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1
Jamaladdeen, Rawaa. "Investigation on Wildfire Flashovers in the Mediterranean Climate Regions with Emphasis on VOCs Contributions." Electronic Thesis or Diss., Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2023. http://www.theses.fr/2023ESMA0015.
Abstract:
Cette thèse apporte des réponses aux demandes de la communauté des pompiers d'étudier les facteurs probables responsables de l'intensification des régimes de feux de forêt jusqu'aux flashovers en utilisant des approches expérimentales numériques et thermochimiques. Le modèle numérique est un modèle de dispersion de gaz validant les données expérimentales des essais en soufflerie pour résoudre la controverse quant à savoir si les accumulations de composés organiques volatils (COV) dans des topographies confinées finissent par induire des incendies de forêt. Il comprend un front de feu se propageant calculé à l'aide du modèle semi-empirique de feu de surface en régime permanent de Rothermel et de la transition de Van Wagner vers les critères de comportement des feux de cime, avec un taux instable intégré d'émissions de COV simulant ceux évoluant à partir de la combustion de la végétation dans le front de feu. Pour synchroniser nos travaux avec les données de terrain, des expériences thermochimiques ont été menées sur diverses espèces de végétation méditerranéenne afin d'examiner leurs taux d'émission de COV dans des conditions environnementales normales et stressantes, car elles pourraient finir par définir différents scénarios d'inflammabilité lors d'incendies de forêt. Premièrement, deux espèces d'arbustes méditerranéens : Cistus albidus et Rosmarinus officinalis sont explorées pour leurs émissions de COV et leurs changements physiologiques après avoir été soumises à des stress abiotiques (sécheresse et chaleur), à l'aide d'analyses par chromatographie en phase gazeuse par pyrolyse et par spectrométrie de masse (Py-GC/MS). Deux autres espèces forestières méditerranéennes : Quercus suber L. et Cupressus sempervirens horizontalis L. ont été étudiées pour leurs caractéristiques d'inflammabilité distinctives à l'aide d'analyses thermogravimétriques et thermiques différentielles (TG/DTA), couplées à une analyse Py-GC/MS pour identifier les gaz émis. lors des pics exothermiques. Cette étape vise à mieux comprendre les descripteurs d'inflammabilité de ces espèces dans le cadre d'une stratégie de gestion forestière plus efficace par laquelle, en favorisant la plantation de certaines espèces moins inflammables dans les mesures sylvicoles, on pourrait protéger d'autres espèces plus inflammables mais économiquement précieuses, des dangers des incendies de forêt et leurs comportements extrêmes. Les espèces de la végétation méditerranéenne sont d'importants émetteurs de COV, en particulier lorsqu'ils sont provoqués par des stress externes lors d'incendies de forêt. Cependant, certains COV biogènes (COBV), plus particulièrement les sesquiterpènes, ne sont pas encore complètement couverts pour leurs caractéristiques d'inflammabilité, telles que leurs limites inférieure et supérieure d'inflammabilité, leur auto-inflammation, températures, points d'éclair, etc. Une telle lacune scientifique qu'il a fallu enrichir en étudiant les limites d'inflammabilité du β-Caryophyllène, l'un des plus importants sesquiterpènes émis par la végétation méditerranéenne. Des tests préliminaires pour mesurer les pressions de vapeur du β-Caryophyllène sont menés en vue d'expérimenter ses limites d'inflammabilité dans une bombe sphérique comme plans futurs. Les travaux de cette thèse doivent être considérés comme la première étape d'une approche plus globale qui devrait fournir aux personnels opérationnels de lutte contre les incendies un outil d'aide à la décision complet, capable de façonner leurs stratégies de gestion forestière pour protéger les milieux naturels et les pompiers des dangers des comportements extrêmes des incendies de forêtRequests from the firefighting communities are increasing urging the scientific communities to create operational protective and preventive tools that help them understand extreme wildfire behaviors considering not only the atmospheric conditions but also topography, and vegetation characteristics. Thus, our objective was to provide answers to such requests by investigating the probable factors responsible for intensifying wildfire regimes to flashovers using numerical, and thermobiochemical experimental approaches. The numerical model is a gas dispersion model validating experimental data from wind tunnel tests to resolve the controversy of whether or not the volatile organic compounds (VOCs) accumulations in confined topographies end up inducing wildfire flashovers. It comprises a propagating fire front calculated using the Rothermel semi-empirical steady-state surface fire model, and Van Wagner transition to crown fire behavior criteria, with an integrated unsteady rate of VOC emissions simulating the ones evolving from the vegetation burning in the firefront. To synchronize our work with field input, thermochemical experiments were conducted on various Mediterranean vegetation species to examine their VOC emission rates in normal and stressful environmental conditions as they may end up defining different flammability scenarios in wildfires. First, two Mediterranean shrub species: Cistus albidus and Rosmarinus officinalis are explored for their VOC emissions and physiological changes after being subjected to abiotic stresses (drought and heat), using pyrolysis-gas chromatography and mass spectrometry (Py-GC/MS) analyses. Two other Mediterranean forest species: Quercus suber L. and Cupressus sempervirens horizontalis L. were investigated for their distinctive flammability characteristics using thermo-gravimetric