Start-up Sequence Research Articles

Experimental investigation of a FSFC variable speed pump-turbine prototype - Part1: penstock fatigue reduction and fast active power regulation

Abstract The Z’Mutt pumping station is located in Canton Valais-Wallis, in Switzerland and is part of the Grande Dixence hydroelectric scheme. The unit 5 of this station has recently been upgraded with a 5 MW variable speed reversible Francis pump-turbine equipped with Full Size Frequency Converter, FSFC, allowing the unit speed to be adjusted from −100% to +100%. This paper presents the methodology based on 1D numerical simulations including CFD/FEM runner damage hill chart to optimize the turbine start-up sequence to minimize both runner and penstock fatigue by taking advantage of the FSFC variable speed technology. FSFC allows for precise start-up trajectories in the n11-Q11 frame, to avoid runner high damage operating points, while reducing penstock pressure variations as compared to a classical fixed speed technology. This methodology resulted in the definition of 6 different FSFC start-up sequences, as well as the classical fixed speed start-up, which have been successfully implemented and tested on site. Site tests of fast transition from turbine to pump and vice versa are also showcased. Finally, fast active power regulation tests performed in pump mode are presented to show the ability of FSFC variable speed technology to provide ancillary grid service in pump mode.

On the modelling of the fatigue-induced damage in Francis turbines start-up sequences

Abstract The European Green Deal is prescribing a very ambitious rise in the annual production of renewable energy sources, and grid regulation services are increasingly important in the course of a massive integration of intermittent renewable energy sources. Although hydropower effectively regulates power, the growing demand for flexibility in the coming decades means that hydroelectric technologies must be adaptable, often operating in conditions for which they were not originally designed to ensure availability and system reliability. This also includes a significant increase of the number of start-ups per year. To address these challenges, this paper suggests a two-fold forecasting method to predict damage due to fatigue in the runner blades of Francis turbines. Firstly, stresses during transient operations are predicted using a quasi-steady approach that concatenates measurements from steady-state operations through Voronoi tessellation. Following that, a neural network is trained on an existing dataset of recorded blade stresses during transient operations. The effectiveness of both approaches is validated against measurements in a reduced scale model of a Francis turbine. The comparative analysis highlights the strengths and weaknesses of each method, offering a detailed understanding of dynamic damage accumulation during start-up sequences compared to steady-state operations.

Analysis of mode-switching of a contra-rotating pump-turbine based on load gradient limiting shutdown and startup sequences

Abstract The contra-rotating pump-turbine (CRPT) is investigated as a runner configuration enabling more efficient low-head pumped hydro storage (PHS). To enhance the flexibility of low-head PHS with a CRPT, it is important to examine mode-switching. This study examines two mode-switching sequences for the CRPT, one turbine-to-pump and one pump-to-turbine. The mode-switching sequences are made as a combination of shutdown and startup sequences of each mode. The goal is to avoid pump and turbine brake modes while maintaining smooth load gradients. The turbine shutdown of the turbine-to-pump mode-switching involves a multi-stage valve closure to reduce the rotational speed of the runners, followed by the pump startup based on a previously optimised sequence. The pump shutdown of the pump-to-turbine mode-switching involves a gradual valve closure and rapid speed down of the runners at the end of the sequence. This is followed by the turbine startup, where a valve opens to generate sufficient flow over the runners before increasing the rotational speed of the runners simultaneously. Both mode-switching sequences require approximately 5 s each, and the largest loads are experienced during the pump mode parts of the sequences. The analysis is carried out using transient computational fluid dynamics with the OpenFOAM open-source software.

Evaluation of the fatigue-related influence of start-ups on Pelton turbines based on reduced scale model stress measurements

Abstract In recent decades, the electricity industry has undergone a significant transformation from a vertically integrated supply system to a market-regulated structure. This shift, along with the intermittent nature of increasingly prevalent non-dispatchable renewable energy sources, induces system operators to redistribute portions of the power generation included in the market schedule to preserve the energy balance within the power system. For hydropower plants, this translates in increasingly frequent operations in transient condition, with significant fatigue-related consequences on the lifetime of hydraulic machines. The understanding of fatigue phenomena during transient operations requires therefore experimental investigations, modeling and optimization of such operations, representing today a relevant research subject. This paper proposes the comparison between two methodologies which aim to estimate and optimize the operational cost, with respect to the lifetime of a Pelton turbine, of the specific case of the back-to-back start-up of a multistage pump performed with the Pelton runner of the same ternary group. These methodologies are developed on data collected during an experimental campaign performed with the reduced scale model of the investigated turbine, homologous to the real test case pumped-storage power plant. Despite the substantial distinction in the adopted approaches, the two methodologies show common features in terms of the fatigue damage trend as a function of the turbine operating conditions, and of the optimal strategy minimizing the structural impact of start-up sequences.

