Blown Transformer Cutout

mbrooke

Batteries Not Included
Location
United States
Occupation
*
What is a POCOs typical approach/policy for a blown pole pig fuse with no bird or squirrel in sight? How do you determine the unit is good?
 

hillbilly1

Senior Member
Location
Atlanta,Ga
They keep replacing the fuse until something starts burning! LOL!
had that on a large pad mount, after a storm, they came out and replaced the fuse, about 10 minutes later the transformer caught on fire burning off the secondary wires down to ground level. Expensive fix, eight sets of 750 cu at 250’ each!
 

mbrooke

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United States
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*
They keep replacing the fuse until something starts burning! LOL!
had that on a large pad mount, after a storm, they came out and replaced the fuse, about 10 minutes later the transformer caught on fire burning off the secondary wires down to ground level. Expensive fix, eight sets of 750 cu at 250’ each!
Did the equipment inside at least survive?
 

bwat

EE
Location
Western PA
Occupation
EE
Many years ago when I was an intern at a POCO, one of my main tasks was looking at dist. devices (like fuse cutout or reclosers) that had operated X amount of times within a month or two. For that company, at least, a single fuse opening up was usually ignored and replaced as long as nothing looked suspicious. If it happened twice.. then something usually HAD to be done to at least show action being done even if nothing else seemed wrong. Squirrel protection.. tree trimming.. etc.. those were often the “default” action if no one could come up with any other cause.
 

mbrooke

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United States
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*
Many years ago when I was an intern at a POCO, one of my main tasks was looking at dist. devices (like fuse cutout or reclosers) that had operated X amount of times within a month or two. For that company, at least, a single fuse opening up was usually ignored and replaced as long as nothing looked suspicious. If it happened twice.. then something usually HAD to be done to at least show action being done even if nothing else seemed wrong. Squirrel protection.. tree trimming.. etc.. those were often the “default” action if no one could come up with any other cause.

Bird guards get undone btw.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Bird guards get undone btw.
???
what does that even mean?

if It isn’t obvious, such as an animal, wind and trees, etc. then it’s best to look at the pressure relief at the upper rim of the XF.
Especially after a lightning storm. If there’s oil dripping out, the transformer is shiny, or a little brown spot on the pressure relief it’s shot.
There’s always a reason. Overloaded? Don’t just assume and throw in a fuse the next size up. Especially on the bigger pots or pad mounts. TTR is cheap compared to blowing up or further damaging a bigger unit. For a 25 and below on the rural residential, look for obvious as mentioned above. They cheap enough to try it one time.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
???
what does that even mean?

if It isn’t obvious, such as an animal, wind and trees, etc. then it’s best to look at the pressure relief at the upper rim of the XF.
Especially after a lightning storm. If there’s oil dripping out, the transformer is shiny, or a little brown spot on the pressure relief it’s shot.
There’s always a reason. Overloaded? Don’t just assume and throw in a fuse the next size up. Especially on the bigger pots or pad mounts. TTR is cheap compared to blowing up or further damaging a bigger unit. For a 25 and below on the rural residential, look for obvious as mentioned above. They cheap enough to try it one time.
I put in a 1200 amp single phase service for a store (owner was too cheap to get three phase, even though it was available at the pole) the poco left the same transformer that was used for the old 400 amp service (it was loaded to 390 amps before the addition) Blew the primary fuse, they throw a bigger fuse in, next day, the transformer went in a big way! LOL!
 

mbrooke

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Location
United States
Occupation
*
???
what does that even mean?

😂 The animal guard on the bushing somehow opened up. Its one of those hinged types where the two halves lock together. One half is open exposing the terminal.

if It isn’t obvious, such as an animal, wind and trees, etc. then it’s best to look at the pressure relief at the upper rim of the XF.
Especially after a lightning storm. If there’s oil dripping out, the transformer is shiny, or a little brown spot on the pressure relief it’s shot.
There’s always a reason. Overloaded? Don’t just assume and throw in a fuse the next size up. Especially on the bigger pots or pad mounts. TTR is cheap compared to blowing up or further damaging a bigger unit. For a 25 and below on the rural residential, look for obvious as mentioned above. They cheap enough to try it one time.

Makes sense.

