Showing papers in "IEEE Electrical Insulation Magazine in 2002"

Review of condition assessment of power transformers in service

Abstract: As transformers age, their internal condition degrades, which increases the risk of failure. To prevent these failures and to maintain transformers in good operating condition is a very important issue for utilities. Traditionally, routine preventative maintenance programs combined with regular testing were used. The change to condition-based maintenance has resulted in the reduction, or even elimination, of routine time-based maintenance. Instead of doing maintenance at a regular interval, maintenance is only carried out if the condition of the equipment requires it. Hence, there is an increasing need for better nonintrusive diagnostic and monitoring tools to assess the internal condition of the transformers. If there is a problem, the transformer can then be repaired or replaced before it fails. An extensive review is given of diagnostic and monitoring tests, and equipment available that assess the condition of power transformers and provide an early warning of potential failure.

Vegetable oils for liquid-filled transformers

Abstract: Several billion litres of transformer oil are used in transformers worldwide. To meet the challenges posed by environmental concerns, fully biodegradable vegetable oils have been developed for use in electrical equipment, particularly in transformers. Against this background the author discusses the development of vegetable oils for transformer use, their biodegradability, decomposition products, functional life test, fire hazard tests and the special challenges presented by cold weather. Further exploitation of these fluids for use in capacitors and cables needs further study and tests.

A review of faults detectable by gas-in-oil analysis in transformers

Abstract: IEC Publication 60599 provides a coded list of faults detectable by dissolved gas analysis (DGA): PD = partial discharges; D1 = discharges of low energy; D2 = discharges of high energy; T1 = thermal faults of temperature 700/spl deg/C. The IEC TC10 databases of DGA results corresponding to faults identified by visual inspection of faulty transformers in service have been presented in a previous paper (see IEEE Elec. Insulation Mag., vol. 17, no. 2, p.31-41, 2001). The present paper reviews these DGA results in a more user-friendly graphical form. It also reviews the DGA results of laboratory models attempting to simulate these faults, as published in the scientific literature or technical reports. The specific case of on-load tap changers (OLTC) is reviewed much more extensively, and separately, since DGA interpretation in this case must take into account the large background of residual gases resulting from the normal current-breaking operation of the OLTC. Particular attention is also given to DGA results related to PDs and low-temperature thermal faults.

Automated wavelet selection and thresholding for PD detection

Abstract: Presents a discussion of some important and unresolved issues related to previous work to provide a more comprehensive understanding of the practicability of wavelet-based denoising.

Challenge of mixed insulating liquids for use in high-voltage transformers.1. Investigation of mixed liquids

Abstract: The aim of this work is to present results of investigations into mixtures of two insulating liquids, recently proposed as alternatives to mineral oil. The mixtures are a combination of the widely available mineral oil and a specific amount of ester liquid, which has similar electrical properties combined with fewer environmental risks but high hygroscopicity. The water saturation limit of esters is more than 40 times larger than that of mineral oils. Esters absorb water vapor from the air in larger quantities than mineral oil, and this hygroscopicity reduces the moisture content in solid insulation due to diffusion from the solid into the liquid, while the dielectric properties of ester liquids are only slightly changed . Although the life of an oil in service depends primarily on its initial quality, service conditions need to be considered also. The investigations have therefore been carried out on unaged mixed liquids as well as on specimens under severe ageing conditions. Pure liquids have also been investigated to provide baseline data for comparison purposes. The first part of the investigation compares the properties of the mixed liquids with those of pure liquids. The second part of the investigation, will evaluate the compatibility of the mixed liquids with insulating papers used in high-voltage transformers.

Understanding FACTS-concepts and technology of flexible AC transmission systems [Book Review]

