History of Power Transformers in Japan
Description of Related Historical Materials

and2

Toshiyuki Yanari■ Abstract
The development history of transformer technology in Japan can be divided into three eras.
The first era, “from copying to domestic production” dates from the start of transformer production in 1893
through to the post-war era. Japanese technology started out being manufactured based on copies of overseas
technology or produced through licenced technology contracts. By the 1920s, Japan had absorbed thesetechnologies and grown to the point of becoming almost independent in its technology production; in the
1930s, Japan caught up to the level of technology that was available in the leading countries.

The next era, “breaking away from overseas technology” extends from the post-war era through to themid-1970s. Japan’s post-war rebuild period was a time of revitalising its technical cooperation with othercountries and actively introducing new technology from overseas. This was followed by the economic boom
and a growing demand for electricity, which led to the achievement of high-capacity technology at almost
the same level as the technology available overseas, as well as the achievement of higher voltage 500kV
transformers. High capacity is accompanied by the issue of flux leakage. Overseas technology offered nosolutions to this issue, since Japan had reached almost the same level of technology as that which wasavailable overseas; Japan had to solve the problem for itself. There was also the issue of countermeasures forthe newly-introduced partial discharge testing for high voltage; this took ten years to solve. These solutions
proved to be the trump card in revolutionising manufacturers’ awareness of quality issues, bringing Japan to
the forefront of other countries in terms of problem-solving.

The third and final era, “development of independent technology”, dates from the late 1970s through to thepresent day. Frictional static electricity generated between insulators and transformer oil, used as a coolant in
the 500kV transformer since 1972, caused flow electrification, leading to dielectric breakdown. The lessons
learned while attempting to solve this issue proved very useful in later development of independent
technology in Japan. Specific examples include the development of UHV transformers and UHV insulation
technology within a far more limited scope of freight transport than other countries and the successful
development of the world’s first high-capacity gas-insulated transformer. These achievements were made bytakingdevelopment

back

to

the

basicsanddown-to-earth

validation.

The

new

style

of

disassembled-for-transport transformer, which came about out of the very limited transportation conditions
and the demand for high product reliability, was superior to the existing partition type transformers both incost and in function and was expected to become widely adopted.

1

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan■ Profile■ Contents

Toshiyuki Yanari
Chief Survey Officer, Center of the History of JapaneseIndustrial Technology, National Museum of Nature andScience1.
2.

March 1962

4.

Graduated from the Department of ElectricalEngineering,
FacultyofEngineering,
University of Tokyo
April 1962
Started working at Tokyo Shibaura ElectricCo., Ltd. (now Toshiba Corp.)
Worked on designing and developing powertransformers for the next 40 years
October 1985 Awarded a degree from the University ofTokyo for research on the long-term insulation
reliability of UHV transformers
April 1990
Chief engineer
August 2001 Retired from Toshiba Corp.
April 2003
Doctor of Engineering; Chief Survey Officer,
National Museum of Nature and Science

3.

5.

6.
7.

Introduction
Overview of the Developmental History of Transformer
Technology in Japan
From Copying to Domestic Production (Pre-War
Transformer Technology)
Breaking Away from Overseas Technology (Post-War
Rebuild to 500kV Transformers)
Development of Independent Technology (Overcoming
Flow Eletricification and the Challenge of New
Technology)
Technology Systematisation
Transformer Conservation

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

2

1. Introduction

To transmit high-capacity electricity from a powersimple glossary at the end), long-term reliability,

station to a distant point of consumption, electricity

maintenance and life span, flow electrification,is sent out at high voltage due to the current

voltage regulation, earthquake proofing and disastercapacity limitations of the power lines. Near the

proofing. The topic of high capacity includes

point of consumption, this voltage is stepped downtransportation problems, as well as other issues,and then transmitted to the consumer. Power

such as cores, coil winding and cooling. Hightransformers are used to convert the voltage. In

voltage focuses on winding and insulation issues

order to coordinate power from many different

and touches on insulating materials and insulation

power stations and to network this system,

treatments. The main points under environmental

switching stations and substations are set up to

issues are noise and fire proofing. The accessories

supply consumers with reliable electricity with no

topic covers tap changers, coolers and radiators,

power outages. The current transmission voltage inconservators and bushing.

Japan is 500kV; the transformers that connect toBelow is a three-stage overview of transformers

this supply have the capacity to convert enoughand their development history.

voltage to supply one million ordinary households(1)each. While transformers have all kinds of uses, as

CopyingtoDomestic

Production(Pre-War Transformer Technology)

outlined in the appendix, this report traces the(2) Breaking Away from Overseas Technology

history of technology and systematically examines(Post-War Rebuild to 500kV Transformers)

power transformers, which have played a constant(3) Development of Independent Technology

leading role in the transformer category.

(Overcoming Flow Eletricification and theThis systematic examination categorises the main

Challenge of New Technology)transformer technologies under discussion from

Chapter 2 provides an overview of the history offive perspectives: high reliability, high capacity,transformer development in Japan; Chapters 3 to 5

high voltage, environmental issues and accessories,

address the respective technological interests andexamining each perspective era by era. The points

technological developments in each era in detail.

examined under the topic of high reliability include

Chapter 6 re-examines the entire period from aexperimental

systematisation perspective and traces the history ofverification,lightningprotected

design (technical terms in italics are explained in a

3

From

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japantransformer technology development.

2. Overview of the Developmental History of Transformer Technology in Japan
2.1 From Copying to Domestic Production

domestically-produced transformers. At this point,
Japanese transformer technology could be regarded(1) Early Transformers

as standing on its own.

Japanese transformer technology began with thecopying of overseas products. In 1893, eight years(2) Developments on the Korean Peninsula

after the transformer as we know it today first

The early Showa Period, in which there were major

appeared, Miyoshi Electric started making its own

developments in Japanese transformers, was also

copies of products from the United Kingdom. In

the time in which the technology spread across to1900, engineers employed in American companies

the Korean Peninsula and made progress there. This

returned to Japan and started producing their own

started with the supply of 36MVA units in 1928.

oil-filled transformers using American-style designs.

Given the success of this arrangement, a succession

While these first started out being used for lighting,of electrical facilities was established from 1935

there was an increasing demand for their use in

onwards;

power supply into the 1900s. As they began to be

extremely-high voltage product in the East wasused for long-distance transmission of extra-highcompleted in 1939, while the 100MVA for Sup’ung

voltage, they needed to be capable of handling highPower Station, with record-breaking capacity for a

voltage and high capacity. Silicon steel sheets andpre-war product, was completed in 1940. Largetransformer oil began to be used from 1910,

volumes of these transformers were sent to theenabling transformers to meet these demands.

Korean Peninsula and Manchuria until around 1943,

From 1911, technology from technical cooperation

when the war became too intense.

with overseas began to be incorporated into designs.

During this time, Japanese transformers came to

Early transformers – even overseas ones – werestand equal with those from leading countries, both

mostly shell-type transformers, but in 1918,

in terms of high voltage and high capacity. Without

American company GE discovered an effective

a doubt, the expansion into the Korean Peninsulabarrier insulation system using an insulationand Manchuria significantly boosted Japanesecylinder to separate the oil gap between coils,

transformer technology.

the

220kV

transformer,

the

first

thereby enabling a shift to core-type transformers.
Japan started making these as well and they later(3) Lightning Protected Design and Impulse

began to grow in their scope of application.

Testing

The 10MVA high-capacity transformer went into

The greatest matter of technical interest at this time

production in the 1920s, with 154kV transmissions

was understanding the behaviour of transformer

beginning in 1923. At first, American-madecoils in lightning surges and the development oftransformers were used, but in 1926, Japan’s firstlightning-protected coils. A paper on the behaviour

domestically produced 154kV transformer was putof transformer coils in lightning surges wasto use with a 6.667MVA unit for Nippon Electric

published in Germany in 1915. From then on,

Gifu Substation. The success of this transformer led

research was carried out in various countries;

toresearch on lightning-protected coil structures was

the

later

near-universal

adoptionofToshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

4also being carried out at the same time. In Japan,

suspended because of the war; it resumed in 1952

there was a negative attitude towards adopting

and new technology that had been worked onlightning-protected coils developed overseas; there

overseas during and after the war made its way into

was little advantage to it, since the transmission

Japan. Some of this technology was worked out andsystem was configured differently. While the coils

implemented purely from information such as

used at the time emulated the structure ofliterature,

reinforced insulation at the ends of the coils, a

collaboration

standard

surge-proof

information gained on observation tours of overseas

winding or partially shielded winding began to befactories, and some was developed by own

adopted after a study of potential distribution

technology fostered during the war. This new

carried out in the 1930s confirmed that this would

technology poured into Japan from the mid-1950s

have the same improved potential distribution

to the 1960s. Many of these new technologies are

effect as lightning-protected coils, even on thestill in use today.

Japanese system. Impulse testing began on these

The technology that was to have the greatest impact

lightning-protected design transformers in 1930 inon the later development of the transformer was thethe United States. It was first used in Japan in 1937

adoption of grain-oriented silicon steel sheetsat 154kV and 18MVA for the Ministry of Railways.

introduced from the United States and theThis was the first proof of the validity of theintroduction of the frame-shaped core that used

lightning-protected design transformers. Impulse

characteristics of new material. These had magnetic

testing became standard in 1945 as the war wasproperties that were superior to the hot rolled

ending.

silicon steel sheets that had been used since 1910

windingsystemcalled

some

was

with

workedoverseasoutthroughpartners

andand could achieve high magnetic field strength with
2.2 Breaking Away from Overseas Technology

minimal excitation current. The magnetic fieldstrength was also increased from 1.3T or less to(1) The Appearance of Extremely-High Voltage

1.6-1.7T, which helped significantly to downsize(EHV) Transformers and the Introduction of

the transformer.

Overseas Technology

5

The epoch of technology that immediately followed(2) Increased Capacity for Power Station

the war saw the beginning of 275kV transmission

Transformers

on the Shin-Hokuriku Trunk line, worked on by

The Japanese economy grew rapidly after theKansai Electric Power Company. The transformers

Korean War. The increased demand for electricity

that were put into this system included pre-war

resulted in the successive establishment of hightechnology as well as new, post-war technology.

capacity thermal power stations. For the main

Given that these also underwent the standard

equipment, such as generators, American-madeimpulse testing issued in 1945, this was a test of the

products were usually used for the primary unit,

technologicalcompanies

while secondary and subsequent units were usually

involved; they were the combined result of all

domestically-produced through licenced technology.

possible efforts from all sides at the time.

However,

Technical cooperation with overseas had been

domestically-produced from the start. Of course,

capabilities

of

all

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanthetransformers

were

all

many of these used new technology introduced

improved coil space factor and a sudden rise in thefrom overseas.

capacity

The rate of capacity development for power stationtransformers.

transformers was very quick, rapidly increasing

improved to the point that a 300 MVA transformer

from 200MVA in 1958 to 300MVA in 1960,

could be transported in the same space that could

430MVA in 1963, 680MVA in 1966, 870MVA in

only have accommodated a 39 MVA transformer

1971 and 1100MVA in 1973. Since this capacity

before the war.

speed was about the same as what was happening

In addition to the existing distribution transformers,

overseas, there were no solutions overseas to thethere was also a need for power transformers to

issues that accompanied high capacity; Japan had tohave on-load tap changers to improve the quality

solve these on its own. In particular, Japan often

of the power. Around this time, German company

had cases requiring high impedance in its

MR was developing an on-load tap changer (LTC)

configuration; making these transformers capablebuilt into the transformer tank. This receivedof high impedance added further complication toworld-wide attention; its introduction and adoption

the issue of high capacity. In such cases, there wasin Japan through technical cooperation fulfilled thelittle to be gained from continuing technicalwishes of the power companies. The MR LTC is

cooperation and Japan gradually steered away fromstill being produced today through technicalits reliance on licenced technology.

cooperation, albeit later, updated models of it. This

limitsof

By 1963,

assembled-for-transport
the technology had

is the only remaining instance of licenced
(3)

High

CapacityofTransformers

fortechnology in Japan’s transformer industry.

Transformer Substations and On-Load Tap
Changing Devices(4) The 500kV Transformer for Export andOnce power stations were capable of high capacity,

Partial Discharge Testing

substation transformers had to be capable of highTransformers increased in capacity and, whencapacity as well. Combined with the strong demand

275kV transformer technology took a steady holdfrom power companies to further reduce thein the 1960s, discussions began on the next stage ofinterval between factory shipping and commencing

transmission voltage, inspired by the achievement

operation,

this

meant

disassembled-for-transportadeparturefromof 400kV transmission in Europe. It was decidedtransformers,

whichthat the next transmission voltage would be 500kV.

were the norm for high-capacity units,

to

This

assembled-for-transportA

manufacturers into development; they carried out

three-phase, five-limb core was adopted, using

model validation assuming that freight cars would

grain-oriented silicon steel sheets to drasticallybe the means of transportation. In 1966, a prototype

reduce the size of the iron core and the hight of

was built and sent for demonstration testing to thetransportation. Special freight cars were put to use,

Ultra High Voltage Laboratory in Takeyama on themaking effective use of the dimensions inMiura Peninsula. Since the aim was to build up an

accordance with rail transport limitations. New

operating record overseas rather than adoption oflightning-protected

newthe technology at home, Japanese manufacturers

insulating materials were adopted, meaning ancompeted for overseas orders of 500kV and 400kV

coiltransformers.

structures

andofficial

decision

of

500kV

spurredToshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

6transformers for overseas schemes at the time; thistransformers and model coils showed that thesucceeded in bringing in many orders forinsulation breakdown was caused by a discharge oftransformers from overseas. The transformer

static electricity built up on the insulator throughspecifications immediately encountered insulation

the flow of transformer oil.

trouble on commencing 500kV transmission in the
United States. Tests were introduced to monitor

2.3. Development of Independent Technology

long-term partial discharges at a slightly higher
voltagethantheoperatingvoltage.

(1) Overcoming Flow Electrification

Countermeasures against partial discharge wereThe

unknown at the time, so it took a great deal of effort

transformers was as yet unknown, so determining

to solve; it took nearly another ten years to find thethe cause of this was purely by trial and error. A

perfect solution.

number of models were built, from full-scale tophenomenon

of

flow

electrificationinbasic, and conditions were varied to determine the(5) 500kV Transformers for Domestic Use

causal factor. After two years of investigation, theIn the 1970s, Tokyo Electric Power decided on aleading cause of the build-up of static electricity

500kV

determining

was found to be the flow rate of the oil, the shapetransformer specifications, producing pre-testingof oil duct and its susceptibility to electrification.

equipment and carrying out testing. Development

The size of the AC electric field and the surface of

was more intense in Japan than in the West; Japanthe insulating material were also found to be factors,

also had to work with the rail transport limitations,and countermeasures were put in place for each of

meaning a number of improvements had to be madethese issues. The susceptibility of transformer oil toto the existing export-market transformers in terms

electrification was confirmed to be due to trace

of

While

substances in the oil becoming activated by

specification decisions had to be made from an

dissolved oxygen and copper ions in the oil andeconomic perspective, there was a major focus on

significantly altering the degree of electrification ofreliability. Decisions were made on the positioning

the oil; to date, little more is known about this. Thisof the taps, the transformer configuration and also

is one difficulty of using petroleum oil, which is a

the test voltage. This reliability-focusing thinking

blended mixture in itself. Tests were carried out on

continued until the end of the 1980s and had a huge

the basic design of the problematic transformers to

impact on the direction of Japanese transformer

determine the extent to which this was happening,technology.

e.g. there was a new trend to try to determine

Such was the introduction of the 500kV transformer.

another insulating structure, having traced it back to

Insulation

the electrical discharge. This contributed greatly totransmission

coil

structures

programme,

andbreakdown

insulation.

occurred

duringpre-implementation voltage impression testing inlater technological developments in Japan.

1972, thereby delaying the commencement of

7

500kV operation a year until 1973. Further(2) The Development of UHV Transformers

insulation breakdown occurred during voltage

and UHV Development Technology

impression testing in 1974; a breakdown analysis

Once Japan’s 500kV transmission network wasandestablished in the late 1970s, discussion turned toadetailed

investigation

of

the

actualSurvey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, JapanUHV transmission – the next level of voltage – andgas-insulated switchgear (GIS) was becoming

development began. The idea was to develop a

more widely used, there was a rise in demand fortransformer

gas-insulated

that

was

subject

to

the

same

transformers

forundergroundtransportation limitations as the 500kV transformer,

substations and for underground railways, as they

but was capable of twice the voltage. This wasallowed for more compact substations. Laterachieved through the use of new insulating material

improvements in coil cooling systems, etc. enabled

thanks to the aforementioned research tracing backthe production of self-cooling models up toto the electrical discharge phenomenon, as well as

30MVA; these even began to be used by power

advances in computer-aided analysis technology,

companies for distribution.

which was then becoming more powerful and more

Initiatives to increase the capacity of gas-insulatedcommonplace. A prototype was built at the end oftransformers began in the United States, with thethe 1970s. Meanwhile, an investigation committee

idea of developing and implementing 300MVA

had been launched to work on implementing UHVclass transformers in the early 1980s. However,transmission and investigate technology challenges.

those plans were interrupted and development was

Throughout this time, various tests were being

cut short. Investigation into increased capacity

systematically carried out as more long-term

began around that time in Japan, leading on fromreliability measures were being incorporated tothe development that had started in the United

withstand a higher level of operating stress thanStates, with various companies working on

ever before. The results of these tests formed thedeveloping a transformer that used a liquid calledbasis for later decisions on test voltage in Japan.

perfluorocarbon as the coolant and PET film andHowever,of UHV was

SF6 for insulation. As the various companies

postponed due to changes in economic growth;

worked on their developments in their own way,

manufacturers

developed

Toshiba completed a 154kV, 200MVA transformer

technology into 500kV models or lower, with thefor Tokyo Electric Power in 1989. This was

idea of downsizing these and reducing the amountfollowed by 275kV, 250MVA and 300MVA

of loss. This technology also succeeded in gaining

transformers produced by Hitachi, Toshiba andsome overseas orders for 765kV transformers.

Mitsubishi respectively in 1990. These differed

the implementation

built

the

newly

completely
(3)

The

Developmentof

Gas-Insulatedin

structure

from

the

existing

oil-immersed transformers and had many technicalTransformers

issues needing to be solved, but these hurdles were

The first gas-insulated transformer with SF6 gas assystematically cleared. They passed reliability

the insulating material appeared as early as 1967.

verification and were put to practical use, the result

However, there was little demand at the time forof the basic technology capability that had taken

non-flammable transformers and competition withroot since the flow electrification incidents.

PCB transformers meant even less demand was to

However, although gas-insulated transformers that

follow. They reappeared in 1978 with film

used this cooling method did exist, they were more

replacing the existing paper to insulate theexpensive

conductors, which greatly improved the impulse

transformers because they required special coolingwithstand voltage, which had been lacking. Just as

equipment and expensive coolants; it was therefore

than

the

existing

oil-immersed

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

8difficult

to

bring

use.

bank capacity of 3000MVA, the same rating as

Nevertheless, Toshiba had developed shunt reactors

expected in actual machines in the future.

needed for underground substations and had

Technically, it was completed in 1993 using the

researched gas cooling because the transformer

insulating technology developed in the 1980s, but it

cooling method of incorporating a cooling panel

then underwent two years of testing at thewould not work for cooling the cores of blocked

Shin-Haruna Substation. Several new issues wereshunt reactors. During the course of that research,encountered during that process, making thisToshiba found that gas cooling could also be used

testing process significant.

on300MVAthem

generalThiswas

The plan at the time was to commence UHV

establishingthetransmission at the beginning of the 21st century,

technology to analyse gas flow through coils,

but the current schedule was suspended due to thedeveloping the technology toequalise heatslump in power demand when the bubble economy

distribution and combining this with existing

burst. It is not clear when UHV will behigh-pressure, high-capacity gas blowers, highimplemented.

successfully

class

into

transformers.

achievedbypressuregas

vesselsandthermalinsulation;

in

1994,

300MVA gass

upgradedcooling(5) Changes in Transport Conditions and thetransformers were supplied to the Tokyo Electric

New Disassembled-for-Transport Transformers

Power Higashi-Shinjuku Substation. The cost of theSince the appearance of the 500kV transformers,

transformer was kept down by using SF6 forpower companies in Japan have placed a strong

cooling and for insulation. There were benefits todemand on reliability, avoiding dealing with thehaving gas devices for the entire substation and theinternal workings of the transformer on site ascost margin narrowed to the point that it was nomuch as possible. By the late 1970s, downsizing of

longeroil-immersed

the main transformer had progressed to the pointtransformers. After that, gas-insulated transformers

that the use of a transport cover, which was thenreplaced the existing oil-immersed transformers as

replaced by a proper cover on site, was hardly seen,

the main transformers used in undergroundmuch less the disassembled-for-transport system

substations.

practised until the 1960s. Meanwhile, transformers

lessattractive

thanwere expected to reproduce factory quality on site(4) UHV Demonstration Testing Equipmentst9

and were freighted in their factory inspection state;

During the 1990s and the early 21 century, thewhere transportation conditions were tough, theUHV programme that had been put on hold in thenumber of transformer partitions increased, as did

1980s came back to life at Tokyo Electric Power,

the number of corresponding cases. Site conditions

with a sudden plan to carry out two years of

andverification testing from 1995. Full-scale model

particularly pumped storage stations, gradually

verification and transformer specification decisions

worsened; despite an increase in transformer

were carried out on the basis of production that had

partitions, the cost of transportation drastically

stopped in the 1980s; the testing equipment ordered

increased, meaning certain measures had to be

successively from Hitachi, Toshiba and Mitsubishi

taken. The first companies to work on this issuecomprised 1050/525/147kV transformers with awere Kansai Electric Power and Mitsubishi Electric.

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japantransport

conditionsforsubstations,

They proposed a new disassembled-for-transportchambers, fieldsystem, which included various ingenious ideas,

investigations and field testing equipment. By 1994,

such as packing all the coils together in a film pack,the 500kV, 1000MVA transformer, which had beenusing a moisture-absorption-eliminating structure

three single-phase structure, was three-phase.

for disassembly and onsite reassembly, cutting

Besides being far cheaper, it also had the benefits

down the level of dryness onsite and emulatingof less installation space and less loss, providing

factory conditions for the iron core and onsite

the impetus for later expansions in its application.

assembly. This method was later adopted byIts applications are thought to continue to expand invarious companies; it became standard practice tofuture, regardless of how it is transported.

test requirements,

test casehave improved iron cores, dust-proof working

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

103. From Copying to Domestic Production (Pre-War Transformer Technology) (1)3.1. Early Transformers(1) The Age of Copying
The transformers that first appeared in Japan were
500-lamp,

125Hz,

1000V,

30kVA generators

imported by Osaka Electric Light Company fromthe United States in 1889. From when AC
distribution began, British-made transformers were
imported.
The transformer had its origins with Michael

Photo 3.2. The Shell-Type Transformer Displayed

Faraday’s validation of electromagnetic induction

at an Exhibition in Budapest by Ganz (1885)

in 1831. However, the basic closed magnetic loop
core structure of today’s transformers was invented

While the first domestically-produced transformer

by an engineer at Ganz Electric Works in Hungary

in Japan is said to have been an 1893 copy made by

in 1885. This was displayed at an exhibition held in

Miyoshi Electric, founded by Shoichi Miyoshi in

Budapest that year and began to be hugely

1883, of a British-made transformer, there is no(2)

successful as a power source for electric lights .

detailed record of this, since Miyoshi ElectricThis invention triggered the expansion of the AC

closed down in 1898. The following year, in 1894,

power system, forming the basis for the later

Toshiba’s predecessor Shibaura Engineering Works

high-capacity,

supplystarted producing single-phase 0.375-10kVA andsystems. Photo 3.1 shows a model of Faraday’s

three-phase 1-30kVA transformers to step down

electromagnetic induction experiment; Photo 3.2

from 1000V or 2000V to 100V, emulating a productshows the first transformer displayed at themade by British company Ferranti. This productexhibition in Budapest.

was displayed at the Fourth National Industrial

high-voltage

electricity

Exhibition in Kyoto in 1895. Since it was
air-cooled, the transformer was long and thin, so it
was known as the ‘pagoda tower’. The shape of it
cannot be confirmed, as there are no surviving
photographs of it. Photo 3.3 shows a contemporary
product

madebyFerranti(3).

Meidensha

Corporation also started producing transformers in1897 with a 50-100 lamp capacity of 10
candlepower.
Photo 3.1. A Model of Faraday’s Electromagnetic
Induction Coil (1831)

11

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

Photo 3.4. Shibaura 50kV Testing Transformer
Exhibited at the 1904 World’s Fair
Photo 3.3. Ferranti’s 150hp Shell-Type Transformer
In 1905, he produced the first 11kV, 150kVA

Supplied to a London Substation (1891)

extra-high-voltage transformer for Kofu Electric.
(2) The Start of Oil-Immersed Transformers

Extra-high voltage had been introduced to Japan in

The end of the age of copying and the transition

1899, using American-made transformers. Fig. 3.1

into independent design came when Zentaro Iijima,shows the progress of domestically-produced

who had been employed by US company Wagnertransformers in terms of high voltage and highElectric Corporation, returned to Japan to work forcapacity. A 22kV, 250kVA transformer was

Shibaura Engineering Works and introduced an

produced in 1906; in 1907, Tokyo Electric Light

independent

American-styleCompany started its first 47-mile long-distanceoil-immersed transformer. As well as distribution

55kV, 15MW transmission from Komahashi Powertransformers, Iijima also branched out into theStation to Waseda, using a 2000kVA transformer

design and manufacture of testing transformers andmade by American company GE. In 1908, Shibaura

extra-high-voltage

heEngineering Works supplied Hakone Hydroelectric

produced a 50kV, 4kVA testing transformer (shown

Power with a 44kV, 500kVA transformer. In 1909, a

in Photo 3.4), which was displayed at the World’s

shell-type,water-cooled,

Fair in St Louis the following year, winning a gold

1500kVA

transformer

medal and invigorating the Japanese electricalEngineeringWorksindustry.

Hodogayasubstation,

designforantransformers.

In

1903,

single phase,
supplied

to

44kV,

by

Shibaura

Yokohama

Electric’s

aground-breaking

domestically-produced product for the day, usedvacuum drying for the first time(4). Special lectures
were held at the Institute of Electrical Engineers ofJapan (IEEJ); records at the time show production
up of extra-high-voltage transformers until 1910 as
34 15350kVA transformers at 30kV, 75 7815kVAtransformers at 20kV, and 19 417kVA transformers
at 10kV. The number of transformers completed by
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

12Shibaura Engineering Works is based on acontemporary testing ledger examined by theauthor; there were found to be 3800 mostly
distribution transformers, meaning the company
already had quite a substantial production capacity

Nippon Electric, Gifu, 154kV
Nippon Electric, Ozone, 13,333kVATokyo Electric Light Company, Tabata, 110kV

Photo

Kyushu Hydroelectric, 66kVTokyo Electric Light Company,
Tabata, 4,400kVA
Kyushu Hydroelectric, 2,500kVA

Capacity (kVA)

Voltage (kV)at the time.

Yokohama Electric, 1,500kVA
Kofu Electric, 11kV

High capacity made possible bysilicon steel sheets

3.5.

The

OldestExtra-High-Voltage

Transformer in Existence (13.2kV, 100kVA; madein 1910 by Shibaura for Shinano Electric)

This transformer has water droplets forced to thetank surface; as the water evaporates,

Kofu Electric, 150kvA

theevaporation temperature dissipates a lot of heat.
This was a novel attempt at high capacity in an age

Fig. 3.1. High Capacity and High Voltage Progress

when radiators had not yet been implemented. Thisof Early Transformers

was a priceless resource at a time when thin mild
steel was still being used for the core. Photo 3.6

Hitachi started manufacturing transformers in 1908shows Hitachi’s first transformer supplied toand Mitsubishi in 1910, marking the beginning of

Hitachi Mine in 1910, which was then used forsignificant progress in Japan’s domestic production

another 50 years.

of transformers. Photo 3.5 shows a transformer
thought

tobeevaporation-cooled,theoldestoil-immersed,

patentedself-cooling,single phase, 60Hz, 100kVA, 12/13.2kV-3.3kV
extra-high-voltage transformer in existence, madein 1910 for Shinano Electric.

Photo 3.6. 5kVA Transformer for Hitachi Mine(made in 1910 by Hitachi)

13

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

(3) Establishing a Network of Transformer

Both companies started manufacturing transformers,

Manufacturers

thereby establishing a Japanese network

Shibaura Engineering Works entered into technicaltransformer manufacturers.

ofcooperation with American company GE in 1909
and began incorporating the new technology into its(4) Summary of the Early Developmental

designs from 1911. In 1910, silicon steel sheets

Periodwere imported from the United Kingdom and

The early developmental period of transformers intrialled on pole-mount transformers. In 1911,

Japan was the time leading up to the Great Kanto

silicon steel plates made by American company

Earthquake of 1923. The first transformers started

Allegheny were imported along with transformerout as copies of products imported from overseas;

oil from Vacuum Oil Company. Transformers ofthese developed as far as the use of independent

3300V or higher were oil-immersed, while 2200V

technology learned in the United States to produce

or

type.

extra-high-voltage oil-immersed transformers. With

Transformers of 500kVA or higher were shell-type

the import of industrially-produced silicon steeltransformers.

sheets and insulating oil in the 1910s and an

In

lower

1911,

transformers

were

Hitachi completed

water-cooled,drya single-phase,inelectricity

usage,

transformers

developed further to handle higher capacity andproduced a 66kV, 2500kVA transformer in 1912higher voltage. There was an increase in theand a 22kV, 4000kVA transformer in 1916 fornumber of transformer manufacturers during thisKyushu Hydroelectric, as well as 110kV, 4400kVA

period, as well as the beginning of technicaltransformers for Inawashiro Hydroelectric andcooperation with overseas companies. While theTokyo Electric Light Company’s Tabata substation

earliest recorded products were generally imports

in 1917. Records leading up to the Great Kanto

from overseas, domestic production began within

Earthquake of 1923 show that a single-phase, 66kV,

two to six years of their introduction. This period

6000kVA transformer appeared in 1920, followed

saw the introduction of not only the existingby a three-phase, 66kV, 8000kVA transformer theshell-type transformers, but also the technology forfollowing year. In any case, the first high-capacity,core-type transformers, which gradually expanded

high-voltage products of the time were imports

in scope to become the main technology used in thefrom the United States; domestically-produced

industry – also during this period. In other words,

products followed two to six years later.

this early period dates from the introduction of

Up until this point, high-capacity transformers weretransformers through to the establishment of ashell-type transformers, as previously mentioned;

transformer

however, in response to GE policy changes in 1919,

beginnings of independence.

startedtransformer.

increase

Shibaura

Shibaura

1500kVA

themakingmanufacturing

network

andthecore-typemedium-capacity transformers, which gradually

3.2. Domestic Production of Technology

began to expand in their scope of application.
Mitsubishi entered into a technical cooperation with

(1) Completion of the 154kV Transformer

American company WH in 1923; Fuji Electric did

Production of the first high-capacity transformers

the same with German company Siemens in 1925.

over

10MVA started

withthe single-phase,Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

14

water-cooled, 77kV, 13.333MVA transformer madeThe existing 10MVA-level transformers had to be

in 1924 for the Nippon Electric Ozone Substation;

disassembled for transport; they were reassembled

this was followed by an 80kV, 15MVA transformer

on site and re-dried. The new 77kV, 10MVA

for Toho Electric the following year. Transmission

transformerof 154kV began in Japan in 1923 between Keihin

Shinyodogawa

Electric’s Ryushima Power Station and the Totsuka

transported by sea already assembled and immersed

Substation, while the first domestically-producedin oil. This was the first time to transport a heavy

154kV transformer was a single-phase, 6.667MVA

item in this manner and it was the forerunner of theunits made (by Shibaura) for the Nippon Electric

later assembled-for-transport system. The exterior

Gifu Substation in 1926. In the foreword ofis shown in Photo 3.8.

Shigenari

Miyamoto’s

Henatsuki(Progress of the Transformer)

no

built

for

the

Daido

Power

StationinElectric

1926

was

Shimpo(1), Sadaji Momota,

former president of IEEJ, recalls that “thistransformer was the first 150kV-level transformer
produced in Japan and it had very good operating
performance; when you think about the fact thatnearlyall

150kV-leveltransformers

weredomestically-produced and that there were only one
or two overseas products available, this is a verysignificant achievement in the history of thetransformer in Japan.” This was followed by seven
10MVA transformers for the Yanagigawara Power

Photo 3.8. Assembled-for-Transport 10 MVA

Station and seven 13.333MVA transformers for the

Water-Cooled Transformer for Daido Electric

Komaki Power Station. Photo 3.7 shows a 165kV,

Shinyodogawa Power Station (made in 1926 by

12.5MVA transformer for the Showa ElectricShibaura)

Sasazu Substation; this was the highest tap voltage
product available at the time.

(2) Cooling Methods
The main cooling method used in the high capacitytransformers at this time was water cooling,whereby water pipes were mounted on the upper
inside of the tank and the water flow would directly
cool the oil. As cooling design technology
advanced, developments were made in large-scale
radiator manufacturing technology around the
mid-1920s. This expanded the scope of applicationfor

15

naturalcirculation

self-coolingmethods,

Photo 3.7. A 165kV, 12.5MVA Transformer for

whereby the oil would cool inside a radiator. The

Showa Electric Sasazu Substation (1928, made byradiator was invented and put to practical use by

Hitachi)

Stanley of the USA in 1916; it became more widely

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanadopted around this time because advances inRiver; the first power station had a three-phase,welding technology for thin steel sheets reduced thewater-cooled, 115kV, 36MVA transformer, suppliedamount of oil leaks from the welded areas. A record(by Shibaura) in 1928. At the time, this was a

10MVA self-cooling transformer was supplied toworld-record-breaking water-cooled transformer.

Ujigawa Electric in 1927; the following year in

Since a crane lift could not be used during factory

1928,

nine

single-phase

22MVA,

assembly, the interior was assembled atop the base

three-windingtransformers

tank, which was situated in a pit, with an ingenious

were supplied to the Showa Electric Yao Substation

method of construction whereby the tank was cut(made by Shibaura). This was world-record

into slices and then fitted in place.

capacity, beating the American record at the time.

With the development project on the Pujon River(3) Insulating Material

being more successful than expected, development

Insulating materials at the time were improving

started on the Changjin River. Seven three-phase,worldwide as the electric supply voltage increased.

water-cooled, 110kV, 40MVA transformers were

For example, cotton thread was used as an earlysupplied to the first power station in 1935; three

insulator for coil conductor; manila paper tapethree-phase,wrapping began to be used from around 1915.

transformers were supplied to the second power

Laminated insulating cylinders made from paper

station in 1936; three three-phase, water-cooled,hardened with resin began to be used from around

154kV, 60MVA transformers were supplied to the

1910;

by

second power station in 1937. Work commenced on

concentrically arranging these insulating cylinders

the Heochun River, with the first extremery-highalong the oil channel provided effective insulation.

voltage power supply of 220kV in the East. The

With this understanding, GE switched from thefirst Heochun River power station was completed

previous shell-type transformers to core-type

in 1939, with a three-phase, water-cooled, 220kV,transformers in 1918. Following suit, Shibaura also

80MVA transformer supplied by Shibaura. This had

switched to core-type transformers, as mentioned

a total mass of 225 tons and was the world’s

previously. In 1928, an L-shaped insulator called ahighest-capacity water-cooled transformer. Photoflanged collar started being used to increase the

3.9 shows the exterior of the first 220kV

insulation at the ends of the coils.

transformer.

140kV-87kV-11kV

theinsulating

barrier

formedwater-cooled,

110kV,

45MVA

3.3. Development on the Korean Peninsula andthe Success of the Transformer(1) Hydroelectricity Development Programmeon the Korean Peninsula
Japan Nitrogenous Fertilizer planned a programmefor developing hydroelectric power on the Korean
Peninsula. Changes to the Yalu River basin would
allow for a vast volume of water and a high drop. It
began with a 300,000kW development on the Pujon
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

16supplied in Japan (by Toshiba). These 100MVA
transformers operated at 50Hz as well as having a
50Hz/60Hz duplexer; they were completed in
1940-1941 and had the highest capacity in theworld at the time, although Japan was nine years
behind Germany with the 15/230kV, three-phase,forced-oil, water-cooled style of transformer(5)(Photo 3.10).

