Air Gap Discharge Characteristics of 1 000 kV Transformer Area of Converter Station with Hierarchical Connection Mode

As the voltage level of 800 kV UHV converter station network side increases from 750 kV to 1 000 kV, the insulation requirements for UHV converter station on network equipment should also be increased. The optimization of 1 000 kV air gap on network side is of great significance to controlling the length of valve hall, ensuring safe and reliable operation of converter station, reducing the occupancy of converter station, and reducing project cost. Consequently, we experimentally investigated the discharge of air gap between various charged conductors in the 1 000 kV converter area of the low voltage valve hall network of station. The 50% operating impulse discharge voltage test curve of the corresponding air gap was obtained. Moreover, according to the calculation results of 1 000 kV switching overvoltage on the network side of converter station under different types of conditions, the 50% switching impulse discharge voltage of air gap in 1 000 kV converter area on the network side was analyzed. According to the air gap test curve and the maximum 50% discharge voltage of phase-to-phase and phase-to-ground operation, the value of the key air gap at the network side of the converter station was obtained. The calculation shows that the minimum air clearance of the casing equalizing ring is 7.1 m for the valve hall wall, the minimum air clearance of the casing equalizing ring for the roof of the valve hall wall is 6.6 m, the minimum air clearance of the casing equalizing ring-lightning arrester equalizing ring is 8.2 m, and the minimum air clearance of the pipe bus to split conductor and the casing equalizing ring is 7.8 m. The research results have guiding significance for the selection of the 1 000 kV air clearance on the network side. © 2021, High Voltage Engineering Editorial Department of CEPRI. All right reserved.