基于实测甩负荷的水轮机力矩特性曲线拟合

水电站过渡过程计算中,水轮机特性曲线对计算结果有着十分重要的影响。由于水轮机模型试验得到的综合特性曲线仅包含了水轮机工作的相对高效率区、导叶大开度下水轮机特性,无法满足甩负荷过渡过程计算的要求,需要对特性曲线进行拓展得到水轮机在导叶小开度区、低效率区及制动工况区的特性。目前对于水轮机特性曲线的处理主要根据经验和数学方法对力矩特性进行拓展和拟合,其仿真结果与实测结果存在较大的差异,无法满足对甩负荷过渡过程精确仿真的要求。虽然通过内特性或CFD的方法能够增加水轮机特性的仿真精度,但是需要能够获得详细及准确的水轮机结构及尺寸参数,实际情况中这些参数往往无法准确获取,不利于工程应用。该文基于真机甩负荷实测结果对水轮机力矩特性曲线的拟合进行了研究,通过甩负荷实测数据得到导叶零开度线下的水轮机力矩特性,结合最小二乘法对整个力矩特性曲线进行拓展和拟合。将利用该处理方法得到的水轮机力矩特性曲线与传统处理方法得到的结果进行对比,结果表明,在导叶大开度、高效率区及水轮机正常运行范围内2种特性曲线基本重合,而在导叶小开度下2种特性曲线存在较大的差异,原因在于本文中零导叶开度线上的力矩特性通过甩负荷实测结果得出其更加精确,零导叶开度线力矩特性的差异导致了特性曲线拟合中边界条件的不同。利用本文处理方法得到的特性曲线对不同调速器参数下的甩负荷过渡过程进行了计算,并分析了调速器参数对甩负荷过渡过程的影响,计算结果表明,调速器参数对甩负荷中导叶开度的快关过程和机组转速的上升下降过程无影响,其主要影响机组转速接近稳态后的调节过程,调速器参数设置不当会造成调节系统的调节品质变差,甚至会导致水轮机调节过程失稳。分别采用2种特性曲线对水电机组甩负荷过渡过程进行仿真,并将仿真结果与实测结果进行对比,结果表明,相比传统处理方法得到的特性曲线,本文处理方法得到的特性曲线能更准确反映机组在导叶小开度下的力矩特性,机组频率仿真结果中,传统特性曲线计算结果与实测结果最大偏差达到了15.74%,本文特性曲线计算结果与实测结果最大偏差为1.05%;导叶开度仿真结果中,传统特性曲线计算结果与实测结果最大偏差为36.07%,本文特性曲线计算结果与实测结果最大偏差为9.74%。通过对比可以看出,本文所提出的特性曲线拟合方法可大大提高甩负荷过渡过程计算精度,能够有效指导水电机组的安全运行。

Fitting of hydro turbine torque characteristic curves based on load rejection test

Abstract: In hydropower station transient process calculation, the hydro turbine characteristic curve had a very important impact on the calculation results. At present, the torque characteristic curve of hydro turbine is extended and fitted by the experience and mathematical methods. The simulation results are different from the test results, and it is unable to meet the requirements of accurate simulation of load shedding transient process. In this article, the treatment method of hydro turbine torque characteristic curve was studied based on load shedding test. The torque characteristic of the zero guide vane opening was identified by the shedding test data, and the whole torque characteristic curves were extended and fitted combined with the least square method. The curves were compared with the torque characteristic curves obtained by the traditional method. The results showed that the two characteristic curves are basically coincided under the large guide vane opening and relatively high efficiency, and different in the small guide vane opening. The characteristic curve obtained in this article was used to calculate the load shedding transient process under the different governor parameters, and the influence of the governor parameters on the load shedding transient process was analyzed. Two characteristic curves were used to simulate the load shedding transient process of a hydropower unit, and the simulation results are compared with the test results. Through the analysis, it is found that the characteristic curve obtained by this article can reflect the moment characteristic of the unit more accurately than the traditional method under the small guide vane opening, it is used to simulate the load shedding transition process, and the calculated results were compared with the test results, the maximum deviation of the calculated frequency is 1.05%, and the maximum deviation of the guide blade opening is 9.74%, and the simulation accuracy of the transient process is greatly improved. The research of this article can effectively guide the safe operation of hydroelectric unit.