核电多相角形无刷励磁系统旋转二极管开路故障特征分析

多相无刷励磁系统是大容量核电机组的首选励磁方式,其整流二极管处于高速旋转状态,在实际运行中二极管故障时有发生,对二极管故障特征的准确把握是实现对其可靠灵敏保护的前提。首先,通过理论分析得到旋转二极管正常运行、一管开路及一相开路时励磁机转子电枢电流的解析表达式。进一步,基于电枢反应磁势对定子励磁绕组作用的分析,得到了3种运行情况下励磁机定子励磁电流的谐波特性。最后,对某11相角形无刷励磁机样机进行了负载工况下二极管正常运行、一管开路及一相开路实验,电枢电流和励磁电流的实验结果验证了理论分析的正确性。实验与理论分析均表明:旋转二极管正常运行时励磁机定子励磁电流主要含直流分量,一管开路时出现基波和各次谐波分量,一相开路时出现各偶数次谐波分量。

Characteristic Analysis of Open-circuit Fault of Rotating Diode in Nuclear Multi-phase Angular Brushless Excitation System

Multi-phase brushless excitation system is the preferred excitation mode for large-capacity nuclear power units. Its rectifier diode is in high-speed rotating state. Diode faults frequently occur in actual operation. Accurate grasp of the characteristics of diode faults is the premise to achieve reliable and sensitive protection. Firstly, the analytical expressions of armature current of the exciter rotor are obtained by theoretical analysis when the rotating diode is in normal operation, one-tube open circuit and one-phase open circuit. Furthermore, based on the analysis of the excitation effect of armature reaction on the stator excitation winding, the harmonic characteristics of excitation current of exciter stator under three operation conditions are obtained. Finally, experiments are carried out on an eleven-phase model machine with load when diode is in normal operation, one tube is open-circuit and one phase is open-circuit. Experimental results of armature current and excitation current verify the correctness of the theoretical analysis. Experiments and theoretical analysis show that the stator excitation current of the exciter mainly contains DC component when the rotating diode is in normal operation, fundamental and harmonics components appear when one tube is open-circuit, and even harmonics components occur when one phase is open-circuit.