Why do electric transformers explode?

Sixty milliseconds is fast. But sometimes, it's not fast enough. That's the gist of a great explainer by Cassie Rodenberg at Popular Mechanics, which answers the question, "Why do transformers explode?"

Before I link you over there, I want to add a quick reminder of what transformers actually are.

Although giant robots that turn into trucks do also explode from time to time, in this case we are talking about those cylindrical boxes that you see attached to electric poles. (Pesco posted a video of one exploding last night.) To understand what they do, you have to know the basics of the electric grid.

I find that it's easiest to picture the grid like a lazy river at a water park. That's because we aren't just talking about a bunch of wires, here. The grid is a circuit, just like the lazy river. Electricity has to flow along it from the power plant, to the customers, and back around to the power plant again. And, like a lazy river, the grid has to operate within certain limits. The electricity has to move at a constant speed (analogous to what engineers call frequency) and at a constant depth (analogous to voltage). This is where transformers come in.

Although the single circuit is easiest to picture, the grid is actually made up of lots of interconnected and redundant circuits. And those circuits aren't all at the same voltage.

Imagine that the water park has a couple different rivers — one for little kids that's really shallow, and another that's deeper. What if you wanted to take your inner tube directly from one to the other? To do that, you might follow a channel that slowly descends to a greater depth. Then, you could flow from the shallow river to the deep one without getting out of the water.

That's essentially what transformers do.

But when flooded with too much electricity, the sudden surge can cause a transformer explosion. As transformers detect an energy spike, they're programmed to turn off, but it can take up to 60 milliseconds for the shutdown. However fast those milliseconds may seem, they still may be too slow to stop the electrical overload.

A chamber full of several gallons of mineral oil keeps the circuits cool, but given too much electricity, the circuits fry and melt, failing in a shower of sparks and setting the mineral oil aflame. Mineral oil, in turn, combusts explosively and rockets transformer scything into the air.

All it takes is a trigger, a corroded or faulty wire, and the circuits surge will get ahead of the breaker ...

This explainer comes from 2010, but it's describing the same stuff you see in the current videos of transformers exploding all over New York in the wake of Hurricane Sandy.

To go back to the lazy river analogy, if there's a sudden rush of water pouring down the channel, it's likely to overflow. When that happens on the electric grid, what you get is an exploding transformer.

Read the full Popular Mechanics piece

Image: Taken by user georgeweld on Instagram. Found via Buzzfeed.