Insulation Characteristics of SF6/N2-Filled GIS Spacers under Lightning Impulse with DC Voltage Superimposed

The insulation characteristics of spacers with surface charges accumulation under DC voltage is important for the development of DC GIL. Nowadays, GIL filled with mixed gases has become the current study trend. However, little attentions were paid on the characteristics of SF
6
/N
2
-filled GIS spacers in the previous studies. The paper experimentally tested the breakdown characteristics of SF
6
/N
2
-filled GIS spacer under lightning impulse voltage with DC voltage superimposed. An experimental setup of full-scale cone-type spacer breakdown voltage measuring platform is designed. The conical spacer is placed in SF
6
/N
2
-filled coaxial electrode arrangement. In order to get the composite breakdown voltages, the cone-type spacer is pre-stressed a constant DC voltage for a given time, and then get lightning impulse superimposed. The insulation properties of cone-type spacer under composite voltage are influenced deeply by the duration of pre-applied DC voltage and polarities of the composite voltage. In order to promote the reliability of the SF
6
/N
2
-filled GIS spacer, the performance under composite voltage need to be considered for optimizing insulation design.