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.

Impact of Sensor Technology for Line Protection Performance

The paper has presented the impact on the line protection performance with the introduction of MUs （merging units） in the process bus level. The paper begins with the introduction on modem digital substation structure and process bus. Then, the paper describes the performances of different sensors such as CTs （current transformers）, CVTs （capacitive voltage transformers）, FOCS （fiber optical current transducers） and FOVS （fiber optical voltage transducers）. With the use of above transducers together with MUs, the performance of distance protection function and line differential protection function have been investigated and presented. Finally, conclusions based on the study are presented in the paper.

Traveling Wave Characteristics Based Pilot Protection Scheme for Hybrid Cascaded HVDC Transmission Line

The hybrid cascaded high-voltage direct current(HVDC)transmission system has various operation modes,and some operation modes have sharply increasing requirements for protection rapidity,while the traditional pilot differential protection(PDP)has poor rapidity,and even refuses to operate when faults occur on the DC line.Therefore,a novel pilot protection scheme based on traveling wave characteristics is proposed.First,the adaptability of the traditional PDP applied in engineering is analyzed for different operation modes.Then,the expressions of the forward traveling wave(FTW)and backward traveling wave(BTW)on the rectifier side and the inverter side are derived for different fault locations.From the theoretical derivation,the difference between the BTW and FTW on the rectifier side is less than zero,and the same is true on the inverter side.However,in the event of an external fault of DC line,the difference between the BTW and FTW at nearfault terminal protection installation point is greater than zero.Therefore,by summing over the product of the difference between BTW and FTW of the rectifier side and that of the inverter side,the fault identification criterion is constructed.The simulation results show that the proposed pilot protection scheme can quickly and reliably identify the short-circuit faults of DC line in different operation modes.

基于初始电流行波相位的多端混合直流线路单端保护方案

为了解决LCC-MMC型多端混合直流系统线路保护存在的问题,提出一种基于初始电流行波相位的多端混合直流线路单端保护方案。首先基于多端混合直流输电线路发生不同位置和类型的故障工况,推导直流线路入射电压行波的解析式并计算其高频段相位。其次结合线路边界行波折反射原理和测量波阻抗特性,提出利用初始电压行波相位的区内外识别判据,并根据雷击和短路故障的入射行波低频相位特性构建雷击干扰判据。在PSCAD/EMTDC中搭建昆柳龙多端混合直流系统模型进行验证,证明所提方案仅利用单端量信息即可满足故障判断和选线要求,满足速度性的同时具备一定的抗过渡电阻能力(500Ω)。

基于行波电流极性差异的交直流混联系统纵联方向保护方法

交直流混联系统中逆变站的换相失败使交流线路发生频率偏移,导致工频量纵联方向保护的可靠性受到影响。提出了一种基于行波电流极性差异的交直流混联系统纵联方向保护方法,利用线路区内、外故障时,传播到两端保护的电流故障初始行波波头之间极性差异构成纵联保护。该方法仅利用电流初始行波极性差异进行方向判别,消除了电容式电压互感器无法准确传输宽频带电压信息导致保护的低可靠性问题,且利用高频电流进行计算,避免了交直流混联系统频率偏移的影响。仿真结果显示,基于行波电流极性差异的纵联方向保护方法能够准确、快速地识别单相故障和多相故障,适用于交直流混联系统。

逆变型新能源场站送出线时域方向元件

逆变型新能源暂态故障特征可能导致送出线保护近区故障时现有距离保护方向元件不正确动作。基于逆变型新能源故障期间输出的正序无功电流特征,文中提出了适用于逆变型新能源场站送出线的故障方向判据,通过比较故障时保护安装处正序无功电流计算值与参考值之间的欧氏距离区分正、反向故障。仿真结果表明,提出的方向元件在各种故障场景下都能够准确地判断保护近区故障方向。

基于衰减指数的主动配电网纵联保护新方法研究

根据光伏并网系统中光伏与大系统电源故障输出特性的差异,提出一种基于电流衰减指数的主动配电网保护新原理.首先对采集的保护线路首、末端电流进行滤波、去噪,以避免噪声造成Prony计算不精确的问题;再将线路首、末端电流衰减指数作差与给定门槛值比较,以便判断故障区域;最后通过改变故障位置、故障距离以及光伏渗透率,验证该方法在不同情况下的适用性.通过Matlab仿真实验表明本文提出的方法能够准确判断线内、线外故障,并且其对判断故障相有一定效果.

