ABSTRACT
This chapter reviews the basic concepts pertaining to ac circuits. Because electrical components of a power system predominantly are three-phase units, the chapter focuses on three-phase systems. It pays special attention to power in ac circuits. In an ac power system under steady-state, alternating voltages (and currents) vary sinusoidally at a fixed frequency. Most of the commercial electrical power produced in this country is generated in three-phase systems. A three-phase system requires the generation of three balanced sinusoidal voltages which by definition will have the same magnitude and frequency, but will be displaced from each other by 120° in phase. In working with balanced three-phase systems, computations are usually made on a per-phase basis, and then the total results for the entire circuit are obtained on the basis of the symmetry and other factors which must apply. Thus, each generator seems to supply only its own phase, and the computations on a per-phase basis are therefore legitimate.
