Optimization of a Three-Phase Coaxial 10 kV/1.5 kA HTS Power Cable for Balancing 3-Phase Current Distribution

With the increasing power load of urban power grid, the upgrading of conventional cable is facing with the problem of space resource shortage. Three-phase coaxial high temperature superconducting cable has the advantages of compact structure, low loss, and nearly 2/3 reduction in the consumption of HTS tape, which provides a new prospective solution for urban expansion. However, due to the different radius of each phase of the three-phase coaxial HTS cable, the symmetry of electromagnetic parameters of each phase are affected, resulting in the imbalance of the three-phase current, which will reduce the transmission efficiency. Based on the multi-loop method, we establish the differential equation of three-phase coaxial superconducting cable in this paper, by calculating the parameters of three-phase inductance and capacitance by a numerical method, and obtain the instantaneous variation rule of voltage and current in the three-phase coaxial HTS cable. We propose a novel two-section Particle Swarm Optimization to solve the problem of three-phase current imbalance in HTS cable. The algorithm divides the C-phase conductor and the copper shield layer into two segments with the same radius but different pitches and twist directions, which increases the variable by one-half. By changing the pitches and winding directions, considering the thickness of the insulation, optimization of current distribution of three-phase coaxial HTS cable is achieved. Finally, we designed a 10 kV/1.5 kA three-phase coaxial HTS cable. The results show that the current imbalance ratio of the superconducting cable is reduced from 41% to 1% after the two-section Particle Swarm Optimization. The mathematical model and the imbalance optimization algorithm of three-phase coaxial HTS cable both are verified. The optimization results provide important reference for the structural design and experimental research of three-phase coaxial HTS cable for urban power grid.