基于T区中低频衰减特性构成方向元件的特高压三端混合直流输电线路单端方向保护研究

将保护装置安装在T区两侧,基于T区中低频衰减特性构成方向元件,提出一种特高压三端混合直流输电线路单端方向保护方法。分析特高压三端混合直流输电系统整流侧、T区以及线路末端逆变侧三端边界频率特性,发现T区边界对故障电流暂态信号中低频分量有一定的衰减作用、整流侧边界和线路末端逆变侧边界对故障电流暂态信号高频分量有明显衰减作用。利用小波分解,根据T区两侧线路暂态电流中低频能量差判断故障方向,并提出故障方向判据。当T区左侧发生故障时,利用线路L1末端所检测到的高频暂态电流能量与低频暂态电流能量的比值来判别整流侧区内、外故障;当T区右侧发生故障时,利用线路L2首端所检测到的高频暂态电流能量与低频暂态电流能量的比值来判别线路末端逆变侧区内、外故障;T区发生故障时,判定为线路区外故障。给出基于T区中低频衰减特性构成方向元件的特高压三端混合直流输电线路单端方向保护方案,最后在PSCAD/EMTDC仿真平台搭建昆柳龙特高压三端混合直流输电系统模型并对所提保护方法进行验证,仿真表明该文所提保护方法能实现特高压三端混合直流输电线路全线速动保护。

架空-电缆混合线路接地故障距离保护整定研究

针对架空线与电缆的线路参数不均一,提出了架空-电缆混合线路接地距离保护的整定优化方法。分析了零序电流补偿系数对测量阻抗的影响,两侧保护分别采用从母线起混合线路全长70%的正序阻抗和零序阻抗来计算零序电流补偿系数;分析了故障处于不同位置时,架空线侧和电缆侧的保护所采集的故障相电压波形特征,发现电缆侧保护所采集的故障相电压含有较大幅值的非整次谐波,故架空线侧保护采用从母线起线路全长70%的正序阻抗作为整定阻抗,而电缆侧保护采用整条线路正序阻抗的70%作为整定阻抗。利用PSCAD建立了架空-电缆混合线路模型并进行故障仿真,结果表明,该方法可有效提高架空-电缆混合线路接地距离保护Ⅰ段的灵敏性。

基于高阻接地距离继电器的零序电流保护选择性提升方案

交流线路零序电流保护最末一段均采用300 A定值,存在无序跳闸风险。因此,文中提出了基于零序电抗线和非故障相极化的高阻接地距离继电器原理。继电器采用先选相、后测量的技术路线,选相元件将零序电抗线与非故障相极化方法相结合,构成多种组合判据,以分工完成选相。由于保护安装处零序电流与故障点零序电流存在相位差异,单相接地故障的故障相和相间接地故障的超前相的零序电抗线在故障点位于整定点附近时存在混叠区。区内近端、低阻单相接地故障时非故障相工作电压大幅变化,不利于区分混叠区的两类故障,故将选相元件分为低阻模块和高阻模块。低阻模块采用下偏的零序电抗线,用于识别近端、低阻故障;经低阻模块辅助后,高阻模块只需针对性处置故障点位于整定点附近的故障,可有效区分两类故障。选相完成后,通过非故障相极化的方法获得故障前工作电压,从而确定继电器的动作特性。高阻距离继电器的耐过渡电阻能力远超规程要求,提高了接地后备保护对高阻接地故障的选择性。

