The March/April Issue of the Electrical Insulation Magazine has been released. Use the accordion headings below to explore this issue’s content, and visit the IEEE Xplore for full magazine access.
Characterization of Oil Flow Within Radial Cooling Ducts of Disc Type Transformer Windings Using Particle Image Velocimetry
M. Daghrah, Z. D. Wang, Q. Liu, C. Krause, and P. W. R. Smith – Xplore Link
Experience with Capacitive On-Line Sensors for Moisture Evaluation in Transformer Insulation
Ivanka Atanasova-Höhlein, Maja Končan-Gradnik, Tim Gradnik, Biljana Čuček, Piotr Przybylek, Krzysztof Siodla, Knut Brede Liland, Senja Leivo, and Qiang Liu – Xplore Link
Influence of Employing Different Measuring Systems on Measurement Repeatability in Frequency Response Analyses of Power Transformers
Satoru Miyazaki, Yoshinobu Mizutani, Mehran Tahir, and Stefan Tenbohlen – Xplore Link
Palm Fatty Acid Ester as Biodegradable Dielectric Fluid in Transformers: A Review
The transformer is one of the most vital and expensive apparatus in an electric power system and its reliability is of highest importance. The transformer’s performance depends heavily on its electrical insulation system, as insulation failure almost always renders the transformer failure. Therefore, the electrical insulation is perhaps the most critical transformer internal part. In transformer failure surveys, the windings, tap changer and bushing related failures were the major contributors, followed by lead exit related failures, irrespective of application or manufacturing period [1-2].
The physical foundations for electromagnetism were laid through the experimental work by H.C. Oersted (1820), A.M. Ampere (1822) and M. Faraday (1831), which was later expanded theoretically by J.C. Maxwell (1861). The first practical transformer employing the principles of electromagnetism was invented in 1884 and patented in 1885 by the team of K. Zipernowsky, M. Déri and O. Bláthy, from Ganz Companies in Budapest (then Austro-Hungarian Empire). Practically at the same time, similar development of transformers took place in the USA by W. Stanley, working with G. Westinghouse (1886) and by S. de Ferranti in England. In 1889, M. Dolivo-Dobrovolsky developed the first three-phase transformer at AEG in Germany [3-5]. Since then, during more than a 130-year long history, the transformer fundamentals remained the same, however this apparatus underwent dramatic changes as far as basic parameters and new applications are concerned. The rated operating voltage increased from several kV to 1200 kV (AC) and 1100 kV (HVDC). The rated power increased from several kW to more than 1000 MW [6-7]. In order to achieve such high values of rated parameters, the marked progress in transformer engineering, insulating materials, magnetic materials, conductors (oxygen-free copper and large continuously transposed cables), high voltage technology, thermal-hydraulic theory and cooling technology, etc., was required.
While the small power transformers represent the largest part of the power transformer market, primarily due to its use in various applications, the large power transformers – as a result of recent advancements in their power ratings – represent the fastest growing segment. With emphasis on reducing the transmission losses, the implementation of high voltage transmission technologies such as EHV, UHV, and UHVDC has also significantly increased, especially in China and India. To give an example of the largest transformers, one may take a closer look at a recently built and tested 1100 kV HVDC, single phase, 587 MVA unit with dimensions: 37.5 meters length, 14.4 meters height, 12 meters width, and close to 900000 kg weight. This unit passed dielectric tests at the following levels: AC applied voltage at 1292 kV, switching impulse at 2100 kVp, lightning impulse 2300/2530 kVp (FW/CW), DC applied 1786 kVdc, and polarity reversal +/- 1384 kVdc. (see a photograph of this transformer on the front cover of this magazine) [8-9].
In general, the dielectric strength of a liquid-cellulose insulation system depends on the duration of voltage application, polarity of voltage, field enhancement factor, area and shape of electrodes, kind and degree of contamination of the oil, its temperature and pressure, type of insulating liquid (mineral oil, natural or synthetic ester). The transformer insulation design should be prepared with careful consideration for all these aspects. Ongoing development of insulating structures utilizing the molded or formed pressboard parts allows for operation at higher electric stresses and results in a reduction of size, weight and cost of transformer. The transformer designers optimize the pressboard barrier structures using the two- and three-dimensional electric field calculations. Materials commonly used in power transformer insulation systems are (i) insulating fluid: mineral oil, synthetic, or vegetable esters, (ii) conductor insulation: paper (cellulose-based kraft, synthetic aramid – Nomex®, mixed aramid and cellulose), or enamel coating, (iii) ‘solid’ insulation, dividing and supporting the winding sections and spaces between the windings, i.e. barriers, blocks, spacers, made of pressboard for high voltage units, transformer wood (densified laminated wood) or pure wood (maple or beech wood) for lower voltage applications [e.g. 10-12].
The magnetic material commonly used in large power transformer design is cold-rolled grain-oriented steel (CRGO), characterized by high permeability, low loss and low magnetostriction. The losses generated in the CRGO steel can be divided into (i) a hysteresis loss, dependent on grain size and orientation and (ii) an eddy loss, dependent on the sheet thickness and silicon content. The classical eddy loss – as described by theoretical dependence on the squared values of frequency, thickness and magnetic induction – is, in reality, higher than calculated by theoretical equation and this additional loss, generated by domain wall motion, is called an anomalous or excess eddy current loss and may be as high as 50% of total core loss [13-14]. Therefore, the CRGO steel manufacturing processes are focusing on reduction of the anomalous eddy loss through surface modifications reducing the size of magnetic domains. This may be achieved by mechanical or chemical means, but the best results are obtained by laser irradiation (scribing) [15-16]. The modern CRGO steel sheet thickness used in low loss, large power transformers was for several decades 0.23 mm or 0.27 mm, and recently was reduced to 0.20 mm, allowing for further loss reduction . Very important is the interlaminar sheet insulation created by the surface coating, typically based on inorganic substance with ceramic fillers. Critical to core performance is proper cutting of the sheets, without excessive burrs, achieved with computer-controlled shearing machines. The air gaps between laminations should be as small as practically possible, which is achieved by experienced personnel during the core stacking process or – more and more often, especially for lower power units – by automatic core stackers. All these core features are extremely important, as any problem with insulation, burrs or large air gaps can result in conditions allowing for the core current circulations leading to overheating and gassing of the core during the factory test or in service.
