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The temperature and field dependencies of electric conductivities of two types of silicone rubber-based polymers intended for use in high voltage direct current applications are presented and discussed. The conductivities obtained with the standard method by measuring a current through the material sample placed between metallic electrodes in response to the applied voltage are compared with those deduced from the measured potential decay on pre-charged material surface in an open circuit configuration. The measurements were conducted in the range of the applied electric field strength (0.5–5) kV/mm and temperatures ranging from 22 °C to 70 °C. It is shown that the values of the conductivities obtained by the two methods are in agreement and their temperature dependences obey Arrhenius law yielding similar activation energies. [ABSTRACT FROM AUTHOR]

To design reliable high voltage cables, clean materials with superior insulating properties capable of operating at high electric field levels at elevated temperatures are required. This study aims at the electrical characterization of a byproduct-free crosslinked copolymer blend, which is seen as a promising alternative to conventional peroxide crosslinked polyethylene currently used for high voltage direct current cable insulation. The characterization entails direct current (DC) conductivity, dielectric response and surface potential decay measurements at different temperatures and electric field levels. In order to quantify the insulating performance of the new material, the electrical properties of the copolymer blend are compared with those of two reference materials; i.e., low-density polyethylene (LDPE) and peroxide crosslinked polyethylene (XLPE). It is found that, for electric fields of 10–50 kV/mm and temperatures varying from 30 °C to 70 °C, the DC conductivity of the copolymer blend is in the range of 10−17–10−13 S/m, which is close to the conductivity of crosslinked polyethylene. Furthermore, the loss tangent of the copolymer blend is about three to four times lower than that of crosslinked polyethylene and its magnitude is on the level of 0.01 at 50 °C and 0.12 at 70 °C (measured at 0.1 mHz and 6.66 kV/mm). The apparent conductivity and trap density distributions deduced from surface potential decay measurements also confirmed that the new material has electrical properties at least as good as currently used insulation materials based on XLPE (not byproduct-free). Thus, the proposed byproduct-free crosslinked copolymer blend has a high potential as a prospective insulation medium for extruded high voltage DC cables. [ABSTRACT FROM AUTHOR]