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When a transformer is energized, inrush currents whose magnitudes may reach tens of its nominal current occur and may affect the power quality of the distribution system. When a large transformer owned by a customer is connected to a distribution system, the impact of possible inrush currents on the distribution system has to be assessed by the distribution system operator (DSO). To carry out detailed electromagnetic transient (EMT) simulations of inrush currents, the current−flux curve of a transformer is required. However, obtaining the current−flux curve of a customer-owned transformer is not an easy task for DSOs, since manufacturers provide current−time data of transformers only and do not provide their current−flux curves. Considering this point, the present paper proposes a method to estimate the current−flux curve of a transformer from its current time data so as to enable detailed EMT simulations for DSOs. As a preliminary study, the proposed method is validated using test results of a single-phase transformer in this paper.

Frequency Response Analysis (FRA) is capable of detecting troubles of transformers, such as deformation of winding, displacement of winding and deformation of iron core, by detecting change of transfer function. However, interpretation of the change with reference to the trouble is not clear. In this paper, an identification method of the troubles are proposed based on investigation using a model transformer. Furthermore, proposed method is applied to a real transformer to identify trouble caused by short-circuit tests. The identification agrees with the result of dismantling investigation.

We have proposed a flat type of the superconducting fault current limiter (FCL) which is a modified version of a magnetic shielding type of the fault current limiter. The flat type FCL basically consists of a pancake coil and doughnut-like form high Tc superconductor (HTS) disk, each of which works as a primary winding and a secondary one-turn winding, respectively. In order to clarify the static current-limiting performance of the flat type FCL, the magnetic field analyses were carried out for the small modules of the FCL. The inductance values of the FCL in the superconducting state and normal-conducting state of the HTS disk, L o and L limit , were calculated and their ratio L limit/L o was estimated. The high performance of the FCL must be brought about by the large inductance ratio. It was confirmed that lower L o was derived by sandwiching the pancake primary winding with two HTS disks and by using thin spacer between them, and larger L limit a is produced by connecting the built-up pancake primary windings in series. This suggests that a full-scale FCL may be designed and produced by building up many modules whose pancake winding is sandwiched with the HTS disks.

To cope with the increase in electric power demand and provide an alternative technology to conventional electric power transmission cables, it is hoped that high-temperature superconducting (HTS) cables would be developed. A protective layer has been adopted in HTS cables as a countermeasure against short-circuit current. This protective layer is established in parallel, and is connected to the HTS cable at both ends of the cable. However, this protective layer is not effective for quenching the local degradation of HTS wire in the overload-current domain, which slightly exceeds the rated current in real cables with lengths of several km. Therefore, of concern is the possibility in which the generation of bubbles via an exothermic reaction affecting the electrical insulation, when local quenching occurs. In a 500-m HTS power cable, we applied an external magnetic field to a part of the HTS cable, and the superconducting cable was locally quenched. Quench propagation features and electrical insulation characteristics based on this enforced quenching were determined experimentally.

The 500 m high temperature superconducting (HTS) cable developed by the Super-ACE (R&D of fundamental technologies for superconducting ac power equipment) project included copper layers as protection against short circuit current. The design policy was that liquid nitrogen would not vaporize when it was exposed to the short circuit current of 31.5 kA with 0.5 s. In order to establish the design policy, we have made nine 10 m samples with the same construction of the 500 m HTS cable and set three cables in the liquid nitrogen vessel. Both of balanced fault of three-line grounding (3LG) and unbalanced faults of one line grounding (1LG) and two-line grounding (2LG) have been set and fault currents have been applied to the HTS cables. After each fault, the critical current has been measured and we have confirmed no variation of Ic before and after each fault. HTS cables have not been damaged mechanically by the fault current of 31.5 kA with 0.5 s.

We have proposed an inductive (magnetic shielding) type of superconducting fault current limiter which consists of a high Tc superconducting plate in doughnut shape and spiral coil as the primary winding. In this paper, the current density distribution in the superconducting plate was theoretically investigated to understand the fundamental performance of this type of current limiter. For the analysis, we developed the calculation method for the current density. The current density is distributed almost uniformly in the superconducting plate. The impedance of the current limiter changes every moment not only in current limiting operation but also normal operation. That is because the resistance in the superconducting plate and magnetic coupling condition in the current limiter also change with time. Relatively large impedance rapidly appears in the current limiter when the current density in all the area of the superconducting plate attain to the critical current density.

