induction motor, once the rotor is pulled into synchronism with its magnet, the squirrel cage has no current induced in it and so plays no further part in the operation. In more recent times, the use of variable frequency controls permits synchronous motors to start slowly and deliver more torque. Further reading Institute of Electrical and Electronics Engineers, "Analysis and Control of subsynchronous resonance : presented at the IEEE Power Engineering Society 1976 winter meeting and Tesla symposium". Piscataway, N.J., IEEE, c1976. 76CH1066-O-PWR. LCCN 77153757 //r842 Electric motors