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     

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     

Study of shunt type SFCL equipped with electromagnetic repulsion switch for large capacity

Using a high‐temperature superconductor, we constructed and tested a model Superconducting Fault Current Limiter (SFCL). The SFCL that we proposed has a vacuum interrupter with electromagnetic repulsion mechanism. We set out to construct a high‐voltage‐class SFCL. We produced an electromagnetic repulsion switch equipped with a 24‐kV vacuum interrupter (VI). However, the opening speed becomes slower, because the larger vacuum interrupter needs a heavier‐weight contact. For this reason, the current which flows in a superconductor may not be interruptible within a half cycle of current. In order to solve this problem, it is necessary to change the design of the coil connected in parallel and to strengthen the electromagnetic repulsion force at the time of opening the vacuum interrupter. Thus, the design of the coil was changed, and in order to examine whether the problem is solvable, a current limiting test was conducted. We carried out a current limiting test using second‐generation (2G) HTS wire. The element used in this experiment has a stainless steel stabilizer on both sides of the wire. In the experiment we succeeded in interrupting the current of a superconductor within a half cycle. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(4): 20–27, 2010; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21039     

Relationship between current waveform just before current zero and interruption ability of high‐speed VCB

A high‐speed vacuum circuit breaker which forces the fault current to zero was investigated. The test circuit breaker consisted of a vacuum interrupter and a high‐frequency current source. A vacuum interrupter with an axial magnetic field electrode and a disk‐shaped electrode was tested. The arcing period of the high‐speed vacuum circuit breaker is much shorter than that of a conventional circuit breaker. The arc behavior of the test electrodes immediately after the contact separation was observed by a high‐speed video recorder. The relation between the current waveform just before the current zero point and the interruption ability was investigated experimentally by varying the high‐frequency current source. The results demonstrate the interruption ability and the arc behavior of the high‐speed vacuum circuit breaker. Effective current interruption is made possible by a low current period just before the current zero point, even though the arcing time is short and the arc is concentrated. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 172(2): 20–27, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20915     

Development of a high-speed current limiter for a 6 kV distribution system and evaluation of its effectiveness

We have developed a high-speed fault current limiting equipment for a 6 kV distribution system. The main components of this equipment are a high-speed vacuum switch (VCB) and gate turn-off thyristors (GTO) connected in parallel, and a current limiting impedance with low linear resistance in parallel with the switch. The usual load current is carried by the VCB. In case of a power system fault, the fault current is commutated to and interrupted by the GTO on opening the VCB. Tests confirm that the equipment can interrupt an estimated short-circuit current of 13 kA_rms by limiting to less than 3.5 kAp. The interrupt time was less than 2 ms. This response is about 100 times faster than that of conventional mechanical circuit breakers. The fast interruption current limiter can protect distribution systems within a few ms of a severe short circuit fault occurrence. The primary operational benefit of this equipment is the reduction of instantaneous voltage drop at the bus or on sound lines and of current stress on power system equipment during a power failure. © 1998 Technica, Electr Eng Jpn, 125(3): 11–21, 1998     

Superconducting DC breaker

The scheme of a superconducting fault current limiter (SFCL) rated for operation in the DC electric networks at the maximum current of 300 A, is proposed. This device incorporates a module based on 2G high-temperature superconductors and a quick-action vacuum DC interrupter. Authors present the investigation results relating both to the current-limiting capacity of DC SFCL and to recovery time of the super-conducting state after current disconnection at the voltage of 3.5 kV.     

AC losses in superconducting coils

AC superconducting wire is being developed for such electrical equipment as superconducting transformers and superconducting generators. AC loss reduction is of primary concern in the development of such high-efficiency equipment. In reducing ac losses, it is necessary to develop assessment methods for ac loss in test samples which have shapes similar to the end-product equipment. This paper describes a least-square calculation of ac losses of superconducting wire as a function of frequency and magnetic field strength measured in test coils. Two sample solenoid coils were made to test the influence of different capacities and winding methods on ac losses in ac superconducting coils with rated capacities of 500 kVA and 20 kVA, and impregnated (epoxy resin) and nonimpregnated windings. The ac losses in the superconducting coils were measured by a calorimetric method using the evaporating rates of liquid helium. Estimated ac losses in the superconducting wire of the two coils were compared with Joule losses of copper conductors at ambient temperature. As a result of this comparison, a low-loss ac superconducting wire winding can be made for electrical equipment rather than employing conventional copper winding when used under low magnetic fields under 0.5 T.     

