Materials In Electrical Engineering Research Articles

Modelling and measuring of temperature distribution in explosive cladded materials under induction heating

The work focuses on the modelling and experimental verification of induction heating systems with multilayered loads made of paramagnetic materials obtained through explosive cladding. The research is driven by the industry’s increasing interest in multilayered materials in electrical engineering and electronics. In this case, two- and three-layered configurations, as well as a cylindrical-shaped work coil, were considered. The main parameter subjected to verification was the surface temperature of the batch and its distribution. Due to relatively high temperatures, three measurement methods were used for temperature verification and effectiveness comparison: thermal imaging camera, pyrometer, and thermocouple. Additionally, the developed numerical models will provide a better understanding of the phenomena occurring in multilayered materials under the influence of rapidly changing electromagnetic fields and their impact on the heating process of the entire load. The article also addresses the issue of constructing models with a high discretisation level.

Realization of a Test Tool for Diagnosis of Contact Resistance and Measurement of Selected Types of Conductive Materials

Contact connections in electrical machines and apparatus are important elements in the whole power supply network and a high level of reliability is expected there. Contact resistance is a fundamental criterion in the design of an electrical contact or contact system. The contact resistance should be as low as possible to minimize losses due to the current passage and the related heating of the contact connection. The value of the contact resistance depends on the material used, the value of the applied force, the type of contact, and, last but not least, the quality of the surface and chemical layers. In this paper, an initial diagnosis of the contact material is performed based on the determination of the sample’s specific resistivity by the four-wire method and the evaluation of the measurement uncertainty. The work is followed by the design of a testing device that uses crossed bars to measure the change in contact resistance as a function of the magnitude of the applied force. An analysis of the sample mounting method is performed here using FEM simulations of the current field and shows the interaction between the holder and the sample in terms of current line transfer. The proposed system is then used for experimental measurements of the material-dependent coefficient KC for verification of existing or newly developed materials in electrical engineering, where the values of the KC coefficient are not known. Finally, the paper also deals with the measurement of fritting voltage for individual contact pairs having surface quality corresponding to brushing.

Measurement and Simulation of Magnetic Properties of Nanocrystalline Alloys under High-Frequency Pulse Excitation

In order to broaden the application of nanocrystalline soft magnetic materials in electrical engineering under extreme conditions, nanocrystalline alloys must also have good characteristics under high-frequency and nonsinusoidal excitation. In this paper, the magnetic properties of Fe-based nanocrystalline alloys excited by high repetition frequency pulses were measured. Excitation frequency and duty cycles are two important factors in the study of magnetic properties under pulse excitation. With the amplitude of the pulse remaining constant, different local hysteresis curves were obtained by changing the frequency and duty cycle. The experimental results proved that the higher the frequency is and the smaller the duty cycle is, the narrower the local hysteresis loop is. Finally, the finite element method (FEM) was used to model the magnetic core coupling with an impulse circuit based on the measured magnetic properties. Compared with the experimental results, the simulation results showed that the field-circuit coupling analysis model can effectively reflect the influence law of the frequency and duty cycle on magnetic properties.

Rainer Waser – A Pioneer of Fundamentals of Resistive Switching Memories

Rainer Waser – A Pioneer of Fundamentals of Resistive Switching Memories

Mechanically robust epoxy with electrical breakdown healing capability for power equipment insulation via dynamic networks

Electrical breakdown is a classical failure mod of epoxy when applied as insulating materials in electrical engineering, which greatly threatens the reliability of power equipment. However, as a stiff polymer, the healing of epoxy is usually considered to be inaccessible. In this study, new epoxy networks with electrical breakdown healability were developed for power equipment insulation. The dynamic networks are generated by amine-terminated ring-opened epoxies and bi-functional isocyanates, which endows good reprocessability and healability. Artificial puncture was first made to simulate electrical breakdown features and clarify the influence of failure shape on healability. Electrical damage was carried out afterwards, the thru-hole generated by electrical breakdown is able to be recovered after healing within 10 min. A high healing efficiency of about 90% based on breakdown strength is observed. With temperature and pressure stimulation, the network dissociated reversibly to rejoin the separated surface of the breakdown holes. Meanwhile, the carbon residue generated by electrical discharge is squeezed and isolated by flowed chain segments. Moreover, by replacing bisphenol-A epoxy resin with the hydrogenated epoxy resin of a lower C/H ratio, less carbon residue can be detected after electrical breakdown and improved healability on morphology and insulation properties is discovered.

