Performance Of Composite Insulators Research Articles

Temperature effects on the sheath-core bar interface of composite insulators: a molecular dynamics and DFT study

The functioning condition of composite insulators is greatly influenced by the sheath-mandrel interface. In this work, the effects of temperature on the sheath-mandrel system are examined using molecular modeling, taking into account both density functional theory (DFT) and molecular dynamics (MD). The system’s interfacial free volume, HOMO/LUMO, number of hydrogen bonds, bond order, center-of-mass distance, and other characteristics define its degradation mechanism. The findings demonstrate that elevated temperatures have the potential to increase the interfacial free volume, the center-of-mass distance, and significantly reduce the number of hydrogen bonds. In addition, DFT simulations show that the bonding strength and non-bonding forces between the interfaces weaken with increasing temperature. High temperatures significantly boost the reactivity of the epoxy resin and silicone rubber chains, indicating that the system’s response with some intruders will be catalyzed by the temperature increase. This work looks at the temperature dependence of the sheath-core bar interface degradation from a microscopic perspective, which is important for enhancing the overall performance of composite insulators.

Simultaneous enhancement of thermal and dielectric properties of Ba0.8Sr0.2TiO3 and h‐BN co‐doped epoxy hybrid composites under high frequencies and temperatures

AbstractEpoxy resin (EP) is widely employed in power systems and electronic devices due to its low cost and easy processing along with good insulative and adhesive properties. However, EP insulation properties are compromised at elevated frequencies and temperatures because of its negative temperature coefficient effect (NTC) and poor thermal characteristics. In this context, barium strontium titanate (BST‐60), a positive temperature coefficient (PTC) filler, and hexagonal boron nitride (h‐BN), a thermally conductive filler, both surface‐modified with dopamine, are added in EP to simultaneously improve thermal and dielectric insulation properties at high temperatures and high frequencies. This study finds that below the Curie point of BST, the insulating properties of h‐BN fillers significantly contributes to improving insulation properties. Conversely, above the Curie point, the insulating nature of BST fillers leads to an improvement in the insulation performance of composites. Furthermore, at elevated frequency and temperature, the nano h‐BN enhances thermal conductivity of EP by establishing a thermally conductive network, while micro‐BST suppresses the NTC effect of EP by regulating electrical resistivity above the Curie point. The Heywang model elucidates the PTC effect of BST fillers, while a proposed heat conduction‐dissipation mechanism explains the behavior of incorporated fillers at different temperatures.Highlights PDA‐modified Ba0.8Sr0.2TiO3 and h‐BN co‐doped epoxy composites are prepared. Negative temperature coefficient effect of epoxy is mitigated by PTC fillers. The optimal wt.% of filler enhances both dielectric and thermal properties. Dielectric properties are explored at high frequencies and temperatures. Optimized epoxy composites are suitable for high‐frequency applications.

Study on material and mechanical characteristics of silicone rubber shed of field-aged 110 kV composite insulators

Composite insulators have excellent performance and are more and more widely used in power grid. The performance of composite insulators with different service duration will decline in varying degrees, which could pose a threat to the safe operation of power grid. In order to investigate the influence of service duration and electric field strength on insulator shed performance, the sheds at different positions of insulators with different service duration are sampled. The hydrophobicity, material and mechanical properties of the samples are tested, and then the micro material properties tests are performed in terms of SEM, FTIR and XPS tests. Based on the above test results, the aging law and its mechanism of silicone rubber sheds are analyzed. The results reveal that the performance of insulator shed gradually decline with the increase of service life. The hydrophobicity and hardness of high-voltage end insulator are similar to that of middle section insulator, while other parameters are obviously different, indicating that the electric field can aggravate the aging. FTIR results show that the main chain and hydrophobic side chain of silicone rubber are destroyed, and the oxygen-containing groups increased, indicating that thermal oxygen aging occurred during operation. XPS and SEM results show that the crosslinking degree of silicone rubber increases and the porosity increases. The above changes in the microstructure of silicone rubber lead to the decline of insulator performance.

