Abstract
The upgrade of Akkats power station in Sweden included a new, separate waterway for the addition of a 75 MW generating unit. The vertical intake of its headrace was formed by means of lake tapping. A physical model was used to help understand the blasting process involving fragmented rock, water, air, and gas. Upon commissioning of the unit, swirling flows occurred unexpectedly at the intake, which gave rise to negative consequences including limitations in power output. Echo-sounding showed that the blasted piercing resulted in an irregular intake. A hydraulic model, as part of the design process, was built to examine potential countermeasures for vortex suppression. The final solution was a segmented barrier between the intake and the dam. It effectively suppressed the intake flow circulations; only minor intermittent vortices were left. The fabricated steel segments were anchored into the bedrock, stretching to 1.0 m below the lowest legal reservoir level. The local intake headloss was also reduced. The implemented solution was tested under full turbine loading and the result was satisfactory. Even during winter seasons with ice cover above the wall, the power station ran normally. The case study is expected to provide guidance for solving similar problems with vortex formation.
Highlights
Akkats hydropower station is located on the Lule River in North Sweden
The power production amounted to 590 GWh annually, 26 GWh of which was attributable to the increase in the turbine efficiency
Its intake was formed through lake tapping, a complex dynamic phenomenon involving constructed
Summary
Akkats hydropower station is located on the Lule River in North Sweden. The facility, constructed between 1969−1973, was equipped with one 150 MW unit at a 45 m gross head and a 385 m3 /s turbine flow rate. Follow forThe laboratory model studies; could only beThere examined approximative purposes of Underwater tunnel piercing was a be complex process.inIt an involved four phases of solid rock, water, studies; the phenomenon could only examined approximative manner. The purposes of blasted pre-filling in the headrace and theamaximum upsurge height in the acting shaft, ato identify the risk of blasted rock transport downstream into tunnelshape and the load upon model studies were to work outthe suitable of thedynamic stone pit, to determine properthe levelconcrete of water sealing rock transport downstream into the tunnel and the dynamic load acting upon the concrete pre-filling in the headrace and the maximum upsurge height in the shaft, to identify the risk of blasted sealing wall [10,11]. A tank with a size of 200 × 200 cm formed the upper reservoir
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