| 1. |
- Bengtsson, Magnus, et al.
(författare)
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Fluorescence lidar imaging of fungal growth on high-voltage outdoor composite insulators
- 2005
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Ingår i: Optics and Lasers in Engineering. - : Elsevier BV. - 0143-8166 .- 1873-0302. ; 43:6, s. 624-632
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Tidskriftsartikel (refereegranskat)abstract
- Remote fluorescence imaging of fungal growth on polymeric high-voltage insulators was performed using a mobile lidar system with a laser wavelength of 355 nm. Insulator areas contaminated by fungal growth could be distinguished from clean surfaces and readily be imaged. The experiments were supported by detailed spectral studies performed in laboratory using a fibre-optic fluorosensor incorporating an optical multi-channel analyser system (OMA) and a nitrogen laser emitting radiation at 33 7 nm.
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| 2. |
- Blennow, Jörgen, 1966, et al.
(författare)
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Comparative study of dielectric spectroscopy measurements and anayses of oil and paper samples from a transformer undergoing repair
- 2005
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Ingår i: In Proc. of 19th Nordic Insulation Symposium, Trondheim, Norway, June 13-15.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- New methods, based on characterisation of dielectric response measurements, for assessing moisture content of pressboard and paper are gaining ground. However, there is a need for calibrating results with results from other techniques. This communication presents results from a study of a 19.5/6.8/6.8 kV - 40 MVA power transformer, which was opened on-site during maintenance work, thus allowing for collecting paper samples. Dielectric spectroscopy measurements were conducted before and after its opening. Results were compared with measurements on oil and paper samples. These showed that the moisture levels in the interior of the solid insulation were unchanged. Further, it was found that FDS measurements gave more accurate estimates of moisture levels than estimates based on oil analyses and equilibrium curves.
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| 3. |
- Blennow, Jörgen, 1966, et al.
(författare)
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Sequential Comparative Study of Dielectric Response and Analyses of Oil and Paper from a Power Transformer Undergoing Repair
- 2005
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Ingår i: In Proc. 14th International Symposium on High Voltage Engineering.
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Konferensbidrag (refereegranskat)abstract
- Methods, based on characterisation of dielectric response, for assessing moisture content in pressboard and paper are gaining ground. However, there is a need for calibrating obtained results with results from other techniques. This communication presents results from a study of a 50/10 kV - 40 MVA power transformer, which was sent to a workshop for repair, thus allowing for collecting samples of the solid insulation. Dielectric spectroscopy measurements in frequency domain were conducted at several occasions before and after the repair. Moisture estimation based on dielectric response measurements as well as on titration of oil samples yielded similar results to those obtained by direct titration of paper samples, as long as appropriate temperature values were used in all the analyses mentioned. The temperature value during measurements should be used for the analysis of the dielectric response, while in-service temperature of oil should be used for the evaluation based on Karl Fisher titration.
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| 4. |
- Dernfalk, Andreas, 1975
(författare)
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Diagnostic Methods for Composite Insulators with Biological Growth
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Composite insulators have a number of advantages compared to conventional insulators, but the fact that they are more prone to aging is a major drawback. For instance, biological growths, like algae and fungi, have been found to colonize composite insulators, and possibly effecting the insulation performance. So far there is a lack of diagnostic methods capable of detecting material changes of composite insulators in the field, and developing new diagnostic methods has thus become very important. One of the main aims of the work presented in this thesis was to elucidate on the influence of biological growth on the electrical performance of composite insulators. To do this, fungi originating from insulators installed in Sweden were grown on silicone rubber insulators and material samples in a climate chamber. The performance of the insulators were studied through leakage current measurements conducted occasionally during a period of one and a half years and wet flashover voltage measurements at the end of the test. It was found that presence of growth reduced the average flashover voltage by 30 %, and increased the leakage currents by 3-4 times, compared to clean reference insulators. Insulators colonized in service showed a lower influence of growth. In the field of diagnostics, laser-induced fluorescence spectroscopy has been explored as a tool for detection of changes on surfaces of composite insulators. Measurements were conducted in laboratory as well as remotely outdoors. These revealed that the fluorescence response was influenced by properties like the hydrophobicity of the surface, presence and type of growth, material composition. As an example, it was found that algae readily could be identified from a distance of 60 m through fluorescence of chlorophyll. To characterize the distribution of (bio)contamination, tools based on digital image analysis were applied. The initial experiments were carried out by using photographs of flat material samples with fungal growth, but later the investigations were expanded to parts of real insulators as well. Measures for characterizing growth patterns were explored, and methods for estimating the length of creepage distance not covered by growth were investigated. Finally, techniques for automatic identification of insulator sheds, based on Hough transform, were developed. This allowed for use of a shed model, taking surface curvature into account when estimating covered area.
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| 5. |
- Dernfalk, Andreas, 1975
(författare)
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Image Analysis for Diagnostics of Insulators with Biological Contamination
- 2002
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Composite insulators have a number of advantages compared to conventional insulators. However, the fact that they are more prone to aging is a major drawback. For instance, biological growths, like algae and fungi, have been found to colonize composite insulators, and possibly effecting the performance of the materials. So far there is a lack of diagnostic methods capable of detecting material changes of composite insulators in the field, and developing new diagnostic methods has thus become very important. One of the main aims of the work presented in this thesis was to elucidate on the influence of biological contamination on the electrical performance of composite insulators. To do this, fungi were grown on silicone rubber insulators and materials samples in a climate chamber, and leakage current measurements were performed occasionally during a period of one year. The measurements were performed under clean fog conditions when applying ac-voltage. In parallel photos of the surfaces of samples and insulators covered with the growth were taken. To characterize the distribution of this contamination, tools based on digital image analysis were applied. The first experiments were performed on images of flat material samples with fungal growth, but later the investigations were expanded to parts of real insulators as well.From the current measurements, it was found that the contaminated insulators always suffered from higher leakage currents than the clean ones. Moreover, discharge activity could be observed on the insulators with fungal growth. Regarding the application of digital image analysis, parameters like total covered area, area of largest cluster and number of clusters were found to be useful in characterizing the distributions. Finally, methods for estimating the length of creepage distance not covered by growth were developed.
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| 6. |
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| 7. |
- Dernfalk, Andreas, 1975, et al.
(författare)
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Laser-induced fluorescence spectroscopy for detection of biological contamination on composite insulators
- 2003
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Ingår i: In Proc. 13th International Symposium on High Voltage Engineering, Delft, Netherlands.
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Konferensbidrag (refereegranskat)abstract
- A new technique for remote detection of biological contamination on high-voltage outdoor insulators has been investigated. The technique, which is based on laser-induced fluorescence (LIF) spectroscopy, has been applied to study surfaces of real silicon rubber insulators from a distance of approximately 60 m. Measurements were performed outdoors on a number of clean, as well as, biologically contaminated insulators. Several types of biological contamination were included, as five of the studied insulators had become covered when installed in Sweden, and another three had been contaminated by fungal growth in laboratory. Fluorescence spectra obtained from the surfaces of the described insulators are presented and the applicability of the technique is discussed and compared with photographic methods.
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