Electrical Insulation Materials Research Articles

A Review of Polyolefin-Insulation Materials in High Voltage Transmission; From Electronic Structures to Final Products.

This review focuses on the use of polyolefins in high-voltage direct-current (HVDC) cables and capacitors. A short description of the latest evolution and current use in HVDC cables and capacitors is first provided, followed by the basics of electric insulation and capacitor functions. Methods to determine dielectric properties are then described, including charge transport, space charge, resistivity, dielectric loss, and breakdown strength. The semicrystalline structure of polyethylene and isotactic polypropylene is described, and the way it relates to the dielectric properties is discussed. A significant part of the review is devoted to describing the state of art of the modeling and prediction of electric or dielectric properties of polyolefins with consideration of both atomistic and continuum approaches. Furthermore, the effects of the purity of the materials and the presence of nanoparticles are presented, and the review ends with the sustainability aspects of these materials. In summary, the effective use of modeling in combination with experimental work is described as an important route toward understanding and designing the next generations of materials for electrical insulation in high-voltage transmission. This article is protected by copyright. All rights reserved.

A smart insulation material achieving self-reporting and autonomous repairing against electrical and mechanical damages based on targeted controllable microcapsules

Under the long-term action of electrical and mechanical stresses, irreversible micro-damages, such as electrical trees and cracks tend to occur inside solid insulation materials, leading to insulation failures, which have no effective countermeasures. This study develops a multi-responsive, target-controlled microcapsule to endow the epoxy resin with dual functions of self-reporting and autonomous repair against internal damage even under strong electric fields without human intervention. A turn-on mechanism for self-reporting signals is designed, to be applicable to electrical tree damage inside an epoxy matrix. In situ UV emissions generated by the partial discharge during electrical treeing are employed to automatically cure the microcapsule core material released into the damaged channel. This triggers aggregation-induced emission (AIE) signals and simultaneously repairs the damaged matrix. The polyurethane hybrid shell filled with magnetic particles endows the microcapsules with magnetic response characteristics. Under the control of a directional magnetic field, the microcapsule is concentrated around the vulnerable areas, obtaining high fluorescence emission intensity under low doping content without affecting the matrix performance. This method enables the autonomous inspection and maintenance of electric equipment and electronic devices under live working and provides new insight into the bionic intelligence of electrical and electronic insulation materials.

Influence of amine surface treatments of carbon nanotube and boron nitride hybrid fillers on the thermal and mechanical properties of flexible amine‐based acrylate composites via 3D vat photopolymerization

AbstractOwing to the rapid advancement in electronic devices, thermal interface materials have been introduced to solve the thermal dissipation and electrical insulation problems in electronic parts and packaging materials. In this study, flexible thermally conductive acrylate‐based composites were fabricated via 3D vat photopolymerization. The effects of amine functional groups on the thermal and mechanical properties of acrylate polymers were explored. Surface‐treatment agents, namely, (3‐aminopropyl)triethoxysilane (APTES) and octadecylamine (ODA), were selected to enhance the poor dispersibility of fillers in the resin matrix caused by aggregation. The APTES‐treated carbon nanotube (CNT)–boron nitride (BN) hybrid composite exhibited the highest thermal conductivity of 0.990 W m−1 K−1, which was remarkably 482.35% higher than that of the matrix owing to the addition of 30 wt% BN, 0.5 wt% CNTs, and APTES treatment. The ODA‐treated CNT composite, which contained only 0.5 wt% CNTs, exhibited a thermal conductivity of 0.540 W m−1 K−1, which was 217.65% higher than that of the matrix. The electrical insulation properties of the composites were characterized, and the composites exhibited low electrical conductivity as electrical insulation materials. The advantages of the 3D‐printed flexible thermally conductive acrylate polymers usher in a new era of using polymer composites to address heat dissipation problems in complex structures.

