Hi Prasad,
It is a 3 phase 4 wire system with 230V rms between phase and neutral (Indian 3 phase system ). We want the 3.3V supply to function even if one of the phases fail.
I don’t know right now if current imbalances between phases will have an effect on the power supply operation. I am not sure about this. The only reason we want a 3 phase Input is to increase the reliability of the system and avoid a single point failure.