The breakdown characteristics of the novel eco-friendly insulating gas CF3SO2F are fundamental to the design of gas-insulated equipment. In this paper, the gas mixture parameters for CF3SO2F were optimised for different ambient temperatures in order to ascertain the insulation performance and liquefaction temperature constraints. To further assess its insulation properties, breakdown experiments were carried out under power-frequency voltage (50 Hz), considering the influence of buffer gas types, the molar ratio of CF3SO2F and pressure. The results demonstrate that the breakdown voltage of CF3SO2F is 1.2–1.5 times that of SF6, and it increases with pressure in the range of 0.1–0.4 MPa. When compared to air and CO2, N2 exhibits a superior synergistic effect with CF3SO2F. At an absolute pressure of 0.5 MPa, the 60% CF3SO2F/40% N2 mixture shows similar insulation strength to SF6, but it can only be applied in environments above 10°C. Furthermore, the 12% CF3SO2F/88% N2 mixture at an absolute pressure of 0.8 MPa has an insulation strength comparable to that of 0.5 MPa SF6, with a liquefaction temperature of −25°C. The results demonstrated great potential of industrial applications. At this configuration, global warming potential (GWP) of the gas mixture is only 4% that of SF6. The research provides a new solution for SF6 gas substitution in gas-insulated equipment.
{"title":"Research on Power Frequency Insulation Properties and Configurations of CF3SO2F Gas Mixture for Industrial Applications","authors":"Shubo Ren, Wenjun Zhou, Yu Zheng, Dongxin Hao, Wei Liu, Keli Gao","doi":"10.1049/hve2.70131","DOIUrl":"https://doi.org/10.1049/hve2.70131","url":null,"abstract":"The breakdown characteristics of the novel eco-friendly insulating gas CF<sub>3</sub>SO<sub>2</sub>F are fundamental to the design of gas-insulated equipment. In this paper, the gas mixture parameters for CF<sub>3</sub>SO<sub>2</sub>F were optimised for different ambient temperatures in order to ascertain the insulation performance and liquefaction temperature constraints. To further assess its insulation properties, breakdown experiments were carried out under power-frequency voltage (50 Hz), considering the influence of buffer gas types, the molar ratio of CF<sub>3</sub>SO<sub>2</sub>F and pressure. The results demonstrate that the breakdown voltage of CF<sub>3</sub>SO<sub>2</sub>F is 1.2–1.5 times that of SF<sub>6</sub>, and it increases with pressure in the range of 0.1–0.4 MPa. When compared to air and CO<sub>2</sub>, N<sub>2</sub> exhibits a superior synergistic effect with CF<sub>3</sub>SO<sub>2</sub>F. At an absolute pressure of 0.5 MPa, the 60% CF<sub>3</sub>SO<sub>2</sub>F/40% N<sub>2</sub> mixture shows similar insulation strength to SF<sub>6</sub>, but it can only be applied in environments above 10°C. Furthermore, the 12% CF<sub>3</sub>SO<sub>2</sub>F/88% N<sub>2</sub> mixture at an absolute pressure of 0.8 MPa has an insulation strength comparable to that of 0.5 MPa SF<sub>6</sub>, with a liquefaction temperature of −25°C. The results demonstrated great potential of industrial applications. At this configuration, global warming potential (GWP) of the gas mixture is only 4% that of SF<sub>6</sub>. The research provides a new solution for SF<sub>6</sub> gas substitution in gas-insulated equipment.","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"58 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2026-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146122228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mi Zhou, Xiaoyu Lei, Li Cai, Jianguo Wang, Weihan Zhao, Jinxin Cao, Denglei Duan, Maorong Geng, Yadong Fan, Jianping Wang
Data from five rocket-triggered lightning flashes are adopted to analyse the correlated transient response of buried cables and lightning channel radiations. These five flashes have the same termination point that is right above the buried cables and involve a total of 32 return strokes. Research objects here include armoured four-core cables with two layout forms: a 40-m cable arranged in an L-line (termed as L-shaped cable) and 20-m cable arranged in a straight line (termed as straight cable), each with a diameter of 1.08 cm and buried underground at a depth of 70 cm. Results show that voltage of both cables exhibits a double-peak signature, with the first pulse peaking at a higher value, 227–1023 V. The layout form has a remarkable influence on the rise time and half-peak width of cable voltages. The averaged voltage rise time for the straight cable is 2.4 μs, and the half-peak width is 2.4–5.8 μs, whereas those for the L-shaped cable are smaller, being 0.8 μs and 1.2–1.8 μs for the former and latter, respectively. Moreover, it appears that the L-shaped layout form can, to some extent, reduce the amplitude of cable voltage. Furthermore, parametric correlation analyses show that the peak voltage of buried cables is approximately directly proportional to the peak time derivative of the magnetic field documented at a distance of 75 m from the lightning channel, whereas the peak channel luminosity, also measured at a distance of 75 m from the lightning channel, is directly proportional to the square of peak cable voltage.
