To investigate the ultrasonic signal distribution characteristics of partial discharge due to metallic defects in gas insulated switchgear（GIS） and obtain defect recognition method based on the distribution characteristics

an ultrasonic measurement system is constructed.Four models of typical metallic defects in GIS are designed

i.e.tip on high-voltage electrode model

floating potential model

particle on insulator model

and tip on ground electrode model.Plenty of ultrasonic signals are acquired with the ultrasonic measurement system.Based on these data

some methods for recognizing types of typical defects in GIS are proposed by employing four parameters of pulse number N

ultrasonic amplitude u

time interval Δt

and phase angle Ph

as well as g-u

N-Δt

and N-Ph curves.And the ultrasonic distribution characteristics of the metallic defects in GIS are analyzed.Experimental results show that distribution modes of ultrasonic signal characteristics can be used to recognize types of metallic defects.