Space Charge Characteristics of Epoxy Resin during Accelerated Aging Process

The space charge in dielectric materials is closely related to the aging of insulating materials under DC voltage. In order to further reveal the aging process of ultra-high voltage direct current (UHVDC) dry bushing, it is necessary to study the space characteristics of epoxy resin used in the bushing during aging process. The epoxy resin samples were prepared in vacuum condition. The samples were aged for 24 hours under the dc stress of 60 kV/mm at different temperature (40, 60, 80 and 100 °C). The space charge in the samples during the aging process was simultaneously measured with improved pulsed electro-acoustic (PEA) system. When the temperatures are less than or equal to 60 °C, there are only homocharge accumulations in the sample bulks. When the temperatures are higher than or equal to 80 °C, the homocharge accumulations near both of the electrodes are the same as the conditions at low temperatures at first. Then subsequently, with the increase of aging time, the positive charge accumulation gradually occurs near the cathode at high temperatures. The higher the temperature is, the sooner the positive charge accumulated near the cathode appears, and the larger the amount of the positive charge is. The characteristics of space charge play an important role in distorting the electric field distribution. With the change of the space charge polarity, the position of the maximum electric field in the samples changed.