Transmission lines distance protection using artificial neural networks

This work presents the development and implementation of an artificial neural network based algorithm for transmission lines distance protection. This algorithm was developed to be used in any transmission line regardless of its configuration or voltage level. The described ANN-based algorithm does not need any topology adaptation or ANN parameters adjustment when applied to different electrical systems. This feature makes this solution unique since all ANN-based solutions presented until now were developed for particular transmission lines, which means that those solutions cannot be implemented in commercial relays.     

Application of a distance relaying scheme to compensate fault location errors due to fault resistance

This paper proposes a distance relaying scheme based on the current phase jump behavior during fault conditions to improve the apparent impedance estimated by the distance relay. For a nonpilot protection scheme, the measured impedance is affected by error due to the combined effects of fault resistance and prefault load. An experimental relation between the current phase jump introduced with fault inception and the X/R ratio seen by the distance protection is deduced. The phase jump correction factor obtained is an exponential function of the X/R ratio of the line. This factor is applied to the apparent impedance measured by the relay and it allows mitigating the adverse effect of prefault power. The relaying scheme improves significantly the accuracy in estimation of the resistive fault location. The application of this scheme does not require communication links from the remote end of line and is applicable to all types of fault.     

Strengths and limitations of a new phasor estimation technique to reduce CCVT impact in distance protection

This paper evaluates the performance of a new least squares approach that improves the accuracy and speed of convergence of the voltage phasors estimated during CCVT transient conditions. A justification of the validity of the linear mathematical model for the CCVT used is provided together with a short study about the risk of transient ferroresonance. Also, a discussion is presented about operating times of numerical distance relays and the importance of the new phasor estimation considered. The methodology followed to achieve a realistic evaluation in a variety of scenarios is presented. The results show the improvements achievable in most conditions, but also highlight an example scenario where the new method has limitations.     

Realistic insights into impedance seen by distance relays of a SSSC-compensated transmission line incorporating shunt capacitance of line

In practice, the series compensation is applied to medium-/long-length transmission lines. Such lines include significant shunt capacitance, neglecting of which is expected to noticeably influence the impedance seen by distance relays. Taking the shunt capacitance of a transmission line compensated by the static synchronous series compensator (SSSC) as well as other affecting factors into account, this paper derives precise mathematical expressions governing the apparent impedance seen by the distance relay of the line. Through the acquired expressions, the research conducts sensitivity studies considering different compensation scenarios and locations for the SSSC. The studies make an attempt to produce realistic insights into ideal tripping characteristics of the distance protection of the under studied line, and also into the susceptibility of the impedance seen to output parameters of the SSSC. In addition, the research’s findings well demonstrate the extent to which neglecting the shunt capacitance of the line would contribute to mis-operation of the distance relay.     

基于递归型定频采样变数据窗离散傅氏算法的大型旋转电机启机保护

介绍了大型旋转电机在变频工况下的启机保护。针对现有启机保护存在抗干扰能力不足和计算量偏大的问题,提出一种基于递归型定频采样变数据窗离散傅氏算法。该算法在保证计算精度的前提下,大幅减少计算量。首先根据系统频率,确定数据窗长,然后采用递归型离散傅氏算法计算模拟量幅值。当经过一个固定时间或频率变化后,插入一次非递归全波傅氏校验,消除累计误差。在此基础上,以变频启动工况下的调相机启机保护为例,将新算法与常规峰值算法相结合,对启机保护进行改进。在保护装置上对改进后的调相机启机保护进行了实验验证。结果表明在不同系统频率下保护均能够准确计算故障中的基波分量,且递归型变数据窗傅氏算法与峰值算法相结合能够确保启机保护的可靠性。