Effect of MWCNTs Content on the Voltage Coefficient of Resistance of Insulating Materials Coated with Semiconducting Coatings

The DC voltage standard device serves as the essential equipment for ensuring precise measurement of the operating voltage within the UHV DC transmission and transformation system. During the measurement of voltages exceeding the 800 kV level using the DC voltage standard device, the equivalent resistance of the insulating casing surrounding the standard device exhibits a nonlinear decrease, which adversely affects the accuracy of the measurements. A viable solution to this issue involves the application of semiconducting coatings. In this study, MWCNTs/EP semiconductive coatings with varying contents of MWCNTs were prepared and applied to the outer surface of epoxy insulating cylinders. Following the curing process, the resistance and voltage coefficient of resistance (VCR) of the samples were evaluated. The results indicated that the resistance of the semiconducting coatings consistently decreased with increasing MWCNTs filler content at a constant voltage, while the VCR exhibited a general upward trend in absolute value. For samples containing 0.1 wt% and 0.2 wt% MWCNTs, the conductive mechanism was primarily governed by field emission theory. In contrast, for samples with 0.3 wt%, 0.4 wt%, and 0.5 wt% MWCNTs, the conductive mechanism shifted to being dominated by over permeation theory.