Electrical Insulation Magazine - Nov/Dec 2019

The November/December 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.

For a list of upcoming conferences, please visit the conference page or check out the events calendar.

This issue also contains an overview of the Liquid Dielectrics Technical Committee, which can be viewed here.

CIGRE work on impregnated insulation systems for transformers

In many ways one can say that the International Council on Large Energy Systems, in short CIGRE, is an organisation for information and collaboration on the utilities’ own premises. My viewpoint is from that of CIGRE’s Study Committee D1 “Materials and emerging test technologies”. We have an advisory group on impregnated insulation systems. The committee group has a formal collaboration and liaison with the Study Committee A2 “Transformers”. Essentially, our mission is to provide the transformer community with knowledge on insulation materials used in transformers, concerning both service and design. Our work also serves as pre-studies for later standardisation in IEC. The advisory group recommends what work should be initiated by the study committee. The group’s members come from materials suppliers, transformer manufacturers, utilities, service providers and academia from sixteen different countries. Technical brochures from the established working groups are identified by a number (TBNNN) and may be downloaded from www.e-cigre.org.

After having spent nearly forty years studying the insulation systems of a component that already has a 100-year good track record, one might expect that there should be clear answers and conclusions to the questions raised by the transformer community. But we are still searching for better understanding of and improved models for materials’ behaviour under varying transformer stresses.

Foremost, we face two problems: on one hand the ageing transformer populations, which have a potential for an extended lifespan, and on the other hand, the need to control the quality of new transformers, which are increasingly more optimized. There is a strong trend towards more monitoring, maintained by the trust in big data and analytics’ ability to reduce failure rates and optimize service life. Furthermore, new materials and changes in the processing of traditional materials are introduced, and service stresses changes towards more dynamic loading patterns and impact from power electronics.

Much of the work concerns life span assessment and ageing of transformers. Using conventional oil tests, data is collected from transformers in service. Also, evaluation of new techniques and new monitoring equipment is needed. There are unlimited possibilities for amassing of data, but the questions remain the same: Which parameters carry significant information, how should the data be collected, and based on this, when to act. In the working groups, many laboratories contribute to investigate and compare diagnostic methods for service aged transformers.

Diagnostics from service aged equipment is one cornerstone of the work that is performed. Maintenance method techniques for oil reclamation and dehalogenation has been discussed (TB413). A series of studies on dissolved gas analysis (DGA) have been published. Evaluation of online gas monitors (TB409), and on DGA for tap changers and non-mineral oils (TB443) has been reported. The latest brochure (TB771) addresses new, improved rules for interpretation of DGA. Work has been done on markers for cellulose ageing. A brochure on furanic compounds has been published (TB494), and another on the new methanol markers and on temperature corrections for markers is imminent. Under study committee A2, a brochure which recommends the investigating of decommissioned transformers (TB735) in order to learn more about ageing during service, has also been published. Feedback of experience from service will improve the accuracy of chemical analysis.

In the future, one certainly must prepare for the use of data analytics to improve the monitoring schemes. There is confidence in the big-data approach. However, I doubt that any one utility can provide the big data sets required. Collaboration will still be wanted. We will need consensus on which data are significant and on unified data formats to collect from this collaboration, and especially to establish any correlation to failure incidents and scrapping investigations.

There is a steady flow of new proposed diagnostic methods that needs evaluation. Working groups have been active in the reviewing and development of diagnostic methods used both during service and during commissioning. Two reports address the measuring of moisture in cellulose using dielectric spectroscopy (TB254, TB414), and a study relating to HVDC applications, exposed difficulties in the development of test methods for high field conductivity of liquids (#646). Measurement and interpretation of partial discharge was thoroughly described (TB676). Recently, a brochure was published on the application and interpretation of the measuring of water content in oil using online moisture sensors (TB741).

Specification and characterisation of materials is important for controlling the quality of a transformer. For the end user, reference to material standards is required when working on transformer specification. A good standard provides relevant methods in characterizing a material’s quality and ability to fulfil its function. However, there are examples of suggested parameters for standardisation that lack relevance to a function. For instance, it is not clear and documented how differences in the inception of PD in a liquid relates to the withstand voltage, even if very interesting from a scientific point-of-view. On one hand we have the old well-tested materials, which often are lacking in test methods and proven standards of their functional behaviour. On the other hand, there are new materials for which test methods used for the conventional materials may not always apply. We try to focus our resources on the most important issues.

One group has worked on the ageing of mineral oil impregnated cellulose, mainly for life assessment, but this work is also relevant for design and specification. The work was extended also to include ester impregnated systems (TB738). It documented the importance of water and acids as ageing drivers. Though not perfect, an Arrhenius relation may be used to model ageing in the early stages of the degradation. However, the parameters in the ageing model are seen to vary, and one realizes that insulation paper is not a sufficiently standardized product. In high temperature tests on different cellulose insulation systems, we also see that the combined effects of ageing kinetics and water partitioning results in widely differing acceleration factors. This does not allow for the use of simple Arrhenius models for ageing. Further work is needed here, and I believe that improvement on the understanding of the basic chemistry of the ageing mechanisms is needed in order to reach a sound test regime for the ageing process of cellulose in the various feasible insulation systems.