and differential thermal analyses (TG/DTA), coupled with Py-GC/MS analysis to identify the gases emitted during the exo-thermic peaks. This step aims to better understand the flammability descriptors of these species as a part of a more efficient forest management strategy by which, favoring the plantation of certain lesser flammable species in silviculture measures may protect other more flammable but economically valuable species, from the dangers of wildfires and their extreme behaviors. Mediterranean vegetation species are important VOC emitters especially when provoked by external stresses during wildfires however, some biogenic VOCs (BVOCs), more particularly sesquiterpenes, are still not thoroughly covered for their flammability characteristics, such as their lower and upper flammability limits, auto-ignition temperatures, flashpoints, etc. Such a scientific lack we found it necessary to enrich by studying the flammability limits of β-Caryophyllene, one of the most important sesquiterpenes emitted from Mediterranean vegetation. Preliminary tests for measuring the vapor pressures of β-Caryophyllene are conducted in preparation for experimenting its flammability limits in a spherical bomb as future plans. The work in this thesis should be considered as the first step in a more global approach that should provide operational firefighting staff, with a comprehensive decision-making tool capable of shaping their forest management strategies from wildfire characteristics themselves and protecting wildlands and firefighters equally from the dangers and extreme behaviors of wildfire flashovers
2
Gerini, Francesco. "Locating lightning strikes and flashovers along overhead power transmission lines using electromagnetic time reversal based similarity characteristics." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Abstract:
Questo lavoro di tesi si pone l’obiettivo di analizzare, verificare e implementare un nuovo metodo per la localizzazione di guasti in rete e fulminazioni basato sulla teoria ”Electromagnetic Time Reversal”. L’applicabilità della teoria è inizialmente discussa, successivamente utilizzando le classiche equazioni delle linee e le basi della teoria EMTR viene proposta una soluzione analitica per la localizzazione del guasto e/o della fulminazione. La accuratezza del metodo utilizzato viene discussa in relazione al numero di misure necessarie alla localizzazione mettendo in evidenza pro e contro rispetto alle tecniche attuali. Viene in seguito presentato un secondo metodo di localizzazione anch’esso basato sulla teoria EMTR ma non ancora verificato su un grande numero di casi, chiamato Similarity Property Method. Utilizzando il software EMTP per l’analisi di transitori e con l’ausilio di MatLab entrambi i metodi vengono testati su diverse tipologie di reti e con diverse condizioni al contorno. Infine una analisi conclusiva viene proposta, indicando come e se i metodi presentati possono essere da considerare migliorativi delle attuali tecniche di localizzazione di guasti e/o fulminazioni.
3
Feasey, R. "Post-Flashover Design Fires." University of Canterbury. Civil Engineering, 1999. http://hdl.handle.net/10092/8266.
Abstract:
This report reviews the modelling of post-flashover fires and compares the various methods of predicting temperature versus time in post-flashover compartment fires, including the historical development of theoretical approaches.
The report specifically addresses the use of the COMPF2 model as implemented in the
COMPF2PC computer programme, as a prediction tool for post-flashover fire temperatures. Aspects of the computer code are compared with theory and experimental data. The results of many COMPF2PC simulations are compared with test fire data, in order to determine how best to characterise the input data to achieve the best simulation results with the computer programme.
It is found that with careful selection of input data, COMPF2PC can provide good prediction of post flashover fire temperatures for compartments with a fire load of greater than15 kg of wood per square metre of floor area, and for ventilation factors
A˯√H/A˕ ≥ 0.04. Reliability of temperature prediction is poorer for ventilation factors
(A˯√H/A˕) significantly less than 0.04.
Guidelines for use of the COMPF2PC programme are provided.
Based on the methodology developed during simulation of test fires, generalised fire temperature versus time curves are developed for a single compartment size and a range of compartment material properties. The generalised COMPF2PC temperature versus time curves are compared with those of alternative models in common use.
It is found that for a fire of fire load 1200 MJ m-² of floor area, in a compartment of medium thermal inertia, depending on ventilation, the COMPF2PC model predicts fires which either have a significantly higher maximum temperature or longer duration (or both), than those predicted by the Eurocode Parametric fire, and the "Swedish" fire model of Magnusson and Thelandersson. This may have a significant impact on the calculation of time equivalent fires.
Recommendations for future development of the COMPF2PC programme are provided.
4
Chen, Aiping. "Empirical and experimental studies of flashover in compartment fire." Thesis, University of Central Lancashire, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410489.
5
Benwell, Andrew L. "Flashover prevention on polystyrene high voltage insulators in a vacuum." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/5018.
Abstract:
Thesis (M.S.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 18, 2008) Includes bibliographical references.
6
Kamel, Sherif I. (Sherif Ibrahim). "Mathematical modeling of wet flashover mechanism of HVDC wall bushings." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28792.
