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15 pages, 5674 KiB

Open AccessArticle

Study on the Ageing Characteristics of Silicone Rubber for Composite Insulators under Multi-Factor Coupling Effects

by Xinran Li, Yuming Zhang, Lincong Chen, Xiaotao Fu, Jianghai Geng, Yunpeng Liu, Yijing Gong and Simin Zhang

Coatings 2023, 13(10), 1668; https://doi.org/10.3390/coatings13101668 - 23 Sep 2023

Cited by 6 | Viewed by 2036

Abstract

Due to long-term exposure to high electrical field strength, heavy loads, and the complex climatic conditions in tropical coastal areas of China, widespread abnormal heating phenomena often occur in the operation of composite insulators in power transmission lines, posing a threat to the [...] Read more.

Due to long-term exposure to high electrical field strength, heavy loads, and the complex climatic conditions in tropical coastal areas of China, widespread abnormal heating phenomena often occur in the operation of composite insulators in power transmission lines, posing a threat to the safe and stable operation of the power system. To study the ageing process of the silicone rubber sheath of composite insulators in the high-field, high-humidity, high-temperature, and high-salt-density environments along the coastal regions, this paper establishes a humidity–heat–electricity–salt spray accelerated ageing test platform and conducts ageing tests on silicone rubber materials for composite insulators under the coupled effect of multiple factors. The ageing characteristics of silicone rubber materials are analyzed using scanning electron microscopy, Fourier infrared spectroscopy, thermogravimetric analysis, and other methods. The results show that the coupled ageing factors have an impact on the surface morphology of silicone rubber. The continuous depolymerization of PDMS molecular chains leads to a decrease in the content of groups related to the hydrophobicity of the material, resulting in a deterioration of its hydrophobicity. Moreover, the degradation of silicone rubber materials and the enhanced moisture absorption capacity lead to an increase in the dielectric loss tangent of the saturated moisture-absorbing medium, thereby causing abnormal heating of the sheath at the end of the composite insulator. The research findings of this study are of significant reference value for revealing the degradation mechanism of composite insulator silicone rubber sheaths in tropical island environments and improving the service life of composite insulators. Full article

(This article belongs to the Special Issue Advances in Dielectric Coatings)

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13 pages, 6132 KiB

Open AccessArticle

The Leakage Current Characteristics of High-Gradient MOA Plate and Its Heating Analysis with Coatings under High-Frequency Overvoltage

by Jixing Sun, Yongzhi Fan, Kun Zhang, Jiyong Liu, Xin Wang and Shengchun Yan

Coatings 2023, 13(3), 497; https://doi.org/10.3390/coatings13030497 - 24 Feb 2023

Cited by 1 | Viewed by 1397

Abstract

High-frequency overvoltage generated in railways results in explosions of Electric Multiple Units’ (EMUs) arrestors. To solve this problem, the leakage current characteristics and heat transfer process of high-gradient MOA plates under high-frequency overvoltage has been studied. The leakage current characteristics of arrestor plates [...] Read more.

High-frequency overvoltage generated in railways results in explosions of Electric Multiple Units’ (EMUs) arrestors. To solve this problem, the leakage current characteristics and heat transfer process of high-gradient MOA plates under high-frequency overvoltage has been studied. The leakage current characteristics of arrestor plates under high-frequency voltage was obtained and the element distribution has been analyzed. Heat transfer distribution and the thermal properties of the Metal Oxide Arrestor (MOA) have been modelled. According to the results, for a given voltage, the higher the harmonic frequency, the greater the leakage current of the arrestor valve plate, and the greater the resistive component of the leakage current. The Zn and O elements in high-gradient MOA plates are more uniform. Under the same leakage current as conventional ones, the undertake voltage of a high-gradient MOA plate will increase by 10%. Longtime high-order harmonic action will still significantly improve the core rod temperature when MOA plates are coated. The temperature rise in the power supply section of EMUs during operation is roughly 35 °C. This result will provide a foundation and supporting data for the applicability of high-gradient valve plates in railroads and coating improvements for traditional arrestor plates. Full article

