Space charge characteristics in cross-linking polyethylene under electrical stress from dc to power frequency

The space charge characteristics in cross-linking polyethylene (XLPE) are investigated under various electrical stresses from de to power frequency. The pulsed electro-acoustic method is improved to meet the needs of measurement under ac voltages. The frequency and phase angle dependences of the space charge are studied by means of phase-locking and frequency-converting techniques. Test results show that space charge can develop and accumulate in XLPE under an ultralow frequency voltage. The critical frequency of the applied ac voltage is less than 0.02 Hz. The mechanism of the formation of space charge in XLPE under an ac voltage is discussed through degassing of a sample in vacuum.