Ceramic Insulators Research Articles

An analytical and numerical investigation into conductive-radiative energy transfers in evacuated honeycombs. Application to the optimisation and design of ultra-high temperature thermal insulation

Ultra-high temperature thermal and latent energy storage technologies offer a potential solution to the decarbonisation of the energy sector. However, uneconomical thermal energy losses are a barrier to their development and where significant, their minimisation requires knowledge about the different modes of thermal transport and their interaction in a given structure. In this paper, evacuated rectangular honeycomb structures are investigated as candidates for efficient ultra-high temperature thermal insulation.First, a theory is laid out along with its numerical implementation for the modelling of coupled non-linear conduction and radiation in three-dimensional cuboid multi-media structures with rarefied gaseous and opaque or semi-transparent solid media. The model is then applied to the study, optimisation and design of efficient ultra-high temperature thermal insulation based on rectangular honeycomb structures.A dimensionless number Nrc is defined and an analytical thermal analysis of rectangular honeycombs is developed which correlates Nrc to the optimal geometry and equivalent thermal conductivity of a honeycomb insulator. A numerical optimisation procedure is then presented and the correlations are validated, and thus constitute simple practical design tools for honeycomb insulators. Finally, it is shown that with an appropriate choice of geometry and materials, thin-walled honeycombs have the capacity to outperform existing high-temperature thermal insulation technologies with thermal conductivities lower than 0.01 W/m/K at 1600 K. In particular, a wall thickness of 50μm on a titanium alloy honeycomb would suffice to outperform ceramic fibre insulation over its entire range of operating temperatures.

High Temperature Corrosion Stability of Ceramic Materials for Magnetohydrodynamic Generators

Abstract Corrosion by alkali metals and their compounds poses a significant challenge to the long-term material stability and service life for both metal alloys and ceramics at high operating temperatures. Chemical reactivity between alkali metals and materials underlie numerous industry challenges ranging from fireside corrosion in biomass-fired boilers to reaction with silica-based refractory ceramics in glass furnaces. The problem is particularly significant in magnetohydrodynamic (MHD) generators, where potassium or cesium compounds are introduced to improve the electrical conductivity of the working fluid. Thus, resistance to attack by alkali metal vapor is an important consideration in the selection and fabrication of ceramic electrodes and insulators for MHD generators. We evaluated several refractory ceramics to assess phase stability and known reactions with potassium and its compounds at high temperatures (T > 1,200 °C). Refractory ceramics were tested for potassium vapor corrosion using a modified ASTM standard test method with in situ monitoring of gas composition. Unlike other materials, the magnesia (MgO) and ceria (CeO2) samples did not exhibit corrosion, and no phase or mass changes were observed. This indicates that CeO2 and MgO could exhibit long lifetimes as plasma facing components in MHD generators. Ultimately, this development provides valuable data in evaluating critical materials performance issues that can attest to the viability of high temperature direct fired MHD generator applications.

ASSESSMENT OF UTILIZATION OF CERAMIC WASTE AS A SUBSTITUTE TO CONCRETE CONSTITUENTS – A REVIEW

Due to high consumption of concrete constituents namely, natural aggregates and cement, their de-pletion is observed globally. Over the years, many researchers have come up with alternatives to these basic constituents of concrete. Ceramic waste (CW) generated from ceramic industries (indus-tries producing tiles, sanitaryware, ceramic refractories, ceramic insulators, ceramic crockery) have not found any reuse and is deposited as landfills, which further increases land pollution and also give rise to health issues. The CW can be easily grinded as per required size, which have interested many researchers to use it in the production of concrete. Till date CW has been used as partial re-placement to cement, fine aggregates and coarse aggregates. This review paper discusses the poten-tial of CW as replacement to concrete constituents in the production of concrete and its effect on mechanical and durability properties. The literature review is carried in three parts – review on use of CW to replace cement, fine aggregates and coarse aggregate. The study shows different research-es using different sources of CW having varied properties being used as partial replacement. The effect of replacement on concrete strength and durability is reported

Parameters Optimization of UAV for Insulator Inspection on Power Transmission Line

