What is an Electric Motor?

Figure 1: Various types of electric motors.

An electric motor is a machine that uses the principle of electromagnetic induction to convert mechanical energy into electrical energy, or vice versa. It can be divided into generators and electric motors, the former converts mechanical energy into electrical energy and the latter vice versa.
The electric motor is an important part of the transmission and control system. With the development of modern science and technology, its focus in practical application has begun to shift from the simple transmission in the past to the complex control, especially the precise control of the speed, position and torque of the motor.

Types of Electric Motors

There are many types of motors and various ways of classification. The following are the classifications of several common types of motors:
1. According to the type of working power supply: direct current (DC) motor and alternating current (AC) motor.

2. According to the structure and working principle: DC motor, asynchronous motor, synchronous motor.

Figure 2: Comparison of an asynchronous motor and a synchronous motor.

3. According to the application: motor driver and motor controller.
a) Motor drivers can be divided into: power tool motors, household appliance motors and motors for other general-purpose small mechanical equipment.
b) Motor controllers can be divided into: stepper motor and servo motor, etc.

4. According to the structure of the rotor: squirrel cage induction motor and wound rotor induction motor.

5. According to the operating speed: high speed motor, low speed motor, constant speed motor, and speed control motor. Low speed motors are further divided into gear reduction motors, electromagnetic reduction motors, torque motors and claw-pole synchronous motors.

There are various classifications of motors, but the most basic and common classifications are that between DC and AC, synchronous and asynchronous, and controller and driver motors.

What do an Electric Motor Do?

Figure 3: Electric motors applied in a factory.

Electric energy is extremely convenient in production, transmission, distribution, use, control and energy conversion. In modern industrialized society, all kinds of natural energy are generally not directly used to production. Instead, it is converted into electrical energy first, and then the electrical energy is converted into the required energy (such as mechanical energy, thermal energy, sound energy, light energy, etc.) for use.

The main function of the electric motor is to generate driving torque as a power source for electrical appliances or various machinery. They are the main equipment in power plants and substations, responsible for production, transmission and distribution in the electric power industry. And in industry and agriculture, transportation, national defense and other departments and living facilities, various electric motors are widely used to drive production machinery, equipment and appliances. In addition, they are increasingly used in various control systems to achieve automation and intelligence.

Common Electric Motor Failures and the Causes

Figure 4: Causes of electric motor failures of different frequencies.

1. The electric motor cannot be started
1) Unconnected power supply;
2) Circuit breaking of winding;
3) Grounded winding or inter-phase short-circuit;
4) Wrong winding connection;
5) Melt blown;
6) Wrong wiring of the control equipment.

2. After the motor is pulled into the power supply, the melt is burned
1) Single-phase start;
2) Overloaded or stuck motor;
3) Inappropriate cross-sectional area of the melt;
4) Short-circuited connection between the power supply and the motor.

3. The motor does not start and buzzes after it is powered on
1) Overloaded or stuck motor;
2) Inadequate power supply;
3) The voltage being too low;
4) As for small motors, the grease is too hard or the fit is too tight.

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