{"title":"Moisture dynamics during high-load fluctuations in transformers: Localised accumulation and interfacial transfer within oil/pressboard insulation","authors":"Shaoqi Wang, Qiaogen Zhang, Chong Guo, Yuhan Sun, Zhicheng Wu","doi":"10.1049/hve2.12486","DOIUrl":"https://doi.org/10.1049/hve2.12486","url":null,"abstract":"<p>Power systems grapple with the challenges of high load rates and intermittent new energy sources integration. Transformers, as vital equipment, employ oil/pressboard (oil/PB) insulation. Uneven moisture distribution in this insulation can jeopardise safety thresholds, necessitating precise moisture assessment for grid stability. A novel mathematical model, adsorption–desorption and porous media moisture transfer (ADP-MoT), is presented. This model incorporates adsorption and desorption processes within the porous pressboard, enabling a description of the dynamic moisture transfer between the oil and pressboard. Using this mathematical model, simulations for moisture dynamics were performed on a 750-kV transformer across four typical days. The results indicate that temperature fluctuations are the primary driving factor for moisture migration at the oil/PB interface. Convection and diffusion contribute to moisture movement towards cooler regions. Fluid properties and structural characteristics induce a distinctive streamline-shaped moisture flow within horizontal oil channels, with localised moisture accumulation in specific areas. Moreover, the analysis of 96 transient results uncovers potential free-state moisture formation during severe conditions, underscoring the importance of monitoring the pressboard at winding bases during high load fluctuations. In conclusion, this study significantly contributes to scientifically identifying and addressing risks tied to new energy sources integration in power systems.</p>","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"9 6","pages":"1221-1233"},"PeriodicalIF":4.4,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1049/hve2.12486","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143253150","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High VoltagePub Date : 2024-09-27DOI: 10.1049/hve2.12488
Yongming Xu, Ziyi Xu, Congrui Ren, Yaodong Wang
{"title":"Research on temperature distribution characteristics of oil-immersed power transformers based on fluid network decoupling","authors":"Yongming Xu, Ziyi Xu, Congrui Ren, Yaodong Wang","doi":"10.1049/hve2.12488","DOIUrl":"https://doi.org/10.1049/hve2.12488","url":null,"abstract":"<p>Due to the complex structure and large size of large-capacity oil-immersed power transformers, it is difficult to predict the winding temperature distribution directly by numerical analysis. A 180 MVA, 220 kV oil-immersed self-cooling power transformer is used as the research object. The authors decouple the internal fluid domain of the power transformer into four regions: high voltage windings, medium voltage windings, low voltage windings, and radiators through fluid networks and establish the 3D fluid-temperature field numerical analysis model of the four regions, respectively. The results of the fluid network model are used as the inlet boundary conditions for the 3D fluid-temperature numerical analysis model. In turn, the fluid resistance of the fluid network model is corrected according to the results of the 3D fluid-temperature field numerical analysis model. The prediction of the temperature distribution of windings is realised by the coupling calculation between the fluid network model and the 3D fluid-temperature field numerical analysis model. Based on this, the effect of the loading method of the heat source is also investigated using the proposed method. The hotspot temperatures of the high-voltage, medium-voltage, and low-voltage windings are 89.43, 86.33, and 80.96°C, respectively. Finally, an experimental platform is built to verify the results. The maximum relative error between calculated and measured values is 4.42%, which meets the engineering accuracy requirement.</p>","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"9 5","pages":"1136-1148"},"PeriodicalIF":4.4,"publicationDate":"2024-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1049/hve2.12488","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142540879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High VoltagePub Date : 2024-09-25DOI: 10.1049/hve2.12487
Kai Liu, Shibo Jiao, Guangbo Nie, Hui Ma, Bo Gao, Chuanming Sun, Dongli Xin, Tapan K. Saha, Guangning Wu
