核电站控制棒驱动机构电源系统建模及故障分析

Modeling and Fault Analysis of Power Supply System for Control Rod Driving Mechanism in Nuclear Power Plant

大型核电站控制棒驱动机构的电源系统由两台带飞轮的电动发电机组成,励磁方式包括自并励和相复励。某自并励机型棒电源系统曾发生一机失磁,与之并联的另一机过流保护抢先动作的严重事故。实际核电站中大量棒电源系统采用相复励机型,为了探究此次事故原因并判断棒电源系统中是否存在保护失配的共性风险,有必要对相复励棒电源系统故障特点进行研究。文中从相复励系统的全补偿公式出发,理论分析了机端短路电流变化趋势与相复励系统参数的关系,然后建立了棒电源系统的PSCAD模型。发现机端短路故障的仿真计算与理论分析相吻合,并通过动模机组单机机端短路实验共同验证了仿真模型的正确性。文中仿真分析了棒电源系统单机失磁时的故障特点,提出利用稳态等效电路估算棒电源系统失磁故障时机端电流的大小。结合制造厂家的真机实验验证了估算方法的有效性,同时说明了事故棒电源系统过流与失磁保护失配的原因,为核电棒电源系统保护装置改造奠定了基础。

The power supply system of the control rod driving mechanism in large-scale nuclear power plants consists of two electric generators with flywheels. The excitation modes include self shunt excitation and phase compound excitation. A serious accident occurred in an rod power supply system of self shunt excitation when one generator lost excitation and the overcurrent protection of the other generator in parallel operated first. In actual nuclear power plants, a large number rod power supply systems use phase compound excitation. In order to explore the cause of the accident and determine whether there is a common risk of protection mismatch in the rod power system, it is necessary to study fault characteristics of the rod power supply system of phase compound excitation. Based on the full compensation formula of the phase compound excitation system, this paper theoretically analyzes the relationship between the change trend of the generator terminal short-circuit current and the parameters of the phase compound excitation system, and then establishes the PSCAD model of the rod power supply system. It is found that the simulation calculation of the terminal short-circuit fault is consistent with the theoretical analysis, and the correctness of the simulation model is verified through the single-terminal short-circuit experiment of the dynamic simulation unit. In this paper, the fault characteristics of a single rod power supply system with loss-of-field fault are simulated and analyzed. Combined with the real machine experiment of the manufacturer, the effectiveness of the estimation method is verified, and the reason for the mismatch between over-current and loss-of-field protection of the accident rod power supply system is explained, which lays a foundation for the improvement of protection devices of nucleon rod power supply system.