Successful Field Tests of the World’s Longest 500-m High-Tc
Superconducting Power Cable
by Masashi Yagi*, Shinichi Mukoyama*, Noboru Ishii*2, Osamu Sato*2, Michiharu Ichikawa*3,
Toshihiro Takahashi*3, Hiroshi Suzuki*3, Akio Kimura*4 and Kenji Yasuda*4

Furukawa Electric has completed, in cooperation with CRIEPI (Central ResearchInstitute of Electric Power Industry) and Super-GM (Engineering Research
Association for Superconductive Generation Equipment and Materials), all predetermined items in the field test of the world’s longest 500-m high-Tc superconducting (HTS)
cable, thereby succeeding in establishing basic technologies for practical application of the HTS
cable in the future. This test project has been carried out as a part of Super ACE (Research andDevelopment of Fundamental Technologies for Superconducting AC Power Equipment) projectof METI (the Ministry of Economy, Trade and Industry), being commissioned by NEDO (the New
Energy and Industrial Technology Development Organization) to Super-GM.
In practical application of the HTS cable, it is required to cool the cable several km in length
using liquid nitrogen, making it necessary to study the details of basic operation characteristics
and the issue of long distance circulation of liquid nitrogen. We have laid a 500-m HTS cablemanufactured by Furukawa Electric in the premises of the Yokosuka Research Laboratory ofElectric Power Engineering Research Laboratory, CRIEPI, and have been conducting since April
2004 various tests including those for basic characteristics, rated loading characteristics, load
fluctuation characteristics, and limiting and overloading performance. Recently, the tests havebeen completed successfully, and the results will be briefly reported in this paper.

ABSTRACT1.

INTRODUCTION

The HTS power cable, which enables high-capacity powertransmission with its compact size, is expected to bringabout significant advantageous effects in future, because
it is capable of responding to the needs of power systems
including suppression of CO2 emission, improvement inenvironmental harmonization, enhanced system stability,
and cost reduction.
Realization of the HTS cable systems requires that longdistance HTS cables should be cooled using liquid nitrogen, so that system problems such as cooling characteristics of the HTS cable and long-distance circulation
behavior of liquid nitrogen have to be appropriately
solved. With regard to the cooling section of the HTS
cable, given the fact that the cooling sections for existingnormal-conducting power cables are several km in length,
it was assumed that the existing cooling equipment would
be replaced with refrigerators for the HTS cable and thatpractical HTS cable systems would have cooling sections
Ecology and Energy Lab., R&D Div.
VISCAS Corporation*3 Central Research Institute of Electric Power Industry*4 Engineering Research Association for Superconductive
Generation Equipment and Materials**2

equivalent to the existing ones in length. Accordingly, it
was decided to adopt a cable section length of 5 km for
the HTS cable to be developed here and a cable length of
500 m which is the minimum length to enable accurate
simulation of the cooling and thermo-mechanical characteristics. This cable length of 500 m is thought to correspond to a suitable jointing distance, i.e. manhole distance, for cable laying whereby cable units of this length
are jointed to constitute a 5-km cable section. Thus,
behavior confirmation using the 500-m cable will obviously permit scale expansion into an integrated HTS cablesystem.
A 500-m HTS cable was manufactured and laid by
Furukawa Electric, and tested jointly by CRIEPI andFurukawa Electric at the premises of the Yokosuka
Research Laboratory of Electric Power Engineering
Research Laboratory, CRIEPI.

2.

STRUCTURE OF HTS CABLE

Figure 1 shows the structure of the HTS cable andTable 1 its specifications. It is a 77-kV, 1-kA power cableconsisting of single-core, cold electric insulation andsuperconducting shield layer, and has an outer diameterof 133 mm to be accommodated in a cable duct 150 mm
in diameter. The core former consists of a stainless steel

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Successful Field Tests of the World’s Longest 500-m High-Tc Superconducting Power Cable

Structure

Outer
diameter(mm)

SUS spiral pipe
Conductor layer

FormerStranded conductorof hollow copper wire
(250 mm2)

28

HTS conductor layer Bi2223 tape

30

Insulation layer

Insulator (8 mmt)