The use of high temperature materials, such as aramid papers and boards, as well as ester fluids, resulted in the design and manufacture of large emergency units, or mobile substations. Recently, Con Edison, New York City’s energy utility, requested a spare power transformer that was mobile, versatile in its applicability, and at the same time quick to install and environmentally friendly, allowing to restore the electric power within a few days instead of weeks. A solution was a bank of three single-phase units, enabling reconnection to the 335/136 kV system (300 MVA) or the 132/68 kV system (150 MVA), with compact dimensions and relatively low weight of 95000 kg [17-18]. More conventional mobile transformers and substations utilizing high-temperature insulation and compact design, allowing reconnection to different service voltages on both HV and LV sides are more and more commonly used (Figure 1).
The concept of a mobile solution was taken to extreme through the Saudi National Grid’s request to design and build a 400 kV substation . This enormous mobile substation consists of seven large trailers, carrying the three single-phase power transformers, the 400 kV and 132 kV circuit breakers, the SCADA and telecommunication equipment, and the connection tools and gantries (Figure 2). These mobile substations allow fast and reliable deployment, either for temporary or standby emergency electrical power transmission as well as in new and fast track projects. In some circumstances the mobile substation may be used as a permanent transmission solution, e.g. in remote and challenging areas.
For small power units, the solution that saves land, reduces overhead grids, eliminates fencing, reduces maintenance and outages associated with wildlife, weather and trespassers, utilizing the most recently available quick connection and monitoring methods was introduced . The skid mounted concept and solution, a portable outdoor distribution substation (PODS) was designed, assembled, completely tested and commissioned in the factory and delivered in one or two pieces reducing on-site assembly to a few days. PODS are of a dead front design, often integrated with a vacuum type on-load tap changer, fluid containment, primary or feeder protection using reclosers or circuit breakers with controls configured with IEC 61850 communication protocols and DC batteries and backup. Another similar concept is a high voltage pad-mount transformer (HVPT)  which employs a modular dead front transformer connected underground to other apparatus or components, each located on their own pad. This concept accommodates using standard and approved apparatus and components arranged as preferred by each user, with high voltages up to 230 kV with secondaries 48 kV and less (Figure 3).
The transformer manufacturing processes are under continuous development. Physical phenomena influencing the status of the insulation during assembly, drying, during and after oil impregnation are carefully considered to ensure the designed dimensions of the windings and active parts and required clamping forces .
The transformer in operation is subjected to numerous phenomena affecting its insulation. Aging processes – pyrolysis, hydrolysis, and oxidation, as well as partial discharges, gradually weaken the solid insulation. Precise assessment of the status of the insulation, especially in operation under overload conditions, is still a challenge to power utilities, since available methods (DGA, furan analysis, methanol analysis, partial discharge detection and location, etc.) are not perfect. Nonetheless, they are in constant development bringing new methods (e.g. Duval pentagon) or improved monitoring systems (PD location using electrical, acoustic and UHF methods), comparing the test results to the performance in service, etc. [e.g. 23-30].
One may summarize that in the second century of transformer technology existence, the progress is still happening and very much needed in the future.
 Transformer Reliability Survey, Cigre Technical Brochure 642, 2015
 Ziomek W., Editorial, IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 19, No. 6; December 2012
 Allan, D. J., “Power transformers – the second century”, IEE Power Engineering Journal, January 1991
 Halacsy, A.A., “Von Fuchs GH “Transformer invented 75 years ago”, AIEE Transactions, Part III, Power Apparatus & Systems, June 1961
 Jeszenszky, S., “History of transformers,” IEEE Power Engineering Review, Dec. 1996, pp. 9–12.
 “Designing Hvdc Grids for Optimal Reliability and Availability Performance”, Cigre Technical Brochure 713, 2017
 Zehong, L., et al., “R&D progress of ±1100kV UHVDC technology”, Cigre Session 2012, B4-201, 2012
 “World’s first 1,100 kV HVDC transformer”, Nuremberg, Germany, Jan. 2018 available at https://www.siemens.com/press/en/feature/2018/energymanagement/2018-01-1100kv.php
 Wimmer, R. et al “Introduction of a new level of HVDC to UHVAC linked systems with respect to main component transformer technology and design”, Cigre Session 2018, B4-216, 2018
 Moser, et al., Transformerboard, Scientia Electrica, 1979
 Tschudi, D. J., “AC Insulation Design”, in Proc. of WICOR Insulation Conference, Rapperswil, Switzerland, Sept.1996
 Ziomek, W., Vijayan, K., Boyd, D., Kuby, K., Franchek, M., “High Voltage Power Transformer Insulation Design”, IEEE Electrical Insulation Conference Record, Annapolis, MD, USA, 2011
 Bertotti, G. Hysteresis in Magnetism, Academic Press, 1998
 Gao, Y et al “Investigation on Simple Numeric Modeling of Anomalous Eddy Current Loss in Steel Plate Using Modified Conductivity”, IEEE Transactions on Magnetics, VOL. 48, NO. 2, Feb. 2012
 Nippon Steel “Electrical sheets” Tokyo, Japan, 2018, available at http://www.nssmc.com/product/catalog_download/pdf/D003jec.pdf
 JFE Steel Corp., “Electrical steel sheets”, available at http://www.jfe-steel.co.jp/en/products/electrical/catalog/f1e-001.pdf
 “Resilience power transformer installed in NY in record time”, Transformers Magazine, Feb.2017, available at https://www.transformers-magazine.com/tm-news/4014-siemens-installs-resilience-power-transformer-in-ny-in-a-record-time.html
 “Enabling resilience: Mobile resilience transformers”, Siemens, 2016, available at https://www.energy.siemens.com/us/pool/hq/power-transmission/Transformers/grid-resilience/downloads/react/Case-Mobile-resilience-transformers.pdf
 “CG inaugurates world’s first fully integrated 400 kV mobile substation”, available at https://www.powertransformernews.com/2018/11/09/cg-inaugurates-worlds-first-fully-integrated-400-kv-mobile-substation/
 “Portable outdoor distribution substation, PODS”, PTI Transformers LP, Regina, Canada, available at https://www.partnertechnologies.net/wp-content/uploads/2016/04/PODS.pdf
 “High Voltage Padmount Transformers”, PTI Transformers LP, Regina, Canada, available at https://www.partnertechnologies.net/products/hv-padmount/
 Bengtsson et al, “CIGRE Reference Paper: Insulation condition during transformer manufacturing”, Cigre 2018
