Apparently there was a transformer meltdown in New York last night. The whole sky lit up bright blue and social media went straight to aliens - when my wife showed me the video I started gibbering "Ooh, big fault! Arcing! BIG FAULT!"
So to understand this news, and to understand why this is so rare, and to understand the post-19th Century world in general, how DOES a transformer work, anyway? Well...
1. When we send current through a wire, it creates a magnetic field around the wire, made up of "waves" of strength. You can see the shape of the waves by putting a piece of paper over a magnet and sprinkling some iron filings over the top.
2. When we wrap wire round and round a spindle (like a thing of sewing thread), these waves overlap in the middle and add up to a stronger force. This round-and-round wire is called a coil or solenoid.
3. When we put current through the coil, it turns into a magnet.
4. It works backwards too - when we move a magnet through the middle of the coil, we get some electricity out!
5. Electricity in this context is a unified flow of free electrons. The magnetism pushes the electrons through the wire. So the magnetic field has to be MOVING in relation to the coil in order to MOVE the free electrons around.
6. In alternating current, the polarity changes fifty or sixty times a second.
7. So a magnetic field created by alternating current through a coil of wire will be constantly moving even if the coil physically stays in the same place.
8. A transformer is two coils of wire wrapped around an iron frame. The first coil accepts a given AC voltage as input.
9. The iron frame helps "channel the magnetism" into the second coil, where it moves electrons around to create electricity.
10. The two coils aren't electrically connected together at all!
11. The voltage you get out of a transformer depends on the relative number of turns of wire in the secondary coil versus the primary. If the secondary coil has fewer turns of wire, you'll get out a lower voltage. If it has more, you'll get a higher voltage!
12. Transformers are thus used to change a low voltage to a high one for long-distance transmission, and vice versa for local electricity distribution.
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