小电阻接入城市配网方式影响分析

小电阻在城市配网的接入方式会影响主变保护动作情况和配网零序网络。针对输配电网中2种不同等级的变电站,分析了曲折变接于变低套管与变低开关之间和接于变低10 kV母线2种接线方式下,配网接地故障时保护的动作情况,比较了10 kV自投动作后2种接线方式对配网零序网络的改变。得出当110 kV变电站曲折变接于变低开关和变低套管之间时,曲折变本体故障不会影响10 kV母线,同时主变跳闸切除多余曲折变,能保证10 kV配网在备自投动作后零序网络稳定。220 kV变电站中曲折变通过开关接在母线上,若曲折变故障后开关拒动,变低后备动作隔离故障,不影响变中供电可靠性。为了维持城市配网接地点的唯一性,保证曲折变保护正确动作,建议10 kV备自投联切曲折变。

Effect of low-resistance connection to urban distribution network

The mode of low-resistance connection to urban distribution network will affect the action of main transformer protection and the zero-sequence network of distribution network.The actions of protection during grounding fault in substations of two different levels in transmission and distribution grid are analyzed for two connection modes of winding transformer:between low-voltage switch and low-voltage bushing of main transformer in 110 kV substation;with 10 kV bus in 220 kV substation.The changes of zero-sequence network after the action of 10 kV ASD(Automatic Switching Device) are compared for both modes.In the first mode,the body failure of winding transformer will not affect 10 kV bus while the redundant winding transformer of main transformer will be tripped to keep its zero-sequence network stable.In the second mode,when the winding transformer fails,if the switch refuses to act but the low-voltage backup protection of main transformer acts to isolate fault,the supply reliability will not be affected.To maintain the uniqueness of grounding point for urban distribution network and ensure the correct action of winding transformer protection,it is suggested the 10 kV ASD to trip the redundant winding transformer.