Single-phase-to-ground fault protection based on zero-sequence current ratio coefficient for low-resistance grounding distribution network

Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to their high settings of the action value when a high-impedance grounding fault occurs.In this study,the relationship between the zero-sequence currents of each feeder and the neutral branch was analyzed.Then,a grounding protection method was proposed on the basis of the zero-sequence current ratio coefficient.It is defined as the ratio of the zero-sequence current of the feeder to that of the neutral branch.Nonetheless,both zero-sequence voltage and zero-sequence current are affected by the transition resistance,The influence of transition resistance can be eliminated by calculating this coefficient.Therefore,a method based on the zero-sequence current ratio coefficient was proposed considering the significant difference between the faulty feeder and healthy feeder.Furthermore,unbalanced current can be prevented by setting the starting current.PSCAD simulation results reveal that the proposed method shows high reliability and sensitivity when a high-resistance grounding fault occurs.

Single-phase earth fault current distribution between optical fiber composite overhead ground wire and ordinary ground wire in transmission system

It is important for the safety of transmission system to accurately calculate single-phase earth fault current distribution.Features of double sided elimination method were illustrated.Quantitative calculation of single-phase earth fault current distribution and case verification were accomplished by using the loop method.Influences of some factors,such as single-phase earth fault location and ground resistance of poles,on short-circuit current distribution were discussed.Results show that:1) results of the loop method conform to those of double sided elimination method;2) the fault location hardly influences macro-distribution of short-circuit current.However,current near fault location is evidently influenced;and 3) the short-circuit current distribution is not so sensitive to the ground resistance of poles.

The Research on Grounding Protection for 110kV Resistance Grounding Distribution System

Using the neutral grounding method by the resistance in 110?kV system, it can limit the voltage sag and short circuit current when one-phase grounding fault occurred, but it will change the sequence of the network structure and parameters. This paper analyzes the size and distribution of zero sequence voltage and current when one-phase grounding fault occurred in the 110 kV resistance grounding system, and puts forward the grounding protection configuration setting principle of this system combining the power supplying characteristics of 110?kV distribution network. In a reforming substation as an example, the grounding protection of 110 kV lines and transformer have been set and calculated.

Protection of Zero-Sequence Power Variation in Mountain Wind Farm Collector Lines Based on Multi-Mode Grounding

The arc-suppression coil(ASC)in parallel low resistance(LR)multi-mode grounding is adopted in the mountain wind farm to cope with the phenomenon that is misoperation or refusal of zero-sequence protection in LR grounding wind farm.If the fault disappears before LR is put into the system,it is judged as an instantaneous fault;while the fault does not disappear after LR is put into the system,it is judged as a permanent fault;the single-phase grounding fault(SLG)protection criterion based on zerosequence power variation is proposed to identify the instantaneous-permanent fault.Firstly,the distribution characteristic of zero-sequence voltage(ZSV)and zero-sequence current(ZSC)are analyzed after SLGfault occurs in multi-mode grounding.Then,according to the characteristics that zero-sequence power variation of non-fault collector line is small,while the zero-sequence power variation of fault collector line can reflect the active power component of fault resistance,the protection criterion based on zero-sequence power variation is constructed.The theoretical analysis and simulation results show that the protection criterion can distinguish the property of fault only by using the single terminal information,which has high reliability.

Fault protection method of single-phase break for distribution network considering the influence of neutral grounding modes

With the rapid development of modern distribution network and the access of distributed generation,the network structure is becoming increasingly complex.Frequent single-phase break faults have seriously affected equipment and personal safety and stable operation of the power system.However,with the development and application of the composite neutral grounding modes,the protection of single-phase break fault is facing new challenges.This paper proposes a protection method of single-phase break fault for distribution network considering the influence of neutral grounding modes.The characteristics of neutral voltage and sequence current are analyzed under normal operation and single-phase break fault with different grounding modes.Following this,the protection criterion based on neutral voltage and sequence current variation is constructed.The protection method of singlephase break fault for distribution network is proposed,which is applicable for various neutral grounding modes.Theoretical analysis and simulation results show that the protection method is less affected by system asymmetry,fault location and load distribution.The method has higher sensitivity,reliability and adaptability.

