Excitersystem

An excitersystem, or excitation system, is a subsystem of a synchronous generator or motor that provides the direct current (DC) to the rotor winding to establish and control its magnetic field. The field current determines the generated voltage, reactive power, and dynamic response of the machine. Excitation systems can be broadly categorized as brushless or brush-type (external or static) and are integrated with automatic voltage regulation to maintain stable operation under varying load and network conditions.

Brushless excitation uses a rotating exciter mounted on the generator shaft, together with a rectifier assembly on the rotor that feeds DC to the main field without electrical brushes. Static or brushless schemes use power-electronic devices, such as thyristors or IGBTs, and an automatic voltage regulator (AVR) that senses terminal voltage and adjusts the excitation current. In brush-type systems, a DC generator or a thyristor-controlled rectifier supplies the field through slip rings and brushes.

Main components include a power source for the DC field (rotating or static), a field regulator (AVR), sensors for voltage and current, and protection and control circuits. The AVR adjusts field current to control terminal voltage and reactive power flow, contributing to voltage regulation, transient stability, and fault response. Systems may include supplementary controls for speed, power factor, and governor interactions.

Applications include large synchronous machines in power plants, microgrids, and industrial facilities. They require reliability and protection features; trends include brushless excitation, digital AVRs, and remote monitoring. Maintenance considerations include insulation, brush wear for brush-type systems, and coordination with governors.