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Polypropylene (PP) is regarded as a recyclable material for high-voltage direct current (HVDC) cable insulation due to its high melting point and electrical resistivity. This work focuses on the effect of the β-nucleating agent content on the electrical tree growth characteristics in isotactic PP (iPP) insulation. The results demonstrate that adding β-nucleating agents promotes the growth of β-crystals while limiting the α-crystal content. The crystallinity improves with the reduction in the average size of spherulites due to the addition of a β-nucleating agent with 0.1 wt% content. Electrical tree experiments show that the electrical tree growth rate declines as the nucleating agent content rises from 0 to 0.1 wt%. Meanwhile, the expansion coefficient increases with higher nucleating agent content. Continuous increases in the nucleate agent content result in the upward growth rate of electrical trees. When the nucleating agent content is below 0.1 wt%, the α–β-crystal interface introduced by the agent suppresses carrier migration and limits impact ionization, leading to the slower growth rate of the electrical tree. Further addition of the nucleate agent induces a β–β-crystal interface with weak coupling in carriers. It is concluded that β-nucleating agent-modified PP with 0.1 wt% content has potential application in HVDC cable insulation. [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]

The non-homogeneous electric field distributions in the cross-linked polyethylene insulation of 330 kV power cable with multi-conductor core depending on the electrical conductivity and thickness of the semiconducting screen as well as at different frequency of applied voltage (from 50 to 104 Hz) are studied by finite-element analysis. As shown, taking into account the periodic structure of core surface, the electrical conductivity of the material of internal semiconducting screen should exceed 10–6 S/m and its thickness should be at least 1.5 mm in order to obtain the uniform electric field in the basic insulation of the cable at the boundary with the screen. The paper also considers the effect of various types of the surface and volumetric defects in the semiconducting screen on the electric field inhomogeneity in cable insulation. It is shown that the defects in the screen can lead to a significant increase of the electric field in the local zones of their location (up to 5 times as compared to the field without defects) and therefore contribute to the formation and development of treeing structures in the insulation. The revealed results explain the reasons for the micro- and macrolevel degradation of power cable insulation and confirm the need to ensure the uniform structure, smooth surface of both semiconducting screen and core during the technological process of manufacturing the power cables with crosslinked polyethylene insulation [ABSTRACT FROM AUTHOR]

Cross‐linked polyethylene (XLPE) cables are commonly used for constructing urban power lines due to their superior properties. Insulation defects can cause partial discharge (PD) and electrical tree, which can negatively impact the insulation performance of the cable and even lead to insulation failure. During operation, cables undergo hot and cold cycles, and the temperature of the insulation layer can affect the PD and electrical tree. An experimental platform with a needle‐plate electrode was developed to investigate this phenomenon. The platform was used to detect PD activity and electrical tree propagation in XLPE under a 50 Hz voltage at various temperatures. The results indicate that an increase in insulation temperature leads to an increase in the number of PDs and a decrease in the inception voltage. Simultaneously, it has been observed that a rise in temperature can facilitate the spread of electrical trees. To explicate the aforementioned PD result, a finite element analysis (FEA) model has been developed. Additionally, a molecular dynamics (MD) model of XLPE material was developed to clarify the phenomenon of electrical tree propagation. This study's findings aid in investigating the impact of temperature on XLPE defects, which is critical for assessing power cable performance. [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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

