Study on Discharge Characteristics Between Damping Capacitors in Converter Valve at Different Altitudes

Damping capacitor is an important component of DC converter valve, which plays a role in suppressing thyristor switching overvoltage and providing energy for thyristor control unit. Its operational reliability determines the safe and stable operation of the converter valve. Therefore, it is urgent to study the gap insulation characteristics of damping capacitors in converter valves at different altitudes. This article focuses on the damping capacitor gap inside the converter valve and conducts experiments using a true model to verify its margin. The switching impulse, lightning impulse, DC and AC discharge tests of damping capacitors gap in converter valve were carried out in Beijing (altitude of 55 m), Qinghai (altitude of 2500 m) and Tibet (altitude of 4300 m). Comparative analysis was conducted on the discharge voltage of small gaps in damping capacitors at different altitudes and gap distances. The results show that with the increase of altitude, the air density decreases, and the discharge voltage between damping capacitors decreases. At the same altitude, the 50% lightning impulse discharge voltage is the largest. Compared with the lightning impulse discharge voltage, the 50% switching impulse discharge voltage decreases by about 9%, the DC discharge voltage decreases by about 16%, and the AC discharge voltage decreases by about 42%. For the gap distance between damping capacitors, the equipment parameters provided by manufacturers in China have a large margin, and the margin is greater than 227%, which can meet the actual needs of engineering at different altitudes. This article provides an important theoretical basis for improving the insulation reliability of ultra-high voltage DC converter valve towers and optimizing the design of converter valve insulation under minimum safety margin.