Ceramic Insulators Research Articles

Reaction of aerogel containing ceramic fibre insulation to fire exposure

SummaryAerogel containing ceramic fibre insulations represent a newly developed high performance insulation material applied in industrial installations and recently expanding rapidly into the construction industry to reduce the heat transfer through walls and ceilings. As a rather expensive material they are preferentially used in cases where slim layers of insulation are needed mainly in refurbishing of existing buildings especially those under heritage protection. The reaction to elevated temperatures in case of fire is a decisive property for building applications. The present article investigates the reaction to fire of an aerogel containing ceramic fibre insulation already available on the market. This reaction was monitored experimentally by means of temperature sensors at different depth in the material when subjected to the standard ISO fire. The measured temperature evolutions are discussed with respect to radiative heat transfer in an optically thick medium, temperature induced changes in density because of mass loss and the occurrence of endothermic and exothermic reactions detected by thermal analysis and compared with simulation results. Copyright © 2016 John Wiley & Sons, Ltd.

Novel technique for electric stress reduction across ceramic disc insulators used in UHV AC and DC transmission systems

In the recent years there has been a considerable increase in the demand for electrical power requirement across the globe. The transmission voltage levels have increased to 765kV ac and ±800kV dc. Further HVDC transmission is becoming increasingly viable as it is more economical for long distance transmission and can carry large amount of power compared to same voltage levels as of HVAC. One of the major problems encountered by the utilities is the failure of overhead transmission insulators due to the pollution/contaminated conditions. The insulator failure rate is observed to be higher in DC as compared to the AC transmission systems. The present work is intended to focus on a practically new technique which enhances the surface potential and electric field strength for the existing ceramic disc insulators used for both HVAC and DC transmission. With this technique, substantial reduction in the discharge activity is obtained near the high voltage end of the disc insulator. It is known that faulty discs may alter the field conditions of the remaining discs in a sting, to study the redistribution of field and potential an attempt is made to compute the surface potential, electric field across the ceramic disc insulator string by using developed Surface Charge Simulation Method (SCSM) code. Simulation study is conducted for 1200kV ac and ±800kV dc systems under normal, with string containing faulty discs at arbitrary locations and for different contaminated conditions. Interesting results are obtained from the study; it is believed the results presented will be useful to the utility and design engineers.

Mathematical Modeling of Critical Parameters on the Polluted Ceramic Insulators Under AC Voltage: Based on Experimental Tests

In this paper, a mathematical model of critical parameters on the polluted ceramic insulators based on experimental analysis has been presented. In these cases, the effect of pollution and humidity on the leakage current and applied voltage of the insulators has been investigated. Also, the effect of the insulator shed on the critical parameters has been considered as the factor M. The profile factor M is the ratio of top level leakage distance to bottom leakage distance of insulator. Indeed, the value of the factor M has been defined as a criterion in experimental tests to determine the insulators’ electric strength. As well, to determine the constants of electric arc, the theoretical and experimental results have been compared, thus values of these constants have been determined. So, by presented mathematical model the critical parameters will be predicted. The closeness of results between proposed mathematical model and experiment confirms the veracity of the presented model.

Desempenho físico-químico de filmes hidrofóbicos de AlN e de Ti nanoestruturado crescidos por plasma frio sobre superfícies de isoladores cerâmicos de porcelana tipo pino

Resumo A resistência mecânica e a propriedade dielétrica de isoladores cerâmicos são características fundamentais para o suporte das redes de distribuição de energia elétrica. Porém, tanto a umidade quanto o teor de poluentes na atmosfera podem vir a ser prejudiciais e causar falhas na entrega de energia por elevação da sua corrente elétrica de fuga. O vidrado do isolador tem grande afinidade com a água resultante da interação da superfície do vidro com a atmosfera. No presente trabalho, foi realizada a deposição de filmes de nitreto de alumínio sobre o vidrado de amostras de isoladores elétricos cerâmicos, via plasma "magnetron sputtering" pulsado, de corrente contínua, e com uma mistura dos gases argônio e nitrogênio e de Ti sobre isoladores tipo pino para classes de tensão de 15 kV. A morfologia dos filmes e o desempenho dos isoladores foram medidos por MEV-FEG/EDS, AFM, máxima corrente de fuga RMS e grau de hidrofobicidade. O comportamento dos filmes depositados medido pelo grau de hidrofobicidade reduziu nas amostras de CM6 para CM4, com AlN, e de CM7 para CM3 quando foi depositado o Ti. A máxima corrente de fuga RMS medida nos isoladores sem e com filme nanométrico à base de Ti foi superior nos dispositivos sem a proteção, alcançando valores medidos de 5 mA e com desligamento do sistema computadorizado de medida (após 3 dias em Sauípe e 3 meses em Pituba) em consequência desta ter superado o intervalo de segurança de curto circuito estabelecido nos dispositivos eletrônicos de proteção (surtos superiores a 300 mA). Com a deposição dos filmes em 7 isoladores, foram verificadas alterações de comportamento em dois destes, com picos de máxima corrente de fuga atingindo 2,4 mA no campo. A maioria dos isoladores analisados teve como variações de correntes de fuga RMS, no período de medida, entre 0,2 e 2 mA, em condições adversas de clima (com chuva e diferentes velocidades de vento).

