How torque is produced in a induction motor?

Answer 1

Torque is a Force applied at a Moment Arm. Or a force applied to a bar of a set length. Torque is a unit of Foot-pounds. If you have a ratchet wrench that has a 1 foot handle and you use it to torque a Bolt by applying a force of 20 lbs this will produce a 20 ft-lb torque load to the bolt. ( 1 Foot X 20 Lbs). This can be converted to 240 inch-lbs. The torque produced by car engines are also measured in terms of foot-pound of torque. This defines the power that the engine produces at the Shaft. This is convenient to use in calculating how much power is delivered to a car's transmission or wheels to allow the engineer to determine how fast the car will go, etc.

Answer 2

it will have two windings

one winding will be phase shifted with a capacitor to set up the rotating field to start the motor

depending on size of the starting winding and load sometimes one the motor is at speed the second winding is disconnected

capacitor start-run motors both windings are the same size and the capacitor provides the 90 degree shifted field all the time

sometimes a bigger capacitor is added for higher torque starts

Answer 3

Simply put torque is produced by the interaction of the resultant magnetic fields on the stator and rotor. For all electrical machines it the cross product of these two quantities.

Different machines utlise different ways in which to create these magnetic fields on the stator and rotor but all conform to same principle. An induction machine uses both the temporal and spatial distribution (conceived by Nicola Tesla) of the three phase windings to create resultant magnetic fields on both the stator and rotor which even though they both rotate are stationary relative to one another.

The high levels of flux required to realise such strong magnetic fields are a property of the ferro-magnetic materials used for the stator and rotor lamination's. The stator and rotor windings only serve to excite (induce) the high level of flux density present within the material due to magnetic domain alignment within the lamination material . This is the principle of induction that is referred to in induction motor. We use the stator and rotor current to excite / induce very high flux densities within the ferro-magnetic iron laminations and not the windings themselves.