Photo

3.9.

Japan’sFirst

220kV,

80MVA

Transformer for Heochun River (made in 1939 by
Shibaura)

Besides this, the second power station had awater-cooled, 40MVA transformer; there was athree-phase, water-cooled, 80MVA transformer inDongheungnam as a receiving substation, a
80MVA

Photo 3.10. The World’s Highest-Capacity 230kV,

transformer in Ryonghung and a three-phase,

100MVA, Water-Cooled Transformer for Yalu

oil-immersed,

River Sup’ung Power Station (made in 1940 by

three-phase,forced-oil,water-cooled,forced-air

cooled,80MVAtransformer in Chongjin. This transformer for

Toshiba)Chongjin was Japan’s first transformer with aseparately mounted radiator. Since this 220kV

The coils reached a height of 3.5m; insulating

power line was Japan’s first attempt at an EHVcylinders of these dimensions could not besystem, many experts were called in to test it, withproduced domestically; instead, insulating paper

many tests carried out, such as arc suppression test.

specially ordered from Oji Paper Company’s

Instead of the existing voltage application test forfactory

dielectric strength, an induced withstand voltage

manufacturing and testing equipment had to be

test was carried out for the first time on aremodelled and expanded to manufacture these.

transformer.

The three receiving substations had six three-phase,

Next, development commenced on the Yalu River

forced-oil,itself, starting with the magnificent Sup’ung Power

100MVA transformers; this was the first finned unit

Station, equipped with seven (and one spare) of thecooler system made in Japan (Photo 3.11). Fig. 3.2

world’s highest-capacity 100MVA transformers.

shows the developments in transformer capacity on

While some of the generators were ordered fromthe Korean Peninsula during the Showa Period.

Germany, the transformers were all produced and17

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanin

Sakhalin

forced-air

wascooled,used.

Factory

220kV-66kV,

Tokyo Electric Light Company Tsurumi Thermal
No. 1 Power Station, while in 1938, a 154kV,
50MVA transformer was completed for the Tokyo
Electric Light Company Wadabori Substation. Thistransformer took Japan’s record for forced-oil,forced-air cooled systems, with a special radiator
comprising steel pipes wound in a solenoid shapeand a vertical blower positioned in the centre(Photo 3.12). Forced-oil, forced-air cooling systems
were mainly developed in Europe; the first one inJapan was on an 80kV, 12.5MVA transformer for
Kansai Power Distribution in 1926.
Photo 3.11. Forced-Oil, Forced-Air-Cooled, 220kV,
100MVA Transformer (made in 1941 by Toshiba)

Yalu River, Sup’ung, 100MVA
Pyongyang

Capacity (MVA)

Heochun River, 80MVA
Tokyo Electric Light

Chongjin, Yonggang
Changjin River, No. 2

Nippon Electric,

Changjin River, No. 2
Changjin River, No. 1

Chosen Nitrogen
Pujon River
Toho Electric, 15MVA

Photo

3.12.

The

First

Fig. 3.2. Developments in Transformer Capacity on

Forced-Air-Cooled Transformer

the Korean Peninsula during the Showa Period(TokyoElectric

Light

Company

Forced-Oil,

Wadabori

Substation 154kV, 50MVA, made in 1938 by(2) Advances in Cooling

Shibaura)

In Japan, 10MVA was surpassed for the first time in1924 in a transformer for Nippon Electric’s Ozone(3) Lightning-Protected Design

Substation, while a record 22MVA self-cooling

Major technical considerations in the pre-war era

transformer was completed in 1928 for the Showa

were the development of potential vibration

Electric Yao Substation. A 72kV, 43.75MVA

analyses and lightning-protected coils for lightningtransformer for Nippon Electric’s Tsurumi Thermal

surges and also impulse testing. In 1915, German

Power Station in 1930 used a forced-oil pump toengineer Karl Wagner published a paper in EuM

circulate the oil, while the radiator used special

journal entitled “The Penetration of Travellingalloy steel and ocean water for cooling. In 1935, a

Waves into a Coil with Inter-Winding Capacitance,”

66kV, 63MVA transformer was completed for thepresenting the basic ideas on the internal potential

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

18

vibration of transformer windings(6). This prompted

prompted a discussion on insulation coordination.

a series of research in the United States, Germany

This argument made it necessary to prove thatand Japan from 1915 to 1920, which established thetransformers were resistant to impulse surge

fact that transformer windings can be considered tovoltages greater than the coordination gap. In 1930,

be distributed constant circuits. A lot of results wereGE carried out the first impulse testing. Thispublished in Japan during this time, particularly byprompted the establishment of a standardisation

universities.

acommittee in the United States, with the first draft

lightning-protected coil structure to reduce winding

presented in 1933. Meanwhile, Japan established an

vibration was first proposed in 1921 by Risaburō

investigation committee in 1936 to investigate

Torikai of Kyoto University in an article in the UK

impulse surge testing, with the first draft presented

Journal of the Institution of Electrical Engineers

to the committee in 1937. At the same time,(JIEE)

inJapanese Government Railways recorded in a

Transformer and its Remedy” . Rather thanspecification document that the transformers used

distributing

earth

in the Senju Power Station and Musashi-Sakai

capacitance uniformly, this design aligned initial

Substation, then under construction, should havecapacitance and final capacitance by adjusting the“insulation against surge waves in the form ofearth capacitance in inverse proportion to thecoordination gaps, bushing and windings to

distance from the ground and adjusting the series

improve its proof strength.” Impulse surge testing

capacitance in proportion to that distance, thereby

had to be implemented to ensure this. Impulse

preventing oscillation and improving the electricaltesting was implemented in Japan on a single-phase,

gradient. While this theory was not immediately

18MVA, 154kV transformer (made by Shibaura) in

applied to transformers, GE drew some attention

1937(8). The exterior is shown in Photo 3.13, thewith

non-resonantinterior in Photo 3.14 and the impulse voltage

transformer in 1929. Although all kinds ofgenerator at the time in Photo 3.15. Around 1938,

lightning-protected structures were being proposed

the testing was also implemented on 31MVA

throughout the world at the time, winding structurestransformers for the Senju Power Station. Thesesuch as those typified by the non-resonanttransformers had the aforementioned standardtransformer were not used in Japan, because thedesign of the time, with reinforced insulation at theneutral points were not directly grounded, meaningends of the windings, but despite some issues

a high-resistance ground. The measures generally

arising with poor materials used in the wooden poletaken followed those from around 1920, such as

for operating the tap changer, they passed the test,

reinforcing the insulation at the ends of the winding

proving the validity of the lightning-protectedcircuit. However, other methods gradually began toinsulation design used at the time. In 1940, the first

adopted, such as surge-proof winding, partiallyextremely-high voltage impulse test was carried out

shielded winding and multiple cylindrical winding.

on a 230kV transformer bound for Manchuria.

A

entitled

specificdesign“Abnormalfor

Pressure-rise
(7)

its

seriescapacitanceannouncement

of

a

and

(4) Impulse Testing
In 1926, the reinforcing of line insulation in a
220kV system in Pennsylvania, United States,
19

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

However, around this time, a trend emerged
towards using the lightning-protected coil structure
in Japan as well. Mitsubishi implemented surge
potential distribution measurements in 1933 andpromptly used surge-proof windings developed by
WH in 1932 to a 165kV, 7.5MVA transformer for
Taiwan Electric. While Shibaura did not place theentire coil in a large shield, as GE did with its
non-resonanttransformer

distribution

measurements

in

1934,

potential

confirmedtheeffectiveness of its partially shielded winding (ribPhoto 3.13. The 154kV, 18MVA Transformer forshield winding), which covered the ends of its coils

the Japanese Government Railways Musashi-Sakaiin a partial shield to adequately provide the same

Substation (made in 1937 by Shibaura), on which

effect. This system was used in a 154kV, 39MVA

the First Impulse Testing was Carried Out

transformer for the Tokyo Electric Light Company
Shinano River Power Station in 1939 and was later
used universally. In 1941, Hitachi also confirmed
the effectiveness of the partially shielded winding
in a prototype.
Shibaura took note of a non-resonant winding(multiple

cylindricalwinding)developedby

German company AEG in 1937 and from 1940
began its own developments and applied for testing
trasformers which are grounded in neutral andarc-suppression reactor’s coil winding. However, it
was not until after the war that this was used in a
Photo 3.14. Photograph of the Interior of thepower transformer.

18MVA Musashi-Sakai Transformer(5) Transformer Regulations
A set of draft transformer impulse surge testing
regulations was announced in 1940; following a
draft revision in 1944, these were issued as
JEC-110 in 1945. JEC-106 on impulse surge tests
and JEC-107 on impulse surge measurement
techniques were also issued in 1944.
The

processofformulating

regulationsfortransformers began with the establishment in 1922
Photo 3.15. An Early Impulse Test Voltage

of JEC-9, which prescribed electrical equipment

Generator

standard regulations for all electronic goods,
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

20including rotators. This was followed by the

Chosen Power Transmission Pyongyang Substation

establishment of JEC-36 in 1934, comprising

was transported using nitrogen instead of oil tostandard regulations for transformers, induced

reduce the weight, the first time such a method wasvoltage regulators and reactors, and in which

employed.

transformers were targeted separately. During thetransformers appeared in 1936 with the creation ofwar, JEC-36Z was issued as a wartime standard;

the concave-style Shiki-60. Photo 3.16 shows

this relaxed the limits on temperature rise. Japanfreight being transported using the Shiki-60. In

Standard JES31 was issued in 1926 for standard

1939, this railcar was used to transport a 154kV,transformers. A Japanese Engineering Standard

39MVA transformer for the Tokyo Electric Light(JES) was issued in 1941 on transformer oil. The

Company Shinano River Power Station, packed inaforementioned JEC-110 added impulse testing tonitrogen using a temporary transport tank. This was

JEC-36 as a type test.

recording-breaking pre-war rail transport.

Specialrailcarsfortransporting(6) Assembled Rail Transport
Assembled transportation of transformers in Japan
lagged far behind Europe. Most of the highcapacity transformers at the time, including the
aforementioned record-breaking products in Korea,
weredisassembledfortransportation,

thenreassembled and dried on site, which meant a lot of

Photo 3.16. Assembled Transportation by theSpecial Shiki-60 Railcar

time was spent working onsite. However, to reduce21

the amount of time spent on onsite reassembly,(7) On-Load Voltage Regulating Transformers

Japan set its sights on assembled transportation. As

Another technology developed during this era wasmentioned previously, the 10MVA high-capacity

the on-load voltage regulating transformer. On-loadtransformer

Electric

tap changers were developed in the United States

Shinyodogawa Power Station in 1926 was the firstaround the mid-1920s using a current limiting

high-capacity transformer to be transported by sea

reactor to suppress crossflow while switching to thealready assembled and immersed in oil. In 1928, anext tap. This was followed by the development in

7.5MVA transformer built for the Toho Electric

Germany of a method to suppress resistance.

Najima Substation was transported by rail already

Various companies in Japan adopted the American

assembled

1932,

reactor method, which was first used in 1930 in asingle-phase, 77kV, 22MVA transformers bound for

450kVA transformer for China Joint Electric (madethe Toho Electric Kizu and Iwakura Substations

by Shibaura)(9). The next couple of years saw awere immersed in oil and sent by rail on low-floor

sudden flurry of progress and the creation of arailcars. However, to keep within the height

110kV, 12MVA transformer for Kumamoto Electric

limitations of the time, the laborious task had to be

in 1931. Photo 3.17 shows a load voltage regulating

undertaken of removing half of the core upper yoketransformer of the day, a three-phase, 6.3MVA

and then reattaching it onsite still immersed in oil.

transformer

In 1935, a 154kV, 15MVA transformer for the

Nakamaizuru Substation. The first voltage phase

built

and

for

the

immersed

in

Daido

oil;

in

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

for

the

Kyoto

ElectricLightregulator was installed at the Kansai Joint Powertransformer cores as well as the huge advances in

Amagasaki Power Station in 1933 to control power

Manchuria and on the Korean Peninsula. Whileflow, with a regulating capacity of 9MVA and a line

there were fewer rail transport limitations than on

capacity of 88.5MVA. The German resistancethe Japanese mainland, high capacity transformers

method was introduced by Fuji Electric in 1935 andwent

used in an 11kV, 3MVA, on-load tap-changing

transportation, so disassembled transportation wastransformer for an electric furnace for Japanthe norm. The cores at the time had 90˚ alternately

Nitrogenous Fertilizer.

stacked joins; factory and onsite production quality

farbeyond

the

scope

of

assembled

control was nowhere near comparable to what it istoday. Damage to the core while running,inadequate drying onsite and faulty core sheets
insulation led to increased loop electromotive force
when forming each loop, as well as a highcirculating current, causing melted cores. Many
instances of melted cores, including outbreaks offires, occurred from 1938 onwards among thehigh-capacity transformers supplied to Korea. Thiscan be explained as transformer design and
Photo

3.17.

Transformer

On-LoadfortheVoltage
Kyoto

Regulating

ElectricLight

Nakamaizuru Substation (1932, made by Hitachi)

production technology not keeping up with the
speed of capacity increase. Fig. 3.3 shows a sketchof core damage at the time, while Photo 3.18 shows
an external view of a damaged 60MVA transformer.

(8) Summary of the Early Showa Period andMelting of Transformer Cores
With the advent of the Showa Period, the Japanesetransformer industry began to become self-reliant.
This started with the 154kV transformer in the
Nippon Electric Gifu Substation. The design of thistransformer was difficult for the time, combining
the features of existing American-made units to

The melted iron flows into this area at the sameprovide the capability to switch its low voltage

height as a 2” thick crossbar

77/11kV. While it could be considered to be
dependent on licenced technology, various separate
designs resulted in it no longer using any of thosetechnologies. Since this transformer worked well,most of the later 154kV transformers were
produced domestically; this also led to the laterboom on the Korean Peninsula.

Approximate volume of this area is 8,000cm3

However, we must not forget about the melting ofFig. 3.3. Diagram of Melted Core

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

22

Lightning-protected design and impulse testing also
appeared during this era. Uniform insulation was
normal in Japan due to the different configuration.
Although the lightning-protected coil structuresdeveloped in Europe could not be directly used inJapan at first, they were gradually introduced once
their effect was validated. Japan also kept awatchful eye on impulse testing trends in the
United States and other developed countries; it
continued to prepare for standardisation andmanaged to issue standards during the Second
World War, thereby laying a foundation for a fresh
start after the war.
Photo 3.18. 60MVA Changjin River Transformer
with a Melted Core (1938, made by Shibaura)

23

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan4. Breaking Away from Overseas Technology (Post-War Rebuild to 500kV
Transformers)

4.1. Post-War Rebuild and the Achievement ofExtremly-High Voltage Transformers

From the end of the 1930s and throughout the
1940s, domestic orders for new high-capacitytransformers dropped off, with the main orders
being to repair and restore the transformers that had
been damaged during the war. Nevertheless, orders
for new transformers began to trickle in fromaround 1948. A 22MVA transformer completed in1949 for the Japan Electric Generation andTransmission Company’s Ozone Substation was thefirst to undergo impulse testing following the

Photo 4.1. The First Domestically-Produced 275kV

issuance of JEC-110. This transformer had aTransformer, Kansai Electric Power Company

newly-standardised partially shielded winding as its

Narude Power Station (1951, made by Hitachi)

lightning-protected coil structure.
specialThe 70MVA transformer made by Hitachi for the

procurements for the Korean War and business

Narude Power Station (Photo 4.1) had a primary

quickly boomed again, accompanied by an increase

winding of 154kV, 50MVA, a secondary winding of

in demand for electricity. A 275kV transformer for

257kV, 70MVA and a tertiary winding of 11kV,

the Kansai Electric Power Company Shin-Hokuriku

40MVA, with the EHV neutral point directly

Trunk line started operating in 1952, the first in the

grounded. Accordingly, the ends of the EHVTheadventpost-war

of

epoch

the

(10)

.

1950s

This

domestically-produced

broughtwasJapan’s

extremely-highfirstwinding were positioned at the centre of thevoltage

winding height and it was easy to insulate. This wastransformer and it was also impulse-tested intheaccordance with the new standard. Four major

medium-voltage winding of 154kV; this wascompanies were in charge of manufacturing.

insulated together with the high-voltage winding

(11)

first

structure

in

Japan

to

have

a

Hitachi oversaw 70MVA transformers

for theusing the partially shielded winding method that

Narude99MVA

had been developed in the 1940s.

Powertransformers(12)

Station,for the Hirakata Substation, Toshiba(13)

for the Shin-Aimoto

99MVA transformers
Substation

Mitsubishi

winding of 250kV, 90MVA, a secondary winding offor the Tsubakihara Power Station.

77kV, 99MVA and a tertiary winding of 10.5kV,This took much ingenuity, combining accumulated

45MVA; this had an equivalent capacitance of

pre-war technology with new post-war technology.

117MVA,

(14)

Fuji

Electric

the Hirakata Substation (Photo 4.2) had a primary

45MVA

transformers

andThe 99MVA transformer made by Mitsubishi formakingitthehighestcapacityToshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

24transformer ever. The primary neutral point wassystem of connecting the insulation tube to the coildirectly grounded. The primary winding was abysurge-proof winding, which was becoming theelectrostatic-capacitor electrode to prevent the coilnorm for shell-type transformers. The tank also hadfrom increasing in size. The medium-voltage

a new form-fit design. Mitsubishi also built a

154kV winding was also a standard partially

72.5MVA transformer for the Maruyama Powershielded winding. Fig. 4.1 shows a diagram of theStation.

winding structure.

ofHigh-voltage winding

Medium-voltage winding

Low-voltage winding

means

a

solid-insulation,

Rib shield
Shielding
Stack shield

Photo 4.2. Japan’s First 275kV Transformer, Kansai
Electric Power Company Hirakata Substation (1951,

Fig. 4.1. Diagram of a Non-Resonant Transformer

made by Mitsubishi)

Winding Structure

Toshiba’s

25transformer

for

the

Shin-Aimoto

Fuji Electric’s 45MVA transformer for Tsubakihara

Substation had a primary winding of 275kV,Power Station also used a new structure. Since this

90MVA, a secondary winding of 166kV, 99MVA

one was for a power station and the high-voltage

and a tertiary winding of 11kV, 45MVA, giving it

and low-voltage windings were opposite each other,

the same equivalent capacitance as the Hirakata

a non-resonant winding (multiple cylindricaltransformer, the highest capacity transformer ever.

winding) developed by German company AEG wasWith the primary neutral point directly grounded, it

used. With the neutral points being directly

was the first to have the non-resonant transformer

grounded and the high-voltage neutral point and thestructure developed by GE before the war. Anotherlow-voltage winding opposite each other, it was

reason for this was that it was difficult to use apossible to minimise the main gap between the highmultiple cylindrical winding for the high voltage, as

and low voltage windings. This was the first use in

was commonly used in the West at the time,

Japan of a main-gap-filling insulating structure

because it had a high medium-voltage winding ofreportedly used in post-war Europe, reducing the

166kV. Unlike the GE design, the stack shield forsize of the main gap and adapting well to thethe non-resonant winding had some ingenious

low-impedance specifications of the transformer.

innovations. Besides the coil itself, it also had a

Due

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japantotransportation

constraints,

all

these

transformers were disassembled for transport andinreassembled/re-dried on site. Toshiba used somepreviously. Japan’s level of transformer technology

newly-developedforcapability grew considerably, with clarification on

onsite assembly. Since the aim was to reduce thepotential vibration, the knowledge that the impulse

amount of lifting equipment on site as much as

resistance of paper insulation is key to high series

possible, assembling and erecting the core on top of

capacitance windings, the development of high air

the lower tank made it possible to make do withtight wire insulating paper, and damper-shield

only a 25 ton crane on site. Meanwhile, Mitsubishi

windings and other lightning-protected windings

developed a new method of drying its form-fit tankindependently developed in Japan. Capacitor

structure by heating the tank through induction

coupling shield windings, a later improvement on

while also blowing hot air onto it.

damper-shield windings, were even licenced tocore-erecting

equipment

the

first

275kV

transformer,

mentioned

manufacturers in the United Kingdom, formerly a
4.2. The Revival of Technical Cooperation andleaderthe Increase in Proprietary Technology

aforementioned transposed cables were also put tointransformer

technology.

Theuse in some equipment in 1957 based on
Technical cooperation with overseas manufacturers

information from overseas, which contributed

revived once more in 1952, having been suspended

greatly to their wider adoption later on.

during the war. This brought with it new technology

Thethat had been developed overseas during and after

introduced after the war was grain-oriented silicon

the war. Some of this technology was worked out

steel sheets, developed by American company

and implemented purely from information such as

Armco in 1935. They were first used in 1955,

literature,imported from Armco. However, the full potential

some

was

workedout

through

most

impactingoverseas

technology

andof the grain-oriented silicon steel sheets was not

information gained on observation tours of overseas

realised, as they were used with the right-angled

factories, and some was developed overseas during

joins of the existing core structure. It was not until

the war. This new technology poured into Japan

1956 that a frame-shaped core was used to makefrom the mid-1950s to the 1960s. To give a few

full use of the characteristics of the grain-oriented

examples,silicon steel sheets, in a 6MVA transformer for thecollaboration

withoverseas

partners

vapour-phase-drying

methods,

frame-shaped cores, coil forced cooling, transposed

Tokyo

cables and many other technologies that are still

Substation. Once Yawata Iron & Steel obtained aused today were introduced at this time. High series

technology licence from Armcocapacitance windings, developed in 1950 in the

full-scale production in 1958, it began to increase

United Kingdom, became the focus of independent

in use. However, it was not until around 1962 thatinvestigation based on the UK information with thedomestically-produced grain-oriented silicon steel

aim of making a proprietary product in 1951.

sheets appear on the market and the JapaneseMain-gap-filling insulating structures, used intransformer industry transitioned completely from

Europe, underwent further development based on

the existing hot-rolled T-grade silicon steel sheets

information from overseas; this technology wasto frame-shaped cores made from cold-rolled

able to be implemented in 1951 and was also used

G-grade grain-oriented silicon steel sheets. While

ElectricPower

Company

Kichijoji

and

began

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

26the magnetic field strength used was initially 1.3T,
not very different from the T-grade material, it grew
to 1.6-1.7T from around 1962, which greatly
contributed to increasing the capacity of thetransformer through significant downsizing of thecore.
Photo 4.3. A 66MVA Transformer for the Tokyo
4.3.

High

Capacity

andAssembled

Electric Power Company Keihoku Substation

becometheNormTransported by the Shiki 140 Schnabel Car (1954,

Transportation

forTransformers
(1)

High

made by Hitachi)
Capacity

andAssembled

A special three phase system was developed inTransportation of Substation Transformers

1955 and used on a 275kV, 93MVA transformer forWith an increasing demand for electricity in thethe Electric Power Development Company Sakuma

1950s, primary substation transformer capacity was

Power Station (Photo 4.4).

increased to 30-60MVA; to make it quicker andeasier to install these high-capacity transformers onsite, it became normal for them to be transported
assembled using special freight cars. Muchingenuity was devoted to that purpose.
It started in 1951 with the adoption of form-fit tankat the shell-type transformer. A 45MVA transformer
for the Kyushu Electric Chikujo Power Station wastransported, fully assembled, sideways using the
Shiki 100. The low-floor Shiki 120 was brought out

Photo

the following year in 1952, and used to transport a

Transformer, a 93MVA Transformer for the Electric

65MVA transformer for Chikujo thePower Development Company Sakuma Powersame way on

its side. A 39MVA transformer for the Tokyo

4.4.

The First Special Three Phase

Station (1955, made by Mitsubishi)Electric Power Company Higashi-Chiba Substation
was transported on its side with a form-fit tank. In

The same year, a three-phase, five-limb core was1954, a 66MVA transformer for the Tokyo Electricused in a 99MVA transformer for the Chubu

PowerElectric

Company

Keihoku

Substation

was

Power

Companytransported using Japan’s first Schnabel railcar, theSubstation. This was transported assembled using

Shiki 140 (Photo 4.3).

the Shiki 170 Schnabel car. Photo 4.5 shows thecore and coils of this transformer.

27

Higashi-Nagoya

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

Fig. 4.2 shows the post-war advances in thecapacity of assembled-for-transport transformers
for substations. This was undergirded by the
introduction of the Schnabel car to make the mosteffective use of rail transport limitations, thedownsizing of the core through the use ofgrain-oriented silicon steel sheets and the adoptionof the five-leg core structure. The use of gradedinsulation on the 154kV neutral point under
JEC-120issued

in

1952

and

significant

Photo 4.5. A 99MVA Transformer for the Chubu

improvements to the winding coil space factor due

Electric

to lightning-protected winding structures also

Power

Company

Higashi-Nagoya

Substation, the First to Use a Five-Leg Core (1955,

greatly contributed to this improvement.

made by Toshiba)

continued

toimprove.

Transportationofhigh-capacity transformers progressed, with thetransportation a 180MVA transformer for the
KyushuElectricPower

Company

Nishitani

Capacity (MVA)

from 1957 to 1959 and freight transport capacity

Tokyo Electric Power Company
Boso Substation, 1500/3MVA

Tokyo Electric Power Company
Kohoku Substation, 450MVA

Successively larger Schnabel cars were produced

Chubu Electric Power Company
Nishi-Nagoya Substation, 300MVA
Electric Power Development Company
Nishi-Tokyo Substation, 264MVA
Kyushu Electric Power Company
Nishitani Substation, 180MVA
Chubu Electric Power Company
Higashi-Nagoya Substation, 99MVA

Substation in 1958, a 275kV, 264MVA transformer
for the Electric Power Development Company

Yearin theNishi-Tokyo Substation in 1959, and a 262.5kV,

Fig.

300MVA transformer for the Chubu Electric Power

Assembled-for-TransportCompany Nishi-Nagoya Substation in 1963 (Photo

Substations

4.2.

Advances

Capacity

Transformers

of
for

4.6).
Sea transport was also used. In 1956, a 160MVA
transformer for the Tokyo Electric Power Company
Chiba Power Station was shipped with the use of afloating crane (Photo 4.7). With the later increase insingle-unit capacity of transformers for thermal
power stations, it became possible to transport
assembled three-phase transformers.
Photo 4.6. A 300MVA Transformer for the Chubu
Electric Power Company Nishi-Nagoya Substation,
the Highest Capacity Transformer to be Transported(1963, made by Hitachi)

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

28

capacity record continued to be broken again eachyear, with a 200MVA transformer for the Chiba
Thermal Power Station in 1958, a 270MVA
transformer for the Chubu Electric Power Company
Shin-Nagoya Thermal Power Station in 1959 and a
300MVA transformer for the Tokyo Electric Power
Company Yokosuka Thermal Power Station in 1960.
The progress in power station transformer capacity
is shown in Fig. 4.3.
Photo 4.7. A 160MVA Transformer for the Tokyo
Tokyo Electric Power Company
Kashiwazaki-Kariwa Power Station, 1450MVA
Japan Atomic Power Company
Tsuruga Power Station, 1260MVA
Kansai Electric Power Company
Ooi Power Station, 1240MVA
Tokyo Electric Power Company
Kashima Power Station, 1100MVA
Tokyo Electric Power Company
Fukushima No. 1 Power Station, 870MVA
Tokyo Electric Power Company
Anegasaki Power Station, 680MVA
Chubu Electric Power Company
Owasemita Power Station, 430MVA
Tokyo Electric Power Company
Yokosuka Power Station, 300MVA
Tokyo Electric Power Company
Chiba Power Station, 160MVA

Electric Power Company Chiba Power Station

Meanwhile, there was a growing demand for
distribution

transformers

tobeable tobetransported whole by trailer, particularly in urban
areas.

This

transformer

started
in

with

1958.

At

a

66kV,
the

Capacity (MVA)

Shipped with the Use of a Floating Crane (1956)

10MVA

same

time,

vehicle-movable transformers were also introduced;
these could be moved in emergency situations.

Year
Fig. 4.3. Progress in Power Station Transformer(2) Increased Capacity of Power Station

Capacity

Transformers

29

The pace at which power station transformers

Meanwhile, large-scale hydroelectric dams wereincreased in capacity is surprising.

being built, requiring high capacity transformers for

While many thermal power stations used importedhydroelectric power stations. However, sincemachines for their primary turbines and generators,

hydroelectric power stations often present major

they were using domestically-produced equipment

constraints on rail or road transport, a method wasrather than imported equipment for their primarydeveloped in 1955 of transporting each of the threetransformers, since even before the war Japan had

phases separately; this method later became

reached a world-record level of technology in thiscommon. Examples include a 93MVA transformer

area. One such pre-war record product was afor the Electric Power Development Company

63MVA transformer at the Chubu Electric Power

Sakuma Power Station (Photo 4.4)

Company Meiko Thermal Power Station, while an

133MVA transformer for the Electric Power

85MVA transformer was completed in 1955 for theDevelopment Company Okutadami Power Station,

Chubu Electric Power Company Mie Thermal

completed in 1959(16). However, in many cases,

Power Station and a 160MVA transformer was

they

could

not

meet

the

size

or

completed in 1956 for the Tokyo Electric Power

specificationsfortransport

and

were

Company Chiba Thermal Power Station. The

disassembled for transport, such as a 95MVA

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

(15)

and a

weightstill

transformer

for

the

KansaiElectricPowerhigh-capacity

undergroundsubstation,

using

Company Kurobegawa No. 4 Power Station

imported rubber pouches. With rubber diaphragms

completed in 1960. The system of disassembly forlater being domestically manufactured, thesetransportation gradually declined following thesuperseded the nitrogen-filled tank system byappearance of the 500kV transformer and thearound the mid-1960s.

emphasis on transformer reliability in the 1970s.
4.4. Accessories and On-Load Tap-Changing
Transformers(1) Cooling Systems and Conservators
Let us now examine transformer accessories. In
terms of cooling systems, water cooling was themain system used in pre-war Japan. These weresuperseded by forced-oil cooling systems that had
long been common in Europe. The issue of coolant
preservation in substation transformers had a major
influence on this change. A 66MVA transformer for
the Tokyo Electric Power Company WadaboriFig. 4.8. A 66MVA Transformer for the Tokyo

Substation completed in 1951 (Photo 4.8) was

Electric Power Company Wadabori Substation, thesimplified to have the cooler mounted directly onto

First to Use a Unit Cooler (1951, made by Toshiba)

the body of the transformer; nowadays it iscommonplace to have a unit cooler cooling system(2) On-Load Tap-Changing Transformers

with a cooler and pump combined. Conservators

Another technological advance during this era was(17)

have a nitrogen-filled tank system. Whilethepopularisationofon-loadtap-changing

nitrogen-filled tank system conservators were firsttransformers to provide a constant voltage supply toused in 1942, at that time they were not widely

boost the quality of the electricity available. The

used for economic reasons. After the war, they wereon-load tap changers at this time were mainly

more widely adopted in recognition of their

American-style reactor-type LTCs, while someeffectivenessthewere the German/Janssen-style resistor-type LTCs.

three-chamber structure was common at the time, A

Some transformers had a load voltage regulator

66MVA transformer comprised a floating tank,(LVR) connected in series to the main transformer,

which was the standard structure until the transition

while some were load ratio control transformers

to the diaphragm structure in the 1960s. The(LRT), with a tap winding inside the transformer

diaphragm structure was also licenced technology,

itself. At the time, these were mainly used forfrom American company GE. The first transformer

electricity distribution. However, in the late 1950s,

to apply this technology was in 1960, with aon-load voltage regulation began to be carried out

100MVA transformer for the Tokyo Electric PowerbyCompany

substations. The two methods used were LVR andin

conserving

Chiyodaoil.

Substation,

While

the

first

high-capacitytransformers

atprimary

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

30

LRT; examples using LVR include a 90MVA
transformer (LVR: 220kV±10, ±j30kV) for the
KyushuElectricPower

Company

YamaieSubstation in 1956 and an 80MVA transformer(LVR: 77kV±5%) for the Hokuriku Electric Power
Company Fushiki Substation in 1957. Examples
using

the

LRT

systemincludea

66MVA

transformer for the Chugoku Electric Power
Company Tokuyama Substation in 1957 and a
75MVA transformer for the Tokyo Electric Power

Photo 4.9. A 300MVA Transformer for the Tokyo

Company Kuramae Substation in 1959, using an

Electric Power Company Kita-Tokyo Substation,embedded LRT.

the First to Have a Built-in MR Resistor-TypeThe 1960s saw a greater trend towards using LTCs

Tap-Changer (1962, made by Mitsubishi)

in primary substation transformers, while on-load
tap changers were being built into transformertanks. There was an increasing demand from powercompanies for LRTs that could be transported
assembled, like the transformers themselves. There
was also a growing demand to use highly practical
LTCs with longer lifespans and fewer maintenancerequirements. German company MR received
worldwide attention at the time as being the mostsuited to meeting these demands. In 1963, three
Japanese transformer manufacturers entered into
technical cooperation with MR and after thatmodels developed by MR became the main ones
used in Japan, a trend which continues to thepresent

day.

Photo

4.9

shows

a

Photo 4.10. F-Type Tap-Changer by MR

300MVAtransformer for the Tokyo Electric Power Company

4.5. Elephant Bushing

Kita-Tokyo Substation, the first to have a built-in
MR LTC, while Photo 4.10 shows the LTC itself(18).

To meet the increasing demand for electricity, a66-154kV system was directly introduced to urban
centresthroughconnected
undergroundtocables,sometimes

transformers
substations.

bydirectly

means

of

Undergroundhydroelectric power stations were planned, with thegenerated voltage stepped up by undergroundtransformers; in some instances, the electricity wastransmitted underground by means of oil-insulated
31

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japancables. In such cases, it was usual to have the cablevacuum infusion method. However, around thatend terminal connected to a transformer bushing bytime, the resin spacer developed by GIS began to bemeans of overhead wires. Meanwhile, by aroundused for their compactness. After that, various types

the mid-1940s it was becoming increasinglyof bushings were used in various combinations.

common in the West to connect the cable to thetransformer in oil. In 1958, a 66kV transformer
became the first in Japan to be connected in oil; in
1960, an oil connection with a so-called elephantbushing was used to connect 154kV to a 100MVA
transformer for the Tokyo Electric Power Company
ChiyodaSubstation,

the

first

high-capacity

underground urban substation, and 275kV on a
133MVA transformer (Photo 4.11) for the ElectricPower Development Company Okutadami Power
Station, an underground power station(16). For the

Photo

purposes of clarifying

Transformer

differences in onsite

4.1.

A

275kV

Direct-Cable-Coupledassembly time and load sharing, the elephant

133MVA Transformer for the Electric Powerbushing structure mainly used in Japan has theDevelopment Company Okutadami Power Station

cable head connected to the transformer in a

(1960, made by Toshiba)connection duct using an oil-oil bushing. In thiscase, the length of the bushing pocket and4.6. The Appearance of Ultra-High Capacity

connection duct must be made as short as possible

Transformers

to reduce the amount of space used in theunderground substation. The bushings used at the(1) The Appearance of Ultra-High Capacity

time transitioned from the oil bushings withTransformers

insulation tube barriers, predominant since before

The advent of the 1960s saw a sudden boom inthe war, to oil-impregnated paper condenser

demand for electricity as Japan entered a period ofbushings.

bushings

rapid economic growth. While single-unit capacity

developed in Europe were smaller in size yet still

expanded at a rapid pace from the perspective ofeffective, so this system began to be adopted

capital investment efficiency, the speed at which

through technology imports. However, the drythermal power station transformers expanded wascondenser bushings did not use a vacuum infusion

amazing. Fig. 4.3 shows the progress of transformer

for the resin, so some tiny voids remained. Latercapacity in Japan; this figure shows a sudden climb

testing that showed that this was prone to partialfrom the 1960s to the early 1970s.

discharge, which was difficult to distinguish fromThe completion of a 300MVA transformer for thepartial discharge from the transformer itself. This

Tokyo Electric Power Company Yokosuka Powerwas reported along with the fact that the operating

Station in 1960 was followed by the successive

voltage would drop in quality after extended use;completion of a 370MVA transformer for thearound the mid-1970s, this was replaced by the

Kansai Electric Power Company Himeji No. 2

Resin

(dry)

condenser

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

32Power Station, a 420MVA transformer for the
Tokyo Electric Power Company Yokosuka Power
Station and a 430MVA transformer for the Chubu
Electric Power Company Owasemita Power Stationin 1963, and the completion of a 680MVA
transformer for the Tokyo Electric Power Company
Anegasaki Power Station in 1966 (Fig. 4.12)(19).
Following the provision in 1964 of a 100MVA
transformer to the Japan Atomic Power Company
Tokai Nuclear Power Station – Japan’s first nuclear

Photo 4.13. An 1100MVA Transformer for the

power station – a 490MVA transformer wasTokyo Electric Power Company Kashima Power

completed for the Tokyo Electric Power Company

Station (1973, made by Toshiba)

Fukushima No. 1 Nuclear Power Station in 1969,
with an 870MVA transformer provided to the same

Since this pace of capacity increase was around thepower station as a secondary transformer in 1971.

same as that found in the United States and various

In 1973, a 1100MVA transformer supplied to theother countries, Japan could no longer take the step

Tokyo Electric Power Company Kashima Thermalof introducing technology developed or establishedPower Station became the first transformer tooverseas before establishing its own technology as(20). A 680MVA

it had done in the past with high voltage; it had totransformer and an 1100MVA transformer were

try to solve the issues that accompanied highcompleted for the Tokyo Electric Power Company

capacity on its own.

