Showing papers in "IEEE Electrical Insulation Magazine in 2014"
TL;DR: Dissolved gas analysis (DGA) has been used to assess the condition of power transformers as mentioned in this paper, which uses the concentrations of various gases dissolved in the transformer oil due to decomposition of the oil and paper insulation.
Abstract: Dissolved gas analysis (DGA) is used to assess the condition of power transformers. It uses the concentrations of various gases dissolved in the transformer oil due to decomposition of the oil and paper insulation. DGA has gained worldwide acceptance as a method for the detection of incipient faults in transformers.
267 citations
TL;DR: In this paper, a new method is presented using 5-gas ratios in a "pentagon" representation applicable to mineral oil-filled equipment, where carbon oxides CO and CO petertodd 2>>\s are examined separately as in other methods.
Abstract: Several methods are available for the interpretation of dissolved gas analysis (DGA) results in oil-filled electrical equipment. These methods use ratios of the five main hydrocarbon gases formed, namely H
2
, CH
4
, C
2
H
6
, C
2
H
4
, and C
2
H
2
, either 2-gas ratios, e.g., in IEEE [1] and IEC [2]; 3-gas ratios, in Duval Triangles 1 to 7 [3]; or 4-gas ratios in [4]. In this article a new method is presented using 5-gas ratios in a "pentagon" representation applicable to mineral oil-filled equipment. Carbon oxides CO and CO
2
are examined separately as in other methods.
144 citations
TL;DR: In this paper, a new kind of oil-paper insulation system, with higher dielectric strength and smaller volume compared with conventional insulation systems, was developed to reduce the volume and mass of high-voltage power transformers and improve their long-term operational reliability.
Abstract: Given the adoption of ultrahigh-voltage ac and dc power transmission, it is desirable to develop a new kind of oil-paper insulation system, with higher dielectric strength and smaller volume compared with conventional insulation systems, in order to reduce the volume and mass of high-voltage power transformers and improve their long-term operational reliability [1], [2]. Methods of improving the dielectric properties of the oil-paper insulation have therefore been widely investigated [3], [4]. The most influential factors affecting the performance of oil-paper insulation systems are the low dielectric strength of transformer oil and its degradation caused by water and other contaminants [5]. The dielectric strength of oil-paper insulation may be increased by filtering the oil in order to remove water and other contaminants [6]. However, further increase in the dielectric strength of the oil is required in order to achieve reduction of transformer volume and mass.
105 citations
TL;DR: Electroporation of a cell membrane can be made permeable to various molecules by carrying out a procedure called electroporation, which requires electroporators and electrodes.
Abstract: As described in Part 1, a cell membrane can be made permeable to various molecules by carrying out a procedure called electroporation [1]. This procedure is being successfully used in biology, biotechnology, and medicine [2], [3]. It requires electroporators and electrodes. An electroporator generates short HV pulses of specific shape, amplitude, duration, number, and repetition frequency [4], and the pulses are applied to the target cells or load through the electrodes [5]. The energy delivered to the load is governed by the number of pulses and the pulse voltage, current, and duration. In biomedical applications that energy can be several joules; in biotechnology, where electroporation is used for treatment of agricultural products and water, it can be several kilojoules.
89 citations
TL;DR: In this article, the aging of paper insulation in order to prolong the life of transformers is discussed. But the paper becomes severely degraded, it loses its mechanical strength and thus its ability to insulate the windings.
Abstract: Utilities need to understand the aging of paper insulation in order to prolong the life of transformers. If the paper becomes severely degraded, it loses its mechanical strength and thus its ability to insulate the windings.
69 citations
TL;DR: In this paper, a transformer consists of a magnetic iron core with primary and secondary copper windings, and the alternating current flowing in the primary winding induces a magnetic flux in the core, which in turn creates a current in the secondary windings.