Semi-synthetic paper

48

Shielding layer

HTS shield layer

Bi2223 tape

58

Inner cryostat pipe

SUS corrugated pipe

92

Vacuum insulation
layerSuper insulation (SI)

Outer cryostat pipe

SUS corrugated pipe

Cryostat pipe

Anti-corrosion layer PVC

124
133

spiral pipe and copper strands, on the surface of which a
conductor layer comprised of Bi2223 tape is positioned.
Around the core former, intervened by an electric insulation layer 8 mm in thickness, a shield layer of Bi2223 tapeis provided. This is surrounded by a protective layer onwhich an optical fiber for measuring temperature distribution over the cable length is wound together with a heaterwire for calibrating the cable AC loss. The cryostat pipe
has a structure of vacuum thermal insulation whereby
super insulation (SI) is multilayered between double corrugated pipes of SUS, aimed at a heat invasion rate of 1
W/m or less. With its outermost layer of PVC protective
layer, the cable weighs 14 kg/m, lighter than conventional
cables.
In addition, the cable incorporated foil electrodes forpartial discharge measurement and Pb indicators forcable behavior identification.

3.

MANUFACTURE OF HTS CABLE

3.1 Manufacture of HTS Core
Because of its small thickness of 0.2 mm and its brittle
property, Bi2223 HTS tape is subject to degradation in
critical current I c if excessive tension or bending isapplied. Therefore, in the forming process of multiple conductor tapes around the core former, winding tension oneach tape was optimally controlled individually, thereby

3.2 Manufacture of Cryostat Pipe
Stainless steel corrugated pipes for the cryostat pipe were
manufactured by welding stainless steel sheet into a pipe,
which was subsequently corrugated. With regard to thesuper insulation to be provided as a thermal insulation
layer between the inner and outer cryostat pipes, researchand development study was carried out beforehand
aimed at realizing a low heat invasion rate of 1 W/m, andthe pipe system was implemented under the optimum
conditions thus obtained. Simultaneously, a factory-based
manufacturing technology 1) was newly established thatenabled producing the optimum conditions over theentire length of 500 m. What is more, the thermal insulation layer has to maintain a high degree of vacuum so as
to realize high performance in thermal insulation. In theformation process of the thermal insulation layer, therefore, proper care should be taken including cleaning thesurface of the cryostat pipe by washing, dehumidification
by humidity control, and elimination of cracks and pinholes at the welded seam, making it essential to establish
such technologies as the pinhole-free welding technology
100
80
60
40
20

HTS conductor
HTS shield0

Figure 2

g

Item

Aft
er
lay
in

Specifications of the HTS cable.

ipe
Aft
er
co
mp
let
ion

Table 1

Structure of HTC cable 1).

Inn
er
cry
os
tat
p

Figure 1

HT
Sc
ore

Former,Stranded conductor of copper, 250 sq.

fo r
mi
ng

Conductor layerof HTS tape (Bi2223)

To
tal

Insulation layer of semi-synthetic
paper, 8 mm thick

Co
nd
uc
tor

Inner cryostat pipe of stainless steel
Shield layer of HTS tape (Bi2223)

minimizing the strain on the tape. The electric insulation
layer was created by winding multiple layers of semi-synthetic paper (PPL paper) using the conventional paper
winding machine for OF cables. The HTS shield layer was
also formed by winding Bi2223 HTS tape on the electric
insulation layer while controlling the winding tension.
During its manufacturing process, the HTS cable waswound on drums a number of times to be transferred to
the next process, undergoing bending strains each time.
Thus it was necessary to confirm whether there was acable degradation caused by strains such as those during
the HTS tape winding or drum winding, and accordingly,
critical current Ic was measured with the test pieces cut
from the cable end, using those 1-m long after every
major process and 20-m long after the final process.
Figure 2 shows the changes in Ic of the HTS conductor
and shield layers at each process, taking the summationof original Ic of all HTS tapes as 100 %. As the result, it
was confirmed that there was virtually no degradation andthat manufacturing of the 500-m HTS cable was successfully completed.

Ic/Ic total (%)

Outer cryostat pipe of stainless steel
and anti-corrosion layer,
Super insulation

Critical current Ic of test pieces after each manufacturing process 1).

