Search Results (66)

The increase in power generation facilities from nonprogrammable renewable sources is posing several challenges for the management of electrical systems, due to phenomena such as congestion and reverse power flows. In mitigating these phenomena, Power-to-Gas plants can make an important contribution. In this paper, a linear optimisation study is presented for the sizing of a Power-to-Hydrogen plant consisting of a PEM electrolyser, a hydrogen storage system composed of multiple compressed hydrogen tanks, and a fuel cell for the eventual reconversion of hydrogen to electricity. The plant was sized with the objective of minimising reverse power flows in a medium-voltage distribution network characterised by a high presence of photovoltaic systems, considering economic aspects such as investment costs and the revenue obtainable from the sale of hydrogen and excess energy generated by the photovoltaic systems. The study also assessed the impact that the electrolysis plant has on the power grid in terms of power losses. The results obtained showed that by installing a 737 kW electrolyser, the annual reverse power flows are reduced by 81.61%, while also reducing losses in the transformer and feeders supplying the ring network in question by 17.32% and 29.25%, respectively, on the day with the highest reverse power flows. Full article

To reduce carbon emission levels and improve the low-carbon performance and economic efficiency of Integrated Energy Systems (IESs), this paper introduces oxy-fuel combustion technology to transform traditional units and proposes a low-carbon economic dispatch method. Considering the stepwise carbon trading mechanism, it provides new ideas for promoting energy conservation, emission reduction, and economic operation of integrated energy systems from both technical and policy perspectives. Firstly, the basic principles and energy flow characteristics of oxy-fuel combustion technology are studied, and a model including an air separation unit, an oxygen storage tank, and carbon capture equipment is constructed. Secondly, a two-stage power-to-gas (P2G) model is established to build a joint operation framework for oxy-fuel combustion and P2G. On this basis, a stepwise carbon trading mechanism is introduced to further constrain the carbon emissions of the system, and a low-carbon economic dispatch model with the objective of minimizing the total system operation cost is established. Finally, multiple scenarios are set up for simulation analysis, which verifies that the proposed low-carbon economic optimal dispatch strategy can effectively reduce the system operation cost by approximately 21.4% and improve the system’s carbon emission level with a total carbon emission reduction of about 38.3%. Meanwhile, the introduction of the stepwise carbon trading mechanism reduces the total cost by 12.3% and carbon emissions by 2010.19 tons, increasing the carbon trading revenue. Full article

This article proposes a high-efficiency isolated three-port resonant converter for DC microgrids, combining a dual active bridge (DAB)–LLC topology with hybrid Pulse Width Modulat-Pulse Frequency Modulation (PWM-PFM) phase shift control. Specifically, the integration of a dual active bridge and LLC resonant structure with interleaved buck/boost stages eliminates cascaded conversion losses. Energy flows bidirectionally between ports via zero-voltage switching, achieving a 97.2% efficiency across 150–300 V input ranges, which is a 15% improvement over conventional cascaded designs. Also, an improved PWM-PFM shift control scheme dynamically allocates power between ports without altering switching frequency. By decoupling power regulation and leveraging resonant tank optimization, this strategy reduces control complexity while maintaining a ±2.5% voltage ripple under 20% load transients. Additionally, a switch-controlled capacitor network and frequency tuning enable resonant parameter adjustment, achieving a 1:2 voltage gain range without auxiliary circuits. It reduces cost penalties compared to dual-transformer solutions, making the topology viable for heterogeneous DC microgrids. Based on a detailed theoretical analysis, simulation and experimental results verify the effectiveness of the proposed concept. Full article

This study examines the asymptotic stability of a continuous stirred tank reactor (CSTR) used for poly(methyl methacrylate) (PMMA) polymerisation, utilizing nonlinear fractional-order mathematical models. By applying Taylor series and Laplace transform techniques analytically and incorporating real plant data, we focus exclusively on the chemical reaction effects in the kinetic constants, disregarding mass transport phenomena. Our results confirm that fractional derivatives significantly enhance the stability and performance of dynamic models compared to traditional integer-order approaches. Specifically, we analyze the stability of a linearized fractional-order system at steady state, demonstrating that the system maintains asymptotic stability within feasible operational limits. Variations in the fractional order reveal distinct impacts on stability regions and system performance, with optimal values leading to improved monomer conversion, polymer concentration, and weight-average molecular weight. Comparative analyses between fractional- and integer-order models show that fractional-order operators broaden stability regions and enable precise tuning of process variables. These findings underscore the efficiency gains achievable through fractional differential equations in polymerisation reactors, positioning fractional calculus as a powerful tool for optimizing CSTR-based polymer production. Full article