Experimental investigation of a FSFC variable speed pump-turbine prototype – Part2: runner fatigue reduction

Abstract The demonstration of flexibility technologies to enhance ancillary services of Hydropower Plants (HPPs) is showcased by the XFLEX HYDRO H2020 European Project. The potential of Full Size Frequency Converters (FSFC) is numerically and experimentally assessed by a case study on the Z’Mutt HPP. The investigated unit is a 5 MW variable speed reversible Francis pump-turbine fed by a FSFC that provides full speed control from −100% to +100%, allowing for fast start-up and mitigation of damage caused to different components. In this context, several turbine start-up sequences with controlled guide vane opening and rotational speed are developed, implemented, and tested on prototype scale. The definition of the different sequences, their impact on penstock fatigue and further FSFC capabilities like fast active power control in pump mode and fast power reversion are presented in part 1 of this contribution. Part 2 deals with fatigue damage investigations of the runner with respect to variable speed operation in generating mode using coupled numerical and experimental techniques. Strain signals from the runner blades are extrapolated to the critical areas to assess the relative fatigue damage induced by each turbine start-up. The scaled normal stress approach is applied, which is a critical plane method, adapted for multiaxial stress states. The results reveal that runner damage is mitigated by more than two orders performing a variable speed start-up compared to a classical one with fixed speed technology. Simultaneously, the delay for active power provision is significantly shortened. Thus, the study approves that fast and frequent turbine start-ups are realizable without affecting the runner’s service life thanks to the FSFC.

Influence assessment of shut-in duration and well startup sequence in different geological and field conditions

During 2019-2021, about half of well stock at West Siberian oil fields were shut down for a long period (up to one and a half year) due to oil production restrictions under the agreement between Russia and OPEC (Organization of the Petroleum Exporting Countries). There have never been such large-scale and prolonged shutdowns before. After starting from a long-term shutdown, the flow rate of some wells increased, while others decreased.The main aim of research is to assess the geological and technological factors affecting the results of starting wells after a long shutdown. Statistical methods were used, including multivariate regression analysis, assessing the influence of parameters on each other using trend lines on cross-plots, as well as constructing and comparing maps of geological and technological parameters.As a result, the influence of the duration of downtime, the simultaneity of shutdown of production and injection wells and compensation of production by injection was determined. That will help to reduce losses in case of repeated production restrictions by selecting optimal candidates for shutdown.

On the prediction of the induced damage by the start-up sequence of Francis turbines: On operational resilience framework

The number of transient operations in hydraulic machinery connected to power grid, notably start-ups and shut-downs, has observed a substantial increase in recent decades, primarily driven by the global shift towards intermittent renewable energy sources. Simultaneously, advancements in MW power converter technology and its cost-effectiveness have altered the operational paradigms of hydropower plants. These transformations offer novel opportunities for asset management within the industry. This study introduces a new method aimed at forecasting stress during start-up procedures, leveraging steady-state measurements acquired from a reduced scale model of the hydraulic turbine. Through a dedicated modular telemetry measurement system and the integration of strain gauges onto the reduced-scale runner blades, a tool is devised to predict dynamic loads characteristic of these transient operations. Utilizing steady-state measurements and a Voronoi cell tessellation, the transient predicted stress signal is constructed by concatenating the information from each encountered cell, thus providing an estimated projection of the stress likely to occur during the sequence. The proposed methodology demonstrates a robust forecast of the stresses on the runner blades during steady-state and transient operations of Francis turbines. Its immediate value lies in the ability to correctly estimate the lifetime of the runner as well as the possible integration into an optimization framework for stress reduction, thereby potentially extending the operational lifespan of the unit, from the runner structure perspectives.

