Electrical Tree Research Articles

New Diagnosis Method for Space Charge-Dependent Interfacial Electrical Tree in Packaging Insulation Using Current Integrated Charge Measurement

New Diagnosis Method for Space Charge-Dependent Interfacial Electrical Tree in Packaging Insulation Using Current Integrated Charge Measurement

Quantitative Analysis of Electrical Tree Growth with Partial Discharge Characteristics of PCB Double Layer under AC Voltage

Quantitative Analysis of Electrical Tree Growth with Partial Discharge Characteristics of PCB Double Layer under AC Voltage

Electrical Tree Growth in Fiber Reinforced Epoxy Composites for GIS Insulation Rod

Electrical Tree Growth in Fiber Reinforced Epoxy Composites for GIS Insulation Rod

Исследование влияния магнитного поля на характеристики частичных разрядов

The paper is devoted to the study of the dependences of the characteristics of partial discharges on magnetic induction. The design of the experimental setup has been developed. It allows applying both high voltage and current comparable to the operating one. The setup includes a high voltage source (dielectric tester), a current flow circuit, a high voltage current transformer and a sample of XLPE insulated cable. The operation of the electrical circuit of the experimental setup is simulated using software. The modeling has shown that if the operational electrical strength of the current transformer insulation is present, the high-voltage potential cannot contact the current flow circuit. After this, modeling of the magnetic field inside the insulating layer is carried out. Based on the developed design, an experimental setup is created. To record partial discharges, an artificial defect is created in a cable sample. The results of magnetic field modeling made it possible to estimate the magnetic induction in the field of an artificial cable defect. Next, experimental studies are carried out to assess the influence of the magnetic field of the cable core current on the characteristics of partial discharges. The measurement results have showed a decrease in the average apparent charge of partial discharges and partial discharge power with increasing current. In addition, waveforms are compared, but no significant differences are found. The magnetic field of the current may influence the PD performance in the long term due to its possible influence on the direction of growth of the electrical tree structure.

Partial Discharge Activity During Electrical Tree Growth in Epoxy and its Nanocomposites

Partial Discharge Activity During Electrical Tree Growth in Epoxy and its Nanocomposites

Effect of Bending Deformation on Electrical Tree Properties of Polypropylene Copolymer and Blend Insulation for HVDC Cables

Effect of Bending Deformation on Electrical Tree Properties of Polypropylene Copolymer and Blend Insulation for HVDC Cables

Electrical Tree Characterization in Silicone Rubber Under Different Numbers of Lightning Impulse Shot

Electrical Tree Characterization in Silicone Rubber Under Different Numbers of Lightning Impulse Shot

Electrical tree properties and mechanism of modified aramid/epoxy composites

Electrical tree properties and mechanism of modified aramid/epoxy composites

Effect of nucleating agents on the electrical properties of cross‐linked polyethylene under tensile stress

AbstractDuring the operation of high‐voltage cables, external stress and residual stress can affect the aggregated structure of insulating materials and lead to significant deterioration in their electrical performance. To investigate the evolution characteristics of the electrical properties of cross‐linked polyethylene (XLPE) under mechanical stress, this paper explains the relationship between the aggregated structure of XLPE and its electrical properties and proposes a method for improving insulation performance under mechanical stress. The results show that metallocene polyethylene used as a nucleating agent can promote crystallisation through heterogeneous nucleation and increase Young's modulus by non‐uniform nucleation, increasing crystallinity and reducing interplanar spacing, resulting in more complete crystal forms and reduced damage to the aggregated structure during the tensile process. After nucleating agent modification, the XLPE crystallisation becomes more uniform, and interfacial adhesion forces increase. The weakened interface damage process between the amorphous and crystalline regions under tensile stress effectively inhibits the process of molecular chain polarisation turning and reduces trap density. The modified XLPE crystal structure shows a tendency towards densification and enhanced molecular chain interactions, which can reduce the damage to the aggregated structure under tensile stress, while the reduced free volume inside the material and the shortened average free path of carriers can weaken the damage of high‐energy electrons to molecular chains, thereby inhibiting the process of electrical tree degradation. The results show that nucleating agents have great potential for maintaining the stable operation of XLPE cables under mechanical stress.

Research on the Growth Characteristics of the Electrical Tree at Polyethylene/Silicone Rubber Composite Interface Under Power Frequency Voltage

During operation, the composite interface of the cable joint will experience a tangential electric field. When the composite interface has insulation defects, it is easy to experience interface discharge. Electrical tree is a phenomenon of electrical degradation and it’s a precursor of polymer breakdown. It is observed in the laboratory that under the power frequency voltage, the electrical tree will initiate at the composite interface, and the tree growth will finally lead to the interface breakdown. This paper investigates the development of an electrical tree at the composite interface of polyethylene/silicone rubber under power frequency voltage through microscopic observation. The results show that the air gap of the interface is the weak position of insulation, and the electrical tree will be initiated from the triple junction of the air gap and the impacted area of the two materials. The increase in voltage amplitude will speed up the initiation. High amplitudes also promote the electrical tree. The electrical tree shape will be changed from a branch structure at low voltage to a single branch structure at high voltage. The study on the electrical tree at the interface provides a visual display of the degradation process of the material before the breakdown at the composite interface.

