The January/February 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.
SF6-Free Gas-Insulated Switchgear: Current Status and Future Trends
Combination of Adjustable Inverter Level and Voltage Rise Time for Electrical Stress Reduction in PWM Driven Motor Windings
It is a new year and a new team is now handling the editing of your Electrical Insulation Magazine. We were fortunate to have the excellent team of Stan Gubanski and Resi Zarb managing the Magazine for the last 3 years, and as president of DEIS I want to extend to them our thanks for their commitment to excellence and their dedication. The quality of the Magazine has never been higher, so the new team has a tough act to follow.
The IEEE and DEIS should be volunteer organizations. There are paid staff members at headquarters and the larger Societies with larger budgets can afford some staff support, but for small Societies like DEIS everything that happens should be the result of unpaid volunteers contributing their time and effort. I submit that member willingness to voluntarily serve in key rolls is more important to the success of our society than technical ability in our field of interest. You don’t need to be a Tom Dakin or an Eric Forster or any of the other giants from our past history to make meaningful contributions. Unfortunately, all volunteer tasks are not created equal. There are many jobs that need to be done if the society is to continue serving the needs of our community (that includes our members and non-members). Some of these jobs require only a modest investment in time and effort while others are significantly more demanding. The tasks associated with managing the production of the Society publications (the Magazine and the Transactions) are among our most time-consuming. As a result, we should expect relatively high turnover in these assignments. If we don’t provide adequate resources we shouldn’t be surprised when we find it difficult to recruit replacements. For a number of years, the editors of our Magazine and our Transactions have been technical experts from our Society but they have been paid to perform their tasks. This situation is no longer sustainable because our ability to compensate them is not adequate considering the time commitment required. Therefore, we are making changes to how we will manage production of the Magazine going forward with the goal of significantly reducing the workload.
Identifying new volunteers willing to take on the job of Magazine Editor-in-Chief (EiC) has proven to be difficult. The search committee has so far been unable to find an acceptable candidate from the small number of individuals who expressed any interest in the position. Therefore, to keep the Magazine going Peter Morshuis, the chair of our Publications Committee, stepped in and was appointed as interim EiC, and several changes were put in place in how we manage the magazine. These changes were approved by the Administrative Committee and include the following:
To significantly reduce the workload of the EiC of the Electrical Insulation Magazine by
- Having all copy-editing done externally;
- Involving the Editorial Board to assist the interim EiC;
- Using a detailed description of the desired article scope and format for potential authors (including, e.g., a template);
- Accepting only proposals for papers, not full manuscripts. The EiC, in consultation with the Editorial Board, will then decide whether the author will be invited to submit a full paper. The EiC and the members of the Editorial Board will also actively solicit contributions from suitable authors;
- Making use of an electronic submission and review system;
- Seeking input and support from the Society leadership, the DEIS conferences, and the Technical Committees;
- Per general IEEE policies, make the position of EiC of the Electrical Insulation Magazine a volunteer position with a generous expense reimbursement, in line with the reduced workload.
The EiC search committee will continue to function and we will continue to advertise, making it clear that the position is open and a permanent replacement is desired. We are also soliciting quotes from several outside publishing houses to determine the costs involved in upgrading our support services.
There was a time when serving as the EiC of an IEEE publication was considered a prestigious position. With the current proliferation of publications, that may no longer be universally true but it is our intention to reduce the workload to a manageable level and maintain the quality of the Electrical Insulation Magazine so that serving as EiC is a job that any of our members would enthusiastically accept. Not everyone is at a point in their career where she or he can consider taking on the responsibility of serving as EiC of an IEEE publication. We don’t expect dozens of applications, but we hope that those who are capable of taking on this type of responsibility will give it further consideration. As we develop the improved method of operation and add new support resources, we believe the job will become more desirable.
So, in the meantime what can you do to help? The simplest thing all authors who wish to make a contribution to the magazine can do is read and follow the new submission guidelines. This issue will be the first that spells out exactly what we want, and this will be the requirement going forward. The most significant change is that we will now only accept proposals for articles mentioning in a clear way why the proposed article is of significance to a broad audience. I am sure that with the support of the Society membership we can continue to publish the Electrical Insulation Magazine for years to come. This magazine is critical to the success of our society. It provides an outlet for IEEE news, Society news, industry news, relevant technical information structured for a wide audience, and many other features. It is an important platform for outreach to non-members who are concerned with our field of interest. Survival of the Magazine is not an option; it is a necessity.
