Posted By: Kalash Sinha

June 18, 2016
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Overview

The dynamos at earlier days were small machines driven usually at 1000 to 1500 revolutions per minute by a belt from the flywheel of a reciprocating engine. Parsons required a dynamo that could be driven directly by his turbine at a speed of 18,000 revolutions per minute, in order that the combination should constitute a small, simple and self-contained generating unit. Both electrical and mechanical problems had to be solved, for the alternations of magnetism in the core were vastly more rapid than in any machine yet built, while the centrifugal force of 5.5 tons was developed by every pound of metal at the surface of the armature. Parsons would have attained high fame for his electrical work alone had not this been overshadowed in the minds of the public by the spectacular developments of his steam turbine. By 1900 he was building generating sets of 1000 kW capacity, while in 1912 he undertook to build a turbo-alternator with an output of 25,000 kW, by far the largest and most efficient generating unit in the world at the time. This machine was installed in the Fisk Street Power Station of the City of Chicago, and it proved so successful that in 1923 Parsons was entrusted with the contract for a unit of 50,000 kW for the same city. He lived to see an output of more than 200,000 kW delivered by a single turbo-generator. The growth of electricity supply consequent upon the invention of the turbine created a demand, not only for larger generating units, but also for higher transmission voltages in order that more extensive areas might be economically served. In the early days the practice had been to generate at about 2000 volts, and to step up this voltage when required by means of transformers. The first real advance towards modern conditions was made by Parsons in 1905 when he supplied a pair of 1500 kW turbo-alternators generating at 11,000 volts to the Frindsbury Power Station in Kent. As before, when higher voltages were required for transmission they were obtained by the use of transformers, which were commonly attached permanently to the machines they served. There was, however, to Parsons' mind, something illogical in generating at 11,000 volts or thereabouts when the whole current might have to leave the station at a higher voltage. He therefore attacked the problem with the result that in 1928 he produced a 25,000 kW Turbo-alternator designed to generate directly at 36,000 volts. The windings of the machine were constructed in accordance with an entirely new principle, which made it Parsons, again, was the first engineer to take practical advantage of the possibility of effecting an improvement of the thermodynamic cycle of a steam turbine plant by the regenerative heating of the feed water, a development for which he acknowledged his indebtedness to the original proposal of Mr James Weir in 1876. The result of these advances, enabled him to construct generating units capable of operating with a heat consumption of no more than 9280 B.T.U. per kW hour (2338.5 Kcal/Kwhr), a figure that even to-day could hardly be surpassed by the largest and most efficient machines in existence. The cheapness of electricity produced by a steam power station depends mainly upon three factors, namely the quantity of fuel required to generate it, the capital charges on the station and equipment, and the expenses of running and maintaining the plant. On all of these the influence of turbine machinery has been profound.

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Nitin

February 9, 2017
nice article...very informative...
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