At a loss

[FirtstKnight]

I am a Maintenance man. I also hold a journeyman's license. but I am at a loss on this one. I have 2ea 50 hp air compressor. Both seem to be having a similar problem. .
they are both 230 VAC 3 Phase with a wild leg . Power comes in to the compressor shed from 150 amp breaker to a 200 amp disconnect with 150 amp fuses. then it is run through a manual switch that allows me to switch from one to the other. . One of theses compressors is approx 2 yrs old ( Com -05) the other is 20+ ( Com-01) Com -01 will
Run 5 -6 hrs then it will Trip the motor overload.. by the time get there I am able to reset the overload and it will run another couple of hrs maybe then do it again.
I have replaced the entire motor starter with overload and thermal units . I have replaced oil temp switches. and most recently sent the motor out for evaluation. They did $1300.00 of work on it. we reinstalled it on 6/30/21 and got the same result. Com -05 generally runs ok but back in April while i was on vacation it blew 1 150 amp fuse and tripped the breaker. then when I got back it blew just one fuse (not the same fuse) then on 6/30/21 it tripped the breaker and blew a fuse. I have an amp draw on both compressors left to Right A phase = 100 amps B phase = 87 amps and C phase = 88 amps soo I'm not sure what to do next any help would be appreciated

 

[UNG]

Have you done an IR and continuity check on the motor windings

 

[James]

There is a large difference in the phase currents.
check voltage and current to each of the motor phase cables, any imbalance needs to be investigated.

 

[PEG]

Hi,i take it that your "amp draw" is measured clamp style,while running? or is it a power monitor?

Knowing the stage at which the overload occurs,would be helpful,for example,at start,or near end of cycle.