Control of rotary exciter with series and separetly excitation windings excitation system of generator a2 at power plant “Kostolac A”

摘要

In this paper, the excitation control with rotary exciter of generator A2 in Thermal Power Plant “Kostolac A” is presented. Excitation system under consideration consists of a main exciter, an auxiliary exciter and power semiconductor rectifiers. The main exciter is a synchronous-reluctance generator with windingless toothed rotor. That excitation system is specific due to the fact that the main exciter has three excitation windings and three phase output a.c. windings, all located at stator. Series excitation is serially connected with rotor winding of the synchronous generator, while other two separate excitations are realized by independent windings, each of them generating the flux pointing in opposite direction. In the main three phase a.c. windings the 500 Hz frequency currents are induced. Auxiliary exciter is a 400 Hz permanent-magnet synchronous generator. It supplies separate excitation windings of the main exciter by means of thyristor rectifier bridges. The main aim of the control algorithm is to accomplish the magnetomotive force balance of all three excitation windings in order to regulate generator terminal voltage. In addition to the main outer voltage control loop, the inner local stabilizing current loop is added in order to achieve the satisfactory transient performance of the regulation. Control algorithm sets the values of the firing angle of the thyristors in two three-phase rectifier bridges, in order to produce corresponding excitation currents of separate excitation windings.