Special Issue

Smart Grid

The Development of 275 kV-3 kA YBCO High-Tc
Superconducting Power Cable
Masashi Yagi*, Shinichi Mukoyama*, Takaharu Mitsuhashi*,Ten Jung*, Liu Jin*, Mitsuo Suzuki*, Hirao Hirata*, Tomoya Nomura*,
Ryo Nakayama*, Noboru Maesato*, Takeshi Okuma*2, Osamu Maruyama*2

In response to the increase in the supply and the demand of the electric power,
Furukawa Electric has been developing a 275 kV-3 kA High temperature
Superconducting (HTS) Power cable. This test has been commissioned by the New Energy andIndustrial Technology Development Organization (NEDO) since 2008. The cable is able to transmit a large capacity of electricity of 1.5 GW which is the equivalent amount of power capacity ofa single thermal power plant with low loss, and is expected to be put to practical use an electric
power trunk line in the future.
The fundamental technology for the designing the HTS cable has been accumulated based on
the result of such tests as the alternative current (AC) loss test, the withstand voltage test, thepartial discharge test, and the over-current test. The 30 m HTS cable for a long-term electricalvoltage and current load test was designed and manufactured according to the technologies.
The insulation thickness was determined on the basis of the designed stress from the tests andthe test conditions for the superconducting cables specified in standards such as IEC, JEC. The
cable was also designed to withstand the over-current of 63 kA-0.6 sec and to satisfy therequirement to have the total of the dielectric loss and the AC loss under transmission current beless than 0.8 W/m at 275 kV-3 kA. The 30 m HTS cable was made under the above mentioned
specifications, and evaluation was made on the attributes of the surplus length. It was confirmedthat it satisfied the designed performance.
Furukawa Electric installed the 30 m HTS cable, the end termination and the normal joint at
Shenyang Furukawa Cable. The long term electrical voltage and current load test at 200 kV for
one month was completed successfully.

ABSTRACT1.

INTRODUCTION

The superconductive material features two characteristics: a zero electrical resistance and a high current density. The efficient electric instrument is obtainable based on
the former characteristic and the powerful magnetic field
is an outcome of the latter characteristic. The examples ofusing the latter characteristic are the magnetic resonanceimaging (MRI) of the medical apparatus, the nuclear
fusion technology, the accelerator for high energy physics, etc. and the superconductive metal technology inwhich area Furukawa Electric has a very good reputation.
In order to utilize the former property, we need to lower
the cooling cost for the superconductivity. The cooling* R&D HTS Project Team, HTS Engineering Department*2 International Superconductivity Technology Center
Superconductivity Research Laboratory (ISTEC SRL)

system for the metal superconductor using the liquid helium (-269°C) is not useful from an economic perspective.
Since the high-Tc superconductive material is utilized at
liquid nitrogen temperature (-196°C), it is expected to beefficient, light weight, compact and energy-saving.
Furukawa Electric Group is not only the first runner in themetallic superconductor technology but making progressin the development of the High-Tc superconductor.
Furukawa Electric group has been developing a superconducting cable based on the superconducting technology
and an accumulation of the power electric transmission
technology. The conventional power electric transmission
technology is sought for the utilization of the extra highvoltage power line and is progressing to lay the powerlines underground, in the tunnel or the conduit in the city.
However the tunnel is already fully occupied with thecables and the old cables need to be changed new ones.
It would be economic advantageous if the superconductFurukawa Review, No. 43

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The Development of 275 kV-3 kA YBCO High-Tc Superconducting Power Cable

ing cable which has larger capacity and lower loss than theconventional cable could be installed in the vacant spacein a tunnel or a conduit not being used at the moment.
Furukawa Electric has been developing a 275 kV extra
high voltage superconducting power cable commissioned by the NEDO since 2008. The cable is targeted tohave three times larger capacity and low loss comparedto the conventional 275 kV cable. For a superconducting
cable of 275 kV rated voltage and 3 kA of the current
capacity, the transmission capacity for one line is equivalent to the power capacity of a single thermal plant of 1.5
GW (275 kV /√3 × 3 phase × 3.15 kVA). The cable consisted of a YBCO, which is expected to apply to various
types of the electric instruments because of its cost performance, and its lower loss of one quarter to one fifth ofthe conventional cable even when considering the loss ofcooling of the superconducting cable.
Table 1 shows the target of the development and thatthe targeted cable could perform at a better merit than theconventional cable.
Table 1Ag
YBCOSuperconductor
wireIntermediate
layer

Hastelloy
substrate

TargetFeatureTotal loss of the AC loss
and the dielectric loss isless than 0.8 W/m

One quarter to one fifth ofthe conventional cable evenwhen considering the lossof cooling of thesuperconducting cable

Figure 1 Laser cutting of both edges of YBCO wire.