Low-Temperature Deposition of Diamond Films by MPCVD with Graphite Paste Additive

Modern integrated circuits (ICs) take advantage of three-dimensional (3D) nanostructures in devices and interconnects to achieve high-speed and ultra-low-power performance. The choice of electrical insulation materials with excellent dielectric strength, electrical resistivity, strong mechanical strength, and high thermal conductivity becomes critical. Diamond possesses these properties and is recently recognized as a promising dielectric material for the fabrication of advanced ICs, which are sensitive to detrimental high-temperature processes. Therefore, a high-rate low-temperature deposition technique for large-grain, high-quality diamond films of the thickness of a few tens to a few hundred nanometers is desirable. The diamond growth rate by microwave plasma chemical vapor deposition (MPCVD) decreases rapidly with lowering substrate temperature. In addition, the thermal conductivity of non-diamond carbon is much lower than that of diamond. Furthermore, a small-grain diamond film suffers from poor thermal conductivity due to frequent phonon scattering at grain boundaries. This paper reports a novel MPCVD process aiming at high growth rate, large grain size, and high sp3/sp2 ratio for diamond films deposited on silicon. Graphite paste containing nanoscale graphite and oxy-hydrocarbon binder and solvent vaporizes and mixes with gas feeds of hydrogen, methane, and carbon dioxide to form plasma. Rapid diamond growth of diamond seeds at 450 °C by the plasma results in large-grained diamond films on silicon at a high deposition rate of 200 nm/h.

A sol-gel strategy for constructing a hydroxyapatite nanowire/aramid nanofiber electric insulating composite with excellent flame retardancy and mechanical property

With the increasing demand for high power and miniaturization of modern large-scale electrical equipment, preparing high-performance electrical insulation materials with high thermal stability and excellent mechanical properties has become an urgent problem. In this study, hydroxyapatite (HAP) nanowires and aramid nanofibers (ANF) multifunctional composites were prepared by sol-gel-membrane strategy. Aramid fibers containing an amide structure and HAP can form an ordered hydrogen bonding network and exhibit strong hydrogen bonding. The prepared HAP/ANF nanocomposite films with nanowire/nanofiber network skeleton and laminate structure have good tensile strength (69.6 MPa), dielectric breakdown strength (65.7 kV mm−1), and processing properties. Particularly emphasized is that the multifunctional HAP/ANF nanocomposite films are fireproof and high-temperature resistant, and the interfacial hydrogen-bonding enhancement between HAP nanowires and aramid fibers facilitates the construction of multifunctional insulating materials.

Latest Trend and Front Line in Research Field of Dielectrics and Electrical Insulating Materials

Latest Trend and Front Line in Research Field of Dielectrics and Electrical Insulating Materials

Requirements for cables as categories of construction products and thermal resistance of power cables

Introduction. One of the main driving factors of the demand for cable and conductor products is the modern trend of urbanization, which leads to an increase in cities with significantly increased requirements for electrical networks of transportation and distribution of electrical energy. This requires the development of appropriate infrastructure with significant demand for electricity in the commercial, industrial and residential sectors. The construction industry uses a wide range of cables with an appropriate set of electrical and mechanical properties, resistance to the influence of external climatic factors, and, first of all, must meet fire safety requirements. Increasing construction activity is stimulating the market for fire-resistant cables in the construction industry. According to the Construction Products Regulation, power, telecommunication cables, data cables, control and management, fiber optic refer to construction products in the EU member states. These cables are intended for the supply of electrical energy and communication, which are permanently installed in buildings and other engineering structures. Power, telecommunications, data and control cables are considered construction products, and are the only electrical products classified as construction. Over the next 15 years, Eastern Europe is expected to see increased growth in the construction industry, as the end of the war in Ukraine requires nearly $1 trillion in reconstruction. A strategic task in the reconstruction of the country is the use of cable and conductor products with increased operational properties, including in the construction industry. Significant efforts and investments in innovation and certification of cable and conductor products require manufacturers to create construction products of the «Power, control and communication cables» category with a high level of fire safety in accordance with the Euroclassification of cables in terms of reaction to fire depending on the level of safety. Purpose. Analysis of fire safety requirements for cables as a category of construction products and determination of thermal resistance of power cables based on experimental thermal studies of modern electrical insulating compositions. Methodology. The thermal stability of power cables with a voltage of 0,66/1 kV was determined, depending on the design, based on the conducted experimental studies of the thermal stability of electrical insulation materials, between the core filling and the polymer sheath, removed from the cable samples. On the basis of the conducted correlation analysis between thermal resistance and fire load, which are important parameters for confirming the quality and safety of the entire cable, it has been proven that the efficiency of halogen-free compositions to meet fire safety requirements increases with the increase in the cross-section and number of cores in the cable. Practical value. Determining the heat load and fire resistance of cables of various designs and areas of application based on the obtained experimental data on the heat of combustion of polymer cable materials is necessary and justified at the stage of mastering and determining the prospects for the production of cables with modern halogen-free electrical insulation compositions in accordance with fire safety requirements.