 Kachler, A. J., Hohlein, I., “Aging of cellulose at transformer service temperatures. Part 1: Influence of type of oil and air on the degree of polymerization of pressboard, dissolved gases, and furanic compounds in oil”, IEEE Electrical Insulation Magazine, Volume: 21 , 2005
 Oomen, T. V., Prevost, T., “Cellulose Insulation in Oil-Filled Power Transformers: Part II —Maintaining Insulation Integrity and Life”, IEEE Electrical Insulation Magazine, Vol.22, No2, Mar-Apr 2006
 Boss, P., “Presentation of Cigre SC A2 ‘Transformers’; Technical developments and inputs from present activities”, Electra No 242, 2009
 Schaut, A., Eeckhoudt, S., “Identification of early-stage paper degradation by methanol”, CIGRE, Paper A2-107, 2012
 Duval, M et al “The Duval Pentagon—A New Complementary Tool for the Interpretation of Dissolved Gas Analysis in Transformers”, IEEE Electrical Insulation Magazine, 2015
 Rajotte, C. “Experience with transformer loading tests and direct temperature measurements in laboratory and in service”, PaperA2-110, Cigre 2018 Session,
 Min, BW et al “Development of Power Transformer Defect Location Detection Technology using UHF Partial Discharge Monitoring System”, paper A2-201, Cigre 2018 Session
 Fuhr J et al “Localization of PD Sources in Transformers by Analysis of Signals in Time- and Frequency Domain”, paper A2-205, Cigre 2018 Session
Since 2015, Dr. Waldemar Ziomek works as Director of R&D for PTI Transformers LP, a Canadian manufacturer of large power transformers. In 2013‐2015, he worked for CG Power Systems, an international T&D equipment company, as a global senior expert, specializing in large power transformers and high voltage insulation. Before 2013. he was employed by CG Power Systems Canada Inc. (formerly Pauwels Canada Inc.) as Manager of Engineering, where he started in 1997 as a transformer electrical designer. Since 2001 he is also an Adjunct Professor at The University of Manitoba. Dr. Ziomek authored and co-authored more than 70 scientific and technical papers. He is a member of IEEE, CSA, IEC and CIGRE.
From The Editors
We are excited to let you know that the Electrical Insulation Magazine is now available on the DEIS website. On the home page you will find a link to the most current issue. The link will guide you through the various sections of the magazine and provide links to the Featured Articles through IEEE Xplore. We invite you to give us your comments on how to improve this experience.
Up-and-coming professional, Elizabeth Foley, shares experiences with us regarding mentorship and Dr. James Pilgrim updates readers on the Smart Grid Technical Committee.
This issue of the Magazine brings a series of articles dedicated to diagnostic and material issues for power transformers. Before presenting the featured articles, we introduce the issue with an Editorial written by Waldemar Ziomek from PTI Transformers in Canada, in which he presents the most recent achievements as well as trends in further developments of transformer technology and the interrelated system solutions.
The first article entitled “Characterization of Oil Flow within Radial Cooling Ducts of Disc Type Transformer Windings Using Particle Image Velocimetry” is jointly authored by Muhammad Daghrah, Zhongdong Wang and Qiang Liu from the University of Manchester, UK, Christoph Krause from Weidmann Electrical Technology AG, Rapperswil, Switzerland and Peter Smith from Shell Global Solutions, Manchester, UK. It reports on the application of Particle Image Velocimetry (PIV), a technique applied in fluid mechanics and aerodynamics to study flow patterns, to measure and document oil flow distribution within an experimental setup imitating either directed cooled transformers or naturally cooled transformers. Power transformers are cooled by allowing dielectric oils to circulate through their active parts, understanding the oil flow distribution within the winding cooling ducts is essential for predicting the location and value of the so-called hot spot temperature. In real transformers, it is not feasible with current technology, to directly measure oil flow distribution within the winding cooling ducts. Therefore, experimental models are often used with various measurement tools. The use of a PIV system allowed the experimental capture of the oil flow profile in cooling ducts, including complex phenomena like oil reverse flow and oil recirculation at duct entrances. It is also highlighted that a 3D flow component is noticeable within radial cooling ducts under certain conditions and special care should, therefore, be taken when measuring flow rates in cooling ducts using point-based techniques, such as hot wire anemometry or laser Doppler velocimetry.
The second article in this issue is on “Experience with Capacitive Online Sensors for Moisture Evaluation in Transformer Insulation”, authored by an international team of researchers participating in a round robin test performed by CIGRE Working Group D1.52, which aimed at determining moisture saturation coefficients in different insulating liquids, including mineral oils, ester liquids, and a silicone oil and comparing them with results of traditional analyses by means of Karl Fisher titration. The team consists of Ivanka Atanasova-Höhlein from Siemens AG, Germany, Maja Končan-Gradnik, Tim Gradnik and Biljana Čuček from Milan Vidmar Electric Power Research Institute, Slovenia, Piotr Przybylek and Krzysztof Siodla from Poznan University of Technology, Poland, Knut Brede Liland from SINTEF Energy Research, Norway, Senja Leivo from Vaisala Oyj, Finland and Qiang Liu from the University of Manchester, UK. Capacitive sensors, which measure the relative moisture saturation in insulating liquids, have increasingly been used to monitor moisture content in power transformers and the availability of such measurements and their correlation to operating conditions opens up new diagnostic possibilities. Experiences showed, however, that an effective integration of capacitive sensors into transformer on-line diagnostic systems requires fulfilment of various conditions, including installing the sensors at appropriate locations, gathering adequate amount of data on both moisture and temperature distributions and evaluating the data by comparisons to historical records. The article discusses possibilities and restrictions related to convertibility of the results obtained by either Karl Fischer titration or by capacitive sensor measurements as well as uncertainties of such a conversion, which is possible when using the characteristic for different insulating liquids moisture saturation coefficients. Moreover, the article demonstrates a possibility to derive evaluation criteria for transformer condition based on the correlation between dielectric strength and relative moisture saturation in dielectric liquid. It also shows, based on practical examples from measurements in service, that the behavior of the relative saturation/temperature hysteresis also indicates the wetness of transformer insulation.
