What is the excitation?The main purpose of excitation system for generator is to supply the power source to the rotor field coil.Excitation system produce the field current and it controlled by the automatic voltage regulator (AVR).I already discuss about automatic voltage regulator on my last post.
This field current controller is important to ensure the generator running in the suitable voltage.It also controlled the value of current when generator connected to a large load.It will receive or delivery the required level for reactive power ( kVAr).
We must ensure several factor for the good running condition for generator.The important thing is for the combination of excitation system and automatic voltage regulator.We must ensure the requirement following :-
1) Control the machine voltage accurately in response to slow changes in power or reactive var demand.
2) Limit the magnitude of voltage excursions in response to sudden changes in load.
3) Maintain steady-state stability.
4) Ensure transient stability in response to system faults.
Excitation system for generator
The standard method to supply field current used the direct current ( d.c ) generator and connected with the synchronous machine using shaft.
For high speed generators,normally it used a gearbox to reduce the exciter speed to standard speed around 700 until 1000 r.p.m.The main purpose for this method is to avoid commutation have a problem with d.c generator.
Slip ring method is the common practice to feed the exciter output with generator rotor.The exciter is installed separately from the direct coupled of pilot exciter.The main exciter controlled the field current value for the generator excitation system.