Abstract:
HVDC wall bushings constitute a basic component of converter stations and their adequate performance is vital to insure a highly reliable level of operation. Service records show that the number of flashovers in converter stations has increased substantially during recent years and that the majority of flashovers occurred on HVDC wall bushings. This work presents the first mathematical model to provide the necessary and sufficient conditions for flashover of HVDC wall bushings under nonuniform wetting. The model suggests that the onset of streamers bridging the dry zone and initiated by the nonuniform voltage distribution along the bushing triggers the process of flashover. Fast voltage collapse across the dry zone due to the energy stored in the bushing internal and external leakage and stray capacitance leads to impulsive stressing of the wet part of the bushing. The nonuniform distribution of that impulse and the process of streamer bridging, fast voltage collapse as well as subsequent recharging of the bushing capacitance may lead to consequent discharges and arc propagation along the bushing and eventually to a complete flashover.The random processes associated with the wetting dynamics and pattern as well as the air gaps breakdowns are accounted for in a novel statistical approach to model the flashover process of the HVDC wall bushings under the proposed mechanism.
The work is supported by an experimental investigation into surface resistance and minimum flashover stress of full scale HVDC wall bushings under nonuniform rain.
The findings of the model have been satisfactorily compared with experiments and field observations and can for the first time account for the following aspects of flashover mechanism: critical dry zone length, polarity effect, specific leakage length, wet layer conductance, dry zone position as well as DC system voltage. The model was also used to assess the performance of RTV coated bushings and to compare the strength or an SF$ sb6$ bushing to that of a conventional oil-paper design under nonuniform rain.
7
Martini, Pietro. "Live-line working and evaluation of risk on 400kV transmission line." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/liveline-working-and-evaluation-of-risk-on-400kv-transmission-line(b19247d6-22cc-4815-b865-d80a957dfd7b).html.
Abstract:
Power industries in transmission and distribution level are obligated to maintain and replace their electrical equipment. Maintaining the quality and continuity of supply is their priority to avoid customers' complaints and financial penalisation. Live-line working as one of the most important methods of maintenance has been used since the 1900s where the new methods in 1960s made the live-line workers enabled to work on the higher voltage levels up to 800kV. Various industries adopt different techniques to calculate the minimum approach distance (MAD) during the live-line work. A suitable method reduces the risk to live-line workers and provides adequate safety distances between the live parts and linesmen. Therefore, setting an appropriate safety distance between the linesmen and live parts ensures the safety of the workers and minimise the risk of flashover. In this thesis, different methods of calculation of the minimum approach distance are described, and results from overvoltage simulations are used as an input to the methodology outlined in IEC 61472. Also, this thesis highlights and investigates the impact of a range of factors within 400kV transmission line on the minimum approach distance (MAD). Factors examined include the time to crest of the overvoltage (wave shape), the fault type, the probability of occurrence of each type of fault, fault level and the type of overhead line and towers. Furthermore, the minimum approach distances and also associated risk due to each factor and scenario have been calculated. The calculated risk in this thesis presents the risk of failure of a gap against the switching overvoltages due to the simulation of sources of overvoltage. A new set of estimated equations is developed to consider the influence of wave shape in the calculation of the minimum approach distance (MAD). This thesis does not propose a method to replace the international standards, but it could be used in many situations including where utility companies wish to develop a complete understanding of the risk associated with live-line working. Calculation of the minimum approach distance (MAD) within the National Grid UK is based on the methodology described in the IEC 61472, whereas EDF Energy uses the IEEE method to calculate the minimum approach distance. The choice of a smaller / larger minimum approach distance (MAD) using different methods will have an impact on the risk associated with live-line working. Previous works intend to investigate the magnitude of switching overvoltages on one part of a network and calculate the appropriate minimum approach distance for the work in that section. This work is based on the examination of the switching overvoltages under the worst case scenarios. As a result, the simulated overvoltages in this work are higher than expected overvoltages in National Grid network. Also as in practice, the magnitude of switching overvoltages in National Grid network is controlled by different protections equipment therefore, the simulated results and the calculated minimum approach distances in this work are very conservative.
8
Okubo, Hitoshi, Kenji Tsuchiya, Hiroki Kojima, and Tsugunari Ishida. "Development mechanism of impulse surface flashover on alumina dielectrics in vacuum." IEEE, 2010. http://hdl.handle.net/2237/14535.
9
Patni, Prem K. "Review of models which predict the flashover voltage of polluted insulators." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq23449.pdf.
10
Nielsen, Christian. "An Analysis of Pre-Flashover Fire Experiments with Field Modelling Comparisons." University of Canterbury. Civil Engineering, 2000. http://hdl.handle.net/10092/8284.
Abstract:
Firstly, this report investigates the behaviour of pre-flashover fires conducted in a two-compartment structure. Secondly, it looks at preliminary field modelling results of the pre-flashover fires using the SMARTFIRE program.
A two-compartment structure was built so that pre-flashover fire experiments could be conducted. Each room in the compartment measured 2.4 m wide, 3.6 m long, and 2.4 m high. A doorway, with dimensions 2.0 m high and 0.8 m wide separated the rooms.
