Search Results (44)

Zinc oxide (ZnO) varistors are a core component of surge arresters; their failure can directly affect the secure and reliable operation of power equipment. Therefore, this paper conducts an impulse degradation test on ZnO varistors, combining electrical and microstructural tests to systematically explore the intrinsic correlation mechanism between the electrical properties and microstructural characteristics. Test results show that this type of ZnO varistor is susceptible to side-glaze surface flashover under an impulse current with a waveform of 8/20 μs and an amplitude of 27 kA, and the discharge branches exhibit an extension from the negative electrode towards the positive electrode. Moreover, surface flashover causes the formation of local conductive channels in the side glaze layer, resulting in a significant drop in the direct-current (DC) reference voltage U_1mA. However, the residual voltage U_10kA increases slightly with an increase in the number of impulse groups, with a change in amplitude of less than 1.5%. Additionally, the microstructural testing reveals that the impulse currents cause the bismuth (Bi) element in ZnO grains to precipitate and form more Bi-rich phases at the grain boundaries. This results in an increase in the thickness of the grain boundary layer, which is negatively correlated with the U_1mA. Meanwhile, the grain morphology and size distribution of brand-new samples, samples with different degrees of degradation, and samples with side-glaze surface flashover damage are not significantly different. This is consistent with the fact that the change range of the residual voltage U_10kA during impulse degradation is very small. This test phenomenon indicates that the failure of this type of ZnO varistor to withstand an impulse current with a waveform of 8/20 μs and an amplitude of 27 kA is mainly due to changes in the volt-ampere properties of the small-current regions caused by ion migration within the grain boundary layer. This research provides an experimental basis and theoretical support for improving the impulse withstand capacity of ZnO varistors in their design. Full article

Direct current (DC) surface flashover on polystyrene (PS) remains a critical bottleneck that impedes its reliable application in high-voltage insulation apparatus. To circumvent the protracted processing durations and stringent film-forming conditions inherent in conventional surface modification techniques, this study proposes a novel “liquid-film-assisted in situ rapid plasma curing” strategy. By harnessing atmospheric-pressure dielectric barrier discharge (DBD) technology within an argon ambient, the rapid (<6 min) and efficient deposition of a fluorosilane (FAS-13) functional coating onto the substrate was achieved. Microscopic characterizations coupled with isothermal surface potential decay (SPD) measurements reveal that this coating substantially mitigates the detrapping and surface migration of charge carriers. Macroscopic DC flashover testing corroborates that, under the optimal modification ratio, the surface breakdown voltage of PS is elevated to 14.04 kV, yielding an insulation gain of 26.94%. To elucidate the underlying physical mechanisms, density functional theory (DFT) calculations were conducted, revealing that the energy band misalignment between the wide-bandgap fluorinated layer and the substrate facilitates the construction of a high-density deep trap network (with a depth of ~0.8 eV) at the coating–substrate interface. By robustly anchoring primary electrons and inducing the formation of a homopolar space charge shielding layer, these deep traps physically arrest the evolution of the secondary electron emission avalanche (SEEA). Consequently, this work not only establishes a viable engineering framework for the rapid, large-scale surface reinforcement of DC insulation equipment but also provides profound quantum chemical insights into interfacial trap regulation within all-organic dielectrics. Full article

This paper systematically investigates the failure characteristics and mechanisms of insulating materials in DC voltage dividers under combined high-frequency voltage and high-temperature conditions via simulations and experiments. The results showed that high-frequency harmonics severely degrade the insulation strength of polypropylene/paper/polypropylene (PPLP) at 10 kHz, in which the bulk breakdown strength of PPLP decreases by over 50%. Furthermore, the surface flashover voltage in oil is reduced by 17.7% under high-frequency voltage alone, and by as much as 51% when white flocculent substances are present in the oil. The dielectric properties of PPLP strongly depend on frequency and temperature, which aggravate the heat accumulation of the divider under high-frequency voltage. Furthermore, the multilayer structure of PPLP introduces deeper trap levels due to interfacial states, which reduce the breakdown strength and flashover voltage of PPLP. Electro-thermal coupling induces a rapid temperature rising to 98 °C at 25 kHz caused by dielectric loss, leading to oil turbidity and white precipitation, consistent with finite element simulations. Consequently, a failure mechanism is proposed as follows: prolonged electro-thermal stress causes chain scission in styrene-containing materials, releasing monomers that repolymerize into white polystyrene deposits. Their porous structure and dielectric mismatch distort the interfacial field, trigger partial discharge, and aggravate surface flashover. Full article