Abstract: Weddle’s Job-Seeker’s Guide to Employment Web Sites 2001 P.D. Weddle AMACOM Books 1601 Broadway New York, NY 10019 U.S.A. Phone: +1 800 714 6395 Fax: +1 212 903 808 http://www.amacombooks.org ISBN 0-8144-7097-1 184 pp. $12.95 (Softcover), 2001 For anyone looking for a job or just interested in what jobs are paying, Weddle’s Guide to Employment Web Sites provides an organized and welldescribed listing of many job Web sites, saving you valuable time searching for the right site. The book lists 350 of the top employment Web sites in 2001, covering a wide range of jobs. This book not only includes an organized list of Web sites, but each site has a half-page of key information providing details like the types of jobs found through the site, site owners, date started, site description, who post the jobs—employers, headhunters, or staffing firms—and other information regarding the details of how resumes are handled. The most useful aspect of this book is in the index, where all the major job areas are categorized. This made it easy to review technical job sites, which is what the majority of our readers are generally interested in. There are 20 sites listed under engineering, eight under science/scientists, and 42 under general. While the well-known general sites, like monster.com and hotjobs.com are listed, there are many other high-quality specialized sites listed. Another useful feature is in the regional index list. Here the Web sites are broken down into regions in the United States. Therefore, if you were looking in a specific area of the U.S. these would provide another place to research. While it appears that many of the sites are in the U.S., there is a separate index listing 22 international Web sites (five in Canada). This book is a great resource for today’s job searcher since so many jobs are listed on the Internet and the Internet provides quick and easy access to all the listings.

Transfer function-based partial discharge localization in power transformers: a feasibility study

Abstract: Statistical studies have shown that failures of bushings, winding insulation, and online tap changers are the main causes for long-duration outages of transformers. This article investigates the development of an instrument for supervising the conditions of transformer units. The use of sectional winding transfer functions (SWTFs) for online PD evaluation in power transformers has several advantages: localization of PD sources, discrimination between PDs inside or outside of the transformer, and evaluation of actual PD amplitudes along the winding. Direct measurement of SWTFs-when different points along the coil are accessible-and use of these SWTFs for PD evaluation and localization has shown excellent results. In order to use this method at transformers on site, an appropriate modeling method is needed for the computation of the SWTFs using only measurements at the transformer terminals. A detailed modeling approach based on discrete RLC circuit elements has been studied and different algorithms used for parameter estimation and optimization. This model is applicable in practical cases for a limited frequency range if genetic algorithms (GAs) are used for parameter optimization. A new method based on traveling wave theory has been investigated using genetic algorithms to search for the optimum parameters of a partial differential equation that describes the transient behavior of the coil. This method has shown potential in solving SWTF calculation problems for different transformers.

Challenge of mixed insulating liquids for use in high-voltage transformers. II. Investigations of mixed liquid impregnated paper insulation

Abstract: As society depends more and more on electrical power, the demands for highly reliable power supplies are increasing. This paper examines the compatibility of oil mixtures with cellulose and aramid papers that are used in transformer insulation.

Recognition of discharge sources using UHF PD signatures

Abstract: This paper investigates utilizing zero span UHF PD detection. The findings suggest that the technique is a practical solution for on-line PD monitoring of transformers in the presence of noise and also permits the use of existing knowledge on PD defect signatures.

Effective diagnostics for oil-filled equipment

Abstract: The author describes an approach used in Russia to develop diagnostic techniques to assess the condition of oil-filled power equipment. He considers that the most useful parameters to estimate remaining life are the partial pressures of dissolved gases and water in the oil and the water content in the solid insulation. Gas chromatography is used to determine these parameters from oil samples taken from equipment in service.

The relationship between partial discharge current pulse waveforms and physical mechanisms

Abstract: Partial discharge (PD) measurements have long been recognised as an important tool for detecting and predicting dielectric breakdown (BD). However, as a result of their small amplitude and wide bandwidth, the relationship between the physical mechanisms of gas breakdown and PD signal generation has not been clarified fully. We have investigated the relationship between PD current pulse waveforms and physical mechanisms to provide a basis for improved PD-based diagnostics.

HVDC gas insulated apparatus: electric field specificity and insulation design concept

Abstract: This paper demonstrates the field model and time domain calculating methods and some of their important applications, helping advance an understanding of the complicated charge accumulation phenomena and its effect on the dielectric strength of a HVDC SF/sub 6/ insulation system.

Suspended particles in the liquid insulation of aging power transformers

Abstract: This paper examines some theoretical aspects of the relationship between the aging of oil and the deterioration of the internal insulation of the windings, and looks at some new findings that might provoke fresh consideration of the relationship between the analytical properties of liquid insulation and the dielectric properties of windings.

