Short‐circuit current calculation and performance requirement of HVDC breakers for MMC‐MTDC systems

To evaluate the performance requirement of high‐voltage direct current (HVDC) breakers for modular multilevel converter (MMC)‐MTDC (multi‐terminal high voltage direct current) systems with high efficiency, the equivalent model for calculating the maximum short‐circuit current is presented in this paper. First, the short‐circuit current is decomposed into the steady‐state component and the fault component according to its physical dynamics. Second, the steady‐state component is determined by solving the direct current (DC) network; the fault component is calculated by an equivalent network in which the converters are replaced by a reactance, a resistance, and a capacitance in series. Then, the complete procedure for evaluating the performance requirement of HVDC breakers is described based on short‐circuit current calculation. Verifications have been carried out based on a three‐terminal 800 MW/±400 kV bipolar MMC‐MTDC system. The results show that the proposed methodology is efficient and effective. Lastly, based on the same system, the performance requirement of HVDC breakers and the influence by the sub‐module (SM) capacitance and the smoothing reactor have been studied with the proposed methodology. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Effects of output power fluctuation on short‐circuit current of induction‐type wind power generators

Effects of the fluctuation inherent in wind speed are studied by a probabilistic method. The random variation in wind speed is responsible for random behavior in output power and internal voltage of a wind power generator. In case of fault occurrence at the instant of high internal voltage, the resultant short‐circuit current will be big, and vice versa. The DC component is also affected. According to the study, 2.4% and 1.3% increase of short‐circuit current in AC and DC components are observed respectively in a large variation case. This implies that the wind speed variation should be considered for accurate short‐circuit study. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(3): 27–36, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20721     

Advanced closing switch for three‐phase short‐circuit test of a very fast current limiter

Advanced closing switch for three‐phase short‐circuit test was developed for very fast current limiter using power electronics devices. The conventional short‐circuit test method was used for verification of the current interrupting device with longer time duration to interrupt fault current after the separation of contacts. In the conventional short‐circuit test method, a deviation of the closing time between each phase closing switch with a mechanical driving was regulated so that the breaking performance of the conventional switching device could be examined. However, in the new current limiter with very short fault current interruption time, the deviation time between each phase must be reduced less than the regulated time by the conventional test method. For this purpose, the advanced closing switch for three‐phase short‐circuit test method was developed. In the advanced test method, power electronics devices were used for the initiation of three‐phase short‐circuit fault. Results of the short‐circuit test showed that the advanced circuit had very small deviation time between the initiation of each phase fault. Also, the very fast current limiter with power electronics devices was shown to have an intended interrupting performance. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 68–75, 2000     

Calculation of sudden three‐phase short‐circuit current of turbine generators by 3D magnetic field analysis

Sudden three‐phase short‐circuit current of a turbine generator was calculated by a three‐dimensional magnetic field analysis. That analysis takes into account the rotation, magnetic saturation, and eddy current at a rotor part. To compare test results and calculated results, a method was proposed for short‐circuit phase estimation at sudden three‐phase short‐circuit test by line voltage waveform of the test results. The calculated results of short‐circuit current waveform are in good agreement with the test results. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(1): 54–62, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20110     

Efficient output waveform evaluation of a CMOS inverter based on short‐circuit current prediction

A novel approach for obtaining the output waveform, the propagation delay and the short‐circuit power dissipation of a CMOS inverter is introduced. The output voltage is calculated by solving the circuit differential equation only for the conducting transistor while the effect of the short‐circuit current is considered as an additional charge, which has to be discharged through the conducting transistor causing a shift to the output waveform. The short‐circuit current as well as the corresponding discharging current are accurately predicted as functions of the required time shift of the output waveform. A program has been developed that implements the proposed method and the results prove that a significant speed improvement can be gained with a minor penalty in accuracy. Copyright © 2002 John Wiley & Sons, Ltd.     