{"title":"Correlated Transient Response of Buried Cables and Lightning Channel Radiation of Return Strokes of Five Rocket-Triggered Lightning Strikes","authors":"Mi Zhou, Xiaoyu Lei, Li Cai, Jianguo Wang, Weihan Zhao, Jinxin Cao, Denglei Duan, Maorong Geng, Yadong Fan, Jianping Wang","doi":"10.1049/hve2.70135","DOIUrl":"https://doi.org/10.1049/hve2.70135","url":null,"abstract":"Data from five rocket-triggered lightning flashes are adopted to analyse the correlated transient response of buried cables and lightning channel radiations. These five flashes have the same termination point that is right above the buried cables and involve a total of 32 return strokes. Research objects here include armoured four-core cables with two layout forms: a 40-m cable arranged in an L-line (termed as L-shaped cable) and 20-m cable arranged in a straight line (termed as straight cable), each with a diameter of 1.08 cm and buried underground at a depth of 70 cm. Results show that voltage of both cables exhibits a double-peak signature, with the first pulse peaking at a higher value, 227–1023 V. The layout form has a remarkable influence on the rise time and half-peak width of cable voltages. The averaged voltage rise time for the straight cable is 2.4 μs, and the half-peak width is 2.4–5.8 μs, whereas those for the L-shaped cable are smaller, being 0.8 μs and 1.2–1.8 μs for the former and latter, respectively. Moreover, it appears that the L-shaped layout form can, to some extent, reduce the amplitude of cable voltage. Furthermore, parametric correlation analyses show that the peak voltage of buried cables is approximately directly proportional to the peak time derivative of the magnetic field documented at a distance of 75 m from the lightning channel, whereas the peak channel luminosity, also measured at a distance of 75 m from the lightning channel, is directly proportional to the square of peak cable voltage.","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"13 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2026-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146122230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A reduced-order model (ROM) for the temperature field based on time-space proper orthogonal decomposition (POD) is presented to improve the computational efficiency of transient temperature rise in oil-immersed power transformers with a complete oil natural convection cooling loop. This approach utilises data obtained from a full-order simulation model operating under the transformer's rated conditions as input. This paper first examines the reduction characteristics of the proper orthogonal decomposition (POD) method and subsequently introduces the time-space POD framework. The time POD method is used to select a robust snapshot set, which is subsequently integrated with space POD and Galerkin methods to establish a rapid computation model for the transient temperature field prediction of the transformer under various loading conditions. Compared to traditional finite element models, this method can generate a highly accurate computational model with a small number of snapshot samples, significantly reducing the computation time required. The presented examples demonstrate the exceptional computational accuracy and efficiency of this method. Therefore, this approach offers a workable solution for the digital twin application of transformer temperature assessment by attaining second-level computing efficiency for the entire transformer temperature field.