In recent years, Unmanned Aerial Vehicle (UAV) technology has been widely used in power transmission line inspection. UAV operating parameters determine the quality of the acquired insulator image, which directly affects the efficiency of transmission line inspection. Regarding the inspection of ceramic insulators, this work establishes a three-dimensional (3D) model of ceramic insulators, and simulates the changes in shooting distance, angle, and height of the UAV through three geometric transformations: rotation, translation, and scaling. The influence of those three UAV operating parameters (the shooting distance, angle, and height) on the integrity of the ce-ramic insulator steel cap is studied. In the infrared zero value detection of 110kV ceramic insulators, It is found that the best setting for obtaining the maximum steel cap area is: shooting distance of 3 - 7 meters, shooting height of 1 meter below the center of the insulator string, and a shooting depression angle of 0°. The UAV operating parameters setting method proposed in this paper will provide theoretical and practical basis for the in-depth intelligent inspection of transmission line insulators.

Improving Thermal and Mechanical Properties of Concrete by Using Ceramic Electrical Insulator Waste as Aggregates

Improving Thermal and Mechanical Properties of Concrete by Using Ceramic Electrical Insulator Waste as Aggregates

Numerical Analysis and Experimental Study of the Laser Cleaning of Ceramic Insulator Contamination

Contamination flashover of insulators is one of the main threats to the safety of power systems, and regular cleaning of insulator surface pollution is an effective solution to this problem. In this paper, the laser cleaning of ceramic insulators is studied via simulations and experiments. The adhesion between a contamination layer and an insulator surface is estimated. A laser cleaning model for contaminated insulators is established, and a numerical analysis of the thermal stress field distribution characteristics of laser cleaning is carried out. Various factors that affect the thermal stress field distribution, including the laser power, laser scanning speed and thickness of the contamination layer, are also analysed. The optimal cleaning parameters for the best performance of laser cleaning are obtained through simulation and experiments. The result shows if the equivalent salt deposit density (ESDD) is 0.05 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the nonsoluble deposit density (NSDD) is 0.25 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the best cleaning effect could be achieved when the laser power is 100 W and the scanning speed reached 6000 mm/s.

Feasibility Study on Electrical Properties of 20 kV Polymeric Insulator Dry Test and Rainwater Test

Insulator is a very important equipment in an electric power system. Ceramic insulators have been widely used to support conductors in 20 kV power lines. The problem of ceramic insulators is that they are heavy, easily contaminated on the surface and require a lot of energy in the manufacturing process. Therefore, polymer insulators were developed. This paper presents the design of an epoxy resin polymer insulator with Titanium Dioxide (TiO2) as a nanofiller. The leakage current test was carried out in a high voltage laboratory by applying an AC high voltage of 50 Hz to the insulator dry conditions and the insulator wetted by rainwater contaminants. The results of the leakage current test in dry conditions are 487.6 μA, rainwater contaminated conditions are 594.93 μA, insulation resistance in dry conditions is 2.07 G-Ohms, and contaminated conditions are 1.41 G-Ohms. Based on the test results show that the insulator leakage current increases up to 22% when the surface of the insulator is contaminated with rainwater. Meanwhile, the insulation resistance decreased by up to 32% in conditions contaminated with rainwater. The value of leakage current and insulation resistance indicates that the epoxy resin insulator with TiO2 as filler is electrically feasible to use.

Anti-aging characteristics of RTV-SiR aided HV insulator coatings: Impact of DC polarity and fillers

Room temperature vulcanized silicone rubber (RTV-SiR) coating is applied globally on conventional ceramic insulators to combat pollution flashovers. The present research was intended to see how the polarity of direct current (DC) voltage and filler incorporation affect the aging performance of RTV-SiR based composites coating when seen in the overall context of multiple environmental stresses. Accordingly, RTV-SiR based specimens were fabricated through loading of micro, nano, and micro-cum-nano fillers in the base matrix and subjected to the multi-stress environment in a specially designed weathering cell. Keeping the rest of the parameters common (fixed), aging was carried out under both polarities of DC voltage for 10,000 lab hours. Results revealed that the coating sample with hybrid micro/nanofillers retained the highest hydrophobicity class under both polarities. Fourier transforms infrared (FTIR) spectroscopic analysis asserted that hybrid samples showed the maximum intactness in essential chemical bonds with minor oxygen-hydrogen (OH) hydroxyl content i.e. 56.01% for positive and 26.9% for negative DC. It also measured the lowest leakage current 5.3 μA and 4.61 μA for positive and negative voltage, respectively. Weight-loss and hardness measurements depict improved performance of filled samples. Moreover, the water absorption properties of all investigated samples were assessed through water permeation tests. The study elucidated that hybrid composite performed distinctly superior showing the highest resistance against collegial stresses. As other aging parameters were common, we could single out the effect of polarity showing positive polarity to be relatively more determinantal to aging.

