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Thread: Trane RTAA217

  1. #14
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    RTAA 217 Starters

    Luce, and whoever else is interested:

    It sure looks like you have part winding start on those chillers. I could not see the contactor portion of the wiring diagram but from what you discribe, and the fact that you have some Star-Delta starters (which are different), leads me to think you are correct. I have never seen one on those machines but Trane did use P-W start on some of their recips.

    Let me try to clear the waters a bit as I have met old timers in the business who did not really understand P-W, Star-Delta, Primary Reactor, Auto- Transformer, Solid State, VFD or the difference between open and closed transition. All of these terms apply to Trane, Carrier, York, W-House (McQuay) and any others. They also apply to sewage pumps,fans, the pumps trying to keep New Orleans dry, or any other large motor (read big electrical inrush load).

    The motors you are talking about are 6 lead motors ( six terminals in the terminal box). Basically (as stated earlier) you have two seperate three phase moters in one housing. Remember the Ohm readings you got? The two motors are not interconnected inside the casing. but their ends are brought out to where we can get to them to perform our little tricks.

    The simplest starter is an across-the-line. One contactor closes and "Bang" it's running at 100% torque and current draw. This may not be a good thing so we go to a P-W start. The simpelist of these requires two contactors. When C-1 closes the motor starts with only 65% current draw, but only has 48% of the torque. Hence the "unloaded " start. When C-2 pulls in we are at 100% torque and current draw.

    A Star-Delta Starter requires a third contactor (and may have 4 along with big resistors in the starter).

    Hope this helps a little and keep one hand in your pocket when working in these things, they wiil bite you.

    The pur

  2. #15
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    Don't just rely on the number of leads or terminals to tell you what kind of motor you are looking at. Star-Delta and also two speed motors can be six leads or terminals.
    God Bless our Veterans

    God Bless the USA

  3. #16
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    As Jayguy accurately stated the "Part-Winding" compressors are actually 2 identical and totally seperate motors that are Delta-Wound and Wye connected to the motor terminals.
    A 40 H.P. compressor would then have 2 seperate 20 H.P. motors inside.
    The "Part-Winding" start scheme therefore reduces the Inrush(Locked-Rotor) by 50% of that with a X-Line start.
    Whilst' the Wye-Delta start reduces the Inrush current to a paltry 130% of Full Load.
    An across the line motor would inrush around 500% of the FLA....
    The Part-Winding scheme would be in the neighborhood of 250% Inrush current of the Full Load Amps.
    Ain't "None" of us as smart as "All" of us..

  4. #17
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    Quote Originally Posted by Chiller Guy View Post
    A Star-Delta Starter requires a third contactor (and may have 4 along with big resistors in the starter).

    Hope this helps a little and keep one hand in your pocket when working in these things, they wiil bite you.
    Just to clarify one thing. The resistors carry the load during the transition period.

  5. #18
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    Quote Originally Posted by graham View Post
    Oh boy this could be interesting ????? Luce . its called wye delta or star delta or reduced inrush starter. it does excactly that reduces the inrush amps to get the motor running . What I cant understand is why techs get themselves into situations where they are working on equipment that is clearly beyond their knowledge or ability . I suggest you take a training course or at least pick up the IOM and read it and understand it before you work on this stuff . High voltage/wye delta starters and inexperienced techs do not mix . Find another tech to go to the site with you and help you and hopefully you wont hurt or even worse kill someone ???? I know this may sound harsh but sometimes the truth just has to be said !!!!!!!!!!!!!!! Are you even a service tech????
    Have to agree with Graham on this one, if a tech cannot instantly recognise the type of starter being used they should'nt even be opening the panel.?
    I wonder how many techs of this level are going to get fryed when they encounter an "inside the delta starter configuration"

  6. #19
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    Quote Originally Posted by edward j View Post
    Have to agree with Graham on this one, if a tech cannot instantly recognise the type of starter being used they should'nt even be opening the panel.?
    I wonder how many techs of this level are going to get fryed when they encounter an "inside the delta starter configuration"
    Are you saying that every panel you've ever opened, you've known what all the components were and exactly how they worked?.....
    Pay no attention to the man behind the curtain.
    jogas

  7. #20
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    I always like the look on the electrician when you show him an inside delta starter and how all the motor terminals are hot with the motor off.
    God Bless our Veterans

    God Bless the USA

  8. #21
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    Quote Originally Posted by Randy S. View Post
    I always like the look on the electrician when you show him an inside delta starter and how all the motor terminals are hot with the motor off.

    I feel your pain, and they want to take our work! At least in your State.
    A few years ago I had a Sparky tell me on a new chiller start up that the Wye-Delta starter would not work. That there was a direct short.
    He proceeded to show me the K3 contactor, I just thanked him and told him I would take care of it.

  9. #22
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    Randy,

    What do you mean about the motor terminals being "Hot" when the motor is "off"?

  10. #23
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    In an inside delta starter, the contact or the soft start SCR is in series with each delta connected winding. Each terminal will be hot, but the starter completes the circuit to run. There is also a shunt trip breaker on the soft started ones in case an SCR shorts. Even that relies on the soft start electronics to shunt trip the breaker.

    Every one I've ran into was a soft start. The whole idea is to allow the use of a smaller soft start. A real bargain if you cook a very expensive chiller stator.
    God Bless our Veterans

    God Bless the USA

  11. #24
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    Quote Originally Posted by Randy S. View Post
    I always like the look on the electrician when you show him an inside delta starter and how all the motor terminals are hot with the motor off.
    not just electricians either!!

    good luck.
    You either love bacon or you are wrong.

    4 gallons of gas, 2 miles of travel, teaching my daughters how to drive in the high school parking lot...priceless!

  12. #25
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    Randy,

    OK, I am with you now! I was still in the Star-Delta thinking mode and you threw me a curve with the " inside the delta". Here we just call it a solid state starter. The bleed through on the SCR's will truly keep some parts energized and spoil your day if not careful.
    In fairness to the electricians, most are not trained for control or service work and never get into these units.

  13. #26
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    Not just bleed through

    On an inside delta, it's not just bleed through. The starter is actually inside the delta, and only has to be rated for 67%.

    Draw a 6 lead delta configuration with one SCR block of the soft start in series with each winding, and you'll see what I mean. Each phase goes to one end of a winding, and also to the line side of another SCR block in series with another winding.

    McQuay did it for a while on centrifugals in the 90's and then gave up, going to a "conventional" soft start of the delta configuration at full amperage.
    God Bless our Veterans

    God Bless the USA

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