Delta Wye Transformer - motor rotation

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kwired

Electron manager
Location
NE Nebraska
If you have a Balanced Delta Wye transformer, if you switch two of the primary leads, does it affect all the motors already connected on the secondary side.
All of the three phase direct connected to the line motors - yes. VFD supplied motors and single phase motors won't be affected.
 

kwired

Electron manager
Location
NE Nebraska
why don't you switch it at the motor??
Maybe I misunderstood the OP intended question?

I thought he meant swapping two primary leads, if he meant simply opening two leads -there would be no current in the delta primary and the result would be no secondary voltage at all.
 
Yes - swapping primary leads.

Yes - swapping primary leads.

Maybe I misunderstood the OP intended question?

I thought he meant swapping two primary leads, if he meant simply opening two leads -there would be no current in the delta primary and the result would be no secondary voltage at all.

We are having to swap primary incoming power from a local power plant, even though the building have been in place and used this way for years. Apparently two of the main feeds were reversed for a long time, and don't match the rest of the campus. It is affecting about 8 buildings, out of 100's. We are having a outage soon and swapping the incoming primary's on the affected buildings delta-wye transformers(pretty sure they are all delta-wye). The debate at work is weather we have to change the secondary side to match motor rotation. We are going to check secondary rotation before and after the primary side has been switched, to verify, and then if needed switched the secondary. It has been a big debate leading up to the outage wether it will affect the secondary's, and I have been trying to form my own opinion and both camps have sound reasons why it will or won't be affected. I was just going to post on this forum and get some peoples opinion outside of work. I will update this forum after it has happened and let everyone know what the actual result was.
 
If it was something simple like one or two motors being affected I could just switch it at the motor. But these are established building and it has the potential to affect lots of motors and various other things. Let me explain a little more. We have our own power plant and have hundreds of buildings. Apparently there are about 8 building that have been reversed for a long time, and the power plant wants to switch the primary incoming building power to those 8 building to match the rest of the campus. From what I was told all the building have large delta-wye transformers supplying power to the buildings. Before we have the power outage we are going to check rotation on the secondary side, and then verify secondary side rotation after the swap has been made and if needed swap the secondaries also. We are having an outage and turning off the building MDP's so nothing inside the building will be affected. The debate at work has been wether changing the primary side leads will affect the secondary side rotation. I have heard sound logic from both camps as to why and I am not completely understanding which sides logic is flawed. I was just posting on the forum to gather more opinions. I am leaning towards having to change leads on both sides to match rotation. Either way it will be checked, verified, and switched if needed so there shouldn't be any problems in the end. I was just trying to gather more info and understand why.

After the change over has been completed, I can reply to this post and let everyone know the results.
 

kwired

Electron manager
Location
NE Nebraska
Swapping any two lead upstream will reverse the three phase rotation.

I can understand the want to make all the distribution the same for possible future issues, if you can reverse a common supply being effected by this someplace else it will eliminate the need to go to subfeeders and branch circuit levels at multiple locations to put those back to original rotation. Like swapping two leads on the secondary of the transformer or at the main disconnect of a building, instead of having to go through all feeders or branch circuits in the building and verifying necessary rotation changes.

Of course if you are dealing with much more then 200 amp maybe 400 amp feeds, the difficulty level of doing that starts to factor in as well.
 

Besoeker

Senior Member
Location
UK
We are having to swap primary incoming power from a local power plant, even though the building have been in place and used this way for years. Apparently two of the main feeds were reversed for a long time, and don't match the rest of the campus. It is affecting about 8 buildings, out of 100's. We are having a outage soon and swapping the incoming primary's on the affected buildings delta-wye transformers(pretty sure they are all delta-wye). The debate at work is weather we have to change the secondary side to match motor rotation. We are going to check secondary rotation before and after the primary side has been switched, to verify, and then if needed switched the secondary. It has been a big debate leading up to the outage wether it will affect the secondary's, and I have been trying to form my own opinion and both camps have sound reasons why it will or won't be affected. I was just going to post on this forum and get some peoples opinion outside of work. I will update this forum after it has happened and let everyone know what the actual result was.
If you need the rotation of the fixed speed motors to remain the same, and most applications do, you will have to change both.
You haven't said what the motors are driving. Fans, pumps, elevators......?