We see new liquids arrive, and production of mineral oils change. The demands from environmental policies influence the refining processes of mineral oils; less sulphur and polyaromatics are allowed. There is a general trend to shift from uninhibited oils to harder refined inhibited mineral oils, which in principle should be more well-defined products. At the same time, we see new esters and synthetic liquids being introduced. With such a wide range of chemical compositions, we may expect great differences in their functional properties. One working group discussed the chemistry, test methods, standards and experiences of oxidation stability of different liquids (#526). More work on the new liquids has begun. One new working group address fire and environmental testing and properties of liquids. Another group addresses the dielectric performance of liquids. In this group it is seen that functional properties, like time to breakdown, heavily depend on chemical composition of the liquid.

To illustrate the problems with the existing standards for testing breakdown of liquid, I can mention that we observe that impulse breakdown voltage testing of liquids (IEC 60897) does not distinguish between liquids’ ability to withstand short duration impulses in long point-sphere gaps. The standard needs revision. Furthermore, there is also a discussion on whether a test executed with highly non-uniform field is the only relevant test for the function of a liquid used in an insulation system with low degree of non-uniformity. The other standard used for transformer mineral oils (IEC 60156), tests ac breakdown voltage in a uniform field. There is shared agreement that these test results mainly reflect water and particle content and do not depend on liquid composition. It only has relevance for the monitoring of transformer condition. Still, in literature one may see that this standard is used to characterise the voltage withstand of various liquids for all kinds of applications.

Undoubtedly, there is a need for more and improved standards regarding the materials used in a transformer. The standards should, if possible, be based on models of the chemical and physical mechanisms that govern their behaviour. Even if we learn about the differences in performance and can establish standards that distinguish the functional performance of a material, standards become more robust when based on a good understanding of the fundamental mechanisms.

In most cases the functional requirements depend on the application. There are huge differences between the conditions in a transformer with large gaps, ac stress, and a uniform field to that of a power converter with small dimensions, non-uniform fields, and square wave voltages.

In our culture there is increasingly more control and regulations. For many materials, new and improved standards for the most important functions are needed, and this work will continue in small steps. We should be careful and avoid introducing standards that do not exhibit the desired functionalities. On this area, there is still a need for much more work. To advance this, utilities as end users should not rely on industry alone to deliver this but ought rather to support academia in the basic and neutral research.

From The Editors

: Stanislaw Gubanski, Editor-in-Chief stanislaw.gubanski@chalmers.se

: Resi Zarb, Co-Editor resi.zarb@ieee.org

From the Editors’ Desk
November-December 2019

The Electrical Insulation Magazine often publishes reports about DEIS conferences. It has come to our attention that a report about the 16th International Symposium on Electrets held in Leuven, Belgium in September 2017, has been missing. We, therefore, include this report in this issue of the magazine.

Reports on research activities related to the reliability and diagnostics of power transformer insulations occupy a large part of recent IEEE technical and scientific conferences on electrical insulation systems. We bring in this issue four articles illustrating work related to this subject. We also present an editorial written by Lars Lundgaard of SINTEF Energy Research in Trondheim, Norway elucidating the work on impregnated insulation systems for transformers within the International Council for Large Energy Systems (CIGRE).

The first feature article in this issue is entitled “Analysis and Mitigation of Australian and New Zealand Power Transformer Failures Resulting in Fires and Explosions”. It is jointly authored by Daniel Martin of the University of Queensland in Australia, Chris Beckett of United Energy in Australia, Jon Brown of Transpower in New Zealand and Shawn Nielsen of Queensland University of Technology in Australia. The article presents statistical analyses of power transformer fires and explosions occurring in both countries. Since many transformers in this region are entering the later years of their useful lives, a question posed is whether fires and explosions will become more likely with age. If it does, then this will have implications on replacement policy. A recent study found that the age-related failures begin to occur after around twenty years, prompting a close analysis of whether the likelihood of a catastrophic failure is also age dependent. While many utilities keep data on asset failure, the likelihood of a transformer fire or explosion is so low that a local utility is unlikely to experience enough of these types of failure to evaluate statistically. Consequently, a survey was performed to compile the necessary information from as many utilities as possible. Data on 6,552 power transformers in operation since 2000 onward is gathered, equating to 92,119 service years of operation. Within this period 22 fires or explosions were reported by the owning utilities. The data was sorted into distribution, sub-transmission and transmission voltage classes, and then evaluated using statistical techniques. While the catastrophic failure rate does appear to be related to age, the annual number of fires occurring has fallen off from 2004 onward. Whereas in the past bushings have been identified as the leading cause of fires, many utilities have had programmes in place to mitigate this failure mode, and so bushings are no longer the primary cause of a fire.