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Successful Field Tests of the World’s Longest 500-m High-Tc Superconducting Power Cable

for cryostat pipes and the in-process pinhole detection
technology. Furukawa Electric had already established amanufacturing technology of long-length stainless steel
corrugated pipes for sheathing the stainless steel
sheathed cables currently in use, so that it was possible
for the Company to manufacture high-reliability cryostat
pipes by expanding the above mentioned technologies
and by establishing the eddy current flaw detection technology that allows in-process detection of pinholes at thewelded seam. Moreover, a helium leak test was conducted after pipe manufacturing with a sensitivity higher than
10-9 Pa·m3/s confirming no leaks, and, in addition, a pressure test was carried out with a pressure that is 1.5 times
the design pressure (1.1 MPa) validating air tightness.
Figure 3 shows the appearance of the manufactured HTS
cable, which looks like an ordinary cable due to its PVC
sheath.

vibration with 3 G and 7 Hz was continuously applied for
3 hr, and the change in Ic before and after the test wasmeasured. Although no decrease in Ic was found denying
troubles from land transportation, it was decided to adopt
sea transportation to be on the safe side. Thus the cable
was transported by ship for approximately 50 km from
Ichihara wharf to Yokosuka port, then from there by asemi-truck for 10 km. See Figure 4. The vertical and horizontal accelerations during the transportation were measured using accelerometers mounted on the cable drum,
and the results showed that horizontal acceleration was
virtually 0 G, vertical acceleration during sea transportation was 0.2 G or less, vertical acceleration during landtransportation was 1.0 G or less, and a maximum acceleration of 1.5 G occurred only once in the premises of the
CRIEPI Laboratory, indicating that the transportation
exerted virtually no effect on the cable in view of theresults of the vibration test.

5.

Figure 3

4.

Appearance of the 500-m HTS cable.

TRANSPORTATION OF HTS CABLEASSEMBLY OF TERMINATION

A termination, which had been developed jointly by
Furukawa Electric and Chubu Electric Power Co., wasused in this test. Its structure is shown in Figure 5 andappearance in Figure 6. The termination has a three-segment structure comprising a thermal gradient tank, a former tank and an outer-core tank, and it is movable onrails preventing excessive strains due to thermal contraction.
The HTS cable and the termination are so configured
as to have partitioned vacuum sections, and the cable
was evacuated for its thermal insulation layer during theperiod of termination assembly. The assembly work comprised provision of foil electrodes for partial discharge
detection, optical connectors for optical fiber and hermetic sealing of various wires for measurement.

The manufactured HTS cable had to be transported, forthe purpose of field test, from the Furukawa’s plant inIchihara, Chiba Prefecture to the CRIEPI’s laboratory in
Yokosuka, Kanagawa Prefecture. It was anticipated that,during transportation, the cable core would vibrate inlarge amplitudes due to the different diameters of thecable core and cryostat pipe, and this could result in any
damage in the cable core. Accordingly, a vibration test
using test pieces was carried out beforehand in order toinvestigate the effects of vibration during transportationon the cable, in which, assuming all-land transportation,

Figure 4

Transportation of the 500-m HTS cable.

Figure 5

Structure of termination 2).

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Successful Field Tests of the World’s Longest 500-m High-Tc Superconducting Power Cable

Figure 6

6.

Appearance of termination.

Figure 8

Test line of the 500-m HTS cable photographed fromthe U bend section (1).

Figure 9

Test line of the 500-m HTS cable photographed fromthe termination.

