High Voltage Insulation Material Research Articles

Surface Microstructure Study on Corona Discharge-Treated Polyethylene Using Positron Annihilation Spectroscopy.

The microstructure and chemical properties of the corona discharge process could provide an effective method for predicting the performance of high-voltage cable insulation materials. In this work, the depth profile of the microstructure and chemical characteristics of corona discharge-treated PE were extensively investigated using Doppler broadening of position annihilation spectroscopy accompanied with positron annihilation lifetime spectroscopy, attenuated total reflectance Fourier transform infrared spectra, Raman spectra and contact angle measurement. By increasing corona discharge duration, the oxygen-containing polar groups, including hydroxyl, carbonyl and ester groups, strongly contribute to the deterioration of hydrophobicity and the enhancement of hydrophilicity. And the mean free volume size, with a broadening distribution, decreases slightly. The line shape S parameter decreases because of the decrease in free volume elements and the appearance of oxygen-containing groups. Also, the thickness of the degradation layer, determined from the S parameter with positron injection depth, increases and diffuses into the PE matrix. A linear S-W plot within the degradation layer of different corona treatment duration samples indicates the defect type does not change. The S parameter decreases and the W parameter increases with an increasing corona duration. Using a slow positron beam, the nondestructive probe can be used to profile the microstructure and chemical environment across the corona discharge damage depth, which is beneficial for investigating the surface and interfacial insulation materials.

Laser-Induced Breakdown Spectroscopy Analysis of Sheet Molding Compound Materials

Sheet Molding Compound (SMC) materials are extensively utilized as high-voltage insulation materials in electrical equipment. SMC materials are prone to aging after long-term operation. Conducting non-destructive testing to assess their electrical and physicochemical properties is crucial for the safe operation of electrical equipment. This study identifies the optimal equipment parameters for testing SMC materials using Laser-Induced Breakdown Spectroscopy (LIBS) technology through experimental investigation and also explores the ablation characteristics of SMC under various laser parameters. The results indicate a significant positive correlation between the ablation depth and laser pulse number, while there is no correlation with single laser pulse energy. However, the ablation area demonstrates a strong positive correlation with both single laser pulse energy and laser pulse number. Additionally, LIBS spectral analysis provides elemental results comparable to Energy Dispersive Spectroscopy (EDS), facilitating the examination of variations in Na, Ti, Fe, Mg, Ca, and C elemental contents with depth. Moreover, an enhanced iterative Boltzmann plot method is suggested for calculating the plasma temperature using 21 Fe I spectral lines and the electron density using the Fe II 422.608 nm line. The variations of these plasma parameters with laser pulse number are documented, and the results show consistent trends, confirming that the laser-induced SMC plasma adheres to local thermodynamic equilibrium.

Glass fiber network reinforced polyethylene terephthalate composites for support insulators

Epoxy resin has long been used as an insulating material in high-voltage apparatus, although its poor recyclability greatly limits its future application. Fiber network reinforced polyethylene terephthalate (PET), as a low-cost and recyclable material, has great potential to substitute epoxy resin as a high-voltage insulation material. The enhanced fiber network combined with the PET matrix form a semi-‘steel-reinforced concrete’ structure, and can collaboratively improve the tensile strength by more than 50% and the dielectric strength by 25.4%. Furthermore, the breakdown path as well as the fiber distribution are clearly rebuilt in 3D coordinates based on a 3D x-ray microscope for the first time. Experimental and computational evidence show that the fiber network lengthens the breakdown path and improves the dielectric strength. This work provides new perspectives for subsequent research on the electrical properties of bone-enhanced dielectric polymer composite.

