Electrical Insulation Research Articles

High thermal conductivity and low dielectric loss of three-dimensional boron nitride nanosheets/epoxy composites

Electronic power devices are moving towards high frequency, high integration, and high power, which urgently needs to develop high thermal conductive encapsulating insulation materials to improve the heat dissipation of electronic devices. Herein, we propose to modify the commercialized encapsulating materials of epoxy resin (EP) by incorporating three-dimensional hydroxylated boron nitride nanosheets (3D-BNNSs). The cryogel and vacuum freeze-drying techniques are employed to prepare the 3D-BNNSs using agarose. The results show that the constructed high thermal conductive structure of 3D-BNNSs can effectively enhance the thermal conductivity of EP and reduce the interfacial thermal resistance between BNNSs fillers. The thermal conductivity of 3D-BNNSs/EP composites with 33.03 wt% BNNSs reach 2.54 W/(m·K), which is 13.11 times higher than that of EP (0.18 W/(m·K)). Meanwhile, the resultant composites remain outstanding electrical insulation and dielectric properties. Because agarose contains numerous hydroxyl groups that can form hydrogen bonds with the hydroxyl groups on the surface-functionalized BNNSs, hydrogen bonding can lead to strong intermolecular interactions, which is conductive to accelarate phonon transport. Additionally, agarose can cross-link with the molecular chains of epoxy, impeding the movement of molecular chain segments and resulting in composites with low dielectric loss at high frequencies. This study demonstrates that the 3D-BNNSs/EP composites have great potential for application in thermal management of electronic components.

Metal ion-crosslinked thermoconductive sugar-functionalized graphene fluoride-based cellulose papers with enhanced mechanical properties and electrical insulation

Thermally conductive papers with electrical insulation and mechanical robustness are essential for efficient thermal management in modern electronics. In this study, we introduced a metal ion-assisted interfacial crosslinking strategy to strengthen sugar-functionalized graphene fluoride (SGF) and cellulose nanofibers (CNF) by hydrogen bonding and metal ion crosslinking that leads to simultaneous enhancements in thermal conductivity and mechanical properties. The facile sugar-assisted ball-milling exfoliation method was developed to achieve the exfoliation of graphite fluoride and hydroxyl group functionalization on the surface of graphene fluoride. Thanks to the good dispersibility of the SGF sheets in water, the flexible SGF/CNF composite papers with hydrogen bonding were prepared via vacuum-assisted filtration. We introduced hydrogen bonding and metal ion crosslinking into SGF/CNF papers to obtain densely packed composite papers. Ca2+ or Al3+ ion-crosslinked SGF/ CNF papers exhibited superior thermal and mechanical properties owing to hydrogen bonding and metal ion crosslinking. SGF/CNF-Ca2+ and SGF/CNF-Al3+ papers at 50 wt% of SGF yield in-plane thermal conductivities of 72.93 and 75.02 W m–1 K–1, and tensile strengths of 121.5 and 135.7 MPa, respectively. A thermal percolation value was observed at 12.6 vol% of SGF filler content. In addition, the SGF/CNF papers exhibited electrical insulation properties. These remarkable characteristics of the metal ion-crosslinked SGF/CNF papers are attributed to the densely packed structures caused by the strong interfacial interactions from hydrogen bonding as well as metal ion-crosslinking that could promote phonon transport. High-performance metal ion-crosslinked SGF/CNF papers with these fascinating advantages offer great potential for the thermal management of flexible electronics.

