Motors And Generators

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Electric Motors and Generators, group of devices used to convert mechanical energy into electrical energy, or electrical energy into mechanical energy, by electromagnetic means. A machine that converts mechanical energy into electrical energy is called a generator, alternator, or dynamo, and a machine that converts electrical energy into mechanical energy is called a motor.
Two related physical principles underlie the operation of generators and motors. The first is the principle of electromagnetic induction discovered in 1831 by the British scientist and inventor Michael Faraday. If a conductor is moved through a magnetic field, or if the strength of a magnetic field passing through a stationary conducting loop is made to vary, a current is set up or “induced” in the conductor. The converse of this principle is that of electromagnetic reaction, first observed by the French physicist André Marie Ampère in 1820. If a current is passed through a conductor located in a magnetic field, the field exerts a mechanical force on it.
The simplest of all dynamoelectric machines is the disc dynamo developed by Faraday. It consists of a copper disc that is mounted so that part of the disc, from the centre to the edge, is between the poles of a horseshoe magnet. When the disc is rotated a current is induced between the centre of the disc and its edge by the action of the field of the magnet. The disc can be made to operate as a motor by applying a voltage between the edge of the disc and its centre, causing the disc to rotate because of the force produced by magnetic reaction.
Generally, in larger machines, electromagnets are employed. Both motors and generators consist of two basic units: the field, which is the electromagnet with its coils; and the armature, which is the structure supporting the conductors that cut the magnetic field and carry the induced current in a generator, or the exciting current in a motor. The armature is usually a...