VFD on reciprocating compressor 1

[davor2]

Hi everybody!
Does anyone of You have some expiriance with installing VFD
on reciprocating compressor for decresse speed of compressor?

 

[DickDV]

Experience, yes. You should size the drive output amps to be not less than 150% of motor FLA due to the need to get past the first compression stroke at near-zero speed.

 

[ozmosis]

As with DickDV, yes. In addition to DickDV's comments:
If they are small recip.compressors (i.e.<4cyclinders) then speed control with a VFD will introduce a torque pulsation effect and therefore you need a high performance VFD (the 'vector' control type)to combat this if the need is there to use a VFD.
You should always consult with the manufacturer of compressor and they will advise any lubrication issues as well.

 

[itsmoked]

Yes as below some speed you will have inadequate lubrication and the fan over the heads may stop providing enough cooling, which will result in piston scuffing and possibly detonation.

These things can be dealt with you just have to consider them.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

I think you should start by evaluating why you are putting a VFD on a recip compressor. Many people do it thinking it will inherently save energy compared to staged unloading of the cylinders and are often disappointed with the results. I'm no compressor expert, but I do know that although it can be done, it takes someone who has a very detailed knowledge of part loading cycles etc. It isn't as cut and dry as applying a VFD to a centrifugal machine.

 

[DickDV]

I certainly concur with jraef's comments on this application

 

[OdessaEE]

DickDV: I am not sure why you need to size the VFD for no less than 150% of the motor FLA? I have used 3000HP drives to start 6000HP reciprocating compressors. Obviously you can't load the compressors, but for motor starting the drive rated current actually can be ~40 - 50% of the FLA of the motor.

As for my experience I have only started reciprocating compressors with VFDs. I have usually found that a VFD causes to many problems than what the savings is worth.