Application study of a high‐temperature superconducting fault current limiter for electric power system

Using high‐temperature superconductors, a superconducting fault current limiter (SFCL) was fabricated and tested. The superconductor and a vacuum interrupter serving as a commutation switch were connected in parallel with a bypass coil. When a fault occurs and excessive current flows, the superconductor is first quenched and the current is transferred to the bypass coil because of the voltage drop of the superconductor. At the same time, since a magnetic field is generated by the current flowing in the bypass coil, the commutation switch is immediately driven by an electromagnetic repulsion plate connected to the driving rod of the vacuum interrupter (VI), and the superconductor is separated from this circuit. Using the test model, we were able to separate the superconductor from the circuit by the movement of the VI within a half current cycle and to transfer all current to the bypass coil. Since the operation of the commutation switch is included in the current limiting operation of this test model, it will be a useful circuit in the development of SFCL in the future. Moreover, since it can make the energy consumption of the superconductor small during the fault state due to the realization of a high‐speed switch with simple composition, the burden on the superconductor is reduced compared with the conventional resistive type of SFCL and it is considered that the flexibility of SFCL design is increased. Cooperation with a circuit breaker was also considered; trial calculations of the parameters and energy of operation were conducted and a discussion of the installation of the SFCL in an electric power system is presented. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 20–29, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20265     

Development of NbTi superconducting strands and cables for the field winding of a 200‐MW‐class high‐energy‐density superconducting generator

The NbTi superconducting strands and cables for the field winding of the 200‐MW‐class high‐energy‐density‐type superconducting generator are developed. They are composed of Cu/Cu‐10wt%Ni/Nb‐46.5wt%Ti superconducting strands and the 10‐kA (at 5 T)‐class 9‐strand compacted cables. The diameter of strands is 1.33 mm, and the 9‐strand compacted cables are 2.4 mm thick and 6.0 mm wide. In order to produce high‐current‐density NbTi strands, we made strands under controlled aging heat treatments, the total and final strains, and the strains between heat treatments, by using large‐scale extruder. Moreover, in order to produce high‐stability and low‐AC‐loss NbTi strands and cables, the matrix ratio of strands and the cross sections of strands are optimized. The current density of NbTi filaments for the four‐time‐aging manufactured 1.33‐mm‐diameter strands was J_C=3150 A/mm² at 5 T, 1150 A/mm² at 8 T. The critical current of the 9‐strand compacted cable is 10.7 kA at 5 T. The AC losses of the final compacted cables are less than 100 kW/m³ at 5 T, 5 T/s, that is, decreased to less than half of the target of the AC loss value (< at 5 T, 5 T/s). Compared with the strand (Cu ratio 1.77), the minimum quench energy (MQE) of the strand (Cu ratio>2) increased about 40% at the operation mode current of the superconducting generator. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(3): 24– 31, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20266     

Design study of a high‐temperature superconducting transformer

Many research and development projects on high‐temperature superconducting apparatus such as a transformer, fault current limiter, and cable are being actively pursued in the power field as a result of performance improvement of Bi silver sheath high‐temperature superconducting (HTS) wire. HTS transformers are considered to be among the most promising applications in view of efficiency improvement, the interface with cryogenic cable and normal temperature devices, incombustibility, overload capability, the function as a reactor, and the possibility of use as a fault current limiter. The necessary technical development items of an HTS transformer in order to achieve performance superior to conventional devices are examined. For this purpose, three‐phase 66‐kV 100‐MVA transformers were designed for the comparison of an HTS transformer and a conventional one with oil cooling. The desirable development items are an HTS wire current density of about 40 A/mm², an allowable winding strain of about 0.5%, a percent impedance of 7.5%, an air gap flux density of about 0.3 T, and AC losses of about 0.3 W/km‐A. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(1): 25–31, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10087     

Quantitative evaluation of perpendicular‐field losses in stacked high‐Tc superconducting tapes

