Brush less Digital Excitation & Control system for 500KW to 60MW Synchronous Machine

Click on image to enlarge

The Digital Excitation Control System is intended for providing controls and protection for the Excitation control of HT & LT AC Generators.

The Digital Excitation Control System provides necessary controls and protection to operate the Generator in

1. Solo mode
2. Parallel with other generators (Droop Mode)
3. Parallel with the grid (PF or VAR Mode)

The system is built with 15/20 Amp Excitation controller, which has multiple control functions. The digital AVR has a soft start feature with a user-adjustable setting to govern the rate at which the generator voltage is allowed to buildup. The output voltage of AC generator is maintained at the set point by controlling the exciter field current.

In this 15/ 20 Amp Excitation system with one auto and one manual mode i.e. Field Current Regulator mode (FCR mode). This FCR mode will be useful at the time of commissioning for OCC & SCC and when the Auto mode operation develops problem.

The VAr / Pf control module of the Digital AVR is employed to provide a constant Pf or Constant VAr operation when operating in parallel with the Grid during Auto mode. This module will keep the Power Factor / VAr constant (depending on the mode selected) at the set value against normal grid voltage variation and MW load variation.

The limiters used are Minimum Excitation and Maximum Excitation Limiter. The UEL (Under Excitation Limiter) protects the generator by quickly increasing the excitation should the generator Pf goes leading beyond limit where the Generator could slip out of synchronization. The Stator Current limiter (SCL) puts a limit to the stator current (lag) and will not allow the generator to be over excited to the point of damaging the generator field windings.

The protection features offer fully adjustable tripping levels and time delays. The protection features provided are i) Generator Over Voltage ii) Generator Under Voltage iii) Field Over Voltage iv) Field Over current v) Loss of sensing vi) Loss of field and vii) Exciter diode monitor viii)Watch Dog Timer. The protection relays if enabled will send signals to trip the breaker through 86G. The 86G in turn will shut down the Controller output and hence the Excitation system after the circuit breaker opens out.

Extreme conditions of operation or fault conditions are latched with a Hooter alarm to help the user to identify the cause for tripping of the excitation system. The parameters are also viewable via the front System LCD display of the AVR unit. Password protection offers restrict access for changing the parameter setting. The oscillographic data recording feature can be used to record the generator voltage, current, frequency, kW, Power Factor, exciter field voltage and exciter field current.