Using Tan Delta and Dielectric Constant as Criterion for the Selection of Suitable Insulation Materials for HV Cable Joints

Abstract

High-voltage cable joints are critical components where electric stress concentration often leads to insulation failure. This study evaluated three materials to find optimal configurations for controlling stress in 33 kV applications: PVC tape, stress-grading mastic, and semiconductive rubber tape, with initial relative permittivities of 2.96, 2.66, and 5.07, respectively. Dielectric measurements using a Schering Bridge at voltages of up to 3700 V determined material properties and breakdown characteristics. Semiconductive rubber withstood the highest voltage of 3700 V, while mastic failed at 1350 V. Finite element simulations showed that baseline configurations without proper insulation had a peak stress of 4.3 kV/mm. Simulations of individual materials identified non-linear resistive compounds, such as ZnO-based materials and carbon-black-filled polymers, as the most effective for stress control at conductor interfaces. A three-layer graded design, arranging materials by decreasing permittivity from the conductor outward, reduced the peak stress by 33% to 2.9 kV/mm. These results demonstrate that strategic permittivity grading combined with appropriate material selection ensures uniform field distribution and improved reliability in HV cable joints.