Influence of output power out of a synchronous generator installed in a customer system on current limiting effects due to a fault current limiter

In this paper, it was assumed that a synchronous generator in a customer system was connected to a distribution system via the fault current limiter (FCL). We theoretically investigated the influence of the output power of the generator on the limiting effect of the fault current when a three‐phase short‐circuit fault occurs. It was shown that the fault current out of the customer system, limited by the FCL, rises with the output power of the generator. It was found that the larger the output, the higher the fault current at the fault point is when the limiting resistance is less than 15 Ω in the case of the resistive‐type FCL. On the other hand, the fault current at the fault point decreases with an increase in the output power for a limiting resistance more than 15 Ω. In contrast, it was found that the suppressing effect on the fault current at the fault point due to the inductive‐type FCL hardly depends on the output power. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(3): 15–24, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10357     

Operating characteristics of a superconducting fault current limiting transformer (SFCLT) and enhancement of electric power system stability

We have been investigating the feasibility of a superconducting fault current limiting transformer (SFCLT) with the functions of fault current suppression and system stability improvement. This paper discusses these functions with consideration of overvoltage and thermal characteristics of SFCLT, and their dependence on recovery time into superconducting state after the quench of SFCLT. Simulation results using EMTP suggested that SFCLT would be coordinated with the background power system under the appropriate superconducting recovery time. The operating parameters of SFCLT were also optimized in a simplified power transmission model system. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(2): 40–47, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10070     

Breakdown of YBCO thin films during current limiting and methods of improving current limiting performance

We performed fault current limiting tests using YBCO thin films and investigated the reasons for their breakdown during current limiting. There were two patterns of film breakdown. One occurred immediately after current limiting and the other occurred during current limiting. In film breakdown, the quench propagation speed showed almost no change with increasing energy consumption per unit time, but the energy consumption per unit area increased with increasing energy consumption per unit time. Therefore, local areas of the film reached the melting point and arcing occurred. It is therefore concluded that the performance of the films can be improved by decreasing the energy consumption per unit time. Connecting a parallel capacitor to the film in order to limit the energy consumption per unit time is proposed and tested as a measure to improve the current limiting performance of thin films. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(1): 20–27, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20709     

Self-rehealing characteristics of a sodium current limiter and its overcurrent coordination for low-voltage distribution system

The sodium current limiter developed and applied for low voltage use is not a current limiting fuse but a new type of reusable current limiting device that utilizes metallic sodium as a fusible element. Excellent current limiting performance and quick self-rehealing properties of the sodium limiter allowed highly reliable electric power systems to be obtained economically and compactly. Here we examine experimentally the rehealing properties of the sodium limiter after current limiting operation and discuss the overcurrent coordination of the sodium limiter for a low-voltage distribution system. The results are summarized here:

• 1 (1) The resistance of the sodium limiter, being between about one thousand and several thousand times its normal resistance r₀ at room temperature during a current limiting operation of short circuit fault currents, changes abruptly to 30 to 40 times its r_o value just after the disappearance of the fault current and falls steadily to r_o.
• 2 (2) The sodium limiter can recover current-carrying capability for an overload current even immediately after a current limiting operation and maintain its capability for the following normal load current. The upper limit of the recovery of the sodium limiter is given by its overcurrent against the time characteristics under the normal condition.
• 3 (3) The self-rehealing characteristics of the sodium limiter presented here give the ability to design a low-voltage motor control center using the sodium limiter which maintains maximum service continuity up to high fault currents.

     

超导限流器基本概念和发展趋势

超导限流器是多年以来人们在超导电力技术领域的研究焦点之一,也是被认为最有可能率先实现工业化应用的超导电力设备。本文在介绍超导限流器的基本概念、组成要素和功能特点的基础上,讨论了超导限流器设计和应用相关的一些重要技术参数和性能指标。文章还较系统地分析了电阻型和饱和铁心型两种目前发展水平较高的超导限流器的工作原理和应用情况,并比较了两者的优缺点。随着性能的进一步完善,可靠性和可用性的进一步提高,超导限流器有可能成为理想的电网短路故障限流装置。作者期待在不远的将来超导限流器会在各种电网中得到广泛的应用,并由此推动电网的深刻技术革命。     

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     

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     

Experimental studies of the improvement of power system stability by superconducting fault current limiters