TEST LINE AND COOLING SYSTEM

Figure 7 shows the test line layout 2). The test line configured on a race track consisted of a 10m-high rising andfalling section simulating river-crossing bridges, an offset
section aimed at relaxation of thermal contraction, and anunderground section simulating conduit-based laying,
and the terminations were installed on rails rendering it
movable along with thermal contraction.
Figures 8 and 9 show the views of the test line.
The cooling system for the HTS cable circulates liquid
nitrogen for cooling the cable, and the coolant also serves
as an impregnant for the electric insulation layer, i.e.
paper insulation layer impregnated with liquid nitrogen. To
prevent gasification of liquid nitrogen which can initiate
dielectric breakdown of cryogenic electric insulation, thecoolant is pressurized to circulate in the state of singlephase flow, i.e. subcooled state, thereby cooling the cabletaking advantage of its thermal capacity.
The cooling system for the 500-m HTS cable employedsix Stirling refrigerators with a cooling capacity of 1 kW at
77 K, allocating four for the cable and two for the termination cooling. A storage tank was used to pressurize liquid
nitrogen to a subcooled state, and two circulation pumps
were utilized to circulate liquid nitrogen to the HTS cableand the termination respectively. This configuration of two
partitioned cooling systems each equipped with circulation pumps and a refrigerator is advantageous since itallowed, at the initial stage of cooling, prevention of heatinvasion from the termination and the cable individually,
thereby shortening the initial cooling time. Moreover, bypressuring the storage tank to maintain a subcooled state
all over the system, it is possible to reduce the outlet pressure of circulation pumps thus improving the cooling efficiency thanks to the decreased pumping loads. It
becomes also possible, in case of accidents such as
pump malfunction, to continue operation for a specified
time without damaging the cable.

Offset section (length: 15 m)
U bend section (2)(bending radius: 5 m)

U bend section (1)(bending radius: 5 m)
Termination
10m-high rising andfalling section
Stirling refrigerator

Underground section(length: 80 m, depth: 60 cm)

LN2
storage tank
LN2 pump

Figure 7

Test line layout with cooling system 2).

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Successful Field Tests of the World’s Longest 500-m High-Tc Superconducting Power Cable

7.

RESULTS OF FIELD TESTThe field test was carried out at the CRIEPI Laboratory
according to the schedule shown below. Laying test of
the HTS cable was conducted in November 2003, basic
characteristics test from March through June 2004, rated
loading test from September through December, load
fluctuation test and limiting and overloading test fromJanuary through February 2005, and cable removal andresidual performance test from February through March
2005.
Test results will be presented in outline in terms of laying efficiency, basic characteristics, rated loading characteristics, load fluctuation characteristics, and limiting andoverloading performance.
7.1 Cable Installation Test
In the cable installation test, the cable was investigatedwhether it could be laid in duct just like conventional
cables.
In the cable laying, a pulling eye that had been preliminarily mounted at the cable end was used to lay the cablein the duct for approximately 170 m including the underground and 5-m radius U bend sections, and subsequently, the whole 500-m length was laid using a haulingmachine and ball rollers. While the front end of the cable
was subjected to a tension of 16 kN corresponding to 90% of the allowable tension at the beginning of laying, it
was found that, as a result of a critical current measurement for the specimens taken from the front end of thecable that underwent laying, there was no degradation incharacteristics between before and after cable transportation and laying. Furthermore, it was confirmed that thecable pressurization conducted at the time of manufacturing using dry air maintained a positive pressure even after
cable laying, and being supported by the result of argon
leak test that was carried out later, it was verified that
there was no leak whatever in the cryostat pipe.
7.2 Basic Characteristics Test
The basic characteristics test was conducted focusing on
confirming the thermal behavior at cooling and temperature rise, cooling characteristics or amount of heat invasion, electric characteristics including initial withstandvoltage, critical current, and AC loss.
7.2.1. Cooling and Temperature Rise Test
To cool the HTS cable from room temperature down to
the liquid nitrogen temperature of -196°C, nitrogen gas of
low temperature was used first for gradual cooling andthen liquid nitrogen in turn in the latter half period of cooling. Temperature distribution was measured by means ofan optical fiber wound around the HTS cable core.
The time required for cooling was 117 hr for gradualcooling using nitrogen gas in addition to 21 hr for liquid
nitrogen cooling, totaling 138 hr, i.e. about six days.
Temperature rising was effected by releasing liquid
nitrogen through the bleeder valve provided at the returnline of liquid nitrogen. Because the underground section