Flexible fabrication of a novel SiO2/AF/ZIF-L composite embedded with MOF structure and its thermal insulation properties

ZIF-L, a metal-organic framework (MOF) material, has a two-dimensional (2D) foliation, a large specific surface area, excellent thermal stability and CO2 adsorption performance, respectively. In this work, in order to further improve the thermal insulation performance of SiO2 aerogel composite fabrics, ZIF-L powder was first prepared as a reinforcing particle, and then added to silica aerogel. Finally, SiO2/AF/ZIF-L composites were obtained by solution impregnation method. The influence of different ZIF-L concentrations on the insulation performance of composites and their influencing factors were studied. Furthermore, these composites were fully characterized using BET measurement, Instron 5967, precision transient thermal performance tester, infrared thermal imager, insulation performance test, thermogravimetric analyzer, and dynamic thermomechanical analyzer. The results showed that 0.12% SiO2/AF/ZIF-L composites had excellent thermal insulation performance, with a thermal conductivity as low as 0.029 W/(m·K). In addition, SiO2/AF/ZIF-L composites fabricated by atmospheric drying method had the best thermal insulation performance under the conditions of gel time of 24 h, hydrolysis time of 5 h, and polycondensation pH value of 5–6.

Influence of water penetration on glass fiber-epoxy resin interface under electric field: A DFT and molecular dynamics study

Water penetration is a primary cause of composite insulator core rod deterioration. The performance of the glass fiber-epoxy resin (GFEP) interface plays a crucial role in determining the overall performance of the core rod, and the interface is also affected by an electric field. In this study, molecular dynamics (MD) simulation, reactive force field (ReaxFF), and density functional theory (DFT) simulation techniques were employed to analyze the changes in various parameters, including interface binding energy, free volume, Mayer Bond Order (MBO), hydrogen bond number and distribution, chemical groups, radial distribution function (RDF), and others. The influence of the electric field on these parameters was investigated based on the operational conditions. The results showed that the electric field yielded little effect on the dry GFEP model. However, in the presence of water penetration, the system exhibited a “swelling-collapse” phenomenon under the electric field, and the free volume will increase with the increase of the electric field strength. Analysis of hydrogen bond number, water molecule dipole moment, and water molecule RDF indicated that the electric field could induce the polarization of water molecules, causing their migration towards the epoxy resin ester groups and glass fiber, and form hydrogen bond interaction with them respectively. Consequently, the effective hydrogen bond between the glass fiber and epoxy resin decreased. Additionally, DFT simulation showed that the electric field altered the energy of frontier molecular orbitals, promoting the decrease in the MBO of the epoxy resin ester group C-O bond and water molecule O–H bond, thereby increasing the chemical reactivity between the epoxy resin and water molecules, and facilitated the hydrolysis of the glass fiber and epoxy resin. The synergistic effects of these processes ultimately led to interface failure. This research sheds light on the effects of water penetration on the interface between glass fiber and epoxy resin under the influence of an electric field, which is important for improving the overall performance of composite insulators.

Design and Implementation of Transmission Line Insulator Online Monitoring Platform Based on Image Analysis

The safe operation of insulators directly determines the safety level and reliability of the entire system. In this paper, digital image processing technology is used to analyze and process insulator images, and the performance of composite insulators is comprehensively evaluated from three aspects: degree of deterioration, surface pollution, and degree of water repellency, which is used as the basis for judging insulator detection. For this purpose, an insulator online monitoring system based on telemetry image analysis is specially designed to determine the degree of aging, surface pollution, and hydrophobicity of insulators and to conduct practical tests. At the same time, the system can realize the offline operation of the insulator live, avoid the danger of climbing and live trial operation, and ensure the personal safety of power maintenance personnel. The system hardware uses advanced integration technology and high-performance and reliable equipment. The software is developed using popular development tools, is simple to operate, and has important engineering value.

