电缆分布电容对出口继电器动作的影响分析及应对措施

摘要

《国家电网公司十八项电网重大反事故措施》从设计角度对继电器动作功率和动作电压提出了要求,但在发生直流接地或交流窜入时,若控制电缆的分布电容超过临界值,出口继电器仍旧会误动作.从设备运维检修的角度,设计了一种电缆分布电容的在线监测系统,实现对该类风险的预警,并给出了相应的控制措施.该监控系统通过向直流系统注入低频交流信号,以交流电流为量测量,计算其分布电容并与临界值比较.为实现分布电容的平稳准确测量,基于磁饱和原理和磁通感应原理,设计了一种测量微小交直流信号的电流互感器;采用直流电子负载中的恒阻模式,设计了一种电压均衡模块来平衡直流母线电压.%Eighteen major anti-accident measures taken by State Grid Corporation of China make the corresponding requirements on relay operating power and action voltage from the point of view of design.But if direct current (DC) grounding fault or alternating current (AC) intruding happens,when distributed capacitance of control cables exceeds the critical value,the export relay may still malfunction.The on-line monitoring system of distributed capacitance of control cables is built to realize early warning of the risk: firstly,the low-frequency alternating current signal is injected into the DC system;then,the AC current value is measured and the distributed capacitance is calculated;finally,the measured value is compared with the critical value.In order to measure the distributed capacitance accurately and steadily,a small AC and DC measurement current transformer is designed using the magnetic saturation principle and flux induction principle.Based on constant resistance mode of DC electronic load,a voltage equalization module is designed to balance DC bus voltage.