Breakdown behaviour of polyethylene at dc voltage stress

The paper deals with breakdown voltage characteristics of polyethylene in homogeneous electric fields. The breakdown voltage characteristic is measured with foils in a sphere-sphere arrangement both with dc voltage and with impulse voltage superimposed on dc voltage. The electrical strength was found to be dependent on the pre-applied dc stress and the polarity of the impulse voltage at the instant of their superposition. The impulse breakdown voltage of dc prestressed samples was compared to impulse breakdown voltage superimposed on dc voltage. The influence of insulation thickness and a lamination of polyethylene foils on dc breakdown behaviour was investigated. Moreover, the breakdown voltage was measured in short circuit experiments. The influence both of fall time and of rise time of dc recovery voltage is discussed in connection with the space charge effect.