phase rotation

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brentp

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I need help understanding the following. A utility transformer was installed with ABC clockwise rotation, it failed. A temporary transformer was installed with identical connections, rotation turned up counterclockwise. New transformer was 'repaired' and replaced, back to clockwise. It failed again! Back to temp transformer, counterclockwise. 'New transformer' repaired & replaced, clockwise.

Now my question. Why is rotation different from one trans (or motors) to another? I would like to share with others so the the simplest answer would be appreciated.

Thanks
Brent
 
Why didn't your switch the A to C to C to A connections at the motor ? I assume to get your desired counterclock-wise rotation ?:roll:
 
Sounds to me like the transformers had different bus stab arrangements and who ever hooked them up payed no attention to which one was H1, H2, H3-X1,X2,X3. For instance when facing the transformer one might have terminals let to right like above. The other could have H3,H2,H1- X1,X2,X3. Transformers do not magically change rotation.
 
stickboy1375 said:
I can't believe the POCO did not check rotation before and after the fact!!!
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Well I can't beleive they didn't switch poles before a "TRANSFORMER" was brought in ...:rolleyes:
 
rotation

rotation

Check to see that the winding with the highest volage applied is not the lead closest to the first wrap around the iron core this will cause undue stress to the xformer winding insulation. In other words the grounded side should be near the iron core and the high voltage side should increase gradually as the voltage gradient wraps around the core so the stress of the voltage is not 13k right next to the grounded iron core. The voltage gradient should be gradual and uniform. 13k farthest winding gradually winding down to the grounded zero iron core. I doubt that rotation is your problem here. Rotation is incedental. Which came first the chicken or the egg? Cluck!
 
I am not on the jobsite to see this first hand. I'm getting info from a co-worker. A cracked insulator on the pri side was the reason given for the failures. Twice!

From what I gather, TRANS A was connected 3 times being clockwise. TRANS B was connected 3 times being counterclockwise. Supposedly the transformers were connected identically each time, ABC-H1,H2,H3. Rotation was never any 'problem', just got us thinking. Is rotation incidental between the 2 transformers, or should they have the same rotation if connected identically?

What I need to do is go back and read up on my electrical theory 101 book, if I can find it. :)
 
Nick said:
Sounds to me like the transformers had different bus stab arrangements and who ever hooked them up payed no attention to which one was H1, H2, H3-X1,X2,X3. For instance when facing the transformer one might have terminals let to right like above. The other could have H3,H2,H1- X1,X2,X3. Transformers do not magically change rotation.
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If they were simply reversed rotation then Nick's explantion is probably correct. You need to check to nameplates and compare them to each other, I think you will solve the dilemma. A phase diagram may be needed to see the whole picture.
 
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