{"title":"On image transformation for partial discharge source identification in vehicle cable terminals of high-speed trains","authors":"Kai Liu, Shibo Jiao, Guangbo Nie, Hui Ma, Bo Gao, Chuanming Sun, Dongli Xin, Tapan K. Saha, Guangning Wu","doi":"10.1049/hve2.12487","DOIUrl":"https://doi.org/10.1049/hve2.12487","url":null,"abstract":"<p>Partial discharge (PD) detection of cable terminals is crucial for the safe operation of the traction power system in trains. However, similar PD signals in complex train-operating environments cause difficulty to recognise the insulation defects. Therefore, a PD signal image transformation recognition method is proposed for PD detection of cable terminal defects to identify defects in cable terminals with similar PD characteristics accurately. In the proposed method, the raw PD signals are firstly transformed to images via the Gramian angular field (GAF) representation. This can reveal the discriminative characteristics embedded in the original PD signals and subsequently facilitate differentiating the PD sources, which exhibit similar characteristic in the time domain. The obtained GAF representation of PD signals (named as PD GAF images) is extracted from local and global features to train an efficient MobileVIT model, which is then utilised to identify similar types of PD sources in cable terminals. The results show that the proposed method achieves 97.5% recognition accuracy in the field experiment, which is superior to other methods.</p>","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"9 5","pages":"1090-1100"},"PeriodicalIF":4.4,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1049/hve2.12487","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142540849","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Introducing deep trap states for high dielectric strength of aramid-based composite films","authors":"Wenqi Zhang, Qibin Wang, Guangyi Shen, Sidi Fan, Xiaozhou Fan, Rui Yang, Yunpeng Liu, Xiang Yu, Fangcheng Lv","doi":"10.1049/hve2.12483","DOIUrl":"https://doi.org/10.1049/hve2.12483","url":null,"abstract":"<p>Aramid nanofiber (ANF)-based composites have drawn tremendous interest in high-voltage electrical systems due to their superior insulation strength, thermal stability, and mechanical endurance. However, the filler agglomeration and interface compatibility have retarded further improvement of the dielectric performance. Herein, the nano-titanium dioxide (TiO<sub>2</sub>) particles treated by aminopropyl triethoxysilane (APTES) serve as the inorganic fillers, which are doped in the ANF to prepare the composite nano-paper via the blade coating method. The electrostatic interaction between the ANF and fillers highly promotes their uniform distribution. Compared to the pure ANF paper, the composite paper has a denser structure with reduced pores and defects, which significantly improves its dielectric performance with inhibited partial discharge development. At a filler loading of 3 wt% (mass fraction), the breakdown strength is increased by 70.5% to a maximum value of 358.1 kV/mm, while the bulk conductivity is minimised to 5.2 × 10<sup>−17</sup> S/m, representing an 88.1% decrease. By analysing the energy band structure of each component, energy barriers at the interface for electrons (1.48 eV) and holes (0.40 eV) are determined. These values indicate deepened trap energy levels, which greatly strengthen the carrier trapping effect for improved dielectric performance.</p>","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"10 1","pages":"197-207"},"PeriodicalIF":4.4,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1049/hve2.12483","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143536045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High VoltagePub Date : 2024-09-25DOI: 10.1049/hve2.12484
Teng Gao, Dongxin He, Zhe Xu, Junyu Wei, Shijie Xie, Gilbert Teyssède, Zhizhen Liu, Bin Cui
{"title":"Degradation induced by charge relaxation in silicone gels under the ultra-fast pulsed electric field","authors":"Teng Gao, Dongxin He, Zhe Xu, Junyu Wei, Shijie Xie, Gilbert Teyssède, Zhizhen Liu, Bin Cui","doi":"10.1049/hve2.12484","DOIUrl":"https://doi.org/10.1049/hve2.12484","url":null,"abstract":"<p>The insulating properties of silicone gel used for silicon carbide-insulated gate bipolar transistors encapsulation may deteriorate seriously under ultra-fast pulsed electric fields. The essence of insulation degradation lies in the deterioration of materials caused by dynamic phenomena at microscopic scale, such as charge trapping and detrapping. Different from the steady-state operating condition, insulating materials exhibit a sharp decrease in their insulating properties when subjected to a rapidly changing electric field. To investigate the insulation failure of silicone gel materials under an ultra-fast pulsed electric field, Marcus hopping mechanism for charge response is proposed. By calculating the relaxation time with different defects, we characterise the degradation of the materials. According to the force analysis of space charge, the authors establish a relationship between insulation failures and charge relaxation time. Combined with the experimental results on electrical treeing in silicone gel, the feasibility of the theory is verified. The experimental phenomenon can be well explained, that is, the initial voltage of the electrical trees decreased sharply with shortening the edge time of the pulsed electric field, especially on the nanosecond time scale.