Abstract Hydroelectric units can be operated in synchronous condenser mode to provide reactive power to the electrical power system (EPS) for voltage regulation. In this operating mode, the hydraulic turbine consumes active power and in case of hydroelectric units equipped with a Francis turbine, pressurized air is injected in the draft tube to decrease the tailwater level below the runner for decreasing the friction losses. Several dynamic phenomena have been recorded during full-scale hydraulic turbine operation due to the air–water mixing causing pressure and torque fluctuations which may compromise the operation and safety of both the hydraulic machine and the EPS. In this paper, the study of the dynamic response of a Francis turbine prototype during synchronous condenser mode operation is performed to evaluate the transposition of the machine behaviour from the homologous reduced scale model to the full-scale prototype. Measurements of the pressure in draft tube cone, machine vibrations, and torque are performed in both full scale prototype and reduced scale model. The analysis of the dynamic behaviour of the hydraulic turbine focuses on the critical vibrations and power fluctuations. The onset of a sloshing wave in the draft tube cone is highlighted as predicted by the reduced scale model tests. Rotor–stator interactions (RSI) are analyzed and compared to the RSI during generating mode operation. The advantages of decreasing the pressure in the vaneless gap between the runner blades and the closed guide vanes by installing a draining pipe are emphasized to limit the amplitude of the fluctuations and to avoid unwanted two-phase flow phenomena in the vaneless gap which can perturb the machine operation and safety.

中文翻译：

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电力系统电压调节过程中混流式水轮机的动态行为

摘要 水力发电机组可以在同步凝汽器模式下运行，为电力系统（EPS）提供无功功率进行电压调节。在这种运行模式下，水轮机消耗有功功率，对于配备混流式水轮机的水力发电机组，在尾水管中注入加压空气以降低转轮下方的尾水位，从而减少摩擦损失。由于气水混合导致压力和扭矩波动，这可能会危及液压机和 EPS 的运行和安全，因此在全尺寸水轮机运行期间记录了几种动态现象。在本文中，在同步冷凝器模式运行期间对混流式水轮机原型的动态响应进行研究，以评估机器行为从同源缩小模型到全尺寸原型的转换。在全尺寸原型和缩小比例模型中对尾水管锥体中的压力、机器振动和扭矩进行测量。水轮机动态行为的分析侧重于临界振动和功率波动。正如缩小比例模型测试所预测的那样，尾水管锥体中晃动波的开始被突出显示。转子 - 定子相互作用 (RSI) 被分析并与发电模式运行期间的 RSI 进行比较。