This paper analyzes a typical partial discharge defect case of a high voltage indoor switchgear in a substation.The abnormal partial discharge signal in the high voltage chamber is determined by transient earth voltage（TEV） and ultrasonic test data.In order to realize the precise location of the fault location

the method of TEV location

UHF local discharge detection and location is adopted.The fault location range is given by the above method combined with the internal structure of the type switchgear

and the correctness of the defect diagnosis analysis is confirmed by the blackout check.The test shows that the internal defect TEV detection is more sensitive than the ultrasonic detection.As the detection distance increases

the amplitude of the UHF signal and the TEV signal can be reduced

and the location of the local source can be located through this principle.As the detection distance increases

the arrival time of the UHF signal and the TEV signal becomes longer.Experience has been accumulated for the treatment of similar cases.