Let me close with a more encouraging announcement. The EiC search committee was successful in recruiting a new leader for the Society’s other publication, the Transactions on Dielectrics and Electrical Insulation. Prof. Michael Wübbenhorst of KU Leuven has accepted the position. Michael is the Head of the Section on Soft Matter and Biophysics at KU Leuven and has published extensively in the TDEI and other prestigious journals. We look forward to continued success with the Transactions under Prof. Wübbenhorst’s direction. I also want to thank Prof. Ed Cherney, our departing editor, for his service to the Society over the last 3 years. The impact factor of the Transactions is an important metric and it has improved under Ed’s tenure, so we are in a good position to continue making improvements.
If there are any questions or comments, please do not hesitate to reach out to any member of the Society leadership. We welcome all input from the Society membership.
Paul C. Gaberson President, DEIS January, 2021
From The Editor
There is a rainbow at the end of the tunnel and I wish all of you, wherever you are, to see it.
This issue of the Magazine was produced with a tremendous effort from the Editorial Board and I want to thank them for their support and dedication. The featured articles this time are focused on the quest for clean, SF6-free insulating systems and on the challenges related to the electrical insulation of inverter-fed motors.
The first article is entitled “SF6-free gas-insulated switchgear: Current status and future trends”. It is written by a team from the High Voltage Laboratory of ETH, Zürich, Switzerland: Christian Franck, Alise Chachereau and Juriy Pachin. It provides an overview of research activities to find SF6 alternatives for electric power equipment, newly introduced SF6-free technologies for medium and high voltage levels, and ongoing legal developments to support the introduction of these new technologies. SF6-free solutions are important because SF6 is a potent greenhouse gas (GWP 23,500) with a long atmospheric lifetime (>850 years). The rate of rise of atmospheric SF6 concentration is increasing annually, and the electric power sector is accountable for the majority of these emissions. Therefore, SF6-free solutions are needed. The authors first provide an introduction into the fundamentals of gaseous insulation. Then they describe the ways of identifying new alternative gases and how these are experimentally characterized. The introduction of a new insulating gas requires a large initial effort because a vast array of experimental tests are needed to measure all the relevant properties such as the electric strength, the thermodynamic properties, and investigate the toxicity, the safety aspects and the environmental impact. Computational screening methods can identify promising new insulating gases, typically by their electric strength and boiling point. However, these screenings have limited usefulness because some gas properties cannot be computed, and because they consider only pure gases, whereas insulating gas mixtures are more promising. An overview is provided on the current status of SF6-free technology and it is shown that in the past decade competitive solutions became increasingly available. Over the last years, SF6-free equipment has become commercially available for an increasing number of applications and voltage ratings. The offered portfolio of SF6-free products today consists of a variety of different gas mixtures, but also solid and liquid insulation. With the emergence of SF6-free solutions for an increasing number of applications, legal and regulatory measures around the world are intensifying the pressure on industry to refrain from using SF6, or even phase out SF6 completely. The authors conclude that it is now a question of politics and legislation to support the change away from SF6-technology.
The second article in this issue presents a study on PWM voltage source design, titled “Combination of adjustable inverter level and voltage rise time for electrical stress reduction in PWM driven motor windings”. It is authored by Thomas Hammarström from Chalmers University of Technology, Gothenburg, Sweden. In the article it is described how the shorter rise times obtainable by new SiC and GAN semiconductor technologies utilized in PWM inverters have been observed to increase the stress of high voltage motor insulation systems. In this paper, the author approaches this problem by exploring the advantages of employing a PWM inverter with adjustable inverter level and rise time during operation. To demonstrate and explore the value of this approach, it is investigated what influence the choice of inverter levels as well as rise time has on the partial discharge (PD) characteristics within motor windings. The test objects were subjected to either three or five level inverter voltage waveforms utilizing the same test-set up. A simple twisted pair test-object and a complete motor stator are investigated, both showing similar advantages with the presented solution. In particular, it is shown that the total peak and summed PD magnitude (exposure) drops considerably when applying an increased rise time only at the voltage flanks where PD have been observed. In some cases, the presence of PD can even be eliminated during operation if the applied voltage is close to the extinction voltage level (PDEV). The author made a comparison with similar magnitude 50 Hz sinusoidal voltage waveform for both insulation systems and suggests that similar stress can be obtained with controllable rise time and inverter levels.
