Why do transformers fail violently?

[Gnophos]

I've heard that lightning or extreme heat can make transformers blow. Well, I've had it happen near me twice recently, and neither time was due to lightning (AFAIK) or heat (it's winter).

One time coincided with a car hitting a pole (actually, the supporting wires that are keeping it from falling over). The force caused the wires to oscillate quite a bit, so I have to assume that it caused the transformer to blow, about a quarter mile away, and we lost power. But why? Why would a physical jolt take out a transformer?

The other time was on a really windy day. The transformer outside our workplace blew and we lost power. Again, the same factor, physical motion, seems to be at work here. Can someone explain to this ignorant one why transformers like blowing up so much?

 

[DaveC426913]

The heat referred to is generated internally, probably through corroded insulation. Sometimes this is caused by vermin. We recently had one here in Toronto where the culprit was a raccoon. (Now an ex-raccoon, not merely resting.)

Physical jolts bring wires that are poorly insulated into contact with each other, shorting the system. Whether or not the short itself blows the system, the heat generated by the short will rapidly snowball.

 

[WFO]

I've heard that lightning or extreme heat can make transformers blow. Well, I've had it happen near me twice recently, and neither time was due to lightning (AFAIK) or heat (it's winter).

As mentioned, "heat" refers to the transformers' temperature, not the ambient temperature. Winter loads typically overload transformers.

One time coincided with a car hitting a pole (actually, the supporting wires that are keeping it from falling over). The force caused the wires to oscillate quite a bit, so I have to assume that it caused the transformer to blow, about a quarter mile away, and we lost power. But why? Why would a physical jolt take out a transformer?

It probably slapped the phases together and blew a tap fuse back up the line. The transformer most likely wasn't involved.

The other time was on a really windy day. The transformer outside our workplace blew and we lost power. Again, the same factor, physical motion, seems to be at work here. Can someone explain to this ignorant one why transformers like blowing up so much?

Again, was it the transformer failed,or a tap fuse back up the line? Wind typically blows tree limbs into lines causing temporary faults. In either case, if the transformer actually faulted, they would have had to physically replace it. Did this happen?

 

[Averagesupernova]

When a fuse link blows, maybe that's not correct terminology, it is a pretty loud bang. However, when a transformer blows, it is usually a VERY bright flash and fireball. Usually the fire department puts it out. An exploding transformer can be seen from many miles away. I tend to agree with you WFO, I am wondering if it was actually a transformer that went.

 

[david90]

is it true that the transformers are filled with kerosine?

 

[Danger]

is it true that the transformers are filled with kerosine?

...

 

[enigma]

Winter loads typically overload transformers.

A few years ago, there was an icestorm which blew out power to almost the entire area but I still needed to be at work at 5:30am. It was kind of surreal driving on a dark highway watching green and purple flashes everywhere from transformers blowing up.

 

[WFO]

is it true that the transformers are filled with kerosine?

No.
The oil used in transformers is designed for its dielectric properties, not its lubricity. However, it is close enough to diesal that it can be mixed and run in a diesal engine.

 

[WFO]

A few years ago, there was an icestorm which blew out power to almost the entire area but I still needed to be at work at 5:30am. It was kind of surreal driving on a dark highway watching green and purple flashes everywhere from transformers blowing up.

I'm still thinking what you saw were the lines slapping together in the high winds and snapping from the weight of the ice, not asploding transformers.

 

[Gnophos]

Well, I don't know that the transformers blew up; I just assumed that a loud bang meant that had happened.

Apparently it could be this "tap fuse" you speak of that makes that noise. When the one on our street blew, I looked at the nearest transformer, the one I thought had blown, and nothing seemed out of place, so I was confused.

So where is the tap fuse? Along with the transformer or somewhere else?

 

[WFO]

So where is the tap fuse? Along with the transformer or somewhere else?

Typically you will have a main 3 phase feeder coming down a street. There may be transformers directly on this line and each one will be fused (usually to about twice its full load rating).
There will also be single phase lines "tapping" off of the 3 phase going down alleys, across pastures, etc. Each of these taps are often fused depending on how long they are, and, of course, there are additional fused transformers coming off this line.
During a storm, you will see lots of these fuses on the taps blowing from the wind whipping the lines together or knocking branches into them. Lightning will often pop the tap fuses and the transformer fuses. Nine times out of ten, you can refuse them and nothing is wrong. It was the transient condition taking them out.
And even when a distribution transformer does fail, it often just blows the fuse with no other outward signs.

On the other hand, when they do fail violently (catastrophic failure) it's quite impressive. Check out this site and play the video.
http://video.google.com/videoplay?docid=-2674646408572574875&q=voltage