Significance reduction in characteristic dimension and weight of energy conversion system is urgently needed for developing outstanding-energy-density dielectric materials. For conventional single-layer configuration, huge enhancments in dielectric constant (K) was achieved in polymer nanocomposite system by the introduction of high- K fillers at the expense of the breakdown strength (E b). Herein, we reported that the crafting of core-shell structured BT@TP NPs and BN@TP NSs was used as the nanofillers to achieve a sandwich-structured nanocomposite that one high- K layer of BT@TP-TP was sandwiched by two high- E b layers of BN@TP-TP. In comparison to unmodified BT NPs and BN NSs, the crafting of core-shell BT@TP NPs and BN@TP NSs is beneficial for improving dispersion quality and thus endure high- E b in the matrix P(VDF-TrFE-CTFE) (TP). The newly designed sandwich-structured polymer nanocomposites are capable of balancing the contradict factors of high- K and high- E b. In addition, the enhanced interfacial polarization was directly detected by piezoelectric force microscopy, and the formation of electric trees was well displaced by FEA simulation. Outstandingly, the sandwich-structured nanocomposite 3BN@TP-TP/4BT@TP-TP/3BN@TP-TP exhibits a discharged energy density of 10.3 J/cm3 and dicharged-charged efficiency of 71.2 % at a field of 270 MV m−1, which is 5-fold higher than that of commercial BOPP. [Display omitted] • The core-shell structured BT@TP NPs and BN@TP NSs were successfully synthesized by a nonsolvent induce phase separation. • The newly designed sandwich-structured polymer nanocomposites are capable of balancing the contradict factors of high- K and high- E b. The nanocomposite 3BN@TP-TP/4BT@TP-TP/3BN@TP-TP exhibits a discharged energy density of 10.3 J/cm3 at a field of 270 MV m−1, which is 5-fold higher than that of commercial BOPP. • In the finite element simulation, high electric field was mainly focused on the BN@TP NSs and interfacial TP shell on the BT NPs, which is able to impede the charge injection and then high breakdown strength was attained in the nanocomposite. • The enhanced interfacial polarization was directly detected by piezoelectric force microscopy. [ABSTRACT FROM AUTHOR]

Coupling high dielectric inorganic nanofillers is an effective approach to enhance the energy storage density of polymer dielectric, but the electric field distortion between nanofillers and polymer matrix often leads to polymer dielectric breakdown prematurely, severely limiting their application in the modern electronic industries. Herein, the MgO with moderate permittivity was deposited on surface of BaTiO 3 (BT) nanofibers via coaxial electrospinning, aiming to alleviate the dielectric constant mismatch between BT nanofibers and polyetherimide (PEI) matrix. The experimental and simulation results demonstrate that the MgO effectively inhibits the growth of electrical tree along the electric field direction, and the movement of charge carriers at the interfaces between BT nanofibers and polymer matrix is hindered. Meanwhile, the interfacial polarization in core-shell region endows PEI/BT@MgO composites a higher polarization ability. At room temperature, the PEI/BT@MgO composite containing 1 vol% BT@MgO nanofibers deliveries the maximum discharge energy density, the value reaches 3.27 J cm−3 at 550 MV m−1 that is 36.3 % and 86.9 % higher than PEI and PEI/BT composite with same filler content, respectively. Even at 150 °C, it still achieves the energy density of 2.19 J cm−3 at 450 MV m−1, exhibits a potential value as a high-temperature polymer dielectric. [Display omitted] • Novel core-shell BaTiO 3 @MgO nanofiber was prepared via coaxial electrospinning method. • The mismatch of electric field between PEI matrix and fillers was effectively regulated by the MgO shell layer. • Excellent dielectric stability over a wide temperature range. • The dielectric and breakdown enhancement mechanism were systematically explained. [ABSTRACT FROM AUTHOR]

The article titled "Power Cable Status Evaluation Method Based on Electrical Tree Growth and Data Association Rules" has been retracted by the journal Processes. The authors of the study raised concerns about major scientific limitations and errors in their work. The Editorial Board and the authors agreed that these limitations and errors compromise the validity of the findings, leading to the decision to retract the publication. The retraction was approved by the Editor-in-Chief of the journal. [Extracted from the article]

Partial discharge (PD) induces degradation in filament-like channels of electrical trees (ETs), leading to a significant reduction in material strength and lifespan. To enhance the assessment of insulation status in polyethylene (PE) based on PD characteristics during ET growth, a dynamic health monitoring evaluation model is developed. This model enables early critical warnings for insulation states. Findings reveal that during the rapid growth phase of ETs, the Dynamic Health Index of PE fluctuates within the range of [62%, 11%], with a failure rate reaching 54.30%. The transition point from the retardation stage to the rapid growth stage is identified as the critical warning threshold for insulation failure based on PD characteristics during ET growth. Utilizing linear fitting slopes of apparent discharge magnitude and ultra-high frequency amplitude in the time domain, the frequency bandwidth of ultra-high frequency signals, and average energy distribution facilitates effective differentiation between the retardation and rapid growth stages of ETs. This work establishes a robust foundation for developing an intelligent insulation state evaluation system, thereby enhancing the reliable operation of insulation systems. [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]

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]

