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.

Featured Articles

Calculating the residual life of insulation in transformers connected to solar farms and operated at high load

D. Martin; F. Zare; G. Caldwell; L. McPherson — Xplore Link

Condition assessment of 132/220 kV oil-paper current transformers in Sri Lanka

S. Kumara; M. Fernando; T. N. Aravinda; D. S. Daulagala; A. P. Bandara; K. Bandara; P. Nandasena; G. A. Jayantha — Xplore Link

Gas-in-oil analysis and evaluation criteria for synthetic esters in offshore and traction transformers

Ivanka Atanasova-Höhlein; Carolin Schütt — Xplore Link

Potential of coconut oil as a dielectric liquid in distribution transformers

Anu Kumar Das; Dayal Chandra Shill; Saibal Chatterjee — Xplore Link

Mechanical energy harvesting with ferroelectrets

Xiaoqing Zhang; Heinz von Seggern; Gerhard M. Sessler; Mario Kupnik — Xplore Link

Dan Martin

Innovation Project Engineer, ETEL Transformers
CIGRE NZ.A2 Transformers Convener
Auckland, New Zealand
daniel.martin.au@ieee.org

What is the future for transformer insulation?

The 2020s are going to be an exciting decade of change in terms of how people interact with the electricity grid. In Australia and New Zealand, the electricity systems are decarbonizing, driven by economics and government policies. New technologies such as rooftop PV, solar, and wind are entering the system. Electrical transport and batteries are expected to become mainstream soon as costs continue to decline. The question is, therefore, what are the challenges and opportunities that this presents to the users of transformers and its electrical insulation?

The utilities understand that if the connection of new technologies is unmanaged, there could be problems such as over loading assets leading to impending failure, or investments becoming stranded if they are no longer needed. The utilities must, therefore, ensure that their infrastructure can cope with these new technologies and community expectations while maintaining public safety. They must assure the regulators that any network adaptation costs are prudent and customer money is well spent. The new environment of low-carbon technology presents opportunities for creative thinking and innovative solutions, which is the focus of this article.

ETEL is a manufacturer of transformers and is part of the Unison group of companies, where Unison is a utility supplying part of the east coast of the north island of New Zealand. Unison manages an NZ$550M asset base and supplies 110,000 customers. Unison and ETEL are working together to understand how networks will change, and any improvements to products and services that the Australian and New Zealand networks will require. The operation of Unison is overseen by the Hawke’s Bay Power Consumers’ Trust. Anybody who has a power account for a property linked to Unison is a shareholder, receiving an annual dividend. This is a very different model from the Australian utilities which are either owned privately or by state government. Regardless, both models seek to improve value to the owner such as optimal investment in transformers.

The purpose of my engineering role at ETEL is to manage and complete innovation projects, collaborating with other departments to deliver novel solutions and to implement them with customers. A key part of my role is to understand how networks must change in the 2020s, and then apply this learning to develop new products and services.

When a utility has purchased an asset, such as a transformer, they assign a “standard life” for valuation and depreciation purposes. If the asset must be replaced earlier than at its standard life, there is undepreciated value which is a loss. Consequently, having advanced warning of insulation problems is beneficial for the utility to act and perhaps extend life.

The Australian and New Zealand networks are similar due to the same set of engineering standards being followed (e.g. AS/NZS 60076/7 loading guide for oil immersed power transformers). Thus, transformer technology is similar. A striking difference between these networks has been the historic generation mix. Whereas one is undergoing a transformation to renewables, the other was set up with this type of generation in mind. In New Zealand nearly 60% of the electricity generated is from hydro and another 17% from geothermal, whereas for Australia only 7.5% is from hydro and a negligible amount geothermal. Australia has only recently begun a significant change to renewables, as these are built and as coal fired generators reach the end of their commercial lives and exit the market. In Australia the transmission and subtransmission networks will need to be augmented to make the best use of renewables because the new solar, wind and hydro is unlikely to be in the same place as the coal generation. Consequently, this will likely drive innovative thinking about how to optimize the use of the existing transmission grid, including transformers, to incorporate new resources before expensive grid upgrades are performed. The utilities report transmission grid construction costs of around AU$1M per kilometre before transformer costs are considered.

So, what will happen into the future? In Australia the Federal government’s target of 20% of electricity being renewable by 2020 has been met mainly from wind, hydro and small-scale solar PV. The Australian states have committed to further decarbonization through more of this generation mix. An important question for the generator and transmission utility is: how will they manage their power transformers to the end of their technical life, but with uncertainty about how much longer the generator will be operational. While the energy regulator publishes figures showing the expected closure dates of generators, they can choose to leave earlier if they wish, for instance if market conditions result in the plant being uneconomical to run.