Nanosecond pulse-driven atmospheric-pressure plasmas for polymer surface modifications: Wettability performance, insulation evaluation and mechanisms

Epoxy resin (EP) is one of the most widely-used insulating support materials in electrical power systems, with its insulating performance playing an important role in high-voltage engineering. In this study, a nanosecond pulse-driven Ar/Octamethylcyclotetrasiloxane (OMCTS) plasma jet is developed for fabricating nanocomposite dielectric materials to enhance their EP properties. It is demonstrated that the plasma-enabled polymerization effectively modifies the physical morphology and chemical composition of EP surfaces, where the surface roughness greatly increases with the deposition of less-polar silicon-containing films. Moreover, with an increased OMCTS carrier gas flow rate, the surface conductivity of the EP increases by two orders of magnitude, which is directly related to the appearance of shallow traps in the dielectric surface after Ar/OMCTS plasma treatment. Results show that the trap depth of the electron decreases from 1.21 to 0.99 eV post-treatment, with the OMCTS fragments becoming shallow trap points for charge detrapping and transportation processes. Moreover, the addition of a controlled amount of OMCTS increases the plasma discharge intensity, promotes silicon film deposition, and thus significantly improves the insulation and wettability performance, with higher flashover voltages and water contact angles (WCA). By contrast, excessive addition of OMCTS inhibits the plasma discharge due to the absorption and consumption of energetic electrons by OMCTS molecules. Quantum chemistry calculations are further developed to explore the mechanisms of plasma-induced surface modifications. Overall, the proposed plasma polymerization strategy offers a promising fabrication technique and provides guiding insights into the fabrication of nanocomposite dielectric materials in electrical engineering.

Interaction between copper and thermally expanded graphite during mechanical alloying and spark plasma sintering

Copper and graphite currently serve as electrical engineering materials. For example, either can be used to make electrodes and contacts. Composite materials (including copper-graphite composites) offer better performance — i.e. relative electroerosion resistance and productivity. However, the scope of their application is limited and further research into them is necessary. This research aims to examine the effect of mechanical alloying of the copper – themally expanded graphite powder system followed by spark plasma sintering on the structure of particles and materials and on their physico-mechanical properties. The experimental study into the structure and properties of composite powder materials involved using the methods of X-ray phase analysis, Raman spectroscopy, atomic-force spectroscopy, metallography, spark machining, etc. Powders of high-conductivity copper PMS-1 (per GOST 49-60–75) and thermally expanded graphite produced by Novomet-Sealur were used to make the composite materials. The compositions included 1 wt. % (4 vol. %) of graphite. The process involved mechanical alloying for 1, 2 and 3 hours in a SAND planetary mill (Russia) with the powder-to-balls weight ratio of 1:25. The process resulted in the structural breakdown of graphite and the formation of solid solutions of carbon in copper. Following the process of spark plasma sintering in a Dr. Sinter SPS-1050 unit (Japan) at 900 oС, the latter experienced partial decomposition. This paper demonstrates the role of copper in the restoring of graphite structure during mechanical alloying. Copper-based materials have been developed which have lower electrical resistivity than copper. Intercalates formed in graphite may serve as one of probable mechanisms for decreasing the electrical resistivity. A larger copper-graphite phase contat area and a higher deformation degree of graphite during mechanical alloying lead to higher electrical resistivity in composite materials. A correlation was established between the relative spark erosion wear and the electrical resistivity in copper-graphite composite materials. Thus, the relative spark erosion wear of the best compositions was 20–30% lower than in the case of cast copper M1. The feasibility of using copper-graphite EDM electrodes can be reached due to reduced cost of the EDM electrodes that offer high wear resistance combined with higher performance.This research was funded by the Ministry of Education and Science of Russia under the programme of the World-Class Science & Education Centre Rational Use of Mineral Resources.

Nonlinear Electrical Conduction in Polymer Composites for Field Grading in High-Voltage Applications: A Review

Applications of polymeric materials in electrical engineering increasingly require improvements in operating voltages, performance, reliability, and size reduction. However, the resulting increase on the electric field in electrical systems can prevent achieving these goals. Polymer composites, functionalized with conductive or semiconductive particles, can allow us to reduce the electric field, thus grading the field within the system. In this paper, a comprehensive review of field-grading materials, their properties, and recent developments and applications is provided to realize high-performance high-voltage engineering applications.

Design of Novel High-Frequency 2-D Magnetic Properties Tester for Nanocrystalline Alloy

To broaden the applications of promising nanocrystalline magnetic materials in electrical engineering at high frequency, the materials must be characterized well at a wide range of frequencies and fields. This paper proposes a novel two-dimensional (2-D) magnetic properties tester up to 20 kHz. The finite element method is used to optimize the tester design by calculating the magnetic field distributions in the specimen and yokes. Considering the dimension and physical properties of the specimen, a particular B - H sensing structure is designed to measure the flux density and field intensity in the specimen. Furthermore, a frequency-domain feedback control system is integrated into the measurement system in order to control the waveform of flux density. Moreover, the paper discusses the factors which impact on the experimental results. This paper demonstrates that the novel tester is reliable to study the magnetic properties of materials. At last, the 2-D rotational magnetic properties of nanocrystalline alloy are preliminary measured.

