Lars E. Lundgaard
Bio: Lars E. Lundgaard is an academic researcher from SINTEF. The author has contributed to research in topics: Breakdown voltage & Conductivity. The author has an hindex of 16, co-authored 42 publications receiving 1388 citations.
TL;DR: In this article, the effects of moisture, oxygen, and acidity upon the aging of Kraft and thermally upgraded ("Insuldur/spl reg/") papers have been studied in detail.
Abstract: The effects of moisture, oxygen, and acidity upon the aging of Kraft and thermally upgraded ("Insuldur/spl reg/") papers have been studied in detail. The results for Kraft are consistent with the kinetic model and parameters proposed earlier by Emsley et al., and with the principle that moisture promotes acid-hydrolysis by causing carboxylic acids to dissociate. Moisture is released during the aging of Kraft and, hence, its aging is auto-acceleratory. In contrast, Insuldur consumed moisture under the same conditions, aged more slowly, and its aging was less accelerated by added moisture. 2-Furfuraldehyde (2FAL), which is a dehydration product of pentosans and, hence, an index of moisture production, is also released from Kraft during aging, but not from Insuldur. Acids are, however, produced from both types of paper. Theoretical explanations for these findings are proposed, and their practical implications for transformer maintenance are discussed.
TL;DR: In this paper, frequency domain spectroscopy has been applied to oil-impregnated paper and pressboard with and without moisture and/or acids added, and to paper at various stages of aging.
Abstract: Dielectric response is a non-invasive diagnostic method with a potential to give information about the status of the solid insulation in a power transformer. To investigate what conditions the method can and cannot reveal, frequency domain spectroscopy has been applied to oil-impregnated paper and pressboard with and without moisture and/or acids added, and to paper at various stages of aging. Water and carboxylic acids are important aging indicators. It is found that moisture is clearly detectable. Also low molecular weight carboxylic acids will affect the dielectric response in a way similar to moisture, but high concentrations are needed for a contribution comparable to that of moisture. It is difficult to tell moisture and acids apart from the responses obtained. High molecular weight carboxylic acids make little or no contribution to the dielectric response of the solid insulation in a paper/pressboard - oil system. It was also observed that keeping paper or pressboard at elevated temperatures had a conditioning effect on the response
01 Jan 2008
TL;DR: In this article, it was shown that in spite of low water content in the oil indicated by normal oil sampling procedures, a large amount of water can be revealed within a transformer.
Abstract: • Uncertainty in effectiveness of methods available to assess a health of an equipment. In  e.g. is shown that in spite of low water content in the oil indicated by normal oil sampling procedures a large amount of water can be revealed within a transformer. How to rank the transformer, which needs drying? How to assess a critical level of water contamination to prevent failure or to determine permissible operating conditions, e.g. overloading?
TL;DR: In this paper, the effect of several factors on the electrostatic dehydration process of water-in-model-oil emulsions was studied, including application time, waveform, strength and frequency of applied electric field, and temperature.
Abstract: The effect of several factors has been studied in order to determine their influence on the electrostatic dehydration process of water-in-model-oil emulsions. Not only application time, waveform, strength and frequency of the applied electric field, but also temperature were all found to play a non-negligible role in the process. The results obtained have been correlated to observed phase separation measured with a Turbiscan Lab instrument.
TL;DR: The paper, prepared by CIGRE WG D1.03 (TF 09), presents the guidelines for risk assessment procedure on defects in GIS based on PD diagnostics based on the estimated dielectric failure probability and failure consequences that can be different in case of on-site testing or in service activity.
Abstract: The paper, prepared by CIGRE WG D1.03 (TF 09), presents the guidelines for risk assessment procedure on defects in GIS based on PD diagnostics. The procedure, described in detail in CIGRE Technical Brochure 525, starts with sensitive PD measurement to detect the critical defects and follows with identification of the type of the defect and its location inside the GIS. This information taken together with other essential data from laboratory measurements, manufacturer's experience, design aspects and trend analysis of the PD activity, are the base for the estimation of the criticality of the defects. Finally, the risk assessment is performed based on the estimated dielectric failure probability and failure consequences that can be different in case of on-site testing or in service activity.
TL;DR: In this article, the authors assess the relative importance of either biotic or abiotic oxidation of biomass-derived black carbon (BC) and characterize the surface properties and charge characteristics of oxidized BC.
