For partial discharge in transformer

every single detection method has its limitation and cannot solve all the problems perfectly. To overcome the limitation of single detection method and improve the reliability of partialdischarge detection

this study proposed a combined detection technology based on the ultra-high frequency method

HFCT method and the ultrasonic method. The effectiveness of the combined detection method was confirmed by ex-periment

and the result shows that: 1)the discharge signal and interfere signal can be distinguished by the combineddetection method effectively

and good anti-interfere performance is obtained;2)based on the combined detectionmethod

different kinds of pattern recognition methods could be developed to improve the accuracy of pattern recogni-tion;3)the discharge source location method based on the time-delay of ultrasonic signal to UHF signal has high pre-cision;and 4)the high-frequency signal of discharge can be obtained to calculate apparent charge

thus the level of discharge can be evaluated exactly.