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The study of insulation degradation processes is crucial for the reliable operation of power equipment and electronic devices. The phase field method has been widely used in recent years to simulate the degradation process of insulation materials. However, the effect of space charge was ignored. In this paper, a novel phase field method based on the bipolar carrier transfer model is suggested. This model can simulate degradation under different temperatures and DC or combined AC/DC voltage. The cases under AC and combined AC/DC voltage at different temperatures are simulated by COMSOL. Methods to ensure model convergence are proposed. The results show that the field strength distribution under a combined AC/DC field is more uniform, especially for negative polarity. For the same voltage form, temperature and breakdown time show an exponential relationship. The results are consistent with those of previous experimental studies, proving the usability of the model. In addition, the processes of initiation, growth, and breakdown stage of the dielectric degradation process, as well as the stagnation period, are explored theoretically. The stagnation time at low temperatures under combined AC/negative DC voltage is long. The research in this paper is useful for insulation optimization design, condition assessment, and longevity prediction. [ABSTRACT FROM AUTHOR]

Dielectric materials are foundational to our modern-day communications, defense, and commerce needs. Although dielectric breakdown is a primary cause of failure of these systems, we do not fully understand this process. We analyzed the dielectric breakdown channel propagation dynamics of two distinct types of electrical trees. One type of these electrical trees has not been formally classified. We observed the propagation speed of this electrical tree type to exceed 10 million meters per second. These results identify substantial gaps in the understanding of dielectric breakdown, and filling these gaps is paramount to the design and engineering of dielectric materials that are less susceptible to electrostatic discharge failure. [ABSTRACT FROM AUTHOR]

To evaluate the deterioration degree of insulation material by monitoring partial discharges (PDs), it is necessary to fully understand the PD behavior prior to breakdown. We performed measurements of temporal variations in the number and magnitude of PDs in a void of epoxy resin. It was found that the number of PDs with larger magnitude is less before breakdown and that there is a decreased tendency of the number and magnitude of PDs with the elapsed time. The tendency is remarkable as the applied electric field is small. Additionally, the time to breakdown becomes short when the scattering of the number of PDs per unit time decreases. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Highlights The capacitive energy‐storage capacity of most emerging devices rapidly diminishes with increasing temperature, making high‐temperature dielectrics particularly desirable in modern electronic systems. In this work, calcium niobate (Ca2Nb3O10, CNO) nanosheets have been added into poly(vinylidene fluoride‐hexafluoropropylene) (P(VDF‐HFP), PVHP), forming PVHP/CNO nanocomposites with exceptional temperature stability and ultrahigh energy storage density. Especially, at 80°C and 450 MV/m, the PVHP/0.3 wt%CNO nanocomposite shows an excellent Wrec of 10.81 J/cm3 which is higher than previous PVDF‐based composite films at high temperatures. Because of the high dielectric permittivity of CNO nanosheets and the way that the parallel organization of the nanosheets blocks the course of electrical trees, nanocomposites exhibit greater dielectric constants and breakdown field strengths simultaneously. These findings, will be helpful in the development of flexible, high‐energy‐density capacitors that have stable performance at high temperatures. A record‐high high‐temperature Wrec is obtained. Excellent temperature stability from 25 to 80°C is achieved. The incorporation of Ca2Nb3O10 nanosheets significantly enhances Eb. [ABSTRACT FROM AUTHOR]

Under divergent electric fields, space charge is locally accumulated and controls the initiation and evolution of insulation degradation phenomena, such as electrical trees and partial discharge. The space charge profiles provide crucial information for evaluating the insulation performance. However, the existing space charge measurement methods are not directly applicable under divergent electric fields. In this paper, a method combining experiment and simulation is proposed to evaluate the space charge distribution around a needle electrode. An experimental system is established, and the acoustic waves are measured with a hydrophone placed on the symmetric axis. In order to obtain the space charge distribution, the space charge injection process is simulated using the bipolar charge transport model to reduce the freedom of the distribution. Then, calculations are made for the acoustic waves produced by the simulated space charge distributions. Using the signals without the contribution of internal charge, a correspondence between the experiment and simulation is established. For each experimental signal, the matched calculated signal is obtained using the zero-crossing time as a reference. A perfect match between them is presented after the amplitude compensation, which indicates that the space charge distribution in the experiment is identical to that in the simulation model. [ABSTRACT FROM AUTHOR]

Due to the rapid development of science and information technology, electricity information acquisition system has been widely used in the electricity data collection of users. With the massive electricity data collection, it is difficult to adopt traditional data processing methods to meet the abnormal data processing. In order to effectively mine abnormal information in electricity consumption data, an anomaly detection model based on the Isolation Forest (iForest) algorithm is proposed. Firstly, the daily load curve with strong regularity is used as the characteristic index of anomaly monitoring, and the users with abnormal electricity consumption data are preliminarily screened. Secondly, on the basis of electrical variables, the suspected abnormal users are further analyzed, and the anomaly identification model of electricity data is established to automatically classify the voltage at the metering point. Moreover, combined with the current data, the abnormality of the electric energy metering device is identified, and then the validity of the model is determined through on-site verification. Finally, according to the participating voltage of the fault phase, the 96-point voltage data frozen during the failure period is analyzed and the correction coefficient is adjusted. The results reveal that the electricity data detection model based on the iForest algorithm has significant advantages in computational efficiency. Through the cumulative recall and Precision-Recall (P-R) curves of the model, it is found that the majority of abnormal users can be detected only by detecting a few users with high abnormal scores, which shows that the model has high efficiency. The decision tree algorithm combined with the current data can effectively identify the anomalies of the energy metering device, which verifies the validity of the anomaly identification model of the electricity consumption data. [ABSTRACT FROM AUTHOR]

