Long feed-line calculation

[Maurice442]

Hi eveybody, I am new to this site and I really like the feedbacks of all involved. My question is: One of our customer wants to supply 240v to a remote (1200ft) location in open terrain using underground approved wiring to supply (2) 7 1/2 hp pumps located a few hundred feet apart. He has no 600v available, only a 600Amps 240v main. He wanted to buy (2) 600v to 240v transformers and connect the two 600v winding together to boost his voltage to 600v and down again to 240v to minimize line losses but I`m not sure it`s the best way to do it. I was inclined to suggest a big feedline but maybe somebody has a better idea.

Thank you all
Maurice442

 

[busbar]

You may be able to get a transformer-manufacturer’s rep to help you with comparative calculations. Don't forget that starting and running are figured separately. Make sure you understand the figures he provides, and exactly what assumptions he made in the process.

Then do your own cost comparison versus "large" conductors. Aluminum cable may be cost effective, but I would not install any without hydraulic-compressed terminations.

Fifteen horsepower is not a large load compared to standard sizes of drytype transformers.

 

[mpparent]

Personally, I think you should go w/ larger feeders rather than purchasing a transformer. You could tell your client that it's just one more thing that can fail or maintain. As dpc said, if you go aluminum, use those compression lugs along w/ some NO-OX.

Mike

 

[jbartos]

Suggestion: The larger conductors, e.g. aluminum, could be a reasonable solution as posted above, especially, if one considers excavation and the equipment rental or services cost, e.g. equipment and labor. Then, the price difference in the conductor sizes could be tolerable.

 

[SANRAMON]

I think the method to boost the voltage is better ,the current will be 23A for two pumps,and the distance (1200ft)is relevative long,you have to think about the line losses and voltage losses,the two pumps maybe not work propperly because of the voltage losses .and there maybe another choice ,the voltage you boost can be higher just depending on the prices of the transformer the line and future need of your client.

Jhone

 

[electrifire]

My preference is to use the step-up step-down transformer arrangement fot the following reasons:
1. voltage drop during motor starting, about 6 time running curent, at low power factor starting conditions may not provide adequate torque to start the motors.
2. Transformers with taps provied some insurance of obtaining adequate voltage for operations.
3. Transformers decrease the operating and starting voltage drop with smaller wire due to the higher voltage.

Larger conductors without the step-up transformers fot this small loae will probably be less expensive to install and own.

You should consider open delta connection of transformers to reduce transformer cost if these are three phase motors. This may reduce transformer cost.

 

[mpparent]

I think we'd all agree that in any case, a motor starting analysis should be done to determine if voltage drops, starting requirements, torque demands, motor start times, etc. are all within equipment tolerances.

Mike

 

[BJC]

Run 350 Aluminum with a bare neutral - just like the utility runs to your house.
Depending on which voltage drop calculator i use it comes up to about 10-12 volts at 80 amps.
Thsi would work best a soft start for the pumps and that would take care of starting currents and water hammer. Your going to need some kind of starter anyway so buy one that does some good.
I the pumps are not already purchased the Soft starts have the capability to use three phase motors - which are cheaper and more reliable than single phase.

 

[Ares]

If the motors are not purchased yet combine all of the above suggestions and buy 600V motors with soft starters.
If you are talking about three phases you may be ok with 3#6AWG
You MUST also THINK about GROUNDING that becomes a problem at this distance, adding transformer will let you ground the power at the remote location, which is vital for safety. You will safe $$ on grounding wire and have perfectly safe installation.
There is also a cost associated with sending electricity over 1200ft.
Use voltage drop calc from

http://members.rogers.com/g.cygalski/vdrop.htm

that will aid you do the math, and has built in all the data you will need

 

[jbartos]

Suggestion: This project probably needs good budgetary prices for all variations mentioned above. E.g. if one obtains a good price for an appropriately sized aluminum cable for 240V motor feeder runs, it will be the simplest solution with the minimum parts count, and minimum operation and maintenance cost down the road.

 

[AAK]

In addition to the valuable replies above, I'd like to mention that one key issue here would be if there will be any future load on the 1200Ft far away side to utilize the available 144KW at the source. If this is the case, then It's recommended to step up and then step down the voltage. Otherwise, with a 15hp pump load, a direct feed would be the best solution with due consideration to the voltage drop caused by the starting current of the motors. Good luck. Best regards,
AAK

 

[jbartos]

Suggestion to the previous posting: To bring somewhere 144kVA (600V x 240V, single phase) needs some kind of load in the middle of nowhere with the present projected load of 15HP.