Design of breakdown tests on transformer oil

The design of the breakdown test was evolved on the basis of exploratory experiments, so that the test yields data suitable for statistical analysis. The control of- the test equipment was made automatic so as to avoid the distortion of the inherent distribution of breakdown strengths which may result from manual control. The exploratory experiments revealed that breakdown in a small oil volume represents a random stationary process. They further showed that, fora given gap length, particle impurities greater than a certain size, led to erratic behaviour of the breakdown strengths. The latter follow the extremal distribution of the smallest values based on initial exponential distribution. The material and the gap length of the electrodes affect the parameters of the distribution of breabdown strengths.