Influence of the characteristics of semiconducting materials in high frequency on electric-field distribution in cable accessory

The cable accessory is the key to ensure the safety of transmission lines. Existing researches indicate that cable accessories always break down in the process of switching. Except the high-frequency transient overvoltage, the high frequency characteristics of the cable accessory are worthy to be paid more attention. In this paper, based on the measurements of the dielectric spectroscopy of insulating materials of ethylene propylene diene monomer (EPDM), silicone rubber (SIR), the cross-linked polyethylene (XLPE) and their semiconducting materials in ranges from 1 MHz to 1 GHz, we simulated four models of the electric field distribution in cable accessory under 35kV DC voltage and AC voltage, and respectively superimposed transient voltage. The results show that the conductivity of insulating materials of EPDM, SIR and XLPE increases about two to three orders of magnitude with the increase of the frequency, while their permittivity hardly changes. However, the conductivity of semiconducting materials of the three increases and the permittivity decreases. Among the three semiconducting materials, the conductivity and permittivity of the outer semiconducting material of the XLPE cable vary more. The simulations show that the electric field strength at the interface between the cable and the cable accessory is above security threshold under high-frequency transient voltage. The electric field distribution in cable accessory is within the safety threshold when frequency is 1 MHz. However, the electric field strength at the interface between the cable and the cable accessory is 2.765 kV / mm and 5.613 kV / mm respectively when the frequency increases to 100 MHz and 1000 MHz, which may cause interface breakdown and seriously influence the reliability of the cable accessory.