测量阻抗轨迹和阻抗继电器性能的研究

为了精确计算测量阻抗随过渡电阻变化的轨迹,本文利用解析分析的方法对双端系统不同故障类型下送、受端正反向故障时的测量阻抗轨迹进行了详细的计算分析,并以姆欧继电器和四边形特性的距离继电器为例简要分析了其稳态动作行为。本文所得到的测量阻抗随过渡电阻变化的轨迹为分析阻抗继电器的动作行为提供了理论依据,对距离继电器的设计制造部门也具有一定的指导作用。     

新型自适应距离继电器

距离保护测量到的阻抗由于受对侧系统助增电流的影响会偏离故障线路的实际值,从而引起距离保护发生超越或者缩短保护距离。实际应用中往往利用零序电抗元件来解决这个问题,但对于相间故障则无能为力。通过分析发现,无论对于相间故障还是接地故障,当线路经过渡电阻故障时,距离保护测量阻抗随着过渡电阻变化的轨迹是一段圆弧,利用故障前保护测量到的电压、电流量可以估算出其圆心和半径。文中利用对阻抗变化轨迹的估算,提出了一种基于自适应电抗元件的四边形距离继电器的原理以及实施方案。理论分析和仿真计算都表明,所提出的自适应距离继电器除了能够有效防止区外经过渡电阻故障时发生超越,在区内故障时其耐受过渡电阻的能力也较常规四边形继电器有所提高。     

过渡电阻对距离保护的影响

分析了过渡电阻对单相接地和相间故障时距离保护测量阻抗的影响,提出了通过采集同一时刻故障线路两侧电流、母线电压的补偿算法,消除过渡电阻对测量阻抗的影响。     

现代距离保护技术的最新发展——高阻接地故障保护

文章基于负序电流、零序电流和负序零序复合电流,提出了一种适用于单相接地故障的距离继电器故障阻抗测量新原理。新原理基于假设:输电线路故障时,过渡电阻是纯电阻性的,故障点电压和故障分支电流同相位。新算法不受过渡电阻、负荷电流、系统振荡的影响。PSCAD仿真表明本文算法的精确性。     

基于阻抗轨迹估计的自适应相间距离继电器

在双电源系统中，由于对侧系统助增电流的影响，保护测量到的阻抗会偏离故障线路的实际值，从而引起距离保护发生超越或缩短保护距离。正向经过渡电阻故障时，距离保护测量阻抗随着过渡电阻变化的轨迹可以利用故障前保护测量到的电压、电流，经过估算得到。通过对阻抗变化轨迹公式的推导和分析，提出一种基于阻抗轨迹估计的自适应四边形距离继电器的原理及实施方案。该继电器利用故障前系统正常运行时电压和电流的测量值，实时估计出阻抗变化轨迹，并自动调整继电器的动作特性。理论分析和仿真计算表明，提出的自适应距离继电器可应用于相间距离保护，可有效防止区外经过渡电阻故障时发生超越，同时在区内故障时提高耐受过渡电阻能力。     

一种消除过渡电阻影响的阻抗测量方法

双端供电系统当线路发生单相接地故障时,由于过渡电阻的存在会造成阻抗测量不准确,引起距离保护的不正确动作。首先运用相量图的方法,定性分析了保护位于送电侧和受电侧时,过渡电阻引起阻抗测量误差的原因;为了减小过渡电阻引起的测量阻抗误差,基于全周傅氏算法提出了利用保护安装处负序电流相位代替故障点处故障电流相位的方法,并通过传统阻抗测量方法的改进,在高阻接地的情况下也能够比较准确地求得测量电抗值。EMTDC仿真表明,与传统的计算方法相比,该算法能有效地减小过渡电阻对测量阻抗的影响,保证测量阻抗的准确性。     

高压长线的分布参数模型与测量阻抗

本文介绍了分布参数的数学模型计算高压长线故障的方法，并以线路单相故障为例进行故障计算，探讨了接地阻抗继电器感觉的阻抗和负荷状况，接地电阻对测量阻抗的影响。     

正序电压极化阻抗继电器的保护失效边界模型

提出一组以故障距离和过渡电阻大小为核心因子的保护失效边界模型,用以评估阻抗继电器的耐受过渡电阻能力,同时用于探讨阻抗继电器因过渡电阻而拒动和误动的真实原因。重点分析正序电压极化的阻抗继电器,其具有保护区稳定、耐受过渡电阻能力强等优点。定义了能够使继电器正确动作的最大耐受过渡电阻值为保护失效边界电阻。根据保护失效边界模型计算出保护失效边界电阻值和相应的故障距离,用以绘制保护失效边界电阻曲线,再引入保护失效系数的概念,以此评估该继电器的耐受过渡电阻能力以及抗风险能力。PSCAD仿真结果表明,该模型可准确计算出继电器能承受的最大过渡电阻数值。     

