Study on the influence of gases on white marks and carbonized tracks generated by partial discharge in transformer oil-paper insulation

Partial discharge (PD) in oil-paper insulation of transformer is considered to be a serious fault condition. The movement of excessive charge over pressboard may result in mechanical and chemical damage to material through thermal and electronic action. With the development of PD, gases, white marks and tracks appeared. To research the relationship among the gases white marks and carbonized tracks, a needle-plate electrode configuration was set in laboratory. Pressboards with grooves of varying depths were made to release the gases. And all the pressboards were dissected layer by layer so as to observe carbonized tracks inside the pressboard. Besides, the phenomena of gases, white marks and tracks were recorded by taking photos. The experiment showed that: with the development of PD, carbonized tracks appeared on the pressboards. And as the decomposition of the insulation oil and pressboards, a large amount of gases were generated and overflowed through the pressboard pores, then white marks were formed; Moreover, due to the existence of residual gases, the surface of pressboard was raised where PD happened; As the gases loosed and even broke the pressboards´ structure, PD took place more easily. As a result, carbonized tracks grew to be more.