Motor KW Readings
Motor KW Readings
(OP)
We are commissioning the plant and carrying out no load run 3 similar 6KV / 1000 KW / 8 poles / 118A / motors. For 2 motors we have seen the motor KW of 28KW but for one of the motor motor KW of 13 KW. The no load current of motor per data sheet is 42A at 6000KV. We have seen 46 A for all three motors at 6400 V.
Attached are the motor current and voltage waveform captured through relay and plotted in excel file. As seen for good motor, current and voltage phase sequence is RYB. But for bad motor, voltage phase sequence is RYB and current phase sequence is RBY.
What can be the issue here? - incorrect Current transformer phase sequence? or phase sequence is correct but there is polarity for C phase is reversed? Did not see any temperature rise in relay or through RTD measurement during the 2 hours run.
Please share your thoughts.
Attached are the motor current and voltage waveform captured through relay and plotted in excel file. As seen for good motor, current and voltage phase sequence is RYB. But for bad motor, voltage phase sequence is RYB and current phase sequence is RBY.
What can be the issue here? - incorrect Current transformer phase sequence? or phase sequence is correct but there is polarity for C phase is reversed? Did not see any temperature rise in relay or through RTD measurement during the 2 hours run.
Please share your thoughts.





RE: Motor KW Readings
Phase angle (assuming same reference for VT and CT) is very close to 90 degrees (I get around 87.5 degrees) which is OK for an idling machine. Could actually even be a bit better.
There is some voltage distortion, which reflects in current. Voltage distortion is from outside. Not caused by MUT. Distortion components not in-phase and not 100% in synch. Do you have any large machines with high slip nearby? Or cascade drives?
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Motor KW Readings
RE: Motor KW Readings
My sincere thanks for sharing your views.
ScottyUK - You are correct. This being new plant and not in service, the incoming voltage is higher (@10%) than rated voltage. Once plant is in service and more load comes in, we expect it to come down <5%.
Skogsgurra - You observations are correct - motor PF is very low - this is low RPM motor and running on load. I also believe that CT polarity is reversed.
Thanks again for your help.
RE: Motor KW Readings