3 Phase or Single Phase

[westex]

I am installing a 200 amp 3 phase 480v service for a reverse osmosis water system on a poultry farm. The owner was questioning me if it would save money on his power bill if he installed 480v 3 phase to 240v single phase stepdown transformers to feed the rest of his farm. The rest of the farm is on 8 separate 200 amp single phase services. I could not answer the question.

If he could talk the Coop into enlarging his 3 phase service would there be enough savings or any savings to justify the purchase stepdown transformers?

Is there a formula or calculation that can be used to calculate this scenario?

 

[Jraef]

Energy is energy. Single phase or three phase makes no difference. But the one aspect that might is that if you HAVE 480V 3 phase and have to SERVE some 240V single phase loads, you need transformers and those transformers will have a small amount of losses associated with them. If he ALREADY has 240V single phase service drops from the utility for those other loads, then the transformers are owned by his utility, so THEY are absorbing those losses, not the user. If he increases the size of his 480V service and HE has you add the 8 transformers, then HE owns the losses in those transformers. Depending on loading, sizing, type of transformer and numerous other factors, those losses can amount to anywhere from 4-10% of the single phase power going through them. That can add up over time.

 

[winnie]

As jraef says, energy is energy. There are two potential sources of saving: 1) if the 240V loads are all over a large farm, distributing 480V might save in distribution losses. 2) tarrifs: the co-op might charge differently for 480V versus 240V, 3 or 1 phase, or multiple service drops/meters. The latter can help or hurt, depending on the exact rules involved.

It might pay to see if any of the various loads can be converted to 480V use. Some motors are dual voltage, for example.

-Jon

 

[petersonra]

It might pay to see if any of the various loads can be converted to 480V use. Some motors are dual voltage, for example.

Is that typically true with 240 V single phase motors?

I would bet by the time you add it all up it will be really hard to make an economic case for it.

you would need to get a larger 480V 3 phase service for one thing. In this case something like 800 Amps. And often such services come with demand meters and they can be a real expensive proposition.

Having said that demand meters are pretty much coming to everyone, and not to long down the road.

 

[Jraef]

... Some motors are dual voltage, for example.

-Jon

Wouldn't apply to single phase though...

... The rest of the farm is on 8 separate 200 amp single phase services.

 

[westex]

Thanks for the input. I know the Coop does charge a monthly use fee on 3 phase but being a Farmer they do get cheaper connection fees and new construction fees for primary runs than a home owner or commercial.

The farm owner was under the impression that it would greatly reduce his monthly bill. That does not sound like the case. Thanks again.

 

[Jraef]

Thanks for the input. I know the Coop does charge a monthly use fee on 3 phase but being a Farmer they do get cheaper connection fees and new construction fees for primary runs than a home owner or commercial.

The farm owner was under the impression that it would greatly reduce his monthly bill. That does not sound like the case. Thanks again.

it's a common misconception. Yes, current goes down at 480 vs 240V, but you are not billed for current, you are billed for wattage. Watts = watts = watts.

 

[electrofelon]

it's a common misconception. Yes, current goes down at 480 vs 240V, but you are not billed for current, you are billed for wattage. Watts = watts = watts.

But arent "residential" rates usually more per KWH? I think often you pay less per KWH for a commercial account, but you also have to pay for demand of $7-$9 per KW.

 

[Ingenieur]

might cost more
the util absorbs xfmr losses now
if he took service at 480/3 and stepped down to 120-240/3 he would own the xfmr losses
could be substantial
assume 50% load at each 200 A 120/240/1 service or 24000 kva
that might be 500 w in losses or 12 kwh per day (2% losses)
at $0.10 kwh $440/yr x 8 ~ $3500

 

[retirede]

Most COOPs have a fairly significant fixed monthly charge for each service just for the privilege of being connected. In my area it’s about $40 per month.
Be sure to include that in your calculation if you can eliminate one of the services and hence that charge.

 

[kwired]

Is that typically true with 240 V single phase motors?

I would bet by the time you add it all up it will be really hard to make an economic case for it.

you would need to get a larger 480V 3 phase service for one thing. In this case something like 800 Amps. And often such services come with demand meters and they can be a real expensive proposition.

Having said that demand meters are pretty much coming to everyone, and not to long down the road.

Though it can vary from place to place, what I have seen around here is demand metering doesn't really kick in until you get over certain kVA level regardless of whether you are supplied with single or three phase and voltage doesn't really matter. Which makes sense if you are demanding 100 kVA it is still 100 kVA regardless of what voltage it is or number of phases. About 100 kVA and up seems to be where those demand charges start to kick in. Now it is somewhat rare, but not impossible to see single phase service that large.

 

[petersonra]

He might be looking at upwards of 500 KVA in total. that's a pretty substantial service I think just about every place that would be on a demand meter of some sort.

 

[kwired]

He might be looking at upwards of 500 KVA in total. that's a pretty substantial service I think just about every place that would be on a demand meter of some sort.

I agree.

And don't forget when you have demand metering and charges - you often also pay a minimum demand charge whether you use that minimum amount of energy or not. That is partly because of the higher kVA infrastructure they supplied for you - they invested some $$ on it and might expect to earn some revenue from usage, but if you seldom or never utilize that capacity it doesn't pay back for them very well, and at least a part of the reason for minimum demand charges. Though those higher capacity users may have that minimum demand charge - they often have lower energy rate then other customers, or even a tiered rate that changes at certain levels of usage.