In order to cope with the increase in the electric power demand and an alternative technology to the conventional electric power transmission cables, it's hoped that high temperature superconducting (HTS) cable is developed. In case the HTS cable is introduced into the actual power grid, its length can extend up to several kilometers. The flow properties of liquid nitrogen (LN2) that is a coolant of the HTS cable have not been understood yet. Thus, CRIEPI, Furukawa Electric and Super-GM had constructed an HTS cable test system with its length of 500 m. The rated voltage is 77 kV corresponding to one of the major voltage level of medium-voltage transmission lines. The rated current is 1 kA. We had carried out a numerous set of tests such as measurement of LN2 flow properties, current flow properties, electrical insulation properties, thermal insulation properties and so forth. In addition, short-circuit test was carried out using 10 m HTS cables that is same structure as the 500 m HTS power cable. The test was conducted with the supply voltage of 16 kV and the prospective short-circuit current of 31.5 kA using a short-circuit generator.

Electrical insulation is one of the essential technologies for the electric power apparatus. Determination of testing voltages and design method of the electrical insulation layer are inextricably linked each other, and are critical to developing and realizing a cold dielectric (CD) type high-Tc superconducting (HTS) power cable. The authors had proposed the electrical insulation design method with concepts of partial discharge-free designs for ac voltage condition. This paper discusses the testing voltages for a 77 kV 1000 A HTS power cable with a length of 500 m, and describes results of various voltage withstand test. As a result, it is concluded that the proposed electrical insulation design method is appropriate for the HTS power cable.

A high- T c superconducting cable (HTS cable) can transmit more power with lower loss than conventional cables. HTS cable is expected to be a compact and economical transmission line to meet the increasing electrical demands of cities. However, some technical problems must be solved to bring the HTS cable into practical use. Demonstration and verification tests of the world’s longest (500 m) HTS cable have been carried out as part of the Super-ACE project. The 500 m cable was a single-core, cold-dielectric type with a small enough diameter to be installed inside a 150 mm cable duct. We have already successfully completed the production and installation required for the field tests at the Yokosuka laboratory of CRIEPI. The test layout included a 10 m high section, an underground section and an offset section for absorbing the thermal contraction, so as to simulate real transmission lines. Over the course of a year, CRIEPI and Furukawa Electric have conducted numerous experiments on the thermo-mechanical behavior and operating characteristics of the cooling system and the electrical and superconducting properties of the cable, both at its rated load and with a fluctuating load and an overload.

A high-temperature superconducting (HTS) power transmission cable is considered as one of the next-generation power transmission technologies. The introduction of HTS cables into the actual power grid requires a long-distance cooling tube, due to the location of the cooling stations at intervals of several kilometers along the cable length. Therefore, it is essential to understand the flow property of the liquid nitrogen as a coolant for the HTS cable, the current flow properties, electrical insulation characteristics, thermal insulation properties and mechanical behavior for the HTS cable taking into account its long length. This paper provides a brief summary of the HTS cable test system with a length of 500 m constructed in the Yokosuka area of CRIEPI.

A 500-m single-core high temperature superconducting (HTS) cable system has been constructed and tested in Yokosuka area, CRIEPI, by CRIEPI, The Furukawa Electric and Super-GM. In the actual power grid, the HTS cable distance extends sometimes several km. And has to be cooled down from about room temperature to liquid nitrogen temperature. As, the HTS cable is contracted and suffers mechanical stress. In the case of the long distance HTS cable, it remains a major development issue. The HTS cable constructed in this test system has an offset section for absorbing the thermal contraction. In this paper, we describe the validity of that offset section and the thermomechanical characteristics on the cooldown and warm-up test. The offset functioned successfully as designed.

We have proposed a flat type of the superconducting fault current limiter (FCL) which is a modified version of a magnetic shielding type of the fault current limiter. The new FCL basically consists of a doughnut-like form high Tc superconductor (HTS) plate and spiral coil, each of which works as a secondary one-turn winding and a primary winding, respectively. The FCL modules can be easily built up to make a large scale FCL. This simple construction may enable us to reduce the manufacturing costs. We made two small modules of the flat type FCL with Bi2223 bulk plate and YBCO thin film plate and investigated the generation of the limiting impedance due to an excess current. Higher ratio of the limiting impedance to normal one was produced by the YBCO thin film plate than by the Bi2223 bulk plate.

