抽汽背压式给水泵汽轮机系统电功率超限原因分析与对策

Cause analysis and countermeasures for over limit of electric power of BEST feed water pump steam turbine system

为降低机组汽轮机(简称大机)抽汽的过热度,减少换热过程的不可逆损失,提出并应用一种由变流器主控带小发电机的抽汽背压式给水泵汽轮机(BEST)系统,该汽轮机(简称小机)在驱动锅炉给水泵的同时,其多余功率由配套的小发电机消纳转换,产生的电能供厂内设备使用,从而有效降低厂用电率。实际应用中发现,BEST小机剩余功率过大,触发“电负荷超限”保护动作,小机进汽调节阀关小,带来锅炉给水流量的大幅波动,机组因“给水流量低”保护动作而跳闸。分析运行曲线,认为小机背压异常偏低,蒸汽焓降过大,导致BEST小机剩余功率超过设计值,引起小发电机“负荷超限”。通过优化调整抽汽回热系统投运方案,逐步建立起小机的合理背压,使得小机在各转速下的剩余功率均处于正常范围,BEST给水泵系统电负荷超限问题获得妥善解决,有力保证了机组后续试运工作。相关调试调整经验可供同类型机组参考。

In order to reduce superheat degree of the extraction steam of steam turbine(large turbine)and decrease the irreversible loss in heat exchange process,a back pressure extraction feed pump steam turbine(BEST)system with small generator and controlled by converter is proposed and applied.While driving the boiler feedwater pump,the excessive power of this steam turbine(small turbine)is absorbed and converted by the supporting small generator,the generated electric energy is used by the equipment in the plant,so as to effectively reduce the auxiliary power consumption rate.In practical application,it is found that the residual power of the BEST small turbine is too large,which triggers the“electric load overrun”protection action,and the steam inlet regulating valve of the small turbine is turned down,resulting in a large fluctuation of the boiler feedwater flow,and the unit trips due to the“low feedwater flow”action of the boiler main protection.By analyzing the operation curves,it is considered that the back pressure of the small turbine is abnormally low and the steam enthalpy drop is too large,which leads to the residual power of BEST small turbine exceeding the design value and the“load overrun”of small generator.By optimizing and adjusting the operation scheme of the steam extraction and regenerative system,reasonable back pressure of the small turbine is gradually established,so that the residual power of the small turbine at each speed is in normal range,and the problem of electric load overrun of the BEST feedwater pump system is reliably solved,which effectively ensures the subsequent commissioning of the unit.Relevant commissioning and adjustment experiences can be used as a reference for units of the same type.