Why Do Transformers Explode in Ice Storms?

Factual Questions
1

Something my wife and I have wondered for over a decade now, and she suggested would be a good GQ…

I can fully understand why people lose power during an ice storm – power lines down, either from the weight of the ice or from tree limbs and such breaking them, transformers being dislodged by the weight of the ice, and so on.

But it’s been our experience that quite often what will happen is that the lines are intact, sagging a bit but still connected, and the transformer is in place – but the buildup of ice on it causes it to “blow” – short out or something, and stop feeding power to the places connected to it.

Why does this happen? Given that it does, why do power companies use transformers that keep doing it?

2

I don’t know, but around here transformers tend to blow up in the middle of summer when everyone has their AC cranked on…

3

It’s all part of a sinister plot by Megatron … .

4

The stress on the insulators will cause them to break and expose the actual conductor, or, the live buss inside the XFMR. Once these are exposed they can be grounded (bad) to the XFMR casing causing the windings to either fuse open or short out and take out the fuses that protect the XFMR. Ice speeds up the grounding process. The XFMR`s are built pretty tough, they (the Power Company) has to balance cost with durability. Considering there are thousands of them throughout the city, the failure rate is not very high.