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]

of this work proposed a mathematical model and three types of solutions for conductive electrical tree growth in dielectrics. In this section, experiments are presented using a cone-plane electrode and nanosecond voltage pulses to investigate the electrical tree growth in polymethyl methacrylate (PMMA) samples. The results show that the tree length ${l}$ is proportional to the tangent of the pulse number ${N}$ under high-voltage pulses but ${l}$ approaches a limiting length under relatively low voltage pulses. These results agree with those predicted from the model. Therefore, the mathematical model for conductive electrical tree growth in dielectrics is verified. [ABSTRACT FROM AUTHOR]

By postulating that the electrical tree growth rate ($\textit {dl} / \textit {dt}$) is proportional to the rate of destruction due to partial discharges (PDs), a mathematical model for conductive electrical tree growth in dielectrics is put forward. Three types of solutions are presented for this mathematical model, which predict three cases of electrical tree growth in dielectrics; namely, the development case, the stagnation case, and the transition case. The physical nature of the three cases is presented, which is the comparison of the local field (${E}_{\text {loc}}$) and the critical field (${E}_{c}$) caused by the space charges due to a PD. When ${E}_{\text {loc}} > {E}_{c}$ , $\textit {dl}/\textit {dt} > {0}$ and the electrical tree develops. When ${E}_{\text {loc}} < {E}_{c}$ , $\textit {dl}/\textit {dt} < {0}$ and the electrical tree stagnates. When ${E}_{\text {loc}} = {E}_{c}$ , $\textit {dl}/\textit {dt} = {0}$ and the electrical tree stays at a transition state. [ABSTRACT FROM AUTHOR]

The growth and partial discharge (PD) characteristics of electrical tree in crosslinked polyethylene (XLPE) needle-plate electrode samples are investigated under constant dc voltage at different temperatures. The results reveal that under the experimental conditions, the electrical trees are all branch trees, and the discharge intensity fluctuates with time. The increase in temperature promotes the growth of electrical tree as well as the intensity of PD. Five texture features of PD ${q}$ - ${t}$ histogram are extracted and used as the elements to evaluate the insulation status of XLPE needle-plate electrode under dc voltage based on the gray correlation degree. The area ratio and lateral tree ratio of electrical tree is extracted based on the gray histogram. The lateral tree ratio increases with the increase in temperature, which is closely related to the intensity of PD. Gray correlation theory is used to evaluate the status of XLPE insulation. The results reveal that the evaluated insulation statuses based on the gray correlation degree are the same as those based on experience, which indicates that the proposed diagnosis method of XLPE insulation status based on the gray correlation degree with ${q}$ - ${t}$ histogram texture features as elements has a high accuracy. [ABSTRACT FROM AUTHOR]

Influence mechanism of side group types on the macroscopic electrical properties of silicone rubber (SiR) are analyzed based on the experimental comparison and the molecular simulation. The insulation properties of SiR with different side group types (vinyl, phenyl, and trifluoropropyl), as well as binary compound SiR (vinyl/phenyl and vinyl/trifluoropropyl) are compared and studied experimentally. Further, the effect of side groups on the movement of the molecular chain is analyzed by calculating the free volume, the mean square displacement (MSD), and the end distances. Then the mechanism of its influence on the macroscopic properties of SiR was studied. The experimental results indicated that the resistance and breakdown performance of the phenyl SiR surpasses both vinyl SiR and fluorosilicone rubber owing to the conjugated structure of benzene ring, which has a high electron affinity and reduces free charges and carrier migration rate. Besides, when 10wt% phenyl SiR was mixed into vinyl SiR, the resistivity increased by one order of magnitude, and the breakdown field strength increased by about 8%. In the aspect of dielectric properties, the fluorosilicone rubber is more qualified than the vinyl SiR and the phenyl SiR due to the addition of trifluoropropyl as a polar group to the non-polar dielectric SiR to boost its dielectric constant and dielectric loss. The molecular simulation results indicated that the SiR containing phenyl has a tiny free volume and weak molecular chain movement, the fluorosilicone rubber has the strongest molecular chain movement. The work has important guiding significance for improving and modifying SiR in power equipment. [ABSTRACT FROM AUTHOR]