(This article belongs to the Special Issue Advances in Dielectric Coatings)

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14 pages, 3590 KiB

Open AccessArticle

Evolution of Elements on Electrode Surfaces in Gas-Insulated Systems under Electrical Heating

by Jixing Sun, Kun Zhang, Kaixuan Hu, Jiyong Liu, Yu Tian, Xin Wang and Shengchun Yan

Coatings 2023, 13(1), 33; https://doi.org/10.3390/coatings13010033 - 25 Dec 2022

Cited by 1 | Viewed by 1640

Abstract

Accidents always occur in gas-insulated switchgears (GIS) and gas-insulated lines (GIL) since filmed joint electrodes are produced when internal gases react with the electrode’s surface when there is a discharge or when internal electricals overheat. To solve the problem, this paper analyzed the [...] Read more.

Accidents always occur in gas-insulated switchgears (GIS) and gas-insulated lines (GIL) since filmed joint electrodes are produced when internal gases react with the electrode’s surface when there is a discharge or when internal electricals overheat. To solve the problem, this paper analyzed the evolution of elements on the contact electrode. The reaction of the SF6 and electrode’s surface under breakdown currents and overheating conditions was obtained, and the discharge time and discharge current effects upon the transfer of the element were proposed. It was found that the mobility of the F element on the electrode’s surface typically increases after electrical heating. The number of interruptions and short-circuit currents are important factors affecting the transfer of the F element to the electrode. The flashover current is the essential factor that accelerates the transfer of the F element to insulating materials. Frequent switching is a main factor that accelerates the transfer of the F element to the contact. It was also found that Al has little correlations with the breaking process, and metal fluorides become the main components on the electrode’s surface under discharge heating. The research provides a theoretical basis and data support for GIS/GIL surface optimization treatments and the improvement of fault detection methods. Full article

(This article belongs to the Special Issue Advances in Dielectric Coatings)

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21 pages, 17891 KiB

Open AccessArticle

Measurement and Interpretation of the Effect of Electrical Sliding Speed on Contact Characteristics of On-Load Tap Changers

by Xingzu Yang, Shuaibing Li, Yi Cui, Yongqiang Kang, Zongying Li, Hongwei Li and Haiying Dong

Coatings 2022, 12(10), 1436; https://doi.org/10.3390/coatings12101436 - 29 Sep 2022

Cited by 6 | Viewed by 1852

Abstract

This paper analyzes the effect of sliding speed on the electrical conductivity and friction properties of the contact pair of an on-load tap changer (OLTC). Reciprocating current-carrying tribological tests were carried out on a rod–plate–copper–tin–copper contact galvanic couple at different sliding speeds in [...] Read more.

This paper analyzes the effect of sliding speed on the electrical conductivity and friction properties of the contact pair of an on-load tap changer (OLTC). Reciprocating current-carrying tribological tests were carried out on a rod–plate–copper–tin–copper contact galvanic couple at different sliding speeds in air and insulating oil media. The results show that as the sliding speed increases from 24 mm/s to 119 mm/s, the average contact resistance in air increases from 0.2 Ω to 0.276 Ω, and the average contact resistance in insulating oil also increases from 0.2 Ω to 0.267 Ω. At 119 mm/s, the maximum contact resistance in insulating oil reaches 0.3 Ω. The micro-topography images obtained by scanning electron microscopy show that with the increase in sliding speed, the wear mechanisms in the air are mainly abrasive wear and adhesive wear, and the wear mechanisms in oil are mainly layered wear and erosion craters; high sliding speed and arcing promote contact surface fatigue and crack generation. X-ray photoelectron spectroscopy was used to analyze the surface. The copper oxide in the air and the cuprous sulfide in the insulating oil cause the surface film resistance, and the total contact resistance increases accordingly. In addition, the test shows that 119 mm/s in air and 95 mm/s in insulating oil are the speed thresholds. Below these speed thresholds, the increase in contact resistance is mainly caused by mechanical wear. Above these thresholds, the increase in contact resistance is mainly caused by arc erosion and chemical oxidation processes. Non-mechanical factors exacerbate the deterioration of the contact surface and become the main factor for the increase in contact resistance. Full article

