NEIEP Electrical Theory and Application (430) Practice Exam

Power factor is how much of the current is in phase with the voltage. Inductive loads draw current that lags the voltage, creating a lagging power factor and higher current for the same useful power. A capacitor placed in parallel provides reactive current that leads the voltage, which offsets the lagging reactive power of the inductors. The total reactive power becomes Qtotal = QL − QC, so as the capacitor’s reactive power approaches the load’s, the angle between voltage and current shrinks, cosφ increases toward 1, and the current drawn for the same real power decreases. In short, the capacitor supplies leading reactive power to cancel part of the inductive reactive power, improving the power factor without changing the real power. This effect isn’t achieved by increasing current, dropping voltage, or increasing resistance.