Rated Operating Conditions Research Articles

Tribological analysis of rotor system startup considering deformations of high elastic rubber bushings and grease lubricated plastic bearings

To achieve a compact design, reduced noise, and extended operational lifespan of the air conditioner indoor unit, a novel motor rotor system was implemented. This system utilizes three engineering plastic bearings, encased in high-elasticity rubber bushings and lubricated with grease. Yet, the absence of a simulation model that accurately represents the structural and material properties of this bearing-rotor assembly hampers the precise evaluation of how design parameters influence system performance. As such, in the present study, an innovative tribo-dynamics model was established using a coupling approach that integrates dynamics and tribology. This model encompasses a 4-degree-of-freedom rotor dynamics framework and a grease elastohydrodynamic model, which accounts for the deformation of both rubber bushings and plastic bearings. Utilizing this tribo-dynamics model, the effects of the elastic modulus of the bushing on the tribological properties of the system were explored. The results show that a small elastic modulus of the bushing effectively reduced the local high contact pressure between the journal and the bearing during startup. However, the elastic modulus cannot be excessively low, as it would adversely affect the range of journal motion and the film thickness under rated operating conditions.

Hydrodynamic Characteristics of Preloading Spiral Case and Concrete in Turbine Mode with Emphasis on Preloading Clearance

A pump-turbine may generate high-amplitude hydraulic excitations during operation, wherein the flow-induced response of the spiral case and concrete is a key factor affecting the stable and safe operation of the unit. The preloading spiral case can enhance the combined bearing capacity of the entire structure, yet there is still limited research on the impact of the preloading pressure on the hydrodynamic response. In this study, the pressure fluctuation characteristics and dynamic behaviors of preloading a steel spiral case and concrete under different preloading pressures at rated operating conditions are analyzed based on fluid–structure interaction theory and contact model. The results show that the dominant frequency of pressure fluctuations in the spiral case is 15 fn, which is influenced by the rotor–stator interaction with a runner rotation of short and long blades. Under preloading pressures of 0.5, 0.7, and 1 times the maximum static head, higher preloading pressures reduce the contact regions, leading to uneven deformation and stress distributions with a near-positive linear correlation. The maximum deformation of the PSSC can reach 2.6 mm, and the stress is within the allowable range. The preloading pressure has little effect on the dominant frequency of the dynamic behaviors in the spiral case (15 fn), but both the maximum and amplitudes of deformation and stress increase with higher preloading pressure. The high-amplitude regions of deformation and stress along the axial direction are located near the nose vane, with maximum values of 0.003 mm and 0.082 MPa, respectively. The contact of concrete is at risk of stress concentrations and cracking under high preloading pressure. The results can provide references for optimizing the structural design and the selection of preloading pressure, which improves operation reliability.

Thermodynamic performances of a power-to-X system based on solar concentrating photovoltaic/thermal hydrogen production

100% renewable power-to-X (fuel, power, and heat products) systems have great application potential for the achievement goal of carbon neutrality. However, the extensive chain of the power-to-X system could result in low energy utilization efficiency. A novel composite-parabolic-concentrating photovoltaic/thermal-collector-based power-to-X system utilizing 100% solar energy is proposed, which integrates proton exchange membrane electrolysis cells and proton exchange membrane fuel cells to provide heat, electricity, and hydrogen. Thermodynamic models for each subsystem are established, and energy and exergy efficiencies are assessed in the thermodynamic laws. Three operation modes are analyzed to adapt to the variations of solar radiation and a residential building is used as an application scenario to evaluate its thermodynamic and economic performances in dynamic variations of solar radiations and energy demands. The effects of key operating parameters, such as solar radiation intensity, photovoltaic coverage ratio, current density, and operating temperature, on the performances are investigated. The maximum exergy destruction of the concentrator photovoltaic/thermal collector is 93.20% at the rated operating conditions, and the system exergy and energy efficiencies are 9.11% and 48.97%, respectively. The economic results demonstrate that the levelized costs of solar power, hydrogen, and fuel cell power are 0.2936 $/kWh, 21.70 $/kg, and 2.1520 $/kWh, respectively.

Experimental investigation of performance, emissions, combustion characteristics, cyclic variations, and exergy efficiency of CI engine fueled with Karanja-camphor oil blends and diesel-camphor oil blends.

