If single phase power is 220 volts, why is 3 phase 440 ...
Your question doesn't seem right. It has a couple of mistakes. you said "single phase power is 220 volts . Volts is not unit of power,it is an unit of voltage (potential diference). Three phase kvA is 3 times to its single phase kvA. Its voltage and current rating depend on the type of winding arrangement .