Power transmission
From Wikipedia, the free encyclopedia
Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful work.
Power is defined formally as units of energy per unit time. In SI units: 1 watt = 1 joule/s = 1 newton * metre/second (1W=1J/s=1N·m/s).
Since the development of technology, Transmission and storage systems have been of immense interest to technologists and technology users.
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[edit] Electrical power
With widespread establishment of power grids, power transmission has came to be associated most often with electric power transmission. Alternating current is normally preferred as its voltage may be easily stepped up by a transformer in order to minimise resistive loss in the conductors used to transmit power over great distances; another set of transformers is required to step it back down to safer or more usable voltage levels at destination.
Power may also be transmitted by changing electromagnetic fields or by radio waves; microwave energy may be carried efficiently over short distances by a waveguide.
[edit] Mechanical power
Electrical power transmission has replaced mechanical power transmission in all but the very shortest distances. From the start of the industrial revolution until the end of the 19th century mechanical power transmission was the norm. Factories were fitted with overhead driveshafts providing rotary power. Drivebelts would provide power to individual machines on the shop floor.
Mechanical power may be transmitted directly using a solid structure such as a driveshaft; transmission gears can adjust the amount of torque or force vs. speed in much the same way an electrical transformer adjusts voltage vs current.
Hydraulic systems use liquid under pressure to transmit power; canals and hydroelectric power generation facilities harness natural water power to lift ships or generate electricity. Pumping water or pushing mass uphill with (windmill pumps) is one possible means of energy storage. London had a hydraulic network powered by five pumping stations operated be the London Hydraulic Power Company, with a total effect of 5 MW.
Pneumatic systems use gasses under pressure to transmit power; compressed air is commonly used to operate pneumatic tools in factories and repair garages. A pneumatic wrench (for instance) is used to remove and install automotive tyres far more quickly than could be done with standard manual hand tools.
A pneumatic system was proposed by proponents of Edison's direct current as the basis of the power grid. Compressed air generated at Niagara Falls would drive far away generators of DC power. The War of Currents ended with alternating current (AC) as the only means of long distance power transmission.
[edit] Chemicals and fuels
Power (and energy) may be transmitted by physically transporting chemical or nuclear fuels. Possible artificial fuels include radioactive isotopes, wood alcohol, grain alcohol, methane, synthetic gas, cryogenic gas, hydrogen gas (H2) and liquefied natural gas (LNG).
