In order to realize proper condition maintenance of switchgear

it is very important to improve the state perception ability of the switchgear. Ultrasonic

transient earth voltage and ultra high frequency（UHF）detectionmethod for partial discharge are widely used in the condition detection of switchgear. In this paper

the principles ofthe several detection methods of the partial discharge in switchgear are analyzed

and a typical case of comprehen-sive detection and diagnosis technology of partial discharge defects in switchgear is presented. In a routine inspectiontest

the results of the transient earth voltage detection in a PT switchgear are abnormal

and then the tracking is car-ried out through UHF detection for a long time to verify the existence of internal defects. Then the position of the de-fect is clearly defined by the precise location of the UHF signal and the internal structure of switchgear. Finally

theoutage maintenance is carried out to replace the defective lightning arrester

which eliminates the defects successful-ly. Hence

the reliability of the power supply is ensured. The analysis of the principle and the typical case has accu-mulated valuable experience for the switchgear operation and maintenance. Therefore

this paper further proves thatthe comprehensive detection and diagnosis of partial discharge defects in switchgear is very important for ensuring the safety of switchgear operation and improving the reliability of switchgear.