BTW, can this injure someone in a bucket?

https://www.reddit.com/r/Lineman/comments/hbg91e
 

MD Automation

Member
Location
Maryland
Occupation
Engineer
Hi Mbrooke,

If you recall this recent thread I started…

https://forums.mikeholt.com/threads/my-poco-transformer-failed.2554091/

I had this situation happen at my own house at the end of May. Namely the primary cutout opened up – out of the blue on a beautiful sunny day. No crazy storm or insane wind.

The first lineman that responded eyeballed the ground around the pole for bbq squirrel or roasted birds. He then went up in the bucket with an ordinary handheld Fluke and checked primary and secondary connections for dead shorts. He found no shorts – and I also assume that he found the primary winding open. He was immediately suspicious of the health of that little 25 kVA pot since it was leaking oil from the XO secondary bushing. But even measuring an open primary and seeing oil on the outside he still threw a new fuse in the cutout, grabbed a short hotstick and earmuffs and gave it a go from his bucket. Luckily, what happened was the exact opposite of your TikTok video above, meaning literally nothing. Fuse held, but no output on the secondary. So time for a new transformer.

For a 25 and below on the rural residential, look for obvious as mentioned above. They cheap enough to try it one time.

Yes…this lineman indicated that unless something was clearly obviously amiss, they would almost always try to re-energize it. At least once anyway. Of course this was for a little single phase rural transformer with just my little house on the downstream side, they probably don’t come much smaller?

Btw… those are some crazy long hotsticks in that video. They must be 50 or 60 feet in length or longer! I wonder how hard it is to control the business end to hang the cutout or find the ring to close or open it? I assume you have to assemble something like that from 2 or 3 shorter lengths?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
They keep replacing the fuse until something starts burning! LOL!
Kinda. Years ago, I was at my mom's one evening, the lights went out, and about one second later: ka-boom!

The POCO arrived relatively quickly, so I followed the yellow lights to a 1ph line going underground, feeding two or three pad-mounts behind the townhouses, my mom's building being on the last one on the string.

The guy extended the hot stick, brought down and renewed the fuse, replaced and closed it, and KA-BOOM!

He deduced by the delay that he check the last transformer first, and he was right: the underground cable bushing had been chewed on, and there were remnants of a furry creature.

He remade the termination, renewed the fuse again, and all was well.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
But even measuring an open primary and seeing oil on the outside he still threw a new fuse in the cutout, grabbed a short hotstick and earmuffs and gave it a go from his bucket. Luckily, what happened was the exact opposite of your TikTok video above, meaning literally nothing. Fuse held, but no output on the secondary. So time for a new transformer.
That wasn’t very smart at all. It actually shows inexperience IMO...


Btw… those are some crazy long hotsticks in that video. They must be 50 or 60 feet in length or longer! I wonder how hard it is to control the business end to hang the cutout or find the ring to close or open it? I assume you have to assemble something like that from 2 or 3 shorter lengths?
it gets real fun trying to put that finger in the end of a hot line clamp 35-40 feet in the air with a breeze.
 

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mivey

Senior Member
We look for indicators like dead animals, burnt limbs, damaged equipment, etc. Many times the dead animal may disappear (easy meal for some other critter) or just be hard to find.

Missing indicators will result in a try-it fusing of small units. No short sticks for this. PPE isn't bullet proof. Hiding in the bucket can help but oof. Larger units will be tested on site or swapped out for testing in shop.

I will drop a circuit with an automated recloser, breaker, or gang switch before putting someone at abnormal risk.

30 ft is about my limit on hot-stick fusing. The swaying is too much and my eyesight is not what it used to be nor is my steadiness.
 

mbrooke

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United States
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Epic replies, thank you!



I will drop a circuit with an automated recloser, breaker, or gang switch before putting someone at abnormal risk.
Smartest reply ever- but not always possible if the feeder has large retail, office buildings, hospitals, schools, ect.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Epic replies, thank you!





Smartest reply ever- but not always possible if the feeder has large retail, office buildings, hospitals, schools, ect.
It’s always possible if someone’s life is at risk.
If it’s a choice between your convenience and my safety, you’re going to lose every time.
 

mbrooke

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Location
United States
Occupation
*
It’s always possible if someone’s life is at risk.
If it’s a choice between your convenience and my safety, you’re going to lose every time.

Try telling that to linemen/companies who just send it in. Remember those leaning poles we spoke about?
 
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