Pollution flashover accidents of transmission line insulators have a wide impact and low reclosing success rates, posing a serious threat to the safe and stable operation of the power grid. The existing pollution discharge and flashover models of insulator based on equivalent salt deposit density (ESDD) present significant differences from the actual situation. To address this issue, the conductivity of electrolyte solutions experiments is carried out in this paper, and the quantitative functional relationship between conductivity and concentration of typical components is obtained. On this basis, the concept of effective salt deposit density (SDD_e) is introduced to characterize the actual mass of pollution participating in surface conduction per unit area. A DC discharge dynamic model for polluted insulators is established and verified based on SDD_e combined with the discharge development process. Research results indicate that the average difference between the calculated flashover voltage and experimental value is less than 7%. The deviation of flashover voltage between the SDD_e basis model and measured salt deposit density (SDD_m) basis value increases with the increasing proportion of slightly soluble components. With the increase of insulator surface water adhesion, the flashover voltage obtained by the proposed model decreases while the corresponding SDD_m basis value remains constant. The effects of factors such as slightly soluble pollution and surface water adhesion are considered in the proposed model sufficiently. The application of the model based on SDD_e can improve the accuracy of the insulator discharge process and flashover voltage prediction, especially for the complex pollution area. During the generation and propagation of the arc, the leakage current under SDD_m is relatively higher and the pollution layer resistance is lower compared to that under SDD_e; the variations in the pollution layer resistance and leakage current with arc development under SDD_m do not adequately reflect the actual conditions. Full article

High voltage direct current (HVDC) gas-insulated equipment (GIE) has become a critical component in long-distance power transmission projects, owing to its advantages such as compact structure and high reliability. However, the gas–solid interface insulation of DC GIE under long-term operation faces charge accumulation phenomenon, which will distort the electric field distribution and cause insulation flashover. Due to the lack of technical guidelines for the insulation design of DC gas-insulated equipment, the method of insulation design usually adopts increasing the insulation structure size to ensure sufficient creepage along the surface, which greatly increases the dimensions and manufacturing costs of the final equipment, and fails to fully leverage the unique advantages of GIE in compactness and lightness. Therefore, it is of importance to clarify the mechanism of charge accumulation on the surface of insulators under HVDC, and to propose an insulation design method that can effectively inhibit the charge accumulation and adjust the electric field distribution at the gas–solid interface, which holds practical significance for the safe application of large-scale DC GIE projects. In view of this, this paper firstly summarizes the characteristics of surface charge accumulation at gas–solid interface, and then reviews the existing research progress from two perspectives: surface charge suppression of insulation structure and gas–solid interface electric field regulation, providing theoretical and technical support for optimizing the design of GIE insulation structure, formulating scientific operation and maintenance measures. Full article

This study primarily simulates the flashover phenomenon between the metal fittings (rods) and the skirt surface (plates) of insulators when water droplets traverse between them under heavy rain conditions. High-speed cameras recorded droplet deformation and breakdown processes, while electric field simulation software modeled the air gap’s electric field distribution. The effects of air gap length, axial position of the water droplet, droplet conductivity, droplet diameter, and voltage polarity on the DC breakdown voltage were analyzed. Results indicate that a larger air gap leads to a greater reduction in droplet breakdown voltage and lower electric field uniformity. The breakdown voltage is essentially independent of changes in the axial position of the droplet and the droplet’s conductivity. The breakdown voltage exhibits no significant correlation with droplet diameter. Droplets rarely break down when voltage is applied to the electrodes, indicating that flashover at the low-voltage end of insulators during rainfall occurs infrequently. This research holds significant importance for elucidating the flashover mechanisms of water droplets at both ends (high-voltage and low-voltage) of the insulators and for guiding the design of external insulation for power equipment. Full article