Next generation power system needs dielectrics with increased dielectric energy density. However, the low energy density of dielectrics limits their development. Here, an asymmetric trilayered nanocomposite, with a transition layer (TL), an insulation layer (IL), and a polarization layer (PL), is designed based on poly(vinylidene fluoride)-polymethyl methacrylate (PVDF-PMMA) matrix using KNbO3 (KN) and TiO2 (TO) as the nanofillers. The morphology and defect control of the two-dimensional nano KN and nano TO fillers are realized via a hydrothermal method to increase the composite breakdown strength (Eb) and the composite energy density (Ue). The asymmetric trilayered structure leads to a gradient electric field distribution, and the KN and TO nanosheets block charges transfer along z direction. As a result, the development path of the electrical trees is greatly curved, and Eb is effectively improved. And the Ue value of the nanocomposites reaches 17.79 J·cm−3 at 523 MV·m−1. On the basis, the composite Ue is further improved by defect control in TO nanosheets. The nanocomposite KN/TO/PVDF-PMMA containing TO with less oxygen vacancy concentration (calcined at oxygen atmosphere) acquires a high Ue of 21.61 J·cm−3 at 548 MV·m−1. This study provides an idea for improving the energy storage performance by combining the design of the composite dielectric structure and the control of nanofillers' defect and morphology. [ABSTRACT FROM AUTHOR]

Copyright of Przeglad Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Przeglad Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, we report the effects of a multilayer architecture on the electrical breakdown strengths and ferroelectric characteristics of 45 nm thick aluminum scandium nitride (AlScN) films. Multilayered films (three-layer, five-layer, and seven-layer) are deposited via sequential deposition of Al0.72Sc0.28N and Al0.64Sc0.36N while maintaining constant volume ratios in all three samples. The effect of the increased number of interfaces is compared to 45 nm single layer Al0.72Sc0.28N and single layer Al0.64Sc0.36N films. The Weibull analysis shows an increase in the characteristic breakdown field from 5.99 and 5.86 MV/cm for single layer Al0.72Sc0.28N and Al0.64Sc0.36N to as high as 7.20 MV/cm in the seven-layered sample. The breakdown field to coercive field (EBD/Ec) ratios also increase from 1.37 and 1.26 in single layer Al0.72Sc0.28N and Al0.64Sc0.36N to up to 1.44 in the seven-layered sample with no significant change in remanent polarization. The enhancement of the characteristic breakdown field can be understood as the propagation of the electrical tree being deflected by multilayer interfaces and/or being slowed by the relative compressive stress in the alternating layers. [ABSTRACT FROM AUTHOR]

Polymer‐based dielectric nanocomposites with excellent high‐temperature energy storage performance are highly desirable in advanced electronic and power systems, but it remains a challenge to achieve superior breakdown strength at elevated temperatures. In this work, two‐dimensional (2D) magnesium oxide nanosheets (MgO NSs) are prepared by a hydrothermal method and used as fillers to fabricate MgO NSs/polyetherimide (PEI) dielectric nanocomposites. The effect of MgO NSs addition (1–4 wt%) on breakdown strength of MgO NSs/PEI nanocomposites is studied from 25 to 150°C. As a result, the nanocomposites containing 3 wt% MgO NSs obtain maximum breakdown strength of 538 kV mm−1 at 150°C, which is 25% higher than that of pure PEI and remains 92% of the room‐temperature value, accompany with an excellent discharged energy density of 3.66 J cm−3. The enhancement of breakdown strength could be attributed to the 2D structure and wide band gap (~7.8 eV) of MgO NSs, which act as barriers to suppress the electrical tree growth and create deep traps to capture charge, thus inhibiting the migration of charge carriers and suppressing electrical conduction. This work provides an effective approach for developing high‐temperature polymer‐based dielectric nanocomposites with high breakdown strength and discharged energy density. [ABSTRACT FROM AUTHOR]

Polymer-based dielectrics with excellent processability are essential for dielectric capacitors applications in modern electronics and electrical power systems. Although significant advances in capacitive storage have been achieved by adding inorganic fillers that are synthesized primarily by liquid-phase technology, this method faces considerable challenges for the industrial production of scalable capacitor films that requires easy process conditions. Herein, P(VDF-HFP) nanocomposites with cost-effective inorganic 0.7[0.955(Bi 0.5 Na 0.5)TiO 3 -0.045Ba(Al 0.5 Ta 0.5)O 3 ]-0.3CaTiO 3 nanoparticles (BNT-BAT-CT nps) that are prepared by a combination of solid phase approach and sieving, are constructed via a scalable and practical mechanical process. Both experimental and simulation results verify that the appropriate BNT-BAT-CT nps can significantly suppress the leakage current density, improve the dielectric constant, and block the penetration of the electrical tree, thus generating substantial enhancements in the breakdown strength and capacitive performance. A large discharge energy density (∼10.82 J/cm3) is realized at 580 MV/m in 3 vol% BNT-BAT-CT/P(VDF-HFP) nanocomposites, which is approximately 2.17 times larger than that of pristine P(VDF-HFP). More significantly, unlike previous polymer nanocomposites incorporated with high-cost nanofillers, the designed nanocomposites contain low preparation cost of nanofillers. Combined with the merits of high energy-storage performance and simple and cost-effective preparation, this work offers a viable method towards the large-scale production of polymer-based high-performance dielectrics. [ABSTRACT FROM AUTHOR]

In order to improve the electrical tree resistance of epoxy resin, composites were prepared using dihydroxydiphenylsilane and a novel silicone modifier modified epoxy resin and micron silica, and the composites were subjected to accelerated thermal aging test and electrical tree test and recorded the growth process of electrical trees to further obtain the characteristic parameters of electrical trees in the experimental samples. The results show that the silicone‐modified epoxy resin/silica composite has better thermal stability and electrical tree resistance than the unmodified epoxy resin/silica composite and pure epoxy resin. Analysis of the scanning electron microscope (SEM) and breakdown field strength results show that the introduction of the modifier enhanced interfacial properties between the epoxy resin and silica. At the end of the electrical tree test, the length of the electrical tree in the silicone‐modified epoxy resin/silica composite was at a minimum 25.31% of the length of the electrical tree in the unmodified epoxy resin/silica composite with the same silica filling ratio, and 9.19% of the length of the electrical tree in the pure epoxy, while the electrical trees in the silicone‐modified epoxy resin/silica composite have lower expansion factors, as well as higher fractal dimensions, compared to those in the resin without added silica. [ABSTRACT FROM AUTHOR]