A utility, therefore, may see the value in services where they can extend the life of a transformer by a few years, where a like-for-like replacement would have been a more cost effective decision if there were a guarantee that the generator was staying. Such procedures include online dryout, or more monitoring to provide the data on which to continue usage. Online monitoring can be beneficial as it provides the data on which a decision can be made to keep a fault-free asset in service. However, online monitoring can cost a utility over $100k per transformer, and it would not be considered an effective use of cash to spend this on a transformer nearing retirement when the cash can be put towards a new unit.

New Zealand already has the transmission infrastructure in place to handle renewables, and so there is not the need to adapt the transmission grid in the same way as Australia. However, the New Zealand government has a holistic strategy to decarbonize by 2050, where other forms of carbon-intensive energy will be replaced. The electrification of the transport sector is viewed as essential for this aspiration. The New Zealand transmission authority, Transpower, believes that electricity demand will double by 2050 (from 40 to 90 TWh) to meet this electrification goal, which will be sourced from a diverse range of intermittent renewables balanced with gas generation and batteries. The average age of this utility’s power transformers is 40 years. Consequently, there may be a focus on understanding how their reliability and residual life will be affected by the expected increase of load. The Australian utilities will probably face similar proportional increases if the take up of electric transport is similar.

To keep integration costs low, many solar farms are being connected to the MV side of power transformers owned by the distribution utilities, where the voltage is stepped up to transmission or subtransmission voltages. In Australia, solar farms are typically being installed inland where solar insolation is best and land is cheap. However, the inland network was not set up with large power flows in mind. Many of the power transformers on these networks were installed decades ago and have very limited monitoring, for instance a single sample of oil taken every couple of years for laboratory analysis. This lack of monitoring while the load is low is not a problem because the insulation is not exposed to high operating temperatures. However, if the objective becomes to export as much energy as possible from the solar farm through the transformer, then oversight of the transformer’s operating temperature becomes desirable.

By using temperature, the utility can understand the trade-off between energy exported and transformer insulation life consumption. In this magazine issue, you can read case studies calculating the residual life of five power transformers now connected to solar farms. This project was initiated to better understand the costs incurred by a distribution utility when large scale solar is connected to their network. A solar farm operator may wish to have an output as large as possible for economies of scale. However, the utility has to ensure that their assets can cope with the raised demand.

Distribution networks were historically unmonitored to minimize costs. This is a suitable strategy if power flows in one direction only because measurements of downstream loading can be made at the zone substation. With the possibility now for customers to export energy to the grid as well as consume it, that underlying assumption no longer holds, and new monitoring strategies may be required. It is important for the utility to understand loading because this heats up the insulation potentially shortening its life. When designing a distribution network, the utilities usually make assumptions on how much power a house will require using after diversity maximum demand (ADMD), which is usually between 2 and 5 kW per house on local networks. Transformers are sized by considering the number of houses to be connected and their ADMD. A utility can optimize the choice of transformer capacity between choosing a larger transformer which costs more to procure but will not heat much, and a smaller cheaper unit which may run hotter and not last as long.

Rooftop solar generally displaces load in daylight hours, leading to a “duck curve”. This can have the advantage of unloading substations during the hottest part of the day where there is a significant air conditioning load, and so the insulation heats less extending life. There might still be an evening peak, however, this is in the cooler part of the day. If there is too much rooftop PV, parts of the LV and MV networks could be overloaded. In Queensland, where one in three homes has rooftop PV, this potential overloading was prevented by capping rooftop PV export to 5 kW, corresponding to the after diversity maximum demand (ADMD) of the network.

As electric vehicles (EVs) enter networks the consumer may demand a limit for charging higher than that of the ADMD. In New Zealand the industry expects that the significant uptake of electric vehicles will begin in Auckland, the largest city in New Zealand. The interest in EVs appears stronger in New Zealand than Australia, perhaps because petrol costs approximately 50% more. Consequently, both the Auckland distributor (Vector) and Transpower have been studying the potential impacts of these new technologies on their systems. Respectively, they report their findings in the publicly available documents EV Network Integration, Vector Electricity Asset Management Plan 2019-29 and Te Mauri Hiko, Energy Futures (references given in the reading list).

Vector reports the following possibilities for its distribution network in their current asset management plan:

(1) An increasing number of lower voltage networks will be required “that will support customer technology adoption and enablement through integration with the network”. They will need to monitor the uptake of new technologies.

(2) Advances in energy storage such as improvements to battery capacity and cost. A tipping point for mass adoption is expected, but when is unknown, which creates uncertainty in planning.

In Vector’s asset management plan the trialling of some 50 kW rapid chargers is discussed to build an understanding of how charging technology interacts and impacts the network, and they believe that it is only a matter of time before charging puts pressure on the network. AstheADMDisonly2.5kW,a50kW rapid charger is comparable to adding 20 homes. Vector writes how they are aware of another possible use of an EV: utilising its battery to power either the grid (V2G) or home (V2H). This could be used by the owner as a cheaper source of power during peak consumption, or to supply homes during outages. A utility could, therefore, consider how to use these batteries to reduce load on transformers during peak times if coordination can be achieved.