A power-to-methanol (P2M) system is a promising energy storage approach in transforming surplus renewable energy into a chemical product while utilizing the captured CO₂ from conventional thermal power units. Most of the traditional methods for the optimal configuration of IES use the steady-state model of the equipment, while ignoring the dynamic deviation of the thermal power unit under variable operating conditions. This study enhances the steady-state model of the P2M system by incorporating feedback-based dynamic control for the thermal power generation (TPG) unit. A closed-loop state-space model of the TPG unit is introduced as an additional constraint within the optimization framework. Furthermore, a dynamic deviation index for the TPG unit is formulated and integrated into a mixed-integer linear programming (MILP) model. Together with the system’s annual operating cost over its life cycle, this index constitutes an objective function, aiming to minimize both the dynamic deviations and operating costs, thereby optimizing the capacity configuration of the P2M system’s components. The optimal results indicate that in the dynamic configuration, the hydrogen storage tank capacity increases by 94.73% and the electrolyzer capacity remains almost consistent, which shows the energy storage potential of the P2M. The optimized scheduling results show that the electrolyzer can effectively absorb the intermittency of renewable energy. This method of dynamic configuration planning can effectively suppress the thermal power unit output fluctuation, smooth the schedule curve, and realize the effect of peak shaving and valley filling. Full article

The gas relay is a common non-electric protection device inside transformers, installed on the connecting pipeline between the transformer oil tank and the oil conservator. When the transformer malfunctions and the oil flow value reaches the heavy gas setting value of the gas relay, a heavy gas alarm is triggered. Therefore, accurately analyzing the heavy gas action characteristics and the setting value of the gas relay directly affects the accuracy of the heavy gas alarm. The BF(Bi-Float) type double float ball gas relay uses steady-state oil flow to calibrate the setting values of heavy gas action. In reality, transformer faults cause transient oil flow. To explore the relationship between the oil flow state and gas relay flow velocity setting values, a dynamic model of the heavy gas action process of BF type double float ball gas relay was first established, and the influence of the oil flow state on the gas relay baffle action process was analyzed. Then, a transient oil flow impact test bench was developed to experimentally study the heavy gas action characteristics of gas relays under different intensities of transient oil flow impact. Theoretical and experimental research results indicate that different oil flow impact states have a significant effect on the flow velocity setting values of gas relays. The flow velocity setting value of the BF type double float ball gas relay used in this study under transient oil flow impact is 0.8 m/s, which is lower than its factory flow velocity setting value of 1 m/s. These research results have positive significance for optimizing the performance of gas relays and improving the operational reliability of power transformers. Full article

The protective effect of polyurea (PU) coatings on polymer matrix composite (PMC) panels subjected to high-velocity ballistic impacts, particularly as a potential replacement material for large power transformer (LPT) tanks, has not been extensively reported in the literature. This study addresses the gap by presenting a numerical investigation into the ballistic performance of PMC panels with PU coatings. Due to the complex nature and high cost of experimental testing, this research relies on finite element modeling to predict the panels’ responses under impact. Glass fiber/epoxy and carbon fiber/epoxy composite panels were tested individually and in hybrid configurations while being subjected to simulated 400 m/s steel projectile impacts. This study first investigates the impact damage evolution in uncoated panels, analyzing the arrest depth as a function of the panel thickness. It then evaluates the effect of PU coatings on the ballistic response. The results demonstrate that PU coatings are three times more effective in protecting both glass and carbon fiber panels from penetration compared to simply increasing the panel thickness. Additionally, the utilization of PU coatings led to a reduction in cost, mass, and thickness while still preventing penetration of the projectile in the models. Full article

The prediction of dissolved gas concentrations in oil can provide crucial data for the assessment of power transformer conditions and early fault diagnosis. Current simulations mainly focus on the generation and accumulation of characteristic gases, lacking a global perspective on gas diffusion and dissolution. This study simulates the characteristic gases produced by typical faults at different flow rates. Using ANSYS 2022 R1 simulation software, a gas–liquid two-phase model is established to simulate the flow and diffusion of characteristic gases under fault conditions. Additionally, a fault-simulation gas production test platform was built based on a ±400 kV actual converter transformer. The experimental data show good consistency with the simulation trends. The results indicate that the diffusion of dissolved gases in oil is significantly affected by the oil flow velocity. At higher flow rates, the characteristic gases primarily move within the oil tank along with the oil circulation, leading to a faster rate of gas dissolution in oil and a shorter time to reach equilibrium within the tank. At lower flow rates, the diffusion of characteristic gases depends not only on oil flow circulation but also on self-diffusion driven by concentration gradients, resulting in a nonlinear change in gas concentration across various monitoring points. Full article

