Long-term DC voltage test method of HVDC wall bushing with resin impregnated paper capacitor core considering electro-thermal coupling coefficient

HVDC wall bushing connects the valve hall and the DC field in the converter station, which is the core equipment in HVDC transmission system. The resin impregnated paper capacitor core inside the bushing withstands long-term full DC voltage and full load DC current during operation. Thus, 2 hours long-term DC voltage test and temperature rise test are required to verify its insulation and thermal performance. However, internal discharge faults caused by overheating of current carrying structure still occur frequently in recent years, which means the insulation and thermal defects of the bushing under long-term electrothermal coupling stress can not be completely inspected only IEC standard test. In this paper, the influence of temperature on internal partial discharge measurement and electrical field calculation of resin impregnated paper capacitor core of HVDC bushing are carried out, and the electro-thermal coupling coefficient is given. Finally, a new long-term DC voltage test method during manufacturing process is proposed. This new method has important theoretical significance and engineering application value for internal defect evaluation, discharge or thermal fault diagnosis, as well as estimation of the reliability of both insulation and thermal performance in the life cycle of bushing.