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Old 11-27-2011, 01:14 PM   #1
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How do Transformers Connect / Cause of outages (transformer fire)


HI Guys!

Hope everyone is well! This morning a bit after midnight, I lost power. 6th time this year I've lost power for various reasons, none of the times was the transformer that feeds my house damaged.

So last night, the transformer that burned was about a block away, see photos:
Photos of burning transformer

So my question isn't directly related to a DIY project, but I am hoping you would indulge me, as I think a number of home owners would find the answer to this very interesting.

What I would like to know is why / how a transformer down the line will also take out my power, even though the main line (at the top of the pole) is not off. I made this little drawing to show what I am talking about. All 3 transformers shown take power off of the same main line from the top of the pole. Since the pole on the right (Red with Green Dot) stayed energized, then that top line must have stayed live. What I can't understand is why did I lose power if that main line was still on?



Since the main line had to be on, why / how would the transformer a block away being down cut my power, but not cut the power to the transformer that is tapped off of the same line just another block away?

I hope that makes sense the way I described it. I'm really curious about what is happening in a situation like this, as there have been similar situations multiple times this year, where that transformer / street light shown on the right of my picture stayed on, but then my house is out along with the next transformer being out. (and in none of the outages did they come and do any work on the transformer that feeds my house)

Thank You

Jamie

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Old 11-27-2011, 01:30 PM   #2
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How do Transformers Connect / Cause of outages (transformer fire)


Assuming you are all on the same phase of power the fuse that tripped when the transformer caught fire was probably between the one that stayed on and your house. Or maybe not a fuse but a disconnect that was opened manually the kill power for the repair.

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Old 11-27-2011, 01:38 PM   #3
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How do Transformers Connect / Cause of outages (transformer fire)


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Originally Posted by joed View Post
Assuming you are all on the same phase of power the fuse that tripped when the transformer caught fire was probably between the one that stayed on and your house. Or maybe not a fuse but a disconnect that was opened manually the kill power for the repair.
There is a pole in between those 2 points, I'll look at it and see if I can see a disconnect / fuse on there.

Thanks.
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Old 11-27-2011, 01:42 PM   #4
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How do Transformers Connect / Cause of outages (transformer fire)


In simple terms there are 2 connections on a transformer. One is called the primary, it is usually the high voltage. It is usually connected to the higher lines on the pole. The other connection is the secondary, that is usually the low voltage that feeds your house (120/240). So it is possible that the high voltage lines were still energized. The power going to your house was out due to the burned transformer.
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Old 11-27-2011, 01:48 PM   #5
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How do Transformers Connect / Cause of outages (transformer fire)


There are typically 3 wires which run on the top on electric poles.

Walk down the line in a residential neighborhood and you will see one transformer connected to the 1st line. Then next transformer connected to the 2nd line, the transformer after that connected to the 3rd line, etc.

The 3 wires at the top are called "3 phase". And they "balance" the load on those 3 wires.

Follow the line further and you will see fuses to each of those 3 lines. They look like this...



If a transformer on one of those 3 lines shorts out, the fuse for that line will blow and that one line will then be dead after that fuse. But the two other lines will still be live. (And the transformers on the line with the blown fuse will be dead.)
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Old 11-27-2011, 06:46 PM   #6
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How do Transformers Connect / Cause of outages (transformer fire)


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Originally Posted by Billy_Bob View Post
There are typically 3 wires which run on the top on electric poles.

Walk down the line in a residential neighborhood and you will see one transformer connected to the 1st line. Then next transformer connected to the 2nd line, the transformer after that connected to the 3rd line, etc.

The 3 wires at the top are called "3 phase". And they "balance" the load on those 3 wires.

Follow the line further and you will see fuses to each of those 3 lines. They look like this...



If a transformer on one of those 3 lines shorts out, the fuse for that line will blow and that one line will then be dead after that fuse. But the two other lines will still be live. (And the transformers on the line with the blown fuse will be dead.)
Correct.

