变压器DCD型差动保护误动行为分析

鲁南热电厂3号Y0/Y-10型主变压器装设了DCD型差动保护[1],运行10余年来只要110kV系统区外发生单相接地故障时该保护则误动跳闸。原因是变压器110kV侧的中性点接地运行,当110kV系统单相接地时,进入继电器高低压侧的电流相差1/3,两侧电流失去平衡而动作作跳闸。断开110kV中性点的接地刀闸,变压器作为不接地方式运行可以回避问题的出现。但采用微机型的差动保护,从算法上可以补偿掉高压侧零序电流所造成的单相接地时的差电流。最后更换为微机型差动保护,运行结果表明误动现象得到彻底解决。

Analysis on DCD Transformer Differential Protection Malfunction

DCD transformer differential protection has been applied on Lunan power plant No.3 main transformer. The protection equipment has always miss tripped as long as the out-regional single-phase ground fault happened in 110kV system during the past 10 years. Because the neutral point of 110kV side is directly grounded, high differential current enter the protection relay when a single-phase ground fault happened in 110kV system, which caused the miss trip. The problem can be solved, if the grounding disconnecting link of the 110kV neutral point is opened. If microcomputer differential protection is adopted, the high differential current can be compensated by algorithm so that the miss trip problem can be solved thoroughly.