The study on flow electrification of oil-cellulose insulating system in large power transformer

Electrical breakdown due to charge accumulation from transformer oil flow has caused many failures of large power transformers world wide. The problem is due to the entrainment of diffused electrical double layer charges into circulating transformer oil. As the charges accumulate on the surface of solid insulating materials and in volume oil, static potential builds up. If the rate of charge accumulation is greater than the rate of charge relaxation, harmful spark discharge may occur. By employing a pressboard pipe model, the study carried out revealed the influence of higher oil flow rate and upstream charge on flow electrification By simulating an actual transformer internal structure, it is noticed that there is a probability of partial discharge inception under higher oil circulation velocity. However, the upstream charge and dry zone can lead to a great increase of electric field strength, which may become important potential causes of partial discharge inception under the condition of relative low oil velocity