Nanosize Filler Effect on Propagation of Electron Avalanche in Terms of Waveform Characteristics of Partial Discharge

Nanocomposite materials have excellent insulating properties, such as improved treeing resistance. The propagation properties of electrical trees are often determined using optical observations and partial discharge (PD) characteristics regarding phase angle distribution patterns. There is a limit to confirming the effects of physical barriers on the PD by optical observation alone. Conversely, there is a high possibility that the PD waveform reflects the characteristics of the electron avalanche in the discharge space. In this study, we constructed a PD measurement system with the widest possible frequency range and acquired 1000 PD waveforms along the time series. Although the acquired waveforms have a single peak or multiple peaks, adding nano-fillers increased the observation ratio of the waveform with multiple peaks. Furthermore, the multiple peaks suggested that the electron avalanche progresses with difficulty considering that the nano-fillers easily captures electrons. We investigated the effect of adding nano-fillers from the viewpoint of the waveform characteristics. The time difference between the peaks and the peak ratio is also supported by the property changes in the electron avalanche because of the electron capture by nano-fillers.

Electrical Tree Initiation Prediction in Thermally Aged DC XLPE for Cable Insulation

Electrical Tree Initiation Prediction in Thermally Aged DC XLPE for Cable Insulation

Investigations of the Electrical Tree Growth at Different Voltages and Frequencies

Investigations of the Electrical Tree Growth at Different Voltages and Frequencies

Antiferroelectric nano-heterostructures filler for improving energy storage performance of PVDF-based composite films

Incorporating high permittivity inorganic ferroelectric in polymer dielectrics is the most prevalent and straightforward approach to improve their energy storage capacity, which has an extensive application prospect in power electronic circuits owing to their higher power density. However, the discharged energy density attained with these materials are mainly restrained by the high remnant electric displacement of ferroelectric and the large discrepancy in permittivity between inorganic and organic substance. Herein, we proposed a novel antiferroelectric (Pb0.875La0.05Sr0.05)(Zr0.595Sn0.4Ti0.005)O3@Al2O3 (PLSZST@AO) nano-heterostructure as fillers to fabricate nanocomposite films, wherein the Al2O3 layer with wide band gap and dielectric constant close to that of the PVDF matrix was encapsulated onto the antiferroelectric nanoparticle PLSZST to alleviate the discrepancy in permittivity and enhance the breakdown strength. Especially, the experimental results and computational simulations confirmed that the presence of Al2O3 layer is capable of effectively enhancing the electric displacement and breakdown strength, while reducing the remnant displacement and impeding the formation of electrical trees. As a result, the nanocomposite films exhibited an impressive discharged energy density of 18.2 J/cm3 along with a remarkably enhanced energy storage efficiency of 70 % near the high electrical breakdown strength of 594.7 MV/m when the fillers content was 3 wt%, which was far surpassed the pristine PVDF (Ud = 5.34 J/cm3 and η = 51.8 %). Together with its excellent mechanical strength, the monolayer film was verified to be an outstanding performance dielectric material, outperforming the current PVDF-based composite dielectrics for high-power energy storage capacitors. This work allowed for more versatility in designing and manufacturing flexibility nanocomposite films, which can contribute to improving their performance and practicality.

Modeling EV Charging Station Loads Considering On-Road Wireless Charging Capabilities

Electric vehicle (EV) customers are expected to charge EV batteries at a rapid EV charging station or via on-road wireless EV charging systems when possible, as per their charging needs to successfully complete any remaining trips and reach their destination. When on-road wireless EV charging systems are considered as an alternative charging method for EVs, this can affect the load of a rapid EV charging station in terms of time and magnitude. Hence, this paper presents a probabilistic framework for estimating the arrival rate of EVs at an EV rapid charging station, considering the availability of on-road wireless charging systems as an alternative charging method. The proposed model incorporates an Electric Vehicle Decision Tree that predicts the times when EVs require rapid charging based on realistic transportation data. A Monte Carlo simulation approach is used to capture uncertainties in EV user decisions regarding charging types. A queuing model is then developed to estimate the charging load for multiple EVs at the charging station, with and without the consideration of on-road EV wireless charging systems. A case study and simulation results considering a 32-bus distribution system and the US National Household Travel Survey (NHTS) data are presented and discussed to demonstrate the impact of on-road wireless EV charging on the loads of an rapid EV charging station. It is observed that having on-road wireless EV charging as complementary charging to EV charging stations helps to significantly reduce the peak load of the charging station, which improves the power system capacity and defers the need for system upgrades.