(a)

63 kA – 0.6 sec.

No breakdown at the worst
case

Outer
diameter

150 mmThe same as the diameterof the conventional 275 kV
2500 mm2

OthersEMI free by thesuperconducting shield

No leak field on the highcurrent transmission

DEVELOPMENT FOR THE REDUCTION
OF THE ALTERNATIVE CURRENT (AC)LOSS

The electrical resistance is zero for the superconductor
for the direct current (DC), however the alternative AC
loss occurs on the AC when superconducting. The variable magnetic field based on the AC transmission is present in the superconductor and, thus, the loss is generated. Since the loss becomes load to the refrigerator used
for cooling the superconducting cable, it has to be
removed. The magnetic field penetrates from an edge ofthe tape-like superconductor wire and the characteristicof the edge is very important to solve the magnetic field.
The AC loss is ten times larger in the case of limited characteristic of the superconductivity of the edge. The characteristic was improved by cutting the edge with a laser
due to its low thermal impact.
Figure 1 shows the laser cutting of the edge of the yttrium series superconductor wire and the whole wire included the cut edge is plated with copper.

10

5-C
I c =5550 A at 73.0 K
I c =4530 A at 75.5 K
I c =3860 A at 77.3 K
Caluclation

-9
6
4
2

10

-10

3-C
I c =9200 A at 68.7 K
I c =8550 A at 70.0 K
I c =6700 A at 72.5 K
I c =4700 A at 77.3 K

6
4
2

10-11

Calculation

60.235 W/m at 3 kA

4

0.2

0.4

0.6

0.8

1.0

I t (peak current) /I c(b)

HTS conductor at 2010
I c =9200 A at 68.7 K
I c =8550 A at 70.0 K
I c =6700 A at 72.5 K
I c =4700 A at 77.3 K

2Normalized AC loss [J/m/cycle/A2]2.

2

Normalized AC loss [J/m/cycle/A2]

of aElectric The development
design is the same asa normal joint and The
insulation cable,
the conventional cablean end terminal
Overcurrent

Laser

Target and merit of 275 kV – 3 kA HTS cable.

Item
Loss

Figure 2(a) shows the AC loss normalized with the critical current (Ic). 5-C was the assembled superconductor
wires with the width of 5 mm having the limited edge performance and 3-C is the assembled superconductor
wires with 3 mm width produced by cutting edges with
1 mm each with a laser. The difference of AC loss wasmore apparent in the low use rate (It/Ic), the value of 5-C
was five to ten times higher than 3-C. The loss value of
3-C obtained was 0.235 W/m at 3 kA. The numbers of theused superconductor wire were increased and the loss
per a single superconductor wire was decreased to 0.124
W/m at 3 kA, as shown in Figure 2(b), which is the lowest
attained value in worldwide.

10

-9
6
4

Calculation

2

10-10

0.235 W/m at 3 kA

6
4

HTS conductor at 2011

2

10-11
6

0.124 W/m at 3 kA

4

0.2

0.4

I c =9020 A at 73.7 K
I c =8150 A at 74.4 K
I c =6270 A at 77.3 K
Calculation

0.6

0.8

1.0

I t (peak current) /I c

Figure 2 AC loss of HTS conductor.
(a)The comparison of loss between 5-C and 3-C, 3-C
using the laser-processed YBCO wires.
(b)Further reduction of loss by adjusting the radius of
the conductor.

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The Development of 275 kV-3 kA YBCO High-Tc Superconducting Power Cable

3.