Abstract: The objectives of this study were to assess the relative importance of either biotic or abiotic oxidation of biomass-derived black carbon (BC) and to characterize the surface properties and charge characteristics of oxidized BC. We incubated BC and BC–soil mixtures at two temperatures (30 °C and 70 °C), with and without microbial inoculation, nutrient addition, or manure amendment for four months. Abiotic processes were more important for oxidation of BC than biotic processes during this short-term incubation, as inoculation with microorganisms at 30 °C did not change any of the measured indicators of surface oxidation. Black C incubated at both 30 °C and 70 °C without microbial activity showed a decrease in pH (in water) from 5.4 to 5.2 and 3.4, as well as an increase in cation exchange capacity (CEC at pH 7) by 53% and 538% and in oxygen (O) content by 4% and 38%, respectively. Boehm titration and Fourier-transform infrared (FT-IR) spectroscopy suggested that formation of carboxylic functional groups was the reason for the enhanced CEC during oxidation. Analysis of surface properties of BC using X-ray photoelectron spectroscopy (XPS) indicated that the oxidation of BC particles was initiated on the surface. Incubation at 30 °C only enhanced oxidation on particle surfaces, while oxidation during incubation at 70 °C penetrated into the interior of particles. Such short-term oxidation of BC has significance for the stability of BC in soils as well as for its effects on soil fertility and biogeochemistry.
TL;DR: In this paper, the authors investigated changes in molecular form and surface charge of black carbon (BC) due to long-term natural oxidation and examined how climatic and soil factors affect BC oxidation.
Abstract: The aim of this work was to investigate changes in molecular form and surface charge of black carbon (BC) due to long-term natural oxidation and to examine how climatic and soil factors affect BC oxidation. Black C was collected from 11 historical charcoal blast furnace sites with a geographic distribution from Quebec, Canada, to Georgia, USA, and compared to BC that was newly produced (new BC) using rebuilt historical kilns. The results showed that the historical BC samples were substantially oxidized after 130 years in soils as compared to new BC or BC incubated for one year. The major alterations by natural oxidation of BC included: (1) changes in elemental composition with increases in oxygen (O) from 7.2% in new BC to 24.8% in historical BC and decreases in C from 90.8% to 70.5%; (2) formation of oxygen-containing functional groups, particularly carboxylic and phenolic functional groups, and (3) disappearance of surface positive charge and evolution of surface negative charge after 12 months of incubation. Although time of exposure significantly increased natural oxidation of BC, a significant positive relationship between mean annual temperature (MAT) and BC oxidation (O/C ratio with r = 0.83; P
01 Jan 2010
TL;DR: A critical review of the current state of knowledge regarding the effects of biochar application to soil on soil properties and functions is provided in this paper, where the main focus is providing a sound scientific basis for policy development, to identify gaps in current knowledge, and to recommend further research relating to biochar applications to soils.
Abstract: Biochar application to soils is being considered as a means to sequester carbon (C) while concurrently improving soil functions. The main focus of this report is providing a critical scientific review of the current state of knowledge regarding the effects of biochar application to soils on soil properties and functions. Wider issues, including atmospheric emissions and occupational health and safety associated to biochar production and handling, are put into context. The aim of this review is to provide a sound scientific basis for policy development, to identify gaps in current knowledge, and to recommend further research relating to biochar application to soils. See Table 1 for an overview of the key findings from this report. Biochar research is in its relative infancy and as such substantially more data are required before robust predictions can be made regarding the effects of biochar application to soils, across a range of soil, climatic and land management factors. Definition In this report, biochar is defined as: “charcoal (biomass that has been pyrolysed in a zero or low oxygen environment) for which, owing to its inherent properties, scientific consensus exists that application to soil at a specific site is expected to sustainably sequester carbon and concurrently improve soil functions (under current and future management), while avoiding shortand long-term detrimental effects to the wider environment as well as human and animal health." Biochar as a material is defined as: "charcoal for application to soils". It should be noted that the term 'biochar' is generally associated with other co-produced end products of pyrolysis such as 'syngas'. However, these are not usually applied to soil and as such are only discussed in brief in the report. Biochar properties Biochar is an organic material produced via the pyrolysis of C-based feedstocks (biomass) and is best described as a ‘soil conditioner’. Despite many different materials having been proposed as biomass feedstock for biochar (including wood, crop residues and manures), the suitability of each feedstock for such an application is dependent on a number of chemical, physical, environmental, as well as economic and logistical factors. Evidence suggests that components of the carbon in biochar are highly recalcitrant in soils, with reported residence times for wood biochar being in the range of 100s to 1,000s of years, i.e. approximately 101,000 times longer than residence times of most soil organic matter. Therefore, biochar addition to soil can provide a potential sink for C. It is important to note, however, that there is a paucity of data concerning biochar produced from feedstocks other than wood, but the information that is available is discussed in the report. Owing to the current interest in climate change mitigation, and the irreversibility of biochar application to soil, an effective evaluation of biochar stability in the environment and its effects on soil processes and functioning is paramount. The current state of knowledge concerning these factors is discussed throughout this report.
