Technology

Technology

Railway Technology Today 3 (Edited by Kanji Wako)

Railway Electric Power Feeding Systems
Yasu Oura, Yoshifumi Mochinaga, and Hiroki Nagasawa
Introduction

Electric power technology in the railway
industry refers to the means of supplying
good-quality electric power to the electric motors. It primarily consists of power
conversion technology at sub-stations,feeding circuits for DC and AC feeding
systems, and the structure, materials, measurement, and maintenance of the electric overhead lines.
Power collection via the overhead line
and pantograph, introduced nearly 100
years ago early in the history of electricrailways, remains basically unchanged inphysical appearance. However, technological developments during the past century have done much to greatly increase
the current capacity, speed, and safety.
Today, the capacity is more than sufficient
to drive modern super high-speed trains.
This article discusses all aspects of electric power supply systems for railways,
ranging from the history of electrificationof Japanese railways to today’s sophisticated power supply facilities. It also compares them with their counterparts in othercountries.

World Railway
Electrification Systems
Table 1 shows various feeding systems
around the world and the electrification
distances.
The history of electric railways dates backto 1835 when T. Davenport fabricated amodel electric car powered by voltaic
cells and put it on public exhibition. The
first practical electric cars debuted in 1879
when a 150-V dc, 2.2-kW, bipolar motor
pulled three passenger cars at a maximum
speed of 12 km/h at the Trades Exhibition
in Berlin. In 1881, Siemens Halske built
the world’s first electric railway in
Lichterfelde marking the first passenger
electric railway.
Electric operation is often preferred on

48

Japan Railway & Transport Review 16 • June 1998

and other countries to minimize rectification failures. Later advances in siliconcommutator technology paved the way for
AC feeding systems using commercial frequencies in France and elsewhere. The
25-kV system is used widely around theworld while Japan relies on a 25 kV system for shinkansen and a 20-kV ac feeding system for ‘conventional’ railways. (Inthis article, ‘conventional’ means all JNR/
JR narrow-gauge lines, all non-JR railways,
and the Akita and Yamagata shinkansen,
which were converted to standard gauge
from narrow gauge.)
The three-phase, alternating-current feeding system is used with induction motors
in Europe for railways with steep mountain grades, while a 600-V system, featuring speed control by a power converter,is used in Japan for new urban transit systems.

railways with many long tunnels or onunderground railways because the energy
efficiency is higher than steam or diesel
locomotives and does not involve onboard combustion. The high tractive force
also makes electric operation suitable forlines running through hilly regions. As aconsequence, electric train operation
made remarkable progress. It started firstwith direct-current feeding systems capable of driving a DC motor directly andoffering high tractive force and easy speed
control.
Although a 3000-V dc feeding system iswidely used in many other countries,
some Japanese railways using DC rely on
a 1500-V dc system.
The other alternating-current feeding system originated in Europe using a singlephase, commutator-type motor. Special
low frequencies such as 25 Hz and 16.66
Hz were introduced in Austria, Germany,

Table 1World Electric Railway Feeding Systems and Electrified Distances(1996)

System TypeJapan1World (including Japan)

km

%

km

%

Less than 1,500 V

915

5

5,106

2

Germany, UK, Switzerland, USA

1,500 V to 3,000 V(Mostly 1,500 V)

10,484

61

22,138

9France, Spain, Netherlands, Australia

3,000 V or more
(Mostly 3,000 V)

78,27633

Russia, Poland, Italy, Spain, South Africa

Single- 50 Hz Less than 20 kV•
phase
60 Hz 20 kV
AC

245

0

France, USA

DC

Main Countries

3,741

22

3,741

2

2,037

12

84,37636

Russia, France, Romania, India, China

50 kV

1,173

0

USA, Canada, South Africa

25 Hz • 11 kV to 13 kV

1,469

1

USA, Austria, Norway

120

0

Switzerland

35,461

15

Germany, Sweden, Switzerland

43

0

Switzerland, France

3,668

2

Kazakhstan2, France

25 kV

16.66 Hz

11 kV
15 kV

Three-phase AC

30

Unknown
Total
Notes: 1
2

17,2070

100 235,816 100

Statistics include Japanese subways and AGTs.
Kazakhstan is 3,528 km (3,000 V dc and 50 Hz 25 kV ac) but details are not known.

