Eigenanalysis of oscillatory instability of a hydropower plant including water conduit dynamics

This paper presents a linearized mathematical model of hydraulic conduit taking the water compressibility and the conduit elasticity into account. The model is for studying the oscillatory instability of a hydropower plant with a 50-m-long penstock, 355-m-long tunnel, but no surge tank. Combining the hydraulic subsystem with the mechanic and the electric subsystems, the results of our investigation by the use of eigenanalysis are reported in this paper. From the study, Water Elasticity and Mechanic-water Oscillation Modes have been identified. This concept leads to an insight of the impacts of water conduit dynamics on stability of hydraulic generating units. Although one of the important causes of the instability lies in the hydraulic system, it is demonstrated that the excitation control, i.e. Power System Stabilizer (PSS), is very effective to overcome the instability problem.