The partial discharge (PD) analysis method has remained one of the key technologies for cable condition assessment to diagnose cable operation state. In this paper, two power cable status evaluation methods are proposed based on electrical tree growth and data association rules, respectively. First, in the field of molecular thermodynamics, based on the law of energy conservation of electrical tree growth, this paper studies the relationship between PD signals in cable insulation and the length of the electrical tree. By using the length of electrical tree growth to calculate the probability of PD failure of cables, a cable state assessment method based on electrical tree growth is proposed. Second, for power cable status evaluation, the strong concealment characteristics of cables result in a long power supply recovery time and a serious threat to power supply reliability. Therefore, a group of comprehensive cable status parameters are set by analyzing the status parameters based on data association rules. The comprehensive state of power cables is divided into four elements, and the weight coefficients of cable states are calculated based on data association rule methods. Finally, the simulation results verify the effectiveness and accuracy for the two different power cable status evaluation methods. [ABSTRACT FROM AUTHOR]

The development of high‐precision, non‐destructive, and three‐dimensional (3D) in situ imaging of micro‐scale damage inside polymers is extremely challenging. Recent reports suggest that 3D imaging technology based on micro‐CT technology causes irreversible damage to materials and is ineffective for many elastomeric materials. In this study, it is discovered that electrical trees inside silicone gel induced by an applied electric field can induce a self‐excited fluorescence effect. Based on this, high‐precision, non‐destructive, and 3D in situ fluorescence imaging of polymer damages is successfully achieved. Compared with the current methods, the fluorescence microscopic imaging method enables slicing of the sample in vivo with high‐precision operation, realizing the precise positioning of the damaged area. This pioneering discovery paves the way for high‐precision, non‐destructive, and 3D in situ imaging of polymer internal damage, which can solve the problem of internal damage imaging in insulating materials and precision instruments. [ABSTRACT FROM AUTHOR]

Improving the electrical treeing resistance of polymer is of great significance for insulation reliability. To achieve this, a solution-based method is employed to introduce a voltage stabilizer with high electron affinity into the silicone rubber (SiR). Experimental findings demonstrate the voltage stabilizer's ability to improve the tree initiation voltage and provide evidence of their migration within the SiR. Additionally, by combining a finite element method, it has been confirmed that voltage stabilizers can migrate through dielectrophoresis in non-uniform electric fields and adaptively reposition themselves in response to changes in electric field distribution during the growth of the electrical tree. [ABSTRACT FROM AUTHOR]

Silicone gel is widely used to encapsulate power modules, and improvement of its dielectric strength has been required. So, the purpose of our research is to improve dielectric strength of silicone gel encapsulant, and we focus on crosslinking degree of silicone gel. Previous studies have shown that growth mechanism of electrical tree changes with crosslinking degree of silicone gel. This suggests the possibility that the presence of the interface by different crosslinking degrees inhibits the tree growth. In this paper, we have investigated the tree growth and breakdown characteristics in silicone gel—crosslinking degrees graded layer materials. The interfaces in our study are arrange as being vertical to the line of electric force. Consequently, it was clarified that barrier effect of interface by different crosslinking degrees and the relaxation of electric field in low crosslinking degree region retards on tree growth, which improves the dielectric strength. [ABSTRACT FROM AUTHOR]

The development of renewable-energy-based microgrids is being considered as a potential solution to lessen the unrelenting burden on the centralized utility grid. Furthermore, recent studies reveal that integrated multi-microgrid cluster systems developed in urban communities maximize the effectiveness of microgrids and greatly decrease the utility grid dependence. However, due to the uncertain nature of renewable energy sources and frequent load variations, these systems face issues with unintentional islanding operations. This can create severe damage to the microgrid's performance in its stable operating condition and lead to undesired transient responses. Hence, islanding must be identified rapidly to take preventive measures to address the issue. This requires the development of a suitable anti-islanding technique that is faster in terms of accuracy and timely detection. With this intention, this paper proposes a decision-tree-based fuzzy logic (DT-FL) controller for the rapid identification of islands in an urban community multi-microgrid cluster. The DT-FL controller's operation includes two steps. First, the decision tree extracts the electrical parameters at the point of common coupling of the multi-microgrid system. Second, these extracted parameters are utilized for the online tuning of the fuzzy logic controller, for the fast detection of islanding. The multi-microgrid cluster under study, along with the proposed islanding technique, is implemented in the MATLAB-2021a software. The efficacy of the proposed DT-FL controller is validated by comparing its performance with that of the conventional fuzzy logic controller under different test scenarios. From the results, it is observed that the proposed DT-FL controller shows superior performance in terms of the islanding detection time as well as the transient response of the system when compared with the conventional controller. [ABSTRACT FROM AUTHOR]

Scanning thermal microscopy is used to perform direct imaging local conductive path and dynamic behaviors in the degraded multilayer ceramic capacitors (MLCCs) due to the thermal conductivity difference between the dielectric layers and the conductive regions. For local conductive path, its electrical tree dynamic growth behaviors under the dc bias on and off state are clearly obtained in the thermal image. Such phenomena reveal that space–charge‐limited current mechanism dominates in local conductive path region of MLCCs. The results give a strong demonstration of scanning thermal microscopy as a powerful tool for imaging local conductive behavior in MLCCs, which provides us a direct, unique view to clarify local breakdown mechanism and enriches our insights in the insulation resistance degradation and the reliability of MLCCs. [ABSTRACT FROM AUTHOR]

