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Positive/Negative/Zero Sequence voltages/currents

  1. Jun 21, 2012 #1
    What does it mean when one refers to,

    • Positive
    • Negative
    • Zero

    sequence voltages/currents in relation to 3 phase power system?

    My blunt understanding is that in say positive sequence voltages, as we rotate around the phasor diagram in a clockwise manner we see the voltages in the following sequence:

    A, B, C, A, B, C... And so on.

    In negative sequence voltages the sequence is reversed like so,

    C, B, A, C, B, A... And so on.

    Am I understanding this correctly?

    Why do we chose to make such a distinction anyways?

    Also, what does one mean when they refer to zero sequence quantities?

    Thanks again!
  2. jcsd
  3. Jun 21, 2012 #2


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    I believe these sequences are used when analyzing unbalanced systems with the Symmetrical components method.

  4. Jun 21, 2012 #3
    I read the wiki page you linked and it added some clarity, but its still not obvious to me why they are called symmetrical components.

    Why the word symmetrical?

    What does one mean when they refer to, "symmetrical sets of balanced phasors"?

    Thanks again!
  5. Jun 21, 2012 #4
    The reason for using symmetrical components is that a 3 phase unsymetrical system can be analyzed by three symmetrical system/circuits. That is +, - and 0 sequence.

    It is (purely?) a mathematical decomposition, and has no physical meaning. (To my knowledge)
  6. Jun 21, 2012 #5


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    From the wiki Symmetrical components page:

    When looking at electric power system faults,

    bold by me,
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