VFD / Eddy Current Drive and Automatic Power Factor Correction Relay

The power factor will be related to motor load when using EC coupling, so at lower speeds for a constant torque application the pf will be quite low. The load current will be mostly motor current but you will also have EC losses additionally.

Using VFD, the input Displacement Power Factor will be near unity so will not need correcting for this reason. The input power will be more closely related to the load since VFD losses are relatively low compared to total power.

If using VFD and you are concerned re power quality, a DC choke is a good cost effective benefit.

Eddy current couplings have mostly been superceded by VFD which are very easily available with a lower running cost. The coupling itself adds complexity to the driveline and size and weight. VFD has some downside as it normally needs fitting in an enclosure and introduces high levels of RF and lower order harmonics. If you use a RF filter and have a strong supply this is normally not a real problem. The VFD means you have no inrush current to deal with so sequenced starting is not needed for this reason.

Ultimately, a choice or comparison is really application and environment specific and you don't outline your application, site conditions and your concerns, so its pretty difficult to give better advice without much more information.

The above is just a rough guide as a starter - hope it helps.

Thank you sir. I have more questions and will comeback soon.

T J Shah