Electrical equipment that converts electrical energy into mechanical energy is collectively called an electric motor. An electric motor utilizes the principle of electromagnetic induction to achieve this conversion. A device that converts mechanical energy into electrical energy is called a generator, while a device that converts electrical energy into mechanical energy is called an electric motor.
Classification of motors
According to the type of power source, motors can be divided into DC motors and AC motors.
1) DC motors can be classified into brushless DC motors and brushed DC motors according to their structure and working principle.
Brushed DC motors can be classified into two types: permanent magnet DC motors and electromagnetic DC motors.
Electromagnetic DC motors can be classified into: series-wound DC motors, shunt-wound DC motors, separately excited DC motors, and compound-wound DC motors.
Permanent magnet DC motors can be classified into three types: rare earth permanent magnet DC motors, ferrite permanent magnet DC motors, and AlNiCo permanent magnet DC motors.
2) AC motors can be further divided into single-phase motors and three-phase motors.
According to their structure and working principle, motors can be divided into DC motors, asynchronous motors, and synchronous motors.
1) Synchronous motors can be classified as: 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 classified as: three-phase asynchronous motors, single-phase asynchronous motors, and shaded-pole asynchronous motors, etc.
AC commutator motors can be classified as: single-phase series motors, AC/DC universal motors, and repulsion motors.
Based on starting and operating methods, they can be divided into:
Capacitor-started single-phase asynchronous motor, capacitor-run single-phase asynchronous motor, capacitor-start-run single-phase asynchronous motor, and split-phase single-phase asynchronous motor.
According to their application, electric motors can be divided into drive motors and control motors.
1) Electric motors for driving can be divided into: electric motors for power tools (including tools for drilling, polishing, grinding, grooving, cutting, and reaming), electric motors for household appliances (including washing machines, electric fans, refrigerators, air conditioners, tape recorders, video recorders, DVD players, vacuum cleaners, cameras, hair dryers, electric shavers, etc.), and electric motors for other general-purpose small mechanical equipment (including various small machine tools, small machinery, medical devices, electronic instruments, etc.).
2) Control motors are further divided into stepper motors and servo motors, etc.
Based on rotor structure, they can be classified as follows:
Squirrel-cage induction motors (formerly known as squirrel-cage asynchronous motors) and wound-rotor induction motors (formerly known as wound-rotor asynchronous motors).
With such a wide variety of electric motors available, how do you find the right one for you ?
Choosing the right motor is extremely important, considering its power, type, and model. When selecting a motor, the actual load and operating environment should be taken into account. The motor's power should be matched to the load as closely as possible; it should not be too large, nor too small.
1. Power selection
The power of the motor should be selected according to the load conditions. If the power is too large, although it can ensure normal operation, it is not economical and the efficiency and power factor of the motor will not be high. If the power is too small, it will not be able to guarantee the normal operation of the motor and the production machinery, and the efficiency of the production machinery will not be fully utilized. It will also cause the motor to be damaged prematurely due to overload.
(1) Selection of motor power for continuous operation:
For continuously operating electric motors, first calculate the power of the production machinery, and then select an electric motor whose rated power is equal to or slightly greater than the power of the production machinery.
(2) Selection of motor power for short-time operation:
If a suitable motor specifically designed for short-term operation is unavailable, a motor designed for continuous operation can be used. Due to thermal inertia, overload is permissible during short-term operation. The shorter the operating time, the greater the overload that can be. However, the motor's overload capacity is limited. The power of the motor for short-term operation is typically selected based on an overload factor l. The motor's rated power 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 motor type takes into account factors 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, an AC motor should generally be used.
② Choice between squirrel-cage type and winding type
Three-phase squirrel-cage asynchronous motors are simple in structure, robust and durable, reliable in operation, inexpensive, and easy to maintain. However, they are difficult to adjust in speed, have a low power factor, and poor starting performance. Therefore, squirrel-cage motors should be used as much as possible for driving general production machinery that requires relatively stiff mechanical characteristics but does not have special speed adjustment requirements.
Therefore, wound-rotor motors are only used when it is inconvenient to use squirrel-cage induction motors.
(2) Selection of structural type:
Electric motors are commonly manufactured in the following structural forms:
① Open type
It has no special protective devices in its construction and is intended for use in dry, dust-free locations. Ventilation is excellent.
② Protective
There is a ventilation cover under the casing or end cover to prevent debris such as iron filings from falling in. Some casings are also made into a baffle to prevent raindrops from splashing in at a certain angle.
③ Closed
Its casing is tightly sealed and cooled by its own fan or an external fan, with heat sinks on the casing. It can be used in dusty, humid, or acidic environments.
④ Explosion-proof
The entire motor is sealed and is used in locations with explosive gases.
3. Selection of installation structure type:
① The base has feet, and the end cover has no flange (B3)
②The base does not have feet, and the end cover has a flange (B5).
③ The base has feet, and the end cover has a flange (B35).
4. Selection of voltage and speed
① Voltage selection
The selection of the motor voltage rating depends on the motor type, power, and the power supply voltage at the location of use. Y-series squirrel-cage motors only have a rated voltage of 380V. Only high-power asynchronous motors use 3000V and 6000V.
②Speed selection
The rated speed of an electric motor is selected based on the requirements of the production machinery. However, it is usually not lower than 500 r/min. This is because, for a given power, the lower the motor's speed, the larger its size, the higher its price, and the lower its efficiency. Therefore, it is more cost-effective to purchase a high-speed motor and a separate speed reducer. Asynchronous motors typically use four poles, meaning a synchronous speed n0 = 1500 r/min.
