In order to improve the diagnose ability of insulation defects of gas insulated switchgear（GIS） and improve the detection experience of ultra-high frequency（UHF） method in the field

detailed tests and diagnosis of multiple voids discharge of 550 kV GIS insulation spacer were performed in this paper. Firstly

the abnormal signal of 550 kV GIS insulation spacer

presenting a characteristic of void discharge

was detected on field by the UHF method. After the replacement of the insulation spacer

the tests of withstand voltage

partial discharge

lightning impulse and X-ray detection were employed to investigate the void discharge of insulation spacer. Meanwhile

the UHF and pulse current methods were used to detect the PD signal of the insulation spacer. The discharge characteristics were compared after the lightning impulse. Finally

further diagnostic analyses were carried out by using time difference location statistics and multi-source discharge separation methods. The results show that there are 8 voids in the insulation spacer

which are linearly distributed. The amplitudes of the signals are positively correlated with UHF and pulse current method. With the increment of applied voltage amplitude

the discharge spectrum gradually changes from single void discharge to multiple voids discharge. The partial discharge initial voltage decreases and the extinguishing voltage does not change after the lightning impulse. The UHF signal amplitude and discharge amount will increase under the same voltage after the lightning impulse. The time difference location statistics and multi-source separation indicate the insulation spacer behaves as multiple discharge source characteristics

which is consistent with the X-ray results. The results can provide field experience for GIS UHF detection and diagnosis.