A general impact of EVs on the loading of a transformer is that if customers all try to charge at once, the nearby distribution transformer may run at an elevated temperature shortening the residual life of the insulation. Another concern is that one transformer could become overloaded by a high export current from a group of buildings with rooftop PV, which then passes through another distribution transformer to supply houses with EV charging. In this case, because no current is supplied by the upstream zone substation, which is the only point at which measurements are currently made, the utility is unaware of this overloading and subsequent overheating of distribution transformer insulation.

Some companies in Australia have begun installing large batteries (e.g. 8 MWh) in urban networks connected to the 11 kV power system. The aim is to charge up the battery cheaply around midday when the energy from nearby rooftop PV is abundant, and then sell the energy back to the grid in the evening peak when the price is higher. This battery is likely to reduce the load on the upstream power transformer as the excess energy from the rooftop PV is no longer exported. However, the strategy is reliant on the consumer exporting their excess energy to the grid. Once batteries or EV’s enter the system the consumer may decide not to supply their energy to the grid, which will once again load the power transformer as the large-scale battery charges and discharges.

As distribution transformers are loaded more, their inspection and maintenance periods may need to change. Currently this period is typically between five and ten years. Consequently, there could be a high degree of unnoticed insulation ageing occurring within this inspection interval. A utility could be proactive in preventing unexpected ageing by installing sensors and developing models to identify the distribution transformers at risk in order to take pre-emptive action. This calls for greater understanding of the economics of monitoring and early replacement, or maintenance, versus no intervention and run-to-failure.

Another uncertainty around inverter based supplies is how they generate high frequency harmonics and the effect on transformers. There is an IEC study committee, 77A, which is working to define limits of permissible harmonic currents produced by individual pieces of equipment. The heating effect of harmonics on the eddy currents within a transformer is related to the product of the square of the frequency with the square of the current, which can become significant at typical inverter switching frequencies (e.g. 3 kHz). The industry will have to ensure that insulation does not degrade faster due to extra heat from harmonics.

A significant unknown is whether the pulse width modulation (PWM) outputs of inverters will promote partial discharge (PD) damage in insulation. The inception voltage of partial discharge is strongly related to the rise time and repetition rate of the waveform. A recent CIGRE brochure (D1.43) commented that the electrical insulation of motors can be degraded by PD. One sign of PD is when chemical reactions generate hydrogen gas, which dissolves into the oil. Our studies on transformer insulation connected to solar farms (presented in this issue) did not find any abnormal gassing of hydrogen. However, this mechanism requires further study to ascertain when it might happen.

My vision is a network optimized by smart distribution transformers. The smart controls will optimize the rating so that the temperature of the insulation, and therefore its residual life, is managed, even as more EVs and batteries enter the system. Monitoring the oil condition will help proactively prevent outages by enabling optimized maintenance and refurbishment activities. Traditionally, a barrier for monitoring small transformers has been cost. Distribution transformers are sometimes viewed as cheap disposal items by the utilities, which are easy and quick to replace when they fail. However, there are many of them so costs mount up, e.g. in public domain literature an Australian utility operates 150,000 distribution transformers, in 2018 spending AU$60M on replacement and only AU$3M on maintenance. More monitoring can help the utility spend less on replacement if transformers are kept in service for longer.

There has been an increasing use of fault-rated metal enclosures to house distribution transformers in urban environments, referred to as kiosk substations. The metal housing improves public safety by containing any faults. A need identified by the local utilities was to develop a smart kiosk, which could anticipate faults, facilitate the adoption of new consumer technologies, and permit enhanced life cycle asset management practices [1], [2].

Some of the utilities are known to have installed larger distribution transformers than necessary, for instance to handle peak load, load growth, or for emergency loading conditions. However, local research noted that this might not be an efficient use of capital because most transformers only experience 50- 70% of their rated load [1]. A general effect of operating a transformer at low load is that the residual life of its paper insulation will be much longer than the expected standard life of a transformer (e.g. 40-50 years). Consequently, a dynamic-rating algorithm was developed locally allowing the insulation to operate periodically at higher temperatures while ensuring that its residual life does not fall below what is considered acceptable by the utility.

In the future we expect to be applying these dynamic rating algorithms with electric vehicle charging. The charger is likely to be connected to the upstream grid through a transformer. How should this transformer be sized? It may be designed so that it runs hot during charging, then cools once the battery has been charged or when there are no EVs. The algorithm will ensure that the transformer can deliver the maximum load while ensuring that the insulation does not degrade prematurely.

