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Thread: AF Safety concerns: 150kVA pad mount xfmr boosting 208 => 480 in Data Center

  1. #1
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    AF Safety concerns: 150kVA pad mount xfmr boosting 208 => 480 in Data Center

    Some concerns about a 20x25 room with one exit and a
    150kVA pad mount xfmr boosting 208 => 480 in Data Center
    https://1drv.ms/f/s!AkuU8mYuf3eEgV_krr3OkdkHYYEi
    Click image for larger version. 

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    We only have one exit door in the server room.
    Server room is classified as S2 Low Hazard Storage because the xfmr, but the batteries on the UPS could bring it up to H3 - which would require less than 25' to the exit door.
    What is the actual Arc Flash danger here?
    There is no present danger in my opinion, but there is a question of whether this is intrinsically unsafe to have the xfmr in a room that may have unqualified people in it.
    If the doors on that xfmr are not opened, is there a danger to anyone in the room?
    I've put my hands on the effects of AF when it happened with the doors shut, and its usually holes burned in the cabinet, but the doors didn't get blown off or anything.
    I've got to call square d and ask them

    The next OCP before the xfmr is a 400a main disconnect. The xfmr is tapped from that bus.
    The only load on the 480 [secondary side] is a pair of intermittently used 90a 3p cbs


    square d 35149-17232-023 150t3hb instruction manual three phase insulated transformer

    Watchdog® Low Temperature Rise
    • Designed for low energy losses at loads greater than 50% of
    nameplate rating.
    • Extra long life expectancy using 220 oC insulation system
    designed for full load operation at a maximum temperature rise
    of 115 oC or 80 oC instead of 150 oC.
    • Continuous emergency overload capability of 15% on 115 oC
    rise and 30% on 80 oC rise.
    NOTE: These products are obsolete and can no
    longer be ordered. The information in this table
    is for reference only.
    Click image for larger version. 

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    "A problem clearly stated is a problem half solved."

  2. #2
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    Speaking outside of my training/experience level:

    IMHO the transformer itself presents no more arc flash hazard than any other utilization equipment at that voltage and power level. IMHO there will only be a significant arc flash hazard when the equipment is being worked on...and it should not be worked on while energized.

    But to actually evaluate the hazard you will need to know the available current on the feeder supplying the transformer.

    -Jon

  3. #3
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    It's a 240 V 400 amp
    Cutler Hammer
    three-phase large mainframe
    molded case Breaker
    pretty old I have to go and look at the label
    "A problem clearly stated is a problem half solved."

  4. #4
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    NFPA70E pretty much requires that your company perform a Risk Analysis. For instance; the 'task table' methodology now starts with a Yes or No table for PPE being required.

    There are several methods available for you to calculate what amount of Incident Energy might result from an arcing fault event. But this is simply the hazard. It
    You must also evaluate the 'likelyhood' or possibility that the hazard occurs.

    It it probable you will reach the same conclusion that many others have - there is no inherent danger in simply being near the majority of enclosed 480V equipment.
    Just because you can, doesn't mean you should.

  5. #5
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    If I have any concerns regarding this, the only concern I really have is that when a lot of current is flowing that main switchgear there is some little buzzing noise could be from loose busbars
    I really want to turn it off
    take it all apart
    Turn it back on
    run at Hard and at least do a FLIR camera test on it
    but nobody ever wants to turn it off.

    It's just the buzzing
    I put my hand on it when I was buzzing and try to see if I can silence the vibration
    But nothing that was accessible in the lower part of the cabinet was vibrating
    "A problem clearly stated is a problem half solved."

  6. #6
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    I don't think I have ever heard a "quiet" transformer.

    Cute Data Center, BTW.

  7. #7
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    Quote Originally Posted by Chamuit View Post
    I don't think I have ever heard a "quiet" transformer.
    Sort of by definition???

  8. #8
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    Quote Originally Posted by GoldDigger View Post
    Sort of by definition???

  9. #9
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    Quote Originally Posted by Chamuit View Post
    I don't think I have ever heard a "quiet" transformer.

    Cute Data Center, BTW.

    Hey it's only 20 x 25!
    &
    That was back when they were just moving in.
    And it's not the transformer that buzzing
    Humming
    it's the busbars at the main that feed the transformer
    They sound a little strained
    Have A great weekend!
    "A problem clearly stated is a problem half solved."

  10. #10
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    Quote Originally Posted by wyreman View Post
    Hey it's only 20 x 25!
    &
    That was back when they were just moving in.


    Quote Originally Posted by wyreman View Post
    And it's not the transformer that buzzing Humming
    it's the busbars at the main that feed the transformer
    They sound a little strained
    Okay, makes more sense now. I have very limited experience with bus duct, so I'll go back to lurking. Although, have you put your ear to connection points, so to speak, to localize the noise?

    Quote Originally Posted by wyreman View Post
    Have A great weekend!

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