Enhanced dielectric and mechanical properties of CaCu3Ti4O12/Ti3C2Tx MXene/silicone rubber ternary composites

Dielectric polymer composites with conducting fillers would have great potential for diverse applications if their severe leakage loss could be addressed. In this regard, ternary composites using both ceramic and conducting materials as fillers might be an enabler for high dielectric constant and low dielectric loss. Herein, ternary composites with both Ti3C2Tx MXene conducting nanosheets and CaCu3Ti4O12 (CCTO) dielectric particles embedded in silicone rubber were studied. It was found that a ternary composite with 1.2 wt% (0.40 vol%) Ti3C2Tx MXene and 12 wt% (2.58 vol%) CCTO could provide an overall superior performance that include a high dielectric constant of 8.8, low dielectric loss of less than 0.0015, good thermal stability up to 450 °C, and excellent mechanical properties with tensile strength of 569 kPa, elastic module of 523 kPa and elongation at break of 333%. The outstanding performance is attributed to the improved uniform dispersion and good interfacial compatibility of mixed fillers in the polymer matrix, suggesting ternary composites might be a better option over their binary counterparts in preparing high performance dielectric composites.

Fabrication of sandwich-structured PPy/MoS2/PPy nanosheets for polymer composites with high dielectric constant, low loss and high breakdown strength

Polymer-based dielectric nanocomposites with high dielectric constant and low loss have been widely used for energy storage applications in power electronics and power delivery systems. However, there are still changes in preparing polymer-based dielectric nanocomposites with the suppressed loss (tan δ) and maintain breakdown strength (Eb) through simple compound method. In this work, a simple approach to fabricate outstanding comprehensive performance dielectric composites was proposed by cooperating molybdenum disulfide-polypyrrole (MoS2-PPy) hybrids with polyvinylidene Fluoride (PVDF). The MoS2-PPy hybrids were prepared by in situ polymerization of pyrrole with exfoliated MoS2 nanosheets, showing a “sandwich-like” structure of PPy/MoS2/PPy. MoS2-PPy hybrids significantly influenced the dielectric properties of their composites. As result, PVDF/MoS2-PPy composites achieved high dielectric constant (149.5@1 kHz), suppressed dielectric loss (0.19@1 kHz) and high breakdown strength (250.6 MV m−1). The emphasized reasons of high dielectric property are the enhanced interfacial polarization and formation of nano- and micro-capacitor networks. This work could provide an effective method to design and improve the performance of polymer-based dielectric nanocomposites for power system and energy storage applications.

Enhanced dielectric properties of sandwich‐structured biaxially oriented polypropylene by grafting hyper‐branched aromatic polyamide as surface layers

AbstractThis work represents multilayer films with sandwich structure by grafting hyper‐branched aromatic polyamide (HBP) on both sides of biaxially oriented polypropylene (BOPP) (HBPBOPPHBP). BOPP serves as the middle layer to offer high breakdown strength and HBP acts as surface layers to boost the dielectric constant. As a result, the dielectric constant increases significantly from 2.2 of control BOPP to 5.5 (almost increased 1.5 times) after grafting 2.06 μm HBP surface layers, while the dielectric loss still remains at a very low level (<0.03). In addition, all HBPBOPPHBP sandwich‐structured films show higher charge energy density than that of unmodified BOPP. For instance, the discharge energy density of HBPBOPPHBP (1‐20‐1) film is up to 2.38 J/cm3 at an applied electric field of 400 kV/mm, which increases about 36% over that of pure BOPP (i.e., 1.75 J/cm3). Meanwhile, charge–discharge efficiency retains about 90%. This work offers a simple strategy to fabricate polymer‐based high performance dielectric composites.

