Power supply arm protection scheme of high-speed railway based on wide-area current differential

When fault occurs on cross-coupling autotransformer(AT)power supply traction network,the up-line and down-line feeder circuit breakers in the traction substation trip at the same time without selectivity,which leads to an extended power failure.Based on equivalent circuit and Kirchhoff’s current law,the feeder current characteristic in the substation,AT station and sectioning post when T-R fault,F-R fault,and T-F fault occur are analyzed and their expressions are obtained.When the traction power supply system is equipped with wide-area protection measurement and control system,the feeder protection device in each station collects the feeder currents in other two stations through the wide-area protection channel and a wide-area current differential protection scheme based on the feeder current characteristic is proposed.When a short-circuit fault occurs in the power supply arm,all the feeder protection devices in each station receive the feeder currents with time stamp in other two stations.After data synchronous processing and logic judgment,the fault line of the power supply arm can be identified and isolated quickly.The simulation result based on MATLAB/Simulink shows that the power supply arm protection scheme based on wide-area current differential has good fault discrimination ability under different fault positions,transition resistances,and fault types.The verification of measured data shows that the novel protection scheme will not be affected by the special working conditions of the electrical multiple unit(EMU),and reliability,selectivity,and rapidity of relay protection are all improved.

Study on the instantaneous protection reliability of low voltage circuit breakers

This paper outlines the significance of enhancing the instantaneous protection reliability of low voltage circuit breakers and describes their main failure modes. The instantaneous failure mechanism of low voltage circuit breakers was analyzed so that measures to improve instantaneous protection reliability can be determined. Furthermore, the theory of the instantaneous characteristics calibration device for low voltage circuit breakers and the method of eliminating the non-periodic component of test current are given in detail. Finally, the test results are presented.

Influence of DFIG Wind Turbine Protection and Control during Voltage Dip on Circuit Breaker Operation

This paper analyzes a DFIG （doubly fed induction generator） WT （wind turbine） fault current after a symmetrical network voltage dip. The goal is to identify the factors determining how fast the first zero crossings of the fault current occur. This is an important subject because the ftmdamental property of the CB （circuit breaker） is that it breaks the current when the current is very near zero. The study was conducted using a hardware-in-the-loop test environment constructed using two real time simulators （dSPACE and RTDS） and a commercial protection relay. It is found that the reactive current injection during a voltage dip demanded by the grid codes enhances the operation of the WT protection because the zero crossings of the currents through CB are attained earlier. In addition, the size of the crowbar resistance has a significant influence on the zero crossings.

A Novel Crowbar Impulse Current Circuit for Testing the Switch-Type SPD

A crowbar impulse current circuit for testing the switch-type surge protective device （SPD） is presented. The crowbar circuit consists of a computer control circuit, a trigger voltage pulse generator, a main discharging switch, and a crowbar pseudospark switch. The active trigger technology was studied in the crowbar impulse current circuit. The circuit monitors the main discharging current and generates a trigger signal at a proper time for the crowbar pseudospark switch operation. The trigger characteristics of the main discharge switch and the crowbar pseu- dospark switch were investigated. By monitoring the preset applied capacitor voltage, the gap distance of the main discharging switch could be adjusted to ensure a discharging delay time less than 2 μs. Equipped with a surface ttashover trigger device made of high relative perimittivity dielectric material BaTiO3 （εr = 3460）, the discharge delay time of the crowbar pseudospark switch is less than 85 ns, and the minimum operating voltage is less than 1% of its self-breakdown voltage. With a storage capacitor of 9 μF , an inductor of 18 μH and a crowbar pseudospark switch, a load of 30 mΩ and an applied capacitor voltage of 40 kV, an impulse current waveform of maximum 25 kA was generated with a rise time and time to half peak value of 17.2 μs and 336μs respectively.

Protection of Low Voltage CIGRE Distribution Network

High quality electricity services are the prime objectives in the modern power systems around the world. One of the main players to achieve this is the protection of the system which needs to be fast, reliable and cost effective. The study about the protection of the Low Voltage (LV) CIGRE distribution grid and networks like this has been proposed in this paper. The main objective of this paper is to develop protection against short circuit faults which might appear anywhere in the network. The protection of the power networks that comprises of renewable energy generation units is complicated because of the bidirectional flow of the current and is a challenge for the protection engineers. The selection of the protection devices in this paper is made to protect the network against faults in grid connected and island mode of operation. Ultra-fast fuses are proposed in order to protect the inverters used for Photovoltaic (PV) and battery applications. The disconnection of the PV solar panels when in island mode is made by proposing switch disconnecting devices. ABB is currently using these kinds of disconnection devices for the purpose of protecting solar panels against over voltages in the case of islanding. The over speed protection of the existing Wind Turbine Generator (WTG) in the CIGRE network in case of grid loss is also proposed in this paper.

