Case study: Damaging effects of increasing the installed capacity in an existing hydropower plant

摘要

This paper presents a case study of the 960 MW Tonstad hydropower plant, in which the installed capacity was increased from 640 to 960 MW in 1988. In combination with installing new turbine governors, this upgrade resulted in several problems due to higher water discharge and amplified hydraulic transients. Due to high headloss, rapid change of produced power, or a combination of these, free surface flow occurred in a sand trap and flushed sand, gravel and rocks down into the turbines. In addition, high pressure on the downstream side of the reservoir intake gates is observed and has caused uncertainty regarding the structural safety of the gate frames and blades. These problems have resulted in restrictions on operation, and economical loss due to repair and reduced power production revenue. In this work, the layout of the power plant and an analysis of the incidents are presented, and a discussion on how this situation could occur and how it can be avoided in other power plants is conducted. It is concluded that in hydropower plants with complex tunnel systems, very detailed studies are necessary to understand the hydraulic behaviour and to foresee potential problems.