All fires were placed in one room (the fire room) where seven fire experiments were conducted consisting of four differently sized fires. Six of the fires, 55 kW, 110 kW, and 160 kW in size were located in the centre of the fire room. The seventh fire was located in the corner of the fire room and was 110 kW in size. Thermocouple trees were located along the centre-line of the compartment so that vertical temperature profiles could be measured; floor and ceiling thermocouples accompanied the thermocouple trees. In addition, gas sampling points measuring O₂ and CO₂ concentrations were positioned evenly throughout the compartment.
Temperature profiles in the fire room revealed constant cool lower layer and hot upper layer temperatures with a sharp temperature gradient between the two layers.
Temperatures in the upper layer for the centrally located fires reached 130°C for the 55 kW fire, 200°C for the 110 kW fire, and 250°C for the 160 kW fire. Temperature profiles in the upper layer for the comer fire were not constant with height but showed a temperature gradient, where the temperature reached 335°C near the ceiling. Temperature profiles in the room next to fire room (the adjacent room) showed constant temperature profiles that were close to the ambient temperature in the lower layer. The upper layer temperature profiles displayed temperature gradients that continued up to the ceiling. Temperatures in the upper layer for the centrally located fires in the adjacent room reached 110°C for the 55 kW fire, 160°C for the 110 kW fire, 200°C for the 160 kW fire, and 225°C for the comer fire.
Preliminary simulations of the four different fire experiments were conducted using the SMARTFIRE field modelling program. Each fire size simulated twice - one with and one without the six-flux radiation sub-model. A qualitative analysis revealed temperatures in the lower layer of the fire room were under predicted. Temperature gradients were predicted for the upper layer temperature profiles for the centrally located fires, rather than the constant upper layer temperature profiles that were seen experimentally. Overall, simulations predicted closer temperature profiles to the experimental results when the six-flux radiation sub-model was incorporated.
11
Tsuchiya, Kenji, Hitoshi Okubo, Tsugunari Ishida, Naoki Hayakawa, and Hiroki Kojima. "Development Process of Impulse Surface Flashover on Alumina Dielectrics in Vacuum." IEEE, 2011. http://hdl.handle.net/2237/20729.
12
Zhou, Jianping. "A study of charge accumulation and spacer flashover in compressed gas insulation." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/32116.
Abstract:
Compressed gas insulated substation (GIS) and transmission line (GITL) equipment have been developed rapidly throughout the world during the past decades. Compactness is the main advantage of GIS and GITL over conventional air-insulated substations and transmission lines. Sulphur hexafluoride (SF₆) is used as an insulation gas in GIS and GITL because of its excellent insulating properties. Supporting spacers are identified as the most likely places for flashover to occur and they often determine the overall strength of a system. For energized system, surface charges have been observed on spacer surfaces and are considered to play an important role for anomalous flashover of a GIS or GITL system. The purpose of this research is to study the mechanisms and factors governing the magnitude and distribution of surface charges and their influence on flashover voltage.
In this investigation, experiments to study surface charge accumulation under different experimental conditions have been conducted, with a rod-spacer-plane electrode system. The parameters varied are applied voltage levels, insulating gases, gas pressures, spacer materials, rod electrode diameters, and the duration of applied voltages. Experiments with impulse voltage pre-charging were also conducted. It was found that the mechanisms of surface charging are corona, gas conduction, and photoionization. Surface charge magnitude and distribution
are strongly field dependent and are related to the duration of voltage application. Spacers in SF₆ gas accumulate less charges on the surface than in air and nitrogen , for a given geometry, spacer material, voltage, and gas pressure.
In order to determine the effect of surface charges on overall electric field, a surface charge simulation program (the SSM program) was developed to calculate the overall electric field when there are surface charges on a spacer surface. The calculation results show that surface charges significantly distort the overall electric field magnitude, field direction, and distributions, which may explain the anomalous flashover in GIS/GITL systems. It was found that the flashover propagation field on a PTFE spacer surface may be between 6 kV/cm and 10 kV/cm.
High speed photographic observations, with an image intensifier, are suggested
to examine the propagation of a flashover. It may, therefore, be possible that, a reasonable model to predict flashover in SF₆ gas can be built by comparing the flashover propagation model with the electric field pattern on a spacer surface.
The role of photoionization near the spacer surface in charge accumulation should also be studied in greater detail.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
13
Hill, Kenneth Harvey. "Estimation of positive polarity switching surge flashover voltage of compact transmission lines." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0013/MQ41715.pdf.
14
Tsuchiya, Kenji, Hitoshi Okubo, Tsugunari Ishida, Hidenori Kato, and Katsumi Kato. "Influence of Surface Charges on Impulse Flashover Characteristics of Alumina Dielectrics in Vacuum." IEEE, 2009. http://hdl.handle.net/2237/14600.
15
Kato, Hidenori, Katsumi Kato, Ayumu Morita, and Hitoshi Okubo. "Influence of Surface Charges on Alumina Dielectrics on Impulse Flashover Characteristics in Vacuum." IEEE, 2008. http://hdl.handle.net/2237/12132.
16
Farzaneh-Dehkordi, Jalil. "Experimental study and mathematical modeling of flashover of EHV insulators covered with ice." Thèse, Chicoutimi : [Rimouski : Université du Québec à Chicoutimi ;. Université du Québec à Rimouski], 2003. http://theses.uqac.ca.
