Synchronous and asynchronous electric motors: principles of operation and differences in characteristics

Electric motors are machines that convert electricity into mechanical energy. The converted energy drives the rotor of the motor in rotary motion, which transfers the rotation through the transmission directly to the shaft of the actuator. The main types of electric motors are synchronous and asynchronous motors. The differences between them determine the possibilities of use in various devices and technological processes.

Work principles

All electric motors have a fixed stator and a rotating rotor. The difference between asynchronous and synchronous motors lies in the principles of creating the poles. In an induction motor, they are created by the phenomenon of induction. All other electric motors use permanent magnets or current coils to create a magnetic field.

Features of synchronous motors

Leading units of a synchronous machine - armature and inductor

. The stator is the anchor and the inductor is located on the rotor. Under the action of an alternating current, a rotating magnetic field is formed in the armature. It interlocks with the magnetic field of the inductor formed by the poles of permanent magnets or DC coils. As a result of this interaction, the energy of electricity is converted into kinetic energy of rotation.

The rotor of a synchronous machine has the same rotational speed as the stator field. The advantages of synchronous electric motors:

• Structurally, it is used both as an engine and a generator.
• Load-independent speed.
• Great efficiency.
• Low labor intensity in repair and maintenance.
• High degree of reliability.

Synchronous machines are widely used as high power electric motors for low speed and constant load. Generators are used where an independent power source is required.

The synchronous machine also has disadvantages:

• A constant current source is required to power the inductor.
• There is no initial starting torque, an external torque or asynchronous start is required for starting.
• Brushes and collectors fail quickly.

Modern synchronous units contain in the inductor, in addition to the winding supplied with direct current, a starting short-circuited winding, which is designed for starting in asynchronous mode.

Distinctive features of asynchronous motors

The rotating magnetic field of the stator of an induction motor induces induction currents in the rotor, which form its own magnetic field. The interaction of the fields drives the rotor into rotation. In this case, the rotor speed lags behind the speed of the magnetic field. This property is reflected in the name of the engine.

Asynchronous motors are of two types: with squirrel-cage and with phase rotor.

Household appliances such as a fan or vacuum cleaner are usually equipped with squirrel-cage motors, which are squirrel-cage motors. All rods are closed by discs welded on both sides. The interaction of the stator magnetic field with the induced currents in the rotor generates an electromagnetic force that acts on the rotor in the direction of rotation of the stator field. The torque on the motor shaft is generated by all electromagnetic forces from each conductor.

A wound rotor motor uses the same stator as a squirrel cage motor. And the windings of three phases are added to the rotor, connected in a "star". When starting the engine, you can connect rheostats to them that regulate inrush currents. With the help of rheostats, you can also adjust the engine speed.

The advantages of asynchronous motors include:

• Powered directly from AC mains.
• Simplicity of the device and relatively low cost.
• The ability to use in household appliances using a single-phase connection.
• Low energy consumption and economy.

Serious disadvantages - complex speed control and high heat loss. To prevent overheating, the casing of the unit is ribbed, and an impeller is installed on the motor shaft for cooling.

Difference in the characteristics of electric motors

The design features and performance of electric motors are decisive in the selection of units. The design of transmissions and all power units of mechanisms depends on this. When choosing an engine, you need to rely on commonality and the main differences in the properties of machines:

• The main difference between a synchronous and an asynchronous motor lies in the design of the rotor. It is a permanent or electric magnet. In an asynchronous motor, magnetic fields in the rotor are induced by electromagnetic induction.
• For synchronous motors, the shaft speed is constant; for asynchronous motors, it can change when the load changes.
• Synchronizers have no starting torque. To enter synchronization, an asynchronous start is required.

Synchronous and asynchronous electric motors are used in different ways. Synchronous motors are recommended for use wherever high power levels are present. continuous production process and does not need to frequently restart units or adjust the frequency rotation. They are used in conveyors, rolling mills, compressors, stone crushers, etc. A modern synchronous electric motor has the same quick start as an asynchronous one, but it is smaller and more economical than an asynchronous one of equal power.

Asynchronous electric motors with a wound rotor are used where a large starting torque and frequent stops of units are needed. For example, in elevators and tower cranes. Asynchronous electric motors with a squirrel-cage rotor are widely used due to the simplicity of the device and ease of use.

Using the advantages of different units and how a synchronous motor differs from an asynchronous one, you can make an informed choice of one motor or another when designing machines, machine tools and other equipment.