  The use of high-temperature superconductors in electric machines offers
potentially large gains in performance compared to conventional conductors, but
also comes with unique challenges. Here, the electromagnetic properties of
superconducting electric machines with bulk HTS trapped-field magnets in the
rotor and conventional copper coils in the stator are investigated. To this
end, an analytical model of the electromagnetic field in radial air-gap
synchronous electric machines is developed and validated, taking into account
the specific difficulties that occur in the treatment of machines with bulk
HTS. Using this model, the influence of pole pair number, stator winding
thickness, rotor surface coverage, and air gap width on the machine's Esson
coefficient is calculated. In contrast to numerical simulations, the method
presented here can provide results within minutes, making it particularly
useful for work in early development and systems engineering, where large
parameter spaces must be investigated quickly.

Applied Physics;Superconductivity