Research on the Insulation Performance for High Voltage Lead Exit of Ultra-high Voltage Transformers Under Long Duration Power Frequency Withstand Voltage

The test scheme was established according to the V-t characteristic of oil-filled transformer insulation.The long-term insulation property under the 10-hour and power frequency voltage was proposed as the test condition to evaluate the insulation margin of UHV lead exit.The insulation margin test system was designed and manufactured,which allows the lead exit to be tested independently from the transformer or reactor.The partial discharge(PD) level was taken as the characteristic parameter to study the electrical performance of the lead exit under long duration voltage.The two connection mode of PD test circuit was adopted.Based on the analysis of PD circuit,a method of distinguishing the PD position was presented to exclude the interference of bushing PD so as to accurately evaluate the test result.The test result shows that the self-developed UHV AC lead exit in China has good insulation performance without any partial discharge under the long duration power frequency withstand voltage.