Pump running in SF 4

[itsmoked]

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 -

http://www.flaminsystems.com

 

[btrueblood]

BigInch, you forgot halitosis.

 

[itsmoked]

Was this a new pump?

10hp down hole centrifugal pump.
New.

we still do not know the height of the water level over the pump

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

but I think we had 30 feet of water over the pump and a setting of 40 feet. That makes the TDH 10 feet plus 140 PSI plus ? If this is a municipal system or even an industrial install, it is common to see one or two spring loaded checks installed just above the pump. I think the pump is hitting the curve very well.

Yes! You have it. This is an agricultural site.

They very seldom do the exact same as the cut sheet curve says they should.

"Close" counts in horseshoes, hand granades and ... pump curves.

Yep.. This same pump was called a 90L10 when quoted and by the time it was ordered it had changed along with all the others in the series up 5 to a 95. Pure marketing BS.


So does the fact that we have to crank down the output valve to 1/5th open make sense to the throttling idea? I'm thinking it does because of the large head it's pumping against.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

Could be, or maybe the valve is enormous relative to the flow through it. Depends on the valve trim too, although if this is really an isolation valve rather than a control valve then don't expect any kind of linear relationship between valve lift and flow.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[BigInch]

If its a ball valve, it makes sense. You get little to no control until the valve is 25% open, then most of the remaining flow control action occurs between 10% and 0%

You might replace the valve with globe or a plug valve with a better control pattern. Something that will give you a more linear response, or whatever response you're looking for. There is no worse control response than from a ball valve.

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

"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.com

 

[MikeHalloran]

Try to estimate the DP across the throttling valve at the desired flow rate, compute the Cv, then remove it and replace it with an equivalent orifice.

OR

Install the equivalent orifice in series with the valve, leaving the valve full open, so random twiddlers will think the valve is already in the optimum position, and can do no harm with their random twiddling.

On that last option, I have gone so far as to place such controlling orifices in places where no one would look for one, and in places where they're very difficult to reach if found.



Mike Halloran
Pembroke Pines, FL, USA

 

[Artisi]

This is starting to sound like the "Never ending story", but that's OK as it is of interest and keeping a few of us entertained.

I had a bit of spare time and have re-read all the posts and would like to summarise the application as I see it.

I will make a couple of assumptions
1. the flow is 90GPM
2. the discharge pressure taken at some point at ground level is 140PSI
3. the pump is set at 40ft with 30 ft of water over the inlet - making the water level 10 ft below grade.
4. pump efficiency is 72%

What is unknown
1. how accurate is the flow measurement.
2. how accurate is the pressure measurement.
3. how accurate is the power measurement.
4. what is the hydraulic loss from the pump discharge to the above ground pressure measuring point.
5. what is the standing water level during pump operation.
6. is the pump performing to the publish curve.

Using the assumed Q, H and efficiency the power at the pump duty point is;

[140 x 2.311] + 10 x 90 / 3960 / 0.72 = 10.528 HP

So what does this mean, well the pump is running somewhere on its curve at an unknown flow and total head consuming approx. 10.5hp which is above the nominal rating.
In my “neck of the woods” we don’t have SF rating on electric motors however; it seems that operating above nominal is OK according to our North American colleagues. This being the case and as the motor is submerged and probably cooled sufficiently to operate in its SF it should, as pointed out by others, be OK to run.

Should you wish to reduce input power there is a couple of options, increase the head on the pump or pull the pump and reduce the impeller diameter on the final stage which will reduce the flow a little head a bit more and power at a greater ratio.

On the point of having a system resistance curve I agree with Johnny Pellin, there is no need to have this for an existing installation unless you are going to modify the system by changing the pipe work, operating conditions or changing pump speed or impeller diameter. If a pump is running smoothly, is free of cavitation, etc it is operating somewhere on its H/Q curve at a measurable flow, head and power input, it might not be where you want it to be or expect it to be – but it is somewhere on the H/Q curve.

But I guess the story will continue ---

 

[ccfowler]

If this pump has already been running for at least several hours and the motor hasn't been cooked yet, it is probably OK to just let it run.

ScottyUK is right, all that matters is motor temperature. This is apparently a pump intended for pumping water from a well with the pump being cooled by the flowing water. Do you have any specifications regarding the water temperature range for which the pump & motor was designed for continuous operation? If the water temperature is near the upper limit, then the somewhat high current may be an issue. If the water temperature is well below the upper limit, the motor is probably running cool enough to not be a source of worry.

Artisi's listing of assumptions and unknowns is important. Nothing is known with enough precision to adequately deal with the level of precision that is of concern here.

