The cars are pulled at a speed synchronous with the speed of the track's field.
Active power delivered to the line is proportional to slip above the synchronous speed.
At synchronous speed of 1800 rpm, generator will produce no power.
Torque generated by the drive causes the induction motor to run at synchronous speed less the slip.
Some include a squirrel-cage structure to bring the rotor close to synchronous speed.
The motor then runs at synchronous speed as if the rotor were a permanent magnet.
Speed control (by brush-shifting) is possible from 75% below synchronous speed to 10% above.
Thus at synchronous speed the rotor is "locked" to the rotating stator field.
At synchronous speed these poles lock to the rotating magnetic field.
Once started at synchronous speed, the motor can operate with sinusoidal voltage.