20Hz注入式定子接地保护在扩大单元接线发电机组上的应用

Application of injecting 20Hz source-based stator ground fault protection for generators in expanded unit connection

针对目前注入式定子接地保护不具备选择性,无法应用在扩大单元接线发电机组的问题,提出了一种新的注入式定子接地保护方案。该方案首先计算发电机组接地电阻的值以判断是否存在接地故障,当检测到接地故障后,以注入的20Hz电压的相位为基准,将测量到的发电机中性点与机端处的20Hz电流作差后的相位与之比较,通过这个相位关系来判断故障发电机,实现选择性停机。仿真结果验证了新方案计算接地故障过渡电阻和判断故障发电机的准确性,实现了注入式定子接地保护在扩大单元接线机组上的应用。

At present,the stator ground fault protection of generator through injecting 20 Hz voltage cannot be used in generators connected to expansion units due to lack of selectivity.This paper proposes an improved protection scheme to realize the selectivity. The proposed scheme firstly calculates the ground resistance value of generators to determine whether ground fault occurs. When the ground fault is detected,the 20Hz differential current between the neutral and terminal of each generator can be obtained .The phase relationship between the 20Hz differential current and injected 20 Hz voltage is derived.The new protection scheme can determine the fault generator according to the phase relationship,so that it can achieve a selective shutdown.The simulation results verify the accuracy of calculating the grounding transition resistance and selecting the fault generator,whichrealizes the application of the injecting stator ground fault protection in the generators connected to expanding units.