Fault Line Selection Method Considering Grounding Fault Angle for Distribution Network

In the distribution network system with its neutral point grounding via arc suppression coil, when single-phase grounding fault occurred near zero-crossing point of the phase voltage, the inaccuracy of the line selection always existed in existing methods. According to the characteristics that transient current was different between the fault feeder and other faultless feeders, wavelet transformation was performed on data of the transient current within a power frequency cycle after the fault occurred. Based on different fault angles, wavelet energy in corresponding frequency band was chosen to compare. The result was that wavelet energy in fault feeder was the largest of all, and it was larger than sum of those in other faultless feeders, when the bus broke down, the disparity between each wavelet energy was not significant. Fault line could be selected out by the criterion above. The results of MATLAB/simulink simulation experiment indicated that this method had anti-interference capacity and was feasible.

Accident of Large-scale Wind Turbines Disconnecting from Power Grid and Its Protection

There were many accidents of large-scale wind turbines disconnecting from power grid in 2011.As singlephase-to-ground fault cannot be correctly detected,single-phase-to-ground fault evolved to phase-to-phase fault.Phase-to-phase fault was isolated slowly,thus leading to low voltage.And wind turbines without enough low voltage ride-through capacity had to be disconnected from the grid.After some wind turbines being disconnected from the grid,overvoltage caused by reactive power surplus made more wind turbines disconnect from the grid.Based on the accident analysis,this paper presents solutions to above problems,including travelling waves based single-phase-to-ground protection,adaptive low voltage protection,integrated protection and control,and high impedance fault detection.The solutions lay foundations in theory and technology to prevent large-scale wind turbines disconnecting from the operating power grid.

风电场集电线路单相接地故障柔性电压消弧与动态保护新原理

为解决风电场集电系统长期存在的线路单相接地故障处理难题,提出风电场中性点柔性接地方式,理论推导获得柔性接地风电场三序等效电路,与集电线路单相接地故障复合序网模型,建立风电场零序电压柔性调控理论,提出集电线路单相接地故障柔性电压消弧方法,可主动将故障点电压及故障残流迅速抑制到零,实现单相接地故障电弧的可靠消除。进一步提出基于零序电流动态增量的高阻故障辨识与保护方法,通过柔性调控零序补偿电流,逐渐放大故障残流,实现永久性单相接地故障的灵敏感知与保护。利用PSCAD/EMTDC搭建含双馈异步风电机(doubly-fedinduction generator,DFIG)的规模化风电场模型,模拟多种运行与故障条件对所提方法进行验证,仿真结果表明,该方法能够在考虑系统不平衡电压的情况下精准调控集电线路故障点电压,实现瞬时性单相接地故障快速可靠消弧,动态感知并持续抑制永久性单相接地故障残流,实现集电线路高阻接地故障的灵敏保护。该技术有望提升风电场运行灵活性与故障防御能力,有力保障新能源电能外送的持续性、可靠性。

基于单端分支系数的四端柔直环网线路保护方案

为提升直流线路保护在柔性直流环网中的速动性与可靠性,提出一种基于单端分支系数的保护方案。分析了不同故障位置下各换流阀提供的故障电流分量,并根据单端换流阀极线电流突变量构造分支系数,结果表明线路保护区内故障下的单端分支系数小于区外故障,利用该特征构造区内、外故障识别元件。在线路高阻接地致使主保护失效时,根据桥臂最大允许电流决定线路纵联后备保护的开放时限,以优化现有主、后备保护方案之间的时序配合方案,保障各种直流线路故障工况下,换流阀不间断运行。保护方案不依赖线路边界元件,算法简单,大量仿真结果表明,该方案有良好的耐受过渡电阻能力,能在换流阀闭锁前实现故障区域可靠识别。