Abstract:
Thèse (M.Eng.) -- Université du Québec à Chicoutimi, programme extensionné a l'Université du Québec à Rimouski, 2004.Bibliogr.: f. 97-104. Document électronique également accessible en format PDF. CaQCU
17
Yii, Ee Hieng. "Modelling the effects of fuel types and ventilation openings on post-flashover compartment fires." Thesis, University of Canterbury. Civil Engineering, 2002. http://hdl.handle.net/10092/7728.
Abstract:
This thesis describes the details used to model a post-flashover fire compartment as a well-stirred reactor. In particular, it examines the two foremost important variables that dictate post-flashover fire behaviour inside the fire compartment. These two variables are: (1) the mass flow rate of air into the compartment via the vent opening and (2) the fuel mass loss rate inside the compartment.
The vent flow analysis shows that the orifice analogy typically used to describe compartment vent flow is restricted to small wall opening applications. For large wall openings, such as a window occupying one whole wall, the flow rate is dictated by the plume entrainment with a flow rate -60% of the flow rate estimated from the orifice theory.
A series of fire experiments using a reduced-scale compartment were conducted to study the vent flow behaviour in a compartment with a horizontal roof opening and a vertical wall opening. Based on the analytical and experimental studies, it is shown that in the case where the roof vent opening is not excessively large and a wall opening having a small downstand, the neutral-plane exists below the soffit of the wall opening giving outflow and inflow through the wall opening and outflow through the roof opening. In such a case, the flows through these openings can be adequately described using an extended form of the vent flow formulation that includes the roof vent opening. The area of the roof vent and the depth of the downstand between the ceiling and the soffit of the wall opening are found to be significant in determining the extra air inflow induced due to the existence of the roof vent opening.
The cellulosic and pool fuels each have different burning behaviour inside a compartment. However, compartment fire temperatures and fuel mass loss rates, from both fuel types, are strongly dependent on the available fuel surface area to ventilation opening ratio and the fuel surface to enclosure area ratio. In the case of thermoplastic pool fires, the ratio between the heat of combustion of air for the fuel and the heat of gasification of the fuel is also found to be influential on the resulting fires.
A post-flashover fire computer program, CFIRE, has been developed that incorporates these findings. The simulation studies performed using the CFIRE computer program show that the fire time-temperature histories of wood fires are highly dependent on the remaining fuel surface area over time. In the case of thin wood, a shorter and hotter fire is expected as it has greater surface area than thick wood, even with the same fuel load. The study also shows that for small ventilation opening, a pool fire inside a fire compartment is less severe than a wood fire because the thermoplastic fuel is easily vaporised under the radiation feedback from the hot surrounding environment and discharged outside the compartment. In the case of large openings, pool fires are more likely to produce a hotter fire in the compartment than wood fires because wood fuel would not have sufficient fuel surface area to achieve ventilation controlled burning.
By comparing these simulated fires with the Eurocode parametric fires, the Eurocode parametric fires do not provide realistic decay rate. With the modified parametric fires, these fires are conservative as they provide envelopes for the simulated fire curves. However, these parametric fires do not clearly describe the fire behaviour of realistic furnishing inside the fire compartment.
18
Rezazada, A. Qayoum. "Modeling of the effect of reduced air pressure on AC flashover voltage of polluted insulators." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=55644.
19
Andersson, Lucas. "Thermal Exposure Caused by the Smoke Gas Layer in Pre-flashover Fires : A Two-zone Model Approach." Thesis, Luleå tekniska universitet, Byggkonstruktion och brand, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-60971.
Abstract:
A pre-flashover fire is very different from a post-flashover fire. The main difference is that in a pre-flashover fire the gas temperature and the radiation temperature differ. One thing that makes it a lot different is that the thermal exposure induced by a pre-flashover fire is largely affected by the smoke gas layer. These smoke gases can be very hot and therefore they emit heat radiation to their surroundings. The theory used, to calculate the thermal exposure of a pre-flashover fire, in this thesis relies on using thermal resistances to describe the heat transfer from the smoke gases. By doing so it is possible to calculate the temperatures of the smoke gases and the surfaces in touch with the smoke gases. Another approach is to use CFD software to numerically calculate the temperatures and in this thesis the two-zone model are compared to FDS, a CFD software. The two-zone model are also compared to a reduced-scale test. The comparisons gave good results, the two-zone model produced similar results compared to re reduced-scale test and FDS. This method of calculating thermal exposure can thereby be used to evaluate evacuation safety and save a lot of calculation time compared to calculating the thermal exposure with CFD software such as FDS.
20
PEREIRA, Carlos Simões. "Processo de attachment, densidade de raios e a ocorrência de flashover em linhas de transmissão de eletricidade." Universidade Federal do Pará, 2014. http://repositorio.ufpa.br/jspui/handle/2011/6555.
