Transformer Polarity

Status
Not open for further replies.

SG-1

Senior Member
I have a transformer, let?s assume for the moment that the terminals are all correctly identified, H1, H2, X1, X2. The manufacturer says the transformer is additive. Is there any electrical test I can use to prove this ?

Let?s say for the sake of this thread that adjacent & opposite terminals do not physically exist. I just have four wires hanging out.

I think a scope could tell. If additive, then the input & output waveforms would be in phase. If subtractive, then the input & out waveforms would be 180 degrees out of phase. Do I have that backwards ?

Is there any simpler way to test, just using a voltmeter for example ?
 

Smart $

Esteemed Member
Location
Ohio
I have a transformer, let?s assume for the moment that the terminals are all correctly identified, H1, H2, X1, X2. The manufacturer says the transformer is additive. Is there any electrical test I can use to prove this ?

Let?s say for the sake of this thread that adjacent & opposite terminals do not physically exist. I just have four wires hanging out.

I think a scope could tell. If additive, then the input & output waveforms would be in phase. If subtractive, then the input & out waveforms would be 180 degrees out of phase. Do I have that backwards ?

Is there any simpler way to test, just using a voltmeter for example ?
Yes. See page 2 of the following pdf...

https://www.idc-online.com/technical_references/pdfs/electrical_engineering/Transformer_Polarity.pdf
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
141003-2111 EDT

SG-1:

A simple way, but not real good, is to use a battery and a Simpson 260 in DC.

Identify a secondary terminal by a DOT (conventional notation). With the Simpson selector switch set to +DC, the red test lead from the 260 + terminal to the secondary DOT terminal, and the black test lead from the 260 COMMON - to the secondary non-DOT terminal, then connect a low voltage battery - terminal to one primary terminal. Pick the primary terminal that you assume is the primary non-DOT.

Pick a Simpson voltage range that should be safe for the meter. Very monentarily connect the battery + terminal to the assumed primary DOT terminal. If the meter first jumps positive, then the primary assumed DOT selection is correct. If the first meter pulse is negative, then the primary assumed non-DOT termainal is the primary DOT terminal.

On a 175 VA 120 V input and 8 V output transformer I used a 12 V battery and the 2.5 V Simpson range and got only a very small blip of the meter needle.

A better way is to use a 6 V or lower 60 Hz AC source to power the primary and an oscilloscope to check the secondary phase relationship.

.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
I have a transformer, let?s assume for the moment that the terminals are all correctly identified, H1, H2, X1, X2. The manufacturer says the transformer is additive. Is there any electrical test I can use to prove this ?

Let?s say for the sake of this thread that adjacent & opposite terminals do not physically exist. I just have four wires hanging out.

I think a scope could tell. If additive, then the input & output waveforms would be in phase. If subtractive, then the input & out waveforms would be 180 degrees out of phase. Do I have that backwards ?

Is there any simpler way to test, just using a voltmeter for example ?

I love it when it is a good day to learn. :thumbsup:

I've never heard the term "additive" used to describe a transformer. What does that mean? Is there any connection between the X winding and the H winding? Help me out here

As for transformers:
I'm thinking any transformer (single phase is under discussion) can be connected as an additive autotransformer or a subtractive autotransformer - as in a buck-boost.

As for tests:
Say H1, H2 is the 120V primary, and X1, X2 is the 16V secondary.

Connect H2 - X1. Connect H1, H2 to 120VAC.

Measure between H1, X2. Voltage will either be 104V or 136V

If 136V, then H1---->H2 is the same polarity as X1--->X2.

ice
 

SG-1

Senior Member
141003-2111 EDT

SG-1:

A simple way, but not real good, is to use a battery and a Simpson 260 in DC.

Identify a secondary terminal by a DOT (conventional notation). With the Simpson selector switch set to +DC, the red test lead from the 260 + terminal to the secondary DOT terminal, and the black test lead from the 260 COMMON - to the secondary non-DOT terminal, then connect a low voltage battery - terminal to one primary terminal. Pick the primary terminal that you assume is the primary non-DOT.

