Blown Transformer Cutout

mivey

Senior Member
Another scenario. Dual-feed circuit. We are in alley behind Joe's. Is the open point here or there? We think it is circuit 123 but it might be 124. Buzz line and call for open on circuit 123. Line no longer buzzes. We dropped the correct circuit and it is good for safety grounding.

Still gets grounded for work. No buzz doesn't mean there isn't a lower voltage or static present so only an idiot would grab it unless protected.

Buzzing is a useful tool. But not the only tool for all situations.
 

mbrooke

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Another scenario. Dual-feed circuit. We are in alley behind Joe's. Is the open point here or there? We think it is circuit 123 but it might be 124. Buzz line and call for open on circuit 123. Line no longer buzzes. We dropped the correct circuit and it is good for safety grounding.

Still gets grounded for work. No buzz doesn't mean there isn't a lower voltage or static present so only an idiot would grab it unless protected.

Buzzing is a useful tool. But not the only tool for all situations.

I'll take your word. I mean it is still being done after all.

How well do hook stick meters work in such a case?

BTW, your POCO seems to drop circuits all to often!
 

mbrooke

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Just fine given the right circumstance. But a zero doesn't necessarily mean zero voltage present. It too must be verified.

I'll give you that. Zero doesn't mean zero.

Given your frame of reference, I'll take that for what its worth. :)
I disagree. Some POCOs don't de-energize unless they really have to. Others de-energize at lower thresholds.[/QUOTE]
 

paulengr

Senior Member
In relation to what though? Remember that 15-50kva pole pigs are often overloaded to 200-300% capacity during peaks.

Fuses reflect that, and their time current curves start at around 200% of the link rating.

Nothing stop the oil from getting hot- fuse pops- then linemen sends it in with hot oil.

You've never seen CSP units with their red signal lights lit up all over town when the units are under 10 years old? The bulb burns out before anything else.
The high current limits on primary fuses are because of magnetization current. Nothing stops you from using a smaller fuse except the fact that it will nuisance trip.

For line fuses I like using the free Coordinaide web app S&C has. It works great and I don’t have to dig out my key and do a lot of setup for SKM. It plots magnetic inrush currents and most common utility fuses. Everythjng even arc flash is worked on time current curves.
 

mbrooke

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The high current limits on primary fuses are because of magnetization current. Nothing stops you from using a smaller fuse except the fact that it will nuisance trip.

For line fuses I like using the free Coordinaide web app S&C has. It works great and I don’t have to dig out my key and do a lot of setup for SKM. It plots magnetic inrush currents and most common utility fuses. Everythjng even arc flash is worked on time current curves.
Isn't loading behind the larger links?
 

mivey

Senior Member
I disagree. Some POCOs don't de-energize unless they really have to. Others de-energize at lower thresholds.
You have no information about quantiy, qualifiers, or circumstance. Even if you had information to compare, your inexperience would still mean your frame of reference is inadequate to determine if it is too often or not.
 

mbrooke

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You have no information about quantiy, qualifiers, or circumstance. Even if you had information to compare, your inexperience would still mean your frame of reference is inadequate to determine if it is too often or not.

There are POCOs that kill power just for cutting a few spans of tap. Common.
 

paulengr

Senior Member
Alright.




Fuzzing a line doesn't get you much of a response on 4.8kv delta.
Why are you doing it on a 4160 line? If there is any question obviously don’t do it. I mostly work 4160 and below so I carry a tic and a meter. Also I started off talking about it but I thought it was clear most work rules forbid using it at all because of mistakes made. Obviously you have two issues...identifying the voltage AND presence/absence. Start with the first part.

So if I can’t identify voltage do I test it with the 9 V battery test (tongue) or the best (safest) voltage detector on the truck I have? That’s the thing about voltage testing. Some tests work better than others in certain situations but not in others. You can’t use a tic for everything or any other test for that matter.
 

mbrooke

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Why are you doing it on a 4160 line? If there is any question obviously don’t do it. I mostly work 4160 and below so I carry a tic and a meter. Also I started off talking about it but I thought it was clear most work rules forbid using it at all because of mistakes made. Obviously you have two issues...identifying the voltage AND presence/absence. Start with the first part.

So if I can’t identify voltage do I test it with the 9 V battery test (tongue) or the best (safest) voltage detector on the truck I have? That’s the thing about voltage testing. Some tests work better than others in certain situations but not in others. You can’t use a tic for everything or any other test for that matter.
My point was that linemen could enter a 4160 volt segment and still mistakenly believe they are on 12kv. Not everyone has nice AMI/prints or working in their own territory after a storm. At 4kv fuzzing is less indicative of power.
 

paulengr

Senior Member
Right. So why does lightning still kill transformers?
Because lightning arresters protect against a percentage of strikes, not every strike, and because VERY frequently the wiring is insufficient.



Or because the transformer is located outside the static lines or the static lines are under built instead of overbuilt and maybe not mounted high enough. Tons of reasons that surge arresters “don’t work”. They definitely do when installed correctly and maintained. But especially installations and sizing are done incorrectly.

