Transformer polarity

[Timcorny]

Hi everyone-

I was researching the additive vs subtractive polarity thing, and found a link (http://www.kilowattclassroom.com/Archive/TransfPol.pdf) that I suspect will answer the "why do we have additive and subtractive" question. I found the link to be dead. Does anyone have another link to this .pdf? Or the answer from another source?

Thanks,
Tim

 

[rbalex]

Do a google search on Lenz's Law.

 

[Timcorny]

Clarification

Clarification

I should restate my question...I understand polarity, know the difference between additive and subtractive. My question is, why did the powers that be not settle on one polarity for all transformers? They chose a 200kVA / 8660V threshold for some possibly arbitrary reason between additive and subtractive. Is there a reason that they are not all additive or subtractive?

 

[rcwilson]

Additive- subtractive refers to relative physical position of H1-H2 and X1-X2 on single phase transformers like the pole top units. It makes a difference when single phase units are wired into 3-phase banks or paralleled. An additive unit in a subtractive bank will have the wrong polarity if it is wired in the ?normal? way.

The story I got was each manufacturer had their own standard. When a consensus national standard was being developed more manufacturers of small units had subtractive polarity and more suppliers of large units used additive. (That might be backwards). The committee picked a kVA number and split the standard so there was the least amount of disruption to the installed base.

 

[mbeatty]

The story I got was each manufacturer had their own standard. When a consensus national standard was being developed more manufacturers of small units had subtractive polarity and more suppliers of large units used additive. (That might be backwards). The committee picked a kVA number and split the standard so there was the least amount of disruption to the installed base.

I never heard this but, in a strange way, I guess it makes some sense. :?