Study On Influence Factors Of The Breakdown Voltage Of The Tip Plate Electrode Under Composite AC And DC Voltage

HVDC transmission technology has developed rapidly in recent years in china,and the voltage level has gradually increased.As an important equipment of the HVDC transmission system,the converter valve suffers from greater volume of composite AC and DC voltage with enhancement of voltage level.High electric field may cause discharge even breakdown in converter valve.At present,the breakdown characteristics of air gap under composite voltage have been short of research.It can optimize the internal insulation of the converter valve by studying the air gap breakdown characteristics of the tip-plate electrode under composite voltage.In this paper,a composite AC and DC voltage breakdown experiment platform with is built.In order to study the breakdown characteristics of extremely non-uniform electric fields,the tip-plate electrode is used as the experiment electrode.A gas discharge model based on fluid dynamics is established,and the validity of the model is verified by an example.The effect of the electrode spacing and the DC component on breakdown voltage of the tip-plate electrode under the composite positive DC and AC voltage is studied by applying the composite voltage to the plate and grounding the tip.The experimental results show that at the same distance,the composite breakdown voltage first remains unchanged and then gradually decreases as the DC component voltage decreases from the DC breakdown voltage to 0.The DC component also has a large effect on the distribution of breakdown voltage and the positive discharge pulse before breakdown is an important reason for the significant change of breakdown voltage.The influence of the positive discharge pulse on the insulation of the air gap is analyzed by simulating the positive discharge of the tip-plate electrode and the experimental results are explained.The effect of the electrode spacing and the DC component on breakdown voltage of the tip-plate electrode under the composite negative DC and AC voltage is studied by applying the composite voltage to the tip and grounding the plate.The experimental results show that the composite breakdown voltage first remains unchanged and then gradually decreases with the decrease of the DC component when the electrode spacing is 1～2cm,the composite breakdown voltage decreases continuously with the decrease of the DC component when the electrode spacing is 2.5cm.The DC component also has a large effect on the distribution of breakdown voltage and the negative discharge pulse before breakdown is an important reason for the significant change of breakdown voltage.The influence of the negative discharge pulse on the insulation of the air gap is analyzed by simulating the negative discharge of the tip-plate electrode and the experimental results are explained.