Power loss minimization considering short‐circuit capacity in distribution system with decentralized distributed generation

In the future, a large number of distributed generators are expected to be connected to the distribution system. However, with the connected capacity of distributed generation (DG) increasing, the problems of short‐circuit capacity (SCC) over the interrupting capacity of the circuit breaker (CB) and power loss increases due to reverse power flow from DG are inevitable. In this paper, a reconfiguration methodology based on an optimal algorithm is applied to the distribution system with DG to minimize power loss, taking into account the SCC. Moreover, in order to further reduce the loss, the daily load variation is also considered and the optimal model decided by calculations. Finally, to illustrate its application, the methodology is applied to a case study of a 33‐bus system with decentralized DG units. The results show that this method is obviously able to reduce power loss and make the network operate in the optimal mode with normal load variation, at the same time decreasing the SCC within the interrupting maximum of the faulty CB. Moreover, the whole voltage profile is also improved. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Fault current limiting system for 500‐kV power systems

Recently, expansion in the scale of power systems and development of localized power sources are leading to an increase in fault current of 500‐kV systems. In the future, it is quite likely that the fault current at the interconnection of such power systems may exceed the rated short‐time current of existing electric power facilities. As one of the solutions of this problem, a thyristor‐controlled series‐resonant‐type fault current limiter (FCL) is proposed to restrain the fault current. This paper deals with the FCL system configuration, the placement method of the FCL in power systems, the outline of the FCL's specification, and the operation method of the protective relay in the multimachine system. Finally, the effectiveness of the FCL is evaluated from the viewpoints of limiting the fault current by simulation analysis. The FCL is shown to be a useful protection device for large, high‐capacity power systems. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 11–22, 1999     

基于功率协调的交直流并联系统可靠性评估

提出一种基于功率协调的交直流并联系统可靠性评估方法。在求得交流、直流线路的最大输送功率后，对交直流系统功率进行合理的协调，得到整个系统输送功率满足负荷要求的概率性指标，用Monte Carlo模拟法对可靠性指标进行统计计算。文中同时给出进行交直流并联系统可靠性评估的算法，通过交直流并联系统的仿真计算，证明所提方法和算法的有效性。     

Analytical estimation of propagation delay and short‐circuit power dissipation in CMOS gates

An efficient analytical method for calculating the propagation delay and the short‐circuit power dissipation of CMOS gates is introduced in this paper. Key factors that determine the operation of a gate, such as the different modes of operation of serially connected transistors, the starting point of conduction, the parasitic behaviour of the short‐circuiting block of a gate and the behaviour of parallel transistor structures are analysed and properly modelled. The analysis is performed taking into account second‐order effects of short‐channel devices and for non‐zero transition time inputs. Analytical expressions for the output waveform, the propagation delay and the short‐circuit power dissipation are obtained by solving the differential equations that govern the operation of the gate. The calculated results are in excellent agreement with SPICE simulations. Copyright © 1999 John Wiley & Sons, Ltd.     

影响电力系统短路计算结果的原因分析

电力系统短路计算是电力部门经常进行的基本计算,其计算结果是设备选择、继电保护定值整定的依据。无论使用调度自动化中的短路计算软件,还是使用继电保护定值整定软件,各种软件或算法的计算结果可能出现差异。产生差异的原因较多,分析表明主要原因有:(1)近似计算中各节点的正序正常电压处理不一致;(2)近似计算中变压器模型的等值阻抗处理方法不同;(3)详细计算中,由于未考虑分接头影响,至使变压器模型选择不当。变压器模型对短路计算的影响很大,建议采用C IM变压器模型,该模型具有原理正确和使用方便的特点。     

计及控制策略的并网型微电网可靠性评估

当上层配电网故障或电能质量不满足要求时,微电网可通过控制策略切换等调度各微电源的出力,实现微电网孤岛运行。孤岛运行时,不同控制策略直接影响微电网的供电可靠性。通过对微电网最常见的两种控制策略（主从型和对等型）的分析,建立了计及控制策略的并网型微电网功率模型;通过对上层配电网进行最小路等值,建立微电网不同控制策略下的故障影响矩阵,提出了基于时序蒙特卡洛的并网型微电网可靠性评估方法。以此方法对改进的IEEE-RBTS系统进行可靠性评估,分析了两种控制策略对配电网可靠性指标的影响。算例表明：微电网加入配电网后可改善系统可靠性性能;对等型微电网比主从型微电网的可靠性要高。     

高压直流输电系统可靠性评估研究

高压直流输电系统可靠性是现代电力系统可靠性研究的重要研究领域之一,介绍了高压直流输电系统主要可靠性指标,根据相关文献对高压直流输电系统可靠性评估方法、安全性与充裕度的综合评估等进行了系统评述,并展望了今后的研究方向.     

