Overloading utility provider transformer. Is this a good idea?

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space_cat

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Huntington Beach, CA
I'm dealing with a bit of a situation with the utility company regarding my industrial building. I have owned my building and run a manufacturing business out of it for almost 20 years now. When I bought the building it came with 3 metered panels (3-phase, 480v). One rated for 800 amps and 2 more rated for 400 amps each, totaling 1600 amps.

My business manufactures wheels for cars and as our production moved to China a while back, we started using much less power. Recently, we ran into a problem when we discovered that our pad mounted transformer is only rated at 225 KVA for our entire building (there wasn't any label on the transformer so we always assumed it was much larger). The last few years we have been growing like crazy and have been scaling our operation, but we can't fire up any of our new equipment since we will overload the transformer.

I know you can overload the utility transformer for short periods of time, but we have several CNC machines that run for hours at a time. I want to pressure the power company to upgrade our transformer so we can use more than 1/8th of what our building was permitted for.

What would happen if I overloaded the pad mounted transformer provided by the POCO at 120%/150%/200% load for many hours or days straight?

If I "accidentally" broke the power companies transformer they provided, would they install a larger transformer?

If I push the transformer as close to 100% load as I can 24 hours a day for a while will that provide any pressure on the power company to upgrade my infrastructure?

I am using the proper channels currently to get a larger transformer, but I have a lot of angry customers and I am losing a lot of money. Any advice on the situation would be amazing!

Thanks in advance!! :thumbsup:
 
This is very common. Your setup sounds "average". Very roughly, and making a sweeping generalization, you will find utilities size their transformers to around 40% of the NEC service size. Do you have an electrician on staff who can do some measurements to see what your actual load is? I think that would be a good first step. I predict you will find you are not overloading the transformer on a long term continuous basis. I would say if you are going to 150% for short periods, or even 125% continuously, you are probably fine. A utility guy told me once they dont actually go by current, they have some formula the calculates temperature. If you really are dangerously overloading the transformer, I would provide a new load sheet to the utility and let them take it from there. I bet it is somewhere in the utility requirements that you are supposed to inform them of new loads anyway.
 
electrofelon said:
This is very common. Your setup sounds "average". Very roughly, and making a sweeping generalization, you will find utilities size their transformers to around 40% of the NEC service size. Do you have an electrician on staff who can do some measurements to see what your actual load is? I think that would be a good first step. I predict you will find you are not overloading the transformer on a long term continuous basis. I would say if you are going to 150% for short periods, or even 125% continuously, you are probably fine. A utility guy told me once they dont actually go by current, they have some formula the calculates temperature. If you really are dangerously overloading the transformer, I would provide a new load sheet to the utility and let them take it from there. I bet it is somewhere in the utility requirements that you are supposed to inform them of new loads anyway.
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Yeah we have an electrician and we had an electrical engineer come in to draw up plans/load schedule for the POCO. I'm in the Los Angeles area and there is a lot of red tape so getting through the whole process could take months. I just want to see if there is a way to speed the process up if the utility company sees we are pushing their transformer.

With our new machines, we can have a continuous load of 500 amps at 480v three phase for up to 6 hours. Right now I keep a lot of them off so I don't break the pad mount transformer. Some of our customers want really complicated designs which can run for hours at a time. We are also upgrading some of our digital infrastructures and want to also add a small server room, that that is out of the question at this time with the limited power.
 
180124-1324 EST

space_cat:

How many CNC machines? What HP on air compressor? What is typical HP advertized on outside of machine in big numbers? What do the CNC load meters usually read? How many lathes, and mills? Are you using LED lights?

Most mills are not heavily loaded. Lathes have high inertia loads usually.

With all machines and lights off what is line voltage? With all machines and lights you want to run on at once when operating normally what is a typical low voltage?

In our area at our shop we have about 175 kVA of transformers, two in an open delta. If these were to be overloaded the power company would add another transformer.

You need information, meaning make measurements under what you think is your maximum load, then extrapolate to more machines. Nameplate amperes don't mean much relative to your actual load.

Lighting could be a big part of your load.

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Generally, you TELL the utility what you need, and they deal with it. You will often find that they will decide on their own to "over duty" a transformer beyond what YOU would be able to get away with. But they own it, they make their own rules and they don't have to abide by the NEC.

Then if you have told them your needs and the transformer fries because THEY decided not to upgrade it, you get to claim the losses against them. But as a general rule you can't tell them what to do in advance.
 
Honestly, nothing may happen. Even with everything running (new gizmos included) the load might not even exceed 60%. NEC load calcs are grossly oversized as well as the data plates on most machines. Factor in load diversity and that POCO transformers can sustain 200 to 300% overload for short times provided load is cyclic its usually a none issue.
 