Polyethylene Based Ionomers as High Voltage Insulation Materials

AbstractPolyethylene based ionomers are demonstrated to feature a thermo‐mechanical and dielectric property portfolio that is comparable to cross‐linked polyethylene (XLPE), which may enable the design of more sustainable high voltage direct‐current (HVDC) power cables, a crucial component of future electricity grids that seamlessly integrate renewable sources of energy. A new type of ionomer is obtained via high‐pressure/high‐temperature free radical copolymerization of ethylene in the presence of small amounts of ion‐pair comonomers comprising amine terminated methacrylates and methacrylic acid. The synthesized ionomers feature a crystallinity, melting temperature, rubber plateau modulus and thermal conductivity like XLPE but remain melt‐processable. Moreover, the preparation of the ionomers is free of byproducts, which readily yields a highly insulating material with a low dielectric loss tangent and a low direct‐current (DC) electrical conductivity of 1 to 6·10−14 S m−1 at 70 °C and an electric field of 30 kV mm−1. Evidently, the investigated ionomers represent a promising alternative to XLPE‐based high voltage insulation, which may permit to ease the production as well as end‐of‐use recycling of HVDC power cables by combining the advantages of thermoset and thermoplastic materials while avoiding the formation of byproducts.

Preface

The 2022 International Conference on Power Engineering and Electrical Technology (ICPEET 2022) was successfully held in Nanjing, China from July 22nd to 24th, 2022 in the form of online conference. The conference aimed to provide a platform for experts and scholars in the fields of power engineering and electrical technology to share research achievements and cutting-edge technologies, understand academic development trends, broaden research ideas, strengthen discussion, and promote industrial cooperation of academic achievements.We had the honor of having invited Prof. Hongwei Li from Southwest Petroleum University, China to serve as our Conference General Chair. About 160 individuals and enterprises all over the world attended the conference. Divided into three parts, the conference agenda covered keynote speeches, oral presentations, and online Q&A discussion. Firstly, keynote speakers were each allocated 30-45 minutes to hold their speeches. Then in the oral presentations, the excellent papers we had selected were presented by their authors one by one.During the conference, we were delighted and honored to invite three sophisticated keynote speakers to address their speeches. Among them, Assoc. Prof. Kwan Yiew Lau from Universiti Teknologi Malaysia delivered a speech on the topic: Tailoring Dielectric Properties of Polymer Nanocomposites. To address the problems hindering the use of nanocomposites as practical high voltage insulation materials, he proposed nanofiller/polymer interface modification techniques to tailor the dielectric properties of nanocomposites. The importance of the local material structure in determining the dielectric properties of nanocomposites was also discussed. Additionally, Professor Yiming Zhang from Fuzhou University gave a report on Foreign Object Detection Technology in Electric Vehicle Wireless Charing System. In the report, different foreign object detection techniques were reviewed and a new metal object detection system with novel coil layouts and topologies was proposed. The wonderful and dramatic speeches of each keynote speaker had triggered heated discussion. Moreover, every participant praised this conference for disseminating useful and insightful knowledge.The proceedings of ICPEET 2022 is a compilation of the accepted papers and represent an interesting outcome of the conference. These papers feature but are not limited to the following topics: Electric Power Allocation, Smart Grid and Technologies, Power System, Electric Vehicle Technology, Electromagnetic Compatibility, etc. All the papers have been checked through rigorous review and processes to meet the requirements of publication.On behalf of the conference organizing committee, we would like to express our heartfelt appreciation to all the keynote speakers, peer reviewers, and all the participants. In particular, we would like to acknowledge the Journal of Physics: Conference Series, for the endeavor of all the colleagues in publishing this paper volume. We firmly believe that all the attendees have had fruitful discussions and gained valuable knowledge, and will enjoy the opportunity for future collaborations.List of Committee member is available in this pdf.

