Vattenfall (Sweden)

Prefabricated modular substations could help DSO:s to shorten the project execution time by up to 50%. This paper describes the DSO, Vattenfall Eldistribution’s, ongoing development pilot where the viability of this concept will be examined. The pilot includes prefab modular buildings for 46 and 12 kV metal-enclosed air insulated switchgear and the protection automation control system (PACS). Two different business models will be introduced in separate substation projects. Key technical and economic expectations from a pilot study are discussed. Preliminary results that support these expectations are presented. The methodology of the development pilot, including continuous status reports and building know-how, is described.

Abstract With wind turbines approaching or surpassing their designed operational lifespan of 20-25 years, the exploration of lifetime extension potentials becomes crucial. This paper presents a reliability-based assessment of steel support structures for offshore wind turbines, utilizing measured data from various sources to evaluate structural integrity. The proposed methodology adheres to IEC Standards and DNV guidelines, introducing a structural reliability format and identifying uncertainties associated with extending turbine life based on measured data. Traditionally, the assessment of a lifetime extension potential has relied on aero-elastic simulations, which are updated to represent actual structural, environmental and operational conditions. However, this paper proposes a novel data-driven approach that utilizes measurement data to predict the lifetime extension potential. A significant aspect of this methodology is virtual sensing, which is known as a cost efficient method to obtain the complete structural response based on a limited number of accelerometers in the wind turbine tower. The cost efficiency enables structural response monitoring of all wind turbines in a wind farm, providing the essential input to the data-driven reliability format suggested in this paper. The proposed data-driven approach integrates three types of data: measured load-response data (virtual sensing), operational data (SCADA), and environmental data (Metocean). By establishing a robust framework for data collection, integration, and validation, it provides a novel method to predict the structural reliability of offshore wind turbine support structures based on measurements. The methodology is validated using data from a wind farm in the Baltic Sea, showcasing a highly reliable and cost-efficient approach for assessing lifetime extension. By comparing virtual sensing predictions with actual strain gauge measurements, the accuracy of this data-driven method is confirmed, ensuring reliable assessments of structural integrity and lifetime extension potentials.

Anthropogenic barriers fragment Portuguese rivers, threatening endemic freshwater fish communities. This study compiled national inventories and peer-reviewed research (2002–2024) to quantify fishway implementation, evolution and typology, while evaluating fish performance from published research. One hundred fishways built between 1950 and 2024 were recorded, half of which were constructed after the implementation of the Water Framework Directive in Portugal (29 Dec 2005), tripling the annual construction rate. Fishways were found to be associated mainly with weirs (46%) and small hydropower plants (44%), with typology being dominated by the pool-type design (67%), nature-like facilities (18%), fish locks and combined systems (6% each), fish lifts (2%) and a single eel pass. Forty scientific contributions addressed fishway effectiveness; three-quarters dealt with pool-type facilities, while 12.5% and 10% focused on nature-like fishways and lifts, respectively. Experimental and field studies highlighted species-specific hydraulic preferences, the benefits of vertical slot and multislot configurations, and the potential of retrofitting fishways with macro-rugosities (i.e., fixed structural elements placed on the bottom) to improve non-salmonid fish passage. However, low attraction efficiency, limited multi-season monitoring and risks of aiding invasive species remain a concern. Research needs are proposed, including the refinement of species-specific hydrodynamic criteria, and the development of standardized efficiency metrics and of selective passage solutions, to advance fishway performance under Mediterranean hydrological constraints.

To meet future nitrogen removal targets, Henriksdal wastewater treatment plant (WWTP) will require external carbon addition, estimated at 8 tons COD/day by 2040, due to low influent BOD/TN ratios, precipitation chemical use, and low temperatures. Methanol, the projected option, is fossil-based and contributes to indirect greenhouse gas emissions. This study evaluated a volatile fatty acid (VFA)-based fermentate produced from primary sludge and food waste in a 2 m3 mesophilic fermenter as a carbon source for denitrification. The filtrated fermentate was tested as carbon source in both batch denitrification tests and pilot-scale MBR (4.5 m3/h), where it was dosed for 70 days, replacing glycerol currently used at Henriksdal and Henriksdals WWTP. In batch tests, the fermentate achieved a 40% higher denitrification rate than glycerol. Pilot trials showed a 30% higher denitrification rate and 50% lower carbon consumption while maintaining effluent concentration below 3 mg NO3- -N/L. Microbial analysis revealed no significant community changes with the carbon source transition, indicating effective VFA uptake by existing microorganisms. Full-scale projections suggested that replacing methanol would require 10% of the plant's primary sludge plus food waste. Although this sludge use would reduce biogas production, methane potential tests showed that recycling of the fermentate solid fraction would result in only 2% lower biogas production, representing a minor trade-off.