The second article entitled “Influence of Copper on Gassing Properties of Transformer Insulating Liquids” is authored by a team of researchers representing academic and industrial institutions from USA and Japan. It is authored by Ivanka Atanasova-Höhlein of Siemens Transformers in Germany. It describes problems encountered when evaluating evolution of gases in liquid insulated equipment and especially on the so-called stray gassing of insulating liquids in transformers. The latter is a phenomenon found in new as well as in aged transformers and in most of the cases in free breathing transformers, generally filled with an uninhibited type of mineral oil. The effect is characterized by a relatively quick increase of hydrogen and/or saturated hydrocarbon concentrations at rates slowing down with time to near zero. The classical interpretation by means of dissolved gas analysis (DGA) data indicates, in such cases, the presence of a hot spot below 150°C, despite that transformers operate far below their nominal rating. At the same time the lower than expected oxygen content in the oil suggests an on-going oxidation. Test methods to address this problem have been developed by CIGRE and ASTM and attempt to provoke stray gassing by oil treatment at elevated temperatures (120°C or even higher). They, however, do not reproduce the phenomenon completely, as the tests at such temperatures, which by far are not typical for service conditions, contradict strongly the real experiences. The article shows clearly that presence of copper plays a decisive role and presents a newly developed laboratory method to evaluate the effect of stray gassing in various types of insulating fluids under lower operating temperatures.

The third article in this issue is entitled “Evaluation of Mechanical Condition of Transformer Paper Insulation after Factory Drying” and is authored by George Frimpong and Lena Meltzer of ABB, respectively in the US and Sweden. The article sheds some light on a problem met when determining Viscometric Degree of Polymerization (DP) of transformer paper according to ASTM D4243 or IEC 60450 standards, a well-established method used in the transformer industry to track degradation of the paper insulation used inside transformers. Both the standards require the tested paper sample to fully dissolve in the solvent solution for a proper measurement. However, there is no clear guidance within these standards on how to determine DP if the paper cannot be fully dissolved in the solvent, which has become evident through experiments performed in recent years, especially on new paper after factory drying. This phenomenon has been observed for different paper types, paper dried using different drying methods, different types of pulp and measurements made at different laboratories. To investigate this phenomenon, various samples of transformer paper originating from two manufactures were dried along with windings of ten transformers in five different factories. The transformers were carefully chosen to provide variability in size and duration of processing. The samples from each transformer were sent to four different laboratories for DP measurements. The findings show that new (undried) paper readily dissolves in the solvent used for DP measurement, while all the laboratories had great difficulty getting the dried paper to fully dissolve in the solvent. Furthermore, an attempt to quantify the amount of undissolved cellulose in solution as described in ASTM D4243 was mostly unsuccessful for the dried papers. These difficulties introduce large uncertainties in the DP measurements and if DP is to be reliably used to assess the condition of paper after factory drying, it is important that the main standards bodies provide modifications to the measurement protocols that ensures heavily bonded cellulose fibers to fully dissolve.

The fourth article in this issue is entitled “Condition Monitoring of In-service Oil Filled Transformers: Case Studies and Experience” and reports on field experiences from periodical condition monitoring of 37 oil-filled transformers belonging to a Canadian power company and a rubber bladder sealed reactor of a Uruguayan power company. It is authored by Mohan Rao and Issouf Fofana of the University of Quebec at Chicoutimi, Canada, Amidou Betie of the National Polytechnic Institute Felix Houphouet-Boigny, Ivory Coast, Mohammed Senoussaoui and Mostefa Brahami of University of Sidi Bel Abbes, Algeria, and Eduardo Briosso of CTM Salto Grande, Uruguay. Rates of degradation of insulation systems of the transformers and reactors (three individual phases) are reported while considering the influence of oil reclamation and inhibitor replenishment. The impact of oil reclamations on the physiochemical parameters and significant aging markers is elucidated. For the transformer fleet, the aging markers are interfacial tension, acidity, moisture content, dielectric strength, and furan content. For the reactor, dissolved gas analyses, acidity, interfacial tension, dielectric losses, breakdown voltage, moisture content, and furan analysis are analyzed and reported for all the three individual phases. The key aspects are 1) some of the transformers have been in service for more than 70 years at an average temperature of around 2°C and 2) adopted maintenance strategies include regular reclamations, which helped maintain the units beyond their theoretical design life. Since reclamation not only removes decay products but also anti-oxidants, regular inhibitor replenishments have helped to keep the units in good condition. The lesson learned from the rubber bladder reactor case study indicates that a continuous monitoring is also essential.

