# When a pole transformer goes bad



## Yoyizit (Jul 11, 2008)

KE2KB said:


> I'm just wondering whether there's any truth to rumors that the lids or pieces of these things fly off with great force, and sometimes end up blocks from the pole, or is this just a myth?
> 
> *Plus, they throw out hot oil.*
> 
> ...


A customer of mine had voltage dropouts, so I called PoCo to put a recording voltmeter on the line. Probably it was squirrels meeting their Maker because of bad insulation.

A very angry guy showed up with a meter and said the voltage was fine. I reiterated, "recording voltmeter." 
So, PoCo's first line of defense was intimidation.

PoCo hooked it up and after a week said the recorder didn't show any problems (but after that my customers didn't have any more dropouts). 
So the second line of defense was probably deception.

The money that is supposed to go to infrastructure goes to the mistresses of the CEOs. :laughing: This shows up occasionally in your newspaper.

I called PoCo once, and before I even asked, the receptionist told me that they are under absolutely no obligation regarding the quality of the power that I am paying for (but they sort of promise 114v to 126v).

Possibly the health of one of these huge transformers can be judged by doing an (unpowered) insulation test. Powering down all your neighbors for this reason probably won't be very well received.


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## rgsgww (Jul 5, 2008)

The inside wires will breakdown over time, causing a short. At this time, depending on which side is shorting, you may experience dim lights, or extremely high voltage. Soon the oil gets very hot, and starts to boil. At this moment the pressure inside the transformer exceeds a safe amount and a side will open up. Once the hot oil gets out, an arc may ignite it and you will fire and some sparking and arcing. You may hear a loud bang after the thing exploded, this is probably the disconnect/fuse going. But since its so old, it may not. If it doesn't go, you might see some arcing afterwards, until the power is shut off. If power isn't cut, the wires will get hot enough that they pull apart. Once they pull apart, they fall and touch each other. You will see a shower of sparks and it will be over.

Ive seen this before...you will know its getting bad as soon as your gfcis start tripping and resetting themselves.

No, they don't usually don't throw pieces very far, but I would not want to be under it when it happens.


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## Ultrarunner2017 (Oct 1, 2008)

Yoyizit; Thanks for your quick reply.
This isn't something I "worry" about, but it's on my mind every now and then, especially when the weather gets bad.
I'm also wondering, since these transformers are so old whether they contain PCB's, and we could have them replaced solely on that issue.
As for the wiring, I'm not as concerned about it as I am of the transformer. At least when the wiring fails, power simply goes out (most of the time), but when a transformer blows, it may be spectacular.

As for the POCO and their attitude, there was an incident this past summer in our town involving a house that exploded due to leaking gas. Several residents had reported a gas odor for weeks prior to the incident, but the POCO came, and left, saying they didn't find anything. Their last visit had been only hours before the explosion. 
Then all of a sudden, the house explodes, nearly killing a couple of people who just happened to be walking nearby.

I still haven't heard about where the gas was leaking from. It was probably inside the house, but still, shouldn't the company have asked the resident for permission to check out his house. The guy was killed in the explosion! I'm always asking myself why he didn't report the gas odor himself. There's something wrong with that whole story.


After that incident, the company has been very careful, and attentive to gas leaks. One night, a month or so ago, they were digging up the street not far from our house during the night because someone had smelled gas. It never got so bad that I caught any of it, but I'm sure the POCO isn't taking any chances.

You talk about the nasty disposition of the POCO worker. That seems to be the norm for people like that, doesn't it. After that explosion, there were several follow-up articles in our local newspaper with residents stating how poorly the POCO had reacted to their complaints on that issue, and others.
I recall once when I was about 13 years old, I was riding my bicycle up and down our block, and smelled gas at a certain location. My mom called the gas co (which is also the electric co) and reported it. The next morning (not the same day) a guy comes by early in the morning, acting as though I had brought him out here on his day off or something (very nasty) and demanded that I show him where I smelled the gas.
Later in the day, a crew was digging and repairing the leak. Then the guy (probably not the same one as in the morning) told me that I should come to work with them with my super-sensitive nose <g>

Back to the transformer issue: I did send an e-mail to a general address (very hard to find one that's not specifically designed for reporting a street light out, or move-in move-out request). I mentioned PCB's when I told them about the transformer.
It is possible, though not probably that I can have all of the transformers in town replaced by law, if we passed anything about PCB's in these transformers.

