In this paper, the aramid fiber surface was modified by plasma, and the effects of plasma on the interfacial properties of aramid fiber reinforced epoxy resin (AFRP) was studied. The shear strength between aramid fiber and epoxy resin is notably enhanced after undergoing plasma treatment. Additionally, the AC breakdown strength of the treated samples can reach up to 33.2 kV/mm, which is 13.7% higher compared to the untreated samples. After treatment, the conductivity and dielectric constant of the samples decreased to some extent within a certain range. When compared with untreated samples, this provides a method to enhance the interfacial properties of aramid fiber reinforced epoxy resin composites. This could be a valuable development for using such materials in HV (high voltage) electrical equipment.
The ultra-high frequency (UHF) method has found widely application in the field of partial discharge (PD) detection in gas insulated switchgear (GIS). UHF sensor is an essential component and whose performance highly correlates with the effectiveness of PD detection. In this paper, a microstrip antenna is designed as a new UHF sensor for PD detection by adopting coplanar waveguide feeding. The geometric model is firstly established based on electromagnetic theory. The key dimension parameters are optimized considering the demands of PD detection. A trident-shaped feeding strip is loaded to further enhance the sensor performance. Obtained results demonstrate that the working band of the proposed UHF sensor is 500-1120 MHz with an acceptable size, while the radiation characteristics are good with a peak gain of 4.6 dB. PD experiments are carried out for two typical artificial defects of corona and internal air-gap discharge to verify the effectiveness of the designed sensor. It is indicated that the sensor can effectively detect PD signals, and is expected to be used for PD detection in GIS.
Polypropylene (PP) insulation material displays higher melting point, high breakdown strength and volume resistivity, which meets the needs of high voltage cable insulation in the future. This paper focuses on the influence of crystallization characteristics on the resistant performance of electrical tree of polypropylene (PP). The sample of PP insulation are non-isothermally crystallized at different cooling rate and isothermally crystallized at different temperatures. The spherulite size of PP insulation samples decrease with the increase of cooling rate. The electrical tree of the sample cooled with a rate of 10 K/min has short trunks and many branches. While as the cooling rate slowed down and the spherulite size increased, the electrical tree branches decreased, the length increased, and the electrical tree deterioration increased. It is found that the electric tree tends to grow along the spherical crystal boundary.
Based on the density functional theory, the interaction between the decomposition products of $\mathrm{C}_{4}\mathrm{~F}_{7}\mathrm{~N}/\mathrm{CO}_{2}$, a new type of environmental protection insulating gas, and epoxy resin monomer was studied from the microscopic point of view. The potential adsorption sites of $\mathrm{C}_{4}\mathrm{~F}_{7}\mathrm{~N}/\mathrm{CO}_{2}$ mixture decomposition products and epoxy resin monomer were determined by electrostatic potential analysis. The interaction strength and charge transfer of gas-solid bimolecular model were calculated. The results showed that the adsorption energy of $\mathrm{C}_{4}\mathrm{~F}_{7}\mathrm{~N}/\mathrm{CO}_{2}$ mixture decomposition products and epoxy resin monomer was less than 0.06eV, the charge transfer amount is less than $0.05e$ and the adsorption process was mainly physical adsorption. The interaction strength of gas decomposition products and epoxy resin monomer was weak, and the chemical stability of gas-solid interface was good.
The use of polypropylene (PP)/elastomer blend in HVDC cable insulation is widespread due to its eco-friendliness. However, the low thermal conductivity of this material limits its application due to the temperature gradient caused by Joule heat from the current in the cable conductor. To address this issue, boron nitride (BN) nanosheets with high thermal conductivity and excellent insulation performance were added to the PP/propylene-based elastomer (PBE) blend. Threedimensional (3D) thermal conductive pathways were created by a self-support and pressure-reinforced method. Thermal and electrical conductivities were measured at 30, 60, and 90°C. The results showed that the addition of BN improved the thermal conductivity and reduced the electrical conductivity of the PP/PBE blend. As the temperature increased, the thermal conductivity of the PP/PBE/BN nanocomposite sample decreased. However, samples with the 3D structure exhibited better thermal conductivity performance at high temperatures. The electrical conductivity increased with the temperature, and the electrical conductivity dependence on temperature was reduced by the introduction of BN. It is suggested that the technique of incorporating the 3D thermal conduction pathways established by thermal conductive nanoparticles into the PP/elastomer blend is advantageous in enhancing its thermal conductivity and insulation performance.