The structural changes and very-low-frequency (VLF) nonlinear dielectric responses are measured to evaluate the aging state of cross-linked polyethylene (XLPE) in power cables under various thermal aging conditions. For this purpose, the accelerated thermal aging experiments were performed on XLPE insulation materials at 90 °C, 120 °C and 150 °C with different durations of 240 h, 480 h and 720 h, respectively. The Fourier transform infrared spectrum (FTIR) characterization and differential scanning calorimeter (DSC) were tested to analyze the influence of different aging on physicochemical properties of XLPE insulation. Besides, the VLF dielectric spectra show that the permittivity and dielectric loss change significantly in the VLF range from 1 mHz to 0.2 Hz. A voltage–current (U–I) hysteresis curve referring to a standard sinusoidal voltage and the response current were introduced to characterize the nonlinear dielectric properties of XLPE insulation caused by thermal aging. [ABSTRACT FROM AUTHOR]

The harshness of the submarine environment represents a serious threat for immersed high voltage power cables, extensively used for offshore wind farms, which in turn are supposed to last for at least 20 years for their total investment to be economically viable. The Crosslinked Polyethylene (XLPE) used for the insulating layer of the cables may suffer different degradation phenomena, leading to unexpected breakdowns and rises in costs. In this work, numerical simulations have been developed to study the mechanisms by which micrometric pores inside XLPE can enlarge and coalesce (namely, water treeing) when the insulation is subjected to the intense electric field generated by hi-voltage wires. The study aim is to predict material plasticization next to voids, which is supposed to represent the onset of coalescence of neighboring pores. A microscale-level finite element coupled electro-mechanics model has been developed to describe the interactions between the intense electric fields and the subsequent Maxwell stresses in a dielectric. The roles of different influencing parameters such as distance, relative volumes, and the shape of two neighboring voids in a representative unit volume are considered. Finally, the behavior of a generic microstructure characterized by randomly distributed voids immersed in an electric field is simulated. [ABSTRACT FROM AUTHOR]

Electricity load forecasting is one of the important tasks of the power marketing department, and accurate load forecasting is extremely important to ensure real-time dispatch and security of the power system. In order to obtain accurate and reliable load forecasting results, an ultra-short-term power load forecasting model based on an improved random forest regression algorithm is proposed in this paper. First, data pre-processing is performed on the original dataset. Then the pre-processed time data and historical load data are used as inputs to the model, and optimization of the model using the Gaussian mixture-based tree-structured Parzen estimator algorithm is carried out. Finally, the final prediction results were derived. Experimental analysis was conducted with real load data from a region of China, and the experimental results show that the method has better prediction accuracy than the original random forest algorithm and other traditional machine learning algorithms. [ABSTRACT FROM AUTHOR]

Electrical treeing is one of the main degradation mechanisms in high-voltage polymeric insulation. Epoxy resin is used as insulating material in power equipment such as rotating machines, power transformers, gas-insulated switchgears, and insulators, among others. Electrical trees grow under the effect of partial discharges (PDs) that progressively degrade the polymer until the tree crosses the bulk insulation, then causing the failure of power equipment and the outage of the energy supply. This work studies electrical trees in epoxy resin through different PD analysis techniques, evaluating and comparing their ability to identify tree bulk-insulation crossing, the precursor of failure. Two PD measurement systems were used simultaneously—one to capture the sequence of PD pulses and another to acquire PD pulse waveforms—and four PD analysis techniques were deployed. Phase-resolved PD (PRPD) and pulse sequence analysis (PSA) identified tree crossing; however, they were more sensible to the AC excitation voltage amplitude and frequency. Nonlinear time series analysis (NLTSA) characteristics were evaluated through the correlation dimension, showing a reduction from pre- to post-crossing, and thus representing a change to a less complex dynamical system. The PD pulse waveform parameters had the best performance; they could identify tree crossing in epoxy resin material independently of the applied AC voltage amplitude and frequency, making them more robust for a broader range of situations, and thus, they can be exploited as a diagnostic tool for the asset management of high-voltage polymeric insulation. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Polymeric insulation employed in electrical power industry undergo irreversible and unpredictable ageing due to partial discharges (PDs). In particular, the dielectric properties of polyethylene (PE) used in high voltage cables are often compromised by the formation of electrical trees. In this work we assume that the propagation of treeing channels involves the injection of carbonic material into the gas interacting with the surface of the defect. Experimental characterizations proved that, in certain conditions, disordered graphitic carbon can form in some areas of the electrical trees, thus increasing surface conductivity and inhibiting PDs. The chemical mechanism involved in this process is yet to be clarified. Here we propose a model for this process. By means of a series of molecular dynamics simulations, we show how the chemisorption of gaseous molecules on a PE surface can lead to a bidimensional carbonic structure. The characterization of the density of states of such systems suggests that the presence of pure carbon adsorbed on the polymer causes an increase in surface conductivity. [ABSTRACT FROM AUTHOR]

Dielectric capacitors are fundamental energy storage components in electronics and electric power systems due to their unique ultrahigh power density. However, their relatively low energy storage density is a long‐standing challenge which greatly limits their practical application range. Chitosan (CS) and montmorillonite (MMT) are two kinds of materials that exist abundantly on the earth with natural surface charges. The positively charged CS and negatively charged MMT can be self‐assembled into the typical sandwich‐structured CS/MMT/CS 2D structure through an electrostatic attraction. Loading these surface‐charged sandwich‐structured nanosheets into poly(vinylidene fluoride)‐based composite with a weight fraction as tiny as 0.3 wt.%, an ultrahigh energy storage density of 32.5 J cm−3 accompanied with a high efficiency of 64% are concurrently achieved with a very low cost and scalable process. Guided by finite element simulation, it is revealed that a number of electric potential wells that exist in the charged sandwich nanosheets impede the acceleration of internal charges and hinder the growth of electrical trees. The results offer a novel paradigm for exploring ultrahigh energy storage density capacitors in an economical way. [ABSTRACT FROM AUTHOR]