The growing integration of inverter-based resources (IBRs) provides net-zero-emission benefits. However, it also introduces new instability challenges that arise from interactions with the power system or other IBRs. Identifying this phenomenon in advance drives the analysis to methods such as those in the frequency domain, where global information can be gathered. The scientific literature contains many IBR representations that do not consider DC-side dynamics or in which such dynamics are embedded within specific models. This complicates their extraction and use in the representation of other IBRs. This paper suggests a general modeling technique to define DC-side dynamics as a function of AC-side variables and sources. The method is verified against a static synchronous compensator (STATCOM), represented using a switching model. The verification is then extended to an aggregated offshore wind power plant model based on type-4 wind turbines with point-to-point HVDC transmission to shore. The approach provides a fundamental building block defining voltage-source converter DC-side dynamics: a capacitor and two ideal controlled current sources, one for charging and the other for discharging. The model is a nonlinear differential equation with states accessible from the AC side. The simulation results show that it is possible to synthesize the DC dynamics uniquely for the three applications considered, and potential extension for DC systems is possible.

Assessing harmonic distortion measurements in the electric railway power systems (ERPS) requires evaluating the time-varying behavior, interactions, and performance in different time scales. This paper aims to map and assess harmonic voltage levels in 13 traction converter stations for the Swedish railway power supply system, with findings that have direct practical implications. For that, measurements from the public and railway grid sides for 69 weeks are analyzed. Statistical values are explored for the harmonic voltage spectra and total harmonic distortion (THD) variation. The public grid side measurements are investigated using 95th percentile weekly values, and performance is evaluated by comparing the recommended planning levels of IEC 61,000–3–6. The intraweek variation complements the information about the time-varying behavior of the THD. The 95th percentile, minimum daily values, and intraday variation are explored to understand the time-based behavior since there are no reference limits from standards for comparison, looking to the railway grid side. Extended analysis is placed on the railway grid side to highlight some aspects of measurement time-aggregation based on 10-min values, and time-series trend analysis is used to confirm traffic planning impact. Discussion and findings regarding railway operation, the technology deployed at the traction converter station, time-varying behavior, traffic planning impact, measurement time-aggregation, and spectra patterns were presented.

Abstract Hydraulic axial turbines are more frequently utilized for grid regulation purposes. Sometimes, they must be operated at speed-no-load (SNL) conditions, which is characterized for some machines by a varying number of large vortical flow structures extending from the vaneless space to the draft tube, introducing detrimental pressure pulsations throughout the turbine. A recent study shows that the vortices can be mitigated by individually controlling the guide vanes. Since optimization of the distributor layout is linked with a large degree-of-freedom, machine learning is deployed to assist in finding an optimal setup cost-effectively. A reduced numerical computational-fluid-dynamics (CFD) model is built and used to generate input for Gaussian process regression surrogate models by performing 2000 steady-state simulations with varying distributor layouts. The surrogate models suggest that the optimal layout is to open seven out of 20 guide vanes in succession while keeping the remaining ones closed. However, this configuration induces large radial forces on the runner, and after implementing some modifications by trial and error, detailed time-dependent CFD simulations show that placing 4 + 3 opened guide vanes on opposite sides of the runner axis is better; it reduces the pressure peaks corresponding to a two- and three-vortex configuration, and the maximal pressure pulsations by as much as 88% in the vaneless space compared to regular SNL operation. Meanwhile, the radial force on the runner is reduced by more than 83%, and pressure pulsations on the runner blades by more than 55%, compared to the surrogate models' optimal layout prediction.

Fuel performance codes are used to forecast fuel behavior and ensure safe operation. These analyses must typically include prediction uncertainties, and fuel performance models need calibration. Consequently, code calibration must derive the best estimates and corresponding uncertainties of model parameters for subsequent propagation.Bayesian calibration is popular for generating the probability distribution of model parameters. However, model inadequacy disrupts these techniques, typically resulting in underestimated uncertainties. Earlier research showcased the incorporation of model inadequacy by model parameter inflation. The method demands cheap code predictions and derivatives, which required further research to develop differentiated Gaussian process surrogates.This work combines those techniques into a complete methodology. We demonstrate it by calibrating Transuranus against fission gas release and cladding oxidation data. The result is model parameter uncertainties that primarily explain the discrepancies between the predictions and corresponding measurements, except when the output behaves highly non-linearly.