Abstract: The AVC substation in power plant side receives the instruction of power plantside 500kV bus from the AVC main station of province dispatch center through the remote terminal unit. After considering various restraint conditions sufficiently, the center control unit calculates relevant width of the control pulse, and sends the calculation result to the executing terminal of the AVC system. The executing terminal output the increase or decrease excitation signal to the DCS. The DCS gives the instruction to the excitation system to regulate the reactive power of the generator set. The reactive power output and the terminal voltage of the generator are influenced by the excitation current. When the excitation current varies, the reactive power output and the terminal voltage of the generator will increase or decrease with the variation of the excitation current; and by the transformer beside the generator, the bus voltage will increase or decrease. The increase or decrease of the excitation current can be realized by adjusting the settings of the excitation regulator (AVR).

Key words: automatic voltage control (AVC) system, distributed control system (DCS), excitation system