Book Reviews

Magnetic Communications – From Theory to Practice

F. Hu, Editor

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
http://www.crcpress.com
ISBN 978-1-4987-9975-1
305p. $119.95 (Hardcover), 2019

Today, wireless communication is most commonly made possible through radio frequency (RF) waves propagating through air. However, applications such as underwater, underground, or medical communication, RF communication is not effective or possible due to the rapid attenuation of RF waves. For example, acoustic signals can travel over 1 km in water with little signal loss while RF waves will be attenuated in a very short distance. Magnetic induction has been used to provide wireless high-speed communications for underwater applications at propagation speeds of 3 x10⁷ m/s with data rates of Mb/s and transmission distances of >50 m.

This book introduces acoustic and magnetic communication from an engineering design perspective. It is divided into two parts – magnetic communications and acoustic communications. The magnetics topics cover wireless data and energy transfer and magnetic communications models. Wireless charging of cell phones and electric vehicle charging principles are described along with data-sharing applications. Efficiency between induction coils and upper bounds on high-speed data communications between induction coils are also detailed.

Communications for underwater and mining applications using acoustic transmission methods detail network routing protocols, hybrid RF and acoustic transmission and propagation models. Since acoustic links have a much longer propagation delay time as compared to over air RF signals, conventional media access control (MAC) cannot be used. A new MAC schedule-based collision avoidance method is explained. Hybrid systems, using acoustic transmission for underwater and RF communication for above the water surface, are described in detail. These systems have complex network bandwidth management challenges and protocol controls that are also covered in detail. The propagation mathematical models describe the acoustic signal fading characteristics in free space and water.

This book can provide research engineers who design underwater and underground communication systems with the latest insights and knowledge into non-RF networking schemes for improving existing products. With the latest technology and emerging topics discussed, electrical engineering communications students could also use this book for exploring ideas for research topics in this area or to just learn about the fundamentals of magnetic induction and acoustic communications.

Superconducting Fault Current Limiter – Innovation for the Electric Grids

P. Tixador, Editor

World Scientific Publishing Co.
5 Toh Tuck Link
Singapore 596224
US Office:
27 Warren Street
Suite 401-402
Hackensack, NJ 07601
http://www.worldscientificpress.com
ISBN 978-981-3272-97-2
405p. $138 (Hardcover), 2019

A superconducting fault current-limiter (SCFCL) can be used as a circuit breaker in a MV power distribution system. Its properties are such that it behaves as a variable impedance which is a function of the current passing through the device. As the current exceeds a critical current density, the impedance of the device rapidly increases from near zero to a high level, thereby providing inherent current-limiting capability. The need for cryogenic cooling increases the cost and complexity of this device, however, the development of high-temperature superconducting (HTS) materials has greatly reduced this cost and complexity, so much so that there are a number of SCFCL is operating the field today.

This book, a collection of well-organized chapters written by various authors, describes the technical details and operation of resistive SCFCL’s and how they could be integrated into a MV power distribution system. The book begins with a description of the requirements of an existing power grid in general to illustrate the requirements necessary in a SCFCL. This is followed by a description of superconductivity in general but with a focus on the important properties needed for a SCFCL switch. Two superconducting materials (BSSCO and REBCO) used in today’s SCFCL’s are discussed. Next, the design of a resistive based SCFCL is discussed and modeling the SCFCL using EMTP-RV software to study its effect on the switching properties in a power grid. Cryogenic systems are reviewed to show what is involved with these systems including operation, maintenance and costs. The remainder of the book reviews the impact of the location of the SCFCL in the grid for both AC and DC grids, some SCFCL project examples through the world and some new developments such as the direct flow diverter concept and a sapphire coated wire substrate.

There is a wealth of technical details on SCFCL’s included in this book, but its strong point is in the information it provides on the implementation of the SCFCL into the power grid. Field operating examples give very interesting details on the behavior and maintenance of these devices in real-world applications. The poor grammar, prevalent throughout the book, and the occasional unclear writing can be annoying, but generally the intended message is clear. While the title implies innovation for a new electric grid, there is no new information presented on what future electric grids might look like. In fact, the entire design of the SCFCL presented is based on the characteristics and requirements of the existing power grid with no real insight into what a future power grid might look like and how that may affect the design of a SCFCL, except that it will contain a SCFCL.

Despite these limitations, this book would be very interesting to researchers who want to learn about SCFCL’s or those working in this field. The collection of this data in one book makes this book a very convenient resource for those working on this technology.

Creep and Fatigue in Polymer Matrix Composites, 2^nd *Edition***

R.M. Guedes, Editor

Woodhead Publishing
An imprint of Elsevier
50 Hampshire Street
5^th Floor
Cambridge, MA 02139
http://www.elsevier.com/books-and-journals
ISBN 978-0-08-102601-4
587p. $252 (Softcover), 2019

Creep or cold flow, is the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses. It can occur from long-term exposure to high levels of stress that are still below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods and generally increases as they are near their melting point.