High emissivity MoSi2–ZrO2–borosilicate glass multiphase coating with SiB6 addition for fibrous ZrO2 ceramic

To develop a high emissivity coating on the low thermal conductivity ZrO2 ceramic insulation for reusable thermal protective system, the MoSi2–ZrO2–borosilicate glass multiphase coatings with SiB6 addition were designed and prepared with slurry dipping and subsequent sintering method. The influence of SiB6 content on the microstructure, radiative property and thermal shock behavior of the coatings has been investigated. The coating prepared with SiB6 included the top dense glass layer, the surface porous coating layer and the interfacial transition layer, forming a gradient structure and exhibiting superior compatibility and adherence with the substrate. The emissivity of the coating with 3wt% SiB6 addition was up to 0.8 in the range of 0.3–2.5μm and 0.85 in the range of 0.8–2.5μm at room temperature, and the “V-shaped grooves” surface roughness morphology had a positive effect on the emissivity. The MZB-3S coating showed excellent thermal shock resistance with only 1.81% weight loss after 10 thermal cycles between 1773K and room temperature, which was attributed to the synergistic effect of porous gradient structure, self-sealing property of oxidized SiB6 and the match of thermal expansion coefficient between the coating and substrate. Thus, the high emissivity MoSi2–ZrO2–borosilicate glass coating with high temperature resistance presented a promising potential for application in thermal insulation materials.

High voltage studies of inverted-geometry ceramic insulators for a 350 kV DC polarized electron gun

Jefferson Lab is constructing a 350 kV direct current high voltage photoemission gun employing a compact inverted-geometry insulator. This photogun will produce polarized electron beams at an injector test facility intended for low energy nuclear physics experiments, and to assist the development of new technology for the Continuous Electron Beam Accelerator Facility. A photogun operating at 350kV bias voltage reduces the complexity of the injector design, by eliminating the need for a graded-beta radio frequency �capture� section employed to boost lower voltage beams to relativistic speed. However, reliable photogun operation at 350 kV necessitates solving serious high voltage problems related to breakdown and field emission. This study focuses on developing effective methods to avoid breakdown at the interface between the insulator and the commercial high voltage cable that connects the photogun to the high voltage power supply. Three types of inverted insulators were tested, in combination with two electrode configurations. Our results indicate that tailoring the conductivity of the insulator material, and/or adding a cathode triple-junction screening electrode, effectively serves to increase the hold-off voltage from 300kV to more than 375kV. Electrostatic field maps suggest these configurations serve to produce a more uniform potential gradient across the insulator.

Structural Performance of Porcelain and Polymer Post Insulators in High Voltage Electrical Switches

AbstractPost insulators are key components of most electrical substation equipment, but they are vulnerable during earthquakes. To better understand the seismic response of post insulators, this paper presents an experimental program that involved two types of 230-kV disconnect switches post insulators. Several solid ceramic (porcelain) and hollow-core composite (polymer) insulators were tested. The experiments consisted of static loading and dynamic shaking table tests. The static cyclic-loading, resonance-search, and pull tests—including material characterization—allowed the determination of the insulators lateral stiffness, fundamental frequency, and mode of failure. Moreover, failure loads and corresponding displacements and strains were determined. Additionally, the shaking table tests involved substructured dynamic tests of single porcelain and polymer post insulators. The main objective of the static and dynamic tests was to compare the behavior of porcelain and polymer post insulators under latera...