If you change just the primary they will run backwards and that could cause damage - or even be dangerous depending on the driven load.
I strongly advise aganst what appears to be the "suck it and see" approach that you are suggesting.
 
We are not just going to switch it and let it affect everything down stream. We are having a power outage at all building the feeds are supplying power to. We are isolating it at the buildings main distros. Checking rotation at the on the secondary feeds. Removing power upstream at the plant level. Switching primary feeds. Checking secondary again for rotation. If the rotation is reversed like most people say it will be, myself included, removing power from the plant level, checking rotation again to verify correct rotation. Then and only then returning power to the buildings main.

the buildings do include elevators, and many other applications where a reversed motor would be catastrophic.

mainly just wanted a break down on a engineering level of why or why not the secondary needs to be flipped. Not just, yea it needs to be flipped. I am on the side and I would say 97% of us are also on the side that the secondary needs to be swapped also, which is why we are isolating and taking precautions to not hurt anything down stream.
 
Swapping any two lead upstream will reverse the three phase rotation.

I can understand the want to make all the distribution the same for possible future issues, if you can reverse a common supply being effected by this someplace else it will eliminate the need to go to subfeeders and branch circuit levels at multiple locations to put those back to original rotation. Like swapping two leads on the secondary of the transformer or at the main disconnect of a building, instead of having to go through all feeders or branch circuits in the building and verifying necessary rotation changes.

Of course if you are dealing with much more then 200 amp maybe 400 amp feeds, the difficulty level of doing that starts to factor in as well.

we are doing it on the main distro side of the building. See comment below. We just have like 8 building we are having to switch. We are not doing lots of branch level switching.
 

Besoeker

Senior Member
Location
UK
We are not just going to switch it and let it affect everything down stream. We are having a power outage at all building the feeds are supplying power to. We are isolating it at the buildings main distros. Checking rotation at the on the secondary feeds. Removing power upstream at the plant level. Switching primary feeds. Checking secondary again for rotation. If the rotation is reversed like most people say it will be, myself included, removing power from the plant level, checking rotation again to verify correct rotation. Then and only then returning power to the buildings main.

the buildings do include elevators, and many other applications where a reversed motor would be catastrophic.

mainly just wanted a break down on a engineering level of why or why not the secondary needs to be flipped. Not just, yea it needs to be flipped. I am on the side and I would say 97% of us are also on the side that the secondary needs to be swapped also, which is why we are isolating and taking precautions to not hurt anything down stream.
I thought I gave you an explanation in relation to fixed speed motors. They will run backwards and you seem to have agreed with that. In operation, cage motors have a rotating field in the stator which induces current thus producing torque. They will run in the oposite direction if the applied three-phase rotation is reversed.The secondary needs to be reversed to retain the original phase rotation applied to equipment sensitive to that rotation.

Of course check rotation on the secondary feeds - testing is important. People can and do make errors for various reasons.

But I have a question. Assuming the connected plant is operating satisfactorily now, albeit with the opposite phase rotation to other sites what is the problem are you trying to fix?
 
But I have a question. Assuming the connected plant is operating satisfactorily now, albeit with the opposite phase rotation to other sites what is the problem are you trying to fix?

That sir is another question I never had answered. I am assuming there is some sort of problem that I have not been told. I am just an electrician that is working from the secondary side. We have other utility electrical workers who will be working on the primary side and their bosses were we ones who thought it needed to be fixed in the first place. I am just a employee on the bottom of the totem pole trying to understand why, but hey it's easy overtime since we're taking down the buildings at hours no one else will be there.
 

kwired

Electron manager
Location
NE Nebraska
I thought I gave you an explanation in relation to fixed speed motors. They will run backwards and you seem to have agreed with that. In operation, cage motors have a rotating field in the stator which induces current thus producing torque. They will run in the oposite direction if the applied three-phase rotation is reversed.The secondary needs to be reversed to retain the original phase rotation applied to equipment sensitive to that rotation.