Interface phenomena in stator winding insulation - challenges in design, diagnosis, and service experience

Abstract: Technically and economically optimized insulation systems can only be offered today if there is complete knowledge of phenomena in the winding insulation that determine its service life. This paper describes how such mechanisms are influenced by operating conditions, how they are detected using modern diagnosis methods, and how they can be intentionally influenced by the design of the insulation.

Recovery of SF/sub 6/ from N/sub 2//SF/sub 6/ gas mixtures by using a polymer membrane

Abstract: The investigation of gas recovery from N/sub 2//SF/sub 6/ gas mixtures using a polymer membrane has been reported It has been shown that the purity of recovered gas, the recovery loss, and the gas handling speed depend on various parameters such as original gas mixing ratio, gas feeding pressure, gas flow rate, and temperature of the membrane A gas recovering system with two membrane separators connected in cascade has proved to be very efficient in attaining high purity in a recovered gas, with negligibly small recovery loss and high handling speed for practical use Furthermore, this system could be applied for CO/sub 2//SF/sub 6/, He/SF/sub 6/ and even for ternary mixtures such as N/sub 2//CO/sub 2//SF/sub 6/ without any modification in the system, where we expect much better performance in comparison with N/sub 2//SF/sub 6/

Numerical simulation of partial discharge propagation in cable joints using the finite difference time domain method

Abstract: In this second of a series of three papers, the authors investigate partial discharge (PD) detection and propagation in cable joints. The complex nature of cable joints leads to errors when PD analysis is carried out using conventional equivalent circuits. The authors use the finite difference time domain method to determine the transient electromagnetic fields caused by simulated PD in model cable joints.

Clean electricity from photovoltaics [Book Review]

Abstract: Polymeric Materials—Structure, Properties, Applications G.W. Ehrenstein Hanser Gardner Publications, Inc. 6915 Valley Ave. Cincinnati, OH 45244-3029 Phone +1 800 950 8977 Fax +1 513 527 8950 http://www.hansergardner.com ISBN 1-569900-310-7 277 pp. $39.95 (Softcover), 2001 With an increasing number of applications using polymeric materials, there is a need for understanding the relationship between polymer structure, properties, and processing. By better understanding material properties and the effects of processing on performance, one can make better design choices and material selection. Understanding how the chemical and physical characteristics of polymers are affected by the design and process parameters leads one to better end products. Optimizing mold design, flow conditions, fiber type, orientation, and process conditions result in improved physical properties of the final part. This applications-oriented book reveals the necessary materials, design, and process conditions necessary to obtain desired properties. This book is filled with practical examples intended not only to show the reader the “how to,” but to add physical understanding. It clearly shows common techniques used to produce various plastics and how the effects of temperature, fiber reinforcement, water absorption, crosslinking, aging, plus many others factors affect the physical properties. The book is loaded with many photographs of microtomed and etched sections of plastics that illustrate how the physical properties of a polymer are altered and what physical changes actually occur. The book provides a quick way to learn about the practical aspects of polymers and the parameters that are important to an applications engineer. Coverage includes molecular structure and synthesis of polymers, polymer structure, thermomechanical properties, mechanical behavior, aging, and stabilization. All types of polymers including thermosets, thermoplastics, elastomers, and blends are covered. The author does an excellent job at clearly showing the practical side of polymer characteristics. Application engineers involved with plastic materials will find this book to provide valuable insight into polymer characteristics allowing for optimization and good material selection.

Principles of Electronic Materials and Devices, 2nd Edition [Book Review]

