Influence mechanisms of pulse duration on transformer oil breakdown characteristics

The paper presents results of optical and statistical studies of pre-breakdown phenomena and electrical breakdown strength of transformer oil in a quasi-uniform field. The breakdown strength of transformer oil are studied over a wide range of pulse width. It can be seen from the breakdown results that the functional relation between breakdown field strength of transformer oil and the impulse effective time teff in double-logarithmic coordinate can be divided into three regions, and the critical value of which is about 0.5μs and 50μs. A new formula is derived to describe this relationship in a wide time range. Secondly, a high speed shadow graphic visualization system with high magnification is built to detect the initiation processes of streamers in transformer oil. Three different pulses are used to study the streamer processes. The discharge characteristics of transformer oil is determined by the competition of two different mechanisms. With the increase of field strength or the decrease of pulse duration, it becomes easier for the streamers initiate from the anode. There are three different breakdown modes with the pulse duration.