The influence of stacks of Bi‐2223 multifilamentary tape‐shaped wires without twisting on AC losses observed in an external magnetic field perpendicular to their wide faces is investigated. The perpendicular‐field losses decrease with increasing number of tapes in the range of small field amplitudes. At larger amplitudes, on the other hand, the AC losses have little dependence on the stack number. This can be attributed to the effect of magnetic interaction between wires. By taking into account effective demagnetization factors on the basis of theoretical consideration, the perpendicular‐field losses are plotted on a master curve for the maximum magnetic field applied to the wires. Furthermore, the perpendicular‐field losses measured as a function of the field amplitude are well reproduced by the numerical evaluation of AC losses for a slab with infinitely wide surfaces. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 50–57, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10050     

Verification tests and insulation design method of cold dielectric superconducting cable

A High‐Temperature Superconducting (HTS) cable has a bulk power transmission capacity as a candidate for the replacement of aged cables and/or for the increase of the power transmission capacity, and its diameter is preferred to be smaller than the inner diameter of the duct for the existing cables. To reduce the diameter of HTS cable, the cold dielectric (CD)‐type electrical insulation in which a cable core is immersed into liquid nitrogen (LN₂) should be adopted, and the thickness of its electrical insulation layer has to be optimized. Since a partial discharge (PD) in the electrical insulation layer of the CD‐type HTS cable is considered as a major cause for the aging of the insulation layer, PD‐free design must be adopted for the CD‐type HTS cable. This paper describes a design method for the electrical insulation layer of the CD‐type HTS cable adopting the PD‐free design under AC stress, based on the experimental results such as a PD inception stress (PDIE), an impulse breakdown stress, and PD extinction characteristics under AC stress superimposed with an impulse stress. Moreover, the proposed design method was applied to a 500‐m HTS cable and was verified by a field test. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(2): 25–36, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20512     

Proposal of flux‐lock‐type fault current limiter with high‐TC superconducting element

This paper proposes a new type of fault current limiter (FCL), which consists of a high‐T_C superconducting (HTS) element and two coils wound on the same core without any leakage magnetic flux. In this FCL, either the limiting impedance or the initial limiting current level can be controlled by adjusting the inductances and the winding direction of the coils. Therefore, this FCL could relax the material restrictions on high‐T_C superconducting FCL. A current‐limiting experiment by a model FCL was carried out, and the limiting performance was observed. The initial limiting current level of the model FCL was 1.7 times higher than the critical current of the HTS element, and the fault current is suppressed to 52% immediately after the short‐circuit in the test. Considering voltage–current characteristics of a high‐T_C superconductor in a computer simulation, the calculated results almost agreed with the experimental results. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 31–38, 1999     

Recovery time to superconducting state after quench in superconducting fault‐current limiter

Since fault current tends to increase with electrical power demand, current‐limiting technology for overcurrents has been investigated. As a promising candidate, the superconducting fault‐current limiter (SC‐FCL) is expected to be introduced into power systems. One of the most important features of the SC‐FCL is recovery to a normal operating mode, that is, superconducting state rapidly after current interruption. In this paper, the recovery time of an SC‐FCL introduced into a distribution power system is discussed. To obtain the fundamental data, the recovery time of short Nb‐Ti superconducting cables was measured. We developed a method of calculation of the recovery time and it was confirmed that the calculated results agree with the measured ones. We studied the recovery characteristics of an SC‐FCL in a 6.6‐kV distribution system for the short‐circuit fault near the substation. We considered 3 and 17 cycles as the period from fault occurrence until current interruption. As a result, the superconducting cable length required to recover within the high‐speed reclosing time of 0.3 s are more that 270 and 480 m for 3 and 17 cycles, respectively. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 34–44, 2000     

Development of a 70‐MW‐class quick response excitation superconducting generator

A superconducting generator is expected to be a next‐generation machine due to its many advantages over a conventional generator. Super‐GM has been promoting R&D of 70‐MW‐class superconducting model generators to verify the basic technologies required for the design and manufacture of a 200‐MW‐class superconducting pilot generator. Verification tests of the third model generator, quick response excitation type C generator, were finished in June 1999. The excellent characteristics as a superconducting generator were verified through the series of tests. We report main test results such as “open and short‐circuit test,” “loaded test,” “quick excitation test,” “negative‐phase sequence overcurrent test,” and “sudden short circuit test.” © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(1): 22–29, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10029     