Abstract:
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Esta tese refere-se ao uso de modelos de attachment de lideres (Leader Progression Model – LPM) para estimativa da distancia de salto, que, junto com dados de densidade de raios como coletado pelo sistema de detecção de raios do SIPAM, são usados para estimar a taxa de flashover em linhas de transmissão de eletricidade na Amazônia. O modelo de progressão de líder desenvolvido nesta tese é denominado ModSalto, que, para estimar a distancia de salto: 1- integra a densidade linear de cargas elétricas devida ao líder, proporcional a prospectiva corrente de primeira descarga (1º stroke) Ip, para determinar o campo elétrico produzido pelo líder descendente na estrutura sob estudo (para-raios, arestas, condutores, etc.); 2 – integra a distribuição imagem do líder descendente, fazendo uso da característica de poder das pontas como fator de estimulo e intensificação do campo elétrico devido a streamers nas partes aguçadas das estruturas sob estudo, para temporizar o momento do processo de attachment. O gatilho para o líder descendente, por hipótese, se deve a ejeção aleatória de pacotes de cargas elétricas em domínios turbulentos no interior das nuvens que recebem energia por processos de cascata da turbulência geral, e o comportamento do líder descendente, deve obedecer à equação da força de Lorentz, no espaço de campos cruzados elétrico devido às nuvens a cima e o campo magnético da Terra, que obriga as cargas do líder a desenvolverem movimentos cicloidais que podem explicar a natureza tortuosa do trajeto do líder descendente. Com o objetivo de formalizar dados consistentes de densidade de raios é feita uma reanalise do conjunto de dados coletado pelo LLS SIPAM de outubro de 2006 a julho de 2008 na região amazônica, com cerca de 3 milhões de eventos, comparando-os com dados de torres instrumentadas para evidenciar-se sua qualidade e usabilidade. Dados de elevação de terreno do SRTM da NASA são usados para gerar formula do raio de atração (Ra) das estruturas passiveis de serem atingidas por raios e para gerar formulas de área de atração, usadas para quantificar o numero de raios que provavelmente atingirão determinada estrutura, baseado no valor de densidade de raios (raios/km2/ano) na área em estudo.
This thesis refers to the use of leaders attachment model (Leader Progression Model - LPM) in the estimation of striking distance values and jointly use of lightning density data gathered by a LLS System to estimate the flashover rate of electricity transmission lines in the Amazon region. The leader progression model developed here is called ModSalto, and to estimate the striking distance, it: integrate the linear density of the leader electric charge proportional to the prospective lightning first stroke (Ip) to estimate the electric field produced by the descending leader, in the tip of the structure under study (arrester, electric conductor, etc.); makes integration of the image leader charge distribution and makes use of the power of tips as a stimulus and intensification factor for the electric field due to the streamers on the edge of the structure under study, to time the attachment process. The trigger of the descending leader is hypothesized to be on behalf of packets of charges turbulent domains in cloud, and the leader's behavior on the descending path is hypothesized to obey the equation of the Lorentz force in the space of movement of electric charges of the leader, influenced by crossed electric field due to the electrification of the clouds and the Earth's magnetic field, which imprints a cycloid motion on the leader’ tip electric charges which may explain the stepped and tortuous nature of the downward leader. The LFR parameters (Lightning Flashover Rate) is presented as an estimate of the probability of occurrence of flashover induced by lightning on an electric transmission line, that may be derived by a defined parameter Jv (Vulnerability Window) as a quantifying factor to the probability of insufficient protection provided by the EGM model to the transmission line, protected against lightning with use of shielding conductors (shield wire). With the aim to get a usable lightning density data, we do a reanalyze of the dataset of occurrence of lightning collected by LLS SIPAM, from October 2006 to July 2008 in the amazon region, with over 3 million hits, comparing them with data from instrumented towers allowing an assessment of the quality of such data. Terrain elevation data (SRTM) from NASA are used to generate attraction radius (Ra) formulas that takes into account the height of the structures and jointly with Log Normal distribution parameters describing the statistical behavior of first pulse current values (stroke) of the lightning, as estimated by LLS SIPAM, to generate a summation or integration area of attraction formula, used in the quantification of the number of lightning which are likely to hit a given structure, depending on the density of lightning (lightning / km2 / year) at the study site.
21
Fielding, Trevor J. "An investigation of the field electron emission processes responsible for the flashover of high voltage vacuum devices." Thesis, Aston University, 1986. http://publications.aston.ac.uk/8050/.
22
Kleinhans, Kevin. "Investigation into possible mechanisms of light pollution flashover of 275kv transmission lines as a cause of unknown outages." Thesis, Link to the online version, 2005. http://hdl.handle.net/10019/1071.
23
Studhalter, Jakob. "A probabilistic comparison of times to flashover in a compartment with wooden and non-combustible linings considering variable fuel loads." Thesis, University of Canterbury. Department of Civil and Natural Resources Engineering, 2012. http://hdl.handle.net/10092/7650.
Abstract:
Prescriptive fire safety codes regulate the use of combustible room linings to reduce fire risk. These regulations are based on classification systems which designate materials according to their relative hazard when exposed to a standard fire scenario. However, no quantitative data sets on the fire risk of wooden lining materials exist which take into account relevant uncertainties, such as movable fuel loads in compartments.
