With the rapid increase of the capacity of single synchronous generator

the excitation current for providing magnetic field for electromagnetic induction is also greatly increased

and how to ensure the rapidity

safety and reliability of the de-excitation under extreme conditions such as system failure and no-load faulty forced excitation has become a problem that needs to be solved.Power electronic soft-switching technology provides new ideas and methods for the optimization of de-excitation performance.In this paper

the excitation system of the three Gorges generator is taken as the object of study

and the selection and parameters optimization of the nonlinear resistor are carried out.On this basis

the soft-switching technology is introduced to create the zero-crossing point of excitation current

and the timing coordination of voltage establishment

commutation

energy shifting and energy consumption in the process of de-excitation are analyzed and optimized.Theoretical analysis and simulation show that the zero-current shutdown of the de-excitation circuit breaker is realized

and the safety and reliability are improved on the basis of ensuring the fastness of de-excitation.The time of de-excitation on no-load faulty forcing excitation is1.048 s

the overvoltage of the excitation winding is limited to 3 500 V

and the overvoltage of the de-excitation breaker is limited to 2 000 V.