We have been developing an inductive type superconducting fault current limiter with a superconducting cylinder. For practical use, a high critical current density (Jc) is needed in a large diameter. To achieve these items, we have developed a Bi-2223 thick film on a MgO substrate, with a Bi-2212 buffer layer. This cylinder was 450 mm in diameter and 120 mm in length. We describe the superconductive characteristics of this cylinder, and the limiting properties of the fault current limiter using these cylinders.

Superconducting fault current limiter (SCFCL) is expected to be a first application of high-TC superconductors to electric power systems. We have been developing a magnetic shielding type of SCFCL. In this paper, we propose a design method for the magnetic shield SCFCL. The method is based on a newly developed computer program which can evaluate the dynamic thermal and electromagnetic behaviors of high-TC superconducting cylinder in fault current limiter operation. As an example, the trial design of a model system, which is 6.6 kV (rms) in rated voltage, 400 A(rms) in rated current, and 12.5 kA(rms) in maximum prospective short-circuit current, is shown. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(2): 50–57, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10197

Fault current limiters for electric power systems have been researched. We have studied a inductive type superconducting fault current limiter. The limiter has superconducting cylinder as active element. We developed a high Jc Bi-2223 thick film on a MgO cylinder. Jc was over 5800 A/cm/sup 2/ at 77 K. We made a inductive type superconducting fault current limiter with the Bi-2223 thick film cylinder and investigated limiting performances.

Fault current limiters for electric power systems have been researched. We have been studying on a inductive type superconducting fault current limiter. The limiter has superconducting cylinder as active element. It is necessary for practical use of the superconducting fault current limiter that superconductor has high critical current density (Jc). So as to get high Jc, we tried Bi-2223 as a material for the superconductor, and prepared Bi-2223 thick film. Raw paste of Bi system was coated on a polycrystalline MgO substrate and then was sintered in the air with intermediate pressing by a cold-isostatic-pressing (CIP) technique. The sintered Bi-2223 thick film had good crystal orientation. The Jc of the 500 /spl mu/m thick film was over 6000 A/cm/sup 2/ at 77 K.

Superconducting fault current limiters have been researched to protect electric power systems. We have developed a superconducting fault current limiter. As the active element, we choose Bi-2212 thick film for the superconductor cylinder. In order to attain practical use of the superconducting fault current limiter, larger scale superconducting cylinders must be developed. Processing energy increases as the size of the limiter is increased. If there are local defects in the superconducting cylinder and the processing energy is concentrated on them, there is a possibility that the cylinder will be damaged. We therefore investigated the thermal runaway propagation of the Bi-2212 thick film from a local heat point and how local defects affect the current-carrying capacity. The result is that the velocity of the thermal runaway propagation in the thick film from the local heat point is very slow. Thermal runaway doesn't propagate within a few milliseconds. If there are local defects such as cracks in the superconducting cylinder, the current will concentrate at the tip of the defect and the Joule temperature rises. The cracks then grow as the result of thermal stress. When a crack runs from end to end on the cylinder, superconductor on the cylinder melts due to arc discharge.

Superconducting fault current limiter (SCFCL) is expected to be the first application of a high-temperature superconductor (HTS) to electric power systems. The authors have been developing a magnetic shielding type of SCFCL that uses a cylindrical Bi-2223 HTS bulk. Short-circuit fault tests in a small SCFCL model were performed experimentally. A computer program based on the finite element method (FEM) taking the voltage-current (E-J) characteristics of the bulk material into account was developed to analyze the performance in the short-circuit fault tests and to investigate the dynamic electromagnetic behavior within a bulk superconductor. Because the E-J characteristic of HTS bulk depends on temperature and magnetic field, they investigated experimentally the E-J characteristics of a bulk superconductor in various operating temperatures and magnetic fields. The computer program considering the measured E-J characteristics simulated the electromagnetic behaviors in an SCFCL test model successfully (BiPb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/.

