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Pump running in SF 4

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itsmoked

itsmoked

Electrical
Feb 18, 2005
19,114
10hp down hole centrifugal pump.
New.
Set at about 70 feet.
Pressure measured and found at center of BEP.
Rated flow 90g/min.
Actual measured flow 85g/min.
230V 3ph.
Supply voltage 241V - all phases within 0.5V
Wire size from measured point to pump 6AWG.
Rated current 30A
Actual current [red]31A,31A,34A[/red]

Why?


Keith Cress
kcress -
 
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So far the "real" data (flowrate and 70 ft head) only accounts for a hydraulic horsepower load of 1.5 HP. I assume you have more than 70 ft head on that pump. I'd expect to see a differential head of something like 350 ft, or 150 psi.

"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.

"Being GREEN isn't easy." Kermit[frog]
 
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Is there a pressure reading available at the discharge?

=====================================
(2B)+(2B)' ?
 
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Also, is there possibility that some flow is discharged upstream of the point where flow is measured.

=====================================
(2B)+(2B)' ?
 
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Some additional hydraulic and installation data might help with getting a meaningful answer.
 
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I have problems with that.. The FLA on a motor's plate already includes that. If the load tapered off a little the PF may drop a little increasing the "measured" current. But, increasing it to more than the FLA? I'm thinking no.

Keith Cress
kcress -
 
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For a given amount of work done by an induction motor, high current is often a symptom of low voltage. I see you've already raised the topsde voltage to compensate for cable drop. Any possibility that the pump manufacturer already accounted for likely cable volt-drop and this is really wound as (say) a 210V motor in the knowledge that the topside voltage will be 230V? In that case you might be saturating the core iron. IIRC submersibles usually aren't in the slightest bit generous with their core designs because they need to minimise the motor diameter, so a slight over-volatge would lead you into saturation quite quickly.


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I am with BigInch on this. With the given condition, assuming 50% pump efficiency (for multistage bore pump), you get about 1.5 HP.

Did you check the direction of rotation? Debris?

 
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Once again it is somewhat meaningless to examine a pump performance curve without taking into account the relevant system curve. As already noticed by others with data passed on to us one would expect a hydraulic horsepower load of 1.5 HP. Your pump seems to be overrated.
Could you post the pump performance curve and the system curve?
 
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This seems to come up a lot and I would like to understand the use of the system curve better. If I am sizing a pump for a service with no controls, I need to know the system curve to estimate where the pump will run. If I have a control system that controls the pump to a constant pressure or flow, I need to know the system curve in order to design the control valve. But, once the system is built and the pump is running, I have almost never seen any need for the system curve. Once I have the ability to directly measure the suction and discharge pressure, the pump operating point is known. I know the flow and I know the head. The pressure drop in the downstream piping does nothing to change either of these. Please help me understand the value of the system curve in this situation.

For the particular question, I think most of the important questions have already been asked. The possibilities that occur to me are these:

Low voltage
Incorrect motor speed (50 Hz motor running in 60 Hz system)
Incorrect rotation
Incorrect pump (too many stages or wrong impeller pattern)
Alternate flow path.
Bad data.

I would suggest that you very carefully verify the data you are using for this analysis. The flow meter could be set up incorrectly or not calibrated. The pressure readings could be in error. The depth down to the pump could be different that you were told.


Johnny Pellin
 
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Just wondering how the data reported by the OP could match with a 10 hp pump running close to BEP
 
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In looking at the data, I see one potential problem. He states that the pump is "set at about 70 feet." I would interpret this to mean that the pump is 70 feet down the hole. The pressure at the surface is probably not zero. If it is pumping into any back-pressure, then this needs to be added to the pump head. So, if this was a well pump in my plant, the pump might be down 70 feet with 100 psi pressure at the surface. The head pressure that the pump needs to overcome would be about 300 feet. Pumping 85 gpm at 300 feet of head with 70 percent efficiency would calculate out to 9.1 BHP. This would start to look a bit more reasonable for running FLA on the 10 HP motor.

Johnny Pellin
 
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That's exactly why we asked for a system curve, to know the discharge pressure at all flowrates, not just at BEP. You can eliminate the guesswork 100 psig, which could just as easily be as low as 35 psig, or again just as easily higher than 100. Without it, we're just guessing and our time just as easily wasted.

"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.

"Being GREEN isn't easy." Kermit[frog]
 
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I have interpreted the 70 ft as a total differential head, but if that number refers to a suction lift…..
Well I think a system curve could dispel some doubts and eliminate the need of assumptions.
 
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I suppose my perspective on system curves may be particular to my industry. But, in the best example I can see in my plant that relates to the original question, a system curve is both impossible and unnecessary. Our well pumps pump into headers that may be fed from many sources and deliver water to many users. The header is pressure controlled with one or more pumps that are on some sort or pressure control. There may be some variability in the pressure of the header. But, it can't be put into the form of a system curve. I could spend a month trying to model the system with all combinations of contributors and users.

But, as I said, the system curve for my well application would also be unnecessary. If the header is pressure controlled to run between 95 and 105 psi, then I know all I need to know. I have almost never seen an application in my plant where a system curve is important except at original design or redesign. But, with vary rare exception, all of our streams are flow controlled. And, when I need to evaluate pump performance, it is done at discrete points in time where I only need to know the suction conditions, discharge conditions, product properties and flow rate. If I had a problem that might require evaluating a system curve, it would probably be a situation where the control valve reached 100% and the flow controller couldn't reach set-point. Then I would need a system curve (or at least a couple of points on a system curve) to determine if I can achieve the target flow rate best by making changes to the pump, control valve or system.


Johnny Pellin
 
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JJ If you have a disch pressure control, you only have one backpressure for all flowrates; your system curve is a flat line, so its pretty easy to guess how that system will react to any flowrate you want to put into it; output is a flat line; same pressure for all flowrates. Most systems have a more complex requirements, such as various discharge pressures for running different products in a pipeline running up and over a large hill. Diesel pressure will be much greater than gasoline, given the same flowrate. If you ran it on a flat backpressure, your flowrate would slow down when pumping diesel and increase when flowing gasoline. And no matter what the product, before you can design that control valve, you must know what head loss it must supply at any flowrate that is possible to get through that system. Then, and only then, will you will be able to correctly select that valve. After you select it and run the system as you apperantly do, the output from your pressure controled "black box" is always a flat line, but somebody had to design what went into the inside of that "black box" using a system curve, so they could get the valve parameters set correctly to give you that flatline pressure output at all flowrates. Using an electrical analogy, without that system curve, you'd have no idea what kind of variable resistor you'd need to put inside that black box to get the same voltage at all currents. Afterward, as long as that resistor didn't burn out, I'd imagine you could be eternally happy as a clam continually watching your 12VDC flatline output coming from that box.

"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.

"Being GREEN isn't easy." Kermit[frog]
 
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Alright'y folks, more info.

The pump is a Gould 95L10.
Here's the curves and everything else:


More data with some corrections:
The voltage is 242~243V across all the phases.
The motor is a Hitachi.
It's FLA is 29A.
The motor is drawing 31A, 31A, 34.5A
All leads were rolled with no change.
Open delta. 12kV/240V - two transformers on the pole running ONLY this pump.

Correction: Pump set at 40 Feet with 30 feet of water above its intake.

Static pressure is about 105psi with pump off.
Gauge at well head reads 140psi.
Flow checked with two flow meters. 85~90gpm

An identical well a hundred yards away feeds the same main. They both ultimately feed a tank way up on a hill.

What say you now?
And thanks folks.



Keith Cress
kcress -
 
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