Centrifugal pump anomaly
Centrifugal pump anomaly
(OP)
I have a system that uses a 480V 3ph motor driving a submerged centrifugal pump. The system is flushing at the moment and the discharge goes to 8 different bearings. The pump when deadheaded is right on with the pump curve. When all of the valves are open allowing maximum flow, the pump also matches the pump curve. As the valves are closed one by one, there for restricting the flow, the pump discharge pressure increases as expected. The anomaly here is that the amp draw on the motor increases as well. I am dealing with bearings at different elevations but the kicker is that the last valves to be closed at those at the highest elevation which should even more so decrease the flow and decrease the amp draw on the motor. Any ideas?





RE: Centrifugal pump anomaly
RE: Centrifugal pump anomaly
Steve
RE: Centrifugal pump anomaly
is it an open impeller design?
sometimes, you have to look at internal leakages to explain kW disappearing
RE: Centrifugal pump anomaly
RE: Centrifugal pump anomaly
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Centrifugal pump anomaly
Regards,
SNORGY.
RE: Centrifugal pump anomaly
RE: Centrifugal pump anomaly
So far the story here seems to be that he's on the backside of the power curve, which would typically indicate he's operating out of the normal range of something.
So, roricaja what say you?
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Centrifugal pump anomaly
M.N.Ball
Process Engineer
CSSBB
RE: Centrifugal pump anomaly
As you reduce the load on an induction motor the power factor gets worse. Often MUCH worse. This greatly increases the motor's excitation current demand. This causes the clamp-on ammeter to see little decrease and occasionally, even an increase - as is happening here.
If you clamp-on and see the current reduce as you lower a motors load fine! You see what you expect, though it's not really correct. If you reduce the motor's load and see little reduction or an increase, then that particular motor's power factor changes more than the typical and you need to pitch the ammeter and switch to a power meter. Specifically a Watt meter.
Get a hold of a Watt meter roricaja23 and repeat your test. Tell us what you see then.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Centrifugal pump anomaly
This may not be an anomaly at all.
RE: Centrifugal pump anomaly
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Centrifugal pump anomaly
for small size motors, cos phi is everything but constant.
so with a rising amp meting and a falling cosinus phi,
the kW might be falling
RE: Centrifugal pump anomaly
Keith Cress
kcress - http://www.flaminsystems.com
RE: Centrifugal pump anomaly
You may want to check your pump curve and adjust for shaft speed variations. Commonly, the pump curve is generated for a constant shaft speed, often a synchronous speed such as 1800 rpm for the 60 Hz part of the world. Since you are presumably using an ordinary induction motor, the "slip" (which, of course, varies according to the load) can have enough of an effect to make some of the numbers look a bit off.
Was the pump curve that you are using established by a special test by the manufacturer, or is this a generic curve for this pump series? If it is just a generic curve, some modest variations in performance can be expected.
Similarly, how well do you know the motor's actual performance characteristics. Are you working from nameplate data, or do you have actual performance test data.
RE: Centrifugal pump anomaly
RE: Centrifugal pump anomaly
Furthermore the OP has left the room...
Keith Cress
kcress - http://www.flaminsystems.com
RE: Centrifugal pump anomaly
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Centrifugal pump anomaly
Patricia Lougheed
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RE: Centrifugal pump anomaly
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/