It's called 'coordinated tripping'.

This means that if a fault develops the fuse/breaker closest to the fault is the only one that opens the circuit. Big buildings have this scheme on their feeder breakers too, as well as all hospitals.

The fuse things (that the arrows are pointing at) are called 'cutouts'. They have fuse elements inside a porcelain tube, and can be removed and installed from the ground using a fiberglass pole called a 'hotstick'.

If you look at the cutouts real close, there's a round eye on the top. This is where the hook of the hotstick is placed, and it is pulled down and out. There's a type of hinge at the bottom, that is arranged to release it when it's hanging down. Just push up, but not out, and the entire assembly will be released, and you can lower it to the ground to replace the fuse element.

There's another eye in the bottom of the cutout, this is what you use to re-install it. It's a real trick to get one back in from the ground.

Most of us greatly prefer a bucket truck and an 8' hotstick.

The reason most cutouts are not vertical is because if you close it into a fault, it'll blow sparks down. If it's straight down, you'll be showered by the sparks.

When you open or close a cutout under load, don't just mess around, snap it in or out.

When a fuse like this blows, it sounds just like a 12 gauge shotgun. Really loud!


Rob
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Old 11-27-2011, 07:06 PM   #7
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How do Transformers Connect / Cause of outages (transformer fire)


What is really good about our city owned utility, is that they already know on most outages, before you even get a chance to call in. I got the pleasure of seeing the transformer five doors down leaking oil, and as the supervisor that was sent out to check it out, the fuse blew just as he was calling it in. He said that it was lucky that it did not catch on fire.

I heard the can lid pop, but power was still on, until of course the fuse popped.
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Old 11-27-2011, 08:10 PM   #8
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How do Transformers Connect / Cause of outages (transformer fire)


Do the wires run through the woods as shown, or do they really follow the roadways?

Are you sure that the transformer closest to your house really supplies your house? Sometimes the 120/240 volt lines (the lines are sometimes called secondaries) for a particular house might come from a transformer other than the closest transformer. About 3/4 way up the pole you see a bundle of wires, two hots wrapped around a bare neutral/ground/messenger. This seemingly goes pole to pole all the way down a long street but if you look closely you will see that every so often, perhaps every ten houses, the two hot secondary wires come to an end and are taped off and another two hot wires, also taped off, contineu on from that point, fed by the next transformer.

Or maybe there is a fuse (cutout) in the primary line (at the top of the pole) between the green dot (transformer still energized) and the all-red dot (your transformer) and that fuse blew when the yellow dot transformer caught fire.

Generally each transformer has its own fuse, which should blow first, before a cutout in the primary line blows.
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Last edited by AllanJ; 11-27-2011 at 08:23 PM.
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Old 11-27-2011, 09:17 PM   #9
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How do Transformers Connect / Cause of outages (transformer fire)


Quote:
Originally Posted by AllanJ View Post
Do the wires run through the woods as shown, or do they really follow the roadways?
Yes, the wires run as shown. It just regular residential area with mature trees. They do tend to run lines through the middle of blocks, though peoples yards, just as shown in the drawing I made. They also tend to put transformers in peoples back yards many times.


Quote:
Originally Posted by AllanJ View Post
Are you sure that the transformer closest to your house really supplies your house?
The transformer was replaced about 4 years ago due to a direct lightning strike. I was told by the crew that replaced it that it was for my house, so I am fairly certain that it accurate. To me, it does physically look like the lines from the closest transformer are the ones that head to and are tapped off to my house.

