ABSTRACT
The usage of a three-phase voltage supply is very common for the generation, transmission and distribution of bulk electrical power and is most commonly used by electric grids worldwide. Most of the industrial loads are supplied by three-phase power for its advantages over single-phase systems such as cost and efficiency for the same amount of power transmission. In principle, any number of phases can be used in a polyphase electric system, however a three-phase system is simpler from the design and construction point of view of power system and its components.
In this chapter, the behaviour of three-phase systems under different conditions of voltages and currents is analysed, and related important terms are explained in detail. The components of three-phase power under balanced, unbalanced and harmonic conditions are described and illustrated through examples. A component of power, i.e., instantaneous reactive power is introduced using the αβ0 transformation, which is related to instantaneous reactive power and Budeanu's reactive power. The unbalanced three-phase system is described in terms of three balanced sets of voltage components, i.e., positive, negative and zero sequence components and accordingly sequence powers are derived using symmetrical components. Based on the definition of apparent power, the expressions for various power factors such as arithmetic, vector, and effective power factors are developed. The equivalence of a three-phase balanced and unbalanced load based on the same output power and losses in the feeder is discussed. From this equivalence, it is inferred that the power factor of the balanced equivalent circuit is the same as the effective power factor, which can be used to design the feeders in an electrical system.