Global experience of HVDC composite insulators in outdoor and indoor environment

Abstract High-voltage direct current (HVDC) transmission is known as green-energy transfer technology and has recently become an attractive alternative of high-voltage alternating current (HVAC) due to its high-power transmission capability and lower power loss. Use of composite insulators on direct current (DC) transmission lines experienced rapid growth in recent years due to their high hydrophobicity and better performance in contaminated environment than conventional ceramic insulators. During their service operation on DC lines, insulators are prone to more accumulation of contaminants due to unidirectional electric field. The contaminants under wet conditions allow leakage current to flow on the insulator surface. Being organic in nature, polymeric insulators have a tendency to age under the combined effects of electrical and environmental stresses. To fully understand the long-term aging performance of DC composite insulators, a detailed survey was considered necessary. Towards that end, this paper critically summarizes worldwide experience of aging performance of composite insulators in the field as well as in laboratory conditions.

Performance of Composite Insulators Used for Electric Transmission under Extreme Climatic Conditions

Composite or polymeric insulators are being used in various parts of the world for high-voltage transmission and distribution lines. In some parts of India, places in the states like Rajasthan and Gujarat experience an increase in the daytime temperature up to 50 degrees C, while the nighttime temperature reduces as low as 3-5 degrees C. Because of these extreme temperature variations along with electric stress and humidity conditions, composite insulators have to perform well over their lifetime to ensure the reliability of the transmission network. In the present work, experimental conditions are simulated with temperature variation from 50 to 3-5 degrees C along with electrical stress, humidity variation, pollution, and ultraviolet radiations. Accelerated aging studies with these stresses are conducted to understand the degradation on the insulator similar to the field conditions. Surface resistivity measurements, leakage current analysis, and surface degradation studies using thermogravimetric analysis, scanning electron microscopy, energy-dispersive x-ray, and Fourier transform infrared spectroscopy (FTIR) are conducted. Some interesting results obtained from the study are presented. Experimentation under extreme conditions with polluted insulators showed considerable degradation which was inferred from the material testing analysis. The insulator slabs on which electrical stress was not applied showed a considerable peak at 1500 cm(-1) in the FTIR spectra, indicating the generation of low molecular weight PDMS chains from the bulk due to UV aging and thermal stress, while the degradation pattern of non-polluted sample was severe compared to the slab treated but was considerably less severe in comparison with the polluted insulator sample exhibiting pollution can considerably increase degradation rate.

The frequency independent functionalized MoS2 nanosheet/poly(arylene ether nitrile) composites with improved dielectric and thermal properties via mussel inspired surface chemistry

To obtain high performance dielectric composites, novel functionalized MoS2 nanosheet/poly(arylene ether nitrile) (PEN) nanocomposite films were demonstrated. For this purpose, the MoS2 nanosheets prepared by hydrothermal method were modified via mussel inspired co-modification and crosslinking of polydopamine (PDA) and polyethylenimine (PEI), followed by incorporating into the PEN matrix to form the MoS2@(PDA + PEI)/PEN nanocomposite films through a simple solution casting method. The surface modification of MoS2 nanosheet was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). The effect of functionalized MoS2 mass fraction on the performance of PEN composites was also detailed investigated. Owing to the well interfacial compatibility between MoS2 nanosheet and PEN matrix, the resulting PEN nanocomposite film with 10 wt% MoS2@(PDA + PEI) exhibited excellent comprehensive performance, including high dielectric constant of 8.3, low dielectric loss of 0.02 at 1 kHz and outstanding frequency stable. Moreover, it also showed excellent thermal stability (T5% > 490 °C) and mechanical properties that the tensile strength and modulus reached 120.3 MPa and 2468.2 MPa, respectively. Such remarkable performance may be suitable for dielectric applications in special demand. Our study provides a new strategy to obtain high-performance dielectric materials.

Improved Current Sensor for Water Diffusion Testing of Composite Insulators.

