核电站控制棒电源系统相复励发电机短路故障的解析计算

针对核电站控制棒电源系统，现有保护仅采用以额定电流为定值的定时限过流保护作为短路后备保护，导致该系统已发生多起过流保护抢先动作与失磁保护失配的事件。解决保护失配问题的关键在于对控制棒电源系统发电机短路故障电流的准确解析，解析重点在于考虑发电机实际采用的相复励无刷励磁方式对故障电流的影响，而相复励励磁电流由并励电压对应的励磁分量和复励电流对应的励磁分量合成产生。经过合理的假设与模型简化，结合发电机基本方程和励磁系统数学模型，推导得到了并励电压分量作用下的三相短路电流。引入复励电流分量作用，根据励磁电流变化对短路电流进行修正，得到了包含暂态分量和稳态分量的相复励发电机三相短路电流时域解析表达式。由正序等效定则扩展得到两相短路电流的时域解析表达式。基于PSCAD/EMTDC平台建立了控制棒电源系统电磁暂态模型，对理论分析结果进行了验证，进一步对保护优化方法进行了讨论。

Analytical calculation of short circuit fault of phase compound excitation generator in control rod power system of nuclear power plant

For the control rod power supply system of nuclear power plant, the existing protection only uses the fixed time overcurrent protection with rated current as the backup protection for short circuit fault, which has led to several events of overcurrent protection preemptive action and mismatch with loss of excitation protection in this system. The key to solve the protection mismatch problem is to accurately analyze the short circuit fault current of generator in the control rod power supply system. The key point of the analysis is to consider the influence of the phase compound brushless excitation mode actually adopted by generator on the fault current, and the phase compound excitation current is composed of the excitation components corresponding to the shunt excitation voltage component and the compound excitation current. Through the reasonable assumption and model simplification, combined with the basic equations of the generator and the mathematical model of the excitation system, the three-phase short circuit current under the shunt excitation voltage component is derived. The compound excitation current component is introduced to modify the short circuit current according to the variation of excitation current, and the time-domain analytical expression of three-phase short circuit current of phase compound excitation generator including transient component and steady-state component is obtained. The time-domain analytical expression of two-phase short circuit current is obtained by extending the positive sequence equivalent rule. The electromagnetic transient model of the control rod power supply system is established based on PSCAD/EMTDC platform to verify the theoretical analysis results, and the protection optimization method is further discussed.