The electrical equipment that converts electrical energy into mechanical energy is collectively referred to as a motor. Electric motors use the principle of electromagnetic induction to achieve the mutual conversion of electrical energy and mechanical energy. The device that converts mechanical energy into electrical energy is called a generator, while the device that converts electrical energy into mechanical energy is called an electric motor.

Classification of motors

According to the type of working power supply, it can be divided into DC motors and AC motors.

1) DC motors can be divided into brushless DC motors and brushed DC motors according to their structure and working principle.

Brushed DC motors can be divided into permanent magnet DC motors and electromagnetic DC motors.

Electromagnetic DC motors are divided into series excited DC motors, parallel excited DC motors, separately excited DC motors, and compound excited DC motors.

Permanent magnet DC motors are divided into rare earth permanent magnet DC motors, ferrite permanent magnet DC motors, and aluminum nickel cobalt permanent magnet DC motors.

2) AC motors can also be divided into single-phase motors and three-phase motors.

According to their structure and working principle, they can be divided into DC motors, asynchronous motors, and synchronous motors.

1) Synchronous motors can be divided into permanent magnet synchronous motors, reluctance synchronous motors, and hysteresis synchronous motors.

2) Asynchronous motors can be divided into induction motors and AC commutator motors.

Induction motors can be divided into three-phase asynchronous motors, single-phase asynchronous motors, and shielded pole asynchronous motors.

AC commutator motors can be divided into single-phase series excited motors, AC/DC dual-purpose motors, and repulsion motors.

Divided by starting and operating modes:

Capacitor starting single-phase asynchronous motor, capacitor running single-phase asynchronous motor, capacitor starting running single-phase asynchronous motor, and phase separated single-phase asynchronous motor.

Divided by purpose: drive motors and control motors.

1) Electric motors for driving can be divided into: electric motors for power tools (including drilling, polishing, grinding, slotting, cutting, expanding, etc.), electric motors for household appliances (including washing machines, electric fans, refrigerators, air conditioners, recorders, video recorders, DVD players, vacuum cleaners, cameras, hair dryers, electric shavers, etc.), and electric motors for other general small mechanical equipment (including various small machine tools, small machinery, medical equipment, electronic instruments, etc.).

2) Control motors are further divided into stepper motors and servo motors.

According to the structure of the rotor, it can be divided into:

Cage induction motors (formerly known as squirrel cage asynchronous motors) and wound rotor induction motors (formerly known as wound type asynchronous motors).

There are a wide variety of electric motors, how can you find the one that suits you in this vast sea of motors?

The correct selection of electric motor, power, type, and model are extremely important. When choosing an electric motor, it should be selected based on the actual situation of the load and usage environment. When selecting, attention should be paid to matching the power of the motor with the load as much as possible, and it should not be "large" or "small horse pulling large cart".

1. Power selection

The power of the electric motor should be selected according to the load situation. Choosing a larger power can ensure normal operation, but it is not economical as the efficiency and power factor of the electric motor are not high; Choosing a smaller size cannot guarantee the normal operation of the motor and production machinery, cannot fully utilize the efficiency of the production machinery, and may cause premature damage to the motor due to overload.

(1) Selection of power for continuous operation of electric motors:

For a continuously running motor, first calculate the power of the production machinery, and the rated power of the selected motor should be equal to or slightly greater than the power of the production machinery.

(2) Selection of Short term Operating Motor Power:

If there is no suitable motor designed specifically for short-term operation, a continuous operation motor can be selected. Due to thermal inertia, overload can be tolerated during short-term operation. The shorter the working hours, the greater the overload can be. But the overload of the electric motor is subject to * * *. The power of the motor for short-term operation is usually selected based on the overload coefficient l. The rated power of the electric motor can be 1/l of the power required by the production machinery.

2. Selection of Types and Forms

(1) Selection of types:

The selection of the type of electric motor is based on considerations such as AC or DC, mechanical characteristics, speed regulation and starting performance, maintenance, and price.

① Selection of AC and DC motors

Unless otherwise specified, AC motors should generally be used.

② The choice between squirrel cage and wire winding

The three-phase squirrel cage asynchronous motor has a simple structure, is sturdy and durable, works reliably, is inexpensive, and is easy to maintain. However, it is difficult to adjust speed, has a low power factor, and poor starting performance. Therefore, for general production machinery that requires hard mechanical characteristics without special speed regulation requirements, squirrel cage motors should be used as much as possible for dragging.

Therefore, wound motors are only used when it is inconvenient to use squirrel cage asynchronous motors.

(2) Selection of structural types:

Electric motors are often made into the following structural types:

① Open type

There is no special protective device in the structure, used for dry and dust-free places. The ventilation is very good.

② Protective type

There is a ventilation hood under the casing or end cover to prevent debris such as iron filings from falling in. Some also make the shell into a baffle shape to prevent rainwater droplets from splashing into it at a certain angle.

③ Closed type

Its shell is tightly sealed, cooled by its own fan or external fan, and equipped with heat sinks on the shell. It can be used in places with high dust, humidity, or acidic gases.

④ Explosion proof type

The entire motor is tightly sealed and used in places with explosive gases.

3. Selection of installation structure type

① Machine base with feet, end cover without flange (B3)

② The machine base does not have feet, and the end cover has a flange (B5)

③ Machine base with feet, end cover with flange (B35)

4. Selection of voltage and speed

① Selection of voltage

The selection of voltage level for electric motors should be based on the type, power, and power supply voltage at the location of use. The rated voltage of the Y series squirrel cage motor is only 380V. Only high-power asynchronous motors use 3000V and 6000V.

② Selection of rotational speed

The rated speed of the electric motor is selected according to the requirements of the production machinery. But usually the speed is not less than 500r/min. Because when the power is constant, the lower the speed of the motor, the larger its size, the more expensive it is, and the efficiency is also lower. Therefore, it is more cost-effective to purchase a high-speed electric motor and equip it with a reducer. Asynchronous motors usually use four poles, with synchronous speed n0=1500r/min.