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Significantly enhanced flashover voltage of epoxy in vacuum by graded surface roughness modification

High Voltage 2023年第5期8卷 997-1010页

作者： Inzamam Ul Haq Feipeng Wang Shakeel Akram Muneeb Ahmed Muhammad Tariq Nazir State Key Laboratory of Power Transmission Equipment&System Security and New Technology Chongqing UniversityChongqingChina College of Electrical Engineering and Control Science Nanjing Tech UniversityNanjingChina State Key Laboratory of Electrical Insulation and Power Equipment Xi'an Jiaotong UniversityXi'anChina School of Engineering RMIT UniversityMelbourneVictoriaAustralia

The flashover strength of epoxy(EP)insulations in the High voltage direct current applications of future energy grids can be improved by tailoring their surface *** work aims to improve the DC surface flashover characteristics of EP after being treated with sandpaper of different *** with virgin EP and homogenously modified EP considering varying surface roughness(R_(a)=0.54,3.16,5.24,and 8.35μm)are *** experimental characterisations,such as water contact angle,surface intrinsic conductivity,surface voltages,flashover strength,and trap distributions are conducted and evaluated to analyse the difference between virgin and treated ***,based on the obtained experimental results of homogenously treated EP and theoretical analysis,the concept of surface functionally graded materials(SFGMs)is put *** flashover voltages of homogenously treated EP are augmented significantly compared to virgin EP regardless of the voltage polarity and enhanced by enhancing the surface *** sample T_(Model‐C) with SFGM design shows a 45.02%and 43.75%improvement in the negative and positive flashover voltages than that of the virgin *** the end,COMSOL simulations are conducted to justify the experimental findings and to analyse the difference between virgin and modified samples in terms of electric field distribution.

关键词： flash graded roughness

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Autonomous-synergic Voltage security Regions in Bulk power systems

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Journal of Modern power systems and Clean Energy 2023年第2期11卷 686-692页

作者： Fan Li Tao Niu Lin Xue Yuxiao Li Tianen Huang Zhenjie Wu Key Laboratory of Power Transmission Equipment&System Security and New Technology Chongqing UniversityChongqing 400044China Zhejiang University Hangzhou 310058China Grid Hangzhou Power Supply Company Hangzhou 310020China

Determining security/stability boundaries is a common and critical means of preventing cascading failures induced by voltage-related issues,which represents one of the major challenges in bulk power ***,traditional approaches suffer from conservative issues and heavy computational *** address these challenges,the concept of an autonomous-synergic voltage security region(AS-VSR)and the corresponding dynamic constraint coefficient pruning(DCCP)computation method,which fully consider the volt/var characteristics of bulk power systems,are proposed in this *** linearized and nonlinearized robust optimization problems are introduced to obtain accurate *** computational accuracy,time cost,and advantages of autonomous-synergic control are observed in the simulation results.

关键词： Voltage security region cascading failure dynamic constraint coefficient pruning(DCCP) bulk power system robust optimization

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Effect of Thermal Field on Moisture distribution Characteristics of Ester Oil-paper Insulation Interface: Insights From Molecular Dynamics 22

Effect of Thermal Field on Moisture Distribution Characteris...

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22nd IEEE International Conference on Dielectric Liquids, ICDL 2023

作者： Zhou, Jian Wang, Feipeng Wang, Qiang Chongqing University State Key Laboratory of Power Transmission Equipment and System Security and New Technology Chongqing China

ISBN: (纸本)9798350302172

Ester insulating oils, which are used in environmentally friendly transformers, have been found to exhibit different performance characteristics from traditional mineral insulating oils due to their molecular structure. The mechanisms behind the thermal aging of ester oil-paper insulation systems are being investigated, with moisture being identified as a significant factor that impacts insulation. However, it is difficult to observe the dynamics of moisture at the oil-paper insulation interface through macroscopic experiments. In this study, the authors used molecular dynamics simulations to model the diffusion behavior of moisture at the interface of ester oil-paper insulation at various temperatures (298-373 K). The results showed that at 298 K, water molecules in the ester insulating oil tend to form clusters, but as the temperature increases, these molecules diffuse from the oil to the paper and accumulate at the oil-paper interface. The diffusion coefficient of water molecules in the normal direction of the interface was found to be significantly smaller than its tangential direction diffusion coefficient, with a minimum value at 343 K. The authors also observed that the binding capacity of the insulating oil to water molecules decreases with increasing temperature as the molecules diffuse from the oil to the paper. These findings provide valuable data for improving our understanding of the thermal aging of ester oil-paper insulation systems and may inform the design of experimental prediction and testing schemes for this system. © 2023 IEEE.

关键词： Molecular dynamics

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Preparation of Graphene Loaded Cobalt Catalyst and its Oxygen Evolution Performance 4

Preparation of Graphene Loaded Cobalt Catalyst and its Oxyge...