Multilayer dielectric stacking structure are widely used in various fields of electrical insulation applications to satisfy multiple thermal and electrical insulation requirements. The accurate information of thermal resistance between dielectric films is essential for effective thermal management of electrical equipment, which is helpful to obtain the internal temperature distribution of devices to ensure the operating stability. However, it will be difficult to obtain the accurate interface information by using the traditional method. In this work, a novel method is proposed to measure the thermal resistance between ultra-thin films based on dielectric transient current. A multilayer sample structure including a dielectric film sensor is utilized. The target interface thermal resistance between ultra-thin films was determined by analyzing the pyroelectric currents signal generated by dielectric film. Several group samples with different interfaces were prepared by changing the contact surface roughness and the thermal interface materials (TIM). The results show that the simulated pyroelectric current curve coincide with the experimental current curve, and the goodness of fit is more than 99%. The trend of the obtained data is consistent with the theoretical expectations.
In order to repair the surface properties of cracked ethylene propylene diene monomer (EPDM) without any impurity element addition, an atmospheric pressure plasma jet (APPJ) repair system with C-H based media (styrene) was established and surface characterization tests are carried out. The results show that a typical polystyrene film is fabricated on EPDM surface after Ar/styrene APPJ treatment, and the surface hydrophilicity is improved significantly, where the water contact angle decreases from 104.21° to 9.79°. In addition, cracks on EPDM surface can lead a decrease in the flashover voltage, but the plasma treatment recovers the electrical properties of the damaged EPDM from 10.2 to 13.4 kV. It is noted that the styrene addition in plasma has a significant effect on EPDM surface properties, where the best modification effect generally occurs at the appropriate medium concentration (20 mL/min). Plasma-driven polymerization of styrene results in the C-H containing films on EPDM surface, which accounts for improvement of hydrophilicity and recovery of electrical insulating properties.
Abstract-The moist air inside the HV switchgear can cause partial discharge (PD) on the surface of the post insulator, damaging the insulation performance. This paper explores the impact of humidity on the PD of post-insulators, analyzing the PD spectra and related parameters under varying humidity. The results show that when relative humidity is 40 %, the average discharge increases with voltage, yet the PD spectra remain similar under different voltages. When relative humidity reaches 60 % or 80 %, the spectra display diverse PD sources related to the distribution and movement of drops on the post insulator’s surface at different voltages.
The breakdown accident for the cable line caused by the defect of the buffer layer poses a challenge to the maintenance and operation of the cable. The long-term operation of cable will cause the changes in physical properties of the buffer layer and affect the stable operation of the cable. Therefore, this paper establishes an distributed electric network model for analyzing the discharge defect of buffer layer under different states. The calculation methods of each component in the model are proposed. The axial distribution of potential between the corrugated aluminum sheathing and the buffer layer under different contact conditions was analysed. The results show that the continuous development of the corrosion product in the axial direction will increase the voltage between the corrugated aluminum sheathing and the buffer layer. The discharge risk can be effectively reduced by injecting rejuvenation fluid between the metal sheath and the buffer layer. The effectiveness of the rejuvenation method can be quantified by using the distributed electric network model.
Grafted-modified polypropylene (PP) has been studied widely due to thermostability and hard breakdown. The dielectric properties of grafted polypropylene affect the long-time usage directly in AC voltage. In this paper, methyl mechacrylate grafted polypropylene (PP-g-MMA) in different grafting proportions were prepared by water-solid phase suspension grafting method. The wide frequency dielectric spectrometer was used to test the dielectric properties of PP-g-MMA, including permittivity and dielectric loss. The results have shown that the overall trend of permittivity and dielectric loss tangent $(\text{tan}\delta)$ of PP-g-MMA is similar at different temperature. The permittivity increases with the increasing grafting proportion. With the increasing grafting proportion, the $\text{tan}\delta$ of PP-g-MMA increases in the low frequency, and decreases in the middle and high frequency. It lays the foundation for the subsequent study in properties and parameters.
