Studies on the active SISFCL and its impact on the distance protection of the EHV transmission line

The active saturated iron-core superconductive fault current limiter (SISFCL) is a good choice to decrease fault current. This paper introduced the principles and impedance characteristic of the active SISFCL. Then, it shows the current-limiting effects of the SISFCL. Besides, the impact of the active SISFCL on the distance protection of the EHV transmission line is evaluated. Based on that, the coordination scheme of the distance protections is proposed. A 500 kV double-circuit transmission system with SISFCLs is simulated by Electro-Magnetic Transients Program including DC (EMTDC). Simulation tests demonstrate the correctness and validity of theoretical analyses.     

Jiles–Atherton Hysteresis Approach in Analyzing the Effect of Field Suppression in Saturated Iron-core Superconducting Fault Current Limiters

Saturated iron-core superconducting fault current limiters (SISFCL) are becoming more popular in the recent years due to their ability of reliable, effective and instantaneous fault limiting. With a superior performance than conventional current limiting methods, the SISFCL is finding its application in modern transmission lines and distribution system. In the SISFCL, the iron core is forced into saturation using a superconducting coil carrying DC current. During a fault in the system, the high fluxes set up in the AC coils interact with the DC flux, thereby reducing the flux density abruptly. This sudden change in the flux density induces a high voltage across the DC coil, which may damage the DC current source as well as the superconducting material. As a protective measure, a field suppressor unit is used that disconnects the DC supply following a fault. In this paper, a mathematical model of the SISFCL is developed considering hysteresis and the effects of the field suppressor unit have been analyzed. The paper also aims to highlight the effects on the performance of SISFCL with varying hysteresis loops of the core material.     

计及故障点两侧零序电流相位差的新能源送出线路接地故障时域距离保护研究

新能源电源故障电流呈现弱馈性、强受控性并具有大量的间谐波,导致现有工频量距离保护可靠性下降,而时域距离保护主要根据方程求解故障距离,受新能源短路电流特性影响较小。针对新能源送出线路较长时,线路分布电容对零序电流相位的影响不可忽略,进而导致故障距离的计算产生较大偏差的问题,提出了一种计及故障点两侧零序电流相位差的新能源送出线路时域距离保护改进方案。首先,计及故障点两侧零序电流相位差的影响,将过渡电阻等效为过渡阻抗。然后,通过列写故障回路方程并求解故障距离,形成保护判据。最后,基于PSCAD/EMTDC大量仿真实验,验证了所提时域距离保护方案计算故障距离的误差较小,可以较好地适用于新能源经中长距离交流线路送出的场景。     

安装固态短路限流器后距离保护整定的改进方法

故障限流器在电力系统中应用时将对继电保护尤其是距离保护产生一定的影响。以带旁路电感变压器耦合三相桥式固态限流器为例,详细分析了其对距离保护产生的影响,提出了一种应用于装设固态限流器线路的距离保护整定新方法,并通过仿真验证了所提出的方法可以有效消除限流器对距离保护的不利影响。     

Analysis on the fault characteristics of three-phase short-circuit for half-wavelength AC transmission lines

Half-wavelength AC transmission(HWACT) is an ultra-long distance AC transmission technology, whose electrical distance is close to half-wavelength at the system power frequency. It is very important for the construction and operation of HWACT to analyze its fault features and corresponding protection technology. In this paper, the steady-state voltage and current characteristics of the bus bar and fault point and the steady-state overvoltage distribution along the line will be analyzed when a three-phase symmetrical short-circuit fault occurs on an HWACT line. On this basis, the threephase fault characteristics for longer transmission lines are also studied.     

正常运行方式下跨电压等级四回线零序电流补偿系数整定

跨电压等级同塔四回线路中某一条线路发生接地短路时,故障线路不仅受到同一电压等级非故障线路零序互感的影响,还受到不同电压等级线路零序互感的影响,同时对于超高压线路多采用长距离输电,电容电流的影响也不容忽视。综合分析了四回线路正常运行方式下,一线路发生接地短路时非故障线路零序互感和长线路零序电容电流对零序电流补偿系数的影响,根据公式提出了新的零序电流补偿系数整定方式。最后利用PSCAD仿真结果验证了本文方法更能准确地反映故障位置,且能使两侧的距离Ⅰ段保护范围有交叉,提高了线路接地距离保护性能。     

基于站域信息的同杆双回线接地距离保护优化方案

基于单间隔电气量的接地距离保护由于受到同杆双回线线间互感的影响,存在故障线路距离测量不准确、非故障线路易发生反方向误动和末端故障超越等问题.利用智能变电站中跨间隔站域信息高度共享的特点,构建了同杆双回线单元式保护配置方案,设计了过程层信息获取及交互的实现方案.利用双回线的断路器位置和接地刀闸位置信息自适应地选择零序补偿系数;利用双回线六相电流信息和六序分量法实现故障选线和选相,根据选线结果实现对故障线路的接地距离保护的邻线零序电流自适应补偿,而对非故障线路不再使用邻线零序电流补偿.理论分析和数字仿真验证表明,所提单元式配置和接地距离保护优化方案可以实现双回线中故障线路接地距离保护的自适应邻线零序电流补偿,并解决了盲目进行邻线零序电流补偿造成的非故障线路反方向误动的问题.     

