Calculation of a.c. losses in a type II superconductor

A method of calculating a.c. losses in a type II superconductor is discussed, which is applicable to a variety of simple problems. Equations are derived which should be useful in calculating the losses in electrical machines with superconducting windings. These equations show the dependence of the loss on the magnitude and direction of the magnetic field and on the magnitude and phase angle of the transport current. The mathematical assumptions and models involved are considered in detail, and a comparison is made of calculations using the London and Kim approximations to the relationship between critical current density and magnetic field. Finally, the calculated losses are compared with published experimental measurements.