A transformer is labeled additive when the primary & secondary windings are wound opposite each other around the core. H1 & X1 still have the same instaneous polarity.
Subtractive indicates that both primary & secondary windings are wrapped in the same direction around the core. H1 & X1 still have the same instaneous polarity. ....
I did not know that. (only one of many things today - there will be a new list tomorrow)
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.
A transformer is labeled additive when the primary & secondary windings are wound opposite each other around the core. H1 & X1 still have the same instaneous polarity.
Subtractive indicates that both primary & secondary windings are wrapped in the same direction around the core. H1 & X1 still have the same instaneous polarity. ....
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".
I think this also follows $S's post:
... "Transformers with subtractive polarity normally have the primary and secondary windings wound around the core in the same direction. However, the transformer can have subtractive-polarity terminal markings with the primary and secondary coils wound in the opposite directions if the internal winding leads are reversed."
You have been given some sound advice here.
Normally I'd use a 'scope. ...
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'm just a little curious as to why the polarity matters in your application?
... Instrument transformers are subtractive.
One source stated that additive polarity has an advantage in larger transformers, because there is less core loss.
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