</p>","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"9 6","pages":"1383-1392"},"PeriodicalIF":4.4,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1049/hve2.12484","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143253474","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Effect of accelerator on properties of epoxy resin re-prepared from alcoholysis recycling","authors":"Xin Zhao, Wendong Li, Xiong Yang, Wenrui Li, Fangzheng Zou, Wang Guo, Guanjun Zhang","doi":"10.1049/hve2.12481","DOIUrl":"https://doi.org/10.1049/hve2.12481","url":null,"abstract":"<p>Alcoholysis has emerged as a crucial method for the degradation of anhydride-cured epoxy resin, and the degraded epoxy resin (DER) can be reused to prepare a new resin. Accelerator is commonly employed in the preparation of epoxy resin to expedite the curing process. However, the effect of accelerator content on the re-prepared resin's performance has remained unexplored. Hence, DER is used to replace part bisphenol A diglycidyl ether to prepare new resins with varying accelerator contents, and the comprehensive properties of new resins are investigated. The results demonstrate that the accelerator-free re-prepared resin exhibits a performance that is comparable to that of the original resin. After accelerator is added during the preparation of new resins, the curing temperature of the reconstituted resin shows a decrease, and two peaks appear during the curing exothermic process. Besides, as the accelerator content increases, the insulation performance initially improves and then deteriorates, while the mechanical and thermal properties continue to decline. Through characterisation and chemical simulation analysis, it is believed that excessive accelerators are detrimental to the cross-linking reaction of DER. Therefore, the accelerator content in the new epoxy resin should not be high.</p>","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"10 1","pages":"208-218"},"PeriodicalIF":4.4,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1049/hve2.12481","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143536046","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High VoltagePub Date : 2024-09-20DOI: 10.1049/hve2.12482
Hesham S. Karaman, Eman G. Atiya, Diaa-Eldin A. Mansour, Mohsen Ghali, Z. M. S. Elbarbary, Manal M. Emara
{"title":"New insights on thermal ageing of electrical insulating oils as revealed from photoluminescence and absorption spectroscopy","authors":"Hesham S. Karaman, Eman G. Atiya, Diaa-Eldin A. Mansour, Mohsen Ghali, Z. M. S. Elbarbary, Manal M. Emara","doi":"10.1049/hve2.12482","DOIUrl":"https://doi.org/10.1049/hve2.12482","url":null,"abstract":"<p>Recently, significant efforts have been exerted to replace mineral oil with environmentally friendly oils due to safety and environmental issues. However, there is a need to clarify the physical mechanisms behind the ageing impact of these oils. The authors use advanced optical spectroscopy techniques in correlation with dielectric measurements to understand the ageing processes in environmentally friendly oils as well as mineral oil. Firstly, different samples of environmentally friendly oils and mineral oil were utilised to investigate the ageing mechanism. The samples were subjected to different ageing periods using a thermal accelerated ageing process. Secondly, the severity of the produced byproducts due to the oil degradation is examined based on several measured properties representing macroscopic and microscopic categories. The macroscopic category was evaluated through dielectric properties, including breakdown voltage, dielectric permittivity, and dissipation factor. The microscopic category, on the other hand, was assessed using techniques such as ultraviolet–visible absorption spectroscopy and photoluminescence spectroscopy. These techniques enabled a deep understanding of the molecular-level changes occurring in the oil under ageing conditions, thereby getting new insights into oil ageing mechanisms. It is worth mentioning that natural ester oil demonstrated the most favourable performance across various properties under ageing conditions.</p>","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"9 5","pages":"1033-1045"},"PeriodicalIF":4.4,"publicationDate":"2024-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1049/hve2.12482","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142540839","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High VoltagePub Date : 2024-08-26DOI: 10.1049/hve2.12448
Ji Li, Jingfeng Tang, Yuqing Lou, Haoran Zhang, Lu Wang, Tianyuan Ji, Daren Yu, Ximing Zhu
