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Hydro-abrasive erosion in hydraulic turbines is critical and one of the prominent issue due to its association with maintenance costs and production losses in the hydropower plant. IEC 62364:2019* standard guide focuses mainly on hydroelectric powerplant equipment and provides the standard on particle abrasion rates on several combinations like operating conditions, component materials properties, water quality among many factors. With the consideration of different critical parameters, a theoretical model of abrasion rate on hydraulic turbines is proposed by IEC 62364:2019. Present study is conducted to elucidate the several terms used in the theoretical model of abrasion rate for Francis turbine as per the guidelines. The work has taken account into run-off river (RoR) hydropower plant consisting of Francis runner operating in sediment laden rivers in the Himalayan area. Theoretical expected erosion depth for runner inlet, runner outlet, guide vanes facing plates and labyrinth seals is calculated. Characteristic velocities of runner (Wrun) and guide vanes (Wgv) were estimated to be 32.26 m/s and 35.05 m/s respectively. Particle load was calculated based upon the sampling data available from the site. Measurement data from field observation during overhauling was used for comparison with the data calculated from empirical relation. For 229 hours operation of turbine, observed abrasion depth varies from 8.1 mm in guide vanes to 1.5 mm in labyrinth ring corresponding to calculated values of 7.53 mm and 1.89 mm for same components. Results shows good correlation among calculated values from IEC and measured values from the site. An optimized solution can thus be devised based on the evaluation of hydro-abrasive erosion along with energy production and maintenance expenses. *IEC 62364:2019. Hydraulic machines - Guidelines for dealing with hydro-abrasive erosion in Kaplan, Francis, and Pelton turbines. Edition 2.0 (March 2019) International Electrotechnical Commission, Geneva, Switzerland [1]

AlternaFuture has been a multidisciplinary research project in Hydrocen to investigate the potential of extreme upgrading of existing hydropower system with a positive effect on the environmental conditions. The project is a desk study and is carried out through developing future scenarios of an extreme upgrading of an existing hydropower system, to create potential for new innovations and solutions from the multidisciplinary scientists within the project. The existing hydropower system in the Mandal river has been applied as a case-study, where the current situation has been the baseline for developing alterative future scenarios and evaluating the economic and ecological results. The project has been divided in three main activities; (A1) mapping the current situation and defining environmental restrictions for reconstruction, (A2) developing physical scenarios consisting of hydropower projects, environmental projects and use of new innovations, and (A3) economic and environmental evaluation of the scenarios. Three main scenarios were developed for the Mandal river; (1) triple installed capacity, (2) maximum flexibility, and (3) flood protection. The hydropower optimization program ProdRisk was used to compare the hydropower operation and water management in present situation with the three scenarios. Energy price forecasts from HydroCen where used to assess the economic income from hydropower production, which in turn where compared with the estimated construction costs of each scenario to consider the economic feasibility. Thereafter, the impacts on the environmental status and recreational value in different parts of the watercourse, including reservoirs, lakes and river reaches are evaluated for three hydropower scenarios and compared with the present situation. In conclusion, it is found possible to realize extreme upgrading of existing hydropower systems, and at the same time in sum have a positive effect on the environmental conditions. It is noted that the positive effects require a significant effort in mapping and planning the environmental measures. For such upgrading consisting of multiple projects, single projects that have severe negative ecological impacts must be cancelled and cannot be included in the final scheme. Planning of such upgrading projects therefore must include environmental experts from the very beginning. The main conclusions from the AlternaFuture research project are presented below. 1. Extreme upgrading of existing hydropower systems can be done while also in sum improving the environmental conditions. 2. Extreme upgrading of hydropower systems that include pumped storage plants are economically feasible if the energy price variability increases sufficiently. For the Mandal river, the necessary increase is in between the 2030 price forecast and the 2030-scaled forecast as described in Memo 1. 3. It is the pumped storage plants that generate the main increase of revenue in the upgrading scenarios. Extreme upgrading without pumped storage plants has not been found economically feasible for any price forecast. 4. The pumped storage plants result in a reduction of the total energy production for the hydropower system, but a higher income. In the current tax regime, the pumped storage plants result in reduced taxation to the local municipalities because some of the Norwegian hydropower taxes are related to produced energy. The taxation to the central government increases depending on the economic profit from the pumped storage plants. 5. There is potential to find new hydropower projects in existing hydropower systems. 6. It is possible to construct a flood power plant to mitigate the flood challenges in the Mandal river. The flood power plant is not found to be economically feasible only from hydropower production, and the remaining costs have to be financed by other stakeholders such as insurance companies or local municipalities. The flood power plant can reduce a 200-year flood to a 20-year flood. 7. The extreme upgrading scenarios have a positive impact on flood mitigation owing to new reservoirs and pumped storage plants. This positive impact has not been quantified in this project. 8. Recommended future work includes developing a best-practice guideline for environmentally friendly upgrading of existing hydropower systems based on the methodology developed and applied in this project. In addition, 18 new research projects have been proposed and are described in Memo 5. © NTNU 2020. The publication may freely be cited with source acknowledgement.