The third article entitled “Influence of Employing Different Measuring Systems on Measurement Repeatability in Frequency Response Analyses of Power Transformers” presents result of a collaboration between Japanese and German researchers. The authors are Satoru Miyazaki and Yoshinobu Mizutani from Central Research Institute of Electric Power Industry in Japan together with Mehran Tahir and Stefan Tenbohlen from the University of Stuttgart in Germany. FRA measurements on power transformers provide valuable information, especially as it relates to their mechanical integrity. Concerns had, however, been raised in relation to the measurement repeatability, which evoked much international debate and various attempts to simultaneously measure and compare transfer functions of transformers by using several measuring systems. The results revealed that the differences in the measuring impedance introduce certain variation among them. This article analyzes the influence of employing different measuring instruments and different measuring lead connections by introducing a comparison method that combines cubic-spline interpolation and piecewise linear interpolation to the measured transfer functions. This results in employing a numerical index that can objectively evaluate the extent of disagreement among the compared responses. The applied method is experimentally validated and it is shown that the influence of different measuring systems becomes negligible in practical applications as long as the way of connecting the measuring leads remains the same as in reference measurements.
The fourth article is “Palm Fatty Acid Ester as Biodegradable Dielectric Fluid in Transformers: a Review” and is authored by Junko Tokunaga and Masanori Nikaido from Lion Specialty Chemicals Co. together with Hidenobu Koide and Tomoyuki Hikosaka from Fuji Electric Co., Japan. The authors present advantageous properties of palm fatty acid ester liquid, a new biodegradable dielectric fluid for transformers, in comparison with mineral oil and other natural ester oils. Comparative reports are summarized on electrical properties of the liquid and mineral oil on thermal aging of cellulose components impregnated in them, and on possible fault diagnoses for transformers filled with this liquid. The advantageous characteristics of palm fatty ester acid liquid include better cooling performance, higher oxidation stability and breakdown voltage. Apart from the advantages provided by other vegetable fluids, such as environmental friendliness and cellulose protection, the better cooling performance the liquid has been verified by tests on real transformers. Also the high oxidation stability makes it applicable in air sealed pole transformers. In addition, the lower risk of flow electrification, higher hydrolytic stability and no reduction of breakdown voltage in the degraded fluid, increase the safety assurance of transformers.
The last article in this issue is “Transformer Condition Assessment using Fuzzy C-means Clustering Technique” by Samuel Eke, Guy Clerc and Thomas Aka-Ngnui from University of Lyon, France and Issouf Fofana from University of Quebec at Chicoutimi, Canada. The article describes how to obtain a general classification of transformer condition according to the available data, to identify groups of units requiring extensive investigation or basic maintenance. It proposes grouping of transformers according to the similarities in the data characterizing the condition of each unit. In the considered example, the parameters of the feature vector are those generally used in the context of the predictive maintenance of transformers from standard oil analyses. Data analyses are subdivided into the following steps. The most relevant parameters are firstly selected by applying Laplacian Score. Then, the transformers are grouped according to their similarities by Fuzzy C-means algorithm, and finally, each group is interpreted and a hierarchy depending on the gravity of the observed fault is established. It is, however, important to stress that the proposed method has its constraints and limitations, which depend on the quality of available data. In order to ensure sufficient quality, it is important to consider a group of transformers with similar characteristics and operating under similar conditions.
News From Japan
Development of a Clay Coating on Metal as a New Electrical Insulating Substrate
For various industrial purposes, a combination of metal and inorganic substance coated on it is widely used. Typical objectives of such coatings would be functional, decorative, or both. Although the adjustment, addition, or improvement of strengths of adhesion, wettability, anti-corrosion, water-resistance, wear-resistance, and antimicrobial activity are the main purposes of functional coatings, ceramic or oxide coatings on metals are also adequate for use as a substrate of a power electronic module . Ceramic coatings on metals for this application must have superior thermal durability, high thermal conductivity, and good electrical insulating ability.
Ichinen Chemicals Co., Ltd., Fujisawa, Japan, has recently developed a method to coat clay on the surface of metal such as stainless steel. Stainless steel is one of the most popular and useful metals for industries and in our daily life. Because of its high corrosion resistance and good processability, stainless steel has been widely used for making a vast variety of products ranging from daily commodities such as tableware to industrial goods such as structural frames and piping. In order to enhance the corrosion resistance or surface electrical insulation performance further, proper ceramic coating must be done on the surface of stainless steel.
A variety of methods to coat stainless steel are known. First, organic polymers or paints are usable for simple and light coating. However, organic coats have relatively poor heat resistance and weak wear-resistance. Secondly, sol-gel methods are suitable to make thin inorganic compound coatings. However, they are not adequate to make a dense and thick ceramic coating, because a crack would occur during the calcination of the gel precursor. Sputtering and laser deposition are also good methods to fabricate inorganic thin films, but their feasible sizes and growth rates are not adequate for most industrial purposes. With these backgrounds, the development of a simple, low-cost, and easy-handling process that can coat a ceramic or inorganic layer on the surface of metal is desirable.
Ichinen Chemicals uses clays to fabricate various kinds of ceramics through a calcination process. Clays are easily dispersed in water to make their pastes for use in wet coating. One typical starting aqueous solution is a mixture of 10 wt% synthetic hectorite Na0.3(Mg,Li)3Si4O10(OH)2, with an average particle size of approximately 60 nm, 0.4 wt% polyoxyethylene lauryl ether, 1.5 wt% ethanol, 4 wt% ethylene glycol monobutyl ether, and 84.1 wt% ion-exchanged water.
After the hectorite clay was immersed in the ion-exchanged water for 20 min, all organic additives were added to the solution and mixed for 20 min. Then, the solution became an aqueous paste of clay as shown in Figure 1. Here, the organic additives help the dispersion of the clay in water, by which we can control the viscosity of resulting paste. Next, the clay paste was spin-coated onto an utrasonically cleaned stainless steel plate. All these processes were conducted at room temperature. Then, the plate samples were dried for 1 h at 105°C and succeedingly calcinated for 2 h at 600°C in an oven. In some cases, half of the plate surface was covered with transparent tape to prevent coating on that portion.