A parameter which affects the residual life of paper insulation is its water content. This measurement is rarely performed on distribution transformers by the Australian or New Zealand utilities because its cost is high in proportion to the value of the unit. Future developments in this area could be to develop lower cost monitoring technology. A new application of fibre optic sensors has been to measure the water content of insulation. These sensors use Bragg grating technology, where the strain on a fibre can be measured. A coating is applied which absorbs water and swells slightly, straining the Bragg grating. The main key benefit of fibre optic technology is its immunity to electromagnetic fields. In 2012, I supervised a student thesis project at Monash University investigating the fabrication of fibre optic sensors to measure water. These days such sensors can be purchased off the shelf. Use in transformers is promising [3]. However, a challenge is reducing the cost of the light source and interrogator.

Analytical software which collects and collates data from a fleet of distribution transformers is needed because of the potentially very large quantity of data. As an example, the Brisbane utility Energex reports that approximately half of its 50,000 distribution transformers have power quality monitoring installed. Some fleet-measures involving insulation that could be incorporated into such software include:

• A list of expected replacements and maintenance based on the expected consumption of insulation residual life.

• A statistical approach to proactively determine when to upgrade a distribution transformer before consumer loads necessitate a change.

• General health of insulation which utilities can use to plan inspection activities.

As new customer technologies dominate the grid, and there is a move to low-carbon generation sources, the push to optimize the use of insulation with transformers run at higher loads is apparent. In the future there is likely to be less spare transformer capacity available, and transformers will be safely and economically run at higher temperatures during peak load or emergency events. What is required to realize this optimization? More emphasis on models and low cost, robust sensor monitoring. As part of this monitoring there will be an increased use of analytics to interpret data, and provide the information which utilities can use to effectively manage and plan their networks.

This is an exciting prospect for me, since my career as an expert in transformer asset management has increasingly involved the development of new algorithms to enable utilities to analyse data about their transformers. In the past I have developed improved models for the ageing of transformer insulation, particularly by incorporating the effects of water, as well as a new statistical model for probability of transformer failure based on Australian and New Zealand data. I look forward to building on this to develop the analytic techniques needed for a low-carbon future.

We acknowledge Dr. Bhaba Das, who as the R&D Engineer, developed ETEL’s smart transformer technologies from 2014 until 2018.

All information in this paper about specific company activities and initiatives are within the public domain.

References

[1] B. Das & S. Phadnis, “ETEL Smart Transformer: One Year of Operation”, EEA Conference & Exhibition, New Zealand, 2017.

[2] B. Das, S. Phadnis & T. Jalal, “Smart Transformer Kiosk for Australian and New Zealand Utilities”, EEA Conference & Exhibition, New Zealand, 2016.

[3] M. A. Ansari, D. Martin & T. K. Saha, “Investigation of Distributed Moisture and Temperature Measurements in Transformers using Fiber Optics Sensors”, IEEE Transactions on Power Delivery, vol. 34, no. 4, pp. 1776-1784, 2019.

Further Reading

Energex, Distribution Annual Planning Report, Australia, 2019.

Powerlink Queensland, Transmission Annual Planning Report, Australia, 2019.

Transpower, Te Mauri Hiko, Energy Futures, New Zealand, 2018.

Vector, Electricity Asset Management Plan 2019-2029, New Zealand, 2019

Vector, EV Network Integration, New Zealand, 2017.

From the Editors’ Desk November-December 2020

The time has come for us to bid farewell to the Editorship of this Magazine. We have enjoyed contributing to its development for the last two and a half years, but we will be leaving it in capable hands and you will continue to receive interesting and relevant reading.

We would like to thank all the people who have helped us to bring noteworthy reading to all the DEIS membership. Specifically, we want to thank our regular contributors – Yoshi Ohki for all the news from Japan; John Shea for the book reviews to enlighten and educate us; and Davide Fabiani and Frank Hegeler for the regular updates on our Conference schedule. Without the contributing authors, however, there would be no magazine. Thank you to all of you and all of the reviewers of these featured articles. As a point of interest, over the last couple of years, we have published 47 articles from all over the world including Sweden, Canada, Japan, Brazil, USA, UK, Switzerland, Germany, Slovenia, Poland, Norway, Finland, France, Italy, Spain, Netherlands, China, Qatar, Australia, New Zealand, Ivory Coast, Algeria, Uruguay, Ethiopia, Sri Lanka.

This issue of the magazine presents feature articles on two subjects. Four are dedicated to transformer issues, which seems to still be a hot topic for industry and academic researchers. The other subject is on practical applications of active polymers, a very interesting and fast developing area and unfortunately not often present among our publications. A good completion to this subject can also be found in our News from Japan.

