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  1. #1
    Join Date
    Jan 2005
    Location
    Houston TX
    Posts
    866

    Wye-Delta skelter

    I am not an electrical engineer and I don't play one on TV. I am working on a Trane CVHA-025, with a wye-delta closed transition starter. The motor design is 208 volts, 392 RLA, 3860 LRAD, 1265 LRAY, OLTA is 425. The Allen-Bradley time inverse overload is calibrated to trip at 247amps and to hold 1278 amps for 41 seconds at start up. The overload point of 247 amps is not the question, the high amperage, which is more then the lock rotor wye is what I am concerned about. I know under certain starting conditions it may take a motor a while to come up to speed, but allowing it to draw more then lock rotor for 41 seconds sounds a bit extreme. Also the Cutler- Hammer contacts are cooked, but not just the contact area the copper bridge is discolored from heat as are the copper bases of the 2 mounted contacts. This is on the three major contactors, all contacts.The contactors are rated at 250 amps @ 480 volts (1M and 2M) and 200 amps @480 volts (shorting). The chiller starts okay but the shorting contactor sounds like there is arcing going on as the motor starts and begins to come up to speed (last about 10 seconds) I am thinking the contacts are undersized for the load. The 1M and 2M are Cutler-Hammer C32LN-3, and the shorting is C/H C32KN-3 and both are series A-1. The motor itself checks out okay any of the 6 t-legs to ground show 475 meg ohms to ground and 1 gig ohm between the 3 windings. I believe the chiller came with this equipment from Trane back in 1982 when the chillers were installed.

  2. #2
    Join Date
    May 2001
    Location
    Western Wa
    Posts
    1,754
    Theoretically the "main" and "delta" contactors each only carry 67% of the rated full load when running.

    The "star" and "main" would be the ones taking the most beating on start up.

    Is there a big voltage drop at start up?
    God Bless the USA

  3. #3
    Join Date
    Sep 2004
    Location
    Kansas City, Kansas, United States
    Posts
    13,817
    i thought it was 57.5%?????????

    Quote Originally Posted by Randy S. View Post
    Theoretically the "main" and "delta" contactors each only carry 67% of the rated full load when running.

    The "star" and "main" would be the ones taking the most beating on start up.

    Is there a big voltage drop at start up?
    I WILL SELL WORK,GENERATE BUSINESS, GO GET NEW CUSTOMERS!
    YOU SHUT THE HELL UP AND QUIT RUNNING YOUR MOUTH!

  4. #4
    Join Date
    Apr 2009
    Location
    In the south
    Posts
    30
    Sound like you are hearing alot of noise from the shorting contactor is that right? If so pull the front off the contactor and see if the ring has come out of the magnetic frame. If it has this causes the magnetic field pulling in the contactor to get screwed up and causes the contactor to make a loud buzzing noise.

  5. #5
    Join Date
    Jan 2005
    Location
    Houston TX
    Posts
    866

    Wye-Delta Duex

    Randys, a minimal voltage drop of 2 volts and the motor doesn't hesitate it does come right up to speed in wye configuration. When I look at the size of the contacts 1M & 2M are 1/2" in diameter and the shorting is about 1/2" square and the amount of current that has to pass thru them and the copper support for the stationary and bridge of the movable 1270 amps seems way too much to pass thru unimpeded. I have another account that has 5, 208 volt Tranes CVHE's and they have contacts as big as your fist. They are 500 Tons each and each contactor has it's own enclosure. They are about the size of a old phone booth. The ironic thing is these machines are very slow starters and the LRA on those machines isn't much greater for a machine 2 and 1/2 times the machines I'm talking about(200) ton CVHA's. Tranetek, all the shorting rings are epoxied to the armatures. Thanks-GEO

  6. #6
    Join Date
    Jun 2009
    Location
    Lawng Eyeland
    Posts
    97
    Those meg readings don't sound so hot to me. When was the last time the bearings been changed?

  7. #7
    Join Date
    May 2001
    Location
    Western Wa
    Posts
    1,754
    How about the shading coils on the iron core of the contactor?

    The copper loop thingy.
    God Bless the USA

  8. #8
    Join Date
    Jun 2009
    Location
    Lawng Eyeland
    Posts
    97
    Definitely agree Randy, dis-colored copper is never good. Always clip back my motor connections. Good pick-up.

  9. #9
    Join Date
    May 2001
    Location
    Western Wa
    Posts
    1,754
    Possibly, it has something to do with the size of the transformer feeding the building.

    As others have said, the 208 current draw when starting is tremendous, and it just may be to do with the sizing of the starter contactors.
    God Bless the USA

  10. #10
    Join Date
    Dec 2003
    Location
    Half way between North pole and Equator
    Posts
    947
    It is probably safe to assume that these are not the original contacts in contactors due to the age of chiller.
    Have they been replaced recently, when did this problem begin?
    Have you been the only one working on it, doing repairs?
    If they are not the original, or OEM replacement contacts they may be some aftermarket knock offs that have slightly different dimensions.
    This can cause less than adequate pressure between contact surfaces resulting in arcing.
    Someone may have elected to get "cheaper" contacts, or the originals were no longer available.
    Be carefull, you could be playing with an Arc Flash incident waiting to happen.

  11. #11
    Join Date
    Jan 2005
    Location
    Houston TX
    Posts
    866

    Wye-Delta part lV

    Randy, that is my thought too! But why is the 2M also burnt ? I think I'm going to try and contact Cutler-Hammer with the part #'s and see what they think. If you look at the large wire size involved compared to how small the contact area is. I would have thought I would get a lot more voltage drop at start-up and a slower acceleration time, but thats not the case at all. The contactors do say they can carry 1400 amps locked rotor, but that's at 480 volts. Anyway I appreciate your advice. Thanks-GEO.

  12. #12
    Join Date
    Jan 2005
    Location
    Houston TX
    Posts
    866

    Wye-Delta part V

    First off an apology to acjourneyman, I should learn to read a little closer. These are the original contactors according to the starter manufacturer Cutler-Hammer and the Trane starter ID #. That's why I plan on contacting them on Monday, hell I may call Trane also. The more the merrier. Guys, thanks alot for all your advice. It is truly appreciated-GEO

  13. #13
    Join Date
    Jan 2005
    Location
    Houston TX
    Posts
    866

    Wye-Delta Grand Finale'

    As promised I got all my answers today. The contactor size has nothing to with amps or volts (go figure) NEMA sizing only has to do with motor horsepower. The motor I'm dealing with is 240 horsepower and that is border line between a size 5 and 6 contactor, not a size 4 as is in there now. That would explain all the extra burnt contacts sets I found laying on the work bench. I think they have been changing contacts every year since 1982. That year also played a key role to my fact finding. That's the year Trane change venders with their starters from G/E to Cutler-Hammer, now Eaton, Cutler-Hammer. Ironic part of it all is the customer won't want to spend the money to upgrade to the right size contactors. It is their chiller and I'm only the messenger. Again thanks to all.-GEO

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