In Figure 2, the lower half shows the portion coated with the clay, while the upper half shows the portion not coated but covered by the tape. We can see an interference pattern only on the lower portion, which shows clearly that a transparent thin coating of clay, or ceramic derived from clay, was formed on the surface. It is also clear that the coat can protect the surface of stainless steel from oxidation at the high temperature of 600°C during the calcination, because the coated portion maintained the metallic glory or silver color of the original stainless steel in contrast to the uncoated portion that became dark brown in color.
The pencil hardness test was conducted on the coating using a conventional tool to estimate the adhesion of the clay or ceramic coating to the stainless steel substrate. In the test, a weight of 750 g was loaded on pencils with various values of hardness from 6B to 6H. Then, the pencil was put on the clay-coated stainless steel plate at an angle of 45°. The presence of scratch on the clay surfaces was checked to determine the pencil hardness. As a result, the pencil hardness of the coated surface was found to be 6H, which is sufficiently hard enough to be peel-proof, confirming that the developed clay or ceramic coating has excellent adhesion to the stainless steel.
Figure 3 shows the X-ray diffraction (XRD) patterns obtained with CuKα radiation of the coated samples before and after the calcination at 600°C. Both patterns exhibit the (00L) lines of clay, which means that clay fragments were present in the coating. The interlayer space of the clay fragments was calculated from the (001) lines and was found to change from 1.4 to 1.0 nm. This indicates that the thermal dehydration occurred between the layers of the clay. Other (00L) lines appear more clearly after the heat treatment, indicating more packing and densification of the clay fragments, which brought about a hard coat.
To examine the interface between the coating and the stainless steel substrate, a cross-section of the coated surface was exposed using focused ion beam bombardment. The exposed surface was then characterized by transmission electron microscopy (TEM) together with energy dispersive X-ray spectrometry (EDX). Figure 4 shows a cross-sectional bright field TEM image of the coating on a stainless steel plate calcined at 600°C. A smooth coating with a thickness of 0.6 μm, with no cracking, is clearly seen on the stainless steel substrate. Inside the coating, it appears that clay fragments were stacked. The presence of voids is also evident. As mentioned above, the present clay-derived ceramic coating was prepared using a wet coating process of the clay paste, which formed bubbles due to the release of solvent or surfactants during the drying and calcination processes. These processes might have caused the irregular stacking of the clay fragments, which resulted in the voids. The interface between the coating and the stainless steel surface has excellent adhesion without peeling or voids. Based on the EDX analysis of the interface region, iron (Fe) was confirmed to be present. Since the original clay contains no iron, iron was clearly diffused from the stainless steel into the coating at the high temperature, which seemingly adhered the coating tightly to the stainless steel.
To summarize, Ichinen Chemicals has succeeded in the fabrication of a clay-derived ceramic coating on a stainless steel substrate with a submicron thickness using a simple wet coating process using an aqueous clay paste followed by calcination at 600°C.
This article was completed with the help of Dr. Yukinori Noguchi of Ichinen Chemicals, Co., Ltd.
Interval Finite Element Method with MATLAB
S. Nayak and S. Chakraverty
Academic Press; An imprint of Elsevier
525 B Street, Suite 1800, San Diego, CA 92101-4495
Tel: +1 619 231 6616; Fax: +1 619 699 6422
ISBN 978-0-12-812973-9; 162p. $105 (Softcover), 2018
Finite element method (FEM) is a well-known numerical method that is used to model many different types of engineering problems including structural, mechanical, fluid dynamics, weather, and many other subject areas. It generally contains well-defined boundary conditions, fixed initial conditions, and well-defined input values. However, oftentimes there may be incomplete information available or the input parameters can have some uncertainty in their value. These uncertainties can occur due to vague, imprecise, and/or incomplete information concerning the variables and parameters being used in the model due to measurement errors, different operating conditions, observations, operator error, tolerances, stochastic processes, experimental errors, and/or other sources of uncertainty.
Two methods to handle uncertainty are the interval method or stochastic method. The challenge with stochastic method is that generally, a large data set is required that includes data obtained that involve all conditions over a sufficient period of time to insure all outliers are included in the data set. This method is generally not possible or desired. Frequently beta site testing or prototype testing in the field is done to obtain this type of information. This can take a very long time and still may not contain all the conditions necessary to produce all outcomes.
The interval method can be used to model uncertainty without having to obtain large data sets. By including uncertainty in the governing differential equations in a finite element method, the equations become interval finite element method (IFEM) equations. These uncertainties can be classified into two categories, those due to randomness and those due to lack of information. A combination of uncertainty values with finite element methods used to create the IFEM are described in the book. Modification of the elements in a finite element mesh are done using a range of values, leading to a more generalized solution resulting in a more realistic and accurate model.
This book explains how this uncertainty method can be incorporated into a MATLAB program using the finite element method. It provides simple examples to illustrate the IFEM method. These examples cover various structural problems including a spring mass, bar, truss and frame with numerical solutions and corresponding MATLAB codes. A systematic approach to MATLAB codes was used to study these problems. The book also introduces the reader to the basics of interval arithmetic and hybridization with FEM using MATLAB.
Readers who use finite element methods to generate models might we very interested in this method to handle uncertainty in model input parameters. Oftentimes, the model uses assumptions for input parameters and these values are not well-know. This method may help to generate more realistic models that better represent the expected range of response of a system under real-world conditions.
Measurements and Analysis of Overvoltages in Power Systems
John Wiley & Sons, Inc.
111 River Street, Hoboken, NJ 07030
Phone: (877) 762-2974; Fax: (800) 597-3299
ISBN 978-1-119-12899-1; 376p. $130 (Hardcover), 2018
Protection of transmission lines from overvoltages is critical to the reliability and continuity of power systems. Real-time measurements of power system overvoltages can provide crucial information for designing protection equipment for power systems as well as a way to provide real-time monitoring for improving system operation.
This book presents a blend of theory and practical application information on overvoltage protection methods, mainly for high voltage transmission lines. It introduces overvoltage simulation studies, provides experimental data, and develops a pattern recognition method for the development of an overvoltage algorithm that can be implemented in hardware and used for real-time monitoring of power systems.
The book consists of eight chapters. Chapter one contains information on overvoltage mechanisms in power systems, with an emphasis on lightning strikes and the affects that can be produced by a lightning strike on or near a power system. Some of the topics cover transmission line traveling wave, overvoltage classifications, induced overvoltages from ground strikes, and many other topics.
