Dynamo
Today, the simpler alternator dominates large scale power generation, for efficiency, reliability and cost reasons.
Also, converting alternating to direct current using rectifiers (such as vacuum tubes or more recently via solid state technology) is effective and usually economical.
The principle, later called Faraday's law, is that an electromotive force is generated in an electrical conductor which encircles a varying magnetic flux.
This design was inefficient, due to self-cancelling counterflows of current in regions of the disk that were not under the influence of the magnetic field.
This counterflow limited the power output to the pickup wires, and induced waste heating of the copper disc.
Later homopolar generators would solve this problem by using an array of magnets arranged around the disc perimeter to maintain a steady field effect in one current-flow direction.
The spinning magnet was positioned so that its north and south poles passed by a piece of iron wrapped with insulated wire.
Pixii found that the spinning magnet produced a pulse of current in the wire each time a pole passed the coil.
As with electric motors of the period, the designers did not fully realize the seriously detrimental effects of large air gaps in the magnetic circuit.
Antonio Pacinotti, an Italian physics professor, solved this problem around 1860 by replacing the spinning two-pole axial coil with a multi-pole toroidal one, which he created by wrapping an iron ring with a continuous winding, connected to the commutator at many equally spaced points around the ring; the commutator being divided into many segments.
Around 1856, six years before Siemens and Wheatstone, Ányos formulated the concept of the dynamo, but did not patent it as he thought he was not the first to realize the idea.
The modern dynamo, fit for use in industrial applications, was invented by Henry Wilde with his paper presented to The Royal Society by Michael Faraday on 26th March 1866 [9].
It was independently invented by Sir Charles Wheatstone, Werner von Siemens and Samuel Alfred Varley.
Varley took out a patent on 24 December 1866, while Siemens and Wheatstone both announced their discoveries on 17 January 1867, by delivering papers at the Royal Society.
[12] Further improvements were made on the Gramme ring, but the basic concept of a spinning endless loop of wire remains at the heart of all modern dynamos.
[14][15] After dynamos and motors were found to allow easy conversion back and forth between mechanical or electrical power, they were combined in devices called rotary converters, rotating machines whose purpose was not to provide mechanical power to loads but to convert one type of electric current into another, for example DC into AC.
The technology of rotary converters was replaced in the early 20th century by mercury-vapor rectifiers, which were smaller, did not produce vibration and noise, and required less maintenance.
Rotary converters remained in use in the West Side IRT subway in Manhattan into the late 1960s, and possibly some years later.
[18] The invention of the dynamo principle (self-induction) was a major technological leap over the old traditional permanent magnet based DC generators.
The discovery of the dynamo principle made industrial scale electric power generation technically and economically feasible.
Both types of self-excited generator, which have been attached to a large external load while it was stationary, will not be able to build up voltage even if the residual field is present.
Dynamos, usually driven by steam engines, were widely used in power stations to generate electricity for industrial and domestic purposes.
Large industrial dynamos with series and parallel (shunt) windings can be difficult to use together in a power plant, unless either the rotor or field wiring or the mechanical drive systems are coupled together in certain special combinations.