The third article reports on a new method for detecting defects in inverterfed motors, entitled “Detection method of inter-turn insulation defects of inverterfed motors under induced impulse voltage”. The paper is authored by Xuezhong Liu, Ping Liu, Tianlong Zhang, Pengfei Yuan from Xi’an Jiaotong University, Xi’an, China and Hugh Zhu, consultant in Boston, USA. The inter-turn insulation of inverter-fed motors is stressed by repetitive steep-fronted pulse voltages which can reduce its lifetime. The voids and cracks, which may exist in the interturn insulation, can produce partial discharges. In this paper, the authors present a novel method, aimed at the detection of both inter-turn shorts and partial discharges at the inter-turn insulation using induced impulse voltage. Experiments and electromagnetic transient calculations were carried out to optimize the impulse induction testing schemes. Four parameters were proposed to evaluate the effectiveness of the impulse induction testing schemes. A near-field sensor with a flexible thin framework was designed to measure response signals from interturn insulation defects under induced impulse voltages. This sensor can be temporarily mounted at the straight portion of the end-winding region of a target coil of a motor and is sensitive to high-frequency current signals. The authors present experimental results obtained on the coils of a 300 kW/2 kV inverter-fed traction motor indicating that the sensor can detect both inter-turn shorts and partial discharges from voids in the inter-turn insulation. The authors conclude that the method can be used to detect inter-turn insulation defects in machine and manufacturing during the maintenance of machine windings.
News from Japan
John J. Shea
Phase Change Material-Based Heat Sinks
S. Rangarajan and C. Balaji
Taylor & Francis Group
6000 Broken Sound Parkway–NW, Suite 300
Boca Raton, FL 33487-2742 http://www.crcpress.com
220 pp., $99.95 (Hardcover), 2020
When a material undergoes a phase change such as a solid turning into a liquid, generally energy is absorbed by the material in order to change from a solid to a liquid. This energy absorption, at the phase change point, can be utilized to enhance a heat sink capacity during transient events to control the temperature rise in an electronic component. Phase-change materials (PCM) can be incorporated into a heatsink to provide the additional energy absorption and heat dissipation during these transient thermal events in electronic components to allow for great operating range.
This book presents the results of experimental studies of different types of PCM-based composite heat-sinks, their thermal performance, and the amount of time for the liquified PCM to re-solidify. The book starts by introducing readers to (PCM) and heat-sink optimization when using PCM. It provides an introduction to thermal cooling applications for electronics and provides a critical review of the state-of-the-art in PCM thermal cooling.
After a general introduction to PCMs and an introduction to thermal management in electronics for both active and passive technologies, the literature review shows the current state-of-the-art in PCM used for heat sinks. A convenient table, provides the reader with all the relevant PCM used for heat sinking applications to date. This can save a researcher many hours who would otherwise have to collect all this information on their own.
n-eicosane PCM with thermal enhancers added, experimental setup, and methods used to characterize this material for heat sink applications are presented. The results of a prototype heat sink, optimized for various objectives (i.e. minimize temperature rise, geometry) is also presented. Active rotational heat sinks and a numerical analysis for heat sinks using thermosyphons (e.g. heat pipes) as a thermal conductivity enhancer (TCE) also give the reader some other options to consider when designing heatsinks. Future studies are provided but are rather limited, without any detail and do not provide many new areas of study.
An interesting book for researchers involved with designing heat sinks for electronics, especially high-power electronics (e.g. Si, SiC or GaN) power semiconductors since many of the applications that use these devices are limited by the device temperature during transient overcurrent. PCM may be able to extend the current range of many of these devices and lead to even higher current ratings, especially for wideband gap materials since they have a higher operating temperature rating than Si-based devices.
