柔性低频输电系统的故障分量特征及保护适用性分析

Analysis of Fault Component Characteristics and Protection Applicability on Flexible Low Frequency Transmission System

柔性低频输电系统由于运行频率的改变以及柔性低频换流站的控制机理,其故障特征以及对保护原理的影响较为复杂。为了分析故障分量保护原理在柔性低频输电系统中的适用性问题,基于柔性低频换流站的控制架构,建立了以故障限流为故障控制策略的双端型低频输电模型。计及该系统线路发生三相故障的控制特性,分析了不同情况下的低频故障分量阻抗特性,并推导出低频等值阻抗的量化计算式,进而从理论上分析其对传统故障分量保护元件的影响机理。最后,在PSCAD/EMTDC平台上搭建了双端低频输电测试模型对理论分析进行仿真验证。研究结果表明:柔性低频输电系统在一定故障条件下可造成故障分量保护范围缩小,甚至使得保护元件完全失效,研究结果对于低频系统继电保护研究的开展具有一定的参考作用。

Due to the change of operating frequency and the control mechanism of flexible low-frequency converter station,the fault characteristics of flexible low-frequency transmission system and its influence on protection principle are complicated.In order to analyze the applicability of fault component protection principle in flexible low-frequency transmission system,a double-terminal low-frequency transmission model with fault current limiting as fault control strategy is established based on the control architecture of flexible low-frequency converter station.After considering the control characteristics of the system when three-phase fault occurs in the line,the impedance characteristics of low-frequency fault component in different situations are analyzed,and the quantitative calculation formula of low-frequency equivalent impedance is deduced,and then the influence mechanism on traditional fault component protection components is analyzed theoretically.Finally,a double-terminal low-frequency transmission model is built on PSCAD/EMTDC platform to verify the theoretical analysis.The research results show that the flexible low-frequency transmission system can reduce the protection range of fault components and even completely fail the protection components under certain fault conditions,which has a certain reference for the development of relay protection research in low-frequency systems.