Over the last years, there have been several incidents with cracks in high head Francis turbines. These cracks are understood to be related to pressure pulsations, vibration modulus and the combination of these. In this paper, a setup for the investigation of pressure pulsations in a low specific speed model turbine is presented with the use of onboard pressure sensors. Earlier onboard measurements have mainly utilized blade-mounted sensors. In this paper, a setup with hub-mounted pressure sensors are described. In addition, a position sensor is utilized to analyse the pressure data relative to the angular position of the runner. The setup is considered as a good reference for computational fluid dynamics validation and is considered less extensive for evaluating the onboard pressure pulsations compared to blade-mounted sensors. Open Access. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

The Horizon 2020 Project ‘Increasing the value of Hydropower through increased Flexibility (HydroFlex)’ aims towards scientific and technological breakthroughs to enable hydropower to operate with very high flexibility in order to utilise the full power and storage capability. The project will create the environmental, social and technical basis for successful future industrial developments by performing well-focused research and innovation activities on the key bottlenecks of hydropower units that restrict their operating range and thus limit their flexibility. One objective of the HydroFlex project is to develop a water turbine capable of doing a significant number of starts and stops per day. Work package 2 aims to investigate if there is a demand for such a turbine in the future power system, for example from an economical perspective in the power markets or from a technical perspective in terms of grid operation and short term system stability. To fulfil this task, simulations of the future European power system are needed. As the future development of the European power system is subject to uncertainty, this report defines three European energy scenarios as a framework to cover various future developments in the simulations. At first, this report explains the status quo of electricity generation in Europe as well as fundamental knowledge related to the term flexibility. Flexibility provision needs to meet certain demands caused by different elements of power systems. This report also presents different flexibility options able to cover these demands for flexibility. Although all provide individual advantages, this report identifies hydropower, especially pumped storage hydropower, to be a very flexible, diverse option and a technology capable of facing flexibility challenges set by the increase of intermittent renewable energy sources. Hydropower is especially common in the Nordic and Alpine countries and might provide flexibility. Assessments of future possibilities regarding this technology should therefore consider hydropower located in these countries. In order to evaluate requirements for hydropower providing flexibility, factors are described, which are essential to the future success of this possibility. As the future is subject to uncertainty, numerous outlines of the future European power system are available, designed by different parties involved in power systems. This report examines existing scenarios on possible opportunities of hydropower based on the mentioned factors. Finally, this report defines three scenarios, the Green Hydro, Reference and Prosumer scenario, which are specifically designed as suitable input for the following computational simulations of the European power systems. To evaluate the possible profitability of hydropower and to achieve HydroFlex’s main objective, the scenarios describe different contexts for Nordic hydropower.