初始运行工况对水泵水轮机飞逸过渡过程水力特性的影响

飞逸过渡过程是抽水蓄能电站可能发生的一类事故工况。此过程中水泵水轮机的转速、流量和压力大幅改变,转轮流态极易恶化,可能引发剧烈压力脉动和转轮受力失衡。水泵水轮机初始运行工况是飞逸过程的重要控制因素之一,但其对此过程中机组水力特性的影响尚不明确。本文用一维管道与三维水泵水轮机耦合的数值模拟研究了某模型抽水蓄能系统中水泵水轮机从两个不同初始运行工况发生飞逸过程时水力特性的差别。结果表明,相对于流动条件较好的额定工况,由流动条件较差的部分负荷工况开始的飞逸过程更容易引起水泵水轮机运行轨迹的剧烈跳动以及流道压力脉动和转轮径向水推力的幅值突增,原因是在此过程中更易形成转轮流动失稳,机理是过渡过程中的瞬时流态保留有相应初始工况的部分流动特征,即瞬时流态的演化存在迟滞效应。因此,在当前不断拓宽抽水蓄能机组运行范围以满足电网容量调节需求的背景下,应充分考虑初始运行工况对可能发生的飞逸过程的影响。

Influence of the initial working condition on the hydraulic performance of the pump-turbine during runaway transient scenario

Runaway is one of the accident transient scenarios in pumped-storage power stations. During this type of scenario, the pump-turbine operating status varies significantly, inducing increases of pressure pulsations and hydraulic loads on the runner easily. The initial working condition is one of the controlling factors of the runaway scenario, however, its influence on the hydraulic performance of the pump-turbine has not been clear. In this study,the influence was analyzed by the coupled numerical simulations between the one-dimensional pipes and the three-dimensional pump-turbine of a model pumped-storage power sys-tem. The results show that the runaway scenario starting from the part-load working condition evidences abrupt variations in the operating trajectory, pressure pulsations, and runner blade radial forces of the pump-turbine; these phenomena do not appear during the runaway scenario starting from the rated working condition. The abrupt variations of the hydraulic performance can be attributed to the transition of runner flow patterns from the stable status to the unstable one during the runaway scenario starting from the part-load working condition. The mechanism of this phenomenon can be attributed to the hysteresis effect of the transient flow patterns, i.e., the instantaneous flow patterns during transients can maintain the corre-sponding initial flow features to some extent. Therefore, the influence of the initial working condition on the pump-turbine runaway performance should also be considered in the pumped-storage power station, es-pecially when broadening the working range of the pump-turbine.