水泵水轮机低水头起动过程水力特性分析

Study on Hydraulic Characteristics During Low Head Startup Process of Pump-turbine

抽水蓄能机组在低水头并网发电过程中常会由于水力不稳定性和其自身的反“S”特性导致并网失败,严重影响电力系统的调节品质。为探究水泵水轮机低水头起动过程的水力特性,基于力矩平衡方程控制转轮实时转速,采用增量式比例–积分–微分(proportion integration differentiation,PID)算法对活动导叶开度进行实时控制,借助动网格技术和计算流体动力学方法开展考虑PID控制的水泵水轮机低水头起动过程数值模拟,建立水泵水轮机内部流动演变与外特性变化的关联机制。研究表明:转轮所受压力在起动过程初始阶段最高,叶片表面压力系数为1.22,经过PID调节后减小至1.08。起动过程中转轮力矩的变化主要受叶道涡及驻点位置改变的影响,驻点在叶道内沿逆时针方向移动。水头的变化与转速和回流形态的演变密切相关,表现为转速主导影响了水头的变化频率,而回流的具体形态则影响了压力场的分布,进而决定了机组段水头的数值大小。研究成果可为提高水泵水轮机在低水头起动并网成功率提供参考。

Pumped storage units often fail to connect to the grid in the process of low head generation due to hydraulic instability and their own anti-S characteristics,which seriously affects the regulation quality of the power system.The speed of the runner is controlled based on the torque balance equation,and the opening of guide vanes are controlled by using the incremental proportion integration differentiation(PID)algorithm in real time.By means of the dynamic mesh technology and computational fluid dynamics(CFD)numerical simulation method,the low head startup process of pump�turbine considering PID control is simulated.The correlation between the evolution characteristics of the internal flow details in the pump-turbine and the changes of external characteristics is established.The results show that the pressure on the runner peaks in the initial stage of the starting process,and the blade pressure coefficient reaches 1.22.After PID adjustment,the value decreases to 1.08.The change of runner torque is mainly affected by the change of blade passage vortex and stagnation position.The variation of head is closely related to the evolution of rotational speed and backflow pattern,which is mainly reflected as that the rotational speed dominates the variation frequency of head,while the specific backflow pattern affects the distribution of pressure field,and then determines the specific value of head in unit section.This paper provides reference for improving the success rate of grid connection of pump-turbine in the low head startup process.