Sodegaura Power Station as 500kV transformers to

As well as high capacity, there were increasing

step up the power supply directly at the power

demands for transformers to have higher impedance

station to feed into a 500kV network that had alsoof around 1.5 times the existing specifications tocommenced operation in 1973.

limit the short-circuit capacity of the networks.

exceed 1000MVA (Photo 4.13)

Consequently, one of the most significant issues
with high-capacity transformers was that of cycliccurrents within the structure due to leakage flux inthe windings and the loss and heat caused by thesecurrents.
(2) Dealing with Leakage Flux
Windings started to counteract leakage flux in 1958
with multiple cylindrical windings, which had
improved

insulation

andbetterproduction

Photo 4.12. A 680MVA Transformer for the Tokyo

conditions, as well as the widespread use of

Electric Power Company Anegasaki Power Stationtransposed cables as the conductor within these(1966, made by Toshiba)

windings. Transposed cables have two lengths ofthin conducting material twisted at a pitch of

33

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanaround10cm,

makingstrongshielding for core clamp, the use of double

mechanically. They also effectively halve theconcentric winding arrangements, the introduction

fringing flux at the ends of the winding and are stillof cyclic current reduction or preventive measures,

widely used today.

such as preventing multi-point grounding or using

The greatest difficulty in counteracting leakage flux

insulation, the use of structures to prevent

is preventing selective heating of the tank. Cyclic

incomplete contact, the use of tank magnetic

currents are generated in the tank not only due toshields

leakage flux from the winding, but also due to thedevelopment of low-voltage high current bushing,magnetic field of the high current lead wire.

and measures to prevent overheating of theMagnetic tank shields were used to deal with this inconnection between the low-voltage isolated phaseshell-type transformers from 1952 onwards, while

bus and the low-voltage bushing pocket. Into thecore-typealuminium

1980s, it became more common to use a computerelectromagnetic shields from 1958. However, there

to analyse the electromagnetic field; this increased

were issues with the structure and scope ofaccuracy went a great way to solving the leakage

mounting these; these issues were eventually solved

flux issue; however, since transformers are complex

through repeated trial and error on several products.

in shape they are generally difficult to analyse.

Selective heating from cyclic currents flowing

Even today, some aspects of this issue have notwithin the inner structure of the tank due to leakage

been fully resolved.

flux or the magnetic field of the high current lead

The pace of transformer capacity increase later

wire made things difficult, as this could not beslackened off. Nuclear power stations placed orders

immediately detected externally. In many cases, thefor transformers, with a 1200MVA transformer for

issue appeared and was dealt with on site.

the Japan Atomic Power Company Tokai Nuclear

Gas-in-oil analyses are commonly used these days

Power Station in 1975, a 1240MVA transformer for

to detect selective heating; this technology is thethe Kansai Electric Power Company Ooi Nuclear

result of these early processes. As mentioned

Power Station in 1976, a 1260MVA transformer forpreviously, the conservator system used in Japanthe Japan Atomic Power Company Tsuruga Nuclear

from the 1960s onwards was the diaphragm system.

Power Station in 1985 and a 1450MVA transformer

Japan had very high analytical precision infordetecting even the tiniest amount of dissolved gas

Kashiwazaki-Kariwa Nuclear Power Plant in 1994

in oil, meaning it could make its evaluation criteria(Photo 4.14)(21). More recently, a 1510MVA

very strict regarding flammable gas generated bytransformer was completed for the Chubu Electric

overheated oil, which contributed greatly toPower Company Hamaoka Nuclear Power Plant ineliminating the causes of flammable gas generation.

2002 (Photo 4.15)(22), the current world record

Determining the presence or absence of selective

holder for the highest capacity transformer in theheating began in the late 1960s, with gas-in-oil

world.

transformers

them

used

very

the

(for

core-type

Tokyo

Electrictransformers),

Power

the

Company

analyses during temperature rise tests at factories.
Thus, from the late 1960s to the 1970s, various
countermeasures were adopted, such as the use of aslit structure for core tie plate, the use of magnetic
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

34

4.7. Transformer Exports and the Developmentof 500kV Transformers(1) Post-War Transformer Exports
Post-war transformer exports were often based oninternational yen loans. At first, these were aimed at
India and Taiwan, until around 1960. At this point,
research and development began on the next levelof supply voltage: the idea of the 400kV power
supply such as was implemented in Europe andother areas. Based on these developments, Japan
succeeded in securing an order for a 330kV
transformer for Australia in 1960, followed by
Photo 4.14. A 500kV, 1450MVA Transformer fororderstheCompanytransformers in 1961. These orders were sent by

Kashiwazaki-Kariwa Nuclear Power Plant (1994,

Hitachi and Toshiba. Photo 4.16 shows the exterior

made by Hitachi)of the 330kV, 100MVA transformer. This could be

TokyoElectric

Power

for

330kV,

160MVA

and

100MVAsaid to be the beginning of Japan’s officialtransformer exports. These transformers were also
Japan’s

first

on-loadtap-changing

auto-transformers, with the tap changing at the endof the medium-voltage 132kV line. The windings
incorporated the latest technology, being both the
newly-developed damper-shield windings as wellas high series capacitance windings(23)(24). This wasa time of adopting new technology, including theuse of thermal upgraded insulating paper, the use ofcrêpe paper and flexible copper twist wire for thelead, and crimped lead terminals.

Photo 4.15. A 500kV, 1510MVA Transformer for
the Chubu Electric Power Company Hamaoka
Nuclear Power Plant (2002, made by Mitsubishi)

35

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japantransformers

were

distinctive

in

that

the

specifications required partial discharge testing in
addition to the existing insulation tests.

Photo 4.16. A 330kV, 100MVA, On-Load Tap
Changing, Auto-Transformer for Australia (1961,
made by Toshiba)(2) Initiatives towards 500kV Transformers and
500kV Transformers for Export

Photo 4.17. A 500kV, 10MVA Transformer Used

Japan’s decision in the 1960s to move up to 500kV,for Voltage Impression Testing

the next level of supply voltage, spurred on

Central Research Institute of Electric Powerdevelopment. By 1963, development was fully

Industry Yokosuka Research Institute (1966, madeunderway, with the creation of full-scale models

by Mitsubishi)with the assumption that these would be transported
by rail. By 1966, Hitachi, Toshiba and Mitsubishi
had sent 500kV, 10MVA prototypes to the
Takeyama Ultra High Voltage Laboratory fordemonstration testing (Photo 4.17)(25). Further,since the aim was to build up experience overseas
before applying the technology in Japan, by 1965
each company had successfully secured orders forhigh-capacity 500kV transformers from Canada,followed by the United States and Australia, as wellas orders from Mexico for 400kV transformers.

Photo 4.18. Core and coil of Japan’s First 500kV

Photo 4.18 shows the inside of Japan’s first 500kV

Transformer, a 100MVA Transformer Bound fortransformer, a 100MVA transformer bound for

Canada (1967, made by Toshiba)

Canada. As a result of a series of insulation faults
not long after putting US-made 500kV transformers(3) Initiatives towards Partial Discharge Testing

into operation early in the 500kV stage, theseIn those days, design/production and testing toToshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

36

prevent partial discharge was completely by trial

is a clear difference between the work environment

and error. Tentative measures were taken, such as

and workers’ ethic in Japan and that in othereliminating concentrated electric fields from thecountries.

electrodes, testing and improving the insulating
materials

used,increasingawarenessofdust-proofing by painting the inner structures inlightcolours,

introducing

newinsulating

improvingtheproduction

technology,

andenvironment

throughtheintroductionofCompletionofDomestic

500kV

Transformers and Flow Electrification Incidents(1) Development of 500kV Transformers for theDomestic Market

cleanrooms and low-humidity working chambers.

In 1970, Tokyo Electric Power Company finally

While these were successful to some extent, it was

decided to go to 500kV transmission and decisions

rare to pass a test the first time around and the

got underway on transformer specifications. Whileinterior of the transformer was repeatedly cleaned

some specifications had been adopted for anwith transformer oil to remove foreign bodies.

interconnected grid between Kansai Electric Power

Various other countermeasures were later adopted,

Company and Chugoku Electric Power Company,

such as the use of voidless insulating materials, themost transformers in Japan were almost firstremoval of

metallic contaminants from theapplication of auto-transformer type with ainsulation, the introduction of insulation moisturecapacity bank of 1000MVA. While many of the tap

control, and controls to prevent the enter of foreignchangers were positioned on the medium-voltage

bodies. While acoustic corona location technology

terminal on a auto-transformer, as often done

became established, as well as technology thatoverseas, there was little precedent for this on

identified the point of corona discharge, this was

275kV, many transformer faults had occurred in the

not enough to radically solve the issue of partial

LTC and there were reliability issues with using(26). This was issue completely solved

them with a voltage as high as 275kV. Accordingly,

from the mid to late 1970s onwards when 500kV

the neutral switch method was adopted, despite thetransformers were launched in Japan, thanks to an

fact that this means larger equipment due to tap

understanding of partial discharge inception fieldcore excitation, the fact that this would make thestrength in oil, configuration and management of

tap step voltage uneven and other shortcomings.

allowable electric field values, outfitting ofMoreover, the tap winding was placed separately as

dust-proof machine rooms, complete awareness ofthe on-load voltage regulator, enabling the main

dust protection among workers and a lot oftransformer to be moved independently in the event

Japanese-style quality control. It took nearly ten

of failure near the LTC.

years to completely solve this issue. Nowadays, it isLightning impulse test voltage was set at 1550kV, astandard practice in Japan to use partial discharge

step lower than the 1675kV used in lightning

testing to ensure no internal partial discharge. This

impulse testing on 500kV transformers in the Westguarantees the reliability of the insulation of theat the time. Switching impulse testing was alsotransformer. While criteria such as IEC standards

adopted at first, with a test voltage set at 1175kV.

are more relaxed elsewhere than in Japan, thisWhile in the West it was usual to determine the ACcannot be said to be unrelated to the fact that there

test voltage in way that linked to the lightning

discharge

37

4.8.

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanimpulse test voltage, but based on 275kV running
results in Japan, it was set at 840kV, quite highcompared to that used in the West. Decisions onpartial discharge testing were carried out withreference to overseas precedents, with a test patterndetermined of 1.5E (E: normal operating voltage) 1
hour, 2E 5 minutes, 1.5E 1 hour. AC testing wasdetermined while carrying out testing on priortesting equipment. Thus, 500kV transformers inJapan were based on the running results of 275kVtransformers; specifications were set in order toimprove reliability, forming the start of the later
reliability-centred principle that continued until the
1990s. Kansai Electric Power Company, which
followed Tokyo Electric Power Company inPhoto 4.19. The First Domestic 500kV Transformer

commencing 500kV transmission, set its AC test

A 1000/3MVA Transformer for the Tokyo Electric

voltage at 680kV, having linked it to lightning

Power Company Shin-Koga Substation (1971,

impulse testing as in the West; however, it

made by Toshiba)

ultimately set it at an intermediate 750kV duringlater test voltage standardisation.
(2) Completion of 500kV Transformers
The first 500kV transformers in Japan were
supplied to the Tokyo Electric Power Company
Shin-Koga and Boso Substations in 1971 by
Toshiba and Mitsubishi, with three banks each(27)(28).
Photo 4.19 shows the exterior of a 500kV
transformer for the Shin-Koga Substation, while
Photo 4.20 shows the interior of the same. Around1972, during testing prior to commencing operation,
there were two successive insulation breakdowns at
the Boso Substation. Once these were investigatedand repair, 500kV transmission commenced inJapan in 1973.

Photo 4.20. Core and Coil of the Shin-Koga
Substation 1000/3MVA Transformer

These 500kV transformers essentially comprised
the windings and insulation structured usedsuccessfully in the 500kV transformers for export.
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

38

However, a more compact design was required,

the insulation had leaked out when exchanging the

given the different rail transport limitations and duetransportation cover for the main cover on site,

to the high AC test voltage values, the heavy use of

making it susceptible to water absorption. However,barrier insulation arranged alternately between oil

during prolonged voltage impression at the factory,

gaps and the insulating material was adopted.

one of the transformers emitted a sound from

Further, while dust protection was being reinforced

within that coincided with the electrical signal. As

with the building or relocating to new factories,

light from electrical discharge could be confirmed

dust protection was not thoroughly enforced andfrom the testing observation window, it wasworkers had little awareness of this issue, so it was

concluded that electrical discharge was taking placerare to pass partial discharge testing the first time

inside the transformer. It was also concluded thataround.

this was due to static shock from the oil flow, since

A auto-transformer built in 1974 for Kansai Electric

the discharge varied with the operation of the pump.

Power Company had the tap winding built into the

The oil industry had experienced issues such as

main transformer, with the tap winding woundtanker explosions and pipeline fires from staticaround the side leg of the single-phase core. Whileelectricity, but nobody at the time expected oil flow

power companies had differing views on reliability,

toeven Tokyo Electric Power Company adopted theinsulation-oriented machine such as a transformer

system of winding the tap winding into the mainto the point of insulation breakdown. Tracing the

body of the transformer for its 500kV and 154kV

cause of this meant re-investigating static electricity

system transformers, rather than the LVR system.

from the ground up. In 1974, soon after research on

There was a difference in importance between theflow electrification started, another insulation

154kV and 275kV networks.

breakdown occurred during voltage impression

In 1974, transformers were first used to directly

testing on a transformer for the Shin-Tokorozawa

step up to 500kV from the generators at the Tokyo

Substation. This time, too, there was a lot ofElectric Power Company Sodegaura Power Station

damage inside the transformer so the cause couldandnot be determined, but when another insulation

theKansaiElectricPower

Company

Okutataragi Pumped Storage Power Station.

cause

electrostatic

discharge

insidean

breakdown occurred on a second transformer
during subsequent voltage impression testing, the39(3) 500kV Transformer Accidents and Flow

possibility of electrostatic discharge was considered.

Electrification

A detailed examination of the intact coils of theDuring testing at the Boso Substation in 1972, two

three arranged in parallel with the legs showedtransformers in succession experienced insulation

tracking in the insulation, probably due to a lot of

breakdown, as mentioned earlier. An investigationelectrostatic discharge in the oil flow channel in thewas launched on all the transformers from thelower part of the coil. It was determined that thefactory, including the two that had broken down,

insulation breakdown in this transformer was frombut no clear cause was found at the time. It waselectrostatic

concluded that the insulation breakdown was

flashover. Right before this incident, electrostatic

probably caused by increased moisture content indischarge had successfully been induced in a

the insulation, since the transformer oil infused insimulated cylindrical coil inlet on a cylindrical

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japandischarge

developing

into

AC

full-scale model. By comparison with this, it wasdetermined that electrostatic discharge was thecause of this incident. Fig. 4.4 shows the site ofoccurrence of tracking marks from electrostatic
discharge. Photos 4.21 to 4.23 show example
tracking marks.

Medium Voltage
Low Voltage

High Voltage
Photo 4.22. Ibid. Tertiary Winding Basic Insulation
Cylinder Inner Side View

Photo 4.21

Yoke

Oil Flow
Clamp

Tank

Fig. 4.4. Site of Occurrence of Electrostatic
Discharge Marks

Photo 4.23. Ibid. High-Voltage Winding Basic
Insulation Cylinder Inner Side View

Photo 4.21. Electrostatic Discharge Marks(Medium-Voltage Multiple Cylindrical Winding
Terminal Shield)

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

40

5. Development of Independent Technology (Overcoming Flow Electrification and theChallenge of New Technology)

5.1.

Overcoming

Flow Electrificationand(29)(30)(31)

Back-to-Basics Development

flow electrification were established, researchcontinued on the degree of electrification oftransformer oil and on agents to control it. Since(1)

Investigating

theCausesof

FlowElectrification IncidentsTo

determinethetransformer oil is refined from petroleum oil, it is a
mixture of various chemical compositions and it

cause

of

this

incident,

remains

impossible

toidentify

the

trace

manufacturers changed all kinds of conditions

components leading to the degree of electrification.

using actual transformers, full-scale models andStill, experimental results show that changes in thebasic models. This confirmed that the susceptibility

electrification of transformer oil can be controlled ifof transformer oil to electrification, the shape of the

benzotriazole (BTA) is added to it at an amount ofoil channel, the local flow velocity, the AC electric

10ppm. This practice of adding BTA to transformer

field and the surface state and moisture content ofoil has been commonly adopted in Japan since thethe insulation all have an electrostatic discharge

1980s; the transformer oil standards also include ancausative effect. Different transformer oils varied inappendix on BTA-added oil.

the degree of electrification of the oil; it was later
confirmed that there were variances in time. While(2) Reflecting on Flow Electrification Incidents

it is still not known what substance causes thisand Later Developments

timewise variation, the electrification is thought to

At the time, it was impossible to predict this flow

vary dramatically due to trace substances in the oilelectrification

being activated by dissolved oxygen and copper

incorporating oil into the coil, the designs at theions in the oil. Consequently, differences in thetime only gave thought to the cooling of the coiltime between oiling and voltage impression isand overlooked the oil flow. Problems occurred inthought

betweenareas with high local flow velocity. For one thing,transformers in the degree of electrification andthis led to a reflection on the underlying idea thatwhether or not electrostatic discharge will occur. As

parts designed according to design standards fora result of a flurry of research by various

imported

companies,

flow

back-to-basics consideration. A trend emerged andelectrification were established in 1976. The results

took hold to ensure no such oversight would occurofintroducedwith the high-capacity, high-voltage progress of, but received little attention attransformers. This played a major part in later

to

this

resultindifferences

countermeasures

study

were

againstalso(32)(33)(34)(35)

overseas41

phenomenon.

overseasIn

technology

terms

lackedofany

the time. However, in the 1980s, various places

development of new Japanese technology.

around the world reported trouble thought to be

In this period, the inner structures of transformers

from electrostatic discharge. It started to receive

changedmore attention and continues to be a major issue

non-oil-immersed insulating materials such aseven today. Even after countermeasures against

paper laminate compounds were superseded by

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

dramatically.

Problematicoil-immersed pressboard laminated material or

From the late 1970s to around the mid-1980s, Japanreinforced wood. Insulation materials mainly usedbegan full-scale development on UHV. Research onin Europe, such as craft board moulded insulation

this was being carried out all around the world atand pressboard insulation cylinders, made their way

the time as the next stage of voltage and Japan

to Japan. Examination of the insulating properties

expected to implement it as well.

of winding structures resulted in simple continuous

This required a transformer that could withstanddisc winding and minimal shielding between turns

twice the voltage of the 500kV transformer whileat the end of the winding rather than elaborate

being subject to the same rail transport size andwindings such as the high series capacitancemass limitations. Initiatives commenced to achieve

windings previously often used for high voltage. It

this objective, using strategic placement of thewas possible to apply this to windings of 275kV

aforementioned new, compact insulating material.

and over, so it quickly expanded in use. Computers

By the end of the 1970s, various companies had

became more widely used at this point, having areported building prototypes(36)(37)(38).

significant impact on the increased accuracy ofInpotential vibration analyses.

Transmission was put together from experts in

1978,variousthe Special Committee on

fieldsandinvestigation

UHV

began

on

5.2. The Development of UHV Transformers

implementing UHV. Besides manufacturing within

and UHV Development Technology

the rail transport limitations, another technical issue
with UHV transformers was ensuring absolute(1) Development of UHV Transformers

reliability against operating voltage stress during
500kV

extended operation and all kinds of abnormaltransmission began with Chubu, Chugoku andvoltage stress due to having a greater electric field

Kyushu Electric Power Companies, while Tokyoon the oil channel during operation than existingElectric Power Company worked on increasing its

transformers. To deal with this, various long-termbank capacity from 1000MVA to 1500MVA. The

reliability

production side had been thoroughly immersed in

implemented, with the results reported to thetheaCommittee. This is reflected in the later revisions ofcountermeasure against partial discharge. Rigorous

Japan’s test voltage standards and enabled Japan tocontrol and increased awareness among workers

haveAroundthe

mid-1970s,

importanceofdomestic

dust-proofingas

checksunique,werehighlylater

designedreliableandinsulation(39)(40)(41). Photo 5.1 shows a UHV

through QC activities has finally led to thestandards

standardised production of partial-discharge-freeprototype transformer undergoing reliability checks

transformers.

using prolonged voltage impression in a factory

Major advances in various electric field analyses

field.

and potential vibration analyses using large-scale
electronic computers has been characteristic of thisperiod. Collation of the results of these analyses
and results of model experiments has increased
understanding of oil insulation and made it possible
to have more compact insulation.
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

42model (Photo 5.3). The transformers for South
Africa had a bank capacity of 2000MVA, thelargest ever for a substation (Photo 5.4).

Photo 5.1. UHV Prototype Transformer (1979,
made by Toshiba)

Photo 5.2. The First 765kV Transformer, an
805/3MVA Transformer for Venezuela (1982, made(2) Adoption of UHV Development Technology

by Mitsubishi)

The implementation of UHV was later pushedforward due to the economy transitioning fromrapid growth to stable growth in the 1980s. This
technology is reflected in transformers of 500kV
and lower among various manufacturers, withmodel changes to downsize and reduce loss. For
example, existing core-type 500kV, 1000/3MVA
transformers had had two coils in parallel and asingle-phase, four-leg core; the adoption of thistechnology enabled a single coil and a single-phase,
three-leg core, which significantly reduced both
mass and loss.
This technology was also used to tender for 765kV

Photo 5.3. A 765/500kV, 1650/3MVA Transformer

transformers for overseas; a Japanese alliancefor Brazil (1988, made by Toshiba)(Hitachi, Toshiba, and Mitsubishi) succeeded ingetting an order for 765kV transformers for
Venezuela.

The

first

shipment

of

a

UHV

transformer was sent in 1982 (Photo 5.2). Orders
for 765kV transformers were also later successfullyreceived from Brazil and South Africa. The
transformers bound for Brazil had a medium
voltage of 500kV and a high-voltage impulse test

43

voltage of 1950kV, the same as that expected for

Photo 5.4. A 765kV, 2000/3MVA Transformer for

UHV in Japan; it was thus later viewed as a priorSouth Africa (1985, made by Fuji)

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan5.3.

Popularisation

Substations

and

of

Underground

Transformer

Disasterperspective of downsizing the substation, this was
extremely effective.

(42)(43)

Prevention Measures(2) Transformer Disaster Prevention Measures(1) Popularisation of Underground Substations

With Tokyo Electric Power Company’s progress on

As high-voltage electrical cables began to develop

a 275kV network, the short-circuit capacity for theand spread, a movement developed around the end

system in the 1980s exceeded the initially-plannedof the 1950s to bring direct high-voltage systems in

10GVA. When transformers broke down internally,

to urban centres and construct high-voltage

it was a high-energy incident. Accordingly, there

networks in cities. The Tokyo Electric Powerwas a fear of the worst case scenario, in which theCompany Chiyoda Substation was completed inpressure on the transformer tank would exceed its(44). This was equipped with a 100MVA,

breaking pressure before a circuit breaker could

154kV transformer. Since it was underground, theisolate the system, thereby breaking the tank andheight of the transformer would affect thecausing a fire. It was necessary to set someconstruction

strictcountermeasures in place. A collaborative study

constraints and various ingenious methods were

between manufacturers and power companies

used, such as onsite assembly. Photo 5.5 shows it in

conducted an experiment using gunpowder toassembled in the factory.

simulate increased tank pressure in an internal

1960

costs,

sothispresented

breakdown and then examined the transformation.
This resulted in the proposal of a countermeasure tohave tanks separated into single phases joined by an
upper duct and sharing a common duct andconservator; larger holes between the tank and theduct relieve pressure increase. This became thestandard

structureforfutureunderground(43)

substations.

Regarding explosion-proofing of transformers, theinternal tank pressure was obtained and the
Photo 5.5. The First High-Capacity Undergroundacceptable accident level determined from theSubstation Transformer

correlation between the amount of gas emitted andA 154kV, 100MVA Transformer for the Tokyo

the amount of expansion in the tank throughElectric Power Company Chiyoda Substation (1960,

collaborative research between power companies

made by Toshiba)

and manufacturers in 1975(42). However, since
underground substation transformers had a special

Later, in 1969, shipments were made of 275kV

three-phase structure, they had a low amount of

substation transformers. The Shinjuku and Jonantank expansion. It was necessary to develop a new

Substations started operating in 1971. Gas insulated

structure, as this could not withstand a short-circuit

switchgears (GIS) began to be used in these 275kV

capacity of 15GVA.

underground substations and later. From the
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

445.4. The Addition of High-Capacity Shunt

shunt reactor later became the standard shunt

Reactors

reactor structure adopted by all companies. In 1994,
the first 500kV reactor was set up by the Electric(1) The Necessity for Shunt Reactors

Power Development Company, while the first

With high-capacity underground substations thus

250MVA reactor was set up by Chugoku Electric

built in urban centres and cable systems connected,

Power Company and Shikoku Electric Power

at night, when the load was low, a leading load

Company. As far as exports go, a record highwould occur due to cable capacitance. To avoid this,capacity 765kV, 400/3MVAshunt reactor wasunderground substations started being fitted withdispatched to South Africa in 1985 (Photo 5.7).

high-capacity shunt reactors. At first, this was puton the transformer’s tertiary circuit and provided
compensation indirectly, but later shunt reactors

Core Yoke

Core Yoke

Core Leg

Gap

were directly connected to the 275kV system.
(2) Introduction of Radial Core Shunt Reactors
When 275kV was introduced to Japan in 1952, thefirst 15MVA shunt reactor was introduced toWinding

Hirakata Substation for compensation. Later, otherWinding

relatively low-capacity shunt reactors of 30MVA
were introduced from time to time. However,(a) Transformer

increased cable systems led to the installation of(b) Air-Core Reactor

Core Yoke

150MVA reactors at outdoor substations connected

Block Coreto underground substations from 1975 onwards.
The main reactors at the time were the air-coreGaptype; these had magnetic shieldings around the coil.
However, this type had relatively high loss;

Winding

connecting a shunt reactor would always give a
100% current flow. To reduce loss, due to thestrong demand for electricity, a transition began to(c) Core Reactor

the radial core structure that was standard in

Fig. 5.1. Internal Schematic Diagram of aEurope at the time and had been in production by

Transformer/Shunt Reactor

Japanese manufacturers from around 1960. Thiswas developed further in the early 1980s. In thiscase, a spacer made from material with a highYoung’s modulus, such as ceramic, was placed
between the block core, thereby avoiding variations
due to magnetic attraction. Fig. 5.1 shows aschematic diagram of the internal structure of atransformer and shunt reactor. The radial core type45

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanbasement substations in urban centres. However,
the issue of PCB toxicity meant a strong trend to
ban the use of PCB worldwide; in Japan, the use of
PCB was declared prohibited in 1974. However,there was not enough demand for PCB transformers
to create a demand for a PCB replacementtransformer, so everyone soon got by with
oil-immersed transformers.
(2) The Appearance and Spread of Gas
Insulated Transformers

Photo 5.6. Radial Core Assembled

The first SF6 gas insulated transformer appeared
even before gas insulated switchgears were used.
This first transformer was produced by Toshiba
based on introduced technology through technicalcooperation with American company GE. Rather
than using SF6 as a coolant for direct gas cooling,
this transformer had an evaporator built into thetank and ran a heat exchanger using fluorocarbons.
This 66kV, 3000kVA transformer was supplied toDaiichi Life in 1967 (Photo 5.8).

Photo 5.7. A 765kV, 400/3MVA Shunt Reactor forSouth Africa (1985, made by Toshiba)
5.5.

Fire-Proofing

Development

Transformers

of

Gas

and

Insulated(45)(46)

Transformers(1) Fire-Proof Transformers

Photo 5.8. Japan’s First Gas Insulated Transformer

Before the war, transformers with polychlorinated(Daiichi Life, 66kV, 3MVA) (1967, made bybiphenyl (PCB) insulating oil had been produced

Toshiba)from time to time for use indoors at power stations.
Since PCB had the same cooling and insulation

At the time, it was quite difficult to design

properties as mineral oil, it was in high demand,

insulation

particularly in the United States. In Japan,

technology; like the oil-immersed transformers,

6-10MVA PCB

produced

paper was used for insulation and it had a low

sporadically from around the mid-1950s forimpulse withstand voltage. The film-type gastransformers

were

–

there

was

no

film

insulation

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

46

insulated transformers of today appeared in 1978;

H-class aramid paper were also used. Whilethese were adopted on the Jōetsu Shinkansen

forced-air cooling systems were normal for 10MVA(Photo 5.9).

transformers at the time, there was also a strong
demand for natural cooling. This was met by
improving the winding cooling systems, using
highly heat-resistant film and other means and a
20MVA, self-cooled, gas insulated transformer was
produced in 1987, followed by a 30MVA version in
1989. The popularity of gas insulated transformers
grew as they were widely adopted as replacements
after a series of substation fires around the

Photo 5.9. A 66kV, 10MVA Gas Insulated

mid-1980s. Fig. 5.2 shows a typical gas insulated

Transformer for the Jōetsu Shinkansen (1978, madetransformer structure(46).

by Meidensha)
Bushing
Tank

After this, there was a growing demand forCore

SF6 Gastransformers for basement substations and subways.

Cooler

In 1982, on-load tap changers were implemented
for gas insulated transformers with vacuum valves.

Winding

The first of these were placed in the Sapporo City

Partition Plate

Air
Air

Transportation Bureau (Photo 5.10).

Gas Blower
SF6
Fig. 5.2. General Structure of a Gas Insulated
Transformer(3) Dry-Type Transformers
While dry-type transformers were used since before
the war prior to the popularisation of gas insulatedtransformers in lower voltage/capacity applications,such as indoor use. In the 1960s, moulded
Photo 5.10. A 66kV, 11MVA On-Load Tap

transformers from polyester resin, then epoxy resin,

Changing

were developed in Europe for these applications as

Transformerfor

SapporoCity

well. Research began in Japan as well from the late

Transportation Bureau (1982, made by Fuji)

1960s and epoxy resin moulded transformers wereAt first, the main film used was E-classintroduced in 1974. After that, as capacity steadily

heat-resistant polyethylene terephthalate (PET).

increased, the existing dry-type transformers were

Later,

replaced (Photo 5.11).

B-classheat-resistantPET,

F-classheat-resistant polyphenylene sulphide (PPS) and47

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanseparate cooling system for directly cooling thewinding, using aluminium sheets developed byAmerican company GE for the windings, PET film
for the insulation, rolling up metal cooling plates
inside the winding and passing perfluorocarbon
liquid through it. Hitachi also started working on
perfluorocarbon transformers together with Chubu
Electric Power Company. They came up with animmersion cooling system, whereby a tub madePhoto 5.11. A 22kV, 13MVA Moulded Transformer

from FRP cylinder around the interior in the tankfor Tokyo City (1994, made by Fuji)

was filled with perfluorocarbon liquid to directly

5.6.

From

Liquid-Cooled,Gas

Insulatedcool the interior. The general structures and features

Transformers to Gas-Cooled, Gas Insulated

devised by each company are given in Table 5.1(46).

Transformers

All the companies’ methods had to solve a numberof points, which took time to develop and(1)

DevelopmentofHigh-Capacity

Gas

implement.

In

1989,

Toshiba

succeededinInsulated Transformers

developing the world’s first 154kV, 200MVA,

High-capacity gas insulated transformers were firsthigh-capacity, gas insulated transformer for the

researched in the United States. In the early 1980s,

Tokyo Electric Power Company Asahi Substationplans were revealed to develop and implement a(Photo300MVA transformer,

later

development of 275kV, 300MVA and 250MVA

suspended due to financial curtailing by the US

transformers in 1990 by Tokyo Electric Powergovernment. Development in Japan commenced byCompany, Kansai Electric Power Company andKansai Electric Power Company and Mitsubishi

Chubu Electric Power Company(47)(48)(49).

but

these

were

5.12).

ThiswasfollowedbytheElectric, inspired by the American plans. At first,
SF6 gas alone was thought to be inadequate forcoolinghighcapacitytransformers

andconsideration was given to other liquids for cooling.
Mitsubishi came up with an evaporative coolingsystem developed by American company WH,
whereby perfluorocarbons were dropped downfrom above the winding, cooling them by heatabsorption as they evaporated. In 1980, a 77kV,
40MVA transformer was delivered to Hokusetsu

Photo 5.12. The World’s First High-Capacity Gas

Substation. Later, work began on changing to liquid

Insulated Transformer

flow-downtransformers.

A 154kV, 200MVA Transformer for the Tokyo

Meanwhile, from 1983 onwards, Toshiba began

Electric Power Company Asahi Substation (1989,

work on development, together with Tokyo Electricmade by Toshiba)forhigh-capacity

Power Company. This involved the adoption of a
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

48Table 5.1. Overview of Liquid-Cooled, Gas Insulated Transformer Structures
Liquid-Cooled

Cooling System

Flow-Down
Distributor
CoolerImmersion

Separate

Separator
Tank
SF6 GasCompressor SF6 Gas

PFC Fluid
CoolerConfiguration
Winding

Winding Structure

Tank
Pressure
Regulator

Rectangular

Plate

Winding

Feed
Pump

Winding
SupportInsulation
cylinderCoolerFeed Pump
Cooling Pipe

Disc Winding

Sheet WindingCore Structure

Shell TypeCore TypeCore Type

Voltage (kV)

275

275

154, 275

Capacity (MVA)

300

150, 250

200, 300

0.1-0.2

0.35

0.4

80-10023.4, 24.4

130, 135PFC Fluid

PFC Fluid

PFC Fluid

PPS Film

Aramid Paper

PET Film

SF6 GasPFC Fluid

PET Film

SF6 GasSF6 GasSF6 GasForced Circulation

Forced Circulation

Forced Circulation

Mix of SF6 Gas andSF6 Gas and Coolant

SF6 Gas and Coolant

Coolant

Separate

Separate

NominalPressure

(MPa)
Main

Body

Gas

3

Capacity (m )Cooling Medium
Winding

Insulation

Coating
Insulating
MediumWinding
Interior
GroundCoolant Circulation
SystemCharacteristics

49

Core

Feed Coolant
Pump

Sheet Winding

Winding
Insulation cylinder SF6 Gas
Core
Static Shield for
H.V wdg.

Gas
Storage

ExampleMagnetic Core
Cooling Panel
ShieldCoolant
Pressure
Pressuriser
VesselLow

operating

Core

and

Core and winding cooled

coolant

by cooling panelpressure by means ofimmersedpressure regulator

inside insulation tub

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japaninwinding(2) The Challenges of Liquid-Cooled, Gas

the heat resistance of the insulation, developing a

Insulated Transformers

high-capacity, high-pressure gas blower, keeping an

These were completely different in structure fromeven winding temperature by controlling the gas

the existing oil-immersed transformers. While eachflow inside the winding, and various other

had numerous issues to be solved in various ways,

technology. Japan’s capabilities in developing newthese hurdles were systematically cleared. The flow

technology contributed greatly to this achievement.

electrification

Currently, Tokyo Electric Power Company is using

incidents

had

left

Japanese

researchers and developers with well-groundedthese

technology development capabilities, which saw

oil-immersed transformers in its undergroundthem through all the reliability testing right to thesubstations. This system was also adopted in a

implementation stage.