All-natural, thermally conductive, flame-retardant electrical insulating lignocellulose-mica composite film fabricated via in-situ mineralization

Miniaturized, integrated, and functional electronic devices generate a large amount of heat accumulation during operation, which significantly affects the reliability, durability, and safety of electronic devices. In severe cases, it may even lead to fires. Therefore, the development of insulation composite materials with thermal conductivity and flame-retardant properties is particularly important. In this study, we propose an in-situ mineralization strategy to prepare insulation composite materials with thermal conductivity and flame-retardant properties. By dissolving and preparing a gel film, Al3+ and Zn2+ retained inside the lignocellulose are in situ mineralized to form Al(OH)3 and ZnO, and introducing inorganic blocks with high insulation performance (industrial waste mica tailings and synthetic mica). The prepared film has excellent tensile strength (117.4 MPa), low dielectric loss, high dielectric strength (83.8 kV mm−1), high insulation resistance, four times higher thermal conductivity than the unmineralized film, and excellent flame-retardant properties. Meanwhile, the environmental impact of the composite film is much lower than that of petrochemical-based plastic films and can easily degrade under natural conditions within 32 days. It is a composite material that meets the standards of the new electrical insulation field, and the in-situ mineralization strategy can also provide ideas for the preparation of high-performance lignocellulose-based materials.

Nano-BN and nano-cellulose synergistically enhanced the mechanical, thermal, and insulating properties of cellulose insulating paper

The complex and demanding environments of high humidity, heat, altitude, and intricate electric fields necessitate higher standards for the mechanical, thermal stability, and electric insulation properties of insulating paper. However, a single nanomaterial alone struggles to enhance overall performance. Hence, we propose employing two-phase nanomaterials with distinct dimensions to synergistically enhance the performance of cellulose insulation paper. Accordingly, “simulation design directly guided experimental research” was utilized in constructing nano-BN/nanocellulose/cellulose (nano-BN/NFC/cellulose) models through molecular dynamics simulation, and its mechanical parameters, dielectric properties, thermal stability, and so on were simulated and calculated. Based on simulation results, suitable proportions of nano-BN/NFC/cellulose insulating paper were prepared. Nano-BN and NFC synergistically enhance the mechanical properties of insulating paper. The nano-BN, CNF, and cellulose are arranged layer by layer under the action of gravity, allowing the fillers to overlap diagonally along the plane, synergistically forming a thermally conductive network conducive to heat transfer. Additionally, a strong interfacial effect is formed between the three-phase materials, reducing the overall structure's polarization effect and charge accumulation, and synergistically enhancing electrical insulation performance. The 12%nano-BN/NFC/cellulose (P12) exhibits optimal overall performance and is expected to be used in power equipment operating in special environments with high humidity and heat.

Covalent bond-assisted continuous interface structure for high thermal conductive polyimide composite films

Polyimide (PI) is widely used in electronic, electrical and communication fields because of its outstanding mechanical properties, electrical insulation and thermal stability. However, the lower thermal conductivity limits their application. Here, PI composite films with high thermal conductivity are obtained by utilizing reactive groups on the carbon nitride nanosheets (CNNS) surface to form covalent bond with PI matrix. The thermal conductivity of CNNS/PI composite films can reach 5.84 W∙m−1∙K−1, which is about 10 times higher than that of pure PI (0.56 W∙m−1∙K−1). This is attributed to the covalent bond between CNNS and PI matrix acting as a “thermal bridge” to connect the discontinuities at the interface, thereby reducing the interfacial thermal resistance between CNNS and PI. The heat transfer mechanism of composite film is further revealed by finite element analysis. This work provides a viable solution to improve the thermal conductivity of PI, allowing for a wide range of potential applications for PI in electronic devices.

A processable high thermal conductivity epoxy composites with multi-scale particles for high-frequency electrical insulation

The solid-state transformer (SST) in the renewable energy grid is developing in the way of high voltage and high frequency, which often results in a sharp increase in heat production of the equipment and accelerates the failure of the insulating materials. Epoxy resin (EPR) is commonly used as an insulation material for SST due to its excellent electrical insulating properties, processing performance (viscosity), and low price. However, the thermal conductivity of EPR is only about 0.2 W/(m·K), which leads to poor insulating performance under high frequency and temperature. To enhance thermal conductivity, a substantial quantity of highly thermally conductive particles is incorporated into the EPR, accompanied by a severe increase in electrical insulation defects and viscosity. This study utilized a multi-scale particle-filled approach to investigate the thermal conductivity, processing characteristics, and high-frequency electrical insulation performance of composites. The composite, filled with 25 µm BN and 5 µm SiO2 particles, enhances thermal conductivity to 0.732 W/(m·K) and demonstrates superior electrical insulating properties at both 10 kHz and 20 kHz bipolar square waves (with an increase of 131.76% and 163.97% in relative EPR, respectively), as well as good processability. Meanwhile, it is found that the dielectric loss, thermal conductivity, and electric field distribution of the composite are the main factors affecting the electrical insulating properties from 10 to 20 kHz under high voltage.Graphical

