MUSTAFA SAMY EL_HEBIRY

AC motor

AC MOTORS

 An AC motor is an electric motor driven by an alternating current .

TYPES OF AC MOTORS There are two main types of AC motors,

depending on the type of rotor used.The first type is the induction motor, which runs slightly slower than the supply frequency. The magnetic field on the rotor of this motor is created by an induced current.The second type is the synchronous motor, which does not rely on induction and as a result, can rotate exactly at the supply frequency or a sub-multiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet. Other types of motors include eddy current motors, and also AC/DC mechanically commutated machines in which speed is dependent on voltage and winding connection.

CONSTRUCTION

ROTOR1. Salient pole It is used in low and medium speed alternators2. Smooth cylindrical It is used for steam turbine driven alternators. The rotor consists of a smooth solid forged steel cylinder having a numberSTATORIn alternator, it is used for holding the armature stampings and windings in position

AC motors typically feature rotors, which consist of a laminated, cylindrical iron core with slots for receiving the conductors.The most common type of rotor has cast-aluminum conductors and short-circuiting end rings. This ac motor "squirrel cage" rotates when the moving magnetic field induces a current in the shorted conductors. The speed at which the ac motor magnetic field rotates is the synchronous speed of the ac motor and is determined by the number of poles in the stator and the frequency of the power supply: ns = 120f/p, where ns = synchronous speed,    f = frequency, and     p = the number of poles.