It's probably a very long shot to have anything done on on a pre-emptive basis, but I guess it never hurts to make someone aware.
My next step would be to write an article for our local paper. If they like it, and start to spin it, we could have all new transformers by next spring 

Now if I really believe that, I'll commit myself to the "funny farm".:jester:
Sorry for being so long, and straying a bit off the original subject, but it seems to have created a torrent of thoughts from my mind.


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## Ultrarunner2017 (Oct 1, 2008)

rgsgww said:


> The inside wires will breakdown over time, causing a short. At this time, depending on which side is shorting, you may experience dim lights, or extremely high voltage. Soon the oil gets very hot, and starts to boil. At this moment the pressure inside the transformer exceeds a safe amount and a side will open up. Once the hot oil gets out, an arc may ignite it and you will fire and some sparking and arcing. You may hear a loud bang after the thing exploded, this is probably the disconnect/fuse going. But since its so old, it may not. If it doesn't go, you might see some arcing afterwards, until the power is shut off. If power isn't cut, the wires will get hot enough that they pull apart. Once they pull apart, they fall and touch each other. You will see a shower of sparks and it will be over.
> 
> Ive seen this before...you will know its getting bad as soon as your gfcis start tripping and resetting themselves.
> 
> No, they don't usually don't throw pieces very far, but I would not want to be under it when it happens.


Thanks for that info. I'll look out for GFCI's tripping without reason (especially if more than one trip at once).


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## rgsgww (Jul 5, 2008)

KE2KB said:


> Thanks for that info. I'll look out for GFCI's tripping without reason (especially if more than one trip at once).



I think the mov (metal oxide varistor) the gfcis surge suppressing device, was diverting a surge, they were hot! I was very lucky that I unplugged all of my equiptment before it happened. There was a storm with 90-100 mph wind, so I unplugged my stuff beforehand.

The gfcis will trip like that when something is very wrong. I tested the volts-it was changing so fast that the meter couldn't get a reading.

It took the poco about 4 hours to reconnect 1 wire...


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## Yoyizit (Jul 11, 2008)

rgsgww said:


> I think the mov (metal oxide varistor) the gfcis surge suppressing device, was diverting a surge, they were hot!


Electricians in our building hooked up something wrong and stunk up the whole place by frying all the surge suppressors; MOVs can only handle transients, not continuous overvoltage.


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## Yoyizit (Jul 11, 2008)

KE2KB said:


> As for the POCO and their attitude, there was an incident this past summer in our town involving a house that exploded due to leaking gas. Several residents had reported a gas odor for weeks prior to the incident, but the POCO came, and left, saying they didn't find anything.


I had a problem with the gas company, so I wrote them a letter along the lines of
"Can you imagine sitting in a Board of Inquiry explaining that there was a gas explosion because you didn't feel like looking through nine years of old records regarding this gas line hookup?"

They fixed the problem.

Then, incredibly, they tried to invite me to defraud them (so they could nail me later). They didn't have anything on me so they tried to get something on me.


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## jerryh3 (Dec 10, 2007)

Yoyizit said:


> I had a problem with the gas company, so I wrote them a letter along the lines of
> "Can you imagine sitting in a Board of Inquiry explaining that there was a gas explosion because you didn't feel like looking through nine years of old records regarding this gas line hookup?"
> 
> They fixed the problem.
> ...


So your employer has been out to get you, the electric company has been out to get you, the gas company has been out to get you... you may want to look out your windows for some black helicopters..


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## Ultrarunner2017 (Oct 1, 2008)

Well, at least if (when) the pole transformer goes, I can say "I told you so"
That of course means diddly, since the POCO has a policy of fix when it's broke, right?
It would probably make the Guinnes Book if they did replace a transformer before failure on my part!

