Breakdown characteristics in transformer oil under the controlled effect of thermal and electric strength

Summary form only given. This paper deals with the breakdown characteristics in commercial transformer oils effected by both controlled thermal and electric strength (controlling the field efficiency factor) under DC voltage. The experiments are done under the normal practical operation condition in Thailand. The results are compared with the manufacture's specification. The commercial transformer oil from a main transformer plant is very carefully investigated in laboratory with the controlled environment similar to site condition, particularly, ambient temperature, oil moisture and purification, and temperature rise up to 100 celsius, with the test voltage up to 300 kV. The results have shown that, the such insulators has a linear characteristic in withstand with the test voltages, whereas the temperature are increased, and field factors varied.