Ac losses in superconducting coils

AC superconducting wire is being developed for such electrical equipment as superconducting transformers and superconducting generators. AC loss reduction is of primary concern in the development of such high-efficiency equipment. In reducing ac losses, it is necessary to develop assessment methods for ac loss in test samples which have shapes similar to the end-product equipment. This paper described a least squares calculation of ac losses of superconducting wire as a function of frequency and magnetic field strength measured in test coils. Two sample solenoid coils were made to test the influence of different capacities and winding methods on ac losses in ac superconducting coils with rated capacities of 500 kVA and 20 kVA, and impregnated (epoxy resin) and nonimpregnated windings. The ac losses in the superconducting coils were measured by a calorimetric method using the evaporating rates of liquid helium. Estimated ac losses in the superconducting wire of the two coils were compared with Joule losses of copper conductors at ambient temperature. As a result of this comparison, a low-loss ac superconducting wire winding can be made for electrical equipment rather than employing conventional copper winding when used under low magnetic fields less than 0.5 T.     

一起电网系列过电压事故的分析

断线过电压一般发生在配网中,与配网导线较细、杆塔较低、宜受外力破坏有关。本文介绍了一起发生几率小、容易被忽视的因真空灭弧室真空度下降造成的断线过电压情况,并对其发生过程进行了详细分析,提出了防范措施。     

Development of a new 6.6 kV/ 1500 A class superconducting faultcurrent limiter for electric power systems

A superconducting current limiter comprising a noninductively wound AC superconducting coil (trigger coil) connected in parallel with a limiting coil was developed. A model electric power system for the application of this type of superconducting current limiter was created, 400 V/100 A class model superconducting current limiters were fabricated, and various current limiting tests were performed with respect to short-circuit currents and phases varied over a wide range. The results demonstrate that the proposed current limiter possesses performance characteristics fully adequate for application to the model system. A 6.6 kV/1500 A class superconducting trigger coil was developed, with a scale permitting, in principle, validation tests of applicability to actual power systems. This coil was demonstrated to be capable of limiting short-circuit currents by a factor of 1/30, and was subjected to detailed evaluation of current-limiting characteristics     

Jiles–Atherton Hysteresis Approach in Analyzing the Effect of Field Suppression in Saturated Iron-core Superconducting Fault Current Limiters

Saturated iron-core superconducting fault current limiters (SISFCL) are becoming more popular in the recent years due to their ability of reliable, effective and instantaneous fault limiting. With a superior performance than conventional current limiting methods, the SISFCL is finding its application in modern transmission lines and distribution system. In the SISFCL, the iron core is forced into saturation using a superconducting coil carrying DC current. During a fault in the system, the high fluxes set up in the AC coils interact with the DC flux, thereby reducing the flux density abruptly. This sudden change in the flux density induces a high voltage across the DC coil, which may damage the DC current source as well as the superconducting material. As a protective measure, a field suppressor unit is used that disconnects the DC supply following a fault. In this paper, a mathematical model of the SISFCL is developed considering hysteresis and the effects of the field suppressor unit have been analyzed. The paper also aims to highlight the effects on the performance of SISFCL with varying hysteresis loops of the core material.     

直流SMC铁心高温超导故障限流器的研究

分析了直流电力系统保护的发展现状,设计了一种铁心型高温超导故障限流器。为了尽量延长限流的时间,限流器的铁心采用软磁复合材料(SMC)。限流器在系统正常工作时对电力系统影响很小,当短路故障发生时,它会很快表现为大阻抗以限制短路电流。基于磁场有限元与电路耦合的计算方法,首先对限流线圈在短路过程中的非线性电感进行精确计算,然后结合计算结果,在电路仿真程序中计算短路电流。通过对比SMC与硅钢铁心材料限流器的限流情况,可以看出SMC铁心限流器对于直流电力系统短路故障的限流效果更好。在短路故障发生后8 ms时,该限流器能将短路电流限制到最大值的12%。     

五种纵向磁场真空灭弧室触头磁场特性分析比较

用三维有限元法研究了线圈、杯状,两极和四极及双线圈五种纵磁真空灭弧室触头的纵向磁感应强度分布、触头片上涡流分布和纵向磁场滞后时间.研究表明:(1)电流峰值时纵向磁场由强到弱依次排列为:线圈式触头、两极式结构、双线圈式触头、杯状和四极式触头;(2) 电流过零时剩余磁场由弱到强依次为:四极式触头、两极式触头、杯状触头、双线圈式触头和线圈式触头; (3)纵向磁场较强处滞后时间由小到大依次为:两极式触头、四极式触头、线圈式触头、双线圈式触头和杯状纵磁触头.     

