New approach to teaching instantaneous powers in steady-state AC circuits

By transforming the differential equation to an algebraic equation using complex variables, phasor representation is the most suitable and powerful method for analysis of steady-state single-phase alternating-current (AC) circuits. Although the actual phasor representation leads to a fast solution when computing the amplitude and phase of steady-state AC circuit currents and voltages, active, reactive and apparent powers, it does not provide an appropriate way to fully understand and explain the instantaneous power. In this paper, the rotating phasor of current for steady-state single-phase AC circuits is introduced to handle and improve the teaching methodology of instantaneous powers in power undergraduate courses. Terms such as instantaneous active and reactive powers and complex instantaneous apparent power are also defined. Various application examples are provided to assess the pertinence of the proposed teaching approach.