常规直流逆变站交流送出线路距离保护适应性分析与对策

常规直流逆变站交流送出线路故障通常会引发换相失败,存在故障电压和电流波形畸变等问题,可能导致工频相量距离保护性能劣化。首先,分析了工程中广泛应用的正序电压极化距离保护在常规直流逆变站交流送出线路中的适应性,分析结果表明,当逆变站运行于单回交流出线工况时,传统正序电压极化距离保护不再适用;然后,基于交流线路的RL模型,提出了基于波形相关系数的时域距离元件,可以不受逆变站非线性输出特性的影响,并针对时域距离元件存在的出口近区故障方向判别问题,利用电流畸变程度判断故障方向;最后,通过仿真验证了时域距离保护方案的有效性。

Single-end Protection Scheme Based on Transient Power Waveshape for Hybrid HVDC Transmission Lines

The recent in-depth development of hybrid highvoltage direct current(HVDC) transmission systems poses looming adaptability challenges to protection. The various and disparate direct current(DC) transmission topologies can profoundly affect the operating characteristics of DC transmission networks, which result in the lack of performance of conventional DC protection schemes in such topologies. This significantly limits the application of hybrid HVDC technologies. This paper proposes a single-end protection scheme based on the transient power waveshape for fast and sensitive detection and classification of different types of DC faults in hybrid HVDC transmission lines. The fault characteristics and their causes under different fault conditions are analyzed in detail with a pre-introduced linearized transient model of a hybrid HVDC transmission system, demonstrating that the formation of the fluctuation characteristics of local measurements is mainly determined by the buffering and absorption effects of lumped-parameter reactors on transient traveling-wave(TW) energy. Simulation results verify the sensitivity, rapidity, reliability, and anti-interference ability of the proposed scheme when applied to hybrid HVDC transmission lines. Furthermore, it is confirmed that the proposed scheme is adaptable to symmetric voltage-sourced converter(VSC) and conventional line-commutated converter(LCC) based HVDC transmission lines.

A Similarity Comparison Based Pilot Protection Scheme for VSC-HVDC Grids Considering Fault Current Limiting Strategy

In the voltage source converter based high-voltage direct current(VSC-HVDC)grids,fast and reliable protections are the key technologies.The traditional protection schemes are easily affected by fault resistance,line distributed capacitance,etc.Meanwhile,the influence of fault current limiting strategy(FCLS)has not been fully considered.In this paper,the fault characteristics under FCLS and the feasibility of traditional travelling wave protections are analyzed.To improve the reliability and sensibility,a similarity comparison based pilot protection scheme is proposed,which focuses on the relationship between the fault characteristics and the state of the protected transmission line,with the establishment of a precise frequencydependent transmission line model.The criteria based on the similarity comparison calculated by cross-wavelet can identify the fault effectively.Meanwhile,the protection scheme can also endure the influence of error synchronization.Finally,the protection performance is verified in the PSCAD/EMTDC under different fault conditions.

基于故障串电流反向突变判据的光伏阵列线间故障保护方案

光伏阵列发生线间故障时故障电流较小,过电流保护无法有效清除故障。提出一种基于光伏串输出电流反向突变特性的光伏阵列线间故障保护方案。基于光伏串输出电流-电压曲线定性分析了光伏阵列发生线间故障时输出电压、电流的变化特性,得到光伏阵列线间故障下光伏串输出电流反向减小特征。通过光伏串等效电路模型,建立了光伏串输出电流与光伏串故障电池数量之间的量化关系。以最小故障电池数量的电流突变为阈值,提出了基于故障电流反向突变的保护判据。该保护判据可快速准确地定位光伏阵列中的故障串,且只需要测量光伏串的输出电流信号以及光伏阵列输出的电压信号,保护配合只需要跳闸信号。最后,通过时域仿真以及现场测试有效验证了所建立判据的准确性以及所提出的保护方案的正确性。

