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- 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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| 2. |
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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. |
- Blennow Tullmar, Peter, et al.
(författare)
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Niobium-doped strontium titanates as SOFC anodes
- 2008. - 4
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Ingår i: Advances in Solid Oxide Fuel Cells III. - 9780470196359 ; 28, s. 203-214
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Konferensbidrag (refereegranskat)abstract
- Sr-vacancy compensated Nb-doped SrTiO3 with the nominal composition Sr0.94Ti09Nb0.1O3 has been evaluated as part of a solid oxide fuel cell (SOFC) anode material in terms of redox stability, electrical conductivity, as well as electrochemical properties. Sr0.94Ti0.9Nb0.1O3 has been synthesized with a recently developed modified glycine-nitrate process. The synthesized powders have been calcined and sintered in air or in 9% H 2 / N2 between 800 - 1400 °C After calcination the samples were single phase Nb-doped strontium titanate with grain sizes of less than 100 nm in diameter on average. The phase purity, defect structure, and microstructure of the materials have been analyzed with SEM, XRD, and TGA. The electrical conductivity of the Nb-doped titanate decreased with increasing temperature and showed a phonon scattering conduction mechanism with σ > 120 S/cm at 1000 °C (in 9 % H2 / N2). The electrochemical properties of Sr0.94Ti0.9Nb 0.1O3 and a composite electrode of Sr 0.94Ti0.9Nb0.1O3/YSZ have been investigated by using a symmetrical cell configuration. The tests indicated that the electrodes were redox stable and showed a potential ability of the Nb-doped titanates to be used as a part of a SOFC anode. However, the catalytic activity of the materials was not sufficient and it needs to be improved if titanate based materials are to be realized as constituents in SOFC anodes.
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