Effect of oil quality and field configuration on steep-front breakdown strength of processed pressboard

The surface and puncture strength of flat processed pressboard samples have been measured under application of steep fronted short duration pulses in uniform and nonuniform field configurations. With the latter configuration the strengths have also been measured with new, field aged and reclaimed mineral oil. Tests have also been conducted to simulate retrofilling of transformers in the field with reclaimed oil. It is shown that with the exception of tests conducted with new mineral oil, a similar strength is obtained under all of the above conditions; with new oil higher strengths are obtained