Remarkable improvement of organic-to-inorganic conversion of silicone rubber at elevated temperature through platinum-nitrogen catalytic system

Organosilicon materials with high capacity of organic-to-inorganic conversion at elevated temperature are always favorable in the field of high-temperature-resistant materials, flame retardant materials, chemical engineering and functional materials in electrical engineering. In this work, it was found out that the platinum-nitrogen catalytic system could obviously enhance the organic-to-inorganic conversion efficiency of silicone rubber (SiR) at elevated temperature. The residual rate of Pt/N/SiR (SiR containing 0.33 phr Karstedt's catalyst (Pt) and 2 phr nitrogenous silane (N)) at 1000 °C was significantly improved from 3.0% to 44.8% in comparison with SiR and its thermal stability was also enhanced. DLS, TEM and UV–vis absorption spectrometry revealed that the platinum in Karstedt's catalyst would aggregate at elevated temperature and deteriorate its catalytic activity for organic-to-inorganic conversion of SiR. And the addition of nitrogenous silane can efficiently inhibit the aggregation and retain the high catalytic efficiency of platinum. A thorough TG-FTIR study, together with SEM/EDX and XPS analyses suggested that the platinum-nitrogen system might suppress the intramolecular cyclic transition and enhance the radical coupling between polymer chains of SiR during thermal degradation, which resulted in the high capacity of organic-to-inorganic conversion of Pt/N/SiR at elevated temperature.

Anomalous Loss Modeling and Validation of Magnetic Materials in Electrical Engineering

By using statistical approaches, a calculation model of anomalous loss in magnetic materials is built on the basis of the production of anomalous loss and domain wall motion. Based on that, a macrophysical interpretation of this model is described in detail, and a testing method to determine the microstatistical characteristic parameters is proposed due to the pure anomalous loss obtained by the separation of total experimental core losses in electrical steel sheets. Meanwhile, the characteristics of the coefficient of anomalous loss are analyzed. In addition, rotating anomalous loss can be extended in this model. Therefore, under trusted error range, the separated and predicted values of alternating and three-dimensional rotating anomalous losses are compared and analyzed, respectively. The results clearly underline the necessity of achieving more accurate loss coefficients.

Enhancing the thermal and electrical performance of epoxy microcomposites with the addition of nanofillers

Polymers are widely used insulating materials in electrical engineering because of their good dielectric properties, low cost, light weight, and ease of production. However, polymers exhibit a relatively low thermal conductivity that ranges between 0.1 and 0.6 W/mK. An approach to improve the thermal performance of polymers is the addition of high loadings of microsized fillers with high thermal conductivity [1]–[8]. However, most of the time, microcomposites exhibit inferior electrical properties such as higher relative permittivity and/or lower breakdown strength, compared with neat materials or microcomposites with lower fill grades [2], [4], [9]–[11]. In the last years, much research has been carried out to evaluate the potential advantages that nanosized fillers can offer to polymers [12], [13].

A Residential Interactive End-Use Electric System with Electrical Engineering Materials Based on RTP and Load Forecasting

As smart grid has been under rapid construction in China, this paper proposes an interactive information system according to the interaction feature of smart grid. End users are able to exchange electricity usage information with power utilities by using this system. Structures and functions of this system are demonstrated first. Smart meter plays a key role in the whole system and it is connected with other parts of the system by GPRS and serial communicating paths. Subsystems both of grid side and users side are designed in details. Information of real-time pricing(RTP) and load forecasting is applied to motivate users to participate the operation of the grid actively so that energy resources could be optimized and finally goals of economical and high-efficient using of energy can be achieved.