was located lower in elevation than the bleeder valve, thissection was slower in temperature rising due to the residual liquid nitrogen. The whole cable sections took 211 hr,i.e. about nine days, to reach room temperature. Thistemperature rise time considerably depended on ambient
temperature and sunshine, so that in case of low ambient
temperature and weak sunshine, it took a longer time due
to a significant reduction of heat inflow from the termination.
7.2.2. Measurement of Thermal Loss
Heat invasion into the cryostat pipe was determinedbased on the measurements of temperature and pressure
differences between the upstream and downstream
points, i.e. 0 m and 500 m from the origin, while circulating liquid nitrogen at a constant flow rate. The results
showed that the thermal loss including viscosity loss of
the 500-m HTS cable was 1.23 W/m, and the thermal loss
due to heat invasion from outside the cryostat pipe was
1.21 W/m.
At the U bend section, heat invasion was seen to befour to six times larger than that in straight sections. Thisis due to the fact that the cable core is pressed against
the inner cryostat pipe because of the thermal contractionof the core, reducing the thickness of the thermal insulation layer thus decreasing its thermal performance. Figure
10 shows the X-ray photographs of the U bend andstraight sections of the HTS cable taken perpendicularly.
At the bent section, the thermal insulation layer is seen to
be pressed tight due to thermal contraction, indicating
mechanical lateral pressure and increase in heat invasion.
At the straight section, on the other hand, it has been
confirmed that the HTS cable developed here possesses
thermal insulation performance equivalent to 1 W/m orless, achieving the initial target.
7.2.3. On Pressurization of Cooling
During the circulation of liquid nitrogen, an X-ray photograph taken at the 10m-high rising and falling section
showed a shadow image which was attributed to a gas
phase. See Figure 11. In this cooling system, the storagetank is pressurized with gas in order to maintain, even incase of pump malfunction, the inner pressure thus preventing occurrence of dielectric breakdown. At the beginning, helium gas having a boiling temperature lower thanliquid nitrogen was used as a pressurizing gas, but it was
found that, since helium gas dissolves into liquid nitrogen,the dissolved helium gas gasified as the temperature ofliquid nitrogen rose in low pressure, producing a mass of

Figure 10 X-ray photograph of cable sections during LN2 cooling. (Left: straight section, Right: U bend section)

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Successful Field Tests of the World’s Longest 500-m High-Tc Superconducting Power Cable

functioned satisfactorily. At the time of temperature rise, inthe meantime, the final returning length of the cableremained at a value of 490 mm. This may be attributed to
the fact that the cable was moved mostly to the underground section where the temperature rising was slow at
the time of temperature rise 3).

Inner cryostat pipe
Level of liquid nitrogen
HTS core

Figure 11 X-ray photograph taken at the 10m-high rising andfalling section.

gas 1). Existence of this helium gas mass raised concerns
about significant reduction in the electric insulation performance of the cable core. Accordingly, a method wasdevised in which nitrogen gas was efficiently used as apressurizing gas in place of helium gas, and it was confirmed that stable circulation of liquid nitrogen wasachieved.
7.2.4. Thermo-Mechanical Behavior
When cooled from ambient temperature to liquid nitrogen temperature, the cable core that constitutes the conductor contracts by about 0.3 % due to thermal contraction 5). Stress would be generated unless this contraction
was smoothly effected, so that a serpentine offset wasprovided in the cable line aiming at relaxing stresses dueto thermal contraction. Figure 12 shows the structure of
the offset.
The movement was checked using X-ray over the whole
500-m length, and it was confirmed that the cable moved
sufficiently according to cooling and temperature rise andthat the offset absorbed a contraction length of about 690
mm between before and after cooling. This length was ingood agreement with the predicted value which was calculated assuming that the offset took care of almost all
the thermal contraction of the 200-m long straight section,and it was confirmed that the mechanical stress relaxation
5 mR

5 mR

90°

45°

45°
15.7 mFigure 12 Structure of cable offset.