DEVELOPMENT FOR SOLVING THE
OVER- CURRENT

Since an over-current of about ten times the rated current
flows into the superconducting cable during the short circuit fault, it is necessary for the superconducting cable towithstand the over-current when the cable is used in the
power line system. Even though the withstand conditionof the over-current for 275 kV system is determined on a
specification from the customer, we adopted the value of
63 kA according to JEC 2350 of AC circuit breaker.1)
The duration time adopted is 0.6 seconds as the worst
case scenario according to the technical report of theInstitute of Electrical Engineers of Japan.2) The value of
63 kA is 20 times larger than the rated current of 3 kA
used in the development of the superconducting cable.
As the over-current is shunted for the protection of the
conductor, the superconductor wire is protected. The
structure of the superconducting cable is shown in Figure
3. The copper stranded former fills the role of the protection conductor for the superconducting conductor sideand the braided copper wire fills the role of the protector
for the superconducting shield side. The current flows
through the superconducting conductor and the superconducting shield at steady condition but the commutation from the superconductor to the copper occurs on theover-current and the superconductor is protected. The
cross surface area of the copper for the protection conductor is discussed later. The larger surface area of theprotection copper conductor is decreases the temperature rise on the over-current, however the compactness isdecreasing. An optimization of the cross surface area forthe protection conductor is needed.

Generator

Figure 4 Closed circuit for the over-current test.

The right side cable in Figure 4 had a normal joint andthe withstanding performance of the joint was checked.
Figure 5 shows the shape of the normal joint. With
respect to the conductor side, the reed shaped superconductor wire was installed parallel in the longitudinal direction and jointed. As for the shield side, the joint was carried out on the reinforced insulation layer and the joint
method was the same as in the conductor side.

Figure 5 Normal joint of HTS for the over-current test.

Figure 3 Structure of HTS cable.

In the case of the conductor current in the direction of
the red arrow, the conductor shield current flows in the
direction of the blue arrow.
The over-current test of the superconducting cable isshown in Figure 4. Two cables were installed in parallel
and the superconducting conductor was connected withthe generator and the shield circuit was assembled toinduce the current in the superconducting shield.

Figure 6 shows the waveform for the over-current of
63 kA. A peak of the first wave was set at 158 kA in consideration of the DC component, which was 2.5 times ofthe over-current. On the other hand, the amplitude of theshield current was 80% of the conductor side. The amplitude of the shield current for the cable without a normal
joint was 90% under the same test system. The difference
occurred with or without the normal joint because of themagnetic connection at the normal joint.
Since the superconducting shield was installed on thereinforced insulation in the normal joint and the distance
between the conductor and the shield of the joint was longer than the cable part, the magnetic connection was
weaker. Furthermore the resistance of the terminal was
not ignored because the test circuit was short. The ampliFurukawa Review, No. 43

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The Development of 275 kV-3 kA YBCO High-Tc Superconducting Power Cable

Current [kA]

tude of 80% was relevant according to the above conditions. The real superconducting transmission line will
have the normal joint at interval of 100 m and the shieldcurrent can be 100% of amplitude of the conductor current.

150
100
50
0
-50
-100
-150
0.00

Superconductor
wires

Liquid Nitrogen

Insulating paper

Kraft paper
0.02

0.04

0.06 0.08
time [s]

0.10

0.12

0.14
Kraft paper

Figure 6 Waveform for the over-current of 63 kA.

An increasing temperature and a recovery time to theinitial stage were checked by the duration time of theover-current of 63 kA as a parameter. With respect toincreasing of the temperature, it was less than 5 K for
0.05 seconds (3 cycles) and less than 8 K for 0.1 seconds(7 cycles). The recovery to the initial stage was less than
3 seconds for both cases and the result suggested thatthe cable would be recovering smoothly after the accident. The increasing of the temperature and the recovery
time to the initial stage for 0.6 seconds (36 cycles) wereless than 20 K and ten minutes respectively and the valueof Ic checked after the recovery did not deteriorate. These
results showed the cable having enough tolerance for theover current.

4.

