Evaluation of degree of oil impregnation in HDLP pressboard using partial discharge detection

Degree of impregnation of pressboard samples was investigated using partial discharge detection method. A PD detector instrument was used. Changes in inception voltage level were taken as means of impregnation degree estimation. First, the samples were under drying and vacuum treatment for several days, and electrode holes were drilled according to IEC 60243-1.The applied voltage was a sinusoidal voltage of 50 Hz. In carrying out this experiment, it was found that impregnation degree could only be measured when oil reached the area between electrodes. So, in order to measure inception voltage as soon as impregnation started, sample was put into oil, and oil was allowed to leak into the electrode holes. The voltage level was increased gradually while the pressboard sample was under continuous impregnation process. The inception voltage and the discharge (PD) levels were recorded. The results of the measurements show that impregnation degree can be estimated using partial discharge detection, where the inception voltage increases during impregnation process