By Faraday's law of induction, a magnetic flux is generated in a conductor through which an electric current is flowing, when a changing magnetic field is superimposed on it, due to a changing current. Thus, if AC and DC circuits are connected in series, DC power can be obtained from an AC source, and if the AC current is continuous, the DC power is constant.
AC induction motors use the principle of Faraday's law of induction (as just described), but in contrast to the DC motors just described, the winding that forms the magnetic field is not connected to the return circuit for the AC current that is flowing, so it is said to be a shunt winding.
The squirrel cage rotor is made up of a number of copper bars that are wrapped around a core of hardened steel and known as the squirrel cage laminations. These are held together by a squarish casting between the center of the rotor and the outermost squirrel cage bars. The rotor connecting rings provide additional support.
This is really just a small motor with variable speed drive capability. The rotor turns in both directions with the same torque (pitch) by using the windings of one side of the motor to start the rotor turning in one direction then reversing the winding (and so reversing the direction of rotation) and start it spinning in the other direction, giving it the ability to rotate with either direction equally well.
By far the most common starting arrangement is to connect a d-c motor directly to the start winding of the piston. The motor will attempt to rotate with the piston, since they have the same inertia. However, friction of gearing, of the piston rod rubbing against the overhead, and of the diaphragm spring, will reduce the speed to a level that is lower than the normal speed for the motor. d2c66b5586