Dual‐Network Assembled Nanopaper towards Extremely Harsh Conditions

AbstractAramid nanofibers (ANFs) exhibit desirable lightweight and excellent properties, while their strength has to be sacrificed to further improve their electrical insulation and fire resistance so as to meet the special demands of extreme environments. Herein, Zylon nanofibers (ZNFs) with analogous structure compatibility but superior performance are employed to construct an assembled dual‐network structure to improve the overall properties of ANFs. A facile in situ structure restoration (ISSR) strategy is proposed to achieve ZNF aqueous dispersion for the first time by deprotonation of ZNFs, which significantly avoids the corrosive acid system and facilitates the papermaking process. The composite ANF@ZNF nanopaper exhibits incredible tensile strength (233 MPa) and toughness (14.7 MJ m−3), increased by 108% and 584% compared with pure ANF nanopaper due to the dense entangled dual‐network and tremendous hydrogen bonds. Moreover, it presents superior breakdown strength of ≈128 kV mm−1, which is 6 times higher than that of commercial Nomex T410 insulation paper with a thickness of 50 µm. Besides, it exhibits surprising flame resistance (endure 1000 °C burning) ascribed to the excellent thermostability of ZNFs. This work provides promising possibilities for expanding the applications of aramid‐based composites for advanced electrical insulation and thermal protection in extremely harsh conditions.

Glass frit and method of forming electrical insulating coatings on steel substrates of film heaters

Electric film heaters (EFHs) applied on flat steel substrates show promising potential in the production of heating devices. The basis for manufacturing EHFs is heat-resistant steel, the surface of which is coated with a heat-resistant electrical insulation coating. These coatings are glass crystalline and are applied mainly by screen printing. Compared to screen printing, the electrophoretic method of coating is more productive. In this work, glass in the MgO–CaO–B2O3–SiO2 oxide system was chosen for obtaining glass crystalline coatings. The paper provides a description of the material composition and the method used to prepare a suspension for еру electrophoretic deposition of coating. The main technological parameters for forming electrophoretic coatings with a specific thickness are determined based on experimental results. Utilizing calculated data on the properties of the selected glass, the study substantiates the most rational temperature and time regime for coating firing. These conditions promote crystallization and result in the production of heat-resistant coatings with sufficient electrical insulating properties for steel substrates of EFHs.

Simultaneous measurements of temporal evolutions of the voltage and the current on the load of the Seoul National University X-pinch device using the optics-based systems.

Optics-based measurement systems have been developed to measure the voltage and the current on a load of the Seoul National University X-pinch device [Ryu etal., Rev. Sci. Instrum. 92, 053533 (2021)]. A lithium niobate crystal that changes the polarization state of the propagating laser beam due to the Pockels effect induced by the electric field across the crystal, thus capable of measuring the voltage, is located next to the load. For the current measurement, an optic fiber is wound around the load to detect the change in the polarization state of the propagating laser beam due to the Faraday rotation induced by the magnetic field. As both voltage and current measurement systems utilize optical effects, the sensors, i.e., the lithium niobate crystal and the optic fiber, do not require any electrical grounds, in contrast to circuit-based probes, such as voltage dividers or Rogowski grooves. This facilitates an easy access to shield other required electronic devices, such as lasers and photodetectors, from the electromagnetic interference generated by the X-pinch power system. In addition, the sensors can be placed in close proximity to the load with fewer concerns on the electrical insulation. Temporal evolutions of the simultaneously measured voltage and current on the load of the X-pinch are successfully obtained and discussed.