{"title":"Energy regulation of impulse current generator modulated DC arc discharge","authors":"Ji Li, Jingfeng Tang, Yuqing Lou, Haoran Zhang, Lu Wang, Tianyuan Ji, Daren Yu, Ximing Zhu","doi":"10.1049/hve2.12448","DOIUrl":"https://doi.org/10.1049/hve2.12448","url":null,"abstract":"<p>This paper proposes a method of impulse current generator modulated DC arc by combining the advantages of pulse and the RF to solve the low electron energy problem of direct current arc. Through experimental analyzing the electrical, spectral, and optical characteristics of the arc, the effect of impulse current generator (ICG) on improving electron energy is discussed. The results show that the ICG consumes more energy to enhance the strength of arc discharge, and therefore electron energy is increased in a microsecond scale. In addition, it is found that the electron energy of the arc discharge can be adjusted by varying inductance, capacitance, and discharge tube: increasing the inductance or capacitance can increase the electron energy firstly and then decrease it. In adjusting the three adjustable components, adjusting the inductor is the most effective method, followed by adjusting the capacitor, and adjusting the repetition frequency has the least effect. The reason is discussed, and it is believed that the results are related to leakage inductance and distributed capacitance.</p>","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"9 5","pages":"1046-1058"},"PeriodicalIF":4.4,"publicationDate":"2024-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1049/hve2.12448","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142540959","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High VoltagePub Date : 2024-08-23DOI: 10.1049/hve2.12480
Tian Liang, Zhijin Zhang, Xingliang Jiang, Jianlin Hu, Qin Hu
{"title":"A method for simulating powdering of silicone rubber composite insulator in coastal areas","authors":"Tian Liang, Zhijin Zhang, Xingliang Jiang, Jianlin Hu, Qin Hu","doi":"10.1049/hve2.12480","DOIUrl":"https://doi.org/10.1049/hve2.12480","url":null,"abstract":"<p>In recent years, the powdering phenomenon often has been found in suspension composite insulators operating in outdoor environments, and there is currently a gap in research on the composition and formation process of powdered substance. A method for simulating powdering of silicone rubber (SiR) in a high humidity salt-fog environment is proposed, and the obtained powder is compared with the natural powder. Test results show that the powder obtained from artificial environments is similar to the natural powder in coastal areas, which proves that this method is reasonable to simulate the powdering process. Powdered substances are generally composed of two types of substances, Type I is an inorganic filler and its dehydration product and Type II is a small molecular siloxane. The average particle size of artificial powder is 8–10 μm, while that of natural powder is 3–5 μm. All the dielectric properties of powdered SiR decreased, and after 12 h of ageing, the dielectric properties of the artificial sample were close to those in coastal areas, and the element composition was also similar. Aluminium hydroxide (Al(OH)<sub>3</sub>) crystals were detected in both powders. The change trend of the characteristic functional groups in the infrared spectrum of the artificial powder is consistent with that of the natural powder, but the degree of molecular chain bond destruction is lower.</p>","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"9 6","pages":"1336-1346"},"PeriodicalIF":4.4,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1049/hve2.12480","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143253226","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Stress grading system optimisation for an inverter-fed rotating machine","authors":"Peng Wang, Wenhuan Zhao, Yue Zhang, Shuai Yang, Andrea Cavallini, Chaofan Yu, Chizhou Cheng, Yingwei Zhu","doi":"10.1049/hve2.12478","DOIUrl":"https://doi.org/10.1049/hve2.12478","url":null,"abstract":"<p>Stress grading systems using non-linear resistive coatings are a key component to suppress surface corona in the end-windings of rotating machine. Compared to a sinusoidal-fed motor, the high slew rate of the voltage at the flanks of the repetitive square voltages from the inverter cause large capacitive currents to flow in the main wall insulation. These large currents, if not properly considered in the design phase, lead to severe electrothermal stress of the grading system. Experiments and simulations were conducted on a stress grading system whose structure arises from limitation posed by the motor structure. Measurements performed with different rise times show that the maximum potential along the conductive armour tape (CAT) increases non-linearly with increasing axial distance, and the potential at the edge of the CAT reached nearly twice the peak-to-peak voltage at 500 ns rise time, leading to corona inception. As metal plates are used in the machine to dampen vibrations in the end-winding, similar plates were also fastened to the stress grading system, worsening the already inadequate corona suppression performance. The stress grading system was therefore modified, avoiding the surface corona while, at the same time, reducing the temperature in the grading system to acceptable levels.</p>","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"9 5","pages":"1115-1124"},"PeriodicalIF":4.4,"publicationDate":"2024-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1049/hve2.12478","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142540941","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}