Excitation System in Turbo Generator

Excitation System provides DC to Field Winding of Generator so that Magnetic Flux is produced by it. DC can be provided by External Source. But if it fails, Generator won't work. Self Excitation is always preferred. Self Excitation means that the Exciters are coupled to the Generator by Coupling.
In earlier times, DC Excitation was used. DC was produced by DC Generators and supplied to Rotor of Turbo Generator via Slip rings. This system had number of disadvantages e,g, Sparking, Brush Wear etc. However, this system still exists at number of places, hence DC Excitation is also covered in this Video.
In DC Excitation, Pilot Exciter was self excited and supply DC Current to Field Winding of Main Exciter. Main Exciter is separately excited and supply DC to Generator Rotor.
Brushless Excitation means that DC is supplied to Generator without Brushes. Pilot Exciter has Permanent Magnets on Rotor. AC produced in its Stator is rectified by Thyristor Bridge and fed into Stator of Main Exciter. It uses rotating Diodes to convert AC produced in Rotor of Main Exciter to DC which is supplied to Field Winding of Generator.
Automatic Voltage Regulator (AVR) regulates the Output Voltage. Output Voltage of Generator is stepped down and compared with Reference Voltage in Comparator. The error Voltage is amplified and converted into Pulses by Gate Control.
When a Terminal Voltage of Generator changes, Gate Control advances or retards the pulses. Thyristor is triggered earlier or later and its output changes. Field Current of Main Exciter changes thus changing Field Current of Generator Rotor. Thus Terminal Voltage of Generator changes.
There is a provision of Manual Control also in AVR.

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