Monitoring and prediction of thermal failure of high-voltage switchgear insulation materials by studying the thermodynamic properties of FR-4 epoxy resin and the characteristic gas of thermal decomposition

FR-4 epoxy resin is a common material used as internal parts in high voltage switchgear. In this paper, we adopted the accelerated thermal aging method to explore the thermal aging behavior of FR-4 epoxy resin, simulating the practical application of this material in high voltage switch. The effects of thermal aging on the thermodynamic properties and thermal decomposition characteristic gases of FR-4 epoxy resin were characterized by FT-IR, DSC, TG and GC-MS analyses. The experiment results showed that thermal aging could destroy the internal crystal structure of FR-4 epoxy resin, which could lead to this material easier to be decomposed after heating. We also detected that the thermal decomposition rate of FR-4 epoxy resin aging was greatly accelerated compared with the materials that had not been aged. In addition, unaged FR-4 epoxy resin could release 9 main volatile gases under 120°C, and irreversible defects or structural damages occurred in the materials along with the volatilization of small organic molecules. Furthermore, after continuous thermal aging at 120 °C for 672 h, the molecules of FR-4 epoxy resin were more cracked and volatilized, we observed a more obvious phenomenon of thermal decomposition in this materials. In total, we compared the types of thermal decomposition gases and the decomposion mechanism of aged and unaged FR-4 epoxy resin. In application, our results can provide reference for condition monitoring and fault prediction for this material in high voltage switchgear in the future.

Influence of phosphorus-based flame retardants on polypropylene insulation for high-voltage power cable applications

For high voltage (HV) power cable applications, various studies have been performed to improve the mechanical and electrical properties of polypropylene (PP)-based insulation materials to replace crosslinked polyethylene. However, studies on the effect of additives to yield additional PP properties are still lacking. Herein, we prepared PP blends by melt-mixing widely used commercial flame retardants for PP with isotactic PP (iPP) and investigated their electrical breakdown, flame retardancy behaviors, and UV stability. Among the five kinds of flame retardants employed, aluminum hypophosphite (AHP), aluminum diethyl phosphinate, melamine pyrophosphate, ammonium polyphosphate (APP), and APP treated with silane, AHP was very effective in minimizing the decrease of the direct current breakdown strength of iPP at both 25 °C and 110 °C in the range of 5–20 phr. Particularly, only AHP afforded V-2 grade flame retardancy to iPP, and the flame retardancy was maintained even when the content was reduced to 3 phr. Furthermore, upon exposure to ultraviolet (UV) rays for 5 d, the tensile strength of pristine iPP decreased by approximately 44%, while that of a blend with 3 phr AHP decreased by only 10%. The study results will contribute to the optimization of power cable products through the use of appropriate flame retardants in the design of high-performance PP-based HV insulation materials.

The study of the effect of the pores on the electric field distribution inside alumina ceramic

Alumina ceramics are widely used as high-voltage insulation material due to its good electric insulation. As we all know that the defects inside the ceramic have great impact on the insulation property of the ceramics, especially the pores. For a better understanding of the effect of the pores, we carried out the fundamental study of how the pores affect the electric field distribution inside alumina ceramics by simulation and theoretical analysis. The results showed that the electric field strength inside the pore is higher than that without any pores inside the ceramic and the increased proportion is almost constant which is not relative to the size and location of the pore.

Design and Management of High Voltage Power Systems and Insulation Materials

To satisfy the fast-growing electricity demand, high-voltage power systems with higher performance and better stability are required, which raises challenges including the design of power systems, the control of high-power electronics, the synthesis and preparation of high-performance insulation materials, evaluation of the insulation conditions, dielectric insulation tests, material modification, environment protection, etc [...]

