As with an induction motor, when the stator coils of a multi-phase induction generator are connected to an alternating current grid, by transformer action a voltage is induced into the rotor windings, or the conducting bars of a squirrel cage rotor, with the frequency of this induced voltage in the rotor being equal to the frequency of the applied stator voltage. When the individual rotor windings are short circuited, or connected together through an external impedance, (the conducting bars of the squirrel cage rotor are already short-circuited together), a large current flows through the coils creating a magnetic field, which by Lenz's Law has a polarity opposite to stator field. This causes the rotor to rotate, being dragged along by magnetic attraction behind the rotating field created by the stator. The magnitude of the torque on the rotor depends on the magnitude of the relative speed between the rotating rotor and the rotating field created by the stator, commonly called the slip. The rotor thus accelerates up towards the synchronous speed set by the frequency of the grid suppy reaching a maximum when the magnitude of the induced rotor current and torque balances the applied load, while at the same time, the frequency of the currents induced in the rotor windings are reduced, keeping in line with the slip frequency. But the faster the rotor rotates, the lower is the resulting relative speed difference between the rotor cage and the rotating stator field, or the slip, and thus the voltage induced into the rotor winding. As the rotor nears synchronous speed, its torque decreases in line with the slip reducing the acceleration as the weakening rotor magnetic field is insufficient to overcome the friction losses of the rotor in idle mode. The result is that the rotor remains rotating slower than synchronous speed. This means that in motor mode, an induction machine can never reach its synchronous speed because at that speed there would be no current induced into the rotors squirrel cage, no magnetic field and thus no torque.