利用电压变化特征的识别电力系统振荡的方法

电力系统发生振荡时交流线路距离保护的测量阻抗会进入动作区,导致距离保护误动作。目前我国线路距离保护I段和II段采取了振荡闭锁措施,以防止保护误动作,但是需要人工计算静稳电流定值,整定难度大;此外,线路处于重负荷状态时,会误闭锁距离保护,闭锁期间,线路故障无法切除。该文分析了系统振荡期间保护安装处电压余弦分量(Ucosφ)特征,系统振荡期间,Ucosφ变化范围是[-1 p.u.,1 p.u.];正常运行时,|Ucosφ|变化范围是[0.707 p.u.,1 p.u.];线路发生故障后,Ucosφ固定且数值较小,根据上述特征差异,提出了利用Ucosφ识别系统振荡与线路故障的方法。该方法利用Ucosφ替代静态稳定电流,无需人工整定,自适应识别系统振荡及线路故障,在系统振荡且会导致距离保护误动时,闭锁距离保护;线路故障时,可靠不闭锁距离保护,利用实时数字仿真系统进行了仿真验证。

基于自定义电流突变量的高压直流输电线路纵联保护原理

直流线路保护是直流输电技术发展的关键问题,其主要技术难点在于快速可靠地识别线路故障。电流差动保护受分布电容电流影响明显,需要延时、动作速度慢;而现有的其他纵联保护在对边界元件的依赖程度、过渡电阻耐受能力和抗干扰能力上仍有提高空间。针对上述问题,分析了高压直流输电线路电流突变量的故障暂态特征,并定义了一个新的电流突变量概念,利用自定义电流突变量的极性特征识别区内外故障;在此基础上,提出了一种基于自定义电流突变量的高压直流输电线路纵联保护方案。最后,通过PSCAD/EMTDC仿真模型对所提保护方案进行了仿真验证。仿真验证表明,所提保护无需延时即可正确识别区内外故障,还带有故障选极的效果,且不依赖于边界元件,过渡电阻耐受能力高、抗干扰能力强,具有较高的灵敏性和可靠性。

地铁直流进线振荡电流识别算法研究

针对地铁直流进线的振荡电流容易引起继电保护系统频繁误动作的问题,文章提出以变分模态分解、样本熵、TOPSIS为核心的故障诊断分析算法,并搭建实时数字仿真试验平台,以地铁继电保护装置为应用场景,通过将改进的进线保护算法与传统逆流保护算法进行试验对比分析,验证了方法在工程实践中的可行性和有效性。结果表明,该方法可有效识别直流进线特殊振荡电流,提高继电保护的可靠性。

±800 kV直流线路工程邻近带电体架线施工防护研究

考虑直流输电线路邻近带电体架线施工风险,利用表面电荷法得到导线表面电场强度数学模型,应用有限元计算了邻近±800 kV直流输电线路和T型塔的空间电场分布情况,给出了架线施工时邻近线路和T型塔的最小关注距离。研制了直流电场安全监控报警装置并用于验证有限元仿真结果;依托昌吉–古泉±1000 kV特高压直流工程甘3标段完成了装置功能验证,结合验证结果给出了邻近带电体施工管控措施。研究结果可为邻近带电体架线安全施工提供技术参考。

简析室外道路照明电缆截面积的选择

结合实际案例,阐述选择室外道路照明电缆截面积时,除考虑电缆载流量及线路电压损失外,还应考虑断路器的保护灵敏性,通过分析影响断路器保护灵敏性的因素,提出室外道路照明电缆截面积的选择建议。

基于电磁抑制法的架空输电线路防雷装置研究

为进一步提升架空输电线路耐雷水平,解决传统防雷装置在降低雷电流幅值方面存在的不足,采用电磁抑制法可有效降低雷电流波形陡度和入地电流峰值的新型防雷装置。对新型防雷装置结构及电气进行了设计,研究了通流线圈及装置制造工艺,最后制作了装置样机并开展模拟试验。结果表明,相较于传统防雷装置,新型防雷装置雷电流波形陡度降低幅度达54%,雷电流入地峰值降低幅度达26%,且适应于多种铁塔角钢尺寸、方向的安装,可有效降低架空输电线路遭受雷电绕击和反击概率。