Abstract: Power transformers are utilized to convert high voltages normally used in electrical power transmission to lower voltages more suitable for consumers. A transformer consists essentially of a magnetic iron core with primary and secondary copper windings. The alternating current flowing in the primary winding induces a magnetic flux in the core, which in turn creates a current in the secondary windings. If there is a difference in the number of turns in the primary and secondary windings, the secondary voltage will be scaled up or down proportionally to the ratio of the turns. In this way, a high voltage can be transformed to a low voltage. However, the desire to convert increasingly greater electrical loads using smaller power transformers results in both higher electrical and thermal stresses. The materials utilized to insulate the different electrically conductive components from each other must be designed to withstand those stresses. The insulating media often consist of pressboard and an insulating liquid. The liquid performs a double duty as it not only insulates the conductive parts but also functions as a liquid coolant. Here we are primarily interested in the oil as an insulating medium.
54 citations
TL;DR: In this article, physical electrical parameters of the transformers should be analyzed in addition to support the current frequency response assessment. But the authors do not consider the impact of the electrical parameters on the reliability of the diagnostics.
Abstract: The standard frequency response analysis (FRA) is not fully efficient for diagnostics of mechanical failures in power transformers. The article recommends that physical electrical parameters of the transformers should be analyzed in addition to support the current FRA assessment.
34 citations
TL;DR: In this article, partial or full bridging of the leakage distance occurs for moderate ice-accretion levels and reduces insulator reliability during melting in saturated conditions, and the DEIS has played an important role as a forum for exploring icing flashover physics.
Abstract: During the last 50 years a significant technical advance, namely in our understanding and control of switching-surge overvoltages, has had some unintended and adverse consequences when designers took full advantage of the possibility of reduced insulator dimensions. Glaze ice accretion can produce harmful effects, especially on closely spaced or large-diameter station post insulators and bushings. Partial or full bridging of the leakage distance occurs for moderate ice-accretion levels and reduces insulator reliability during melting in saturated conditions. Colocation of HV or EHV substations with roads or expressways on which deicing salt is spread has proved particularly problematic. The DEIS has played an important role as a forum for exploring icing flashover physics and as a sponsor of improved test methods and applications guidance.
34 citations
TL;DR: In this paper, the authors investigated the insulation strength of gas-insulated switchgear (GIS) under transient overvoltages (VFTO) with frequencies ranging from 1 to 100 MHz and amplitudes up to 2.5 p.u.
Abstract: Gas-insulated switchgear (GIS) is widely used today in electrical power systems because of its reliability, compaction, long maintenance cycle, and small impact on the environment [1]. In its use the normal operation of the disconnector generates very fast transient overvoltages (VFTO) with frequencies ranging from 1 to 100 MHz [2] and amplitudes up to 2.5 p.u. [3]. For systems above 330 kV, the insulation strength of the GIS under VFTO is of concern as insulation failures caused by VFTO have exceeded those caused by lightning impulse (LI) [4]. This characteristic has attracted the attention of researchers worldwide and currently is a hot topic in the field of ultra-high-voltage (UHV) GIS insulation.
28 citations
TL;DR: In this article, the thermal performance of two nominally identical transformers, one filled with standard mineral oil and the other with natural ester Envirotemp FR3 oil, was compared.
Abstract: In this article the authors present the results of their studies comparing the thermal performance of two nominally identical transformers, one filled with standard mineral oil and the other with natural ester Envirotemp FR3 oil.
28 citations
TL;DR: In this paper, the authors describe a system that uses data from online diagnostic systems to calculate the remaining lifetime of an electrical insulation system and also presents experimental accelerated aging data and use them as input data for remaining-lifetime calculations.