The rate of deformation is a function of the material’s properties, exposure time, exposure temperature and the applied structural load. Depending on the magnitude of the applied stress and its duration, the deformation may become so large that a component can no longer perform its function and eventually fail. Creep can occur in polymers which are considered viscoelastic materials. With the viscoelastic/visco-plastic nature of a polymer, damage can accumulate and propagate, especially with a fiber reinforced polymer matrix, progressively degrading the strength and stiffness of the material. Catastrophic and premature failure of fiber reinforced polymer structure can occur well before its estimated lifetime if conditions that the materials are exposed to are not fully considered in the original design of the material. Also, much of the failure mechanisms and creep properties are not fully understood and can be very difficult to create a predictive model to estimate expected lifetime and performance of a material. Oftentimes a combination of theoretical modeling based on experimental results is used to determine creep and fatigue performance of a material.

This book reviews some of the latest experimental and theoretical approaches to creep and fatigue in polymer matrix composites. It provides many mathematical models that attempt to describe and predict creep and fatigue in polymer composites as well as numerous tables and graphs of experimental results.

The book is divided into three parts. Part I deals with time-dependent models of the viscous nature of the polymer matrix. Some of the specific topics cover the fundamentals of creep and stress relaxation in polymers and polymer composites. This part of the book is very beneficial for those who do not have the background in the fundamentals of creep and fatigue in polymers. This part goes on to describe more advanced topics including; time-temperature effects for predicting the long-term response of linear viscoelastic materials, the effects of moisture, modeling piezoelectric composites, predicting behavior of nanocomposites, and creep analysis using visco-plastic models.

Part II covers creep rupture which includes the time-dependent nature of failure mechanisms in carbon-fiber reinforced polymer composites, composite structures, and laminates.

Part III details fatigue modeling, characterization, and monitoring. This part describes accelerated testing methods for determining long-term creep and fatigue properties of polymer composites. Other topics include the modeling, analysis, and testing of the viscoelastic properties of shaped memory polymer composites and methods used to monitor the structural health of structural polymer composites.

This book would appeal to the material scientist, polymer chemist, and structural engineers who want to learn about the latest information for testing and modeling the creep and fatigue properties of various composite polymeric materials used for structural applications. It contains background on fundamentals to orient a beginner in this area and advanced modeling information with theory and experimental results to satisfy in-depth detail desired by more experienced readers in this area of research.

Electrical Machine Drives

C.M. Franchi

CRC Press
Taylor & Francis Group
6000 Broken Sound Parkway – NW, Suite 300
Boca Raton, FL 33487-2742
http://www.crcpress.com
ISBN 978-1-138-09939-5
400p. $129.95 (Hardcover), 2019

The AC induction motor is a workhorse of industry. Many processes in industry, as well as other applications, use induction motors. Many of these applications require precise speed and torque control of the motor, while other applications do not have to have as tight a control. A variable speed drive is one way to bring precise control of motors.

This book presents commonly used methods for protecting and starting AC power induction motors. The book begins by presenting the fundamentals of induction motor design. A comparison of the DC and AC induction motors (single-phase and three-phase) fundamentals along with motor selection factors are first presented, followed by in-depth three-phase motor fundamentals which include construction, operation, operating characteristics, cooling, and various other parameters. The electrical power basics (power factor, causes of low power factor and methods to improve the power factor) are also described.

The remainder of the book describes starting and controlling methods for AC induction motors. These begin with direct on-line (DOL) methods including fuse selection, fuse sizing, overload relay characteristics, selecting and sizing contactors (ratings, and features), and auxiliary relays. These are the basic components used for DOL starting and motor protection and are very commonly used for many motor applications today. The information provided will help the engineer not only understand the uses for each these components but also help in selecting and sizing the correct values for a given application. After detailing the basic components of a motor starter and the DOL starting method, other starting methods are covered which include soft-start and variable frequency drives (VFD).

The operating principles of soft-start methodology are presented, parameter description (voltage ramping, start pulse, and current limitation), typical circuit topologies, and phase control methods.

The VFD operating principles include details on how VFD circuits work, including the control methods for firing the IGBT gates for pulse width modulation control, protection of VFD’s (overcurrent, earth leakage, thermal overload, and fault protection) along with installation information. Good practice for installing VFD provides the reader with recommendations for preventing or minimizing undesired effects when using VFD. Some other problems address harmonics, selecting a switching frequency, and protecting motors against high frequency switching. The final chapter provides details on sizing drives, according to the type of load, and some application examples.

This is a book for power engineers who specify, utilize, or design motor starters for AC induction motors. It ties together a fundamental understanding of the theory of AC motors and motor controls with a pragmatic view that allows the reader to fully appreciate the uses of three different starting methods for AC motors and their protection.