But I'll be sure to have my Nikon aimed at the thing while it's exploding! With the 300mm tele I just bought, I should be able to do it at a safe distance<g>


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## rgsgww (Jul 5, 2008)

KE2KB said:


> Well, at least if (when) the pole transformer goes, I can say "I told you so"
> That of course means diddly, since the POCO has a policy of fix when it's broke, right?
> It would probably make the Guinnes Book if they did replace a transformer before failure on my part!
> 
> But I'll be sure to have my Nikon aimed at the thing while it's exploding! With the 300mm tele I just bought, I should be able to do it at a safe distance<g>



Yeah it seems that way...

I remember you saying about the old wires...If they did short, the power would still be flowing. Those transformers only have a fuse before them.

When it does, I'd love to see the pics.


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## HandyPete (Mar 23, 2008)

Dude, open yourself a micro brew and relax. I'm a POCO electrician and have seen hundred of these pop-tops explode. So far everything that's been said is true (especially the hot oil).

Don't do anything, buy anything, say anything, change anything, heck, think anything! honestly, in my opinion your OK.

-pete


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## Yoyizit (Jul 11, 2008)

jerryh3 said:


> So your employer has been out to get you, the electric company has been out to get you, the gas company has been out to get you... you may want to look out your windows for some black helicopters..


The Men in Black have already been by with that flashy thingy. . .so I don't remember making those posts.:laughing:


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## Ultrarunner2017 (Oct 1, 2008)

HandyPete said:


> Dude, open yourself a micro brew and relax. I'm a POCO electrician and have seen hundred of these pop-tops explode. So far everything that's been said is true (especially the hot oil).
> 
> Don't do anything, buy anything, say anything, change anything, heck, think anything! honestly, in my opinion your OK.
> 
> -pete


I have to have something to worry about<g> If I didn't, the things I didn't worry about would happen without my having worried about them, and I would be telling myself that if I had worried about them, they wouldn't have happened, because it's usually the things you don't worry about that happen, while the ones you do worry about never happen!:jester:

Now you must really think I'm gone nuts! I think you're right!

edit: That microbrew is starting to sound real good right now, but all I've got is warm Maybe stick it in the freezer for an hour and it'll be cold enough


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## WFO (Nov 5, 2008)

Yes, your transformer can explode. On the other hand, you can get hit by a meteor.
When a transformer fails (and they do fail) 99.44% of the time they blow their fuse. You hear a POP and the lights go out. Very little drama unless there are 30 seconds left in the Super Bowl with the score tied when the TV goes off.
Yes, older transformers can contain PCB's. If you don't cook with PCB's (like the Japanese that had so many birth defects), you'll be OK.
Transformers have no moving parts so there's not much to wear out. Cellulose insulation in an oil bath can last an awful long time if not abused (i.e., overheated/overloaded). It would be like trading in your car at 100,000 miles. Is it worn out? Only if its been abused....otherwise, it's good to go for another 100,000.
And contrary to popular belief, POCO employees are not perverted, drug snorting pedophiles looking to screw over their customers. 

Living in fear of your transformer ranks up there with being abducted by aliens, getting swallowed by a python, and winning the Power Ball Lottery. Don't hold your breath:thumbsup:


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## frenchelectrican (Apr 12, 2006)

I allready did see poletoppers { pole mounted transformer(s) } go bad the same as pad mounted { for underground laterals } the padmounted are not too bad on failure rate but not any worst than poletoppers failed.

I just saw one padmounted transfomer went bad due one mantanice did make a major screw up with connection { I was in diffrent building when the big padmounted transformer failed } I heard the transfomer shurdder a little but yeah I did heard the conductors really slapping in the conducts and next thing a loud bang I knew the fuse just kicked out called the POCO to come out and change the padmounted transfomer plus clean up the ground { oil leak }.

Most poletopper don't fail very fast unless serious overload or direct short circuit then it will do pretty good show with it.

Merci,Marc


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## Ultrarunner2017 (Oct 1, 2008)

Well, maybe I have talked a bit too much again<g>
In regards to POCO employees, I have never personally had a bad experience with any of them. It was other residents of my town who were making those statements in the newspaper. It wasn't the employees themselves, mainly higher management I think they were complaining about.

As far as living in fear of pole transformers, I don't. I just think about these things from time to time. If I were in charge, I probably would have replaced the wiring and transformers on my block by now, but then, my company probably would have to be bailed out by the gov<g>.