F-DQN: an optimized DQN for decision-making of generator start-up sequence after blackout

F-DQN: an optimized DQN for decision-making of generator start-up sequence after blackout

A comparative analysis of organic substrates from industrial wastewater streams for enhanced electricity production using a double chamber microbial fuel cell (DCMFC)

This study investigates the startup sequence of a Double Chamber Microbial Fuel Cell (DCMFC) for the treatment of diverse industrial wastewater streams, including biorefinery, dairy, and mixed sources. It presents a comprehensive startup and calibration procedure for the essential electrical components, utilizing MATLAB-SIMULINK to establish typical resistance calibration curves and correlate measured electrical parameters with expected values. This approach enables a robust experimental startup protocol for the DCMFC under psychrophilic and thermophilic conditions. The study explores the impact of fundamental operating parameters on determining the experimental Hydraulic Retention Time (HRT) of the DCMFC. Specifically, it examines the effects of catholyte type (Phosphate PO43−buffer) and three distinct organic substrates: dairy wastewater, biorefinery wastewater, and mixed substrates (50% v/v dairy).Electricity production is evaluated in terms of voltage yield (mV), Columbic efficiency (CE) (%), and overall growth yield (Y). The study also assesses the COD (Chemical Oxygen Demand) mass balance component's influence on COD removal efficiency to establish a viable operating HRT during the startup phase. Key findings include startup experimental voltage yields of 145.2 mV for biorefinery, 85 mV for mixed wastewater, and an impressive 357 mV for dairy wastewater. Columbic efficiencies of 0.92%, 0.77%, and 0.02% were respectively achieved. Furthermore, the study reveals a viable experimental HRT, ranging from 72 to 96 hours, for both biorefinery/mixed and dairy/mixed wastewater sources, facilitating startup electricity generation and efficient removal of organic contaminants. These findings contribute to the advancement of sustainable wastewater treatment and bioelectricity generation, offering valuable insights for practical applications.

Energy-Saving Control Strategy for Multisleep States of CNC Machine Tool Considering Components Priority

As the representative energy-consuming equipment in the manufacturing industry, machine tools consume lots of energy during the non-machining period, which leads to low energy efficiency. The existing strategies do not consider the startup sequence among components, which causes the control parameters to fail to run during the practical startup process, and this paper conducts energy-saving research to address the issues. The relationship of priority among components was used as the constraint to obtain an energy-saving control strategy for multi-sleep states of machine tools considering components priority. Furthermore, the improved whale algorithm was applied to solve the energy-saving control strategy of the machine tool, and the search and convergence ability of the algorithm was improved by introducing the chaotic convergence factor and adaptive weight coefficient. Finally, the energy-saving strategy was utilized with a vertical CNC machine tool as an experimental example to mill the end face of the randomly arriving workpieces. The results show that this changed algorithm has a better solution speed and effect than the ordinary whale algorithm and some other improved whale algorithms. Compared with the practical control process and other control strategies, the control strategy considering components priority can obtain more stable productivity and better energy-saving effect.

Novel Start-up for Moving Bed Biological Reactors for Nitrogen Removal with High C/N Influent by Heterotrophic Nitrification and Aerobic Denitrification

A novel start-up strategy for MBBR systems was implemented that achieved removal rates of ammonia and total nitrogen of more than 90% and 70%, respectively, with influent C/N ratio of nine. The strategy consists of operating the MBBR with non-nitrified secondary effluent (C/N=2) until ammonia removal is sustained and gradually increase the C/N ratio of the feed to the target value of nine, when the MBBR system is fed primary effluent. Before using the start-up sequence, the MBBR system treating primary effluent (C/N=9) showed negligible ammonia removal after 120 days of operation, indicating the absence of nitrifying bacteria. It was assumed that heterotrophs were outcompeting autotrophs, and the C/N ratio was decreased to allow autotrophs to proliferate. Genomic analysis indicated the presence of bacterial and fungal populations, which can perform nitrification and denitrification. The most abundant heterotrophs observed were Proteobacteria at 31%, Bacteroidetes at 22%, and Actinobacteria at 8%. The most abundant fungal population belonged to Ascomycota (10%), Basidiomycota (10%), and Mucoromycota (1%). Heterotrophic nitrification and aerobic denitrification were found to play an important role in nitrogen removal at C/N=9. Autotrophs may have proliferated at lower C/N ratio as total nitrogen removal was low, but at higher C/N a shift in microbial population should have taken place as indicated by the dominance of heterotrophs.

