Unusally High Compressor LRA

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clsarmiento

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A 75HP, 480V, 3-phase compressor motor (85.5FLA) is drawing 460-500 amps LRA on start up, and giving out a very loud noise. The feeder size is 3 #1/0 cu. & #6 cu Gnd. It is connected to a variable speed drive provided by mechanical. What seems to be the problem? Is there a grounding issue maybe? Thanks!
 
460 to 500 amps does not seem to excessive for locked rotor amps for a compressor.

Typically 6 times the full load amps is what the LRA will be.

85.5 X 6 = 513 amps.

Chris
 
lakee911 said:
If on a VFD, ramp up slowly and there shouldn't be much amperage, no?
Click to expand...

for rotary screw type compressors, I would say yes, but reciprocal compressors have a high torque motor requirement, I have never seen VFD on them, and the fact the OP did say it has a VFD, which I seem to remember Sullair Sullscrews are now provided with a VFD on some of there models, so I would bet he has a screw compressor, and anything could be wrong, from contaminated screw oil, bad bearings, to many electrical problems, some of what I listed before, but like number five "need more input":D

Here's a link to Sullairs VSD's:
http://www.sullair.com/corp/details/0,,CLI1_DIV61_ETI5679,00.html
 
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Unusually High LRA on Compressor

Unusually High LRA on Compressor

I don't have much data on this compressor but here's what I got from the electrician on the field: "The compressor is having like a nuetral drop with no neutral to the ground, we recommend that 2 ground rods be put in to create a grounding field for the compressor motor, 'cause it is drawing 460-500 amps on start up on LRA".
 
clsarmiento said:
I don't have much data on this compressor but here's what I got from the electrician on the field: "The compressor is having like a nuetral drop with no neutral to the ground, we recommend that 2 ground rods be put in to create a grounding field for the compressor motor, 'cause it is drawing 460-500 amps on start up on LRA".
Click to expand...

Suggest finding a different electrician or maybe in this case an electrician.
 
clsarmiento said:
I don't have much data on this compressor but here's what I got from the electrician on the field: "The compressor is having like a nuetral drop with no neutral to the ground, we recommend that 2 ground rods be put in to create a grounding field for the compressor motor, 'cause it is drawing 460-500 amps on start up on LRA".
Click to expand...

Installing ground rods will do nothing to fix the problem.

Chris
 
lakee911 said:
If on a VFD, ramp up slowly and there shouldn't be much amperage, no?
Click to expand...

I absolutely agree, if the VFD is driving a rotary screw compressor. IMHO, I believe that VFD driven reciprocating compressors can be problematic due to the varying mechanical forces. I have seen applications where a higher rated VFD has been utilized to handle the recip requirements.
Regards,
Mark
 
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