Influencia de la sobrevelocidad en las sobrepresiones que se presentan en los sistemas hidráulicos de las centrales hidroeléctricas equipadas con turbinas Francis

Abstract

At initial stages of a hydroelectric plant study, besides to perform the design of civil works, important non-permanent flow analyses must be carried out. Such analyses comprise the operation of the hydraulic system and the electro mechanic equipment, including the study of overpressure and over speed that may occur during a load rejection of turbines. When a power plant is equipped with Pelton turbines, the flow variation during the shutdown can be studied applying the sequence of injectors and its rating curve; while for reaction turbines, the analysis is more complex, as the flow rate depends, not only on the opening of wicket gates, but also on the speed of rotation, which increases rapidly during load rejections as the generator torque disappears. To overcome the strong limitation on turbine data availability, several researchers have developed simplified methods to replace the use of turbine characteristic curves by simpler equations. One of them is the so called variable discharge orifice method (Ramos, 2002), developed to be applied to small power plants. Present article analyzes the applicability of the method for designing medium and large hydroelectric power plants, by comparing its performance with measurements made in two prototypes.