Epoxy-based composites are crucial insulating and structural materials for superconducting magnets, providing mechanical strength, winding fixation, and heat transfer. However, future superconducting devices with higher integration and power will place even higher demands on their toughness, thermal conductivity, electrical insulation, and radiation resistance at low temperatures. Otherwise, problems such as cracking, detachment, and low heat dissipation efficiency will arise, which may lead to quenching of low-temperature superconductors (Nb₃Sn, NbTi) and a decline in the performance of high-temperature superconductors (YBCO). Research focuses on summarizing the recent progress in modifying epoxy resin to address these issues. The current strategies include formula optimization using mixed curing and toughening agents to enhance mechanical properties, incorporating functional fillers to improve cryogenic thermal conductivity and reduce the coefficient of thermal expansion. Studies also evaluate cryogenic electrical insulation performance (DC breakdown strength, flashover voltage) and radiation resistance under cryogenic conditions. These advancements aim to develop reliable epoxy composites, ensuring the stability and safety of superconducting magnets in applications such as particle accelerators and fusion reactors. Full article

Under the DC field, live contamination is more likely to deposit on the surface of insulators due to the action of the external electric field. The deposition of dirt on the surface of Ultra High Voltage (UHV) insulators can lead to the occurrence of flashover phenomena, causing significant economic losses. Due to the particularity of UHV insulators, many traditional surface anti-pollution technologies designed for normal voltage insulators are not applicable to them. In order to prevent the harm of contamination accumulation affecting the safe operation of transmission lines, in this study, tetragonal BaTiO₃ was mixed into room-temperature vulcanized silicone rubber for the first time to prepare a composite coating with piezoelectric properties. This coating can use the piezoelectric effect to remove the contamination adhering to the surface of UHV insulators under a DC field. In this study, the piezoelectric properties of the prepared tetragonal BaTiO₃ were verified through material characterization. The results show that the introduction of piezoelectric fillers can significantly accelerate the dissipation of charges on the insulator surface under slight disturbances, which helps to reduce the accumulation of charged pollutants on the insulator surface. The anti-pollution performance under electric field conditions was verified through a simulation experimental device. Finally, through experiments in a real converter station environment, the anti-pollution effect of the insulator under actual working conditions was verified. Full article

Surface charge accumulation is an important cause of flashover accidents for DC pillar insulators and the failure of DC gas insulation equipment. In this paper, the DC pillar insulator is taken as the research object, and a surface potential measurement system is built. The surface potential distribution of the pillar insulator under different voltages is measured. An inversion algorithm based on the B-spline basis function is proposed. The electric field simulation model of the DC pillar insulator considering the gas’s weak ionization and surface conductance is established. The surface charge accumulation characteristics of the pillar insulator under different DC voltages are studied. The results show that the surface potential of the DC pillar insulator presents an oscillating distribution in the axial direction, and the potential distribution is approximately mirror symmetry under positive and negative voltages. The surface charge density is non-uniform in the axial direction, and the surface charge distribution is different under different voltages. In addition, the current density on the solid side gradually approaches and exceeds the current density on the gas side with the increase in the applied voltage, which promotes the accumulation of charges on the insulator surface with the same symbol as the electrode to weaken the field strength and balance the normal electric field components on both sides. Full article