This article compares the influence of blending the low-viscous oxygenated camphor oil with hydrocarbon diesel fuel and high-viscous oxygenated Karanja oil. The experiment is conducted in a four-stroke one-cylinder naturally aspirated Kirloskar compression ignition (CI) engine coupled with an eddy current dynamometer. The three types of fuel blends are prepared by blending the camphor oil with Karanja oil on the volume ratio of 30:70 (C30K70), 50:50 (C50K50), and 70:30 (C70K30), and the other three types of fuels are prepared by blending the camphor oil with diesel on the volume ratio of 30:70 (C30D70), 50:50 (C50D50), and 70:30 (C70D30). The experimental efficiency results show higher thermal efficiency of 31.86% and 30.84% for C70D30 and C70K30 at rated operating conditions. The brake-specific energy consumptions of C70D30 and C70K30 were found to be 11.29 and 11.67MJ/kWh, respectively, at rated operating conditions. The lowest CO, CO2, HC, and smoke emissions are found for C70D30 at rated operating conditions, which are 96.58%, 6.15%, 34.20%, and 7.59% lower than diesel. However, the NO emissions were found to be 27.62% higher for C70D30 than diesel at full load. The rate of pressure rise, net heat release rate, and cyclic variations were found to increase with increase in proportion of the camphor oil. The P-v diagram also confirms the lower heat addition period for the C70D30 and C70K30 with an increase in brake thermal efficiency. The actual compression ratio and the actual cutoff ratio are found to have a reasonable correlation with the thermal efficiency of the engine. The exergy efficiency of C30K70 is found higher which is 2.11% higher than diesel fuel at rated power. Second-order polynomial equations were obtained for the engine characteristics using the curve fitting method, and the characteristic equations confirmed the confidence level of 95%.

Investigation on hydraulic loss characteristic of Kaplan turbines based on entropy generation theory

Abstract In this paper, the hydraulic losses of a Kaplan turbine under optimal and rated operating conditions are investigated through the theory of entropy generation. The results show that hydraulic loss values calculated using pressure drop and entropy generation theory are similar. The hydraulic losses are mainly concentrated in runner and draft tube. However, when the operation condition of Kaplan turbines deviates from the optimal condition, the proportion of hydraulic loss in draft tube increases. The hydraulic loss in draft tube is mainly composed of entropy generation caused by turbulence fluctuation, which is the result of unstable flow induced by vortex rope. The hydraulic losses of other parts are mainly composed of entropy production caused by wall shear. The high entropy production of the runner concentrated on the shroud, hub, blade surface, and blade trailing edge, while entropy production caused by wall shear is concentrated on blade pressure surface and shroud near blades when the turbine strays from optimal operating condition.

Numerical simulation of fish damage in a bulb tubular turbine with different guide vane openings

Abstract Tubular turbines have advantages in developing low-head hydropower, however, the development of hydropower shouldn’t forget to maintain a balance with ecology. In this paper, a three-dimensional model of the flow channel of a low-head power plant bulb tubular turbine unit is established using Unigraphics NX, and the hydraulic characteristics and fish damage mechanisms of the turbine under different guide vane openings of 45∼85 mm in rated operating conditions are simulated and analyzed using STAR-CCM+, and it is found that the fish mainly suffers from impact damage and pressure damage in the downstream process with the highest probabilities of 15.73% and 15.72%, respectively. Furthermore, with the increase of the opening of the guide vane, the probability of shear damage to the fish first decreases and then increases, while the probability of pressure, pressure gradient, and impact damage all gradually increase, and the probability of all four types of damage reaches the highest when the opening of the guide vane is 85 mm. Although the unit will have a large output at large opening operating conditions, from the point of view of fish protection, it is better for such turbines not to be operated with large opening of the guide vane for a long time.

