Transformer Polarity

SG-1

Senior Member
Just considering the physics, I don't see any way to check the winding direction other than checking the leakage field - as done by both your compass or gar's hall effect xdcr. Or a Mag-Probe. I wonder how many other devices could do it ?



Okay test to see if I have this right:
Case 1 - Additive
Orient the core so we are looking down one arm, along the axis of the windings.
Starting with H1 close to us, wind clockwise to the other end of the arm - label H2.
Starting again at the end close to us, label X2, wind CCW to the other end - label X1.
X1, H1 are the same polarity, xfm is called "additive".​

Case 2 - Subtractive
Orient the core so we are looking down one arm, along the axis of the windings.
Starting with H1 close to us, wind clockwise to the other end of the arm - label H2.
Starting again at the end close to us, label X1, wind CW to the other end - label X2
X1, H1 are the same polarity, xfm is called "subtractive".​
It would be best to actually wind yourself a crude transformer or two & experiment as we did. Core loss was horrendous.

I think this also follows $S's post:
Smart linked an excellent PDF. Many transformers have opposite &/or adjacent terminals for physical reference.



I've got a 4-ch isolated input scope. I can tell the polarity but not the winding direction - same as I could with a volt meter. Bes - is there something I'm missing here?
I think he was just thinking of detecting polarity, not winding direction. This question was unusual.





I'm curious as well. I can see how this could matter to an mfg - they want to produce the best product (actually - the best looking specifications) they can for the minumim money. But why does this matter for the end user? If the xfm has the required specs, accuracy for an instrument xfm or losses for a power xfm, why would the winding direction matter?

ice
Winding direction does not matter that much. To us what matters most is that it is labeled correctly. I work for a large manufacturer.
 

Smart $

Esteemed Member
Location
Ohio
The comments below figure 16.1 is basically what started this. Not only were the winding leads switched internally, they were labeled incorrectly. H1 & X2 had the same electrical polarity.
Is there an all-encompassing convention which requires single phase transformer terminals to be marked a particular way?
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Winding direction does not matter that much. To us what matters most is that it is labeled correctly. I work for a large manufacturer.
As I understood you to say, additive or subtractive is based on winding direction.

Polarity is based on labeling the the leads correctly.

Additive or subtractive won't burn up equipment as long as the polarity is correct.

So, your only concern is polarity?

Keep in mind, I'm not telling you - I'm telling you this is what I'm hearing.

ice
 

SG-1

Senior Member
Is there an all-encompassing convention which requires single phase transformer terminals to be marked a particular way?
There is for instrument transformers, C57.12 or 13.
The search is on for the dry type transformer, which is one of the two mentioned above.


There seems to be a standard on terminal layout. H1 & X1 on the same side if subtractive. H1 & X2 on the same side if additive. Just like in the PDF you posted. All other references show simular. The transformer type in question does not follow the above physical layout, that my be why they say additive on the nameplate.

Funny the things we don't know about such a common device !
 

SG-1

Senior Member
As I understood you to say, additive or subtractive is based on winding direction.

Polarity is based on labeling the the leads correctly.

Additive or subtractive won't burn up equipment as long as the polarity is correct.

So, your only concern is polarity?

Keep in mind, I'm not telling you - I'm telling you this is what I'm hearing.

ice
From the beginning this thread asked how to test a transformer to see if it is wound additive or subtractive.

Polarity is easy.

The transformer that started this had the terminals mismarked. In addition, we were wondering how one proves the additive claim on the nameplate, short of dissecting an epoxy cast transformer. It seemed to us that it should be possible to prove this with some electrical test.

This exercise started out as academic.
 
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