Phase failure alarm

Discussion in 'General Electronics Chat' started by sparkyozz, Feb 20, 2011.

  1. sparkyozz

    Thread Starter New Member

    Feb 20, 2011
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    Hi all im trying to make a phase failure alarm for a 3 phase refrigeration unit. im struggling with what parts i need and how to get the low voltage output to trigger the siren
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Use a relay rated for ur operating voltage.
     
  3. debe

    Well-Known Member

    Sep 21, 2010
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    Like R!f@@ said, if 240V Id use 3 relays 1 for each phase to neutral so contact closes if any one phase goes down & trigers the siren.
     
  4. alim

    Senior Member

    Dec 27, 2005
    113
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    Can you say what type of three phase voltage powers the unit is it WYE or is it DELTA?
     
  5. Hagen

    Active Member

    May 8, 2010
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    Phase failure protection is a little trickier than you might think. For example, if a 3 phase motor is running, and one phase goes down (perhaps a fuse blows), a relay connected from line to neutral, even on the dead phase, will remain energized due to a voltage from the other phases via the motor windings.
    Though I'm sure many on this forum could tackle this problem, many solid state devices today can provide this protection, along with overload protection if desired.
     
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    a current transformer around each phase could work. As Hagen mentioned, if your load is a 3ph motor or heater, voltage from the other 2 phases will be present on the 3rd phase, but if there is an open, no current will be flowing & the transformer will detect this. I also think a current transformer would be a better option since it's analog, and you mentioned wanting a "low voltage" indication. If you know how many watts your equipment draws, then you could translate a drop in current to a drop in voltage.

    something like this
     
    Last edited: Feb 20, 2011
  7. BillB3857

    Senior Member

    Feb 28, 2009
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  8. sparkyozz

    Thread Starter New Member

    Feb 20, 2011
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    i was planning on linking someting out of the 3 phase isolators there are 2 refridgeration units fed seperatly, they only draw a low current 15a or so. i only really need to know if the power fails to the units rather than an actual phase drop i suppose. im out of my depth a bit with this..

    i could do with a simple wiring diagram.??!! this is all a bit technical for a domestic electician

    thanks for all your inputs though .. muchly appreciated
     
  9. sparkyozz

    Thread Starter New Member

    Feb 20, 2011
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    its delta that powers the refridgerator units
     
  10. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Whats wrong with this?
    it works with wye
    it trips on undervoltage, overvoltage, and phase loss - pretty much any kind of power failure.
    Only thing I see is your amperage requirement. you got your keywords now "3 phase line monitor relay". Shouldn't be too hard to find one that fits your amperage needs.

    as far as the wiring diagram, you should have 3 big wires going to the reefer unit (isolate power) cut these, insert relay.
     
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