Sources: (1) Railway Electrical Engineering Association of Japan, vol.8, no.10, pp.3–5, Oct. 1997
(2) Ibid., vol.8, no.11, pp. 77–78 and pp. 81–83, Nov. 1997

Copyright © 1998 EJRCF. All rights reserved.

Shinkansen
AC, Conventional railways
DC, Conventional railways
Fin
an
cia
l

Re
str
uc
tur
dL
ing
on
Pla
gR
n
an
ge
Pl
an

3r

6,000

ye

Electrification
ratio
53.9%

ar
Pl

lan

rP

ea

an

-y

0

Conventional
railways
9,897.3 km

Conventional railways
AC electrification
3,682.3 km

5-

4,000

t5

20

Shinkansen
2,036.5 km

d

40

8,000

JN
R1
0-y
ear

1s

Copyright © 1998 EJRCF. All rights reserved.

60

10,000Electrified Distance2nCommercial operation of electric railways
in Japan dates back to 1895 when a 500V dc tram system was started in Kyoto.
The first electric railway owned by theJapanese Government Railways began operation in 1906 between Ochanomizu
and Nakano in Tokyo, which used to belong to Kobu Railways before being purchased by the government. The 600-V
dc system was later replaced by a 1200V dc system to prevent voltage drop. In
1922, it was replaced again by a 1500-V
dc system when the section between
Yokohama and Kozu was electrified. The
1500-V dc system is still used today by
all DC electric railways in Japan.
The postwar increase in transportation
demand in Japan led to the introductionof more powerful electric locomotives
around 1950. At that time, it was fearedthat the 1500-V dc system had reachedits limit, and a study was started on railway electrification based on commercialfrequency, single-phase alternating
current. After a successful demonstration
test on the Senzan Line, the first commercial operation using an electric locomotive started in 1957 on the Senzan andHokuriku Lines, soon followed by a 20kV single-phase, alternating-current
system using a step up or boosting transformer (BT) to minimize inductive interference in telecommunication lines.
In 1964, the Tokaido Shinkansen began
operations using the BT feeding system,
marking the first high-speed train operation with a maximum speed of 210 km/h.
However, it soon faced maintenance andother technical problems associated withthe large collection current requiring complex anti-arcing designs. This led to a
study of the auto transformer (AT) feeding
system, which was introduced on the
Yatsushiro-Nishi Kagoshima section of the
Kagoshima Line in 1970, and on the Shin
Osaka–Okayama section of the Sanyo

12,000Electrified Distance (km)History ofRailway Electrification in Japan

Electrification Ratio (%)

Figure 1 History of Railway Electrification in Japan*

2,000

Conventional railways
DC electrification
6,215.0 km

nce
dista
rifiedElecttion ratio
Electrifica

01906 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995

Year
Note:
* Including Japanese Government Railways, Japanese National Railways (JNR, from June 1949
to March 1987) and JRs, but excluding private railways

Shinkansen in 1972. Today, the AT feeding system is the standard for all AC electric railways in Japan.
Figure 1 shows the history of railway electrification in Japan from the era of the Japanese Government Railways until thepresent JRs. Figure 2 maps the various
systems in Japan. Roughly speaking, the1500-V dc system is used on the conventional railways in Honshu (Kanto, Tokai,
Kansai, and Chugoku districts) and
Shikoku, while the 20-kV ac system ismainly used in Hokkaido, northern
Honshu (Tohoku and Hokuriku districts),
and Kyushu. All shinkansen use the 25kV ac system. In contrast, most private
railways rely on the 1500-V dc system,
while the 600- or 750-V dc system is usedby subways and some other railways.