DEVELOPMENT OF THE 275 KV INSULATION

4-1 Superconducting Cable Insulation for 275 kV
The insulation of the superconducting cable is a composite insulation consisting of the insulating paper and theliquid nitrogen shown in Figure 7. The insulation composition is similar to the oil-filled paper insulated cable (OFcable) consisting of the oil and the insulating paper. The
electric design of the insulation is the same as the OF
cable. The electric stress is the highest on the conductor
and the insulation thickness is designed for the electric
stress to be less than the designed stress. The insulating
paper shown in Figure 7 is the semi-synthetic paper consisting of the polypropiren film (PP film) sandwiched withthe thermal laminated kraft paper. The dielectric loss of
the insulating paper is not ignored for the 275 kV system.
If the insulating paper used for the 66 kV superconducting cable is applied to the 275 kV system, the loss reaches 0.8 W/m and does not meet the target shown in Figure
1. Therefore a semi-synthetic insulating paper, changing
the component ratio of PP film from 40% to 60%, wasapplied.

Polypropylene film

Figure 7 Structure of the electrical insulation for thesuperconducting cable.

With respect to the electric design, a partial discharge
free (no partial discharge) at an abnormal voltage under
the operation and withstand against the impulse lightening voltage were considered. The test condition wasdetermined on the basis of IEC620673) of the international
standard, JEC34084) of Japanese electrical standard andthe other superconductor test standard. The determination was done at the committee of the NEDO project
attended by the professors and the electric power
experts.
The partial discharge test voltage was determined to
310 kV taking into consideration the electrical fault voltage, the target and no partial discharge at the test voltage. The value of 310 kV was determined as the 300 kV of
the highest line voltage between two conductors times
the voltage increased magnification on the load rejection(1.79/ √3 ).
The test voltage of lightening impulse was 1155 kV
which had a margin of 1.1 times of the withstand impulse
voltage of the 275 kV electrical device.
The model semi-synthetic paper insulated cables having
the insulation thickness of 1 mm, 10 mm and 20 mm were
manufactured and the cables were tested. The designed
electrical stress was determined according to the test
result.
The result of the partial discharge test is shown in
Figure 8. The semi-synthetic paper insulated cable
immersed in the liquid nitrogen under absolute pressureof 0.2 MPa was tested for the partial discharge. The electrical stress detected an inception of the partial discharge
while increasing in voltage was plotted in Figure 8. The
result for the cable with the thickness of 1 mm was closely
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The Development of 275 kV-3 kA YBCO High-Tc Superconducting Power Cable

Cumulative probability [%]same as the cable with 10 mm thickness. Furthermore,
the cable with the thickness of 20mm had no partial discharge at 300 kV (25.4 kV/mm) nor at 310 kV (26.2 kV/mm). The result suggested that the partial discharge
inception voltage was independent from the insulation
thickness. The inception voltage was obtained from theresult of the thickness of 1 mm. The electric stress at theprobability of the inception of 0.1% was 22 kV/mm andthe electric stress was used as the design value.
Figure 9 shows the result of the impulse breakdown
voltage test. The result of the sample with the insulation
thickness of 1 mm was compared with the result of thesample with 10 mm insulation thickness. It suggested thatthe impulse breakdown voltage was dependent on theinsulation thickness. Assuming the variation of theimpulse property of 10 mm thickness is the same as
1 mm thickness, the design stress for the impulse breakdown of 83 kV/mm was determined. The outer diameterof the 275 kV cable was designed at 35.4 mm and thethickness of the insulation was 22 mm. The 275 kV cable
was confirmed to withstand the target impulse voltage of1155 kV.

99.99
99
90
70
50
30

1 mmt model cable
10 mmt model cable

20 mmt model cablePD free at 300 kV(25.4 kV/mm)

10
5
3
1

20 mmt model cablePD free at 310 kV(26.2 kV/mm)

