roto phase 240v 3 phase

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chefiam1

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Centerville,pa
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retired 20yrs electrician
900 ft run 110/220 single phase what size wire for 200 amps?
i came up with two sets of 500 mcm?
what i'm trying to do is not have 3 phase power dropped to the property.thats 26,000.00 dollars
so, i need to run a 3 phase 20 h p pump and a 110/220 200 amp single phase that is 900ft from power.
and use a roto phase to supply pump.can i put the roto phase at the start of run? and run 3 phase 900 ft or
do i run 110v/220 single phase is it worth running single phase?

first time doing this type of calculation HELP thanks, Chef
 
I suggest stepping the voltage up to 480 or 600 v and then back down to 120/240. For your 20hp motor, a oversized vfd can convert 1 ph to 3 ph.
 
thanks, tom i have been pulling my hair out . to explain it to my father in law who has a golf course
and wants to run a pump out of a large pond but it is 1000 ft from power pole. so, 220v single phase service drop to a step up trans
then run 900 ft then step down to a VFD
 
chefiam1 said:
can i put the roto phase at the start of run? and run 3 phase 900 ft or
do i run 110v/220 single phase is it worth running single phase?
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I'd say definitely put the VFD or rotary converter at the load. And I agree on stepping up to a higher voltage for the run.

You might be able to find a VFD that will accept the stepped-up voltage, and not have to buy a second transformer.

Added: If there is no utility transformer yet, you might be able to ask for a higher voltage from the power company.
 
I dont see step up/step down being worth it. You probably only need 500 AL for the single phase run. I just bought some triplexed 500/500/(1/0) AL USE (just pulled it yesterday, 600 feet) and IIRC it was 3.60/ft - there are you two transformers right there.
 
Voltage drop is worse with current. If you run the single phase out to the load, the current of that circuit will be 173% of what the current will be at 3 phase, so the VD would be worse. So for example a 20HP 230V 3 phase motor, rated at 54A FLC, will draw 93A from the single phase supply. So you will have to base your VD on 93A (plus transformer losses) if you run the single phase to the load, vs basing the VD on 54A f you run the 3 phase out to the load.

But on the 3 phase, you have to run 33% more conductors. So pick your poison.

Stepping up to the higher voltage works best if the pump can be reconnects for 460V, but if not, then you have to add the costs of a transformer at each end, plus OCPDs, disconnects etc. and more VD through those transformers.

If you want to do it with a VFD, it should be as close to the load as possible for reasons other than VD. So you still have the 93A issue running out to the VFD, then you will have to buy a VFD rated for at least 108A if doing phase conversion. Typical VFD sizes jump from 96A to 125A, so you would need the 125A drive (50HP), NEMA 3R enclosed with a breaker, etc., figure $12-15k for the VFD alone (maybe less for some off-brand no-name Chinese drive, but you take your chances). Weigh that against the cost of the RPC, but also remember that for the end user (in this case your F.I.L. that you will have to see at holidays), the RPC loses significant energy in running the idler motor, so more long term operating costs.
 
We see single phase 480 drops often enough. Run that out to your 480v roto phase for the motor. Tap a transformer from the single phase 480 large enough for the actual 240/120 single phase load. If you need the 200, pay for it and quit waffling.

The mfgs selling name brand phase converters , static or rotory, know what they are doing. Ask.
 
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