The first article in the transformer group is entitled “Calculating the Residual Life of Insulation in Transformers Connected to Solar Farms and Operated at High Load”. It is written by a team of authors from Australia: Dan Martin and Firus Zare of the University of Queensland, Greg Caldwell of Energy Queensland and Lindsay McPherson of Essential Energy. Since in Australia many large-scale solar PV farms are being installed, the preferred sites are inland where the insolation is best, and land is readily available. However, the grid infrastructure in these areas is not set up to support large power flows. To minimise connection costs the utilities operate existing assets for as long as economically prudent. Consequently, there is a focus on optimising the usage of power transformers. The researchers of the University of Queensland have over the past three years worked with two local distribution utilities on modelling the remnant insulation life of highly loaded power transformers. The approach was to analyse data using the new IEC 60076/7 transformer loading guide and to verify the expected change in insulation condition using field measurements. A verification of the calculations is made by using oil quality measurements.

The second article of this group presents a summary of experiences arising from “Condition Assessment of 132/220 kV Oil-Paper Current Transformers in Sri Lanka”. It is authored by a team of researchers, engineers and consultants: Sarath Kumara, Manjula Fernando and Thanuja Aravinda of the University of Peradeniya, with Dileepa Daulagala, Asanka Bandara, Kapila Bandara and Pradeep Nandasena of Ceylon Electricity

Board and Gawasinghe Jayantha of EnPower Engineering Consultants. This article summarizes findings from current transformer (CT) condition monitoring activities conducted since 2005 by the Sri Lankan electricity utility, Ceylon Electricity Board. Series of laboratory and field investigations were performed, including analyses of oil quality and by testing whole units. In the case of oil quality investigations, various electrical and chemical tests were used to assess the condition of 25 field and laboratory aged oil samples. In the case of investigations on whole CT units, dielectric response measurements were performed on a fleet of 149 CTs, including new, field aged and laboratory aged units. It is concluded that by using the chemical, physical and electrical parameters and classifying them according to IEC 60422:2013, ambiguity in result interpretation may sometimes be achieved. At the same time, results of dielectric response measurements on the insulation system of whole CT units show that the technique provides an alternative route for condition assessment. It is thus suggested that a combination of loss tangent value at 10 mHz together with results of oil color test and dissolved gas analysis can well be used as performance indicators of CTs.

The third article is on “Gas-in-Oil Analysis and Evaluation Criteria for Synthetic Esters in Offshore and Traction Transformers”. It is written by Ivanka Atanasova-Höhlein and Carolin Schütt of Siemens Gas and Power in Germany. As it is generally recognized that dissolved gas analysis (DGA) is a powerful tool in the diagnosis of insulating liquid filled power equipment, there exist numerous evaluating schemes for condition assessment of mineral oil filled equipment. Nevertheless, the experiences show that a fine tuning and revision of the schemes is required for equipment filled with synthetic esters. This concerns both the testing methods and the result evaluation. Absolute methods, like total gas extraction, require considering the contribution from partial pressure of moisture to the total extracted gas content because esters can dissolve a much higher amount of moisture in comparison to mineral oils without deterioration of their dielectric properties. As synthetic insulating liquids in transformers of offshore wind farms or traction applications usually operate at high temperatures, one has to consider not only the generally known rules for gas formation under electrical and thermal faults but also the thermo-oxidative gassing (known as “stray gassing“) of the liquid itself that appears at the contact with copper. Different experimental schemes are being used to calculate the values and ratios at thermal and dielectric faults, however, they remain of limited validity for real cases because of different energy intensity and thermal distributions involved. Thus, in practical evaluation, a combination of concentration threshold and ratio values seems to be the most pragmatic and reasonable way to adopt. This article presents the recommended gas threshold values and ratios for the transformer fleets of interest, which were developed based on service data as well as the common knowledge available from generally approved mineral oil analyses.

The fourth and last article in this group is entitled “Potential of Coconut Oil as a Dielectric Liquid in Distribution Transformers”. It is authored by researchers from India: Anu Kumar Das and Dayal Chandra Shill of North Eastern Regional Institute of Science and Technology, Nirjuli, as well as Saibal Chatterjee of National Institute of Technology, Mizoram. The authors present a review of test results available in literature and claim that dielectric liquids based on coconut oil can be used as a potential alternative for distribution transformers, especially in tropical climates, since they have shown similar and sometimes better physicochemical, thermal and dielectric properties to mineral oils or other natural ester based dielectric liquids. However, it is stressed that more studies need to be conducted to ensure a safe and reliable operation of coconut oil filled distribution transformers. These should include validating the expected high oxidation stability of coconut oil as per IEC 61125, evaluating its fire properties and dielectric strength when mixed with a small content of mineral oil, material compatibility of the oil at elevated temperature, and stray gassing behavior.

