Pump problem

[operatorjoe]

First off I know nothing about electrical engineering so please (yes and no) answers or explain as if I were 5 years old.
I work at a water pumping facility that has had a lot of trouble with 1 pump that has been offline for 3+ years.
Basic information 1. 200HP 20MGD low lift submersible mid-level voltage 4160v. This pump has been rebuilt 3 times in 2 years. first 2 times when reinstalled it would not even start. the 3rd time it started and ran 5 days was shut down but then failed on restart. This pump is a small pump for this facility (the rest are 400 hp). piping and wiring to this pump are set up for easy upgrade to 400 hp pump. (wiring and starter is same as other 400hp pumps) Distance from motor control (starters) to pump is 1200+ feet. Question Could the 1200 feet of wire between starter and pump be contributing to this ongoing problem? I have seen problems on lower voltage VFD systems where distance caused failure. These pumps are not VFD and are relatively new 2002-2005. I will verify any hazy or inconsistent facts here that come into question. Thank you!

 

[waross]

Are the other pumps at long distances also?
What gauge size wire is running to the pump?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Current on a 200HP 4160V motor is so low, it's hard to imagine there being a significant voltage drop, especially if everything is sized for a motor twice as big. Has anyone meggered the motor leads? I'd be suspicious of cable insulation breakdown.

But what do you mean by "failed to start"? Given that you are thinking voltage drop, I'm suspecting that it stalls? That's why I'd think in terms of failing conductors.



"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[GroovyGuy]

Hey Joe
Voltage-drop (on the motor feeder) will not be an issue, it's only 1200ft. This is nothing for a 4kV motor.
What were the causes of the previous failures? (ie stator, rotor, bearing)
What was the current (at time of failure)? Any chance that the motor was overloaded (although the protective relay should have picked up on that condition).
I think we can assume that the 3-voltages are balanced, else you would be having difficulties with the other 400hp motors). Correct?
GG

I am forever learning and changing.
W.E. Deming

 

[operatorjoe]

I am still trying to find the size of wire inside armored cable,
Difference in distance of travel for wire Probably no more than 50 feet.
Failure for last repair was at point of connection at motor, Could have been bad connection/insulation for install.
Thanks for your input. I hoped that if there were some glaring problems this forum would be a good place to start search.

 

[Artisi]

You really need a lot more technical description, failed to start / restart - why? - was the cable continuity checked, are all 3 phases balanced, was or did the pump seize, did overloads trip, is the pump running the correct direction, what was the mode of failure for "Failure for last repair was at point of connection at motor, Could have been bad connection/insulation for install of failure" doesn't tell us anything -- etc etc.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[jraef]

400HP @ 4160V is going to be about 55A max, so if the wire is #6 or better you are fine. I've never seen 5kV rated cable sold as less than #6. it's not Voltage Drop on the wire based on size.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Artisi]

operatorjoe:
You would be better off with this is the pump engineering forum, wider range of people understanding pumps who may well not see this post in this forum.
You can ask management to remove this post and you could repost it. Click on the red flag (report) and ask.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[waross]

You may have an issue with workmanship or termination methods.
This is the correct forum for motor problems regardless of what the motor is driving.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Artisi]

waross - your are correct if a motor / electrical fault - however - I feel the pump end should be reviewed as well - is the pump locked - insufficient pump clearances - 2 occasions pump wouldn't start -- I time ran for 5 days - shut down and wouldn't start -- electrics or mechanical??

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LionelHutz]

You need to provide a better technical explanation because just telling us it failed to start is quite useless. What happened when it didn't start and what was the reason for rebuilding it?

 

[Marke]

The first question to ask, is was the pump rebuilt, or was the motor rebuilt.
Is it a sump type pump, or is it a bore hole pump?

Common problems with bore hole pumps are:
1. Pump needs to get up to pumping speed within 2 seconds to lubricate the thrust bearings.
2. Pump needs to get up to pumping pressure quickly to prevent it from a) operating of the end of it's curve and b) to ensure that the pump mechanism is lifted off the thrust washer.
3. Pump needs to operate with sufficient water above the pump inlet to always exceed the NPSHr of the pump. Operation below the NPSHr will result in uplifting and damage to the wet end and thrust washers.
4. Pump needs to be always operated with sufficient flow to cool the motor/pump. That can be in the order of 33% of the pump rating. Low flow can result in overheated iron with plastic insulation extruding out of the stator winding and into the gap.

There are many possibilities for operation that can cause failure and prevent a start.
More detail on what was repaired would give us a clue.

Best regards,
Mark

Mark Empson
Advanced Motor Control Ltd

 

[Artisi]

Think we can assume its a low lift sump pump as pointed out in the first post.
But I wouldn't get too excited as the O.P. seems to have vanished anyway

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[operatorjoe]

Sorry for extended lapse on this subject. Thank you for your help and I will try to address these questions soon.