距离保护特性元件躲过渡电阻能力分析与研究

对距离保护元件,由于存在过渡电阻,单侧电源线路经短线路出口故障或双侧电源的线路故障,容易引起距离保护拒动或误动。分析了过渡电阻对距离保护工作的影响,探讨了接地及相间距离继电器这种受过渡电阻影响较大的元件阻抗圆特性躲过渡电阻能力改进,以及几种较好的躲过渡电阻特性,指出将这些特性组合起来将具有很好的躲过渡电阻的能力。     

高压输电线路距离保护克服过渡电阻能力研究

高压输电线路中存在较大的过渡电阻,很容易引起距离保护拒动或误动.分析特高压单侧电源经长线路出口故障和双侧电源长线路出口故障时过渡电阻对距离保护工作的影响,探讨单侧电源助增电流网络、外汲电流网络中过渡电阻对测量阻抗的影响,并给出2种网络结构在不同地点处保护测量阻抗的计算公式.研究能较好躲过渡电阻特性的零序电抗继电器、自适应接地距离继电器、神经网络距离继电器,分析比较不同方法的优缺点及适用场合.     

基于改进小波包熵的SSSC串补线路故障位置识别

静态同步串联补偿器(SSSC)的应用会对距离保护的测量阻抗产生影响,使得距离保护发生拒动或超越.文中采用改进小波包熵分析了SSSC串补线路保护安装处的暂态故障电流特征,结果表明:故障点在SSSC之前和之后时串补线路的小波包熵值明显不同,故障点在SSSC之前的小波包熵值远大于故障点在SSSC之后时的小波包熵值.根据该特征...     

静止同步串联补偿器控制方式及特性研究

基于dq同步旋转坐标系建立静止同步串联补偿器(static synchronous series compensator,SSSC)的数学模型,采用电压外环电流内环的双环控制实现对SSSC的控制。基于IEEE次同步谐振第1标准测试系统,考虑仅由固定电容提供串补及其中部分由SSSC提供串补的2种补偿方案,利用测试信号法计算2种补偿方案下发电机组的次同步阻尼特性,并进一步分析SSSC在次同步频率范围内的阻抗特性。研究表明：次同步频率下串有SSSC支路的阻抗特性与串有等值电容支路的阻抗特性相似,但SSSC所呈现的容抗小于固定电容的容抗,且SSSC还呈现较大的电阻分量。因此,串有SSSC的系统次同步谐振点将偏移,且谐振点附近的负阻尼大大减小,这将有利于缓解次同步谐振(subsynch- ronous resonance,SSR)。     

基于功率传递的同期并列装置实现SSSC功能的仿真

本文针对基于功率传递的电网间同期并列装置转换为静止同步串联补偿器的复合系统,建立了并网装置转换为SSSC后的等效模型,根据SSSC既可进行容性补偿又可进行感性补偿的双重补偿的特点,分析了SSSC调节潮流的过程以及接入SSSC前后输电线路电流的变化情况。为减小短路故障情况下短路电流对系统的影响,本文利用SSSC可等效为感性阻抗的特点对不同短路故障电流进行了限制,从而提高了现有设备的综合利用率。在PSCAD/EMTDC中搭建了含SSSC的等效模型,仿真结果表明SSSC可有效调节线路输送的潮流,并验证了当系统发生短路故障时SSSC具有一定的限流功能。     

Digital distance protection of transmission lines in the presence of SSSC

In this paper the impact of Static Synchronous Series Compensator (SSSC) on the impedance calculated by distance relay is investigated. Analytical results are presented and verified by detailed simulations. Six different phase to phase and phase to ground measuring units of the distance relay are simulated to resemble the behavior of the relay. It is shown in this paper that zero sequence of the injected voltage by 48 pulse SSSC converter has the most impact on the apparent impedance seen by the phase to ground fault measuring unit and cause under reaching of distance relay. It can be concluded from the results that SSSC located in the middle of the transmission line cause to divide trip characteristics of distance relay into two separate parts. It is also shown that the over-reaching operation of distance relay might happen in some cases in the presence of SSSC. All the detailed simulations are carried out in MATLAB/Simulink environment.     

