The Main Components of AC Motors


Since their introduction in 1887 by Nikola Tesla, Alternating Current (AC) motors have continued to develop, and now are commonly used in most household appliances and industrial machines. Motors operate by turning electrical energy into a usable torque, employing the principles of magnetism and electric current. AC motors, as differentiated from Direct Current (DC) motors, run with variable power supply. They are composed of two basic electrical components --- a stator and a rotor.


  • The primary winding component of an AC motor is called the stator. It is the stationary part which is connected to the power supply. A set of electromagnets are placed on the inside surface of the hollow, cylindrical stator. One pole of each of these magnets is set facing the hollow center, where the rotor will be positioned. The poles on the stator are also designed in a way where they can both repel and attract the poles installed on the rotor. This is done in order to create a continuous magnetic field that allows the rotor to turn without stopping.


  • The secondary and rotating component of an AC motor is the rotor, which is also shaped like a cylinder but is solid with a shaft on its center. The rotor contains a set of electromagnets that have their poles facing the poles of the electromagnets arranged on the stator. The magnetic interaction of these poles will induce the rotating motion of the rotor and the shaft. A basic rotor only contains two poles; the North and the South Pole. The rotor turns because the poles on the stator continuously attract and repel the poles on the rotor, creating a magnetic field that makes it possible for an AC motor to run.


  • The mount is also a component of an AC motor, and is the part of the frame which holds the stator. Depending on how it is fixed on the base frame, the mount can be of several types, like rigid base, resilient base, or National Electrical Manufacturers Association (NEMA) C face. A rigid base is fixed on the frame by bolts, welds or casts, while a resilient base is designed to counter noise and vibration by attaching isolation rings between the mounting hub and the frame base. A NEMA C face mount has a customized design enabling motors to be directly mounted. Bolts will be used to fasten the motor to the mount.


  • Enclosures are motor casings designed to protect the motor and control heat generated by the motor windings. The two most common types of enclosures are "Totally Enclosed Fan Cooled" (TEFC) and "Open Drip Proof" (ODP). TEFC enclosures have dust-tight and water-seal features. They are equipped with external fans, situated on the motor's rear shaft, that cool the surface of the casing and motor windings. ODP casings, on the other hand, are made of simple metal sheets with intake and exhaust vents. These have internal fans that cool the motor windings through the vents.


  • Photo Credit motors image by Dusan Radivojevic from
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