Design and Optimization of Air-Core HTS Pulse Transformer for Series-Type Hybrid Circuit Breaker (S-HCB)

This paper discusses the design and optimization of a unique HTS air-core pulse transformer for the new class of dc series type hybrid circuit breakers (S-HCBs) operating in the liquid nitrogen (LN2) under cryogenic environment. The HTS secondary windings of the new pulse transformer carry a dc load current offering ultralow power loss during the normal operation unlike the conventional solid state circuit breakers (SSCBs). Unlike the prior-art HTS power transformers and the superconducting fault current limiters (SFCLs), the new pulse HTS transformer is uniquely designed to prevent the HTS tapes from quenching despite the set of constraints imposed by the S-HCB operation including a large pulse current up to 6kA and high mechanical stress. A new transformer optimization methodology is proposed using the genetic algorithm (GA) in MATLAB coupled with SIMULINK and a finite element model (FEM) in COMSOL to find the optimal transformer design meeting the overall 10kV/150A S-HCB design requirements within the electromagnetic constraints of the HTS. A 10kV/150A HTS transformer prototype is built and the electrical parameters are measured and found consistent with the simulated parameters. The S-HCB with the HTS transformer is tested at 600V/30A and 5kV/150A to validate the design. The experimental and COMSOL simulation results showed the successful operation of the HTS transformer and the fault currents of 30A and 150A were forced down to zero within10μ sand remain as a small ripple current for200μ sbefore a series mechanical switch opens arclessly and with no damage caused to the HTS windings.