220kV, 300MVA transformer for Chugoku Electric

However, in contrast to the simple structure of thePower Company as well as the first 345kV,

existing oil-immersed transformers, which the same

400MVA transformer for export to Australia. The

oil

these

latest liquid-cooled, gas insulated transformer was atransformers required a special structure for cooling

275kV, 450MVA transformer – the highest capacity

the winding, which was costly, and also used verygas insulated transformer for an underground

expensive perfluorocarbon fluid for cooling. These

substation – completed by Hitachi in 1998 with antransformers cost two to three times more than theimmersion system and supplied to Chubu Electric

existing oil-immersed transformers, which made it

Power Company (Photo 5.15).

for

both

insulationandcooling,gas

insulatedtransformers

insteadofdifficult for them to be widely adopted.
(3) Achievement of High-Capacity, Gas-Cooled
Transformers
Underground substations required shunt reactors aswell as transformers. Toshiba started researchingdirect gas cooling, as it was having difficulty using
a separate cooling system incorporating a blocked
core cooling panel for gas insulation of thesereactors. The success of this gave hope to the ideaof300MVA

gas-cooledtransformers,andPhoto 5.13. A Gas-Cooled, 275kV, 300MVA

development changed direction. In 1994, a 275kV,Transformer

300MVA transformer for the Tokyo Electric Power

Company

Company

made by Toshiba)

Higashi-Shinjuku

Substation

was

for

the

Tokyo

Higashi-Shinjuku

ElectricPower

Substation(1994,

successfully produced with a gas cooling system.
Photo 5.13 shows the exterior of this transformer,
while Photo 5.14 shows the interior, which looks nodifferenttoanoil-immersed

transformer(50).

Previously thought impossible, gas cooling wasachieved by increasing the gas pressure, increasing
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

50

achievesufficiently

reliableequipment.

Thedevelopment of high performance zinc oxidearresters also meant that the test voltage could be
reduced and rationalised by 70%(39). Although aconclusion was reached on UHV transmission in
1982, the economy transitioned from high growth
to stable in the 1980s, which meant a major delayin the implementation of it and a suspension ofstudies on UHV.
Photo 5.14. Interior of the Higashi-Shinjuku

However, the postponed UHV plan began to be

Substation Transformer

implemented by Tokyo Electric Power Company inthe 1990s and the early 2000s. In 1995, a proposal
suddenly emerged for two years of demonstration
testing. Testing began on full-scale models based on
the production models that had been abandoned in
the 1980s to eliminate technical issues anddetermine specifications.
(2) UHV Demonstration Testing Transformers
The

rated

valuesPhoto 5.15. The Highest-Capacity Gas Insulatedtransformers

wereTransformer, a 275kV, 450MVA Transformer for1050/525/147kV, bank capacity of 3000MVA, andthe Chubu

tap range of 7%. Hitachi, Toshiba and Mitsubishi

Electric Power Company Meijo

Substation (1998, made by Hitachi)

fordemonstration

set

at

testing

voltagesofworked on one phase each. The designs emulated
the already-developed insulation technology, with

5.7. UHV Demonstration Testing Equipment

single-phase 1000MVA on a two-tank structurewith bushing out between the two tanks. Prior to

51(1) Resumption of UHV Transmission Plans

the demonstration testing models, a single tank test

Steps

technology

piece was produced, with the actual model being

development for UHV transmission, including the

produced following limit tests. The demonstration

establishment of the Special Committee for UHV

testing model was completed in 1993 and it was

Transmission in 1978, basic studies, developmental

tested

had

been

taken

towards

for

two

(51)

.

years

Photo

at

5.16

the

Shin-Haruna

shows

the

UHV

research and demonstration testing. This also

Substation

included the selection of 1000kV as the nominal

demonstration testing model in site. During testing,voltage and 1100kV as the maximum voltage.

issues emerged with the field test circuit and with

Detailed conceptual designs and studies on basic

flow electrification of a different type than thatspecifications for UHV as well as manufacturers’

experienced with the 500kV transformer. The newstudies on component models and prototype

issues discovered with UHV implementationtransformers made it clear that it was possible todemonstrated the significance of carrying out

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japandemonstration testing. While current UHV lines aremercury arc valves made in Sweden. In 1970,

operated at 500kV, there are new issues emerging

Electric Power Development Company continued

that did not occur previously, such as connected

prolonged

500kV transformers experiencing insulation failure

Japanese-made thyristor valves in place of mercury

due to lightning surges – investigation into thearc valves. Hitachi and Toshiba also took part incause of which showed that voltage on UHV lines

manufacturing conversion transformers. Technicalenters transformers with a longer wavetail than aissues with conversion transformers at the timenormal waveform, causing greater stress within the

included DC bias magnetism in the core due to thetransformer.

excitation current being ridden by the DC

demonstration

testingusing

component caused by differences in valve control
angle between each phase, increased noise due tothis, problems insulating the DC voltage, andfurther loss and temperature increase on harmonic
currents. The first thyristor valves in operation werein-tank, oil-immersed thyristor valves at the Tokyo
Electric Power Company Shin-Shinano Frequency
Converter Station. To allow compatibility between
Tokyo Electric Power Company and Chubu Electric
Photo

5.16.

UHV

Demonstration

Testing

Power Company, DC conversion was used between

Transformer at the Tokyo Electric Power Company

the 50Hz and 60Hz converter stations. The

Shin-Haruna Substation (1993, from left made bytransformers had a rated value of 187MVA,

Toshiba, Mitsubishi and Hitachi)

275kV/110kV.

Initially, the plan was to begin operation at the startof the 21st century, but that plan is now on hold and
it is unclear when UHV will be implemented, due
to the plateauing demand for electricity following
the bursting of the bubble economy.
5.8. DC Conversion Transformers and DC
Transmission
Photo 5.17. The First Frequency Converter
(1)

The

EmergenceofDC

Conversion

Transformer at the Electric Power Development

Transformers

Company Sakuma Frequency Converter Station

The first DC conversion transformers in Japan were(1964, made by Mitsubishi)

275kV, 368MVA and 353MVA transformers madeby Mitsubishi Electric in 1964 for the Electric(2) The Start of DC Transmission

Power Development Company Sakuma Frequency

DC transmission started in Japan in 1979 on the(52)

Converter Station (Photo 5.17). These used

ElectricPower

Development

Company

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology52

Hokkaido-Honshu connection. In 1978, Hitachi

substation for stabilising the network between

supplied the Hokkaido transformer, while Toshiba

Chubu Electric Power Company and Hokuriku

supplied the Honshu transformer. These had rated

Electric Power Company, interconnected on thevalues of 187MVA, 275/125kV, about the same assame frequency. Most noteworthy here is the DC

the Shin-Shinano transformer. At the second phase,link between Shikoku and the Kii Peninsula andthe DC voltage was raised ±250kV, while the DC

DC transmission aimed at providing Kansai

withstand voltage was doubled to ±450kV. Since

Electric Power Company with power generated by

DC insulation had different voltage distribution

Shikoku Electric Power Company and Electric

ratios from AC insulation for the insulating material

Power Development Company. While the plan was

and the oil duct, the insulation structure had to be

to initially operate at ±250kV, it was alreadydifferent from the existing AC insulation. Modelequipped for future ±500kV operation, with DC

testing was carried out on insulation structures withreactors, etc. In preparation for this, development

double the DC withstand voltage, followed bybegan on 500kV equipment, with manufacturers

actual production units. The second phase wascarrying out model testing on DC insulation andshipped out in 1979. Photo 5.18 shows the exteriorreliability checks carried out through long termof a 250kV DC transmission transformer.

experimenting at the Kansai Electric Power
Company Yamazaki Laboratory. Hitachi, Toshibaand Mitsubishi produced these transformers andreactors, supplying them in 1997-1998 (Photo 5.19).
The DC transmission transformers have rated
values of 872MVA, 500kV – the highest evercapacity for conversion transformers.
UHVTransmission
Line(i
Pl i )
500kV

Network Connection Facilities
Substations

Transmission

Photo 5.18. A 250kV DC Transmission Transformer
Hokkaido-Honshu
HVDC, 300-600MW(1993)

at the Electric Power Development Company
Hakodate Converter Station (1979, made by
Shin-Shinano Frequency Converter
Station, 300-600MW (1992)

Hitachi)Minami Fukumitsu Back to
Back Converter Station,
300MW (1999)

(3)

Power

Compatibility

and

500kV

DC

Transmission
Further

expansions

SakumaFrequency

were

made

to

enhancecompatibility between power companies. Fig.

Kii Channel DC
Transmission,
1400MW (2000)

Higashi-Shimizu Converter
Frequency
Station, 300MW
Converter Station, (1993)
300MW (2001)

5.3(53) shows a distribution map of converter
stations accompanying DC conversion in Japan.
There are two DC transmitters, three frequency
converter stations (including one that had not yet
started operating) and one back to back converter
53

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

Fig. 5.3. The Electrical System Structure in Japan

companies competed to reduce loss. Applying
technology developed for UHV to machinery built
for 500kV and under made it possible to reduce themass and simplify the structure of those machines;
accordingly, various companies competed to apply
this technology to reduce the mass and simplify the
Photo 5.19. A 500kV DC Reactor at the Shikoku
ElectricPower

CompanyAnanstructure of their products.

Frequency

Converter Station (1997, made by Mitsubishi)(3) Measures to Reduce Core Loss
Measures to reduce core loss started with the use of

5.9. Reducing Losshigher quality materials for the core, followed by
the use of magnetic-domain-refined silicon steel(1) Transformer Loss Evaluation

sheetsFor quite some time it has been normal overseas

mechanically by lasers, and the use of thinnerwhen operating a transformer in a network tosilicon steel sheets than the standard 0.35mm withcalculate the price of loss produced by thatthicknesses of 0.3mm, 0.27mm or 0.23mm.

transformer as an associated cost and add it to the

Structural changes included the use of step-lap jointpurchase price of the transformer when estimating

cores, in which the core junction takes a staircase

its value. While there are differences between load

pattern. Another effective method to reduce coreloss and no-load loss in this estimate, the estimates

loss is to reduce the transformer mass by reducing

increased after the 1973 oil crisis. For somethe dimensions of the insulation. The most effective

countries, particularly those that depended on

way to reduce core loss is to reduce mass of coreenergy from other countries, the price quadrupledmaterial. However, reducing the loss in the copper

to $7000/kW no-load loss, $3000/kW load loss.

wire is not very effective. Reducing core loss byThis meant the loss estimate had a greater

improving core materials has mainly been done inweighting than the price of the unit, resulting in a

Japan since the introduction of grain-oriented

situation in which the main competitive advantage

silicon steel sheets. The technological strength ofwent to how much the loss could be reduced by.

Japanese steel manufacturers has led the world with

withmagnetic

domains

markedout

the development of high grain-oriented silicon steel(2) Reducing Losssheets in 1968, the introduction of 0.23mm sheets

In the 1980s, the domestic market entered a time ofand the development of magnetic-domain-refined

long-term low growth due to changes in demandsiliconstructure.

manufacturers

manufacturers virtually have the monopoly on

intensified over the smallest of matters. Japan had

high-quality materials. Transformer manufacturers

not familiarised itself with loss price evaluation likewere quick to adopt these materials, giving them anoverseas and price was evaluated in terms of costadvantage against overseas competition. The

only. However, given this situation, companies

materials used today have around two-thirds thesoon learned that the amount of loss as well as costloss than in the 1960s, when grain-oriented silicon

was a key factor in gaining orders; the various

steel sheets were first used. Taking into account theCompetition

betweensteel

sheets.

Currently,

Japanese

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

54reduced loss from improvements in insulation

to implement. The use of transposed cables withtechnology and other factors in the materials used,thin conducting wires made it possible to reduce

it is around 50% better.

eddy current loss, which accounted for as much as
30% of resistance loss, by more than half at high(4) Measures to Reduce Load Losscapacity. Such improvements to insulation greatly

In contrast to core loss, improving materials has

contributed to workability and loss reduction.

little effect in reducing load loss. Reduction in load
loss is mainly achieved by reducing eddy current

5.10.

loss

Transformers

in

the

windings

through

the

use

of

multiconductor cables, containing several thin
conducting

wires

all

insulated

together,

Popularisation
andSoundproofing Measuresof

Low-Noise

Simplification

of

(54)

or

transposed cables, with an odd number of(1) Necessity of Low-Noise Transformers

conducting wires positioned in two rows and joined

The demand for low-noise transformers emerged

mechanically at a fine pitch. Other methods include

sporadically in the 1950s, but in very limited

mounting a magnetic shielding for stray load loss

circumstances. However, as society later became

occurring in the tank or inner structural materials,

more affluent, there were more sensitive reactions

narrowing the width of the iron materials, orto industrial pollution issues, including noise. Noise

creating a slit. Where transformers for export werereduction was first carried out on transformers at

expected to have very high loss evaluation, asecondary substations located near residential areas.

method was adopted of decreasing the current

In the 1970s, urban noise control regulations were

density and thereby reducing the resistance loss,

made stricter and even high-capacity transformers

even though the price of the transformer increased

at primary substations in the outskirts of urban

as the mass increased.

areas had to reduce their noise omissions at night to

It was possible to reduce load loss in machines such

45dB at the substation boundary line. Air-insulated

as 500kV substation transformers, which had amachines

single-phase structure and could alter the number ofswitchgear (GIS) in the 1970s, drastically reducing

windings in parallel, by applying technology

the land area occupied by substations. Since thedeveloped for UHV. The amount of copper wire

noise specifications imposed on transformers wereused in the 1000/3MVA transformers could beobtained by calculating backwards from the level atgreatly reduced by changing them from a two-main

the boundary, this meant even lower values thanleg structure into a one- main leg structure, but thisbefore, e.g. 60dB.

were

supersededby

gas-insulated

was less effective in other transformers. Existing55

insulation designs had concentrated on minimising(2) Low-Noise Measures and their Changes

potential

capacitance

Measures taken on transformers to meet thesewindings did not have a very workable structure;

specifications include surrounding the tank area

results from investigating potential vibration andwith sound barriers such as steel sheets, concrete or

failure mechanisms in windings made it possible toconcrete panels, or reducing the amount of noiseuse ordinary continuous disc windings at 275kV

generated through magnetic distotion of the core.

and higher, which was previously thought difficult

Other methods included reducing fan rotations tovibration.

High

seriesSurvey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanreduce the noise produced by the cooling system, or

5.20 shows the exterior of a 300MVA transformer

fitting the cooler with a soundproofing wind tunnel

operating at 60dB without a sound barrier.

lined with sound absorbing material.
While many ingenious methods were used to makeit easier to assemble transformer sound barriers

Tank Reinforcing
Materialaround transformers on site, foundation work andassembly required a lot of time and effort, which
did not match the course of action prescribed bypower companies at the time of keeping onsite
work as simple as possible.
During this time, work began on improving the

Directly Mounted
Soundproofing
Plate
Tank Side Plate

Transformer Tank

core material, which was a source of noise. Highgrain-oriented silicon steel sheets had better crystal

Fig. 5.4. Structural Diagram of a Direct-Mountedorientation as well as better magnetic andSoundproofing Plate

magnetostrictive properties and better tensile
strength from the insulating film. Accordingly, it

Air

Oil

could reduce the noise generated by the existing

Tank Reinforcing Material

grain-oriented silicon steel plates by 2-4dB. Thishas been adopted as the norm since the late 1970s

Solid-Bourne Vibration

to the present day. While step-lap joint cores werethese also reduce the disturbance to the magnetic
flux flow at the joint and consequently reduce theNoisemagnetic and electromagnetic vibration, which was
found to reduce the amount of noise by up to 15dB,

Tank Side
Wall(Vibrating
Body)

Soundproofing Plate(Compound Plates)
Resin

Highly EfficientSoundproofing Plateinitially used as a means of reducing no-load loss,

Frame-Shaped Added Mass

Thin Steel Sheetdepending on the circumstances. These were firstused in secondary substation transformers and thenbecame the norm for 30MVA transformers with nosound barriers. These were also used for highFig. 5.5. Detail of an Example Installation of acapacity and gradually increased in use, although

Direct-Mounted Soundproofing Plate

this meant poor core stacking workability. By using
this

in

conjunction

with

a

direct-mounted

soundproofing plate attached to the tank beam, or
combining it with a reduced magnetic flux density,
it was possible for even 300MVA transformers tooperate at low noise levels of 60dB without soundbarriers, thereby drastically reducing the amount of
onsite work. Figs. 5.4 and 5.5 show the structure ofa direct-mounted soundproofing plate(54). PhotoToshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

56reproduction of the factory product. In some cases,
the transformer capacity was equal to two or three
generators combined. Accordingly, designing andmanufacturing a product that would fit within thesize and mass constraints for transportation could
only be done by increasing the number ofpartitions; sometimes a single-phase unit would be
Photo 5.20. A 300MVA Transformer Operating at

split into two or three partitions. A 500kV, 680MVA

60dB without a Sound Barrier (Tohoku Electrictransformer manufactured in 1977 for the Kansai

Power Company Ishinomaki Substation) (1992,

Electric Power Company Oku-Yoshino Pumped

made by Hitachi)

Storage Power Station had a nine-part structure,with a single phase split into three partitions.

Thus, in recent times, large-scale sound barriers

Includingrequiring a lot of work on site are only used incomprised 12 partitions (Photo 5.21). By the 1980s,

specifically-designated low-noise circumstances.

both pumped storage power stations and substations

Generally, onsite work has been simplified throughfaced stricter limitations on transport routes due tothe use of direct-mounted soundproofing plates andthe rationalisation of freight transport, as well ascore structures or through magnetic flux density.

stricter size and mass restrictions for transportation.

theon-loadvoltageregulator,itWith an increasing number of substations being
5.11. Changes in Transportation Conditions

located in remote rural areas far from urban centres

andas well as growing difficulties with road transport,

the

New

Disassembled-for-Transport

Transformers

transportation costs rose significantly. In the eventof a fault with an existing transformer that meant it(1) Changes in Transformer Transportation

had to be returned to the factory for repairs, there

Conditions

were fewer and fewer means of transporting it.

There is a major difference between electricity use

Something had to be done to resolve this.

during the day and during the night. An increasing
proportion of electricity is generated throughpumpedstoragetocombatpeakloads.

High-capacity pumped storage power stations havebeen being built since the 1970s, while the greatest
issue has been the transportation of high-capacity
equipment due to the limitations imposed by thelocation of these power stations. At a time whenequipment reliability was a top priority for

57

transformers, it was unthinkable to adopt the old

Photo 5.21. A Transformer Transported in Nine

disassembled-for-transporttransformers

Partitions, a 680MVA Transformer for the Kansai

had to be transported in their factory-tested

Electric Power Company Oku-Yoshino Powercondition, with the onsite product an exact

Station (1977, made by Toshiba)

system;Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

(2)

The

New

Disassembled-for-Transporttransportation limitations, it also reduced the time

Transformers

required for onsite assembly, as well as other

The first endeavour to solve this issue wasbenefits. This system is likely to increase in use

undertaken by Kansai Electric Power Company andregardless of any future transportation difficulties.

Mitsubishi Electric. In contrast the previous
disassembled-for-transport system, they packed thecoils together in film using a structure thatprevented moisture absorption during disassemblyand onsite reassembly, thereby omitting any onsite
drying. Further ingenuity with the core provided astructure that was easier to dismantle andreassemble, while the use of a dustproof working
chamber meant that onsite assembly conditions
could match those at the factory. This provided a

Photo 5.22. A New, Integrated Three-Phase,

structure and working system that showed concern

Disassembled-for-Transport, 500kV Transformer atfor power companies’ emphasis on reliability. In

the1984, a 275kV, 300MVA transformer was supplied

Substation (1996, made by Toshiba)

to the Kobe Substation as a model case

Chubu

ElectricPower

Company

Seibu

(55)

. Thismove was later taken up by other power companies

5.12. Diagnosing Deterioration and Prolonging

and manufacturers, who worked on new core

Lifespan(56)structures,

madeimprovements

todustproof

working chambers, investigated the necessity ofIn the 1990s, amidst the slumped demand for

onsite field testing as well as what should be tested,electricity and the liberalisation of the electricity

and also brought out testing equipment. In 1994,

market in the wake of the burst of the bubble

the existing 500kV, 1000MVA transformer, which

economy, power companies starting trying to get

had comprised three single-phase structures, wasmore from their investments in power distribution

configured into a three-phase structure. As well as

facilities. One of the measures taken was to reduce

dramatically reducing transport costs, this also

expenditure by prolonging the lifespan of their

reduced installation space and loss, meaning it

transformers, many of which were set up during the

could benefit power companies. From then on,booming post-war demand for electricity and weremore and more power companies adopted this

now reaching the end of their 30-year lifespan.

system and it became the norm. Photo 5.22 shows

Specifically, they would calculate the remaining

an integrated three-phase, 1000MVA, 500kV

lifespan of the transformer and use it to the verytransformer. The adoption of this system meant noend. Despite a higher likelihood of damage to themore specialised railcars. It could be transported ontransformer, they would keep using it until thean ordinary truck trailer and could be transported

damage actually did occur. This was a dramaticfrom the factory or nearest port, meaning that thechange of direction from the previous approach oftime and labour required to operate special railcars

emphasising reliability. It became common to

was also no longer required. As well as eliminatingcollect insulating material from ageing transformers,

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

58specifically, the insulation from the winding

low average load factor resulting from their use as

thought to be the most degraded, determine thepeak load generators rather than base load

degreegenerators.

ofdegradation

by

the

degreeoftransformers

that

were

polymerisation and the tensile strength of the paper,

manufactured earlier on operate less efficiently andnote down the data and compare it to data fromare uneconomical; these are steadily being scrapped,

sampleswith an increasing number of facilities being shutofinsulationfrom easily

accessedcomponents inside the transformer, such as leads,

down.

and use the correlation between the two to simply

Meanwhile, with the previous emphasis on

determine the lifespan of the transformer andreliability, there is an excessive number ofcalculate the remaining lifespan. Power companies

substation transformers compared with those foundand manufacturers collaborated to standardise theoverseas. These are operated in such a way as toevaluation criteria for determining the lifespan of

avoid an overload even in the event of a breakdown,transformers; these were published in 1999

(56)

.

so the average load factor is lower than for power

Currently,

arestations. Even transformers that have reached their

beginning to be updated with the view that they

lifespan of 30 years have little degradation, so

would need to be updated anyway due to the highprovided there is no major change in electricity

usage load factor on them since the 1970s and also

demand, these are expected to continue being usedin light of the fact that they can then be expected tofor a long time, while being checked for

operate for another 30 years. However, fossil fueldegradation.

nuclearenergytransformers

power transformers are not being updated, due to a

59

Further,

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

6. echnology Systematisation

6.1. Pre-War Transformers

natural cooling was sufficient, high voltage andhigh capacity required two stages of cooling:(1) Transformers in the Early Developmental

cooling the interior and overall cooling of the entire

Periodtransformer. The natural convection of the oil was

To this point, we have examined the course ofused to cool the interior, but heat radiation from thetechnological progress on transformers stage bytank alone was not sufficient for overall cooling.

stage. Let us now systematically examine theSince radiators had not yet been developed, atechnology in each period.

water-cooling method was introduced, with water

The early developmental period began by copying

pipes built into the tank. Radiator cooling started

technologyonwith the development of the radiator in 1916, buttransformers began about 10 years after thissince the welding of the laminate was by no means

copying started. Initially, electricity distribution

perfect, there were often oil leaks, meaning thisstarted out at low voltages of around 1000V andmethod was not yet widely adopted. In the 1920s,

was used for lighting. As other uses for electricity

improvements in cooling designs and radiator

began to develop, transformers began to be adapted

production technology saw an increase in use offor higher voltage and higher capacity. While they

self-cooled transformers; by the late 1920s, Japan

were air-cooled and air-insulated to begin with, oil

had made a transformer with world-record-breaking

was soon proposed as a medium for insulation andcapacity. After that, as further progress was madecooling and mineral oil was put to use. However,on capacity, forced-oil systems became morecore materials at the time consisted of laminatedcommonly used to cool the interior, forcibly

mild steel sheets, which carried the problem ofcirculating oil with a pump. While Germany andsignificant loss, as well as properties that change

other countries had long used forced-oil, forced-air

over time to add to the loss. This problem wascooling systems, Japan did so much later in 1926.

significantly improved with the invention of silicon

The cooling unit system commonly used today was

steel sheets in 1900 by Robert Hadfield of the

adopted in the 1940s.

fromoverseas.

Development

United Kingdom; these were industrialised andused in transformers in 1903. High capacity(2) Post-War Success of the Transformer

transformers made rapid progress in Japan with the

The Showa Period saw in the age of transformer

import and application of silicon steel sheets indevelopment. This was triggered by Japan’s first1910.

domestically-produced 154kV transformer, broughtTechnical

manufacturers

cooperation

beganaroundwiththisoverseastime

andout in 1926, three years after the first imported ones.

technology developed overseas began to be

Following the continued successful operation of

introduced to Japan, accelerating the progress of

this transformer, overseas imports dropped off as

development of transformer technology in Japan.

domestic

Another issue with high capacity was cooling.

predominance. Further development of electricity

While at first, transformers generated little heat andon the Korean Peninsula played a major role in the

products

gainedalmostexclusive

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

60spread of transformers. Given the success of the(3) Lightning-Protected Design and Impulse

first large-scale power generation projects, otherTesting

power generation projects steadily got under way,

A major technical consideration in the pre-war era

with some record-breaking products manufactured.

was how to protect transformers against accidents

One of these was the implementation of the firstfrom lightning surges. Following a publication in

extremely-high-voltage 220kV transformer in the1915 by German engineer Karl Wagner stating that

East, a 220kV, 80MVA transformer completed in

the behaviour within a transformer in response to a1939. Later, a 100MVA transformer was produced

surge can be interpreted through travelling wave

– equal to the highest capacity transformer in thetheory in the same way as power lines, studies were

world at the time. In some respects, Japanesecarried out in many countries on lightning surges

transformer production technology had reached

and windings. These studies were carried out inworld-class level. However, although the level ofJapan as well, mainly at universities. Since thetechnology at the time might not have been a far

areas near the ends of the transformer windings

cry from world-class, given the incidents of melted

were often the parts that were damaged, a methodcores, inadequacies in production technology andwas adopted in Japan around 1920 of reinforcing

quality control, the strain of pushing to the limit

the insulation around those areas, while otherand producing a record product started to show.

countries developed their own particular windings

The first high-capacity transformers of 10MVA andto withstand surges. However, unlike the West,over were disassembled for transport, having nowhich had a directly-grounded neutral point, Japanother means of transportation. They were thenused high resistance grounding; accordingly, thereassembled and re-dried onsite. This meantvoltage distribution from lightning surges would beassemblythedifferent. These windings were not adopted as it

high-capacity transformers on the Korean Peninsula

was thought that they could not be. However,were disassembled for transport, and the lack ofmanufacturers later took potential distribution

sufficient work management and drying during

measurements and confirmed that surge-proof

onsite assembly was thought to be one cause of thewindings and partially shielded windings did

melting cores. While assembled transportation got

actually improve potential distribution; theseoff to a slow start due to more limited rail transport

windings were gradually introduced in the 1930s.

constraints than in the West, in the late 1920s,

However, the transformers at the time using thisassembled transportation began to be the trend,

design were not actually proven to have any special

with special railcars that made effective use of thelightning resistant properties. In the 1920s, debate

transportation limitations as well as methods tobegan in the United States on the issue of insulation

reduce the mass of the load transported bycoordination between power lines and transformers,

substituting oil with nitrogen. In this way,etc. In the 1930s, GE started carrying out the firsttransformers up to 39MVA had been transported by

impulse tests with the aim of finding proof on thisrail before the war.

issue. Impulse testing later became standardised in

took

several

days.

All

of

the United States; inspired by this, Japan also
formed a standardisation committee and published
its own standards, following much discussion, in61

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

1945, just before the war ended. Impulse testing
was first carried out in Japan in 1937 on a 154kV(6) Setting Standards

transformer

Japanese

Reliability-based standards began in 1922 with theGovernment Railways. This had a winding

setting of Standard JEC-9 for electrical equipment

structure with reinforced insulated ends andincluding rotating machines. Standard JEC-36 fordemonstrated

transformers was established in 1934, thereby

for

the

what

was

validity

then

of

the

insulating

structures of the time.

ensuring uniform quality for transformers as aindentproduct.

Japan

Standard

JES31

was

(4) On-Load Tap Changers

established in 1926 for pole-mount transformers,

Another technical topic of this period was thestandardising their characteristics, structure, etc.

development of on-load tap changers. On-load tap

JEC-36Z was issued as a wartime standard to easechangers, which changed taps during operation toup the temperature restrictions of JEC-36 during

maintain a fixed voltage to balance the changes in

the war. JEC-110 on impulse testing was issued justthe load, were developed around the mid-1920s to

before the end of the war, as mentioned previously,

temporarily bridge a different tap position while thelayingtap is changing. A system of using a current

commencement of extremely- high-voltage power

limiting reactor to suppress cyclic current duringtransmission.

theframework

for

the

post-war

this process was first developed in the United States,
followed by a method developed in Germany using(7) Systematisation of Pre-War Transformer

resistance. The American current limiting reactor

Technology

system was first adopted in Japan, with the firstThe

product built in 1930. The next few years after thattechnology is shown in Fig. 6.1. Figs. 6.2 and 6.3

saw rapid development and the implementation ofshow the timewise trends in technology andhigh capacity, with voltage regulators introduced in

production in terms of the major transformer issues

1933 to control the flow of electricity. The

of

German-styleenvironment and accessories. Fig. 6.2 shows theresistancetapchangers

were

implemented in Japan in 1935.

above

reliability,

outlinehighofpre-warcapacity,transformer

high

voltage,main technology developments for each of theseissues and also notes the technological progress of(5) Non-flammable Transformers

the period. The numbers to the top right corner of

Polychlorinated biphenyl (PCB) was developed in

the balloon boxes correspond to the numbers on the

the United States in the 1920s as a non-flammable

photographs in the main text. Fig. 6.3 shows theinsulating oil. This was later produced in Japan andtimewise trends in major technologies. The shaded

first used in a transformer in 1940. However, theareas represent technologies that were used

war ended without it coming into widespread use

concurrently with other technologies but mainly

due to the issue of cost. While dry-typeused in high-capacity transformers. Areas marked

transformers

aswith diagonal borders indicate that it took some

non-flammable transformers, they were also nottime to switch to these technologies. Table 6.1

widely adopted due to cooling and voltage

shows the development period for the main

limitations.

technologies and products.

had

also

long

been

used

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

62

(Fig. 6.1. Systematisation of Transformer Technology (from Copying to Domestic Production))

63

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

(Fig. 6.2. Transformer Technology Trends (from Copying to Domestic Production))

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

64

(Fig. 6.3. Timewise Trends in Main Technologies)

65

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

Table 6.1. Main Transformer Technologies and Products (pre-1950)
Pre-1900

1900s

1910s

1920s

High
reliability

TestingStandards

High
capacity- JEC-9 electricalequipment
standard
regulations
established 1922
- Transformer
standard JES-31
issued 1926

Transformer
production starts
1893

Oil-immer
sedtransformer
production
starts 1900
- 1500kVA
transformermanufactu
red 1909

Core

CoolingModesandmethodsoftransport- Air
cooling1893

Oil-immer
sed
self-coolin
g 1900- Use ofwater
coolingaround1909- Start ofuse ofcore-typefor high
capacity
1919- First transformer
over 10MVA
produced 1924

- Start ofuse ofsiliconsteel
sheets1910- Start of domestic
production ofsilicon steel sheets
1922- Start of use ofdomestically-prod
uced silicon steel
sheets 1928
- Use offorced-oil,forced-air cooling1926- Self-coolingused on highcapacity 10MVA
1927- 10MVA
transported by sea
with interior
assembled 1926
- 7.5MVA
transported in oil
1928

1930s
- Potential
distribution
measurements
1933- Impulse voltage
generators 1934
- Impulse testing
implemented
1937- JEC-36
established 1934
- Wartimestandard JEC-36Z
issued 1938

- Forced-oil,water-cooled
30MVA 1930

1940s

- JES onmineraltransformer
oil issued
1941- Impulse
testing
standard
JEC-110
issued 1945

- First use of
bankedradiatorsystem 1940
- First use offinned unitcooler 1941
- First use ofunit-cooler
1948- 22MVA sent byrail immersed inoil 1932- First use of
nitrogenimmersedtransportation

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

66

1935
- Concave railcar
produced 1936
- Assembled
transportation by
special railcar
1939
High
voltage
Winding
method- First use oflightning-protecte
d winding
structures 1928

Insulationmaterial

Insulation
technology- Start ofuse ofvacuumdrying1909- Start ofimport anduse oftransforme
r oil 1911
- Start ofdomestic
productionoftransforme
r oil 1913
Extensivestudies on
potential
vibrationaround1916- First use ofsurge-proof
windings 1932
- Start of use ofpartially-shielded
windings 1939

- Use of flange
collar 1928

- First 154kV
produced 1926

- First 220kV
1939

Environment
Low-noise
structures
Fire-proofing

AccessoriesOn-loadtapchangers

Conservat
67- First use ofmultiplecylindricalwindings
1940- First use ofneutralinsulated
method1948

Non-flammable syntheticoil (PCB)transformer
1940- Firstinducedvoltageregulator
produced
1912- First use

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan- First on-load
voltage regulatingtransformer 1930
- Resistance-type
on-load tapchangers
introduced 1935
- First use of

ors

of
conservato
rs 1914Coolers,
radiators
Bushing
Typicalproducts- 11kV,
150kVAfor Kofu
Electric
1905- 44kV,
1500kVA r
forYokohama
Electric
1909- 66kV,
2500kVAr for
KyushuHydroelectric 1912- 500kV
testingtransforme
r for the
Universityof Tokyo1915- 110kV,
4400kVA
forInawashiro
Hydroelectric 1917

nitrogen-filledconservators
1942- First condenser
bushing 1926
- 77kV,13333kVA r for
the Nippon
Electric Ozone
Substation 1924
- 154kV,
6667kVA for the
Nippon Electric
Gifu Substation
1926- 140kV, 22MVA
self-cooled for theShowa ElectricYao Substation
1928- 450kVA LVR
for Chugoku
Electric Power
Company 1930
- 140kV, 39MVA
assembled-transp
orted for Tokyo
Electric Light
Company 1939
- 220kV, 80MVA
for Changjin
River
Hydroelectric
1939- 230kV,
100MVAfor Yalu
River
Hydroelectric 1940Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

686.2. Post-War to 1975

Kingdom were soon developed and incorporated
into Japanese technology; these were late used as a(1) 275kV Transformers and Introduction of

powerful tool for changing to higher voltage. These

Overseas Technology

windings made particularly well-insulated windings

The first post-war technology epoch was thewhen combined with the newly-developed high-air

completion of the Kansai Electric Power Company

tight wire insulating paper. Other completely

Shin-Hokuriku Trunk Line 275kV power line andoriginal Japanese windings, such as damper-shield

the completion of the transformers for that line.

windings, were also developed and contributed to

These transformers were subject to impulse testing

the change to higher voltage. By adopting thisunder the new regulations; to achieve this, eachtechnology, the 275kV transformer introduced incompany used1952 could have even more compact insulation inits

accumulationofpre-wartechnology and also incorporated the latest

thetechnology.

windings with transposed cables made it possible toNewtechnologies

included

1960s.