Application of hydrophobic coating to reduce leakage current through surface energy control of high voltage insulator

A hydrophobic coating was applied using atmospheric-pressure plasma to solve the problem of leakage current caused by the attachment of pollutants to transmission line ceramic insulators. After applying coatings on quartz and ceramic substrates using HMDS:N, C4F8, anti-fingerprint, and CH4 materials, hydrophobicity was determined through water contact angle analysis. In the case of ceramic substrates, the AFM analysis results show that the value of roughness, Ra, determined by the contact angle according to Wenzel's law, of the surface was 63.1–76.4 nm. As a result of XPS and FT-IR analyses, hydrophobic characteristics were observed when C-H bonding was large and Si-O bonding and oxygen content were small. The finite element method analysis shows that when a hydrophobic coating material possessing a high contact angle is used, the adhesion density of contaminants with conductivity is lower than that of a ceramic insulator with hydrophilicity. This reduces the leakage current. It is difficult to artificially clean an insulator in the installation environment, and fewer pollutants will attach to a hydrophobic surface because of rain, snow, or wind in the natural environment.

A Study of Possible Reasons of the Damage by Electric Current of Traction Induction Motors Bearings of Electric Trains Lastochka and the Ways to Prevent This

There is a problem of damage of bearings of traction induction motors of electric trains Lastochka by electric current. Based on the fact that the bearings have a ceramic insulation coating, and the cases of its electrical breakdown is not fixed, the authors put forward a version that a high-frequency current flows through the bearing as through an electric capacitance. The analysis show that the cause of the current can be a radio standard GSM-R. The proposed technical solution against the damage of bearings: the use of grounding shaft rings, replace the bearings on the other with ceramic rolling elements, arrangement of separate high-frequency grounding for the GSM-R antenna.

Iron encapsulated carbon nanotube composites embedded in alumina with enhanced magnetic properties

Alumina is an essential ceramic insulator, while carbon nanotubes (CNTs) have intriguing mechanical, thermal, electrical, and magnetic properties. We report on the synthesis of CNTs/Al2O3 nanocomposites using the chemical vapor deposition (CVD) process using iron as a catalyst. The as-prepared composite's structure and morphology are characterized by transmission electron microscope, scanning electron microscope, X-ray diffractometer, thermogravimetric analyzer, and Mössbauer spectroscopy. The experimental results show that these composites contain CNTs of an average diameter of 40 nm distributed homogenously within the alumina matrix. The percentage of CNTs within the composites is at 7%. The CNT/Al2O3 nanocomposites demonstrate a dramatic enhancement of ferromagnetic properties during vibrating sample magnetization measurements. As compared to the magnetization of 0.03 e.m.u./g at an applied field of 1.5 T for the Fe-catalyzed Al2O3, the saturation magnetization of CNT/Al2O3 is 1.78 e.m.u./g, which represents an increment of ∼5800%. The coercivity of CNTs/Al2O3 composites increased from 0.036 T at 300 K to 0.285 T at 5 K. This study provides a relatively simple approach to blending the magnetic properties with potential thermoelectric materials.

Degradation analysis of RTV-SiR based composites under both polarities DC voltage for insulators coating

In a high voltage transmission system, insulator pollution highly affects the reliability of operation. Air pollutants from surrounding environment accumulated on insulator surface after some time during field operation. Which ultimately polluted the insulators and severely affects their performance in high voltage lines. To combat the pollution effects, high voltage ceramic insulators are coated with room temperature vulcanized silicone rubber (RTV-SiR) as a one-time interminable solution these days. In this study, an attempt has been made to investigate the aging behavior of several composite coatings. Different test samples for coating with various loading concentrations of alumina tri-hydrate (ATH) and silica (SiO2) were fabricated and subjected to multi-stress aging under both polarities of DC voltage. A weather cycle representing a heavily polluted region of Pakistan was simulated in a chamber for 10,000 h. Various diagnostic techniques of aging like hydrophobicity assessment, leakage current monitoring, Fourier transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were utilized. The aging effect on investigated composites was also evaluated through measurements of mechanical properties. Considering the cumulative effect on aging detected through the measurement of several relevant parameters, it has been established that hybrid composite is most resistant to aging. Further, the polarity effect on aging was manifested showing positive polarity as having a more adverse effect on aging as compared to negative polarity.