Study of hydraulic turbine flow-induced noise distribution law based on defective runner blade

Abstract In order to analyse flow-induced noise distribution law under the defective runner blade, this paper performs defective treatment on the runner blade according to the HLA855a-LJ-250 hydraulic turbine model. Two kinds of blade models, intact blade and outlet side abrasive blade, are established respectively, and the Realizable k-ε turbulence model and broadband noise source model are used to simulate the hydraulic turbine under rated operating conditions. The simulation results show: 1)Double-row leaf grilles and runner blade are the main dipole flow-induced noise sources; 2)Significant differences in the distribution of the acoustic power levels of the double-row leaf grilles’ characteristic blades and the runners’ characteristic blades under different Schemes; 3)Runner defective blades have less effect on the acoustic power level of spiral case, the rest of the overflow components acoustic power level has a tendency to increase, especially the runner has the greatest impact. The maximum increase in acoustic power level of the runner is almost 17 dB, followed by double-row leaf grilles with an increase of around 8 dB. Therefore, critical attention needs to be paid to the abnormal noise signals of runner and double-row leaf grilles.

Going beyond BEM with BEM: an insight into dynamic inflow effects on floating wind turbines

Abstract. Blade element momentum (BEM) theory is the backbone of many industry-standard wind turbine aerodynamic models. To be applied to a broader set of engineering problems, BEM models have been extended since their inception and now include several empirical corrections. These models have benefitted from decades of development and refinement and have been extensively used and validated, proving their adequacy in predicting aerodynamic forces of horizontal-axis wind turbine rotors in most scenarios. However, the analysis of floating offshore wind turbines (FOWTs) introduces new sets of challenges, especially if new-generation large and flexible machines are considered. In fact, due to the combined action of wind and waves and their interaction with the turbine structure and control system, these machines are subject to unsteady motion and thus unsteady inflow on the wind turbine's blades, which could put BEM models to the test. Consensus has not been reached on the accuracy limits of BEM in these conditions. This study contributes to the ongoing research on the topic by systematically comparing four different aerodynamic models, ranging from BEM to computational fluid dynamics, in an attempt to shed light on the unsteady aerodynamic phenomena that are at stake in FOWTs and whether BEM is able to model them appropriately. Simulations are performed on the UNAFLOW 1:75 scale rotor during imposed harmonic surge and pitch motion. Experimental results are available for these conditions and are used for baseline validation. The rotor is analyzed in both rated operating conditions and low wind speeds, where unsteady aerodynamic effects are expected to be more pronounced. Results show that BEM, despite its simplicity, can adequately model the aerodynamics of FOWTs in most conditions if augmented with a dynamic inflow model.

Temperature field analysis and equal-amplitude temperature rise constraint current control method under open-circuit fault-tolerant operation for five-phase permanent magnet motor

The phase redundancy and freedom of the five-phase permanent magnet motor (FPPMM) enhance the reliability of the motor system. However, the temperature rise and torque reduction issues of the motor during open-circuit fault operation need to be further studied. In order to study the temperature distribution characteristics and the output capability of the motor under fault operation subject to temperature rise constraints, a 3-D global temperature field model containing a complex heat dissipation structure has been established. And the equal-amplitude temperature rise constraint current control method is proposed under open-circuit fault-tolerant operation to improve its output capability. The temperature distribution of the motor during steady state operation under rated operating conditions is analyzed with emphasis. Based on this, the temperature field changes of the motor during single-phase and two-phase open-circuit fault-tolerant operation are investigated. Then, the proposed equal-amplitude temperature rise constrained current method is introduced in detail to ensure the safe operation of the motor. An experimental platform is built, which verifies the accuracy of the temperature field calculation, as well as the correctness of equal-amplitude temperature rise constrained current method.

Optimizing the economic viability of proton exchange membrane fuel cells operated with oxygen-enriched cathode air for residential hydrogen energy storage systems

The recovery and utilization of oxygen in residential hydrogen energy storage systems significantly impact economic factors. This study introduces an algorithm tailored to optimize oxygen concentration (fraction) across varied operational conditions, encompassing considerations for both efficiency (positive aspect) and lifetime (negative aspect). Initially, an enhanced air supply system (ASS), functioning with oxygen-enriched cathode air, is devised following the forefront scheme. Moreover, a dynamic model is formulated based on MATLAB/Simulink® software for the proton exchange membrane fuel cell (PEMFC) system. The model enables quantitative assessment of system gains in relation to various current densities and oxygen fractions, and its accuracy is partially validated through experimental data. Further, a model correlating stack lifetime to oxygen concentration (fraction) is established using experimental data obtained from other researchers. Finally, the optimal oxygen fractions are determined and managed, with a comparison of the effects before and after optimization. The optimized results indicate a 13% improvement in stack net power at rated operating conditions and a 24% improvement at peak operating conditions, and the system efficiency is improved by 24% and 43% at rated and peak operating conditions, respectively. In addition, the minimum value of system efficiency is observed to be 54%, and there is a notable attenuation of the concentration polarization phenomenon. This approach contributes to mitigating the challenge of lower system efficiency in normal PEMFCs for residential hydrogen energy storage systems (RHESSs) attributed to inadequate gas supply pressure.

