Experimental study of pressure pulsation in a large-scale hydropower plant with Francis turbine units and a common penstock

Abstract

The effects of partial load operation on pressure pulsation and pressure pulsation propagation to off-operation units are significant • Pressure pulsation measurements are provided for an actual hydropower plant. • Rotor-stator interactions and draft tube vortex rope were studied simultaneously. • Pressure pulsation propagates from operating units to off-operation units. • In partial loads, the most significant wave in waterway is draft tube vortex rope. • The turbine rotor-stator interaction waves are localized and flow rate dependent. As a limiting factor in power generation, especially in part-loads, turbulence is considered an important phenomenon in hydropower plants. In this study, the pressure pulsation measurements are done for Darian Hydropower Plant in Iran, which is composed of three 70 MW units with a common penstock. The frequency spectrum for different features such as rotor-stator interactions, draft tube vortex rope, and surge tank fluctuations is obtained and discussed in detail. Pressure pulsation measurements were obtained while one of the units (i.e., Unit I) was in operation, and the other units (Units II, III) were out of operation. In addition to the in-operation units, the effect of pressure pulsation on the out of operation units is also studied comprehensively. The results show that to avoid the destructive effect of pressure pulsation, the output power of the in-operation unit should not be lower than 55 MW (i.e., a part load lower than 78% of the full load). Results demonstrate that at lower power levels pressure pulsation is significant likely because the flow characteristics are rather significantly different than the conditions considered for the design of the plant. Moreover, it is found that most of the pressure waves generated by the turbulent flow of the in-operation unit waterway have considerable impacts on the neighboring units. A very good agreement between the expected theoretical frequencies and measured frequencies are observed for various pressure pulsation phenomena, as well.