Abstract: IEEE Electrical Insulation Magazine need to be aware of the potential limitations that could be imposed on lead-based products and be aware of alternative lead-free solders. A wide range of various lead-free solders are described in this book along with underlying fundamentals that are key to practical applications. The book begins with reasons why lead is toxic to the environment, industry trends, and current legislation. The next chapter covers fundamental technology, including conventional lead-containing solder technology, physical properties, metallurgical properties, failure modes, alloy design, and thermomechanical fatigue of solders in general. This technical background lays the foundation for understanding solder requirements. The next 14 chapters cover a variety of solder alloy compositions and properties. These include binary, ternary, quaternary, and higher-element systems. Examples of these alloys use tin, silver, bismuth, copper, indium, zinc, and gallium in various ranges and percentages. There are phase curves and stress-strain curves for alloys described. There are also high-temperature and low-temperature (relative to 63Sn/37Pb alloy) alloys. The remaining chapters are devoted to applications and various aspects of the industries that use solders. There are details on PCB surface finishes, intermetallics, microstructure of SnAg, reliability, conductive adhesives, tin coating chemistry, role of bismuth, and production defects. This reference text is a practical handbook containing a wealth of information on lead-free solders and can serve as a guide to selecting the most appropriate lead-free solder alloy for a given application. Those working with solder—especially lead-based solders—will find this a very interesting and practical book for not only finding a replacement solder but for understanding the physical and metallurgical requirements of solders in general. This book could also be used in a graduate materials science curriculum. Principles of Electronic Materials and Devices, 2 Edition S.O. Kasap McGraw Hill 1221 Avenue of the Americas New York, NY 10020 Phone +1 800 352 3566 Fax +1 212 512 4105 http://www.mhhe.com ISBN 0-07-239342-4 745 pp. $100 (Hardback), 2002 As electronic accessories become more common in a variety of applications, there is a greater need for engineers and scientists to develop and advance electronic materials and devices. This text contains a broad range of topics in electronic materials and devices, mainly intended for an undergraduate course. While in-depth detail is not intended, the author injects a wonderful, semi-quantitative level of description in the text. Concepts presented with many detailed illustrations and superb writing are presented in a way to convey the physical ideas with a minimum of mathematics. Unlike many college level texts, there are more than 130 worked-out examples to reinforce learning and understanding. There are over 470 professionally prepared illustrations and a CD, included with the book, contains all the figures in color PDF and PowerPoint formats, making it easier for overhead or electronic presentations. The broad range of topics covers materials science concepts, electrical and thermal conduction in solids, quantum-physics, theory of solids, dielectric materials and insulation, and magnetic and optical properties of materials. For example, there is a good comparison of different capacitor types illustrating the physical mechanisms and dielectric properties of electrolytic, mica, polyester, ceramics, tantalum, and others. There is even a section, although very basic, on dielectric breakdown in solids, liquids, and gases. The book reads more like a physics book, filled with practical, well-illustrated and explained topics that are pertinent to engineers, physicists, and scientists today. Even though the text is intended for an undergraduate course, it could easily be used by the engineering community as general reference text, especially for those who only occasionally use electronic components but need to understand the basic physics behind devices.

Application of Maxwell solvers to PD propagation. I. Concepts and codes

Abstract: This article reviews the basic approaches to solving electromagnetic propagation in the context of PD detection. It also investigates available commercial software, introduces the steps required to obtain trustworthy computational results, and gives an example of detailed analysis of PD propagation.

Mechanical prestressing improves electrical strength

Abstract: There is a strong mechanical influence on the growth of electrical trees in electrical insulation resins. This is not to argue that electrical treeing is exclusively a mechanical phenomenon directly analogous to mechanical cracking. It is obviously an electrically driven process; no volts, no trees. Nevertheless, the mechanical dimension is of sufficient importance for its effects to be exploited to advantage using the prestressing technique. The effect that post-curing at 100/spl deg/C has on the development of prestress, and on the ability of the cured sample to retain its prestress as the temperature is raised, has both positive and negative aspects. On the down side, material cured at 100/spl deg/C requires a greater tension to be applied to the fibers during the casting process in order to achieve the same degree of prestress. On the other hand, the increase in the glass transition temperature from 65/spl deg/C to 113/spl deg/C permits the use of the composite at temperatures up to 80/spl deg/C before any significant loss of prestress occurs, as compared with 40/spl deg/C for material cured at room temperature. As an additional bonus, there is an enhancement of the mechanical strength resulting from the inclusion of cast-in fibers, which is important where the electrical insulation also acts as a structural member in the insulation system.

Accelerated ageing tests on polymeric cables using water-filled tanks - a critical review

Abstract: Accelerated ageing tests in water-filled tanks are gaining more attention because of their capability to provide information on cable life in addition to cable breakdown strength relative to ageing. This paper describes a statistically meaningful test that will meet these two main objectives of ageing.