An improved current sensor aimed at measuring currents of different parts in composite insulator samples was proposed. Conventional current sensors used in water diffusion tests aim to examine the performance of composite insulators, however, it is difficult for the conventional current sensors to locate the defects. Thus, we designed a new electrode structure to measure the currents of different components in short samples of composite insulators. Based on a finite analysis method, the influence of relative permittivity and conductivity on the current was analyzed. New samples with different interfaces and samples after operation were tested using the new and conventional current sensors. The performance of a certain part in short samples can be diagnosed by analyzing the current and phase information extracted from the test results. By comparing the test results of new and traditional current sensors, it was proved that the new electrode structure is more effective in locating the defects of insulators.

Nickel hydroxide as novel filler for high energy density dielectric polymer composites

The preparation of high performance dielectric polymer composites often involves methods which are quite difficult to be used for large scale application due to their complexity. To tackle this, current study demonstrates a novel type of dielectric filler for the preparation of high performance dielectric composites: Ni(OH)2. Due to the abundant OH groups on their filler surface, hydrogen bond is observed between Ni(OH)2 and PVDF matrix, and beta form crystal of PVDF is induced. Among 0D, 2D and 3D Ni(OH)2, the platelet 2D Ni(OH)2/PVDF composite illustrates the highest dielectric constant (16.3), breakdown strength (421 kV/mm) and energy density (17.3 J/m3) with as little as 5 wt% (3.02 vol%) Ni(OH)2 in PVDF matrix. Such value is rather large comparing with many literature results. More importantly, this method does not involve any filler surface modification. Moreover, finite element simulations indicate that the distribution of electric field and energy density for composites containing platelet like Ni(OH)2 is more uniform than the rest, which should be the mechanism for enhanced dielectric performances. This provides a novel type of filler for the preparation of high performance dielectric polymer composites.

The effect of multilayered film structure on the dielectric properties of composites films based on P(VDF-HFP)/Ni(OH)2

High dielectric constant ceramics fillers are widely used as fillers in polymer matrix to prepare high performance dielectric composites. Homogeneous filler distribution in these composites films is found to be quite difficult to achieve balance between high dielectric constant and high breakdown strength. Herein, multilayer structured composites films containing nickelous hydroxide (Ni(OH)2) as fillers, with different multilayered structures were designed and prepared, including 2–5 layers structure with various filler distribution. The effects of multilayer structure on the dielectric performance are explored by keeping the overall filler content constant. Combined with computer simulation, it is suggested that the variation in filler distribution in these films can effectively redistribute electric field intensity. Meanwhile, the dielectric constant and breakdown strength of the overall composites can be adjusted by changing the volume ratio between high filler content layer and low filler content layer. It is noted that at least 1/3 of the overall film volume should be occupied by a high breakdown strength layer to keep rather high overall breakdown strength. Moreover, high dielectric constant layer should be the outer layers to achieve overall high dielectric constant. Among all the layered structures investigated, the maximum energy density of 6.03 J/cm3 is obtained for film with a 3-layer nonsequential arrangement structure, which is 68% higher than single layer film with identical composition. This study provides some reference value for the preparation of multilayered dielectric polymer composites films for energy storage applications.

Enhanced performance of P(VDF-HFP) composites using two-dimensional BaTiO3 platelets and graphene hybrids

Carbon nano-materials e.g. graphene are widely utilized to prepare high-к dielectrics due to their low percolation threshold. However, composites incorporated with conductive carbon nano-materials usually suffer from high dielectric loss. In this work, a strategy is proposed to suppress the dielectric loss of graphene/P(VDF-HFP) composites using two-dimensional BaTiO3 platelets. Large interfacial region is formed in the composites due to the hybrid fillers, which results with enhanced interfacial polarization. The BaTiO3 platelets are aligned in the perpendicular direction to the surface of the composite film after the treatment of tape casting. These aligned BaTiO3 platelets act as isolation belts to block the electron transportation path. In these contributions, composite with a high permittivity of 66.2 and suppressed dielectric loss of 0.048 are simultaneously obtained. This work provide a feasible route to prepare high performance dielectric composites.