Polypropylene is considered to be the material of choice for environmentally friendly high voltage direct current cable insulation. The high power transmission of electrical energy exposes insulating materials to high temperatures and electric fields, resulting in the degradation of material properties. This paper reports that organic molecular semiconductors with strong electron affinity can effectively modulate electrical properties of polypropylene. The charge injection and transport process are analyzed by considering a combination of relations describing various conduction models in dielectrics, including the Richardson–Schottky (RS) emission and the hopping conduction. Based on the performed experiments, a modified Wiesmann–Zeller (WZ) model is proposed to simulate the electrical treeing process of polypropylene. The electrical treeing results are well verified with the simulation results, which offer a valuable tool for further analysis of the effect of intrinsic barrier height, hopping distance, and activation energy on the electrical degradation in the material. This work provides an insightful analysis of multiple charge transport mechanisms affecting the electrical degradation of the polymer, which is crucially essential for the rational design of high-performance insulation materials. [ABSTRACT FROM AUTHOR]

It is difficult to achieve high energy storage density in a low electric field by blending conductive filler composites. Sandwich structure composites with conductive filler were prepared by tape casting. The MXene/PVDF film with a thin thickness was used as two outer layers to enhance the permittivity of the composites. The BN/PVDF film with a thicker thickness was used as the intermediate layer. The growth of electrical trees in the direction of composite thickness is inhibited by interface barrier and high breakdown BN network, which plays a role in protecting the breakdown strength. The results showed that the larger energy storage density (13 J/cm3) is obtained under the low electric field (360 kV/mm) when the MXene content was 0.03 vol%. [ABSTRACT FROM AUTHOR]

Detailed analyses of mechanisms of electrical treeing phenomenon have been carried out yet. In this study, we analyze electrical trees as very thin 3D tubes between a treeing needle and a plate electrode and calculate the energy-release rate to estimate and evaluate the driving force required for crack propagation. This study implements a new method applying an analogy between concepts of fracture mechanics and Maxwell stress to calculate the energy-release rate in a 3D model. As a result, we obtained the energy-release rate around a volume near the needle-electrode and electrical trees. In addition, path independence is verified, and it is found to be conserved only when the path does not include the interface between the needle-electrode and the insulation material. Then, the values of energy-release rate obtained in each condition of tree length and applied voltage were compared, respectively. It is revealed that the 1D-growth of the tree has a small effect on the value of the energy-release rate, and that the value is proportional to the square of applied voltage on the needle-electrode. These results imply that calculating energy- release rate exhibits a potential to mathematically evaluate the growth of electrical trees, connecting its results to experimental results such as partial discharge phenomenon and/or space charge accumulation. [ABSTRACT FROM AUTHOR]

Electrical treeing is one of the major breakdown mechanisms for solid dielectrics when subjected to high electric stress. It is a damaging process due to partial discharge (PD) and progresses through the stressed insulation by chemical degradation whose path resembles the form of a tree root. Numerous methods have been proposed to increase the tree resistance of the insulating materials, such as adding tree inhibitors, reinforcement, and modifying the insulating material. In overcoming this phenomenon, nanocomposites have gained broad interest as insulating materials due to their excellent ability to resist electrical treeing. Introducing nanofiller into the polymer matrix is an impressive and promising method to enhance the electrical tree endurance. In fact, this may increase the resistivity of polymer to suppress the growth of electrical trees inside the insulation medium. This article presents a study on the electrical tree performances with its associated PD and the influence of filler concentration in silicone rubber (SiR) samples filled with silicon dioxide (SiO2) as the nanoparticles for electrical treeing retardant. Previous research that used SiO2 as a filler showed lots of improvement on the breakdown test compared to the unfilled SiR, which prompted this study. The electrical tree performance of SiR nanocomposites containing SiO2 nanoparticles, however, has received limited attention. The electrical tree experiments were carried out by applying a fixed AC voltage of 12 kVrms at a power frequency of 50 Hz to unfilled SiR and SiR nanocomposites containing 1 wt%, 3 wt%, and 5 wt% SiO2 nanoparticles. The outcome parameters investigated to evaluate the electrical tree performances were tree initiation time, tree propagation time, growth rate, and tree breakdown time concerning its associated PD characteristics. This study found that the SiR nanocomposites could suppress the electrical trees better than the unfilled SiR. Moreover, increasing the filler content increased the electrical tree performances of the SiR nanocomposites. This finding suggests that the SiO2 can be exploited as a filler in SiR polymeric insulating materials for inhibition of electrical tree. [ABSTRACT FROM AUTHOR]

Internal partial discharges and electrical treeing are some of the main aging mechanisms of all the polymeric insulating materials present in the power net. A better understanding of this process calls for the development of more sophisticated simulation tools, based on the numerical solution of first principles equations, i.e., a set of partial differential equations. The accuracy of the predictions of these models heavily relies on the quality of the set of physical parameters used as, for example, the swarm parameters. A key aspect is the correct representation of the first electron availability which triggers the discharge. These electrons are mainly injected into the gas from the interface between the gas itself and the solid polymeric matrix by means of the Schottky effect. The work function is a very relevant parameter in defining this effect, and so the entire quality of the simulation process depends on it. In this work, we estimate the value of the work function, using electronic structure calculations, and we perform some parametric analyses to show how the discharge simulations are affected by the variation of this quantity. In particular, we assume that the polymeric material is polyethylene, which is used extensively in the electric power transmission industry. The discharge simulations produce some relevant data that can be compared against experimental data for validation purposes. [ABSTRACT FROM AUTHOR]

In order to improve electrical matching between ethylene-propylene-diene misch-polymere (EPDM) reinforce insulation and crosslinked polyethylene (XLPE) main insulation in direct current (DC) cable accessories, the glyceryl monooleate (GMO) organic compound composed of several polar-groups and one long carbon chain is employed for chemical graft modification on EPDM to ameliorate DC electrical performances. Charge trap characteristics are analyzed by testing thermal stimulation current (TSC) and verified by calculating first-principles electronic properties to elucidate the GMO-graft-modified charge trapping mechanism accounting for DC electric conductance and dielectric breakdown. The grafted GMO molecules introduce substantial shallow charge traps that lead to nonlinear profiles of electric conduction versus electric field and cause hopping transports of percolation conductance. Electric conductance of EPDM is significantly improved by GMO graft for electrical matching with XLPE, while a high level of dielectric breakdown strength is retained sufficiently for reinforce insulation in cable accessories. Shallow charge traps introduced by GMO graft are capable of capturing charge carriers to form homocharge layers near electrodes which can scatter the transporting charge carriers and exclude further charge injections, thus to mitigate the dielectric breakdown strength reduction caused by electric conductivity improvement. Electric field finite-element simulations demonstrate that the electric field in DC cable terminals can be evidently homogenized by using GMO-grafted EPDM as reinforce insulation. [ABSTRACT FROM AUTHOR]

