- Electric Motor Definition: An electric motor is a device that converts electrical energy into mechanical energy using magnetic fields and electric currents.
- Core Functioning: The main principle behind all electric motors is Faraday’s Law of induction, which describes how a force is generated from electrical and magnetic interactions.
- Motor Varieties: The types of electrical motors include DC Motors, AC Motors like Synchronous and Induction Motors, and specialized motors such as Stepper and Servo Motors.
- Application Significance: Electric motors are integral to numerous devices and systems, ranging from household appliances to industrial machinery.
- Historical Evolution: The development of electric motors began with Michael Faraday’s experiments in 1821, revolutionizing how mechanical work is powered electrically.
What is an Electric Motor?
An electric motor (or electrical motor) is a machine that converts electrical energy into mechanical energy. Current in a winding sits in the motor magnetic field and produces torque on the shaft. That force is the Lorentz force on a current in a magnetic field. Faraday’s Law covers induced emf, which matters in induction machines and generators.
Motors run from direct current (DC) supplies such as batteries or rectifiers, or from alternating current (AC) supplies such as inverters, electric generators or a power grid.
Electric motors turn electrical energy into motion in transport, industry and household plant.
Before practical motors, electric supply was used mainly for lighting. Motors made electricity useful as a source of mechanical work.
They appear in cars, trains, tools, fans, air-conditioning, appliances and disk drives. Some electric watches use a tiny stepping motor.
Different types of motors were built for different duties and supplies.
Induction machines follow Faraday’s Law of induction. Every motor still uses a current in a magnetic field to produce torque.
A changing field and an induced current explain induction-motor torque. A DC motor uses a steady field and a commutated winding current.
Motor design has grown from early DC machines to induction, synchronous and electronically controlled types used in modern plant.
The main electrical motor families in use today are set out below.
Types of Electric Motors
The main types of motors include:
- DC Motors
- Synchronous Motors
- 3 Phase Induction Motors (a type of induction motor)
- Single Phase Induction Motors (a type of induction motor)
- Other special, hyper-specific motors
The diagram below groups those motors:
Among the four basic classifications of motors above, the DC motor is the one supplied with direct current.
It is the earliest practical rotary form: torque comes from current in a conductor inside a magnetic field.
The others are AC motors. A synchronous motor runs at synchronous speed in the steady state.
The rotor field locks to the stator rotating field and turns with it. Speed is set by supply frequency (f) and pole number (P): Ns = 120 f/P.
In an induction motor the stator rotating field cuts short-circuited rotor conductors and induces circulating current in them.
Those currents in the stator field produce torque, so the rotor starts and keeps turning below synchronous speed.
This induction motor, also called an asynchronous motor, runs below synchronous speed. Torque and speed follow slip, the difference between synchronous speed Ns and rotor speed Nr,
Induced emf from changing flux density is why it is called an induction machine.
A single-phase induction motor also uses emf induction from changing flux, like a three-phase motor.
Unlike a three-phase motor, it is fed from a single-phase supply.
Starting behaviour is explained by double-revolving-field theory and cross-field theory.
Besides those four basic types, several special electrical motors are in use.
They include linear induction motors (LIM), hysteresis motors, Stepper motors and Servo motors.
Each type was built for a plant duty or a specific device.
Hysteresis motors were used in clocks and turntables because they run quietly at near-synchronous speed. Small watches more often use a stepping motor.
History of Motors
In 1821 Michael Faraday showed electrical energy turning into mechanical motion: a current-carrying conductor in a magnetic field rotated under the torque from current and field.
On that principle William Sturgeon built an early commutator DC machine in 1832. It was costly and did not enter general use.
In 1886 Frank Julian Sprague produced a practical constant-speed DC motor that held speed under a changing load, among the first motors useful for industry and electric traction. Faraday and Sturgeon had already shown earlier laboratory motors.