Polyaniline coated cellulose fiber / polyvinyl alcohol composites with high dielectric permittivity and low percolation threshold

Cost effective, high performance dielectric composites based on polyvinyl alcohol, cellulose fibers and polyaniline were prepared and the dielectric properties were studied as a function of fiber content, fiber dimensions and polyaniline content over a frequency range of 40 Hz to 30 MHz. The short cellulose fibers were size-reduced to micro and nano levels prior to coating with polyaniline. Fiber surface was coated with Polyaniline (PANI) by an in situ polymerization technique in aqueous medium. The composites were then prepared by solution casting method. Short cellulose fiber composites showed a dielectric constant (DEC) of 2.3 x 105 at 40 Hz. For the micro- and nano- cellulose fiber composites the DEC was increased to 4.5 x 105 and 1.3 x 108, respectively. To gain insight into the inflection point of the dielectric data polynomial regression analysis was carried out. The loss tangent of all the composites remained at less than 1.5. Further, AC conductivity, real and imaginary electric moduli of all the composites were evaluated. PVA nanocomposite attained an AC conductivity of 3 S/m. These showed that by controlling the size of the fiber used, it was possible to tune the permittivity and dielectric loss to desired values over a wide range. These novel nanocomposites, combining high dielectric constant and low dielectric loss, can be effectively used in applications such as high-charge storage capacitors.

Graphene encapsulated rubber latex composites with high dielectric constant, low dielectric loss and low percolation threshold

A dielectric composite with high dielectric constant, low dielectric loss and low percolation threshold was prepared by using the combined strategy of encapsulating of graphene oxide nanosheets (GONS) on carboxylated nitrile rubber (XNBR) latex particles and the in situ thermal reduction in GONS at a moderate temperature. The encapsulation of GONS on XNBR latex particles was mainly realized via the hydrogen bonding interactions between GONS and XNBR during latex mixing. A segregated graphene network was obtained at a low content of thermally reduced graphene (TRG), resulting in a low percolation threshold (0.25vol.%). The dielectric constant at 100Hz obviously increased from 23 for pure XNBR to 2211 and 5542 for the composite with 0.5vol.% and 0.75vol.% of TRG, respectively. The dielectric loss of the composites retained at a low value (less than 1.5). Meanwhile, the elastic modulus only slightly increased with the presence of 0.1–0.5vol.% of TRG, keeping the good flexibility of the dielectric composites. This study provides a simple, low-cost and effective method to prepare high performance dielectric composites, facilitating the wide application of dielectric materials.

Preparation and Properties of Aluminum Silicate Fiber Mat Impregnated Silica Sol

Aluminum silicate/SiO2 sol composites are prepared by aluminum silicate fiber mats impregnated with different amount of silica sol. The effect of different impregnation process on impregnation amount of composites are compared, Thermal insulation performance and compression strength of composites are tested in this paper. The results show that: Samples prepared by vacuum impregnation process can get its highest impregnant amount, compressive strength of composites could achieve 241KPa.Thermal insulation performance of composites would be a liitle worse than aluminum silicate fiber products

Study on Properties and Application of PG/CS Composite PCMs

Tris (hydroxymethyl) ethane (PG) as a phase change material, micro-porous xonotlite (CS) as matrix, PG/CS composite PCMs were prepared by melt-soaking method, and the effect of micro-porous structure of xonotlite on heat absorption capacity, bending strength and insulation performance of composites, and the exudation of PG was studied. Otherwise, for the work environment and characteristics of propulsive device of vehicle, this paper explored the feasibility that phase change materials (PCMs) worked as the insulation material in short-time insulation system of the vehicle. Experimental results show that, when the most probable pore diameters of xonotlite was not less than 63nm, the composites presented better and almost same absorption capacities of matrix (CS) to PCM (PG) in different composites; when up to 85nm, the composite exhibited the lowest leakage rate (less than 5%), the optimal mechanical property and thermal insulation performance. This Study proposed a new idea for the design of the insulation material in the thermal protection system of propulsive device of vehicle.