Transformer polarity

[gpang]

I know by industry standards, all single-phase distribution transformers 200 KVA and smaller, having high voltages 8660 volts or less (winding voltage) have additive polarity. All other transformers have a subtractive polarity.

The question is, why are there additive and subtractive polarities for transformers (other than current flow in the windings)? What are the benefits one over the other?

Thanks

 

[Smart $]

Perhaps this document (pdf) will answer your question.

 

[nakulak]

nice link ,

 

[gpang]

Smart $

Smart $

Correct me if I'm wrong, there is no benefit between additive or subtractive transformer polarity. Transformer polarity is basically used for paralleling and identifying transformers.

 

[quogueelectric]

xformer polarity

xformer polarity

I was told by a contractor /MIT engineer about a high volt 2400 xformer that had a polarity because of the way it was wound. The high voltage HOT had to be connected to the side of the winding that was on the outside wraps of the xformer. He told me that if it was hooked up wrong the voltage diference between the grounded iron core and the winding insulating material was too great and it would surely fail. If it was connected properly it would have the neutral grounded conductor attatched to the side closest to the innermost winding therefore creating a gradual and even voltage buildup as the windings wrapped thier way to the outside of the xformer. This was why I always double check before I hook up a strange transformer.

 

[Smart $]

Correct me if I'm wrong, there is no benefit between additive or subtractive transformer polarity. Transformer polarity is basically used for paralleling and identifying transformers.

For a correctly wired xfmr, that is true. It is also true for an incorrectly wired one... i.e. no benefit... but there may be non-beneficial effects in this case :grin:

 

[gpang]

Thanks for all your replies.