As indicated earlier, the fifth article in this issue is thematically different from the previous ones. It is on “Mechanical Energy Harvesting with Ferroelectrets” and is jointly authored by Xiaoqing Zhang of Tongji University in Shanghai in China together with Heinz von Seggern, Gerhard Sessler and Mario Kupnik of Technical University of Darmstadt in Germany. The authors present their work on mechanical energy harvesting for feeding self-sufficient wireless sensor networks (WSN). Initially, the ferroelectret utilized in energy harvesters was cellular polypropylene (PP) with significant longitudinal piezoelectric effect. It became quickly replaced by the thermally more stable fluorinated polyethylene propylene (FEP) in the form of a hybrid structure composed of air-filled cavities and layered FEP films. The transverse piezoelectric effect in such a structure yielded several times larger output than for PVDF. A normalized power of 50 to 100 μW can be for seismic masses between 0.1 to 0.3 g (referred to the gravity of the earth), which is close to the top-performing ceramic systems. The large power output is achieved thanks to adoption of a force enlargement in harvester design. Other advantages of the ferroelectret harvesters are their low cost, mechanical flexibility, environmental compatibility, and better matching of mechanical impedance. All these allow hope for a bright future of such devices.

John J. Shea

Design for Additive Manufacturing

M. Leary
Elsevier
50 Hampshire Street
5th Floor
Cambridge, MA 02139 http://www.elsevier.com
ISBN 978-0-12-816721-2
356 pp., $130 (Softcover), 2020

Additive manufacturing (AM) is an alternative method for producing parts and can be an economical method even when compared to traditional manufacturing methods, especially for low volume and/ or high complexity parts. Over the past decade, process and material advances have greatly improved the quality and robustness of AM parts (also referred to as 3D printing) as well as a greater number of material choices.

This book provides the current state-of-the-art of design for additive manufacturing (DFAM) for research and industrial applications. It covers methods for both polymeric and metallic technologies and ties design optimization with cost and process selection. Best practices are described to illustrate AM design through a series of case studies illustrating advantages and specific limitations of existing DFAM tools.

After introducing a comparison between traditional manufacturing and additive methods by contrasting volume and part complexity crossover points where economies of scale and part geometry determine cost per part, the book delves into specific aspects of DFAM. First, details are provided for producing CAD designs that achieve a given goal for part geometry and desired specifications. Design details are provided for build orientation, support structure generation, file formats, tools paths, and guidelines when using multiple materials. Further optimization of the physical design attributes including materials, geometry, and processing conditions are described. Building upon these aspects, efficient geometrical structures are presented, many of which cannot be achieved with traditional manufacturing methods. Naturally occurring structural geometries, cell structures, readily obtainable in AM, can achieve highly optimized parts by using lattice and zero-mean curvature structures.

Algorithmic methods are presented for topology optimization to insure the best possible structural design for a given part. This chapter in the book helps the designer to think about how to produce the strongest structure by reducing stress concentrators in the part or structure. Generative design (GD) methodology is used to create designs not reasonably achieved by a human designer. These methods are used by the designer to help them create an optimized part or structure by first creating a feasible element and then testing the structure to evaluate the potential feasibility of this solution. This iterative procedure is performed to optimize the solution.

With recent developments, there are many materials and methods to choose from. The use and best practices of thermoplastic extrusion, also known as fused filament fabrication (FFF), includes the effect of the toolpath, part strength, surface roughness, part orientation, and unsupported overhangs is detailed. Material jetting (MJ), like commercial ink jet printing, is another method described for creating not only parts but also for coating already fabricated parts. Vat polymerization (VPP), which uses a liquid UV curable material, and powder bed fusion (PBF) and directed energy fusion (DEF) which use focused thermal energy to fuse materials by melting as they are being deposited, and binder jetting (BJT) are also discussed.

With the in-depth technical descriptions, references and summary at the end of each chapter along with many practical best practices presented, this book could be used by the AM design engineer for part optimization, or by traditional part designers or students who want to learn more about AM practices.

Wide Bandgap Semiconductor Electronics and Devices

U. Singisetti, T. Razzak, and Y. Zhang 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 978-981-121-647-3
257 pp., $128 (Hardcover), 2020

The interest and use of wide bandgap semiconductors (WBS) (i.e. SiC and GaN) continues to increase, driven by increases in power efficiency in power electronics and high-speed communications. These wide bandgap materials exhibit excellent material properties that enable higher efficiency, higher breakdown voltage, faster switching speeds, higher temperature operation, and lower temperature coefficient of resistance as compared to current Si technology. There are even other materials researchers are working on to deliver even higher performance than existing SiC and GaN.

This book discusses a broad range of current topics including fundamental transport studies, growth of high-quality films, advanced materials characterization, device modeling, high frequency, high voltage electronic devices and optical devices with the latest developments in AlGaN, AlN, Ga2O3, and diamond materials.

Currently, SiC and GaN are the main materials of focus for mass production efforts. This book focuses on current as well as promising alternative upcoming materials for even better performance than SiC and GaN. Some of these topics cover new materials such as diamond MOSFET devices and AlN/GaN HEMT devices for communication applications. Other areas described cover radiation hardened field-effect transistors (FET’s), material growth and device fabrication methods for Ga2O3, and the latest developments for AlGaN N-channel transistors and vertical GaN device technology.

