Electrical stress distribution in cable accessories when testing at different frequencies

This paper report on an theoretical investigation using FEA simulations on the stress distribution in medium voltage cable joints. Three different supplies namely 50 Hz sinusoidal, VLF 0.1 Hz sinusoidal and VLF 0.1 Hz cosine square were evaluated. The simulation results show that phase shifts occur in the stresses under 0.1 Hz sinusoidal voltages and that only above 10 Hz sinusoidal no phase shifts occur. With the application VLF 0.1 Hz cosine square the stresses are totally different to normal operating stresses. The reason for these differences is the influence of the volume resistivity and the interfacial polarization during low frequencies. The mechanisms involved to determine the stress distribution in the joint which as a multi layer insulation system is totally different to a cable which is a single layer insulation system. This should be taken into account when the most appropriate test voltage and frequency are selected for commissioning tests.