POWER, WATER - HYDRO SURGE SHAFTS | SECTOR
OPEN AND CLOSED CASE
A new combination of open and closed underground surge tanks is advocated by some hydropower researchers to help power plants respond better, and with more operational flexibility, to the increasing dynamic demands coming from power grids. T&T spotlights the challenge and ideas for tunnel networks and shafts.
A recent paper from hydropower researchers proposes to use combinations of traditional open and closed large surge tank caverns in underground water tunnel systems to help achieve faster and better damping of the large-scale forces that quickly arise from dynamically changing flows. In terms of tunnelling, the recommendation would
suggest more complex underground configurations for hydro projects, and design and excavation of more caverns and shafts each time.
CHALLENGE With more demands coming from electricity grids to hydropower plants, especially pumped storage systems, the power plants would have more oscillations of water masses in their tunnel systems, and sometimes briefly but powerfully. This would result in more hydraulic transients washing through the network of tunnels and requiring damping down. The classic term for such combined pressure wave
transients and mass oscillations is ‘water hammer’. Hydropower systems of all kinds are designed to minimise such effects and the ensuing dynamic forces. Often this is done by a variety of means, such as careful governing of flows through operation of hydraulic valves, guide vanes, blades and turbines. An additional facility, and clearly seen in tunnel layouts of hydropower plants, is to have large surge tanks that are, in effect, pressure relief valves. They help to brake the mass oscillations of water and pressure transients passing along tunnels by offering vastly larger local spaces to expand into and for the flows to churn, so helping to provide the necessary damping of the movement and energy. The surge tanks are large openings, connected to the
principal tunnels, or headraces, in different ways. They are effectively caverns and in many older hydropower project designs, such as in Norway, they have vertical shafts; other orientations can see them as surge chambers, which are more used in projects in more recent decades, and long inclined shafts also are in play. Depending on the project, the hydraulic network can be designed as to have them located at different points, generally upstream of underground powerhouse but there can be an additional one downstream. Some of these underground surge tanks are open (which respond slowly to mitigate the oscillations of
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water mass and transients), others are closed - sealed with a volume of pressurised air inside, above the water surface (and offer faster mitigation).
RESEARCH With those baselines for all hydropower, and noting the potential for the energy generation type to offer more to support decarbonisation, flexibility of large-scale energy storage and electricity grid support in various
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