This document describes the principles of operation of a 3-phase alternator. It discusses how a synchronous generator works using Faraday's law of electromagnetic induction. It also describes the different components of a 3-phase alternator including the stator, rotor, and different winding configurations. The document also discusses how varying the field current can control the output voltage of the alternator and how the number of poles and rotor speed determine the output frequency. Open and short circuit testing characteristics are also summarized.