| 51. |
- Abdulahovic, Tarik, 1976
(författare)
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Analysis of High-Frequency Electrical Transients in Offshore Wind Parks
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, a study of high frequency electromagnetic transient phenomena is performed. Models of various components needed for simulations of high frequency transients, such as transformers, cables and breakers are developed. Also, measurements of high frequency transients are performed in the cable laboratory in ABB Corporate Research in Västerås, Sweden for the purpose of parameter estimation of models and for verification of simulations. Some critical cases where the voltage surges of the magnitude and/or rise time above basic lightning impulse voltage level appear, are identified. Also, some transient protection schemes are analyzed and the performance of different transient mitigation devices is studied. Furthermore, the energizing transient of the Utgrunden wind park is analyzed and the simulation model is verified using the measurements.The energizing transient simulation predicted accurately the magnitude and the frequency of the transient voltages and currents. Simulations of the high frequency transients are in a very good agreement with the measurements obtained in the cable lab. Simulations predicted accurately critical surges with the highest magnitude and matched with good accuracy surge waveform recorded during the measurements. During the testing and simulations, surges which exceed the basic lightning impulse voltage level of dry-type transformers specified by IEEE standards, both in magnitude and rise time are observed even when surge arresters are used. It is confirmed both in simulations and measurements that use of additional transient protections devices such as surge capacitors and RC protection, decreased the magnitude of surges below the critical level.
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| 52. |
- Abdulahovic, Tarik, 1976, et al.
(författare)
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Comparison of switching surges and basic lightning impulse surges at transformer in MV cable grids
- 2009
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Ingår i: Nordic Wind Power Conference, Bornholm, Danmark.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The electric transients generated during the switching of a breaker placed near the transformer in a system with a substantial amount of cables can have a very short rise time and can reach very high magnitudes. In practice, the magnitude of the voltage surges is usually limited using the surge arresters while the rise time of the surge to which the apparatus is exposed, remains unchanged.In this paper, the characteristic of the switching transients generated in the MV cable grids are analyzed. For this purpose, cases with both dry-type and oil insulated transformers are studied. These cases are typical for a MV industrial grid and a wind park (WP) collection grid. Furthermore, the case with and without surge arrester protection is analyzed in order to observe the impact of the surge arresters on the voltage surges.Simulations show that the magnitude of the voltage surges exceeds the basic lightning impulse insulation level (BIL) defined by present standards. Furthermore, the rise time of the voltage surges is much shorter compared to the rise time of the lightning impulse especially in the case of the dry-type transformers and the WP collection grid. When surge arresters are used, the magnitude of the surges is limited to the BIL but the rise times of the surges can be twenty five times shorter compared to the BIL. Only when surge arresters are used with other fast transient mitigation equipment such as RC protection or surge capacitor protection, the magnitude of very fast voltage surges are brought down.
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| 53. |
- Abdulahovic, Tarik, 1976, et al.
(författare)
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Modeling of the energizing of a wind park radial
- 2007
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Ingår i: Nordic Wind Power Conference, Roskilde, Denmark.
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Konferensbidrag (refereegranskat)abstract
- This paper presents measurement and modeling ofthe energizing of a wind park radial. The measurements in this paper are taken from the Utgrunden wind park that consists of seven wind turbines each of 1.5 MW rated power. This park is connected to the Öland 55 kV grid at the Degerhamn station. The wind turbines in the Utgrunden wind park are of the pitchregulated doubly-fed induction generator (DFIG) type. The transient voltage and the energizing current graphs are presented and both active and reactive powers are analyzed as the radials to the wind park is connected. Furthermore, the model of the Utgrunden wind park radial is built using PSCAD/EMTDC software. For the cable model, the frequency-dependent (phase) model built in model is used. A built-in model with the saturation modeling is simulated for the purpose of the transients analysis and the results are compared with measurements. The results show that the measured resonance frequency agrees well with the measurements while the damping is underestimated in the simulations.
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| 54. |
- Abdulhamid, Hussam, 1974, et al.
(författare)
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A combined transient in situ FTIR and flow reactor study of NOx storage and reduction over M/BaCO3/Al2O3 (M=Pt, Pd or Rh) catalysts
- 2006
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 244:2, s. 169-182
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Tidskriftsartikel (refereegranskat)abstract
- Transient in situ DRIFTS and flow-reactor experiments were performed to study the storage and reduction of NOX over Pt/BaCO3/Al2O3, Pd/BaCO3/Al2O3, and Rh/BaCO3/Al2O3 samples using CO, H-2, C3H6, or C3H8 as the reducing agent. The DRIFTS results show that exposure of the examined samples to NO2 results in the formation of nitrite/nitrate peaks over alumina and barium and that the reduction of stored NOX is influenced by the type of precious metal and reducing agent. Using CO as the reductant results in a lower NOX reduction capacity for Pt/BaCO3/Al2O3 compared with Pd- and Rh-based samples, whereas H-2 shows a significant ability to reduce the stored NOX on all samples examined. In addition, the reduction with CO and C3H6 proceeds via the formation of isocyanate species over both barium and alumina sites. The intensity of barium-isocyanate species for Pt/BaCO3/Al2O3 is significantly lower than the corresponding intensity for the Pd- and Rh-based samples, suggesting that the interaction between barium and Pt is lower than the corresponding interaction in the Pd/BaCO3/Al2O3 and Rh/BaCO3/Al2O3 samples. (c) 2006 Elsevier Inc. All rights reserved.
