pump taking high current
pump taking high current
(OP)
hello
we have three similar vertical pump in parallel operation with full load current of 75amps. One pump is taking current more than full load current 75amps. It takes 76-80amps. Others pumps takes 65-69amps @same time for same parameter.generally two pumps always in operation.
I have checked suction/discharge pressure which are same for both pumps. Flow meter is common for all pumps so we cant take individually but i think is same as pressure are same.
There is all parameter (vibration,temperature etc.) are within limit.
can any one suggest ,what may be the probable causes of high amps.
reagrds
pradip
we have three similar vertical pump in parallel operation with full load current of 75amps. One pump is taking current more than full load current 75amps. It takes 76-80amps. Others pumps takes 65-69amps @same time for same parameter.generally two pumps always in operation.
I have checked suction/discharge pressure which are same for both pumps. Flow meter is common for all pumps so we cant take individually but i think is same as pressure are same.
There is all parameter (vibration,temperature etc.) are within limit.
can any one suggest ,what may be the probable causes of high amps.
reagrds
pradip





RE: pump taking high current
Not all "identical" pumps are actually identical.
Your one pump drawing more power will be pumping more flow than either of the other two.
Unless each actual pump has been individually tested to create a unique pump curve you won't find put why. It also makes a big difference on the shape of the pump curve and where on the curve the duty point is.
Less than 10% from duty point is not unusual for parallel pumps.
Can you post the pump curves and mark or note the duty point?
Other issues can be that the inlet to the three pumps is not equal and hence one pump has a lower inlet head than the other. Can you sketch out the physical inlet (it there is one) and outlet headers.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pump taking high current
As I said these pumps are identical and generating same head (same discharge pressure)with same suction pressure.They have common suction and discharge piing.
usually two pumps run parallel.
RE: pump taking high current
One could also be slightly less efficient as well.
If you have the pump curves then post them along with the inlet and outlet headers and then we can see if they really are "identical".
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pump taking high current
Has the running clearance been checked?
What pump type are they? -- vertical pump means nothing without configuration description.
Is o/current reading on all phases, have all electrics been confirmed as Ok?
quoting LittleInch "Remember - More details = better answers"
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: pump taking high current
RE: pump taking high current
hello all
thanks for your interest and reply
I have seen the all pump curves supplied by the vendor and it is similar for all three pumps .I will provide to you pump curve. Here difference in ampere is by 8-10 amps in both pumps which delivering similar head in parallel operation. As I said the pump is delivering same head, it mean flow must be same if it is identical.
layout is like pumps suction from common header first is A then B and then C and in discharge its reverse .
C is taking high current.
RE: pump taking high current
"similar" and "identical" are not the same thing.
also we don't have any process conditions for these units. If the head developed is small, the it won't take much to increase the head of one pump versus another.
Also check Artisis' post and confirm the motor is actually good.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pump taking high current
Are there minimum flow spill-back lines? Does each pump have an individual spill-back or is there one common spill-back for the group? Are there suction strainers or screens? Is this a service prone to fouling, lime formation, trash or solids?
Johnny Pellin
RE: pump taking high current
RE: pump taking high current
Metering in larger pumping stations, particularly at the highest voltage level tends to be more complex and comprehensive than in smaller pumping stations on lower voltage level. Service technicians may need additional instruments to measure and record, for example, circuit and insulation resistance
RE: pump taking high current
Thanks for reply
This pump has closed impeller and we have already checked all 3 phase current and t is like 76 78 & 76 for one pump and 66 67 & 68 for another pump.
These pumps have not any minimum flow lines individually.
is it good idea to check motor by solo run test,before jumping on the pump?
what may be the probable causes for unhealthy motor taking high amps ,I mean, what parameter I should check?
RE: pump taking high current
If possible can you dead head each pump separately for a few seconds and see if you get the same pressure. That will start to tell you if there is actually something different with the basics of each pump.
I don't know enough about motors to know what the tests could be, but try the deadhead thing first. If they are all the same it might be flow related, but you're gradually knocking things off one by one
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pump taking high current
Johnny Pellin
RE: pump taking high current
A slight variation in plumbing could cause a difference in load.
I would not assume that the motors are identical either, unless you have motor test data.
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P.E. Metallurgy, Plymouth Tube
RE: pump taking high current
We are still waiting on pump type / configuration
An installation drawing etc. would assist.