Quote:
Originally Posted by AllanJ View Post
Sometimes the 120/240 volt lines (the lines are sometimes called secondaries) for a particular house might come from a transformer other than the closest transformer. About 3/4 way up the pole you see a bundle of wires, two hots wrapped around a bare neutral/ground/messenger. This seemingly goes pole to pole all the way down a long street but if you look closely you will see that every so often, perhaps every ten houses, the two hot secondary wires come to an end and are taped off and another two hot wires, also taped off, contineu on from that point, fed by the next transformer.
Or maybe there is a fuse (cutout) in the primary line (at the top of the pole) between the green dot (transformer still energized) and the all-red dot (your transformer) and that fuse blew when the yellow dot transformer caught fire.
Generally each transformer has its own fuse, which should blow first, before a cutout in the primary line blows.
I can see that this is very true right in my area from the times we have had outages because houses just several houses away have power.

I'll look at it again and take some photos tomorrow in the day light and post them. I can easily get clear photos of the transformers that are closest to me. Thank You.

Quote:
Originally Posted by micromind View Post
When a fuse like this blows, it sounds just like a 12 gauge shotgun. Really loud!
Rob
Thank You both for all of the information, I will get more photos to help show what I'm looking at.

Rob, I didn't hear it, but I happened to be on the phone at the time and was in a little more inner room, but my fiancee was in bed and she said she heard this huge boom outside. I wondered how the transformer would have made such a loud sound. But it sounds like what she heard was one of those fuses blowing out.
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Old 11-27-2011, 11:14 PM   #10
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How do Transformers Connect / Cause of outages (transformer fire)


The other thing which I am famuair with Jamie's area { not too far from my home in Wisconsin } that he do have intertied secondary line as well so which it mean that there are couple transfomer share the same secondary line.

I know it sound nutty but this one of few common methold which the POCO used on hevey resdentail area so they can actually increase the KW rating by intertied it instead of standard 25 KVA or 37 KVA pigs *{ pole mounted transfomers} so they double it up so it actually boosted up to either 50KVA or 74 KVA or larger depending on how it lay out. { There is both single and triphase verison used in few area }

The major pain in butt is do the polarty setting due you have to interconnect it only one way othewise you will blow the primary fuse pretty quick if you are not carefull with it. { I will save that topic for other time due it can be a long winded details }

Merci.
Marc

Note: * the pigs or pots is the same terms for pole mounted transfomer and that word will varies a bit depending on the area you are speaking of. for underground pad mounted transfomers we called them slugs.( they are differnt than pigs are and hevey beast as well )
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Old 11-28-2011, 02:27 PM   #11
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How do Transformers Connect / Cause of outages (transformer fire)


one thing to remove from the equation are those street lights they are off some place else for the blocked area.... so the town can be billed for them.the TR that burns up has to be yours and the one in front of your property is down stream homes where do the lights stop and houses without power from the burning TR and your near by TR those 3 wires on the horizontal pole to pole are 22,000V primary stepped down pair'd 240V single phase with a neutral from the utility no homes have 3 phase power either 240V or 460V only commercial spaces if there are some on the street or near a coporate park complex
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Old 11-28-2011, 03:51 PM   #12
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How do Transformers Connect / Cause of outages (transformer fire)


I just went and took photos. I updated my little map drawing and put letters on it that are corresponding to the letters I placed on each photo so it is easy to tell where everything is.

There is a limit of 10 photos in a post, so the last of them will be in a second post.





3-Phase feed: (Pole A)







This street light is the one that stayed on.





This light was off:



Transformer to my house:



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Old 11-28-2011, 03:51 PM   #13
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How do Transformers Connect / Cause of outages (transformer fire)


Last of the photos: (continued from prior post)





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Old 11-28-2011, 06:50 PM   #14
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How do Transformers Connect / Cause of outages (transformer fire)


In each picture, what direction is north?

I can't figure out which direction is towards E, which direction is towards A, etc.
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Old 11-28-2011, 08:18 PM   #15
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How do Transformers Connect / Cause of outages (transformer fire)


This is not by chance a area serviced by WE? I got the pleasure of seeing their work while up in Land O'lakes this past weekend. It probably took them about two hours to get a pole back in the ground and wired, with the transformer back online. What amazed me, is that they even put the telco & locally owned catv back on the pole.

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