Phase Current un-balanced problem ..
Phase Current un-balanced problem ..
(OP)
I have a hermitic motor(compressor motor) which is 635KW , FLA 1091A.
DC resistance measured :8.52/8.51/8.50 microohm, which consider as balanced.
but voltage/current strange as below:
389v/390v/389v
609A/652A/608A
Obviously phase B current is higher. I have other 3 motors had the same problem with phase B current higher. It looks motor has no problem, but I was wondering why this could happen? Anyone helps...
DC resistance measured :8.52/8.51/8.50 microohm, which consider as balanced.
but voltage/current strange as below:
389v/390v/389v
609A/652A/608A
Obviously phase B current is higher. I have other 3 motors had the same problem with phase B current higher. It looks motor has no problem, but I was wondering why this could happen? Anyone helps...





RE: Phase Current un-balanced problem ..
RE: Phase Current un-balanced problem ..
Since DC resistance maynot reveal really unbalances, check for reactances (Z and phi/Z).
Motor tester (ALL Test) can help in finding the unbalances (in stator winding or rotor bars).
Varri
RE: Phase Current un-balanced problem ..
For sure it's not related to the motor I think.
Anyone else got opinion/help, thanks.
RE: Phase Current un-balanced problem ..
RE: Phase Current un-balanced problem ..
For the winding ohmics readings and due to the power line rotation results, I think the motors are OK.
The Voltage media is : 389.3 and differences between Vmedia and the real values are: 0.33,0.7 and 0.33.Then the Desbalance Voltage in percent is: (0.7/389.3)x 100= 0.179% this desbalance don´t cause power problems.The amps readings were taken at 50% Load? I am agree with Varri79´s. Also the Rated Voltage, P.F and Efficiency date could help, could you provide?
Regards
Petronila
RE: Phase Current un-balanced problem ..
RE: Phase Current un-balanced problem ..
I got following infomation on one of these motors:
460V/509HP/3555RPM/HERMITIC MOTOR/FLA 572/LR CODE:F /HERTZ:60 /SVC FACTOR:1.0
Test result:
394V/395V/392V
242A/259A/245A
Phase B current higher also. I'm not able to measure reactances right now, neither the phase angel of power line.
This thing really confused me:(
RE: Phase Current un-balanced problem ..
394/395/392>>393.66 ave >>0.422% Voltage
242/259/245>>248.666ave >>4.15% Current
4.15/0.422 = 9.83 times (as expected)
I wonder if a circuit analysis calculation could be atempted using the technic of Symetrical Components for an unbalanced three phase circuit. You will need all the impedance parameters of the motor and phase angles of the voltages.
RE: Phase Current un-balanced problem ..
I think you have to check your power transformer, check the Output voltage and loading, the motor´s Voltage name plate is 460 ,some extrange to me are the voltage readings: if your motors are running at 394,395,392(Below 15%) this is an under voltage operation and this cause effects on the motors efficiency,temperature,current and the motor´s perfomance.I think you have to find if the Voltage problem comes from the Transformer´s Load capability.
Regrads
Petronila
RE: Phase Current un-balanced problem ..
Are you running 50hz?
Jim
RE: Phase Current un-balanced problem ..
The way to find out whether power line affects this current unblance is difficult
RE: Phase Current un-balanced problem ..
RE: Phase Current un-balanced problem ..
RE: Phase Current un-balanced problem ..
609A/652A/608A"
"By the way, I've rotated the power line, A-B-C to B-C-A then to C-A-B, still phase B current higher.
For sure it's not related to the motor I think. "
I assume you rotated at the motor terminals and the power system B phase remained high, even when connected to motor lead T1, T2, T3 right?
Where was the voltage measured? Maybe there is a high resistance connection between the point of voltage measurement and the motor? For example the breaker?
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RE: Phase Current un-balanced problem ..