Control system for suction valves within gas compressors skids located in potentially explosive zones

The paper presents the implementation of a feedback loop controller for the suction valves used within the gas compressors skids manufactured by Romanian Research and Development Institute for Gas Turbines COMOTI. These compressors are installed at beneficiaries, in potentially explosive environments (e.g., gas extraction and transportation applications). The proposed solution addresses the problems observed due to the high suction pressures of screw compressors, which may occur at start-up or during operation, leading to failed start-ups or emergency shutdowns. An automatic sequence implemented in the control software and displayed on the operating panel, could assist the operator during high suction pressures (above 1.2 bar). These pressure conditions normally lead to alarm limits and to performing an automatic shutdown sequence for protecting the compressor. The paper herein discusses the implementation of a start-up sequence in the programmable logic controller’s software, which can be applied without critical interventions on the compressor packages, only through minor control software modifications which can safely extend the inlet pressure range and the exploitation of the compressors. Thus, since no hardware modifications are required, we also ensure maintaining the ATEX certifications of equipment and assemblies.

Structural impact of the start-up sequence on Pelton turbines lifetime: Analytical prediction and polynomial optimization

Structural impact of the start-up sequence on Pelton turbines lifetime: Analytical prediction and polynomial optimization

Experimental study on flow control system of an electric pump-fed cycle for thrust control

An electric pump-fed cycle can enable the electrical control of pump revolutions and rapidly vary the propellant flow rate. This paper proposes the pump control method as a flow control system of an electric pump-fed cycle. In order to evaluate the applicability of the designed flow control system, the test equipment that simulates an electric pump-fed cycle was constructed, including the Li-ion battery power system and communication instruments. The designed PID controller demonstrated rapid flow stabilization and robustness compared to the system without a controller. Meanwhile, under the initial pressurized condition in the run tank that simulated an engine start-up sequence, the controller response delay occurred was more than 500 ms. In addition, the dynamic loads, such as the water hammer effects and overshoot, were identified. The start-up sequence of an EP cycle was adjusted to alleviate those issues. Consequently, the supply stabilizing time and overshoot were adjusted to 400 ms and 1.7 %, respectively. This study can be the first step in utilizing an electric pump-fed cycle for the thrust control technology in the upper stage of a mission.

Determining optimal generator start-up sequence in bulk power system restoration considering uncertainties: A confidence gap decision theory based robust optimization approach

A reasonable start-up sequence of generators considering renewable energy generation integration can effectively improve the restoration efficiency of the power system concerned. The restoration strategy of generators is time-sensitive, however, the computation procedure of existing methods is not fast enough to meet the requirements of practical applications. In this paper, the generator start-up sequence optimization (GSSO) problem is addressed with the integration of wind-solar hybrid systems (WSSs) considered in bulk power systems. Specifically, a deterministic model for GSSO is formulated to maximize the total generation capability during the restoration procedure, in which fewer auxiliary variables are required to promote the computational efficiency. On this basis, in order to deal with the inherent and significant uncertainties of WSSs, a confidence gap decision theory (CGDT) based approach is proposed combining the advantages of stochastic optimization and the information gap decision theory based method while considering the worst-case realization of unknown probability distributions, so that a chance-constrained robust generator start-up solution is thereby attained. Moreover, the formulated CGDT based model is transformed into a mixed integer linear programming problem. Finally, the IEEE 39-bus power system and a modified version of an actual power system in China are employed to demonstrate the feasibility and efficiency of the proposed method.