Plastic Optical Fiber Sensors—Science, Technology and Applications
M. M. Werneck and R. Allil Editors CRC Press
Taylor & Francis Group
6000 Broken Sound Parkway–NW, Suite 300
Boca Raton, FL 33487-2742
420 pp., $200 (Hardcover), 2020
Plastic optical fiber (POF) cables are not only used for information transmission and lighting but can also be used for many different types of sensing applications ranging from measurements of current, voltage, temperature, gas identification and quantity, biological detection of microorganisms, displacement, structural integrity, and radiation levels.
The book begins by describing POF cables, their properties, and how they can be used in sensing applications. Their history and use in various countries is presented in a timeline which gives the reader a background in the progressive development and new applications achieved over time. The operating principles detail refractive index between core and cladding materials and the optical, mechanical, chemical, and thermal properties of POF are described. Five different types of POF and the fabrication of POF, including micro-structured POF are presented. Fiber attenuation and other losses are also characterized.
Applications, for the above-mentioned quantities, provide an overview of the design and examples of typical results for the sensor. Applications of particular interest to our readers may include current, voltage, and temperature sensing with POF. A description of a system using POF for measuring MV levels in a power distribution system is given. Unfortunately, this system uses a battery to provide power to the circuit and thus has very limited lifetime, but it still illustrates the concept of measuring current and voltage with a completely electrically isolated system. Many photos of the components and resulting measurements based on this design are provided. Also discussed is a leakage current monitoring method for 13.8kV distribution lines and 500kV transmission lines. These consist of a capacitive sensor coupled to a POF. Graphs showing how leakage current changes over various times of the day and weather events and sensor diagrams are provided.
The temperature sensing application uses a ruby sensor head as a temperature sensitive material which changes its fluorescence time as a function of its temperature. The ruby sensor head is coupled to the POF to safely measure temperature in HV or other hostile environments.
The fiber Bragg grating method is also described, which could also be of interest to our readers, since it can be utilized for a variety of different measurements that include temperature, strain, pressure, humidity, and magnetic field. POF has many different responses to environmental factors such as temperature and humidity as compared to silica fibers. These differences are described along with the details for making Bragg gratings for the various measurements listed.
This book would interest our readers who have a need for electrically isolated measurements or for those needing sensing solutions in hostile or inaccessible environments. The POF provides a safe and secure method for communicating sensing information when compared to wireless communication, especially when large metal enclosures such as switchgear is involved.
Dielectric Metamaterials— Fundamentals, Designs, and Applications
I. Brener, S. Liu, I. Staude, J. Valentine, and C. Holloway, Editors
50 Hampshire Street, 5th Floor Cambridge, MA 02139 http://www.elsevier.com/books-and-journals
309 pp., $172 (Softcover), 2020
This book provides a review of the current understanding and implementation for designing and creating metamaterials, specifically dielectric metamaterials with a focus on optical antennas and wavefront control for tailoring reflection, transparency, absorption, and phase and polarization of light. The definition for a metamaterial is a material engineered to have properties not found in naturally occurring materials. They can be made from assemblies of multiple structures fashioned from composite materials such as metals and plastics designed to bend light or electromagnetic waves for a desired effect. Unlike a conventional optical glass lens which bends light according to the thickness of the glass and the properties of the glass, metamaterials can have widely varying index of refraction along the optical area resulting in an output that does not resemble an image thorough a conventional glass lens. The materials are usually arranged in repeating patterns, at scales smaller than the wavelengths of the phenomena they influence and they derive their properties, not from the properties of the base materials, but from their newly designed structures.
Their precise shape, geometry, size, orientation and arrangement gives them their ability to control electromagnetic waves by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials and can be modeled using Mie scattering theory. Designs have been made for both visible light and other parts of the electromagnetic spectrum.
Appropriately designed metamaterials can affect waves of electromagnetic radiation or sound in a manner not observed in bulk materials. Those that exhibit a negative index of refraction for particular wavelengths have been the focus of a large amount of research. These are also referred to as double negative or backward wave media. A form of ‘invisibility’ was demonstrated using gradient-index materials.
Potential applications of metamaterials can include optical filters, sensor detection and infrastructure monitoring, smart solar power management, radomes, high-frequency battlefield communication and lenses for high-gain antennas, and even shielding structures from earthquakes. Metamaterials offer the potential to create super-lenses. Such a lens could allow imaging below the diffraction limit of conventional glass lenses.
