In this paper

the comprehensive diagnosis and analysis process of abnormal heating defect of 500kV capacitance voltage transformer is introduced. The defect is considered to be inside of the lower ca-pacitor unit by infrared thermal image detection and capacitance as well as capacitance of dielectric losstest. It is found through disassembly examination that the sealing performance of the equipment is weak dueto lack of sealing ring at the flange connection

causing serious water erosion inside the capacitor unit andpartial capacitor element discharge breakdown besides the weak insulation part of insulation board. The the-oretical calculation result of damage degree of capacitor element is consistent with the disintegration exami-nation. In view of the reason of the defects

such measures as elimination hidden danger of similar equipment

improvement of sealing structure of the equipment and strengthening operation monitoring are made.