Cross-linked polyethylene (XLPE), the most commonly used insulation system in underground cables, and gas-insulated substations are often subjected to high-voltage stresses of time-varying nature. Lightning overvoltages, fast transients, very fast transients, and AC voltages are the most common overvoltages striking the insulation. These stresses cause degradation of insulation, which is called treeing, and are considered as the major cause of the reduction in life of the insulation. The purpose of our work is the development of a stochastic model to inspect the spread of electrical trees under lightning impulse voltage. A numerical solution of Poisson's equation in the material is obtained first. The electric field distributions obtained on the surface of the material are used to compute the path of tree propagation by developing a program based on a probabilistic approach. The key parameters of the damage are evaluated by plotting histograms of the results obtained from many iterations. A statistical analysis of the obtained results has also been done, and the model has been found efficient. [ABSTRACT FROM AUTHOR]

Underground power cables are prone to electrical tree aging and additives loss due to the harsh working environment. In this work, the thermal aged cross-linked polyethylene (XLPE) cables were restored by injecting a newly synthesized voltage stabilizer containing hydrolyzable siloxane groups. The voltage stabilizer functionalized siloxane groups greatly enhanced the electrical tree initiation voltage, significantly reduced the direct current (DC) conductivity and dielectric loss factor. The results of scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) indicated that the voltage stabilizer molecules were distributed in the electrical tree channels of the restored cables. After secondary thermal aging at 150 °C for 360 h, the characteristic electrical tree initiation voltage of the restored cable reached 12.10 kV, which was 66.90% higher than that of the unrestored cable. This indicated that the migration of voltage stabilizers could be inhibited by introducing hydrolyzable groups. This investigation provided a new approach to improve the migration resistance of the voltage stabilizer and the inhibitory effect of the rejuvenation liquid on the electrical tree. [ABSTRACT FROM AUTHOR]

With the rapid development of electronic industry, high‐energy storage density dielectric materials are urgently needed to meet electronic components equipment miniaturized demand. Polymer dielectric materials have the advantages of good flexibility and high breakdown field, however, the energy storage capacity of polymers is limited by its inherent low dielectric constant. To improve the dielectric constant and energy storage density of the polymer material, we synthesized 0D (zero dimension), 1D, 2D lanthanum modified lead zirconate titanate (PLZT) fillers which introduced into polyvinylidene fluoride (PVDF) matrix. The anisotropic of the fillers has obvious improvement on the properties of materials. Compared with 0D fillers, high anisotropic fillers are more effective in enhancing the dielectric performances and energy density of PVDF based composites. The high anisotropic ratios of 2D fillers limit the charge migration toward the electrodes and hold back the growing electric tree during breakdown. Consequently, high breakdown strength (430 MV/m) and high discharge energy density (13.9 J/cm3) for 2D PLZT/PVDF composite films were obtained. This work is of critical significance in making dielectric capacitors for energy storage devices and reveals the influence mechanism for different dimensions fillers on the dielectric and energy storage properties of PVDF based composites. [ABSTRACT FROM AUTHOR]

The increasing integration of renewable sources into distributed networks results in multiple protection challenges that would be insufficient for conventional protection strategies to tackle because of the characteristics and functionality of distributed generation. These challenges include changes in fault current throughout various operating modes, different distribution network topologies, and high-impedance faults. Therefore, the protection and reliability of a photovoltaic distributed network relies heavily on accurate and adequate fault detection. The proposed strategy utilizes the Variational Mode Decomposition (VMD) and ensemble bagged trees method to tackle these problems in distributed networks. Primarily, VMD is used to extract intrinsic mode functions from zero-, positive-, and negative-sequence components of a three-phase voltage signal. Next, the acquired intrinsic mode functions are supplied into the ensemble bagged trees mechanism for detecting fault events in a distributed network. Under both radial and mesh-soft normally open-point (SNOP) topologies, the outcomes are investigated and compared in the customarily connected and the island modes. Compared to four machine learning mechanisms, including linear discriminant, linear support vector mechanism (SVM), cubic SVM and ensemble boosted tree, the ensemble bagged trees mechanism (EBTM) has superior accuracy. Furthermore, the suggested method relies mainly on local variables and has no communication latency requirements. Therefore, fault detection using the proposed strategy is reasonable. The simulation outcomes show that the proposed strategy provides 100 percent accurate symmetrical and asymmetrical fault diagnosis within 1.25 ms. Moreover, this approach accurately identifies high- and low-impedance faults. [ABSTRACT FROM AUTHOR]

This paper presents the effect of addition of dielectric barrier discharge (DBD) plasma‐treated nano‐Al2O3 particles on electrical treeing characteristics of epoxy resin (EP) at 30, 60, and 90°C, respectively. The electrical treeing and simultaneous partial discharge measurements, surface potential decay, scanning electron microscope, Fourier transform infrared spectrograms and differential scanning calorimetry are adopted to analyze the influence of plasma‐treated nano‐Al2O3 particles on the different insulation properties of EP and its composites. The results show that the high temperature adversely affects the electrical tree initiation, growth rate, and discharge activities of the EP nanocomposites. The DBD‐treated nano‐Al2O3 particles increase the electrical tree initiation voltage of the EP nanocomposites compared to the nanocomposite with the untreated nano‐Al2O3 particles. In contrast, the electrical tree growth rate decreases in the EP nanocomposite with the DBD treated nano‐Al2O3 particles at high temperatures. It is found that DBD treated nanoparticles affect the trap density and energy level of the composites by generating new chemical bonds, and then change their electrical properties. A charge carrier transport model is proposed to explain the obtained experimental results. [ABSTRACT FROM AUTHOR]