Chapter 2 deals with equipment used to monitor and measure overvoltages in power systems including capacitive voltage dividers, shielding material selection guidelines, stray capacitance calculations, 3D simulations for capacitive effects, and using Pockels cell devices for measuring voltages.
Chapter 3 covers data acquisition systems used for monitoring overvoltages, including the design of monitoring circuits used to measure and store waveforms and triggering circuit design. Methods, for transferring the acquired information include using wireless GSM networks and 10GB all-optical carrier ethernet are described. Various practical information on serial communication interfaces is also described along with numerous case studies to give the reader a good idea of what type of data acquisition equipment is currently used in the field.
Chapter 4 studies the transient response of lighting. This chapter contains critical practical information on the properties of overvoltages (i.e. wave-shape characteristics) for many different scenarios and equipment, such as how the lighting overvoltage wave-shape changes as it propagates down a transmission line or what the voltage waveform may look like at a substation. This type of information is used to develop algorithms, later in the book, for identifying and classifying overvoltages.
Chapter 5, testing and analysis of UHVDC systems, consists primarily of the effects of overvoltages on parts of a UHVDC system (i.e. connecting/disconnecting converter transformers, overvoltages on the AC side and DC side of the substation).
Chapter 6, digital simulation, shows how to set up circuits to create overvoltage models in a power system. The author shows simulation examples using the ATP (alternative transients program) software.
Chapter 7 shows the dynamic simulation of overvoltages on transmission lines including models for transmission lines, lightning arrestors, and tower geometries.
Chapter 8 provides details on overvoltage pattern recognition, showing how to classify measured waveforms to build algorithms for machine learning capabilities and automated response based on the type of overvoltage measured.
This book would be very useful to a power system engineer involved with developing overvoltage protection and monitoring systems for power systems, especially for lightning protection of transmission lines and UHVDC systems.
Power Microelectronics – Device and Process Technologies, 2nd Edition
Y.C. Liang, G.S. Samudra, and C. Huang
World Scientific Publishing Co.
5 Toh Tuck Link, Singapore 596224
27 Warren Street, Suite 401-402, Hackensack, NJ 07601
Phone (201) 487-9655; Fax (201) 487-9656
ISBN 978-981-3200-24-1; 617p. $145 (Hardcover), 2017
The power electronics field is gaining attention from the combined factors of wideband gap (WBG) semiconductors and the increasing use of power electronic converters and inverters mainly driven by electric vehicles (EVs), uninterruptible power supplies (UPS), marine and ship power distribution, and renewable energy sources. This book introduces the fundamentals of power semiconductor devices and associated fabrication methods. It focuses on detailed descriptions of the various types of semiconductor structures and the physics behind these devices.
The book is organized in four areas. The first area describes semiconductor carrier physics and junction electrostatics involving topics on the effects of carrier concentration and all the associated parameters including drift, diffusion, resistivity, recombination – essential background for understanding semiconductor device physics. Other areas cover device punchthrough phenomena and field grading edge or junction terminations.
The second area of the book, which is the majority of the book, covers the physics and characteristics of specific power devices. The devices discussed are the bipolar junction diode, power MOSFET (Metal-Oxide Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), superjunction structures, SiC and GaN devices. In each case, the design structure, static and dynamics switching characteristics, and device performance parameters are described in detail. Discussions on parasitics and gate drivers provide the reader with very practical information for designing devices and circuits.
The third area describes fabrication and modeling of devices. Topics include lithography, etching, deposition, oxidation, ion implantation, epitaxy, and diffusion. These are the fundamental processing steps for device fabrication. The basic models are described for simulating each of these process steps in order to produce the desired device characteristics.
The final area covers four case studies, two for silicon power devices and two for wideband gap devices. The cases for silicon are a process and design of a PFVDMOS (poly-flanked vertical double-diffused metal oxide semiconductor) device and tunable oxide bypass MOSFET. The WBG study covers process and design of a SiC DIMOSFET (double implanted MOSFET) and the design of a normally-off GaN HEMT (high electron mobility transistor).
This book provides very clear descriptions of many new cutting-edge power electronic devices and as such would be an excellent book for readers interested in learning more about the most recent silicon and WBG materials and devices. The multitude of illustrations along with measured waveforms of critical information that is needed for practical device and application design is provided, making this book well worth reading.
Advanced DC/DC Converters, 2nd Edition
F.L. Luo and H. Ye
CRC Press; Taylor & Francis Group
6000 Broken Sound Parkway – NW, Suite 300, Boca Raton, FL 33487-2742
Phone (800) 272-7737; Fax (800) 374-3401
ISBN 978-1-4987-7490-1; 773p. $160 (Hardcover), 2017
Power conversion technology is becoming an increasingly popular research topic in both academia and industry, due to the popularity of renewable energy sources, energy storage, electric vehicles (EVs), and consumer electronics. Power electronics is at the heart of these applications and with new wideband gap semiconductors also driving new designs in power conversion equipment, many researchers are now focusing their attention on developing new power conversion topologies. DC/DC converters, used to convert from one DC voltage level to another voltage level, are used in these applications.
The purpose of this book is to provide concise, state-of-the-art information on advanced DC/DC converters for electrical engineering students and working professionals. According to this book, there are more than 500 DC/DC converter topologies existing and new topologies are being created every year. The authors have sorted and categorized all these converters into six generations according to their characteristics and sequence of development. These generations are 1st Gen: classical/traditional, 2nd Gen: multiple-quadrant, 3rd Gen: switched component, 4th Gen: soft-switching, 5th Gen: synchronous rectifier, and 6th Gen: multiple-element resonant power converters. This classification and organization allows the reader to easily sort and allocate DC/DC converters and asses and compare specific technical features.
The book is organized into 18 chapters. The first 6 chapters review the 1st generation converters with details on the fundamentals of DC/DC power conversion methods, voltage-lift conversion methods, and super-lift conversion. Buck, boost and buck-boost, topologies are covered and many of the other types of topologies which were invented by one of the authors (Luo). 2nd and 3rd generation topologies are covered in chapters 7 to 10 including multiple-lift push-pull switched capacitor converters. Mathematical modeling methods are also described for modeling the transfer function, stability, efficiency, and time constant of converter designs. Chapters 11 through 19 cover the remaining generation of topologies. The final chapters introduce various DC energy sources (various single-phase and three-phase AC to DC rectifier circuits), gating -signal generators, and EMI/EMC design considerations.