(This article belongs to the Special Issue Advances in Dielectric Coatings)

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24 pages, 3327 KiB

Open AccessArticle

A Novel Mutual-Coupling Dipole Model Considering the Interactions between Particles

by Yongqiang Kang, Jialin Zhang, Zhipeng Shi, Xuhong Pu, Shuaibing Li and Hongwei Li

Coatings 2022, 12(8), 1079; https://doi.org/10.3390/coatings12081079 - 30 Jul 2022

Cited by 4 | Viewed by 1352

Abstract

The interactions between two or more particles and the calculation of the local electric field are widely applied in many fields, such as those of insulation, biology, medicine, and microfluidics. The dipole approximation model, which is a classical electric field calculation method, has [...] Read more.

The interactions between two or more particles and the calculation of the local electric field are widely applied in many fields, such as those of insulation, biology, medicine, and microfluidics. The dipole approximation model, which is a classical electric field calculation method, has been widely used in many fields to solve for the local electric field in a multi-particle system, but it does not consider the interactions between particles; as a result, it is easily limited by the calculation situation, and it generates a large calculation error when the distance between particles is small. Based on the physical essence of an interaction between two particles, a concept of the mutual-coupling dipole moment caused by the interactions between particles is defined for the first time. Moreover, by combining the calculation process of the dipole moment and the electric field of polarization, a novel mutual-coupling dipole model considering the interactions between particles is proposed in this paper, and analytical expressions of the local electric field that consider the interaction between two particles are obtained, thus compensating for the large error in the electric field calculation caused by the dipole approximation model when the distance between particles is small. In this paper, a mutual-coupling dipole model considering particle interactions is proposed. This model can effectively reflect the interactions between particles when the distance between particles D/R is less than 0.6 and accurately calculate the local electric fields of the particles. These results can be effectively used to investigate the interactions between particles and the control of particles in electric fields in many fields, such as in the calculation of the insulation of mixed dielectrics, the microscopic transport of medicines, the control of bio-cells and micro-fluids in electric fields, and environmental governance. Full article

(This article belongs to the Special Issue Advances in Dielectric Coatings)

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14 pages, 5238 KiB

Open AccessArticle

Effect of Particle Trap on Motion Characteristics of Metal Particles in AC GILs and Parameter Optimization

by Shenghui Wang, Huaqi Liu, Kang Ma, Qi Ou, Hui Geng and Fangcheng Lv

Coatings 2022, 12(7), 981; https://doi.org/10.3390/coatings12070981 - 11 Jul 2022

Cited by 4 | Viewed by 1514

Abstract

Metal particle contamination is an important reason for insulation failure of gas-insulated transmission lines (GILs). Particle trap is the common method for particle suppression. At present, research on the motion characteristics of metal particles near a particle trap and the optimization of trap [...] Read more.

Metal particle contamination is an important reason for insulation failure of gas-insulated transmission lines (GILs). Particle trap is the common method for particle suppression. At present, research on the motion characteristics of metal particles near a particle trap and the optimization of trap parameters under AC voltage is insufficient. Based on that, firstly, a dynamic model of metal particles under AC voltage was established, and the motion characteristics of particles in front of the trap were studied, combined with experiments. Then, the influence of trap parameters on the capture effect was analyzed, and the optimization of the trap was realized by simulation. The results showed that, under AC voltage, the randomness of metal particle movement was strong, and the activity was low. The particles mainly moved away from the trap. Among the particles moving towards the trap, some stayed in front of the trap, and some fell into the trap from above. The thickness and height of the trap were the key parameters affecting the capture effect, and with the increase in height and thickness, the capture rate showed a trend of increasing first and then decreasing. The above conclusions can provide a reference for the optimization of a metal particle trap under AC voltage in engineering. Full article

(This article belongs to the Special Issue Advances in Dielectric Coatings)

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12 pages, 2342 KiB

Open AccessArticle

A Study on the Influence of End-Sheath Aging and Moisture Absorption on Abnormal Heating of Composite Insulators

by Xinran Li, Simin Zhang, Lincong Chen, Xiaotao Fu, Jianghai Geng, Yunpeng Liu, Qilin Huang and Zheng Zhong

Coatings 2022, 12(7), 898; https://doi.org/10.3390/coatings12070898 - 24 Jun 2022

Cited by 6 | Viewed by 1562

Abstract

Abnormal heating of composite insulators of high-voltage transmission lines concentrate at its end, especially in a high-humidity environment. In order to study the influence of end-sheath aging and moisture absorption on abnormal heating of composite insulators, in this paper, we first discuss the [...] Read more.