Measuring thermal conductivity using H2-O2 flame on ceramic films prepared by atmospheric chemical vapor deposition

Uneven micron-sized pores on the surface of the polycrystalline alumina (Al2O3) substrates can affect their performance as electrical insulating plates. In this study, we investigated the sealing of these pores with amorphous Al2O3 films deposited via atmospheric chemical vapor deposition. Furthermore, we conducted annealing treatments on the samples. The color change of the deposited Al2O3 films was investigated using the Commission Internationale de I’Eclairage color space. Notably, the deposited films initially changed the sample color from white to orange or brown. However, increasing the annealing temperature and duration reversed this discoloration effectively and restored the original white (colorless) appearance of the sample. We measured thermal conductivity using the flame flash method with the H2-O2 flame to assess the influence of sealing. While the unsealed substrate exhibited a thermal conductivity of 4.66 W/mK in the range of 400–500 °C, the annealed and flattened Al2O3 film deposited on the substrate maintained a comparable thermal conductivity of 4.67 W/mK within the same temperature range. This finding demonstrates that our sealing method successfully filled the pores while having minimal influence on thermal conductivity, which is a crucial property for electrical insulation applications.

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.

Multi‐layer graphene nanosheets bridging binary aluminium oxide for the synergistic enhancement of thermal conductivity and electrical insulation of silicone resin composite

AbstractThe flexible polymer composites usually require high intrinsic thermal conductivity fillers for the applications in thermal management, such as the well‐known graphene, which can, in turn, compromise their electrical insulation properties. Here, the authors developed the silicone resin (SR) composites filled with multi‐layer graphene nanosheets (MGN) and binary alumina (Al2O3), and the microstructure of composites exhibits the dominant skeleton of large‐sized Al2O3 filler and branching of small‐sized Al2O3 fillers features by the size matching effect of optimal binary Al2O3. The introduction of supplementary MGN fillers further increases the face‐to‐face contact probability and bridges the isolated binary Al2O3, which contributes to the high thermal conductivity of 3.0 W·m−1·K−1 under these synergistic effects. The dense and connected ‘Al2O3‐MGN‐Al2O3’ thermal conductive pathway is successfully built, as supported by the numerical simulation and Agari model fitting. Meanwhile, the electrical conductivity caused by MGN can be blocked by the surrounding insulation Al2O3 filler network, exhibiting a high volume resistivity of 1.7 × 1015 Ω · cm. Moreover, the Al2O3/MGN/SR composite films effectively transfer the heat and diminish the hot‐spot temperature by 53.5°C in cooling light emitting diode chip module application.

ВПЛИВ ВЕЛИЧИНИ ЄМНОСТІ ПОСЛІДОВНОГО РЕЗОНАНСНОГО КОНТУРУ НА ПОТУЖНІСТЬ ЕЛЕКТРОТЕХНІЧНИХ СИСТЕМ РЕЗОНАНСНОГО ТИПУ ДЛЯ МОНІТОРИНГУ ІЗОЛЯЦІЇ ВИСОКОВОЛЬТНОГО ОБЛАДНАННЯ

It were analyzed the processes of charging the capacitive electro-technical storage (CES), which can be the electrical insulation of modern high -voltage equipment (in particular power cables) during the current monitoring of its techni-cal condition by the value of leakage currents when applying high voltage to insulation. The transformerless electro-technical system (ETS) of a resonance type, in which resonant inductive-capacitive circuit (ICС) with a high Q -factor carried out a multiple increase in AC voltage, was used to generate such voltage. Analytical expressions were obtained for the steady-state voltage on such CES and transient currents in the ETS circuit its charging. Simulation modeling of transient processes in the circuits of such ETS during CES charging was performed using the LTSpice software pack-age. It is shown that the dependences of the output voltage and current of the ETS on time, obtained by analytical ex-pressions, practically coincide with the results of simulation simulations. The influence of the ratio of the load capaci-tance and the resonant circuit capacitance on the relative load charging time and, accordingly, on the ETS power was studied. It was found that in order to increase the power of high -voltage transformerless ETS of the specified reso-nance type, it is necessary to increase the ratio of the CES capacity to the ICС capacity of the resonant circuit of the ETS. This approach can be used when using ETS with resonant ICCs to create powerful electric discharge installations (EDIs) for the implementation of technologies for obtaining electro-spark micro- and nanopowders with unique opera-tional properties. When creating powerful EDIs, it is suggested to use the value of the above-mentioned ratio at least 10. References 31, figures 5.