22.0 kV/mm

0.5
0.3
0.1
18

20

22

24

26

28

4-2 Normal Joint and End Terminal for 275 kVWith regard to the end terminal of the superconducting
cable, the stress relief cone for electric field relaxation andthe condenser cone to relax the electrical stress for thenormal conductivity part from the atmosphere temperature to the liquid nitrogen temperature were designed anddeveloped. The condenser cone was covered with thecomposite bushing. The composite bushing was consisting of the epoxy based FRP cylinder coated with the silicone rubber and shade, and attached the clasp at theboth side of the cylinder. The electric field analysis for the
combination of the condenser cone and the composite
bushing was carried out, and a relevant design satisfying
the target voltage was determined. The composite bushing achieved downsizing to 80% in length and 20% of
weight reduction comparing to the porcelain bushing.
Furthermore, it was designed so that the superconductor
wire would not get damaged on cooling and rising of thetemperature, based on the solution for thermal expansion
and contraction to prevent the cable from buckling.
Figure 10 shows the outdoor end terminal.
With respect to the normal joint for the super conducting cable, the insulation was designed on the basis of theelectrical stress in the radial direction and in the longitudinal direction. The electrical stress for the insulation
design was obtained from the breakdown test on theinsulation model close to the actual cable and taking into
consideration the tolerance. The joint of the former andthe superconductor wire were carried out as shown in
Figure 5 and the joint had low resistance and withstoodthe over- current.
The end terminal and the insulation part of the normal
joint were designed for withstanding an AC voltage of
400 kV and an impulse voltage of 1155 kV, and a current
carrying part was designed for withstanding the rated current of 3 kA and the over-current of 63 kA-0.6 sec.

30

PD inception stress [kVrms /mm]

Breakdown voltage (Imp.) [kV/mm]

Figure 8 Weibull plot of Partial discharge Inception stress (PDIE)
The design stress of PDIE free was 22 kV/ mm.

140
120
100
80
60

83 kV/mm

40±1155 kV
3 shots

positive(+)
negative(-)

20
0
0

5

10
15
Insulation thickness [mm]20

Figure 9 Impulse breakdown voltage of the model cable.
Design stress of Impulse free was 83 kV/mm.

Figure 10 Termination for 275 kV HTS cable.

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The Development of 275 kV-3 kA YBCO High-Tc Superconducting Power Cable

Former

Hollow stranded conductorof 400 mm2

Superconducting
conductor

Superconducting two layers,
Sixty wires with width of 3 mm
AC loss of 0.124 W/m at 3 kA

Insulation

Semi-synthetic paper withthickness of 22 mm
Dielectric loss of 0.6 W/m

79.4 mmthe conductor and the superconducting shield sealed themagnetic field by the anti-phase current. The disturbanceof the magnetic field created by the superconducting
shield is small because of the distance from the conductor being long and the AC loss of the shield is expected
smaller than the conductor, the value is one-third to onefourth according to our experience. However, the superconductor wire used for the shield has the width of 5 mmwith deteriorated Jc on the edge, the analyzed result suggested that the AC loss of the shield was 60% of the conductor loss.
According to the above result, the total loss was
0.8 W/m associated with the AC loss at 3 kA of 0.2 W/mwith the dielectric loss of 0.6 W/m.
The stainless (SUS) thermal insulated inner pipe andthe super insulation (SI) of the vacuum insulation material
were wound, and the SUS outer pipe with polyethylene
sheath for the cold area, and the target of the total outer
diameter was 150 mm.

Superconducting
shieldSuperconducting one layer
AC loss of 0.076 W/m at 3 kA

81 mm

5-2

Copper shield

Copper braided wire of 210 mm2

Protect layer

Semi-synthetic paper

Double thermal
insulated pipe
Outer sheath

Double stainless pipe, Vacuum
insulation layer, Poly-ethylene
sheath5.

DESIGN AND MANUFACTURING OF 275
KV-3KA SUPERCONDUCTING CABLE

5-1

The Design of the 275 kV-3kA Superconducting
Cable
According to the result described in articles 2 to 4, the275 kV-3 kA superconducting cable was designed andthe designed items were summarized in Table 2.
Table 2Composition

275 kV-3 kA HTS cable.
Specification

Outer
diameter

35.4 mm

90 mm

150 mmThe 400 mm2 hollow copper wire strands was used as
the former. The former can withstand the over-current of
63 kA-0.6 sec. and protect the superconductor, anddecrease the temperature on the line fault. If it is needed
for the temperature to decrease more, the diameter of theformer can be larger.
The superconductor wire having the width of 3 mm anda constant Jc (critical current density) in the cross sectional direction was used for the superconducting conductor and the AC loss at 3 kA was 0.124 W/m.
The semi-synthetic paper insulation consisted of thekraft paper and the PP film, the composite rate of the PP
film being larger than the conventional semi-synthetic
paper was used and the insulation thickness was 22 mm.
The design of the thickness was determined by the electric stress on the conductor shield wound up on the superconducting conductor to be less than the designed stress.
Since the larger conductor makes the insulation thickness
thinner, the capacity becomes larger and the dielectricloss is increased. On the other hand, the smaller conductor makes the insulation thickness thicker and the dielectric loss is decreasing. The insulation design shown in
Table 2 makes the electric loss of 0.6 W/m.
Even though the superconducting shield layer being
one layer, however, since the wound diameter of theshield was larger than the conductor, the numbers of theused superconductor was more than the conductor. An
anti-phase current against conductor current in the superconducting shield was induced by the magnetic field of