This book is an encyclopedic reference for DC/DC converters. It contains very clear and concise descriptions of DC/DC converters in use today. Anyone working or studying DC/DC converter technology would want to have this book as a standard reference source for making comparisons of various DC/DC converter topologies and for having the convenience of a one-source handbook to find all the information needed on a particular DC/DC converter design.
Analog Electronics for Measuring Systems
Wiley & Sons, Inc.
111 River Street, Hoboken, NJ 07030
Phone: (877) 762-2974; Fax: (800) 597-3299
ISBN 978-1-7863-0148-2; 180p. $120 (Hardcover), 2017
Analog sensors are used to measure temperature, light intensity, moisture, and many other physical quantities. Knowing the technical details about a sensor and the electronics that interface the sensor to a measurement system is critical for the electronics engineer who needs to design a system involving an analog sensor.
This book provides a concise introduction to analog measurement technology. It is intended for readers with a general background in electronics and signal processing who want ideas and a basic understanding of analog measurement circuits and signal processing.
It gives a general overview of the fundamentals on analog sensor measurements and provides specific circuit examples of some common designs. Topics cover various types of sensors (thermocouples, photomultiplier tubes, photodiodes, pyroelectric sensors, piezoelectric, strain gauges, and reactive sensors), conditioning circuits, differential and instrumentation amplifiers, active filters, and A/D converters. There is also a chapter on noise and electronic compatibility.
Electronic engineers dealing with instrumentation design would be interested in this book because of the many types of sensors described and the associated op-amp circuits. These provide very good insight into solving many sensor to instrumentation system problems, making this a great resource for designing most instrumentation challenges.
Astrochemistry – From Big Bang to the Present Day
World Scientific Publishing Co.
5 Toh Tuck Link, Singapore 596224
27 Warren Street, Suite 401-402, Hackensack, NJ 07601
Phone (201) 487-9655; Fax (201) 487-9656
ISBN 978-1-78634-038-2; 224p. $98 (Hardcover), 2017
Astrochemistry deals with the chemistry occurring in stars, planets, and interstellar medium including plasma chemistry. This book describes the chemical makeup of the Universe, our solar system, and our planet. It uses the principles of physical chemistry to explain the evolution of the Universe and the complex chemistry occurring both in interstellar space and the planetary systems.
The book is broken down into three major sections – background on the chemistry of the Universe, laboratory-based theory, and laboratory based experiments. The background section covers astrophysical topics on spectroscopy, Doppler shift, the Big Bang theory, star creation, and interstellar chemistry (gas-phase reactions, bond forming reactions, and rearrangement reactions). The principles of the processes used to create various astronomical formations are explained and many examples of measurement data used to confirm theoretical predictions is presented.
The laboratory theory section presents and explains methods used to measure astronomical quantities used to make conclusions about various astrophysical quantities. Some examples include the Grand Challenge of chemical modeling of giant molecular clouds including using spectroscopic data (vibrational, rotational, and transition intensities) and kinetic and dynamical data (i.e. plasma chemistry – collisional cross-sections, impact parameters, angular momentum, and reactions).
Laboratory-based experiments cover methods that can be setup in a laboratory that are used to replicate various aspects of astrophysical quantities. These are used to compare with measured values of astrophysical quantities in an attempt to confirm conclusions. The experiments involve three different areas of study. The first area uses spectroscopy data involving laser-induced fluorescence, microwave spectroscopy, molecular beams, and various absorption spectroscopy methods. The second experimental method covers the area of gas-phase kinetics and dynamical data. These involve ion-cyclotron resonance mass spectroscopy technique, the afterglow technique and neutral reactions. The third area covers dust-grain chemistry. This covers ice structures via infrared spectroscopy and the formation of hydrogen on ice surfaces.
A final section deals with the formation of the solar system and the evolution of the earth. The author steps through the early processes of the Earth formation, explaining the layered structure of Earth, the oceans, fossil formation, and how other solar-systems formed.
The author does a nice job in explaining complex theory and experiments, clearly explained each theory or method, emphasizing an understanding of the fundamental principle and how it applies to astrophysics.
This book is very accessible to many readers but is primarily focused on graduate or advanced undergraduate students in chemistry or astrochemistry or for someone interested in learning more about astrochemistry in general and theories on how the Earth was formed.
Concepts in Physical Metallurgy
Morgan and Claypool IOP Publishing
Temple Circus, Temple way, Bristol BS1 6HG, UK
Distributor in US:
82 Winter Sport Lane, Williston, VT 05495
Phone: (802) 846-9442
ISBN 978-1-6817-4473-8; 169pp. (Softcover), 2017
This book is an introduction to physical metallurgy. It was created from a series of lecture notes taught by the author, from the Department of Metallurgy and Materials Engineering at the University of Technology, Odisha, India. It provides a concise and effective way to understand and realize the behavior of metals from an atomic level.
The book begins with an introduction on how atoms are arranged in metallic materials and the importance of symmetry in materials. Building on this concept of symmetry, other fundamental topics are introduced including the concepts of solidification, crystallization, and defects in metals. The various types of defects in crystalline structures covered include point, line, surface, and volume defects. Causes and uses of certain defect types are explained.
Mechanical properties of materials are also reviewed. Besides the usual properties such as elasticity, ductility, hardness, creep, endurance, and strength, some of the other more techno-mechanical properties discussed are machinability, weldability, hot working, cold working, slip, and recovery processes used to anneal metals.
Phase diagrams provide a medium for understanding the different possible phases of pure metals and alloys influenced by temperature and pressure. The author provides a clear and concise way to understand the details of phase diagrams and the important factors associated with a phase diagram.
The last two topics deal with ferrous and non-ferrous metals. Ferrous materials cover carbon steel and the various properties of carbon steel. These properties describe eutectics, heat treatment, transformation diagrams, quenching methods, tempering, and surface hardening. These are fundamental concepts used to process carbon steels which are essential for a metallurgist to understand. Descriptions of non-ferrous metals touches on copper, copper alloys, aluminum and its alloys, titanium, and nickel alloys, and magnesium.
Reading and studying this book can be a quick way to learn fundamental concepts in metallurgy, and especially the essential processes used to process carbon steels. Each chapter is well written and nicely illustrated to clearly convey essential information. There is also a bibliography at the end of each chapter for more in-depth study.
