Due to the external electromagnetic interference in the working area of a switchgear

the detection accuracy of partial discharge（PD）in the switchgear will be limited.In order to distinguish partial discharge transmission and external interference in switchgear

a simulation model of partial discharge in switchgear is established

and the pulse characteristics of internal discharge and external interference in the switchgear are simulated and analyzed by using the finite element analysis software COMSOL.Simulation results show that the waveform of the discharge inside the switchgear presents multiple oscillations

while the external interference waveform has almost no oscillation phenomenon.To verify the correctness of the simulation analysis

a TEV detection system of internal discharge is set up in laboratory for discharge of internal cavity defect

and the wavelet transform theory is employed.According to the internal and external pulse time-frequency spectrograms of the internal cavity defect

obvious oscillation phenomenon of the internal discharge is observed

but there is no obvious oscillation in the external discharge.This research may provide a reference for distinguishing internal discharge pulse from external discharge pulse.