Electric Motor

The origin of the electric motor can be traced back to 1831 when Michael Faraday demonstrated the fun­damental principles of electromagnetism. The purpose of an electric motor is to convert electrical energy into mechanical energy. Electric motors are efficient at converting electric energy into mechanical energy. If the efficiency of an electric motor is 80%, it means that of electrical energy delivered to the motor is directly converted to mechanical energy at the motor shaft. The portion lost within the motor is the difference between electrical energy input and mechanical energy output.

There is no fundamental difference between an electric dynamo and an electric motor. In the case of the dynamo, mechanical energy is converted into electrical energy, whilst the motor converts electrical energy into mechanical energy.

Electric motors work on the following principle or idea: first, when you place a current-carrying conductor in a magnetic field, the conductor will move because of a mechanical force. In other words, an electric motor converts electrical energy (the current in the conductor) into mechanical energy (the movement caused by the force in a magnetic field).

A basic electric motor has an electrical input of voltage and current. It has a mechanical output in the form of torque and rotation. The motor loses some energy in the form of heat.

An electric motor consists of two main parts:

• a stator, which is the outer frame and does not turn, and
• a rotor, the inner part of the motor that can turn.

The rotor is connected to a shaft, which connects the machine to its mechanical load, for example the fan that turns when you switch the machine on. It is a long piece of metal that sticks out from the rotor and it turns when the rotor turns. Depending on the type of machine, either the stator or the rotor (or both) contain current-carrying conductors wound into coils. These coils are called windings. There are slots cut into the stator and the rotor to contain the windings and their insulation. There is an air gap between the stator and the rotor so that they do not rub against each other. A direct current (DC) motor needs a supply of direct current to work and an alternating current (AC) motor needs a supply of alternating current to work.

Questionnaire:

• What is electric motor? Explain.