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4th IEEE International Conference on Electrical Materials and power equipment, ICEMPE 2023

作者： He, Wenkai Yang, Qing Zhang, Zhaotian Chongqing University State Key Laboratory of Power Transmission Equipment and System Security and New Technology Chongqing China

ISBN: (纸本)9798350334678

The energy crisis is becoming more severe, and energy restructuring is imperative. Hydrogen energy introduction effectively reduces the proportion of fossil energy, and hydrogen production from the water splitting is a core technology to realize low-carbon transition. Transition metal compounds with large reserves and high catalytic activity are considered promising catalysts for oxygen evolution reactions. In this work, CoS2-loaded oxygen evolution catalysts on graphene were prepared by radio frequency plasma treatment. The introduction of two-dimensional structured graphene accelerates the surface electron migration and increases the reaction area. The plasma treatment promotes the loading of nanoparticles on graphene. The plasma etching effect was used to create a large number of carbon structure defects and oxygen vacancy structures on the surface of catalysts, which improve the distribution of CoS2, effectively modulate CoS2 transition state free energy, and improve the oxygen evolution catalytic activity. Electrochemical tests show that the experimentally synthesized CoS2/rGO@30min achieves an overpotential of300 mV at 50 mAc m-2 with excellent OER performance and stability. © 2023 IEEE.

关键词： Graphene

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SiC MOSFETs Junction Temperature Estimation Method Considering Aging Influence 6

SiC MOSFETs Junction Temperature Estimation Method Consideri...

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6th Asia Conference on Energy and Electrical Engineering, ACEEE 2023

作者： Liu, Qiangqiang Du, Xiong Wang, Zhenye Ren, Hongyu Zhou, Junjie Chen, Rui Chongqing University State Key Laboratory of Power Transmission Equipment and System Security and New Technology Chongqing China

ISBN: (纸本)9798350312690

Junction temperature (Tj) is a critical parameter for condition monitoring and lifetime assessment of SiC MOSFETs. As one of the temperature-sensitive electrical parameters (TSEPs), the on-state drain-source resistance (Ron) can be calculated by measuring Vds and Id, making it a widely used Tj indicator in SiC MOSFETs. However, the relationship between Ron and Tj may change with aging of SiC MOSFETs, leading to errors in Tj estimation. Therefore, an improved SiC MOSFETs Tj estimation method considering the influence of aging is proposed to eliminate this error. Back Propagation Neural Network (BPNN) is employed to map the work accumulation to an aging factor, so that to correct the result of Ron-based Tj estimation method. To validate proposed method, a dc power cycling test platform is built. The number of power cycles is taken as work accumulation, which represents the aging state of SiC MOSFETs. The test results shows that the Ron-based Tj estimation method without correction of can result in errors of up to 18°C after 6337 power cycles. However, the proposed method is able to reduce the errors to less than 2°C at the same aging state, confirming the effectiveness of the proposed method. © 2023 IEEE.

关键词： Junction temperature

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Study on Stress Field distribution and Size Influence Characteristics of Bellows in GIS equipment

Study on Stress Field Distribution and Size Influence Charac...

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2023 IEEE International Conference on power Science and technology, ICPST 2023

作者： Li, Ying Hao, Jian Ding, Yilin Liu, Qingsong Li, Xu Zhong, Yao Chongqing University State Key Laboratory of Power Transmission Equipment & System Security and New Technology Chongqing China

ISBN: (纸本)9798350311358

Due to installation errors, expansion and contraction of materials, or foundation settlement, GIS equipment is prone to accidents such as cylinder cracks, support tilt and gas leakage when the bellows are improperly deployed. Therefore, it is of great significance to understand the stress distribution characteristics of bellows and its influencing factors for ensuring the operation safety of GIS equipment. In this paper, stress field simulation research was carried out for GIS bellows, the stress and deformation displacement distribution of GIS bellows were solved, and the influence of wall thickness and wave height on the distribution characteristics of stress and deformation displacement of GIS bellows was studied. The results show that: the stress distribution of the bellows is large at both ends and small in the middle and the stress of the wave crest structure is less than that of the wave trough structure;The distribution of deformation displacement is large in the middle and small at both ends, and the deformation displacement of wave crest structure is larger than that of wave trough structure;in a certain range, reducing the wall thickness and increasing the wave height can reduce the maximum stress value of bellows and improve the temperature compensation ability of bellows. These conclusions provide some guidance for the design and selection of bellows. © 2023 IEEE.

关键词： Finite element method

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Practical Research on a new Type of Electric Field Sensor 4

Practical Research on a New Type of Electric Field Sensor

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4th IEEE International Conference on Electrical Materials and power equipment, ICEMPE 2023

作者： Ke, Kun Yang, Qing Liao, Wei Qiu, Zhenhui Ma, Lewei Chongqing University State Key Laboratory of Power Transmission Equipment and System Security and New Technology Chongqing China

ISBN: (纸本)9798350334678

Aiming at the problems of large size, limited measurement band range and high cost of traditional voltage transformers, this paper designs a new electric field sensor based on the D-dot principle, which is only the size of a coin and the volume is greatly reduced. The static response and frequency characteristics of the sensor are tested by the built sensor performance test platform, and the test results show that the sensor can produce good static response for different waveforms, and the measurement frequency range is between 10Hz-l0kHz and has good linearity, which can not only realize low-frequency measurement but also meet the requirements of high-frequency measurement. Furthermore, the sensor is placed under the simulated transmission line, and the experimental results show that the output law of the sensor is consistent with the simulation results under different spacing and different voltage levels, in line with the electromagnetic field distribution law. Finally, the cost is compared and analyzed, and the analysis shows that the sensor has a high cost performance, which shows that the sensor has broad practical application prospects. © 2023 IEEE.