{"title":"An Efficient Method for Transient Temperature Calculation in Oil Natural Transformers Based on the Time-Space Proper Orthogonal Decomposition","authors":"Haijuan Lan, Wenhu Tang, Zeyi Zhang, Jiahao Gong, Xiongwen Xu, Goran Strbac","doi":"10.1049/hve2.70146","DOIUrl":"https://doi.org/10.1049/hve2.70146","url":null,"abstract":"A reduced-order model (ROM) for the temperature field based on time-space proper orthogonal decomposition (POD) is presented to improve the computational efficiency of transient temperature rise in oil-immersed power transformers with a complete oil natural convection cooling loop. This approach utilises data obtained from a full-order simulation model operating under the transformer's rated conditions as input. This paper first examines the reduction characteristics of the proper orthogonal decomposition (POD) method and subsequently introduces the time-space POD framework. The time POD method is used to select a robust snapshot set, which is subsequently integrated with space POD and Galerkin methods to establish a rapid computation model for the transient temperature field prediction of the transformer under various loading conditions. Compared to traditional finite element models, this method can generate a highly accurate computational model with a small number of snapshot samples, significantly reducing the computation time required. The presented examples demonstrate the exceptional computational accuracy and efficiency of this method. Therefore, this approach offers a workable solution for the digital twin application of transformer temperature assessment by attaining second-level computing efficiency for the entire transformer temperature field.","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"39 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2026-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146110314","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Geng Chen, Jie Wang, Chuanyang Li, Cong Wang, Youping Tu
In gas-insulated high-voltage direct current (HVDC) devices, micro partial discharges (PD) caused by micro-protrusions or surface roughness on conductors or enclosures may not cause immediate insulation system failure due to their weak discharge intensity. However, the continuous charging of carriers generated by the discharges to the insulator is one of the potential triggers of surface flashover of insulators. This work investigates the micro PD characteristics in SF6 at 0.1–0.7 MPa, which is below the lower limit of conventional detection methods, via a highly sensitive micro-discharge measurement platform. The experimental results show that the micro PD exhibits a strong polarity effect. With increasing pressure, the mean amplitude and mean repetition rates exhibited an extremum at 0.3 MPa. As the applied voltage increased, the mean amplitude shifted from negative polarity dominance over positive polarity to positive polarity dominance over negative polarity. Time-resolved PD (TRPD) and pulse sequence analysis (PSA) patterns indicate that the micro PD is characterised by clustered bursts and amplitude stratification. Furthermore, the negative polarity micro PD is more stable than the positive polarity counterpart. The results of this work can provide references to guide the optimized design of gas-insulated HVDC devices.
{"title":"Micro Partial Discharge Characteristics of SF6 Under DC Voltage","authors":"Geng Chen, Jie Wang, Chuanyang Li, Cong Wang, Youping Tu","doi":"10.1049/hve2.70132","DOIUrl":"https://doi.org/10.1049/hve2.70132","url":null,"abstract":"In gas-insulated high-voltage direct current (HVDC) devices, micro partial discharges (PD) caused by micro-protrusions or surface roughness on conductors or enclosures may not cause immediate insulation system failure due to their weak discharge intensity. However, the continuous charging of carriers generated by the discharges to the insulator is one of the potential triggers of surface flashover of insulators. This work investigates the micro PD characteristics in SF<sub>6</sub> at 0.1–0.7 MPa, which is below the lower limit of conventional detection methods, via a highly sensitive micro-discharge measurement platform. The experimental results show that the micro PD exhibits a strong polarity effect. With increasing pressure, the mean amplitude and mean repetition rates exhibited an extremum at 0.3 MPa. As the applied voltage increased, the mean amplitude shifted from negative polarity dominance over positive polarity to positive polarity dominance over negative polarity. Time-resolved PD (TRPD) and pulse sequence analysis (PSA) patterns indicate that the micro PD is characterised by clustered bursts and amplitude stratification. Furthermore, the negative polarity micro PD is more stable than the positive polarity counterpart. The results of this work can provide references to guide the optimized design of gas-insulated HVDC devices.","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"19 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2026-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146110313","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wenyu Ye, Xinhan Qiao, Wentian Zeng, Le Yu, Yinfu Chen, Ke Xu, Jianwen Zhang
