A/C Compressor Current imbalance

[ralft]

I have a re-manufactured hermetically sealed residential 3 phase A/C compressor/motor with rather large current imbalance. The vendor insists that it was tested and in spec. My utility uses the grounded center tap of one winding to provide 240 volt 3 phase and also 120/240 single phase. My voltages are Vab=242. Vac=244 and Vbc =239 and voltages to ground are Va=212, Vb=120 and Vc=119. All of these voltages are within the utility's specs. My compressor motor currents are: Ia=11.5, Ib=8 and Ic=11. All these readings were taken when the utility electric load was low because of relatively less A/C demands. The voltage imbalance calculates to be 1.1% while the compressor current imbalance was 14.3%. The other day I had slightly larger voltage imbalance (1.7%) and greater current imbalance (22%). I have connected a 12 volt single phase source to each of the T lead pairs and the current is always 2.1 amps. I thought that this should pretty much eliminate the motor as being at fault. But then I tried shifting the motor T leads changing the motor leads at the contactor. By doing this I got the current imbalance down to less than 10% and this was with the higher voltage imbalance of about 1.7%. This tells me that the motor may have some inherent imbalance after all.
Is 10% current imbalance going to shorten the life of the motor? Fortunately, the load is only about 2/3 of the motor rating. What about efficiency penalty? What do you all think?

 

[ralft]

A/C Compressor Current imbalance - update

A/C Compressor Current imbalance - update

I tried using my 12 v. single phase source to further test the winding similarity. This time I connected it across 2 T leads and then measured voltage from the 3rd T lead to each of the 1st 2. In the first of 3 tests the voltage was split 50%/50% as expected but in each of the remaining tests, the voltage was split 49%/51%. I just completed a set of voltage and current readings with high afternoon outdoor temperatures which should drive the utility voltages more abnormal. The 3 voltage readings were 241.6, 245.6 & 235.3 (Unbalance factor = 2.3%) and the resultant amps were: 11.5, 8.8 & 10.6 (Unbalance factor = 14.6%). I think that these readings show that my motor is performing as well as can be expected with the uneven voltages. Do you all agree? How can I correct (or get the utility to correct) the unbalanced voltages?