Page - 1117 - in Book of Full Papers - Symposium Hydro Engineering

3.4. SAFETY-CRITICAL APPURTENANT STRUCTURES AND CONTROL TECHNOLOGY The aim is to assess the reliability of the weir gate’s control technology under unusual and extreme conditions. In a run-of-river plant the functionality of the weir gate is of vital importance to avoid overtopping the weir and overflowing of the river banks upstream of the weir. This chapter of the safety assessment describes the control technology of the weir gates, which is under normal conditions fully automated to maintain the head water at the concessionary level. In case of failure of the automatic control and concurrent rising of the headwater level, a backup control system is taking over to open the weir and avoid overflowing. As an alternative or if the backup system should fail, the weir can be operated manually from the control room in the powerhouse or from a separate control station at the weir site. Both plants have a power supply from their own production. In case of failure of the internal power supply, it can be switched to external supply or supply from the emergency diesel generator. The outcomes from the seismic safety assessment demonstrated that the weir structure and powerhouse, which house the hydraulic system, will remain intact. The hydraulic system is therefore with high probability operable also after an earthquake has occurred. In case of failure of the hydraulic aggregate, in Ruppoldingen a fix installed backup aggregate is available. In both plants, a mobile emergency aggregate with its own diesel generator is available. This allows opening of one gate at the time. Regular trial runs of the backup systems including moving of the gates with the help of these systems ensures that for both plants, the equipment is well maintained and the personnel is well trained to use the equipment even in emergency situations. The assessment could conclude that sufficient redundancy is available to safely open the weir gates also under unusual and extreme conditions. 3.5. STRUCTURAL SAFETY ASSESSMENT In this chapter, the safety of all water-retaining structures, i.e. weir, gates and powerhouse are quantitatively assessed. This requires verification of structural stability (sliding, overturning and buoyancy), structural and foundation stress analyses and behavior against reviewed operational and hazard scenarios (load cases). Head and tailwater levels for the same load cases considered at the time of design were updated based on latest hydrological data. The post-earthquake functionality of the gates needs also to be verified. 1117