How AC Motors Are Made

Three phase AC motors are used for most industrial applications. The three main parts of an AC motor are the rotor, stator, and enclosure with working parts being the stator and rotor, while the enclosure protects the motor and serves as its housing.

 

AC motors are used for a wide variety of industrial applications because of their strength, adaptability, endurance, and simplicity of design, which makes for easy maintenance. They can operate an industrial pump or a home mixer and adapt to each function with ease.

 

Stator Core

The stator is the stationary part of an AC motor and the motor's electromagnetic circuit. It is made from laminations, which are thin metal sheets, that are stacked on each other to form a hollow cylinder. The use of laminations reduces the loss of energy.

 

Stator Windings
Stator windings refer to the copper wire that is wound around the stator in its slots. The number of slots in the stator depends on the phases of power that is provided to the coils. A three phase motor has six slots with three pairs of coil windings that are offset by 120o. The term winding is used to describe an entire electromagnetic circuit composed of multiple coils. The coils are of the same shape and size. The more coils a motor has, the more smoothly it will run.

 

The number of electric currents energizing the coils is known as the phase of the motor. A three phase motor can have three, six, or twelve coils.

 

When the motor is activated, the stator is connected directly to the power source, which transforms the coils and stator into an electromagnet.

 

Rotor
The rotor is the part of an AC motor that moves or rotates. The squirrel cage type of rotor construction is the most common type. Much like the stator, a squirrel cage rotor is made by stacking laminations to form a cylinder. The squirrel cage is formed by conductor bars that are evenly spaced inserted into the rotor's slots. The bars for the squirrel cage are made of aluminum or copper.

 

Once the laminations have been stacked and the conductor bars inserted, a steel shaft is pressed into the middle of the assembly.

 

Bearings
The function of bearings on an AC motor are to support and locate the rotor, to keep the air gap small, and transfer loads to the motor. They are able to operate at a variety of speeds while minimizing friction.

 

There are several types of bearings that are used in AC motors, which include ball and roller bearings. The life of a bearing in an AC motor is determined by the number of revolutions or operating hours a bearing can endure. Other factors include operating conditions and lubrication.

 

Air Gap
The air gap is the gap between the rotor and stator, which is a necessary part of the motor and a key to its design. The gap has to be large enough to prevent contact between the surfaces of the rotor and stator accounting for tolerances related to their dimensions, loose bearings, and movement. The air gap has to be as small as possible to enhance the efficiency of the motor since larger air gaps require more power to achieve sufficient magnetization.

 

Fan
In AC motors, heat builds up in the windings. For this reason, AC motors have a built in cooling system. Inside the enclosure, a fan is attached to the shaft of the rotor at the opposite end of the axle that drives the machine that the AC motor is attached to. The fan pulls in cool air and forces it across the windings. Hot air is blown out the rear of the enclosure.

 

Enclosure
The enclosure protects the internal parts of an AC motor from particles and liquids, provides convective cooling, and ensures electrical safety. The amount of protection depends a great deal on the quality of materials used to produce the enclosure. NEMA and IEC have specifications for enclosure designs. An ingress protection (IP) code is used to classify enclosures, such as IP65. The higher the number of the IP code the better is the protection.

 

Some enclosures come with heat fins on the side and do not have a fan for cooling. Totally enclosed fan cooled enclosures have a fan on the rotor shaft.