Excitation systems can be defined as the system that provides field current to the rotor winding of a generator. Well-designed excitation systems provide reliability of operation, stability and fast transient response.
The system that is employed for providing the mandatory field current to the rotor winding of the synchronous machine, such style of system is named associate degree excitation system. In different words, the excitation system is outlined because the system that is employed for the assembly of the flux by passing current within the coil. the most demand of associate degree excitation system is responsibleness underneath all conditions of service, the simplicity of management, simple maintenance, stability, and quick transient response.
Types of Excitation System
The excitation system is mainly classified into three types. They are
- AC Excitation System
- Rotor Excitation System
- Brushless Excitation System
- Static Excitation System
- DC Excitation System
Their types are explained below in details.
1. AC Excitation System
The AC excitation system consists of Associate in Nursing generator and thyristor rectifier bridge directly connected to the most generator shaft. the most exciter might either be self-excited or individually excited. The AC excitation system could also be broadly speaking classified into 2 classes that square measure explained below in details.
a. Rotating Thyristor Excitation System
The rotor excitation system is shown within the figure below. The rotating portion is being boxed by the broken line. this technique consists AN AC exciter, stationary field, and a rotating coil. The output of the exciter is corrected by a full-wave thyristor bridge rectifier circuit and is provided to the most generator coil.
The generator coil is additionally provided through another rectifier circuit. The exciter voltage is often engineered up by victimization it residual flux. the facility offer and rectifier management generate the controlled triggering signal. The generator voltage signal is averaged and compare directly with the operator voltage adjustment within the motor vehicle mode of operation. within the manual mode of operation, the excitation current of the generator is compared with a separate manual voltage adjustment.
b. Brushless Excitation System
This system is shown within the figure below. The rotating portion being surrounded by a broken line parallelogram. The brushless excitation system consists associate degree generator, rectifier, main exciter, and a static magnet generator. the most and therefore the pilot exciter ar is driven by the most shaft. the most exciter contains a stationary field and a rotating coil directly connected, through the chemical element rectifiers to the sector of the most alternators.
The pilot exciter is that the shaft drove static magnet generator having rotating permanent magnets hooked up to the shaft and a three-phase stationary coil, that feeds the most exciter field through chemical element rectifiers, within the field of the most generator. The pilot exciter could be a shaft driven static magnet generator having rotating permanent magnets hooked up to the shaft and a 3-phase stationary coil, that feeds the main’s exciter through 3-phase full wave part controlled thyristor bridges.
2. Static Excitation System
In this system, the availability is taken from the generator itself through a 3-phase star/delta connected transformer. the first of the electrical device is connected to the generator bus and their secondary provides power to the rectifier and additionally feed power to the grid feedback loop and alternative electrical instrumentation.
This system includes a terribly little latency and provides wonderful dynamic performance. this method reduced the budget items by eliminating the exciter windage loss and winding maintenance.
3. DC Excitation System
The DC excitation system has 2 exciters – the most exciter and a pilot exciter. The exciter output is adjusted by AN automatic transformer (AVR) for dominant the output terminal voltage of the generator. this electrical device input to the AVR ensures limiting of the generator current throughout a fault.
When the sector breaker is open, the sector discharge electrical device is connected across the sector winding thus on dissipate the keep energy within the coil that is very inductive.
The main and therefore the pilot exciters are often driven either by the most shaft or individually driven by the motor. Direct driven exciters are sometimes most popular as these preserve the unit system of operation, and therefore the excitation isn’t excited by external disturbances.
The voltage rating of the most exciter is regarding four hundred V, and its capability is regarding zero.5% of the capability of the generator. Troubles within the exciters of turbogenerator are quite frequent thanks to their high speed and in and of itself separate motor driven exciters are provided as standby exciter.