Abstract: It introduces the principle of partial discharge electrified detection such as ultrasonic, ultrahigh frequency（UHF）, high frequency current and time difference location method. The partial discharge phenomenon of No. 2 main transformer in a 110 kV substation is detected by PDS-T90. According to the UHF and high frequency current data, it can initial infer that the discharge type is insulation discharge from the high voltage side cable compartment. PDS-G1500 is used to determine the discharge source in the C-phase cable compartment at the high voltage side after phasing analysis. And then UHF is used to accurately locate the discharge source. The specific discharge location is determined by time difference analysis. Considering the importance of the load in the substation, it is inconvenient to deal with the power outage. After research, it is decided to install the intensive care system PDS-G100 M to track the discharge intensity and growth trend in real time. The results show that the partial discharge signal is stable and there is no obvious growth trend. The electrified detection positioning and tracking technology are used to realize the partial discharge signal tracking, trend judgment, timely warning of transformer and they have scientifically formulated the condition maintenance program. The results show that the partial discharge signal of No. 2 main transformer is stable without obvious increasing trend. So the hidden danger of safety is eliminated and the reliability of power supply is ensured.