System Diagnostics of Supporting-Rod Porcelain Insulation at Digital Substations

This article is dedicated to an important problem of increasing the reliability of supporting-rod porcelain insulation at electric power substations. Porcelain insulation is installed on open switchgears (OSGs) of substations as part of the main switching equipment. Obsolescence and physical wear results in the destruction of supporting-rod porcelain insulators (SRIs), which often leads to serious consequences: shutdown of substation bus systems, emergency shutdown of substation equipment, reduction of power plant loads, as well as they pose a threat to operational personnel during operational switching. When supporting-rod insulation is replaced in due time, it significantly increases the reliability of the main substation equipment. Possible causes of failures were analysed using a graphical technique (Ishikawa diagrams). It has been established that sudden temperature changes of the ambient air are an important negative aspect, especially the transition of temperature values through 0ºC. The work represents a mathematical model of the development of microfractures in the insulation body of a ceramic insulator. The influence of external forces on the insulator leads to the appearance of additional stresses in it, to the destruction of new particles and to the sudden growth of microfractures. The article gives main SRI diagnostic techniques currently used in the electric power industry. According to statistics, it has been established that a relevant approach is the transition to digital technologies, which provides an automated information processing process without deactivating a piece of equipment. The article describes and proves that the proposed system of diagnostics of supporting-rod porcelain insulation at digital substations without deactivating a piece of equipment is a relevant area of scientific development. Within the framework of this scientific study, a patent for invention No. 2743887 dated 20 April 2020 was obtained.

Finite element modeling and assessment of seismic response of electrical substations porcelain post insulators

The study presented in this paper focused on developing accurate computational finite element (FE) model of electrical substations ceramic (porcelain) post insulators. The objective is to investigate the structural behavior and seismic response of these critical equipment through detailed numerical simulations that can replace or minimize experimental qualification tests and optimize future design of electrical equipment. Detailed three-dimensional solid FE modeling was used to capture the complex geometry of post insulators and the brittle nature of ceramics. Dedicated material characterization tests were utilized to define the porcelain nonlinear material model parameters. The developed model was verified using previously conducted experiments and used to perform linear and nonlinear static and dynamic analyses. A sensitivity parametric study was conducted first to calibrate the model and rank the sources of uncertainties in porcelain insulator modeling using the so-called tornado diagram analysis. The calibrated model was further utilized to carry out nonlinear time history analysis under earthquake excitation and capture the dynamic mode of failure, which is not always feasible to achieve using experimental tests. The study concluded with identification of which modeling parameters significantly affect the simulated structural behavior of post insulators, and compared the inelastic response at failure under static and dynamic loading.

Highly porous multicomponent (Hf1/3Ta1/3Nb1/3)C ultra-high temperature ceramic with low thermal conductivity

Fundamental requirements of ultra-high temperature ceramic (UHTC) thermal insulators are excellent thermal stability above 1800 °C, good thermal insulation capability, and high mechanical reliability. We report foam-gelcasting-freeze drying method to fabricate porous multicomponent (Hf1/3Ta1/3Nb1/3)C UHTC with superhigh porosity (90.0-94.0%). The as-prepared samples show low density (0.70–1.17 g/cm3), moderately high compressive strength (0.34–1.34 MPa), low thermal conductivity (0.089–0.098 W/(m•K)), and excellent ultra-high temperature stability (low shrinkage of < 1% after thermal cycles up to 2000 °C). Coordinative mechanisms of multicomponent induced phonon scattering enhancement and low solid skeleton thermal conduction are the main factors that provide excellent thermal insulation capability.

