Got a motor driven pump. 75 HP, 3 phase, 460 V, SF 1.15. Nameplate FLA is 87A. The pump is on a constant flow system.

Amprobed it at 96, 100, 104 amps. Voltages are within 2 volts of each other.

Is this something I should be worried about? 87 X 1.15 is 100. I am not concered with the imbalance as much as the fact that the motor is running at max all the time.

I know next to nothing about pumps so is this something I should worry about? This motor/pump combo is a backup to another pump that just failed. It has not run in about 2 years .

Many thanks

drillman -

You most likely want to be concerned about the imbalance, as it amounts to 4%.

The winding temps of the motor will encrease, efficiency will decrease, and life expectancy of the motor windings will decrease drastically.

Go to This Link

for a good article explaining the adverse effects of unbalanced voltage.

Steve


(edited to add link)



[This message has been edited by electure (edited 05-24-2006).]

drillman -

I read your post last night and "saw" "amps" and then "thought" "voltage".

The info in my previous post does not apply, but I'll leave it in case anyone would like to get info about "voltage imbalance".

I'll email you an article about current imbalance, as I don't think it would cut-n-paste well.

While you have a 4% unbalance, it looks as if you are ok.

It is not unusual to have higher unbalance at no load than when the motor is under load. Were you reading taken under load or no load?

Steve

What is the voltage at the motor?

The fact that this is a backup to a pump that just failed is cause for concern. It could be the pump/motor combination is undersized for the application. Has something been changed since the initial installation? If it is a centrifugal pump, you can throttle the discharge valve a notch or two to drop the current, maybe you will still have acceptable flow with the throttled valve. Either way you should take a second look at the system, compare field conditions with design values. Good luck.