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Phase determination in 3 phase circuits

  1. Aug 12, 2006 #1
    I'm working on a 3 phase induction motor. I need to measure the RMS values of three phase voltages, and single phase current which further feed power to the induction motor. I've implemented the true rms measurement (sum of squares method) algorithm for RMS value calculations and readings are fine. For calculation of power I need to multiply the current with the corresponding voltage. But I don't know in which phase the current is being drawn.
    So, in case of 3 phase circuits, is there any algorithm to determine the phase in which the current flows? One point to keep in mind is that the load will always be inductive and the current always lags the voltage in that phase.
    Please help.

  2. jcsd
  3. Aug 12, 2006 #2


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    Science Advisor
    Homework Helper

    You need the phase angle between voltage and current.
    It's not enough to know that it lags.
    Pick any winding to measure both.
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