Electrical Engineering ⇒ Topic : Power curve in R-L series circuit

Power curve. The power curve for a R-L series circuit is shown in Fig. (a). To make the treatment more illustrative, it is assumed that current lags behind the voltage by 30°i.e. (Φ) = 30°. It is clear that power is negative between 0⁰ and 30⁰ and between 180° and 210°. During the rest of the cycle, the power is positive. Since the area under the positive loops is greater than that under the negative loops, the net power over the cycle is positive.This means that power is being consumed by the circuit. However, it is less than the average power consumed by a comparable circuit where voltage and current are in phase (i.e. pure resistive circuit). The negative area simply indicates that inductance of the circuit returns power to the source during that interval.

                                                                figure (a)