Reliability evaluation considering customized power quality supply in FRIENDS

The authors have proposed a Flexible, Reliable and Intelligent ENergy Delivery System (called “FRIENDS”), which is a new concept for a future power distribution system. One of the most important feature of FRIENDS is to be able to manage the reliability of power supply. In this paper, FRIENDS and a conventional distribution system are compared quantitatively as to supply reliability and cost through time sequential Monte Carlo simulation. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(4): 25–35, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20053     

功率因数校正电路的蒙特卡罗分析

建立一种功率因数校正电路的计算机模型,并对该模型进行了计算机辅助的蒙特卡罗分析,得到了电路中元器件参数的随机误差对电路输出电压的影响,为电路生产过程中确定元器件的误差范围提供了科学依据。     

电网安全稳定控制系统可靠性评估

对电网安全稳定控制系统(简称稳控系统)的可靠性进行评估是开展其可靠性设计的必要前提,对于保障电网安全稳定运行具有重要意义。首先,综述了电网二次系统可靠性评估指标和可靠性评估方法的研究现状,将可靠性评估指标从时间和概率两个方面进行了归类,总结了四种可以研究稳控系统可靠性的分析方法。然后,分别采用马尔可夫状态空间法和蒙特卡罗方法对稳控系统典型工程应用案例进行可靠性计算评估,比较了两种方法在小型稳控系统可靠性分析中的适用性,推导出装置失效率和修复率与系统可用度的数学表达式。最后,通过对比分析前述两种可靠性分析方法的优缺点,提出综合应用各种可靠性分析方法进一步深化研究大型复杂结构稳控系统可靠性的建议。     

特高压对江西电网短路电流的影响

2013年江西电网将建设1 000kV南昌特高压站,以电网规划设计为基础,以电网建设项目进度为条件,对特高压入赣前、后江西电网的短路电流进行详细计算分析,在此基础上分析了特高压对江西电网短路电流的影响,并提出了降低江西电网短路电流和保障电网安全稳定运行的措施和建议.     

多端口直流断路器可靠性评估模型及其应用

多端口直流断路器(MTCB)是未来实现多端换流站联络及故障快速隔离的核心设备,其可靠性直接影响多端直流配电网的可靠性水平.首先分析了MTCB拓扑结构及工作原理.然后以珠海"互联网+"示范工程中应用的三端口混合式直流断路器为例,基于工程可靠性原理并考虑器件冗余建立MTCB可靠性评估模型.然后分析了MTCB对多端直流配电网可靠性的影响.最后基于唐家湾三端直流配电网结构进行算例分析,计算了MTCB在不同设计模式、冗余分析下的可靠性情况,进行了MTCB对多端直流配电网可靠性的影响分析及灵敏度分析,验证了所提模型的正确性和有效性.     

高阻接地的船舶中压电网暂态短路电流计算

针对高阻接地方式的船舶中压电网,提出一种系统化的暂态短路电流计算方法。考虑同步发电机及异步电动机暂态特性,根据故障点位置,基于分层等效方法将系统中所有发电机和电动机等效为一台发电机。对于等效发电机,考虑系统分布电容,用对称分量法求解三相对称及各种不对称故障的暂态电流。用Simulink仿真结果对比验证了该方法的有效性和精确性。     

基于多状态节点贝叶斯网络的HVDC系统可靠性评估

贝叶斯网络具有灵活的推理机制,能深刻地揭示系统内在的机理。该文提出了将贝叶斯网络应用于高压直流系统可靠性评估的方法。该方法采用多状态节点来描述系统及节点的多态性,有效地处理了特殊的备用情况,并提出了信念度矩阵来描述系统内部各层元件之间的连接关系,通过考查给定系统状态对应的信念度,可以评估系统中的薄弱环节。此外,利用贝叶斯网络的自动更新功能,还能根据当前的元件或子系统的状态对系统未来状态作出预测。最后,通过具体的算例对所提方法的有效性进行了分析和验证。     

孤岛状态下含分布式电源的配电系统可靠性分析

分析了孤岛状态下含分布式电源的配电系统可靠性。针对配电网孤岛运行的特点,提出了可靠性分析的复合随机性负荷模型,提出了既能反映系统充裕度又体现动态特性的可靠性计算方法和衡量指标。计算结果表明,所提的模型、计算方法和衡量指标能充分反映分布式电源在不同程度上提高配电系统的可靠性,为系统的规划设计提供了重要参考。