小电阻接地系统馈线自适应零序电流保护原理及装置实现

摘要

小电阻接地系统发生多回线同相复杂接地故障时,零序电流幅值相比于单回线接地故障将显著下降,容易导致馈线首端的零序电流保护拒动,进而造成母线接地变压器的零序电流保护越级误动,扩大停电范围.为此,对小电阻接地系统多回线复杂接地故障的故障机理进行分析,推导了多回线与单回线接地故障下馈线零序电流关系;在此基础上,提出了一种自适应馈线零序电流保护方案,即根据母线电压将多回线接地故障的零序电流实时补偿为单回线接地故障的零序电流值,从而确保了常规的保护动作值整定方式和保护配合能够适用于多回线复杂接地故障,并研发了相应的自适应零序保护装置.基于PSCAD/EMTDC和RTDS对保护原理及保护装置的测试结果表明,自适应零序电流保护在多回线复杂接地故障情况下仍具有较高的灵敏性,补偿精度不受过渡电阻、故障位置的影响.所提保护方案只需在原有零序电流保护方案基础上,增加母线电压信息,容易实现,具有经济性和较高的工程应用价值.%When in-phase grounding fault occurs in multi-circuit lines,the zero-sequence current would significantly decrease compared with that during single line grounding fault,which may cause zero-sequence current relay protection to function improperly and expand the fault range.Therefore,the SPGF(Single Phase Grounding Fault) mechanism of multi-circuit lines in low resistance grounding system is analyzed,and the relationship between feeder zero-sequence current during both multi-circuit line and single-circuit line SPGF is deduced,based on which,a novel adaptive zero-sequence current protection scheme is proposed,i.e.the zero-sequence current during SPGF occurs in multi-circuit lines can be compensated to zero-sequence current during single-circuit line SPGF according to the bus voltage in real time.The protection device based on the proposed scheme is developed.The proposed scheme and the protection device are verified via PSCAD/EMTDC and RTDS,the results show that the proposed scheme has high sensitivity during complex SPGF occurs in multi-circuit line,and the compensation accuracy is not affected by transition resistance and fault location.The proposed scheme can easily be implemented and has economic and high engineering application value since it only needs to add the bus voltage information on the basis of the existing zero-sequence current protection scheme.