Vertical 300hp Well Pump Motor

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Sahib

Sahib

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India
ptonsparky said:
I would imagine the designers know about SF, but it is not considered or even relevant to the end user for this small of system. Some one else has taken responsibility.
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Big or small, pumps obey affinity laws one of which is input power increases with increase in RPM.
 
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GoldDigger

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Sahib said:
Big or small, pumps obey affinity laws one of which is input power increases with increase in RPM.
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Power only increases with cube of speed if you are not limiting the flow in a pressure independent way. With a centrifugal type pump the power essentially goes as the square of the speed (to accelerate the fluid mass to linear speed at edge of impeller) times the flow rate.
Plus frictional losses, of course.

Sent from my XT1585 using Tapatalk
 
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adamscb

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Update on this VFD, it's been installed and it ran just fine uncoupled. However, we coupled it up and we're running into issues. It seems to hover at around 16-20 Hz, but I have the drive set up to only run at 60 Hz (for now of course). At first I thought the acceleration time was too high, so I changed it from 10 seconds to 2.5, but the issue still persists. I believe something is wrong with the pump, either it wasn't coupled properly or there's some other issues. We measured the current on the line and load sides of the VFD. The currents on the line side were in the 20's, and were in the mid 200's on the load side (300 hp motor). Does anyone have any ideas?
 
Jraef

Jraef

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adamscb said:
... The currents on the line side were in the 20's, and were in the mid 200's on the load side (300 hp motor). Does anyone have any ideas?
Click to expand...
That right there is ONLY possible if the VFD is set up to reduce the Hz as a response to a Current Limit setting. But why you would have a CL setting in the "200s" for a 300HP pump is curious.

Also, the math isn't working out correctly. At 20hz (1/3 speed) the 300HP pump is only going to be about 10HP worth of load, which would track at around 20A at the most on the input side, so that part works. But also at 20Hz the voltage should be at around 150V, so 10HP output @ 150V should be demanding MAYBE around 60A on the load side of the VFD. Most likely this is just measurement error in that you have a meter incapable of properly interpreting the complex waveform of the VFD output. You have multiple issues going on here, but I would not trust what any hand-held meter is telling you. What does the VFD display tell you?
 
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adamscb

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Jraef said:
That right there is ONLY possible if the VFD is set up to reduce the Hz as a response to a Current Limit setting. But why you would have a CL setting in the "200s" for a 300HP pump is curious.

Also, the math isn't working out correctly. At 20hz (1/3 speed) the 300HP pump is only going to be about 10HP worth of load, which would track at around 20A at the most on the input side, so that part works. But also at 20Hz the voltage should be at around 150V, so 10HP output @ 150V should be demanding MAYBE around 60A on the load side of the VFD. Most likely this is just measurement error in that you have a meter incapable of properly interpreting the complex waveform of the VFD output. You have multiple issues going on here, but I would not trust what any hand-held meter is telling you. What does the VFD display tell you?
Click to expand...

It says several hundred amps as well I believe, maybe even in the high 200's / low 300's. And I didn't program a Current Limit setting in the drive when commissioning, but I can check just to make sure. This one's got me stumped.
 
M

MattS87

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Yakima, WA
adamscb said:
It says several hundred amps as well I believe, maybe even in the high 200's / low 300's. And I didn't program a Current Limit setting in the drive when commissioning, but I can check just to make sure. This one's got me stumped.
Click to expand...

Might have missed it, but what model is the drive? IIRC the Toshiba G9's are defaulted to current limit setting.
Does the output stay a constant frequency or "hunt"?
You are using 4-20mA to control the drive correct? What are you measuring on that signal?
 
