Study On Excitation Protection And Control Of Synchronous Generator Based On Direct Measuring Power-angle And Transient Energy Function Method

According to the statistical data, more than sixty percent of all the synchronous generator faults are the excitation system faults, which includes partial loss-of-excitation and complete loss-of-excitation. Excitation fault is likely to make the generator lose synchronism and fall into asynchronous operation state with excitation or without, which will damage badly the safety of power system and generator group if the protection or control strategy is incorrect. Excitation protection is complex problem because excitation fault relates to the large-disturbance stability of generator. At the present time, excitation fault protection criterions usually use static stability boundary criterion or asynchronous impedance boundary criterion. The criterions react indirectly generator power-angle and slip through the relationship between generator output electromagnetic power and excitation voltage or generator terminal measuring impedance. So excitation protection working result hasn't been ideal because of protection maloperation or misoperation. At the same time, control subject after excitation fault hasn't been studied deeply. So it's very significant in science and engineering utility to study deeply on the protection and control principle and method of generator excitation fault.In this thesis, theoretical analysis method combined with numerical simulation calculation is used. Firstly, based on generator principle and stability control theory of power system, synchronous generator operation behavior after excitation fault is analyzed by simulation calculation. Secondly, principle shortages of existing loss-of-excitation protection are found through protection criterions analysis. Finally, excitation protection and control principle and method based on direct measuring power-angle and rotor system transient energy function is proposed.The thesis includes mainly the following research findings:①According to the demands of large-disturbance stability analysis, mathematic models of generator unit and its correlative system are given. Based on ALSTOM 700MW hydro generator and QFSN - 600 - 2YHG subcritical turbo-generator, generator terminal parameters varying process after excitation fault are simulated. It provides that excitation field drop will lead rotor rotational speed increase and the generator leaving synchronous speed, especially turbo-generator, will rapidly bring enormous asynchronous active power. So when loss-of-excitation fault is studied, even earlier fault, must consider effects of asynchronous active power on generator electromechanical transient process.②Based on varying process of generator terminal parameters after excitation fault, shortages of excitation protective principle of static stability boundary and asynchronous impedance boundary are analyzed. It proposed that excitation fault research relates to large-disturbance stability. Because dynamic power-angle character of generator after excitation fault is non-sinusoidal, there are differences between dynamic power-angle character and static state power-angle character. So it isn't ideal to protective operation result based on small-disturbance stability and static stability boundary criterion. At the same time, it proposed that asynchronous boundary impedance criterion is a constant reactive power circle moving adown j Xd′. It can ensure complete loss-of-excitation generator measuring impedance enter into the circle, but can't ensure the other condition measuring impedance including impossible losing synchronism enter. So loss-of-excitation protection would be maloperation when system voltage drops short and recovers or generator rejects load.③Based on stability principle, it puts forward setting conditions and calculation method of generator loss-of-excitation protection by direct measuring power-angle. According to large capacity power plant connection configuration, mathematic models of excitation system and its correlative system are given. Generator loss-of-excitation protection by direct measuring power-angle is simulated. The simulate results show that the direct measuring power-angle loss-of-excitation protection can react excitation fault reliably and rapidly.④The relationship between transient energy function of generator rotor system and generator stability is analyzed in the thesis. It proposes load-shedding control method to partial loss-of-excitation generator using transient energy function of generator rotor system. The control method is load-shedding speed proportions measuring real time potential energy of generator rotor system. So it furthest ensures that depth loss-of-excitation generator doesn't loss synchronization and the other condition loss-of-excitation generator keeps larger generating power. The forward method validity is proved by simulation calculation.