Of course check rotation on the secondary feeds - testing is important. People can and do make errors for various reasons.

But I have a question. Assuming the connected plant is operating satisfactorily now, albeit with the opposite phase rotation to other sites what is the problem are you trying to fix?
Would seem someone thinks that all the sub units of the campus need to have same phasing - which is sort of nice, but isn't absolutely necessary either. Having some consistency - say if rotation is clockwise on every switchboard/panelboard may have some advantages with future additions or repair work, but some of us are used to the fact that we never know what rotation will be from one place to another, or even within same building or structure at times.
 

Smart $

Esteemed Member
Location
Ohio
While I agree with others that flopping two primary conductors will necessitate flopping secondary conductors, that presents a problem if you flop secondary at the transformer terminals. Let me explain...

Let's say your primary conductor-terminal pairings are ABC-BAC and your secondary terminal-conductor pairings are abc-abc. When you flop, you'll end up with ABC-ABC and abc-bac. The problem this presents is the NEC requires busing phase arrangement in distribution equipment to be ABC (or abc regarding the secondary), top to bottom, front to back, or left to right.

The only way to correctly do this is to flop primary and affected motors individually. Do not flop secondary even though that would provide the correct motor rotation.
 

Tony S

Senior Member
After spending 25 years on plants with opposing phase rotations it does get confusing so I can understand the desire to have uniformity.

Historically all plants ran BYR as in the 30’s we had our own power plants. When we connected to the local grid it run RYB, simple enough, swap the incoming feeders around.

In the 60’s a number of new plants were built and some genius engineer decided the phase rotation should be corrected. So now 20 plants are running BYR and 6 running RYB.

As the plants expanded they started to overlap, two guesses who ended up as “piggy in the middle” trying to sort the mess out. All we could do was give each piece of distribution equipment a phase rotation identifier.

If it can be sorted as easily and quickly as Nilrem seems to think, go for it but heed the warnings.
 

Besoeker

Senior Member
Location
UK
After spending 25 years on plants with opposing phase rotations it does get confusing so I can understand the desire to have uniformity.

Historically all plants ran BYR as in the 30’s we had our own power plants. When we connected to the local grid it run RYB, simple enough, swap the incoming feeders around.

In the 60’s a number of new plants were built and some genius engineer decided the phase rotation should be corrected. So now 20 plants are running BYR and 6 running RYB.

As the plants expanded they started to overlap, two guesses who ended up as “piggy in the middle” trying to sort the mess out. All we could do was give each piece of distribution equipment a phase rotation identifier.

If it can be sorted as easily and quickly as Nilrem seems to think, go for it but heed the warnings.
Something of an irrelevance to this thread but we don't have RYB here now.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
...the NEC requires busing phase arrangement in distribution equipment to be ABC (or abc regarding the secondary), top to bottom, front to back, or left to right.

There are no industry, or code, fixed A, B, C identifiers for transformer outputs, therefore all that might be needed is some new signage at the transformer. For example: instead of X1=A (brown), X2=B (orange), and X3=C (yellow), it might read X1=B(orange), X2=C(yellow), and X3=A(brown).
 

banion23

Member
Location
US
If you're swapping leads on the primary, I'd check all branch circuits on the secondary and track down all motors on the secondary that are 3-phase and not operating through a vfd, and just swap 2 on those motors. Then test to verify rotation.

Use a phase rotation meter.

Any issues doing this?

Sent from my SM-N920V using Tapatalk
 

Smart $

Esteemed Member
Location
Ohio
There are no industry, or code, fixed A, B, C identifiers for transformer outputs, therefore all that might be needed is some new signage at the transformer. For example: instead of X1=A (brown), X2=B (orange), and X3=C (yellow), it might read X1=B(orange), X2=C(yellow), and X3=A(brown).
I agree, from a compliant-only perspective. From the perspective of customary, that would just be flopping the abnormal-for-on-campus wiring from the primary side to the secondary side... wouldn't it?
 
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