Principles of Forensic Engineering Applied to Industrial Accidents

L. Fiorentini and L. Marmo

John Wiley & Sons, Inc.
111 River Street
Hoboken, NJ 07030
http://www.wiley.com
ISBN 978-1-118-96281-7
515p. 119€ (Hardcover), 2019

Forensic engineering has been defined by Wikipedia as “the investigation of failures – ranging from serviceability to catastrophic – which may lead to legal activity, including both civil and criminal.” Generally, the purpose of forensic engineering investigation is to locate cause or causes of failure with a view to improve performance or life of a component, or to assist a court in determining the facts of an accident. It can also involve investigation of intellectual property claims, especially patents.

This book is a concise introduction of forensics engineering as applied to industrial accidents. It provides a rigorous approach to the discovery of root causes that lead to an accident or near-miss. The approach used helps to identify both the immediate cause(s) as well as the underlying factors that affected, amplified or modified the events and eventual human error.

The book covers simple real cases and an overview of more complex ones, an overview of the most commonly used methodologies and techniques for investigating accidents, methods for collecting and handling evidence, and an overview of the common mistakes that can lead to the wrong conclusion or loss of proof.

Some of the industrial accidents described in this book include Seveso, Bhopal, Flixborough, Deepwater Horizon drilling rig explosion, San Juanico, and the Buncefield disasters. These are all major industrial accidents that have been analyzed to illustrate the forensic methods used to determine the causes and methods used to perform an investigation. Examples of some of these methods cover sample collection and preservation, interviewing techniques, and evidence analysis. Investigative methods explore human factors, human error, root cause analysis and others. These are tools used to help determine the cause(s) for the failure.

The book also provides recommendations for implementing safety improvement and ways to develop recommendations for improving safety. How to handle near misses and how to treat them and how to choose the best corrective actions are some examples of lessons learned.

In addition to the major disasters described earlier in the book, there are also quite a number of case studies described that are on a smaller scale than the previously described major disasters but are more likely to be more frequently encountered. These examples provide insight into what to look for in similar situations. These examples coupled with the methodologies presented provide a sound foundation for learning about forensics engineering.

Thus, this book is suitable as an introductory volume for those who want to know more about forensic engineering methods, especially focused on industrial accidents. These readers might include safety managers, risk managers, engineering consultants, attorneys, authorities having jurisdiction, judges, and prosecutors. While there are more specialized books available on certain topics, this book is intended as an overview and is especially useful as a way to learn from real accidents or near misses to improve safety and understand how failures can occur.

Advanced Topological Insulators

H. Luo, editor

Scrivener Publishing LLC
100 Cummings Center
Suite 541J
Beverly, MA 01915
www.scrivenerpublising.com

John Wiley & Sons, Inc.
111 River Street
Hoboken, NJ 07030
http://www.wiley.com
ISBN 978-1-119-40729-4
413p. $225 (Hardcover), 2019

Topological insulators (TI) are materials that behave as insulators in their interior but whose surface is conductive and robust. Conduction electrons were topologically protected in these materials, which means their surfaces are guaranteed to be robust conductors even in the presence of defects. In experiments, researchers would slice off thin layers from the surface of the material and after each thinning of the material, the surface maintained its conductance without the slightest change. For the thinnest samples, such topological conduction properties were even observed at room temperature, paving the way for practical applications in quantum computing and spintronics. Phenomena such as current induced magnetization switching by spin-orbit torque (SOT) is an important ingredient for modern non-volatile magnetic devices such as magnetic random-access memories and logic devices that are needed for high performance data storage and computing.

This book presents the latest advances in theory, experimentation and applications in TI and it provides a foundation for understanding the technology. It begins by covering the characterization of phase transition points in TI systems. This involves quantum phase transitions and the characterization of electronic and optical properties. It continues by examining theory and experimental results of thin-film TI and topological superconductors. Electronic properties of TI nanoparticles and TI nanowires are also explored. Applications cover using a TI as a saturable absorber in a Q-switched erbium doped fiber optic laser to exploit the wide-bandgap characteristic of the TI. Applications for photonic crystal fibers and patterned 2D thin-films are also described.

This book is written for researchers in physics, materials science, and chemistry with interests in learning about some of the latest advances in TI. It involves a deep understanding of quantum mechanics to fully appreciate the work being presented and some familiarity with TI would also be a prerequisite to get the most out of this book. By bringing many topics on TI into one book, the author makes it easier to for the reader to better understand the complex but fascinating field of TI.

News From Japan

Yoshimichi Ohki

A New 250-kV HVDC XLPE Cable System in Japan

For electric power suppliers, the stability of power supply is a most important and keen issue. Regarding this, a power grid generally becomes more stable with an increase in size. In addition, a grid is more robust when it takes the form of a circle than when it is one-directional. On this point, Japan is not a good country to maintain a stable power grid for many reasons. First, Japan is a small but long archipelago. While its length reaches about 3500 km, its width is only 300 km at the widest point. Secondly, two different commercial power frequencies are used; western Japan uses 60 Hz, while the eastern half uses 50 Hz. Thirdly, Japan is an isolated country surrounded by the Pacific Ocean, Japan Sea, Sea of Okhotsk, East China Sea, and Philippine Sea. Fourthly, building a large international circular power grid is also difficult because of geopolitical situations.

