V20 vfd showing f3 fault after running 1hr

Dear Shaad,

F3 means line voltage too low.
I assume, that the line voltage failed.
I propose as follow:
Measure the three phases put the results on a writer.
Put the fault message of the drive (DO) also on this writer.
Monitor the DC link voltage on a analogue output and transmit it also onto the writer.
By simultaneously monitoring these values the identification when the fault occurs will be possible.

A quick overview might be given by looking all three phases with a multimeter and detect the max / min values by it. 

I don't think, that the drives HW is defective.

Hello,

please check out the V20 operating instruction manual, page 252.
https://support.industry.siemens.com/cs/ww/en/view/109768394

You can find the detailed description of p1210 there.
Please also pay attention to the delay time, maybe your chosen restart attempts doesn`t cover more than 6s of power supply failures.

"Delay Time" is the time between attempts of quitting fault. The "Delay Time" of first attempt is 1 second, then it will be doubled every next attempt."

In this case you can try to use another setting of p1210 or simply increase the value of p1211.