Study on dielectric surface discharge in transformer oil under high voltage nanosecond pulse

Electrical equipments are always subjected to different operating conditions and voltage waves which cause electrical failure on the surface and in the bulk of dielectrics. In this paper, experiments have been carried out to study main factors that influence the characteristic of dielectric surface discharge in transformer oil. Experimental study on flashover of nylon 6 and polymethyl methacrylate (PMMA) under applied voltage ranged from 50 to 250 kV shows that the flashover voltage U is influenced by the insulation structure, rise velocity and pulse width of the applied voltage. Flashover electrical field value E in pulse with rise time less than 10 ns is higher than that in DC and AC voltages. When angle between electrode and the sample is about 45°, nylon 6 and PMMA show the best flashover performance. From these results, the influence of the secondary electron emission and space charges on the electrical breakdown of dielectrics has been stressed.