In AC circuit, there are three concepts of electric power: active power, reactive power and apparent power. KVA stands for apparent power, which includes reactive power and active power. KW stands for active power, and kVar stands for reactive power. The relation between kW and kVar and conversion there is a concept - power factor cos ф, active power kW=UIcos ф, reactive power kVar=UIsin ф, and apparent power kVA=UI(U is voltage, I is current).