Development of Y‐branch joint for 275‐kV XLPE and fluid‐filled cable

When a new UHV substation is built in an urban region, generally, an existing underground transmission line will be diverted and drawn into the new substation. Compared with the latter construction method, enormous cost reduction of switching facilities and cable construction is expected when applying a Y‐branch joint (YJ) which is able to serve as a three‐way joint. The YJ has already been applied for 154‐kV‐class circuit, but it has not been investigated for 275‐kV‐class circuit. Since both XLPE and oil‐filled cable are presently used in 275‐kV‐class underground cable line, a universal design YJ for both cables has been investigated. The YJ was applied in a compact design which was based on our sophisticated electrical stress control technology for 500‐kV prefabricated‐type joint. Furthermore, the design was based on its prefabricated assembling technology. The YJ was verified as to its electrical and mechanical performance as 275‐kV cable joint by completion of its assembling test and a long‐term electrical test. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(2): 18–24, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20514     

Operation of superconducting fault current limiter using vacuum interrupter driven by electromagnetic repulsion force for commutating switch

Using conventional high‐temperature superconducting wire, a model superconducting fault current limiter (SFCL) is made and tested. Solenoid coil using Bi2223 silver sheath wire is so made that inductance is as small as possible and a vacuum interrupter is connected in series to it. A conventional reactor coil is connected in parallel. When the fault current flows in this equipment, superconducting wire is quenched and current is transferred into the parallel coil because of voltage drop of superconducting wire. This large current in parallel coil actuates magnetic repulsion mechanism of vacuum interrupter. Due to opening of vacuum interrupter, the current in superconducting wire is broken. By using this equipment, current flow time in superconducting wire can be easily minimized. On the other hand, the fault current is also easily limited by large reactance of parallel coil. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 52–61, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20315     

Performance evaluation of 6000‐A‐class superconducting field windings for 600‐MW‐class superconducting generators

Superconducting generators have many advantages such as increasing generator efficiency and improving power system stability. In Japan, a national project has been conducted since 2000 which is aimed at the development of fundamental technologies required for high‐output‐density and large‐capacity superconducting generators. This paper describes the results of this project, focusing on 6000‐A‐class field winding development. Copyright © 2004 Wiley Periodicals, Inc. A superconducting generator with a high output density and a large capacity has inherent factors that decrease superconducting stability. These are: (1) increase in the magnetic field in the winding which is caused by the increase in winding current density and (2) difficulty in fabricating windings which increases as a conductor diameter becomes larger. To secure the stability, we adopted a higher‐copper‐content conductor and a design that increases winding fixing pressure, along with devising a winding method that accommodates larger conductor diameter. These improvements were applied to a partial model of a 600‐MW field winding. Test results of the model showed good stability, indicating that design and fabrication technique for a 6000‐A‐class superconducting field winding has been successfully evaluated. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(2): 7– 18, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20332     

冷绝高温超导电缆绝缘层设计研究

通过对冷绝缘高温超导电缆绝缘层的设计、评测及研制工艺过程分析,总结了绝缘失效的原因及研制工艺的缺陷,提出绝缘层研制工艺优化改进的措施及操作方法,可为冷绝缘高温超导电缆的研究提供一定的参考。     

Computation of heat loads in cryogenic parts of high‐temperature superconductor synchronous machines

High‐temperature superconductor (HTS) synchronous machines are expected to have higher efficiency and smaller size than normal conductor synchronous machines, and are being developed mainly in the USA and Germany. This paper describes a computation method of heat loads in cryogenic parts of HTS synchronous machines, and the evaluation study results of heat loads in HTS synchronous motors for blowers, in which Bi‐2223 is used at 30 K, using the computation method. From the evaluated heat loads, the required capacity of the refrigerator for HTS synchronous machines may be determined. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(2): 62–68, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20338     

超导技术的发展及其应用

本文回顾了从 1 91 1年发现超导现象以来超导技术的发展历史和现状 ,包括超导材料、超导线、超导电缆和超导电气设备。对超导电缆和超导变压器作了重点介绍。文章最后提出了今后超导技术的应用前景     

高温超导电缆的研发现状和发展趋势

与常规电缆相比,高温超导电缆具有体积小、重量轻、容量大、电流密度高、损耗低、环境友好等优势,为未来电网提供了一种新的电力传输方式。随着高温超导线材取得的重要研究进展,国际上相继开展了高温超导电缆的研发,已有多条超导电缆工程成功地进行了挂网示范运行。本文介绍高温超导电缆的研发进展情况,并简单对高温超导电缆的发展趋势和关键技术做出展望。     