Polymer‐Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics

Preceramic polymers were proposed over 30 years ago as precursors for the fabrication of mainly Si‐based advanced ceramics, generally denoted as polymer‐derived ceramics (PDCs). The polymer to ceramic transformation process enabled significant technological breakthroughs in ceramic science and technology, such as the development of ceramic fibers, coatings, or ceramics stable at ultrahigh temperatures (up to 2000°C) with respect to decomposition, crystallization, phase separation, and creep. In recent years, several important advances have been achieved such as the discovery of a variety of functional properties associated with PDCs. Moreover, novel insights into their structure at the nanoscale level have contributed to the fundamental understanding of the various useful and unique features of PDCs related to their high chemical durability or high creep resistance or semiconducting behavior. From the processing point of view, preceramic polymers have been used as reactive binders to produce technical ceramics, they have been manipulated to allow for the formation of ordered pores in the meso‐range, they have been tested for joining advanced ceramic components, and have been processed into bulk or macroporous components. Consequently, possible fields of applications of PDCs have been extended significantly by the recent research and development activities. Several key engineering fields suitable for application of PDCs include high‐temperature‐resistant materials (energy materials, automotive, aerospace, etc.), hard materials, chemical engineering (catalyst support, food‐ and biotechnology, etc.), or functional materials in electrical engineering as well as in micro/nanoelectronics. The science and technological development of PDCs are highly interdisciplinary, at the forefront of micro‐ and nanoscience and technology, with expertise provided by chemists, physicists, mineralogists, and materials scientists, and engineers. Moreover, several specialized industries have already commercialized components based on PDCs, and the production and availability of the precursors used has dramatically increased over the past few years. In this feature article, we highlight the following scientific issues related to advanced PDCs research: (1) General synthesis procedures to produce silicon‐based preceramic polymers. (2) Special microstructural features of PDCs. (3) Unusual materials properties of PDCs, that are related to their unique nanosized microstructure that makes preceramic polymers of great and topical interest to researchers across a wide spectrum of disciplines. (4) Processing strategies to fabricate ceramic components from preceramic polymers. (5) Discussion and presentation of several examples of possible real‐life applications that take advantage of the special characteristics of preceramic polymers.Note: In the past, a wide range of specialized international symposia have been devoted to PDCs, in particular organized by the American Ceramic Society, the European Materials Society, and the Materials Research Society. Most of the reviews available on PDCs are either not up to date or deal with only a subset of preceramic polymers and ceramics (e.g., silazanes to produce SiCN‐based ceramics). Thus, this review is focused on a large number of novel data and developments, and contains materials from the literature but also from sources that are not widely available.

Important Role of the Hall Effect Measurement System in a Modified Course of Materials in Electrical Engineering

The course ldquoMaterials in Electrical Engineeringrdquo is a core course in the Mechatronics curriculum at the Faculty of Technical Sciences, University of Novi Sad, Serbia. In the past, this course was comprehensive and mainly theory-based. Teaching methods used in this course had not been changed for many years, and were mainly based on a traditional approach. They were therefore often outdated, and boring for students. In addition, the lack of modern materials characterization equipment was a significant weakness of the course in its early stages. This paper presents the main aspects of the modified course, which features a greater inclusion of modern equipment in its teaching methodology; in particular it introduces the Hall effect measurement system as an indispensable characterization technique in education, research and in the semiconductor industry. This paper also describes how students can be taught to use the Hall effect measurement system to determine the structural and electrical characteristics of different materials. Finally, students' feedback and observations on the modified course and the applied teaching methodology are discussed.

Very high speed micromachining of electrical materials

The advent of micro electro mechanical systems has created a demand for high precision functional products at the microscale. Machining processes must be scaled down accordingly. This paper explains the mechanics of micromachining and how it can be applied to machining electrical engineering materials.

Soft magnetic materials for electrical engineering: state of the art and recent advances

AbstractThis article gives a brief description of the essential characteristics and principal applications of amorphous, crystalline and nanostructured soft magnetic materials in electrical engineering. Copyright © 2005 John Wiley & Sons, Ltd.

Influence of frequency, electrode material and superimposed dc on ac electroluminescence in polymer films

Summarizes new results on the influence of some experimental parameters on ac electroluminescence (EL) of polymers used as insulating materials in electrical engineering. Electroluminescence under a uniform ac field is investigated in low density polyethylene (PE) and polyethylene naphthalate (PEN) films with semi-transparent electrodes on both sides. Particular emphasis is given to polyethylene. The dependence of EL on the voltage frequency is investigated in the range of 10/sup -2/ Hz to 10/sup +2/ Hz with the help of phase-resolved measurements. The influence of the electrode/polymer contact is investigated by changing the electrode material (gold, silver, and calcium). The effect of a superimposed dc bias on the ac voltage is also reported.

Study of rapidly solidified Cu–Cr–RE alloys

Electrical engineering materials of Cu–Cr–RE have been made using the technology of rapid solidification, composite green compacts, extrusion and so on. By means of the analysis of optical metallographs, electron microscopy, physical and mechanical properties as well as electrical properties, and the examining of the hardness, softening temperature, etc. the authors selected Cu–Cr–Y alloy, which has excellent comprehensive properties. The authors have also made a deep study of the chromium and yttrium elements, which affect the structure, the recrystallization temperature, the strength at room and high temperature, the resistivity and contact resistance, and have also compared the properties of the Cu–Cr and Cu–Cr–Y alloy. The results show that rapidly solidified technology and added rare–earth elements not only enhance the fine grain boundary strengthening, but also the second phase strengthening. Cu/Cu–Cr–Y composite material improves the thermal stability and thermal endurance, and also maintains a better electrical conductivity and thermal conductivity.

Book Review: Principles of Electrical Engineering Materials and Devices

Book Review: Principles of Electrical Engineering Materials and Devices