# POCO transformers and kVa sizing.



## don_resqcapt19 (Jul 18, 2010)

The utility companies size their transformers on what they expect the real load to be. They do not base it on the Article 220 calculations. It is often only 1/2 to 1/3 the size that you would expect based on the load calculations. Their sizing is based on years of real world experience and not on the very conservative load calculations found in the NEC.


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## guest (Feb 21, 2009)

What Don said, and the POCO's also allow the tx's to operate under overload conditions with a calculated "loss of life" factored in. An oil colled transformer is surprisingly durable and can withstand a severe overload for a long time without failing right away, but again with some loss of life involved. A 300% overload is not unheard of.


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## BBQ (Nov 16, 2010)

And short time, like few hours may not even reduce the life as the life is reduced by overt temp, not overcurrent. 

An oil filled transformer takes a long time to heat up.


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## kbsparky (Sep 20, 2007)

BBQ said:


> ....An oil filled transformer takes a long time to heat up.


Yup, and when they blow up, they really put on a show!!

http://www.youtube.com/watch?feature=endscreen&v=dr0JpZ80-lE&NR=1


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## socalelect (Nov 14, 2011)

They figure 2 t0 3 kva in my hood per residents svc


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## D-Bo (Apr 15, 2012)

got two 3000 amp services heated up last week. they set 1500kva padmount for each


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## user4818 (Jan 15, 2009)

I counted 15 single family houses on one 50 KVA transformer a few blocks over.


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## socalelect (Nov 14, 2011)

Peter D said:


> I counted 15 single family houses on one 50 KVA transformer a few blocks over.


Pete. In my hood there's 9 houses plus several well meters on a 25 kva. I have bitched about the vd and they will do nothing, they. Wont even replace the 6 gauge lateral that feeds 2. 100 amp panels on my property


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## TOOL_5150 (Aug 27, 2007)

socalelect said:


> Pete. In my hood there's 9 houses plus several well meters on a 25 kva. I have bitched about the vd and they will do nothing, they. Wont even replace the 6 gauge lateral that feeds 2. 100 amp panels on my property


start shooting at the transformer with a 22..... :brows: thatll make em change it.


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## guest (Feb 21, 2009)

TOOL_5150 said:


> start shooting at the transformer with a 22..... :brows: thatll make em change it.


And aim 1/3 of the way up from the bottom of the tank and slightly off the centerline...that is the best spot to short out the coils. I won't say how I know this....:whistling2::laughing:


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## socalelect (Nov 14, 2011)

mxslick said:


> And aim 1/3 of the way up from the bottom of the tank and slightly off the centerline...that is the best spot to short out the coils. I won't say how I know this....:whistling2::laughing:


Slick the only problem is this pot has self destructed 3 times in 5 years yet they put the same little o e back up. My po co is not the brightest


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## BBQ (Nov 16, 2010)

socalelect said:


> Slick the only problem is this pot has self destructed 3 times in 5 years yet they put the same little o e back up. My po co is not the brightest


How do you know it is not being shot at?


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## socalelect (Nov 14, 2011)

BBQ said:


> How do you know it is not being shot at?


Becuz all of my neighbors are anti gun pu$$ys


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## BBQ (Nov 16, 2010)

I live in an 'anti gun' state but our highway signs often have bullet holes. :jester:


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## guest (Feb 21, 2009)

socalelect said:


> Slick the only problem is this pot has self destructed 3 times in 5 years yet they put the same little o e back up. My po co is not the brightest


SDGE or SCE? :laughing: They both have their stupid moments. 

If you are around next time it lets go, you might try to appeal to the trouble crew..sometimes they can contact engineering and get the go-ahead to replace with a bigger pot...as long as it hasn't been shot at.  Offering up a case of beer might help your cause too.  

(Many years ago on the service upgrade to my house I did get the line crew to install a heavier drop for me when I told them that my anticipated load would likely burn down their standard #6 resi triplex.  They ended up stringing what looked like #2 triplex..let's just say I never had voltage drop issues. :whistling2

BTW, how does it fail? Blows fuses, burns up in flames and sparks, or just quits? 

If it has a history of violent failures you can call the POCO and threaten to report them to the PUC and get it changed to a bigger one due to the hazard. Be sure to take time and date stamped pics whenever possible.


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## socalelect (Nov 14, 2011)

mxslick said:


> SDGE or SCE? :laughing: They both have their stupid moments.
> 
> If you are around next time it lets go, you might try to appeal to the trouble crew..sometimes they can contact engineering and get the go-ahead to replace with a bigger pot...as long as it hasn't been shot at.  Offering up a case of beer might help your cause too.
> 
> ...


San diego gouge and extortion 
When. It goes it blows apart. Starts a little grass fire then its a mad scramble to get the generator set up


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## user4818 (Jan 15, 2009)

mxslick said:


> SDGE or SCE? :laughing: They both have their stupid moments.


Here we go again. 

