Overloading utility provider transformer. Is this a good idea?

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Besoeker said:
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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It would but the knock on effect to the customers installation with an increase of the MPFC could be problematic.

A couple of years back I transferred a 800kVA 11/.433kVA transformer from a private network to the local DNO (PoCo) ring, we were within spitting distance of the DNO primary 33/11kV 20MVA substation. The costs spiralled from my budget of £100K to £230K due to the new MV switchgear required because of the MPFC.
 
kwired said:
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.
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The OP's only concern as expressed in his post is whether or not he'll fry the transformer. I'm sure he's well aware of the usage and demand issues; he's the one knocking on the POCO's door for a larger transformer. As others have pointed out, NEC vs. POCO calculations means he may already be using the largest they would spec for his service. Rather than the interminable wait while the POCO mulls over his request, I suggested taking the empirical approach.
 
mbrooke said:
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.
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hence the 'depending on your pu Z'
a PU Z of 3% at 300% OL will have a drop of 43 volts at the sec lugs

you've seen xfmrs with 15% pu Z?
 
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gadfly56 said:
The OP's only concern as expressed in his post is whether or not he'll fry the transformer. I'm sure he's well aware of the usage and demand issues; he's the one knocking on the POCO's door for a larger transformer. As others have pointed out, NEC vs. POCO calculations means he may already be using the largest they would spec for his service. Rather than the interminable wait while the POCO mulls over his request, I suggested taking the empirical approach.
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Yep, the worry of demand charges and such as mentioned above are valid, but as jraef said the POCO has been notified and did nothing.

If the service is rated for the loads, I would run that tranny to the max.

Burns up, oh well.

Yeah I know inconvenient outage possible.
 
Sahib said:
No win for POCO really because overloading a transformer shortens its life.
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Power companies in the US are very savvy on computer use. I'd bet they have a very good idea of transformer loads, especially with a single customer installation such as this. I'd guess than when loads approach some level, maybe 125%, they will act based on a report automatically generated.

They want to schedule maintenance, not respond to emergencies.
 
have someone who knows how run a service load calculation and send that to the utility. they can decide what they want to do with it. that's what they are going to do anyway.
 
GeorgeB said:
Power companies in the US are very savvy on computer use. I'd bet they have a very good idea of transformer loads, especially with a single customer installation such as this. I'd guess than when loads approach some level, maybe 125%, they will act based on a report automatically generated.

They want to schedule maintenance, not respond to emergencies.
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I had a similar experience as the OP. 150 kw transformer with a 700 and a 600 amp panel. The machine shop was constantly overloading the transformer. The POCO said they knew the transformer was overloaded(194 kw). They also said when the machine shop reached 200kw they would replace the transformer. They did. Now the machine shop has an additional 1200 amp panel and they are still on a 500kw transformer.
 
Another issue due to transformer overloading, apart from reduced life, is excessive voltage drop. Perhaps POCO does not care about maintaining their supply voltage within any legal/standard limit at the consumer supply point.
 
Sahib said:
Another issue due to transformer overloading, apart from reduced life, is excessive voltage drop. Perhaps POCO does not care about maintaining their supply voltage within any legal limit at the consumer supply point.
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Correct. However, (usually) POCO transformers in the US have a low impedance for this exact reason. It tends not to be an issue for the most part.
 
electrofelon said:
Yeah, I don't recall the last time I saw voltage at a service more than a volt or two below nominal. Usually it's quite a bit on the "healthy" side
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Even at full load its taken into account. Here are two pole pig tags FWIW:


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Two 300kva padmounts:



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