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power metering accuracy, induction motors

Discussion in 'Electrical Engineering' started by bruce varley, May 11, 2004.

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  1. bruce varley

    bruce varley Guest

    Hi, I have a feeling this has been posted before, but it doesn't show in my
    current postings, as don't the FAQs. Anyway, here goes:

    Can anyone give me an idea on the stability to be expected in determining
    the power input to a 3 phase induction motor from a current measurement of
    one phase, appropriately linearised and calibrated. Ie. the current
    measurement is logged against the output of an accurate, temporarily
    installed polyphase power meter at several working points, then the curve
    between the current test points is interpolated and used to provide an
    ongoing measurement of power. Assume the CT is accurate and the supply
    voltage steady. I'm after variable factors within the drive that would
    affect the relationship, and by how much.

    Drives are 3.3KV 500KW, standard squirrel cage induction. Incidentally, to
    hopefully prevent spurious responses, this relates to a real industrial
    problem, not homework. TIA
  2. SQLit

    SQLit Guest

    Honeywell and JCI, Metasys both have used this method. When we installed 3
    phase utility grade equipment we found the errors as small as 5% and as
    large as 40%. If your really interested in accuracy you will need 3 phase
    current and voltage measurements. If you want a ball park or county accuracy
    then do as you suggest.
    Have fun with your project
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