Since there is no fundamental background presented in this book on WBS and the topics deal with advances in some of the latest WBS and ultra-wide bandgap semiconductors (UWBS) materials, this book is more suited for researchers already familiar with WBS who are interested in developing new WBG materials and devices since it provides the latest developments in new materials and processes and trends for WBS and UWBS technology.

Semiconductor Gas Sensors, 2nd Edition

R. Jaaniso and O.K. Tan, Editors WoodHead Publishing
An Imprint of Elsevier
50 Hampshire Street

5th Floor
Cambridge, MA 02139 http://www.elsevier.com/books-and-journals
ISBN 978-0-08-102559-8
512 pp., $290 (Soft cover), 2020

Gas sensors were first developed many years ago to detect various types of toxic gases for safety reasons. Today, with the advancement of metal-semiconductor gas sensors, many other applications have emerged to allow the detection of gases of different properties, origin, and concentration. Gas sensors are now used for safety, energy savings, health, foods, environmental protection, and other areas.

This second edition on gas sensors provides the most recent information on gas sensor technology for metal semiconductor oxide materials. It contains three parts. Part one describes the basics of gas sensors, providing the necessary background for someone new to this technology. It covers the fundamentals of gas sensors with focus on resistor-type sensors. The conduction mechanism in metal-oxide sensing films is reviewed with response characteristics of p and n- type doped semiconductor films. It also examines the effect of electrode influence on material response.

The second part deals with various types of sensor materials including one and 2-D materials, carbon nanomaterials, InGaN/GaN nanowires, and rare earthdoped oxide materials. Gas sensor material deposition methods and optical probing techniques, used as an alternative to electrical conduction methods, are also reviewed.

Part three covers recent progress into integration of gas sensor materials into devices such as SiC FET’s, micro-machined sensors, and integrated CMOS- based sensors. These recent developments show how gas sensor technology can become low cost electronic components used in a variety of gas sensing applications including automotive and environmental sensing.

The book contains a wealth of recent data and performance measures for many types of new gas sensing materials and devices making it suitable for researchers involved with gas sensor development. It is also appropriate for those who want to learn about gas sensors in general due to the excellent coverage on the fundamentals. However, to fully appreciate the book, it does require some background in chemistry, specifically gas-metal semiconductor oxide reactions.

Ferroelectrics—Principles and Applications

A.K. Bain and P. Chand
John Wiley & Sons, Inc. 111 River Street Hoboken, NJ 07030 http://www.wiley.com
ISBN 978-3-527-34214-3
325 pp., 145,00 € (Hardcover), 2017

Certain classes of dielectric materials possess unusual properties. These properties include pyroelectricity the ability of certain materials to generate a temporary voltage with a temperature change. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. Piezoelectricity, materials which produce an electric field when mechanically stressed, and ferroelectricity, the property of certain materials that have an electric polarization that can be reversed by an electric field. All these fall under the classification of ferroelectric materials.

This book covers the fundamentals of ferroelectrics including the above-mentioned material types along with in-depth technical descriptions of the microscopic properties of these materials. Energy band theory and phonon theory in three dimensions are explained in order to provide the necessary background for understanding the phenomena at work in these types of materials. In addition to the in-depth background on theory, many application examples are provided for each material type. Some of the interesting application examples for those interested in optical switching include electro-optical switch examples and nano-scale ferroelectric devices. These application examples show how to build electro-optical switches using ferroelectric materials.

Researchers and material scientists using ferroelectric materials will find this book useful as a comprehensive source on the topic with the latest topics on laser printed materials and applications covered. Extensive references on ferroelectric and piezoelectric materials make this an invaluable resource to anyone working in this field of research.

Introduction to Wavelet Transforms

N. Bhatnagar
CRC Press
Taylor & Francis Group
6000 Broken Sound Parkway–NW, Suite 300
Boca Raton, FL 33487-2742 http://www.crcpress.com
ISBN 978-0-367-43879-1
472 pp., $129.95 (Hardcover), 2020

Wavelets are used in astronomy, geophysics, mathematics, signal processing and other areas. Some specific areas of wavelet transform use include signal compression for efficient information transmission, signal denoising, storing fingerprint files, speech recognition, image enhancement methods, and analyzing similar signals.

Wavelets are the latest mathematical tools used for constructing functional spaces. Wavelet analysis condenses complex functions into a set of simpler functions. These sets become building blocks to describe the signal being represented by the wavelet transform. A set of coefficients in a series of equations are used to describe a signal. Needing only to transmit a set of coefficients, rather than the entire signal, complex signals can be transmitted to a receiver by simply transmitting the coefficients to the receiver. This requires lower bandwidth as compared to transmitting the entire signal.

