基于软开关技术的大型发电机灭磁性能优化

Optimization of De-excitation Performance of Large Capacity Generators Based on Soft-switching Technology

随着同步发电机组单机容量的迅猛提高,为电磁感应提供磁场的励磁电流也大大增加,如何在系统故障和空载误强励等极端条件下确保灭磁的快速性、安全性和可靠性,已成为亟待研究和解决的课题。电力电子软开关技术为灭磁性能的优化提供了新的思路和方法。文中以三峡发电机组励磁系统为研究对象,对非线性电阻进行了选择和参数优化,在此基础上,引入软开关技术,为灭磁创造励磁电流过零点,对灭磁过程中的建压、换流、移能和耗能等工作环节的时序配合进行了分析和优化。理论分析和仿真表明,灭磁过程中实现了灭磁断路器的零电流关断,在保证灭磁快速性的基础上,提高了灭磁的安全性和可靠性。系统故障下空载误强励的灭磁时间为1.048 s,励磁绕组过电压限制在3 500 V,灭磁开关过电压限制在2 000 V。

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.