Abstract: Electric-power machines such as generators, large rotary machines, and transformers play an important role in electrical energy delivery Since the beginning of electrical-energy distribution to consumers, offline diagnostics of these important machines has been performed In time-based maintenance that is based on offline diagnostics, diagnosis is carried out regular intervals, followed by maintenance or repair as required Personnel have to be transported to the site to perform the measurements Currently, online diagnosis is being used important electric equipment around the globe; measurements are performed continuously, which helps minimize the number of faults and therefore network outages The data collected the diagnostic system, eg, voltage, current, or temperature, are sent via a computer network to the supervisory service In this paper, the authors describe a system that uses data from online diagnostic systems to calculate the remaining lifetime of an electrical insulation system The paper also presents experimental accelerated aging data and use them as input data for remaining-lifetime calculations
TL;DR: In this paper, the authors have observed that EO has higher PDIVs than MO for corona and creepage discharges, but their understanding of the oil/pressboard interface is incomplete.
Abstract: EO has proved to be a viable substitute for MO. Its dielectric performance is always comparable with, if not superior to that of MO, at least when new, dried, and highly purified. The smaller permittivity mismatch between pressboard and EO, compared to that between pressboard and MO, leads to a more uniform field distribution at the oil/pressboard interface. We have observed that EO has higher PDIVs than MO for corona and creepage discharges. However, our understanding of the oil/pressboard interface is incomplete. There is a lack of standardization in PDIV measurements, particularly in the case of creepage discharges. Because industry is striving to provide new insulating oils for use at increased transmission voltages, improving electrical testing techniques and the understanding of the oil/pressboard interface is important.
TL;DR: In this article, experimentally obtained moisture equilibrium charts for paper and pressboard insulations in mineral and natural ester transformer oils were presented. But they were only applied to paper insulations.
Abstract: This article presents experimentally obtained moisture equilibrium charts for paper and pressboard insulations in mineral and natural ester transformer oils.
TL;DR: In this paper, it has been ascertained that space charge plays a fundamental role in DC insulation reliability because of modifications it may induce in the (Poissonian) electric field distribution, especially when heterocharge is formed during voltage application.
Abstract: While HVDC assets are impetuously expanding worldwide, the design of HVDC polymeric insulation systems still contains unknowns. It has been ascertained that space charge plays a fundamental role in DC insulation reliability because of modifications it may induce in the (Poissonian) electric field distribution, especially when heterocharge is formed during voltage application. Heterocharge (charge close to an electrode of opposite polarity to that of the electrode) can increase the electric field at the interface between electrode and polymer, thereby enhancing injection from the electrode. This can cause so large a field concentration as to increase the conductivity abruptly and lead to insulation failure due to the electrical discharge process called, usually, thermal instability breakdown [1], [2].
TL;DR: In this article, a sensitive optical system which can be used to measure accurately the concentrations of fault gases dissolved in samples extracted from transformer oil is described, and some test results are presented.
Abstract: A sensitive optical system which can be used to measure accurately the concentrations of fault gases dissolved in samples extracted from transformer oil is described, and some test results are presented.
TL;DR: In this article, various anti-icing and de-icing methods for insulators currently being investigated in China are discussed with particular reference to the application of semiconductive silicone rubber coatings on insulators.
Abstract: Icing of transmission lines due to extreme weather conditions has caused many failures in power networks worldwide [1]. As China has much of its land 2,000 m above sea level, intense snow and ice storms at this altitude have caused significant losses to the economy, and the harsh conditions have made life very difficult in these regions [2]. The winter of 2008/2009 was particularly harsh with freezing rain, which continued for more than three weeks in the central provinces, causing 218 ice flashovers. In particular, Hunan and Jiangxi Provinces experienced the severest storms resulting in damage to 37% of the 500-kV power transmission towers, collapsing many towers. Considerable work has been done in China on understanding the reasons for, and preventing, the icing flashover of insulators [3]-[10], but in this article the various anti-icing and de-icing methods for insulators currently being investigated in China are discussed with particular reference to the application of semiconductive silicone rubber coatings on insulators.
