Explosive device in high voltage fuse

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tom baker

tom baker

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There is a book out on Weather of the Pacific Northwest by a highly respected meteorologist. He said the high voltage fuses have an explosive device to open the fuse when a hv line shorts (falls to ground). He relates watching fuses explode during a storm.
I am not a HV guy, but have seen the fuses, its just a wire of a certain size, that is held under tension by a spring. On a fault, the fuse explodes and opens.
Right? Is this myth busted?
 
I have seen one explode as I was driving along a power line. It was above a sidewalk. Very impressive, but the only form of explosive needed is electrical energy. This fuse blew on a clear day. I can see why someone who probably does not know about arc flash could think this.

I have had KTK fuses (100,000 or 200,000A) blown apart, out of the holder & across the barn by thunderstorms more than once. Usually one end cap remains in the holder.

Ever hear of a lineman having his hand blown off while taking a new fuse out of a box ?

I say this myth is busted. It would be a good one for the Myth Busters, they could go to a high power lab for the big bang.
 
Don't know. What is an expulsion fuse?
And I may submit this to mythbusters. I watch those shows when I exercise on a treadmill. Makes the time go by really fast!
 
Yup. Sounds like a shotgun blast, or a cherry bomb. :D

It is supposed to eject the fuse from the holder to make it easier for the linemen to find the blown fuse when driving by.

Sometimes, when the weather is clear, and a fuse blows, you can find a dead squirrel or buzzard lying on the ground next to the pole with the blown fuse. ;)
 
I used to have a sub practically in the back yard.

When a fuse would blow, fire would actually shoot out of it.

One time, before I was a real electrican, one of the fuses blew and a few of the neighbors and I decided to get a closer look. I was about 10 feet outside the sub's fence when another fuse blew.

Way cool!

Now, that being said, I did have some experience in the field and being the curious sort, managed to get a blown 400 or 600 amp fuse and take it apart. (600 volt) There was no sign of external fire or spark. Everything was contained in a sand like material sealed in the fuse. This was not a small fuse. But it wasn't a 50k fuse with 44k going through it, either.

This is the first I have ever heard of either explosive or expulsive fuses. Don't trust Mythbusters, though. They 'proved' it was not possible to split an arrow with another arrow shot from a bow. I have a friend that can do it with no problem and has shown me 'double splits' where he split two arrows, one after the other.
 
SG-1 said:
The fuse looks normal, except it has a external muffler built into one end.
Click to expand...
The muffler is usually only used when this style fuse is mounted inside of an enclosure. Open air/pole top units don't need mufflers.

Some peolpe call expulsion style fuses, either boric acid style or solid material (i.e S&C's SM4 fuse).
 
K8MHZ said:
I used to have a sub practically in the back yard.
This is the first I have ever heard of either explosive or expulsive fuses. Don't trust Mythbusters, though. They 'proved' it was not possible to split an arrow with another arrow shot from a bow. I have a friend that can do it with no problem and has shown me 'double splits' where he split two arrows, one after the other.
Click to expand...

That was the "Robin Hood" segment. And yes, with modern aluminum shaft arrows it's not uncommon to stack 'em. However, the myth was that a cedar arrow, or other natural wood could be split from nock to tip. Because the grain in the wood wanders from one side to the other, even when the split was started dead center it would "wander" to one side or the other. I would hazard a guess that your buddy is using aluminum or possibly graphite shafted arrows, yes?
 
Don't the S&C "electronic" fuses use some sort of explosive charge to open the fuse element? I think it is some sort of gas generating charge much like the ones used in automotive air bags.
 
tom baker said:
There is a book out on Weather of the Pacific Northwest by a highly respected meteorologist. He said the high voltage fuses have an explosive device to open the fuse when a hv line shorts (falls to ground). He relates watching fuses explode during a storm.
I am not a HV guy, but have seen the fuses, its just a wire of a certain size, that is held under tension by a spring. On a fault, the fuse explodes and opens.
Right? Is this myth busted?
Click to expand...

Current limiter does employ an explosive device for speed: http://www.gwelec.com/product_current/commutat.cfm

Although expulsion fuses went gases when operating under fault the action could not be called explosion. (The arcing and ionization produces inert gases from the powder it surrounds it. The escaping gases 'blow' the arc therefore lengthening it to the degree when the available voltage is no longer able to sustain it, thus the arc is exhausted and the circuit opens. This action is represented by a smoking puff at the 'puffer' end of the fuse. Depends on the size and voltage of the fuse, it is somewhere between a shotgun and a cannon.;))
 
gadfly56 said:
That was the "Robin Hood" segment. And yes, with modern aluminum shaft arrows it's not uncommon to stack 'em. However, the myth was that a cedar arrow, or other natural wood could be split from nock to tip. Because the grain in the wood wanders from one side to the other, even when the split was started dead center it would "wander" to one side or the other. I would hazard a guess that your buddy is using aluminum or possibly graphite shafted arrows, yes?
Click to expand...

Yes, aluminum was what he was splitting. Graphites were too expensive to waste. I don't recall ever seeing him use a real wooden arrow. It makes sense that an arrow shaft made of wood can't be split all the way by any means unless the grain was perfectly parallel, which does not really occur much in nature.
 
When the "How It's Made" show covered the making of high-voltage fuses they did show that there is a small explosive charge that ejects a small pin to protrude from one end to show the fuse is blown.

And I have been close to one of those expulsion fuses when it let go, it was a very impressive bang. Youtube has lost of videos of expulsion fuses blowing.

Oh, and a major pet peeve of mine is when the news media calls an expulsion fuse acting as a "transformer" exploding. Happens all the time when we get storms or earthquakes.
 
mxslick said:
When the "How It's Made" show covered the making of high-voltage fuses they did show that there is a small explosive charge that ejects a small pin to protrude from one end to show the fuse is blown.

And I have been close to one of those expulsion fuses when it let go, it was a very impressive bang. Youtube has lost of videos of expulsion fuses blowing.

Oh, and a major pet peeve of mine is when the news media calls an expulsion fuse acting as a "transformer" exploding. Happens all the time when we get storms or earthquakes.
Click to expand...

I am curious about whose fuse did they use, since all the ones I know - and I know a few - use a simple spring loaded pin anchored to the fuse element, so when the fuse melts the pin simply pops up.
 
jim dungar said:
The muffler is usually only used when this style fuse is mounted inside of an enclosure. Open air/pole top units don't need mufflers.

Some peolpe call expulsion style fuses, either boric acid style or solid material (i.e S&C's SM4 fuse).
Click to expand...

Hmmm, the explanation I was given that the mufflers are designed as flame/arc arrestor pressure relief ports to prevent external material ignition. Of course it could be different from manufacturer to manufacturer.
 
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