In recent years, arresters in 10 kV distribution transformer areas of the Guangdong power grid have exhibited a rising trend of premature failures, posing a serious threat to distribution network reliability. This paper studied the failure causes of arresters through performance tests on failed arresters and through deterioration tests on new arresters and their prorated sections under typical operating stresses. The failed arresters and their internal varistors displayed varying degrees of physical damage and pronounced degradation in electrical performance, characterized by a strong polarity effect on the DC reference voltage (U_1mA), elevated DC leakage current (I_L) and resistive current (i_R), and excessive residual voltage (U_5kV). In the lightning impulse test, varistors primarily showed pinhole-type damage and significant polarity effects on ΔU_1mA. In the AC aging test, ΔU_5kV increased markedly. In the water immersion test, varistors exhibited salt deposits and aluminum electrode blackening, with ΔU_1mA decreasing, while I_L and Δi_R increased significantly. Overall, internal moisture superimposed on other operating stresses was identified as a major internal cause of arrester failure, while pollution flashover of the housing was considered the primary external factor. Corresponding improvement measures in material optimization, testing and inspection, and operation and maintenance are proposed to enhance arrester reliability. Full article

In direct-current gas-insulated transmission lines (DC GIL), complex heat transfer processes accelerate surface charge accumulation on insulators, causing local electric field distortion and elevating the risk of surface flashover. This study develops a three-dimensional multi-physics coupled mathematical model for ±200 kV DC GIL basin-type insulators. The bulk and surface conductivity of insulator materials were experimentally measured under varying temperature and electric field conditions, with fitting equations derived to describe their behavior. The model investigates surface charge accumulation and electric field distribution under DC voltage and polarity-reversal conditions, incorporating multi-field coupling effects. Results show that, at a 3150 A current in a horizontally arranged DC GIL, insulator temperatures reach approximately 62.8 °C near the conductor and 32 °C near the enclosure, with the convex surface exhibiting higher temperatures than the concave surface and distinct radial variations. Under DC voltage, surface charge accumulates faster in high-temperature regions, with both charge and electric field distributions stabilizing after approximately 300 h, following significant changes within the first 40 h. Following stabilization, the distribution of surface charge and electric field varies across different radial directions. During polarity reversal, residual surface charges cause electric field distortion, increasing maximum field strength by 13.6% and 47.2% on the convex and concave surfaces, respectively, with greater distortion on the concave surface, as calculated from finite element simulations with a numerical accuracy of ±0.5% based on mesh convergence and solver tolerance. These findings offer valuable insights for enhancing DC GIL insulation performance. Full article

To conquer the challenges of charge accumulation and surface flashover in epoxy resin under direct current (DC) electric fields, numerous efforts have been made to research dielectric barrier discharge (DBD) plasma treatments using CF₄/Ar as the medium gas, which has proven effective in improving surface flashover voltage. However, despite being an efficient plasma etching medium, SF₆/Ar has remained largely unexplored. In this work, we constructed a DBD plasma device with an SF₆/Ar gas medium and explored the influence of processing times and gas flow rates on the morphology and surface flashover voltage of epoxy resin. The surface morphology observed by SEM indicates that the degree of plasma etching intensifies with processing time and gas flow rate, and the quantitative characterization of AFM indicates a maximum roughness of 144 nm after 3 min of treatment. Flashover test results show that at 2 min of processing time, the surface flashover voltage reached a maximum of 19.02 kV/mm, which is 25.49% higher than that of the untreated sample and previously reported works. In addition to the effect of surface roughness, charge trap distribution shows that fluorinated groups help to deepen the trap energy levels and density. The optimal modification was achieved at a gas flow rate of 3.5 slm coupled with 2 min of processing time. Furthermore, density functional theory (DFT) calculations reveal that fluorination introduces additional electron traps (0.29 eV) and hole traps (0.38 eV), enhancing the capture of charge carriers and suppressing surface flashover. Full article

