Welcome back to linear circuits. Today, we're going to begin our
discussion of transformers. This lesson is essentially just going to
present transformers as a device and describe the physics on how they work.
This concept of transformers is fairly extensive one and so to help make it a
little bit easier to learn. It's been broken up into several smaller
pieces. So that it is nicely compartmentalized.
In the previous lesson we talked about maximum power transfer in AC systems.
Sometimes to get maximum power transferred, transformers are actually
used for the impedance matching that was discussed.
But we're going to talk about transformers generally and look at that
number of different places that they, they turn off when they're used.
The objectives for this lesson are to identify physical transformers and their
circuit representations and then to describe the physical function of
transformers. This is representative of a transformer.
Here the grey is indicitive of a ferrous metal core.
So ferrous meaning that it's got some iron in it.
And the reason behind it being ferrous is ferrous materials hold magnetic fields
very well. Then we have two coiled wires represented
in these somewhat orangish-colored coils here.
So, this side, as we put a current through it Is going to generate the
magnetic field according to Ampere's Law, which we've already discussed when we
talked about conductors. When the magnetic field is established in
this coil, because of this ferris core, is going to then have an impact on the
other coil. Since now there is a magnetic filed that
is moving. Through this second coil, the second
inductor. So when we put them together in this
configuration, we call it a transformer. It doesn't necessarily have to be quite
like this. The only thing that makes it a
transformer is this idea of mutual induction, that current going through one
coil generates a magnetic field that has an impact or an effect on the other coil.
When we do circuit diagrams they will be drawn somewhat like this where we
basically have 2 inductors that are placed side by side and the dots here are
representative of reference directions. The reference directions that are present
in transformers we with regard to the directions of these coils and.
So it's possible that you could coil this the opposite direction.
In which case, you would move one dot down to the other side.
This lets you know whether this magnetic field is basically working in the same
direction or the opposite direction, that the magnetic field is coming from the
other coil. In these systems, we're typically going
to connect one side to a source and the other side to a load.
So to help distinguish the two sides of the transformer, we'll refer to one side
as the primary winding or the primary And now there's the secondary winding.
And typically, the primary winding relates to the winding that is connected
to your power source, and the secondary winding is connected to some sort of
load. It's entirely impossible to flip the
direction of the transformer. And then you could then change, calling
the other the primary, and then the previous one the secondary.
It really doesn't particularly matter. It's just to keep things clear as to
which side you're referring to. As far as the relationship of magnetic
field and current, first of all, we know about Ampere's Law.
As current flows through the coil, it generates a magnetic field.
The other thing that makes these devices operate is Faraday's Law of Induction.
Faraday's Law of Induction states that a change in magnetic flux leads to a
voltage. We're not going to get in the finer
details of Faraday's Law of Induction but to be able to talk a little bit about it,
we need to have some idea of what magnetic flux is.
So if we take some sort of closed loop, and we make a surface that connects all
the sides of this loop, and then we count the amount of b field, or the magnetic
field that's going through this surface, and then divide it by the area.
That gives us the magnetic flux, which is represented by the, by capital phi.
This is somewhat similar to the way that we calculated currents.
We calculate the amount of charge that was moving through some surface, in time.
So it's a similar kind of an idea. Faraday's law of induction states that
changing Magnetic flux leads to voltages, which means that if the b field here is
constant, there's no changing magnetic flux, so zero voltage, which is why
inductors behave like wires if you let the currents flow through them stay
constant in time. So the implication of this is that
transformers are AC devices. In order for them to work the way that
we've described, you need to have an alternating current.
If the current is DC or if it's constant in time, it doesn't quite have the same
impact as it would if the current were alternating.
There's two primary models for analyzing transformers in a linear sense.
The first is the linear transformer model, where it uses impedances for the
analysis. Impedances for the two coils as well as
impedance for the neutral induction. This is primarily used in communications
applications. The ideal transformer model is primarily
used for power transfer applications. It requires a few different assumptions
to be made. That are never quite, actually true.
But they generally give us a good idea of how the transformer is going to operate
in a certain circumstance. In per ideal transform models, we're
simply going to make use of the voltages and the number of coils turns for the
analysis. To summarize, we just introduced
transformers as a circuit device, described their physical behavior and
introduced the 2 analysis modes. In the next lesson we'll start by talking
about the first of these, the linear transformer model.
To see how we can use it for analysis, until then.