I'm probably more likely to be hit by a falling plane than an exploding transformer. I live under the flight path to a small, but busy airport.


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## Ultrarunner2017 (Oct 1, 2008)

frenchelectrican said:


> I did heard the conductors really slapping in the conducts


What exactly did you mean by that?


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## Gigs (Oct 26, 2008)

My dad once called the power company because his power was out. They said there wasn't any known outage, so they'd send a truck out. When the truck got there, he went up to the door and said "Uh, you didn't notice your transformer and pole are on fire?" :laughing:

At least he got a new transformer (and wire all the way from the state road actually) out of the deal.


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## InPhase277 (Feb 9, 2008)

KE2KB said:


> What exactly did you mean by that?


He heard the conductors jumping around in the conduits. During high current shorts, the magnetic field is powerful enough to move the conductors. Inside large switch gear it is a good idea to wrap the incoming feed with a rope and secure them in place to prevent them from ripping the gear apart.


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## Yoyizit (Jul 11, 2008)

WFO said:


> they blow their fuse


A PoCo guy told me there was no fuse. 
You have a link for what kind of internal (external) fuse this would be?
Just curious.
Thanks.


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## InPhase277 (Feb 9, 2008)

Yoyizit said:


> A PoCo guy told me there was no fuse.
> You have a link for what kind of internal (external) fuse this would be?
> Just curious.
> Thanks.


I don't have a link, but I think they are fused on the primary side, not the secondary. 5 or 10 A I believe. The long white tubes that are parallel with the knife switch cutout on the pole are fuses.


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## AllanJ (Nov 24, 2007)

I would say that nasty behavior from a company (gas station, utility, airline, department store, bank, salon, etc.) employee is grounds for an independent complaint. With no mention of the transformer or gas smell or whatever except to help identify the time and place.

I agree that there is no easy way to predict failure of a transformer.

In many cities, underground power cable failures happen randomly and often accompanied by flames shooting from a manhole. Often the cables are from over half a century ago, insulated with oil soaked paper wrapping (similar to cellulose in an oil bath) and with a lead sheath. Sometimes a post mortem turns up drying up of the paper near where a hole occurred in the lead from corrosion or chewing by rats.


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## Gigs (Oct 26, 2008)

InPhase277 said:


> I don't have a link, but I think they are fused on the primary side, not the secondary. 5 or 10 A I believe.


Also it's just a thermal, so you can still have thousand amp+ shorts on the primary for long enough to really ruin your day, massive amounts of energy.










Looks like 100amp is a common size.


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## rgsgww (Jul 5, 2008)

AllanJ said:


> I would say that nasty behavior from a company (gas station, utility, airline, department store, bank, salon, etc.) employee is grounds for an independent complaint. With no mention of the transformer or gas smell or whatever except to help identify the time and place.
> 
> I agree that there is no easy way to predict failure of a transformer.
> 
> In many cities, underground power cable failures happen randomly and often accompanied by flames shooting from a manhole. Often the cables are from over half a century ago, insulated with oil soaked paper wrapping (similar to cellulose in an oil bath) and with a lead sheath. Sometimes a post mortem turns up drying up of the paper near where a hole occurred in the lead from corrosion or chewing by rats.



I was in NYC awhile ago, when they had 100 degree weather. There were power outages everywhere. They had alot of smoke pouring out of the manholes. I was in the subway and the power went out...its freaky down there...


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## Yoyizit (Jul 11, 2008)

Gigs said:


> Looks like 100amp is a common size.


7200v (?) and 10A (100A) = 72kw (720kw). The I²T  rating and interrupting rating on this fuse must be enormous.

Now I need to count how many houses on a xformer. . .


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## jerryh3 (Dec 10, 2007)

I thought the primaries had 5A fuses.


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## WFO (Nov 5, 2008)

If the transformer has no external fuse, then it is probably a CSP variety. I believe that stands for Completely Self Protected but don't quote me on that.

These have internal protection and can usually be identified by a small ring on a short lever that sits just below the lid. If a CSP trips, the lineman has to pull the ring down and back up to set it just like you do in your house (except he does it with a hot stick). Linemen hate CSP's because there's no external means of telling they're bad, and when one does fail without tripping it's own circuit, it usually takes out the whole line without giving any indication of which transformer is bad.

