Video Transcript
Give two ways to increase the
efficiency of an electrical transformer.
If we sketch out a basic model of
the transformer, we see it consists of three parts. There is a core that connects a
primary coil with a secondary coil of wire. Alternating current through the
primary coil creates a changing magnetic field in the core, which directs these
field lines through the windings of the secondary coil.
It’s the changing magnetic field
through the windings of the secondary coil that induce an emf in this coil and, as a
result, current. If this process were lossless, then
100 percent of the electrical energy contained in the primary coil would be
transmitted to the secondary coil. But there are energy losses
involved. And that’s where we can look to
increase the efficiency of our transformer.
First, one area of energy loss has
to do with the wires themselves that the current travels through. These wires are often very long,
with many hundreds or even thousands of windings around the core material. To an extent, the wires resist the
flow of current through them. And this resistance results in
heating and energy loss.
One way then to increase the
efficiency of an electrical transformer is to use different wires, specifically
wires with lower electrical resistance. But the wires aren’t the only
source of energy loss in this process. The core also has something to do
with it.
The alternating current that runs
through the primary wire is due to a potential difference set up across that
wire. Interestingly, as the magnetic
field through the windings of this wire changes, that can induce potential
differences in the core itself. When a potential difference exists,
charge wants to flow to follow that. And currents are formed within the
core, small loops called eddy currents. These eddy currents involve charge
movement and therefore friction, which does not contribute energetically to the
current in the secondary coil.
Therefore, from the perspective of
transforming energy, this is an energy loss. To minimize this loss and therefore
to increase efficiency, we can design a core in a special way. If we took a side-on view of our
transformer core and if our core was one solid chunk of material, then that would
mean that eddy currents that form have no restriction within the core as far as
where they can exist. They could be as big as the core
self.
But what if we design the core
differently? What if, instead of one chunk of
material, we make it of many thin strips of material called laminas? These laminas, which themselves are
of the same material as our original core, are thin slices of it, which are
electrically isolated from one another.
The fact that the laminas are
electrically isolated means that any eddy currents that form can’t spread from one
lamina layer to another. They’re significantly constrained
and therefore minimized, as well as the energy losses resulting from them. This design of the transformer core
is yet another way to increase the efficiency. We can use thin isolated laminas or
sheets to construct the core.
Now our question only asked for two
ways to increase efficiency, and we’ve come up with two. But in fact, there’s a third way to
raise the efficiency of an electrical transformer. This has to do with the material of
the core itself. Recall that, because of the
changing nature of the current in our primary coil, the magnetic field acting on our
core is constantly changing. Certain materials adjust well to
rapidly changing magnetic fields in them and others not so well.
Some materials, once they’ve
internally aligned with an external magnetic field, are very hard to change from
that alignment. Others though are adept at making
these changes in response to the external magnetic field. The better a core material is at
responding to an external magnetic field, the more efficient it is. There’s less energy loss due to
molecular alignment and dealignment with an external field. We would like then to pick a core
material that does a good job of responding to magnetic fields. And by doing so, we’ll raise the
efficiency of the transformer.
Soft iron, it turns out, is very
good at doing this. So a third way to increase
electrical transformer efficiency is to use soft iron to make the transformer core,
which will minimize energy lost to molecular vibrations in the core. Any two of the three ways we’ve
listed here would be good methods for increasing the efficiency of an electrical
transformer.