The discharge and flashover phenomenon of post insulators in rainy weather has not been given sufficient consideration; however, with the construction of ultra-high voltage power grids, the performance of the external insulation and the ability to withstand special climate conditions need to be guaranteed. Therefore, it is meaningful to conduct studies on the discharge characteristics of contaminated post insulators under rainfall conditions. Moreover, the conventional perception tends to confuse the flashover of polluted insulators in the rain with the pollution flashover that occurs in the fog; however, in fact, the discharge of contaminated insulators that occurs during rainfall has characteristics that can be distinguished from the pollution flashover. In this study, firstly, the current status of research on the external insulation characteristics of post insulators was analyzed through an examination of the available literature. Secondly, the concept of a ‘pollution rain flashover’ of insulators was established and clarified, to distinguish it from the traditional meaning of ‘pollution flashover’ or ‘contamination flashover’. Thirdly, research results on the pollution rain flashover of post insulators used in power stations in recent years were summarized, which included the characteristics and mechanism of the discharge, parameters and factors influencing the flashover voltage, and their influence laws. Particularly, the gap discharge between insulator sheds triggered by raindrops, which is the most significant feature of the pollution rain flashover, and the profile optimization of sheds, which is an effective way to improve the performance, were emphasized in this work. Fourthly, the prevention methods were studied, which mainly include the application of rainproof sheds and the shed optimization for pollution rain flashover of post insulators. Finally, a brief prospect is given for future research. Full article

The advanced Gas Insulated Switchgear/Gas Insulated Lines (GIS/GIL) transmission equipment serves as an essential physical infrastructure for establishing a new energy power system. An analysis spanning nearly a decade on faults arising from extra/ultra-high voltage discharges reveals that over 60% of such faults are attributed to the discharge of metal particles and dust. While existing technical means, such as ultra-high frequency and ultrasonic sensing, exhibit effectiveness in online monitoring of particles larger than sub-millimeter dimensions, the inherent randomness and elusive nature of micron-nano dust pose challenges for effective characterization through current technology. This elusive micron-nano dust, likely concealed as a latent threat, necessitates special attention due to its potential as a “safety killer”. To address the challenges associated with detecting micron-nano dust and comprehending its intricate mechanisms, this paper introduces a micron-nano dust adsorption experimental platform tailored for observation and practical application in GIS/GIL operations. The findings highlight that micron-nano dust’s adsorption state in the electric field predominantly involves agglomerative adsorption along the insulator surface and diffusive adsorption along the direction of the ground electrode. The pivotal factors influencing dust movement include the micron-nano dust’s initial position, mass, material composition, and applied voltage. Further elucidation emphasizes the potential of micron-nano dust as a concealed safety hazard. The study reveals specific physical phenomena during the adsorption process. Agglomerative adsorption results in micron-nano dust speckles forming on the epoxy resin insulator’s surface. With increasing voltage, these speckles undergo an “explosion”, forming an annular dust halo with deepening contours. This phenomenon, distinct from the initial adsorption, is considered a contributing factor to flashovers along the insulator’s surface. The physical mechanism behind flashovers triggered by micron-nano dust is uncovered, highlighting the formation of a localized short circuit area and intense electric field distortion constituted by dust speckles. These findings establish a theoretical foundation and technical support for enhancing the safe operational performance of AC and DC transmission pipelines’ insulation. Full article

During the operation of multi-electric aircraft, the polytetrafluoroethylene (PTFE) material used to insulate the aviation cable is subjected to a high electric field while working under the extreme conditions of high temperatures for a long time, which can easily cause a partial discharge and even flashover along the surface, which seriously threaten the safe operation of the aircraft. In this paper, the electrical insulation properties of PTFE were regulated via modification by the magnetron sputtering of TiO₂ under high temperatures, and modified PTFE with different sputtering times was prepared. The direct current (DC) surface discharge, surface flashover, and electric aging characteristics of modified PTFE were studied under the condition of 20~200 °C, and the mechanisms by which modification by sputtering of TiO₂ and high temperature influence the insulation properties were analyzed. The results show that the surface discharge intensity increases with the increase in temperature, the modification by sputtering of TiO₂ can significantly inhibit the partial discharge of PTFE, and the flashover voltage first increases and then decreases with the increase in the modification time. The modification by magnetron sputtering can effectively increase the surface potential decay rate of the PTFE, increase the shallow trap energy density, effectively avoid charge accumulation, inhibit the partial discharge phenomenon, and improve the surface electrical insulation and anti-aging properties. Full article