hi engineers we have inverter unit have (400 v ac output 500 KVA and dc input 480 v ..... we have battery ( 12 V ,100 AH ) MY QUASTION IS how many battery I need ? for this power ?
It depends on inverter efficiency, for how long you want to load it and at what power level.
The least you need is (ideally) 480V/12V=40 batteries. Assuming 90% efficiency (which is high) and load having PF=1 (VA=W), you can run that system for 480*100*.9 Wh/500 000 W =.0864 hours, or a little more than five minutes.