Abstract:A case of partial discharge defect in 35 kV switchgear cabinet is analyzed. The live detection technologies such as transient earth voltage , acoustic emission and ultra-high frequency is adopted to detect and analyze the defect, and the electromagnetic wave time difference method is used to locate the partial discharge source. Combined with the internal structure of switchgear cabinet, the location range of the partial discharge source is given. The obvious discharge trace between the lead of A-phase arrester and the insulation board is found during the power failure inspection, which verifies the correctness of the defect diagnosis and positioning result. The results show that the live detection technologies for partial discharge can effectively find insulation defects in switchgear cabinet, which provides experiences for similar defects treatment of switchgear cabinet.