Various Feeding Systems

its own hydroelectric power station in
Niigata Prefecture (on the Shinano River)as well as a thermal power station in
Kawasaki City in Kanagawa Prefecture.
These two power stations supply the railways in the Tokyo metropolitan area.
In Japan, the receiving voltage at substations for direct-current electric railways
is usually extra-high tension at 22, 66, or
77 kV. This is converted to 1200 V
by a transformer, and then to direct current by a rectifier at the rated voltage of1500 V (no-load voltage of 1620 V). Subways and some private railways use 600
or 750 V dc.
The receiving voltage for alternating-current conventional electric railways is an
extra-high voltage of 66, 77, 110, or 154
kV. The shinkansen use receiving voltages of 77, 154, 220, or 275 kV. The conventional railways use a feeding voltage
of 20 kV, and the shinkansen use singlephase at 25 kV.

From power station to railway
sub-station
The electric power generated by power
stations is carried to electric railway substations by transmission lines. JR East has

Japan Railway & Transport Review 16 • June 1998

49

Technology

Figure 2 Map of Railway Electrification of JR Group in Japan

Conventional
Railways

AomoriDC
AC

Shinkansen
Asahikawa

Akita

Otaru

Morioka

KushiroMuroran

Murakami
Niigata

Hakodate
Nishi Izumo

KokuraHakataSendai

Tottori

Kinosaki

Fukushima

Kanazawa
Fukui
NaganoKuroiso

Hiroshima
Fukuyama
Iyoshi

SaseboOita
Nagasaki

Yamagata
amagata

Itoigawa

Kochi

Kumamoto

Okayama Himeji
Himeji

Kyoto

Nagahama
Gifu

Shin-Osaka

Utsunomiya
Kofu

NagoyaTokushima

Shizuoka

Omiya
TorideTokyo

Wakayama
ShinguKagoshima

Miyazaki

DC feeding system
Figure 3 Structure of a DC Feeding System
12-pulse Rectifier

6-pulse Rectifier

Three-phase AC

3-phaseAC

Three-phase AC

3-phaseAC

Transformer

Transformer–

Rectifier+–

1,500 V dc
High-speed
circuit breaker+
1,500 V dc

Rectifier

Sectioning
post

FeederContact
wireElectric car

50

Japan Railway & Transport Review 16 • June 1998

Rail

A direct-current feeding system features athree-phase bridged silicon rectifier for
conversion from alternating to direct current. Since the three-phase rectifier uses a
6-pulse system, it causes lower harmonics
in the AC side and distortion in the voltage
waveform, lowering the power quality. To
reduce the harmonics, a more-modern rectifier design using a 12-pulse system featuring two sets of 6-pulse rectifying circuits,
with AC input voltage phases 30° apart,connected in series or parallel, is used.
Figure 3 is an example showing the structure of a DC feeding circuit connected to
the nearest sub-station. Section and tie
posts are sometimes used to prevent voltage drops on double tracks where substations are located far apart. In this case,the up and down tracks are connected by

Copyright © 1998 EJRCF. All rights reserved.

a high-speed circuit breaker. The distance
between sub-stations is about 5 km on
metropolitan trunk lines and 10 km onother lines.
Efforts are being made to introduce regenerative cars on DC electric railways inorder to reduce the weight and save energy. They are designed to convert the
kinetic energy into electric power during
deceleration and return it to the overheadlines. However, the regenerated power
would be wasted if there are no cars inthe section to use it. This loss can be prevented by thyristor rectifiers, thyristor inverters, thyristor chopper resistors, or
simultaneous up and down track feeding
systems. Such devices are used on some
sections; Figure 4 shows an example of athyristor inverter. In this system, the motive power is supplied from a rectifier, andwhen the regenerative power exceeds the
motive power requirement, the inverter
is activated automatically to supply power
to stations, etc.

