History and Principle of Operation
– Alternating current generating systems were known from the 1830s.
– Early alternators were developed by Michael Faraday, Hippolyte Pixii, Lord Kelvin, and Sebastian Ferranti.
– The Ganz Works invented the constant voltage generator in 1883.
– A conductor moving relative to a magnetic field develops an electromotive force (EMF).
– A rotating magnet (rotor) turns within a stationary set of conductors (stator).
– The field cuts across the conductors, generating an induced EMF.
– Alternators can have permanent magnets or field coil electromagnets.
Synchronous Speeds
– One cycle of alternating current is produced each time a pair of field poles passes over a point on the stationary winding.
– The relation between speed and frequency is given by N=120f/P, where f is the frequency in Hz and P is the number of poles.
– Different speeds correspond to different frequencies and numbers of poles.
– Examples of synchronous speeds include 428.6, 514.3, 3,429, 375, and 450 revolutions per minute.
Classifications
– Alternators can be classified by method of excitation, number of phases, type of rotation, cooling method, and application.
– The two main ways to produce the magnetic field are using permanent magnets or field coils.
– Alternators that use permanent magnets are called magnetos.
– Wound field coils form an electromagnet to produce the rotating magnetic field in other alternators.
– There are permanent magnet alternators and permanent magnet generators.
Types of Alternators
– Variation of alternators that use direct current from a battery for initial excitation upon start-up.
– Transformation and rectification method that relies on residual magnetism in the iron core to generate a weak magnetic field.
– Brushless alternators composed of two alternators built end-to-end on one shaft.
– Brushless alternators have a rotating rectifier assembly mounted on the rotor, eliminating the need for brushes and slip rings.
– Varying the current through the exciter field coils controls the output of the main alternator.
Specific Applications
– Alternators are commonly used as generators in power generation stations.
– Automotive alternators charge the battery and power the electrical system in internal combustion engine vehicles.
– Diesel-electric locomotives use alternators to provide electricity for traction motors.
– Marine alternators are designed for the salt-water environment and explosion-proof conditions.
– Aviation and radio transmissions also utilize alternators for specific purposes. Source: https://en.wikipedia.org/wiki/Alternator
An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature. Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines.
An alternator that uses a permanent magnet for its magnetic field is called a magneto. Alternators in power stations driven by steam turbines are called turbo-alternators. Large 50 or 60 Hz three-phase alternators in power plants generate most of the world's electric power, which is distributed by electric power grids.
