Surge tank throttles for safe and flexible operation of storage plants

Throttle surge tanks are a part of high head powerplants. The main consequence of a throttle placement is to introduce head losses by accelerating the flow. They make it possible to manage extreme water levels during mass oscillations while increasing water surge, e.g. water hammer, in the headrace tunnel. This phenomenon happens every time the flow discharge is changed in the waterway. Either throttle is placed during construction to reduce costs or its placement is needed following a refurbishment to adapt the old surge tank geometry to the new design loads. However, the introduction of throttle is often not sufficient to adapt surge tank for important increases of discharge. This article suggests a review of the existing throttled surge tanks and the establishment of a characterization. The non-exhaustive review focuses mainly on existing plants in Switzerland but also to extend to some existing in the world. Good knowledge of throttles allows to reduce the steps and durations of throttle design and construction.