Hydrogen energy plays an increasingly vital role in global energy transformation. However, existing electric–hydrogen coupled integrated energy systems (IESs) face two main challenges: achieving stable operation when integrated with large-scale networks and integrating optimal dispatching code with physical systems. This paper conducted comprehensive modeling, optimization and joint simulation verification of the above IES. Firstly, a low-carbon economic dispatching model of an electric–hydrogen coupled IES considering carbon capture power plants is established at the optimization layer. Secondly, by organizing and selecting representative data in the optimal dispatch model, an electric–hydrogen coupled IES planning model considering the integration of wind, photovoltaic (PV), diesel and storage is constructed at the physical layer. The proposed electric–hydrogen coupling model mainly consists of the following components: an alkaline electrolyzer, a high-pressure hydrogen storage tank with a compressor and a proton exchange membrane fuel cell. The IES model proposed in this paper achieved the integration of optimal dispatching mode with physical systems. The system can maintain stable control and operation despite unpredictable changes in renewable energy sources, showing strong resilience and reliability. This electric–hydrogen coupling model also can integrate with large-scale IES for stable joint operation, enhancing renewable energy utilization and absorption of PV and wind power. Co-simulation verification showed that the optimized model has achieved a 29.42% reduction in total system cost and an 83.66% decrease in carbon emissions. Meanwhile, the simulation model proved that the system’s total harmonic distortion rate is controlled below 3% in both grid-connected and islanded modes, indicating good power quality. Full article

While power transformer manufacturers are well versed in electrical aspects such as ampere-turns and amps per square inch, optimizing electrical efficiency, voltage regulation, and insulation, there is a potential oversight regarding the intricate mechanical challenges associated with electrical design. As transformers evolve in size and capacity, mechanical forces become increasingly significant, necessitating a closer examination of the mechanical aspects of electrical design. This study focuses on the design of power transformer tank walls. To address the challenge associated with larger tank wall deflection (for both the high-voltage and low-voltage sides) during pressure tests, different stiffeners such as flat stiffeners, changed flat stiffener dimensions, flat bar supports for stiffeners, and H-beams were added to the tank wall and modeled for finite element analysis. The tank wall design was optimized for higher mechanical strength, lower deflection, and lower mass by assessing the von Mises stress and deformation of different stiffeners. The findings of this study will contribute to a better understanding of how design adjustments affects mechanical strength, stress distribution, and overall reliability, providing valuable insights for the industry. Full article

Power transformers play a vital role in adjusting voltage levels during transmission. This study focuses on optimizing the structural design of power transformer tanks, particularly high-voltage (HV) tank walls, to enhance their mechanical robustness, performance, and operational reliability. This research investigates various stiffener designs and their impact on stress distribution and deformation through finite element analysis (FEA). Ten different configurations of stiffeners, including thickness, width, type, and position variations, were evaluated to identify the optimal design that minimizes stress and deflection while considering weight constraints. The results indicate that specific configurations, particularly those incorporating 16 mm thick H beams, significantly enhance structural integrity. Experimental validation through pressure testing corroborated the simulation findings, ensuring the practical applicability of the optimized designs. This study’s findings have implications for enhancing the longevity and reliability of power transformers, ultimately contributing to more efficient and resilient power transmission systems. Full article

Partial discharge is a fault that occurs at the site of insulation defects within a transformer. Dual instances of partial discharge origination discharging simultaneously embody a more intricate form of discharge, where the interaction between the discharge sources leads to more intricate and unpredictable insulation damage. Conventional piezoelectric transducers are magnetically affixed to the exterior metal tank of transformers. The ultrasonic signals emanating from partial discharge undergo deflection and reverberation upon traversing the windings, insulation paperboards, and the outer shell, resulting in signal attenuation and thus making it difficult to detect such faults. Furthermore, it is challenging to distinguish between simultaneous discharges from dual partial discharge sources and continuous discharges from a single source, often leading to missed detection and repairs of fault points, which increase the maintenance difficulty and cost of power equipment. With the advancement of MEMS (Micro-Electro-Mechanical System) technology, fiber-optic ultrasonic sensors have surfaced as an innovative technique for optically detecting partial discharges. These sensors are distinguished by their minute dimensions, heightened sensitivity, and robust immunity to electromagnetic disturbances. and excellent insulation properties, allowing for internal installation within power equipment for partial discharge monitoring. In this study, we developed an EFPI (Extrinsic Fabry Perot Interferometer) optical fiber ultrasonic sensor that can be installed inside transformers. Based on this sensor array, we also created a partial discharge ultrasonic detection system that estimates the directional information of single and dual partial discharge sources using the received signals from the sensor array. By utilizing the DOA (Direction of Arrival) as a feature recognition parameter, our system can effectively detect both simultaneous discharges from dual partial discharge sources and continuous discharges from a single source within transformer oil tanks, meeting practical application requirements. The detection methodology presented in this paper introduces an original strategy and resolution for pinpointing the types of partial discharges occurring under intricate conditions within power apparatus, effectively distinguishing between discharges from single and dual partial discharge sources. Full article