With increasing demands for electric power, the electric power system is becoming more and more complicated, and the stable, highly reliable delivery of electric power is encountering two major problems, namely, large fault currents and power system instability. In particular, the fault currents occurring in power systems are tending to increase. To solve this problem, superconducting fault current limiters (SCFCLs) have been developed, and it is hoped that they will also solve the problem of power system stability. This paper describes the results of experiments on the improvement of power system stability and the suppression of fault currents with SCFCLs, performed with power transmission simulators. An experiment using an R‐type SCFCL in a power system was performed. An R‐type SCFCL was simulated by using a resistor and an electromagnetic contactor with thyristors. It was found that the inclusion of an SCFCL in the electric power system gives improved suppression of fault currents and improved power system transient stability. © 2000 Scripta Technica, Electr Eng Jpn, 133(4): 41–52, 2000     

基于高耦合电抗器的500 kV限流器限流特性等效试验

基于高耦合电抗器的500 kV限流器在限流状态下的阻抗较大,而由于试验室电源电压有限,限流状态下的试验电流远小于额定短路电流,因此500 kV限流器在额定短路工况下的限流特性试验和动稳定性考核试验无法直接进行。针对上述问题,提出了一种间接验证限流器限流特性的等效试验方法。通过设计降低阻抗参数的比例缩小样机,在试验室条件下进行全电流的比例缩小样机间接试验,同时结合试验室内500 kV限流器比例缩小样机的低电压试验和500 kV限流器接入实际系统的高电压人工短路试验,综合验证500 kV限流器的限流能力。研究结果表明,500 kV限流器在额定短路工况下的限流幅度满足设计要求,所设计试验方法具有良好的等价性。     

Control of fault current limiter by series‐connected voltage sag compensator

This paper describes a control scheme of fault current limiter by series voltage injection. The current limiter proposed in this study is based on the use of a SMES‐based series‐connected voltage sag compensator, which has been previously studied by the authors, for controlling fault current caused by short circuit on the load side. An algorithm for fast discriminating between power system voltage sag and load‐side short circuit is proposed for the equipment to correctly function either for voltage sag compensation or for fault current limiting purpose. Furthermore, a new control strategy based on output voltage phase control of the series compensator is proposed for current limiting with good waveform characteristics and low active power absorption. Experimental results demonstrated the validity of the proposed strategy. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 64–72, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20128     

饱和铁心型超导限流器的仿真设计方法

分析了饱和铁心超导限流器的工作原理,给出了其正常工作的电磁约束关系.介绍了利用PSPICE进行仿真设计的新方法,为优化产品结构参数、准确预估限流效果提供了有效途径,最后介绍了一个设计实例.     

Realization of a multiport gyrator using current mirror circuits

A current‐mode signal processing circuit is quite attractive for low supply voltage operation and high‐frequency application. A current‐mode continuous‐time filter consists of simple bipolar current mirrors and capacitors, and are quite suitable for monolithic integration. In this paper, we propose a design for a multiport gyrator using current mirror circuits. Using the multiport gyrator and capacitors, we can simulate passive LC filters. The tuning of the filter frequency can be achieved by adjusting the current of a single dc current course. As examples, third‐ and fifth‐order low‐pass filters are designed for frequencies of 20 to 80 MHz, and SPICE simulation results are shown to demonstrate the effectiveness of the proposed method. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(4): 41–47, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1167     

新型混合型限流断路器在直流电力系统中的限流特性研究

针对直流电力系统高di/dt短路电流难以分断的问题,开展了基于高速斥力开关的混合型限流断路器在直流电力系统中的应用研究.对限流断路器的工作原理、参数设计以及高速斥力开关的动作特性进行了分析,采用EMTP仿真分析了限流断路器在不同短路电流上升率下的限流特性.仿真结果表明限流断路器可将预期100 kA、时间常数5 ms的直...     

磁偏置超导故障限流器限流响应模型与并网运行研究

针对电网短路故障限流问题,提出一种新型磁偏置超导故障限流器(SFCL),采用超导无感组件、双分裂电抗器支路两级限流的运行方式,具有自触发、分级故障限流、快速自我恢复等优点.应用MATLAB/Simulink软件,搭建了含磁偏置SFCL的10 kV电网线路仿真模型,提出超导限流组件磁热耦合特性的物理建模方法,并对0°和90°短路故障角下的SFCL并网限流效果进行瞬态仿真和比较.仿真结果表明,在电网0°和90°不同故障短路角电流冲击下,SFCL在首半波中的限流率分别为36.45％和45.89％,随后第2个半波的最大限流率达到78.58％,限流电阻在90°短路故障角下的变化率是0°短路故障角下的1.75倍,实现了较快的限流动作响应和显著的分级限流效果.最后实验验证了磁偏置超导限流技术的可行性.     