TL;DR: In this article, the most commonly exploited demulsification techniques (i.e., chemical, biological, membrane, electrical, and microwave irradiation) of both oilfield and synthetic emulsions, taking into account the emulsion-stabilizing and -destabilizing effects with regard to the dominant parameters plus the emuls composition are discussed.
Abstract: The difficulties associated with transportation and refining of crude oil emulsions and produced water discharge limitations are among the conspicuous clues that have led the oilfield researchers to probe into practical demulsification methods for many decades. Inconsistent research outcomes observed in the literature for a particular demulsification method of a typical emulsion (i.e., water-in-oil or oil-in-water) arise not only from the varied influential parameters associated (such as salinity, temperature, pH, dispersed phase content, emulsifier/demulsifier concentration, and droplet size) but also from the diverse types of emulsion constituents (namely oil, surfactant, salt, alkali, polymer, fine solids, and/or other chemicals/impurities). Being the main component in formation of stabilizing interfacial film surrounding the dispersed phase droplets, surfactant is the most predominant contributor to emulsion stability, extent of which depends on its nature (being ionic or nonionic, and its degree of hydrophilicity/lipophilicity), concentration, and interaction with other surface-active agents in the emulsion as well as on the salinity, temperature, and pH of the system. In this paper, it is endeavored to overview some of the most commonly exploited demulsification techniques (i.e., chemical, biological, membrane, electrical, and microwave irradiation) of both oilfield and synthetic emulsions, taking into account the emulsion-stabilizing and -destabilizing effects with regard to the dominant parameters plus the emulsion composition. Further, the variations occurring in interfacial properties of emulsions by demulsification process are discussed. Finally, the mechanism(s) involved in emulsions resolution achieved by each method is elucidated. Clearly, the most efficient demulsification approach is the one able to attain desirable separation efficiency while complying with the environmental regulations and imposing the least economic burden on the petroleum industry.
TL;DR: The observation of oppositely charged drops bouncing rather than coalescing in strong electric fields should affect the understanding of any process involving charged liquid drops, including de-emulsification, electrospray ionization and atmospheric conduction.
Abstract: The movement of drops in electric fields plays a role in processes as diverse as storm cloud formation, ink-jet printing and lab-on-a-chip manipulations. An important factor in practical applications is the tendency for adjacent drops to coalesce, usually assumed to be favoured if drops are oppositely charged and attracted to each other. Now Ristenpart et al. show that when oppositely charged drops move towards each other in an electric field whose strength exceeds a critical value, the drops simply 'bounce' off one another. This observation calls for a re-evaluation of our understanding of all processes involving electrically induced drop motion. Adjacent drops of fluid coalesce, and oppositely charged drops have long been assumed to experience an attractive force that favours their coalescence. However, here it is observed that oppositely charged drops moving towards each other in a strong electric field do not coalesce when the field strength exceeds a certain value but rather 'bounce' off one another. This observation calls for a re-evaluation of our understanding of processes such as storm cloud formation and ink-jet printing, which involve electrically induced droplet motion. Electric fields induce motion in many fluid systems, including polymer melts1, surfactant micelles2 and colloidal suspensions3. Likewise, electric fields can be used to move liquid drops4. Electrically induced droplet motion manifests itself in processes as diverse as storm cloud formation5, commercial ink-jet printing6, petroleum and vegetable oil dehydration7, electrospray ionization for use in mass spectrometry8, electrowetting9 and lab-on-a-chip manipulations10. An important issue in practical applications is the tendency for adjacent drops to coalesce, and oppositely charged drops have long been assumed to experience an attractive force that favours their coalescence11,12,13. Here we report the existence of a critical field strength above which oppositely charged drops do not coalesce. We observe that appropriately positioned and oppositely charged drops migrate towards one another in an applied electric field; but whereas the drops coalesce as expected at low field strengths, they are repelled from one another after contact at higher field strengths. Qualitatively, the drops appear to ‘bounce’ off one another. We directly image the transient formation of a meniscus bridge between the bouncing drops, and propose that this temporary bridge is unstable with respect to capillary pressure when it forms in an electric field exceeding a critical strength. The observation of oppositely charged drops bouncing rather than coalescing in strong electric fields should affect our understanding of any process involving charged liquid drops, including de-emulsification, electrospray ionization and atmospheric conduction.