Light emission measurements of predischarges in insulating oil

This paper deals with the measurement of the light emissions and the charge occuring during the prebreakdown in insulating oil. For the charge measurement a specific sensor was used which minimizes the influence of the stray capacitances. In addition to the charge measurement a photomultiplier tube was installed in the test set-up which allowed the recording of the light emissions during the pre-discharge growth. For both the positive and negative primacy streamer, a linear rise of the charge could be observed which changes subsequently into a step-wise growth. At positive polarity every new step is correlated with an impulse-like emission of light. This is in contrast to the negative streamer, where a continuous emission of light could be determined.