Transformer Polarity

All transformers actually have a polarity aspect but only rarely does this matter. It is easiest to think of just a single phase transformer to understand what effect winding polarity has. It is also important to consider a non-symmetric input waveform. I'll use a repeating cycle of right triangles known as a sawtooth. When the input of a transformer is driven by a sawtooth waveform voltage if the output wiring polarity matches the input polarity (positive wiring) then a sawtooth output will be on the output. If instead the output wiring is is opposite of the input wiring (negative wiring) then a ramp waveform will be present on the output.

Now this is a broad simplification of what is actually happening. You will have to study the fundamentals of electronics so that you know why this happens and how to use this. I'm also assuming that no frequency roll off happens to these waveforms as they travel through the transformer.

Basically polarities in transformers are determined by how it was physically wound, as well as on how the the start / finish of each windings are interconnected . Also, depending on the transformer type, waveform polarity inversion takes place between the primary and secondary windings of the transformer.

As its AC, polarity does not come into it as its changing polarity 50 times a second! Or 60 times in some areas of the world, it depends where you live....

YOU DID KNOW THAT? Or not?

With AC, we talk about phase, in phase, out of phase, phase difference in degrees, single phase.....

3 Phases means that the phases are at 120° to each other......

Mr. Andy -

My understanding is, In a varying signal once its slope or direction changes, the polarity together with its corresponding phase will appear as compared to a particular point of reference.

In a transformer that reference point can be derived from the same original signal as it passes through the medium, or get shifted to the zero or 'x' axis. The phase angle differences, signal inversions, polarity changes, timing delays or however its labeled comes from the natural characteristics and behavior of the device, its core, inductance, reactances, etc... but will not be merely be dependent on where one lives.

vsar

Did you accidently post on the wrong blog?

No Mr. Andy, my comment applies -

Polarity and Phasing terminologies of AC signals can be used interchangeably or be interpreted as one and the same. Especially true in power applications, where one can encounter catastrophic results if signal polarities or phases are not properly matched, observed and followed before connections are made!

Polarity most definitely does come into play with AC. For an example consider the two isolated primary step down transformer found in many consumer products. When wiring these two primaries in series or parallel correctly and the nominal secondary voltage will be in the middle of the regulation range of the supply circuitry. Wire the input primaries in series or parallel incorrectly and a short circuit happens that cannot be found using an ohmmeter.

I see your point, but I personally have always described that as phasing, in phase or out of phase. I think that the use of the word polarity could mislead someone.....

Over the years I have used this technique a couple of times to make ac voltages/currents from two or more seperate outputs of the same transformer, or even two transformers on the same pysical supply, when what I needed was either not available or I already had a transformer(s) on hand and did not want to buy something else.....

I usuall use a 'scope to validate that I am connecting both windings the correct way round, not having a scope makes the possibility of a dangerous error far more likely......