A probability distribution model for the compressive strength of micro thin-walled hollow glass beads under uniform pressure

Because of their many excellent properties, hollow glass beads (HGBs) are widely used in composite materials; stealth coatings; the aerospace field; the deep-sea field; electrical, thermal and sound insulation materials and military explosives. However, there is currently no method for predicting the strength of HGBs. This paper proposes a probability distribution model for the compressive strength of micro thin-walled HGBs under uniform pressure. The theoretical model was verified by comparing the parameters of 13 types of HGBs. The model showed that compressive strength is inversely proportional to the square root of the radius for the same type of HGBs. Moreover, for different types of HGBs made with identical materials, the compressive strength is only related to the outer diameter and equivalent density. Further study revealed that the particle size of HGBs follows a normal distribution. The failure mode of HGBs under uniform pressure is mode-II. Therefore, the maximum shear stress, which occurs on the inner surface of HGBs, is the dominant factor in the failure process. Furthermore, the shear strength is only inversely proportional to the square root of the radius even for different types of HGBs.

MECHANICAL PROPERTIES AND DANGER OF MICA CRYSTALS FOR THE PRODUCTION ENVIRONMENT

Mica is a group of rocks and minerals with a layered structure created under the influence of volcanic processes. Due to the delamination of the stone, it was used instead of glass. Irkutsk region is an area with the richest reserves of various types of mica. Since the beginning of the 20th century, mica has been used for the needs of electronics as an electrical insulation material. Nowadays, mica is used in aircraft and radio industries. Vermiculite, one of the types of mica, is extremely useful as a concrete filler for obtaining sound and heat protective materials and insulation, as well as for heat insulation of furnaces. Mica is a popular component in the production of agricultural products, the paint and varnish industry, perfumes, and in the cosmetic industry. It is hoped that rare natural qualities of mica, new promising applications and current scientific research in this area can stir interest in this mineral. The lamellar shape of mica crystals is the key property of mica from waste rock. The shape of mica crystals is the basis for solving the problem of mechanical enrichment of mica in the rock mass.

Low-cost and highly thermally conductive silver modified mica-paraffin multifunctional composite phase change materials for photo-thermal conversion and electrical insulation

To improve the utilization efficiency of renewable energy and adaptability of composite materials, a new mineral-based composite phase change material (Ag-Mica/CNF/PW) was designed and prepared by chemically modifying natural mica, attaching silver nanoparticles to the mica surface as functionalized support material, and using paraffin wax as the phase change functional medium. As expected, the thermal conductivity of the composite phase change material (CPCMs) increased significantly to 0.9 W/m k, which was 330.1% higher relative to pure paraffin. With the addition of silver-modified mica, the volume resistivity of CPCMs reached 11.9 × 1012 Ω cm. The relative enthalpy efficiency achieved 104.8%, and the photothermal conversion efficiency reached 91.3%, proving that the silver-modified mica-based CPCM was successful and feasible. The heat resistance index of CPCMs was 137.2 °C, and the enthalpy loss rate after 50 cycles was only 0.7 %, indicating that CPCMs have excellent thermal stability. The designed CPCMs are a promising candidate for developing thermal storage and building thermal management, electrical insulation and solar energy conversion.

