交流量串入直流控制回路造成保护误动的分析和对策

Analysis and solutions of Misoperation when AC Flows into DC Control Circuit

介绍了某发电厂由于间隔二次回路故障引起的主变保护误动事故。通过对主变出口继电器及其回路、二次回路的检查 ,找出了事故的原因 :由于交流量窜入直流控制回路引起中间出口继电器动作从而造成主变保护动作。通过试验对事故进行了分析 ,并提出了 2种防范措施 :方案 1为将出口中间继电器两端的续流二级管改为RC回路 ,从而避免由于交流量引起的中间出口继电器的抖动 ;方案 2为对直流系统进行改造。验证结果表明方案 1不会影响保护的动作特性。现场采用方案 1解决交流量窜入直流回路引起的保护误动问题 。

A misoperation of main transformer relay in a power station caused by the fault in secondary circuit is introduced. Trough the check of the main transformer exit relay, its correlative circuit and secondary circuit, it is found that the misoperation is caused by the AC current flowing into the DC circuit and activating the intermediate relay. The accident is analyzed by experiments and the following two solutions are presented. a. Substituting the freewheeling diode between the two terminals of intermediate relay by RC circuit so as to eliminate the contact bouncing caused by AC; b. Reconstructing DC system. The first solution is tested and it shows that there is no influence on relay performance characteristics. It is used to avoid this kind of misoperation problem in power station and has good effect.