figuring out delta bank rotation from ground

[amhst56]

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!

[reppy007]

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...

[Pootnaigle]

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.

[Lineman North Florida]

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.

[T-Man]

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/university/transbasics/chapter3.html

[reppy007]

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.

[amhst56]

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.

[reppy007]

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.

[Lineman North Florida]

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.

[T-Man]

I may not be following your question, But if you tie all the H1's or tie all the H2's to the floating neutral the connection is a WYE on the high side because there is a comon point tied. Forming a wye or a star connection.

Now on a Delta you would tie an H1 on one tr to an H2 on the next and so on untill all the points are tied in series to form the triangle or delta.

You can wire either of these primary conections to get a wye 120/208 or 240/ 477 four wire secondary depending on the secondary coils of the tubs.

You can also wire the WYE or Delta banks to deliver delta 240 or 480 depending if the internal coils are wired in series for 480 or parallel for 240 (A to C and B to D for 240 - or B to C for 480)

[Lineman North Florida]

I may not be following your question, But if you tie all the H1's or tie all the H2's to the floating neutral the connection is a WYE on the high side because there is a comon point tied. Forming a wye or a star connection.

Now on a Delta you would tie an H1 on one tr to an H2 on the next and so on untill all the points are tied in series to form the triangle or delta.

You can wire either of these primary conections to get a wye 120/208 or 240/ 477 four wire secondary depending on the secondary coils of the tubs.

You can also wire the WYE or Delta banks to deliver delta 240 or 480 depending if the internal coils are wired in series for 480 or parallel for 240 (A to C and B to D for 240 - or B to C for 480) Maybe I should have stated that I was speaking of Wye primary and Delta on the secondary side, every closed Delta bank that I have ever built with Wye primary on the topside, the floating neutral will be tied across the 3 pots on the high side all together meaning all on H1 or all on H2,hopefully this helps clear up my original question.

[reppy007]

Maybe I should have stated that I was speaking of Wye primary and Delta on the secondary side, every closed Delta bank that I have ever built with Wye primary on the topside, the floating neutral will be tied across the 3 pots on the high side all together meaning all on H1 or all on H2,hopefully this helps clear up my original question.

If your saying that if you swapped the floating tie,I wouldnt think it would change the rotation,never heard that asked before,and it is a good question.The incoming phases on the primary side would be the same,and the secondary would remain the same,it would change the polarity,but Id vote no,as far as changing the rotation...now if I was an apprentice again,that is one question I would ask of the supervisors/foreman when at the end of a verbal test,they asked me if I had any questions....did that once when I asked them about what leads what on a capacitor bank.....the reactance or the resistance.I used to know,but i seemed to have even forgotten that one.

[T-Man]

When you change primary connections, you change rotation. So if the leads of the Floating Neutrals were hooked to the H1 bushings you would have one rotation, and if you installed the new bank with the floater hooked to the H2's. the second time the rotation would change.

If you vectored this out you would not only see the rotation change, you would also see the polarity of the three phase bank change also. (do not confuse this polarity change with an additive or subtractive transformer winding) I'm saying in one case the vector diagram of the delta triangle would be pointing up and in the other example the vector diagram would be pointing down.

So if A phase on the secondary was the upper most point of the triangle in example one, it would be the one pointing down in the second example. The left and right points would stay the same. Draw it out and you will see.

[Lineman North Florida]

When you change primary connections, you change rotation. So if the leads of the Floating Neutrals were hooked to the H1 bushings you would have one rotation, and if you installed the new bank with the floater hooked to the H2's. the second time the rotation would change.

If you vectored this out you would not only see the rotation change, you would also see the polarity of the three phase bank change also. (do not confuse this polarity change with an additive or subtractive transformer winding) I'm saying in one case the vector diagram of the delta triangle would be pointing up and in the other example the vector diagram would be pointing down.

So if A phase on the secondary was the upper most point of the triangle in example one, it would be the one pointing down in the second example. The left and right points would stay the same. Draw it out and you will see. And with that being said and back to the original question, it seems to me that on a delta bank no one can call rotation from the ground and be right 100% of the time without checking rotation with a meter.