Silicone rubber (SR), an organic silicon polymer material, is known for its excellent heat resistance and mechanical properties. It is widely used in composite insulators and cable accessory materials. However, the ageing caused by humidity and heat significantly impacts its performance, an issue that cannot be ignored. This paper investigates the changes in the combustion performance of SR insulation materials during wet-heat ageing, focussing on both experimental and simulation-based approaches. Through macroscopic experiments, SR samples underwent wet-heat ageing tests, and the changes in combustion phenomena, oxygen index, afterflame time, and microstructure with varying ageing degrees were studied. Molecular simulation techniques were employed to uncover the mechanism by which structural changes during wet-heat ageing affect SR's combustion performance. The results reveal that as the ageing degree increases, the colour of the SR sample remains largely unchanged, but the surface shows an increasing number of wrinkles, holes, and traces of filler precipitation. The combustion characteristics of SR exhibit a noticeable upward trend as the ageing degree deepens. Using the ReaxFF force field, five distinct structural changes during wet-heat ageing were identified and categorised from ageing degree 0 to ageing degree 5. As the ageing degree increases, the spatial ductility and thermal stability of SR change significantly, which in turn alters the intermolecular forces within the material. These structural changes lead to improved combustion performance of SR. This paper provides theoretical guidance for understanding the evolution of SR's performance during ageing and its implications for future research and material development.
{"title":"Combustion Performance of Silicone Rubber Polymer Insulation Material Under Damp-Heat Ageing Conditions: Molecular Insights Into the Effects of Structural Changes on Macroscopic Properties","authors":"Wenyu Ye, Xinhan Qiao, Wentian Zeng, Le Yu, Yinfu Chen, Ke Xu, Jianwen Zhang","doi":"10.1049/hve2.70165","DOIUrl":"https://doi.org/10.1049/hve2.70165","url":null,"abstract":"Silicone rubber (SR), an organic silicon polymer material, is known for its excellent heat resistance and mechanical properties. It is widely used in composite insulators and cable accessory materials. However, the ageing caused by humidity and heat significantly impacts its performance, an issue that cannot be ignored. This paper investigates the changes in the combustion performance of SR insulation materials during wet-heat ageing, focussing on both experimental and simulation-based approaches. Through macroscopic experiments, SR samples underwent wet-heat ageing tests, and the changes in combustion phenomena, oxygen index, afterflame time, and microstructure with varying ageing degrees were studied. Molecular simulation techniques were employed to uncover the mechanism by which structural changes during wet-heat ageing affect SR's combustion performance. The results reveal that as the ageing degree increases, the colour of the SR sample remains largely unchanged, but the surface shows an increasing number of wrinkles, holes, and traces of filler precipitation. The combustion characteristics of SR exhibit a noticeable upward trend as the ageing degree deepens. Using the ReaxFF force field, five distinct structural changes during wet-heat ageing were identified and categorised from ageing degree 0 to ageing degree 5. As the ageing degree increases, the spatial ductility and thermal stability of SR change significantly, which in turn alters the intermolecular forces within the material. These structural changes lead to improved combustion performance of SR. This paper provides theoretical guidance for understanding the evolution of SR's performance during ageing and its implications for future research and material development.","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"55 3 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2026-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146122229","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents a simplified equivalent circuit model (ECM) for the post-arc sheath stage in DC vacuum circuit breakers and outlines the method for calculating circuit parameters using the particle-in-cell Monte Carlo collision (PIC-MCC) method. The post-arc sheath is modelled as a parallel combination of a variable resistor and a variable capacitor. Based on a specific DC experimental case, the PIC-MCC simulation provides essential parameters of charged particles and electric field data for calculating equivalent resistance and capacitance. The total current through the circuit components is calculated by applying the transient recovery voltage (TRV), and the resulting post-arc current (PAC) waveform is compared with experimental results to validate the simplified ECM and the proposed parameter calculation approach. Further simulations study the impact of the initial drift velocity of charged particles on equivalent circuit parameters and PAC traces, showing that higher drift velocities increase capacitance and decrease resistance, leading to higher PAC peaks. The comparison with experimental data indicates that considering the drift velocity contributes to the simulation accuracy.
