This work investigates the effect of surge tank throttling on governor stability, power control, and hydraulic transients in hydropower plants. The work is intended to be practical, but includes some new research. The practical contributions include a methodology for a combined evaluation of the effects of installing surge tank throttles in hydropower plants, and a demonstration of the throttle effects through a case-study. The research contributions include the evaluation of the throttle effect on power control, and a comparison of the throttle effects on power control for governor systems with speed feedback exclusively versus combined speed and power feedback. Field measurements are used to calibrate a numerical model of the case-study hydropower plant. The results from the case-study show that the throttle has an insignificant positive impact on governor stability. Power control is improved when a throttle is installed; the overshoot of produced power and the time until steady-state conditions occur are reduced. The throttle has a significant effect on the hydraulic transients, and increases the water hammer and reduces the mass oscillations in the system.

This paper presents a technical review of the existing pumped storage plants in Norway. The power system is changing towards integrating more and more renewable energy, especially from variable renewable energy sources, leading to new challenges for the security of supply, power, frequency, and voltage regulation. Thus, energy storage options are a highly researched topic in the current situation. Even though there are many energy storage technologies, most are optimal for short term grid balancing, and few are capable of providing long term (weekly or seasonal) storage. One exception is pumped storage, a mature technology capable of delivering both short term and long term energy storage. In this paper, the ten existing pumped storage plants in Norway are presented, several of which are capable of seasonal energy storage. The Norwegian knowledge and experience with pumped storage plants technology is provided as a basis for future research within the field. The review provides information about energy production and storage capabilities, construction costs, specific costs per kW and stored kWh, electromechanical installation, technical specifications, and operational experience with focus on the design of the tunnel system layout. The data presented in this review are unique and previously unpublished. A discussion and conclusions regarding the current situation, trends, and future outlook for pumped storage plants in Norway within the European power market are provided.

The design and results from a hydraulic scale model of mass oscillations in a hydropower plant with a closed surge tank constructed as an underground rock cavern are presented. The results from the model test of an existing hydropower plant at scale 1:65 are compared with field measurements. The main contributions of this work include (1) an assessment of whether hydraulic models may be applied to evaluate hydropower tunnels with closed surge tanks, (2) a novel approach to scale atmospheric air pressure, and (3) an evaluation of the thermodynamic behaviour in the model and prototype. The hydraulic model is shown to provide an accurate representation of the maximum (first) amplitude, with a relative error of less than 4%. An estimate of the period of the oscillations has a relative error of less than 1%. The model has higher dampening compared with the prototype, resulting in the 20% relative error of the second amplitude. Both the model and prototype reveal approximately adiabatic behaviour of the closed surge tank.

In order to increase the lifespan of hydraulic turbines in hydropower plants, it is necessary to minimize damages caused by sediment erosion. One solution is to reduce the amount of sediments by improving the design of sand trap. In the present work, the effects on sand trap efficiency by installing v-shaped rake structures for flow distribution and rib structures for sediment trapping is investigated numerically using the SAS–SST turbulence model. The v-shaped rake structures are located in the diffuser near the inlet of the sand trap, while the ribs cover a section of the bed in the downstream end. Three-dimensional models of the sand trap in Tonstad hydropower plant are created. The present study showed that integrating rib type structure can reduce the total weight of sediments escaping the sand trap by 24.5%, which leads to an improved sand trap efficiency. Consequently, the head loss in the sand trap is increased by 1.8%. By additionally including the v-shaped rakes, the total weight of sediments escaping the sand trap is instead increased by 48.5%, thus worsening the sand trap efficiency. This increases head loss by 12.7%. The results also show that turbulent flow commencing at the sand trap diffuser prevents the downstream settling of sediments with a diameter of less than one millimeter. The hydraulic representation of the numerical model is validated by comparison with particle image velocimetry measurements of the flow field from scale experiments and ADCP measurements from the prototype. The tested rib design has not previously been installed in a hydropower plant, and can be recommended. The tested v-shaped rakes have been installed in existing hydropower plants, but this practice should be reconsidered.

As power systems include more intermittent renewable energy sources, energy storage solutions are needed to support them. Pumped hydro is a reliable alternative for long-term energy storage. A solution for bringing more pumped hydro into the power system is to upgrade existing hydropower plants into pumped hydro. To investigate this possibility, a case study with a complex tunnel system and multiple surge tanks along both the headrace and the tailrace tunnels is selected. A hydraulic scale model and validation methods were developed. The challenges in developing and validating complex models involving multiple surge tanks, throttles, head loss, and limited prototype information are detailed.