The Electric Field Threshold of Charge Accumulation in XLPE under AC field

Abstract

As a commonly used insulating material, the internal charge of the crosslinked polyethylene (XLPE) may accumulate under the AC electric fields, resulting in insulation aging. To better design insulation and electrical energy transport voltages, it is necessary to study the threshold electric fields for charge accumulation inside polymers at different frequencies. In this paper, by detecting the space charge response of XLPE under AC electric fields at different frequencies, the distribution of space charges and the threshold electric fields for a large amount of charge accumulation at different frequencies are analyzed. The results show that hetero-charges accumulate near the upper and lower electrodes of XLPE under the AC electric fields. The total internal charge accumulation of the XLPE under the AC electric field of different frequencies is Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.01Hz</inf> >Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5OHz</inf> >Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10kHz</inf> . The threshold electric fields of XLPE at 10kHz, 50Hz and 0.01Hz are 6.85kV/mm, 4.54kV/mm, and 6.26kV/mm, respectively. The analysis shows that the hetero-charges accumulated at the sample electrode and the accumulated internal charges of the same polarity as the cathode mainly come from charge injection and impurity dissociation, respectively. The hetero-charges on the surface of the sample reduce the barrier of AC charge injection, so that the AC threshold electric field is lower than that under DC fields. The difference in space charge accumulation at different frequencies may be caused by frequent charge injection and extraction at high frequency, resulting in shallow charge injection depth and less accumulation, while the long effective charge injection time and charge hysteresis at low frequency lead to more charge accumulation.