Pick a Simpson voltage range that should be safe for the meter. Very monentarily connect the battery + terminal to the assumed primary DOT terminal. If the meter first jumps positive, then the primary assumed DOT selection is correct. If the first meter pulse is negative, then the primary assumed non-DOT termainal is the primary DOT terminal.

On a 175 VA 120 V input and 8 V output transformer I used a 12 V battery and the 2.5 V Simpson range and got only a very small blip of the meter needle.

A better way is to use a 6 V or lower 60 Hz AC source to power the primary and an oscilloscope to check the secondary phase relationship.

.

We use center scaled milli-ammeters & DC batteries, usually connected through a bell to perform inductive kick polarity tests.

We are looking for a way to tell if the secondary winding is wound in the same direction as the primary.
 

Smart $

Esteemed Member
Location
Ohio
When we run both tests shown:

Additive test, the transformer is always additive
Subtractive test, the same transformer is always subtractive.

I seek a way to know if the primary & secondary are both physically wound in the same direction.
Not possible. The only difference between additive and subtractive is what the secondary terminals are marked. If you have an additive transformer and reverse terminals labels (X1, X2 to X2, X1) you'd have a subtractive transformer.

Think of it like hooking the transformer as either a buck or boost configuration. Whichever connection gives you a higher-than-primary voltage is in boost mode and additive. The jumpered terminals are opposing ends of winding polarity.

Hook it up so that you get lower-than-primary voltage you are in buck mode and subtractive. The jumpered ends are the same end of winding polarity.

Whether the transformer is additive or subtractive don't really matter if you test this way...
 
Last edited:

Smart $

Esteemed Member
Location
Ohio
...

We are looking for a way to tell if the secondary winding is wound in the same direction as the primary.
Here... I'll make it easy for you.

Connect H1 and H2 to your voltage source (de-energized while connecting of course), and jumper H1 to X1. Mark H1 negative (?) and H2 positive (+). Energize and measure voltage between H2 and X2.

If voltage measured is greater than source, mark X1 positive (+) and X2 negative (?).

If voltage measured is less than source, mark X1 negative (?) and X2 positive (+).
 

fmtjfw

Senior Member
If you get the primary--secondary polarity wrong on one transformer of a 3-transformer bank used to change 12.7kV Delta to 120/208Y you get some pretty strange line-to-line voltages in the secondary.

If it is not your lucky day and you hook it up as delta-delta, you get a pretty good arc, at a minimum.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
141003-2358 EDT

SG-1:

I believe the only way you can determine if both primary and secondary are wound in the same direction is to physically look at the windings.

Why does it make a difference? If there is some detectable difference, then use that difference to determine the direction.

.
 

SG-1

Senior Member
Thanks to all posters for your input. This expedition started several weeks ago when some one detected that H1 & X4 had the same instantinous polarity using the inductive kick method. This CPT also was marked additive polarity. The CPT is constructed such that adjacent & opposite terminals are meaningless. We have determined a scope is also useless for this.

Our final solution was to inject the primary winding with low level DC, H1 being positive. Then watch a compass ( magnet ) turn to align with the exposed portion of the core. The secondary was then injected X1 being positive & the compass was observed a second time. It turned the same direction as before. This indicated both windings were wrapped in the same direction around the core. The transformer is epoxy cast so the windings cannot be examined. They could be with a saw.

A second transformer from a different manufacturer was also tested. The compass turned north then south, indicating the primary & secondary windings were wrapped around the core in the opposite direction. This transformer was also marked additive.

Does anyone see a flaw in our method ?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
If you do not pay any attention to the labels, the primary and secondary are always wound in the same direction. :)
It I'd when you label the ends that the polarity becomes important.
Now you could say that you can distinguish winding CW versus CCW by arbitrarily starting with the end of the winding closest to the core.
 

SG-1

Senior Member
I love it when it is a good day to learn. :thumbsup:

I've never heard the term "additive" used to describe a transformer. What does that mean? Is there any connection between the X winding and the H winding? Help me out here

As for transformers:
I'm thinking any transformer (single phase is under discussion) can be connected as an additive autotransformer or a subtractive autotransformer - as in a buck-boost.

