All,

I need your detailed support on one of my project. I request you all to please answer to all my questions and queries to properly support me on this project.

I have been given a project to install VFD on air compressor. The purpose is to control compressor’s speed according to desired pressure at header. The current compressor control works on loading and unloading of air compressor as per pressure requirement at common header.

There are following types of air compressors installed at site:

a) Screw Air Compressor.
b) Piston Air Compressor.

I am new to this technology and doesn’t know:

1. Is this possible to install VFD on “Piston Air Compressor” as I have heard that only screw compressors are best to go with VFD?
2. What parameters do I need to study for air compressor before installing it with VFD.
3. What possible problem may occur by installing VFD which can easily be resolved by working on it proactively.

Can anyone help?

Reciprocating and screw compressors have a minimum speed that is required for proper lubrication of the bearings. Either compressor has a maximum speed. Hence, high and low frequency settings are needed as well as rate of change tuning to prevent surging. Improved pressure control, reduced vibration, and longer compressor life should be attained as well as modest electrical savings. Screw compressor should work the bast so long as it does not require excessive turn-down. Reciprocating compressor should have a greater turn-down.

Hi Steven,

Thanks for your response.

Now I am looking for what possible items do I need to take into consideration before installing VFD on compressor:

a) Motor - this can be replaced by inverter duty motor.
b) Air Compressor - this is my point of concern now. Is there anything inside compressor unit that must be studied or taken into consideration. I mean to say any compressor unit's part or assembly or anything else related to its configuration & operation before VFD may create problem in operating compressor on VFD.

You can use the screw compressor to get the high flow rate and volume and connect one or 2 piston compressors to boost the pressure based on signal from pressure transmitter or switch

I would suggest you go back to your Supervisor and advise him that you do not have the skillset to complete this project and you need to outsource the project

you to check the motor compatibly with VFD, and the required air capacity with the rate of air consumption per/hr.
you can use screw compressor, with pressure senor switch.

If you can start the compressors in an unloaded condition a VFD can act as a soft starter. This reduces the in rush current and the heating of the motor windings. This improves motor life. The motor may be able to start more often (times per hour) and the insulation isn't damaged as fast. An inverter rated motor is a must.

The only thing we have to take care of is when you are starting the motor with VFD frequently do check its temperature settings as it usually happens motor trips frequently as current rises which causes change in temperature control.

All, I would appreicate your help but this is not what I am asking. I need answer on the following:

2. What parameters do I need to study for air compressor before installing it with VFD.
3. What possible problem may occur by installing VFD which can easily be resolved by working on it proactively.

And then I explained my question in the following para which is linked to point no. 2 & 3 mentioned above here:

b) Air Compressor - this is my point of concern now. Is there anything inside compressor unit that must be studied or taken into consideration. I mean to say any compressor unit's part or assembly or anything else related to its configuration & operation before VFD may create problem in operating compressor on VFD.

Usman, is you company too short on cash to pay a QUALIFIED consultant? If yes, then the answers would be as follows:
2. Air compressor operations 101.
3. Your Air Compressor User's Manual.