Surrogate based optimisation of a pump mode startup sequence for a contra-rotating pump-turbine using a genetic algorithm and computational fluid dynamics

Surrogate based optimisation of a pump mode startup sequence for a contra-rotating pump-turbine using a genetic algorithm and computational fluid dynamics

Bidirectional Charging for BEVs with Reconfigurable Battery Systems via a Grid-Parallel Proportional-Resonant Controller

This paper investigates the potential of bidirectional charging using modular multilevel inverter-based reconfigurable battery systems via grid-parallel control. The system offers several advantages such as modularity, scalability, and fault-tolerance over conventional battery electric vehicle systems. It is designed for seamless integration with the grid, allowing bidirectional power flow and efficient energy storage. Within this study, the battery system is first simulated in Matlab/Simulink and later implemented into a hardware setup. Eventually, the simulation results and the measurements have been compared and evaluated. Thereby, startup sequences and constant current scenarios were investigated. It has been shown that the system is fully capable to charge and discharge the batteries in the grid-parallel connection, thus enabling bidirectional charging with close to full drive system power. The current total harmonic distortion complies with grid regulations and can potentially improve the grid quality. The proposed system offers significant potential for grid-integrated energy storage systems, addressing the challenges associated with renewable energy integration, grid stability, and energy management. In comparison to other publications on this topic, the proposed approach does not need additional dedicated power electronic hardware and has more degrees of freedom for current control.

Bi-Level Coordinated Power System Restoration Model Considering the Support of Multiple Flexible Resources

When power systems encounter outages and large-scale blackouts, system restoration is critical and should be carried out with dedicated schemes. In this past, most studies divided the power system restoration into three stages (i.e., black-start zone partitioning, network reconfiguration, and load restoration) and deal with them separately. After that, few studies considering the three stages together were emerging while the support of multiple flexible resources, i.e., renewable energy source (RES), electric vehicle system (EVS) and energy storage system (ESS), were not considered comprehensively. Therefore, a bi-level coordinated power system restoration (BiCPSR) model is proposed in this work considering the support of multiple flexible resources. In the upper level, two network topology indices that describe the “reachability” and “shortest reachable distance” of buses in power systems, and the restoration characteristics of generators and loads are utilized for optimizing the start-up sequence of generators and network reconfiguration. In the lower level, the uncertainties of RES and EVS are considered by various scenarios and the support of multiple flexible resources is utilized cooperatively for accelerating the restoration process and maximizing the restorable load. Case studies on the revised IEEE 39-bus, WECC 179-bus and the actual Zhejiang power systems are performed to illustrate the basic features of the proposed model and its availability in bulk power systems. The comparisons between the proposed model and other models are also performed to illustrate the strengths of the proposed model.

Challenges for integration of renewable energy in public grid

Integrating renewable energy is one of the current and future subjects for the energy transition to CO2-neutral energy generation. New requirements, including grid and converter perspectives, must be considered as renewable power generation is carried out with power electronic converters. Inverter-based resources (IBRs) must meet grid connection regulations, forecasting options, time scheduling, storage options, and voltage quality. In this article, some essential requirements from the manufacturing perspective are described, and their testing procedure is displayed with the validation of simulation models. This paper further highlights the SICAM Power Plant Controller (PPC) for photovoltaic plants, enabling the plant operator to create generation forecasts for the next 2-3 days of power and energy. To be grid-code compliant, the PPC includes several functions to meet requirements, and its start-up sequence is also described. The system operator gains a grid-compliant model validated against site measurements. The procedures have been successfully applied to several IBR projects. Previews of new concepts to reach the future demands of integrating IBRs into the public grid are presented. Possible impacts on the power generation and components are assessed, and necessary countermeasures are applied with the influence and feasible solution for energy trading with IBRs. Future aspects of supra-harmonics and their impacts on public grids are described and presented as an outlook. This paper highlights the challenges of integrating IBRs and lessons learned based on project executions.

Analysis of the thermal inertia of pipelines in SHIP

Solar Heat for Industrial Processes (SHIP) is one of the most promising alternatives to decarbonize the industry. The present work aims to analyze the influence of thermal pipelines inertia on a small-scale solar concentrator of 20 kW with a phase-change material thermal storage. Two dynamic simulations for this SHIP system integrated into a tube steel factory in Romania were developed with Dymola software: one of them considered the thermal inertia of the pipelines and the other did not. By comparing the simulation results, we have found that the pipeline inertia conveyed delays in the start-up sequence of the system and decreased the temperatures of heat transfer fluids until the steady state is reached. Furthermore, the thermal inertia decreased the total energy produced. Other researchers have also found delays due to the inertia of the pipelines, but the delays were lower than ours. The difference in the delays may be due to the small scale of the SHIP system analyzed in the present work. Finally, we can conclude that dynamic simulation became important in SHIP systems because of the difference found with the non-inertia simulation.