Internal Discharge Characteristics of HVDC Wall Bushing Model with Resin Impregnated Paper Capacitor Core under Long-term DC Voltage of Different Polarity

In the HVDC converter station, the DC wall bushing can spread long-term full DC voltage and current with both positive and negative polarity, from the converter valve, through the wall of valve hall, to connect with DC field. In IEC 65700–2014, the bushing sample is applied with 1.5 times of maximum positive DC voltage during long time operation, and the test time is 2 hours. However, the different polarity of DC voltage is not considered, which is contrary to SF6 filled equipment with weak insulating performance under negative DC voltage. The influence of DC voltage polarity to HVDC wall bushing with capacitor core should be studied, and evaluate the reliability of its insulation status during the life cycle. In this paper, the discharge characteristics of internal capacitor core and external hollow insulator of the bushing sample during 2h long-term DC voltage duration test are studied. The number and value of discharge pulses are two important parameters for evaluating DC partial discharge, positive DC voltage, as well as negative DC voltage shall be used to test the long term DC insulation performance of HVDC wall bushing.