from the Automation List department...
Inverter for Screw Type Air Compressor
Application Questions and Problems topic
Posted by Canan Tas on 28 September, 2006 - 12:40 am
I just want to know that does anyone has done an application such as applying inverter to a screw type compressor (Atlas Copco GA45) in terms of saving energy and cost? If so, what are the advantages and disadvantages for such an application?

Posted by Andy Mitchell on 2 February, 2007 - 10:54 pm
The obvious advantage of fitting an inverter drive to a screw compressor is energy saving - this can regularly be as much as 30% of the absorbed power. Secondly as the machine is almost permanently under load conditions there is less wear and tear on consumables such as inlet valve seals, drive coupling inserts etc. There can be disadvantages such as over-heating of both the motor and compressor air-end during extended low rpm operation. A fixed speed compressor which is converted to be variable speed will only have a limited speed range with a maximum speed reduction to approximately 50% of nominal motor speed. Many purpose built variable speed drive compressors will turn down to as 20% of the maximum speed / compressor capacity. There are many other considerations to take into account also - will the air-end rotors remain efficient at low speed? Slippage back across the rotors increases dramatically in many units at different rev bands.
I would recommend data-logging your application to see how much air you are using and how much demand varies before making a decision. It may be more economical in the long run to buy a purpose built variable speed drive compressor and keep the GA45 as a back up.

Andy Mitchell
Technical Director
Air Services Ltd.

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