Analysis of Action of Transformer Protection Caused by Two Points Grounding Fault

Combined with the action of the protection device,the fault of the action of the transformer protection is analyzed. The fault waveform is particular when two points grounding fault occurred in different phases of neutral non-grounding system,so the fault waveform is further analyzed and the protection action logic is demonstrated fully through the action of the primary equipment. The grounding fault occurs in the phase C of the 35 k V line,and the insulation of the main transformer 35 k V down lead phase A insulating bush declines to form breakdown grounding. The two fault points,one is in the differential protection scope,another is out of the differential protection scope,and then the two fault points supply the channel for fault current and cause the fault. The in-depth analysis and discussion about the reason of waveform provide the reference for such fault analysis.