3 phase AC circuit

Discussion in 'General Electronics Chat' started by chinmey, Mar 2, 2016.

  1. chinmey

    Thread Starter New Member

    Jan 12, 2016
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    How to detect zero crossing in 3 phase without neutral
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Use three detectors.
     
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  3. crutschow

    Expert

    Mar 14, 2008
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    With no neutral, then you detect the zero crossing of the voltage measured across each phase.
    If you want to measure all three phases, then that requires three isolated differential detectors.
    An opto isolator can be used for that purpose (as long as an approximate 1.3V offset in detecting the zero crossing point is not a problem).
    If that's too much offset than a comparator could be added at the input of the opto.
     
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  4. chinmey

    Thread Starter New Member

    Jan 12, 2016
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    please can you help with the below circuit.
     
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  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    I would use the Earth as a reference point and detect between each phase and earth, if you do it between phases you need three circuits.
     
    Last edited: Mar 3, 2016
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  6. chinmey

    Thread Starter New Member

    Jan 12, 2016
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    Thanks for the reply
     
  7. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Um what? Say that again? o_O
     
  8. crutschow

    Expert

    Mar 14, 2008
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    If there's no neutral, then the earth reference is likely to be rather noisy as compared to the phase voltages.

    And how does that reduce the number of required circuits? ;)
     
  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Same number of circuits required, for full zero crossing detection either between phases or PME.
     
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