Impact of Replacing a 37 kW Motor with a 45 kW Motor in a Deep Bore Well Pump Application

You need to check out a lot of things...is the motor failing? overheating? must know the cause...

https://franklinwater.eu/media/467529/aid-i-2019-gb.pdf

I would question who recommended the VFD and why...was/is the motor designed for VFD use?

https://www.lmpforum.com/forum/topic/764-vfds-on-submersible-pumps/

https://electrical-junction.com/blog/post/dol-starters-vs-vfds-which-one-is-the-best-choice-for-your-motor-control-needs

..."For a borehole pump, it's generally better to choose a pump with a VFD (Variable Frequency Drive) as it allows for more efficient operation by adjusting the pump speed based on water demand, leading to significant energy savings compared to a pump without a VFD (inverter) which runs at a constant speed regardless of need; essentially, a VFD provides better control over your water flow and reduces unnecessary energy consumption. "...

Response: Detailed Analysis on Expected Impact of Replacing 37 kW Motor with 45 kW Motor

After further examination, here’s what I’ve calculated regarding the potential impact of replacing Motor-A (37 kW) with Motor-B (45 kW), considering the current operating load and motor specifications:

• Current Motor (Motor-A) Analysis:
• Electrical Power: 40.5 kW
• Mechanical Power: 32.97 kW
• Shaft Speed: 2860 RPM
• Load Torque: 110.08 N·m
• Proposed Replacement Motor (Motor-B) Analysis:
• With Motor-B, there is a slight speed increase from 2860 RPM to 2865 RPM. According to affinity laws, this speed change results in a small torque adjustment to 110.46 N·m, which yields the following:
• Shaft Speed: 2865 RPM
• Torque: 110.46 N·m
• Mechanical Power: 33.14 kW
• Electrical Power: 40.32 kW

Assuming that Motor-B operates at approximately 75% of its rated load, the efficiency improves slightly to 82.2% (from data sheet values).

Key Takeaway:
Despite the increased motor rating, the electrical load is expected to remain close to 40.5 kW, with minor improvements in efficiency and a negligible RPM change. These factors could lead to modest performance benefits, though the overall impact on load should be minimal.

Well the proof is in the pudding, and the devil is in the details...and sometimes the devil eats your pudding...

Aghvel,

It looks like a good job. If you should have the opportunity to occasionally reduce the frequency and power of the motor, that will be a real hit.

Hello,

May I suggest that you are only looking at half the situation.

The pump is also part of the equation and those motor speeds would seem to be the no-load RPM on the 50 Hz supply.

The RPM at the dynamic load of the hydraulic system is also required. Pump suppliers provide published operating curves for pump/motor combinations giving L/sec or Gal/min curves for motor/head combinations for each impeller option.

Then you need the head curve based on flow. Static head plus calculated friction losses at each flow rate. This is specific to your individual pipework design as built.

Where those curves intersect will predict your new operating situation.

For the costs involved with a 45kW motor, it's well worth the cost to involve the pump manufacturer in the discussions.

Also, caution. If the new situation is higher flow, then does that exceed the well production capacity? Pumps don't like to run dry.

I am presuming that your extraction rates are not regulated/licenced like the wells that I deal with, where we monitor draw down on the aquifer during extraction.

"The pump is also part of the equation and those motor speeds would seem to be the no-load RPM on the 50 Hz supply."

No, those speeds are typical full-load speeds. At no-load the speed would be as close to 3000 rpm as makes no difference.

But some more points. OP hasn't said whether the pump performance has been OK, and if so why he's thinking about changing the motor?

Also deep well borehole pumps are an integral unit. It's unlikely the motor could be removed and an uprated one fitted, and why would it be considered? Perhaps the idea is to replace the complete thing, identical apart from the motor.

You never mention if the flow rate and pressure is low or sufficient. That tells me you're only concentrating on the motor, which could be a mistake.

I'm an electrical-instrumentation, not a mechanical, engineer though I self-studied on pump stuff because people kept blaming the motor and the controls every time the pump failed.

The pump has the recommended motor size on its plate. If your motor is smaller than what the pump needs, then you'll get the problem you're experiencing. If your pump and motor are matched but the motor is drawing more power than expected, then your pump and motor are likely undersized for the job.

If you increase the motor power without checking the pump power requirement, you could be overstressing the pump and you'll be damaging that pump sometime in the future.

regards,

Vulcan

If the pump will be running at full speed all the time no need for a VFD for soft start. A VFD brings a lot of problems.Bearings on the pump and motor must have grounding rings installed to prevent arching of the balls and pitting resulting on premature bearing failure,as well as inducing noise on other equipment and controls.How deep and what type of pumping system do you have? "Deep" is a relative term.

After checking out your link,it seems to be a very well designed pump and already designed for VFD,which is good,especially if you have frequent cycling of the pump.However,the system wiring may need to be upgraded to handle the extra current required.This is in addition to the recommendations provided by others.

The running current would be unchanged if the electrical power stays constant at 40.5 kW. If it were started DOL the starting current would be higher, but unlikely to mean wiring upgrade. And with VFD start not an issue IMO.

The key thing is to match the pump and motor characteristic curve with the piping characteristic curve in terms of lift and flowrate, for it is the product of these two things that will determine the power required. If the <...37kW motor...> is already drawing <...40.5kW...> then it is not long for this world. Is there scope to turn the flowrate down a bit (for that will bring the motor back into its operating range)? To do so would mean that the <...45kW motor...> is not needed.

Nothing has been mentioned about the motor cabling and upstream supply. More power means more amps, which means more cable heating, which means shorter lifespan.

How critical is this application?

40.5kW is the electrical input power. At rated output 37kW and efficiency 81.4% electrical power = 45.5kW

We still need to know whether it's working OK now, and why he's thinking about changing the motor.

So, what did the motor manufacturer and the pump manufacturer both say over the telephone?

1. No it wont.

2. You will not be able to measure the difference.

3. This application is quite normal

The change of speed is of little consequence (I doubt that you would be able to measure the changes in the field). Flow (Q) will be increase by 1.0017 times present Q. Head by 1.0034 present H and Power will increase by 1.025 times present power.

I can see no mechanical or flow behaviour problems.

Also don't see any electrical problems as the load remains essentially the same.