Variable frequency drive for NG compressor

This could be taken two ways: either it is:
1. An electric motor driving the compressor (rather than a turbine or diesel/gas engine)
or
2. An electric motor with a variable frequency drive.

So, there are a selection of answers:
1a. if the driver is a synchronous motor there isn't a power factor problem as the motor will be either 1.0 or leading PF
1b. if the driver is induction: check with the motor manufacturer for the power factor vs. load curve AND request from the manufacturer of the recommended maximum PF correction capacitor.

2. If it is a variable frequency drive, check with the VFD manufacturer to see what kind of front end it has, and then validate what the vendor can allow as PF modification equipment placed before the AC drive.

There will need to be a torsional analysis completed with a loaded torque effort curve supplied by the compressor manufacture. This will be necessary for moth motor and coupling to be adequately sized and properly selected. This goes back to the sizing of the variable frequency drive as well. If there are large torque spikes occurring each rotation the drive must be sized to provide adequate amperage. Remember that AC drives are horsepower sized for convenience. They are always sized to the amperage requirement and this application may require 5-7000hp VFD to adequately drive the load with no trip.

The VFD drive manufacture should be consulted on the power factor issue depending on technology used on the rectifier front end. 6, 12 pulse?? CSI, VSI, LCI
A transformer may be required to reduce other issues, such as common mode voltages.