Linear power networks — Three-phase systems

Alternating current (AC) and direct current (DC) are the two main power transmission and distribution systems. Historically, the use of transformers to adapt voltage levels to the power being transmitted led electricians to opt for alternating current to develop large-scale power networks. For both technical and economic reasons, three-phase systems were soon to take on particular importance, from the production to the use of electrical energy. The aim of this article is to describe the operation of three-phase systems, covering balanced operation, single-phase equivalent diagrams and unbalanced operation.