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  1. Default figuring out delta bank rotation from ground

    I use to work with a lineman that said he could figure out the rotation of a closed delta bank by knowing the primary phasing and where the each secondary leg was.

    He was very good with banks, so I don't doubt him, but I can't find any books or from searching the web how it is done.

    Can someone here explain how it work?

    Thanks for the help!

  2. #2

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    Quote Originally Posted by amhst56 View Post
    I use to work with a lineman that said he could figure out the rotation of a closed delta bank by knowing the primary phasing and where the each secondary leg was.

    He was very good with banks, so I don't doubt him, but I can't find any books or from searching the web how it is done.

    Can someone here explain how it work?

    Thanks for the help!
    That can depend on where you are checking the rotation,if its at the meter like us where Im located its basically a guessing game,because of how the electrican has wired his stuff.....but if you know how it is generated and wire your bank in that order,you should be half way there....then you would most likely wire your secondary the same way,A-Phase on the primary side to A-phase on the secondary side,and so on ,then again your polarity can change that...its kind of hard to explain without knowing where you are checking the rotation.....Ive been around lots of people that leave it clock-wise at the bank,weather urd or overhead.....but here that doesnt really apply...

  3. #3
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    Oct 2006
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    South East Texas
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    Ummm there is an always will be a 50% chance that the rotation will be correct regardless. But I would hate to try and explain why I elected to not use a rotation meter to be sure.

  4. #4

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    Quote Originally Posted by amhst56 View Post
    I use to work with a lineman that said he could figure out the rotation of a closed delta bank by knowing the primary phasing and where the each secondary leg was.

    He was very good with banks, so I don't doubt him, but I can't find any books or from searching the web how it is done.

    Can someone here explain how it work?

    Thanks for the help!
    I know on our system that if it is a Wye bank and it is made up correctly, your rotation will be Clockwise ABC or Red, White and Blue at the tx bank, can't say that for a Delta bank on our system, that's not to say that he couldn't do it, just that I don't know how to guarantee the rotation on a Delta bank without using a rotator.

  5. #5
    Join Date
    Feb 2009
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    Wisconsin
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    A,B and C phase are 120 degrees apart right from the generator at the power plant. And the power pland rotates the generator in a clockwise direcion. (I could be 50% right or wrong about that)

    No matter if you work a delta or a Wye connected transformer A phase will always be 120 degrees away from B and C ( draw a 360 degree circle and start at any one degree, them measure 119 degrees away from the first mark and make another. Then mark another spot on the circle to find the third point. Connect those three points in the center and w=each one of those legs represent a phase.)

    Now label one A, one B and one C

    I wish I was at a chalk board!

    If you vector the secondary to the primary and label the connections you will be able to find rotation thru vectoring. Now Poot has a good idea. . .use a rotation meter, But if you want to know why delta is not happy phasing to wye, Vectoring is your answer.

    Here read this:
    http://www.federalpacific.com/univer.../chapter3.html

  6. #6

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    The lineman who knew the rotation,if he was 100% correct,I suggest he go to Las Vegas,it is a 50/50 shot.....I ve worked with guys that left the rotation on the transformers clockwise....the story behind that is kind of funny ......I overheard one saying the rotator didnt work,he mentioned that it was the second one that week that didnt work....well that was a red flag and when I looked to see what they were doing....I found that they were trying to get the rotation from a power transformer on a urd opend delta bank......that wasnt going to work,so I helped them out a bit.....Im sure they forgot a week later what they had been taught,cause they knew close to nothing about how one works or the why question.

  7. Default

    I always use a rotation meter, but it would be nice to figure out where my 1 and 2 legs are going before going aloft.

    Example: we were changing from an open delta to a closed delta and it would have been nice to know if the rotation was going to change by adding that third pot. The guy we use to work with said if you are looking down from above the pole at the phasing of the transformers. Abc, bca, and cab are all clockwise and something about where the 1 and 2 legs are on the lighting pot. Does this ring a bell for anybody? Thanks for the help.

  8. #8

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    Quote Originally Posted by amhst56 View Post
    I always use a rotation meter, but it would be nice to figure out where my 1 and 2 legs are going before going aloft.

    Example: we were changing from an open delta to a closed delta and it would have been nice to know if the rotation was going to change by adding that third pot. The guy we use to work with said if you are looking down from above the pole at the phasing of the transformers. Abc, bca, and cab are all clockwise and something about where the 1 and 2 legs are on the lighting pot. Does this ring a bell for anybody? Thanks for the help.
    On your closed delta bank you will only have to swap the lighter legs for the right rotation,not the high leg.Its either one way or the other.On your 277/480 volt banks you can make one power leg hot,but only temporary connectng the other two to see what kind of rotation your getting,if its wrong just swap the two.Some guys will barley tighten some two bolt clamps,then do the checking...Ive done it that way....another way is taping the connections together,but using that method you must be careful,watching that they are temp.taped well enough and not getting into a ground,or bond wire.

  9. #9

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    While we are talking about banking transformers, A closed delta bank has a floating neutral on the topside, let's say you have an existing bank with the floating neutral tied across the 3 pots on the H1 bushing on the high side, the pole gets changed out and the new bank gets built back exactly like the old bank, same side of pole etc etc, with the exception of the way the floating neutral ties across the 3 pots, it gets tied across on the H2 bushings, in other words the only difference is on the high side. Would it change the rotation? Not talking about banking additive and subtractive pots together either, all pots in both banks are the same polarity 2 bushing pots.

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