Video: Describing Methods to Increase the Efficiency of a Transformer

Give two ways to increase the efficiency of an electrical transformer.


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.

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