The Manufacturing of the 275 kV-3 kA
Superconducting Cable
The superconducting cable was manufactured according
to the design shown in Table 2. The structure of the manufactured cable is shown in Figure 11.

Hollow former
Superconducting conductor layer
Superconducting shield layer

Vacuum thermal insulation layer

Outer diameter Φ150mm

Figure 11 Structure of 275 kV-3 kA HTS cable.

The superconductor wire with a single length of morethan 50 m was used. Every superconductor wire waschecked Ic for the total length. The wire with the width of
3 mm for the conductor with more than 80 A (the averageof 97 A) of Ic and the width of 5 mm for the shield withmore than 100 A (the average of 117 A) were used. The
superconducting cable core with the length of around 50
m was manufactured and the core of around 20 m out of
50 m was applied to the bend test, the structure examination, the withstand voltage test, the over-current test andAC loss test. Figure 12 (a) shows the superconducting
cable core with length of 30 m for a demonstration and
Figure 12 (b) shows the superconducting core covered
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The Development of 275 kV-3 kA YBCO High-Tc Superconducting Power Cable

with the thermal insulated pipe.
The result of the tests for the core of 20 m wasdescribed below. The core had neither break nor ruck on
the insulation after the bend test, the structure examination was satisfied with the dimension of Table 2. The resultof the withstand voltage test was satisfied with thedesigned property. The withstand voltage test was done
immersed nitrogen under the atmospheric pressure being
more severe than the test liquid nitrogen under pressure.
(a)

(b)

6.

6-1

The Installment of the Normal Joint and theTransfer of the Cable
The superconducting cable of 30 m with the normal joint
had been manufactured, and then the terminal for thesuperconducting conductor and superconducting shield
and the stress relief cone were fitted to the end terminal,
and the cable was laid on the pallet shown in Figure 14
and was transported to Shenyang Furukawa Cable located in Shenyang city, Liaoning, of the test yard. The superconducting technology is very interesting in East Asia
where the demand of the energy is increasing tremendously and the test carried out in China would be tobroadcast the Japanese technology to the world and tocontribute to advance the superconducting technology
globally.
With respect to the transportation route, the cable wastransported by road from Chiba to Yokohama, from
Yokohama to Dalian port by sea and from Dalian to
Shenyang by road. The transportation was controlled withan acceleration meter installed on the pallet and the result
was less than 3G, and the shape of the cable appeared
normal after the transportation.

Figure 12 Manufacturing of the HTS cable.
(a) HTS core  (b) HTS core with the thermal insulated pipe

Figure 13 shows the result of Ic measurement. It was
6440 A on the conductor side and 5920 A on the shieldside immersed nitrogen under the atmospheric pressure.
Each result of the Ic was larger than the expected value,
the average of Ic of the superconductor wire times thenumbers of used wires, 5820 A and 5031 A respectively.
The result shows no deterioration of Ic during the manufacturing. With respect to the shield side, the result indicated that the transition from the superconducting to thenormal state occurred slowly and the transition suggested the localized deterioration in the superconductor wirein the longitudinal direction. The suggestion was supported by the Ic measurement result for the superconductor
wire before the cable manufacturing.

A LONG TERM ELECRICAL VOLTAGE
AND CURRENT LOAD TEST AT 275 KV –3KA

Normal joint

Superconducting
cable

Figure 14 Transportation of the HTS cable with the normal joint.

6-2
Generated Voltage [mV]0.5
Conductor : I c =6440 A
Shield : I c =5920 A
Distance between voltage terminal: 1.5 m（1 µV/cm）

0.4
0.3
0.2
0.1
0.0
0

1000

2000

3000 4000
Current [A]

5000

6000

7000

Figure 13 V-I characteristics of the HTS cable sample.

