The application of the pulse discrimination system to the measurement of partial discharges in insulation under noisy conditions

Various methods of eliminating noise from partial discharge measurements are reviewed and it is pointed out that such techniques may not always be applicable due to environmental conditions and cost. It is explained that, by using the pulse discrimination system originally developed by one of the authors, one may reduce or eliminate filtering and screening and undertake partial discharge measurements in the presence of external interference. The original system was rather slow and the paper describes a new faster version which enables partial discharges to be recorded in the presence of interference pulse rates of around 10⁵ per second. The measurement system has a limited bandwidth and any common-mode radio interference entering the system within this bandwidth can be eliminated by the pulse discrimination system. The test results demonstrate that a single small pulse can be detected when it is buried in interference. The paper also shows that partial discharge characteristics taken under quiet conditions are similar to those recorded with considerable radio and pulse interference. When undertaking measurements under noisy conditions, some of the required pulses are lost as they are superimposed on interference. Methods of gathering data over a number of cycles of the supply voltage are therefore considered.