I

Ingenieur

Senior Member
Location
Earth
adamscb said:
Update on this VFD, it's been installed and it ran just fine uncoupled. However, we coupled it up and we're running into issues. It seems to hover at around 16-20 Hz, but I have the drive set up to only run at 60 Hz (for now of course). At first I thought the acceleration time was too high, so I changed it from 10 seconds to 2.5, but the issue still persists. I believe something is wrong with the pump, either it wasn't coupled properly or there's some other issues. We measured the current on the line and load sides of the VFD. The currents on the line side were in the 20's, and were in the mid 200's on the load side (300 hp motor). Does anyone have any ideas?
Click to expand...


did you verify pump rotation?

you measured 20 A into the drive and 250 out?
converted to power 17 kva in = ~ 17 kva so v out ~40 vac
about 17 HP
something does not add up
fla 350 A range

so the pump controls/modulates around 15-20 Hz to maintain the pressure setpoint?
what is the pressure at 20 Hz? 60 Hz?
 
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A

adamscb

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USA
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EE
At this point in the project I'm just trying to get the motor to run and being able to change the frequency from the front HIM keypad. The external 4-20mA signal for the PID is still in progress. When the motor was uncoupled it ran fine and I was able to vary the frequency from the HIM. After we coupled it up, the motor runs in the 16-20 Hz range and will not change frequency when it's in manual, and a speed command change is given from the front HIM keypad. The model is an Allen Bradley PowerFlex 753. What is also pretty odd is the status always says "Accelerating" and doesn't change to "Running". To me that means that the VFD is trying to get it to ramp up to 60 Hz, but something is preventing that.
 
kwired

kwired

Electron manager
Location
NE Nebraska
adamscb said:
At this point in the project I'm just trying to get the motor to run and being able to change the frequency from the front HIM keypad. The external 4-20mA signal for the PID is still in progress. When the motor was uncoupled it ran fine and I was able to vary the frequency from the HIM. After we coupled it up, the motor runs in the 16-20 Hz range and will not change frequency when it's in manual, and a speed command change is given from the front HIM keypad. The model is an Allen Bradley PowerFlex 753. What is also pretty odd is the status always says "Accelerating" and doesn't change to "Running". To me that means that the VFD is trying to get it to ramp up to 60 Hz, but something is preventing that.
Click to expand...

Make sure there is no max speed setting parameter set to only 20 Hz. Such setting often means the drive won't give a higher output regardless of what input frequency reference may be.

I have used min speed setting parameter more often but does about same thing on the other end of operating range - set for min output of 30hz only time you see less is during starting/stopping accel/decel, otherwise give it an input signal that equates to 20 Hz output and it will still run at 30 Hz.
 
I

Ingenieur

Senior Member
Location
Earth
adamscb said:
At this point in the project I'm just trying to get the motor to run and being able to change the frequency from the front HIM keypad. The external 4-20mA signal for the PID is still in progress. When the motor was uncoupled it ran fine and I was able to vary the frequency from the HIM. After we coupled it up, the motor runs in the 16-20 Hz range and will not change frequency when it's in manual, and a speed command change is given from the front HIM keypad. The model is an Allen Bradley PowerFlex 753. What is also pretty odd is the status always says "Accelerating" and doesn't change to "Running". To me that means that the VFD is trying to get it to ramp up to 60 Hz, but something is preventing that.
Click to expand...


it ramped up to 60 Hz motor alone?
but coupled to the pump stops at ~ 20?

did you measure output voltage with pump coupled at 20 Hz?

definitely sounds like a set-up issue
most mfgs will give a quick set-up procedure for a pump, fan, etc
go thru each parameter
250 A out at 40 v is not right

I bet if on site a guy like Jaref could sort it in a few minutes
 
kwired

kwired

Electron manager
Location
NE Nebraska
Ingenieur said:
it ramped up to 60 Hz motor alone?
but coupled to the pump stops at ~ 20?

did you messure output voltage with pump coupled at 20 Hz?

definitely sounds likeva set-up issue
most mfgs will give a quick set-up procedure for a pump, fan, etc
go thru each parameter

I bet if on site a guy like Jaref could sort it in a few minutes
Click to expand...

