合并单元直流偏置对母线保护的影响分析及解决方案

近年来,因合并单元输出直流偏置信号而导致保护动作的事故在智能变电站屡有发生。为解决这一问题,提高合并单元采样值输出的稳定性和安全性,介绍了合并单元工作原理和ADC芯片设计原理,分析了合并单元在采样回路断线时产生直流偏置的原因。基于母线保护装置采样值差动原理,从动作行为方面分析了合并单元直流偏置输出对母线保护的影响。通过改造ADC芯片外围回路,提出了减小合并单元直流偏置的解决方案。搭建了测试系统,通过验证采样值输出值和母线保护动作情况,证明了合并单元直流偏置解决方案的有效性。

Analysis and solution for the influence of DC bias of a merging unit on bus protection

In recent years, accidents in protection action caused by the output DC bias signal of a merging unit have been occurring frequently in smart substations. To solve this problem, we need to improve the stability and security of the sampling value output of the merging unit. The reason for DC bias of a merging unit when the sampling circuit is broken is analyzed by introducing the working principle of a merging unit and the design principle of an ADC chip. Based on the sampling value differential principle of a bus protection device, the influence of DC bias output of the merging unit on bus protection is analyzed from the action behavior. By reforming the peripheral circuit of the ADC chip, a solution to reduce the DC bias of the merging unit is proposed. The test system is built to verify the output value of the sampling value and bus protection action. It proves the effectiveness of the DC bias solution for the merging unit. This work is supported by the National Natural Science Foundation of China (No. U1804252).