M. Schueller, F. Senn, W. Ladstaetter

Isovolta AG, System Development High Voltage, Werndorf, Austria
 

Testing isolation systems of rotating electrical high voltage machines with voltages much higher then the standardized acceptance level of 2·Un + 1kV becomes more and more common these days. This paper describes the effects of high one minute withstand voltages of up to 4.5·Un on the voltage endurance of the insulation system. To evaluate the influence of different AC hipot levels model generator bars have been carefully produced under laboratory conditions. The voltage endurance of reference test bars without prior withstand testing was compared with test bars exposed to four different one minute test voltages between 3.5·Un and 4.5·Un. To obtain further information on the generated energy and thus electrical deterioration mechanisms during the withstand voltage test, partial discharge measurements have been performed simultaneously. As a result of these experiments a significant reduction of the electrical lifetime of the insulation of rotating machines after exposure to high withstand voltage levels could be seen.