Influence of DC Component on DC GIS Gap Breakdown under AC and DC Superimposed Voltages

In UHV (Ultra High Voltage) DC transmission, the valve-side equipment of the converter valve and converter transformer will be subjected to AC and DC voltages as well as AC and DC superimposed voltages with complex waveforms during the working period. The above situation challenges the insulation within the converter valve equipment. Based on the typical insulation structure of DC GIS (Gas Insulated Switchgear), this paper carries out AC and DC superimposed voltage experiments and studies the influence of DC component on the gap breakdown characteristics of DC GIS. The experimental results show that: In the positive polarity of the AC and DC superposition voltage, with the DC component gradually increased, the amplitude of the breakdown voltage by the AC breakdown voltage gradually increased and then remain unchanged. The distribution of breakdown voltage shows the change rule from normal distribution to bimodal distribution and then to normal distribution. In the negative polarity of dc and ac superposition voltage, with the increase of dc component, the amplitude of the breakdown voltage presents the trend of increasing firstly and then maintaining in the vicinity of DC breakdown voltage basically unchanged. And the distribution of breakdown voltage shows the change rule of normal distribution to bimodal distribution and then to normal distribution.