There are many devices in the distribution system, transformers, circuit breakers and various types of power equipment are more susceptible to the external environment, resulting in complex and diverse fault types, which seriously affects the safety and reliability of the power grid. The existing protection equipment lacks a unified algorithm framework to identify and protect multiple faults in the distribution network. Based on this, this paper proposes a comprehensive fault identification model based on long and short term memory (LSTM) neural network algorithm. Firstly, this paper collects experimental data for typical faults such as short circuit, surge, residual current, overload, over-temperature, over-voltage and under-voltage. Secondly, the typical features of various types of faults are analyzed and calculated accordingly. On this basis, a comprehensive fault classification and recognition model combining LSTM and threshold judgment is proposed. Finally, the validity of the model is verified by the data set collected and constructed before. The comprehensive fault identification model proposed in this paper can accurately identify the short circuit, surge, residual current and other faults in the distribution network lines, and then provide targeted protection for the distribution network lines by controlling the circuit breaker to open and close, ensure the normal and stable operation of various power equipment, and effectively improve the safety and reliability of the distribution network.
Insulator flashover in field is a serious threat to the security and reliability of the gas insulated switchgear (GIS), and the metal particles on the surface of GIS insulator are considered to be a main cause of insulation fault. In previous studies, centimeter metal particles are usually examined in a GIS, which is obviously different from the actual field situation. In this study, a GIS insulator experimental platform is established, and the partial discharge (PD) and flashover characteristics of millimeter metal particles on the insulator surface in a 252 kV GIS are studied. The results indicate that under the operating voltage and routine PD test voltage, the discharges of millimeter metal particles are weak and sporadic: the discharge repetition rate is smaller than 60 times/s and the maximum apparent charge is smaller than 3 pC. As the voltage increases, the apparent charge and discharge repetition rate both increase slightly. The discharge is significantly enhanced only within a short time before flashover. This study provides an important reference for understanding the PD and flashover characteristic of millimeter metal particles on insulator surface, and is beneficial for improving the effectiveness of defect detection.
Based on the solid-layer and up-and-down methods, the AC pollution flashover tests are carried out on the bushing external insulation in the artificial climate chamber. The altitudes and pollution degrees of those tests are: at different altitudes (232m, 2000 m, 4000 m) and different pollution degrees (ESDD(equivalent salt deposit density) / NSDD(non-soluble deposit density) is 0.05/0.5, 0.1/0.5 and 0.15/0.5 mg/cm 2 ). The experimental procedure involves measuring the voltage across a divider during AC pollution flashover events and capturing the arc discharge path with a high-speed camera. The experimental data reveal that the bushing external insulation is more susceptible to AC pollution flashover as the altitude and pollution degree increase. The discharge performance of the bushing external insulation at different altitudes and pollution degrees is summarized, which provides guidance and a basis for selecting the bushing external insulation of the UHV AC substation. Finally, combined with the AC pollution flashover performance of the bushing external insulation at different altitudes, the optimization direction of the bushing external insulation is proposed to improve the reliability of the bushing during operation.
Transformer, as an important part of the grid, its failure or not has a direct relationship to the grid. In the transportation, installation or lifting cover process, by the impact, bumps and vibration, etc. may make the transformer winding deformation. In addition to transformer short-circuit fault generated after the electrodynamic short-circuit force will also make the winding deformation of different degrees. The winding deformation will affect the magnetic field distribution of the transformer, and the change of magnetic field will cause the change of force on the winding. Therefore, in order to study the effect of the degree of winding deformation on the magnetic field and force, a full-size model of the transformer was built in the finite element simulation software and then studied in this paper. The following conclusions are obtained: the winding deformation degree has influence on the magnetic field distribution and winding force; The greater the degree of winding deformation, the greater the axial magnetic field between the high voltage winding(hvw) and low voltage winding(lvw) cavities, the more radial leakage in the winding end, and the larger the degree of distortion of the magnetic field; the bigger the winding deformation degree, the smaller the overall force, and the specific force at the upper end of the winding corresponds to the magnetic field distribution.
This paper focuses on the modeling and testing of a thermoelectric generator (TEG) -based energy harvester for powering wireless sensor nodes in a high-voltage direct current (HVDC) converter. The objective is to investigate the feasibility of using an environmental power-based energy harvesting solution for powering wireless sensor nodes in harsh industrial environments. The paper firstly models the thermoelectric generator, and then the experimental validation of the TEGbased energy harvester is carried out in a real HVDC converter module. The results prove the feasibility of using a thermoelectric generator as an energy source for powering wireless sensor nodes in condition monitoring for HVDC converter.
