Previous studies have shown that the waveform characteristics of the transiently radiated fields generated by switching operations in the external space of gas insulated substations（GIS） can reflect the operating state of a switch. In order to verify the idea that the feature analysis of the transiently switching electric fields（E-fields） can be applied to the fault diagnosis of the switch

based on the disconnecting switch（DS） test platform of China Electric Power Research Institute

we measured the transiently spatial switching E-fields under different working states by using a non-invasive 3D radiation E-field measurement system. Then

the correlation between the characteristics of the switching E-fields and the functioning status

including normal working state

inner point discharge and external point discharge was respectively established. The results show that the detailed waveform and the characteristic frequency distribution of the switching E-field pulses under insulation defects obviously differ from the case of normal operating state. Thus

the insulation fault detection for DS can be realized by monitoring and analyzing the transient E-fields due to switching operations. The research provides a new idea for the fault diagnosis domain with respect to switchgear such as DS.