900 HP Motors

[sjk]

I have two different size pumps using the same 900 HP, 2300VAC, 3PH, 60HZ motors. The pump efficiencies were determined using amp readings on the motors, with negligible losses between the motor and pump. Both pumps are determined to be 20% less effiecient than our curves show. We have these pumps in other plants with no efficiency problems. Could we have some sort of electrical problem?

The Transformer and motor starters are in a small building approximately 100 ft from each pump. Both pumps are supposedly hooked up to the same 2400V transformer. The wire size from the control panels to the motors are #4/0 3 wire.

My questions are:

Although these are new motors is it possible that they could be less efficient than stated in their specification?

, and if the motors are OK, Could there be something going on with the 2300VAC transformer?

With both motors being on the same transformer, could there be a problem with the power coming into the control panel?

Phase problems?

We are pretty sure our pumps are working correctly and are not 20% inefficient.

Thanks in advance,

Stan K.

 

[nbucska]

The power is P= V*I*cos(phi) where phi is the phase angle between the voltage and current. You evidently assumed P=V*I which is true only is there is no phase shift. <nbucska@pcperipherals.com>

 

[sjk]

For power I used the following formula:

P = (1.73 x Amps x Volts x P.F. x Eff.)/746

P.F. being the motor Power Factor
Eff. being the motor Efficiency
Amps being the single leg current
and Volts being the motor voltage of 2300

Stan K.

 

[jbartos]

Suggestion: Please, could you provide all nameplate data of those two motors and the measured values of currents. There may be other factors involved, e.g. quality of power supply, oversized motors with respect to the shaft horsepower needed for those pumps, etc.

 

[don01]

hi sjk
some food for thought. I take it the pump performance has been checked by way of power flow rates and pressure. With these size motors you would have good flow meters and valves to create some dp s and flows for checking. We used to use these checks to get an idea of the state of the pumps. not the motors.

If your volts and current are in accord with the base data for the motor It should be fine, check your pf if you can. I take it that by 20% less efficient you mean the motor is using more kw that the pump curve indicates?

Do a draw up into the plant if possible to get a first principke check of the flow measurement system

Regards Don