关键词： Electric power transmission

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Ultrasound Plane Wave Reference Frame Multi-Hypothesis Prediction Reconstruction

Ultrasound Plane Wave Reference Frame Multi-Hypothesis Predi...

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2023 IEEE International Ultrasonics Symposium, IUS 2023

作者： Tong, Lin Wang, Ping Li, Xitao Li, Qianwen Chen, Jinghan Shen, Yue Chongqing University State Key Laboratory of Power Transmission Equipment and System Security and New Technology Chongqing China

ISBN: (纸本)9798350346459

The emergence of ultrasound plane wave technology has driven the development of ultrasonic ultrafast frame rate imaging technology. However, simultaneously, it has placed an increased burden on hardware sampling, transmission, and data storage. Compressed sensing technology is widely employed in ultrasound sparse sampling and imaging. However, it faces challenges in effectively recovering useful signals when the sampling rate is low or the echo noise is excessive. Based on the characteristics of ultrasound echo signals, this paper employs a multi-hypothesis prediction method to reconstruct correlated echo signals. This approach can efficiently reconstruct ultrasound echo signals while reducing the reliance on the sparsity of the original echo signals. On PICMUS experimental data, the image similarity surpasses that of methods relying solely on sparsity or both sparsity and correlation. Without compromising image quality, this paper's method accomplishes signal compression and reconstruction from the perspective of signal correlation. © 2023 IEEE.

关键词： Compressed sensing

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Research on Lifetime Evaluation of IGBT Module in Wave Energy Converter Considering Environmental Uncertainty 6

Research on Lifetime Evaluation of IGBT Module in Wave Energ...

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6th Asia Conference on Energy and Electrical Engineering, ACEEE 2023

作者： Jia, Dongqiang Wang, Jing Du, Xiong Chongqing University State Key Laboratory of Power Transmission Equipment & System Security and New Technology Chongqing China

ISBN: (纸本)9798350312690

Insulated gate bipolar transistors (IGBTs) are one of the weak links of the wave energy converter. Accurate lifetime evaluation is an important support for the reliable operation of the wave energy conversion system. However, the impact of operating environment uncertainty wasn't consider in the current IGBT module lifetime evaluation model. This paper proposes a lifetime evaluation model of IGBT module considering environmental uncertainty, which effectively simulates the uncertainty of environmental temperature and wave energy power generation and improves the accuracy of lifetime evaluation results. Firstly, the Monte Carlo method is used to generate a large number of random scenarios to simulate the uncertainty of operating environment, and the scenario reduction method is introduced to extract typical operating scenarios. The scenario generation scenario and reduction fully balance the contradiction between accuracy and computational complexity of lifetime evaluation model. Secondly, the mission profile is divided into different time scales, and the influence of low frequency junction temperature and high frequency junction temperature on the life loss of IGBT module is quantitatively analyzed. Finally, the effects of different lifetime evaluation methods are compared by simulation, and the simulation results show that the proposed lifetime evaluation model has higher accuracy. © 2023 IEEE.

关键词： Junction temperature

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Coordinated Frequency Control Strategy of Offshore Wind Farm via MMC-HVDC Considering Secondary Frequency Drop 26

Coordinated Frequency Control Strategy of Offshore Wind Farm...

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26th International Conference on Electrical Machines and systems, ICEMS 2023

作者： Zhou, Zhiting Li, Hui Tan, Hongtao Chongqing University State Key Laboratory of Power Transmission Equipment & System Security and New Technology Chongqing China

ISBN: (纸本)9798350317589

Offshore wind farm (OWF) integrated into the onshore grid through Modular Multilevel Converter-based high-voltage direct current (MMC-HVDC) cannot respond to the frequency changes of the onshore grid system under conventional control methods. Furthermore, the wind turbine contributes to frequency regulation by releasing the kinetic energy stored in the rotor, which may cause a secondary frequency drop (SFD) during speed recovery. Therefore, this paper proposes a coordinated frequency control strategy for OWF-MMC-HVDC considering SFD. Firstly, considering the DC voltage fluctuation limit, the coupling relationship between the frequency of onshore grid system and the DC voltage of grid-side converter station is established, and it actively participates in the system frequency control by changing the DC voltage reference value. Secondly, we develop a frequency transfer model for OWF that considers the losses in submarine cables. Additionally, we design a variable-rate speed recovery function, which not only shortens the speed recovery time but also mitigates the occurrence of SFD. Through simulations involving load increases and wind speed fluctuations, we validate that the proposed control strategy successfully prevents SFD. © 2023 IEEE.

关键词： Drops

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