{"title":"Investigation of the Simplified Equivalent Circuit Model of the Post-Arc Sheath Stage in DC Vacuum Circuit Breakers","authors":"Xubin Li, Xingyu Guo, Wen Wang, Xiaoming Liu, Minfu Liao, Jiyan Zou","doi":"10.1049/hve2.70144","DOIUrl":"https://doi.org/10.1049/hve2.70144","url":null,"abstract":"This paper presents a simplified equivalent circuit model (ECM) for the post-arc sheath stage in DC vacuum circuit breakers and outlines the method for calculating circuit parameters using the particle-in-cell Monte Carlo collision (PIC-MCC) method. The post-arc sheath is modelled as a parallel combination of a variable resistor and a variable capacitor. Based on a specific DC experimental case, the PIC-MCC simulation provides essential parameters of charged particles and electric field data for calculating equivalent resistance and capacitance. The total current through the circuit components is calculated by applying the transient recovery voltage (TRV), and the resulting post-arc current (PAC) waveform is compared with experimental results to validate the simplified ECM and the proposed parameter calculation approach. Further simulations study the impact of the initial drift velocity of charged particles on equivalent circuit parameters and PAC traces, showing that higher drift velocities increase capacitance and decrease resistance, leading to higher PAC peaks. The comparison with experimental data indicates that considering the drift velocity contributes to the simulation accuracy.","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"8 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The internal pressure fluctuations caused by vibration in oil-immersed electrical equipment can initiate bubbles within narrow oil gaps, reducing the electrical strength of equipment and giving rise to the problem of abnormal gas production in oil-immersed equipment. This study mainly investigates the dynamic characteristics of cavitation in insulating oil microgaps under varying vibration conditions. A microgap model with vibration is constructed based on fluid mechanics, the fluid pressure within the microgap is derived, and the maximum negative pressures caused by vibration under varying vibration conditions and geometric structures of the insulating oil microgap are analysed. Subsequently, combined with the theories of bubble dynamics, the dynamic processes of the bubble within the microgap during a single vibration cycle under varying vibration conditions are analysed, and the influence of vibration intensity and frequency on the dynamic characteristics of the bubble is also discussed. Finally, the bubbling phenomenon and cavitation processes within the microgap under varying vibration conditions are observed and analysed using an experimental platform of microgap vibration. A better understanding of the development process of cavitation within the microgap structure under vibration is achieved. Furthermore, this study also provides theoretical support for the insulation risk assessment of the microgap structure under vibration and the design optimisation of the internal structure of oil-immersed electrical equipment.
{"title":"Investigating Dynamic Characteristics of Cavitation in Insulating Oil Microgaps Under Vibration: Theoretical Analysis and Experimental Observation","authors":"Jiajun Yang, Tao Zhao, Yunpeng Liu","doi":"10.1049/hve2.70147","DOIUrl":"https://doi.org/10.1049/hve2.70147","url":null,"abstract":"The internal pressure fluctuations caused by vibration in oil-immersed electrical equipment can initiate bubbles within narrow oil gaps, reducing the electrical strength of equipment and giving rise to the problem of abnormal gas production in oil-immersed equipment. This study mainly investigates the dynamic characteristics of cavitation in insulating oil microgaps under varying vibration conditions. A microgap model with vibration is constructed based on fluid mechanics, the fluid pressure within the microgap is derived, and the maximum negative pressures caused by vibration under varying vibration conditions and geometric structures of the insulating oil microgap are analysed. Subsequently, combined with the theories of bubble dynamics, the dynamic processes of the bubble within the microgap during a single vibration cycle under varying vibration conditions are analysed, and the influence of vibration intensity and frequency on the dynamic characteristics of the bubble is also discussed. Finally, the bubbling phenomenon and cavitation processes within the microgap under varying vibration conditions are observed and analysed using an experimental platform of microgap vibration. A better understanding of the development process of cavitation within the microgap structure under vibration is achieved. Furthermore, this study also provides theoretical support for the insulation risk assessment of the microgap structure under vibration and the design optimisation of the internal structure of oil-immersed electrical equipment.","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"158 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146110907","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhenfu Tang, Yihua Qian, Dan Zhou, Wei Hu, Feipeng Wang, Yang Xu