Ceramic Insulation of Bi2Sr2CaCu2O8-x Round Wire for High-Field Magnet Applications

Conductor insulation is a key technology for the development of ultrahigh field superconducting magnets. We have developed a ceramic insulation coating on Bi2Sr2CaCu2O8- x round wire for high field magnet applications. The coating consists of TiO2 nanopowder, polymer binders, and other additives. The insulation is uniformly applied on Bi2Sr2CaCu2O8- x wire by dip coating in ceramic slurries. Its thickness is controllable between 10 and 30 $\mu\text{m}$ . The coating is strongly bonded to the wire and reasonably flexible before heat treatment; therefore, the insulated wires can be wound into coils without cracks or spalling. After Bi2Sr2CaCu2O8- x heat treatment, the coating is sintered to provide reliable ceramic insulation. A few pieces of Bi2Sr2CaCu2O8- x wire (including one over 750 m long) are insulated for our Bi2Sr2CaCu2O8- x high-field magnet development program. In this paper, we present the technical details of our insulation process, including the formulation of the coating slurry, and the coating application method. We also addressed issues with respect to improving coating quality.

The Effect of Controlling Stray and Disc Capacitance of Ceramic String Insulator in the Case of Clean and Contaminated Conditions

Due to their flexibility against the tension force and the easiness of maintenance characteristics of overhead transmission line, one of the biggest problems when using ceramic string insulator is the non-uniform voltage distribution on each insulator disc that connected on the string. This paper analyzes the effect of controlling stray capacitance (Kcsc), disc capacitance (Kcdc) and contaminated pollution (Kccp). In this paper research study considerations, the Electricity Generating Authority of Thailand (EGAT) 115kV overhead transmission line power towers are simulated in EMTP/ATP drawing and the results were analyzed. As it was found that in the clean condition, when the constant (Kcsc) was conducted and adjustment when Kcsc value has low value (decreases), the string efficiency would be high value (increases) for instances Kcsc=0.01 string efficiency=99%, Kcsc=0.50 string efficiency=64%. When the constant (Kcdc) was adjusted; if Kcdc is low, the string efficiency will also be low for instances at Kcdc=0.01 string efficiency=33%, Kcdc=0.50 string efficiency=40%. Nevertheless, Kcdc adjustment utilizes the appropriate value gained from factory that the k=0, so the value will be 90% higher. As for the contaminated condition, when the constant (Kcsc) was adjusted as shown in Fig.11, if Kcsc value is low, the string efficiency will be high for instances Kcsc=0.01 string efficiency=99%, Kcsc=0.05 string efficiency=65%. When the constant (Kcdc) was adjusted; if Kcdc is low, the string efficiency will also be low for instances at Kcdc=0.01 string efficiency=17%, Kcdc=0.50 string efficiency=40%. Considering on Kccp, for example Kccp=0.01 string efficiency=82% Kccp=0.50 string efficiency=55%.

The use of PAP-2 aluminium powder when manufacturing powder composites: the features of technology, structure, physical and mechanical properties of the composites. Part 2: Study of composite properties and structure

This paper shows the possibility to reinforce the Al/Al2O3 laminated cermet matrix with metal fibres of rapidly solidified alloys (steel, titanium, and aluminium), as well as with discontinuous duralumin chips. Several energy-intensive destruction mechanisms resulted in the maximum reinforcement effect achieved by using titanium and steel fibres with their content of 20 and 10 vol.%, respectively. The resulting composites have the following properties: ρ = 2,30÷2,85 g/cm3; σbend = 180÷250 MPa; K1s = 7,5÷15 MPa·m1/2 and KSU = (18÷35)·103 J/m2. The composite «Al/Al2O3 – Ccoke residue» has ρ = 2,21÷2,23 g/cm3 with a very low sliding friction coefficient of 0,17 (the counter-face was a ball made of Steel ShKh-15 loaded by 1 N). The oxide-adhesive type of bonding is formed in the «Al/Al2O3 – alumina grains» composite which allows removing spent grains from the grinding work zone and achieving the self-sharpening mode. The material containing kaolin fibres is an ultra lightweight (0,25–0,5 g/cm3) ceramic insulation with λ = 0,07÷ ÷0,2 W/(m·К) in the 20–1000 °C range. The material comprising alumina spherulites combines both relatively high hardness (σbend = = 10÷50 MPa) and porosity (42–52 %) with high thermal stability which is the result of rapid elimination of the temperature gradient from micron-size structure elements.