I forgot about him mentioning running it uncoupled- max speed setting probably not the problem if it ramped up to 60Hz uncoupled.
 
Jraef

Jraef

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As I said, it’s classic current limit /overload behavior. The default setting is that if it approaches either the CL or hits the OL curve, it backs off on the increase in output frequency in order to shed loading. So why is a centrifugal pump so loaded at such a low speed? My guess is a mechanical binding problem. This is acting as it it is a locked rotor. On verticals, there is often a back-spin ratchet on the top. Are you sure that’s on correctly (or the rotation is correct)?
 
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I

Ingenieur

Senior Member
Location
Earth
but as was noted
if input v=480 and i=20 that is only 20 hp (motor is 300)
output v=? and i=250 (fla~350), but if s in = s out then v out ~ 40

v/hz ~ 40/(15 to 20) ~ 2.5

if out is 40 v and i 250 a then could be an ol since z ~ 0.16 Ohm
very unstable, almost a sc or winding Z

since the issue started when the pump was connect a mech issue is a good place to start
close iso valves and see if it spins freely by hand
 
M

milldrone

Member
Location
Northern California
adamscb said:
I believe something is wrong with the pump, either it wasn't coupled properly or there's some other issues.
Click to expand...

Is the pump shaft rotating? Someone else asked if it was rotating backwards against the anti back rotation device.

adamscb said:
We measured the current on the line and load sides of the VFD. The currents on the line side were in the 20's, and were in the mid 200's on the load side
Click to expand...

When this condition is occurring, what does the HIM display say the output voltage is?

Jraef said:
That right there is ONLY possible if the VFD is set up to reduce the Hz as a response to a Current Limit setting. But why you would have a CL setting in the "200s" for a 300HP pump is curious.

Also, the math isn't working out correctly. At 20hz (1/3 speed) the 300HP pump is only going to be about 10HP worth of load, which would track at around 20A at the most on the input side, so that part works. But also at 20Hz the voltage should be at around 150V, so 10HP output @ 150V should be demanding MAYBE around 60A on the load side of the VFD. Most likely this is just measurement error in that you have a meter incapable of properly interpreting the complex waveform of the VFD output. You have multiple issues going on here, but I would not trust what any hand-held meter is telling you. What does the VFD display tell you?
Click to expand...

Ingenieur said:
did you verify pump rotation?

you measured 20 A into the drive and 250 out?
converted to power 17 kva in = ~ 17 kva so v out ~40 vac
about 17 HP
something does not add up
Click to expand...

Ingenieur said:
it ramped up to 60 Hz motor alone?
but coupled to the pump stops at ~ 20?

did you measure output voltage with pump coupled at 20 Hz?

definitely sounds like a set-up issue
most mfgs will give a quick set-up procedure for a pump, fan, etc
go thru each parameter
250 A out at 40 v is not right
Click to expand...

What is P35 set to?
What is P65 set to?

Jraef said:
As I said, it’s classic current limit /overload behavior. The default setting is that if it approaches either the CL or hits the OL curve, it backs off on the increase in output frequency in order to shed loading. So why is a centrifugal pump so loaded at such a low speed? My guess is a mechanical binding problem. This is acting as it it is a locked rotor. On verticals, there is often a back-spin ratchet on the top. Are you sure that’s on correctly (or the rotation is correct)?
Click to expand...

I have seen similar behavior when the volts/ Hz is not near 7.6 volts to the Hz. Using Ingenieur's calculation the output voltage when the drive is 16/20 hz is somewhere near 40 volts. But as Jraef indicated it should be near 150 volts. Also I have seen the drive attempt to output 20 hz when the voltage was around 40 with a locked rotor. So please double check for correct rotation (not against the backspin ratchet). Another possibility is that after coupling, the impeller is "binding" against the bowls after coupling the two shafts. Either way I'm suspicious of the V/Hz curve.
 
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