Figure 4 Power Regeneration by Thyristor Inverter
Three-phase AC

Distribution
transformer
3-phase 6.6 kV ac bus

Transformer

Transformer

RectifierRegenerative
inverter

Station facilities,
etc.
Harmonic
filter
1,500 V dc
Regenerative car

Figure 5 Scott ConnectedTransformer

Figure 6 Modified Wood-bridge
Connected Transformer

V

T

V

AC feeding system
Since three-phase power from the power
utility is converted to two single phases,
to ensure that the current is as close as
possible to the three lines of the threephase side, one separate phase is fed toeach of the overhead up and down tracks.
Various methods can be used to connect
the feeding transformers. Today, the Scottconnected transformer (Fig. 5) is used toreceive extra-high tension, and the modified wood-bridge connected transformer(Fig. 6) is used to receive extra-high voltage, with the neutral point directly
grounded.
Figure 7 shows the composition of an AC
feeding circuit. It includes feeding AC
sub-stations, sectioning posts for feed sectioning, and sub-sectioning posts for limited sectioning, all located along the
tracks. The feeding sub-stations feed thetwo single phases converted from thethree-phase source by a feeding transformer in the opposite track directions,

Copyright © 1998 EJRCF. All rights reserved.

Feed to overhead line
(UVW is 3-phaseand TF is 1-phase)

T

ST

Teaser transformer

B phase
O

F (N)
U

W
U

W
Earth

T

T

A phaseFF

ST: Step up transformer

F (N)Main phase transformer

Figure 7 Structure of an AC Feeding System
Feeding
sub-station
SS

Sectioning
SubSubpost
sectioning
sectioning
post
post
SP
SSP

Feeding
sub-station
SS

SSP

Down track
Up track: Circuit breaker: Air section: Disconnecting switch: Phase-to-phase changeover section

Japan Railway & Transport Review 16 • June 1998

51

Technology

Table 2

Feeding Voltages and Distances between Sub-stations of
Various AC Feeder Systems in Japan
Feeding voltage (kV)FeedingsystemDistance between sub-stations (km)Conventional
railways

Shinkansen

Conventional
railways

Shinkansen

BT

22

—

30 to 50

—

AT

44

60

90 to 110

20 to 60

Coaxial

—

30

—

10

This design minimizes the inductive interference on telecommunication lines
because the current flows to the rail only
in limited sections.
In particular, when an electric car passes
a BT section, a large arc is generated in
the section, and a large load current cancause a very large arc that can damage
the overhead line. Consequently, capacitors are often inserted serially in the nega-with a 90° phase offset.
Table 2 shows the feeding voltages andthe distances between sub-stations of various AC feeding systems in Japan.

BT feeding system
Figure 8 shows the composition of a BT
feeding circuit. A BT is installed every 4
km on the contact wire to boost the return circuit current on the negative line.

NF capacitor
Boosting
transformer
(BT)

V
I

Boosting
wire

I
Rail

Electric car

Figure 9

In the AT feeding system, the feeding voltage of the sub-station is twice the voltage
supplied to the electric car. An AT, atevery 10 km along the track, cuts the voltage to the overhead-line voltage as necessary. This is very effective in reducing
inductive interference in telecommunications lines. Figure 9 shows the composition of an AT feeding system, and thephotograph below shows an external viewof an AT designed for shinkansen.
In Japan, the AT is designed with a turn ratio of 1:1 and the sub-station feeding voltage is twice the overhead-line voltage. Thissystem is ideal for high-speed and largecapacity electric cars because there are nolarge voltage drops nor arcing sections.

As shown in Figure 10, the coaxial cable
feeding system features a coaxial cablelaid along the track. Every several kilometers, the inner conductor is connectedto the contact wire and the outer conductor is connected to the rail. The cable
itself is very expensive but the conductor

Structure of AT Feeding System

Sub-station
AT
2V
I/2
V

V

Negative
feederContactwire

BT section

AT feeding system

Coaxial cable feeding system

Figure 8 Structure of NF-based BT Feeding System
Sub-station

tive feeder to compensate for the reactance and reduce the amount of current
intercepted by the pantograph, thereby reducing arcing, and also helping to prevent voltage drop.

Auto transformer
AT

AT

Contact
wire

I
CPW

Electric car

Rail

FeederProtective
wire
External view of AT (60/30 kV, 7500 kVA)

52

Japan Railway & Transport Review 16 • June 1998

(RTRI)

Copyright © 1998 EJRCF. All rights reserved.