Combining

multiplecylindricaland

use them as high-voltage windings in high capacity

cylindricaltransformers; from the 1960s to the 1970s, thewindings) developed in Europe, form-fit tankultra-high-capacity 1000MVA transformer was the

structures and core-erecting equipment. In 1952,

prized goal.

main-gap-filling
non-resonant

insulating
windings

structures(multiple

technical cooperation with overseas manufacturers

69

resumed, having been suspended during the war,(2) High Capacity Substation Transformers andbringing with it a wealth of new overseas

LRT

technology that had been developed during andIncreased demand for electricity in the 1950s led tosince the war. This included a lot of technology stillhigh capacity transformers at primary substations.

used today; for example, grain-oriented silicon

Assembled transportation by special railcar became

steelcores,

the norm, since it meant that these could bevapour-phase-drying, forced winding cooling andinstalled on site quickly and easily. This was madetransposed cables. The grain-oriented silicon steel

possible through core materials and structures, as

sheets developed by US company Armco played amentioned previously, as well as other the use ofmajor role in the later downsizing of the core andthree-phase, five-limb cores, the emergence of

proved to be very useful in ushering in highspecial freight cars with higher carrying capacity

capacity transformers. Their magnetic properties

and the development of special three-phasewere superior to those of the hot-rolled T-grade

transformers. Around the mid-1950s, assembled

cores of the time; capable of use at a higher

transportation

magnetic density, they made it possible to downsize

transformers as well; this was assisted by

the core in inverse proportion by 1.3/1.7 (around

improvements76%). The transition to grain-oriented silicon steel

structures resulting in insulation taking up far lesssheets was complete by around 1962, when aspace in the winding. Addoption of gradeddomestic version appeared on the market.

insulation of the neutral point on the 154kV system

In terms of insulation technology, high series

cannot be overlooked either. As a result, while

capacitance windings developed in the United

pre-war railcar transport limitations had meant the

sheets,frame-shaped

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

was

to

carriedout

forlightning-protected

275kV

windingtransportation of nothing greater than a 154kV,

wrapped

39MVA transformer, by 1963 it was possible toaluminium coolers appeared with fins extrudingtransport a 275kV, 300MVA transformer for thefrom aluminium pipes – these became the norm.

Chubu Electric Power Company Nishi-Nagoya

However, there was a transition in the 1970s to iron

Substation.

coolers with heat sinks fitted to iron tubes, due to

While it became the norm during this time forproblems with aluminium coolers corroding from

distribution transformers to have on-load tap

salt-air damage, particularly at coastal powerchangers, there was a growing demand for them atstations, as well as the fact that in the event of a

primary substations as well. The on-load tap

transformer fire, the aluminium would weaken withchangers (LTCs) at the time were mainly thethe heat and damage the adjoining banks as well.

American-stylesome

When urban underground substations began to beGerman-style resistor type ones were also used.

built at the end of the 1950s, a cooling system was

Two systems were used concurrently: connecting

developed that had cooling towers in which water

an on-load voltage regulator in series with thewould circulate and be cooled by the outside air.

transformer, or using load ratio control transformers

This system later became the norm. In 1960, the(LRTs), with a tap winding inside the transformer

first 154kV, 100MVA high capacity transformer

itself. However, in the 1960s, there was a growing

was introduced to an urban underground substation.

trend to use LTCs at primary substations with the

Later, in the 1970s, the introduction of the 275kV

LTC built into the transformer tank; the demand forsystem in urban centres saw the establishment of

LRTs that could be transported together with the

300MVA high capacity transformers. Special

main transformer itself grew as the demand for highthree-phase type transformers were adopted forcapacity transformers grew. The reactor type wasunderground substations due to service accessdeemed unsuited to this demand, while the LTC

limitations, ceiling height limitations and roadmade by the globally-renowned German LTC

transport limitations. Various ingenious approaches

manufacturer MR was deemed to be the most suited

also had to be used to assemble them.

to it. Three transformer manufacturers introduced

Self-cooling

this product through technical cooperation. Sincetransformers of 50MVA or lower. As their scope ofthen, models developed by MR have been the main

application expanded, the existing oval tube shapeones used in Japan.

used to increase the radiator space factor was

reactortype,

althougharound iron pipes; insystemswerethe 1960s,

mainlyusedonreplaced by a flat tube shape in the early 1960s.
(3) Changes in Accessories

This increased the effectiveness of the fans where

Water cooling was the main transformer coolingfans were used, making it possible to increase thesystem before the war. In the 1950s, finned air

rated capacity of the air-cooled type transformers.

coolers began to be fitted directly onto transformers.

In the 1950s, the existing open-type conservators

These were combined with pumps to form coolingbegan to be replaced in standard use byunits. Forced cooling systems were introduced,

nitrogen-filledforcing oil directly into the winding from the pump;

improved the issue of oil oxidation. However, athese later became the norm for high capacity

diaphragm system developed in the United Statestransformers. Coolers first had copper ribbons

was introduced in the 1960s, using a rubber film toconservators,

which

greatly

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

70separate the oil and the air. Around the mid-1960s,

Demandfor

non-flammabletransformers

atfollowing domestic production of these rubber

secondary substations in urban basements appeared

films and validation of their transmission properties,

around the mid-1950s, albeit sporadically. This

the diaphragm system took hold as the norm,

continued until the 1970s, when a pollution issue

contributing greatly to improving installation spacewith a 60kV, 10MVA PCB transformer resulted in

and increasing the analytical precision of gas-in-oil

the banning of the production or use of PCB

analyses, which later became the norm.

transformers.

(4) Response to Environmental Issues(5) Breaking Away from Introduced Technology

Let us finally touch on environmental issues. In

With the growing demand for electricity in the1952, the first low-noise-specification transformer

1960s, a number of high-capacity thermal power

was produced for use in an underground urban

stations were built in various places. Most of thesubstation.

This was a 15MVA distribution

primary equipment, such as power turbines andtransformer. In 1956, a high-capacity 110MVA

generators were imported, while the secondary andtransformer was produced for the Tokyo Electricother lesser equipment was Japanese. PrimaryPower Company Toda Substation (Photo 6.1). At

transformers, however, were Japanese, because by

the time transformers were not bound by urban

this time Japanese transformer technology wasnoise restrictions and so the demand for low-noise

equal to that from overseas, Japan having actively

specifications was sporadic. However, there wascombined new post-war technology with its

demand in special circumstances, and low-noise

pre-war technological capabilities.

transformers with soundproofing structures and

The greatest technical challenge in producing

transformers with concrete sound barrier structurestransformers for high-capacity thermal power

began to appear in the early 1960s. In any case, an

stations was local heating of structural materials

awareness of environmental issues can be said todue to leakage flux from the winding. For example,

have emerged in the early 1950s.

the flange joining the upper and lower tanks would
heat up, burning the paint. Nobody overseas hadenough experience for this issue to be solved
through technical cooperation, so Japan had tosolve the problem for itself. Improvements weremade through trial and error, such as the range andmethod of attaching the electromagnetic tankshielding. In some cases, other problems occurred,
such as a build-up of flammable gas on site.
However, the issues were gradually solved,

Photo 6.1. The First High-Capacity, Low-Noise

resulting in a store of technology able to be used on

Transformer, a 110MVA Transformer for the Tokyohigher capacity transformers.

Electric Power Company Toda Substation (1956,

It also became standard practice to transport

made by Toshiba)

assembled substation transformers by rail. The
insulation had to be compact for the contents of the71

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japantransformer to fit within the rail transporttransformers, which had passed factory testing,limitations. This was difficult to achieve withduring initial operation in the United States. In

introduced technology, which mainly came fromthose days, factories working with insulation andthe United States, (as there was a trend towards

windings were not partitioned off from outside andstandardisation and reducing production costs

people could come in or out without any special

rather than economising materials by compacting),

precautions. It was difficult to re-educate workers

so Japan had to make its own improvements. Thus,

who had been reared in this environment, and it

independent

becametook more than ten years to produce a transformer

established and there was a gradual shift away fromfree of partial discharge. Experienced advice fromtechnology imported from overseas.

overseas test witnesses also contributed greatly to

Japanesetechnology

theachievementofpartial-discharge-free(6) Development of 500kV Transformers

transformers. For example, insulation moisture

Once the rigorous demand for electricity leading

management and oil treatment technology were

into the 1960s had been met, manufacturers started

based on information they provided, and havedevoting their efforts to exporting to keep

become the current norm in Japan. While it took athemselves in work. It had been more than ten years

lot of effort to achieve partial-discharge-freesince the 275kV supply voltage had beentransformers, there was no option to solve it

introduced in Japan; 500kV was considered to bethrough technical cooperation, so Japan had tothe next level of voltage. Manufacturers started

solve it on its own.

testing models in preparation for that.
Various different countries overseas had developed(7)

SystematisationofTechnology

fromplans for supply voltages of 500kV or 400kV; some

Post-War to 1975of these were being planned by national or state

The above outline of transformer technology frompublic corporations and offered a chance forthe post-war period to the domestic development of

unproven manufacturers to make bids. Japanesethe 500kV transformer in 1975 and the transition

manufacturers all placed bids and successfully

away from overseas technology is shown in Fig. 6.4.

received orders for large quantities of 500kV or

Fig. 6.5 shows the timewise trends in the main

400kV transformers from Canada, the United States,

technologies and products for each of the main

Australia, Mexico and other countries. Thesetransformer issues and also notes the technologicaltransformers had to have partial discharge testdevelopment and progress of the period. Table 6.2

specifications, which had been brought in after ashows the development period for the mainseries of insulation breakdowns in some 500kV

technologies and products.

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

72

(Fig. 6.4. Systematisation of Transformer Technology (Breaking Away from Overseas
Technology))

73

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

(Fig. 6.5. Trends in Transformer Technology (Breaking Away from Overseas Technology)
1of2)
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

74

(Fig. 6.5. Trends in Transformer Technology (Breaking Away from Overseas Technology)
2of2)
75

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

Table 6.2. Main Transformer Technologies and Products (1950 onwards)
1950s

1960s

1970s
- Adoption oftank flange
reinforcing
structures 1974
- Developmentof automaticgas analysis
equipment
1977

Standards- JEC-120
established1952- Partial
discharge
test
introduced
1965- Switching
impulse test
introduced
1966- Gas-in-oil
analysis usedin testing1967- Acoustic
coronalocationtechnology
established
1967- JEC-168
established
1966

High
capacity- Use ofmagnetictankshielding1952- First use ofgrain-oriente
d silicon
steel sheets
1955- First use of
three-phase,five-legcores 1955
- First use offrame-shaped cores 1956
Core-erecting equipment
established1958- Core plate
processing

High
reliability

TestingCore- Use ofelectromagn
etic tankshielding
1963- Use ofbound cores
1965

1980s
- Establishment ofseismicproof
design fortransformer
bushing 1983

1990s
- Transformer
deterioration diagnosis
guidelines 1999

- Gas-in-oil analysis
diagnosis guidelines
1999- Methods for
managing flow
electrification 1999

- JEC-204
established1978- Regulationsforseismicprooftransformer
design 1978

- Gas-in-oil
analysismaintenancecriteria established1981- First use ofhighgrain-oriented
silicon steel
sheets 1972
- No-bakecores become
the norm 1975

- GEORG’s
automatic core
cutting machine
introduced 1980
- First use ofmagnetic-domain-r
efined silicon steel
sheets 1982
- First use ofstep-lap cores 1984
- First use of corelegs automatic
loading equipment
1985- JEC-2200
established 1995

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

76

CoolingModesandmethodsoftransport

line
constructed1959- First use offorcedwindingcooling 1956
Developmen
t of cooling
tower watercoolingsystem 1957
- First use ofform-fittanks 1951
- Tanktransported
on its side1951
- First use of
specialthree-phasetransformers
1955- Schnabelcars
produced1955- First use of
a floating
crane 1956

High
voltage

Winding
method77- Use ofmultiplecylindricalwindings fortransformers
1951- First use of
dampershieldwindings
1954- First use oftransposed
cables andmulti-conduc
tor cables
1954

Transformers with inbuilt
LTCs
become thenorm 1963
Transformer
built with six
partitions fortransportation 1968- Air pallettransport
methodintroduced
1975
Transportationof 500kV
transformers
with main
cover onbecomes thenorm 1977- Siteinstallationtransportation
using air pallet
bearings 1978

- First use of new
disassembled-for-tr
ansporttransformers 1984

- First500kV
transformer
produced
1967- 500kVtransformer
produced forthe domestic
market 1971
- UHV test
transformers
completed1978- First use ofheat-sealedtransposed
cables 1975
- Wider use ofcontinuous discwindings for
EHV 1975- UHV technology
applied totransformers of
500kV and under1981- First use of
CC shielded
windings
1966- Large-scalevertical
winding
machines
introduced
1966

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan- UHV field testing
equipment completed
1993

- First use ofhigh seriescapacitancewindings
1956
Insulationmaterial

Insulation
technologyEnvironment
Low-noise
structures- First275kVtransformer
produced1951- First use of
main-gap-filling
structures
1951- First use of
induction
heating
dryingmethod 1951
- First use ofelectrostatic
shieldingsystems1951- First use ofvapor phasedryingmethod 1956

- Low-noisetransformers
produced
1952- Low-noisetransformers- First use ofoil-immersed resinadhesiveinsulation
cylinders1960- First use ofcrêpe
insulation
paper 1960
- First use of
paper woundsoft copperand flexible
copper wires
1960- First use ofheat-resistan
t insulation
paper 1962
- First use ofhourglassinsulation
1962- First use of
E-typeinsulation
1966- Moisturecontrol of
insulationmaterial
introduced
1967
Low-humidity,
air-condition
ed cleanrooms
introduced
1967- Low-noisetransformers
producedwithconcretesound- Use of highdensitypressboard
1972
- New
insulating
materials
become thenorm 1975- First use of
BTA-addedtransformer oil
1980- First use of
low-dielectric-constant pressboard
1989- Volume
theorysystematisation
1971- Flowelectrification
phenomenon
solved,prevention
technology
established1976- Magnetic
field analysis
and potential
vibration
analysistechnology
established1976- Study on various
properties ofcomposite
insulation 1980
- ZnO arresters
used in oil toprotect tap
windings 1982

- Panel-typesoundproof
tanks used
1970
- Noise control
guidelines- First use of highly
effective
soundproof panels
1981- Development of
low-noise

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

78

produced
with soundbarrierstructures
1957
Fire-proofing

AccessoriesOn-loadtapchangers

Conservat
ors

Coolers,
radiators

Bushing

Typicalproducts

79- 275kV,
99MVA
transformer
for theKansaiElectricPower
Company
Hirakata
Substation
1951- 110MVA
low-noisetransformer
for thebarriers 1961

issued 1977

high-capacitytransformers withno soundproof
panels 1984

- First gas
insulatedtransformers
produced
1967- Gas insulatedtransformers
used PET film
produced 1978

- Liquid-cooled
gas-insulated, highcapacitytransformers
produced 1989

- First use of
hot line oil
purifiers
1960
- LTC
technical
cooperation
begins withGermancompany
MR 1963- First use ofdiaphragm
conservators
1960- First use of
double-tube
watercooling 1964
- Use of275kV
cable-connec
tedtransformers
1960
- Dry
condenser
bushing
production
begins 1964
- 154kV,
100MVA
undergroundtransformer
for theTokyo
ElectricPower
Company
ChiyodaSubstation
1960- 275kV,
300MVAtransformer- Gas-cooled,
gas-insulated highcapacity transformers
completed 1994

- First use of MR
new series LTCs
1980
- First use ofgas-insulated LTCs
1982
- High-capacity,
gas-insulated LTCs
completed 1989

- Use of highly
efficient FRP
fan coolers
1979- Development ofvariable speed
cooler control 1982
- First use ofpressboard in-oil
spacers 1984

- 500kV,
333.3MVA
transformers
for the Tokyo
Electric Power
Company
Shin-Koga andBoso
Substations
1971- 275kV,
1100MVA
transformer for
the Tokyo
Electric Power

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan- 765kV,
800/3MVA
transformer for
Venezuela 1982
- 275kV, 300MVA
newdisassembled-transport-typetransformer for theKansai ElectricPower Company
Kobe Substation
1984- 154kV, 200MVA
liquid-cooled,- 275kV, 300MVA
liquid-cooled,
gas-insulatedtransformer 1990
- 300MVA, 60dB
transformer with nosoundproof panel for
the Tohoku ElectricPower Company
Ishinomaki Substation
1992- UHVdemonstration
testing transformer for
the Tokyo ElectricPower Company

TokyoElectricPower
Company
Toda
Substation
1956- 154kV,
75MVA
transformer
with inbuilt
LTC for the
Tokyo
ElectricPower
Company
Kuramae
Substation
1959- 275kV,
270MVAtransformer
for the
Chubu
ElectricPower
Company
Shin-Nagoya
Power
Station 1959
- 275kV,
264MVAtransformer
transported
assembled
for theElectricPower
Development Company
Nishi-Tokyo
Substation
1959

with inbuilt
LTC for the
Tokyo
ElectricPower
Company
Higashi-Tok
yo
Substation
1965- 275kV,
680MVAtransformer
for theTokyo
ElectricPower
Company
Anegasaki
Power
Station 1966
- 500kV,
200MVAtransformer
for Canada
1967- 66kV,
3MVA
gas-insulatedtransformer
for Daiichi
Life 1967

Company
KashimaPower Station
1973- 275kV,
450MVAtransformer
transported byrail for the
Chubu ElectricPower
Company
Sunen
Substation1974- 500kV,
1100MVA
transformer for
the Tokyo
Electric Power
Company
Sodegaura
Power Station
1974- 66kV,
10MVA
gas-insulatedtransformer for
the Japanese
National
Railways
JoetsuShinkansen
1978

gas-insulatedtransformer for the
Tokyo ElectricPower Company
Asahi Substation
1989

Shin-Haruna
Substation 1993
- 275kV, 300MVA
gas-cooled/insulatedtransformer for the
Tokyo Electric Power
Company
Higashi-Shinjuku
Substation 1994
- 500kV, 100MVA
newdisassembled-transport-type transformer for
the Chubu ElectricPower Company Aichi
Power Station 1994

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

806.3. Development of Independent Technology

the appropriate configuration of insulation, made it

since 1975

possible to produce UHV transformers with twice
the voltage of the existing 500kV transformers(1) Overcoming Flow Electrification and UHV

while keeping within the same transportation

Technology

limitations. With UHV implementation delayed,

As discussed in the previous section, Japanese

this technology was put to use in transformers oftechnology capabilities rose swiftly to meet the

500kV and under, contributing to a major reductionneed to develop technology that addressed thein the resources used on these transformers. In lightmajor issues of high voltage and high capacityofduring this period.

transformers at this time and power companies

However, amidst this, there were issues withfocusing more on reliability given the demand for ainsulation breakdown due to flow electrification inreliable power system in a computerised society,the early domestic 500kV transformers. This wasthere was a growing demand for transformers to becaused by the design of the oil channel, based ontransported with the main cover in place, despite

superficial trust in imported technology rather than

the first 500kV transformers having usually been

independentwhen

transported with a temporary transport cover on,

producing high-capacity, high-voltage transformers,

which was then replaced with the main cover.

which went beyond the scope of anyone’s previous

Meanwhile,

experience. It may sound like an excuse, but at thecompanies meant that special allowances were notime no technicians anywhere in the world werelonger made for products such as transformers

aware of the issues with frictional static electricity

being

within transformer: a fact that those who first

resulting in more limited transportation conditions

caused the problem may take some comfort in. It

with smaller dimensions than before. To meet these

took over two years of systematic investigation torequirements,

solve this issue and propose countermeasures. A

rationalisation was used to reduce dimensions ofkeen sense of the importance of back-to-basics

the transformer; transportation with the main coverdevelopment was quickly adopted during thison then became the norm.

ground-up

investigation

theinsulation

breakdowns

rationalisationtransported

the

under

with

of

the

special500kV

railwaylimitations,aforementioned

insulation

process, but the lesson learnt ensured later success81

in developing UHV transformers and developing(2) Development of Underground Substations

and implementing the world’s first high-capacity,

With the increase in urban electricity consumption,

gas-insulated transformers.

extremely high voltage power began to be broughtThis period is an age of major developments inin from outer lines into city centres and thenJapanese transformer technology. In the late 1970s,

supplied to secondary substations. Power cables

research was carried out on in-oil electricalwere used to convey power into city centres,

discharge mechanisms, going back to the basics ofeventuallyforming

networks

oil insulation in response to the severe rail transport

substations

furnishedwithlimitations unique to Japan. This resulted in theundergroundsuccessful development of compact, reliable,

switchgear contributed greatly to the spread ofhighly-insulated structures, which, combined with

these

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanoflarge-scale

275kV,

300MVAtransformers.

undergroundsubstations.

Gas-insulated

A

specialthree-phase format was the norm for transformers

the previous 10MVA to 30MVA as well as

in these underground substations. However, special

self-cooled transformers; these hurdles were cleared

three-phase transformers had less scope forwith the use of more effective winding cooling andexpansion than normal in the event of an internalhighinsulation breakdown. The larger the network, thegas-insulated transformers with a gauged pressurelarger the fault current and there was concern thatof 0.11-0.14MPa are not subject to the regulations

oil would leak from the weakest point – the tankon high-gas-pressure vesells (maximum pressure offlange – and cause a fire before the fault current

at least 0.2MPa) and are currently used for low

could

were

capacity uses, they are being manufactured withandincreasing

capacity,withmanufacturers jointly deciding on disaster-prooftransformerfor

Tohokustructures for underground substation transformers

Company Yanaizu-Nishiyama Geothermal Powerand making appropriate alterations to existingStation produced in 1994 as having the highest

transformers. Meanwhile, research continued into

capacity thus far (Photo 6.2).

beisolated.

investigated,

withCountermeasurespower

companies

thermalinsulation.

the

While

low-pressurea 161kV,

68MVA

Electric Powerthe 1980s on the possibility of a non-flammable,
high-capacity,

gas-insulatedtransformer

andvarious methods were developed.
As cable networks expanded, there was anincreasing demand for high-capacity shunt reactors
to compensate for leading currents caused by the
charge capacity of the cable during light loads atnight. These were first used for compensation in
tertiary transformer circuits, but later 150MVA
high-capacity versions came to be in standard

Photo 6.2. A 161kV, 68MVA, Low-Pressure

demand instead of directly connecting to the 275kV

Gas-Insulated Transformer for the Tohoku Electric

system due to their efficiency.

Power Company Yanaizu-Nishiyama Geothermal
Power Station (1994, made by Toshiba)(3)

Developmentof

Gas-Insulated

Transformers
The

impulseHigh-capacity
properties

ofgas-insulatedtransformers

first

gas-insulated

started being developed in the United States.

transformers greatly improved with the use of film

Progress had been made in the early 1980s to

insulation and they were put to practical use fromdevelop and implement a 300MVA transformer, but

1978, mainly in underground substations for

the Reagan administration suspended the project as

industrial or transport-related uses. A major factor

part of reducing public finance under the “limited

was the compact configuration of substation

government” slogan. Triggered by this project,facilities made possible through the standardisationplans

of GIS in particular. Later, gas LTCs were also

gas-insulated transformer as a means of disasterdeveloped and used in power companies’ secondary

prevention in underground substations. At the time,

substations. This required a capacity increase fromit was thought difficult to cool a high-capacity

were

made

in

Japan

to

developaToshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

82transformer using gas alone, so perfluorocarbons,

significant amount of heat using gas alone, which,used in computers, were proposed as the coolingfollowing testing on a full-scale model, led to themedium. Various ideas were drafted using thisproduction

medium to cool the heat generated by the windings

transformer. The first such transformer was a 275kV,

and core. In Japan, Mitsubishi, Toshiba and Hitachi

300MVA transformer produced by Toshiba in 1994

each developed their own methods. In 1989,

forToshiba successfully implemented the world’s first

Higashi-Shinjuku Substation. This development

200MVA transformer; in 1990, each company had

virtually offset the added cost compared to an

successfullyoroil-immersed transformer against the cost of

250MVA transformers. While these developments

disaster prevention with the added benefit of awere simpler in structure than the existing

greater degree of freedom in the positioning of thetransformers that used oil for insulation and cooling,transformer and GIS. These were deemed suitable

there were a number of problems in partitioning theto275kV,

usedforinsulation

perfluorocarbons

used

for

SF6

gas

developed

300MVA

cooling,

from

the

meaning

the

of

a

Tokyo

replacehigh-capacity

Electric

oil-immersedPower

gas-cooled

Companytransformers

inunderground substations and they later gained morewidespread use.

development and testing took a long time. However,Gas-insulated transformers were higher priced thanthe companies each demonstrated their technicaloil-immersed transformers due to the comparatively

capabilities to overcome these difficulties andhigh cost of the materials while offering noeventually come up with a product. The companies

advantage over oil for cooling. The cheaper

put a lot of effort into long-term reliability testing,oil-immersed transformers were far more common

since these structures had no proven track record.

around the world. There is a demand for

However, the future of these transformers was

gas-insulated transformers in densely populated

concerning. Despite being of comparable productcities in China, Hong Kong, Taiwan and otherdesign with the existing oil-immersed transformers,

places in Asia, and while Japan is currently the only

they were expected to cost over twice as much, as

country with the technological capabilities todifferent materials were used for the insulation andsupply these, it is expected that joint ventures will

the cooling and the cooling in particular was

begin production before long. However, this isexpensive. Power companies could not be expected

purely for transformers of 50MVA or less; there isto adopt these for the disaster-prevention benefits

presently no demand for high-capacity transformers,

alone. However, this led to the development ofalthough a recent decision to use gas-insulated

high-pressure gas transformers, the development oftransformers in underground substations in parks inblowers that could be used with high gas pressure,

Australia resulted in an order from TMT&D for a

the development of PET and other insulation

345kV, 400MVA transformer in 2003.

materials with better heat-resistant properties and83

the development of technology to keep temperature(4) Transformers for UHV Demonstration

distribution within windings as uniform as possible

Testingby analysing gas flow within windings by computer

While the implementation of UHV transformers

and creating optimal channel structures. This madewas postponed, development resumed in the 1990s

it potentially possible to adequately handle aand early 2000s, at the sudden emergence of a

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

proposal by Tokyo Electric Power Company tooncommence UHV operation. Given the strange

transformers operated on a DC voltage of ±125kV,

problem of flow electrification that occurred with

about the same as the Shin-Shinano transformer. At

the initial 500kV operation, Hitachi, Toshiba andthe second phase, the DC voltage was raised to

Mitsubishi produced one phase each of an actual±250kV and operated commenced the following

transformer based on the specifications for theyear, with around 600MW connecting Honshu andexpected rated values and Tokyo Electric Power

Hokkaido. In 1999, DC transmission between

Company scheduled two years of demonstration

Shikoku and the Kii Peninsula started as a result of

testing of that transformer at the Shin-Haruna

joint development between Shikoku Electric Power

Substation, in order to test whether or not someCompany, Electric Power Development Company

new problem would arise. Before producing the test

and Kansai Electric Power Company. Operating attransformer, a half-phase prototype test transformer±250kV at the first stage, plans are in place to raise

was produced to test for any issues and to test forthis to ±500kV at the second stage. Some of theinsulation limits. The two years of demonstrationequipment is already ready for 500kV use. Before

testing have been prolonged, with testing still being

this equipment was manufactured, tests werecarried out. During this time, new problems havecarried out to check for issues with DC insulation,

occurred, meaning that the demonstration testing

including model testing and long-term reliability

has been worthwhile. Starting UHV operation has

checks by power companies.

the

Hokkaido-Honshu

connection.

Thebeen a huge dream for transformer engineers formany years, but even now in the 21st century there(6) Low-Loss Transformers

is little prospect of it coming true as yet.

While the new technologies of UHV, gas-insulatedtransformers and DC transmission were drawing(5) DC Conversion Transformers

attention,

DC transmission in Japan started out in the form ofundergoing changes from the 1980s onwards.

frequency

conversion

for

power

ordinarytransformers

were

also

interchange

between 50Hz and 60Hz zones. It began in 1964

In the 1980s, as the domestic market moved into awith a conversion transformer for the Electric

period of long-term low growth, more attention

Power Development Company Sakuma Frequency

began to be drawn to loss, previously not

Converter Station made by Mitsubishi using

considered to be an issue. Competition ensued to

Swedish-madeLaterreduce loss. When applying UHV technology totransformers had thyristor valves instead oftransformers of 500kV and less, the existing highmercury arc valves. Following the development andseries capacitance windings were largely replaced

testing of domestically-produced valves, in 1977,bythe Tokyo Electric Power Company Shin-Shinanotransposed cables or other multi-conductor cables

Converter Station became the first thyristor

to reduce the winding eddy current. This was able

converter station. Toshiba and Hitachi shared theto more than halve the eddy current loss, which

production of the 50Hz and 60Hz equipment foraccounted for as much as 30% of the total loss inthis converter station, likewise the transformers.

high-capacity transformers. Other improvements

The first DC transmission in Japan started in 1979

included the use of the newly-developed low-loss

mercuryarc

valves.

continuous

discwindings,

which

used

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

84silicon steel sheets as a core material and ofstorage power stations began to be constructed instep-lap joints as a core structure, which allowed avarious places; the main issue with these wassmooth flow of magnetic flux across the joint. The

transportation of equipment, due to geographic

reduction in core materials by adopting UHV

constraints. This was a time when transformer

technology meant a reduction in core loss, morereliability was highly emphasised. Transformers

than halving the amount of loss from the 1960s.

could no longer be transported disassembled as

While previous 500kV transformers had had athey were in the past; increasing demand for them

two-limb parallel winding structure, the adoption of

to be transported in their factory-tested condition

UHV technology made it possible to reduce this towith the factory product reproduced on site meant

one limb, thereby making a significant reduction in

an increasing number of cases of increasing

loss through a significant reduction in materials

numbers of transformer partitions. At the same time,used.

various policies, such as limitations on freighttransportationroutes,(7) Low-Noise Transformers

transportation

dimensions

In addition to low-loss transformers, low-noise

consolidation of freight stations, appeared as atransformers were another distinctive technology ofresult of the rationalisation of railroad freight

this period. Transformer noise reduction was

handling, followed by the privatisation of Japan

becoming

substation

National Railways. An increasing number oftransformers as urban noise restrictions tightened in

substations were located in mountainous areas far

the 1970s, but as the transition of substations tofrom urban centres. Accordingly, transportation also

GIS systems made them far quieter than theadded to the cost, in some cases even amounting toexistingnoise

more than 20% of the overall cost, making some

restrictions that restricted noise levels at thekind of solution necessary.Kansai Electric Powerboundary line demanded lower noise levels thanCompany and Mitsubishi Electric proposed a new

before. In the 1980s, there was a growing trend todisassembled-for-transport method, which was

keep onsite work as simple as possible and atrialled on a 300MVA transformer in 1984. This

demand to simplify soundproofing structures. The

method involved packing the coils together in film

use of high grain-oriented silicon steel sheets asusing a structure that prevented moisture absorption

well as step-lap joints was expected to dramaticallyduring disassembly and onsite reassembly, thereby

reduce noise levels, while a simple sound-proofing

omitting any onsite drying. A new core structure

structure combining this with reduced magnetic

and onsite assembly conditions equal to those at theflux density made it possible to achieve noise levels

factory provided a structure and working systemof 60dB even for high-capacity transformers, thusthat showed concern for power companies’

gradually reducing the size of these formerly largeemphasis on reliability. This move was later takensound-proofing structures.

up by other power companies and manufacturers,

commonair-insulatedfor

primary

substations,newstricterandlimitations

on

mass,

and

who worked on new core structures, made
(8)

85

From

Partitioned

Transportation

toimprovements to dustproof working chambers,

Disassembled Transportation

investigated the necessity of onsite field testing as

From the 1970s onwards, high-capacity pumped

well as what should be tested, and also brought out

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japantesting equipment, resulting in more widespreadfactor, since Japan has put a lot of capital

adoption. While the added complexity of the maininvestment into these to ensure power reliability.

structure and the increased time for disassembly

The load factor also changes at night, which drops

and reassembly meant increased cost, there were

the average load factor by 50%. Accordingly, there

also advantages, including a dramatic reduction inhas been no deterioration despite having been usedtransport costs, an economising of resources by

for more than the generally expected lifespan of 30

having three phases in one structure, reduced

years and there is no pressing need to update them.

installation space and reduced loss. This new

This has meant that there will be a steadily

disassembled-for-transport system is likely todecreasing

increase in use in future.

transformer manufacturers having to merge anddemandfortransformers,withplan for how to survive in future. This trend has(9) Life Expectancy and Prolonging Lifespanbeen happening for more than 20 years in the WestIn the 1990s, there was a slump in the demand forand is increasingly becoming a reality in Japan aselectricity following the burst of the bubble

well.

economy. With the liberalisation of the electricity
market, there was a movement to control costs, and(10) Systematisation of Technology from 1975

power companies starting sharply reducing their

Onwards

capitalLooking back at this period, we see that it started

expenditure.

A growingnumberoftransformers produced post-war also needed to beout

updated as they were coming to the end of theirovercoming this issue, Japan embarked on the roadlifespan. As a result, companies started examining

to developing its own technology and became

the degree of deterioration on these transformers tocompletely independent from overseas technology.

gain an accurate understanding of the lifespan of

It achieved some notable results, establishing UHV

the transformer. The lifespan of the transformer wastechnology and successfully producing the world’s

estimated through the decrease in mechanicalfirst high-capacity gas-insulated transformer. This

strength of the insulating material used due towas also a time for companies to distinguishthermal ageing and the consequent increased

themselves from others by developing new

possibility of internal insulation failure from atechnologies for existing products in areas such as

short-circuit current during an external accident.

low loss, low noise or simplicity of transportation.

Generally, a transformer had reached its lifespan

The long-term slump in the economy since thewhen the strength of the insulating paper reached1990s meant a decrease in new technology

one quarter of its original strength. Nuclear power

developments; as projects continue to be curtailed,transformers used for base load power generation

there is concern transformer engineers will disperse

have a higher load factor; investment is going in toand the technology will go into decline.

with

flow

electrification

incidents.

By

updating the primary ones with the idea that they
will last for 60 years. Lately, many transformers

Fig. 6.6 shows the progress of technology, whilethat have been in operation for more than 30 years

Fig. 6.7 shows the trends in the major technologies

are having their coils replaced.

and products.

However, substations transformers have a light load
Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

86

(Fig. 6.6. Systematisation of Transformer Technology (Development of Independent
Technology))

87

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

(Fig. 6.7. Trends in Transformer Technology (Development of Independent Technology))

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

886.4. Characteristics of Japanese Transformer

testing, which are far stricter than the global

Technology

standard. From the same perspective, Japan also
has far stricter requirements for environmental

Finally, let us discuss the characteristics ofperformance than other countries. Low-noise

Japanese transformer technology. Much of thetransformers have been the norm since noise

Japanese transformer technology after the war was

regulations were tightened in the 1970s, whendeveloped from American technology introduced

transformer substations began to be placed closer tothrough technical cooperation. However, as theresidential areas. The use of GIS at substations has

economy developed, it became difficult to simply

reduced the level of noise at the boundary, resulting

adopt American designs due to differences inin even stricter low-noise specifications fordesign philosophy resulting from differences intransformers. Gas is also being adopted forindustrial structure. Specifically, the high cost of

substations in urban basements or at publiclabour in the United States meant that designs were

facilities such as transport stations in order toas standardised as possible with simple structures,

prevent any fires or oil flow out caused by internalwith priority given to reducing labour hours rather

faults in the transformer. While gas insulation isthan the cost of materials. In Japan, however,possiblematerials were expensive but labour was cheap, so

technology exists only in Japan. The fourth featuredesigns tended to focus on bringing down the costis that most of the electricity consumption is inof materials, even if it meant more labour hours.

cities,Accordingly, in developing the 500kV transformer

transmission from distant power sources. For thisas capacity and voltage increased, designs tended toreason, Japan produces the world’s highest-capacity

be compact with complex structures due to thesingle-unit transformers, capable of 1500MVA, forgreater rail transport limitations in Japan than in theits power stations, while transformers with bank

United States; according to this design philosophy,

capacity of 1000-1500MVA are widely used for

products could not have any room to spare. Thus,

substations.

the primary feature of Japanese transformers is thetechnology has contributed greatly to overcoming

tendency towards compact design due to the unique

the technical issues with high capacity and carrying

size and mass restrictions for rail transport. Thisout

also gave rise to the idea of special three-phaseanalysis. Demonstration testing is being carried out

systems. The next feature is the globally-unrivalledwith the aim of implementing high voltage offactories with their thorough quality control not

1000kV; Japan is completely prepared to put this

only in design but also in production, such as

into operation at any time. Japan can be proud todust-proofing, due to the strong demand fromhave carried out all kinds of reliability tests andpower companies for transformer reliability, in turnestablished the technology for 1000kV UHV

stemming from for a strong demand from society

transmission in particular, despite having stricter

for a stable power supply. One example is Japan’stransportation limitations than other countries.

specified acceptable levels for partial discharge

89

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanforhigh-capacity

requiringhigh-capacity,

Japan’s

preventive

transformers,

wealthmaintenance

thishigh-voltage

of

using

independent

gas-in-oil

7. Transformer Preservation

With regard to the status of power transformer

1910 that have been kept as memorabilia at thepreservation, the author conducted a survey tofactory once no longer used by the client. Products

examinetransformersof this age are relatively small and possible to store;

manufactured by Hitachi, Toshiba, Mitsubishi, Fuji

later products were too big to store and have all

and Meidensha that had had new technologies

been scrapped. The reality is that at the time, there

applied to them or were record-breaking products

was no thought to preserve them. Of the 128 items,

for these companies. The author compiled survey

33 products thought by the author to bedata on products still existing in Japan, excluding

epoch-making products in terms of technology

those exported overseas. There was a total of 128

were selected as candidates for registration, along

data items. While transformers are generally said towith an original product control ledger by test

have a lifespan of 30 years, they are actually used

number, started in 1905, and an original test reportforoldesttaken after the Great Kanto Earthquake. Table 7.1

transformers currently being used in Japan are fromshows an overview of the candidate products forthe early 1950s; any older transformers within theregistration.

the

40-50

current

years.

stateofAccordingly,

therange investigated had all been scrapped. However,two items referred to transformers manufactured in

Acknowledgements
The author is grateful to the many people who cooperated on the “History of Power Transformers in Japanand Description of Related Historical Technology”.
The author received tremendous assistance from Hitachi, Ltd., TMT&D Corporation, Fuji Electric, Co., Ltd.,
Meidensha Corporation and Japan AE Power Systems Corporation, the technical data from whom formed
the basis for this report. The author received various kinds of assistance with the survey, particularly withdrawing up the data, from the following people. The author would like to take this opportunity to express hisheartfelt appreciation.