Polyetherimide for Magnet Wire Applications

<div class="section abstract"><div class="htmlview paragraph">Magnet wire is composed of a conducting core and thin layer of electrical insulation. Copper (Cu) is typically used as conducting core, and various polymers such as polyamideimide, polyimide, and polyesterimide are used for electrical insulation. The role of the magnet wire is related to the interchange between electrical and mechanical energy for energy transformation application such as transformers, motors, generators etc. Currently, the electric vehicles (EV) industry is growing rapidly and demands on related components are therefore increasing. Compared to the combustion engine, EV needs more electrical power with higher voltages or higher currents, which can increase probability of electrical discharge. The degradation of the insulation layer can occur by polymer bond breakage due to electrical stresses under partial discharge. To keep high performance under higher voltage, insulating polymers should have high heat and chemical resistance as well as low water absorption. In addition, the adhesion between the insulating polymer and Cu should be sufficient to prevent crack issues. As an incumbent solution, polyamideimide (PAI) and polyimide (PI) is being used for this application in a varnish form. However, PAI absorbs moisture in humid environments or when immersed in water (up to 5% weight), which can cause reliability issues [<span class="xref">1</span>]. PI shows very poor adhesion strength with the conducting core due to its stiffness and low surface energy [<span class="xref">2</span>, <span class="xref">3</span>], which can cause reliability problems for magnet wires [<span class="xref">4</span>]. Therefore, there are strong demands to solve such issues like improvements in dielectric strength, water resistance, and high heat resistance. In this report, we will share the results of excellent flexibility, adhesion, and electrical performance of polyetherimide (PEI, ULTEM™ resin) based varnish as a high voltage insulation material.</div></div>

Recognition of Fused Partial Discharge Patterns in High Voltage Insulation Systems: A Hybrid DCNN and SVM Based Approach

The performance assessment of insulation materials within the components of a high voltage power system depends upon effective condition monitoring techniques of the insulation. One of the important phenomena to be considered in the diagnostics and performance assessment of high voltage insulation materials is the Partial Discharge (PD) measurement. The improved Deep learning techniques help in the effective identification and classification of various sources of PD mechanism. In this work, Deep Convolution Neural Network (DCNN) technique is proposed for the fusion of several features that are extracted from the PD signals. Three-dimensional Phase Resolved patterns of PD images can be used for training the DNN. For the classification of PD patterns, linear and non-linear type of multi-class support vector machine has been proposed. The results obtained are compared with linear SVM and non-linear SVMs with the polynomial kernel, Radial Basis Function (RBF) kernel, and Sigmoidal kernel. The SVM type with a higher pattern recognition rate is identified to be effective in PD pattern recognition and classification. The results of the proposed work show that the fusion approach of PD patterns supports applying huge PD data sets as input, generated by multiple faults, for effective PD pattern recognition.

Crosslinking-modulated direct-current conductivity of XLPE-PS composite via charge trap characteristics

Low direct-current (DC) conductivity is one of the most desired characteristics for crosslinked polyethylene (XLPE) as a high-voltage DC cable insulation material. In this Letter, a correlation between the DC conductivity and cross-linking characteristics of XLPE-polystyrene (PS) composites at 50 °C was studied. Experimental results show that by adjusting the cross-linking structure, different trap distribution characteristics for XLPE-PS composites were realized. With the increase in the cross-linking agent content, DC conductivities of XLPE-PS composites tend to decrease, and the introduced average trap depth increases correspondingly. An increase of 0.07 eV for average charge trap depth in XLPE-PS composites could be acquired in the test range. It is considered that the increase in the average trap depth reduces the carrier mobility, contributing to the reduction of DC conductivity for XLPE-PS composites. Thus, the DC conductivity and average trap depth of XLPE composites show a strong relevance. The results suggest that the interaction between PS particles and the matrix introduced by cross-linking plays a dominant role in determining the charge conduction for XLPE-PS composites.

Effect of X-ray irradiation on the properties of alumina ceramics

Alumina ceramics are commonly used as high-voltage insulation materials. The alumina ceramic will turn yellow after being irradiated with a certain amount of X-rays. Based on this phenomenon, we focused on the study of the yellowing mechanism and the effect of X-ray irradiation on the electrical insulation properties of alumina ceramics. The results indicate that after X-rays irradiating on the alumina ceramic, the color becomes yellow due to the generation of color centers; within an irradiation dose of 3 mGy, X-rays have no adverse effect on the electrical insulation properties of the alumina ceramic.

