Abstract The grid adjustment is seriously affected by the instability of Pumped Hydro Energy Storage plants (PHES), one of which is the phenomenon of Positive Slope (PS) in pump turbine. In this paper, two positive slopes were experimentally captured on one curve of the discharge-head performance in a pump turbine while only one positive slope is observed on one pump performance curve in general pumps. The similarities and differences of two positive slopes are demonstrated using data obtained with this pump turbine model. It is found that two positive slopes are caused by two different stalls, respectively. For the first positive slope, the stall with five stall cells in the vane-less domain (between impeller and wicket gates) is induced to play a key role. On each pump performance curve, with the smaller opening of guide vanes, the discharge of the first PS is less, until the first PS and the second PS becomes one PS. For the second positive slope, significant complex vortexes in the impeller inlet, the variations of cavitations and a lower signal of pressure fluctuation are observed. The discharges of the second positive slopes almost keep stable with the different wicket gates’ openings. For their common characteristics, hysteresis phenomena are observed in both PS and are influenced by cavitations.

中文翻译：

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一台单泵水轮机两种不同正斜率的实验比较

摘要 抽水蓄能电站(PHES)的不稳定性严重影响电网调整，其中之一是抽水机正斜率(PS)现象。在本文中，在泵涡轮机中的一条排放水头性能曲线上通过实验捕获了两个正斜率，而在一般泵的一条泵性能曲线上仅观察到一个正斜率。使用此泵涡轮模型获得的数据证明了两个正斜率的异同。发现两个正斜率分别是由两个不同的档位引起的。对于第一个正斜率，在无叶片域（在叶轮和闸门之间）具有五个失速单元的失速被诱导发挥关键作用。在每条泵性能曲线上，导叶开度越小，第一个PS的放电较少，直到第一个PS和第二个PS变成一个PS。对于第二个正斜率，在叶轮入口处观察到显着的复杂涡流、空化的变化和较低的压力波动信号。第二个正斜率的放电几乎保持稳定与不同的闸门的开口。由于它们的共同特征，在两个 PS 中都观察到滞后现象，并且受到空化的影响。