TMT&D Corporation:
Eiichi Tamaki, Fumihiko Miyawaki, Masami Ikeda, Toru Nakata, Yoshihito Ebisawa
Japan AE Power Systems Corporation:
Naoki Amano, Yukiyasu Shirasaka, Toshikazu Ito, Yoshiharu Ogawa

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

90

Table 7.1. Overview of Candidate Transformers for Registration
No NameForm Location
Manufactur
.
at
er
1
Transformer test
Actua TMT&D
Shibaura
number ledgerl item Hamakawasaki
Engineering
OfficeWorks

Comments

1905

An early record
ledger that started
managing
transformers by theirtest numbers
The oldest extant
record of atransformer test
reportThe oldest extant
extra-high voltage
transformer

2

Transformer test reportActual itemTMT&D
Hamakawasaki
OfficeShibauraEngineering
Works

1923

3

13.2kV, 100kVA
extra-high voltage
transformerActual itemShibauraEngineering
Works

1910

4

5kVA,single-phasetransformer
Special three-phase,
275kV, 93MVA
transformerActual itemActua
l itemHitachi,Ltd.
Mitsubishi
Electric
Corporation

1910

6

Special three-phase,
275kV, 133MVA
underground power
station transformerActual itemTokyo
Shibaura
Electric
Co., Ltd.

1960

7

275kV, 300MVA,
on-load tap changing
transformerActual itemMitsubishi
Electric
Corporation

1962

8

Three-phase, 275kVA,
680MVA transformerActual itemTokyo
Shibaura
Electric
Co., Ltd.

1966

945dB super-low-noise
180MVA transformerActual itemTokyo ElectricPower Company
Electric PowerHistoricalMuseumHitachi, Ltd.
Kokubu Factory
Electric Power
Development
Company Sakuma
HydroelectricPower Station
Electric Power
Development
Company
Okutadami
HydroelectricPower Station
Tokyo ElectricPower Company
Kita-Tokyo
Substation
Tokyo ElectricPower Company
Anegasaki
Thermal Power
StationKyushu ElectricPower Company
Nishi-Fukuoka
Substation

Meidensha

1967

10

275kV, 300MVA
underground substationtransformerActual itemTokyo ElectricPower Company
Jonan SubstationTokyo
Shibaura
Electric
Co., Ltd.

1969

11

The first
domestically-produced
single-phase, 500kV,
1000/3MVA
auto-transformer
Three-phase 275kV,
1100MVA transformerActual itemTokyo ElectricPower Company
Shin-koga
SubstationTokyo
Shibaura
Electric
Co., Ltd.

1971

Actua
l itemTokyo ElectricPower Company
Kashima Thermal

Tokyo
Shibaura
Electric

1973

5

12

91

Year

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan1955

The first transformer
by Hitachi, Ltd.
The first transformer
to use special
three-phase and theoldest extant 275kVtransformer
Used in an early
underground power
station with a 275kV
cable directconnection structure
The highest capacity
substation LRT and
the first transformer
to use a MR LTC
The highest capacitytransformer at thetime

The first
domestically-produce
d 45dB low-noise,high-capacitytransformer
The first 275kV,
high-capacity
undergroundsubstationtransformer
Japan’s firstcommercial 500kV
transformer

The first 1000MVA
ultra-high capacitytransformer

13

Assembled-for-transpor
t 275kVA, 450MVA
on-load tap changing
transformerActual item14

Forced-gas, forced-air
cooled, 66kV, 10MVA
gas-insulatedtransformer
UHV prototypetransformerActual item16

Single-phase, 500kV,
1500/3MVA
auto-transformerActual item17

Gas-insulated, on-load
tap changing, 66kV,
11MVA transformerActual item18

Evaporation-cooled,
77kV, 20MVA,
gas-insulatedtransformer
Single-phase 500kV,
1000/3MVA
transformer
275kV, 1000MVA,
phase-shifterActua
l item21

New
disassembled-for-transp
ort 275kV, 300MVA
transformerActual item22

2000kV transformer forhermetic seal testingActua
l item23

187kV, 200MVA,
ultra-low-noisetransformer
Liquid-cooled, 275kV,
300MVA, gas-insulatedtransformerActual item275kV, 250MVA,
liquid-cooled,
gas-insulatedtransformer
275kV, 300MVA,
60dB low-noisetransformer with nosoundproof panelActua
l item

15

19

20

24

25

26

Actua
l itemActua
l itemActua
l itemActua
l itemActua
l itemPower Station
Chubu ElectricPower Company
Sunen Substation

Co., Ltd.
Tokyo
Shibaura
Electric
Co., Ltd.

East Japan
Railway Company
Kita-Nagaoka
Laboratory
TMT&D
Hama-Kawasaki
OfficeMeidensha

1978

Tokyo
Shibaura
Electric
Co., Ltd.

1979

Chubu ElectricPower Company
Shin-Mikawa
Substation
Sapporo City
Transportation
Bureau Asabu
Tetsukita
Substation
Kansai ElectricPower Company
Nishi-Shirahama
Substation
Kyushu ElectricPower Company
Buzen Substation
Tohoku ElectricPower Company
Niigata Substation
Kansai ElectricPower Company
Kobe Substation

Hitachi,
Ltd.

1982

Fuji
Electric
Co., Ltd.

1982

The first
gas-insulatedtransformer equippedwith a VCB LTC

Mitsubishi
Electric
Corporation

1984

Toshiba

1984

Toshiba

1984

The first forerunnerof liquid-cooled,
gas-insulatedtransformers
UHV technology
applied to a 500kV
transformer
The world’s highest
capasity phase-shifter

Mitsubishi
Electric
Corporation

1984

Showa Electric
Wire & Cable Co.,
Ltd. Sagamihara
OfficeHokkaido ElectricPower Company
Naebo Substation
Kansai ElectricPower Company
Hirakata
Substation
Chubu ElectricPower Company
Abe Substation

Toshiba

1987

Hitachi,
Ltd.

1988

Mitsubishi
Electric
Corporation

1990

Hitachi,
Ltd.

1990

Tohoku ElectricPower Company
Ishinomaki
Substation

Hitachi,
Ltd.

1992

1974

The highest-capacitytransformer to betransported by freight
car with three phases
in one unit
The first
gas-insulatedtransformer withinsulating film
A prototypetransformer capableof UHV within railtransportation
limitations
UHV technology
applied to a 500kV
transformer

The first transformer
transported by thenewdisassembled-for-tran
sport method
Testing transformer
capable of being
corona free at the test
voltage
Attained a low noiselevel of 45dB using asteel sound barrier
Gas-insulatedtransformer with acoil core cooled byliquid flow-down
Liquidimmersion-cooled,
gas-insulatedtransformer
Achieved low noise
specifications of
60dB using only adirect-tank-mounted

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

92

27

1050kV, 1000MVA
transformer for UHV
field demonstration
testing
Forced-gas, watercooled, 275kV,
300MVA, gas-insulatedtransformerActual item29

Forced-gas, forced-air
cooled, 161kV,
68MVA gas-insulatedtransformerActual item30

New
disassembled-for-transp
ort 500kV, 1000MVA
transformerActual item31

Three-phase 500kV,
1450MVA transformerActual item32

22kV, 13MVA
moulded transformerActual item33

1H DC reactor for
HVDC

Actua
l item34

500kV, 1500/3MVA
underground substationtransformerActual item35

275kV, 450MVA,
liquid-cooled,
gas-insulated,
underground substationtransformerActual item

28

93

Actua
l itemsoundproof barrier
Test transformer withactual specified
values fordemonstration testing
High-capacitytransformer able tobe cooled only byhigh-pressure SF6
gasHighest-voltage,
highest-capacity
low-pressure
gas-insulatedtransformer
500kV, 1000MVA
transformer with an
integrated
three-phase structuretransported by thenewdisassembled-for-tran
sport method
Highest capacitytransformer

Tokyo ElectricPower Company
Shin-Haruna
Substation
Tokyo ElectricPower Company
Higashi-Shinjuku
Substation

Hitachi,Toshiba,
Mitsubishi

1993

Toshiba1994

Tohoku ElectricPower Company
Yanaizu-Nishiyama Geothermal
Power Station
Chubu ElectricPower Company
Aichi Substation

Toshiba

1994

Mitsubishi
Electric
Corporation

1994

Tokyo ElectricPower Company
Kashiwazaki-Kari
wa Nuclear Power
StationTokyo
Metropolitan
Bureau of Public
Cleansing Ariake
Waste Incineration
Plant
Kansai ElectricPower Company,
Electric Power
Development
Company Kihoku
Converter
Substation
Shikoku ElectricPower Company,
Electric Power
Development
Company Anan
Converter
Substation
Tokyo ElectricPower Company
Shin-Toyosu
Substation
Chubu ElectricPower Company
Meijo Substation

Hitachi,
Ltd.

1994

Fuji
Electric
Co., Ltd.

1994

Highest capacity
moulded transformer

Toshiba,
Mitsubishi

1997

DC reactor for
500kV DCtransmission

Toshiba

1997

The first 500kV
undergroundtransformer

Hitachi,
Ltd.

1998

The highest capacity
275kV, gas-insulated
undergroundsubstationtransformer

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan■ Reference Materials 1
Appended Reference Materials 1 provides an overview of the trends in transformer technology in Japan,
showing in chronological order the time of first application or implementation of new technology throughthe efforts of Hitachi, Toshiba, Mitsubishi, Fuji or Meidensha, as well as listing the products to which these
new technologies were applied and also record-breaking products by each company. This report was written
based on this data. Figs. 6.1 to 6.7 and Tables 6.1 and 6.2 are also based on this data. This table also showselectricity-related events in Japan as well as topics related to electricity, transformers and events in global or
Japanese society.
Chronological History of Transformer Technology
Year
Power Situation in Japan
Development of new transformer-related technology
1831
1837
1856
1878
First arc light lit in Japan
1879
1881
1882
1883
1885
1886
Tokyo Electric Light Company founded
1887
Tokyo Electric Light Company No. 2
Branch starts thermal power generation
for business use
1888
Institute of Electrical Engineers of Japan(IEEJ) founded1889
Osaka Electric Light Company starts AC
distribution
1890
1891
Completion of the first hydroelectric
power station for business use, KeagePower Station
1893
The first domestically-produced transformer
manufactured (Miyoshi Electric Factory)
1894
Production starts on air-cooled transformers(Shibaura Engineering Works)
1895
Kyoto Electric Railway started
1896
Tokyo Electric Light Company starts
50Hz transmission (Asakusa Thermal
Power Station)
1897
Meidensha starts transformer production
1899
Adoption of extra-high voltage 11,000V
1900
Production starts on oil-immersed transformers
1903
1904
1905
Test numbers adopted
1906
1907
55kV transmission begins (Tokyo
Electric Light Company,
Komahashi-Waseda)
1908
Hitachi starts transformer production
1909
44kV transmission begins
Vacuum drying adopted(Tonosawa-Hodogaya)
Shibaura Engineering Works starts technicalcooperation with GE
1910
Mitsubishi starts transformer production

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

94

1911
1912
1913
1914
1915
1916

66kV transmission begins (Nagoya
Electric Light Company and others)
77kV transmission begins (Katsuragawa
Electric Power Company)
110kV transmission begins(Inawashiro-Tabata)
Electric furnace steelmaking begins(Daido Steel Company)

1917
1918
1919
1920

Dammed hydroelectricity generation
begins( Nohana-minami)
Japan’s first load dispatching centre(Tokyo Electric Light Company,
Kojimachi)
Main Transformer Products

Silicon steel sheets first used (pole-mounttransformers)
Silicon steel sheets and transformer oil first imported
and used
Production starts on induction voltage regulators
Production starts transformer oil (Nippon Oil)
Conservators first used

Research published on internal potential vibration by
Kujirai, Nishi, Hou
Thesis published on the transformer resonancephenomenon by Nishi, Bekku
Epstein testing introduced for inspecting silicon steel
sheetsFirst use of core-type for high-capacity transformers

Social Situations, Electricity/Transformer
Situation Overseas, Other
Faraday discovers the electromagnetic induction
phenomenon
Masson prevents eddy currents in stacked
laminated cores by mutually insulating thin steel
sheet ribbons
Varley produces a core with a closed circuit ofbundled wires
Edison invents the light bulb
Edison starts an electricity business in New York
Ewing discovers the hysteresis phenomenon in
iron
Gaulard and Gibbs propose AC distribution
First thermal power generation begins (USA)
Stanley discovers the idea of counterelectromotive force
Max Deri patents a transformer for shunt-type AC
distribution and names it the trans-form
Core-type and shell-type transformers
manufactured by Ganz (transformer lighting
exhibited at the Budapest Expo)
Stanley completes a transformers with an annular
core of wire and a laminated sheet core structure
Ganz and Stanley successfully devise parallel
power distribution systems

Wenstrom produces a three-phase, core-typetransformer
First use of transformer oil for insulation 15000V
transmission (Germany)

95

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, JapanAir-cooled system standardised for transformers
up to 30kVA (Shibaura)First Sino-Japanese War

Air-cooled 1-2kV/100V 50-100 lamp capacity(Meidensha)

50kV, 4kVA test transformer developed(Shibaura)

Hadfield invents silicon steel
Silicon steel industrialised in the United Kingdom
Russo-Japanese War

First extra-high voltage 11kV, 150kVA
transformer completed (for Kofu Electric)(Shibaura)
22kV, 250kVA transformer completed(Shibaura)
44kV, 500kVA transformer completed (Hakone
Hydroelectric) (Shibaura)
Shell-type, water-cooled, 44kV, 1500kVA
transformer completed (Yokohama ElectricPower Company Hodogaya Substation)(Shibaura)First use of conservators
Single-phase, water-cooled 1500kVA
transformer (Nagoya Electric Light Company)(Hitachi)
66kV, 2500kVA transformer (Kyushu
Hydroelectric) (Shibaura)

500kV test transformer (University of Tokyo)(Shibaura)
Single-phase, oil-immersed, water-cooled
38kV, 2600kVA transformer (Japan
Nitrogenous Fertilizer) (Hitachi)
Oil-immersed, water-cooled 60kV, 2000kVA
transformer (Kumamoto Electric Power
Company) (Hitachi)
110kV, 4400kVA transformer (Inawashiro
Hydroelectric, Tokyo Electric Light Company
Tabata Substation) (Shibaura)
350kV test transformer (Ministry ofCommunications) (Hitachi)

66kV, 6000kVA transformer completed(Shibaura)

Year

Power Situation in Japan

1921
1922
1923

154kV transmission begins (Keihin
Electric Power Company Koshin

154kV transmission begins (USA)First World War
Wagner publishes the basic concept of internalpotential vibration in transformer windings

200kV transmission begins (California, USA)
Production of 220kV-graded insulationtransformers (USA)New Transformer-Related Technology
Developed
Domestic production of silicon steel sheets
Electrical equipment standard JEC-9 established
Mitsubishi starts technical cooperation with WH

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

96network)
1924

Three-winding transformer produced (Tokyo
Electric Light Company, 10MVA) (Hitachi)
Fuji starts transformer production throughtechnical cooperation with Siemens
77kV, 10MVA transformer transported
assembled by sea (Daido Electric Power
Company Shin-Yodogawa Power Station)(Shibaura)First condenser bushing produced
Japan’s first transformer standard JES31 issued

1925
1926

1927
1928

First use of lightning-protected winding
structures
First use of domestically-produced silicon steel
sheetsFlanged collar insulation used

1929
1930

Radiator valve invented
Multi-dial thermometer used

1931
1932
1933

1934

Pumped-storage power generation
begins

1935

1936
1937

1938
1939

6kV distribution begins (Tokyo
Electric Light Company)

1940

97

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

Potential distribution measured
First use of surge-proof windings (Single-phase,
165kV, 7.5MVA transformer for the Taiwan
Electric Taipei Substation)
Transformer standard JEC-36 established
Impulse voltage generator built
First use of nitrogen immersed transportation(154kV, 15MVA transformer for the ChosenPower Transmission Pyongyang Substation)
Resistor-type on-load tap changers introduced(Jansen-style)Concave railcar Shiki 60 producedFirst impulse testing implemented (154kV,
18MVA transformer for the Ministry ofRailways Musashi-Sakai Substation)
Wartime standard JEC-36 Z issued
Assembled transportation by special freight car
Shiki 60 (39MVA transformer for the Tokyo
Electric Light Company Shinanogawa Power
Station)First use of partially shielded windings (154kV
transformer for the Tokyo Electric Light
Company Shinanogawa Power Station)
Invention of impulsewave waveform viewing
deviceImpulse testing implemented on a 230kVtransformer (Manchuria Electric)
Non-flammable synthetic oil (PCB) immersed
transformer produced (44kV, 4.5MVA
transformer for Manchuria)
First use of multiple cylindrical windings (220kV
arc-extinguishing reactor for the Chosen
Hydroelectric Heochun River Power Station)
First use of a banked radiator (230kV, 80MVA
transformer for the Chosen Hydroelectric
Chongjin Substation)

1941

First use of a finned unit cooler(100MVA
transformer for Chosen Hydroelectric)
Japanese standard on mineral transformer oil
issuedFirst use of a nitrogen-filled conservator
Neutral point graded insulation method
developed
Studies on potential vibration in 220kV
transformers

1942

1943
1944

Load voltage regulator adjusted on thehigh-voltage side produced
The first standard on static induction electric
apparatus impulse testing JEC-110 established
Studies on anisotropic silicon steel sheet core
structures

1945

Main Transformer Products

Social Situations, Electricity/Transformer Situation
Overseas, Other

Three-phase, 66kV, 8,000kVA transformer
completed (Shibaura)
Single-phase, 55kV, 5000kVA transformer (Daido
Electric Power Company) (Mitsubishi)
2kV, 240kVA transformer for a rotary converter(Tokyo Electric Light Company) (Meidensha)
Single-phase, water-cooled 77kV, 13333kVA
transformer (Nippon Electric Ozone Substation)(Shibaura)
80kV, 15MVA transformer (Toho Electric Power
Company) (Shibaura)
Single-phase, 66kV, 1000kVA transformer (Teikoku
Electric Light Company) (Meidensha)
The first 154kV transformer (154kV, 6667kVA
transformer for the Nippon Electric Gifu Substation)(Shibaura)
The first forced-oil, forced-air cooled 80kV,
12.5MVA transformer (Kansai Power Distribution)(Hitachi)Water-cooled 53kV, 10MVA transformer (Kyoto
Electric Light Company) (Fuji)
Self-cooled, 10MVA transformer (Ujigawa ElectricPower Company) (Shibaura)
820kVA transformer with mercury-arc rectifier(Nippon Mining Company) (Hitachi)
77kV, 22.53MVA (Tokyo Electric Light Company)(Mitsubishi)
Self-cooled, single-phase, 140kV-87kV-11kV,
22MVA transformer (Showa Electric Power
Company Yao Substation) (Shibaura)
165kV, 12.5MVA transformer (Showa ElectricPower Company) (Hitachi)
Three-phase, water-cooled, 115kV, 36MVA
transformer (Chosen Nitrogen Corporation Pujon
River No. 1 Power Station) (Shibaura)
Single-phase, 70kV, 7.5MVA transformer
transported immersed in oil (Toho Electric Power
Company Najima Substation) (Mitsubishi)

Non-resonant transformer produced (USA)Great Kanto Earthquake
Inertia transformer produced (US company WH)
Parallel circuit on-load voltage regulatingtransformer (US company GE)
Radio broadcasting begins

Jansen-type cross current suppression systemannounced

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

98

99

The first 154kV, 18.833MVA transformer to bedisassembled for transport (Toshin Electric Power
Company Toyomi Power Station) (Hitachi)
700kV testing transformer (Osaka Togyo) (Hitachi)
Forced-oil, water cooled, 60kV, 4.5MVA, 34.5kA
secondary current for an electric furnacetransformer (Denki Kagaku) (Fuji)
Three-phase, forced-oil, water cooled 72kV,
43.75MVA transformer (Nippon Electric Tsurumi
Power Station) (Shibaura)
The first on-load voltage regulating transformer(450kVA transformer for Chugoku Godou Electric)(Shibaura)
400kV test transformer (Fuji)
On-load voltage regulating, single-phase 110kV,
12MVA transformer (Kumamoto Electric Power
Company) (Shibaura)
Three-phase, water-cooled, 105kV, 23MVA
transformer (Chosen Hydroelectric) (Fuji)
77kV, 22MVA transformer transported immersed inoil (Toho Electric Power Company Kizu Substation,
Iwakura Substation) (Shibaura)
Single-phase, 147kV, 20MVA transformer (Tokyo
Electric Light Company Kawasaki Substation)(Mitsubishi)
On-load voltage regulating, 6300kVA transformer(Kyoto Electric Light Company) (Hitachi)
The first 88.5MVA phase sifter ( Kansai Joint Power
Company Amagasaki Thermal Power Station)
On-load voltage regulating, 2100kVA transformer(Sanyo Chuo Hydroelectric) (Hitachi)
39MVA,178.5kV, disassembled-for-transporttransformer (Toshin Electric Power Company
Shimagawara Power Station) (Hitachi)
Single-phase, 165kV, 15MVA transformer
transported by low-floor railcar immersed in oil(Taiwan Electric) (Mitsubishi)
On-load voltage regulating, three-phase, 77kV,
15MVA self-cooled transformer (Electric Power
Development Company) (Hitachi)
Three-phase, forced-oil, water cooled, 66kV,
63MVA transformer (Tokyo Electric Light
Company Tsurumi No. 1 Thermal Power Station)(Shibaura)
Self-cooled, three-phase, 161kV, 34.65MVA
transformer (Oigawa Electric Company)(Mitsubishi)
Single-phase, 66kV, 1500kVA transformer (Minami
Chosen Electric Power Company) (Meidensha)
Three-phase, 11kV, 3MVA, on-load tap changing
transformer for an electric furnace (Japan
Nitrogenous Fertilizer) (Fuji)

Forced-oil, water cooled, three-phase, 100MVA
transformer (Germany company AEG)
The Great Depression

Water-cooled, 154kV, 60MVA transformer(Chongjin River Hydroelectric Hagi River
Substation) (Shibaura)
Self-cooled, 154kV, 50MVA transformer (ChosenPower Transmission Gyeongseong Substation)

Multiple cylindrical windings (non-resonanttransformer) produced (German company AEG)
Impulse testing regulations issued (USA)Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

Recommendations announced on insulation
coordination (USA)The first impulse testing (US company GE)

Water-cooled, three-phase, 60MVA transformer
produced (USA)Surge-proof windings produced (US company WH)

V-t characteristics published (US company GE, WH)

Grain-oriented silicon steel sheets invented (UScompany Goss)(Shibaura)
Single-phase, 84kV, 31.25MVA transformer(Kansai Joint Power Company Amagasaki No. 2
Power Station) (Hitachi)
Forced-oil, forced-air cooled, 154kV, 50MVA
transformer (Tokyo Electric Light Company
Wadabori Substation) (Shibaura)
Self-cooled, 70kV, 63MVA transformer (Chubu
Joint Power Company Meiko Power Station)(Shibaura)
The first 220kV transformer (220kV, 80MVA
transformer for Chongjin River Hydroelectric
Heochun River No. 1 Power Station) (Shibaura)
500kV testing transformer (Furukawa ElectricCompany) (Fuji)
Three-phase, forced-oil, water-cooled, 230kV,
100MVA transformer (Yalu River HydroelectricSup’ung Power Station) (Toshiba)
Single-phase, self-cooled, 230kV, 37.5MVA
transformer (Manchuria Electric Andong Substation)(Hitachi)Single-phase, 220kV, 50MVA transformer(Manchuria Electric) (Mitsubishi)
On-load voltage regulating, three-phase, 44/44±3.3kV, 150MVA transformer (Mitsubishi)
Three-phase, self-cooled, 161kV, 35MVA
transformer (Nippon Light Metal Niigata) (Hitachi)
Three-phase, forced-oil, forced-air cooled, 230kV,
100MVA transformer (Chosen Hydroelectric Tasado
Substation, etc.) (Toshiba)
Forced-air cooled, 161kV, 70MVA transformer(Hydroelectric Construction Bureau of Manchuria
Songhua River Power Station) (Hitachi)
On-load tap changing, single-phase, 40kV, 5MVA
transformer (Yamaguchi Prefectural Electricity
Bureau) (Meidensha)
Forced-air cooled, three-phase, 240kV, 30MVA
transformer (Kanggye Hydroelectric) (Fuji)
Three-phase, 60kV, 28MVA, 58.4kA second
current, on-load tap changing transformer for anelectric furnace (Japan Nitrogenous Fertilizer) (Fuji)
Forced-air cooled, 230kV, 70MVA transformer(Hydroelectric Construction Bureau of Manchuria
Songhua River Power Station) (Hitachi)
Three-phase, forced-oil, forced-air cooled, triple
winding, 154/77/21kV, 33MVA transformer (Japan
Electric Generation and Transmission Company
Ibaraki Substation) (Hitachi)

Year
1948

Power Situation in Japan

Forced-oil, forced-air cooled, three-phase 220kV,
100MVA transformer transported by railcar (German
company AEG)

Second World War begins

Japan-US war

Main-gap-filling insulation structure (Swiss company
BBC)

New Transformer-Related Technology Developed
First use of unitcooler (78MVA transformer for
Showa Denko)
The first neutral-point graded- insulation transformer(single-phase, 140kV, 25MVA transformer for theElectric Power Development Company Okayama
Substation)

1949

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

100

1950
1951

9 power companies established

1952

275kV transmission begins (Kansai
Electric Power Company Shin-Hokuriku
Trunk Line)
Electric Power Development Company
established

1953
1954

Air circuit breakers implemented

1955

1956

1957

Tokai-Mura No. 1 Nuclear Reactor
ignited1958

101

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

Non-resonant windings (lightning-protected layered
cylindrical windings) developed
275kV transformer producedHigh series capacitance windings developed
First use of form-fit (single-phase, 66kV, 15MVA
transformer for the Tokyo Electric Power Company
Shikahama Substation)
First use of main-gain-filling insulation structures
First use of induction heating drying method
First use of electrostatic shielding (three-phase,
154kV, 33MVA transformer for the Tohoku ElectricPower Company Higashi-Niigata Substation)
First use of non-resonant windings in transformers(multiple cylindrical windings) (154kV, 27MVA
transformer for Tokyo Electric Power Company)
Static induction electric apparatus standard JEC-120
establishedPost-war overseas technical cooperation resumes
Shiki 120 low-floor railcar produced
Use of onsite core-erecting equipment
First use of magnetic tank shielding (shell-type)
Test methods established for the stability oftransformer oil
Shiki 130 well hole railcar producedFirst use of damper-shield windings (120kV,
45MVA transformer for the Kyushu Electric Power
Company Ainoura Power Station)
First use of transposed cables
Use of multi-conductor cables
First use of special three-phase transformers
First use of grain-oriented silicon steel sheets
First use of three-phase, five-limb cores
Schnabel-car-type Shiki 170 produced
Automatic electric field replication technology
Dial-type temperature relays, indirect resistor
temperature detectors and pressure release valves
adoptedDevelopment of gas-in-oil analysis method
Technical cooperation begins with German company
AEG (Meidensha)
First use of vapor-phase drying method
First use of forced winding coolingFirst use of floating cranes
Equipment for viewing AC magnetic properties
First use of high series capacitance windings
First use of frame-shaped core (6MVa transformer
for the Tokyo Electric Power Company Kichijoji
Substation)
Cooling-tower-type water-cooled transformer
developed
Shiki 400 Schnabel car produced
Winding machines fitted with transposed cables
Transformer short-circuit testing (70kV, 2000kVA)
Shiki 300 Schnabel car produced
Multi-conductor cables used
Establishment of erecting equipment for large-scale
coresFirst use of transformers with cable connections

1959

Extremely-high-voltage cross-channeltransmission line built (Kanmon, 220kV)

Main Transformer Products
Three-phase, forced-oil, forced-air cooled, 154kV,
78MVA transformer (Showa Denko) (Mitsubishi)
147kV, 60MVA transformer with 6MVA on-load
voltage regulator (Showa Denko Shiraishi
Substation) (Hitachi)
Three-phase, 115kV, 15MVA on-load tapchanging transformer for export (India) (Fuji)
84kV, 20MVA transformer with a nitrogen-filledconservator (Japan Electric Generation andTransmission Company) (Hitachi)
The first three-phase, 250kV, 99MVA
transformer for 275kV (Kansai Electric Power
Company Hirakata Substation) (Mitsubishi)
The first three-phase, 275kV, 70MVA transformer
for 275kV (Kansai Electric Power Company
Narude Power Station) (Hitachi)
Self-cooled, three-phase 69kV, 45MVA
transformer (Kyushu Electric Power Company
Chikujo Power Station) (Mitsubishi)
Assembled, transported on its side by special Shiki
100 well hole railcar (45MVA transformer for
Kyushu Electric Power Company Chikujo Power
Station) (Mitsubishi)
Non-resonant, 154kV, 27MVA transformer(Tokyo Electric Power Company Hakojima
Substation) (Fuji)
Three-phase, 154kV, 66MVA transformer withcooling unit (Tokyo Electric Power Company
Wadabori Substation) (Toshiba)
Forced-air cooled, 66kV, 37.25MVA transformer(Japan Electric Generation and Transmission
Company Tsurumi Power Station) (Meidensha)
Tripled rated, three-phase, 69kV, 33.75MVA
transformer (Hokkaido Electric Power Company
Sunagawa Substation) (Mitsubishi)
Three-phase, 166kV/275/11kV, 99MVA
transformer (Kansai Electric Power Company
Shin-Aimoto Substation) (Toshiba)
The first 77kV, 15MVA reactor (Kansai ElectricPower Company Hirakata Substation) (Toshiba)
The first low-noise, three-phase, forced-oil,self-cooled, 63kV, 15MVA transformer (Tokyo
Electric Power Company Hibiya Substation)(Hitachi)Assembled, transported on its side by special Shiki
120 railcar (65MVA transformer for Kyushu
Electric Power Company Chikujo Power Station)(Mitsubishi)(elephant type)
Fully equipped 10MVA transformer produced
Moveable transformer producedCore sheet cutting process line built on
400kV, 10MVA transformer prototype tested
Shiki 600 Schnabel car produced
Social Situations, Electricity/Transformer
Situation Overseas, Other
Transistor invented (Bell ResearchLaboratories, USA)High series capacitance windings published(EE, UK)
Korean War
The first successful nuclear power generation(USA) single-phase 250/3MVA (WH),three-phase 138kV, 145MVA (WH)
Treaty of Peace With Japan

400kV transmission begins (Sweden)

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology102Forced-oil, water-cooled, three-phase, 66kV,
42MVA, 10kA second current transformer for anelectric furnace (New Japan Nitrogenous Fertilizer
Company) (Fuji)
Form-fit, assembled ,transported on its side,
three-phase, 147kV, 39MVA transformer (Tokyo
Electric Power Company Higashi-Chiba
Substation) (Mitsubishi)
Non-resonant, three-phase, 275kV, 45MVA
transformer (Kansai Electric Power Company
Tsubakihara Power Station) (Fuji)
Assembled-for-transport, 154kV, 50MVA
transformer (Tokyo Electric Power Company
Kawasaki Substation) (Toshiba)
Double rating of high-voltage, single-phase,
250-154kV 72.5MVA transformer (Kansai
Electric Power Company Maruyama Power
Station) (Mitsubishi)
Fahrbar-type, three-phase, 110kV, 50MVA
transformer (Kyushu Electric Power Company
Chikujo) (Fuji)
Three-phase, forced-oil, forced-air cooled, 230kV,
135MVA transformer (Kyushu Electric Power
Company Kamishiiba Power Station) (Hitachi)
Assembled-for-transport, 154kV, 66MVA
transformer (Tokyo Electric Power Company
Musashino Substation) (Toshiba)
154kV, 66MVA transformer transported
assembled by Shiki 140 Schnabel car (Tokyo
Electric Power Company Keihoku Substation)(Hitachi)Assembled-for-transport, 154kV, 99MVA
transformer (Chubu Electric Power Company
Higashi-Nagoya Substation) (Toshiba)
Special three-phase, 275kV, 93MVA transformer(Electric Power Development Company Sakuma
Power Station) (Mitsubishi)
Low-noise, three-phase, 66kV, 30MVA
transformer (Tokyo Electric Power Company
Sumida Substation) (Mitsubishi)
55dB low-noise, three-phase, 66kV, 30MVA
transformer (Tokyo Electric Power Company Inari
Substation) (Meidensha)
154kV, 65MVA ,three-phase, five-leg coretransformer (JPA-Korea) (Meidensha)
275kV, 132MVA transformer (Electric Power
Development Company Nishi-Tokyo) (Hitachi)
Fully equipped sealed 2MVA transformer(Tohoku Electric Power Company Kitakata
Substation) (Hitachi)
Low-noise 154kV, 110MVA transformer (Tokyo
Electric Power Company Toda Substation)(Toshiba)
The first three-phase, forced-oil, forced-air cooled,154kV, 160MVA transformer with forced winding
cooling (Tokyo Electric Power Company Chiba
Power Station) (Toshiba)
On-load voltage and phase regulating, 220kV

103

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Vapor-phase drying method (GE, USA)

Start of commercial nuclear reactor operation(Calder Hall Nuclear Power Station, UK)
Japan joined the UN
Thyristors released on the market (GE, USA)±10,±j30kV, 90MVA transformer (Kyushu
Electric Power Company Yamaie Substation)(Toshiba)
48dB low-noise, 66kV, 30MVA transformer(Tokyo Electric Power Company Itabashi
Substation) (Hitachi)
Assembled-for-transport, 66MVA transformer
with a five-limb core (Kansai Electric Power
Company Furukawabashi Substation) (Hitachi)
On-load tap changing, 110kV, 60MVA
transformer (Kyushu Electric Power Company
Shinohara Power Station) (Meidensha)
Dry-type, H-grade-insulated, 3000kVA
transformer with tap changer (Kansai ElectricPower Company Dojima Substation) (Hitachi)
99MVA transformer transported assembled by
Shiki 140 railcar (Chubu Electric Power Company
Iwakura Substation) (Hitachi)
78MVA transformer transported assembled by
Shiki 120 Schnabel car (Tokyo Electric Power
Company Suruga Substation) (Mitsubishi)
Cooling-tower-type water-cooled, 66kV, 30MVA
transformer (Tokyo Electric Power Company
Otemachi Substation) (Mitsubishi)
On-load tap changing, 110kV, 66MVA
transformer (Chugoku Electric Power Company
Tokuyama Substation) (Toshiba)
27.5MVA reactor (Kansai Electric Power
Company Shin-Aimoto Substation) (Toshiba)
On-load tap changing, 110kV, 70MVA
transformer (Kyushu Electric Power Company
Omura Power Station) (Hitachi)
Low-noise, 45MVA transformer with soundbarrier structure (Tokyo Electric Power Company
Takanawa Substation) (Hitachi)
On-load tap changing, 154kV, 30MVA
transformer (Kansai Electric Power Company
Shin-Yawata Substation) (Fuji)
Special three-phase, 275kV, 260MVA transformer
with frame-shaped core (Tokyo Electric Power
Company Naka-Tokyo Substation) (Mitsubishi)
Three-phase, 275kV, 200MVA transformer(Tokyo Electric Power Company Chiba Power
Station) (Toshiba)
On-load tap changing, 120MVA transformer
transported assembled by Schnabel car (Tohoku
Electric Power Company Honmyo Substation)(Mitsubishi)
220kV, 180MVA transformer transported
assembled by Schnabel car (Kyushu ElectricPower Company Nishitani Substation) (Hitachi)
2500kVA transformer with Scott connection(Japanese National Railways Tohoku Main Line
Kuroiso Substation) (Hitachi)
The first (elephant) cable connected, three-phase,
66kV, 6MVA transformer (Furukawa Chemical)(Fuji)

