Using partial discharge techniques to characterise transformer oil

The breakdown arc of a negative discharge is preceded by a burst of current pulses. Near to breakdown this burst of current pulses gives information about the size of the discharge and can be used to map its development. This paper develops the idea that, with the advent of fast digitizing oscilloscopes, the recording of such current pulse bursts can provide an alternative approach to the testing of insulating oils. The standard electrical breakdown test for transformer oil continues to be employed for the want of a better test, although it is acknowledged that the information it gives is of limited value. The proposed alternative approach, by avoiding actual breakdowns and testing over a longer period, can give more reliable (and reproducible) information not only about the breakdown voltage but also about the particle content of the oil.