The high voltage test techniques of circuit-breakers and isolators with impulse (lightning or switching) voltage applied to one terminal and the power frequency voltage applied to the opposite terminal are presented.The test circuits
technical measures and theco mparision of attained technical specific ations. with the reley ant standard of IEC are introduced.The opposite phase type fests of imp ulse and po wer frequency voltage had been made on the circuit-breakers type KW 5-220 and KW 5-500.