220 single phase to phase converter 3 phase 220 900 ft to 20 hp motor?

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chefiam1

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Centerville,pa
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retired 20yrs electrician
need 3 phase power 900 ft from road to 20 hp motor/pump and a single phase 110/220 100 amp to a barn.utilities say 26,000 for 3 phase to first pole right by road. so, i'm trying to find the cheapest most efficient way to do this. can a phase converter do this or a buck/boost transformer orn does it have to just be large cables

thanks, chef
 
It isn't worth spending money to get the power company to bring in 3 phase. A VFD will serve you far better; it will take the single phase input power and provide 3 phase to run the pump, and give you better control of the pump as a side benefit.

Now the question is about bringing power to the location.

To run the pumps you are talking about $3 worth of energy per day.

If you run power in an inefficient fashion (25% voltage drop) then it costs $4 per day to run. It would take many days at $1 per day to pay off a large investment in lower power losses in the feeder. Your real question will be how much voltage drop can the _barn_ tolerate.

For running the pumps the VFD will likely tolerate a 10 or 15% voltage drop. You might need to oversize the VFD to account for the single phase input and the increased input current (because of reduced input voltage), but I could imagine running the pump on 2/0 Al conductors (240V at the street, 218V going into the VFD).

But that 100A service to the barn, if the loads really are say 50A with things like ACs starting....you might need parallel 300s....

Have you priced out how much the POCO would charge to run single phase primary to the location of the barn and pumps? That would be the way to reduce voltage drop to reasonable values.

-Jon
 
the barn can be 50 amp nothing with a big power consumption will be at that location. single phase 900 ft i need to check that out with electric company.

thanks chef
 
mpoulton said:
How about three 7.5HP pumps instead, either 1ph or on VFDs with 1ph input? That reduces the starting load quite a bit.
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VFD reduces starting current even with the 20 HP motor.

If drawing water from a well, price to install three wells might make the price to run power into there look cheap.
 
Using a VFD will typically require a 40hp drive for a 20hp motor. Somewhere around 110a 240/1ph full load. You would be pulling paralleled 350 aluminum to be getting 5% voltage drop assuming a 160a max load (110 for motor and 50a for barn).

Might be significantly cheaper to go with a 480 single phase service, and bringing it up to your pump location, getting a 480v drive for the pump. Get a small transformer to feed the barn.



One set of 4/0 aluminum will get you 100a 480v 900ft under 5% voltage drop.

A 15kva 480-120/240 step down is only about $1000. Even if you cant get a 480 service set, the cost of a 50kva 240-480 stup up transformer at the road is still low compared to the increased price of pipe, wire, and the additional labor.

240@ 160a would be running 2 2-1/2" with a 350-350-2/0-2/0 per pipe is about $10 in material fer foot for both pipes
480@ 100a would be running 1 2" with a 4/0-4/0-2 is about $2.75 a foot in material
 
ppsh said:
Using a VFD will typically require a 40hp drive for a 20hp motor. Somewhere around 110a 240/1ph full load. You would be pulling paralleled 350 aluminum to be getting 5% voltage drop assuming a 160a max load (110 for motor and 50a for barn).
Click to expand...

IMHO that is not quite correct.

To run a 20hp motor from a single phase supply, you need to oversize the drive in order to have a large enough capacitor bank and input rectifier. However the drive is still only drawing 20hp (at full load) from the supply. So you are probably looking at 55-60A (at full load) being used by the VFD and pump.

ppsh said:
Might be significantly cheaper to go with a 480 single phase service, and bringing it up to your pump location, getting a 480v drive for the pump. Get a small transformer to feed the barn.
Click to expand...

This is a good point. Going to 480V means half the current to deliver the same power to the load, and twice the available voltage to tolerate the voltage drop. So for the same % drop you get away with much smaller conductors.

A 480V drive will typically cost less than a 240V drive of the same capacity.

This needs to be balanced against how much the utility will charge for a 480V service (will you have a separate monthly base change, will they charge for bringing in the transformer) and the ongoing losses in the step down transformer, and possibly needing to convert the pump motor to higher voltage.

As I see it the list of reasonable options are:

1) bring single phase primary service to the location and use a 240V VFD
2) use fat conductors to mitigate voltage drop
3) tolerate large voltage drop
4) get a 480V single phase service and use a 480V VFD with a step down transformer to supply the barn.

-Jon
 
winnie said:
IMHO that is not quite correct.

To run a 20hp motor from a single phase supply, you need to oversize the drive in order to have a large enough capacitor bank and input rectifier. However the drive is still only drawing 20hp (at full load) from the supply. So you are probably looking at 55-60A (at full load) being used by the VFD and pump.
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A 20hp 3ph 240v motor is 54a FLC.

54 * 1.73 = 93.5a Single phase amperage if we assume no losses within the drive. Fuji is listing 115a input at 1ph for their 50hp, but that drive is rated for 21.6hp, so my number is a little on the high side.
 
ppsh said:
A 20hp 3ph 240v motor is 54a FLC.

54 * 1.73 = 93.5a Single phase amperage if we assume no losses within the drive. Fuji is listing 115a input at 1ph for their 50hp, but that drive is rated for 21.6hp, so my number is a little on the high side.
Click to expand...
Don't forget to include power factor in the calculations.
 
Besoeker3 said:
Don't forget to include power factor in the calculations.
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Power factor should be fairly negligible on the drive input, but what they haven't factored in is motor efficiency.

746 x 20 = 14920 VA / 240 = 62 amps. But motor efficiency is probably going to between .85 to .95 so at full load the supply current may be ~ 73 amps.
 
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