断熱技術：工業炉の排熱削減に寄与する高強度高断熱性多孔質セラミックスの開発

断熱技術：工業炉の排熱削減に寄与する高強度高断熱性多孔質セラミックスの開発

A High-Vacuum High-Electric-Field Pulsed Power Interface Based on a Ceramic Insulator

Improving the flashover voltage in a vacuum interface between a pulsed power system and a vacuum region has been a goal for many years. The interface problem is difficult because of the electrical, mechanical, and vacuum issues that must be satisfied simultaneously. In this paper, according to the theories of vacuum flashover and the design rules for high-electric-field insulators, a ceramic-insulated vacuum interface is presented. The electrostatic field along the ceramic surface was obtained by ANSYS simulations. By optimizing the field shaper and shielding rings, the electric fields were well distributed and the fields around the cathode and anode triple junctions were effectively controlled. The high-voltage test was carried out on an ~600-kV, ~100-ns pulser, and the results show that the vacuum interface can work stably with a holdoff E-field stress of 40 kV/cm. The experimental results agree with the theoretical and simulated results. Finally, the influence of the surface treatment on the ceramic flashover characteristics was also discussed.

Electrical Performance of Distribution Insulators with Chlorella vulgaris Growth on its Surface

<p><span>This paper presents a study about electrical performance of ceramic and polymeric insulators bio-contaminated with alga <span><em>Chlorella </em><span><em>vulgaris</em><span>. The performed tests involve ANSI 55-2 and ANSI 52-1 ceramic insulators and ANSI DS-15 polymeric insulators, all of them <span>used in distribution systems of Colombia. Biological contamination of insulators is realized using a controlled environment chamber <span>that adjusts the temperature, humidity and light radiation. The laboratory tests include measurements of flashover voltages and leakage currents and they were performed to determine how insulators are affected by biological contamination. After a series of laboratory tests, it was concluded that the presence of <span><em>Chlorella vulgaris </em><span>on the contaminated ceramic insulators reduces the wet flashover <span>voltage up to 12% and increases their leakage currents up to 80%. On the other hand, for polymeric insulators the effect of algae <span>growth on flashover voltages was not to strong, although the leakage currents increase up to 60%.</span></span></span></span></span><br /><br class="Apple-interchange-newline" /></span></span></span></span></span></p>

Electrical Performance of Distribution Insulators with Chlorella vulgaris Growth on its Surface

<p><span>This paper presents a study about electrical performance of ceramic and polymeric insulators bio-contaminated with alga <span><em>Chlorella </em><span><em>vulgaris</em><span>. The performed tests involve ANSI 55-2 and ANSI 52-1 ceramic insulators and ANSI DS-15 polymeric insulators, all of them <span>used in distribution systems of Colombia. Biological contamination of insulators is realized using a controlled environment chamber <span>that adjusts the temperature, humidity and light radiation. The laboratory tests include measurements of flashover voltages and leakage currents and they were performed to determine how insulators are affected by biological contamination. After a series of laboratory tests, it was concluded that the presence of <span><em>Chlorella vulgaris </em><span>on the contaminated ceramic insulators reduces the wet flashover <span>voltage up to 12% and increases their leakage currents up to 80%. On the other hand, for polymeric insulators the effect of algae <span>growth on flashover voltages was not to strong, although the leakage currents increase up to 60%.</span></span></span></span></span><br /><br class="Apple-interchange-newline" /></span></span></span></span></span></p>

Development of the water drop–induced corona test method for composite insulators

Historically, line composite insulators have been used with success in relatively clean environments mainly due to the simplicity of handling and better pricing than ceramic insulators. Voltage upgrading and compact design of overhead lines are new typical nisch areas for composite insulators. Hydrophobicity is a key parameter of composite insulators providing insulation performance much higher than ceramic insulators. However, the outstanding hydrophobic properties of composite insulators may be deteriorated not only due to dry-band activity in polluted areas but also due to continuous corona activity on the housing material itself or corona from the metal parts (fitting, grading/ corona ring) onto the housing. In the worst case the insulator may suffer from erosion and other damages [1]. This puts higher importance on protecting the insulator from long-term aging.

Transparent Glazes for High-Voltage Porcelain

The results of development work on the constitution of raw compositions of transparent shiny glaze coatings used for the production of ceramic high-voltage porcelain insulators are presented. The content region of the raw components for forming defect-free coatings with the required dielectric properties is determined.