Solubility and Diffusivity of Polar and Non-Polar Molecules in Polyethylene-Aluminum Oxide Nanocomposites for HVDC Applications

The best commercial high-voltage insulation material of today is (crosslinked) ultra-pure low-density polyethylene (LDPE). A 100-fold decrease in electrical conductivity can be achieved by adding 1–3 wt.% of well-dispersed inorganic nanoparticles to the LDPE. One hypothesis is that the nanoparticle surfaces attract ions and polar molecules, thereby cleaning the surrounding polymer, and thus reducing the conductivity. LDPE-based nanocomposites with 1–12 wt.% octyl-coated aluminum oxide nanoparticles were prepared and the sorption and desorption of one polar compound (acetophenone, a crosslinking by-product) and one non-polar compound of a similar size (limonene) were examined. Since the uptake of acetophenone increased linearly with increasing filler content, whereas the uptake of limonene decreased, the surface attraction hypothesis was strengthened. The analytical functions for predicting composite solubility as a function of particle size and filler fraction were derived using experimental solubility measurements and Monte Carlo simulations.

In situ synthesis of epoxy nanocomposites with hierarchical surface-modified SiO2 clusters

Polymer nanocomposites are often produced using in situ approaches where an inorganic filler (as the dispersed phase) is synthesized directly in an organic matrix. Such an approach generally leads to improved dispersion and reduced agglomeration of the filler material. Epoxy-based nanocomposites have demonstrated promising properties for application as high-voltage insulation materials. In this work, a sol–gel based method has been adapted to synthesize surface-functionalized SiO2 in situ in epoxy. The synthesized SiO2 moieties were dispersed in clusters of 10–80 nm, and formed chemical bonds with the epoxy monomers via a silane coupling agent. Raman spectra show the formation of four-membered D1 rings, which may be part of a cage-like structure similar to that of polyhedral oligomeric silsesquioxanes (POSS). SAXS measurements indicate that the SiO2 clusters consist of a hierarchical structure with an increasing fractal dimension with increasing SiO2 content. The nanocomposites displayed improved thermal stability, while the glass transition behavior varied depending on the structure and content of the SiO2 moieties. While the relative permittivity showed no significant changes from that of pure epoxy, the onset of the dielectric relaxation changed with the SiO2 structure and content, similar to the behavior observed for the glass transition.The synthesis of surface-functionalized SiO2 in situ in an epoxy resin (DGEBA) resulted in a good dispersion and limited agglomeration of the SiO2 in the nanocomposite, with little deviation in the dielectric properties (i.e., complex permittivity). The SiO2 is suspected to have a hierarchical structure based on the SAXS measurements, with the primary structural level consisting of POSS-like cages, and an evolution in the structure from inorganic chains to cross-linked clusters with increasing SiO2 content.

Technical committees

Outdoor insulators have been widely recognized as backbone components installed in the power system in order to maintain a reliable power supply. The ability of outdoor insulating materials to withstand different weathering conditions in different outdoor environment high voltages has been an important task defined for both suppliers and users of outdoor insulators in the power industry. The use of standard material screening methods is an essential step conducted in order to qualify outdoor insulating materials for their targeted high voltage applications. Various standard guides have been developed, but the need remains to update or create new guides addressing new challenges in the power system. The main aim of this technical committee is to develop IEEE guides on evaluation methods of high voltage insulation materials in the outdoors. The following objectives can be highlighted in achieving this aim: • Providing a scheduled forum such as workshops, special sessions and meetings, addressing new challenges in the industry. • Conducting technical activities such as round robin testing and state-of-the-art literature surveys on recent advances. • Publishing review articles, position papers and special issues in the journals of DEIS.

Theoretical Study on the Grafting Reaction of Maleimide to Polyethylene in the UV Radiation Cross-Linking Process.

Theoretical investigation of the reaction of graft maleimide to polyethylene in the UV radiation cross-linking process is accomplished at the B3LYP/6-311+G(d,p) level for high-voltage cable insulation materials. The reaction potential energy surface of the nine reaction channels is identified. The results show that the N,N′-ethylenedimaleimide can connect two 4-methylheptane molecules and act as the cross-linking agent. The calculated reaction potential barrier of forming 4-methylheptane radical by maleimide is higher than that of maleic anhydride. The study is expected to provide a basis for optimizing the UV radiation cross-linking polyethylene process and development more than 500 kV high-voltage cable insulation materials in practical applications.