Abnormal heating of composite insulators of high-voltage transmission lines concentrate at its end, especially in a high-humidity environment. In order to study the influence of end-sheath aging and moisture absorption on abnormal heating of composite insulators, in this paper, we first discuss the appearance test, temperature rise test, and dielectric characteristic test conducted on 110 kV decommissioned composite insulators. Test results indicated the temperature rise in composite insulators increased with ambient humidity, but temperature rise was not severely affected by surface contamination of its shed and sheath; in dry environments, the dielectric constant and dielectric loss factor of high-voltage end sheaths are higher than of those of medium- and low-voltage end sheaths, and the loss effect becomes more severe after moisture absorption in a high-humidity environment. After the tests, the authors established a COMSOL simulation model of composite insulators, to analyze changes in the electric field and thermal field of the end sheath of composite insulators due to the coupling of electric and thermal fields. It was concluded that the dielectric constant of a high-voltage end sheath of the composite insulator increased after moisture absorption, distorting the partial electric field on the surface; meanwhile, the dielectric loss factor increased significantly after water molecules intruded into the aging layer of the sheath as polar molecules. Therefore, the dielectric loss (leakage conductance loss and lossy polarization loss) caused by aging and moisture absorption of the sheath surface under partially high field strength in the high-humidity environment was the leading cause of abnormal heating at the high-voltage end of composite insulators. The conclusion of this paper serves as an important reference for revealing the causes of abnormal heating of composite insulators in high-humidity environments and the influence mechanism of external factors on abnormal heating. Full article

(This article belongs to the Special Issue Advances in Dielectric Coatings)

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Review

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37 pages, 4979 KiB

Open AccessReview

Progress on Current-Carry Friction and Wear: An Overview from Measurements to Mechanism

by Shuaibing Li, Xingzu Yang, Yongqiang Kang, Zongying Li and Hongwei Li

Coatings 2022, 12(9), 1345; https://doi.org/10.3390/coatings12091345 - 15 Sep 2022

Cited by 26 | Viewed by 4197

Abstract

As aerospace, electrified railway, weapon equipment manufacturing, and other fields have leapt forward, the operating environment of current-carrying friction pairs is becoming increasingly severe, and research on the current-carrying friction and wear theory and its vital technologies are progressively in demand. This study [...] Read more.

As aerospace, electrified railway, weapon equipment manufacturing, and other fields have leapt forward, the operating environment of current-carrying friction pairs is becoming increasingly severe, and research on the current-carrying friction and wear theory and its vital technologies are progressively in demand. This study summarizes the relevant research on the current-carrying friction and wear. In this study, the essential characteristics and classification of current-carrying friction and wear are summarized, the effect of working parameters on current-carrying friction and wear performance is clarified, and the generation mechanism, failure mechanism, and factors of current-carrying friction and wear are emphatically investigated. Moreover, the mechanism of arc generation and the effect of environmental conditions and surface facial masks on the friction and wear process are summarized. This paper also introduces the preparation technology of a conductive wear-resistant self-lubricating material, the main factors affecting the conductive wear-resistant property of the coating, and the action mechanism. The simulation and prediction results of the current-carrying friction and wear temperature field and the wear amount are presented. Finally, the problems in the current-carrying friction and wear research are classified, and future research directions in this field are proposed. The future’s critical development and improvement directions are also proposed from the aspects of developing coating quality evaluation equipment, optimizing the coating quality, and studying the coating self-lubricating mechanisms. Full article

(This article belongs to the Special Issue Advances in Dielectric Coatings)

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