The slip ring induction motor has two distinctly separate parts, one is the stator and other is the rotor. The stator circuit is rated as same in the squirrel cage motor, but the rotor is rated in frame voltage or short circuit current. The frame voltage is the open circuit voltage when the rotor is not rotating and gives the measure of turns ratio between the stator and rotor. The short circuit current is the current flowing when the motor is operating at full speed, with the slip rings shorted and the full load applied to the motor shaft.
Qualities Of Slip-Ring Motors:
1. suited for high inertia loads as it caters with excellent starting torque,
2. Low starting current when compared to squirrel cage induction motors,
3. Speed is varied with the help of external resistance, from 50% to 100% of the full speed,
4. Higher brush and slip ring maintenance required,
5. As the brush wears out, it may lead to intermittent contact, and thus heavy sparking.
Thus we have seen in detail the starting arrangement of slip ring induction motors. In my next article, we will discuss on the speed control of slip ring induction motors.