Space Charge Measurements in Low-Density Polyethylene under AC stress by the Pulsed Electro-acoustic Method

Space charge profiles obtained in low density polyethylene under sinusoidal or square AC stress for frequencies going from DC to 10 Hz, temperature from 25 to 50degC and fields of 30 or 40 kV/mm are presented. It is shown that most of the features observed under DC stress (generation of carriers of the two polarities with non-symmetrical amount and velocity) are still active under AC stress. As a matter of fact, it is shown that a negative space charge builds up at 50degC within the whole insulation bulk even with relatively high stress frequency.