The long-term operation of dry-type transformer bushings at high temperatures can impact the performance of their primary insulation material. This article presents an experimental study of the effect of thermal aging time on electrical treeing in the epoxy resin-impregnated paper. The experimental results show that the electrical treeing pattern along the middle path of the electric field and the interlayer creepage along the average direction of the electric field are closely related to the aging time. Under the effect of thermal aging at 150 °C, the tree-starting voltage of epoxy resin-impregnated paper tends to increase and decrease as the aging time increases. An analysis and discussion of the test results in conjunction with scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) tests suggest that the destruction of the cross-linked network of the epoxy resin-impregnated paper at 150 °C is a fundamental reason for the significant decrease in the material’s tree-starting voltage and the change in electrical treeing morphology and interlayer creepage. Long-term operation at high temperatures can seriously impact the primary insulation performance of dry-type transformer bushings and requires attention. [ABSTRACT FROM AUTHOR]

As the key cryogenic insulating material for high-temperature superconductivity equipment, epoxy resin works in the harsh environment of strong electric field and extremely cryogenic temperature, and its operational reliability faces severe challenges. In this article, aiming at bisphenol F epoxy resin for cryogenic insulation of super-conducting power equipment, researches on electrical trees in epoxy resin under lightning impulse voltage at room temperature and cryogenic temperature were carried out. The effects of temperature, impulse voltage amplitude, and polarity on the initiation characteristics, growth morphology, growth rate, and expansion coefficient of electrical trees are discussed. The results show that the electrical tree initiation under impulse voltage in a cryogenic environment also has a polarity effect. The voltage is higher than that under negative impulse voltage, the shape of electrical trees is a typical branch, the color is darker, the tree channel is wider, and the branches next to the channel are simpler. There are fewer branches, and many darker spherical or ellipsoidal cracks appear in the electrical branch channel. [ABSTRACT FROM AUTHOR]

Electrical tree aging problem under high-frequency voltages seriously affects the reliability of packaging insulation for power electronics modules. In this article, boron nitride (BN) sheet/epoxy resin (ER) composites with low doping concentration are prepared and characterized. Varied voltage frequencies (50 Hz–130 kHz) are selected, and electrical tree characteristics of composites at different voltage frequencies are studied. Results show that as the frequency increases from 50 Hz to 130 kHz, electrical tree initiation voltage of pure ER decreases by 39.8%. However, as the frequency increases, tree channels first become denser, and then, the tree branches decrease. Moreover, electrical tree shape presents sturdy single-branch-like tree at 130 kHz. By introducing BN sheet, the tree initiation voltage increases, especially at higher frequencies. The tree scale of BN sheet/ER is smaller than that of pure ER at all frequencies. Combining the dielectric properties and tree results of different materials, the influence of frequency on tree characteristics of ER is discussed, and the role of BN sheet in the bulk is revealed. [ABSTRACT FROM AUTHOR]

Thermal aging causes electrochemical changes in a polymeric dielectric, instigating the formation of microvoids and oxidized carbonaceous layers. These voids increase in number and size with aging time. This and other chemical changes result in weight reduction, change in dielectric constant of the sample, and affect electrical tree growth inside the polymer. The current work aims to understand the electrochemical changes in epoxy resin due to thermal aging and their effect on electrical tree growth. Physicochemical analysis is performed using field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The formation of carboxyl groups and voids encourages space charge accumulation resulting in local field enhancement. Inception of trees occurs in the regions of high field stress. Carbonization of tree tubules due to aging makes the walls conducting and promotes tree growth. Furthermore, thermal aging leads to gap formation and carbonization at the metal–dielectric interface, which also affects the nature of electrical tree growth in aged insulation. [ABSTRACT FROM AUTHOR]

Epoxy resin insulation materials are mainly derived from petrochemical materials which have the disadvantages of resource consumption and environmental pollution. In order to cure bisphenol A epoxy resin, a maleopimaric anhydride (MPA) curing agent was prepared from rosin, a renewable resource, and blended with a petroleum-based curing agent (methylhexahy-drophthalic anhydride). The influence of maleopimaric anhydride content on the initiation and growth characteristics of electrical trees was studied and analyzed in this paper using molecular dynamics simulation (MD) and electrical tree tests at an 18-kilovolt power frequency voltage. When the MPA content used was ≤10%, the free volume percentage of the curing system increased with MPA content, and thus the initiation voltage became lower; when the MPA content was ≥20%, the hydrogenated phenanthrene ring structure content increased significantly with increasing MPA content, and the rigidity of the curing system increased significantly; thus, the initiation voltage gradually increased. MPA4 had an 11.11% higher initiation voltage than the petroleum-based control group. The effect of the polar rigid structure within the curing system significantly inhibited the growth rate and length of electrical trees as MPA content increased. Electrical trees developed into light-colored, thin, and narrow dendritic structures when the MPA content reached 40%. The results show that curing epoxy resin with the rosin-based curing agent maleopimaric anhydride (MPA), in place of a petroleum-based curing agent, can produce environmentally friendly resins with excellent electrical tree resistance and potential application prospects. [ABSTRACT FROM AUTHOR]

Electrical treeing is one of the main causes of crosslinked polyethylene (XLPE) cable failure. The current methods for locating electrical trees are mainly based on the partial discharge (PD) signal. However, PD signals are easily attenuated in the long cable and the PD test voltage may cause damage to the insulation. This work proposes an improved broadband impedance spectrum (BIS) method to locate electrical trees in XLPE cable. A mathematical model of a long cable containing local electrical tree degradation is established. The Gaussian signal is chosen as the simulated incident signal to reduce the spectral leakage. The location spectrum is obtained by multiplying the frequency domain function of the single-ended reflection coefficient and the Gaussian pulse. It has been found that the location spectrum of the local capacitance change can be characterized as a typical double-peak waveform and the spectrum of the local conductance change can be regarded as a typical single-peak waveform. Electrical tree experiments at different temperatures were carried out to initiate different types of electrical trees. A vector network analyzer (VNA) was used to test the high frequency capacitance characteristics in the treeing process. The location spectra of the 20 m long cable containing different types of electrical trees was calculated by the improved location algorithm. The results show that the location error of local electrical tree degradation is less than 3%. The capacitance of the sliced sample decreases with treeing time. The effect of the bush-pine tree on capacitance parameters is greater than that of the branch-pine tree. A typical double-peak is found in the bush-pine tree location spectrum and a single-peak is found in the branch-pine tree spectrum. [ABSTRACT FROM AUTHOR]