Among the four big islands of Japan, the northernmost Hokkaido is the most difficult to build a stable grid, because the Tsugaru Strait between Hokkaido and the Main Island, called Honshu, is the widest of all the major straits in Japan. For these reasons, interconnection of electric power to and from Hokkaido is limited.

Figure 1. Schematic illustration of a map of Japan and locations of new and existing Hokkaido- Honshu HVDC power links.

Table 1. Specifications of this project

As shown in Figure 1, up to recently, the Hokkaido grid and the Honshu grid were interconnected by a bi-pole 600 MW LCC-HVDC link. Here, LCC means a line-commutated converter, which cannot change the direction of the electric current. The reversal of the direction of power flow in a LCC system is achieved only by reversing the polarity of dc voltage at both stations. Since the commencement of operation of Pole 1 in 1979 and Pole 2 in 1993, this power link has been playing a key role in improving reliability as an emergency backup for power shedding and also in contributing to the frequency stability in the Hokkaido power system. It has also been reducing the reserve margin and improving the mutual backup for supply-demand imbalance of each area.

However, Pole 1 of this power link has passed 40 years this year (2019) since the commencement of its commercial operation. This means that it needs to prepare for future replacement. One countermeasure against possible suspension of the link was already partly conducted by installing the world’s highest-voltage ( , as of 2012) XLPE-insulated LCC HVDC submarine cable [1, 2]. This new cable has been operated safely since December 2012. However, building an additional HVDC link that can interconnect more power is still a keen issue. With this background, a new Hokkaido-Honshu HVDC link started its construction in 2014.

Figure 2. Detailed transmission routes and facilities of new and existing HVDC links

The specification and route of the new DC link are shown in Table 1 and Figure 2, respectively. A voltage-source converter (VSC) system is used in this new link. As mentioned above, the former Hokkaido-Honshu Link are LCC lines, which use thyristors. Thyristors are essentially unidirectional switches that need external voltages to reverse the direction of power flow. On the other hand, VSC uses an insulated-gate bipolar transistor (IGBT), by which both turning-on and turning-off the switch can be achieved with no help of an external voltage.

As shown in Figure 2, the new link has two overhead line sections and a tunnel section, where a DC cable is installed. The cable in the tunnel is the longest in the world as an extra-high voltage (EHV) cable installed in a submarine tunnel as of March 2019. The tunnel is a railway tunnel, called Seikan Tunnel for high-speed “bullet” trains connecting Tokyo and Hakodate in Hokkaido. The cables in the sea section were installed directly under the sea in the former HVDC link for all the lines, Pole 1, Pole 2, and the newest one constructed in 2012. Compared to such cases, the installation of the cables in the railway tunnel has many advantages. First, there is no need of compensation to fisheries and no need for environmental assessment. In addition, almost all the processes including installation and maintenance are much easier. Furthermore, there is no risk of cable damage by a ship’s anchor.

The cable that started its operation in December 2012 was manufactured by J-Power Systems Corporation, which was then merged into Sumitomo Electric Industries, Ltd. Since this cable has been operated without any trouble, Sumitomo decided to manufacture the new cable essentially the same.

Table 2. Supply items for this project

Figure 3. Developed XLPE-insulated cable installed in a railway tunnel for a new 250-kV HVDC VSC link.

Figure 4. Pre-molded one-piece joint.

Figure 3 shows the configuration of the developed cable. The wind velocity, ventilation, temperature, flow rates and temperatures of water and drainage, and other environmental conditions were surveyed for one year in 2013. As a result, three different conductor sizes, 800, 1000, and 1500 mm², were decided taking account of environmental conditions. Since the cable length that can be transported is limited, a pre-molded one-piece joint, shown in Figure 4, was adopted for connecting two conductors of the same size and a prefabricated composite joint, shown in Figure 5, was adopted for two conductors of different sizes. As for the insulation, XLPE containing a kind of inorganic filler especially developed for use in DC cables, was adopted.

A test piece of the cable, manufactured exactly the same, successfully passed a type test conducted in accordance with of the CIGRE TB 496 in September 2016. The new HVDC link has been operated with no trouble since March 2019.

A blackout, what is called the first island-wide electric power outage in Japan, happened in Hokkaido on the 6th of September 2018. The blackout continued for a relatively long time; it took about 55 hours before 99% of the outage was restored and two weeks for the complete recovery. The direct cause of the blackout was that a very big earthquake hit Hokkaido and suspended a 1.65-GW thermal power station. However, another point is that the Honshu-Hokkaido HVDC link available at that time is an LCC link as mentioned above. This means that the link needed an external power to restart its operation. Therefore, the link could not take proper action at the power outage. This could be one of the secondary causes. It is expected that the new link, which is VSC-operable, will solve this disadvantage.

Figure 5. Prefabricated composite joint.

