Excitation systems have a powerful impact on generator dynamic performance and availability, it ensures quality of generator voltage and reactive power, i.e. quality of delivered energy to consumers. Following types are common:
- [Brushless excitation systems], with rotating exciter machines and [Automatic Voltage Regulator (AVR)], or
- Static Excitation Systems [SES], feeding rotor directly from thyristor bridges via brushes
Static Excitation System:
In the static excitation system the rotating rectifier is not being used; the supply to the rotor field is being given through the brushes which are static and it is further controlled as the same system as the static excitation system by the excitation transformers and the excitation generators.
Schematic Diagram of Static Excitation System
In this system, the AC power is tapped off from the generator terminal stepped down and rectified by fully controlled thyristor Bridges and then directly fed to the field of the main generator through slip rings thereby controlling the generator voltage output.Here Alternator’s Stator and Rectifier are stationary.
A high control speed is achieved by using an internal free control and power electronic system. Any deviation in the generator terminal voltage is sensed by an error detector and causes the voltage regulator to advance or retard the firing angle of the thyristors thereby controlling the field excitation of the alternator.
The other type of excitation system is
Brushless excitation systems, with rotating exciter machines and Automatic Voltage Regulator (AVR)