Regulation of DC Electric Field Distribution within Insulation Via Positive Temperature Coefficient Material

Negative temperature coefficient(NTC) electrical resistivity of insulating materials causes the distortion of DC electric field, increasing the design difficulty of HVDC equipment. The ceramic(0～35%) with positive temperature coefficient(PTC) electrical resistivity was doped into epoxy resin to weaken its temperature dependence of electrical resistivity(0 ～ 35%). Thermal conductivity, electrical resistivity-temperature characteristics and DC breakdown strength were tested. The electric field and temperature distribution under temperature gradient were simulated. The higher doping of PTC filler has a better electric field distribution. As for epoxy composite with 20% filler, the thermal conductivity increases by 66% and the radial temperature gradient decreases by 55%; the NTC effect weakens and the activation energy decreases by 35%; the maximum distortion of electric field decreases by 58%, while the DC breakdown strength only decreases by 16%. The PTC effect of fillers mitigating the decline of electrical resistivity with temperature coupled with decreased hot-spot temperature suppresses the distortion of electric field. The optimization of electric field distribution within insulation via PTC materials/epoxy composites has potential to be used in HVDC electrical equipment.