Overhead Line Systems

Figure 10 Coaxial Cable Feeding System
Sub-station
Coaxial power
cable

I
V
Electric car

Contact wireI
Rail
Negative feeder

Detecting Feeding Faults
Feeding circuit faults can be caused byelectric car faults, overhead line faults, flying objects, and animals (birds, snakes,etc.). The high voltage causes a high fault
current and, consequently, a protective
relay is used to instantly detect any fault
and trip a power circuit breaker.

DC feeding system
In a DC feeding system, typically, the current for the electric car increases smoothly,
but a fault current always increases
abruptly. A ∆I-type fault selective relay at
sub-stations is used to detect faults basedon this difference.

Copyright © 1998 EJRCF. All rights reserved.

AC feeding system
In an AC feeding system, faults are detected by a combination of a distance relay and an AC ∆I-type fault selective relay(Figure 11). The distance relay monitors
the overhead line impedance from thesub-station and recognizes an event as afault when the impedance falls within apredetermined rectangle on the impedance plane. As with DC systems, the AC∆I-type fault selective relay detects thechange in current.
Furthermore, locators are used to mark fault
points based on the current distribution,so any fault can be corrected promptly.

An electric railway takes its power for theelectric motors, lights, air conditioning,etc., from the overhead line using the pantograph on the roof.
The pantograph is in constant contact withthe overhead line (contact wire) locatedabout 5 m above the rails, whether the
train is moving or not. Therefore, the overhead line must always be located within
the pantograph range, and the pantographmust always maintain contact with theoverhead line to supply uninterrupted,
good-quality power at all times. To meetthese requirements, the overhead equipment is generally designed bearing thefollowing in mind:• Must have characteristics meeting train
speed and current requirements• Must be at uniform height above rail to
optimize pantograph power collecting
characteristics, so entire equipment
must have uniform spring constant andbending rigidity• Must have minimum vibration and

Figure 11 Protective Zone of AC Electric Railway Protective Relayr

Impedance of contact line
g
llin

ca

tro

Reactancelayout is simple, making it ideal for use
where space is limited. Japan is the only
country that uses this system (the Tokyosections of the Tohoku Shinkansen andTokaido Shinkansen).
In comparison to the overhead line, thecoaxial power cable has an extremely
small round-trip impedance. Therefore,
the load current is boosted in the coaxial
power cable from the connection with theoverhead line. This results in a rail current distribution similar to that of the AT
feeding system, significantly reducing theinductive interference in telecommunication lines.

Catenary system

Distance relay

n
co
or g
t
is
yr erinTh ow
P∆l relaySP

PWM controlling car
Powering

SS

Resistance
SS: Sub-station
SP: Sectioning post

Japan Railway & Transport Review 16 • June 1998

53

Technology

Figure 12 Overhead Lines of World High-Speed Railways

18.0 m5.0 m18.0 m

5.0 m

50 m
Shinkansen

1.8 m

9.0 m
65.0 mGerman high-speed line

15 m

15 m

2 3.5
3.5 4.5 4.5

4.5 4.5

63 m

1 m 6.0 m

3.5 2
3.5

1.4 m

French TGV Southeast
60 m
Italian high-speed line
9.0 m
French TGV Atlantic

Table 3Comparison of Overhead Line Constants on Dedicated High-speed Lines
Japan

Item

GermanyTGV Atlantic

Italy

Catenary typeHeavy compound type Stitched and simple

SimpleStitched and simple

Twin stitched and simple

Standard span [m]50

63 (Stitched wire 15)

63

65 (Stitched wire 18)

60 (Stitched wire 14)

Standard wire height [m]

5.0

4.95

4.95

5.3

4.85

System height [mm]

1,500

1,400

1,400

1,800

1,400

Suspended

St 180 mm2(1.450 kg/m)

Bz 65 mm2(0.59 kg/m)

Bz 65 mm2(0.59 kg/m)

Bz11 70 mm2(0.63 kg/m)

