Partial discharge detection is an essential method for insulation condition monitoring and insulation diagnosis of GIS. However

the partial discharge detection sometimes gives false alarm or omits alarm

so it is necessaryto study the detection effectiveness. In this paper

two typical insulation defects of the sphere-plate gap with spineand the metallic particle on contaminated insulator are simulated

and the relationship between partial discharge in-ception voltage and breakdown/flashover voltage are investigated. A partial discharge detection effectiveness factor αis proposed to evaluate the effectiveness of partial discharge detection via the pulse current method. The results showthat both partial discharge inception voltage and breakdown/flashover voltage decrease significantly with the increaseof defect size. For the sphere-plate gap with spine

its partial discharge inception voltage has a big difference from thegap breakdown voltage and its partial discharge magnitude is large. While for the metallic particle on contaminatedinsulator

the partial discharge inception voltage is closer to the flashover voltage and the partial discharge magnitudeis smaller. As a result

the partial discharge detection effectiveness factor for the metallic particle on contaminated in-sulator is smaller than that for the sphere-plate gap with spine

so it is harder to detect the partial discharge of metal-lic particle on contaminated insulator. In addition

the partial discharge detection effectiveness factor becomes small-er with the increase of air pressure

so partial discharge test under reduced pressure can enhance the effectiveness of partial discharge detection.