The superconducting fault current limiter is expected to be the first application of high-TC superconductors to electric power systems. To analyze the performance of the magnetic shielding-type superconducting fault current limiter, the dependence of the voltage-current (E-J) characteristics of high-TC superconducting bulk on temperature and magnetic field have been measured. Short-circuit fault tests with a small limiter model have been carried out. A computer program based on the finite element method was used for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The computer program, considering the voltage-current (E-J) characteristic, successfully simulated the electromagnetic behavior in the fault current limiter test.

The superconducting fault current limiter (SCFCL) is expected to be the first application of high-T/sub C/ superconductors (HTSs) in power systems. To develop a magnetic shielding type superconducting fault current limiter, we have carried out some fundamental experiments concerning the magnetic shielding characteristics of an HTS bulk cylinder. In this paper, the experimental results of magnetic flux penetration into a Bi(2223) cylinder are shown. AC magnetic field is applied to the sample by a primary winding (copper coil) excited by AC triangular- and sinusoidal-waveform currents in the frequency range of 0.1 Hz to 100 Hz. We also developed a finite element method (FEM) computer program for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The results of computer simulations considering the voltage-current (E-J) characteristic are compared with experiments.

The superconducting fault current limiter is expected to be the first application of high-Tc superconductors (HTSs) in power systems. To develop a magnetic shielding-type superconductor fault current limiter, we have carried out some fundamental experiments on the magnetic shielding characteristics of an HTS bulk cylinder. In this paper, the experimental results of magnetic flux penetration into Bi-2223 cylinders are shown. An ac magnetic field is applied to the sample by a primary winding (copper coil) excited by ac triangular- and sinusoidal-waveform currents in the frequency range from 0.1 Hz to 100 Hz. We also developed a finite element method computer program for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The results of computer simulations considering the voltage–current (E–J) characteristic are compared with experiments. Next we carried out a current-limiting test with a small limiter model, and the developed finite element method computer program successfully simulated the electromagnetic behavior in current-limiting operation. © 2000 Scripta Technica, Electr Eng Jpn, 134(1): 17–27, 2001

${\mathrm{Ca}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Li}}_{\mathit{x}}$${\mathrm{CuO}}_{2}$ thin films were grown on ${\mathrm{SrTiO}}_{3}$ (100) substrates by a pulsed-laser-ablation technique. The deposited films were single phase of the infinite-layer structure for 0.15\ensuremath{\le}x\ensuremath{\le}0.45. The lattice parameter a decreased with increasing x, indicating p-type carrier doping into the ${\mathrm{CuO}}_{2}$ plane. In the x-ray-diffraction patterns for these samples, the peak width was quite narrow and Laue functional oscillations were seen around the 001 peak. The peak intensity ratios between 001 and 002 reflections strongly suggested that Li ions were substituted into the Ca ion site of the infinite-layer lattice. Moreover, we observed a lattice image by TEM and determined the composition of a small region by energy dispersive x-ray analysis and true site occupancy by x-ray structural analysis using a four-circle goniometer. The films were found to be almost single crystals without oxygen deficiency.

Single‐phase Sr0.875Nd0.125CuO2−δ (SNCO) thin films of the ‘‘infinite‐layer’’ structure were fabricated by a pulsed‐laser deposition technique. The films directly grown on SrTiO3 (100) substrates had superconductivity onset temperatures around 20 K, but zero resistances were not observed down to 4.2 K. The a‐axis length of the film samples did not exceed the values reported for bulk SNCO samples. It was demonstrated that, when deposited onto a Pr2CuO4 buffer layer formed on a SrTiO3 substrate, the a‐axis length of the thin film SNCO increased up to 0.395 nm which was comparable to that for bulk SNCO. The film sample exhibited a zero resistance state below 7 K. Thermoelectric‐power measurements indicated that the carrier density for the film deposited on a Pr2CuO4 buffer layer was higher than that for the film fabricated without a buffer layer.

The microstructure of Sr1−xCuO2−δ thin films with x=0.00 and 0.10 was investigated by X-ray diffraction and transmission electron microscopy. Both films were single phase of the “infinite-layer” structure. However, in both films certain defects were observed, being extended along the ac-plane. The defect was found to be intergrown Sr2CuO3 crystallites between the infinite-layer structure Sr1−xCuO2−δ crystals. It was suspected that one of the reasons why superconductivity was not observed in these films was that Sr-deficient ab-planes were not observed in these film samples.

