and generators are referred to as electric machines. Electricians are most
frequently concerned with electric motors, due to their extensive application.
must be one of man’s most useful inventions. In the manufacturing industries
they are used in large numbers, to drive lathes, drilling and milling machines,
augers, conveyors, cranes, hoists, lifts, fans and steel rolling equipment. In
the process industries they are used to pump liquids and gases. They are used
in transport to start engines, operate windscreen wipers, open and close
windows and power electric vehicles. In domestic situations they are used in
washing machines, clothes dryers, cookers, fridges, freezers, vacuum cleaners,
food mixers, audio / video equipment, cameras, clocks etc.
Electric motors are
popular because they are compact, reliable, and cheap, need little attention,
and are convenient to use. They can be provided in a wide range of sizes and
can be designed to have different characteristics for various applications.
Also, there is a readily available supply of electricity. The electric motor
may be regarded as an energy converter. It is supplied with electrical energy
and provides mechanical energy as an output as shown in Figure.
There are AC motors and DC motors. There is a number of different types of motor under each heading. They may be classified by their power rating. This may be given in Watts or Horsepower. One Horsepower is the equivalent of 746 Watts. Power ratings range from a few watts, such as those used in electric clocks, through to a few kilowatts, such as those used in domestic, agricultural and light duty industrial situations, to large motors in the order of tens of megawatts. These are used in heavy duty industrial situations such as mining, quarrying and cement plants. Motors are also classified by the way in which their windings are interconnected.
Motors are classified depending on the environment in which they are intended to be used. For example, very high temperature locations, damp locations, dust laden locations and explosive locations.
The basic requirement of an electric motor is that it should provide rotational drive. The motor is fixed in position and drives a mechanical system directly or via gears, belts etc.
Motors depend for their operation on the interaction between two magnetic fields. Electric current, flowing through windings consisting of copper wire produce both of these magnetic fields. Some small motors use permanent magnets to produce one of the magnetic fields.