Effects of volume and surface conductivity on the surface charge and electric field characteristics of the tri‐post insulator in SF6‐filled ± 500 kV DC‐GIL

Herein, the surface charge characteristics of a tri‐post insulator in a ± 500 kV direct current gas‐insulated transmission lines (DC‐GIL) filled with SF6 are thoroughly studied. The influences of volume and surface conductivity of the insulator on the surface charge and consequent electric field distribution are discussed. An improved method is introduced to obtain the distribution of surface charge with considerable accuracy and efficiency for the calculation. It is found that with increasing the volume conductivity, the dominative conduction mechanism changes from surface conduction to bulk conduction, while the inverse variation appears with increasing the surface conductivity. During the variation of electric conductivity, obvious effect of surface charge accumulation is found on the electric field distribution involving the variation of peak electric field strength and its location. Besides, high charge density usually appears along with low peak field strength during this variation. It can be concluded that the surface charge accumulation should be paid special attention when analysing the insulation characteristics of tri‐post insulators. The variation of volume and surface electric conductivity should be thoroughly considered. The influence of volume conductivity and surface conductivity on the surface charge and electric field distribution characteristics of the tri‐post insulator in a ± 500 kV DC‐GIL is studied. The investigation indicates that the volume and surface conductivity should be focused on in the design of tri‐post insulators considering the insulation property during long‐term stress of HVDC.