Surge Arrester

A really big surge?

Bird poop on the arrester?

There are multiple failure modes, the only reliable way to tell is to examine what's left; look for arcing, burning, tracking, how the shell blew apart, if the safety valve operated, etc., then check the system conditions at the time it failed, switching, lightning, protective device operation, etc.

Just remember, a burst arrester is a good thing, it's a sacrificial item just like a fuse.

I've got £5 that says the arrestor manufacturer can, Mildred.

My added WAG is this surge arrestor has not been properly maintained.

That should be classified as a SWAG since utility grade lightning/surge arresters are "install and forget" devices, they get as much maintenance as the conductors and insulators that they protect do. The only "maintenance" they ever get is replacement, unless they are part of a live-line cleaning procedure because they're in an area with a high environmental contamination potential.

They fail because they were improperly engineered, under-specified, over-worked, poorly manufactured, etc. Here's how power engineers view them, check out the bottom of page 9. No Heaviside equations required, all the hard work's been done for the newbies and whannabes.

What was going on when it burst? Conditions are usually unknown when this kind of damage becomes apparent. Consequently, a mystery is born.

Were there any fried critters near the incident? Any tell-tale carbon on it? Have any nasty sun spots when this failed? Nuclear testing? Anything?

By definition, a surge arrestor provides a short circuit to ground during the event that caused it. Not unlike throwing up a brick wall in front of a speeding train. The wall will not make out so well after the train hits it. The train may or may not do so well depending on how thick the wall was.

I've never heard of surge arrestors being a problem at a generation station. Probably due to minimal impedance at the generator. Out in the field, all kinds of impedance is encountered.

Transients can be really ugly in a circuit that is highly inductive. Too little information for anything but guess work.

Because too high of voltage was applied to it due to a line voltage surge.

Or; The surge arrester has reached the end of it's service life.

Perfectly put.

Sadly it probably went right over the head of the idiotic customer, but we here all enjoyed it fully!!

I think I may have added that it was probably caused by an ID-10T error,which is common is such cases.

Of course, a burned-out motor and a non-blown fuse would more aptly fit the question of why the fuse failed.

Exactly, fuses fail⁽¹⁾ when they fail⁽²⁾ to fail⁽³⁾, as I like to tell people unaware of the purpose of 'sacrificial components.'

Then I give them the footnotes:

1. Fail: To not succeed at the assigned task.
2. Fail: To not perform as expected.
3. Fail: To deteriorate, disintegrate or otherwise spontaneously cease to be.
   

Bravo! I think you missed your calling! I am usually so overwhelmed by the stupidity of such a question that I can't think of a reasonable response.

As to whether it was too condescending, that would be in the eyes of the receipt just like it is when someone writes a stupid question here. I think the insult is really derived from the person feeling guilty for his ignorance. After all, I believe that this specific truth works in any language: "Ask a stupid question and you will get a stupid answer".

Unfortunately, it seems the stupid people are the ones left in charge after all the smart people figure out that they have no future in a company full of idiots.

Over the years, I've found that humor is the best way to deal with stupid questions, but it is a very slippery slope into humiliation if the words are not well chosen. That is not to say that a smart person can never be a smart-ass but one has to be careful of how often the stops are removed. People like to retaliate, so every response needs to be measured carefully. And it always helps to know the person, else their tolerance might be easily surpassed.

The checks I try to remember to use are this: (1) No editorializing or opinions, (2) Avoid inflammatory language (I struggle with this one), (3) If you don't know this person well, sugar coat everything no matter how much it makes you gag.

Always remember, even stupid people have feelings. Keep the loathing to yourself.

It did it's job. That is why it is call a surge arrester. Might have been a lighting strike nearby.