In order to analyze the explosion accidents of the CRH5 EMU roof arrester in recent years, an internal temperature measuring platform based on fluorescence fiber was established, and the temperature distribution characteristics under the continuous operating voltage and high-current impulse were analyzed. The test results show that passing section overvoltage and steep impulse overvoltage have higher amplitudes, while high-harmonic overvoltage has a lower amplitude but a longer duration. The maximum temperature rise of the arrester was 5.2 °C under 34 kV for 3 h. The surface temperature of the valve plate column was high in the middle and low on both sides; the maximum temperature difference at different positions was only 2.2 °C. The maximum temperature of the valve plate column rose to 97.6 °C under 105 times of the high-current impulse, and the maximum temperature difference at different positions reached 33.8 °C. Then, the actual overvoltage of the arrester in operation was measured and analyzed statistically, and the arrester simulation model was established. The temperature characteristics of the normal arrester and the arrester with the electric tree were studied under the actual typical overvoltage, and the influence of air velocity on the internal temperature rise was analyzed. The simulation results show that, due to the low amplitude and small current of high-harmonic overvoltage, the internal temperature rise of the normal and defective arresters was very small. Under the effects of passing section overvoltage and steep impulse overvoltage, the internal temperature of the normal arrester can reach 36.57 °C and 241 °C, and the arrester with the electric tree defect can reach 44.75 °C and 536 °C, respectively. The air velocity has little effect on the internal temperature rise of the arrester. Passing section overvoltage and steep impulse overvoltage occur frequently and have an obvious influence on the internal temperature rise of the arrester, so the roof overvoltage of the EMU is an important reason for the arrester burst. [ABSTRACT FROM AUTHOR]

Unlike the term sound insulation, which means reducing the penetration of noise into other areas, sound absorption means reducing the reflection and energy of the sound on the surface. It has become a highly noticed issue in recent years because the noise in our daily life is increasing day by day, and it causes some health and comfort disorders. In many areas, textiles have been used for acoustics control and noise absorption purposes. The purpose of this work is to determine the most effective media for sound absorption performance and its relation to thermal conductivity from needle-punched nonwoven, meltblown nonwoven and hybrid forms in different arrangements of these fabrics. To provide comparable samples, both needle-punched nonwoven and meltblown nonwoven samples were produced from 100% Polypropylene fibres. According to sound absorption tests, the hybrid-structured sample having a composition similar to the needle-punched nonwoven sample placed at the bottom of our study, while the meltblown nonwoven sample placed as a face layer outperformed the rest of the samples in terms of sound absorption and thermal conductivity. 'Meltblown only' samples had remarkably higher sound absorption efficiency than most of the samples, while the 'needle-punched nonwoven only' sample had the lowest sound absorption efficiency in all frequencies. [ABSTRACT FROM AUTHOR]

Phase-control technology, which is also called simultaneous interconnection technology, is one of the latest developments in intelligent interconnection. With the subsequent development of the short-circuit system, which increased significantly, the switching capacity of the switch is tested. Applying arc power to the contact holes during a short circuit also causes extensive damage to the switch contacts, which severely affects the operation and life of the switch. To solve this problem, this paper introduces the branch definition algorithm, describes different types of faults occurring in power systems, proposes a general scheme for fault current phase-controlled breaking, derives a fault occurrence detection method and a phase control method, and performs a simulation analysis of the proposed branch definition algorithm; a single-phase short-circuit current model is built; and the algorithm is tested using simulation data. The oscilloscope acquisition data were simulated and analyzed to obtain the characteristic parameters of the waveform, and the online simulation results obtained were analyzed with the oscilloscope data. The experimental results show that the system designed in this paper can accurately predict the zero value, and the zero values obtained from four experiments conducted are 34.52 ms, 34.46 ms, 29.9 ms, and 29.84 ms, respectively. [ABSTRACT FROM AUTHOR]

Utility vegetation managers need tools to predict tree-related risks and knowledge of the necessary management prescriptions to reduce the risk of windthrow damage to utilities' electrical infrastructure. This review focuses on key studies involving the likelihood of failure of trees, beginning with a description and discussion of failure in trees, followed by an examination of methodologies that have been used to assess tree failure, before concluding with a review of factors which have been found to influence tree failure. Ultimately, a better understanding of the likelihood of failure of individual trees and the relationships governing tree failure and vegetation-related outages may allow for significant advances in the risk management of utility infrastructure. [ABSTRACT FROM AUTHOR]