The effect of adding electron‐buffering voltage stabilizer (1 wt% m‐aminobenzoic acid) on the electrical tree‐induced degradation of cross‐linked polyethylene (XLPE) was studied at high temperatures. The electrical tree inception, growth, and partial discharge characteristics were simultaneously analyzed at 30, 50, and 70°C, respectively. The results showed that the growth rate of electrical tree and partial discharge activity as well as the discharge repetition rate, significantly increased with the temperature for pure XLPE and XLPE stabilizer blend. However, the XLPE stabilizer blend exhibited higher tree inception voltage, lower tree growth rate, and partial discharge activity than pure XLPE. The addition of the voltage stabilizer reduced the carbon layer thickness in the tree channel and offered higher resistance to the electrical tree growth. Surface potential decay demonstrated that the voltage stabilizer addition decreased the trap energy level, but increased the shallow trap density of the XLPE. Quantum chemical calculations showed that the voltage stabilizer enhanced the ability to buffer the high‐energy electrons in the XLPE. A high‐energy electron buffering mechanism was also proposed to explain the effect of voltage stabilizer on the electrical treeing and partial discharge activity in the XLPE at high temperatures. [ABSTRACT FROM AUTHOR]

A nonlinear one-dimensional problem has been formulated for steady heat conduction at a constant difference of electric potentials on the inner and outer surfaces of a cylindrical layer of polymer dielectric with a temperaturedependent thermal conductivity coefficient and specific electrical resistivity. A fixed temperature value on the inner surface of this layer is assumed, and a total thermal resistance between its outer surface and the surrounding environment is assigned. The problem formulation is transformed to integral relations making it possible to calculate distributions of temperature and electric field intensity through the layer thickness. An example is provided of a quantitative analysis of these distributions for a cross-linked polyethylene layer. The results of such analysis make it possible to identify possible areas of application of polymer dielectrics in various electric devices, including those used as electrical insulation of high-voltage direct-current cables and to establish conditions of a thermal breakdown of a dielectric layer. [ABSTRACT FROM AUTHOR]

Epoxy resin has been widely used as the main insulation in power electronic transformers, which, however, inevitably suffer from the detrimental effect of electrical trees. In this paper, bipolar square-wave voltage is applied to the epoxy resin to initiate electrical trees, with the effect of waveform parameters and ambient temperature on electrical tree characteristics explored. All trees observed demonstrate branch-like structures. The electrical tree length, width, extension factor, fractal dimension, and accumulated damage increase with voltage amplitude and frequency, while breakdown time decreases. In addition, the results of gas chromatography show that thermal decomposing occurred during the breakdown of the epoxy resin, inducing small-molecule gases including acetylene, hydrogen, and carbon monoxide. This indicates that the initiation voltage of the electrical tree at 500 Hz decreases from 8 kV to 6 kV when the temperature is elevated from 20°C to 80°C. The results of surface potential decay testing shows that the trap energy depth and the charge mobility are increased at higher temperatures, which also leads to an easier charge injection and results in an enhanced electrical tree evolution. [ABSTRACT FROM AUTHOR]

Insulation failure due to electrical tree degradation is a challenge for epoxy resin (EP) operating in high electric field environments. To provide an experimental basis for the electrical tree inhibition method, we observed the inception times/voltages and growth rates of EP electrical trees at different ambient temperatures in real time using a micro-charge-coupled device, and proposed an in situ nondestructive observation method for obtaining the three-dimensional morphology of the EP electrical tree by fluorescence imaging. We also elucidated the influence mechanism of ambient temperatures on the growth characteristics of electrical trees by the molecular dynamics method. The results revealed that increasing the ambient temperature could increase the fractional free volume of a cross-linked EP system, resulting in increased charge carrier damage to the molecular chains, thus promoting the growth of EP electrical trees. [ABSTRACT FROM AUTHOR]

With the popular application of alternating current/direct current (AC/DC) hybrid power grid, ultra‐high‐voltage (UHV) AC/DC cables of long‐distance and large‐capacity transmission systems have been strongly demanded. Voltage stabilizers are widely used to resist AC electrical tree of cross‐linked polyethylene (XLPE) insulation materials, but poor compatibility with polymer matrix limited improvement of DC insulation performance. In this research, the maleic anhydride‐modified 2,4‐dihydroxybenzophenone as a novel voltage stabilizer 4‐(4‐benzoyl‐3‐hydroxyphenoxy)‐4‐oxobut‐2‐enoic acid (MDVS) was synthesized to improve the electrical properties of XLPE. The XLPE‐g‐MDVS with different contents of MDVS was prepared, and both AC electrical properties and DC electrical properties were tested. The results indicate that the modified XLPE retain the characteristic of voltage stabilizer to resist AC electrical tree and improve breakdown strength, and to exhibit excellent DC insulation performance in a wide temperature range. In the comparison with the pristine XLPE, the graft of MDVS can significantly suppress space charge accumulation and decrease DC conductivity. At 70°C, the maximum amount of space charge density of XLPE‐g‐1.2wt%MDVS is 56.2% lower than that of XLPE, and the DC conductivity decreases by nearly two orders of magnitude. Furthermore, the DC breakdown strength of XLPE‐g‐1.2wt%MDVS materials exhibit higher than that of the pristine XLPE. In addition to the self‐excited energy dissipation of the voltage stabilizer, quantum chemical calculations demonstrated that the improvement of DC performance attributed to the deep traps introduced by MDVS. [ABSTRACT FROM AUTHOR]