We usually fuse our distribution transformers at 200% of rated primary current. 
For example, a single phase 37.5 KVA pot (we call them pots) 7200/120/240 volts pulls about 5 amps primary at rated full load. We'd put in a 10 amp fuse. If it had a 14,400 volt primary, we'd use a 5 amp fuse.


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## WFO (Nov 5, 2008)

Here's a link. It takes awhile to load.

http://www.rousant.co.za/files/csp.pdf


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## frenchelectrican (Apr 12, 2006)

jerryh3 said:


> I thought the primaries had 5A fuses.


 No,..

It depending on the transfomer size , primary voltage those can change a bit depending if hookup on single phase or triphase.

the primary fuse can run anywhere from ¼ amp all the way much as 400 amp or more. again it depending on size.

Most of POCO transfomer on single phase they useally connect L-N format but few do hook up in L-L format for three phase it will be either L-N or L-L depending on the set up { most rather run delta on primary side and on secondary side it will go either way depending on voltage }

Merci,Marc


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## frenchelectrican (Apr 12, 2006)

InPhase277 said:


> He heard the conductors jumping around in the conduits. During high current shorts, the magnetic field is powerful enough to move the conductors. Inside large switch gear it is a good idea to wrap the incoming feed with a rope and secure them in place to prevent them from ripping the gear apart.


 
He is correct on describing on this.,

Yeah belive or not there is documeted case some conduit actally ripped or bent heckva out of line with very hevey short circuit { this more common happend with very large system and with multi parallel conductors }

If you have free hanging conductors you will see them jump up and down or both sideway as well.

The last one I did see it was three freehaning MV conductors { 4160 volts } going to the large trailer mounted air compressor it did make weird shape almost like triangle format with jumping around { that time the motor actally have a serious arc fault ( not bolted fault ) 

Any one who been doing jump start the cars you may notice the jumper cable do move when you crank over the engine it will move due so much current running thru the cable by magatinc foruce.

Merci,Marc


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## WFO (Nov 5, 2008)

For a good example, check out this test on You Tube. All three phases are grounded during the fault and you can see the violent reaction to the intense magnetic field created by the fault current. 

http://www.youtube.com/watch?v=DCyMS7FKCZc&feature=related


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## Ultrarunner2017 (Oct 1, 2008)

When I was a kid, I recall watching Sci-Fi movies and wondering whether the wires really danced like they do in the movies.
Then, I finally got to see one first hand after a storm, when there were lines down. I was in my car, and the POCO and cops were on the scene. I saw a wire dancing on the wet pavement as I drove past.

As for my "pot", I got a response from POCO whom I e-mailed before T-giving. She told me that they did send someone to check it out, and the report came back that all is well.
She told me the transformer is from the 60's (not much older, as I had thought), and that I am probably better off with that one than with a new one owing to their superior construction and ability to withstand overloads than today's models.
She told me also that there are no PCB's in the transformer. It uses mineral oil, and the older ones used linseed oil.
Further, she told me that the open-air wiring is fine. As long as it doesn't get broken, they don't replace it. Being open air, it doesn't pose the overheating problem that twisted would.

I don't know if there really is a fuse on this pot. I'll have to take a look at it.
So, in spite of my worrying, and some of us ranking on POCO, they do respond to customers inquiries and concerns. Perhaps what got me the call-back is that I mentioned PVC's in my e-mail. They want to make sure I don't take this thing one step further and call the EPA or someone.

So, I am satisfied and content. Now I can sleep without worrying about the pot. All I have to do now is talk to someone at NASA to confirm that there are no Earth crossing asteroids that may threaten to put a hole in my head someday<g>


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## rgsgww (Jul 5, 2008)

KE2KB said:


> When I was a kid, I recall watching Sci-Fi movies and wondering whether the wires really danced like they do in the movies.
> Then, I finally got to see one first hand after a storm, when there were lines down. I was in my car, and the POCO and cops were on the scene. I saw a wire dancing on the wet pavement as I drove past.
> 
> As for my "pot", I got a response from POCO whom I e-mailed before T-giving. She told me that they did send someone to check it out, and the report came back that all is well.
> ...


