Influence of the HTS Winding Tape on Limiting the Transient Currents in Superconducting Transformers

The article presents an extended computer model of a HTS (high temperature superconducting) 21 MVA 70/10.5 kV transformer with severalfold compound windings, based on a verified PSpice model of 10 kVA transformer with single windings. Two superconducting tapes: SCS12050 (with a copper stabiliser layer) and SF12050 (without a stabiliser) were used in the windings. The circuit model of the transformer developed in the PSpice environment considers Rhyner's power law and the Jiles-Atherton description of the magnetic hysteresis loop. Two types of transient states were analysed: switching on a superconducting transformer to the network and an emergency short-circuit of the secondary winding. For the first five unidirectional current pulses generated when connecting an unloaded transformer to the network, the values of the pulse duration (gamma angle), the temperature increase in the primary winding as well as the mean and effective values of the switch-on current were calculated. The waveforms of currents, voltages, changes in resistance and temperature during the operation short-circuit were compared for the windings with both types of HTS 2G (high temperature superconductor second generation) tapes. The conducted analysis allowed us to determine the influence of electrical and thermal parameters of the tapes in question on the effective limitation of current in transient states and the possibility of their use in the construction of superconducting transformer windings.