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  1. #1
    Join Date
    Sep 2011
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    BAJA AND CALIFORNIA
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    90

    motor condition in centrifugal chiller

    Hello guys new question related to a motor on centrifugal chillers
    YORK is open drive motor so no question about MEGG the motor
    TRANE low pressure R-123 is a semi-hermetic motor whats the best condition to perform motor MEGGER ??? according to your experience
    CARRIER & MC Quays 134a is semi-hermetic motor whats the best condition to perform motor MEGGER???? according to your experience.
    if you guys have any chart or manual that explain how is the best method to MEGG the motor and under what condition ,i will appreciate your Help.

    Regards

  2. #2
    Join Date
    Mar 2007
    Posts
    3,108
    Why wouldn't you test an open drive Y motor with a megger? It has windings with insulation that can deteriorate the same as any other motor.

    As far as T, C, and M chillers... I don't know of any special procedures for any of them, other than checking from phase to phase in addition to phase to ground. Don't meg any of them in a deep vacuum. Don't use a megger with a solid state starter or vfd connected. Megger readings don't do a whole lot of good without a history. I think T has a chart in the blue service guide?

    As far as a go/no-go rule of thumb for standard motors, I've always used 1 megohm per 1kv + 1 megohm.
    "There is no greater inequality than the equal treatment of unequals."

    -Thomas Jefferson

  3. #3
    Join Date
    Sep 2011
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    BAJA AND CALIFORNIA
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    90
    Rob you right that we need to check all the motors of the chillers , my question is around to the fact of york is open chiller compresor and motor are separate so the motors are under ambient condition , now trane R-123 OR 11 are low pressure and normally with refrigerant the units stoped are in vaccum my question is according to your experience we have to increase the pressure to 0 or 1 psi and then apply the megger or is no problem to megg the motor if the units are in vaccum but with the load of refrigerant???
    Now on the R-134a C,M, or any other centrifugal with positive pressure you can megg the motor of the unit under pressure condition??
    Do you have the blue service book for share??

    regards

    oscar

  4. #4
    Join Date
    Mar 2007
    Posts
    3,108
    The reason they say not to meg a motor in a vacuum is because in a deep vacuum, there is no atmospheric insulation between the phases and from phase to ground. Arcing can occur inside the motor. Even in a low pressure machine that's in a vacuum when it's sitting idle, the refrigerant is the atmosphere that helps to insulate the phases from one another and ground.

    The chart is in CTV-SG-1 and CTV-SB-61. My copy of it is not much good and is mostly illegible.
    "There is no greater inequality than the equal treatment of unequals."

    -Thomas Jefferson

  5. #5
    Join Date
    Sep 2011
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    BAJA AND CALIFORNIA
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    K ROB i will be on tampa next february , if you have time we can meet and buy you lunch do you work for a company or you do yourself??? may be you can give me some advices and recommendations in a chiller side , we have tranes ,mcquay,yorks and carrier under our responsability most of all are screw or centrifugals

    thanks again for your support

  6. #6
    Join Date
    Mar 2007
    Posts
    3,108
    Going to a class or something around here? Tampa's pretty cool, you'll enjoy it. I am always for doing lunch and talking shop with other folks in the business. Glad I could be of assistance, Oscar.
    "There is no greater inequality than the equal treatment of unequals."

    -Thomas Jefferson

  7. #7
    Join Date
    Mar 2007
    Posts
    61
    Quote Originally Posted by Tech Rob View Post
    The reason they say not to meg a motor in a vacuum is because in a deep vacuum, there is no atmospheric insulation between the phases and from phase to ground. Arcing can occur inside the motor. Even in a low pressure machine that's in a vacuum when it's sitting idle, the refrigerant is the atmosphere that helps to insulate the phases from one another and ground.

    The chart is in CTV-SG-1 and CTV-SB-61. My copy of it is not much good and is mostly illegible.

    Motor is to be megged with the stator at ambient temperature after 24 hours of idle standby.

    Meg Phase to Phase with remaining Phase connected to Ground.

    Meg Phase to Ground with remaining Phases connected to Ground.

  8. #8
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    4,389
    Quote Originally Posted by w~p View Post
    ...Meg Phase to Phase with remaining Phase connected to Ground.

    Meg Phase to Ground with remaining Phases connected to Ground.
    nope.
    When I am late for work, I usually make up for it by leaving early.

  9. #9
    Join Date
    Dec 2008
    Location
    Dixiana, AL
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    2,610
    Quote Originally Posted by w~p View Post
    Motor is to be megged with the stator at ambient temperature after 24 hours of idle standby.

    Meg Phase to Phase with remaining Phase connected to Ground.

    Meg Phase to Ground with remaining Phases connected to Ground.
    Where did this instruction come from?

  10. #10
    Join Date
    Oct 2011
    Location
    La.
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    282
    In the IOM manuals the manufactures tell how to meg their motors and the limits that are allowed. Sometimes we need to read. See any York OM manual around page 58.

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