Fabrication and morphology control of highly porous mullite thermal insulators prepared by gelation freezing route

Mullite thermal insulators with high porosities of up to 91vol% were fabricated using a gelation freezing method, resulting in a honeycomb-like morphology with micrometer-sized cells. Mullite particles dispersed gelatin based gels with and without an ice binding protein additives were frozen, dried under vacuum and sintered at 1500°C. Ice binding proteins could inhibit the formation of large ice crystals and reduce cell size in insulators obtained. The thermal conductivity of the obtained thermal insulators ranged from 0.23 to 0.38W/mK at room temperature. The compressive strength was measured to be 1.4–21.7MPa. These properties could be varied by adjusting the process parameters of the gelation freezing. The method proposed here is a promising method of preparing ceramic insulators with very high porosity and improved strength.

Microstructure, radiative property and thermal shock behavior of TaSi2–SiO2-borosilicate glass coating for fibrous ZrO2 ceramic insulation

The objective of this research was to develop a high emissivity coating on the low thermal conductivity ZrO2 ceramic insulation, which can be used in a reusable thermal protective system for short-term applications. The effects of SiB6 and heat-treatment time on the microstructures and radiative properties of the TaSi2–SiO2-borosilicate glass composite coatings prepared on fibrous ZrO2 ceramic with slurry dipping and subsequent sintering method were investigated. The coating prepared in the presence of SiB6 with a heat-treatment time of 15 min maintains a dense structure and infiltrates into the ZrO2 substrate, possessing a gradient structure and good compatibility. The emissivity of the coating is up to 0.9 in the range of 0.3–2.5 μm and 0.8 in the range of 3–30 μm at room temperature. The emissivity mechanism regarding electron transition absorption, lattice vibration absorption and the effect of surface roughness on the emissivity is discussed. The increased roughness leads to the increased emissivity, which can be explained by “circular grooves” and “pyramidal grooves” models. After thermal cycling between 1573 K and room temperature 10 times, the weight gain of the coating prepared with SiB6 is only 0.29%. The high emissivity TaSi2–SiO2-borosilicate glass coatings with high temperature resistance show a promising potential for application in thermal insulation materials.

A Simplified Model for Effective Thermal Conductivity of Highly Porous Ceramic Fiber Insulation

Highly porous ceramic fiber insulations are beginning to be considered as a replacement for firebrick insulations in high temperature, high pressure applications by the chemical process industry. However, the implementation of such materials has been impeded by a lack of experimental data and predictive models, especially at high gas pressure. The goal of this work was to develop a general, applied thermophysical model to predict effective thermal conductivity, keff, of porous ceramic fiber insulation materials and to determine the temperature, pressure, and gas conditions under which natural convection is a possible mode of heat transfer. A model was developed which calculates keff as the sum of conduction, convection, and radiation partial conductivities. The model was validated using available experimental data, including laboratory measurements made by this research effort. Overall, it was concluded that natural convection is indeed possible for the most porous insulations at pressures exceeding 10 atm. Furthermore, keff for some example insulations was determined as a function of temperature, pressure, and gas environment.

Design and Experimental Evaluation of Dual-Anode Electron Gun and PPM Focusing of Helix TWT

A dual-anode convergent electron gun with a perveance of 0.14 $\mu \text{p}$ has been designed and developed for a high-efficiency helix traveling-wave tube (TWT), which would ultimately have application in a satellite communication system. The electron gun with an isolated beam forming electrode and an M-type dispenser cathode of 3.1-mm button diameter has been designed using EGUN, OMNITRAK-3-D, and OPERA-3-D codes. It consists of two isolated anodes, namely, control anode and ion-barrier anode, in addition to a ground accelerating anode to meet the requirement of long life and high reliability. Initially, in cathode selection, life considerations are ignored, and the gun is designed with the available cathode. Periodic permanent magnet (PPM) focusing has been designed using a Sm2Co17 high-intensity magnet in order to reduce the size and the weight of the overall TWT. Confined flow beam focusing has been adopted. A compact, small-size electron gun assembly has been designed using a ceramic insulator and a suitable support structure with due considerations for high-voltage and thermal requirements. A high-voltage analysis has been carried out using ESTAT code, and a thermal analysis has been carried out using ANSYS code. Designed electron gun and PPM focusing has been experimentally validated by developing and testing a beam-stick tube with the application of rated potentials at various electrodes in a gun and a collector. The design and experimental results for the electron gun and PPM focusing have been found in close agreement.