To study the influence of the arrangement of glass fibres on the growth morphology of electric dendrites, this paper conducted experiments on the initiation and cultivation of electric dendrites on insulation specimens with different glass fibre arrangements. The experimental results show that when the electric field is parallel to the glass fibres, the electric dendrites show linear growth with multiple branches; when the electric field is perpendicular to the glass fibres, the electric dendrites show aggregated growth. The analysis suggests that when the applied electric field is parallel to the glass fibre, to release the discharge energy in the main channel of the dendrite, the discharge in the track of the electric dendrite will drive the electric dendrite to grow along the interface area between the glass fibre and the epoxy resin. When the externally applied electric field is perpendicular to the glass fibre, the discharge within the electric dendrite discharge channel is high. To release the energy in the electrical tree channel, the blast in the electrical tree track induces the electrical tree branch to grow along the interface area and forward. [ABSTRACT FROM AUTHOR]

This article attempts to reveal the detection ability of microstrip slot resonator for water and electrical tree defects in insulating samples. The characteristics of microstrip gap resonator are analyzed in high-frequency electromagnetic simulation software. A gap capacitance extraction method is proposed based on two-port transmission theory, and the gap capacitances under different dielectric constants are analyzed based on this method. The resonant frequency of sensor is found to be negatively correlated with the dielectric constant of the materials. In the experimental part, the sensor made of double-sided copper clad plate with medium FR4 was used to detect the water tree and electrical tree in low-density polyethylene (LDPE) samples, and the experiment results showed good feasibility. [ABSTRACT FROM AUTHOR]

For the development of converter transformer applications, research on the discharge characteristics in transformer oil is required. This article presents an analysis of the streamer discharge characteristics caused by a needle-plate electrode in oil-pressboard insulation under ac voltage and discharge images on the time scale of microseconds. Based on the discharge image, a Gaussian filter, image segmentation of the Otsu algorithm, and Canny edge detection are used to detect the edge of the discharge image. By extracting the discharge profile image, the discharge characteristics are effectively identified. The size and quantity of particles in transformer oil during the discharge are analyzed. Research on the characteristics of streamer discharge propagation is not only helpful for understanding the process of discharge but also has important significance for converter transformer design from the perspective of inhibiting streamer discharge. [ABSTRACT FROM AUTHOR]

A phase-field model is developed in this paper based on the similarity between mechanical fracture and dielectric breakdown. Electrical treeing is associated with the dielectric breakdown in solid dielectrics by the application of high voltages. Instead of explicitly tracing the propagation of conductive channel, this model initializes a continuous phase field to characterize the extent of damage. So far, limited research has been conducted for simulating the effect of nanofiller dispersion on electrical treeing. No study has modeled the effect of uniform and nonuniform dispersion of nanofillers with varying filler concentration on treeing. Since electrical treeing tends to decrease the breakdown strength of solid dielectrics therefore, nanofillers are widely used to distract the tree from a straight channel to distribute its energy in multiple paths. Diverting a straight treeing channel into multiple paths reduces the chances of its propagation from live to dead-end hence, improving the breakdown strength. The physical and chemical nature of nanofillers has a crucial impact on increasing the resistance to treeing. In this paper, phase-field model is developed and used to simulate electrical treeing in polyethylene for varying concentrations of alumina nanofiller using COMSOL Multiphysics. Tree inception time, tree-growth patterns, and corresponding changes in dielectric strength is studied for both dispersions. Electrical treeing under different concentrations of alumina nanofillers with uniform and nonuniform dispersion is investigated in polyethylene as a base material. It is observed that fillers with uniform dispersion increases the resistance to treeing and tree inception time. Highest resistance to treeing is observed by adding 1% nanoalumina uniformly in raw polyethylene. Moreover, in uniform dispersion the tree deflects into multiple branches earlier than nonuniform dispersion impeding the damage speed as well. [ABSTRACT FROM AUTHOR]

The purpose of lung recruitment is to improve and optimize the air exchange flow in the lungs by adjusting the respiratory settings during mechanical ventilation. Electrical impedance tomography (EIT) is a monitoring tool that permits measurement of regional pulmonary filling characteristics or filling index (FI) during ventilation. The conventional EIT system has limitations which compromise the accuracy of the FI. This paper proposes a novel and automated methodology for accurate FI estimation based on EIT images of recruitable regional collapse and hyperdistension during incremental positive end-expiratory pressure. It identifies details of the airway tree (AT) to generate a correction factor to the FIs providing an accurate measurement. Multi-scale image enhancement followed by identification of the AT skeleton with a robust and self-exploratory tracing algorithm is used to automatically estimate the FI. AT tracing was validated using phantom data on a ground-truth lung. Based on generated phantom EIT images, including an established reference, the proposed method results in more accurate FI estimation of 65% in all quadrants compared with the current state-of-the-art. Measured regional filling characteristics were also examined by comparing regional and global impedance variations in clinically recorded data from ten different subjects. Clinical tests on filling characteristics based on extraction of the AT from the resolution enhanced EIT images indicated a more accurate result compared with the standard EIT images. [ABSTRACT FROM AUTHOR]