A long secondary linear traction motor analysis based on electromagnetic-thermal-fluid coupling

The temperature analysis of the motor is critical for its functioning and durability as it has a significant impact on enhancing its efficiency. The purpose of this paper is to design a rational water cooling system for the Double-sided Linear Flux Switching Permanent Magnet motor (DLFSPM), thereby reducing the adverse effects of temperature rise. This paper conducts electromagnetic fluid and thermal analyses of DLFSPM. It also designs a rational cooling structure to reduce the temperature rise while running thereby contributing to its operation reliability. The electromagnetic-thermal-fluid coupling model provides a feasible solution for reducing the temperature increase of the DLFSPM motor under rated operating conditions, thereby enhancing its overall performance.

Water cooling structure design and temperature field analysis of permanent magnet synchronous motor for underwater unmanned vehicle

Unmanned underwater vehicles (UUVs) have extremely harsh cooling conditions for permanent magnet synchronous motor (PMSM) due to global sealing and compact space, and an efficient heat dissipation system is essential for the safety and operational reliability of PMSM. Currently, with the introduction of seawater and the addition of heat exchanger, liquid reservoir are typically used for open-circuit heat dissipation, which not only adds weight, but seriously affects the flow characteristics of the UUV. In this paper, a novel dual channel water cooling structure is designed to achieve internal circulating heat dissipation without additional auxiliary devices. The temperature field of the PMSM with different water cooling structures is solved by Computational Fluid Dynamics (CFD) under rated operating conditions. The results show that the cooling efficiency of water cooling structures is more affected by low flow rates, accompanied by increasing the flow rate from 0.5 L/min to 24 L/min, the cooling performance is enhanced, but does not entirely obey a strict linear variation. Furthermore, at a flow rate of 6 L/min, the dual spiral water cooling structure performs the best heat dissipation, the maximum operating temperature of the PMSM is reduced by 51.72 K, the maximum temperature rise suppression rate reaches 53.02 %, and the minimum differential pressure of 10.18 kPa.

Neural Networks Detect Inter-Turn Short Circuit Faults Using Inverter Switching Statistics for a Closed-Loop Controlled Motor Drive

Early detection of an inter-turn short circuit fault (ISCF) can reduce repair costs and downtime of an electrical machine. In an induction machine (IM) driven by an inverter with a model predictive control (MPC) algorithm, the controller outputs are influenced by a fault due to the fault-controller interaction. Based on this observation, this study developed neural network models using inverter switching statistics to detect the ISCF of an IM. The method was non-invasive, and it did not require any additional sensors. In the fault detection task, an area under receiver operating characteristics curve value of 0.9950 (95% Confidence IntervaI: 0.9949 - 0.9951) was obtained. At the rated operating conditions, the neural network model detected and located an ISCF of 2-turns (out of 104 turns per phase) under 0.1 seconds, a speedup of more than two times compared to the thresholding-based method. Moreover, we published the switching vector data collected at various load torque and shaft speed values for healthy and faulty states of the IM, becoming the first publicly available ISCF detection dataset. Together with the dataset, we provided performance baselines for three main neural network architectures, namely, multi-layer perceptron, convolutional neural network, and recurrent neural network.