This isn't a multi-thousand horsepower boiler feed pump where the performance curves have been established by very accurate (and expensive) test bed operation of this specific pump. If this pump's performance is within 10% of the generic curves, that is about all you can expect for accuracy. Unless your instruments have been very accurately tested for their specific calibration, each is likely to be accurate to only about 4% of full scale.

If I was dealing with such a problem and was really concerned about cooking the motor, I would find some way to monitor the temperature differential across the pump and motor by attaching thermocouples in the water flow close to the pump suction and very close after the motor. I would make sure to connect them for differential indication since this would minimize instrument error problems. The potential combined instrument errors associated with simply getting two individual temperture indications can easily approach or even exceed differential temperature range that would be of interest. I would monitor the inlet water temperature with a separate primary element (RTD, thermistor, or thermocouple). Since the discharge pipe is apparently passing through a considerable depth of surrounding water, the water temperature measured above ground may not reflect the discharge water temperature leaving the pump & motor accurately enough to be meaningful. The temperature rise across the pump & motor provides a good indication of net efficiency for the combined pump & motor when combined with accurately measured flow and head.

I've seen "seriously overloaded" motors (125 - 130% of rated load) work well for years when provided with enough extra cooling.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[thewellguy]

From the onwers manual. ....motors perate with a flow rate of .5ft/sec. in water temps up to 95 F without any derating of horsepwoer." If this motor is running in north America then I would guess the water temp to be in the mid 50's to low 60 F.

 

[itsmoked]

Update:

The puzzle remains.

The pump was pulled. The motor changed from a Hitachi to a Franklen. No obvious change in the current. Same imbalance even.

The flow was restricted until FLA was achieved. That was when the 95gal/min pump was throttled clear down to 48gal/min.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ccfowler]

itsmoked,

Since changing the motor left the phase imbalance, my normal response would be to get one or more EE colleagues involved in dealing with the magical characteristics of 3-phase power. I will be the first to state my near-total ignorance of the mysteries of 3-phase power, but from encountering some messy problems in the past, my expectation is that the apparent phase imbalance may be the result of some power factor problem being induced by something other than this motor. Something else nearby (electrically) is probably introducing the problem that you are seeing at the subject motor. There may even be some goofy harmonics in play.

In situations like these, I can't help recalling a professor's remark many years ago that "the most dependable electric motor is a Detroit Diesel 6-71 with an air starter and a large fuel tank." No poly-phase power issues involved!

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[jonr12]

My book shows 32.2 amps at SF Load, your average is 32. Nearly all submersibles run in the service factor. If you rolled the wires and the amp draw stayed the same, the problem is not down hole. I don’t think the amp draw of the pump/motor is too high. I think the unbalance is the only problem. Lots of submersibles run with more unbalance than that. You could throttle a little until the high leg is down to 32.2, but I don’t think that is necessary.

 

[1gibson]

Might be stating the obvious, but if the motor is overloaded then the slip will increase, and you will end up with a speed reduction.

I see your curve is rated 3450 rpm (3600 nominal) which is a pretty good amount of slip to begin with. Get it into the SF and I can see losing another 10-20 rpm, which will show up on the pump curve as below rated.

 

[Artisi]

This is starting to sound like the kid's nursery song, "The wheels on the bus go round and round all day long ___ etc"

You have changed motors and still have the same result, if you don't want to or can't run into the SF then change the pump duty or change the pump.
Long winded discussions and wishful thinking will never reduce the power input for this application as it seems fairly obvious that the flow / head/ efficiency equals more than 10HP as has already been shown.

 

[BigInch]

Red herring trawler needed for extended duty periods.

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

"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.com

 

[tr1ntx]

itsmoked:

Forgive me for weighing in here, I read this post to see if I might learn something or be reminded of something I've forgotten from years ago. It seems like there needs to be a benevolent buttinsky in this conversation. Perhaps one person's choice of words doesn't sink in with someone else (a problem I have all the time).

Your last comment was "the puzzle remains". No, it doesn't.

You had posted: "It's FLA is 29A. The motor is drawing 31A, 31A, 34.5A" Others have posted that the required HP for the flow conditions you give is 10.5~. Your motor's 29A FLA is for operating at 10HP. It is actually putting out 10.5~HP so it's using more than 29A to do so.

"What's up with that?" you might ask. You've already pointed out the marketing BS from the mfg, and others have spelled out the BS in the downhole water pump industry regarding their stated performance. You're apparently able to get the flow output you need, and if, as someone else stated, the motor is not running hot, don't worry about it, it's close enough. I've forgotten what little I once knew about electric motor intricacies, but they often operate slightly above their rated HP. Temperature is the hard limit, melt the insulation and you're done.