视在功率S=P/cosφ=30/0.8=37.5KVA，无功功率Q=√﹙S²-P²﹚=√﹙37.5²-30²﹚=√506.25=22.5KVAR。ΔU=P÷U×﹙R×0.4﹚+Q÷U×﹙X×0.4﹚=30÷0.38×﹙0.92×0.4﹚+22.5÷0.38×﹙0.352×0.4﹚=37.39VΔU%=ΔU÷U×100%=37.39÷380×100%=9.8%