CdCu 153.7 mm2(1.42 kg/m)

Auxiliary suspended

Cu 150 mm2(1.375 kg/m)

Bz 35 mm2—

Bz11 35 mm2(0.31 kg/m)(0.30 kg/m)

Contact wireCu 170 mm2(1.511 kg/m)

CdCu 120 mm2

Cu 150 mm2(1.33 kg/m)

CuAg Ri 120 mm2(1.08 kg/m)

CuAg 151.7 mm2(1.35 kg/m)

Wire
grade

Contact line total density [kg/m]
Suspended [N]Catenary Auxiliary suspended[N]
wire
tensionContact wire [N]

4.34

1.65

1.92

1.71

2.77 × 2

24,50014,00014,00015,00018,40014,7004,000 (Stitched wire)—

2,800 (Stitched wire)

2,900 (Stitched wire)

14,70014,00020,00015,00014,700(53,900)(28,000)(34,000)(30,000)(33,100 × 2)

Wave propagation velocity ofcontact wire [km/h]

355

414

441

424

376

β (train speed/
wave propagation velocity)

0.68, 0.76(= 240, 270/355)

0.65 (= 270/414)

0.68 (= 300/441)

0.59 (=250/424)

0.66 (= 250/376)

Pre-sagNone

1/1,000

1/1,000

1/1,000

1/1,000(Total tension) [N]54

FranceTGV Southeast

Japan Railway & Transport Review 16 • June 1998

Copyright © 1998 EJRCF. All rights reserved.

motion to ensure smooth pantographpassage during high-speed operation orstrong winds• Must have strength to withstand vibration, corrosion, heat, etc., while maintaining balance with reliability andoperating life span
Figure 12 compares the catenary equipment for high-speed trains in different
countries. In Japan, compound catenary
equipment consisting of three longitudinal wires is used for shinkansen, while
simple or stitched catenary equipment isused in Europe. The Italian high-speed
line uses twin catenary equipment to supply the large current for the 3-kV dc electrification. Table 3 compares the constantsof these various catenary systems.
Compound catenary systems feature lesspantograph vertical motion and larger
current capacity but require a larger number of components resulting in a more
complex design.
In Europe, pre-sag is often used to compensate for the large vertical motion of thepantograph in the simple catenary system.
Pre-sag refers to a special design feature inwhich the height of the contact wire islower at the centre of the span by anamount equal to around 1/1000 of the span.
In real terms, generally, the contact wire
height is 20 or 30 mm lower than the supports at the centre of the span, thereby suppressing the pantograph vertical motion.
This design is effective for the overheadlines on the French and German high-speedlines which have a large amplitude, but isless effective for overhead lines with small
amplitudes like the shinkansen and the Italian high-speed line.

Lateral wave propagation
The most critical constants for the mechanical performance of the overhead line
are the weight and tension per unit length.
The total tension is relative to the pushup force of the pantograph and is closely
related to the vertical motion of the overhead line. It is 54 kN for shinkansen and

Copyright © 1998 EJRCF. All rights reserved.

Heavy compound overhead line of Tohoku Shinkansen(RTRI)

Simple catenary equipment of Nagano-bound(RTRI)
shinkansen

28 to 34 kN for the French and German
systems. The Italian system has a total
tension of 66 kN because it uses a twin
catenary system with a larger wire size.
The pantograph push-up force is roughly
70 to 80 N for Japan, 130 to 250 N for
France and Germany, and 200 to 300 N
for Italy. This means France and Germany
have an overhead line amplitude aboutfour times greater than that of Japan.
Generally speaking, greater stability results from smaller overhead line amplitude. It also reduces the fault frequency
and damage to components. The French
and German systems seem to allow larger
amplitudes at the cost of fewer pantographs.
The square root of the ratio of the contact
wire tension to the weight per unit length
represents the velocity of the lateral wave
propagating along the wire. This is the mostimportant parameter in overhead line design. In railway technology, this velocity iscalled the wave propagation velocity andis recognized as the critical speed.
Table 3 shows the wave propagation velocity and the ratio of the train speed to
the wave propagation velocity (β). Simulation and experiments have verified thatas the train speed approaches the wave
propagation velocity, the overhead line
amplitude and local bending increase,making it harder to maintain contact be-