As for tests:
Say H1, H2 is the 120V primary, and X1, X2 is the 16V secondary.

Connect H2 - X1. Connect H1, H2 to 120VAC.

Measure between H1, X2. Voltage will either be 104V or 136V

If 136V, then H1---->H2 is the same polarity as X1--->X2.

ice

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. Instrument transformers are subtractive.

One source stated that additive polarity has an advantage in larger transformers, because there is less core loss.
 

Smart $

Esteemed Member
Location
Ohio
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. Instrument transformers are subtractive.

One source stated that additive polarity has an advantage in larger transformers, because there is less core loss.
And here's a quote from another source:

"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."
 

Besoeker

Senior Member
Location
UK
I have a transformer, let?s assume for the moment that the terminals are all correctly identified, H1, H2, X1, X2. The manufacturer says the transformer is additive. Is there any electrical test I can use to prove this ?

Let?s say for the sake of this thread that adjacent & opposite terminals do not physically exist. I just have four wires hanging out.

I think a scope could tell. If additive, then the input & output waveforms would be in phase. If subtractive, then the input & out waveforms would be 180 degrees out of phase. Do I have that backwards ?

Is there any simpler way to test, just using a voltmeter for example ?
You have been given some sound advice here.
Normally I'd use a 'scope.
I'm just a little curious as to why the polarity matters in your application?
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
141004-0735 EDT

SG-1:

If you forget all the X and H markings and simply apply DOT markings, then:

1. Apply an AC signal to the primary. When the primary DOT is positive the secondary DOT is also positive.
2. Position a Hall magnetic sensor to sense leakage flux, and position so Hall output is positive when plus current is applied to the primary DOT. Next remove primary current and apply a + DC current to the secondary DOT. The Hall device will also read positive.

3. Remove the secondary and rotate it 180 degrees (reverse winding direction). Now in test 1 the secondary DOT will be negative when the primary DOT is positive.
4. Repeat test 2 with the secondary reversed. Now the Hall device reads negative when + current is applied to the secondary DOT.

5. There is no difference in one method over the other.

6. There may be a non-destructive way to determine the answer to your question, but how much is it worth in $ to determine this?

.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
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
 

SG-1

Senior Member
And here's a quote from another source:

"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."

This is interesting, can you supply a link or reference ?
We are trying to get a copy of IEEE C57.12...
 

SG-1

Senior Member
You have been given some sound advice here.
Normally I'd use a 'scope.
I'm just a little curious as to why the polarity matters in your application?

One good reason is so the diagrams supplied to the end user match the eqipment.
For most end users it will not matter, unless they try to parallel with another transformer in the future.

If the power supply of a an Insulgard relay is ever powered from the CPT there could be several thousand dollars worth of confusion. The data has to be phase resolved.

The main reason may be that after this was detected, we wanted to know how & why this transformer was different from other manufactures, so curiosity.
 

SG-1

Senior Member
141004-0735 EDT

SG-1:

If you forget all the X and H markings and simply apply DOT markings, then:

1. Apply an AC signal to the primary. When the primary DOT is positive the secondary DOT is also positive.
2. Position a Hall magnetic sensor to sense leakage flux, and position so Hall output is positive when plus current is applied to the primary DOT. Next remove primary current and apply a + DC current to the secondary DOT. The Hall device will also read positive.

3. Remove the secondary and rotate it 180 degrees (reverse winding direction). Now in test 1 the secondary DOT will be negative when the primary DOT is positive.
4. Repeat test 2 with the secondary reversed. Now the Hall device reads negative when + current is applied to the secondary DOT.

5. There is no difference in one method over the other.

6. There may be a non-destructive way to determine the answer to your question, but how much is it worth in $ to determine this?

.

This might better than sliced bread, now I know what I want for Christmas. Thanks !
A Mag-Probe can also identify north & south poles according to the general application notes. I have one of these to play, er, experiment with.
 
Status
Not open for further replies.
Top