Transient surface charge of SF 6 ‐filled direct current gas‐insulated transmission lines insulator under thermal‐electric coupled fields: effects of ambient temperature, load current and gas pressure

Abstract

The transient surface charge characteristics of a basin-type insulator in horizontally installed SF6-filled direct current gas-insulated transmission lines (DC-GIL) are investigated based on a three-dimension (3D) simulation model under thermal-electric coupled stress. The influence of ambient temperature, load current and gas pressure on the surface charge and electric field characteristics is investigated. Simulation results indicate that the surface charge accumulation process is accelerated due to the promotion of bulk conduction under high ambient temperature, high load current and low gas pressure. The transient field variation is accelerated as the consequence. The highest field strength on the convex surface increases and moves towards the enclosure with increasing time. With increasing load current, the field strength increases due to the influence of charge accumulation and temperature-dependent conductivity of the insulator. It is revealed that the transient surface charge under coupled fields should be focused when dealing with the insulation characteristics of DC-GIL insulators during long-term operation. The mentioned operating conditions should be paid attention. This method introduced in this study can help to evaluate the 3D transient charge and field characteristics under various conditions.