As an introduction to wavelets, this book can serve as a good book for students learning about wavelets as well as signal processing engineers who work with wavelet transforms. It provides a sound basis for understanding wavelet theory and provides information on the latest methods used in wavelet transformations. It provides the basics of wavelet transforms, intermediate topics, signal processing concepts, and mathematical concepts.

The basics cover a comparison of wavelets to Fourier transforms and justification for using wavelets. Continuous and discrete transforms are described along with some examples and applications for signal denoising, image compression, and neural networks.

Intermediate topics cover periodic, biorthogonal, the lifting technique, packets, and lapped orthogonal transforms. Signal processing topics include descriptions of discrete Fourier transforms, z- transforms, continuous and discrete time signal processing.

The mathematic concepts cover sets theory and number theory, matrices, Fourier theory, probability theory and stochastic processes.

This is an interesting book for anyone wanting to learn about wavelets and wavelet transforms. No prior knowledge of wavelet transforms is necessary, but this is a highly mathematical book with limited explanations of practical application of the theory and methods. It does have problems for students to work on making it suitable for a classroom textbook. It is also very useful to have the more familiar methods, Fourier transforms and z-transforms, to help the reader already familiar with these more traditional methods of signal transformation to better understand wavelet transform methods and compare them to these other, more familiar methods.

Power Systems Analysis Illustrated with MATLAB and ETAP

H.M. Shertukde
CRC Press
Taylor & Francis Group
6000 Broken Sound Parkway–NW, Suite 300
Boca Raton, FL 33487-2742 http://www.crcpress.com
ISBN 978-1-4987-9721-4
303 pp., $160 (Hardcover), 2019

Power system analysis begins with accurate models of individual components of a power system. This book provides the reader with theoretical models of power system components with an emphasis on electrical machines and transmission lines and shows how to analyze one-line diagrams under various cases.

After introducing the single line diagram method of modeling, mathematical equations are used to represent synchronous and asynchronous machines and transformers. One specific condition covers transformers used for photovoltaic applications along with some of the factors to consider when designing power systems with distributed energy sources. These factors are discussed and taken into account in the system model.

Other topics cover a transmission line model for various line lengths, network calculations, load flow analysis using the Newton-Raphson method and underground cables. Symmetrical three-phase faults and symmetrical component analysis for fault calculations are also introduced. The Runge-Kutta algorithm is also used for a power system stability analysis method.

Two test cases are covered. The first involves a power load flow analysis using the Newton-Raphson method. The second shows a power system stability study using the Runge-Kutta algorithm. All the methods shown are supported and can be implemented using ETAP and MATLAB software for a convenient and efficient way to model and analyze multi-phase power systems. Examples of MATLAB code is provided in an appendix to show how some of these power system examples can be analyzed.

With questions at the end of each chapter, this book can be used in an undergraduate course in power engineering to teach the fundamentals of power system analysis. It provides concise examples of power system modeling and provides insight into power system behavior especially when motors or generators are involved.

Reliability Engineering and Risk Analysis—A Practical Guide, 3rd Edition

M. Modarres, M.P. Kaminskiy, and V. Krivtsov
CRC Press
Taylor & Francis Group
6000 Broken Sound Parkway–NW, Suite 300
Boca Raton, FL 33487-2742 http://www.crcpress.com
ISBN 978-1-4987-4587-1
522 pp., $120 (eBook) (Hardcover)

This book comes together as a hardback with access to an electronic version of the book for access anytime through CRC press eBook resource or as an eBook only. It contains comprehensive coverage of reliability and risk analysis techniques, containing equations and information used to perform reliability and risk calculations with a focus on reliability analysis. Since reliability is a multidisciplinary subject, this book covers many different engineering disciplines. However, rather than focusing on mathematical derivations of reliability equations, it concentrates on the practical methods used to solve reliability problems especially at the component level of a system, which is the fundamental building block for reliability of a system. It shows how to determine breakdown a system and calculate complex system reliability by determining individual component reliability factors and putting these individual factors together to determine the overall system reliability.

This is a basic text on reliability so there is no necessary background in reliability studies needed to use this book. It begins by introducing the tools used for the basic building blocks of reliability analysis and component reliability. One real-world reality, that many other books on this topic do not recognize, is that the book makes a practical distinction between components in a system that cannot be replaced versus ones that can be replaced in order to calculate the uptime of a system based on these different possibilities. Other practical methods describe human reliability, accelerated life testing, and methods used to calculate product warranties – all very valuable methods for the practicing design engineer to understand. Risk analysis, touched on at the end of the book, shows how to perform a product risk assessment. Again, very practical methods for design and manufacturing engineers.

This is a comprehensive book on reliability analysis focused on practical current topics that would benefit companies who rely on this type of analysis. It could be used by practicing engineers to learn how to perform reliability and risk analysis or for a course on this subject matter since it contains problems at the end of each chapter with a solutions manual available for the instructor by sending a request to the publisher.