Investigating Degradation in Extrusion-Processed Bio-Based Composites Enhanced with Clay Nanofillers

This research investigates the extrusion-based fabrication and characterization of nanocomposites derived from bio-sourced polypropylene (PP) and poly(butylene succinate) (PBS: a biodegradable polymer derived from renewable biomass sources such as corn or sugarcane), incorporating Cloisite 20 (C20) clay nanofillers, with a specific focus on their suitability for electrical insulation applications. The research includes biodegradation tests employing the fungus Phanerochaete chrysosporium to evaluate the impact of composition and extrusion conditions. These tests yield satisfactory results, revealing a progressive disappearance of the PBS phase, as corroborated by scanning electron microscopy (SEM) observations and a reduction in the intensity of Fourier transform infrared spectroscopy (FTIR) peaks associated with C-OH and C-O-C bonds in PBS. Despite positive effects on various properties (i.e., barrier, thermal, electrical, and mechanical properties, etc.), a high clay content (5 wt%) does not seem to enhance biodegradability significantly, highlighting the specific sensitivity of the PBS phase to the addition of clay during this process. This study provides valuable insights into the complex interplay of factors conditioning nanocomposite biodegradation processes and highlights the need for an integrated approach to understanding these processes. This is the first time that research has focused on studying the degradation of nanocomposites for electrical insulation, utilizing partially bio-sourced materials that contain PBS.

Strategies for constructing stable solid electrolyte interface on the surface of lithium metal negative electrodes

Abstract With metallic lithium serving as the negative electrode material, lithium metal batteries are seen as the most promising next generation of high-specific energy batteries. However, the poor stability of the solid-state electrolyte interface (SEI) caused by the spontaneous interaction between metal lithium and electrolyte during battery cycling exacerbates several problems such lithium dendrite formation, lower Coulomb efficiency, and capacity degradation. The practical use of secondary lithium metal batteries is therefore constrained. Consequently, enhancing SEI stability is a focus of extensive study in the realm of lithium metal batteries. The ideal surface electrode should have strong surface electrical insulation, good lithium-ion conductivity, and high mechanical strength in order to manage the even deposition of lithium ions on the surface, facilitate ion transport, and inhibit dendritic growth. Therefore, constructing a functional SEI film is an effective strategy to solve the challenges faced by lithium metal negative electrodes. This article first introduces the formation mechanism and structural composition of SEI. Then, the failure reasons of SEI were analyzed. Finally, the modification strategy of SEI was emphasized, aiming to provide a reference for the research of metal lithium negative electrodes.

IEEE Electrical Insulation Magazine, a Publication of DEIS

IEEE Electrical Insulation Magazine, a Publication of DEIS

The influence of nanocellulose from different plant raw materials on the quality indicators of electrical insulation paper

An urgent scientific and practical task for electrical engineering enterprises is to improve the specific characteristics of component transformers and capacitors that use electrical insulating paper. Electrical insulating paper is characterized by a wide list of special quality indicators, the necessary values ​​of which are achieved due to the use of cellulose with special properties and various chemical auxiliary substances. There are known attempts to use nanocellulose (NC) from wood to reduce the consumption of harmful synthetic chemical auxiliaries, but there are practically no research results on the impact of consumption of NC from non-wood plant materials. Therefore, in the work, a comparative study of the effect of NC from hemp fibers and coniferous wood on the target indicators of the quality of electrical insulating paper was carried out. For this, cellulose, suitable for extracting NC from hemp fibers, was obtained by an environmentally safe organosolv method. NC is obtained as a result of acid hydrolysis of organosolv hemp and sulfate unbleached coniferous cellulose, which is traditionally used in the production of electrical insulating paper. Laboratory samples of electrical insulating paper were made with a weight of 65±3 g/m2 from sulfated unbleached coniferous cellulose with the addition from 1% to 5% NC by weight of paper. The research results confirmed the hypothesis that the addition of NC paper pulp from various plant raw materials leads to an increase in the mechanical and electrical strength of the paper. It has been established that the effect of NC from hemp fibers on the quality indicators of electrical insulation paper is not inferior to the effect on them of NC from coniferous wood, and in some cases even a better result is observed. It was established that the introduction of NC into the composition of paper practically does not reduce its degree of polymerization, which is of great importance for maintaining high reliability and a long duration of work of paper insulation. The obtained results have scientific and practical significance for other types of insulating papers: capacitor, cable, telephone, impregnation, transformer, etc.

