The internal defects of gas insulated switchgear(GIS) equipments seriously threaten the safe and reliable operation of electric power systems. Digital radiography(DR) detection technology can realize visual diagnosis of internal structure of the GIS equipments

and provide strong technical support for equipment fault diagnosis. According to the principle that the X ray absorptivity of different materials can be characterized by transmission intensity ratio of materials

the material density and atomic number were used to calculate the material transmission intensity ratio. Moreover

the feasibility and validity of using the DR detection technology to detect typical defects of GIS equipments were investigated. The effect of applying voltage on the effectiveness of DR detection of internal insulation defects was experimentally studied. Finally

a 220 kV GIS equipment was tested by the DR technology

which proves that it is effective and feasible to use the DR technology to carry out detection and preliminary judgement for internal insulation defects of GIS equipments.