Vertical 300hp Well Pump Motor

[Sahib]

Still the possibility of defective drive may not be ruled out because it is perpetually on start mode without shutting down under load.

What is also pretty odd is the status always says "Accelerating" and doesn't change to "Running".

 

[adamscb]

Pump was stuck...VFD acts like it should now. Still being able to run while under pretty much locked rotor conditions is incredible, in my opinion.

 

[Jraef]

:thumbsup::thumbsup:
Thanks for reporting back!

 

[Ingenieur]

Pump was stuck...VFD acts like it should now. Still being able to run while under pretty much locked rotor conditions is incredible, in my opinion.

what was the issue?
an object jammed in it?
etc

 

[ptonsparky]

what was the issue?
an object jammed in it?
etc

Yes, how?

 

[Besoeker]

Pump was stuck...VFD acts like it should now. Still being able to run while under pretty much locked rotor conditions is incredible, in my opinion.

Excellent that you got a fix...........)
One thing surprises me a bit. With a centrifugal load is the the motor cooling fan is normally shaft driven. With a locked rotor, you would lose that cooling altogether.
Maybe you didn't run it for very long...

 

[adamscb]

The mechanic seemed pretty reluctant to tell me, all I know is that the shaft wouldn't turn by hand. They re-coupled it and were able to turn it by hand then.

And as far as running it when it was stuck, we only ran it for maybe 10 seconds at a time. We knew something was wrong and shut it down immediately. I'm guessing if it was ran for an extended amount of time it would have tripped eventually.

 

[Besoeker]

The mechanic seemed pretty reluctant to tell me, all I know is that the shaft wouldn't turn by hand. They re-coupled it and were able to turn it by hand then.

And as far as running it when it was stuck, we only ran it for maybe 10 seconds at a time. We knew something was wrong and shut it down immediately. I'm guessing if it was ran for an extended amount of time it would have tripped eventually.

Or cooked...

 

[adamscb]

The default setting of that particular drive is for it to attempt to stay running by driving down the frequency and lowering the current limit. If the user did not change that setting (and it sounds probable), that would completely justify what he is seeing. So really, what we DON'T know is why it is a perpetual state of overload. It cannot be that the motor is overloaded from flow, there is none. So it leaves a mechanical problem or a defective drive, and he has run the motor uncoupled from the pump with no issue. I'm going with a mechanical problem here.

Jraef, thanks for this post, you were spot on with this. For ease of troubleshooting, do you think that this parameter should be changed to "Disabled", so something is forced to trip? I see pro's/con's for either way, either letting it trip out or reducing Hz/current to protect the drive, your thoughts?

 

[ptonsparky]

Jraef, thanks for this post, you were spot on with this. For ease of troubleshooting, do you think that this parameter should be changed to "Disabled", so something is forced to trip? In my opinion I think it should be left the way it is to protect the drive, but I'm not our backshift electricians working at 2am.

How often is this likely to occur?

 

[Jraef]

Jraef, thanks for this post, you were spot on with this. For ease of troubleshooting, do you think that this parameter should be changed to "Disabled", so something is forced to trip? I see pro's/con's for either way, either letting it trip out or reducing Hz/current to protect the drive, your thoughts?

If it's an unmanned pump station, I would leave it at the default setting. Once it is up and running, a jammed shaft is unlikely now. That sort of thing generally happens at commissioning. Once it's known to be good to go, tripping at a critical time might present other critical issues, compared to running as well as it possibly can. If you are worried about it, you can set up monitoring of this function top let operators / SCADA system know it is happening.

One thing I like to recommend implementing is to monitor kW and flow and comparing them constantly. If there is a significant divergence in the expected kW/flow ratio, you signal the operators that preventative maintenance is required on the pump because the only thing that should cause that to vary would be mechanical problems. kW/flow ratio drops, there is a blockage, kW/flow ratio rises, bearings are bad, kW/flow ratio spikes, open channel flow (broken pipe) etc. etc.

 

[Ingenieur]

The mechanic seemed pretty reluctant to tell me, all I know is that the shaft wouldn't turn by hand. They re-coupled it and were able to turn it by hand then.

And as far as running it when it was stuck, we only ran it for maybe 10 seconds at a time. We knew something was wrong and shut it down immediately. I'm guessing if it was ran for an extended amount of time it would have tripped eventually.

poor mechanic
how are you to learn from this?
if you mess up own it

do you have a picture of the pump type? google pic is fine
were you there when he did the fix?

 

[adamscb]

poor mechanic
how are you to learn from this?
if you mess up own it

do you have a picture of the pump type? google pic is fine
were you there when he did the fix?

I don't have a picture of the pump type...not knowledgeable enough in pumps...all I know is it's a vertical centrifugal.
And no I wasn't there...all I know is that it was locked up pretty bad.

 

[Bigjabe]

we used vfd's, to limit inrush current, but the sewage pumps always ran at full speed
they were not much more expensive than a SS, but offered more flexibility
our utility REQUIRED anything over 25 HP to have a vfd (or SS), even for constant speed application

best to include the whole post rather than selectively edit and highlight to demean someone
Ingenieur

is the pumping rate constant? head and gpm?
is the drive modulated or running at a constant speed once started?





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everything over 25HP on VFD?! My goodness that could be amazingly expensive... and did you have any harmonics issues?

 

[Ingenieur]

everything over 25HP on VFD?! My goodness that could be amazingly expensive... and did you have any harmonics issues?

usually these were applications with only a few motors that were a small percentage of the total load