350 MW机组给水流量低的停机分析

Analysis on Shutdown of 350 MW Unit for Little Feed Water Flow

锅炉发生MFT保护动作,连锁引起汽机跳闸和发电机解列。锅炉跳闸首出信号为“主蒸汽流量大于360 t/h且给水流量低”,即主汽流量大于360 t/h且给水流量低于324 t/h,延时20 s。原因分析表明,机组运行时发生LVDT连杆脱落缺陷,脱落LVDT连杆弯曲,造成LVDT套筒内部磨损;反馈无法线性显示实际位置,存在反馈值突变至0%的可能;然后,通过伺服卡自动控制回路计算,输出较大控制电流指令,驱动油动机开门进汽。在给水主控的自动控制下,A汽泵迅速减小出力,B汽泵超速至6202 r/min后保护动作跳闸,最终总给水流量迅速降低,触发锅炉MFT保护动作。

MFT protection action of boiler occurred,which caused turbine trip and generator disconnection.The first signal of boiler trip is"main steam flow is greater than 360 t/h and feed water flow is low",that is,main steam flow is greater than 360 t/h and feed water flow is lower than 324 t/h,with a delay of 20 s.The analysis of the cause showed that during the operation of the unit,the LVDT connecting rod fell off,and the LVDT connecting rod was bent,result⁃ing in the internal wear of the LVDT sleeve;the feedback could not display the actual position linearly,and there was the possibility that the feedback value would suddenly change to 0%;then,through the automatic control circuit of the servo card,a large control current command was output to drive the hydraulic servo motor to open the door and feed steam.Under the automatic control of feed water main control,the output of steam pump a is reduced rapidly,when the speed of steam pump B reached 6202 r/min,the protection action tripped,finally the total feed water flow decreased rapidly due to insufficient adjustment,which triggered the boiler MFT protection action.