Numerical investigation of electromagnetic-thermal-mechanical coupling in no-insulation REBCO coils via an improved T–A formulation

Superconducting Magnetic Energy Storage (SMES) systems exhibit significant potential in smart grid and high-dynamics energy storage applications due to their high-power density and rapid response capabilities. This work examines the multi-field coupling behavior of No-Insulation (NI) high-temperature superconducting coils, specifically analyzing their performance evolution during charging and under harsh operational conditions. A 2D axisymmetric multi-physics coupling model of the NI magnet coil was established using an improved lumped equivalent circuit model and T–A formulation under Neumann boundary conditions. The model analyzes the electromagnetic losses, temperature distribution, and mechanical response characteristics under different excitation rates and sudden power-down events. The results demonstrate that an elevation in excitation rate markedly intensifies the angular current delay effect and radial current redistribution, resulting in a large increase in the coil's total electromagnetic losses and temperature. In the event of a sudden power-down, the induced terminal voltage experiences a reverse surge (−15.322 mV), causing a sharp increase in electromagnetic losses. The NI coil effectively mitigates transient loads through a radial current redistribution mechanism. Mechanical analysis indicates that under high-speed excitation, the uneven distribution of shielding currents leads to circumferential stress concentration at the inner radius of the top coil, resulting in turn-to-turn lamination at the unconstrained outer radius and thereby reducing the mechanical performance of the coil. This study reveals the self-carrying operational characteristics of the NI coils under multi-field coupling, providing novel perspectives on the design and application of NI coils in SMES systems.