TL;DR: In this article, thermal and pressure gradients cause cavities to form in the insulation system of mass-impregnated nonraining HVDC subsea cable insulation, during high load and load changes.
Abstract: This article proposes how thermal and pressure gradients cause cavities to form in the insulation system of mass-impregnated nondraining HVDC subsea cable insulation, during high load and load changes.
TL;DR: In this article, failure of the insulation of HV power cables can occur during operation at normal voltage or as a result of a transient voltage spike due to lightning or switching, and failure may occur if localized electrical stresses exceed the dielectric strength or if the insulation is degraded to the point that it cannot withstand the applied voltage.
Abstract: Failures of the insulation of HV power cables can occur during operation at normal voltage or as a result of a transient voltage spike due to lightning or switching. Failures may occur if localized electrical stresses exceed the dielectric strength of the insulation or if the insulation is degraded to the point that it cannot withstand the applied voltage.
TL;DR: In this article, the authors present an analysis over an operational period of 33 years of 34.5kV through 230kV mineral-oil-filled power transformers that have been removed from service because of faults and defects.
Abstract: The article presents an analysis over an operational period of 33 years of 34.5-kV through 230-kV mineral-oil-filled power transformers that have been removed from service because of faults and defects.
TL;DR: In this paper, it was shown that noncorrosive sulfur compounds can become corrosive in oil with dissolved oxygen in the range of a few hundreds to a few thousands of parts per million, producing, for example, metal sulfides, after being exposed to high temperatures, electrical stresses, transient phenomena, DC fields, and hot metal surfaces.
Abstract: In recent years, several documented cases of transformer failures have been attributed to the presence of corrosive sulfur species in the insulating oil [1], [2]. However, all sources of corrosive sulfur in oil have not been completely identified, yet. They can be residuals from the refining process, or they are formed under favorable operating conditions, such as high ambient and operating temperature and low oxygen concentration. It has been recently shown that noncorrosive sulfur compounds can become corrosive in oil with dissolved oxygen in the range of a few hundreds to a few thousands of parts per million, producing, for example, metal sulfides, after being exposed to high temperatures, electrical stresses, transient phenomena, DC fields, and hot metal surfaces. This has been quite commonly found in closed-type transformers (rubber bag or nitrogen blanketed) but can also occur in open breathing transformers, that work under more-or-less constant load, and in this case they breath very little [1], [3].
TL;DR: In this paper, the authors explored a novel method of wind energy generation using an electrostatic wind energy converter or EWICON, which is used to generate electricity from wind energy in the Netherlands.
Abstract: Since ancient times humanity has been harnessing the power of the wind in various forms, such as discovering the planet in sailboats, creating living space in the Dutch polders, or providing bread by flour-grinding windmills. Since 1887 wind has also been used to generate electricity as the shift to renewable energy production is being made [1]. In order to fulfill the long-term carbon emission goals set by, for example, the EU for 2050, the share of renewable energy (wind, solar, hydro, biofuels) needs to increase substantially [2]. Of these various means of renewable energy, wind energy is still the largest part. Therefore, wind farms, both decentralized and bulk, are being constructed. In 2010 wind energy constituted 2.5% of the global electricity production [3]. The article explores a novel method of wind energy generation using an electrostatic wind energy converter or EWICON.
TL;DR: In this article, the authors use electrical testing of cable systems to show the origins of the main test specifications, and they refer throughout the paper mainly to cables with extruded insulation and their accessories.
Abstract: An ever-increasing appetite for electrical energy by industrial, commercial, and household consumers has resulted in a continuously growing demand for transmission capacity and improved reliability of elecricity supply. The reliability of a HV power plant must be maintained at a high level over its lifetime, typically 50 years. All newly manufactured components of electricity networks undergo various types of tests to ensure their reliability and longevity. The tests follow specifications set out in national and international standards. These tests could be described in general terms as: design-verification tests,; production-quality tests, and ; tests after installation. Of all systems in a HV plant, cable systems must satisfy possibly the widest range of test requirements. So in this article we use electrical testing of cable systems to show the origins of the main test specifications. Although we refer throughout the paper mainly to cables with extruded insulation and their accessories, most of the discussion can be generalized to other HV equipment such as power transformers or insulators. We limit our discussion to insulated cable systems built to transmit electrical power in bulk at the subtransmission and transmission voltage levels, i.e., those rated above 30 kV.
