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Basic power analysis confusion

  1. Aug 26, 2008 #1

    Now why does machine 1 act as a motor and 2 as a generator?

    The above question shows that both have current leaving the positive terminal
    - so the generator convention is assumed

    but they both absorb negative Real and Reactive power. Then why is either a generator and a motor?

    Do we consider the other a load once one is assumed to be a generator? Then what happens when we have multiple generators in a network?
  2. jcsd
  3. Aug 26, 2008 #2


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    I think you may just be reading too much into the figure.

    In the absence of anything else, I would assume that machine 2 ("generator") is being turned by a herd of elephants (grad students?--more plentiful) or a waterfall, or a boiler, something which is putting energy into the system. Machine 1 ("load") then spins because of the current output by Machine 2, using up the energy put into the system.

    The current convention just says "measure current going this way", but says nothing about whether or not this is negative (which, in this case, it better be!)--or the complex equivalent of this when dealing with AC stuff.

    In theory, any generator can be used as a motor and vice versa. In practice, they're optimized one way or the other.
  4. Aug 26, 2008 #3

    so once we choose one convention (the generator side in this case), we assume the other device - the receiving end of the current ( whether positive or negative ) to be at the load side.

    Its makes sense now - as device 1 is considered to be on the generator side, its absorbing real and reactive power and hence is a motor

    Then the other device is considered to be on the load side and is delivering Real and reactive power and is hence a generator.

    I see now.

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