# Transformer Basics

#### Mind In Disguise

Joined Jan 27, 2012
1
Hopefully my question is in the right place.

My question is pretty simple, I'm just trying to visualize all of the "ins and outs" of how transformers do what they do.

I understand how the fluctuating voltage (EMF) in a primary sets up a fluctuating magnetic field that is 90 degrees out of phase, which in turn induces another fluctuating voltage (back EMF) that is now 180 degrees out of phase with the initial, thus cancels it out.

What I do not understand is what happens from there. Doesn't that back EMF set up yet another fluctuating magnetic field that in turn cancels out the one set up by the original EMF?

It would seem this is true, but if so then how is it that a transformer is able to operate at all? In the end, wouldn't the setup be no different than a single "secondary" simply wound onto a core?

I understand with a secondary wound also, that is closed circuit with a resistor, there is induction in it as well from the initial fluctuating magnetism. And this of course also sets up an alternate magnetism that is going through both coils and duplicating this whole process of trying to "cancel things out". (I'm envisioning a secondary that is set up to "draw" the same amount that the primary is capable of providing)

It's just when you put all these effects together, you end up with net zero all around. Nothing flowing in the secondary, and flow in the primary prohibited as well.

Is it that a transformer will only work if what is drawn is less than the max theoretically capable? This would seem true and makes sense, but then how do transformers fail?

If it all starts at zero, and limits at zero when the max is reached (secondary loading is equivalent to primary capability), then there must be an optimal peak efficiency in there. And as long as the materials are such to withstand any maximum EMFs and magnetism, along with any maxes resulting in performance (or rather the poor performance past peak efficiency), then it should be impossible to fail. It should just simply quit working altogether and resume once the load is adjusted, right? Is this exactly process behind how blackouts and/or brownouts occur?

I have had circuits class, and aced it, but still don't feel like I "get it".
Any insight is greatly appreciated.

#### thatoneguy

Joined Feb 19, 2009
6,359
The magnetic field is in phase with the current, though current is out of phase with the voltage.