Frequency stability of an islanded grid supplied by hydropower plants

The paper presents the results of a study on the behaviour of a small islanded grid, supplied only by hydro units, following generation and load disturbances. Based on a simplified model of the hydraulic components, the generation units and the electrical network, a system simulator provides values for frequency, loads and surge tank levels during the transients following such disturbances. Suitable power and frequency controllers for the generating units were synthesized, on the basis of geometrical and hydraulic characteristics of the penstock, the opening and closing time of the turbine valve actuator, and the starting time of the network, and then introduced in the model.The results show that, with a correct tuning of the turbine controllers, the grid can withstand large generation and load disturbances, with limited and quickly dampened oscillations both of frequency and surge tank level.