I know this topic can get old at times, but hear me out once.
We are expierencing a large current imbalance on our 2000 amp 480 volt Y service which serves motor only load. We have 10 refrigeration compressors on this service of varying horsepowers between 75 hp and 300 hp. The service and all motors have been checked and all exhibit the same facts:
A phase current middle value
B phase current lowest value
C phase current highest value
Voltage at the service entrance 481,484,482
Neutral current is zero
There is a 13% difference between the low and high readings on the current. The voltages at the incoming service entrance all look good. Entire system including motor starters have all been IR scanned showing nothing.
Every motor has its own microprocessor and displays current readings. All 10 show the current imbalances as described above. The service equipment has it's own metering and shows the same as the motors. All have been checked with a hand held True RMS clamp-on meter
I have checked for harmonic currents riding on the 60hz using a Fluke 41B Power Analyzer. It showed all current to be 60hz, and no harmonic component. The one thing that stood out was the following:
A phase power factor .72pf
B phase power factor .61pf
C pahse power factor .68pf
These measurements were at the service entrance.
I am stumped where to go next. Any ideas are greatly appreciated.