Young Professional Highlight - On Mentoring
Thoughts on Mentoring
Just recently, it occurred to me that I am in a position where I still seek out advice and mentoring from others with more experience, but I’m also being asked to mentor others. It has not been very often where I have sat on both sides of the fence at the same time. I started mulling over what I have learned in each role and put together my top three guiding principles for each role. I wish I could say that I have perfectly mastered all of these lessons or that these are the best guidelines, but I cannot. What I can say is that these principles help me enormously, and I hope they help you too.
As a Mentee
Make sure you want advice. Although this sounds obvious, one of my first snags in being mentored was a mismatch in what I said I wanted and what I actually wanted. I had worked hard to put together my first proposal, and I gave a final draft to my mentor for review. At this stage in the project, the paper had gone through several revisions, and what I wanted was someone to say it was great as is. What I actually got were ways it could be made better. To make matters worse, I argued for why the paper was good enough as it was. Needless to say, it was not a great situation. The entire experience could have been avoided if I had recognized that I did not actually want advice.
Mentoring does not have to be formal. Sometimes there is a formal mentor–mentee pairing, but some of the best mentoring I have had has been much less formal. For example, I had the opportunity to speak with a gentleman who had worked his way up to overseeing several production facilities in multiple countries. I asked him what he learned during his career as a leader. He replied that most people want to come to work and do a good job, but sometimes, they need help knowing what good looks like. What I loved about this insight was that it puts the burden of defining success on the leader and assumes the best intentions in people. This conversation, which lasted less than 30 minutes, had a huge effect on how I approach leadership.
Tell your mentor how you used his or her advice. I seek help when I am facing a situation I am not sure how to handle. Usually, there is also a bit of reluctance because I am about to do something I am not entirely comfortable with. A good mentor will sit down, listen to me, provide suggestions, and nudge me to grow. It takes quite a bit of their time and effort to do that. When I go back to thank them for their efforts, I make sure to tell them how I took their advice and the positive outcome that resulted. I do not always take all the suggestions, but I’m sure to highlight and acknowledge him or her for the bits I did use. Not only does it let my mentor know exactly how helpful she or he was, it also encourages them to be more likely to help me in the future.
As a Mentor
Tailor your advice. Justin Marro was the first person I was asked to officially mentor. Although we work well together, we are different people with different preferences, strengths, and weaknesses. Usually, when we discuss how he is going to handle a situation, I think about what I would do but also take into account that he is not me. In general, my approach is going to be a little more direct than Justin would prefer. So, we discuss whether or not a subtler approach would be effective or if this is an opportunity for Justin to step out of his comfort zone. Ultimately, the final call is Justin’s to make, which leads me to my next point.
Do not take it personally. There have been plenty of times when my mentee does not take my advice or suggestion. Ultimately, the mentee is the one that will be experiencing the consequences, good or bad, and choosing not to take my advice is a valid option. I recently had the experience where a mentee asked me for advice, and I gave it. I could tell that he did not care for my response, so he asked other people for their advice. That was perfectly fine. No one is perfectly suited to mentor every person in every situation. A mentee’s response did not make my advice any less valid, nor did it negatively reflect on my mentoring ability.
Do not avoid constructive criticism. Mentoring can be a lot of fun, especially if I feel that I am passing along solid gold nuggets of advice or seeing someone grow under my tutelage. One of the less pleasant aspects is when I have to point out a mistake or tell someone he or she made a social faux pas. To give constructive criticism, I follow these guidelines: Do it in the moment—waiting increases the perceived severity of the infraction; make it private—keep it between you and your mentee; keep it brief—get to the point and move on; and finally, acknowledge all the work that is going well.
These are just a few lessons that I’ve learned being a mentor and a mentee, but they say nothing about the most important aspect of the mentor–mentee setup, and that is the relationships I’ve built. As I mentioned above, Justin was the first person I officially mentored. Justin credits the mentorship for his personal and professional growth. Although the official mentorship ended when he was promoted, the relationship did not end just because the official program did. Today, he and I continue to bounce ideas off each other, trade advice, and encourage each other. The mentoring experience can be a great one, and I encourage everyone to look for opportunities to be mentored or to mentor someone.
2019 IEEE Electrical Insulation Conference
The 37th IEEE Electrical Insulation Conference (EIC) will be held in Calgary, Canada, June 16 to 19, 2019. The EIC is the primary conference of the IEEE Dielectrics and Electrical Insulation Society that is devoted to the practical application of electrical insulation to electrical and electronic apparatus. Almost 200 abstracts have been accepted for presentation in three parallel oral sessions and two poster sessions at the Hyatt Regency in Calgary. A review of the abstracts shows that the 2019 conference will continue with its strong focus on the practical aspects of new insulation materials, failure mechanisms, and testing. As usual, the papers are from both industry and academia.
The 2019 conference continues a long tradition of the practical application of electrical insulation in assets such as power cables, transmission lines, transformers, rotating machines, and switchgear. The first EIC occurred in Cleveland, Ohio, in 1958. It was jointly sponsored by the IEEE and the National Electrical Manufacturers Association (NEMA). During this early era many new synthetic insulating materials were being introduced. The EIC provided a forum to discuss the manufacture, properties, and application of these new materials, as opposed to the more scientific Conference on Dielectrics and Electrical Insulation.
The EIC, under the auspices of NEMA and the IEEE-DEIS, joined with the International Coil Winding Association in the 1970s to add a major exhibition component to the event. From this time until 2009 the EIC was sponsored by these three organizations. In 2009 IEEE-DEIS became the sole sponsor of the EIC, with a more modest exhibition consisting of about 30 companies from insulation material suppliers, test laboratories, and test equipment suppliers. However, NEMA continues to be active on the EIC Board of Governors and as sponsor of the Golden Omega Award, which recognizes business leaders in the electrical insulation sphere. At the 2019 Calgary EIC, the Golden Omega Award will be presented to a worthy recipient at the Tuesday-night awards dinner.
The EIC was originally a biennial conference and was usually held in the US Midwest. With the EIC merging with the IEEE International Symposium on Electrical Insulation in 2012, the EIC has become an annual event and is held throughout North America.
I hope you will be able to join us at the Hyatt Regency in Calgary. It is a beautiful city for a conference, and this year, the EIC is shaping up to be an outstanding technical conference as well.
Kevin Alewine, 2019 Conference Chair