Nilrem54
Member
- Location
- Norman, Oklahoma, USA
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.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.
Maybe I misunderstood the OP intended question?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.
If you need the rotation of the fixed speed motors to remain the same, and most applications do, you will have to change both.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.
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.
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.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.
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.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?
Something of an irrelevance to this thread but we don't have RYB here now.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.
...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.
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?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).