全线相继速动单端保护新原理

在故障分析的基础上,提出一种新的输电线路单端全线故障速动保护判据。该判据利用非故障相上的故障电流分量的变化来判断对侧的保护动作情况,同时和故障相的距离保护相配合,构成全线相继速动保护。该判据在配置单相重合闸的线路和空载的情况发生故障有明显的优点。ATP仿真实验表明该判据灵敏度高、可靠性好。     

A Fault Location Algorithm Based on Circuit Analysis for Untransposed Parallel Transmission Lines

This paper proposes a fault-location algorithm for ultra-high-voltage untransposed parallel transmission lines that only use the voltages and currents at the local end. The proposed algorithm uses the voltage equation for the faulted phase of the faulted line. The equation contains the fault distance, fault resistance, and fault current. To obtain the fault current, Kirchhoff's voltage law is applied on the loops of three phases consisting of the faulted line and the adjacent parallel line. The fault current can be represented in terms of the fault distance. Inserting the fault current into the voltage equation results in an equation that contains only two parameters (i.e., the fault distance and fault resistance). The fault distance is estimated by solving the equation. Test results indicated that the algorithm accurately estimates the fault distance regardless of the fault resistance and mutual coupling effects.     

风电场送出线等传变距离保护

分析了具备低电压穿越(LVRT)能力的双馈式风电场送出线路故障暂态特性。风电送出线路风场侧保护测得的电压与电流主要频率分量不一致,致使传统的依据工频电压、电流相量的距离保护元件动作性能受到严重影响,无法正常工作。基于输电线路时域模型的解微分方程算法不涉及信号的频域信息,可以克服送出线电压、电流主频不同带来的影响,但受高频分量的影响较大。等传变距离保护相较传统的解微分方程算法,增加了低通滤波及故障点电压重构两个环节,显著改善了算法的测距性能。PSCAD/EMTDC仿真结果表明,线路不同位置处发生不同类型故障时,等传变距离保护算法均可以实现快速、准确测距。     

An accurate fault location algorithm for parallel transmission lines using one-terminal data

An accurate fault location algorithm for parallel transmission lines, using fundamental frequency components of post-fault voltage and current measured at one terminal, is described in this paper. Parallel transmission lines can be decoupled into the common component net and differential component net. In differential component net, the current distributing coefficient is a function of fault distance, and the differential component current at the fault point can be expressed in terms of the current at the local terminal. Therefore, for asymmetrical faults, the phase fault current can also be expressed as a function of local terminal current and fault distance. With the fault boundary conditions for a given fault type, the fault location equations can then be derived. Based on distributed parameter line model, the proposed algorithm achieves superior locating accuracy, with mutual coupling between circuits, source impedance and fault resistance having very little influence on the locating accuracy. The performance of new algorithm is verified by computer simulation results for transposed and non-transposed lines.     

基于PSCAD4.2软件的电力系统距离保护仿真分析

分析了输电线路距离保护的基本原理,并基于PSCAD4.2软件搭建了电力系统距离保护仿真模型,设置了输电线路可能发生的接地故障和相间故障,得出不同故障类型下输电线路的电压、电流以及其他量的变化规律的波形,仿真结果表明,利用该软件建立的模型能够准确反映距离保护的作用机理,即距离保护装置能够快速响应故障信号并动作于断路器,实现输电线路的保护。     

一种耐高阻和抗负荷电流影响线路单相接地距离保护

采用集总参数建模,利用保护安装处测量到的电气量计算保护安装处到接地故障点的电压降,根据线路保护安装处到接地故障点的电压降与故障距离呈线性关系计算接地故障距离和故障线路测量阻抗。该方法原理上消除了过渡电阻和负荷电流对阻抗距离保护动作性能的影响,适用于振荡工况。仿真分析和2套不同电压等级线路的故障录波数据测试表明,所提方法具有很强的耐受过渡电阻和负荷电流影响的能力,具有良好的现场实用价值。     

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.     