I have 2 200 amp square d breaker panels, when ever the 40 amp ac turns on, you can feel the 2/0 service conductors buzzing.

This is the fuse


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## micromind (Mar 9, 2008)

This is an older style installation. 

Around here, the 3 phase 7.2 to 15 kv is one of two systems. The first is 7200 volts to neutral (ground), and 12,470 volts phase to phase. The other is 14,400 volts to ground, and 24,940 volts phase to phase. Commonly called 12.5KV and 25 KV. The phase (hot) wires are above the pots (transformers), and the neutral is below. On all POCO (power company) installations, neutral and ground are the same. 

These are called 'one bushing pots'. On a transformer, any terminal is called a bushing. The top one is the high voltage bushing, and the ones out the side are low voltage bushings. On these pots, the high voltage is connected to the top bushing, and the case is the other side of the high voltage winding. You can see the 3 small wires connected to the neutral wire below the pots. Most modern pots have two high voltage bushings. 

The fuse/disconnect things are called cut-outs. The smaller part on the left is actually the fuse. It is a ceramic tube that holds a fuse element. You make up the element on the ground, and raise it up to the cut-out with a hot-stick (a long telescoping fiberglass pole with a hook on the end). The rings at the top and bottom are where the hot-stick hook goes. As you can imagine, this gets tricky in the wind! While this can all be done from the ground, most of us prefer to go up in a bucket truck, and use an 8' hot-stick. 

If a cut-out is closed in to a short, or a short develops, the fuse element will explode. I mean EXPLODE!! It sounds just like a shotgun blast. Maybe a bit louder. The bottom end of the ceramic tube is open, and fire, sparks, etc., fly out about 10' long. It's quite a sight, you'll never forget it. 

We've all heard how the POCO gets away with grossly overloading wire, and the secondary (low voltage) side of this installation is a good example. The secondary connection here is called a 120/208 3 phase 4 wire wye. Each pot is internally connected to deliver 120 volts. The number 50 on the pots is the KVA rating. 50,000 divided by 120 equals 416 amps. Those wires look like about 2/0 or so. And they're still there after all these years! 

Rob


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## rgsgww (Jul 5, 2008)

micromind said:


> This is an older style installation.
> 
> Around here, the 3 phase 7.2 to 15 kv is one of two systems. The first is 7200 volts to neutral (ground), and 12,470 volts phase to phase. The other is 14,400 volts to ground, and 24,940 volts phase to phase. Commonly called 12.5KV and 25 KV. The phase (hot) wires are above the pots (transformers), and the neutral is below. On all POCO (power company) installations, neutral and ground are the same.
> 
> ...



Reminds me of when a tree fell on a 3 phases outside of my home. Long story short, the wires melted, split apart, touched each other. A shower of sparks fell from the lines and there was a large explosion sound (no, it wasn't the short), I knew exactly what that was. Has happened about three times in the last 6 months around here.


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## Yoyizit (Jul 11, 2008)

*just curious*



rgsgww said:


> I have 2 200 amp square d breaker panels, when ever the 40 amp ac turns on, you can feel the 2/0 service conductors buzzing.
> 
> This is the fuse


Why have three xformers on a pole? Why not just one big one? Isn't there an Economy of Scale?


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## rgsgww (Jul 5, 2008)

Yoyizit said:


> Why have three xformers on a pole? Why not just one big one? Isn't there an Economy of Scale?



Not sure why they do that...I'm not a lineman. Im guessing its cheaper and lighter.


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## InPhase277 (Feb 9, 2008)

Yoyizit said:


> Why have three xformers on a pole? Why not just one big one? Isn't there an Economy of Scale?


Three single phase transformers are cheaper than one three phase. And if one goes bad, you only have to replace that one.


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## Gigs (Oct 26, 2008)

micromind said:


> The number 50 on the pots is the KVA rating. 50,000 divided by 120 equals 416 amps. Those wires look like about 2/0 or so. And they're still there after all these years!


416 amps is really not too much for 2/0 AL under those conditions.

A few back of the envelope calculations for an uninsulated wire suspended in free air gives me an upper bound of 550 amps for a 40C temperature rise in 2/0. 

The NEC is pretty conservative, which is good, you should have a pretty big safety margin for things that are in places where people live and work.


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