Author(s): Aurelie Koch; Yves Keller; Markus Kost; Micheal Muller

Linked Author(s): Aurélie Koch

Keywords: Penstock; Inspection work; Reinforcement work; Hydropower plant

Abstract: The hydropower plant Handeck 1 was built between 1928 and 1930 as the first plant of a complex hydropower scheme owned by the Kraftwerke Oberhasli Ltd. (KWO) in the Bernese Alps of Switzerland. The 90 years old steel lined penstock connects the Gelmer Reservoir to the Handeck 1 power house. It is divided into two underground parts, a steep section with an inclination of 35° followed by a horizontal section leading to the turbines. At that time, the penstock was built with the available steel quality by welding prefabricated drawn steel plates on site. Several problems like cracks, leakages and deformations were reported along the horizontal section and at two bends since the plant operation started, which led to three major engineering works in the late 1940s, in the 1990s and recently in 2020. The inspection of the penstock was carried out in 2019 with visual inspection of the corrosion protection, non-destructive testing at known problem areas and destructive material tests on steel, cast iron and concrete. Furthermore, a static analysis was carried out. The result of the inspection work led to the discovery of unreliable cracks on the outside bend connecting the horizontal section to the valve chamber. The required structural safety of that part was not fulfilled. In 2020 immediate measures were carried out: the reinforcement of the bend and emergency measures in the power house. The reinforcement of the bend consisted in winding 45 prestressed multi-strand tendons around the penstock and embedding them in a reinforced concrete structure to ensure the force transmission between the penstock and the prestressed tendons. The reinforced structure should relieve the steel liner by absorbing the internal pressure. Moreover, the hydropower plant Handeck 1 has been equipped with a system of spillway channels for emergency cases. These temporary measures combined with additional monitoring should allow a safe and reliable operation of the hydropower plant until long-term solutions for the penstock are implemented. Serious inspection work and the implementation of appropriate measures are the key components to optimize the management of old steel lined penstocks. The inspection has shown that the technical lifetime of the entire Gelmer penstock is reached. The implemented measures can ensure a high security level, while guaranteeing the operation of the hydropower plant for a few more years. In 2020, KWO undertook a preliminary study to assess the replacement possibilities of the penstock. Many alternatives were studied and the replacement of the penstock with a new inliner ended up being the best solution from an economical point of view.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221316

Year: 2022