This book provides the reader with an introduction to metamaterials, background fundamentals in Mie scattering theory, and examples of various designs for dielectric nano-antennas, and controlling transmission and reflection of light from surfaces using dielectric metamaterials.
The book provides very good technical depth and as such would be useful for someone wanting to learn not only about some of the latest research in metamaterials but to gain an understanding of the fundamentals. Undergraduate or graduate students or working professionals studying metamaterials would find this book valuable especially for the extensive reference lists provided at the end of each chapter. It covers a new topic in electromagnetic technology but since it uses a great deal of electromagnetic theory, the reader would need a firm understanding of Maxwell’s equations and electromagnetic wave propagation in order to fully appreciate this book, however, the many illustrations and drawings do greatly help to explain the theory.
Current Interruption Transients Calculation, 2nd Edition
D. F. Peelo
John Wiley & Sons Inc.
111 River Street
Hoboken, NJ 07030 http://www.wiley.com
295 pp., $160 (Hardcover), 2020
This book can be used to understand the theory of circuit interruption produced by circuit breakers in power systems. The author shows how to write the equations used to represent the opening of a three-phase circuit under all possible circuit conditions and to translate these equations into an Excel spreadsheet that is used to solve for the transient currents and voltages produced. It covers all the interruption cases for transient current and voltage that can occur on a power system explaining, first using theory, then illustrating with practical examples.
Topics in this edition include: RLC circuits; pole factor calculations; terminal faults; short-line faults; inductive load switching; and capacitive load switching. Appendices also cover differential equations; duality principle; useful formulas; asymmetrical current calculations; shunt reactor switching and generator circuit breaker transient recovery voltages (TRV’s).
While this book contains the necessary theory that can be applied to any type of circuit breaker, many of the examples are focused on the conditions and applications that occur in medium-voltage (MV) and high-voltage (HV) power systems. Many of the capacitive and transmission line effects that can occur in MV and HV systems using transmission lines do not manifest themselves in LV systems since they use relatively short cable or bus distances and have different circuit impedance. However, as mentioned, this book is a great resource for someone who wants to not only understand circuit interruption theory in general but for those engineers who want to quickly learn how to use their computer to accurately calculate and graph transient currents and voltages for 3-phase balanced as well as unbalanced power circuits. As a power engineer, this is an outstanding resource that you will constantly use as a handy reference source for calculating circuit transients and even more importantly, you will gain a better understanding of how to adjust circuit components for a desired outcome.
Fundamentals of High Voltage Engineering
R. Arora and B. S. Rajpurohit
John Wiley & Sons Inc.
111 River Street
Hoboken, NJ 07030 http://www.wileyindia.com
408 pp., INR 499 (Softcover), 2019
There are a number of books on high voltage (HV) engineering and lightning but what sets this book apart from many of the other books is the straightforward explanations that are focused on current topics relevant to today’s power systems. The book provides an excellent way to quickly learn about application of HV engineering for today’s power systems and to grasp many areas of HV design and testing. It would be an excellent book for an undergraduate or graduate class in power engineering and for engineers wanting to quickly grasp many of the key aspects regarding the basics of HV engineering with regard mainly towards insulation breakdown.
The book begins by describing the need for insulation in power systems and the function of insulation in such systems. One of the most attractive features for this book is that the authors relate each of the topics covered to practical aspects of a power system and its relevance. This makes these topics easier to understand in an application. One example is on many of the more commonly encountered situations such as why there are different voltage levels such as 120Vac versus 230Vac and the reasons for various ratings in different system frequencies with an emphasis on dielectric insulation being the enabler for power systems. Another example describes the use of E-glass in composite insulators as the only type of glass used in composites and the reasons why.
The book primarily covers the use of insulating materials for power systems with a focus on the electric field and breakdown mechanisms, power system overvoltages, lightning, generating HV, measurement methods, non-destructive testing, and HV laboratory design.
It contains clear and concise descriptions of the breakdown mechanisms for gas, vacuum, solid, and liquid dielectrics. Phenomena, including partial discharge and streamer breakdown, are clearly explained with descriptions and illustrations and supporting equations when applicable. Each of the key phenomena describing the behavior of dielectrics is covered. For example, in solid dielectrics they are broken down into organic, inorganic, composite, and nano-composite materials and properties pertinent to each class of material is described. For example, the effect of nanocomposite fillers on breakdown is described where the effect of filler materials on composite based materials is described. The trends of other basic properties are also detailed. While there is not a rigorous derivation and supporting descriptions presented and there are no specific materials quoted, the general trends and applications of material are described.