This work is a comparative risk analysis on the influence of wooden linings on the time to flashover in a compartment, considering uncertainties in the fuel load configuration. A risk model is set up for this purpose using B-RISK, a probabilistic fire design and research tool currently under development at BRANZ (Building Research Association of New Zealand) and the University of Canterbury. The risk model calculates fire spread in a compartment between fuel load items and from fuel load items to combustible linings. Multiple iterations are performed considering varying fuel load arrangements and input values sampled from distributions (Monte-Carlo simulation).
The functionality and applicability of the risk model is demonstrated, comparing the model with experiments from the literature. The model assumptions are described in detail. Some of the model inputs are defined as distributions in order to account for uncertainty. Parametric studies are conducted in order to analyse the sensitivity of the results to input parameters which cannot be described as distributions.
Probabilistic times to flashover are presented and discussed for an ISO 9705 compartment considering varying movable fuel loads and different lining configurations. The fuel load is typical for a hotel room occupancy. Effects of suppression measures are not considered. It is shown that flashover occurs approximately 60 seconds earlier if walls and ceiling are lined with wooden materials than if all linings are non-combustible. This value refers to the 5th percentiles of the time to flashover, i.e. in 5% of the cases flashover has occurred and in 95% of the cases flashover has not (yet) occurred. Referring to 50th percentiles (median values), the difference is approximately 180 seconds.
Furthermore it is shown that with wooden wall and ceiling linings in approximately 95% of
the iterations flashover occurs, whereas with non-combustible linings 86% of the iterations lead to flashover. After 900 seconds, in 90% of the iterations flashover occurs if walls and ceiling are lined with wooden materials, and in 77% of the iterations if the linings are non-combustible. Using different wooden lining materials (non-fire retardant plywood, fire retardant plywood, and MDF) has no significant effect on the probabilistic times to flashover. Varying the fuel load energy density has an influence only when all linings are non-combustible and when the fuel load energy density is relatively low (100–200 MJ/m2).
This work contains recommendations regarding the further development of B-RISK, the research into the fire risk connected with wooden room linings, and suggestions regarding the further development of prescriptive fire safety codes.
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Alles, Joan. "Investigations on flashover of polluted insulators : Influence of silicone coating on the behavior of glass insulators under steep front impulse." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC058.
Abstract:
Cette thèse s’inscrit dans le cadre de l’amélioration du comportement électrique des isolateurs de lignes haute tension ; l’objectif est d’assurer une meilleure fiabilité et qualité d’alimentation en énergie électrique. Ce travail a été motivé par la nécessité de répondre à trois questions liées au comportement des isolateurs verre en zone polluée. La première porte sur la recherche d’une méthode permettant de calculer la tension de contournement des chaînes polluées selon le type d’isolateur et ses caractéristiques. La deuxième question concerne la différence de comportement entre les isolateurs en verre et les isolateurs en porcelaine de type « outerrib » ; ce type d’isolateurs présente une forme spécifique adaptée aux environnements à forte pollution. Les tensions de contournement ainsi que les trajectoires de l’arc sur les isolateurs en verre sont très différentes de celles observées avec les isolateurs en porcelaine. Et la troisième question est relative à la défaillance des isolateurs recouverts de silicone lors des essais en chocs (des impulsions de tension) à front raide. En effet, les isolateurs recouverts d’une couche de 0.3 mm (ou plus) de silicone hydrophobe explosent lorsqu’ils sont soumis à des impulsions de tension à front raide d’amplitude très élevée pendant un temps très court. Différents mécanismes pouvant être à l’origine de l’explosion/éclatement des isolateurs recouverts d’une couche de silicone sont discutés. Il ressort des différents tests et analyses que le mécanisme le plus probable semble être la fragmentation par plasma. En effet, suite à l’application d’une tension à front raide, d’amplitude très élevée, des canaux (fissures) microscopiques prennent naissance là où le champ électrique est le plus intense. L’application répétitive des chocs de tension conduit au développement de décharges dans ces canaux (rupture diélectrique de l’air) c’est-à-dire des arcs (canaux de plasma) qui se développent/propagent dans le volume de l’isolateur. La puissance déchargée (c’est-à-dire l’énergie stockée dans les condensateurs du générateur en des temps très courts) dans ces canaux à chaque choc étant très élevée, elle conduit à l’explosion de l’isolateur après quelques chocs (parfois 5 ou 6 suffisent): c’est la fragmentation par plasmaThis thesis deals with the improvement of the electrical behavior of insulators of high voltage lines; the objective is to ensure better reliability and quality of power supply. This work was motivated by the need to answer three questions related to the behavior of glass insulators in polluted areas. The first one concerns the search for method for calculating the flashover voltage of polluted chains according to the type of insulator and its characteristics. The second question concerns the difference in behavior between glass insulators and "outerrib" porcelain insulators; this type of insulator has a specific shape adapted to environments with high pollution. The flashover voltages as well as the trajectories of the arc on glass insulators are very different from those observed with porcelain insulators. And the third issue is the failure of silicon-coated insulators during shock tests (pulses) with a steep front. Indeed, insulators coated with a layer of 0.3 mm (or more) of hydrophobic silicone explode when subjected to very high amplitude steep-edge voltage pulses for a very short time. Different mechanisms that may be responsible for the explosion / puncturing of insulators covered with a layer of silicone are discussed. It appears from the various tests and analyzes that the most probable mechanism seems to be plasma fragmentation (cracking). Indeed, following the application of a steep front voltage, of very high amplitude, microscopic channels (fissures) originate where the electric field is most intense. The repetitive application of impulse voltages (shocks) leads to the development of discharges in these channels (breakdown of the air), i.e.; arcs (plasma channels) which develop / propagate in the volume of the insulator. The discharged power (i.e.; the energy stored in the capacitors of the generator in a very short times) in these channels (cracks) at each shock being very high, leads to the explosion of the insulator after some shocks (5 to 6 sometimes): it is the fragmentation by plasma or plasma cracking
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Byström, Alexandra. "Compartment Fire Temperature Calculations and Measurements." Doctoral thesis, Luleå tekniska universitet, Byggkonstruktion och brand, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-59927.
