Comparative Study of Dielectric Properties of Two Kinds of Insulating Oils in the Oil Gap of the Equipotential Ball

In order to research into the electrical performance of plant insulating oil under pure oil gap, some research institutes applied needle - ball electrode to carry out experimental research under power frequency voltage and lightning impulse, but in the actual transformer, there is no such kind of electrode structure, which shows tiny reference to actual design of the transformer. Based on pure oil gap structure of the typical transformer - equipotential ball to the box wall (ascending flanged base wall), to carry out plant insulating oil and mineral insulating oil under the negative polarity lightning impulse, negative polarity operation impulse together with breakdown and voltage withstanding test under power frequency voltage. The results show that: in the pure oil gap of the equipotential ball, the average breakdown voltage of plant insulating oil under the three kinds of over voltage is lower than the mineral insulating oil; and negative polarity lightning impulse breakdown voltage is the most decentralized, while the breakdown voltage under power frequency voltage shows the minimum dispersion. The dispersion of plant insulating oil is larger than that of mineral insulating oil. Nevertheless, negative polarity lightning impulse breakdown voltage is more sensitive to the oil.