Investigation on Time-Varying Behavior of NI HTS Field Coil for Synchronous Motors Considering Armature Reaction and Slotting Effect

This paper presents calculation results of time-varying behavior of no-insulation (NI) high temperature superconductor (HTS) field coil for synchronous motor considering armature reaction and slotting effect. We selected four NI HTS motor models having different stator topologies for confirmation of armature reaction and slotting effect. Also, before NI behavior analysis, we proposed a wound field synchronous motor (WFSM) dq-equivalent circuit which can be considered as a circuit model of insulated (INS) HTS motor. The circuit model used in this paper contains parameters varying with the position of rotor and dq-axes cross-coupling inductance for describing the armature reaction and slotting effect of practical motor. Next, to investigate time-varying behavior of NI field coil during steady-state operation, simulations of a new circuit model combining proposed dq-equivalent circuit and NI lumped circuit were implemented. Turn to turn radial leak current values of selected models were calculated at different armature current density. Also, torque ripple values of the NI and the INS case were obtained by circuit simulations. It can be confirmed that peak to peak radial current occurs by largest value at the topology having the greatest flux linkage harmonics and torque ripple value of NI motor is smaller than that of INS HTS motor.