Starting performance of saturable three-phase induction motors

The starting currents and torques (at slip S=1) are determined as a function of the terminal voltage of saturable three-phase induction motors from numerical magnetic field solutions. In order to obtain a first approximation for the stator and rotor currents, the unsaturated stator and rotor leakage reactances and resistances are calculated based on the conventional approach. The equality of the fundamentals of the stator and rotor current sheets along the circumference of the machine is used to compute the currents in the rotor bars as a function of the stator current. For this first approximation of the stator and rotor slot currents, the magnetic field and its associated reluctivity distribution within one pole pitch are determined based on the finite-difference formulation. The calculated (frozen) reluctivity distribution is then used to recalculate saturated stator and rotor leakage reactances, which provide a basis for a first and second approximation for the current distributions at starting. Both the measured stator currents and the associated torque agree well with the numerically determined values