Thermal degradation characteristics of oil‐filled cable joint with extremely degraded tan δ oil

Much of oil‐filled (OF) cable has been used for a long time as 66‐ to 500‐kV extrahigh‐voltage cable. Sometimes we can see extremely degraded tan δ oil (several tens of percent of tan δ, for example) in joint boxes, etc. The values of tan δ calculated by a simple combination model of paper/oil show that the oil‐impregnated paper with such a high tan δ oil likewise has an extremely high tan δ, which must result in thermal breakdown. However, such an event has not taken place up to the present in actually operated transmission lines. This fact suggests that some mechanism for the suppression of tan δ has acted in the paper insulation impregnated with degraded tan δ oil. Therefore, we investigated in detail the tan δ characteristics of paper impregnated with extremely high tan δ oil. In addition, based on the investigation results, we developed a method for simulation of heat generation by dielectric loss in an OF cable joint (which has degraded tan δ oil). © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(1): 1–10, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21184     

An over‐current withstanding design of superconducting power cables

In a design of HTS power cables, the over‐current withstanding design is very important. In a conventional case, when one of the 2‐circuit power cables failed, the other cable should transport the previous total power continuously. If we adopt this idea also in case of superconducting power cables, the rating current should be decided carefully. In this paper, the authors show a fundamental idea for a short‐time withstanding over‐current design of HTS power cables. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 34–40, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10051     

Study of Superconductor Recovery Time Characteristics and High‐Speed Reclosing of Electromagnetic Repulsion Switch

Using a high‐temperature superconductor, we constructed and tested a model superconducting fault current limiter (SFCL). The superconductor and a vacuum interrupter serving as the commutation switch were connected in parallel using a bypass coil. When the fault current flows in this equipment, the superconductor is quenched and the current is then transferred to the parallel coil due to the voltage drop in the superconductor. This large current in the parallel coil actuates the magnetic repulsion mechanism of the vacuum interrupter and the current in the superconductor is interrupted. Using this equipment, the current flow time in the superconductor can easily be minimized. On the other hand, the fault current is also easily limited by the large reactance of the parallel coil. This system has many advantages. Thus, we introduced an electromagnetic repulsion switch. High‐speed reclosing after interrupting the fault current in the electrical power system is essential. Thus, the SFCL should recover to the superconducting state before high‐speed reclosing. But the superconductor generates heat at the time of quenching, and it takes time to recover to the superconducting state. Therefore, the recovery time is an issue. In this paper, we study the superconductor recovery time. We also propose an electromagnetic repulsion switch with a reclosing system. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(3): 12–19, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21072     

中压电缆终端高频电热老化试验装置的研制及分析

中压电缆终端被广泛应用于柔性交流输电和作为逆变器和电机的连接中,这些电缆终端可能会遭受到高频谐波电压的冲击,从而导致其绝缘迅速失效.本文研制了模拟电网高频谐波电压和工频大电流的电热老化试验装置.首先,通过信号发生器和功率放大器产生低压大电流信号,再通过高频变压器升压获得高频高压;同时通过工频试验变压器产生工频高压,将工...     

Magnetic field analysis of a 70‐MW‐class superconducting generator by the 3D finite element method

The three‐dimensional magnetic field and eddy current distribution of the 70‐MW‐class superconducting generator was calculated by a finite element method. The condition for the exciting armature coil was calculated by the jω‐method. In the magnetic flux distribution of the armature winding bore, the value obtained by analysis had good agreement with the measurement. An analysis that let the rotor move by the synchronizing speed was also done. The armature voltage for the nonload condition and the armature current for the three‐phase short‐circuit condition obtained by calculations had good agreement with the measurements. The validity of the analytical model for three‐dimensional magnetic field analysis of superconducting generators was confirmed from these results. In addition, the synchronous reactances were calculated using these results with eddy current in the facing. It was found that the facing had the effect of decreasing synchronous reactance by about 5%. © 2000 Scripta Technica, Electr Eng Jpn, 134(2): 53–60, 2001