5 mR

7.2.5. Electric Characteristics Test for Withstand Voltage
and Superconducting Characteristics
The HTS cable developed here can be evaluated for its
performance only when impregnated with liquid nitrogen.
Thus it was during the field test that the cable was confirmed as to whether it could exhibit the withstand voltage
and superconducting characteristics as designed.
(1) Withstand Voltage Test
Conditions for withstand voltage were set out as 95
kVrms for 10 min, in consideration of a time factor of conversion for 30 years. Test voltages were applied in 5
kVrms/min steps until 95 kVrms. And in the mean time, inorder to survey the soundness of the electric insulation
layer, partial discharge measurement by tuning method
was carried out using the foil electrodes installed on thetermination under the condition of a noise level of 100 pC.
As a result of a voltage application of 95 kVrms for 10
min, any partial discharge exceeding 100 pC was notdetected, and this confirmed the validity of the design
methodology 5) for the electric insulation of the present
HTS cable.
(2) Superconducting Characteristics
Figure 13 shows the superconducting characteristics
with its left part of the graphs indicating that no voltage is
induced, i.e. zero electric resistance even at a conduction
current of 1000 A.
Critical current is used to evaluate the state of superconductivity, and it is defined as a current that induces avoltage generation of 1 µV/cm. Because the present cable
is 500 m long, the point of 50 mV corresponds to the critical current. The critical currents at an average liquid nitrogen temperature of 73 K for the conductor core and shieldlayers were 1910 A and 1620 A, respectively 3), and it wasdemonstrated that the cable satisfied the initial specification for critical current of 1000 A or more. Table 2 shows
critical current data for various temperatures, and it canbe seen that the lower the temperature the higher the critical current for superconductivity.
Meanwhile, when a HTS cable is used with an alternating current, alternating-current (AC) loss is generated dueto the alternating magnetic fields. The AC loss for thepresent cable was 1.3 W/m under the conditions of 73 K
in averaged liquid nitrogen temperature and 1000 Arms in
conduction current, showing a rapid AC loss increase
when the current exceeded 900 A 3). Thus it was shownthat the AC loss at 1000 A of the HTS cable manufactured
here is equivalent to the amount of heat invasion throughthe cryostat pipe.
7.3 Results of Rated Loading Test 3)
To confirm the operation characteristics of cooling system and the electric insulation characteristics, a conduc-

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Successful Field Tests of the World’s Longest 500-m High-Tc Superconducting Power Cable
0.10

2000

LN2 temperature:

77K

Conductor current

69K

73K

Shield current

1500

0.08

0.06

Current (A)Voltage (V)1000

1 µV/cm
0.04

500
0
-500
-1000

0.02

-1500
0.00

0

500

1000

1500

2000

2500

Current (A)73K

Voltage (V)

0.06

0.04

0.02

500

1000

1500

2000

2500

Current (A)(b) Shield
Figure 13 I-V characteristics of the 500-m HTS cable.
Table 2

0.04

0.05

0.06

7.4 Results of Load Fluctuation Test 3)
In this test, the current was made to fluctuate simulating
daily load fluctuations in an actual electric power system,and the tracking behavior of the cooling system wasinvestigated. Although certain amount of overshoot wasobserved, the system stabilized in about 3 hr.

1 µV/cm

00.03

test at 95 kVrms was carried out, confirming no occurrence of partial discharge. Thus, it was confirmed that
there was no degradation in terms of electric insulation
performance.

69K

0.08

0.00

0.02

Figure 14 Current waveforms of the 500-m HTS cable.

0.10
77K

0.01

Time (s)(a) Conductor

LN2 temperature:

-2000
0.00

Critical current of the 500-m HTS cable at different
positions and temperatures.

Position

69 K (-204°C)

73 K (-200°C)

77 K (-196°C)

HTS conductor

2290 A

1910 A

1570 AHTS shield

1965 A

1620 A

1350 Ation current of 1000 A was continuously imposed for one
month at a voltage to ground of 70 kVrms under the conditions of averaged liquid nitrogen temperature: 73 K, liquid nitrogen flow rate: 30 /min, and pressure: 0.3
MPa(abs). These conditions were determined assuming
insulation degradation in 30 years.
The present HTS cable has a superconducting shieldlayer in which, taking advantage of perfect diamagnetism
specific to superconductivity, a shield current having aphase opposite to that of the conduction current flows
thus shielding the magnetic field from leaking to the outside. As shown in Figure 14, the shield current was 980 A
at a conduction current of 1000 A in the conductor layer,
confirming also the performance of a cable which is low
in magnetic field leakage.
After the one-month loading test, a withstand voltage