灵活接地配电网单相接地故障全过程特征分析

为进一步明确灵活接地方式下的单相接地故障特征,给新型接地保护原理的研究提供理论依据,通过建立涵盖灵活接地配电网接地故障全过程的等值电路,分析系统内各检测点处典型故障电气量的幅值、相位特征及其在不同阶段内的变化规律。相比于中性点接地电阻投入之前,在不同故障情况下,故障点电流始终增大,系统零序电压及健全线路零序电流始终减小,而故障线路零序电流随故障点接地电阻的增大而先增大后减小。这与灵活接地方式推行的初衷并不完全相符,解释了目前现场常用的传统小电阻零序过电流保护效果不如理想预期的原因。数字仿真与现场人工试验均验证了本文所得结论的正确性。

针对海上风电场汇集线路单相接地故障的柔直侧新型距离保护方案

海上风电场汇集线路发生单相接地故障时,线路两侧短路电流分别由风电机组换流器和柔直换流器提供,由于正序、负序与零序网络串联,在传统大电网存在场景下不受控制影响的零序电流也将像正序和负序电流一样呈现幅值受限、相位受控特性,柔直侧距离保护无法正确识别单相接地故障。该文建立海上风电场汇集线路单相接地故障时的复合序网,分析汇集线路两侧故障特性,在不借助线路双端通信的前提下,利用柔直侧负序和零序电流准确求取风机侧零序电流。基于此,构建关于故障距离的方程,提出柔直侧新型距离保护方案,解决了双端均为逆变型电源的线路中零序电流受控导致距离保护性能下降的问题。此外,所提保护方案受风电场无功支撑策略、过渡电阻大小及性质影响小。测试结果表明,该保护方案可以准确识别海上风电场汇集线路区内外单相接地故障。

超、特高压交流线路反时限零序过流后备保护的整定建议

针对国家电网“六统一”线路保护装置,提出了超、特高压交流线路反时限零序过流保护的整定原则。反时限零序过流保护在保证灵敏性方面并无困难,整定原则的核心问题是解决选择性和速动性的矛盾。根据该保护的原理和逻辑提出了转折电流的概念以及接地距离保护与反时限零序过流保护的配合原则;充分考虑配合时间定值和最小时间定值对保护动作特性的影响,综合超、特高压电网实际短路电流水平和接地距离保护的过渡电阻耐受能力,将反时限零序过流保护低电流区的选择性与接地距离保护高电流区的选择性进行结合,提升了对接地故障全域电流范围的选择性切除能力;提出了方向元件投退原则。通过对某省级电网进行算例分析,验证了整定原则的有效性,该整定原则已经在实际电网中进行了应用。

西北电网330 kV尖樊线人工短路试验中接地距离保护适应性分析

以风电为代表的新能源场站的故障特征对传统距离保护的附加阻抗产生了新的影响,导致保护性能降低。而现有距离保护适应性研究缺乏对单相接地故障场景的分析。为此,结合西北电网于尖樊线进行的2次人工短路试验数据,基于多种控制策略下的风电场故障特征,分析单相接地故障下接地距离保护附加阻抗系数,进而判断保护适应性。研究发现网侧保护附加阻抗系数较小,两侧电源故障电流对保护影响较小;而风电场侧保护附加阻抗系数较大,两侧电源故障电流对保护影响较大,导致保护拒动。

