Comressor-VFD Setting Speed 1

[HamidEle]

The compressor minimum speed is 60%Nominal Speed. We need to set VFD to drive the compressor. I am thinking of setting VFD minimum speed at 30% Nominal Speed. Since we may run the compressor at lower speed later. Anybody can shed some light on me?

Thanks in advance.

 

[jraef]

Compressor minimum speeds often have to do with lubrication. Setting too low may end up costing you the compressor. The people to consult are those who know your specific compressor. Generalizations will not serve you well.


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[HamidEle]

Thanks for the inputs. We are trying to set VFD minimum speed.

 

[HamidEle]

After the second thought, i think we should set at the compressor running limit(minimum speed).This way, we can avoid overheating the motors at lower speeds than the minimum.

 

[ozmosis]

What sort of compressor? Air compressor or refrigeration compressor? Screw/reciprocating/scroll/centrifugal?
as jraef points out, the minimum speed is determined by the mechanical limitations of the system and the recommendations of the manufacturer. A lot depends on lubrication and the impact of running at low speed.

 

[HamidEle]

it is recipracating compressor. We set the minimum speed at which the compressor will be allowed to run.

 

[ozmosis]

Sorry, what is your question? are you asking if you can lower the minimum speed below the manufacturer recommendations?

 

[HamidEle]

My question was, can we set VFD minimu speed lower than Compressor manufacturer recommnended set point?

 

[ScottyUK]

Yes, you can. But if you do consider the following:

Will the compressor manufacturer honour the warranty? Probably not.
Will it break? Probably.

It's your compressor; do what you want provided it remains compliant with the applicable codes, but the manufacturer usually sets these limits because they are safe for the machine.



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If we learn from our mistakes I'm getting a great education!

 

[jraef]

"Can" dos not mean "should".

If only more people recognized that simple fact...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[ozmosis]

HamidEle
As others have said, you can set the VFD minimum speed to whatever you wish but on a reciprocating compressor, this is not a good idea.
The company I work for manufactures both VFD's and recip compressors for refrigeration. Our minimum speed is 40% of rated speed (30Hz on a 50Hz supply and 36Hz on a 60Hz supply). This is specifically for oil regulation. Maximum speed is also limited but for other reasons.
I would stick with the manufacturers advice otherwise it will get very expensive when it fails, and it will fail.