Critical stable cross-sectional area of surge tank in hydropower plant with multiple units sharing common hydraulic system

摘要

The stability of hydropower plant has a significant influence on the safety and quality of electric power. Surge tanks, as one of the most crucial components of hydropower plants, possess the ability to stabilize the fluctuation in hydraulic-mechanical-electromagnetic systems after load disturbance. In this study, hydropower plants with multiple units sharing common hydraulic system (MUCH) were divided into the surge tank-headrace tunnel subsystem (SHTS) and multiple turbine-governor-penstock subsystems (TGPSs) according to the coupling effects. The superposition principle of the SHTS was verified by Laplace transform method to adapt the single input restriction for frequency response analysis. Then, a novel theoretical model of the hydropower plant with MUCH was proposed based on the coupling mechanism of the entire system. Combined with the magnitude-frequency characteristics of the system, superimposed magnitude of hydropower plants with MUCH was drawn, which is a quantifying criterion for the stability analysis. Based on coupling effects of the system and physical meaning of superimposed magnitude, a new practical formular of critical stable cross-sectional areas of surge tanks (CSAT) was derived, where the classical Thoma formula is a special case without considering the turbine characteristics and layouts of hydropower plants.