Assessment of station cable condition using wireless telemetry and diagnostic tests

Abstract: Following the premature in-service failure of a 15 kV, XLPE insulated cable in a hydraulic generating station, a program was devised to: determine the root cause of failure; assess the condition of the remaining cables in the station; and ensure that the field modifications proposed to rectify the problem were effective. The underlying mechanism driving the failure was found to be overheating of the cable sheath as a result of the inadvertent formation of ground loops in the cable support structure, and hence circulating currents. Physicochemical tests of cable sections recovered from the failed circuit showed that the cable had experienced temperatures in excess of 115 /spl deg/C. Electrical diagnostic testing of the affected cable circuits indicated that the majority of the cable length was unaffected by the overheating. However, the portion of the cable within the switchgear cubicle may have undergone some ageing as evidenced by higher dielectric loss values. On-line temperature measurements, including those on the current-carrying components using wireless telemetry, confirmed that one of the sources of the high temperatures was the ground structure in the cubicle.

High electric stress and insulation challenges in integrated microelectronic circuits

Abstract: The insulating layer in the transistor has decreased from 100 nm in the early 1970s to only a few nanometers today. This thin insulating layer gives rise to very high electric fields approaching 1000 kV/mm for an operating voltage of 1 V. Degradation of the insulation during ageing takes place due to the high field and may eventually lead to a breakdown. Currently it seems that the reliability of the insulating layer is one of the factors that may limit a further scaling of the transistor technology. Another threat to the thin insulating layer is electrostatic discharges (ESD) caused by human or machine handling. ESD can generate voltage and current pulses far outside the normal operating regime, and cause breakdown of the insulating layer. This article intends to give a brief introduction to the above-mentioned insulation challenges in integrated microelectronic circuits.

The World's first long-distance 500 kV-XLPE cable line. 3. Underground apparatus

Abstract: This is the final article in a series that introduces the outline of the Shin-Toyosu Substation. In order to respond to the increasing power demand in the central Tokyo area, Tokyo Electric Power Co., Inc. started operation of the Shin-Toyosu Substation-which is the world's first 500-kV underground substation-on 21 November 2000. In this article, some important pieces of apparatus used in the underground substation are briefly introduced.

Numerical distance protection - principles and applications [Book Review]

Abstract: Weddle’s Job-Seeker’s Guide to Employment Web Sites 2001 P.D. Weddle AMACOM Books 1601 Broadway New York, NY 10019 U.S.A. Phone: +1 800 714 6395 Fax: +1 212 903 808 http://www.amacombooks.org ISBN 0-8144-7097-1 184 pp. $12.95 (Softcover), 2001 For anyone looking for a job or just interested in what jobs are paying, Weddle’s Guide to Employment Web Sites provides an organized and welldescribed listing of many job Web sites, saving you valuable time searching for the right site. The book lists 350 of the top employment Web sites in 2001, covering a wide range of jobs. This book not only includes an organized list of Web sites, but each site has a half-page of key information providing details like the types of jobs found through the site, site owners, date started, site description, who post the jobs—employers, headhunters, or staffing firms—and other information regarding the details of how resumes are handled. The most useful aspect of this book is in the index, where all the major job areas are categorized. This made it easy to review technical job sites, which is what the majority of our readers are generally interested in. There are 20 sites listed under engineering, eight under science/scientists, and 42 under general. While the well-known general sites, like monster.com and hotjobs.com are listed, there are many other high-quality specialized sites listed. Another useful feature is in the regional index list. Here the Web sites are broken down into regions in the United States. Therefore, if you were looking in a specific area of the U.S. these would provide another place to research. While it appears that many of the sites are in the U.S., there is a separate index listing 22 international Web sites (five in Canada). This book is a great resource for today’s job searcher since so many jobs are listed on the Internet and the Internet provides quick and easy access to all the listings.

The world's first long-distance 500 kV-XLPE cable line. 2. Joints and after-installation test

Abstract: For pt. 1 see ibid., vol. 18, no. 2, p. 65-67 (2002). In this second part of a three part series introducing the Shin-Keiyo/Toyosu underground transmission line using a 500-kV XLPE cable, the authors describe the specially developed extrusion-molded joints and after-installation test procedures. Based on the results of basic research extensively done to design the 500-kV extrusion-molded joints, the insulation thickness was determined to be 36 mm through careful considerations of various design parameters obtained. As in the case of the cable, the main factors that determine the performance of the joints are contaminants and voids, and their permissible levels are determined. Unlike cables, it is impossible to conduct sampling inspections for the extrusion-molded joints after they were assembled. Therefore, particular emphasis has to be placed on supervision and inspection of conditions during the assembly process.