限流式动态电压恢复器及其参数设计

为优化电网正常运行时的电能质量,针对电力系统短路故障问题,提出了一种限流式动态电压恢复器(Dynamic voltage restorer with fault current limiting,DVR-FCL)拓扑结构。以限流阻抗值为目标函数,考虑直流侧电压整定的参数设计,给出了DVR-FCL的直流侧电压、输出滤波器、串联变压器参数、串联变流器、直流侧电容的整定方法。利用PSCAD/EMTDC仿真软件验证了DVR-FCL对电压跌落及短路故障的动作特性。结果表明,所提拓扑结构和参数设计方法正确,可实现改善电压质量和短路限流的双重功能,保证了电力系统安全性和稳定性。     

混合直流系统中基于平波电抗器与限流电抗器参数优化的限流策略

直流线路正常运行过程中,平波电抗器可以减小电流纹波。当直流线路发生故障时,限流电抗器的快速投入可以抑制故障电流的上升速度。因此,考虑限流电抗器与平波电抗器的协同,不仅可以抑制故障电流的上升速度,而且能够降低直流断路器的切断容量。然而,受到投资成本和系统动态特性的制约,平波电抗器与限流电抗器的电感容量需要保持在合理的范围内。因此,对直流输电系统中平波电抗器和限流电抗器的容量进行优化配置,在保证限流能力的同时降低投资是十分有意义的。首先,建立了交直流混联系统的故障等效模型,并分析直流线路发生双极性短路时两端故障电流的特性。其次,建立了平波电抗器和限流电抗器的优化配置数学模型。最后,基于MATLAB仿真试验对所提限流策略进行了验证。     

采用异步联网限制短路电流的实际应用和分析

500 k V主网短路电流超标问题已成为广东电网近年来运行最突出的问题之一。现有的运行措施可将超标站点短路电流暂时降低至安全水平,但电网整体的短路电流水平仍较高,且牺牲了部分系统安全可靠性,从长远来看通过直流背靠背异步互联限制短路电流是可行的解决办法。以2018年广东500 k V电网为研究对象,建立直流背靠背异步联网模型,从短路电流限制效果、系统可靠性等方面进行仿真计算,并与传统运行措施进行对比,可以得出,采用直流背靠背异步互联措施具有更好的限流效果和更高的安全可靠性,验证了该方案在短路电流限制方面的有效性和优越性。     

饱和铁心型超导限流器压敏电阻的实验

压敏电阻可抑制超导限流器断直流时产生的高压,同时加速直流励磁能量的释放以促使限流器交流侧快速退饱和,进入感性限流状态。为验证其保护和能量吸收作用,用NI采集卡、Labview以及其他电流电压传感器和可控的IGBT器件设计和制造了检测控制系统。对不同压敏电压等级的压敏电阻进行断直流的放电实验以验证其抑制电压的保护作用。结果表明:断直流时储存能量的释放是超导限流器产生高压的原因;励磁储能一定且压敏电阻通流量一定的条件下,压敏电压越大断直流产生的电压也越大,同时电流断开时间越小则能量释放时间越小。所得结果为设计更大容量的超导限流器,选择不同压敏电阻的压敏电压和通流量等级提供了实验和计算参考。     

混合式限流断路器的研究与发展

电力电子技术的进步与新型器件的出现为电力系统的发展提供了新的机会。概括了目前混合式限流断路器(HCLCB)的基本工作原理及其在国内外发展状况,详细介绍了基于不同器件的HCLCB的拓扑结构,诸如自然换流式及强迫换流式HCLCB,并分析了相应的技术特点,同时还从机械结构及故障电流检测的角度阐述了HCLCB设计要点,希望能为HCLCB的设计提供参考。     

Electromagnetic and thermal analysis of high-Tc superconductor in application of current limiting devices

Superconducting fault current limiters (SCFCL) offer an attractive way to limit short-circuit currents in power systems. Analysis into electromagnetic and thermal behaviors of superconductor material is crucial in order to develop a novel design concept of a fault current limiter. A new scheme, which can treat electromagnetic field of the type-II superconductor under transient temperature field, is proposed. In this analysis, one of the critical state models, the Bean model was employed to determine the current distribution in the superconductors and effect of magnetic flux flow was also taken into account. Numerical results indicate that the flux flow strongly affects the stability against the quench in Bi-2212 material. High-T_c superconductor material (Bi-2212) was chosen for the current limiting application. In order to investigate characteristics of the current-quenched Bi-2212 bulk, a 2-dimensional heat transfer equation was numerically solved using the finite element simulation. Heat distributions among the superconductor bars were also simulated and by comparing both the experimental and simulated results, it was found that non-uniformities in a current density or a temperature may exist in the quenching of bulk Bi-2212 superconductor.