TL;DR: In this article, fractal analysis is used to analyze the leakage current that develops on polymer insulators when subjected to pollution and electrical stress, which manifests itself by dryband arcing leading to erosion and possible tracking of the polymeric material.
Abstract: The increased use of polymer insulators on the overhead electrical power system has led to many designs of insulators, with many profiles and materials, but the performance has not always been stellar, particularly in polluted and wet environments, and degradation by tracking and/or erosion has been the main reason for this. In tests, such as the tracking wheel, visual inspection of tracking and erosion is subjective and can be misleading in establishing a quantitative measure of the damage to insulators. In this article fractal analysis is used to analyze the leakage current that develops on polymer insulators when subjected to pollution and electrical stress. Leakage current manifests itself by dry-band arcing leading to erosion and possible tracking of the polymeric material. Leakage current obtained from continuous monitoring of insulators under test is subjected to a methodology based on fractal analysis.
TL;DR: In this article, the authors proposed a continuous search for actions to reduce the possibility of failures in distribution networks, where the power quality refers also to the continuity of the service, which is greatly affected by failures that produce outages of transmission and distribution lines.
Abstract: Along with the increasing complexity of electric power systems, there is an increment on the quality standards of the electric energy supplied. The power quality refers also to the continuity of the service, which is greatly affected by failures that produce outages of transmission and distribution lines. Failures in distribution networks significantly affect the cost and quality of power supplied [1], and there is a continuous search for actions to reduce the possibility of failures.
TL;DR: In this article, the authors present a practical case as to the steps that must be taken by a transformer designer in rating a power transformer on-load tap changer (OLTC).
Abstract: The on-load tap changer (OLTC) is a crucial and expensive component of every power transformer. Its primary function is the dynamic adjustment of load voltage to specified levels without interrupting load current. Apart from thermal limitations at each tap position, the main concern in correctly rating an OLTC is the basic impulse insulation level (BIL). The reason for this is that during the standard BIL test on a power transformer, damaging overvoltage may develop on the regulating winding, which is transferred to the OLTC, which may damage the OLTC, and as a result, fail the BIL test on the power transformer. In regard to the lightning impulse voltage test, since the overvoltage that develops is a consequence of the distributed capacitance and inductance of the regulating winding, and as there are several types of regulating windings, each with different values of distributed capacitance and inductance, the correct rating of the OLTC will depend on the type of regulating winding used. Therefore, the transformer designer must be able to estimate the transferred impulse overvoltage, for the purpose of not only choosing the right type of regulating winding, but also to limit the overvoltage through passive or active means, for example incorporating electrostatic shielding in the regulating winding or installing a MOV surge arrestor. With this aim, computational tools are a powerful aid for assisting the transformer designer, since they allow the computation of distributed capacitance and inductance of the regulating winding, as well as estimating the distributed impulsive voltage. On the other hand, in regard to voltage withstand at power frequency, the induced AC voltage test is also important for determining the BIL of an OLTC. This article presents a practical case as to the steps that must be taken by a transformer designer in rating a power transformer OLTC.
TL;DR: Impedance spectroscopy of dielectrics has a long history, going back to Heaviside, and modern multiphysics finite element analysis packages allow dielectric spectra to be computed from detailed physical models for comparison with measurements.
Abstract: Impedance spectroscopy of dielectrics has a long history, going back to Heaviside. Modern multiphysics finite element analysis packages allow dielectric spectra to be computed from detailed physical models for comparison with measurements.