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| 55. |
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| 56. |
- Abdulhamid, Hussam, 1974, et al.
(författare)
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In situ FTIR study of SO2 interaction with Pt/BaCO3/Al2O3 NOx storage catalysts under lean and rich conditions
- 2006
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 241:1, s. 200-210
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of SO2 with Pt/BaCO3/Al2O3 NOx storage catalysts under lean and rich conditions in the absence and presence of water was investigated by means of in situ FTIR spectroscopy at 350 degrees C. For the lean condition (SO2 + O-2), surface and bulk barium sulfates were formed in addition to sulfites and surface sulfates on alumina. Pt does not appear to play an essential role in the formation of these species under lean conditions. In contrast, under reducing conditions (SO2 + H-2), Pt catalysed the reduction of SO2 with H-2 to form reduced sulfur species that accumulate on both Pt and barium sites. A subsequent treatment with NO2 resulted in the reduction of NO2 in the oxidation of these sulfur-containing species to form bulk barium sulfate instead of being stored over barium sites. Introducing water significantly affected sulfur trapping over the catalyst surface. During the lean conditions, the presence of water resulted in almost no surface barium sulfate formation. Meanwhile, the formation of bulk barium sulfate was increased, probably due to enhanced sulfate formation. However, the presence of H2O under reducing conditions resulted in significantly lower sulfur storage on both barium and alumina in comparison with humid lean exposure conditions.
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| 57. |
- Abdulhamid, Hussam, 1974, et al.
(författare)
-
Influence of the type of reducing agent (H2, CO, C3H6 and C3H8) on the reduction of stored NOX in a Pt/BaO/Al2O3 model catalyst
- 2004
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30-31:1-4, s. 161-168
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, a comparative study for a NOx storage catalytic system was performed focusing on the parameters that affect the reduction by using different reductants (H2, CO, C3H6 and C3H8) and different temperatures (350, 250 and 150 degrees C), for a Pt/BaO/Al2O3 catalyst. Transient experiments show that H2 and CO are highly efficient reductants compared to C3H6 which is somewhat less efficient. H2 shows a significant reduction effect at relatively low temperature (150 degrees C) but with a low storage capacity. We find that C3H8 does not show any NOx reduction ability for NOx stored in Pt/BaO/Al2O3 at any of the temperatures. The formation of ammonia and nitrous oxide is also discussed.
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| 58. |
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| 59. |
- Abdulhamid, Hussam, 1974, et al.
(författare)
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The reduction phase in NOx storage catalysis: Effect of type of precious metal and reducing agent
- 2006
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 62:3-4, s. 319-328
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Tidskriftsartikel (refereegranskat)abstract
- The effect of different reducing agents (H2, CO, C3H6 and C3H8) on the reduction of stored NOx over PM/BaO/Al2O3 catalysts (PM = Pt, Pd or Rh) at 350, 250 and 150 °C was studied by the use of both NO2-TPD and transient reactor experiments. With the aim of comparing the different reducing agents and precious metals, constant molar reduction capacity was used during the reduction period for samples with the same molar amount of precious metal. The results reveal that H2 and CO have a relatively high NOx reduction efficiency compared to C3H6 and especially C3H8 that does not show any NOx reduction ability except at 350 °C over Pd/BaO/Al2O3. The type of precious metals affects the NOx storage-reduction properties, where the Pd/BaO/Al2O3 catalyst shows both a high storage and a high reduction ability. The Rh/BaO/Al2O3 catalyst shows a high reduction ability but a relatively low NOx storage capacity.
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| 60. |
- Abedi, Parisa, 1968, et al.
(författare)
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Inherent safety evaluation in process plants— a comparison of methodologies
- 2005
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Ingår i: Central European Journal of Chemistry. - 1895-1066. ; 3:4, s. 756-779
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Tidskriftsartikel (refereegranskat)abstract
- Abstract A global population increase and an improved standard of living are generally expected. To meet these demands, an increased production of chemicals will be necessary while protecting human health and the environment. However, most current methods of chemical production are unsustainable. New designs must result in plants that assure process and operator safety, the sustained health of workers and the community, and the protection of the environment. Traditional safety precautions and process controls minimize risk but cannot guarantee the prevention of accidents followed by serious consequences. Therefore, the general approach to environmental and safety problems must be changed from reactive to proactive. One way is to further develop the concept of inherent safety. In this paper some methods for inherent safety evaluations are reviewed. The aim of the study is to analyze the different tools available for inherent safety evaluation and identify the most important criteria in determining the inherent safety of a process plant. A model is proposed to show the interactions of different factors on the inherent safety level of a process and the model is illustrated by a case study.
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