Investigation of sintering properties and behavior of sericite ceramifying powder under low temperature

AbstractPolymer–ceramic composites are widely used in refractory cables. The ceramic fillers provide high temperature and fire resistance, while the polymer matrix provides flexibility and improved electrical insulation. The properties of the polymer–ceramic composites are determined by the ceramization‐forming properties of the corresponding ceramifying powders. Properties such as shrinkage, density, and porosity were characterized to compare the effects of different contents of glass powder. The sintering activation energy was calculated using the logarithmic relationship between shrinkage and holding time. The microstructure, cross‐section, and crystalline phases were investigated by scanning electron microscopy (SEM) and X‐ray diffraction analysis (XRD) to explore the ceramization process of sericite ceramifying powder. The ceramization process of ceramifying powder is proposed. The results show that during low‐temperature sintering, the glass powder and muscovite phases melt and partially transform into α‐quartz and albite low during cooling down.

Electrical insulation and dielectric properties of aramid fiber reinforced epoxy composites under mechanical stress

In this work, an in-situ testing platform that could simultaneously apply high voltage (HV) and mechanical stress has been established. The dielectric properties evolution of aramid fiber reinforced composite (AFRC) under different tensile stresses is investigated systematically. The results show that there is a significant influence on the electrical insulation performance of AFRC, when the applied tensile stress reaches 45 % of the ultimate tensile stress (UTS). Elevated tensile stress will induce interface strain concentration inside composites under this condition, which is prone to cause local damage and defects, consequently enhancing charge accumulation under HV. As the tensile stress continues to increase, it is observed that the absorbed charge around defects increases by 49.4 % under 60 % UTS, accompanied by a discernible decline in the partial discharge inception voltage (PDIV) by 46.9 %. With the increase of absorbed charge, the localized intense electric field is formed, thereby fostering partial discharge and breakdown failure. Therefore, it is important to pay more attention to the evolution of dielectric properties of AFRC under mechanical stress in the design and assessment of aramid-based insulation rods. © 2014 xxxxxxxx. Hosting by Elsevier B.V. All rights reserved.

Constructing phonon transport bridges via low-temperature sintering in Diamond@Ag/EP composite to achieve efficient 3D networks structure

The rapid advancement of integrated circuits and electronic devices presents challenges to traditional epoxy molding compound (EMC), necessitating the demand for highly thermally conductive yet electrically insulating composites to address the “hotspot issues” in high-power chips. Here, a low-temperature sintering technology based on metal–organic decomposition is developed to fabricate a three-dimensional interconnected networks structure composite (3D-Diamond@Ag/EP). The in-situ decomposition of the silver amine complex on the surface of the Diamond@Ag hybrid filler forms nano-silver bridges, which facilitate the successful construction of the three-dimensional networks structure. When the Ag reaches 4.0 vol%, the thermal conductivity of the composite (reaches 6.42 W/m·K) breaks out of the low numerical blockade of the epoxy resin (0.18 W/m·K), while maintaining excellent insulation performance. It is noteworthy that the great improvement of thermal conductivity is achieved by the synergistic effect of sufficient thermal pathways and minimizing interfacial thermal resistance along these paths. Moreover, this work obtained composite exhibits other excellent thermal characteristics. It provided a practical route to produce high thermal conductivity polymer-based composites with electrical insulation for heat management in modern electronic devices.