tween the pantograph and overhead line.
It is estimated that the resulting performance drop becomes apparent when the
train speed exceeds 70% to 80% of the
propagation velocity. At this speed, lossof contact with the line increases greatly,
and in extreme cases, the overhead line
itself can be destroyed.
Consequently, the contact wire constantmust be set so that the propagation velocity is significantly faster than the train speed.
The propagation velocity can be increased
by laying a lighter wire at a higher tension.
In the case of a pure copper contact wire,
after considering safety factors, the maximum achievable speed (neglecting wear)
is around 500 km/h. Any further increasein the wave propagation velocity can only
be achieved by using wires with a higher
tensile resistance per weight unit length.
In Japan, wires in use or under development include copper alloys, and other alloys, as well as compound wires such asaluminium-clad steel wire, and copperclad steel wires.
In Table 3, the β values are all 0.7 or lower,
indicating that all countries have selectedvalues within the above-mentioned stablevelocity range for train speeds.
The photograph (above left) shows a heavy
compound overhead line. The Naganobound Shinkansen (Takasaki–Nagano section), which started operations in October

Japan Railway & Transport Review 16 • June 1998

55

Technology

1997, uses the simple catenary overheadequipment found commonly in Europe.
This system was chosen for economy because the less-frequent train operation
consumes only a small proportion of thecurrent-carrying capacity. This shinkansen
uses a 110-mm2 copper-clad steel wire (Fig.
15b) with a tension of 20 kN to withstandthe train operating speed of 260 km/h. Thisis the first simple catenary system for highspeed operation in Japan.

Figure 13 Third Rail Arrangement

Protective plate

Third rail
(conducting steel rail)

Insulator
Running rails

Third-rail conductor

Figure 14 Overhead Rigid Conductor System
Wall (tunnel, etc.)

Tensionless

Insulator

T-shaped mountLong ear

6 m max.
Contact wire
410 mm

In the third-rail conductor system, thecollector is laid next to the rail to save
space in restricted subways. This systemdates back nearly 70 years to 1927 when
it was first introduced on the Ginza Lineof the Tokyo Rapid Transit Authority(TRTA). The voltage is 600 or 750 V. Figure 13 shows the structure. In Japanese
subway systems, it is shielded at the top
and on one side for safety; a flat shoe collects current directly from the top of therail, which is supported by insulators every 2.5 to 5 m. This third rail system islimited to a maximum speed of around
70 km/h due primarily to the undergroundconditions in the Tokyo metropolitan area.
However, experiments show it is capableof serving speeds exceeding 100 km/h.

Overhead rigid conductor system

Overhead rigid conductor system and pantograph

56

Japan Railway & Transport Review 16 • June 1998

(RTRI)The overhead rigid conductor system has
been developed as an overhead line fordirect links between subways and suburban
railways. It features toughness and small
space requirements (Fig. 14 and opposite
photograph) and prevents broken wires andother accidents, especially in the subway
sections.
The maximum speed has been limited to
90 km/h primarily due to the short distances between stations and frequent
curves in the metropolitan subways.
The system runs at a voltage of 1.5 kV toallow direct connections to suburban railway systems. It has been used for nearly
40 years on the TRTA Hibiya Line.

Copyright © 1998 EJRCF. All rights reserved.

weight reduction is critical.
Supports are often made of galvanizedsteel. High-quality, inexpensive porcelain
insulators are common, but polymer insulators with excellent insulation characteristics have been introduced recently.