The insulation performance of composite insulator is reduced due to the possible defects such as air gap, crack and delamination, which leads to serious power grid accidents. Interfacial defect is one of the main structural defects of composite insulator. In this paper, a low-energy active infrared thermography (AIT) method based on chirp pulsed radar (CPR) excitation is studied. And a platform is built to test the silicone rubber (SIR)- epoxy resin sample with artificial flat bottom holes. Use CPR signal to excite and analyze the results. Principal component analysis (PCA), one of the post-processing characteristic extraction algorithms is used to process the thermal wave response signal of the sample to improve the detection accuracy of defects. The signal-to-noise ratio (SNR) of defects is used as an indicator to evaluate the effectiveness of defect detection. The results of pulse thermography (PT) of the sample are used for comparison to verify the detection effect of CPR signal excitation on deep defects.
The epoxy-metal interface is the weakest part in the internal insulation of epoxy insulation parts. Improving the insulation performance of the epoxy-metal interface through material formulation and process modification is an effective way to reduce insulation accidents. In this paper, we investigate the influence of epoxy formulation, semiconductive coating, and surface states of metal inserts on the insulation performance of epoxy-metal interfaces. First, post insulators with four epoxy formulations, two insert electrode surface states, and three thicknesses of semiconductive adhesive coatings were set as samples. Second, the partial discharge characteristics and breakdown voltage of the insulator samples were measured on a non-partial discharge power frequency experimental platform, using the step boost method. According to the calculation results of electrostatic field distribution based on finite element analysis, the maximum electric field strength at the epoxy-metal interface increases with the increasing of the semiconductive coating thickness, but is almost unaffected by its relative permittivity. There is generally no obvious partial discharge signal before internal breakdown of epoxy post insulator without interface defects. Compared with smooth metal inserts, the insulators with knurled metal inserts have a higher breakdown voltage. Besides, the samples with the highest breakdown voltage did not use the epoxy formulation with the highest breakdown electric field strength, which is limited by the compatibility among the epoxy resin material, the semiconductive coating, and the metal insert. The results suggest that in order to improve the insulation strength of the epoxy-metal interface, it is necessary not only to adopt knurling process on the surface of the metal inserts, but also to consider the compatibility among the three materials when selecting the epoxy insulation material and the semiconductor coating.
This paper comprehensively considers the spatial positioning, real-time and other factors of unmanned aerial vehicle(UAV) inspection, and firstly proposes a UAV precise positioning technology based on visual positioning and visual tracking, so as to realize the rapid collection and judgment of information such as location and safety distance. At the same time, aiming at the problems of long positioning and recognition time and poor real-time performance, the improved kernel correlation filter(KCF) tracking algorithm is used to fit the tracking model.
Accurately judging the hydrophobicity classes (HCs) of the composite insulator helps to grasp the antipollution flashover performance of the insulator and prevent accidents in time. Aiming at the problem of low HC recognition accuracy of hydrophobic images and interference of operators’ subjectivity in the feature extraction process, an intelligent HC recognition model of composite insulators based on the Contrast Limited Adaptive Histogram Equalization (CLAHE) image enhancement method and ResNet deep learning network is proposed in this paper. Firstly, composite insulators under varying HCs were simulated by spraying ethanol solutions with different volume fractions, and a series of hydrophobic images under experimental conditions was obtained. To improve the generalization ability of the model on photographic factors (photographing distance, light intensity, insulator color), images were preprocessed with gray processing, cropping, enhancement, and so on. The transfer learning strategy was used for training and verifying the pre-trained ResNet network by applying the preprocessed image dataset so that it is suitable for recognizing the HC of composite insulators. The results show that the CLAHE-ResNet18 model proposed in this paper can still effectively identify each HC under varying photographic factors and complex conditions. This model can maintain an accuracy above 96.74% in the testing dataset, with good generalization ability and application value.
DC bushing is one of the technical challenges that restrict the development of DC power transmission and transformation technology. With the electrification of society towards higher power density, bushings are exposed to extreme electrical and thermal stress superpositions during operation. The adaptive bushing, with a field grading layer, provides additional benefits compared to the conventional bushing. In this paper, an electro thermal coupling field simulation model of adaptive bushing was established. The determination of the parameters of the nonlinear materials in the field grading layer was discussed. Under the electrothermal coupling filed, the electric field distribution and temperature distribution were simulated. With the increase of load current, the temperature gradient intensifies, and the maximum electric field distributed in the main insulation part reverses from inner to outer. Benefit from the field-depended conductivity, the nonlinear materials can introduce negative feedback in voltage distribution, so that the electric field shows good stability even under the extreme temperature gradient. This work will promote the application of nonlinear composites in ultra-high voltage DC bushings.