Radiation-Resistant Electrical Insulation Materials for Superconducting Magnet Applications

To develop radiation-resistant electrical insulation materials suitable for cryogenic temperatures and applications that require radiation resistance such as future nuclear fusion energy systems, a United States Department of Energy Fusion Energy Sciences funded study was undertaken collaboratively by InnoSense LLC (ISL) and the Center for Advanced Power Systems. The goals for the new electrical insulation materials were low gas generation under irradiation, long pot life, high mechanical strength, good flexibility, and high dielectric strength. The development of proprietary metal oxide nanoparticle incorporated organic polymer composites (MOPOC) and their properties are reported. MOPOC consists of organic polyurethane (PU)-polyimide (PI) copolymers, ISL's proprietary and patented phenylated bipyridinium ionic polymers, and metal oxide nanoparticles. The results show the promise of the materials with the desired characteristics of mechanical, thermal, and pot life. Dielectric strength of 44 kV/mm and the suitability for cryogenic temperature application was demonstrated by room temperature and 77 K measurements. Preliminary gamma radiation exposure tests are promising. Further systematic investigations with larger doses on multiple compositions are planned in the next phase of the development with the extension of funding from the Department of Energy Fusion Energy Sciences and the established extended collaboration with the University of California Davis for neutron and proton beam exposure of the insulation samples.

Investigation of the dielectric properties and mechanical stability of lignocellulosic biomass based electrical insulation material for high voltage applications

The laminated insulation pressboards are used in electrical transformers and they are made from pure wood cellulose fibre. It is used in high-voltage transformers for electrical insulation due to its superior electrical and mechanical properties. Many researchers are searching for alternatives to wood raw materials to reduce deforestation. The banana is one of the lignocellulose-based raw materials; the banana fibre contains 48% cellulose. In this work, different frequencies and temperatures are used to investigate the electrical characteristics of epoxy resin composites reinforced with banana leaf fibres, including their dielectric constant, dissipation factor, and loss factor. At frequencies ranging from 1 to 10 kHz and temperatures ranging from 30 to 150 °C, the dielectric properties of several composites containing banana leaf fibre are studied. The composite’s dielectric properties gradually increased with temperature and decreased with frequency. Correspondingly, the mechanical tests involving a banana leaf fibre epoxy composite are conducted for tensile, bending, impact, and water absorption. The banana leaf fibre has been treated with a 5% sodium hydroxide (NaOH) solution to increase its dielectric and mechanical strength. According to this study, the mechanical strength of biocomposites containing up to 60% treated banana leaf fibre epoxy (TBLFE) composites is greater than that of pure epoxy. A thermogravimetric investigation of composites reinforced with banana fibres has revealed remarkable thermal stability up to 220 °C. In a composite made from chemically treated banana fibre pressboard, there is a good bond between the fibres and the matrix. The FESEM surface analysis shows that treated banana leaf fibril insulation boards have a better texture than composites that have not been treated. The testing results depict that banana leaf fibre is one of the good alternatives to wood cellulose for electrical insulation on pressboard for high-voltage applications.