500kV transmission begins (USSR)

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

104Moveable 70kV, 3MVA transformer (Chubu
Electric Power Company) (Meidensha)
Fully equipped, 66kV, 10MVA transformer(Tokyo Electric Power Company Shibue
Substation) (Meidensha)
Three-phase, 275kV, 270MVA transformer(Chubu Electric Power Company Shin-Nagoya
Power Station) (Toshiba)
Special three-phase, 275kV, 264MVA transformer(Electric Power Development Company
Minami-Kawagoe Substation) (Mitsubishi)
70kV, 20MVA shunt reactor (Kansai ElectricPower Company Shikitsu Substation) (Hitachi)
Assembled-for-transport, three-phase, 275kV,
264MVA transformer (Electric Power
Development Company Nishi-Tokyo Substation)(Hitachi)Three-phase 154kV, 75MVA transformer withembedded on-load tap changer (Tokyo ElectricPower Company Kuramae Substation) (Fuji)
Assembled-for-transport, three-phase, 275kV,
200MVA transformer (Kansai Electric Power
Company Higashi-Osaka Substation) (Fuji)
Year
1959
1960

Power Situation in Japan

New Transformer-Related Technology Developed

154kV underground substation (Tokyo
Electric Power Company Chiyoda
Substation)
275kVOF cableFirst use of diaphragm-type conservators
First use of hot line oil purifiersFirst use of 154, 275kV cable-connectedtransformers
First use of oil-immersed resin-bonded insulation
cylindersFirst use of crêpe insulation paperFirst use of paper-wound soft copper twist wires andflexible copper twist wires
Field mapping using resistance paper
UHV testing facility completedFirst use of radial core shunt reactors
Use of hot oil spray drying method
First use of concrete sound barriersFirst use of hourglass insulation
First use of thermal upgraded insulating paper
Technical cooperation on LTCs begins with MR
First use of electromagnetic tank shielding
First use of air-tight kraft insulating paperFirst use of tap winding float prevention resistors
First use of crimping terminal for lead connection
Start of overseas expansion of transformer
technology (joint venture with the Kerala State
Government, India)

1961
1962
1963

Japan’s first nuclear power generation
begins

1964

1965

105

Uniform specifications for on-load tapchanging transformers
500kV transmission line constructed

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, JapanFirst production of dry-type condenser bushings
First use of double-piped cooler (Tokyo ElectricPower Company Babasaki Substation)
First use of aluminium coils
Operating survey conducted and accident statistics
compiled for on-load tap changing transformers(Electric Technology Research Association)

(Tokyo Electric Power Company Boso
Line)
First frequency converter station gridconnection (Electric Power
Development Company Sakuma)

1966

1967

Main Transformer Products

Introduction of partial discharge testingGas-in-oil analysis developed
Adoption of bound cores
Coil assembly rooms fitted with air conditioning
facilities
Development of two-dimensional magnetic fieldcalculation technology
CC shield windings developed and implemented
Introduction of large-scale vertical winding machinesFirst painting of internal structure materials
Winding short circuit vibration analysis programme
developed
Transformer standard JEC-168 established
Adoption of E-type insulation method
Introduction of switching impulse testing
Double concentric winding structures applied tohigh-capacity transformers
Adoption of slit core backing plates
Adoption of clamped magnetic shields
Gas-in-oil analysis introduced to test evaluation
Introduction of high vacuum exhaust systems
Introduction of insulation moisture control
Acoustic corona location technology established
Introduction of corona-free adhesive
Introduction of low-humidity, dust-proof, airconditioned rooms
First hot oil circulation
Pressboard changes from second hand cotton type to
new cotton typeComputerisation of properties calculations
Trial production of resistor-type vacuum switch
LTCs
Transformer technical cooperation with overseas
discontinues (Toshiba)
Social Situations, Electricity/Transformer Situation
Overseas, Other

400kV, 200MVA transformer for testing UHV
circuit breakers (Hitachi Research Laboratory)(Hitachi)Assembled-for-transport, three-phase, 275kV,
260MVA transformer (Tokyo Electric Power
Company Keihin Substation) (Mitsubishi)
Special three-phase, 154kV, 100MVA, undergroundsubstation transformer (Tokyo Electric Power
Company Chiyoda Substation) (Toshiba)
Special three-phase, 275kV, 133MVA, undergroundpower station transformer (Electric Power
Development Company Okutadami Power Station)(Toshiba)
Three-phase, 275kV, 300MVA transformer (Tokyo
Electric Power Company Yokosuka Power Station)(Toshiba)
77kV, 50MVA cable conneted transformer( elephant coupling) (Chubu Electric Power
Company Nanbu-Tairamachi Substation)(Meidensha)
77kV, 20MVA transformer with shunt reactor

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

106

(Kansai Electric Power Company Hirakata
Substation) (Meidensha)
Three-phase, 275kV, 150MVA, cable connectedtransformer (elephant coupling ) (Tokyo ElectricPower Company Yokosuka Power Station) (Fuji)
330kV, 100MVA, on-load tap changing,auto-transformer (Sydney Substation, Australia)(Toshiba)
330kV, 160MVA, on-load tap changing,auto-transformer (Vales Point Power Station,
Australia) (Hitachi)
Low-noise three-phase, 90MVA transformer withconcrete sound barrier (Chubu Electric Power
Company Mizuho Substation) (Fuji)
275/220kV, 200MVA auto-transformer for gridinterconnection (Kansai Electric Power Company
Himeji Substation) (Fuji)
1500kVA, PCB-insulating-oil-immersed transformer(Tokyo Electric Power Company Kawasaki Thermal
Power Station) (Hitachi)
77kV, 180MVA , cable connected transformer(elephant coupling ) transformer (Kansai ElectricPower Company Himeji Power Station) (Mitsubishi)
154kV, 100MVA transformer with diaphragm
conservator (Kansai Electric Power Company
Yokooji Substation) (Meidensha)
220kV, 111.5MVA auto-transformer for gridinterconnection (Electric Power Development
Company Iyo Substation) (Mitsubishi)
Assembled-for-transport, 275kV, 300MVA
transformer (Tokyo Electric Power Company
Kita-Tokyo Substation) (Mitsubishi)
Assembled-for-transport, on-load tap changing,
three-phase, 63kV, 45MVA transformer for anelectric furnace (Denki Kagaku) (Fuji)
Disassembled-for-transport, 200MVA transformer(Chubu Electric Power Company Kawane
Substation) (Hitachi)
On-load tap changing, 220kV, 150MVA transformer
with hot line oil purifier (Chugoku Electric Power
Company Yamaguchi Substation) (Meidensha)
Three-phase, 275kV, 370MVA transformer (Kansai
Electric Power Company Himeji No. 2 Power
Station) (Mitsubishi)
High impedance, three-phase, 275kV, 420MVA
transformer (Tokyo Electric Power Company
Yokosuka Power Station) (Toshiba)
Three-phase, 275kV, 430MVA transformer (Chubu
Electric Power Company Owasemita Thermal Power
Station) (Toshiba)
Assembled-for-transport, 262.5kV, 300MVA
transformer (Chubu Electric Power Company
Nishi-Nagoya Substation) (Hitachi)
Transformer with built-in LTC (Tohoku ElectricPower Company Shin-Sanjo Substation) (Toshiba)
14.7kV, 40MVA reactor (Electric Power
Development Company Minami-Kawagoe
Substation) (Mitsubishi)

107

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

30MVA transformer with Scott connection (Tokaido
Shinkansen line) (Mitsubishi, Toshiba)
275kV, 368, 353MVA frequency convertertransformer (Electric Power Development Company
Sakuma Frequency Converter Station) (Mitsubishi)
Transformer with built-in rotary resistive LTC(Kansai Electric Power Company Shin-Kakogawa
Substation) (Hitachi)
Special three-phase, 275kV, 300MVA transformer(Tokyo Electric Power Company Kita-Tokyo
Substation) (Mitsubishi)
Assembled-for-transport, 275kV, 300MVA
transformer (Electric Power Development Company
Nagoya Substation) (Fuji)
Assembled-for-transport, 275kV, 200MVA
transformer (Tokyo Electric Power Company
Shin-Fuji Substation) (Meidensha)
Low-noise, 140kV, 25MVA transformer withconcrete sound barrier (Tokyo Metropolitan
Government Bureau of Waterworks Asaka
Purification Plant) (Hitachi)
DC66kA rectifier transformer rectifying elementwith embedded in tank (Kanto Denka) (Fuji)
Special three-phase, 345kV, 400MVA transformer(Munmorah Power Station, Australia) (Mitsubishi)
275kV, 300MVA transformer transported withbuilt-in LTC (Tokyo Electric Power Company
Higashi-Tokyo Substation) (Hitachi)
Three-phase, 275kV, 680MVA transformer (Tokyo
Electric Power Company Anegasaki Power Station)(Toshiba)
275kV, 300MVA transformer transported withbuilt-in LTC (Tokyo Electric Power Company Koto
Substation) (Toshiba)
Transformer for 500kV voltage impression testing(Takeyama Ultra High Voltage Laboratory) (Hitachi,
Toshiba, Mitsubishi)
400kV transformers (around 50 3000MVA
transformers for Mexico) (Mitsubishi)
500kV transformers for export (80, 100, 200MVA
transformers for BCHPA, Canada) (Toshiba)
Three-phase, 66kV, 3000kVA, gas-insulatedtransformer (Daiichi Life) (Toshiba)
Three-phase, 275kV, 510MVA transformer with
LVR (Kansai Electric Power Company Himeji No. 2
Power Station) (Mitsubishi)
236kV, 125MVA reactor for export (Canada)(Mitsubishi)
Three-phase, 154kV, 420MVA transformer (Tokyo
Electric Power Company Goi Power Station)(Hitachi)
420kV, 35MVA reactor for export (CFE, Mexico)(Mitsubishi)
Three-phase, 63kV, 50MVA, 112kA secondary
current transformer for an electric furnace (Denki
Kagaku) (Fuji)
Three-phase, 154kV, 53MVA transformer withtransposed cables (Hokuriku Electric Power

Tokaido Shinkansen opens
Tokyo Olympics

New York blackout
735kV transmission begins (Canada)

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

108Company Nishi-Kadohara No. 3 Power Station)(Fuji)
Ultra-low-noise, 220kV, 180MVA, 45dB
transformer (Kyushu Electric Power Company
Nishi-Fukuoka Substation) (Meidensha)
154kV, 100MVA underground substationtransformer (Tokyo Electric Power Company
Togoshi Substation) (Meidensha)
Year
1967
1968

1969
1970

1971

Power Situation in JapanFirst GIS substation

275kVGIS (Tokyo Electric Power
Company Kitatama Substation)

275kV underground substation (Tokyo
Electric Power Company Shinjuku
Substation)

1972

1973

500kV transmission begins (Tokyo
Electric Power Company Boso Line)1974

500kVOF cable introduced

1975

109

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

New Transformer-Related Technology Developed
First actual SF6 insulated transformer introduced
Long-term insulation reliability testing implemented
for 500kV transformers
Silicon steel annealing discontinued
Compact aluminium coolers adopted
Long-term voltage impression testing on 735kV
prototype transformer
Numerical analysis of potential vibration in coils
Panel-type soundproof tank adopted
Moulded transformer developed
Systematisation of volume theory
Production of domestic 500kV transformers
UHV development laboratory built
500ton trailer used
Woodbridge-connected, 220kV, 200MVA
transformer (Japanese National Railways Sanyo
Shinkansen line)transformer winding short-circuit-resistant design
guidelines published (IEEJ Report)
Resin in-oil spacers first used
Electric field analysis using filter paper method
High grain-oriented silicon steel sheets first used
Gas-in-oil automatic monitoring system developed
Investigation begins on the flow electrification
phenomenon
High-density press board adopted
Winding oil flow visualisation technology developed
Expansion overseas (transformer factory operating in
Brazil)Magnetic tank shielding first used (core type)Transformer accidents due to the flow electrification
phenomenon
Three-dimensional magnetic field analysis
technology
Non-magnetic casing eddy current analysis
50dB, forced-oil, forced-air cooled cooling systemdeveloped
Five-leg core adopted for ultra-high-capacitytransformer
Tank flange reinforcing structure adopted
Heat sealed transposed cables first used
Widespread use of new insulation materials such aspress board structural materials, moulded insulation
and reinforced wood
Air pallet transportation method introduced
Maintenance guidelines recommended forhigh-capacity transformers (Electric Technology
Research Association)

1976

275kV gapless arrester commercialised

1977

Substation noise reduction status survey

Main Transformer Products
Special three-phase, 275kV, 222MVA transformer
transported in six partitions (Tokyo Electric Power
Company Azumi Power Station) (Mitsubishi)
Single-phase, 500kV, 400MVA transformer forexport (BPA, USA) (Toshiba)
65dB low-noise transformer (270MVA transformer
for Kyushu Electric Power Company Oita Power
Station) (Hitachi)
Single-phase, 525kV, 900/3MVA transformer forexport (BPA, USA) (Fuji)
275kV, 300MVA underground substationtransformer (Tokyo Electric Power Company Jonan
Substation) (Toshiba)
Single-phase, 400kV, 1000/3MVA transformer forexport (ESKOM, South Africa) (Mitsubishi)
Three-phase, 262.5kV, 490MVA transformer(Kansai Electric Power Company Kainan Power
Station) (Hitachi)
132kV, 4 × 34MVA, DC213.6kADirectory step
down rectifier transformer (ALCAN) (Fuji)
Three-phase, 275kV, 680MVA transformer (Tokyo
Electric Power Company Kashima Power Station)(Mitsubishi)
Low-noise, 275kV, 300MVA transformer (Chubu
Electric Power Company Mikawa Substation)(Hitachi)Single-phase, 525kV, 1000/3MVA autotransformer (BPA, USA) (Hitachi)
275kV, 700MVA phase shifter (Tokyo ElectricPower Company Boso Substation) (Toshiba)
66kV, 10MVA truck-transportable transformer(Tohoku Electric Power Company) (Meidensha)

Tank and bushing reinforcement recommended as ameans of preventing accidents worsening (ElectricTechnology Research Association)
Increased use of continuous disc windings for 275kV
No-bake cores first used
Recommendations for onsite operation methods andcontrol values for 500, 275, 154kV high-capacitytransformers (Electric Technology Research
Association)
Flow electrification solution and prevention
technology establishedTransformer oil charge level management
implemented
Potential vibration analysis technology established
Overseas technology licence (Elektrimunion, Poland)Electric field analysis / magnetic field analysis
technology established
Automatic gas analysis equipment developed
Transportation of 500kV transformers with main
covers on becomes the norm
Guidelines issued on transformer noise reduction
measures (Electric Technology Research
Association)
Social Situations, Electricity/Transformer Situation
Overseas, OtherHigh grain-oriented silicon steel sheets developed(Yawata Iron & Steel Company)

Apollo moon landing

Osaka World Expo

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

110Three-phase, 275kV, 870MVA transformer (Tokyo
Electric Power Company Fukushima No. 1 Nuclear
Power Station) (Toshiba)
Domestic single-phase, 500kV, 1000/3MVA
auto-transformer (Tokyo Electric Power Company
Shin-Koga Substation) (Toshiba)
Domestic single-phase, 500kV, 1000/3MVA
auto-transformer (Tokyo Electric Power Company
Boso Substation) (Mitsubishi)
275kV, 200MVA underground substationtransformer (Tokyo Electric Power Company
Shinjuku Substation) (Mitsubishi)
Special three-phase, 275kV, 335MVA transformer
with six partitions (Tokyo Electric Power Company
Tamahara Power Station) (Mitsubishi)
Three-phase, 262.5kV, 660MVA transformer(Kansai Electric Power Company Kainan Power
Station) (Hitachi)
60MVA transformer for a high-capacity arc furnace(Yahagi Steel) (Toshiba)
66kV, 80MVA reactor (Tokyo Electric Power
Company Jonan Substation) (Toshiba)
Three-phase, 275kV, 1100MVA transformer (Tokyo
Electric Power Company Kashima Power Station)(Toshiba)
On-load tap changing, 275kV, 660MVA transformer(Kansai Electric Power Company Himeji No. 2
Power Station) (Toshiba)
Single-phase, 500kV, 1000/3MVA auto-transformer(Tokyo Electric Power Company Shin-Fukushima
Substation) (Hitachi)
Three-phase, 500kV, 640MVA transformer (Kansai
Electric Power Company Okutataragi Pumped
Storage Power Station) (Hitachi)
275kV, 860MVA transformer with on-load voltage
regulator (Kansai Electric Power Company
Takahama Power Station) (Mitsubishi)
On-load tap changing, 275kV, 450MVA transformer(Tokyo Electric Power Company Kohoku
Substation) (Mitsubishi)
Single-phase, separate-winding, 500kV, 250MVA
transformer (Kansai Electric Power Company
Inagawa Substation) (Toshiba)
On-load voltage phase regulating, 268.8kV,
250MVA transformer (Tohoku Electric Power
Company Niigata Substation) (Meidensha)
154kV, 80MVA reactor (Tokyo Electric Power
Company Ooi Thermal Power Station) (Meidensha)
Special three-phase, 500kV, 640MVA transformer(Kansai Electric Power Company Okutataragi
Pumped Storage Power Station) (Mitsubishi)
Assembled-for-transport, 275kV, 450MVA LRTtransformer (Chubu Electric Power Company Sunen
Substation) (Toshiba)
Three-phase, 500kV, 1100MVA transformer (Tokyo
Electric Power Company Sodegaura Power Station)(Toshiba)
Special three-phase, 345kV, 500MVA transformer

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1973 oil crisis

(Taiwan Electric) (Fuji)
Moulded transformers go on sale (Fuji)
66kV, 15MVA transformer for GIS substation(Tokyo Electric Power Company Fujine Substation)(Meidensha)
Single-phase, separate-winding, 500kV, 250MVA
transformer (Kansai Electric Power Company
Shin-Ikoma Substation) (Hitachi)
60kV, 13.5MVA, Shinkansen booster- transformer(Japanese National Railways Tokuyama Substation)(Meidensha)
275kV, 150MVA reactor (Tokyo Electric Power
Company Kitatama Substation) (Toshiba)
Three-phase, 500kV, 1100MVA transformer (Tokyo
Electric Power Company Sodegaura Power Station)(Mitsubishi)
Three-phase, 275kV, 1200MVA transformer (Japan
Atomic Power Company Tokai No. 2 Nuclear
Power Station) (Mitsubishi)
400kV, 50MVA reactor (Iran) (Mitsubishi)
Single-phase, 500kV, 500MVA auto-transformer(Tokyo Electric Power Company Boso Substation)(Mitsubishi)
Three-phase, 500kV, 1240MVA transformer(Kansai Electric Power Company Oi Nuclear Power
Station) (Mitsubishi)
275kV, 150MVA reactor (Tokyo Electric Power
Company Keihoku Substation) (Mitsubishi)
Three-phase, 275kV, 680MVA transformer (Tokyo
Electric Power Company Anegasaki Power Station)(Hitachi)Single-phase, separate-winding, 500kV, 250MVA
transformer (Kansai Electric Power Company Shigi
Substation) (Mitsubishi)
Moulded transformer production starts (Mitsubishi)
500kV, 50MVA reactor (Brazil) (Mitsubishi)
Three-phase, 500kV, 1200MVA transformer (Tokyo
Electric Power Company Fukushima No. 1 Nuclear
Power Station) (Toshiba)
Single-phase, 500kV, 500MVA auto-transformer(Tokyo Electric Power Company Shin-Koga
Substation) (Toshiba)
500kV, 680MVA transformer transported in nine
partitions (Kansai Electric Power Company
Okuyoshino Pumped Storage Power Station)(Toshiba)
125kV, 187MVA DC conversion transformer(Tokyo Electric Power Company Shin-Shinano
Frequency Converter Substation) (Toshiba, Hitachi)
275kV, 450MVA LRT transformer transported
assembled with built-in LTC (Chubu Electric Power
Company Kitatoyoda Substation) (Fuji)
Year
1977
1978

Power Situation in Japan
Status survey of earthquake damage tosubstation equipment

New York blackout

New Transformer-Related Technology Developed
Widespread use of work-hardened copper wire
UHV test transformer completed

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

112Substation equipment damaged by
Miyagi earthquake

1979

On-load tap changing distribution
transformers standardised
Hokkaido-Honshu DC gridinterconnection started

1980

Investigation into various properties of composite
insulation
UHV test transformer long-term reliability testing
BTA-added transformer oil first used
MR new-series LTCs first used
GEORG’s automatic core cutting machine introduced
Seismic strength testing conducted on substationequipment
Gas-in-oil analysis maintenance criteria established(Electric Technology Research Association)
UHV technology first used on transformers of 500kV
and under
Highly effective direct-mounted soundproofing
plates first used
147kV gas-insulated transformer prototype
completedZnO arresters used in oil to protect tap windings
Magnetic-domain-refined silicon steel sheets firstused
Cooler variable speed control developed
Seismic proof transformer bushing design established(Electric Technology Research Association)
Amorphous transformer developed
Step-lap stacked cores first used
Press board in-oil spacers first used
Low-noise, 275kV, 300MVA, 70dB transformer withno soundproof panels completed
275kV gas-insulated transformer prototype
completed
First use of a new disassembled-for-transport typetransformer
Explosion-proof transformer tank experiments
conducted
Internal pressure analysis method for transformertanks presented (Electric Technology Research
Association)
Automated core-leg stacking equipment first used
Ultra-high-capacity non-partitioned CC shielded
continuous disc winding used

1981

1982

1983

1984

1985

1986
1987
1988

113

Earthquake-resistant transformer design method
specified (Electric Technology Research
Association)
Transformer standard JEC-204 established
Vacuum-valve LTC developed
Computer-based seismic proof analysis method
establishedTransportation for onsite installation by air bearings
Trial use of the new disassembled-for-transportsystem for transformers
High efficiency coolers used with FRP fans

Major black-out in the Tokyo
Metropolitan area
Construction started on UHVtransmission line (Tokyo Electric Power
Company)

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan

Guidelines issued on new insulation design concepts(Electric Technology Research Association)

Main Transformer Products
Single-phase, 500kV, 750/3MVA transformer
transported by rail with main cover on (Kansai
Electric Power Company Minami-Kyoto Substation)(Hitachi)
72MVA transformer for high-capacity arc furnace(Tokyo Steel, Okayama) (Toshiba)
154kV, 20MVA transformer for GIS substation(Tokyo Electric Power Company Naruse Substation)(Meidensha)
GIS direct-coupled, single-phase, 500kV,
1000/3MVA auto-transformer (Kyushu ElectricPower Company Kita-Kyushu Substation) (Toshiba)
GIS direct-coupled, single-phase, 500kV,
1000/3MVA auto-transformer (Kyushu ElectricPower Company Chuo Substation) (Hitachi)
GIS direct-coupled, single-phase, 500kV,
1000/3MVA auto- transformer (Kyushu ElectricPower Company Nishi-Kyushu Substation)(Mitsubishi)
1550/√3kV transformer for UHV transmission
testing (Central Research Institute of Electric Power
Industry, Takeyama) (Fuji)
World’s highest capacity class three-phase, 13.8kV,
67MVA, DC68kA rectifier transformer (Canada)(Fuji)
Three-phase, 525kV, 1100MVA transformer (Tokyo
Electric Power Company Sodegaura Power Station)(Hitachi)
500kV, 50MVA with two-winding, radial core shunt
reactor (Argentina, Uruguay) (Fuji)
World’s highest capacity moulded 22kV, 7.5MVA
transformer (Japanese National Railways, Sendai
Station) (Fuji)
Single-phase, 512.5kV, 1200/3MVA transformer(Canada) (Fuji)
Assembled-for-transport, 275kV, 450MVA
transformer (Chubu Electric Power Company Sunen
Substation) (Meidensha)
Forced-gas, forced-air cooled, 66kV, 10MVA
transformer (Joetsu Shinkansen) (Meidensha)
275kV, 300MVA underground substationtransformer (Tokyo Electric Power Company
Setagaya Substation) (Meidensha)
275kV, 150MVA underground substation reactor(Tokyo Electric Power Company Setagaya
Substation) (Meidensha)
250kV, 187MVA DC conversion transformer(Electric Power Development Company
Hokkaido-Honshu grid interconnection) (Hitachi,
Toshiba)
Forced-gas, forced-air cooled, gas-insulated, 66kV,
10MVA transformer (Asahi Shimbun) (Toshiba)
500kV, 1000/3MVA transformer transported
assembled with in-built LTC (Kansai Electric Power
Company Seiban Substation) (Fuji)
Special three-phase, 275kV, 300MVA underground

Social Situations, Electricity/Transformer Situation
Overseas, Other

Three Mile Island Nuclear Accident
1979 oil crisis

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

114substation transformer (Tokyo Electric Power
Company Nerima Substation) (Fuji)
Special three-phase, 275kV, 150MVA reactor(Tokyo Electric Power Company Nerima
Substation) (Fuji)
80dB, three-phase, 275kV, 680MVA transformer
with no sound barrier (Tohoku Electric Power
Company Akita Power Station) (Hitachi)
275kV, 200MVA reactor (Tokyo Electric Power
Company Niiza Substation) (Mitsubishi)
Evaporation-cooled, gas-insulated, 77kV, 40MVA
transformer (Kansai Electric Power Company
Hokusetsu Substation) (Mitsubishi)
500kV, 120MVA reactor (Argentina) (Fuji)
500kV, 670MVA transformer transported by rail
(Tokyo Electric Power Company Shin-Haruna
Substation) (Fuji)
Single-phase, 500kV, 855/3MVA transformer(Argentina) (Fuji)
Single-phase, on-load tap changing, 500kV,
500/3MVA auto-transformer (Tokyo Electric Power
Company Shin-Okabe Substation) (Hitachi)
2200kV testing transformer (Mitsubishi)
1400kV testing transformer (Toshiba)
1000kV gas-insulated testing transformer(Mitsubishi)
Single-phase, separate-winding, 500kV, 750/3MVA
transformer using UHV technology (Tokyo ElectricPower Company Shin-Hadano Substation) (Toshiba)
1550/√3kV, 6MVA transformer for UHVtransmission testing (Central Research Institute ofElectric Power Industry, Akagi) (Fuji)
525kV, 1200/3MVA transformer (Australia) (Fuji)
765kV, 805/3MVA transformer (Venezuela)(Hitachi, Toshiba, Mitsubishi)
Three-phase, 241.5kV, 680MVA transformer(Thailand) (Fuji)
Single-phase, 500kV, 1500/3MVA auto-transformer
using UHV technology (Chubu Electric Power
Company Shin-Mikawa Substation) (Hitachi)
Three-phase, 525kV, 1200MVA transformer (Tokyo
Electric Power Company Fukushima No. 2 Power
Station) (Hitachi)
Low-noise, 220kV, 650MVA transformer withhighly efficient soundproofing plate (Kyushu
Electric Power Company Shin-Kokura Power
Station) (Hitachi)
Gas-insulate, on-load tap changing, 66kV, 11MVA
transformer (Sapporo City Transportation Bureau)(Fuji)
275kV, 450MVA transformer with variable speed
controlled cooler (Chubu Electric Power Company
Seino Substation) (Meidensha)
525kV, 300MVA transformer with variable speed
controlled cooler (Kansai Electric Power Company
Gobo Substation) (Hitachi)
Gas-insulated, 66kV, 8MVA transformer (Teito
Rapid Transport Authority Mukaihara Substation)

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Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan(Hitachi)
275kV, 1000MVA phase sift regulator (Tohoku
Electric Power Company Niigata Substation)(Toshiba)
New disassembled-for-transport type, 275kV,
300MVA transformer (Kansai Electric Power
Company Kobe Substation) (Mitsubishi)
Evaporation-cooled, gas-insulated, 77kV, 20MVA
transformer (Kansai Electric Power Company
Nishi-Shirahama Substation) (Mitsubishi)
70dB, 275kV, 300MVA transformer with no soundbarrier (Tohoku Electric Power Company Sukagawa
Substation) (Hitachi)
126MVA transformer for an arc furnace(SICARTSA, Mexico) (Toshiba)
Three-phase, 500kV, 1260MVA transformer (Japan
Atomic Power Company Tsuruga Nuclear Power
Station) (Toshiba)
765kV, 400/3MVA reactor (ESKOM, South Africa)(Toshiba, Fuji)
Gas-insulated, on-load tap changing, 66kV, 10MVA
transformer (KDD) (Toshiba)
Gas-insulated, on-load tap changing, 64.5kV,
30MVA transformer (Hokkaido Electric Power
Company Minami-Sanjo Substation) (Mitsubishi)
Single-phase, 765kV, 2000/3MVA, auto-transformer(South Africa) (Fuji)
Three-phase, 500kV, 1200MVA transformer (Tokyo
Electric Power Company Fukushima No. 2 Nuclear
Power Station) (Hitachi)
Self-cooled, gas-insulated, 66kV, 10MVA
transformer (Yokohama City Transportation Bureau
Maioka Substation) (Hitachi)
275kV, 200MVA gapped-core shunt reactor (Tokyo
Electric Power Company Keihin Substation)(Mitsubishi)
Gas-insulated, on-load tap changing, 66kV, 20MVA
transformer (Sapporo City Transportation Bureau)(Meidensha)
2000kV corona-free testing transformer (Showa
Electric Wire & Cable Company Sagamihara)(Toshiba)
Self-cooled, gas-insulated, 66kV, 20MVA
transformer (Sapporo City Transportation Bureau)(Mitsubishi)
3-windings, 525/147kV, 1100MVA transformer for
combined cycle (Tokyo Electric Power Company
Futtsu Power Station) (Hitachi)
400kV, 100MVA reactor (South Africa)(Mitsubishi)
Ultra-low-noise, 187kV, 200MVA,43dB transformer(Hokkaido Electric Power Company Naeho
Substation) (Hitachi)
High-impedance, 500kV, 1500/3MVA transformer(Tokyo Electric Power Company Shin-Keiyo
Substation) (Hitachi)

1150kV transmission begins (USSR)

Tsukuba International Exposition

Chernobyl Nuclear DisasterUS makers withdrawn from US transformer
businesses

Honshu-Shikoku cross-link complete
Japanese National Railways privatised

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

116

Year
1988
1989

1990
1991
1992
1993
1994
1995
1996
1997

Power Situation in Japan

LTCs completed for high-capacity, gas-insulatedtransformers
First use of low-dielectric-constant press board
Studies on DC bias magnetism from magnetic storms

Transformer standard JEC-2200 established
500kV underground substation (Tokyo
Electric Power Company Shin-Toyosu
Substation)

1998
1999

High-capacity transformer factory operating in China

500kV, 250MVA short-circuit test implemented
Transformer deterioration diagnosis guidelines issued(Electric Technology Research Association)
Review of guidelines for gas-in-oil analysis diagnosis
methods (Electric Technology Research Association)
Maintenance management method proposed for flow
electrification (Electric Technology Research
Association)
Ultra-compact, new shell-type transformer completed

2000
2001
2002
2003
Main Transformer Products
Single-phase, 765/500kV, 1650/3MVA
auto-transformer (FURNAS, Brazil) (Toshiba)
275kV, 200MVA reactor (Chubu Electric Power
Company Umemori Substation) (Toshiba)
275kV, 300MVA transformer together with phaseshifter (Tohoku Electric Power Company Akita
Substation) (Mitsubishi)
Liquid-cooled, gas-insulated, 154kV, 200MVA
transformer (Tokyo Electric Power Company Asahi
Substation) (Toshiba)
Self-cooled, gas-insulated, 66kV, 30MVA
transformer (Kyushu Electric Power Company
Yatsushiro Substation) (Toshiba)
New disassembled-for-transport type, 220kV,
250MVA transformer (Kyushu Electric Power
Company Kamishiiba Power Station) (Hitachi)
275kV, 250MVA+20MVAR transformer with
in-built shunt reactor (Chubu Electric Power
Company Toshin Substation) (Mitsubishi)
275kV, 250MVA reactor (Kuwait) (Mitsubishi)
Single-phase, 765/345kV, 1500/3MVA
auto-transformer (FURNAS, Brazil) (Hitachi)
18.5MVA cycloconverter power supply transformer
for variable speed pumped storage (Tokyo ElectricPower Company Yagisawa Power Station)(Toshiba)

117

New Transformer-Related Technology Developed

Survey Reports on the Systemization of Technologies; No. 4, March 2004
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Social Situations, Electricity/Transformer Situation
Overseas, OtherGas-insulated, three-phase, 64.5kV, 30MVA
transformer for waste heat recovery (Tohoku
Electric Power Company Honmachidori Substation)(Fuji)
40kA secondary current, 15MVA transformer for a
DC arc furnace (Daido Steel Company, Hoshizaki)(Toshiba)
Liquid-cooled, gas-insulated, 275kV, 300MVA
transformer (Tokyo Electric Power Company
Shin-Sakado Substation) (Toshiba)
Liquid-cooled, gas-insulated, 275kV, 300MVA
transformer (Kansai Electric Power Company
Hirakata Substation) (Mitsubishi)
Liquid-cooled, gas-insulated, 275kV, 250MVA
transformer (Chubu Electric Power Company Abe
Substation) (Hitachi)
Three-phase, 500kV, 1260MVA transformer(Kansai Electric Power Company Oi Nuclear Power
Station) (Mitsubishi)
Tertiary 50% capacity, single-phase,
separate-winding, 512.5kV, 750/3MVA transformer(Tokyo Electric Power Company Shin-Okabe
Substation) (Hitachi)
Three-phase, 275kV, 1100MVA transformer (Tokyo
Electric Power Company Higashiogishima Power
Station) (Fuji)
Gas-insulated, three-phase, 155kV, 25.5MVA
transformer (Chubu Electric Power Company
Kitamatado Power Station) (Fuji)
High-head-drop, self-cooled, gas-insulated,
three-phase, 75kV, 20MVA transformer (Chubu
Electric Power Company Tokadai Substation) (Fuji)
Low-noise, 268.5kV, 300MVA,60dB transformer
with no soundproof panels (Tohoku Electric Power
Company Ishinomaki Substation) (Hitachi)
New disassembled-for-transport type, three-phase,
275kV, 250MVA transformer (Chubu ElectricPower Company Kita-Matsumoto Substation)(Toshiba)
Forced-gas, forced-air cooled, gas-insulated, on-load
tap changing, 66kV, 60MVA transformer (Tokyo
Electric Power Company Toyosu Substation)(Toshiba)
Single-phase, 525kV, 1500/3MVA auto- transformer
using low-dielectric-constant PB (Tokyo ElectricPower Company Shin-Sakado Substation) (Hitachi)
1050kV, 1000MVA, UHV field demonstration
testing transformer (Tokyo Electric Power Company
Shin-Haruna Substation) (Hitachi, Toshiba,
Mitsubishi)
New disassembled-for-transport type, three-phase,
500kV, 300MVA transformer (Kansai ElectricPower Company Okutataragi Power Station)(Mitsubishi)
500kV, 250MVA reactor (Electric Power
Development Company) (Mitsubishi)
Forced-gas, water-cooled, gas-insulated, 275kV,
300MVA transformer (Tokyo Electric Power

Gulf WarToshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

118

Company Higashi-Shinjuku Substation) (Toshiba)
Forced-gas, water-cooled, gas-insulated, 275kV,
150MVA transformer with shunt reactor (Tokyo
Electric Power Company Katsunan Substation)(Toshiba)
Forced-gas, forced-air cooled, gas-insulated, 161kV,
68MVA transformer (Tohoku Electric Power
Company Yanaizu-Nishiyama Geothermal Power
Station) (Toshiba)
2300kV testing transformer (Hitachi)
New disassembled-for-transport type, 500kV,
1000MVA transformer (Chubu Electric Power
Company Aichi Substation) (Mitsubishi)
Three-phase, 500kV, 1450MVA transformer (Tokyo
Electric Power Company Kashiwazaki-Kariwa
Nuclear Power Station) (Hitachi)
World’s highest capacity moulded three-phase,
22kV, 13MVA transformer (Tokyo Metropolis)(Fuji)High voltage double rated, three-phase, 520(225)kV,
730MVA transformer (Kyushu Electric Power
Company Reihoku Power Station) (Hitachi)
500kV, 250MVA reactor (Electric Power
Development Company Sakaide Power Station)(Toshiba)
Different capacity, three-phase, split-windingtransformer 275kV, 800/450-350MVA transformer(Kansai Electric Power Company Himeji No. 1
Power Station) (Mitsubishi)
Three-phase, 500kV, 1450MVA transformer (Tokyo
Electric Power Company Kashiwazaki-Kariwa
Nuclear Power Station) (Toshiba)
Forced-gas, water-cooled, gas-insulated,
three-phase, 107.5kV, 40MVA transformer(Chugoku Electric Power Company Shimada
Substation) (Fuji)
New disassembled-for-transport type, 500kV,
1000MVA transformer (Chubu Electric Power
Company Seibu Substation) (Toshiba)
Three-phase, on-load tap changing, 275kV,
1050MVA transformer (Tohoku Electric Power
Company Haramachi Power Station) (Toshiba, Fuji)
New disassembled-for-transport type, three-phase,
275kV, 250MVA transformer (Chubu ElectricPower Company Shin-Hokushin Substation) (Fuji)
New disassembled-for-transport type, three-phase,
500kV, 800MVA transformer (Kansai ElectricPower Company Okutataragi Power Station)(Mitsubishi)
Fully transportable, three-phase, 281kV, 380MVA
transformer for (maritime) power station (Tokyo
Electric Power Company Chiba Power Station)(Fuji)
1H DC reactor for HVDC (Kii Channel Anan andKihoku Converter Stations) (Toshiba, Mitsubishi)
1500/3MVA transformer for a 500kV undergroundsubstation (Tokyo Electric Power Company
Shin-Toyosu Substation) (Toshiba)

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Kobe Earthquake155/175MVA transformer for an arc furnace(IMEXSA, Mexico) (Toshiba)
152/182MVA transformer for an arc furnace(ANSDK, Egypt) (Toshiba)
500kV, 872MVA transformer for HVDC conversion(Kii Channel Anan and Kihoku Converter Stations)(Hitachi, Toshiba, Mitsubishi)
Liquid-cooled, gas-insulated, 275kV, 450MVA
transformer (Chubu Electric Power Company Meijo
Substation) (Hitachi)
Split-winding, three-phase, 525kV, 410MVA
transformer x 2 (Tokyo Electric Power Company
Futtsu Power Station) (Fuji)
Three-phase, 525kV, 1100MVA transformer(Electric Power Development Company
Tachibana-wan Power Station) (Fuji)
Single-phase, 765/400kV, 1500/3MVA
auto-transformer (EDELCA, Venezuela)(Mitsubishi)
Single-phase, 525kV, 120/3MVA shunt reactor withsecondary winding (China) (Fuji)
Special three-phase, 500kV, 1500MVA transformer(Kansai Electric Power Company Nose Substation)(Mitsubishi)
New disassembled-for-transport type, 500kV,
1000MVA transformer (Chugoku Electric Power
Company Chizu Substation) (Hitachi)High voltage double rated, three-phase, 525(281.25)kV, 1060MVA transformer (Tokyo ElectricPower Company Hitachinaka Power Station)(Hitachi)Three-phase, 500kV, 1510MVA transformer (Chubu
Electric Power Company Hamaoka Nuclear Power
Station) (Mitsubishi)
Forced-gas, water-cooled, gas-insulated, 345kV,
400MVA transformer (Australia) (TMT&D)
Split-winding, three-phase, 507kV, 525MVA
transformer x 2 (Tokyo Electric Power Company
Kannagawa Power Station) (TMT&D)

New York terrorist attacks

Iraq WarToshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

120

■ Reference Materials 2: Explanation ofTransformer Terminology
Reference Materials 2 provides illustrated
explanations of transformer technology appearing
in this report in order that this may be understoodby non-specialists. Selected terms appear in themain text in italic font. These are provided foryour reference.
Elephant Bushing
A method used to connect a transformer and acable in oil within a duct. Given the possibility ofdifferences in time spent onsite between
transformer
manufacturers
and
cable
manufacturers, and also to clearly define therespective roles of each manufacturer, it iscommon in Japan to have transformer terminals
connected to an oil-oil bushing and thenconnected to a cable within a duct. This type ofoil bushing is called an elephant bushing because
the shape of the duct resembles an elephant’s
trunk.

