10kV小电阻接地系统接地变压器零序电流保护误动分析

Analysis of malfunction of grounding transformer's zero-sequence current protection in 10 kV low resistance grounding system

介绍了小电阻接地系统的原理和运行方式 ,并就某变电所接地变压器零序电流保护误动的原因进行了深入的分析。指出两条馈线同一相先后发生高阻接地时 ,电流的叠加会造成接地变压器零序电流保护误动 ;两条馈线相继发生单相接地时 ,电流、时间的叠加也会造成接地变压器零序电流保护误动 ;馈线、接地变压器的零序电流互感器分别产生正负误差 ,同样会造成接地变压器零序电流保护误动。通过修改保护的定值 ,改善了接地变压器与馈线零序过电流保护的配合 。

The principle and operation pattern of low resistance grounding system were introduced. The reasons of grounding transformer's zero-sequence protection malfunction in a substation were profoundly analyzed. The malfunction is caused by superposed fault currents when two feeders are grounded successively at the same phase through high resistance while the protection of the first one is failed to act, or caused by superposed currents and time when two feeders are grounded successively. When the zero sequence CT of grounding transformer has negative error and that of feeder has a positive one and two currents may be almost equal. Through modifying the protection setting values the matching between protection of grounding transformer and that of feeder is improved and finally the above problems are solved.