抄録
The technique of analyzing the gases dissolved in insulating oil has been widely used to degradation diagnosis of oil-filled equipment such as transformers. On the other hand, oil-filled bushings can not be getting oil because power cut is required. In our study, we found that there are characteristics in frequency components of the electromagnetic wave radiated by partial discharge in oil. By using this characteristic, we have developed a method that can diagnose equipment in hot-line condition. However the cause of the characteristics has not been understood physically. Electromagnetic wave due to partial discharge is caused by the discharge current. It is expected that pulse waveform of current is steep if the velocity of charge is high, but waveform is gentle if the velocity is low. It is also expected that frequency of the electromagnetic wave is higher if the pulse waveform become steeper. Further, the moving velocity of the charge depends on the field strength. In addition, the strength of breakdown electric field depends on the insulating material. Then we forecast characteristic frequency components of partial discharge are affected by the difference of the electric field strength. So we tested the relationship between the rise time of the discharge current and the electric field strength. As a result, we confirmed that the discharge current waveform becomes steep due to the higher field strength. In this paper, we report the test result and developed method. And more, we introduce the examples of diagnostic result in field.