高速铁路10 kV变配电所馈线保护方式优化研究

铁路10 kV变配电所地方进线电源一般为中性点不接地系统。高速铁路变配电所内的馈线、贯通线多为全电缆线路,发生单相接地故障后,馈线电缆零序保护不跳闸只报警,允许故障馈线带故障运行。然而,电力电缆的绝缘裕度比架空线路的绝缘裕度小得多,承受过电压的能力低,一旦发生单相接地故障,易引起永久性的绝缘击穿,进而发展成为相间故障,使故障范围扩大。本文提出高速铁路变配电所故障馈线小电流选线方法,可准确判断出发生电缆单相接地故障的馈线,避免故障扩大。对于高阻接地故障,提出了采用基于暂态量的综合选线方法,除比对故障和非故障线路的零序电流幅值和相位,还利用暂态无功功率方向进行准确选线。

变电站继电保护间歇性弧光接地故障识别方法

传统的间歇性弧光接地故障识别方法主要基于电气量进行故障识别,容易受到系统运行状态、负荷变化等干扰信号的影响,导致故障识别精度低等问题。为解决以上问题,首先需进行接地故障特征分析,然后基于故障特征提取间歇性弧光接地故障信号暂态量,通过包含弧光接地信息的暂态量进行弧光接地故障区段的定位,确定故障位置后即可根据暂态能量变化判别接地故障,实现对间歇性弧光接地故障的识别。试验结果表明:与小波变换法和傅里叶变换法相比,变电站继电保护间歇性弧光接地故障识别方法能识别故障发生的精确位置和持续时间,且识别精度更高,具有较高的实际应用价值。

自动化技术在分布式光伏发电配电网单相接地保护中的应用及经济性分析

基于相电流突变量特征分析方法,构建了一个基于MPC8313处理器与FPGA的自动化系统架构,实现了故障的高效检测和定位。通过实际应用于东南沿海地区的某海滨城市,研究发现该自动化系统显著缩短了故障响应时间,降低了年均故障次数,提高了供电可靠率。经济性分析显示,该自动化技术方案具有高净现值(NPV)和投资回报率(ROI),证明了其经济效益和投资价值。

基于发电机转子接地保护的可靠性分析与建议

上海某燃机电厂的发电机转子接地保护配置了两套注入式保护,分别为工频电压注入式及1~3 Hz低频方波注入式。由于两套转子接地保护之间在原理上相互影响,因此在运行中只投运一套(以1~3 Hz低频方波注入式转子接地保护为主),另一套保护备用。近期该厂#4发电机1~3 Hz低频方波注入式转子接地保护出现过两次保护回路故障报警,均由发电机转子接地碳刷接触不良引起。通过对该保护原理及保护回路逻辑的介绍,找出了转子接地保护回路故障的原因,并对发电机转子接地保护的可靠性进行分析,提出了相应的建议与措施。

路灯配电设计常见问题分析

路灯照明是城市建设中至关重要的一部分,对于保障行人和车辆的安全具有重要意义。而对于路灯照明来说,配电形式的选择和运行状态的稳定性是确保照明系统正常运行的关键。对路灯几种常见的路灯照明配电形式及其可能出现的故障进行分析,结果可为同类项目提供参考。

基于合后零序电压后加速跳闸的配电网保护方法

为提高对配电网小电流接地系统接地故障的处理能力,利用零序电压特征量,研究了一种基于合后零序电压后加速跳闸的配电网保护方法,从系统性、配合性、应用性等方面提供了解决方案,有效解决了当前配电网小电流接地系统的接地故障保护跳闸技术实现方式存在的问题,具有较好的应用效果。

光伏并网对配电网继电保护影响特性分析

光伏发电因其供电可靠性高且投资成本低的特征被广泛应用于发电产业,随着光伏并网规模不断增大,传统的继电保护特性发生改变,原有继电保护方案不再能够满足电网安全运行的要求。对光伏发电的基本特点进行分析。首先,分析了光伏并网前后各位置保护电流的变化特性。然后,基于故障工况分析了光伏并网后保护电流的变化对继电保护正确动作造成的影响,并分析了不同容量光伏电源并入工况下的保护电流变化特性。最后,基于MATLAB仿真软件对前述分析进行仿真验证,结果充分证明理论分析的正确性,研究成果对优化继电保护动作具有指导意义。