Before the power equipment

like transformer and GIS

is put into operation

there are many factors such as transportation

on-site installation that will take some latent damage to its insulation. Thus the field test is an important step to ensure the safety of power equipment. The AC withstand voltage test and its corresponding partial discharge（PD）measurement are inadequate for the detection of all hidden defects in power equipment. Such inadequacy can be compensated by additional impulse withstand voltage test and its PD detection measurement.Oscillating impulse voltage is one voltage waveform that is suitable for field test. In order to study the detection and characteristics of PD under oscillating impulse voltage

the PD detection system is established. The interference resources are analyzed and the anti-interference methods are studied in this paper. The study results show that the interferences from impulse generator are the main ones. The displacement current and the high frequency EM wave from generator switcher action will cause serious interferences. By adopting high pass filtering technology and equivalent time-frequency analyses based on waveform time domain feature

the interferences can be effectively eliminated. And PD signals under oscillating impulse voltage can be detected accurately.