In this work, we study the effect of strong electric fields on a polymer/graphene composite and the resulting morphology upon its dielectric breakdown. Our model system was produced by compounding up to 0.25 wt % graphene nanoplatelets (GNP) into poly(ethylene-co-vinyl acetate) (EVA), which is a soft polymer with low melt viscosity. A strong electric field of up to 400 Vrms/mm was applied to the EVA/GNP composite in the melt. The sample's resistance over the electric field application was simultaneously measured. Despite the low GNP loading, which was below the theoretical percolation threshold, the electric conductivity of the composite during electric field application dramatically increased to >10−6 S/cm over 5 min of electric field application before reaching the current limit of the experimental apparatus. Conductivity growth follows the same scaling relationship of the theoretical model that predicts the rotation and translation time of GNPs in a polymer melt as a function of electric field strength. Since no significant GNP alignment in the composite was observed under transmission electron microscopy (TEM), we hypothesized that the increase in electrical conductivity was due to local electrical treeing of the polymer matrix, which eventually leads to dielectric breakdown of the composite. Electrical treeing is likely initiated by local GNP agglomerates and propagated through conductive channels formed during progressive dielectric breakdown. [ABSTRACT FROM AUTHOR]

Due to the electrical, thermal, and mechanical stress, the insulating materials of cable undergo a slow aging process in service, which leads to the decline of insulation performance. Besides, friction frequently occurs when the cable is moving or vibrating, which will easily cause mechanical damage including frays and chafes. Both aging and damage will cause the characteristic impedance to change. Therefore, it is of great significance for the safe operation of the cable to analyze the variations of characteristic impedance and to make an effective diagnosis. In this article, a two-dimensional model of the cable containing defects is first built, and the characteristic impedance of the model is calculated by the finite-element method (FEM). Meanwhile, a quantitative analysis of the characteristic impedance under two defect types is carried out. Second, combining the space-time focusing of time-reversal and the time-frequency characteristics of reflectometry, the time-reversal time-frequency domain reflectometry (TRTFDR) is proposed to diagnose the cable faults. Based on the distributed parameters calculated by the FEM, the TRTFDR simulation model is established to study the judgment of different faults. Finally, the validity of this method is verified by experiments. [ABSTRACT FROM AUTHOR]

To fully understand the distribution network cable accessories’ moisture fault, the variation in insulation parameters of the cable main insulation of cross-linked polyethylene (XLPE) and the cable accessory reinforced insulation of silicone rubber (SIR) under different moisture conditions are studied experimentally. Furthermore, the effects of typical moisture defect forms and moisture positions on electric field distributions are studied by establishing the interface defect model. The experimental results show that the insulation properties of XLPE after water immersion are more seriously reduced than SIR. The resistivity of XLPE and SIR specimens decreases significantly with the increase in moisture time, decreasing by 90.3% and 48.3% after 720 h, respectively. The relative dielectric constants of the two kinds of specimens increase with different degrees after moisture, increasing by 5.16% and 7.83%, respectively, and the breakdown strength decreases by 18.3% and 13.1% after 720 h, respectively. The simulated results show that the moisture form and position have a great influence on electric field distribution. The electric field distortion caused by water trees’ defect is the most serious, followed by water film defects and water droplet defects. Besides, for different types of moisture defects, the position of the maximum distortion electric field is different. [ABSTRACT FROM AUTHOR]

