Single Pole & Double Pole Voltage Transformer

in single pole, there will be one pole

in double pole, there will be two poles

in three pole. there will be three poles

and so on...

one pole

sorta like this?

Yes, that is a good example of one type. I was thinking more of each winding having multiple taps on it. That way one possible use would be to match the available input voltage to the primary winding. Using a correct pole on the primary winding would permit the same transformer to provide a secondary voltage with very little variation from the stated secondary voltage. The same principal can be used on the secondary winding.

A single pole primary rated for 120v and a secondary rated for 10v would have a secondary voltage of 10v for a 120v actual input, 9.16v for a 110v actual input, 10.8v for a 130v actual input. With a multiple pole primary the primary winding pole closest to the actual input voltage can be chosen to give the secondary voltage closest to what the unit is rated for. In this example it eliminates the need for three different transformers with different primary/secondary ratios and changing the whole transformer to accommodate different variations of the same "labeled" primary voltage.

There are several other ways that this could be obtained with but this is the simplest and easiest to explain.

Good Luck, Old Salt

That's an odd use of the term "pole". Are you referring to the number of terminals, windings, taps, bushings, phases, how it's connected, etc. Please provide a better example of what you are referring to.

RAMConsult-

The term "poles" in reference is not odd but an old school one used more often when electrical distribution was not as consistent in voltage. It was also used for applications where a transformer with multiple voltages, often close together in range on either/and the primary or secondary windings. It was especially used in the control circuits of machine shop or production machines. The use of the term "poles" is in reference to the number of taps that are available in that winding, or course not including the common connection.

With this arrangement, a three pole primary transformer, it can be used with either a 120vac, 208vac or a 220vac supply and always have a secondary voltage of 24vac.

This is different than a transformer with multiple winding, although in some applications they can be used interchangeably with the proper connections and junctures. If this transformer had two independent 12vac secondary windings, it could be used either as two separate windings, 12vac, 12vac, in series 12vac--12vac = 24vac or in parallel 12vac + 12vac = 12vac.

This transformer can not only accept different primary voltages but can also be used to adjust the secondary voltage. For instance, if the primary is connected to the common and the 240vac tap with 120vac applied to it, the secondary voltage would be 12vac. In some cases the term "pole" and "taps" are interchangeable. 220vac to the primary using the common and the 208 terminal will produce a secondary voltage of 25.4vac.

Good Luck, Old Salt

OS,

Oops, I see the source of the confusion, I was not replying to you but asking OP for clarification, if the remark was directed at you it would have been indented and referenced the thread number.

In any event, thanks for the quick refresher on transformers, nice story, I've been doing this for quite awhile and this is the first time I've encountered this. If you scour the web you will find only a few references to "poles" and "transformers", excluding of course "pole mounted transformer" and its derivatives.

Apparently OP is referring to DIN instrumentation transformers similar to or manufactured by Ritz in Germany. The IEC designation for phases is U-V-W. A "single pole" transformer has only a single high voltage terminal designated as U1, a "double pole" transformer has two poles designated as U1 and V1. From the Ritz catalog:

"... Voltage Transformers
	Voltage Transformers have only one iron core with an attached secondary winding. If an open delta circuit is necessary, an additional winding can be provided for the Single Pole Insulated Transformers.
For Single Pole Insulated Transformers the end of the primary winding is grounded as "N" inside of the secondary terminal box and must not be removed during operation..." That second winding would be designated as V1, and U2 and V2 would be connected together to form a delta except where the instrument is attached. I can accept your use of "poles" if you worked on equipment manufactured in Germany, but in the States it is rarely used in the context of transformers, "taps" or "tapping" is the common usage. Hope this explains the terminology for the OP.

RAMConsult-

Sorry about the confusing reply. I have not seen the expression "pole" used as frequently in the last 20-30 years as before that. Although I have not done a historical study on it, I attribute it to the change in power requirement brought on by the proliferation of semiconductors. No longer do we need 350vct @ 800ma to see the picture on a small vacuum tube TV and so forth. No more 120v primary with secondary's of 350v for the vacuum tubes, the 6.3v for the filaments and 5.0 for the 5YG4. Most of the ones I see now are either for door bells, magnetic starters for the control circuit and especially in my "junk" boxes with the troves of transformers left over when my father, the EE, passed away. Many sentimental things there. Most of the modern transformers have multiple secondary windings that can be ganged together if needed or independently.

Good Luck, Old Salt

Single pole

Double pole

The reason for the difference is the transformer size or rated capacity....

In manufacturing voltage transformers with 50KV rated capacities and above, they were made using "I" laminated cores and magnet copper wires size, (comparatively speaking) are sometimes as big as the size of our thumbs. The AWG size or cross-sectional area of the magnet wires used is dependent on the actual rated capacity of the transformer!

Mainly due to the larger size or rated capacity, it is normal for the transformer to have one pole, two poles, three, etc. The physical size, cross-sectional area of the copper materials, transformer configurations are the main determining factors!

The poles typically represents the number of core windings, or legs of the transformer. This holds true for single phase or polyphase devices, Induction or auto-transformer type of transformers.