The p-type carrier doping in infinite-layer structural CaCuO2 thin films was successfully done by substituting Li ions into the Ca site using a laser deposition technique. The lattice constants and X-ray diffraction patterns strongly indicated that the film samples had an infinite layer structure. However, they did not exhibit superconductivity.

Sr/sub 1-x/Nd/sub x/CuO/sub y/ thin films were grown by both RF magnetron sputtering and laser ablation on SrTiO/sub 3/

Sr 1- x Nd x CuO y thin films are grown by a RF-magnetron sputtering technique. The film with x =0 has an “infinite-layer ” structure whose lattice constants are: a =0.390 nm and c =0.347 nm . The resistivity of this film shows a semiconductive behavior. The infinite-layer structure does not form when x exceeds 0.05. For compositions with x less than 0.08, the films contain a multiple number of phases. When x is larger than 0.1, the films have a phase of the Sr 14 Cu 24 O 41 structure. The b -axis of the (Sr, Nd) 14 Cu 24 O 41 crystalline is perpendicular to the substrate surface and the a - and c -axes are aligned in plane with the crystal axes parallel to those of the (1 0 0) SrTiO 3 substrate.

A perovskite related structure was found in the sample of nominal composition of Ba0.5Sr0.5CuOz which was synthesized at a high pressure of 6GPa, when carbonates were used for the starting materials. The space group for the new structure was found to be Pmmm by means of a transmission electron microscopic observation. The lattice parameters were; a=3.92 A, b=3.94 A and c=7.93 A. The cation ordering between Ba and Sr caused to the double stack of the perovskite blocks.

Frequency response analysis (FRA) is a diagnosis method to detect troubles of a transformer, which are deformation and displacement of winging and so, by detecting change of a transfer function compared with that measured when the transformer is normal. However, identification of the troubles detected by FRA is not clear. In this paper, firstly, identification method of the troubles is investigated using a model transformer. Secondly, the proposed identification method is applied to identify a trouble of a real transformer caused by short-circuit tests.

A high-Tc superconducting (HTS) power cable is considered to be a major candidate for the bulk power transmission device in the future. The HTS power cable with a cold dielectric type electrical insulation system can make the outer diameter of the HTS cable compact in order to replace the conventional XLPE cable laid in underground ducts. Therefore, establishment of the electrical insulation design, HV testing and evaluation methods is the most important in the realization of the HTS power cable. From these viewpoints, the electrical insulation design method and determination of testing voltages for a 500-m HTS power cable constructed for verification tests are discussed, and the result of the various tests are described in this paper.

A high-Tc superconducting (HTS) power cable is one of the major candidates for reinforcing power transmission grids dynamically. For operation of the HTS cable, a quench phenomenon would occur due to over-current operation, degradation of the HTS materials, and so forth. In that case, local heating would occur and local evaporation of liquid nitrogen would occur, which may lead reduction of the electrical insulation capability and generate partial discharge (PD) under operational voltage application. This paper deals PD inception characteristics with local heating simulating local quench of HTS material. As a result, it is revealed that there is a time delay from the start of heating to PD generation, and the delay depends on the pressure of liquid nitrogen.

Fault current limiters (FCLs) are expected to reduce fault current and improve stability of power systems. A flat type fault current limiter consisting of the pancake primary winding and a high-Tc superconducting (HTS) disk was proposed as a modified version of a conventional magnetic shield type of the FCL with the superconducting cylinder. The flat type FCL has the advantage of being manufactured smaller than the cylinder type FCL. It is pointed out, from a magnetic field analysis, that the volume of the flat type FCL is smaller than that of the cylinder type FCL with same magnitude of the limiting inductance. Further, the magnetic field analysis suggests that a high inductance ratio can be realized by radially enlarging both the primary winding and the HTS disk, stacking the FCL modules in layers and sandwiching the primary winding with superconducting disks. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

The power application of a superconductor to restrain a fault current has been researched. A superconducting fault current limiter using a Bi-Sr-Ca-Cu-O cylinder has been developed. This limiter consists of the primary winding for generating an AC magnetic field and superconducting cylinder for shielding the field. When fault occurs, the superconducting cylinder quenches and a magnetic circuit is formed inside the cylinder. In the result of that, the limiter has a high impedance thus the fault current is limited. Experiments were carried out in three conditions which are without an iron core, with an iron core, and with an iron core and a copper cylinder as a secondary winding. In each condition, the impedance of the limiter under fault conditions was 1.4 times, 10 times, and 5.9 times as high as the one under normal conditions.