To investigate the effect of the arrangement of glass fibres on the electrical dendrite growth of epoxy resin composite insulation materials. In this paper, specimens of glass fibre reinforced epoxy resin material were prepared, an experimental platform for electric tree discharge of the material under a pin-plate electrode was constructed, and experiments on the initiation and cultivation of electric dendrites were carried out under the working frequency voltage. The partial discharge phase distribution profiles collected by the partial discharge detector were recorded and the effect of glass fibre position on the electrical dendritic properties of the epoxy resin was investigated. When the applied electric field was parallel to the glass fibre, the expansion coefficient of the electric dendrite fluctuated around 1.4, the electric dendrite was mainly developed longitudinally and the growth shape was multi-branched linear growth; when the applied electric field was perpendicular to the glass fibre, the expansion coefficient of the electric dendrite fluctuated around 0.85, the electric dendrite was mainly developed laterally and the growth shape was agglomerative growth. When the electric field is applied perpendicular to the glass fibre, the expansion coefficient fluctuates around 0.85, the electric tree mainly develop horizontally and the growth pattern is agglomerative. The analysis suggests that when the applied electric field is parallel to the glass fibre, to release the discharge energy in the main channel of the dendrite, the discharge in the track of the electric tree will drive the electric tree to grow along the interface area between the glass fibre and the epoxy resin. When the externally applied electric field is perpendicular to the glass fibre, the discharge within the electric tree discharge channel is high. To release the energy in the electric tree channel, the blast in the electric tree track induces the electric tree branch to grow along the interface area and forward. [ABSTRACT FROM AUTHOR]

Polymer nanocomposites have been widely exploited in different engineering applications like high‐voltage engineering application. This is mainly associated with the ease at which they can be tailored toward specific applications. In the present work, alumina‐ and organoclay‐based nanofillers were separately incorporated in cross‐linked polyethylene (XLPE). Different formulations of the XLPE nanocomposites were fabricated with the help of an internal mixer after which they were molded to produce test specimens. The effect of nanofiller variation (0.25 and 0.5 wt% loading) on the electrical treeing phenomenon is reported herein. It was observed that the incorporation of 0.5 wt% alumina significantly enhances the tree inception voltage. In addition, compared to 0.25 wt% alumina‐, 0.25 and 0.5 wt% organoclay‐filled XLPE nanocomposites, 0.5 wt% alumina was found to lower the length and growth of the electrical tree, as well as the expansion coefficient of the XLPE nanocomposite. [ABSTRACT FROM AUTHOR]

In order to improve the aging resistance of epoxy resin insulation materials and the cost-effectiveness and reliability of power apparatuses, a novel silicone-modified aging-resistant epoxy resin insulation material was developed. The modification was achieved via chemical grating, using dihydroxydiphenylsilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane and dicyclohexylamine. Accelerated thermal aging test, accelerated hydrothermal aging test and electrical tree test were carried out to compare the aging resistance of the novel, existing silicone-modified epoxy resin and unmodified epoxy resin under high temperature, humid environment and strong electric fields. The results show that compared with the unmodified resin, the novel material has advantages in thermal, hydrothermal aging resistance and electrical tree resistance. More specifically, after modification, the dielectric strength of the novel material after thermal aging test was improved by 12%; its partial discharge inception voltage (PDIV) after hydrothermal aging test was increased by 19.4% and the growth rate of electrical trees was 12.68% of that in unmodified resin. Compared with the existing silicone-modified epoxy resin, the novel silicone-modified epoxy resin sacrifices part of the hydrothermal properties, but showed better thermal stability, and the growth rate of electrical trees in the novel silicone-modified epoxy resin was 44.26% of that in the existing resin. [ABSTRACT FROM AUTHOR]

In this paper, the packed bed dielectric barrier discharge (DBD) with needle-plate electrode configuration is presented to study the effects of electrical parameters, such as pulse duration and pulse rising and falling time, on discharge characteristics under air and nitrogen. The waveforms of the voltage and the discharge current, discharge evolution images, and the emission spectral of N2 (C3Пu → B3Пg) and N2+ (B2Σu+ → X2Σg+) are collected to investigate the discharge current, as well as the spatial distribution of the discharge modes and the reactive species in the packed bed reactor specifically. It is found that the pulse duration and pulse rising and falling time can regulate the discharge current. Firstly, increasing the pulse duration and the pulse rising and falling time can both increase the discharge duration. Secondly, the peak value of the discharge current has an obvious increasing trend with the pulse duration. Finally, the discharge start time can be delayed by increasing the pulse rising and falling time. A bright discharge channel is distributed at the top of the reactor, while the discharge is diffused at the bottom of the reactor. The generation of N2+ (B2Σu+) tends to depend on the existence of the streamer channel, and N2 (C3Пu) can be generated in the entire discharge area. In addition, the discharge operated in pure nitrogen can reach higher current values, a stronger discharge intensity, and longer existence time for the reactive species than in the air. [ABSTRACT FROM AUTHOR]