Effects of Transient Voltages on Discharge Inception of Tri-post Insulator in DC-GIL

Abstract

Surface charge and electric field distributions of a tri-post insulator in ±800 kV gas-insulated transmission line (GIL) are calculated under the transient voltages (superimposed DC-impulse voltage and the polarity reversal voltage). The theoretical discharge inception voltage of the tri-post insulator under the above conditions is estimated by the volume-time theory. The accumulated homo-charges on the insulator surface significantly relax the electric field at the DC steady state, thus improving the theoretical discharge inception voltage under DC superimposed homopolar impulse voltage but reducing that under DC superimposed heteropolar impulse voltage. When the voltage polarity is reversed in 120 s, the intensified electric field on the insulator surface shifts from the GND electrode towards the vicinity of the HV electrode, in which the maximum electric field grows by 21.4%.