7.5 Results of Limiting and Overloading Test 3)
In this test, in order to evaluate the time limitation of continuous loading test, refrigerators were stopped in simulation of refrigerator malfunction, while continuing the rated
loading test. The test was conducted while monitoringsuch system indicators as temperature, pressure andoccurrence of partial discharge, and it was found that thepressure reached its limitation in 3 hr 30 min under theconditions of 73 K for the averaged liquid nitrogen temperature at the initial stage and 30 /min for the liquid
nitrogen flow rate. This is satisfactory from the standpointof system operation because a refrigerator malfunction
can be settled with no hassles after interrupting powertransmission over the cable.
In addition, additional tests were conducted including
refrigerator stop test assuming refrigerator malfunction,
cooling system stop test assuming refrigerator and pumpmalfunction, overcurrent test whereby a 130-% Ic wasapplied for 1 hr, and overvolatage test assuming anabnormal voltage of 150 kV.
Critical current was measured after each test, and no
degradation was found.
7.6 Cable Removal and Residual Performance Test
Cable specimens 6 m long were taken from the offset
section, U bend section, 10m-high rising and falling section, underground section, and cable end section that
underwent bending, and the specimens were subjected,
in addition to six comparison specimens each 6 m in

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Successful Field Tests of the World’s Longest 500-m High-Tc Superconducting Power Cable

length taken from the straight section, to critical current
measurement and visual inspection. As a result, virtually
no degradation in the critical current was found for the
HTS conductor, while local degradations were seen in the
HTS shield. Although the degree of degradation was within a practically allowable range of about 5 %, this is something that awaits further investigation. Results of disassembly investigation confirmed that there was no damage
in the HTS tapes.

8.

HTS cable was exposed to strong wind and rain at thattime, the cable survived the typhoons allowing us to continue the test. This is thought to be a proof of the robustness of the cable.

ACKNOWLEDGEMENT
This test project has been carried out as a part of Super
ACE project of METI, being commissioned by NEDO to
Super-GM.

CONCLUSION

The HTS cable withstood all the items of this field test
without being damaged. As the result, it has been confirmed that the cable is sound over its entire length andthat owing to its high reliability the cable has withstoodvarious tests including the one for limiting and overloading performance. Furthermore, important achievements
have been accomplished through this series of tests,
which obviously contribute to practical applications of the
HTS cable in terms of design, testing, laying, and operation.
Development of the HTS cable is underway in U.S.,
Korea, China, etc. It is thought to be of great significance
that, ahead of these development programs, we wereable to obtain various data intended for practical applications of the HTS cable.
Incidentally, unprecedented numbers of typhoons landed on Japan during the period of this test including three
big ones that directly hit the test premises. Although the

REFERENCES
1) S. Mukoyama, N. Ishii, M. Yagi, S. Tanaka, S. Tanaka, S. Maruyama,
O. Sato, A. Kimura: “Manufacturing and installation of the world’s
longest HTS cable in the Super-ACE Project”, Applied
Superconductivity Conference 2004, 1LJ03, 2004.
2) T. Takahashi, H. Suzuki, M. Ichikawa, T. Okamoto, S. Akita, S.
Mukoyama, N. Ishii, A. Kimura, K. Yasuda: “Demonstration andVerification Tests of 500-m High-Tc Superconducting Cable”,
Applied Superconductivity Conference 2004, 3LB03, 2004.
3) Ichikawa et al.: “Field Test Results of a 500-m Superconducting
Power Cable”, Proceedings of IEEJ General Conference 2005, 5S15-4, 2005. (in Japanese)
4) S. Mukoyama, H. Hirano, M. Yagi, H. Kimura and A. Kikuchi: “TestResults of a 30 m High-Tc Superconducting Power Cable”, IEEE
Transaction on Applied Superconductivity, 13 (June 2003) 19261929.
5) T. Takahashi, H. Suzuki, M. Ichikawa, S. Akita, S. Maruyama and A.
Kimura: “Dielectric Properties of 500 m High-Tc Superconducting
Cable”, Applied Superconductivity Conference 2004, 1LJ05, 2004.

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