Cable dimension determination using Finite Element Method Magnetic (FEMM) for three-core belted and gas insulated cables

Abstract

A numerical approach utilizing the Finite Element Method (FEM) based freeware Finite Element Method Magnetic (FEMM) is employed to optimize the insulation thickness to diameter ratio (‘T/d’) for a three-core belted cable, enclosed by a grounded sheath, as well as for a gas-insulated cable (GIC) with a common enclosure. The method analyzes the maximum electric field (E-field) within the cable. The minimum E-field magnitude across three critical regions where the E-field at its peak is calculated for different ‘T/d’ ratios, and the optimal ‘T/d’ is identified by selecting the maximum of these minimum values. Analogs to single-core coaxial cable, for a three-core belted cable with a radius of 1 per unit (p.u.), the best ‘T/d’ ratio is 0.80 when subjected to a 1 p.u. Peak potential. Additionally, the optimal conductor radius and conductor-to-cable center dimension for common-enclosure gas-insulated cables are verified to be 0.18 and 0.5, respectively. This study provides a first-time investigation of the best ‘T/d’ ratio for three-core belted cables and verifies CGIC cable parameters using FEMM, where no analytical solutions are available. The results are validated by comparing FEMM with analytical and Charge Simulation Method (CSM) outcomes. Hence, the FEMM provides low computational cost and reliable results compared to commercial software. Through these simulation efforts, the study re-examines the stress within the belted and gas-insulated cables and the parameters that influence it. The FEMM method allows for precise control of both conductor and sheath potentials, ensuring no potential discrepancies between the applied and calculated values across the entire range of T/d ratios.