Hydraulic transients in hydropower plant impact on power system dynamic stability

Futaleufu hydropower plant has 4 Francis turbines rated 118 MW and it is connected to the power system by 2times330 kV lines. Studies carried out in the past did not predict the instable operation of Futaleufu after a 330 kV line fault, when some Futaleufu turbines are automatically disconnected as a consequence of the faulted line tripping. Load rejection caused by disconnected turbines generate large transients in the remaining turbines due to hydraulic coupling through the common conduits. Then, to improve related models and, therefore, to improve studies results of such a line fault it was necessary to make several tests in Futaleufu power plant. Finally, these models were used to conduct studies to design a new automatism, like the gate partial closing of the remaining turbines, to obtain a dynamically stable operation of Futaleufu after the disconnection by fault of a line of 330 kilovolts.