AC Motors are electric motors, these motors are driven by an alternating current. The AC Motors consist of 2 basic parts. The first part: stationary stator having coils that produce a rotating magnetic field with AC current. (Stator is the term to describe the stationery part of a rotor system). The second part is the inside rotor (rotor is the spinning part of a mechanical device), it is given torque by the rotating field and is attached to the output shaft.

There are also 2 types of AC Motors these depend on the type of rotor used:

Type 1 ? Induction Motor

The Induction Motor's magnetic field is created by an induced current and it turns slightly slower than the supply frequency.

Type 2 ? Synchronous Motor

The Synchronous Motor's magnetic field is generated by a permanent magnet or delivered by the current of slip rings. The Synchronous Motor rotates at a sub-multiple of the supply frequency or exactly the same as the supply frequency.

History of AC Motors

A Serbian inventor named Nikola Tesla was the one who identified the rotating magnetic induction field principle in 1882. He generated torque in rotating machines by pioneering the use if this rotating he identified and the induction of electromagnetic field force.

In 1883 the design of a poly-phase induction motor exploited these new found principles and in 1885 a man named Galileo Ferraris researched the concept independently. The Royal Academy of Sciences in Turin was the place Galileo Ferraris published his research, it was published on paper in 1888.

The Second Industrial Revolution was initiated by the introduction of Tesla's motor onwards from 1888. This made possible long distance distribution of electrical energy and efficient generation of electrical energy using the AC (Alternating Current) transmission system, also an invention of Tesla's from 1888.

A man by the name of Michail Osipovich Dolivo-Dobrovolsky was later the inventor of a three-phase cage rotor, this was in 1890. The three phase AC Motor is now used in the majority of commercial applications.

Three Phase AC Induction Motors

The three phase (Polyphase) AC Induction Motor is commonly used where a Polyphase electrical supply is available and is used especially for higher powered motors. The three phases all have differences to the Polyphase electrical supply therefore creating a rotating electromagnetic field.

The electromagnetic field always causes the motor to turn in the same was the field is turning and always rotates slightly behind the phase peek of the stator. This means that the motor always moves slower than the rotating magnetic field that the polyphase supply is creating.

These induction motors have an output of up to about 670 horsepower (500kW) and are the workhorses in industry. They tend to have standardised frame sizes making them interchangeable between manufacturers.

Wind-Tunnel drives, Pipeline Compressors and Overland Conveyor Systems use extremely large induction motors that have the capacity to produce an output of tens of thousands of kW's.