What is an electric motor, and what is the principle of the electric motor?

Nov 16, 2020 | Blog

The electric motor is one of the key reason behind the biggest advancements in the fields of engineering and technology ever since the invention of electricity. Electric motors are an important part of the modern-day life being used in domestic appliances such as dishwashers, fans, mixers, vacuum cleaners to subway system, electric vehicles and so on.

electric motor

Electric motor is an electro-mechanical device or machine that is used to convert electrical energy into mechanical energy by producing a producing rotational force.

The working principle behind the operation of an electric motor mainly depends on two main physical principle — Ampere’s law and Faraday’s law.

  • Ampere’s law states that when a straight current carrying conductor interacts with a magnetic field at a right angle to the magnetic field, then the magnetic field exerts a force on the current-carrying conductor.
  • Faraday’s law states that when the magnetic field around a closed loop or coil of conductor, then a voltage or electromotive force (emf) is induced in the coil.
What is an electric motor, and what is the principle of the electric motor? electric motor 1

In an electric motor, a current-carrying conductor is placed in between two magnets and is connected to a power source. When the power source is turned on, current starts flowing in the conductor,  and magnetic lines of force flow from north to south. By the Fleming’s left hand rule, a downward and an upward force starts acting on the conductor, thereby producing a rotating force.

What are the six parts of an electric motor?

What is an electric motor, and what is the principle of the electric motor? electric motor 2

The six main parts of electric motor are:

  • Stator or Armature: It is a copper winding around the main axis which generates a magnetic field around the rotor.
  • Rotor: It is a moving component which has copper winding on it. The rotor rotates because of a torque is produced around the rotor’s axis when there is an interaction between the magnetic field of the rotor and stator winding.
  • Main shaft: It is a metal component that is extended to allow a place for drive pulley or load attachment. It is actually an extension of the rotor.
  • Brush: It is a small rotary conductor located at the end of the main rotor which transfers electric power between to the main moving rotor, keeps the current flow in the same direction even though the rotor rotates.
  • Bearing: It is a special component required for the smooth rotation of the shaft. It has light friction style so as not to hinder shaft rotation.

Motor housing: Motor housing holds and protects all other parts of motors. It serves the user also from any casualty during high speed rotation of the shaft. Other than that that, the ratings and other vital information about the motor is placed on the electric motor housing.

What are the different types of electric motors?

Depending on the nature of current they are operated on, the electric motor is mainly classified into two broad categories — the alternating current (AC) motor and the Direct Current (DC) motor. The AC motor is powered by alternating current, whereas the DC motor takes direct current as an input.

What is an electric motor, and what is the principle of the electric motor? electric motor 3
  • Alternating Current (AC) motor: This motor converts alternating current into mechanical power. AC motor is further classified into two major categories:
    • Synchronous motor — A synchronous motor changes the alternating current into mechanical power at speed synchronized with the frequency of the supply current; The shaft of this motor rotates at the desired speed, which is synchronized with the supply current frequency. To know more, see Synchronous motor.
    • Asynchronous motor — An asynchronous motor, also known as induction motor can be made without electric connections of rotor. This motor uses the phenomenon of electromagnetic induction to transform electric power into mechanical power to produce torque.   
  • Direct Current (DC) motor:  DC motor is a type of motor that transforms direct current (DC) electrical energy into mechanical energy. It relies on the principle that when a current carrying conductor is placed in a magnetic field, then a force is exerted on the conductor, and torque develops. Nearly all categories of DC motors are fitted with an internal mechanical or electronic mechanism that periodically changes the current’s direction in the motor’s armature part.

How do you know if a motor is AC or DC?

What is an electric motor, and what is the principle of the electric motor? electric motor 4

We can identify whether a motor is AC or DC by observing visually the terminal box, stator and rotor.

  • Terminal box:
    • A delta connected AC induction or asynchronous machine up to around 5 HP (delta connected), has three for line 1, 2, 3 and one for ground total four terminals would be in the box.
    • For higher rating six terminals (R1,2. Y1,2, B1,2.). Two for each of the winding and a neutral, total seven (in slip-ring motor 3 more. Including brush, total ten).
    • For synchronous motors, the rotor field is supplied by slip rings, hence total nine.
    • D.C motors have two armature terminals (A1, A2) and two fields terminals (F1, F2) total four terminals in the box.
  • Rotor:
    • AC asynchronous or induction motor rotor would be caged or wound.
    • AC synchronous motor’s rotor would be round or salient pole and has field winding (F1, F2), and mounted on bearings.
    •  For DC motors the armature or rotor is the wound type rotor, supplied with commutator and brushes, the rated DC, through terminal marked A1 and A2.
  • Stator:
    • AC motors have fins on the surface for stator, and are wound type (producing a rotating magnetic field, and loss in stator)).
    • For DC motors poles are mounted on a cylindrical stator, and are supplied by field (F1, F2) terminals, and they generally have no fins, on the surface.

What are the uses of an electric motor in daily life?

The electric motors have major applications in many industries as the source of mechanical power to the industries. Some time if required they are used as generators also. Motors of medium size and standard dimensions are usually used as generators. The larger motors are used in applications such as in water pumps or ship propellers or pipeline compressors and many more. Some use of electric motor in daily life includes the following:

  • The major applications of electric motor are in the machines such as blowers, fans, machine tools, pumps, turbines, power tools, alternators, compressors, rolling mills, ships, movers, paper mills.
  • The electric motor is an important machine in different applications like HVAC- heating ventilating & cooling equipment, home appliances, and motor vehicles.
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