How about an answer to my earlier question - has this pump always run at higher current yes / no.
Is the o/current pump running over maximum allowed current?
It's looks like developing into one of those enquiries where we need to squeeze every bit of info. from the OP step by step.
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: pump taking high current
These amp reading indicates 3.3kV 3phase line voltage
Vertical turbine pump ? Long shaft ?
A check on design case power for this rated flow of 8925usgpm and h = 424ft at e = 0.81, assuming liquid density is 1000kg/m3 for water tells me design case shaft power is 1185HP and not 519HP ?? What are we pumping here - LPG or LNG?
RE: pump taking high current
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: pump taking high current
yes ,this is running with overcurrent 76-80 amps (More than full load current 75 amps ) always and sister pump with 65-69amps ,it not like spike.This is vertically suspended (V3) centrifugal pump. What do you mean by running clearance ?
phase current already checked and its nearly same for all phase.
RE: pump taking high current
suction / discharge tapping on the same distance from the piping for all pumps and it is just before and after the pump.
Motor is identical in all pumps.
RE: pump taking high current
pump is equipped with 435kw motor ,
pumps running with following data
for pump A Differential pressure is 117psi
for pump C Differential pressure is 116psi
Total flow for both pump is 13805BPH
RE: pump taking high current
RE: pump taking high current
For a pump with an operating point of 4831usgpm (13800bph for 2 pumps), the head curve indicates approx 550ft. If diff press at this point is 116psi, then liquid density must be 485kg/m3. And corresponding operating shaft power is 500HP (373kW), which indicates amps = 71 (approx) at a line voltage of 3300V.
This matches up with the amps on the sister pump at 69-70Amps, so this pump seems to be running as it should be.
Some light liquid being pumped here as suspected ( not disclosed).
But for a motor rated at 435kW, rated amps would be = 82amps, so 76-80amps = 92-98% of motor rating.
The vertical turbine pump running at 76-80amps - intermediate shaft bearing problems?.
RE: pump taking high current
Thanks for reply
Yes you are right ,The process fluid is ethane with sp. gravity 0.435. Motor voltage is 4000V.
It might be problem with intermediate shaft sleeve but I think it should reflect in vibration and vibration is normal.
also we can not open the pump without ensuring all other checks which has potential to creates this problem. I can say overhauling of the pump is the last option .
@ScottyUK: I don't know pump fed from same bus bar or not ,will check with electrical people. If not what we can check ? what will be effect if feeder cable lengths will not similar?
RE: pump taking high current
My summary so far is:
You might have one pump out of three which is operating at a higher flow for the same head and or with lower efficiency, but pumps may not have all been individually tested. If possible do a blocked in pressure test to see if all pumps are running on the same curve. Vendors can allow 3% or more from rated duty and still be "in spec".
Hydraulic power from the curve is remarkably flat, so as noted above maybe the other two pumps are the opposite end of the allowable variation.
Your over amp motor is being fed with less volts than the other two when running ( hence issue of the cable length and bus bars). Try and get an electrician to measure volts when operating at the motor terminals. I'm no sparky, but I've not come across 4000V as a standard voltage before.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pump taking high current
Shaft seals working okay on all 3 pumps? Which API seal flush plan ? Anything different in terms of barrier fluid consumption / seal fluid level depletion ?
RE: pump taking high current
will provide you the drawing .shaft seal is working fine and have plan 13 and 76.No barrier fluid.
RE: pump taking high current
I have NEVER seen an installation with parallel pumps where the piping was identical for each. There is always some variation.
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P.E. Metallurgy, Plymouth Tube
RE: pump taking high current
RE: pump taking high current
I don’t recall seeing how many stages these pumps have. How many stages do these have?
Johnny Pellin
RE: pump taking high current
So, the corrected power consumed should be 500 * 485/438 = 553HP = 413kW
Corrected current then corresponds to 71 * 485/438 = 79Amps
So the high amps pump is performing in accordance with the pump curve.
RE: pump taking high current
Responding to your earlier question -
If one motor has a significantly longer feeder cable than the other then the motor with the long cable will receive a lower voltage at its terminals, resulting in higher current draw. Similarly a small difference in voltage at the busbars can result in differences in line current.
If the supply voltage is abnormally high then the motor current would also rise as the stator core reaches magnetic saturation. This is rare in my experience.
RE: pump taking high current