The appendices contain a very basic introduction to setting up finite element models using COMSOL software for HV geometries and also methods for setting up and calculating traveling waves on transmission lines.
While this book does not contain rigorous mathematical derivations and in some instances, omits details in the explanations, the authors do a wonderful job at clearly explaining the relevance of electrical insulation use in power systems and still provide enough high-level technical detail that allows a student or engineer to fully appreciate the challenges power system designers face when developing power systems.
Short-Range Wireless Communications, 3rd Edition
50 Hampshire Street, 5th Floor Cambridge, MA 02139 http://www.elsevier.com/books-and-journals
472 pp., $99.95 (Softcover), 2019
This book describes the theory and application of short-range RF communication. It provides clear explanations of fundamental theory used to demonstrate the principles presented which can be used for device development. This book is intended mainly for experienced users of wireless communication systems who want to better understand how to modify existing wireless systems or for those who just want to learn more about how short-range wireless communication systems work. The book assumes an engineering background but not specifically a communications or RF engineering background but that of course would help. There a number of Mathcad examples available through a download link, provided in the book, which help guide the reader on various topics. Some examples of these topics include; impedance transformations, helical antenna design, loop antenna design, microstrip patch antenna design, probability for error codes, and a transmission line parameter calculator just to name a few examples. These programs are very useful since they are working examples used to illustrate key principles and to provide useful design calculators.
The key features of this book begin with the theory of radio propagation and continue with extensive coverage of antennas and transmission line theory and design, communication protocols, transmitters and receiver theory and design, digital radios, low-power short-range wireless technologies (e.g. RFID, Bluetooth, personal area networks, ZigBee), radio design, system implementation, Wi-Fi, standards and regulations.
Beside the more widely used communication protocols and systems mentioned above, some new and emerging topics are also described. These include metamaterials, multi-input multi-output (MIMO), loop antenna inductance coupling, very-high-throughput Wi-Fi, low energy Bluetooth, RFID updates, wireless security, location awareness, wireless sensor networks, optical communications, and energy harvesting.
This book “Short-Range Wireless Communication” provides a solid foundation for many of the most popular wireless communication systems and protocols is use today. It presents many clear and practical examples to help the reader understand the technical details and theory of the various methods presented. It will also quickly help anyone wanting to better understand the fundamentals of these communication systems and will provide practical guidance for developing RF components and systems. It is definitely a worthwhile read if you work with these types of systems and devices.
How to be Innovative
P. W. Lednor
World Scientific Publishing Co.
5 Toh Tuck Link
27 Warren Street
Hackensack, NJ 07601 http://www.worldscientificpress.com ISBN 978-981-3222-02-1
203 pp., $88 (Hardcover), 2020
This book provides a framework for those who want to learn about driving innovation within their company. Large companies often have individuals or sometimes small groups that tend to provide the majority of innovative ideas and produce new products for the company. This book provides guidance for those who are tasked with the job of driving innovation within their company, generally in a large company.
The author describes how to build an innovation team. First, selecting inputs for idea generation, developing ideas, and establishing a proof-of concept. This early stage in the innovation process is generally very common to any type of business, no matter what the end product or method. The second area discussed is what to do after establishing a proof-of-concept—covering speed to development and how to measure success. Team dynamics, including balancing efficiency versus effectiveness, enthusiasm versus objectivity, and how to form an effective team and dealing with communication issues are also discussed.
Other areas discussed cover the advantages and disadvantages of open innovation versus the closed innovation processes with examples of each given to illustrate outcomes. Working with universities and dealing with competitors is also reviewed. A broad range of various case studies in many different industries are presented to highlight the process used to successfully create a new product which is in the marketplace. There are discussions on suggestions for making the innovation process more effective and some views on the direction of the future of innovation.
This quick and easy to read book would be most useful for those charged with managing innovation within their companies, with the main focus on larger companies with well-established processes that can sometimes hinder innovation. Individual innovators may also be interested, especially those transitioning from academia to industry to gain an understanding of what is generally expected in industry from the innovation point-of-view.