Can some one guide us in carrying out the investigation for resolving the high amperage problem for some of our newly installed centrifugal pumps? Presently some of the pumps are operating in parallel to avoid tripping due to overload on motors. Will highly appreciate suggestions......

Do they rotate freely?
What type of product?

We definitely need more information

Was this the engineer?

damn.gif (37 Kb, 52 downloads) oh damn!!

The pumps rotate freely. The product is hydrocarbons. The motor sizing is already checked by the pump vendor for undersizing. The product specific gravity has been checked and found according to the pump design.
The pumps performance is OK. The only problem we are facing is that the motors are taking high amperes, i.e. running on overload.
We need to know what else should be checked to find out the root cause?

Have you checked the motor overload trip setting? TQ

If the pump was sized right. And the rotation is right and the voltage is right. Then it's the load. The elec. motor will try to do it's job it doesn't know how big it is. Is the panel set up right with the overloads.

I have seen when the impeler size was wrong by 1/4" and caused overloading. Just because the imperler fits dosen't mean that it's right. Try ajusting the out put and checking the amps.

As an old electric motor shop owner it looks like the load is to much. The question is why.

Greg

What about oversizing?


Check out this link from the mcnally institute

http://www.mcnallyinstitute.com/10-html/10-11.html

The top suspects would be : (sorry if I'm repeating earlier items) actual mechanical overload, low voltage, unbalanced voltage, trip setting incorrect, trip device malfunction.

Measure current on all three phases. Is it balanced? What is the value?
What is the motor nameplate voltage and full load amps (or horsepower)?
If available, what is estimate of the motor terminal voltage (or upstream switchgear voltage).
What is the motor nameplate speed and measured speed (can help us estimate actual power proportional to slip).
If available, what is the pump dp and flow-rate. Those two (along with efficiency) are sufficient to estimate pump shaft horsepower for a normal water pump. For hydrocarbon pump it may be necessary to know the viscosity as well although I wouldn't know how to take that into account. It would stand to reason if your fluid is cooler than normal it will draw more pumping power than normal.

Is the motor driven from a vfd?

Did we ever find out how big the motors are? Are all the motors and pumps the same? Same impellers? OEM parts? The list from the McNally Inst. is great, too.

If they're newly installed, are they still under warranty? Are they paid in full? Holding that last check usually gets a prompt response.

Anyone know why my new post shows up at the top and not the end of the thread? Have we figured out that mystery yet?

quote:

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Anyone know why my new post shows up at the top and not the end of the thread? Have we figured out that mystery yet?

There are two standard ways to set up forums. #1 -The simple way is chronological order. #2 - Another common way is original post on top and reverse chronological after that (has some advantages when you think about it... if it is a long thread you normally want to look only at the newest posts).

On this site everything in the "Posts About Improving Reliability" forum are set up the 2nd way. Everything in the other forums on this site is set up the first way.

I have no strong preference other than we should be consistent within the site. I made some comments about this behavior in the other thread and then flagged it for attention of the admistrator but Terry has not acknowledged he is aware of this.

My suggestion is to check that the system that the pump/s supply does not have too low a resistance to flow.

I will try and attach a test plot of a pump where this happened. It was an ash agitator pump, and the nozzle on the end of the discharge pipe (not visible as it was in the ash pit) had come off. The pump responded by trying to supply more flow, but that pushed its required power above the motor rating and trip setting.

Pump_sys_reduction2.jpg (12 Kb, 25 downloads)

Recirculation, are your non return valves operating correctly

Have you checked that the ammeter is ok? We had many high ampere reports for fans by operators because the ammeter is kaput and not replaced but can be checked at MMC & found okay. TQ

Mohammad,

I've seen this happen when the flappers were left out of the pump discharge check valves, which allowed flow back through the pump that was not running. A quick check is to block in the pump that is not running while you are watching the motor amps on the one that is running.

Hudson you mentioned check valves, are they in place? What about the rest of the system? what appendages are upstream? I know operators who's first action is to throtle valves (especially gate sigh.. ) if they want to control heat exchanger temperature.

This morning I poked around in our KSB manuals and came across:
High amperage, KSB sugestion: Check if actual back pressure is lower then specified. If so, increase back pressure.
Thus it comes back to oversizing or too low resistance to flow as mentioned by Ray BeeBe.

I would compare it to internal combustion engines when you have an overspeed condition, (sudden disappearance of load) or driving a porsche with motorbike brakes. Or am I missing something

quote:

Presently some of the pumps are operating in parallel to avoid tripping due to overload on motors

Makes sense, running two pumps in parallel will increase the back pressure since this is a function of the flow.
Try throtling a valve (not gate or block) in the discharge, probably you have a control valve somewhere?

Is the motor correctly connected in star/delta?

The ARVs (Automatic Recirculation valves) for four of the parallel running pumps were observed passing, causing high capacity flow across the pumps. Therefore leading to high amperage problem. We are presently investigating the reason for the cause of ARV problem.
Thanks for all of you sharing your ideas. Looking forward for more suggestions...
Good day....
Mohammad