How electric transformers work


We recently had a transformer blow in our neighborhood and now my 3 year old is asking me how it works and I honestly don’t know. Can anyone electrical transformers?

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Transformers require alternating current (AC) to operate. That is to say, the voltage/current cannot remain constant, it needs to always be changing. Like the voltage coming out of your wall sockets, which fluctuates in a sine wave 60 times per second (in the USA).

In a transformer, the voltage supply input wire (the “primary”) is typically wound around a core of something like iron. As the voltage/current changes, it creates a magnetic field in the core which is also changing.

The output wire, the “secondary”, is also wound around the same core. That changing magnetic field caused by the primary induces a current in the secondary. The power is transformed from a current, into a magnetic field, and then back into a current.

Those conversions depend on a few factors, one of which is how many times the wires are wrapped around the core. So by changing the ratio of primary/secondary windings, we can also transform the voltages! If the secondary windings end up with a higher voltage than the primary, we call it a “step-up” transformer. If the primary is higher voltage than the secondary, we call it a “step-down” transformer. If they are the same, it’s just an “isolation” transformer.

You can even make transformers with multiple secondaries and get various voltages out of the different ones.

The transformer in your neighborhood was transforming the high voltage transmission levels down to those used in the various houses. High voltage is typically used for transmission because less of the power is lost that way.

Converting between voltages is done by turning electrical energy into a different kind of energy, and then back.

The first way that came to mind for me when I was young was a motor and a generator connected together. The electricity into the motor becomes turning in the shaft, and then that becomes electricity in the other motor. By adding more or fewer coils to the generator, we can adjust the voltage that comes out, since the voltage from each coil adds together.

I was overcomplicating things, though. See, a motor actually turns electrical energy into magnetic energy, then the magnetism pulls on the shaft. We can skip the middleman and take the shaft out, having the motor’s electromagnets right by the generator’s electromagnets.

That’s all a transformer is. Two sets of coils, one input and one output, right next to eachother. The first coil generates a magnetic field from the electricity, and the second one picks it up turning it back into electricity. By adjusting how many loops is in each coil, we control the voltage that comes out.

To understand what they do, you need to understand the electricity grid. High-voltage lines are like slow, steady rivers carrying lots of water, while your home power supply is like a narrow creek.

A transformer takes a big stream and transforms this into narrow streams supplying the entire neighborhood.

But that’s just *what* they do. *How* they work a pretty genius application of electromagnetism and AC current, explaining that is basically impossible if you don’t know how what a magnetic field or electric current is.

Basically, the AC current is like a swing, going back and forth. High-voltage lines swing really high, but with the magic of electromagnets you can “attach” a second swing that swings at the same rate (all power lines in the US swing at 50 times/second), but with much less intensity. This is your 120V end-user power supply).

To do so, you let current flow through a coil, and have a seperate cable mixed into this coil (ie two coils in one). The swinging in one coil creates a magnetic field, which creates swinging in the second coil. But since the second coil is less tightly wound, it swings less intensely there, thanks to ✨electromagnetism✨

I think a more ELI5 response would be to compare it to something hot. If you have one piece of metal that is red hot, if you put it close to another piece of metal it will get warmed up too, but not as hot. You can figure out how hot to make the second piece of metal based off the distance between them, the material that makes it or other factors.

This is like how the magnetic field of the primary of a transformer transfers electricity to the secondary. It creates a magnetic field that induces another magnetic field on the secondary whose voltage is dependant on a variety of factors such as distance, number of turns in the wire that makes up the coil etc.