D.C. dynamic braking of induction motor with a saturistor in its rotor circuit

In this paper two methods, a graphoanalytical method and an approximate analytical method, are presented for the analysis of the d.c. dynamic braking of an induction motor with a saturistor in its rotor circuit. Both these methods take into account the saturation of the magnetic circuit of the motor and the nonlinear nature of the resistance/current and reactance/current characteristics of the saturistor, and allow fairly accurate prediction of speed/torque and speed/current characteristics. The conditions for maximum torque, with given values of stator excitation and magnetising current, have been derived. The nature of speed/torque and speed/current characteristics for different values of stator excitation, different numbers of turns in the saturistor, different resistances in series with the saturistor in the rotor circuit and with d.c. control of the saturistor has been discussed. It is shown that the braking performance with an optimum resistance in series with the saturistor is superior to that when either the resistance, the saturistor or both are omitted.