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     

基于高速SoC单片机的新型调容式消弧调谐控制器

以C8051F为核心,设计了主、从机结构的配电网调容式自动跟踪消弧线圈补偿控制器。调容式消弧线圈是采用晶闸管投切电容器TSC(ThyristorSwitchedCapacitor)技术,通过改变并联于消弧线圈二次绕组电容的大小,等效地实现消弧线圈电感量的调节。介绍了SoC(SystemonChip)技术,同时对控制器的数据采集监控、出口、通信和人机界面等模块的功能和设计进行了详细分析。调容式消弧线圈装置已经通过调试,运行良好,达到了电容电流智能化补偿的要求。     

消弧线圈并联小电阻接地方式下的行波故障测距

中国10～35 kV中性点经消弧线圈接地的中压配电网越来越多地采用消弧线圈与小电阻并联的方案。在发生永久性单相接地故障后投入并联小电阻,使故障电流增大,让保护装置可靠动作并断开故障线路。因此,在其基础上进行单相接地故障的测距技术研究极具发展前景和必要性。并联小电阻后将产生电流行波并在到达故障点后反射,反射电流行波幅值较大、特征明显。文中提出了利用投入并联小电阻产生的电流行波来进行故障测距的方法。深入分析了电流行波在线路上的传输特性,以及利用电流行波零模分量和线模分量进行故障测距的单端测距策略。针对配电网的特点,研究了架空线、电缆混合线路的解决方案以及利用多个检测装置信息的综合测距技术。最后,ATP/EMTP软件的仿真结果证明了所提出的故障测距方法的准确性和实用性。     

Persistent Current Analysis of Superconducting Coils in an Electrodynamic Suspension System

In a superconductive electrodynamic suspension system, superconducting coils experience a space harmonic magnetic field generated by induced current in the levitation coils installed along the guideway. Current in a superconducting coil varies to keep the total magnetic flux constant when the coil is exposed in an external magnetic field. However, superconducting coil current was treated as constant in the conventional analysis because the electromagnetic forces can be estimated easily. The purpose of this paper is to determine the behavior of the persistent current in making reliable and tough superconducting magnets. A simple method to analyze fluctuating persistent current in a superconducting coil is proposed first. Calculated results for the normal running condition showed that the fluctuations of persistent current are less than 1 percent of the initially excited current for the sidewall levitation system, and less than 2 percent for the ground levitation coil system. Even when the null flux guidance cable is short-circuited, the fluctuation is less than 5 percent. Considering that the magnetic shield effects by the conductive cryostat vessels were neglected in this analysis, the fluctuating magnetic field by levitation coils will never affect the stability for a superconducting magnet.     

一种真空断路器真空度在线检测新方法

详细介绍了一种真空断路器真空度在线检测的新方法,其真空灭弧室经过特殊设计,使用内置式双波纹管灭弧室,利用外界气体压力和灭弧室内腔自闭力的平衡原理,当真空灭弧室有漏气时（外界大气压进入）,引起自闭力的变化导致压力元件和位移传感器输出数据发生变化,从而使真空断路器本地闭锁并报警,同时经通用分组无线电业务（GPRS）网络也可实现远程监测报警.采用内置式双波纹管检测技术的真空断路器及其在线检测装置在现场应用情况良好,表明文中特殊设计的真空灭弧室具有推广实用价值.     

Examination of a fault current limiter with conduction‐cooled Nb3Sn screen

We examined the possibility of the practical use of a conduction‐cooled magnetic shield type fault current limiter. A small superconducting fault current limiter was built and the current limiting characteristics were tested. Conceptual design of the conduction‐cooled fault current limiter for a distribution power system was carried out, and we calculated and discussed the temperature rise of shielding coil during a normal and a fault condition. We suggest a protection method for quench due to local disturbances during normal operation. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(1): 20–27, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10164     

真空灭弧室发展分析

阐述了真空灭弧室的发展历史及现状,对决定真空灭弧室发展的4个关键技术:触头材料、电弧控制系统、灭弧室结构及灭弧室制造技术进行了分析,同时对真空灭弧室的发展趋势作了介绍。