You don’t just put a magic pole top decoration up there and things just work, or expect to use whatever one is on hand because it never burns up expecting it to provide enough protection.
 

mbrooke

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Because lightning arresters protect against a percentage of strikes, not every strike, and because VERY frequently the wiring is insufficient.



Or because the transformer is located outside the static lines or the static lines are under built instead of overbuilt and maybe not mounted high enough. Tons of reasons that surge arresters “don’t work”. They definitely do when installed correctly and maintained. But especially installations and sizing are done incorrectly.

You don’t just put a magic pole top decoration up there and things just work, or expect to use whatever one is on hand because it never burns up expecting it to provide enough protection.
FWIW Hv&Lv pointed out several times that the conductor is supposed to hit the arrestor first then the bushing. Most installations are wrong from the start- so so admire him making note of that. As well as you linking to that PDF.

Anyway- you're right- its not perfect as I tihnk about all the factors and variables. Especially considering a direct strike splits trees open.


About the only place I would say is 100% lightning proof is Manhattan. Empire state building gets hit with lightning several times a year and to my limited understanding everything electrical inside survives.


Food for thought- PG&E doesn't put lightning arrestors on their pigs. I've always wondered why?
 

paulengr

Senior Member
You are seriously trying to tell me fuzzing a line is a good idea? Relying on that has gotten linemen killed from what I've read.
As a general practice using your tongue is not safe for testing voltage but can be done safely with 9 V batteries. That doesn’t make it safe for anything else. Even if it was a procedure in the American Electricians Handbook and something my grandfather taught me over 40 years ago,

Fuzzing is totally safe in the right conditions too but not in others. Just as you shouldn’t be using a Fluke multimeter to test 4160 even though it says Fluke on it, even if the idiots on the 70E committee actually stated that this was the only acceptable text until I submitted a correction that was accepted.

Just because it’s something you read about and with zero experience automatically decided is unsafe for you to do it doesn’t mean it applies everywhere. Fuzzing has a limited use just as battery licking does but it is very useful where it can and should be used.

Linemen...actually almost all workers are killed either from lack of training and proper procedures early on or complacency and/or failure to notice when circumstances change later. Our brains have the ability to flat out ignore everything except the task at hand. That’s good until we ignore things that are critical to the task. That’s what tends to create fatalities. Exploding transformers and lightning strikes do happen but much more common is misidentifying what is hot and what isn’t. It comes down to that part of your brain that blanks everything else out so you can focus even to the point of becoming risky behavior.
 

paulengr

Senior Member
Isn't loading behind the larger links?
Yes that too. But initially the coils in the transformer act like a dead short until the magnetic field builds up acting as a counter EMF. Then current quickly backs down. E rated fuses are designed for this.
 

mbrooke

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As a general practice using your tongue is not safe for testing voltage but can be done safely with 9 V batteries. That doesn’t make it safe for anything else. Even if it was a procedure in the American Electricians Handbook and something my grandfather taught me over 40 years ago,

Fuzzing is totally safe in the right conditions too but not in others. Just as you shouldn’t be using a Fluke multimeter to test 4160 even though it says Fluke on it, even if the idiots on the 70E committee actually stated that this was the only acceptable text until I submitted a correction that was accepted.

Just because it’s something you read about and with zero experience automatically decided is unsafe for you to do it doesn’t mean it applies everywhere. Fuzzing has a limited use just as battery licking does but it is very useful where it can and should be used.

Linemen...actually almost all workers are killed either from lack of training and proper procedures early on or complacency and/or failure to notice when circumstances change later. Our brains have the ability to flat out ignore everything except the task at hand. That’s good until we ignore things that are critical to the task. That’s what tends to create fatalities. Exploding transformers and lightning strikes do happen but much more common is misidentifying what is hot and what isn’t. It comes down to that part of your brain that blanks everything else out so you can focus even to the point of becoming risky behavior.

But member I didn't say fuzzing itself was unsafe, rather taking it seriously is unsafe. Lower voltages are less likely to give indication of power. For me anything that is unreliable or not reasonably fool proof ought not be be considered in practice.

I'm still having trouble racking my mind on how its acceptable to close into a transformer that is in an unknown state.
 

mbrooke

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Yes that too. But initially the coils in the transformer act like a dead short until the magnetic field builds up acting as a counter EMF. Then current quickly backs down. E rated fuses are designed for this.

The curves on T fuses go right as much as E fuses if not more... let me check that in coordinate...
 

paulengr

Senior Member
FWIW Hv&Lv pointed out several times that the conductor is supposed to hit the arrestor first then the bushing. Most installations are wrong from the start- so so admire him making note of that. As well as you linking to that PDF.

Anyway- you're right- its not perfect as I tihnk about all the factors and variables. Especially considering a direct strike splits trees open.


About the only place I would say is 100% lightning proof is Manhattan. Empire state building gets hit with lightning several times a year and to my limited understanding everything electrical inside survives.


Food for thought- PG&E doesn't put lightning arrestors on their pigs. I've always wondered why?
Steel and concrete building structures are very good protection from direct strikes. This sort of gives you a cage around the contents as well as anything nearby but below it enough that it is protected by the “lightning rod”.

Then it’s just a matter of avoiding indirect strikes...surges traveling down the conductors outside the building.
 
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