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 exci⁃ tation 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. © 2023 Electric Power Automation Equipment Press. All rights reserved.