核电厂汽轮机甩负荷中调阀阀位反馈与指令偏差超限原因分析

Analysis of Deviation of Medium Pressure Control Valve Position Feedback and Instruction Run Over the Limit in Nuclear Power Plant Turbine Fast Cut Back

某1000 MW核电机组在快速甩负荷(FCB)试验时,中压调节阀(简称中调阀)不能及时关闭,发生中压调节阀阀位反馈值与指令值偏差超限问题,引发跳机保护动作。分析发现,造成这次问题的原因是调节阀弹簧力矩与阀门气动力矩不匹配。利用FLUENT软件对该汽轮机中调阀内的三维流场进行数值模拟,得到阀门气动力矩和阀门开度的变化关系。结果表明:气动力矩随调节阀开度的增加先增大后减小,开度为30°左右时达到最大值;此时,若弹簧力矩与阀门气动力矩不匹配就会发生中调阀关闭动作迟缓甚至卡涩问题,造成阀位反馈值与指令值偏差超限。

In the 1000 MW nuclear power units FCB （fast cut back） test, the medium pressure control valve can not be closed in time, the deviation of the valve position feedback and instruction run over the limit ocurred, which caused the turbine trip protection action. Through the analysis, it was found that the mismatch of the aerodynamic moment and the spring moment was the cause of the problem. The three-dimensional flow field was numerically simulated by FLUENT, and the change regulation of aerodynamic moment was obtained. The conclusion shows that the aerodynamic moment first increased and then decreased with the increasing of opening degrees and the maximum value was reached when the opening degree was around 30°. At this point, if the aerodynamic moment did not match the spring moment, the medium pressure valve would close slowly and even clamped, leading to the deviation of the valve position feedback and instruction run over the limit.