VFDs for Water Well? 1

[CuriousElectron]

Hello,

What are the main reasons why Variable frequenc drives would be used for ~300 HP motors at underground water wells? Two things come to mind:
1. Regulating flow in the discharge line.
2. Tight control deadband. Using variable frequency drives would prevent frequent pump start/stops if floats were implemented on a tight deadband.

Please share your experience.

Thanks,
EE

 

[itsmoked]

I never see them for regulating flow in the discharge though I guess you could.

I definitely see them in not overdrawing a well which at 300HP would be a large problem.

Depending on water usage you could eliminate cycling.

Completely prevent large power line disturbances caused by large motor starting.

Prevent starting surges.

Reduce abuse to foot valves (check valves).

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LittleInch]

a soft start system would reduce most start problems.

~The issue of VFDs is that for systems where the fixed head i.e. the depth you're bring water up, is a large part (50%+) of the required head of the pump the variability in frequency is quite low as it doesn't take much for the pump to be unable to produce the required head.

Centrifugal pump head varies as a square of the rotational speed. hence reduce frequency by 25%, head reduces by 43%.

Far better to run a fixed speed pump and use a control valve to very flow.

Also VFDs consume power - sometimes close to 8%. That's a lot of heat going nowhere.

tight control is possible in many other ways as well.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

We used them often of deep wells (both water and oil) because pumps were deliberately oversized for the well capacity.
The VFD was used strictly to not draw the well down below a specified level.

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P.E. Metallurgy, Plymouth Tube

 

[77JQX]

VFDs can have a place in matching pumping rates to well conditions. As you are probably aware, well capacity can change for many reasons, including interference from nearby wells, reservoir depletion, recharge conditions, etc. I have done the energy savings calculations for several municipal water wells comparing VFDs to control valves in our actual operating conditions, and VFDs generally have slightly lower energy usage when compared to control valves (in our operating conditions). However, I feel control valves are more reliable, and certainly can be repaired more quickly (and with a lower level of talent required) that a VFD. Because of reliability and maintainability, I prefer controls valves to VFDs for regulating well pumping rates.

 

[Compositepro]

Also, starting a pump DOL when the pipe is empty could lead to tripping breakers because of a high initial flow rate. The starting torque on the well pipe would also be high.

 

[CuriousElectron]

Thank you for all who replied!

Is service continuity important for water wells?

Thanks,
EE