Study on space charge behavior of oil-paper insulation under AC-DC combined stress

Abstract

The space charge within oil-impregnated pressboard under AC and AC-DC combined stress were observed with a fast space charge detecting system based on the automatic equipartition phase shift (AEPS) principle. The phase resolution is about 1.79°, i. e. 201 equal division during whole period. Space charge accumulation is not distinct under AC stress at 15 kV/mm. The homocharge accumulates near ground electrode and the density decreases toward the top electrode. It may be associated with the charge injection from electrode. The amount of injected charge and the transfer distance are both depended on the electric field. Space charge accumulation is significant under AC-DC combined stress with the equal component at 15 kV/mm. The negative space charge distribution is dominant within oil-impregnated pressboard during whole period. It is mainly caused by the disruption of balance for electric field and polarization time under AC-DC stress. The polarity reversal, i.e. the voltage crossing 0 V for periodic stress, must be considered when the DC component exceeds a certain range. The space charge accumulated within oil-impregnated pressboard can distort the electric field distribution.