Transient Hydraulic Performance of a Prototype Pump during Starting and Stopping Periods

In order to meet different operational requirements, existing low specific speed centrifugal pumps may have to be run at high speeds. Therefore, it is crucial to understand the transient performance of such centrifugal pumps during high speed starting and stopping. However, there are currently no experiments on the starting and stopping of low specific speed centrifugal pumps. In this paper, transient hydraulic performance experiments during starting and stopping had been carried out on an atypical open impeller centrifugal pump with a rated flow rate of 6 m3/h using an updated test rig. The correlation of speed, flow, head and shaft power with time was obtained for four flow ratios of 0.353, 1.022, 1.654 and 2.343 operating conditions. It was found that the fluctuation of the shaft power curve was the strongest during the starting process, and there was a significant impact phenomenon. The corresponding impact shaft power from small to large flow rates were 0.167 kW, 0.409 kW, 0.234 kW and 0.215 kW, and the shaft power impact phenomenon was the most obvious under rated operating conditions. During the stopping process, the speed, flow rate and head all remain stable for a small period of time, and the time required to decrease to 0 is longer than the time required to reach a stable state during starting. During stopping, the shaft power will instantly decrease, accompanied by varying degrees of fluctuations.

Research on the Hydraulic Characteristics of 1000 MW Francis Runner: Influence of Radial Installation Deviations

This paper focuses on a 1000 MW Francis turbine and conducts a numerical analysis of the entire flow passage using computational fluid dynamics (CFD) under steady-state conditions. Building upon prior research, we further investigate the impact of an uneven gap distribution caused by radial co-directional installation deviations of 0.1 mm, 0.3 mm, 0.5 mm, 1.5 mm, and 2.5 mm on the pressures and radial forces at various locations of the turbine, including the upper crown chamber, the vaneless zone, and the bottom ring chamber, all under steady-state rated operating conditions. By examining the maximum and minimum pressure values under different conditions, we determined that different pressure reading methods should be applied to distinct surfaces. Additionally, we derived the patterns illustrating how different components are affected by radial installation deviations. The significance of this study lies in its comprehensive exploration of the influence of radial installation deviations on the performance of a Francis turbine, particularly under steady-state rated conditions. Through numerical analysis, we elucidated the specific effects of various deviation magnitudes on the pressures and radial forces at different turbine locations. These findings provide valuable insights for the optimization of turbine design and operation. The novelty of this work stems from its in-depth investigation of radial co-directional installation deviations and the extensive results obtained through numerical simulations. These results hold significant implications for improving turbine performance and reliability, surpassing previous efforts in the literature.

Aerodynamic Performance Optimization of Centrifugal Fan Blade for Air System of Self-Propelled Cotton-Picking Machine

To enhance the working efficiency and aerodynamic performance of the centrifugal fan in the air system of a cotton picker, a new type of centrifugal fan blade was designed by extracting the mid-arc section from the prototype blade and integrating an airfoil, which was transplanted and coupled to the mid-arc section. The design aimed to improve the airflow characteristics and performance of the centrifugal fan. By combining experimental data from centrifugal fans used in existing cotton-picker air systems and employing computational fluid dynamics (CFD) methods, the internal flow field structure of the centrifugal fan was simulated. This study focused on investigating the aerodynamic performance of the new centrifugal fan blade and its impact on improving the internal flow patterns within the centrifugal fan. The results of the flow field visualization analysis indicate that the new blade design exhibits excellent aerodynamic performance, improving the flow distribution within the centrifugal fan. It enhances the uniformity of the outlet airflow, reduces the occurrence of localized “jet-wake” phenomena at the impeller’s outlet, suppresses the generation and development of vortices in the flow channel, and reduces local energy losses within the impeller. These improvements contribute to an increase in the fan’s efficiency. Under rated operating conditions, the efficiency of the prototype fan was measured at 60.3%, while the optimized fan achieved an efficiency of 64.8%. This signifies a significant improvement in the efficiency of the centrifugal fan.

FARKLI YÜKLEME ŞARTLARI İÇİN XLPE İZOLELİ DENİZALTI KABLOLARININ ISIL ANALİZİ

Submarine cables are critical assets that play an indispensable role in interconnected power systems, particularly in cross-sea energy transmission and offshore wind turbines. Their importance is further accentuated in exigent situations such as natural disasters and war, which emphasize the need for secure, reliable and uninterrupted energy supply. Furthermore, the investment and operating costs of submarine cables are relatively higher than other power system equipment, making it essential to operate them under the rated operating conditions to prevent possible faults and ensure power system stability. As thermal stress can lead to damage of cable insulation, it is an essential parameter to consider. Overloading increases thermal stress, resulting in rapid aging of the cable insulation and a shorter cable lifetime. Therefore, it is imperative to determine the maximum conductor temperatures and current carrying capacities of submarine cables under varying loading rates and ambient conditions using thermal analysis. In this study, thermal analyses are carried out for a three-phase, 220 kV HVAC, XLPE insulated submarine cable under different loading conditions. The findings demonstrate that the maximum temperature, current carrying capacity, and total losses of the cable are significantly impacted by loading rate, phase imbalance, and seawater temperature.

