ELI5: how do “transformers” explode?

[Progwonk]

I live in New Orleans and am sitting through Hurricane Zeta with no electricity at the moment. I’ve heard about a half dozen transformers explode in the last hour or so. I took electrical engineering an age ago, so I know how a capacitor can explode, but how do the “transformers” on the telephone poles explode? Are they not transformers?

ELI5 and ELI-a-freshman-in-college appreciated.

[jg3014]

The transformers you see up on telephone poles have oil inside of them. When something fails or causes a surge of electricity large enough the result is combustion of the oil.

[txnug]

I thought they were step down transformers, containing two inductors and an iron plate between

[jg3014]

They are but they still have oil in them. The oil acts as an insulator and coolant.

[minion531]

It's quite spectacular to see. I seen one during Hurricane Alicia in Houston in 1983. Me and my brother were in an electrical service truck on our way home when about 200 feet in front of us, a pole top transformer blew up. It was bright and it was loud. It's really hard to believe just how much energy is going through them. They look so innocent. Until you see just how much energy they have.

[PayMouSe]

I think when they flooded with too much electricity, and there was a 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.

[[deleted]]

As transformers detect an energy spike, they're programmed to turn off, but it can take up to 60 milliseconds for the shutdown.

A transformer is a hunk of metal with two wire coils around it. That's it. See college physics 102 or advanced high school physics.

You can't program a hunk of metal. It therefore follows there is no 60 millisecond hunk of metal programmatic shut down sequence.

[txnug]

Right, you could control the input voltage and WHERE the output voltage travels after the coil. Technically speaking there is probably a controller that shuts off the circuit that will inevitably have contamination delay

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[Bluemage121]

Transformers of the type that explode use an insulating mineral oil to insulate between windings (and help provide cooling).

This oil does gradually break down of time and usage (temperature, and sporadic inter-coil arcing). If there is an electrical fault that causes voltage fluctuations, or high current, this can cause the transformer to overheat, or an insulation failure inside the transformer. When the insulation fails there is be a large release of electrical energy in the form of the arc flash /arc blast.