excitator

An excitator, sometimes spelled exciter, is a device or subsystem that provides the excitation current to the electromagnetic field of an electrical machine, most commonly a generator or motor. The excitation current establishes the magnetic field needed for operation and determines the output voltage and torque characteristics.

In power generation, exciters can be brush-type or brushless. Brush-type exciters draw current from the main generator or an external source and feed the field via brushes. Brushless exciters use a small auxiliary generator mounted on the same shaft or an external stator, whose output is rectified (often by rotating rectifiers) to supply the main rotor field without brushes.

Excitation systems may be static or rotating. Static exciters use solid-state devices such as silicon-controlled rectifiers or insulated-gate bipolar transistors to convert AC to DC and regulate current; rotating exciters use a physical generator and rectifier that rotate with the machine. Automatic voltage regulators monitor terminal voltage and adjust excitation to maintain stable output.

Role and issues: Proper excitation is essential for voltage regulation, transient stability, and fault response. Inadequate excitation can cause voltage collapse, excessive reactive power flow, or overheating. Modern plants use integrated excitation systems with digital control, protection schemes, and remote monitoring.

Terminology: The term excitator is common in some engineering communities and is often used interchangeably with exciter; however, exciter is the more widely adopted term in many languages and standards. Other related terms include field winding, regulator, and AVR (automatic voltage regulator).