Detection of partial discharge（PD） is very important role for diagnosing and assessing insulation state of GIS. Different types of PD harm GIS to different degrees

so identification of PD type is vital to safe and reliable operation

insulation condition evaluation

and rational maintenance strategy of GIS. This paper studies the familiar fault types in the operation of three-phase-common GIS

designs four typical insulation defects according to the test conditions

and conducts PD detection for faulty GIS with the UHF method. Typical PD spectrums of four insulation defects are analyzed. This study may provide a basis for stable operation and timely maintenance of GIS.