The Demonstration System at Shenyang
Furukawa Cable Co.
After the test yard was ready, the AC transformer for loading the voltage and the XLPE cable with the conductor
area of 2500 mm 2 for carrying current of 3 kA were
installed preliminarily. The superconducting end reservoir
was installed and the transported superconducting cable
was connected to the reservoir.
The cooling system was also installed and flow diagram
for the cooling system was shown in Figure 15. The liquid
nitrogen for cooling the superconducting cable was on
the closed-loop circulation and the nitrogen was cooled
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The Development of 275 kV-3 kA YBCO High-Tc Superconducting Power Cable

through the sub cooler of the heat exchanger having a
cooling ability of more than 3 kW. The liquid nitrogen in
the sub cooler was cooled based on decreasing the saturation vapor pressure through depressurizing by an air
displacement pump. Since the liquid nitrogen in the subcooler was vacuumed out and consumed, the consumed
nitrogen was resupplied from the cold evaporator.
The Ic of the conductor and the shield, including thenormal joint, was measured after the cooling with the liquid nitrogen immersing. The result was 6800 A on the
conductor and 7000 A on the shield and showed no deterioration occurring after the cable transportation and thecable installation for the long term electrical voltage andcurrent load test. Figure 16 shows the layout of installation of the 30 m cable. The superconducting cable wasbent in the shape of a U and three XLPE cables were connected with one end terminal. This means that the superconducting cable can transfer three times the current.
The loaded voltage and term were determined as 200 kV
by converting the line voltage of 300 kV to a voltage toground, and one month taking into consideration theaccelerated deterioration respectively. The long term electrical voltage and current load test started in November,2012 and was completed in December, 2012. The resultof the partial discharge test for the 275 kV superconducting cable after the long term electrical voltage and current
load test was zero at 310 kV of the designed voltage. It
showed that the cable maintained the initial property after
the accelerated deterioration test equivalent to 30 years.
Further the long term electrical voltage and current load
test is planned to continue for one year.

Safety valve

Safety valve

Safety valve

Safetyvalve

Safetyvalve

Figure 15 Flow diagram of cooling system.

AC Transformer

Coolingsystemhouse

NormalJoint

30 m HTS Cable

Figure 16 Layout of demonstration of 275 kV-3kA HTS cable.

Acknowledgement
The study was commissioned by NEDO and we thank
NEDO associated staff and the International
Superconductivity Technology Center – Superconductivity
Research Laboratory (ISTEC-SRL) for proceeding withthe study and their supply of the superconductor wire. We
also thank Amamiya Laboratory of Kyoto University for
their cooperation for the analysis of the AC loss, Ishiyama
Laboratory of Waseda University for their cooperation for
the analysis of the over-current test and Hayakawa laboratory of Nagoya University for their cooperation for thepartial discharge analysis of the insulation part. The
superconductor wire was a film of YBCO formed on thesubstrate. The YBCO was supplied by SWCC Showa
Cable Systems Co.,Ltd and the substrate was supplied
by Fujikura Ltd., and we thank the both companies.
We thank Mr. Sato, General Manager of Viscas
Corporation for cooperating in manufacturing the superconducting cable of high quality. With respect to the testat Shenyang Furukawa, we thank Mr. Uetake, Chief ofheadquarters for sponsoring the test activities. We also
secured a lot of support from Mr. Li, General Manager ofthe quality assurance department and others for the
installation of XLPE cable, the operation of the long termelectrical voltage and current load test and the partial discharge measurement, etc. We would like to express our
sincere appreciation and gratitude for their support.

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The Development of 275 kV-3 kA YBCO High-Tc Superconducting Power Cable

REFERENCES
1) JEC-2300-2010 AC circuit breaker2) Technical report of the Institute of Electrical Engineers ofJapan(Part II) No. 216 Test method for Gas Insulated Switch Gear
3) IEC62067-2006-03 Power cables with extruded insulation and theiraccessories for rated voltages above 150 kV (Um = 170 kV) up to
500 kV (Um – 550 kV)- Test methods and requirements
4) JEC-3408 High voltage test for Extra high voltage (11 kV – 275 kV)
XLPE insulated cable and joint

Furukawa Review, No. 43

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