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- Arévalo Gonzalez, Liliana
(författare)
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Numerical simulations of long spark gaps – lightning attachment and its application
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Licenciate Thesis presented here is a research work on numerical simulations of two different electrical phenomena: Long gap discharges under switching impulses and the lightning attachment process of positive upward leaders. The development of a positive upward leader and the process of progress of a discharge in long gaps are composed of two intertwined physical phenomena, namely the leader channel and the corona zone. The physical description and the proposed calculations of above mentioned phenomena are based on experimental tests on long gaps. In the methodology proposed here, a geometrical approximation for the representation of the corona zone is used. Furthermore, two different approaches are applied and compared to represent the leader channel. The used methodologies for the computation of the leader channel are an engineering approximation and a physics equation that takes into account the thermoequilibrium process. In order to introduce a more realistic behavior of the discharge, statistical delays for the inception and for the tortuous characteristic of the channel were brought in. A comparison between a model with or without tortuous channel was implemented. A very good agreement was found between the physical model and the test laboratory results. In addition, based on previous works related to the physics of lightning and the lightning attachment process, a new methodology is developed and tested here. The new approach refines previous calculations; the background electric field and the ionized region considered for the advance of the leader segment are computed within an alternative approach. The proposed methodology was employed to test two engineering methods that are accepted international standards, the mesh method and the electro – geometrical method. The results demonstrated that the engineering approximations are consistent with the physical approach. Besides the electrical phenomena mentioned above, one should keep in mind that there are real effects of the lightning attachment process that are not included or are avoided to simplify the calculation. In fact, when a structure is subjected to a strong electric field, it is possible to generate multiple upward leaders from the structure. This effect has not been taken into account in the different numerical models available until now. The published models consider every upward leader as an individual case. And therefore; a first approximation to the process of generation of multiple upward leaders incepted over a structure is presented here. The preliminary results have shown that it is possible to observe an influence on the background electric field when one leader develops simultaneously with other leaders.
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- Arevalo, Liliana, 1978-, et al.
(författare)
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A new static calculation of the streamer region for long spark gaps
- 2012
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Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 70:1, s. 15-19
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Tidskriftsartikel (refereegranskat)abstract
- Different electrostatic approximations have been proposed to calculate the streamer region without going in deep details of the behavior of density of particles under the effect of high electric fields; this kind of approximations have been used in numerical calculations of long spark gaps and lightning attachment. The simplifications of the streamer region are achieved by considering it to be a geometrical region with a constant geometrical shape. Different geometrical shapes have been used, such as cones or several parallel filaments. Afterward, to simplify the procedures, the streamer region was approximated by two constants, one denoted K-Q, called the geometrical constant and in other cases K named as geometrical factor. However, when a voltage that varies with time is applied to an arrangement of electrodes (high voltage and grounded electrodes), the background electric field will change with time. Thus, if the background electric field is modified, the streamer zone could cover a larger or smaller area. With the aim of reducing the number of assumptions required in the calculation of long gap discharges, a new electrostatic model to calculate the streamer region is presented. This model considers a variable streamer zone that changes with the electric field variations. The three-dimensional region that fulfills the minimum electric field to sustain a streamer is identified for each time step, and the charge accumulated in that region is then calculated. The only parameter that is being used in the calculation is the minimum electric field necessary for the propagation of streamers.
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- Arevalo, Liliana, et al.
(författare)
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Attachment process of the discharge of competing grounded electrodes - Experimental observations and modeling
- 2021
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Ingår i: 2021 35th International Conference on Lightning Protection (ICLP) and XVI International Symposium On Lightning Protection (SIPDA). - : IEEE. - 9781665423465
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Konferensbidrag (refereegranskat)abstract
- The lightning attachment discharge process theory is based on studies of the physics of the discharge obtained from high voltage laboratory tests. The process of propagation of positive and negative discharges has been studied independently and then the gathered information has been used to understand and explain the lightning attachment development. In this paper, an experimental set-up is built to describe the dynamic behavior of positive and negative discharges. Electrodes of different dimensions placed at different distances are used as grounded electrodes and a high voltage electrode is subject to negative switching impulses. Test results allow to identify different stages of the dynamic process of attachment of the discharge between a downward negative discharge and a positive upward leader discharge. The principles of physics of discharge for positive and negative polarities are used to model the laboratory test measurements. The model can reproduce in an accurate manner majority of the dynamic processes of the discharge. In addition, statistical results of the effect of nearby and competing upward discharges is obtained.
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