To reveal the formation mechanism of internal overvoltage of electrode line in HVDC

its influence factors

and distribution feature

an overvoltage analysis model of UHVDC transmission project was established in EMTDC/PSCAD. Based on simulation results

the relationship among the amplitude of internal overvoltage

the amplitude and the gradient of current flow through the electrode line was analyzed. It is revealed that the severe fluctuating of unbalance current in electrode lines during faults or conversion of operation mode is the main cause for internal overvoltage. The internal overvoltage is affected by the fault type

the fault position

and the length of electrode line. And its amplitude reduces linearly along the electrode line. Moreover

the optimized configuration method of insulation level of electrode line was discussed. A reasonable and economic method to determine the scales of parallel gaps in electrode line was proposed. At last

a series of suggestions on the design and maintain of electrode line was presented.