I am need of help in giving direction to others on a project where a 29.4kv 600 amp transmission is feeding variable frequency drives (VFD) over unknown (by me) mileage (an oil field). As the main load are these VFD which are poor quality, they generate a large amount of harmonics.

General direction (assumed Federal policy on public lands) requires lines under 33kv to be buried.

I have read in an IEEE article about how the harmonics cause premature failure mostly due to additive voltages, but also affected by the slope of the wave and my questions are as follows:

Is anyone aware of such a Federal policy on Federal lands?

What effect would harmonic filters have on the transmission line?

Based on some info given me the peak voltage due to harmonics on a test was about 75% above normal, would design based on 200%*1.25 insulation be adequate?

Will this effect continue to increase over larger and larger distances?

What ball park effect on the total cost per mileage be?

My stake in this is 3rd party, based on questions posed by fellow engineer, asking him if it is reasonable to waive the burial requirement. I could only give a minimalistic opinion as it is outside my expertise. I will be passing the answers on as a courtesy which would be weighed against asthetic issues.