Test Voltage Frequency Effects on Electric Field Profiles in MV Cable Joints

On-site testing of cable systems is performed to verify the components' integrity and the installation work's quality. Although power cable systems operate at 50 Hz power frequency, they are commonly tested using 0.1 Hz Very Low Frequency (VLF) during on-site commissioning. In that regard, there is a knowledge gap in understanding how electric field stress distribution behaviour within Medium Voltage (MV) power cable systems varies under these 0.1 Hz VLF test conditions. This knowledge gap compromises the reliability of power cable accessories tests. Thus, this study aimed to identify the extent electric stress distribution is affected by variations in test voltage frequency. Finite Element Method (FEM) simulation models of an MV Joint were developed and analysed to compare 50 Hz power frequency to the 0.1 Hz VLF test condition. An equivalent resistance and capacitance (RC) circuit model was developed to validate and interpret the obtained simulation results within the cable joint. It has been confirmed that a change in voltage frequency from 50 Hz to 0.1 Hz causes changes in the electric field profile in the accessories. Questions arise on the efficacy of VLF tests on shielded power cables in comparison with 50 Hz tests.