Partial discharge energy measurements on electrical machine insulation when energised at frequencies between 0.1 Hz and power frequency

The paper describes the measuring equipment and also gives the results of partial discharge (corona) measurements taken on a number of electrical machine insulation samples when energised at frequencies between 0.1 Hz and 50 Hz. The discharge magnitude and discharge energy values were obtained using a pulse discrimination system. The results were plotted on a multi-channel pulse height analyser which enabled integrated discharge values to be determined. The results demonstrate the variation of discharge inception voltage with frequency and show how it is affected by the quality of the insulation being tested. Similar values of integrated discharge magnitude and energy are obtained, if the test voltage is at a known fraction above the appropriate inception voltage. Good comparison is shown to exist over wide frequency and voltage ranges. The results are also in good agreement with those obtained using traditional bridge techniques.