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Thread: 240 3ph ->480 Xfmr

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    240 3ph ->480 Xfmr

    We're getting 3ph open delta from PG&E. We alas have a 480v 3ph 2 hp. pump in place 750ft down.

    So I'm looking at 240->460 transformers. But most I see are wye on the LV side, delta on the 480. As far as I can see, the motor [http://www.franklin-electric.com/res...234-325-94--S] is 3-wire, so feeding that sole load with a delta leaves everything floating.

    What are my options? Obvious would be a non-stock 240 delta-> 460 wye transformer. Others that the electrician & inspector will like...?

    [Don't even ask about swapping the pump motor. $2K+ in labor to pull; & ~that to install a 208/240 one..plus buying it.]

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    You can use one that is wye on the low voltage side and ignore the LV neutral, , however, it will most likely be 208 rated on the LV side and not match your 240 system.
    A 240 delta to 480 delta should be readily available.
    If your HV side is delta, you can elect to ground one phase or use it as an ungrounded system.
    There are specific Code rules for each.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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    This is more of a thought than an answer.

    No bigger than load is, can you set a pair of bucking transformers to drop your 240 to 208 then go with a standard 208 to 480.

    We do not have three phase in our shop. We do have a single phase transformer we reverse feed to get 480 single phase. We then use a 480v VFD to operate those motors that will be running at 480v. Might be a relatively in expensive solution.
    Tom
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    Page 4 of Franklin's AIM manual suggests 2 - 2 kva single phase transformers set up in an open delta configuration as min size. Those should be a stock item in your area.
    Tom
    TBLO

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    Quote Originally Posted by Open Neutral View Post
    We're getting 3ph open delta from PG&E. We alas have a 480v 3ph 2 hp. pump in place 750ft down.

    So I'm looking at 240->460 transformers. But most I see are wye on the LV side, delta on the 480. As far as I can see, the motor [http://www.franklin-electric.com/res...234-325-94--S] is 3-wire, so feeding that sole load with a delta leaves everything floating.

    What are my options? Obvious would be a non-stock 240 delta-> 460 wye transformer. Others that the electrician & inspector will like...?

    [Don't even ask about swapping the pump motor. $2K+ in labor to pull; & ~that to install a 208/240 one..plus buying it.]
    I'm guessing you will spend most of $2K on whatever conversion method you happen to choose. Decision time.

    I like Toms idea of single phase transformer and VFD - remember you will probably need a VFD rated for a 5hp motor to operate it from single phase source.

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    Quote Originally Posted by Open Neutral View Post
    We're getting 3ph open delta from PG&E. We alas have a 480v 3ph 2 hp. pump in place 750ft down.

    So I'm looking at 240->460 transformers. But most I see are wye on the LV side, delta on the 480. As far as I can see, the motor [http://www.franklin-electric.com/res...234-325-94--S] is 3-wire, so feeding that sole load with a delta leaves everything floating.

    What are my options? Obvious would be a non-stock 240 delta-> 460 wye transformer. Others that the electrician & inspector will like...?

    [Don't even ask about swapping the pump motor. $2K+ in labor to pull; & ~that to install a 208/240 one..plus buying it.]
    Do you preceive it as a problem to to use a standard 480D-240D transformer, to corner ground the 480D? Corner ground the delta and run 3w to the motor along with an EGC is you normally would.
    You could use a NEMA 3R TENV encapsulated 3kva such as the Eaton Y48G24T03N which has (2)-5%taps which should be around $1,500.
    I'm sure there are other manufactures who have similar transformers.
    Have you considered a drive isolation transformer? They are availablt as a 230D-460Y/266 w/(1)+5% and (1)-5% taps but are probably ventilated such as the Eaton MD075E89. It's a 7.5kva (an overkill of course) good for 5HP.

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    Many good ideas; thanks. Am open to all suggestions.

    • Considered VFD but long leads; also need load reactor. Also have a long (900+ ft) run to utility shed needing 240/120v. & was entertaining legality/cost of running one leg of 480 to it & putting small stepdown out there; less copper in ground.
    • Ungrounded systems bother me. I can't justify that, it's just my lack of experience with same. Was reading https://forums.mikeholt.com/showthread.php?t=143948 with interest. The only issue with corner ground I can now see with same might be the Siemens EPS200 Solid State Overload Relay; will read up on that.
    • Buck/boost & 208->480 is possible, but more iron/copper, more losses. Cost effectiveness TBD.
    • Had not thought of open delta^2; i.e. two 1∅ 240->480 units. Already concerned about balancing issue; see possibility it would magnify that issue.


    Thanks for all...

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    Quote Originally Posted by ptonsparky View Post
    Page 4 of Franklin's AIM manual suggests 2 - 2 kva single phase transformers set up in an open delta configuration as min size. Those should be a stock item in your area.
    This may well be the best solution, if I can get things balanced. There's a potpourri of less expensive 240-480v single phase transformers in the right KVA. If I can find ones that are tapped....

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    Quote Originally Posted by Open Neutral View Post
    This may well be the best solution, if I can get things balanced. There's a potpourri of less expensive 240-480v single phase transformers in the right KVA. If I can find ones that are tapped....
    Nothing says you can't corner ground that if you want to. If you ground mid point of one phase you still have a wild leg of about 415 volts.

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    I think it's been discussed here previously and I have no technical data to back what I'm saying so you can take it with a grain of salt, but, submersible pumps don't seen to like open delta supplies.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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