Uncle Bobs Tips: Generator Guide

History of Generators

The history of generators starts with the predecessor of the modern day generator, a machine used to change mechanical energy into electrical energy which was discovered in 1831 by Michael Faraday.

The predecessor of the modern day generator, a machine used to change mechanical energy into electrical energy, was discovered in 1831 by Michael Faraday. A British scientist, physicist and chemist who significantly contributed to the fields of electromagnetism and electrochemistry, Faraday discovered that if he moved a magnet through a loop of wire, an electric current flowed in the wire and that the current current also flowed if the loop was moved over a stationary magnet. More formally, he discovered electromagnetic induction: that a potential difference is generated between the ends of an electrical conductor that moves perpendicular to a magnetic field.

Faraday further proposed that electromagnetic forces extended into the empty space around the conductor, but did not complete his work involving this proposal. Faraday's concept of flux lines emanating from charged bodies and magnets provided a way to visualize electric and magnetic fields, a mental model that was pivotal to electromechanical device development that dominated engineering and industry for the remainder of the 19th century. He built the first electromagnetic generator called the Faraday disc, using a copper disc rotating between the poles of a horseshoe magnet producing a small direct current, or DC.

In 1832 Hippolyte Pixii, an instrument maker from Paris, France, discovered the first magneto electric generator based on the principles of Michael Faraday. His device was a spinning magnet, rotated by a hand crank, where the North and South poles passed over a coil with an iron core (the conductor), producing a current pulse each time a pole passed over the coil. He also found that the direction of the current changed when the North pole passed over the coil after the South pole, giving rise to alternating current or AC. Later, by adding a commutator, Pixii was able to convert the alternating current to direct current. (A commutator is an electric switch that periodically reverses the current in an electric motor or a generator).

Both of these designs, however, had a similar flaw: they induced "spikes" of electric current followed by no current at all. Antonio Pacinotti, an Italian physics professor, remedied this problem by replacing the spinning coil with a toroidal one, which he created by wrapping an iron ring. Since some part of the coil was now continually passing by the magnets, it smoothed out the current. A few years later, when designing the first commercial power plants in France in the 1870's, Zenobe Gramme reinvented this model using a ring armature around which was wrapped a coil of wire, producing an even smoother direct current than previously available. Known as the Gramme dynamo, this basic concept of a spinning endless loop of wire remains at the core of all modern dynamos or DC generators. In 1873 it was discovered that a generator could be reversed to serve as a motor, as could a motor be switched to serve as a generator.

A generator, then, is simply a mechanical arrangement for moving the conductor and leading a current to an external circuit in order to activate devices that require electricity. In any generator, the entire assembly carrying the coils is called the armature, or rotor, while the stationary parts constitute the stator. The generator rotor is turned by a device called a prime mover, which may be an engine, steam turbine, water turbine or other medium coupled to the rotor shaft.

The term dynamo is often used for the DC generator. The generator in automotive applications is usually a dynamo. An AC generator is called an alternator. Most alternators produce a polyphase AC, a complex type of current that provides a smoother power flow than does simple AC. Historically, the first commercial electric power transmission (developed by Thomas Edison in the late nineteenth century) used direct current. Since alternating current is more convenient than direct current for electric power distribution and transmission, today almost all electric power transmissions use alternating current.

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