Surge tank design in Austria: Dimensioning-philosophy for flexible hydropower

For high head hydro power plants with tunnels with a significant length, inertia surge tanks are necessary and crucial to allow functional operation of power units. Surge tanks at first allow the controllability of the units and act as surge protection. Due to its placing surge tanks separate the pressurized hydraulic continuum of the power water way and create a demand of balancing water volume. Therefore, a usually significant large construction has to be built often inside the mountain. The size of the surge tank is driven by the water inertia in the power water way expressed in diameter and length, in combination with the demanded loading and unloading time of the power units.
From the first constructed surge tank on until now engineers have been very creative to design surge tanks as small as possible.
This article reflects the development of surge tank designs in Austria and underlines the complexity of the topic. Since there is no standard available, a great emphasis is put on the safety philosophy according to surge designs in Austria. This philosophy depends mainly on the experience of the designers.
In the 1960s Austria started to design its surge tanks with respect of resonance load cases. This accounts for loading and unloading events for most unfavorable mass oscillation interference and water levels in the reservoirs. Complex vortex throttles were invented and are still in use. Mainly throttled chamber surge tanks that create differential effects by both the throttle and the separation effect of the upper chamber are state of the art. In this article the evolution of surge tank facilities in Austria is presented. Recent developments and future outlooks are given how surge tanks can be further optimized. Especially increasing demands from the power market and new pumped storage schemes (PSH) are also reflected in surge tank design aspects. A new development of storage-tunnel surge tanks will also be highlighted in the article.