Sr1−x Nd x CuO y (SNCO) thin films were deposited by a pulsed-laser deposition technique. The quality of the samples were seriously dependent on the quality of the substrate surface. Films containing single “infinite-layer” phase of Sr0.875Nd0.125CuO y were grown on SrTiO3 (100) substrates. The films had onset temperatures of superconducting transition around 20 K. The a-axis length of the SNCO film directly deposited on SrTiO3 did not exceed the largest value ever reported for bulk SNCO samples. It was demonstrated that when deposited on Pr2CuO4 buffer layer fabricated on a SrTiO3 substrate, the a-axis length of SNCO thin film increased up to 0.394 nm which was comparable to that for the bulk material.

Sr1−xCuO2±δ thin films were grown on SrTiO3(001) by sequential deposition of Sr metal and Cu oxide. SrCuO2±δ of the “infinite-layer” structure containing two-dimensional CuO2 sheets was confirmed by in-situ reflection high energy electron diffractmetry (RHEED) and x-ray diffractmetry (XRD). All the samples behaved semiconductive, but electrical resistivity decreased as the amount of defects of Sr, i.e. x, increased. Thus a charge-carrier doping was made for Sr1−xCuO2±δ thin films with x>0.

Hole doping with infinite-layer structural M1−xCuO2 (M;alkaline earth metal) was successfully performed by introducing alkali ions into the M site using a laser deposition technique. The lattice constants and X-ray diffraction patterns were consistent with those for the infinite-layer structural Ca0.91Sr0.09CuO2 which was fabricated at normal pressure. The thermoelectric power for this sample was positive, which indicated hole doping. However, no indication of superconductivity was obtained.

Sr1−xNdxCuOy thin films are grown on SrTiO3 substrates by rf-magnetron sputtering and pulsed-laser deposition. The sputter-deposited film with x=0 has an “infinite-layer” structure whose lattice constants are: α=0.390 nm and c=0.347 nm. When x is larger than 0.1, the films contain a phase of the Sr14CuO24O41 structure. The laser-deposited films of Sr1−xNdxCuOy with x≤.075 were single phase of the “infinite-layer” structure. The lattice parameter c decreased and the lattice parameter αincreased, as the Nd content, x, increased. The films with α=0.10 and 0.125 exhibited superconducting onset temperatures around 26 K. Weak Meissner signals were observed for these films at temperatures below 30 K.

Sr1-x Nd x CuO y thin films were grown on SrTiO3 substrates by a pulsed-laser deposition technique. The laser-deposited films of Sr1-x Nd x CuO y with x≦0.075 were single phase of the “infinite-layer” structure. The lattice parameter c decreased and the lattice parameter a increased, as the Nd content, x, increased. The largest value for the a-axis length did not exceed that reported for superconducting bulk samples. The expansion of the a-axis as x increased was apparently hindered by lattice dimensional mismatch between film and substrate. The films with x=0.10 and 0.125 had onset temperatures of superconducting transition around 26 K. Weak Meissner signals were observed at temperatures below 30 K.

In recent years, interest in the application of superconductivity to the electric power apparatuses has grown rapidly. In ac power apparatuses, loss induced by alternating current is a impeding problem which has to be reduced. A superconducting power cable is one of the promising ways for transmitting huge electric power efficiently in the future. We have proposed the new ac superconducting cable design with a similar electrical insulation structure to the conventional extruded cross-linked polyethylene cable (CV cable). The feature of this cable is to exploit the excellent electrical insulation capability of polymers at cryogenic temperature by separating helium coolant from the electrical insulation. The conductor of the superconducting cable consists of niobium clad over a copper flat wire and niobium tape, which are wound helically in the opposite direction each other on a copper pipe. In order to clarify the ac loss mechanism in this cable design, measurements and analysis of the ac loss of the superconductor have been carried out at the liquid helium temperature.