With increasing demands for fire safety and environmental friendliness, retrofilling transformers with alternative insulating liquids has become a growing trend. However, retrofilling power transformers remains uncertain, as more residual mineral oil compromises K-class flame retardancy, and its impact on environmental performance has yet to be clarified. Meanwhile, there is a lack of evaluation methodology and retrofilling procedure for power transformers. This paper presents a synthetic ester retrofilling conducted on a 20 MVA/110 kV transformer. Kerosene vapour-phase drying was implemented to supplement traditional oil draining, and the insulating liquid achieved a fire point of 304°C, meeting K-class flame retardancy after retrofilling. The estimated residual mineral oil content was less than 0.8 wt%, significantly lower than the typically reported value (e.g., 3 wt%–5 wt%). Standardised testing confirmed that the synthetic ester containing 3.5% mineral oil maintained its environmental performance, achieving 82.6% biodegradability. Additionally, the evaluation methodology and recommended procedure for retrofilling power transformers are proposed in this study. The performance changes of the retrofilled transformer were discussed in detail. A significant decrease in lightning impulse insulation margin and insulation resistance was observed, which should be given particular attention.
{"title":"Evaluation Methodology, Numerical Verification and Retrofilling Procedure for Power Transformers to Ensure K-Class Flame Retardancy and Environmentally Friendly","authors":"Zhenfu Tang, Yihua Qian, Dan Zhou, Wei Hu, Feipeng Wang, Yang Xu","doi":"10.1049/hve2.70127","DOIUrl":"https://doi.org/10.1049/hve2.70127","url":null,"abstract":"With increasing demands for fire safety and environmental friendliness, retrofilling transformers with alternative insulating liquids has become a growing trend. However, retrofilling power transformers remains uncertain, as more residual mineral oil compromises K-class flame retardancy, and its impact on environmental performance has yet to be clarified. Meanwhile, there is a lack of evaluation methodology and retrofilling procedure for power transformers. This paper presents a synthetic ester retrofilling conducted on a 20 MVA/110 kV transformer. Kerosene vapour-phase drying was implemented to supplement traditional oil draining, and the insulating liquid achieved a fire point of 304°C, meeting K-class flame retardancy after retrofilling. The estimated residual mineral oil content was less than 0.8 wt%, significantly lower than the typically reported value (e.g., 3 wt%–5 wt%). Standardised testing confirmed that the synthetic ester containing 3.5% mineral oil maintained its environmental performance, achieving 82.6% biodegradability. Additionally, the evaluation methodology and recommended procedure for retrofilling power transformers are proposed in this study. The performance changes of the retrofilled transformer were discussed in detail. A significant decrease in lightning impulse insulation margin and insulation resistance was observed, which should be given particular attention.","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"143 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146070201","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Thi Thu Nga Vu, Gilbert Teyssèdre, Séverine Le Roy
The worldwide increasing demand for electricity, coupled with the need for more reliable infrastructures and more interconnected networks, has put forward high voltage direct current (HVDC) technologies for energy transmissions. Questions still arise as regards synthetic insulation for cable systems and accessories, as it remains one of the weak points in energy transmission lines. The field distribution in such systems intimately depends upon the electrical conductivity, being temperature and field dependent, and upon the cable/accessory geometry, that is its design. Optimising the design equates to homogenising as much as possible the electric field, particularly the tangential field at the interface between dielectrics, and avoiding field hot spots. Different designs for cable accessory are conceivable that do not necessarily involve the interposition of a field grading layer between the cable insulation and the joint body. In this work, we explore different evolutions of the design, spanning from geometry refinement to setting a two-layers joint body. The idea of keeping the same polymer and using fillers to impart nonlinearity to the conductivity is put forward. Results show that significant reduction of field maxima can be reached with this design. The so-constructed fictive material appears feasible considering literature data. Whether full objects can be produced is an open question.
