Steady State Stability of an Electric Drive (Cont.)

To check the stability at an operating point of the motor, if an increase in speed brings greater increase in load torque than the motor torque, the speed will tend to decrease and return to its original value, so operating point will be a stable point else operating point will be an unstable point.

Various Speed and Torque Curves of Motor and Load

Cases (a), (b) and (c) represents stable operation of drive. Cases (d), (e) and (f) represents unstable operation of drive. Case (g) represents indeterminate condition.