Jraef said:
Generally, you TELL the utility what you need, and they deal with it. You will often find that they will decide on their own to "over duty" a transformer beyond what YOU would be able to get away with. But they own it, they make their own rules and they don't have to abide by the NEC.

Then if you have told them your needs and the transformer fries because THEY decided not to upgrade it, you get to claim the losses against them. But as a general rule you can't tell them what to do in advance.
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Sometimes POCOs deliberately undersize them so they fry after 20 to 30 years. In the end a few premature failures is worth the $$$$ saved from thousands of others that would have been sized larger.
 
Ingenieur said:
depending on pu Z you may have voltage drop problems
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For the Pad? I would agree in that at a certain load point Z will always make itself known, but usually the impedance is deliberately kept low (ie 1-3% instead of 8-15% like with a large power transformer) to allow for heavy overloading.
 
Your CNC machines may take 6 hours to make a part, but unless they are turning shafts for aircraft carriers or hobbing a set of reduction gears, it's unlikely that they will be under continuous full load for that 6 hours. "Really complicated designs" sounds like lots of small cuts, tool changes, etc. - in other words, the machine would be running a light, fluctuating load for a long time rather than a heavy, continuous one, yes?

I wouldnt try to blow up the POCO's transformer by running everything you have. Yes, they will replace it, however you will have down time.

Also, if you truly had 1600A of 480V power, I think you'd get billed demand charges - that size service is capable of running a 10-15 MGD (million gallon/day) waste water plant. and if you are already billed for demand, increasing that 4-5 fold trying to fry the transformer could cost you a small fortune with your power bill - peaks are set in 15 minute intervals.

225kva @ 480V ph is good for 270A on the secondary. How much you can overload that, I dont know, however I'd be willing to bet that a nameplate 500A of CNC mills running at once would average 300A or less with the aforementioned operating conditions.

Electrofelon mentioned "I bet it is somewhere in the utility requirements that you are supposed to inform them of new loads anyway." - probably so.
 
180124-2347 EST

space_cat:

Following are a couple ways to estimate your loading:

Other than for peak voltage drop and any effect this has on your operation your primary concern relative to the transformer is average load.

1. Determine your total electrical energy used for the last year. Divide this by your estimate of the total hours of loading for the year. This is your average power usage. Multiply by some factor to obtain average VA. Extrapolate as needed for the additional machines to be run.

2. Use your electric meter. For each hour the shop is running read kWH from the meter, and record the values. Again apply your multiplying factor to get kVA. Make a judgement of how heavily you are loading the transformer. Again extrapolate as needed.

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Did you pull a permit for all the new equipment.
You should have by code.
If not that will be another can of worms.
You may need to upgrade stuff at your end not just the POCO tranny.
 
180124-2429 EST

space_cat:

Another tool you might have is:

If you have a smart meter and your power company provides you the ability to monitor the meter, then this saves a lot of recording work.

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Sounds like your premises wiring potentially is sufficient, you just didn't have the load to justify a larger transformer before. Along with larger base load comes possibility of higher monthly fees for needed infrastructure, but at same time they should offset any maximum demand factors to some extent.

Probably should do a careful stud of what recent demand data has been and careful projection of what it will look like when running new equipment and make decisions based on those findings.

You also mentioned three meters - might want to find out why that is that way, especially if they are set up for different rate schedules for some reason - might be time to make a change to fit your needs.
 
Starting from whatever you feel is a safe base load, add machines to your production scale incrementally. If the wires at the transformer don't glow red and sag and if the transformer doesn't start smoking when you get to the last machine, just keep running.
 
gadfly56 said:
Starting from whatever you feel is a safe base load, add machines to your production scale incrementally. If the wires at the transformer don't glow red and sag and if the transformer doesn't start smoking when you get to the last machine, just keep running.
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And then go:jawdrop: when you get the bill and get a big penalty for exceeding demand.

You need to look at more then just the capacity of current source, figure out what your expected demand is and set up your arrangements with POCO with what best suits your needs.

Larger power users will have higher base rates - that is necessary for infrastructure costs, they may get some break on energy charges because they are a large user though. Bottom line is if you are going to use it it will cost you, how well you manage things can change how much it will cost you. Might need to have peak production during graveyard shift just to get a better rate, or pay demand charges if you want to do so during usual business hours.
 
A question/thought from the ignorant Brit.

Would it not be in the POCO's interest to give you a bigger transformer so that you can use more electrical energy and they get the benefit of a greater revenue?
 
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