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Thread: 3 Phase or Single Phase

  1. #1
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    3 Phase or Single Phase

    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?

  2. #2
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    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.
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  3. #3
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    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

  4. #4
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    Quote Originally Posted by winnie View Post
    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.
    Bob

  5. #5
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    Quote Originally Posted by winnie View Post
    ... 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.
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  6. #6
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    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.

  7. #7
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    Quote Originally Posted by westex View Post
    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.
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  8. #8
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    Quote Originally Posted by Jraef View Post
    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.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  9. #9
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    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

  10. #10
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    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.

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