Let's see, two of the largest poco's in the country that serve two of the largest cities in the country - again, how on earth do they function without you as their president?


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## user4818 (Jan 15, 2009)

socalelect said:


> Pete. In my hood there's 9 houses plus several well meters on a 25 kva. I have bitched about the vd and they will do nothing, they. Wont even replace the 6 gauge lateral that feeds 2. 100 amp panels on my property


As Don said, their equipment is sized per their historic data, not the NEC.


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## guest (Feb 21, 2009)

socalelect said:


> San diego gouge and extortion
> When. It goes it blows apart. Starts a little grass fire then its a mad scramble to get the generator set up


Something like this?  :


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## socalelect (Nov 14, 2011)

mxslick said:


> Something like this?  :
> 
> <a href="http://www.youtube.com/watch?v=8GdkXbuQfIw&feature=related">YouTube Link</a>


Eh not that spectacular


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## jmsmith (Sep 10, 2011)

Acro,
POCO usually assumes that there will be some 120/240V single-phase use on their service, so the voltage is figured accordingly. On a three- phase transformer, a 500kVA will supply approx. [email protected] Now, a single-phase 500kVA transformer will supply [email protected] An 1800A service will allow 90% load on the transformer. Hope this explains it.
-jim


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## Legion (Oct 19, 2010)

socalelect said:


> Pete. In my hood there's 9 houses plus several well meters on a 25 kva. I have bitched about the vd and they will do nothing, they. Wont even replace the 6 gauge lateral that feeds 2. 100 amp panels on my property


If your voltage drop exceeds your states maximum, and they won't put any monitoring equipment to verify, you can make a public service complaint which forces them too. Once they have the data from their own monitoring equipment and a public service (equivalent) complaint, they'll change it out.


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## socalelect (Nov 14, 2011)

Legion said:


> If your voltage drop exceeds your states maximum, and they won't put any monitoring equipment to verify, you can make a public service complaint which forces them too I
> . Once they have the data from their own monitoring equipment and a public service (equivalent) complaint, they'll change it out.


What is the max drop isn't it 10 percent


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## acro (May 3, 2011)

don_resqcapt19 said:


> The utility companies size their transformers on what they expect the real load to be. They do not base it on the Article 220 calculations. It is often only 1/2 to 1/3 the size that you would expect based on the load calculations. Their sizing is based on years of real world experience and not on the very conservative load calculations found in the NEC.


What Don said, and the POCO's also allow the tx's to operate under overload conditions with a calculated "loss of life" factored in. An oil colled transformer is surprisingly durable and can withstand a severe overload for a long time without failing right away, but again with some loss of life involved. A 300% overload is not unheard of. 


We finally got a contract to look at and it says that our demand shall not exceed 500 kVA.

OK - answer me this. As this is my 1st time dealing with a contract like this, can I be assured that we will not get caught in some technicality?

Nowhere in the contract is there a reference to amps, though that is the units that we used when calculating the load.


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## wildleg (Apr 12, 2009)

don't forget the pocos have years and years of experience blowing stuff up, so they have pretty good ball park ideas of exactly wat will (usually) work


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## acro (May 3, 2011)

Yea, but that's not the way the contract is written. 


It says we are not supposed to exceed 500kVA. But you and I know that by the calculations we are supposed to use, that is nowhere near what we need. I will address it with them, but just wondering what others have seen.

When it is in writing, it's a little different. We are planning on an 1,800 amp service. 



Secondarily, would there be any advantage(for either party) for the contract to state that our facility is different than it actually is?

They have been on site and it is plain to see that it is a stone crushing plant. Yet on the contract, it says it is a trucking facility.

Now, a bunch of resistive heater loads sure is different than a couple of 300hp motors and many smaller ones.


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## acro (May 3, 2011)

acro said:


> It says we are not supposed to exceed 500kVA. But you and I know that by the calculations we are supposed to use, that is nowhere near what we need. I will address it with them, but just wondering what others have seen.
> 
> When it is in writing, it's a little different. We are planning on an 1,800 amp service.



Anybody have an answer for that? I have not gotten any answers from my POCO yet.


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## gesparky221 (Nov 30, 2007)

Responded to an alarm drop at a local school. We get there and right away I notice cutout on pole is open. Call POCO and a line guy shows up. First thing is he replaces the cutout and closes it in. Boom, blows right away. He says must be the underground is bad. Disconnects underground feed to building, puts in new cutout. To disconnect the underground he had to re-pos'n the bucket truck which meant he was over top the xfmr to close the cutout. When he closed the cutout it looked like all hell broke loose. Fire and metal flying everywhere. Don't know how he did not get hurt. After about 3 minutes the fire died down. He sat in the truck for about 15 min. and smoked 4 smokes before he said a word. We stayed on scene until more POCO guys showed up. I looked at the job a couple days later and the can they put up was twice as big as the one that was up there. Must have been all they had on hand at the yard that day.


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