Abstract
In order to clarify the mechanism of the instability phenomenon in an abnormal operation of a pump turbine, the experiment of a pump-turbine was performed. The pressure at inlet and outlet are measured for the various flow rates and rotating speeds. "S-shape curve" was observed in the turbine characteristic curve. The experimental result shows that as the flow rate increases, the torque increases. "S-shape curve" was observed hi a vicinity of the runaway condition. "S-shape curve" in the pump turbine without the guide vane is more clearly observed than that with the guide vane. "S-shape curve" occurs when the increase ratio of the loss is larger than the decrease ratio of the torque.
