Parts of an Electric Motor: A Complete Guide

Electric motors are essential components in countless devices—from household appliances and industrial machines to electric vehicles and power tools. Understanding the parts of an electric motor not only demystifies how these powerful machines work but also helps in troubleshooting, maintenance, and even innovation.

In this blog, we’ll break down the key components of an electric motor, explain their functions, and explore how they all work together to produce motion. 

An electric motor transforms electrical energy into mechanical energy. Typically, an electric motor consists of a stator, rotor, winding, bearings, and casing. The force of attraction or repulsion between the stator or rotor fields causes the motor to rotate. This article provides a detailed description of the components of a motor.

Main parts of an electric motor

        1. Stator

        2. Rotor

        3. Winding

        4. Bearing

        5. Casing

1. Stator

The stator is the stationary part of any electric motor. A permanent magnet or windings may be placed in the stator. In AC motors, the armature is carried by the stator, but in DC motors, the field winding is carried by the stator.  The stator cores of AC motors are built of laminated silicon steel, while the DC motor cores do not necessarily need to be laminated.

Typical stator (Ref.-insideevs.com)

The stator generates a rotating magnetic field that is critical for the motor's function. In AC motors, the stator typically consists of coils that are energized by alternating current to produce the magnetic field.

Function:
The stator generates the magnetic field that interacts with the rotor.

2. Rotor

The rotating part in any electric motor is known as the rotor. Because of the rotary motion it experiences inside an electric motor, the rotor got its name.

Similar to the stator, a rotor can also be a collection of windings (armature) or a single solid component. When windings are involved, they are typically wound around a solid core made of silicon steel or another laminated ferromagnetic material.

Motor rotor (Ref.: lesics.com)

The rotor is the rotating part of the motor, located inside the stator. It's mounted on the motor shaft and spins when acted upon by the magnetic field generated by the stator.

Types of Rotors:

• Squirrel cage rotor (common in induction motors)
• Wound rotor

Function:
The rotor receives torque from the interaction with the stator's magnetic field, which then causes rotation.

3. Windings

The term "windings" refers to coils of wire that typically encircle a metallic core comprised of a ferromagnetic material, such as iron or silica steel. The windings' primary function is to produce magnetic fields. These fields may come from an electric current or a permanent magnet via the electromagnetic effect.

Windings are coils of wire (usually copper or aluminum) that carry electric current. They are found in both stators and rotors, depending on motor type.

Function:

Create magnetic fields when current flows through them.

4. Bearings

An electric motor's rotor and shaft are supported by bearings, which reduces the rotational resistance.  Bearings prevent the motor from being affected by friction, lowering energy losses. This enables the efficient and effective transfer of mechanical energy from the rotor to the load.
Bearing effectiveness is influenced by design, material composition, load, and environmental factors.

Typical bearings (Ref.- emotorsdirect.ca)

Bearings support the motor shaft and allow it to rotate smoothly with minimal friction. They are essential for reducing wear and increasing the motor’s lifespan.

Function:
Facilitate smooth rotation and reduce mechanical wear.

5. Casing/Enclosure

The major purpose of the casing, an external component, is to safeguard the stator and rotor as well as other components of electric motors.  In essence, the casing serves as a barrier between the electric motor's internal structure and the outside world, reducing the impact of physicochemical variables like humidity and temperature on the motor's performance.

Motor casing

The enclosure houses all the motor components, protecting them from environmental factors like dust, moisture, and mechanical damage.

Types of Enclosures:

• Open drip-proof (ODP)
• Totally enclosed fan-cooled (TEFC)

Function:

Provides physical protection and sometimes assists in cooling

6. Commutator

In the DC motor, to maintain a repulsive force between the poles of the rotor and stator, commutators are utilized to switch the direction of current in the rotor. They can be found in any form of motor that needs a DC source to power its rotors. Carbon brushes with a spring-loaded action that are positioned above the commutator apply voltage to the rotor.

Motor Commutator (Ref.- wiraelectrical.com)

The commutator is a rotary switch that reverses the current direction through the rotor windings in a DC motor, ensuring that torque is always in the same direction.

Function:
The commutator reverses the direction of current to ensure continuous rotation in DC motors.

7. Carbon brush

The primary reason brushes are necessary is to transfer electricity from a stationary source to moving parts.  In most cases, an electric motor has two or more brushes. To guarantee that current passes through the motor in the proper direction, these brushes function in conjunction with the terminals (current input points) and commutators.  Typically, brushes are made of copper, graphite, or any other material that satisfies the motor's thermodynamic and electrical requirements.

Typical Carbon Brush (Ref.: electronicscuriosities.com)

In brushed motors, brushes are made of carbon or graphite and maintain electrical contact with the rotating commutator.

Function:
Transfer electric current from the external circuit to the rotor winding via the commutator.

8. Poles

Poles can be thought of as a hypothetical or transient element of an electric motor. They are the locations where the rotor's and stator's magnetic fields have the greatest magnetic influence.  However, pole shoes and pole cores can be used to strengthen the poles in an electric motor. To augment the magnetic affinity of the field windings and the stator core, this section of the stator has ferromagnetic windings installed.

9. Yoke

The yoke is a portion of the housing that covers or shields particular electric motor components like the rotor and stator.  It should be distinct from the casing, which is an all-encompassing external covering that encloses some (or all) of the electric motor's components.

Centrifugal Switch

10. Centrifugal Switch

Essentially, it is a switch that operates based on centrifugal force. It is used to disconnect either the starting capacitor or the starting winding in a single-phase induction motor. 

When the motor reaches between 50 and 70% speed, the centrifugal switch is activated to cut off the starting winding.

If the centrifugal switch is unable to open at 50 to 70 percent of its synchronous speed.  The starting winding of the motor will overheat and burn out; as a result, starting the motor will not be possible.

11. Shaft

The shaft is the component that transfers mechanical power from the motor to the machine or device it's driving. It is directly connected to the rotor.

Function:

Transmits the motor’s rotary motion to the output.

12. Cooling Fan (if present)

Larger or high-speed motors often include a cooling fan to dissipate heat generated during operation.

Function:
Prevents overheating and maintains efficiency.

Conclusion

Electric motors are remarkable machines built from a set of well-coordinated parts. Each component—from the stator to the bearings—plays a crucial role in converting electrical energy into mechanical motion. Whether you're an engineer, hobbyist, or simply curious, understanding the parts of an electric motor is the first step in mastering how they work.