Short-circuit Current Characteristics of Wind Generators

To study the effects of wind generators on distribution system protection,the short-circuit current(SCC) characteristics of wind generators is important.Although there are many researches on the issue,a clear agreement has not been reached so far.The SCC characteristics for different wind generators are studied.PSCAD simulation is performed in the same system integrated with different kinds of wind generators,and their results are compared with those reported in IEEE papers.The detection possibility by overcurrent relay(OCR)is discussed based on the simulation results.

Advancement in Wide Area Monitoring Protection and Control Using PMU’s Model in MATLAB/SIMULINK

A big step forward to improve power system monitoring and performance, continued load growth without a corresponding increase in transmission resources has resulted in reduced operational margins for many power systems worldwide and has led to operation of power systems closer to their stability limits and to power exchange in new patterns. These issues, as well as the on-going worldwide trend towards deregulation of the entire industry on the one hand and the increased need for accurate and better network monitoring on the other hand, force power utilities exposed to this pressure to demand new solutions for wide area monitoring, protection and control. Wide-area monitoring, protection, and control require communicating the specific-node information to a remote station but all information should be time synchronized so that to neutralize the time difference between information. It gives a complete simultaneous snap shot of the power system. The conventional system is not able to satisfy the time-synchronized requirement of power system. Phasor Measurement Unit (PMU) is enabler of time-synchronized measurement, it communicate the synchronized local information to remote station.

多间隔信息融合的母线保护电流互感器断线再开放策略

对于电流互感器(CT)断线后发生金属性故障的情景,现有母线保护采取的闭锁差动保护动作方式将会引发多个变电站停电。此外,当母线区内发生高阻接地故障时,现有母线保护判据可能会将其误判为CT断线故障,不利于电力系统的安全稳定运行。针对这一问题,提出了一种母线保护CT断线再开放策略,该策略基于断线间隔与非断线间隔的零序电流变化量对负荷波动和故障进行区分,并基于非断线间隔的差流有效值和间隔失灵保护信息对区内外故障进行判别。实时数字仿真系统仿真结果验证了所提CT断线识别判据和再开放策略的正确性。

基于钳位型断路器的柔直系统控保协同技术

柔性直流系统以其在输电领域的巨大优势而获得广泛应用.但在直流系统中,短路故障的强冲击性与电力电子器件的脆弱性之间的矛盾异常尖锐,现有保护策略难以同时满足高速动性与高可靠性的要求.本文从控保协同思想出发,基于一种电压钳位原理的直流断路器,提出一种新的故障处理模式,初步探究在柔直系统中控制与保护深度融合的可能性.当发生短路故障时,投入断路器和换流器相配合的限流功能,一方面限制电力电子器件的过流,解决其脆弱性问题;另一方面为保护提供边界,辅助实现故障的快速定位.在甄别出故障线路后,利用断路器的故障切除功能将故障隔离.此方案同时实现了故障限流、保护边界和故障切除3项功能,可有效缓减由于模块化多电平换流器(modular multilevel converter,MMC)器件脆弱性所带来的一系列保护问题.在PSCAD/EMTDC中搭建四端双极柔性直流电网模型,仿真结果表明,本控保协同方案能在5 ms内准确识别并隔离故障线路,而且具有较强的耐受过渡电阻能力.