Figure 15 Contact-Wire Cross Sections

Maintenance of Overhead Lines
Overhead line inspection cars

3 mm(a) Hard-drawn copper

3 mm

3 mm

(b) Copper-clad steel(c) Aluminium-clad steel

Materials in Overhead Lines
The overhead line equipment consists ofthe contact wires, fixtures, and supports.
The contact wire has a round cross section with grooves at the 2 and 10 o’clock
positions, used for hanging the wire froma fixture. Conventionally, contact wires
have been made of hard-drawn copper.
Copper has very low electrical resistanceand excellent corrosion resistance, making it an ideal material for contact wires.
To provide higher mechanical strength, soft
copper is hard drawn into contact wires.
In Japan, contact wires composed of copper with 0.3% tin are used widely to improve wear characteristics. Tunnel
sections often use silver-copper alloy contact wires for extra heat resistance withthe aim of preventing broken wires due
to train fires. Recently, such copper-silver alloy contact wires are being replacedby copper-tin alloy contact wires.
A recent addition to the shinkansen arecopper-clad steel contact wires designed
to increase the wire tension for higherspeed operation. Figure 15 shows crosssections of the conventional type, and thetwo variations: copper-clad steel, and alu-

Copyright © 1998 EJRCF. All rights reserved.

minium-clad steel.
The messenger wire is often made of galvanized stranded-steel wire for economy
and high mechanical strength. Harddrawn copper stranded wires are also usedin many sections requiring larger current
capacity.
Messenger wire fixtures require highstrength and corrosion-resistant materials,
such as stainless steel and copper alloy.
Aluminium alloy is preferred where

External view of diagnostic car for electric facilities

The overhead line is a very long linear
structure and, as such, is subject to sliding stress from the pantograph. It is also
subject to a stress due to rain, wind, snow,
ice, and other natural phenomena. Consequently, the overhead line is a potential source of accidents involving broken
wires due to corrosion and wear. Such
accidents require many hours for repair,so maintenance is essential.
Maintenance begins with accurate diagnosis of the present condition of the overhead line, often performed from a movingcar. The shinkansen overhead lines areinspected every 10 days using ‘Doctor
Yellow’, a seven-car electric facilities andtrack diagnostic system (JRTR 15, p. 43).
Conventional lines use a two-car system.
The measured items include the contact(RTRI)

Japan Railway & Transport Review 16 • June 1998

57

Technology

wire height above rail, deviation, wear,
acceleration of pantograph head, and contact loss. For shinkansen, the measured
data are processed by a central computer
and the results are sent to the relevant
maintenance crews.
Some items cannot be checked from amoving car. These include corrosion of
the feeding wires and loose screws, which
are inspected manually during normal
maintenance work.
When lines need replacement, the work is
performed using special cars. The above
photograph shows a six-car system designed to replace shinkansen contact wires.
Automated diagnosis and repair is a recent topic for railway engineers and special efforts are being made to develop
robots for this purpose.

Contact wire replacement work car(RTRI)

Feeder line inspection robot(RTRI)

Robotics
Overhead line systems require dangerous
work at height. A self-powered feeding
line robot with eddy current sensors has
been developed and put into operation
to locate cross-sectional area loss due tocorrosion.
■

Kanji Wako
Mr Kanji Wako is Director in Charge of Research and Development at RTRI. He joined JNR in 1961 after graduating in engineering from Tohoku University. He is the supervising editor for thisseries on Railway Technology Today.

Yasu Oura

Yoshifumi Mochinaga

Mr Yasu Oura joined JNR in 1967 after graduating in electrical engi-

Dr Yoshifumi Mochinaga joined JNR in 1967. He graduated in elec-

neering from Shibaura Institute of Technology. He is Chief Manager

trical engineering from the Science University of Tokyo in 1980. Heof the Technological Development Department at the Railway Tech-is a Manager in the Power Supply Technology Development Depart-

nical Research Institute, which he joined in 1987.

ment at RTRI, which he joined in 1987. He obtained his doctorate in
AC feeding systems from the Science University of Tokyo in 1994.

Hiroki Nagasawa
Dr Hiroki Nagasawa joined RTRI in 1972 after graduating in mechanical engineering from Tohoku University. He is engaged in development of current collection systems, especially overhead line
materials. He obtained his Ph.D. in tribology from Tohoku University
in 1996.

58

Japan Railway & Transport Review 16 • June 1998

Copyright © 1998 EJRCF. All rights reserved.