Wednesday, April 7, 2010

Three phase circuits - a comment

Conservation of Energy Law in an electric circuit, say 3PH, does not limit you what kind of voltages you are going to apply or produce at the generator points. And this particular freedom, in choosing the shape of voltages, is the root of creativity and inventions in 3PH circuits. Any voltage can be there. We choose, almost axiomatically, a priori, that there will be sinusoidal, periodic voltages.


Pic 1. Three phase systems with generators and loads.

As in any axiomatic system, there is a World #1 and the World #2. The World # 1 determines the reason, motivation why we have the voltages we have. The World #2 accepts those voltages as given, as axioms, as starting assumptions, premises. Finding the reason what voltage shapes we will have usually has nothing to do with the World #2. For instance, we need 3PH voltages to create rotational magnetic field, which in turn, we need to rotate the shaft, which, in turn, we need to move a car. Moving a car is the World # 1, while chosen voltages are the World # 2.


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