3 Phase Alternating Current
The power of alternating current (AC) fluctuates. For domestic use for e.g. light bulbs this is not a major problem, since the wire in the light bulb will stay warm for the brief interval while the power drops. Neon lights (and your computer screen) will blink, in fact, but faster than the human eye is able to perceive. For the operation of motors etc. it is useful, however, to have a current with constant power.
Voltage Variation for Three Phase Alternating Current
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As we learned on the previous page, a full cycle lasts 20 milliseconds (ms) in a 50 Hz grid. Each of the three phases then lag behind the previous one by 20/3 = 6 2/3 ms.
Wherever you look along the horizontal axis in the graph above, you will find that the sum of the three voltages is always zero, and that the difference in voltage between any two phases fluctuates as an alternating current.
On the
next page
you will see how we connect a generator to a three phase grid.
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© Copyright 1997-2003 Danish Wind Industry Association
Updated 12 May 2003 http://www.windpower.org/en/stat/unitsac3.htm |