高压直流输电保护定值整定依据及配合关系探讨

在中国30余年的高压直流输电工程实践中形成了一套高压直流输电保护系统定值体系。文中结合近年来在应用中出现的复杂案例,对以下保护的定值整定依据开展了进一步探讨:阀短路保护启动定值需避开与换流阀并联的阻容回路的充电电流;换流器过流保护过负荷段定值整定依据是直流控制系统失控造成直流运行电流超过控制的过负荷目标值,以及控制目标电流超过所设定的运行时间;直流低电压保护阈值及延时定值的整定需兼顾保护的后备功能,不确保与换相失败保护双桥原理长延时段配合。另外,深入探讨了交直流系统间、金属回线运行方式下直流保护间,以及高压线路再启动与低压再启动间的定值配合问题。最后,提出了高压直流输电保护系统的定值及定值间的配合应有一定的规范性和适度的灵活性的建议。

基于Simulink/MATLAB的实际地铁线路供电系统短路试验仿真分析

直流牵引供电系统在城市轨道交通中扮演着关键角色,其安全可靠的运行对整个城市轨道交通系统的运行至关重要。该文首先介绍地铁牵引供电系统的结构和功能,并建立地铁外部交流电源、整流机组和牵引网络的仿真模型。该仿真模型根据实际地铁牵引供电系统的结构和参数进行构建,旨在研究不同短路情况下的短路特性,包括电源出口短路、近距离短路和远距离短路。通过评估供电系统在短路故障下的稳定性和可靠性,得出若干研究结果。这些结果为地铁供电系统选择合适的一次设备提供理论依据,有助于确保城市轨道交通供电系统的稳定性和可靠性。

大规模新能源接入的交流电网继电保护整定计算研究

新型电力系统高速发展,新能源大量投产,现有忽略新能源电源属性的继电保护传统整定计算方法难以适应。鉴于此,结合新能源的物理特性和整定计算特点,提出了新能源的整定计算实用化模型。讨论了计及大范围新能源接入的短路计算方法,给出了恒流源和受控源接入的短路计算算法,提出了大范围新能源接入后的新能源影响域评价指标,在保证整定计算准确度的前提下提高了整定计算的效率。在前述研究的基础上,详细分析了计及新能源的参数收资、方式设置、保护配置、整定计算原则、重合闸、边界保护管理等内容。所做工作为面向新型电力系统的整定计算业务提供了解决思路,对继电保护整定人员具有借鉴与参考意义。

新能源场站高比例接入下主流类型工频量距离保护比对

新能源场站高比例接入电网后,已有广泛应用的工频量距离保护判据存在无法准确识别电网故障的问题。文章着重从装置中保护判据与工频量提取算法入手,对比分析新能源场站高比例接入场景下不同类型距离保护算法的适应性。针对保护判据,对比分析了方向圆、多边形、比相式以及工频变化量距离保护各自的适应性,明确了能够较好适用于新能源场站高比例接入的距离保护判据。针对工频量提取算法,探究了不同类型新能源场站所提供短路电流中非周期谐波量的变化特性,进一步推导了受谐波量影响的傅里叶算法对工频量提取产生的计算误差,确定了影响工频量提取精度的关键谐波分量。

一种压电换能器热释电防护电路设计

该文探讨了压电材料热释电效应产生的机理,得出压电换能器中压电陶瓷材料受温度变化会产生极化电荷,引起的热释电压会使压电换能器输出信号幅值增大,导致输出失效。因此针对热释电问题提出了两点解决方案。经过对比分析设计了一种ESD保护电路来解决热释电问题。该ESD保护电路通过设计一种改进型二极管钳位电路,针对压电换能器存在的极化电荷构建热释电释放环路,消除了热释电压对有用信号收发的影响。最后,通过对比实验验证了设计方案的可行性。

基于MMC主动限流的VSC-HVDC双极短路故障控保协同策略

直流故障保护是柔性直流输电系统发展面临的主要挑战之一,利用模块化多电平换流器(MMC)的灵活控制实现限流已成为当前研究的热点。MMC的主动限流降低了故障电流变化率和故障电流幅值,易引起故障判断以及保护选择困难。文中以对称单极接线的柔性直流系统为研究对象,采用控保协同思想,将主动限流控制与故障识别相结合,提出了基于主动限流因子的故障区域识别与区分方法实现双极短路故障的区域识别与切除。首先,通过在MMC电流内环控制器中附加故障电流目标预设控制器,在故障发生后可快速跟踪故障电流的变化,自适应地调整MMC输出的直流电压将故障电流控制在预设目标参考值附近;其次,根据不同故障位置时故障电流目标预设控制器输出的限流因子快速确定故障区域。最后,在PSCAD/EMTDC中对四端柔性直流输电系统的不同故障场景进行了仿真分析,验证了所提控保协同策略的可行性和有效性。

