subject: Electric Generator (dynamo) [print this page] Generators are machines used for the large-scale production of electrical energy. In electricity generation, an electrical generator is a device that converts mechanical energy to electrical energy. The generator is based on the principle of electromagnetic induction discovered in 1831 by Michael Faraday. Faraday discovered that if an electric conductor, like a copper wire, is moved through a magnetic field, electric current will flow in the conductor. So the mechanical energy of the moving wire is converted into the electric energy of the current that flows in the wire. Generators were earlier called dynamos, a shortened form of the term dynamoelectric.
The size of large generators is usually measured in kilowatts. One kilowatt equals 1,000 watts. A giant generator can produce more than 1 million kilowatts of electric power. There are two main types of generators. Direct-current (DC) generators produce electric current that always flows in the same direction. Alternating-current (AC) generators, or alternators, produce electric current that reverses direction many times every second.
Their operation is based on principle of electrical induction, whereby a periodic flow of electricity is produced in a loop-type conductor as a result of the periodic variation of the flux of the magnetic lines of force passing through this loop. In order to implement this, we can either cause the loop to rotate in a constant magnetic field or, alternatively the loop can be kept stationary and the magnetic field rotated.
In above mentioned arrangement loop is formed by the armature windings on the rotor which revolves between the fixed magnetic poles of the stator. In the latter arrangement the armature is stationery, and the magnetic poles on magnet wheel revolve instead; the stator consists of an iron ring with induction coils mounted on the inside; the magnetic poles on the rotor move past the ends of these coils at a very short distance from them.
In this case the current produced by the generator is taken direct from the stator, without the aid of special current collectors (brushes). Due to this reason this form of construction is particularly suitable for the generation of high-voltage alternating current. The reverse conversion of electrical energy into mechanical energy is done by a motor, and motors and generators have many similarities. A generator forces electric charges to move through an external electrical circuit, but it does not create electricity or charge, which is already present in the wire of its windings.