This article was completed in cooperation with Hokkaido Electric Power Co., Ltd. and Sumitomo Electric Industries, Ltd.

References

[1] Y. Ohki, “News from Japan – Development of XLPE-Insulated Cable for High-Voltage dc Submarine Transmission Line (1)”, IEEE Electr. Insul. Mag., Vol.29, No.4, pp.65-67, 2013.

[2] Y. Ohki, “News from Japan – Development of XLPE-Insulated Cable for High-Voltage DC Submarine Transmission Line (2)”, IEEE Electr. Insul. Mag., Vol.29, No.5, pp.85-87, 2013.

Young Professionals

The Thesis Formula

Approaching the end of a PhD is painful even for the most studious candidate (at a guess). The sheer volume of work that needs to be completed before we can even begin to fathom the extent of writing that goes into a thesis is scary in itself. Fortunately, throughout my postgraduate life, I have met many kind human beings that have shared their wisdom in finishing the write-up stage as gracefully as possible. So when I was asked to write the young professionals column at EIC 2019 in beautiful Calgary, Alberta, I began thinking about what I could share that might be useful being in my final year – and it was not easy!

My inspiration came after seeing this mind map drawn by world-renowned architect Eva Jiřičná, who exhibited at DOX Prague back in June. The drawing follows the creative process of an architect starting a new project, but to me this perfectly portrays a typical PhD programme or the mental turmoil of project management in general; from the bewildering initial state in an attempt to understand your research narrative, to the periods of complete loss of perspective, to the dead-ends, to the first breakthrough, to the stages where you are drowning in work, but somehow for once science seems to be on your side so you keep going. And finally you reach the write-up stage where you realise the scope of your knowledge in your research area, and just how much you have learnt in this process which has gone way too fast (but also somehow not?).

Although the majority of the PhD process is a big ‘unknown’, the wonderful thing about reaching the write-up stage is that it is a ‘known’ which is based purely on effort and pushing through a repetitive cycle (see “work work sweat sweat work” region in the above figure). I tried to think of what goes into a thesis, and came up with this enigma of a formula, which undoubtedly will not help you the slightest but it may at least remind you to take care of yourself whilst you are writing:

Where motivation will be clear once you have reached this stage of your PhD programme, resilience will have been picked up by now as well, leaving the two areas of interest being work and happy brain. Here are my semi-precious pearls of wisdom.

Writing advice:

TNT (The Next Thing) – leave yourself a roadmap before finishing for the day by writing short notes on your thoughts and questions on which you were pondering, it will make it much easier when you can immediately pick up where you left off in the next writing session.
Create a thesis plan – a bullet-pointed breakdown of: what needs to go into each chapter, work completed, and work outstanding.
Split each chapter into different word documents or LaTeX file – treat each chapter as a long essay that has a deadline at the end of the month for example – visualising the thesis as a handful of long essays truly helps and increases productivity when you finish a chapter.
Writing in 3 stages – a general brain-dump of relevant information, before moving onto to critical analysis of the writing, and finally the editing stage to check the narrative and flow.
For some the Pomodoro technique works, where writings completed in short bursts using a timer, with usually a break is taken every 20 minutes, and repeated until user is broken.
Write your experimental section first – that will help you remember what you did before in terms of experiments and aims/goals, before you move onto the analysis and discussion.
Ignore viva anxieties, and do not try to understand everything as you are writing, you will get to that after you have written up.
There is always more to write and sentences to perfect – send a draft to your PI or supervisor to get regular feedback.

Happy brain advice:

“Music is food for the soul” – if creating working playlists takes time, listen to pre-made playlists and podcasts on online radio such as WWFM/ NTS/ BBC Sounds/ Soundcloud.
Breaking up your working day with something you love – whether that is walking in nature, making time for human contact every day, ring friends and family, doing absolutely nothing…
Self-persuasion with a start or mid-writing coffee/cake/treat of some kind.
Switch up your work environment, preferable away from the lab somewhere communal.
Habit forming is key – procrastinate with absolutely no shame at the start, watch that show you like but get straight back to work afterwards.
Celebrate each little milestone with something that motivates you and cheers you up, maybe even celebrate when you have not reached it yet!
Think about a thesis-free life, how would you feel once this is all finished?

Finally remember that you will be hitting the “target”, as there is no single or correct technique in writing and completing a thesis. Whether it is frequent and allocated writing bursts, or an extensive and complete dive into writing for long periods where you do not see the sun – whatever works for you to keep a sense of direction and motivation is all that you should be doing.

I hope the thesis formula and the mind map doodle encourages someone to take this experience slightly less seriously and to remember that we are all going through the same process, whether this is the start of your postgraduate studies, starting a new research project at work, completing your PhD or you just happen to be stuck in an existential loophole. I also happen to be in the process of writing up, so please get in touch if you have any tips and tricks that work for you! Best of luck ☺

Hasti Haghighi

Hasti.haghighi@manchester.ac.uk