ABSTRACT
Electric generators are devices that convert energy from a mechanical form to an electrical form. This process,
known as electromechanical energy conversion, involves magnetic fields that act as an intermediate medium.
There are two types of generators: alternating current (ac) and direct current (dc). This section explains how
these devices work and how they are modeled in analytical or numerical studies. The input to the machine can
be derived from a number of energy sources. For example, in the generation of large-scale electric power, coal
can produce steam that drives the shaft of the machine. Typically, for such a thermal process, only about one-
third of the raw energy (i.e., from coal) is converted into mechanical energy. The final step of the energy
conversion is quite efficient, with an efficiency close to 100%. The generator’s operation is based on Faraday’s
law of electromagnetic induction. In brief, if a coil (or winding) is linked to a varying magnetic field, then an
electromotive force (emf) or voltage is induced across the coil. Thus, generators have two essential parts, one
creates a magnetic field and the other is where the emf is induced. The magnetic field is typically generated by
electromagnets (thus, the field intensity can be adjusted for control purposes) whose windings are referred to
as field windings or field circuits. The coils where the emf is induced are called armature windings or armature
circuits. One of these two components is stationary (stator) and the other is a rotational part (rotor) driven by
an external torque. Conceptually, it is immaterial which of the two components is to rotate because, in either
case, the armature circuits always ‘‘see’’ a varying magnetic field. However, practical considerations lead to the
common design that for ac generators the field windings are mounted on the rotor and the armature windings
on the stator. In contrast, for dc generators, the field windings are on the stator and armature on the rotor.
Electric generators are electromagnetic devices made of electric and magnetic circuits coupled together electri-
cally and magnetically, where mechanical energy at the shaft is converted to electric energy at the terminals.
