Electric motors are machines that convert electrical energy into mechanical energy. In contrast to this process, generators convert mechanical energy into electrical energy. Their use is widespread throughout the world, so let us see their working principle, motor construction, main types and performance.
Most electric motors operate on the principle of electromagnetic induction, but there are motors that use other electromechanical processes, such as electrostatic force and the piezoelectric effect. The fundamental principle of electromagnetic motors is based on the mechanical force that acting on the conductor through which electric current passes and it is located in the magnetic field. The direction of the mechanical force is perpendicular to the conductor and the magnetic field.
Electric motors have found widespread application in various industrial processes, systems and devices. These are some of the application fields:
- In industrial processes – motors with highly standardized characteristics and dimensions
- Blowers and special pumps
- Household appliances and devices
- Machine and power tools
- Electric watches – with small motors
- Hybrid vehicles (such as Tesla motor)
- Ship propulsion – motors with high capacity and power
- Pipeline compression
- Pumped-storage applications
All electric motors are powered by two sources. They are mainly powered by direct current (DC) sources (batteries, rectifiers or motor vehicles), but some are powered by alternating current (AC) sources (power grid, generators or inverters).
The main components of a typical electric motor are:
- Rotor – The moving part of the motor. It turns the shaft to transfer the mechanical power.
- Stator – The stationary part, which has windings or permanent magnets.
- Air gap – It is the space between stator and rotor.
- Windings – Wires that are wrapped around the iron magnetic core.
- Commutator – The mechanism that switches the input of DC and certain AC machines.
Main types of electric motors
Electric motors can operate on three different principles: magnetic (the most common), electrostatic and piezoelectric. Based on the type of electricity for their work, they can be divided into two categories:
- AC motors – Use alternating current. There are synchronous and asynchronous AC motors. Also, they can be single-phase or three-phase motors.
- DC motors – Use direct current for operation. They differ in how the windings are connected, as well as by their characteristics. The main types of DC motors are: serial, parallel, serial-parallel (compound) motors, brushed DC motors and permanent magnet DC motors.
- Universal AC-DC motors – They can operate on both DC and AC electric power. Universal motors are widely used in household appliances and hand tools (electric drills, grinders, and others).
Also, electric motors can be classified by the type of motion output, internal construction, by operating mode, and so on.
Most of the electromagnetic motors are rotating type, but there are also the linear motors. The windings on the rotor are mounted axially, opposed to the magnetic field that is placed radially. The maximum torque depends on the current power.
The continuous torque density of electric motors is determined by the back-iron depth and size of the air-gap area. It relates to the period of operation and method of cooling. The continuous power density depends on the constant torque speed range and the continuous torque density.