{"title":"Simulation-Based Material Design for HVDC Cable Accessories","authors":"Thi Thu Nga Vu, Gilbert Teyssèdre, Séverine Le Roy","doi":"10.1049/hve2.70155","DOIUrl":"https://doi.org/10.1049/hve2.70155","url":null,"abstract":"The worldwide increasing demand for electricity, coupled with the need for more reliable infrastructures and more interconnected networks, has put forward high voltage direct current (HVDC) technologies for energy transmissions. Questions still arise as regards synthetic insulation for cable systems and accessories, as it remains one of the weak points in energy transmission lines. The field distribution in such systems intimately depends upon the electrical conductivity, being temperature and field dependent, and upon the cable/accessory geometry, that is its design. Optimising the design equates to homogenising as much as possible the electric field, particularly the tangential field at the interface between dielectrics, and avoiding field hot spots. Different designs for cable accessory are conceivable that do not necessarily involve the interposition of a field grading layer between the cable insulation and the joint body. In this work, we explore different evolutions of the design, spanning from geometry refinement to setting a two-layers joint body. The idea of keeping the same polymer and using fillers to impart nonlinearity to the conductivity is put forward. Results show that significant reduction of field maxima can be reached with this design. The so-constructed fictive material appears feasible considering literature data. Whether full objects can be produced is an open question.","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"280 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sihan Wang, Jihang Sun, Jialin Wang, Bin Wei, Guoming Ma
The detection of partial discharges (PD) on the power transformer tank demands higher sensitivity in ultrasonic detection. To target the detection frequency band for sensor optimisation and enhance sensitivity, this paper presents a dual-frequency sensitivity model for optical fibre ultrasonic sensors. Based on coupling resonance principles, the model accounts for the interaction between longitudinal and radial vibrations, yielding two resonant frequencies instead of the single one in conventional models. Through theoretical calculations, the impact of the mandrel’s material and dimensions on the sensor’s sensitivity is analysed, and the sensor structure is optimised accordingly. Experimental validation via a Michelson interferometer reveals that when the aluminium mandrel’s radius and height are 20 mm each, the sensor’s bandwidth can reach 80–200 kHz, aligning well with the typical PD ultrasonic frequency band in power transformers. The experimental results are consistent with the simulation analysis, confirming the validity and accuracy of the proposed model. This advancement not only improves detection sensitivity but also provides a theoretical foundation for designing PD ultrasonic fibre sensors tailored to power apparatus.
{"title":"A Dual-Frequency Sensitivity Model for Optical Fibre Ultrasonic Sensors in Power Transformer Partial Discharge Detection","authors":"Sihan Wang, Jihang Sun, Jialin Wang, Bin Wei, Guoming Ma","doi":"10.1049/hve2.70124","DOIUrl":"https://doi.org/10.1049/hve2.70124","url":null,"abstract":"The detection of partial discharges (PD) on the power transformer tank demands higher sensitivity in ultrasonic detection. To target the detection frequency band for sensor optimisation and enhance sensitivity, this paper presents a dual-frequency sensitivity model for optical fibre ultrasonic sensors. Based on coupling resonance principles, the model accounts for the interaction between longitudinal and radial vibrations, yielding two resonant frequencies instead of the single one in conventional models. Through theoretical calculations, the impact of the mandrel’s material and dimensions on the sensor’s sensitivity is analysed, and the sensor structure is optimised accordingly. Experimental validation via a Michelson interferometer reveals that when the aluminium mandrel’s radius and height are 20 mm each, the sensor’s bandwidth can reach 80–200 kHz, aligning well with the typical PD ultrasonic frequency band in power transformers. The experimental results are consistent with the simulation analysis, confirming the validity and accuracy of the proposed model. This advancement not only improves detection sensitivity but also provides a theoretical foundation for designing PD ultrasonic fibre sensors tailored to power apparatus.","PeriodicalId":48649,"journal":{"name":"High Voltage","volume":"58 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146072622","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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