管道阴极保护电流内检测硬件系统设计

针对传统外检测方法难以在某些特殊管段进行阴极保护电流检测的难题,通过管道内检测法实现管道电流参数的采集,消除了管道阴极保护电流检测盲区。给出了管道阴极保护电流硬件系统设计方案,包括电流放大电路设计、信号转换电路设计、电源方案设计。进行了管道阴极保护电流硬件系统实验测试,获得了阴极保护电流—电压标定曲线。测试结果表明,硬件系统可满足设计要求,为后续管道阴极保护内检测现场应用提供了硬件支持和理论依据。

无刷同步发电机稳态短路电流控制

过载运行能力和突然短路时稳定的短路电流输出能力是无刷同步发电机的重要性能要求。在发电机发生突然短路时,发电机控制器需要配合无刷同步发电机进行短路电流控制,在保证足够的短路电流输出能力的同时也要避免短路电流过大损坏电机。针对无刷同步发电机可能发生的5种短路类型进行了分析,提出梯形电压电流的控制目标曲线,利用无模型自适应控制算法进行短路电流控制,使发电机能在发生各种类型的突然短路故障时输出符合要求的短路电流。建立了发电机和控制器的仿真模型,进行无模型自适应控制方案的仿真验证,同时搭建了实验平台进行实验验证。经过验证无模型自适应算法可以将无刷同步发电机的短路电流很好地控制在目标值,验证了该控制算法在发电机短路电流控制方面的有效性。

PCB罗氏线圈电流传感器积分误差的数字补偿策略

准确可靠的开关电流信息是电力电子变换器实现闭环控制、谐波抑制和短路保护的关键要素,有利于进一步提升功率器件的可靠性。PCB罗氏线圈电流传感器因其高带宽、小体积、低成本和低侵扰的特点,具有重要的研究价值和应用前景。然而,传统积分处理电路存在漂移误差与下垂误差,严重限制了PCB罗氏线圈电流传感器的测量精度。首先,本文采用复位型积分电路以避免漂移误差的持续累积,并消除下垂误差带来的影响。同时,针对复位型积分电路存在的漂移误差与偏置误差提出一种数字补偿策略,该方案采用数字信号处理器控制数模转化模块产生模拟补偿信号,并通过高速减法器消除误差,具有补偿精度高、调整方式简单的优点,可以大幅减小积分误差造成的影响;最后,基于双脉冲测试平台分别进行双脉冲、多脉冲和短路保护实验,验证了所提PCB罗氏线圈电流传感器的性能。

基于自适应滑模观测器的中点钳位型三电平并网逆变器开关管和电流传感器故障诊断

为提高中点钳位型三电平(3L-NPC)并网逆变器故障诊断的准确性和可靠性,针对其开关管开路故障和电流传感器故障,提出一种基于自适应滑模观测器的开关管开路故障和电流传感器故障同时诊断方法。该方法首先针对3L-NPC并网逆变器,设计一种收敛速度快且能显著抑制抖振的自适应滑模观测器来精确估计正常状态下的三相电流值;其次,利用实际电流和估计电流设计了故障检测变量;同时,利用实际三相电流之和以及估计三相电流之和来区分开关管故障和电流传感器故障;在此基础上,构造开关管故障定位变量和电流传感器故障识别变量,实现开关管开路故障的准确定位以及电流传感器故障类型的快速识别。实验结果验证了该文所提诊断算法的有效性和鲁棒性。

脉冲涡流检测激励电源设计

脉冲涡流检测是当前金属材料无损检测主要的方法,激励电源作为系统中的关键部分,其性能将直接影响到检测结果。针对现有材料缺陷脉冲涡流检测方法中激励电源存在关断时间长、无恒流控制、功率小等问题,对非磁性材料的缺陷检测方法进行了研究,提出了一种新的脉冲电源电路,采用线性调整型恒流源,实现恒流与恒压钳位的复合电路拓扑结构。首先对线性单元进行闭环分析,证明了电路的可行性,再通过样机实证,验证了脉冲电源的稳定性和快速性。脉冲电源的幅值在20 A内可调,幅度误差小于1%,能够快速关断,下降时间可达纳秒级。最后利用该脉冲电源组成了一套脉冲涡流检测系统,并对铝合金进行了裂纹缺陷模拟检测实验。通过提取探测器峰值电压发现系统能够准确地识别不同缺陷深度,且具有较高的分辨率。