Partial discharge is an important means for evaluating insulating property of electric equipment and investigating insulation aging.In this paper

the partial discharge interference sources induced by three typical defects

floating potential

high-voltage point discharge

and earth point discharge

are simulated to investigate the features of DC partial discharge waveforms by combining with DC thyristor valve test.The waveform features are induced from four aspects of polarity

phase

amplitude and root number of discharging impulse under increasing DC voltage for identifying the type of defects under DC voltage.