Power invariance transformation in power systems

Many textbooks describe a balanced three-phase circuit by a single-phase eq uivalent representation. Confusion may arise amongst students regarding per -unit values of line-to-line voltages and phase voltages and, therefore, ab out the magnitudes of currents and powers. This paper proposes that student s must first be taught symmetrical components based on power invariance tra nsformation. A balanced three-phase circuit is to be described only in term s of positive sequence components. In the authors' experience, students und erstand this approach better and make fewer errors in per-unit calculation than when they use the single-phase equivalent representation.