THD Value 4%/5%/6%, What Should Be the Counter Measures?

What we think in this instance is of little importance.

The harmonics expectations of your local power authority and regulator are what needs to be reviewed and understood. You could be causing all sorts of distortion in local radio frequencies, you could be causing all sorts of problems with injected ripple controllers used by some power companies.

You need to ask them.

Do some independent research:

Total Harmonic Distortion and Effects in Electrical Power Systems ...

Essential Basics of Total Harmonic Distortion (THD) | EEP

In my opinion, you may follow the

IEEE Std 519-2014

IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems

and/or:

IEC 61000-3-2: Limits for harmonic current emissions (equipment input current <= 16A per phase)

IEC 61000-3-4: Limitation of emission of harmonic currents in low-voltage power supply systems for equipment with rated current greater than 16 A per phase

In order to eliminate the harmonics here may found some of the recommendations:

http://www.engineering.schneider-electric.dk/Attachments/ed/guide/guide_harmonic_detection_and_filtering.pdf

None of the links I've looked at in this thread mention the detrimental effects that the harmonics present in the outputs of many Variable Frequency Drives appear to have on the bearings of the motors being driven. I've seen more than one article recently that indicate that the harmonics contribute to pitting of the balls and races of the motor bearings. These harmonics are on the outputs of the VFDs, but energy laws specify that such harmonics at the output must cause (not necessarily the same) harmonics reflected back into the supply.

These reflected harmonics (as well as harmonics from other sources) could well have some detrimental effects on non-VFD powered motors and their bearings, at least when in the same plant.