The electric motor is a machine capable of converting electrical energy into mechanical energy. The induction motor is the most widely used type of motor because it combines all the advantages offered by the electrical energy such as low cost, easy of supply and distribution, clean handling and simple controls - together with those of simple construction and its great versatility to be adapted to wide ranges of loads and improved efficiencies.
A three-phase system is formed by associating three singlephase voltage system, U1 , U2 and U3 which so the phase displacement between any two of them ch is 120º, which means, the "delays" of U2 relating to U1 , U3 relating to U2 , relating to U3 , are equal to 120º ( considering a complete cycle = 360º ). The system is balanced if the three voltages have the same effective value, U1 = U2 = U
The synchronous speed of the motor is defined by the rotation speed of the rotating field which depends on the number of poles (2p) of the motor and on the line frequency (f) in Hertz. The field makes a complete revolution at each cycle and "f" is the system frequency in cycles per second (Hertz). Winding may have more than one pair of poles which can be alternately distributed (one "North" and one "South") along the circumference of the magnetic core. Since the rotating field runs through one pair of poles at each cycle and the winding has poles or "p" pair of poles
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