First-principle simulations of electronic structure in semicrystalline polyethylene.

In order to increase our fundamental knowledge about high-voltage cable insulation materials, realistic polyethylene (PE) structures, generated with a novel molecular modeling strategy, have been analyzed using first principle electronic structure simulations. The PE structures were constructed by first generating atomistic PE configurations with an off-lattice Monte Carlo method and then equilibrating the structures at the desired temperature and pressure using molecular dynamics simulations. Semicrystalline, fully crystalline and fully amorphous PE, in some cases including crosslinks and short-chain branches, were analyzed. The modeled PE had a structure in agreement with established experimental data. Linear-scaling density functional theory (LS-DFT) was used to examine the electronic structure (e.g., spatial distribution of molecular orbitals, bandgaps and mobility edges) on all the materials, whereas conventional DFT was used to validate the LS-DFT results on small systems. When hybrid functionals were used, the simulated bandgaps were close to the experimental values. The localization of valence and conduction band states was demonstrated. The localized states in the conduction band were primarily found in the free volume (result of gauche conformations) present in the amorphous regions. For branched and crosslinked structures, the localized electronic states closest to the valence band edge were positioned at branches and crosslinks, respectively. At 0 K, the activation energy for transport was lower for holes than for electrons. However, at room temperature, the effective activation energy was very low (∼0.1 eV) for both holes and electrons, which indicates that the mobility will be relatively high even below the mobility edges and suggests that charge carriers can be hot carriers above the mobility edges in the presence of a high electrical field.

Experimental Evaluation and Comparison of Thermal Conductivity of High-Voltage Insulation Materials for Vacuum Electronic Devices

Vacuum electronic devices operate with very high voltage differences between their sub-assemblies which are separated by very small distances. These devices also emit large amounts of heat that needs to be dissipated. Hence, there exists a requirement for high-voltage insulators with good thermal conductivity for voltage isolation and efficient heat dissipation. However, these voltage insulators are generally poor conductors of heat. In the present work, an effort has been made to obtain good high-voltage insulation materials with substantial improvement in their thermal conductivity. New mixtures of composites were formed by blending varying percentages (by volumes) of aluminum nitride powders with that of neat room-temperature vulcanizing (RTV) silicone elastomer compound. In this work, a thermal conductivity test setup has been devised for the quantification of the thermal conductivity of the insulators. The thermal conductivities and high-voltage isolation capabilities of various blended composites were quantified and were compared with that of neat RTV to evaluate the relative improvement.

New diagnostic method of electrical insulation properties based on current integration

We developed a compact system for evaluating the deterioration of insulating materials used in high-voltage dc power apparatuses. The developed system can be used for simultaneous determination of three basic parameters important for evaluating the deterioration of high-voltage insulation materials, i.e., conductivity, dielectric constant, and charge accumulation. Charge accumulation, which is detrimental to high-voltage dc electrical apparatuses, such as power devices, transformers, and power cables, can be evaluated using this system. With this system, the charges accumulated are measured by integrating the current through a capacitor inserted between the highvoltage power source and the high-voltage apparatus to be tested. The obtained information is transmitted to the unit placed at ground potential. The evaluation is carried out by comparing the amount of initial charges in the insulating material with that of charges accumulated at a certain time after application of a high voltage. When the ratio of the charges accumulated at time (t) to that of the initial charge is 1, it is assumed that there was no charge accumulation; thus, no deterioration of the insulating material is assumed. However, when the ratio is greater than 1, the insulating material is considered to have deteriorated. Using the evaluation system, we developed, we examined the deterioration of insulating materials used in coaxial cables by exposure to 1) γ-rays and 2) high-temperature conditions. From these two experiments using the developed system, the deterioration of insulating materials was found to have advanced substantially when the charge accumulation ratio exceeded approximately over 2.0.