Transformer in reverse
- Thread starter patpappas
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As long as it is used within it's rating it will not harm the transformer.
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- PE (Retired) - Power Systems
Every transformer manufacturer has literature available on the "do and don'ts" associated with back-feeding their units. I am not aware of any manufacturer that prohibits this connection except in specific situations.
If they used XO to derive a Neutral for the 480 volt side of the tranformer (or did any other bonding of XO that you would expect to see if the transformer was used in the normal fashion) you have a potential disaster waiting to happen. With most transformers. an improper connection like this will "appear" to work just fine but if you loose a phase of the incoming 208 volt feeder, all hell breaks loose. Do a search on "Reverse fed Transformers" on this site and you should find some lengthy threads on this topic.
One more thing
One more thing
Another thing to remember is that if the dry type transfomrer is "fan" assisted cooling it can not be fed in reverse it will not work properly.
One example is the GE Manufactured TransfMore it is ensientally a dry type distribution transformer de-rated fans added and a higher rating applied. these come in sizes as small as 75Kva I believe. So I guess the common thread is to verify no 277V is required, and verify with the transformer manufacturers recommendation for this practice.
Just for S&G what would happen if you reverse fed a xfmr and connected to the xo to derive 277v it would not work would it because the xo is now on the primary side correct?
One more thing
Another thing to remember is that if the dry type transfomrer is "fan" assisted cooling it can not be fed in reverse it will not work properly.
One example is the GE Manufactured TransfMore it is ensientally a dry type distribution transformer de-rated fans added and a higher rating applied. these come in sizes as small as 75Kva I believe. So I guess the common thread is to verify no 277V is required, and verify with the transformer manufacturers recommendation for this practice.
Just for S&G what would happen if you reverse fed a xfmr and connected to the xo to derive 277v it would not work would it because the xo is now on the primary side correct?
brian john
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I refuse to answer as I have ABSOLUTLY NOTHING POSITVE TO ADD.
http://forums.mikeholt.com/showthread.php?t=93598
http://forums.mikeholt.com/showthread.php?t=93598
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manufacturer's instructions need to be followed or this installation is not just non-compliant, its dangerous or worse. manuf lit should include connection details, o/w get factory rep/engr. to fax you connection details or recommendations (x0). (or as my grandma used to say, xoxo lol)
wasasparky
Senior Member
I keep hearing how reverse feeding D-Y transformers is/can be a really bad idea, but cannot find any specific backup on the www ... anyone got any links?
Just trying to understand...
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- Wisconsin
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- PE (Retired) - Power Systems
wasasparky said:
The only major problem that many people mention has to do with the lack of 277V from the resulting 480V delta connection. Some people do not like the idea of using an ungrounded system or a corner grounded system as they feel that these are confusing to many electricians.
Everything else is primarily an application issue with the primary ones being: The resulting primary X0 should be left floating or elese the transfromer can overheat (even drastically) during periods of imbalance; and the inrush current is extremely high resulting in difficulty in sizing a primary protective device. There are additional issues which should always be addressed.
Go to any manufacturers website and search for reverse connection or feed.
For example:
From ACME
http://www.acmepowerdist.com/pdf/Page%20131-135.pdf
From Hammond Power Solutions FAQ #131
http://www.hammondpowersolutions.com/faqlist.html
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