Finite Element Method Analysis of a Three-Media Submarine Cable Ground Return Impedance at Varying Depth

Submarine power cables are complex systems that are typically hard to model. Identifying the electrical parameters of submarine cables is fundamental for the correct modeling and safe operation of submarine power equipment. Commercial software products for power systems are typically used to calculate electrical parameters of subsea umbilicals. However, this kind of software often uses analytical formulations that might not correctly represent a three-medium ground return impedance. This work presents a Finite Element Method (FEM) analysis of submarine ground return impedances considering a three-medium domain composed of air, seawater, and soil at varying cable depth, which is compared to two-media and single-medium analytical formulations. A tool to estimate the minimal distance between the cable and a medium beyond which this medium can be ignored was also tested. Results show that this distance could be correctly predicted. The two-media formulation results agreed with FEM computed values on low frequencies, but not on high frequencies. On the other hand, single-medium analytical formulation agreed with FEM even at high frequencies, suggesting that the two-media ground return formulation validity could be questioned for submarine cables at high frequencies.