Magnetic field dual responsive blueberry-like microsphere achieving targeted, multiple-cyclic, long-term self-healing against electrical damage in insulating materials

Polymer insulation materials are subjected to a combination of electromagnetic fields, mechanical stresses, long-term light exposure, ambient temperature and other operating conditions that produce mechanical and electrical tree damage which lead to insulation failure. Self-healing technology is a fundamental solution to this problem. However, effective long-term self-healing of mechanical and electrical tree damage to insulating materials is extremely challenging. To address this issue, this work reports a magnetic field dual responsive blueberry-like microsphere (MFDR-BLMS) that makes a breakthrough in the long-term self-healing of mechanical and electrical damage. The microspheres are attracted to the vulnerable area of the insulating material by the directional magnetic field. When the damage come into contact with the microspheres, the high thermal conductivity microspheres as a whole rapidly melt and fill the damage channels under the action of electromagnetic induction heating. This method achieves a magnetically dual-action, non-contact, long-term effective self-healing of mechanical and electrical tree damage after photothermal aging of insulation materials. This is expected to eliminate the requirement for human contact during the repair process under live conditions and provides a new technological idea for the industrial application of self-healing materials for electrical insulation.

Graphene nanosheet stabilized Pickering emulsion and its polystyrene nanocomposites

AbstractHigh thermal conductivity and electrical insulation materials are necessary for packaging materials of miniaturized electronic equipment at present. Graphene nanosheets (GNs) have great potential in polymer composites due to its excellent thermal conductivity. However, the ultra‐high conductivity of GNs will reduce the insulation of polymer composites, so that the GN composites have good thermal conductivity and electrical insulation has become the focus of research. Herein, the closed cell polystyrene nanocomposites are polymerized by using a Pickering emulsion route. Based on the exfoliating effect of pristine graphite at the oil–water interface and the amphiphilic properties of GNs during the preparation of emulsion, the resulting graphite can achieve good dispersion in the polystyrene resin. Furthermore, the high heat transfer rate of the resulting graphite makes the temperature of polystyrene resin increase by 60.2°C at room temperature within 1 min. Meanwhile, the high volume electrical resistivity (3.63 × 109 Ω·m) and breakdown strength (33.8 kV·mm−1) confirms the PNGL0.610%/PS composite keep excellent electrical insulation at 10.0 wt% filler loading.

Performance Analysis of Nyamplung Oil (Calophyllum Inophyl-lum) as an Alternative Liquid Electrical Insulation Material to Replace For Power Transformer Oil

In the operation of electric power distribution, the transformer can be said to be the heart of the transmission and distribution of electric power. In recent years the use of vegetable oil is increasing. The purpose of this study was to test and analyze a mixture of transformer oil and nyamplung oil (Calophyllum Inophyllum) as transformer insulation and also to obtain the best composition of nyamplung oil which can be used as an alternative to transformer oil. This research method tested the parameters of nyamplung oil and a mixture of nyamplung oil and mineral oil (Shell Diala S4), such as; viscosity, flash point, density, pour point, acidity, moisture content and breakdown voltage. The sample test results are then compared with standard mineral oil according to IEC 60296-2003. From the analysis conducted, it was found that TRNY10 oil mixture (10% transformer oil and 90% mineral oil) has the best potential as power transformer oil.

Enhanced thermal conductivity and rheological performance of epoxy and liquid crystal epoxy composites with filled Al2O3 compound

The heat dissipation capability of electrical insulation materials has been the bottleneck affecting the development of high power density electrical equipment and electronic devices. In this study, we investigated the effect of filler compounding, filler surface treatment and liquid crystal structure on the microscopic morphology, rheological performance, thermal conductivity and dielectric performance of the epoxy resin (EP) and liquid crystal epoxy resin (LCEP) composites. The results show that the composite with 45 μm and 3 μm Al2O3 compound fillers at a ratio of 3:2 showed a reduction in viscosity for about 1/3-1/30 and an enhancement in thermal conductivity for about 10%–40% compared to the other filler compounds with different filler size and ratio. The filler surface treatment by silane coupling agent diminished the viscosity by up to 90% and simultaneously enhanced the thermal conductivity of the composite by about 10%. The composite with LCEP matrix showed a thermal conductivity up to 2.47 W/(m·K) at 80 wt% filler loading, which is about 0.54 W/(m·K) higher than that of EP based composite. Moreover, the filler surface treatment can improve the electrical breakdown strength and volume resistivity of the composites. The results indicate that filler compound optimization, filler surface treatment and LCEP matrix can significantly improve the thermal conductivity, rheological and dielectric properties of the composites.

