High ampere and low flow problem
High ampere and low flow problem
(OP)
We have one newly installed pump. Its a between bearings, axially split casing, single stage centrifugal pump. Suction is from a flooded tank. Pump is tripping at overload even at a flow lesser than 50% of the rated discharge. Saw its power curve. Input power vs flow curve slopes downwards. Is it possible for any pump that on increasing its dis flow, it starts taking lesser current? If its possible, kindly advise how to start such a pump.





RE: High ampere and low flow problem
So how extensive have the electrical checks on the system been?
Things to check would be:
Are the overloads set correctly.
Is the motor and overloads the coreect size for the pump.
Is the voltage correct for the motor.
Are the supply cables the right size.
Are all three phases available.
Are all the terminals tight.
How long does the pump operate for before it trips on overload? I suspect by what you are saying that its tripping very quickly.
Has the pump been checked to make sure there is not some sort of mechanical defect?
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
RE: High ampere and low flow problem
This will save a lot of time in useless speculation.
first off please make sure yourself, by physically seeing the shaft that the pump is going the right way around. Very easy to get a three phase motor going the wrong way.
Might need the coupling guard to be temporarily removed.
Is it tripping on start? Do you have a motor starter which allows for excess current on start?
Are you starting against a closed valve?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: High ampere and low flow problem
Johnny Pellin
RE: High ampere and low flow problem
Suction and discharge pressure wouldn't go astray at this point.
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.)
RE: High ampere and low flow problem
RE: High ampere and low flow problem
Most of the things that you have suggested have already been checked. Like
* Direction of rotation
* Alignment and freeness of the pump
* Motor is of adequate rating. Voltage also checked.
* There seems no mechanical rubbing
* Suction strainer also checked.
* Electrical team has checked from their end (connection, cable etc)
* overload setting are right
* Pumping fluid is clean water only
* This is happening with all three pumps installed in parallel. We tried operating them in parallel as well as separately.
Littleinch Sir,
It trips as soon as flow reaches 50% of the rated flow.
Mr. JJPellin sir,
Yes, Its a low head pump. We will try to start the pump with discharge valve opened (Earlier i also thought to do so)as you suggested. But as per start-up procedure given in the O&M manual, pump has to started with discharge valve closed.
One important point i had forgot to mention is that pump was running normal for 3..4 days since its commissioning.
Also please tell how come power decreases on increasing the flow.
I have attached data sheet, sectional drawing and performance curve of the pump.
RE: High ampere and low flow problem
RE: High ampere and low flow problem
You ask how come power goes down as flow goes up? Your pump has quite a large drop in head as flow goes up coupled with a massive change in efficiency as flow increases. These two functions outweigh the flow increase to the extent that power should be going down.
Things to think about. You say the suction is flooded but the npsh is quite high at 7m so worth a check as with an inlet filter, even if empty and a long suction line you could be cavitating the pump. Maybe you've already wrecked the impellor? ? Or something has happened to decrease the efficiency.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: High ampere and low flow problem
Johnny Pellin
RE: High ampere and low flow problem
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: High ampere and low flow problem
I think someone else has asked, but maybe the head is still high which means that the flow is less than required and the power is still high. The head needs to be checked. If it worked for a couple of days , has anything (anything at all including electrical settings) changed in that time? What are you pumping into?
Are the overloads set at the motor rating?
Ask the electrical team what they have actually checked?
What sort of motor starter is fitted?
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
RE: High ampere and low flow problem
Thank you for explaining how power can go down when flow go up.
Tank level is more than 5 meters above suction line and suction line is hardly 5 meters long. So NPSH doesn't seem to be problem.
Motor KW rating is written on motor name plate. Its 75 KW only.
Also impeller MOC is SG Ni resist, so little chances of impeller getting wrecked in a week.
We will take another trial and record all the parameters as suggested by you. I will post it soon.
JJPellin Sir,
Voltage has already been checked by electrical engineer. Its ok.
Will ask electrical guy to check ampere and voltage on all three legs during next trail.
Ashtree Sir,
Exactly, there has to be something common in all there machines.
No work was done on pump or motor since its commissioning.
OEM is also supposed to visit the site in 2/3 days.
Thanks
RE: High ampere and low flow problem
RE: High ampere and low flow problem
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.)
RE: High ampere and low flow problem
RE: High ampere and low flow problem
Keith Cress
kcress - http://www.flaminsystems.com
RE: High ampere and low flow problem
It smoked - This ones a little odd as the power requirement at 50% is more than that at full flow, so starting current and initial flow uses more amps.
How and why the system apparently ran for 3-4 days then not seems to be a key issue.
Did the flow reduce over time? If so the motors would have been operating at a higher power.
Are these motors definitely tripping on excess amps or temperature? you need to measure running voltage and amps, not just volts at rest.
How do you know what the flow is through this single pump when it apparently a new pump in a three pump parallel operation?
Also do you have the test results for this actual pump ( and not a "typical" or computer generated curve?)
This is a curious one - even if you work it out and fix it, please respect us and let us know what you found. Thanks.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: High ampere and low flow problem
If the wire size is too small, the amps will increase.
The pump motor may also not be large enough so that the motor is being overloaded. An overloaded motor will also cause the amps to increase.
RE: High ampere and low flow problem
The drawing indicates a typical double inlet centrifugal pump, so I would expect to see a rising power versus flow curve. Could there be an error in technical data for the pump you have?
Walt
RE: High ampere and low flow problem
Here is some general info about expected shape of bhp vs flow curve for various types of pump.
FAQ237-1543: How does hp change with flow for a "centrifugal pump"
I don't associate that pump curve with that type pump you have... very skeptical that they match.
Maybe you're working off a pump curve that does not correspond to the installed pump (and if there is incorrect pump data floating around, maybe it was used to set your overloads).
=====================================
(2B)+(2B)' ?
RE: High ampere and low flow problem
To a crude first approximation an induction motor is a constant power load over a small range of speeds, so if the terminal voltage drops then the current goes up to compensate. Long cables can be fine from a thermal rating (i.e. they won't melt when carrying operating current) but introduce signficant volt-drop between the source and the motor. Get someone fresh to this problem to run the cable sizing calcs.
Make sure the source itself is healthy too - the MCC should at least have a voltmeter. See how far it falls when you run the pumps.
RE: High ampere and low flow problem
The pump curve that you have presented is for an axial-flow pump. However, the drawing shows a split case pump.
Compare the pump curves:
Here is another pump curve from a spilt case pump.
Please present the pump curves with the pump model number on them.
RE: High ampere and low flow problem
The pump manufacturer and model might clear some of the misunderstandings
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.)
RE: High ampere and low flow problem
RE: High ampere and low flow problem
Just chalk it up to another wheel spinning exercise.
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.)