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Old 11-27-2008, 01:44 AM   #16
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When a pole transformer goes bad


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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Old 11-27-2008, 06:49 AM   #17
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When a pole transformer goes bad


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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Old 11-27-2008, 07:04 AM   #18
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When a pole transformer goes bad


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Originally Posted by frenchelectrican View Post
I did heard the conductors really slapping in the conducts
What exactly did you mean by that?
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Old 11-27-2008, 07:42 AM   #19
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When a pole transformer goes bad


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?"

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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Old 11-27-2008, 08:51 AM   #20
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When a pole transformer goes bad


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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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Old 11-27-2008, 09:13 AM   #21
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When a pole transformer goes bad


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Originally Posted by WFO View Post
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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Old 11-27-2008, 09:22 AM   #22
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When a pole transformer goes bad


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Originally Posted by Yoyizit View Post
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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Old 11-27-2008, 10:09 AM   #23
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When a pole transformer goes bad


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.

Last edited by AllanJ; 11-27-2008 at 10:15 AM.
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Old 11-27-2008, 10:55 AM   #24
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When a pole transformer goes bad


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Originally Posted by InPhase277 View Post
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.

Last edited by Gigs; 11-27-2008 at 10:57 AM.
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Old 11-27-2008, 11:10 AM   #25
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When a pole transformer goes bad


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Originally Posted by AllanJ View Post
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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Old 11-27-2008, 11:18 AM   #26
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When a pole transformer goes bad


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Looks like 100amp is a common size.
7200v (?) and 10A (100A) = 72kw (720kw). The IT 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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Old 11-27-2008, 11:41 AM   #27
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When a pole transformer goes bad


I thought the primaries had 5A fuses.
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Old 11-27-2008, 07:45 PM   #28
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When a pole transformer goes bad


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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Old 11-27-2008, 07:55 PM   #29
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When a pole transformer goes bad


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

http://www.rousant.co.za/files/csp.pdf
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Old 11-28-2008, 02:15 AM   #30
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When a pole transformer goes bad


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Originally Posted by jerryh3 View Post
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 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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