Active power based distance protection scheme in the presence of series compensators

Flexible ac transmission system (FACTS) controllers, especially the series-FACTS controllers, affect the operation of distance relays and can lead to the relays under/over-reaching. This paper aims to demonstrate the effects of static synchronous series compensator (SSSC) and series capacitive compensation (SCC), as two important series compensators, on the distance protection using theoretical and computational methods. The results of the investigation are used to develop a feasible and adequate method for eliminating the negative effects of these devices on the distance relays. The developed method measures the voltages at terminals of the SSSC and SCC by phasor measurement units (PMUs) which are then transmitted to the relay location by communication channels. The transmitted signals are used to modify the voltage measured by the relay. Different operation types and conditions of SSSC and SCC, and different faults such as phase-to-phase and phase-to-ground faults are investigated in simulations. Since the modeled distance relay can measure the fault resistance, trip boundaries are used to show the performance of the presented method. Results show that the presented method properly eliminates the negative effects on the distance relays and prevents them from mal-operation under all fault resistance conditions.     

Optimal economic operation of isolatedcommunity microgrid incorporatingtemperature controlling devices

Flexible ac transmission system (FACTS) controllers, especially the series-FACTS controllers, affect the operation of distance relays and can lead to the relays under/over-reaching. This paper aims to demonstrate the effects of static synchronous series compensator (SSSC) and series capacitive compensation (SCC), as two important series compensators, on the distance protection using theoretical and computational methods. The results of the investigation are used to develop a feasible and adequate method for eliminating the negative effects of these devices on the distance relays. The developed method measures the voltages at terminals of the SSSC and SCC by phasor measurement units (PMUs) which are then transmitted to the relay location by communication channels. The transmitted signals are used to modify the voltage measured by the relay. Different operation types and conditions of SSSC and SCC, and different faults such as phase-to-phase and phase-to-ground faults are investigated in simulations. Since the modeled distance relay can measure the fault resistance, trip boundaries are used to show the performance of the presented method. Results show that the presented method properly eliminates the negative effects on the distance relays and prevents them from mal-operation under all fault resistance conditions.     

Impacts of the SSSC control modes on small-signal and transient stability of a power system

In order to accomplish specific compensation objectives a static synchronous series compensator (SSSC) may be controlled by several ways. The most common control modes of the SSSC are: (1) constant voltage mode, (2) constant impedance emulation mode, and (3) constant power control mode. Moreover, to improve the dynamic performance of the system, a SSSC may be equipped with supplementary controllers, such as damping controls. Therefore, this paper investigates the impacts of different SSSC control modes on small-signal and transient stability of a power system. The performance of different input signals to the power oscillation damping (POD) controller is also assessed. The stability analysis and the design of the SSSC controllers are based on modal analysis, non-linear simulations, pole placement technique, and time and frequency response techniques. The results obtained allow to conclude that the usage of the SSSC in the constant impedance emulation mode is the most beneficial strategy to improve both the small-signal and transient stability.     

A new method for measurement of earth fault loop impedance

A novel method for accurate and quick measurement of earth fault loop impedance in a low-voltage system is presented. The theoretical principle of the method is based on sampling of the tested circuit voltage at properly chosen moments. The method makes possible the simultaneous measurement of impedance, resistance, and reactance. The digital display is calibrated such that quantities can be read directly     

H桥级联式SSSC阻抗补偿域及准稳态模型

根据电压源模型及电流源模型的各自特点,提出了在数学分析中将外接系统等效为电流源模型,而在仿真中采用电压源模型的静止同步串联补偿器(SSSC)电力系统分析等效方法.根据调制比的变化规律,计算出了考虑稳态最大允许电流的H桥级联式SSSC在不同调制方式下的阻抗补偿域.计及直流侧电压波动及脉冲触发时刻,推导了在一定参考阻抗下H桥级联式SSSC输出电压的准稳态数学模型.最后,通过RTDS及EMTDS/PSCAD仿真及实验验证了计算结果的正确性.     

STATCOM与SSSC改善电力系统阻尼的比较研究

电力系统故障过程中暂态能量的消失速率可以作为系统能否快速到达静态平衡点的一个标准,同时也可以看作系统阻尼的一个指标。基于这个理论,针对静止无功补偿器(STATCOM)和静止同步串联补偿器(SSSC)在系统故障过程中对系统作用的不同,分析并得出了一个单机无穷大系统故障过程中STATCOM与SSSC向系统提供的附加阻尼的表达式。仿真结果表明,STATCOM与SSSC都能够显著改善系统阻尼,但SSSC比STATCOM能更好地为系统提供阻尼,改善系统动态性能。