Influence of corundum content on integrity of porcelain after long-term exposure to thermo-mechanical fatigue environments

Ceramic insulators experience thermo-mechanical fatigue and deterioration when exposed to outdoor environments. Therefore, the constituent porcelain materials must have excellent durability. In this study, the effect of the corundum content on the microstructure of porcelain was analyzed, and its thermal and mechanical properties were determined. As the corundum content increased, the coefficient of thermal expansion decreased, which mitigated the thermal stress. In addition, the role of corundum particles in reducing the residual stress and cracks generated during the sintering process was analyzed. Tensile tests on real-field insulators confirmed that excellent integrity was maintained with an increase in the corundum content.

APPLICATION OF DIFFRACTIVE OPTICAL ELEMENTS FOR OPTICAL-ELECTRONIC DIMENSIONAL INSPECTION SYSTEMS

The work is devoted to the application of diffractive optical elements in systems using the structured illumination method to the geometric parameters inspection of industrial articles. The objects of inspection in these systems are: weapon barrels, fuel pellets, fuel elements, spacer grids, ceramic ring insulators. The used diffractive optical elements are computer-synthesized holograms that focus laser radiation into geometric shapes, the configuration of which is optimally combined with the inspected objects shape.

Fire performance of non‐load‐bearing double‐stud light steel frame walls: Experimental tests, numerical simulation, and simplified method

SummaryDouble‐stud light steel frame (LSF) walls provide an enhanced insulation performance when exposed to fire conditions. However, the behavior of different configurations of such assemblies under fire is not well understood. Thus, this study aimed to assess the fire resistance of non‐load‐bearing double‐stud LSF walls subjected to ISO834 standard fire. The walls were lined with one or two type F gypsum plasterboards on each side, using cavity uninsulated or insulated with ceramic fiber. The experimental tests revealed that a wider cavity slows the heat transfer through the cross‐section, delaying the temperature rise on the unexposed surfaces. The use of ceramic fiber insulation substantially increases the fire resistance of the wall and when the cavity is partially filled with this material, if the blanket is placed towards the exposed side, enhanced insulation fire resistance is achieved. Based on the finite element method, a numerical validation was conducted using a special hybrid approach that used experimental temperature values inside the cavities or insulation blankets. This approximation was essential to improve the numerical results. Also, the employment of an air layer, located at specific regions of the models, helped to improve the numerical results, introducing an extra thermal resistance. A new simplified approach was proposed based on the improved design model available in the literature, and the results obtained are consistent with the experimental results. The predicted insulation fire resistance of the numerical and simplified methods agreed well with the experimental results and useful information is supplied to support further numerical and experimental studies.

Probabilistic analysis of the failure of high-voltage insulators based on compositional analysis

High-voltage insulators operating at 154 kV and 25,000 lbs and having service periods ranging from 0 to 53 years were considered to study the failure mechanism based on the composition of ceramic materials. Thermal and mechanical load tests (T&M) were conducted to accelerate the aging and determine the remaining mechanical strength of the aged insulators. Based on load tests (M&E), it was observed that 38 cristobalite samples approaching or completing 50 years of service failed the mechanical load test and exhibited degraded microstructures and insulation resistances of 1200 and 970 MΩ, respectively. Alumina insulators showed a 4% improvement in mechanical strength and 11% increase in hardness compared with the cristobalite samples. A compositional study (X-ray fluorescence) was performed to determine the elemental composition of both the superior and inferior samples to correlate their probabilities of failure P(F) with the wt (%) of SiO2, Al2O3, and Fe2O3 present in the ceramic insulators.

Effects of non-Fourier heat conduction and surface heating rate on thermoelastic waves in semi-infinite ceramics subject to thermal shock

Non-Fourier heat conduction has been observed in many fast heating experiments. This paper studies the thermoelastic fields of semi-infinite ceramics subjected to surface heating shock based on non-Fourier C–V model, which may have its root application for future thermal protection system of space vehicles. To simulate the surface heating process, a family of exponential functions is presented. Furthermore, the ratio of heating duration to thermal relaxation time, and the ratio of thermal wave speed to elastic wave speed are introduced to study the coupling effects of heating rate, non-Fourier heat conduction and inertia. Firstly, the time horizon and spatial scale where the non-Fourier effect is significant has been delimited. Secondly, it is demonstrated that the thermal stress component along depth increases and converges as the depth increasing. Thirdly, the domain where the maximum thermal stresses influenced by non-Fourier heat conduction are drawn by the critical lines in the plane of dimensionless heating duration vs thermoelastic wave speed. This study may be useful for designs of ceramic heat insulations.