Acoustic Corona Location
A system of estimating the location of partial
discharge within a transformer where the partial
discharge is accompanied by sound. The
waveform of the sound is recorded using three ormore microphones while also recording the
waveform of the electrical partial discharge; thetime difference between the sound waveforms andthe electrical discharge waveform allow an
estimation of the location of the partial discharge.
Differences in the distance between the source ofthe sound and the microphones create differencesin travelling time; altering the position of the
microphones makes it possible to determine thelocation of the partial discharge quite accurately.
Frame-Shaped CoreA core structure that makes the most of theproperties of grain-oriented silicon steel sheets;
the sheets are cut at 45˚ angles and placed against
the core limbs and yoke. The core is so named
because the angle of the joins resembles a frame.
The joins are alternately arranged with a
20-30mm deviation to ensure a smooth flow ofmagnetic flux.

Oil bushingTransformer
Winding

Oil cable head

Frame join

Cable

SF6 GasRecognised for its superior insulation properties
in the USA in the 1930s, this was first used in gas
circuit breakers. Its application in transformers
was later examined and it was commercialised intransformers in the 1950s. It is widely used today
in gas-insulated switchgear. While it is classed asa greenhouse gas, there is as yet no appropriate
substitute for SF6, so it is still used with the main
countermeasure being to reduce the emissions
into the atmosphere as much as possible.

121

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National Museum of Nature and Science, Japan

Voltage Application Test
A means of AC insulation testing for transformers,
wherein a specified test voltage is applied to awinding in a test transformer.
Gas-Insulated Switchgear (GIS)
The general term for a device that makes up thecircuit configuration within a substation, from thetransmission line intake to the connection to thetransformer, encompassing all non-transformer
substation equipment (e.g. circuit breakers,
arresters, disconnecting switches and current
transformers) and the transformer connection
busbar within a pressurised vessel.

Shell-Type Transformer
A structure widely used when transformers werefirst developed, wherein the windings wereassembled first, then the core was wrappedaround them. So named because the core islocated on the outside.

WindingCoresusceptible to magnetisation of the crystal grains[100] than the existing grain-oriented silicon steel
sheets; these are a high quality material currently
in general use in transformers.
High ImpedanceTransformers are represented in a circuit as
impedance. Therefore, in the event of a ground
fault, for instance, in the system, the fault current
is limited by the sum of the transformer
impedance and the system impedance, since thefault current flows through the transformer.
Accordingly, where the system fault current is
expected to be greater than the circuit breaker canhandle, the transformer impedance is designatedto be higher than normal. For 275kV devices, theimpedance was usually designated as 14%; highimpedance devices were designated as 20%.
Alternately Stacked Joins
Frame-shaped cores are joined at the corners of
the frame, usually with the joins on every
alternate two steel plates 20-30mm apart.

Uniform Insulation
An insulation structure wherein the ends of thewire and the neutral point have the same
insulation strength.
Vapour-phase-Drying Method
A method of drying the interior of a transformer,
whereby the insulation is heated to expel its
moisture content as quickly as possible. Thisdrying method uses heat to facilitate the increasein temperature of the insulation by bring thevapour of kerosene, a type of lamp oil, into
contact with the cold insulation, where it liquefies
and transmits latent heat to the insulation. Theliquefied kerosene is retrieved once heating iscomplete, and the insulation vacuumed in a
furnace to evaporate and dry out any remaining
moisture content.
Silicon Steel Sheets
Steel sheets developed in the United Kingdom in1900 with superior magnetic properties; these areused to make cores for transformers and rotatingmachinery. Mixing around 3% of silicon with thesteel produces a high magnetic flux density with avery small magnetising current. Since thisdramatically reduces incurred loss, thiscontributed greatly to the upsizing of machinery
following this invention.
High Grain-Oriented Silicon Steel Sheets
Developed in Japan in 1968 for transformers,
these silicon steel sheets were designed to
improve the amount of incurred loss by having
the rolling direction aligned in a direction more

Conservators
The purpose of conservators is to regulate
volumetric change in transformer oil due tochanges in temperature from a box located in theupper part of the transformer tank. Since hot oil
can deteriorate in quality very rapidly whencoming in contact with the air, a thin pipe is used
to connect it to the transformer so that the oiltemperature in the conservator does not rise toohigh. Using inert nitrogen as an intermediarylayer or using a rubber membrane partition areways to prevent oil coming into contact with theair, so as to avoid deterioration of the oil.
Currently, the rubber membrane partition method
is most commonly used in high-capacitytransformers.
Condenser Bushing
Bushing is used as an intermediary for connecting
the ends of the transformer winding protrudingfrom the tank to the power source or the load.
Condenser bushing is one such insulation
structure commonly used for high voltages of
30kV and higher. This bushing has insulating
paper wrapped around the central conductor, withmultiple threads of capacitor foil weaved into it tocontrol the potential. The potential distribution in
the axial and radial directions can be controlled

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
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122

by adjusting the size of the foil threads and the
distance between them.

Sound-absorbing
material (prevents
sound escaping)Oil-impregnated paper or
Measuring terminal
solid insulator
Capacitor foil
GroundCentralCondenser bushing core

conductor

Concrete Sound Barrier
A sound barrier structure involving a transformer
placed within a housing structure made ofconcrete, as shown in the figure, usually used
when it is necessary to reduce transformer noiseby 20dB or more. Consideration is given to letting
no noise escape from the openings for the bushingpockets or oil pipes. Used less frequently more
recently due to factors such as installation spaceand onsite work.
Sound-absorbing
material(prevents soundescaping)
Oil pipe
openingBushingBushing pocket
opening
Muffler-shaped
air vent(exhaust)

Sound barrier(Steel sheet)(Concrete)Sound-absorbing
material
Rubber gasket(prevents soundescaping)

Main tankBase frame
Anti-vibration
fittings

Anti-vibration
rubberSurge-proof windings
A typical lightning-protected winding structure
for shell-type transformers, having a large
electrostatic shielding plate at the ends of thelines. It has the same properties as the multiple
cylindrical windings for core-type transformers.

Shielding plate

Exhaust fan
Expansion
joint
Oil pipe(Concrete)
Anti-vibration
joint Main tankSound barrierSound-absorbingmaterial

Mufflershaped
air vent(intake)
Forced oil pump
Anti-vibration rubber
Base anti-vibrationmaterial

Concrete Panel Sound Barrier
A sound-proofing structure prefabricated bypouring concrete into a steel plate panel, which
can then be mounted onto a transformer frame
after the transformer has been installed. These canbe expected to reduce noise by 15-20dB.

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Three-Phase, Five-Leg Core
A structure in which the magnetic flux of themain legs (Φ1, Φ2, Φ3) is divided between theyokes (Φ5, Φ6) and the side legs (Φ4, Φ7) so as toreduce the height during transportation. In termsof the magnetic flux sine wave, this can reduce
the height of the yoke by 1/√3. In fact, if themagnetic flux is given a constant density in orderto superimpose harmonics onto the magnetic flux,
the cross-section of the yoke can be reduced by
up to 50%.

Time (degrees)

A test when a transmission line has groundedthrough an arc to confirm whether sending the
ground current through an arc-suppression coilconnected to the neutral point has extinguished
the arc current, returning it to 0, and eliminatedthe ground fault.

Three-Chamber Conservator
A type of nitrogen-filled conservator, so named
because the inside of the conservator is divided
into three parts, as shown in the figure. While thenitrogen-filled type was widely used initially, it
had the major disadvantage of a large tank and it
was gradually superseded by the floating-tank
type.

Main-Gap-Filling Insulation Structure
A structure within the insulation structure
between the high- and low-voltage windings
filled with highly insulating-strength solid
insulation without any oil gap. The axial oil duct
for cooling the windings is built within thewindings. However, this method is currently
hardly used, because it is difficult to constructwindings with no oil gap and partial discharge
may occur in these tiny gaps during testing inhigh electrical fields.

Core

Insulating
paper
flangeElectrostatic ring

NitrogenAir

Nitrogen

Air
Moisture
absorption
respirator(b) Horizontal
three-chamber
type

Moisture
absorption
respirator(a) Verticalthree-chamber
type

Magnetic-Domain-Refined Silicon Steel Sheets
High grain-oriented silicon steel sheets with theaxial direction aligned with the direction of therolling for ease of crystal magnetisation. To
further enhance these properties, the surface ofthe sheets is divided into magnetic domains byusing a laser to make fine cuts with very hardedges.
Vacuum Drying
A drying process to remove moisture content
from the insulation as well as any moistureattached to the core, during which the contents ofthe transformer are heated with hot air and thenthe entire drying oven is vacuumed to hasten theextraction of moisture and to thereby reduce thedrying time.

Low-voltage
windingHigh-voltage
winding
Axial oil duct
Oil ducts
between coils

Insulating paper
Insulation cylinder

Degree of Polymerisation
A scale used in examining the deterioration ofcellulose insulation material. Cellulose forms along chain of hydrocarbons, which gradually
breaks down through heat and reduces inmolecular weight. The degree of polymerisation
is a scale used to determine the extent of the
reduction in molecular weight.
Step-Lap Joint
A joint structure joining the legs and yoke in sucha way that the steel plate battens of the core
sheets are arranged in a stepwise manner, as
shown in the figure. This smoothens the flow ofmagnetic flux, which has the effect of reducing
noise and incurred loss.

Arc Suppresion Test

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

124Insulation Coordination
Establishing appropriate respective protective
equipment for transmission lines and machinesconnected to them, determining the level ofprotection and the appropriate reasonable level ofinsulation. Establishing lightning arresters near
the in-points for transmission lines and neartransformers and limiting the amount of lightning
voltage to equipment. Designing equipment towithstand lightning surges of higher voltages thanthat controlled by the arrester.

Low-voltage winding or coreDamper-Shield Winding
A lightning-protected winding developed by
Hitachi. A continuous disc winding with a shieldconductor wound between each turn to improve
the potential distribution, the winding has
increased electrical capacitance between turns.
The shield conductor potential is split into four
sections and connected to the current-carrying
conductor, which is split into two sections. Later
named the CC shield winding with the discovery
that the same effect is produced without theconnection to the current-carrying conductor.
Currently used mainly for 500kV-level windings.

Lightning-Protected Design

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Multiple Cylindrical Winding (Non-Resonant
Winding)
Coils are wrapped cylindrically around theinsulating cylinder, with the oil ducts outside ofthem. Insulating paper is wrapped at thenecessary thickness, followed by anothercylindrically-wrapped coil; this is repeated forseveral layers, with the outer layer surrounded byan electrostatic shield at the same height as thecoil and the shield connected to the lead at theend of the wire. Methods of connecting between
layers include having a lead coming out andconnected to the outer part, having the end ofeach internal layer coming through the oil duct
and the insulating paper and onto the next layer,or having a tapering thickness in the insulating
paper, where the next layer is wrapped the otherway at the end of each wrap. The final two
methods require varying thicknesses of insulating
paper as the voltage is applied to two layers.

Low-voltage winding

Step-Lap Joint

When lightning surges penetrate into atransformer winding, the voltage is very high andabrupt, throwing out the uniformity of the voltage
distribution of the winding. When there is a low
ratio between the electrostatic capacitanceconnected to the winding and the electrostatic
capacitance to the ground, most of the voltage
converges near the ends of the winding;historically, this was dealt with by reinforcing theinsulation in this area. Various other methods
were later proposed to increase the ratio and astructure was developed that could keep thevoltage distribution as uniform as possible
without reinforcing the insulation at the ends ofthe windings. This is what is meant by insulation
design against lightning surges.

Insulating
paper
betweenlayersShieldTank Transported Sideways
Since the core surrounded the core and coil ofshell-type transformers and could provide solid
support for the interior within the tank, it waspossible to support the mass of the core and coilduring transportation even with the tank on its
side. Some shell-type transformers were taller
than they were long, so there were advantages tohaving them sideways in these cases. This methodof transportation was adopted in the 1950s.

Diaphragm-Type Conservator
A type of conservator adopted in the 1960s, which
separated the oil from the outside air with anylon-filled rubber membrane or rubber pouch.
Characteristically separating the oil and the air,
this type of conservator is currently in standard
use in Japan. The rubber membrane is embeddedwith a film of nylon or other substance to prevent
air seeping through it. This means very little gas
is dissolved in the oil; the gas-in-oil analysis
currently commonly used for transformer
maintenance has a very high degree of precisionin analysing trace gases and has contributed to thediscovery of abnormal phenomena.

(1) Oil expansion tank(6) Automatic safetyvalve(2) Air pouch(7) Oil level gauge

Auto-Transformer
A method of transformer connection. Whiletransformers usually have separate high-voltage
windings and low-voltage windings at thenecessarycapacity,
auto-transformers
characteristically have the high-voltage andlow-voltage windings together. This achieves thesame capacity as a double-winding transformer,
where the high voltage capacity is equal to(high-voltage voltage – low-voltage voltage) x(high-voltage current) and the low voltage
capacity is equal to (low-voltage voltage) x(low-voltage current – high-voltage current). By
making these values equal and ultimately using a
auto-connection in contrast to an ordinarytransformer, high-voltage transformer capacity
reduces to (high-voltage voltage – low-voltage
voltage) / (high-voltage voltage). For example, if
we compare a 500kV and 275kV single-windingtransformer to one with separate windings, thetransmission capacity is the same at(500-275)/500=0.45, requiring less than half theactual transformer capacity. This actual capacity
is called self-capacity. Auto-transformers were
universally adopted in Japan with the introductionof 500kV, because they cannot be used unless thesystem has the same ground network.
Right-Angled Joins
A core joint structure used until around the 1960s
while hot-rolled silicon steel sheets were being
used; the cores were joined together as shown in
the figure.

(with alarm contact)(3) Moisture absorption(8) Drain and filtering

respirator for air pouch

valve(4) Connecting pipe

(9) Bushing support(5) Valve(10) Drain valve

Magnetic Tank Shielding
Magnetic shielding attached to the surface of thetank to prevent overheating and increased loss
from leakage flux from the coil; a silicon steel
sheet from several millimetres to around 30mm
thick. The shield either comprises silicon steel
bands with widths equal to the required thickness
stacked on the coil at the appropriate width, withthe cut edges spot welded together, or a100-150mm wide silicon steel sheet the sameheight as the coil stacked to the necessary
thickness and joined with epoxy or similar; these
are then attached to the tank through various
methods. The thickness depends on the amount ofmagnetic flux penetrating through the surface ofthe tank.

Neutral Point
Where the ends of a three-phase winding areconnected, the commonly-connected area whereanother end connects to the circuit through a starconnection is called the neutral point. This area
has a ground potential of 0.

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126

Nitrogen-filled tank Conservator
A conservator filled with inert nitrogen to stop thetransformer oil coming into contact with theoutside air, thereby preventing deterioration of theoil; there are three-chamber types andfloating-tank types.
DC Bias Magnetism
The magnetic flux of a transformer core forms asine wave that reflects the excitation current. Thisis usually positive-negative symmetrical and has
no DC portion; however, when a DC current
flows through the transformer winding fromoutside, the magnetic flux waveform becomes
biased, with a phenomenon occurring in which
the magnetic flux density increases to only one
peak per cycle. This is called DC bias magnetism.
In such a case, surges in the excitation current andincreased noise and vibration occur, while thenoise and vibration form a distorted wave with a
lot of higher harmonics, due to positive-negative
asymmetry in the magnetostriction of the core.
Rail Transport Limitations
Size restrictions for transporting freight by rail,
limited by tunnels, signals and station platforms.
While size and weight limitations vary according
to the transport route, transportation is carried out
by special freight cars according to a service
planning diagram with special specifications inaccordance with limited dimensions of a
maximum width of 3.1m and a maximum heightof 4.0m, as shown in the figure below.

Transformer coreand coils

Transportation
limitations

Tank

Voltage Phase Regulator (Phase Shifter)
Used to control the flow of electricity on atransmission line. Designed to shift the phaseangle at the same time as the voltage. Voltage
regulators act in phase with the main winding,while phase regulators generally regulate thevoltage in quadrature to the main winding andalter the phase of the main winding by vector
synthesis.

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Transposed Cables
Transformer cables comprising an odd number ofpolyvinyl-formal-coated flat copper wires
arranged in double file and twisted together at a
pitch of around 10cm using a special machine toform a single bundled conductor, which is theninsulated. Often used in high capacitytransformers in order to reduce eddy currents loss
caused by circulating currents generated byleakage flux from windings crossed to the
conductor.

Cross-sections at each of the points A, B, C…

Electromagnetic Shielding
A magnetic shield attached to the surface of thetank in order to prevent overheating and increased
loss on the surface of the tank due to leakage flux
from the coil. A good conductor such asaluminium or copper is used on the tank surface;where magnetic flux occurs, a current passes
through the shield to negate it, thereby repellingthe magnetic flux. It prevents overheating andincreased loss on the surface of the tank, which
would be caused by the altered flow of leakage
flux if the tank surface were used without a shield.
Since the repelled leakage flux eventually enters
the internal structure or core and increases theloss in that area, the shield has little effect onoverall loss reduction. However, in the past,electromagnetic
shields
were
used
in
high-capacity transformers as a means ofpreventing the tank from overheating from large
current leads also.
Steel Sound Barrier
There are two types of prefabricated steel soundbarriers, A-type and B-type. A-type covers only
the tank and has a noise reduction effect of up to
10dB. B-type covers the entire transformer withsteel panels and can reduce noise by up to 15dB.

Sound-absorbingCorematerial (prevents
sound escaping)

Eave
Anti-vibration rubber(Steel sheet)Sound-absorbing material
Rubber gasket (prevents
sound escaping)

Winding

Sound barrierSound barrier(Steel sheet)Sound-absorbing
Main tankmaterial
Rubber gasket(prevents soundescaping)

Main tankBase frame

Base frame
Anti-vibration rubber

Anti-vibration rubber
Anti-vibration fittings

A-typeB-typeExtra-High Voltage
Voltage of 10,000V or more.
Equivalent Capacity
Used to express the capacity of multiple-windingtransformers with three or more windings. Where
the rated capacity of each winding is P1, P2, P3,
etc., the equivalent capacity is obtained asfollows.
P = (P1+P2+P3)/2
Special Three-Phase System
A method of easing transportation limitations by
having a three-phase transformer composed ofthree
separately-transported
single-phasetransformers, which are then each positioned as
close as possible to a common base during
installation under a shared top cover with athree-phase lead connection. Proposed in the
1950s, this system has often been used in Japanfor transformers with unfavourable transportation
conditions, such as underground substationtransformers or hydroelectric power stationtransformers.

Double Concentric Winding Arrangement
A type of core-type transformer winding
arrangement, where either the high-voltage or
low-voltage winding is divided into two and theother winding arranged concentrically between
the two parts of the divided winding. The
arrangement can be low voltage-high voltage-low
voltage or high voltage-low voltage-high voltage.
The divided winding is connected in series. Used
as a countermeasure against leakage flux inhigh-capacity transformers because low-voltage,high-current lead-out is easier than in a concentricarrangement.
High Series Capacitance Winding
A lightning-protected winding developed by UK
company EE. With a cleverly-designed conductor
winding method to increase the electrostatic
capacitance in series with the winding as a meansof improving potential distribution, with theconductor rotated twice in two sections of the discwinding and having an adjacent separate potential
conductor. Also used in UHV windings. Also
called interleaved windings.

Core-Type Transformer
A transformer structure that has increased inworldwide adoption since first being adopted by
US company GE in 1910 along with the barrier
insulation method and is now used by mostmanufacturers. The core is assembled first
without the upper yoke, then the upper yoke isassembled after the windings have been put on
from above. So named because the core legs areconcealed inside the windings.

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

128Perfluorocarbons
A non-flammable coolant used for coolingliquid-cooled, gas-insulated transformers, usuallywith a molecular formula of C8F18 or C8F16O.
With boiling points of 100-130˚C, these have no
flash point, lower dynamic viscosity and higher
density than transformer oil. Used as atransformer coolant because they are thermostable
and are very compatible with other materials usedin transformers.
Barrier Insulation
An insulation structure used to improve thebreakdown electric field of the oil gaps by having
multiple insulation cylinders dividing the gap
between the high-voltage winding and the
low-voltage winding and alternately positioning
the oil gaps and the insulation cylinders.
Currently in standard usage.
Coil clamping plate
Press board barrier
Flanged insulation
cylindersHigh-voltage
terminal lead
Rib shield
Oil flow
Oil flowCore
Low-voltage
windingHigh-voltage
winding

Insulation
cylinders

Non-Resonant Transformer
A lightning-protected winding developed by US
company GE with an electrostatic shield attachedto the exterior of the winding so that its initialpotential distribution becomes linear, thereby
improving its potential distribution and increasing
its series electrostatic capacitance. Characterisedby a skirt-like shield called a stacked shield on theexterior of the winding.

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Non-Resonant Winding
A multiple cylindrical winding developed byGerman company AEG in the 1930s. So named
because the winding has a high series electrostatic
capacitance and a low ground electrostatic
capacitance, meaning it has linear initial potential
distribution.
On-Load Tap Changer
A method of voltage regulation by tap changing
while a transformer is carrying a load; one such
system has the tap winding incorporated into thetransformer itself, while another system has avoltage regulating transformer in series with themain transformer.
There are two methods of supressing cycliccurrents when the tap changer changing the taps
bridges between taps while changing: one using areactor and the other using resistance. The resistor
type is currently more commonly used around theworld because it is compact and can be built into
the body of the transformer. As shown in the
figure, the tap changing operation takes aroundtwo seconds to change. Since arcs can occur
while the current is switching over, thechange-over switch is housed in an oil tankseparate from the oil used in the transformer
itself.

Partially Shielded Winding
A structure in which the outer part of the coil near
the ends of the wires is wrapped with an insulated
shield conductor; also called a rib shield winding.
The electrostatic capacitance between the shield
and the coil is series capacitance, thereby
improving the potential distribution near the endsof the wires.

lines and cables systems have a high groundelectrostatic capacitance and a low load current.
Shunt reactors are used to compensate for this andare mainly used during light loading. There areiron core shunt reactors and air core shunt
reactors; the iron core type has less incurred loss
and is currently used more commonly.

Low-voltage winding or coreForm-Fit Tank
A shell-type transformer tank structure thatminimises the space between the core and coils
and the tank, wherein the core and coils areassembled on top of the lower tank and then theupper tank is put on top, with the tank itself also
serving as a core clamp.
Bushing

Core
clamp

Upper tank
CoilSpacerCore
Welded area
Lower tank andlower casing

Coil

Coil cradle

Partial Discharge
A state of partially deteriorated insulationaccompanied by microdischarges, occurring when
an electric field converges where electrodes arepoorly shaped, when there is a void in theinsulation or when there is dust or other foreign
matter present. Partial discharge occurs at lower
voltages than the voltage breakdown occurred.
Partial discharge is viewed as a precursor
phenomenon to transformer breakdown and there
is a trend towards structures and operational
procedures that do not generate partial discharge.
Shunt Reactor
A reactor placed between the system and theground to create a leading load for electrostatic
capacitance and an accompanying rise in voltage
when long-distance high-voltage transmission

Grain-Oriented Silicon Steel Sheets
A commercial product based on the discovery that
if the silicon steel sheets developed by US
company Armco in the 1930s were cold rolled
instead of hot rolled as they had been, and heat
treated appropriately to decarbonise andrecrystallize them, the direction of the edge
susceptible to grain magnetisation would alignwith the rolling direction; with a little morerolling and heat treatment to roughen up the
crystal grains, the amount of loss could be
reduced.
Polychlorinated Biphenyl
A non-flammable transformer oil developed in the
United States in the 1930s and widely used there
due to its superior cooling properties and its
insulation properties equal to mineral oil. It wasalso commercialised in Japan in the 1940s andused in transformers, but due to its toxicity
production of it was banned in 1972 and use of it

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology130was banned in 1974. For transformers, it was used
mixed with 40% trichloride benzol to lower its
congealing point and viscosity. It was often usedin condensers due to its large dielectric tangent.
UHV Transmission
UHV is an abbreviation for Ultra High Voltage
and generally refers to AC power of 765kV or
higher. While 765kV transmission is in operationin various places around the world, 1000kVtransmission started in the Kazakhstan region of
the USSR in the 1980s and remains the only placein the world to have it operating.
Induced Withstand Voltage Test
A transformer AC insulation test, wherein apower source is connected to a low-voltage
winding and induction of no more than twice thenormal voltage is carried out on a test transformer,
producing the voltage specified at the test
terminal. This is done at higher frequency thanthat used for commercial purposes (usually 3-4time higher) so as not to saturate the core. The
potential of the terminals other than the test
terminal is adjusted where necessary.
Oil-Impregnated Paper Condenser Bushing
A commonly-used type of condenser bushing thatuses insulation paper at the core; once thecondenser core is formed and dried, it is infusedwith transformer oil. Widely used up to UHV of
30kV or higher due to the stability of theinsulation.
Radial CoreA core structure used in reactors, in which thecore batten is arranged in a radial shape, as shownin the figure, with the effect of suppressing eddy
currents resulting from core fringing flux
generated in the gap.

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Fringing flux

Flow Electrification
A phenomenon in which the oil and insulation inforced-oil transformers generate frictional static
electricity in the oil flow from the operation of thepump. The static electricity generated builds up anegative charge in the insulation and a separate
positive charge in the oil. When the charge in theinsulation goes beyond a certain limit, creeping
discharge occurs, which intensifies until the AC
insulation breaks down. Static electricity is mostcommonly generated near the oil intake at thelower part of the coil and is significantly affectedby the shape of the flow path in this area.
Electrostatic discharge also generally occurs near
the oil intake at the lower part of the coil. While
the positive charge in the oil dissipates with time,
if a large amount is generated it builds up in theupper space; once a large amount builds up in theupper space, it generates a high voltage anddevelops into a discharge along the surface of theinsulation in this area.
Resin Condenser Bushing
A type of condenser bushing that can either be a
dry-type resin bushing, in which the condenser
core is formed by impregnating the insulating
paper with resin when the bushing core ismoulded, or the resin can be vacuum-impregnatedafter the condenser core is moulded frominsulation paper. The former is hardly used any
more because of partial discharge occurring as aresult of microscopic voids present in the core.
These are now often used for oil-oil bushings
because they are shorter and have smaller bushingpockets, since they do not require porcelain
insulator.

■ Appendix
An outline of the intended applications fortransformers and their classifications.
The intended applications for transformers can be
categorised in the following six ways.
A. Voltage/current conversion
B. Input/output circuit isolation, polarity reversal
C. Using and converting impedance values
D. Voltage/current regulation
E. Surge transfer, noise suppression
F. Power distribution
Transformer classifications can also be
categorised by intended usage as follows.
1. Power transformers
All intended applications from A to F.
Power Transformers(Power transmission transformers)
Power station transformers
Substation transformers(Distribution transformers)
Secondary substation transformers
Pole-mount transformers
Underground transformers
Pad-mounted transformers
Industrial transformers
Power-receiving transformers
High-current transformers
Semiconductor
power
conversion
transformers
Traction transformers
Vehicle transformers
Medical transformers
Power transformers
Consumer transformers
Power transformers
2. Insulating transformers
Intended applications A, B, C and E.
Connected to a circuit to eliminate noisecaused by potential difference, in turn caused
by interlinkage magnetic flux in the circuit;used to ground the circuit at one point.
3. Grounding / arc supressing transformers
Intended application is C, impedance use.
Grounding transformers are used to provide aneutral ground point in the circuit; arc
suppressing transformers are groundingtransformers combined with a secondary
reactor and used for the same purpose as arc
suppression coils.
4. Starting transformers
Intended application is C, impedance use.
Used to start electric motors smoothly.

5.Testing transformers
Intended applications are A and D,
voltage/current conversion and regulation.
6. Instrument transformers
Intended application is A, voltage/current
conversion.
7. Leakage transformers
Intended application is C, impedance use.
Used when a large leakage reactance isrequired to provide a load with negative
voltage/current properties, such as arc welding
or neon tubes.
8. Induction voltage regulators, phase shifters
Intended applications are A and D,
voltage/current conversion and regulation.
Changes the positional relationship of the
primary and secondary windings by rotationand continuously varies the voltage or phaseof the secondary winding.
9. Communication transformers (pulse / signaltransmission)
Intended applications are A, B, C and E. Usedfor voltage, current, and impedance
conversion, polarity reversal, potential
separation between circuits, conversion ofbalanced-unbalanced circuits, etc. during
signal transmission using transformer circuit
constants based on conversion characteristics,
inductance and electrostatic capacity.
10. Noise/high frequency suppression / switching/ lightning protected transformers
Intended applications are B and E. Used tosignificantly reduce surges from the supply
circuit and the transfer of noise to thesecondary side.
The purposes of each transformer and the maintechnologies applied are summarised as atechnology chart in the appended figure.
There are other ways to categorise transformers,such as:Classification by installation site
OutdoorIndoorClassification by cooling and insulation medium
Oil-immersed
Dry-type
Gas-immersed
Classification by manner of voltage regulation
Terminal block tap changer
No-voltage tap changer

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology132On-load tap changer(On-load) voltage regulator
Classification by operating principle
Two-winding transformers, multiple-windingtransformers
Auto-transformers
etc.

As will also be seen from the above study, powertransformers are technically related to everything;
it is a field that has attracted much interest for along time and has played a leading role intechnology. Accordingly, the author selected
power transformers for the present systematic
examination.

Appended Figure: Transformer Technology Chart
PurposeA.

B.

Voltage/current

E.

Input/output circuit

V, VI, VII, VIII, IX
2.

transformers

Using and converting

A, B, D, E

I.
I, II, III, IV,magnetic properties
II.

Winding structure,connections

III. Insulation material and
II, IVinsulation properties
IV. Surge properties

Voltage/current

transformers

V.

regulation

C
4.

Power distribution

5.

V

6.

C

V

VII. Voltage regulation

Test transformers

VIII. Electromagnetic

II, III, IV, IX

Voltage transformers
I, II, III, IV

Leakage transformers
C

8.

flux
VI. Cooling and heating

A
7.

I, V

Induction voltage regulators, phaseshifters
A, D

9.

Impedance and leakage

Starting transformers

A, D

I, II, VII

Communication transformers(pulse / signal transmission)
A, B, C, E

I, II, IV, V

10. Noise/high frequency suppression /switching / lightning protectedtransformers
B, E

133

Core structure and

Grounding / arc supressing

Surge transfer, noise

3.

Main Technology

Insulating / lightning protected

reversal

suppression
F.

Power transformers
A, B, C, D, E, F

impedance valuesD.

1.

conversion

isolation, polarity

C.

Transformer Classification

I, II, IV, V

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japanmechanical force
IX. Transportation

■ Reference List
(1) Miyamoto, Shigenari: Henatsuki no Shinpo [Transformer Progress], Ohmsha, Ltd. (1952).
(2) Ganz transformer since 1885, Ganz Electric Works Budapest (1978).
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No. 12, p. 656 (1955).

Toshiyuki YANARI; History of Power Transformers in Japan and Description of Related Historical Materials
Center of the History of Japanese Industrial Technology

134(16) Yamajo, Takashi: “Chika Hatsudensho-yō Chōkōatsu Henatsuki: Okutadami Hatsudensho-yō 133MVA,
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135

Survey Reports on the Systemization of Technologies; No. 4, March 2004
National Museum of Nature and Science, Japan(32) T. Takagi et al, “Reliability Improvement of 500kV Large Capacity Power Transformer” CIGRE SC12,
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Center of the History of Japanese Industrial Technology136Non-Flammable Transformer]”, IEEJ Transactions on Power and Energy Vol. 115, No. 4 (1995).
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137

Survey Reports on the Systemization of Technologies; No. 4, March 2004
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