Effect Of Test Geometry, Permittivity Matching And Metal Particles On The Flashover Voltage Of Oil/Solid Interfaces

The 60 Hz and lightning impulse flashover voltages of various pressboards, polyethylene and polypropylene in transformer oil were studied. Except for one discrepancy the two widely different test geometries used generally grade the materials in the same order. It is concluded that the difference between materials is due to different discharge propagation properties, and that the propagation is assisted by permittivity mismatch between liquid and solid. Surface structure can also affect the flashover, especially at impulse voltages. At 50 Hz the introduction of solid surfaces can increase the flashover voltage. Metal particles on the interface can reduce average values of the flashover voltage by at least 20 percent and minimum values even more.