Research on Temperature Dependent Threshold of Epoxy/paper Composites through Space Charge Measurements

High voltage direct current (HVDC) dry-type bushing is the key equipment in the ultra-high voltage direct current power transmission system. The temperature of its central conductor can go up to 105 °C under electrical/thermal working stresses. In order to study the effect of temperature on the dielectric performance, the space charge characteristics of epoxy/paper composites at different temperatures (20, 40, 60 and 80 °C) have been measured using a PEA method. Due to the discontinuity of permittivity and acoustic impedance at the interface of epoxy/paper composites, space charge distributions were preprocessed before analyzation. The experimental results show that a threshold (Eth) which directly reveals the inflection point of space charge accumulation is inversely proportional to temperature. Moreover, the direct-current (DC) steady state conductance currents were obtained under high electric fields at various temperatures. The threshold derived from conduction current measurement decreases as temperature increases, which is similar with the space charge measurement. Due to the measurement accuracy and the interference of pulse source, the threshold of space charge is generally smaller than that of conductance current.