OPERATING HYDRO TURBINES WITH AAR INDUCED GROWTH IN CONCRETE DAMS - OTTO HOLDEN GENERATING STATION

摘要

Otto Holden Generating Station located on the Ottawa River, Ontario, Canada has been in operation since 1952. It has eight generating units with total capacity of 243 MW. Alkali Aggregate Reaction (AAR) has been identified as a probable cause for concrete movement and growth since early 1970s. The effects of concrete induced movement were noticed during turbine and generator component alignments performed as part of major unit overhauls on all eight units during the 1980s. AAR was confirmed after concrete analysis in 1999 and instrumentations were installed at various locations in the dam to monitor the concrete growth. Units were operated in off-plumb condition due to relative horizontal movement between the headcover and bottom ring till the late 1990s. G8 encountered problem of sticky wicket gates in 1999 and this initiated second set of major overhauls for all units in 2000. During these overhauls, the headcover and bottom ring were placed eccentrically and bottom ring was modified with a unique design of in- situ adjustability to compensate for its future relative horizontal movement without dismantling the unit. At the beginning of 2014, turbine assessment program was initiated to evaluate the current condition of the units. As a part of this assessment, turbine clearance data and concrete instrumentation data was analysed, Finite Element Analysis (FEA) of turbine components and concrete dam structure was conducted and it led to better understanding of the effects of AAR on turbine alignment caused by distortion of the speed ring and stay vanes. A third set of overhauls is being planned to mitigate unit alignment problems and to extend the operating life of the station. In these overhauls the top speed ring will be freed up from its connection with the concrete, anchor bars, and the pit liner so that it can recover its horizontal offset elastically. This will improve unit alignments and reduce the frequency of unit overhauls.