Magnetic shunts efficiently mitigate losses caused by leakage currents in the tank walls of power transformers. Transformer manufacturers frequently utilize vertical magnetic shunts positioned on the inside surfaces of the transformer tank walls. This study investigated the optimum use of horizontal shunts in a power transformer. A 50 MVA power transformer, manufactured on a commercial scale and featuring optimized vertical magnetic shunts integrated into the wall structure, was analyzed using the 3D finite element method for 100 ms at full load. Simulations for analyses were performed using a commercial ANSYS Electronics Desktop 2021 R1 FEM software program. The model’s validity was demonstrated by verifying the analysis results with experimental tank loss values. Tank loss samples were obtained by analyzing the transformer tank for two milliseconds with vertical magnetic shunts only on the long front wall and the short side wall. Using these loss samples as a reference, parametric analyses were performed for two milliseconds with horizontal magnetic shunts only on the short side wall and only on the long front wall of the tank. A tank model with horizontal magnetic shunts of an appropriate location and size was obtained via the parametric analyses. This model was analyzed for 100 milliseconds at full load and compared with the experimental results of the transformer manufacturer’s vertical magnetic shunt transformer. According to the results, a saving of 25.83% was achieved in the horizontal magnetic shunt volume compared with the vertical magnetic shunt volume. The maximum magnetic flux density was lower in the horizontal magnetic shunts, and the maximum current density was lower in the transformer tank with horizontal magnetic shunts. Full article

The power transformer is one of the most crucial pieces of high-voltage equipment in the power system, and its stable operation is crucial to the reliability of power transmission. Partial discharge (PD) is a key factor leading to the degradation and failure of the insulation performance of power transformers. Therefore, online monitoring of partial discharge can not only obtain real-time information on the operating status of the equipment but also effectively predict the remaining service life of the transformer. Meanwhile, accurate localization of partial discharge sources can assist maintenance personnel in developing more precise and efficient maintenance plans, ensuring the stable operation of the power system. Dual partial discharge sources in transformer oil represent a more complex fault type, and piezoelectric transducers installed outside the transformer oil tank often fail to accurately capture such discharge waveforms. Additionally, the sensitivity of the built-in F-P sensors can decrease when installed deep within the oil tank due to the influence of oil pressure on its sensing diaphragm, resulting in an inability to accurately detect dual partial discharge sources in transformer oil. To address the impact of oil pressure on sensor sensitivity and achieve the detection of dual partial discharge sources under high-voltage conditions in transformers, this paper proposes an optical fiber ultrasonic sensor with a pressure-balancing structure. This sensor can adapt to changes in oil pressure environments inside transformers, has strong electromagnetic interference resistance, and can be installed deep within the oil tank to detect dual partial discharge sources. In this study, a dual PD detection system based on this sensor array is developed, employing a cross-positioning algorithm to achieve detection and localization of dual partial discharge sources in transformer oil. When applied to a 35 kV single-phase transformer for dual partial discharge source detection in different regions, the sensor array exhibits good sensitivity under high oil pressure conditions, enabling the detection and localization of dual partial discharge sources in oil and winding interturn without obstruction. For fault regions with obstructions, such as within the oil channel of the transformer winding, the sensor exhibits the capability to detect the discharge waveform stemming from dual partial discharge sources. Overall, the sensor demonstrates good sensitivity and directional clarity, providing effective detection of dual PD sources generated inside transformers. Full article

The explosion-proof performance is an important index for oil-immersed transformers. The nitrogen-sealed transformer is a new type of transformer with nitrogen gas in the upper space, which can buffer against internal stress increase caused by arc faults. However, the pressure changes in the transformer under internal faults are unclear. The authors of this study propose a method based on finite element simulation to analyze the pressure changes and the stress on the tank. First, the calculation process of arc energy and the pressure of the bubbles caused by the arc are derived. Second, the dynamic pressure wave propagation model and acoustic-solid coupling model are established. Last, the finite element simulation model is built to analyze the pressure characteristics. Taking the winding turn-to-turn and phase-to-phase short circuit faults as the analysis situations, the pressure changes in the 110 kV/20 MVA nitrogen-sealed transformer are simulated. Due to the pressure wave refraction and reflection, the pressure changes show oscillatory characteristics with time after the occurrence of an internal short circuit fault. The pressure wave travels from the arc fault position to the periphery. Compared to the conventional transformer, the pressure changes with slower variations under an internal short circuit fault and the tank suffer less stress, which indicates that the nitrogen-sealed transformer is more effective in the explosion-proof performance. Full article