D−π−A Strategy to boost dielectric breakdown strength of polyimide insulation

Polyimide (PI) possesses multiple advantages including excellent thermal stability, mechanical property and chemical resistance, which has been considered as one of the promising candidates for high-performance electrical insulation materials. Optimizing the polymer structure such as extending the band gap can yield high intrinsic breakdown strength, attributed to the inhibition of impact ionization. However, in most cases, large band gap is achieved at the cost of reducing the backbone coplanarity and rigidity or the intermolecular interaction, resulting in undesirable thermal and mechanical performance. Herein, we introduce an effective strategy to produce thermally stable and mechanically strong polyimide insulation with high breakdown strength through introducing aromatic donor groups into the main chains to construct a D−π−A structure. On the one hand, the formation of D−A effect increases the materials polarization and enhances dipole-induced scattering. On the other hand, enhanced intermolecular interaction via π−π stacking decreases free volume in PIs. Then, increased conjugation degree of the backbone and high packing density between the polymer chains benefit to thermal stability and mechanical properties. Based on this strategy, N-arkyl carbazole groups are preferred, in which the soft alkyl side groups can occupy the pores between the polymer chains to further decrease free volume. As a result, we afford polyimide insulation with significantly improved breakdown strength from 291 kV mm−1 to 570−632 kV mm−1, as compared to the reference PI ODA-PMDA. Simultaneously, the resultant PIs, such as PI-Bu, preserve high Td5% above 524 ℃, high Tg above 364 ℃ and tensile strength above 80 MPa.

Latest Trend and Front Line in Research Field of Dielectrics and Electrical Insulating Materials

Latest Trend and Front Line in Research Field of Dielectrics and Electrical Insulating Materials

Leakage current detection method of electrical insulation materials based on windowed-added Fourier transform

In order to effectively solve the disadvantages of low accuracy of leakage feature recognition and low accuracy of detection results in traditional leakage current detection methods, a leakage current detection method of electrical insulating materials based on windowed Fourier transform is proposed. Firstly, the windowed Fourier transform process is analysed to judge the related properties of leakage current signal. Then, the leakage current detection unit is designed by using the insulation equivalent model, leakage current detector, self-excited oscillator, second-order low-pass filter and windowed Fourier transform process. Finally, based on the leakage characteristics of electrical insulation materials, the leakage current detection process is designed to complete the leakage current detection of electrical insulation materials. The results show that the recognition accuracy of leakage characteristics is always above 95%.

Resistance evaluation of electrical insulating polymer materials used in flexible cables to operational impact

The article presents the test results of polymer material properties taking into account the possibility of their application for flexible cables insulation. The main types of cable constructions and their operation features are considered. Existing test determination methods of insulation resistance to thermal, mechanical, electrical and environmental conditions are analyzed. Requirements for laboratory equipment and test conditions are given. Evaluation criteria of test results are noted. Experimental evaluation was carried out for change degree in the properties of the main types of electrical insulation materials used currently during the flexible cable production: polyvinyl chloride compound (PVC), rubber, ethylene propylene rubber (EPR), thermoplastic elastomer (TPE), fluoropolymer. Tests were carried out under the influence of high and low temperatures, aggressive environments, ozone, mechanical loads. The main processes that determine the changes in electrophysical, physical and mechanical properties of the studied materials are described. Resistance of EPR, TPE and fluoropolymer insulation to a wide range of temperatures, mechanical loads, diesel fuel and transformer oil are shown. An increased resistance of EPR to ozone was also noted. Rubber and PVC compound did not pass the tests under the influence of low and high temperatures, showed "poor" resistance to aggressive environments, but passed the mechanical stress tests. Recommendations on tests and application of polymer insulation taking into account the specifics of flexible cables working are presented.