The DC voltage divider serving for Xiangjiaba-Shanghai ±800 k V HVDC project in Fulong and Fengxian stations often occurs an abnormal phenomena

which the secondary voltage jumping frequently in rain and hazy weather. According to these characteristics

based on studying the working principle of DC voltage divider

calculating the internal heating of resistance and analyzing the external electric field distorting under the coupling interaction between resistance heating and external pollution

the failure mechanism of UHVDC voltage divider is investigated. The results show that the short-circuit of RC elements in DC voltage divider caused by radial discharging is just the reason for the secondary voltage jump abnormally. When the voltage difference in radial direction between internal resistance voltage and external insulator voltage is too large the discharge takes place. Superficially

the serious external electric field distortion of insulator is the direct of cause of radial discharge. In fact

the defect of DC voltage divider configuration which results in high temperature rise and temperature gradient changing dramatically in vertical direction is the real reason for the fault in contamination and wet condition. Under the action of electric field

the coupling effect between gradient thermal distribution and surface contamination in insulator causes extremely voltage difference between external and internal divider along radial direction

when the difference voltage exceeds the breakdown voltage of the insulating medium the discharge appearing inevitably. To avoid occurring such failure

it should pay high attention to the design deficiency exciting in DC divider and some measurements should be taken to optimize the configuration of the DC divider

such as enhancing the heat dissipation segment to minimize the gradient of thermal distribution in vertical direction utmost.