Studies on corona in transformer oil by measurement of space charge

Studies were carried out for needle-plane gaps with a comparatively long separation in transformer oil. Relations between needle voltages and space charge quantities due to coronas by lightning impulse and AC voltages were obtained. It was found that the charge quantities for AC voltages were larger by 1.2 times and 6 times than that for the positive and the negative impulse voltages respectively. It was also found that the space charges by impulse voltages were reduced considerably by back-discharge phenomena.