What are self-excited generators with shunt and series fields called?

Self-excited generators that have both shunt and series fields are referred to as exciters. These exciters are essential components in many electrical systems, as they provide the necessary excitation current to maintain the generator's output voltage.

In these types of generators, the shunt field winding is connected in parallel with the load, allowing it to respond quickly to changes in load conditions. The series field winding, on the other hand, is connected in series with the armature and helps to increase the generator voltage output under high-load conditions. By creating a balance between these two fields, self-excited generators can maintain a stable voltage output despite variations in load.

Exciters play a crucial role in the functionality and stability of larger power systems, particularly in applications where consistent voltage regulation is vital. This makes them an essential part of generator systems, in contrast to the other options presented, which serve different purposes. Transformers, for instance, are used to change voltage levels in AC systems, SCR drives are solid-state devices that control the power flow to electric motors, and diodes are semiconductor devices used for allowing current flow in one direction only.