A modular multilevel DC active power filter scheme based on optimal parameter design for the CFETR N-NBI accelerator grid power supply

A DC active power filter (DAPF) based on a modular multilevel converter scheme is proposed for the accelerator grid power supply (AGPS) in a neutral beam injector system, to reduce the DC bus voltage ripple of AGPS. It works better than adding capacitors directly to the DC bus. This will help reduce the output voltage ripple of the AGPS at rated operating conditions, improve the focus state of the extraction beam, and reduce the occurrence of breakdown conditions. The scheme is special in that each module can compensate one frequency component of the ripple current, and the maximum switching frequency is not more than 4 times the ripple frequency. The electrical parameters of all DAPF modules (switching states and module capacitor voltages) are optimal values obtained through an optimal parameter design algorithm. In the process of applying the algorithm, two types of APF modules are distinguished, which have different switching frequencies and ripple suppression effects to adapt to different occasions. The simulation results show that each module can reduce the relative frequency component of the ripple by about 80% under the optimal parameters. Similar results are obtained by the 400V AGPS prototype and 20 V DAPF prototype. The ripple reduction scheme can be applied to other high-power applications with DC bus.

Numerical Simulation Study on the Influence of Yaw-to-Wind Angular Velocity on Wind Turbine Aerodynamic Characteristics

In this paper, the wind turbine of NREL 5MW wind turbine is used as the research object, and the wind turbine is simulated from yaw-to-wind angle 30°-0° at different yaw angular velocities (0.5°/s, 1°/s, 2°/s) under rated operating conditions by using the slip grid model in fluent solver and custom UDF function program. The output characteristics and aerodynamic characteristics of the wind turbine under dynamic wind conditions are studied, and the effects of yaw angular velocity and yaw-to-wind angle on the output power, and near wake speed of the wind turbine are analyzed. The results show that the smaller the yaw angular velocity of the wind turbine is, the better the output power of the wind turbine can be obtained when the yaw angular velocity is 0.5 °/s 1 °/s 2 °/s. By analyzing the wake velocity, it is found that the smaller the yaw angular velocity is, the greater the larger the wake velocity loss area is.

Techno-economic evaluation of green hydrogen production with low-temperature water electrolysis technologies directly coupled with renewable power sources

It is obvious that green hydrogen production needs to increase to solve climate change issues, but green hydrogen has not been actively produced due to economic disadvantages. In order to secure the economic feasibility of green hydrogen production, it is necessary to find the optimal combination of renewable power sources and water electrolysis types. In this study, the combinations of three types of renewable power plant such as offshore wind, onshore wind, and onshore photovoltaic and two types of water electrolysis such as alkaline water electrolysis (AWE) and polymer electrolyte membrane water electrolysis (PEMWE) are analyzed in the economic evaluation. Previous researches on economic evaluation of green hydrogen production have only been conducted under rated operating conditions, but this study conducted realistic calculations by considering partial load operation according to fluctuating power generation. Accurate hydrogen production efficiency was derived by using actual renewable energy generation data for year with sample time of 1hr, and water electrolysis system simulation results according to power input. The offshore wind power generation data was generated using a wind power generation prediction model using a machine learning method. LCOH for each case was calculated using cost data of system components, and the impact of each price component on LCOH was analyzed through sensitivity analysis. As a result of the calculations, the onshore wind power-AWE case has the lowest LCOH with 7.25 $/kg while PV-PEMWE case has the highest LCOH with 13.44 $/kg. The capacity factor of renewable energy is shown to have the greatest impact on LCOH by sensitivity analysis, followed by the capital expenditure (CAPEX) of the renewable power plant or the operating expenditure (OPEX). This study provides an insight to establish the methodology finding out the most efficient green hydrogen production system based on water electrolysis dedicated to renewable power sources.