Abstract: In the Guangdong Zhuhai Jinwan Power Generation Company Limited, during the test of the generatortransformer unit protection device G60, it was found that the protection 'all stopping when 500kV switch tripped' configured in the protection device acted incorrectly. Based on indepth analysis, it was considered that the main reason of the fault is the malfunction of the generatortransformer unit protection device. The improvement method of the protection logic was put forward; the protection malfunction happening again was avoided, and a serious hidden danger of the generatortransformer unit protection device was eliminated.

Key words: generator-transformer unit, malfunction of protection, G60 device, reason analysis, improvement of protective logic