Torque from hysteresis machines with type-II superconducting segmented rotors

Abstract

Electrical machines having rotors constructed from different numbers of type-II superconducting segments have been modelled numerically. The hollow cylindrical rotors are subjected to a rotating applied field that induces currents in the superconducting pieces and the resulting torque is evaluated. The mathematical technique used is based on the critical state model and solves for the current and field distributions within the superconducting pieces using the finite element method. In a two-pole rotating field, a rotor made from two half-ringed pieces is found to behave like a reluctance machine, having a larger peak torque than hysteresis type rotors constructed from other numbers of segments. In general, splitting the rotor up into more segments is advantageous when the flux penetration is small since this increases the hysteresis loss and equivalently, the torque. The modelling results indicate the number of segments which will result in the largest torque for a given rotor size, material critical current density and applied field amplitude. Such information is valuable when considering the performance optimisation of such machines.