多串补线路保护动作性能分析

从理论上分析了多串补线路故障后的电气量特征,随着故障点的变化,线路多处会发生电流反相和电压反相,故障后电气量中存在多个低频暂态分量。研究了线路保护(电流差动保护和距离保护)的动作性能,提出了串补线路保护配置方案,并给出2点改进建议:一是采用保持记忆电压作为距离保护的极化电压,防止电压反相造成距离保护误动作;二是通过比较故障电流和记忆电压的相位来识别电流反相,当故障后电流相位超前记忆电压,判断为电流反相,闭锁电流差动保护。利用RTDS系统搭建了1 000 kV输电线路模型并进行了仿真验证,仿真结果与理论分析一致。     

Effects of VSC based HVDC system on distance protection of transmission lines

The priority to reactive power contribution from the Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) connection to support the grid during faults as suggested by the modern Network Code (NC) for HVDC affects the distance protection of transmission lines. Moreover, suppressing the negative sequence current during an unbalanced condition also interferes with the proper operation of the distance relays. This is because the current contribution from the converter is limited in magnitude and modified in the waveform in order to protect the power electronic devices during the fault in comparison to the synchronous generator fault current characteristics. This paper discusses the cause as well as the severity of the problems faced by the distance protection of transmission lines connected to the VSC based HVDC system by analyzing the apparent impedance analytically and in the simulation. The response of the relay to balanced and unbalanced faults lying on transmission lines is investigated. It is shown that the VSC limited reactive support and suppressed negative sequence current affect fault detection, forcing the relay to malfunction. The results of this paper can be used as a reference for understanding the effects of VSC-HVDC system on the operation of the distance protection during faults.     

Fault section detection system for 275-kV XLPE-insulated cableswith optical sensing technique

An on-line fault section detection system, which continuously monitors a 275-kV cross-linked polyethylene-insulated underground transmission line and instantaneously determines the section of fault at a ground fault, was developed. In the case of a ground fault, the system detects the fault current which flows from the power source to the point of ground fault and determines the fault section from the magnitude and phase information of the fault current. Optical magnetic field sensors based on the Faraday effect are used for detection of fault current, and optical fibers are used for signal transmission eliminating effects of electromagnetic induction due to a large ground fault current (5000-50000 A) or switching surges on signal transmission lines. The distance between an optical magnetic field sensor and the fault section detector/indicator can be as long as 10 km without the use of any repeaters     

Adaptive algorithm for transmission line protection in the presence of UPFC

The presence of flexible ac transmission system (FACTS) controllers in transmission lines causes mal-operation of distance relays. The series-shunt FACTS devices have larger influence on the performance of the relays compare to the other FACTS controllers. Furthermore, high-resistance fault is another factor that relay become under-reach and cannot correctly identify the fault. In this paper, a method is provided based on synchrophasors to eliminate the effects of unified power-flow controller (UPFC) and fault resistance on the distance relay. In the presented method, the data of voltage and current signals of buses will be sent to system protection center (SPC). In SPC, an algorithm is provided based on active power calculation in buses which is able to eliminate the effects of both mentioned factors. The main advantage of the proposed method, in addition to the simplicity of the algorithm, is the ability to operate in all types of faults and in high-resistance faults. Furthermore, a technique is presented in this paper to calculate UPFC data. A comparison has been performed between this technique and another method where UPFC data is directly transmitted to SPC by communication channel. In modeling of UPFC, detail model is used based on 48-pulses voltage source converters.     

混压同塔四回线跨电压不接地故障下的距离保护适应性分析

混压同塔多回线输电方式因其具有传输容量大、占用土地资源少等优势,在国内外得以较多应用。两个不同电压等级线路间的跨电压故障是混压同塔输电方式下的一种常见故障形式,已有文献开展了跨电压接地故障对距离保护的影响研究。但对于跨电压不接地故障,因其分析更为复杂,尚未见相关研究。以跨电压不接地故障为研究对象,分析了其对接地距离保护和相间距离保护的影响。基于复合序网的混压同塔多回线跨电压故障分析方法,计算分析了跨电压不接地故障时测量阻抗的变化规律,得出其大小与故障点位置和两不同电压系统特殊相电源相角差有关的结论,并进一步指出其与接地故障下的测量阻抗区别及其原因。同时对非完全故障相的相间距离保护的动作情况进行了讨论,指出其存在误动的可能性。最后,在PSCAD中构建了500 kV/220 kV混压同塔四回输电线路模型,通过大量仿真实验,验证了理论分析的正确性。     

用于特高压输电线保护的能量方向元件

传统能量方向元件在特高压线路中不能正确判别故障方向,同时当线路出口发生故障时由于系统内阻很小而导致有功能量方向元件也不能做出正确的判断。提出了一种应用于特高压长距离输电线路的故障分量式能量方向元件,并且提出了相应的方向纵联保护原理,用贝瑞隆算法加以实现;从而使保护的可靠性大大提高;分析了保护判据及其动作特性。通过数字仿真证明了所提方向元件原理和保护判据的正确性和可靠性,该元件具有不受系统暂态过程、过渡电阻、串补电容等因素影响的特性,而且其灵敏度不受故障类型及故障位置等因素的影响,同时动作速度也较快,不大于20ms。