3 Phase Induction Motor

A. Three phase induction motor

A motor is an electromechanical device which converts electrical energy into a mechanical energy. There are mainly two types of motor one is synchronous motor the other is induction motor. The induction motor is the workhorse of the industry. Every Motor consists:

(a) Stator: Stator of three phase induction motor is made up of cast iron. There are number of slots in the stator winding which are there to have three phase winding. The three phase winding are arranged in such a manner that they produce a rotating magnetic field when a 3 phase AC supply is provided to them.

(b) Rotor: The rotor is the moving component of the induction motor it is made up of laminated steel in the core with evenly spaced bars of copper

When the stator winding is connected to a 3 phase AC source, it establishes a rotating magnetic field rotating at the synchronous speed. It is based on the Faraday’s Law of electromagnetic induction which states that wherever a conductor is placed in a time varying magnetic field emf are induced which are called induced emf, if inductor circuit are closed, currents are also induced which is called induced current. As the rotor winding in an induction motor are either closed through an external resistance or directly shorted by end ring, and cut the stator rotating magnetic field, an emf is induced in the rotor copper bar and due to this emf, a current flow through the rotor

Machines having more than three phases exhibit the same properties, but those with one or two phases do not. This was one of the clinching arguments that led to the universal adoption of three phases for electrical power systems, more than a century ago. However, increasing numbers of induction motors are not connected directly to three-phase supplies. Instead, they derive their excitation from a power electronic converter, the input stage of which is connected to a three-phase supply. The output stage of the converter and the stator winding of the motor must have the same number of phases but provided this simple requirement is met, any number of phases may be used. Three is still the common choice, however, not only for the reasons given above but also because the mass production of three-phase motors for the main excitation keeps their unit cost low and standardization enables motors to be sourced from any manufacturer. Despite the above, there has been an upsurge of interest in multiphase machines that is machines with more than three phases. There are several reasons for this, the principal ones