motor over-amping

[usgreg]

hello again, and thank you In advance. I have a 1998 M&M 150 hp. screw skid setup for a cooler/freezer/spiral application that has recently started inhibiting load from motor over amping. I am not the onsite operator, and there is none. It has been online at this facility for about a year. I have been involved for about four months. We had the motor checked and cleaned and new bearings installed. compressor is getting louder in my opinion. Setpoint is 11 psig (and now will not go below 20psig) and head pressure is in the 175 psig range with 2) 75 hp vilter recip's running in common with this screw (93oF outdoor ambient). ammonia injection for oil/discharge cooling set at 120oF, and running 125oF. no oil failures. VI is set at 3 and has been since I have been involved and screw had no problem maintaining suction setpoint. I closed suction valve to reduce flow and would not stop overloading the motor until valve was closed with maybe 1/16th open (just cracked open). I have not found any hot gas bypassing anywhere in system to overload suction. It appears that any volume at all, is now overloading motor, could compressor be bad. Thank you

[RANGER1]

Usgreg,
You may want to check that the amps are true to the readings in your comptroller.
Also motor can run at maximum nameplate amps all day, so check settings in controller.
Your ambient is not to bad so also eliminate possible air in system as well as condensers are doing 100%, sprays, fans etc.
Can you tell us compressor model exactly complete with amps & pressures at that time.

[sgull]

Hi Usgreg.
Compressor wear could be a possibility. As you state that you have liquid injection oil cooling, as the compressor wears the discharge line will start to heat up this results in more liquid injected to keep the discharge cool. The additional liquid would result in higher power consumption. You should check the rotor end clearance on the compressor to check for excessive wear. Also check the rotor seal for wear. If the VI is automatic you should also check that the calibration of this.
Regards
Denis

[Magoo]

as per Ranger1, compare actual motor amps with display amps, one current transformer out of spec can upset whole control system.

[RANGER1]

Usgreg, If amp reading OK try increasing discharge/oil temp to 130 F.
If machine sounds abnormal & it's possibly due for overhaul, you can only recommend it.
Oil analysis or any metal in filters might help make decision.