Using a submersible pump on buck boost transformer

[sparkieone]

I have a well with a 2 HP single phase 240 volt submersible pump that needs to be replaced. The pump is 600 ft. down in the well. It has #8/3 cable feeding it now

I would like to replace it a 3 HP submersible pump. On a pump manufacturer's your web site they show the maximum depth for a 3 hp pump on #8 is 470 ft.

I have not been able to find the full load amps for the pump on to the pump manufacturer's web site so I used 17 amps from table 230.248 of the National Electrical Code for a 3 hp single phase motor for my calculations

The voltage drop for 17 amps motor load at 600 ft at 240v single phase is 15.4 volts exceeding the voltage drop of 3 percent allow for a branch circuit by the National Electrical Code and also 600 ft is deeper than a 3 hp pump will operate according to the pump manufacturer's web site

My question is can I use a buck and boost transformer ahead of the new controller to boost the voltage by 12 volts to 252 volts to operate the 3 hp pump on my existing #8 cable.

The pump motor is my main concern if controller components fail prematurely they can be easily replaced.

This is more of a technical question than a code question but input on both would be appreciated

Please excuse the long post

Thanks

 

[itsmoked]

I can't speak to the code but sure you can boost at the top of the cable. You may even want more that 12V Maybe 16V.

The one concern I would have is that when the 3HP starts the starting current will cause a really large voltage drop down that hole. If the pump cycles often this could be a problem.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

To size the transformer, the primary voltage should be the available voltage.
the secondary voltage should be the amount you want to boost the voltage.
The current rating of the secondary should exceed the Full load current rating of the motor.
You will find that the KVA rating of the transformer is much less than the KVA of the motor.
respectfully

 

[resqcapt19]

Can the pump produce the ~260 psi that will be needed to get the water to the surface?

 

[sparkieone]

In reply to:

Can the pump produce the ~260 psi that will be needed to get the water to the surface?

Yes the pump 10 gpm at 50 psi at 600 ft

 

[itsmoked]

You might want to rethink this!

Your pumping costs are going to 'shoot up'.

This is because your piping losses will rise and your wiring losses are rising substantially. Plus your transformer eff adds in. That voltage boost times the current is coming right out of the operating budget pif! A better solution might be a bigger tank on the surface allowing the 2HP to run longer but still provide for the requirement.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Another point to add to itsmoked's concerns. With the bigger pump, the draw-down in a deep well is often greater, resulting in a higher static head and as a result a greater dynamic head. This is hard to predict as the greater dynamic head results in less flow, less current and less line losses, but this is overcome by longer running time. The net result will probably be more losses again.
respectfully