Modulating polarization and carrier migration characteristics via constructing sandwich-structured heterojunction interfaces for achieving excellent high-temperature energy storage properties in polymer nanocomposites

Dielectric polymer nanocomposites are ideal choices for electrostatic energy storage due to their high power density and reliability, but they cannot operate efficiently at high temperature. To solve this issue, herein, we designed and developed sandwich-structured montmorillonite (MMT)/polyetherimide (PEI)-(Pb,La)(Zr,Sn,Ti)O3 (PLZST) antiferroelectrics (AFEs)@dopamine (DA)-MMT/PEI nanocomposites. On one hand, compared to current wide-band gap fillers, i.e., TiO2, Al2O3, ZrO2, and MgO, two-dimensional MMT nanosheets possess unique electrically insulating performances along the thickness direction, and thus can effectively stop charges injecting and migrating, causing low conduction loss, and large breakdown strength (Eb). On the other hand, PLZST AFEs with orthorhombic structure can exhibit high maximum electric displacement (Dmax) and small remnant electric displacement (Dr) at high temperature, which is beneficial for achieving large Dmax-Dr in the nanocomposites. In addition, large dielectric constant differences between MMT/PEI and PLZST@DA/PEI layers can inhibit electrical tree growth, resulting in further raised Eb. Finite element simulations on electrical tree evolving confirm experimental breakdown results. The sandwich-structured nanocomposite displays impressive high-temperature (150 °C) capacitive performances possessing meanwhile a high Eb of 5265.9 kV/cm, large discharged energy density (Ue) of 7.1 J/cm3, being about 6 times that of the commercial biaxially oriented polypropylene, and large charge-discharge efficiency (η) of 81.6 %, which exceeds obviously latest polymer and polymer composites in terms of overall energy storage performances. More encouragingly, it displays an ultrahigh power density of 15.63 MW/cm3 and ultrafast discharge rate of 19.2 ns at 150 °C, indicate its excellent application potential in high-temperature pulse power systems.

Improved energy density and efficiency of polymer nanocomposites by filling ultralow amounts of 2D Ni(OH)2 nanosheets and building sandwich structure

Currently, the application of polymer dielectric capacitors is largely limited by their low energy storage density. Herein, novel sandwich-structured composite films with simultaneously enhanced energy storage density and efficiency are fabricated, which combine outer layers of inorganic nanosheets Ni(OH)2/poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) with high permittivity and intermediate layer of polycarbonate (PC) with high breakdown strength. The trilayer film with only 1 vol% Ni(OH)2 exhibits an excellent energy storage density of 7.322 J/cm3 accompanied with a high efficiency of 72.1 % at 605 kV/mm, which are 120 % and 113 % of pure P(VDF-HFP). Furthermore, hindrance effect of micro-interfaces and macroscopical-interfaces on electrical trees is well revealed through finite element simulation. These excellent characteristics of composite films suggest that this design strategy is effective to realize concurrent high energy density and efficiency.

Phase field study on electrical treeing under combined AC/DC voltage based on bipolar barrier transfer model

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.

Electrical tree modelling in dielectric polymers using a phase-field regularized cohesive zone model

Electrical treeing is a leading cause to the eventual breakdown of dielectric polymers under high voltages. This paper presents a simulation scheme developed based on the phase-field regularized cohesive zone model (PF-CZM) for electrical tree modelling. By using the electrical analog of the crack propagation, the localized breakdown is modelled by the evolution of surface energy, and the electrical treeing is driven by the competition between the surface energy and the stored energy following the laws of thermodynamics. The microscopic Weibull distribution of the dielectric breakdown strength is the key factor resulting in the fractal structures of the electrical tree. The model developed is mesh independent and length-scale insensitive when the mesh size is no greater than 2.5μm. The validity of the model was confirmed through experiments, which strengthens its credibility. Three types of composites are designed and compared. The results indicate that the epoxy resin enhanced with 5 vol% silica and 1 vol% graphene sheet has a 3.5 % longer dielectric breakdown time and a 29.2 % higher thermal conductivity than the pure epoxy resin. Overall, the model provides a valuable tool for understanding the physics of electrical treeing and designing new dielectric materials with high withstand voltages.

Electric tree intrinsic self-healing epoxy insulating materials based on disulfide bond

Epoxy resin is one of the most commonly used insulating materials for electricians. Nevertheless, the emergence of localized damage or subtle microcracks within the material poses a formidable challenge in terms of detection and subsequent repair. The safe operation of power equipment is seriously jeopardized. In this study, driven by the need for self-healing insulating materials in power equipment applications, the successful synthesis of high-performance epoxy insulating materials featuring varying disulfide bond contents was achieved. Mechanical properties such as tensile strength and elongation at the break of epoxy insulations are enhanced by small amounts of disulfide bond. While an elevated content of disulfide bond diminishes the heat resistance and electrical characteristics of epoxy insulating materials, it is noteworthy that the prerequisites of epoxy resins for electrical applications remain adequately fulfilled. The results of the mechanical damage Self-healing test showed that the optimal repair efficiency reached 81.23 %. Simultaneously, the differentiation of electric tree branches can be inhibited by a disulfide bond. The diminishment of electric tree damage extent within epoxy resin is optimized, and the impairments of electric trees are repaired. Grounded in a disulfide bond, the viability of utilizing self-healing epoxy resins as insulating materials for electrical equipment is substantiated in this paper.