DC Flashover Voltage Characteristics of Contaminated Insulatirs

An investigation was made of the influence of the dc power source on the withstand voltage ofntam-contaminated insulators. A thyristor-controlled power source was found stiff enough for the tests. DC contamination tests on various insulators were also carried out. The dc withstand voltage is generally lower than the ac one (rms). There seems to be a tendency that the rate of decrease in dc withstand voltage becomes larger as the contamination degree increases. The dc withstand voltage depends more strongly than the ac one on the insulator shape. The leakage distance per unit withstand voltage increases with the diameter of the insulator. The dc withstand voltage was also affected by the kind and the amount of insoluble material used, as is the case with ac. The withstand voltage decreases with an increase in the deposit density of insoluble material even at the same ESDD. The dc withstand voltage of the insulators ilators with noniform contam-contamination was not less than that based on ESDD assuming uniform contamination. Shown finally is then-conceptual design of insulator assemblies for the ±600 kV dc class.