Abstract:
This thesis is devoted to heat transfer and fire dynamics in enclosures. It consists of a main part which summarizes and discusses the theory of heat transfer, conservation of energy, fire dynamics and specific fire scenarios that have been studied. In the second part of this thesis, the reader will find an Appendix containing seven scientific publications in this field. In particular, one- and two-zone compartment fire models have been studied. A new way of calculating fire temperatures of pre- and post-flashover compartment fires is presented. Three levels of solution techniques are presented including closed form analytical expressions, spread-sheet calculations and solutions involving general finite element temperature calculations. Validations with experiments have shown good accuracy of the calculation models and that the thermal properties of the surrounding structures have a great impact on the fire temperature development. In addition, the importance of the choice of measurement techniques in fire engineering has been studied. Based on the conclusions from these studies, the best techniques have been used in further experimental studies of different fire scenarios.Denna avhandling behandlar problem kopplade till värmeöverföring och branddynamik i slutna utrymmen med tonvikt på värmeöverföring mellan gaser och utsatta konstruktioner. Avhandlingen består av en huvuddel och ett appendix innehållande sju vetenskapliga artiklar. I huvuddelen sammanfattas och diskuteras grundläggande teorier och principer inom värmeöverföring och branddynamik samt studier av ett antal specialfall av brandscenarion som baseras på dessa teorier. I de avslutande bilagorna (Artiklar A1-A3 och Artiklar B1-B2) finns sju vetenskapliga artiklar som grundligare beskriver de ovan nämnda specialfallen. Huvudfokus i avhandlingen ligger på temperaturutveckling vid brand i slutna utrymmen. I avhandlingen studeras i synnerhet en- och två-zonsmodeller för brand i slutna utrymmen, och en ny metod för att beräkna brandgastemperaturer före och efter övertändning i rumsbränder är framtagen. Validering av dessa modeller med experiment visar att deras noggrannhet är bra. Modellerna visar också att de termiska egenskaperna hos de omgivande ytorna har stor inverkan på brandtemperatursutvecklingen. I tillägg studeras i denna avhandling betydelsen av val av mätmetoder i brandtekniska tillämpningar. På grundval av slutsatserna från dessa studier har de främsta mätteknikerna använts i ytterligare experimentella studier av olika brandscenarier.
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Wardman, John Blackburn. "Vulnerability of Electric Power Systems to Volcanic Ashfall Hazards." Thesis, University of Canterbury. Geological Sciences, 2013. http://hdl.handle.net/10092/8014.
Abstract:
Volcanic eruptions are powerful natural events which impact strongly on society. As human populations grow and expand into volcanically active areas, their exposure and vulnerability to volcanic hazards is also increasing. Of all volcanic hazards, ashfall is the most likely to impact lifelines because of the large areas affected. The widespread dispersal of ash can cause large-scale disruption of vital infrastructure services, aviation, and primary production. Electric power supply is arguably the most crucial of modern infrastructure systems, especially considering the dependence of other sectors on electricity to maintain functionality.
During and immediately after ashfalls, electric power systems are vulnerable to a number of impacts, but disruption from volcanic ash-induced insulator flashover (unintended, disruptive electrical discharge) is most common. This thesis investigates the vulnerability of electric power systems to volcanic ashfall by examining impacts to the different sectors of the modern power system and exploring appropriate mitigation strategies. Analogue laboratory trials using a pseudo (synthetic) ash are undertaken to verify the environmental, volcanological and electrical parameters that most affect electrical conductivity and therefore the flashover mechanism in these experiments. While dry ash is highly resistant to the flow of electric current, increasing moisture content, soluble salt load, and compaction (bulk density) will reduce this resistance and, in turn, increase the potential for flashover.
Volcanic ash is an acute form of airborne pollution for areas downwind of active volcanoes. Results from laboratory experiments in this thesis suggest that insulator pollution (volcanic ash) performance (dielectric strength) is primarily dictated by (1) the conductivity of the ash, and (2) insulator material, profile (shape) and dimensioning. Composite polymer insulators tested herein effectively minimise sinusoidal leakage current and partial discharge activity and also exhibit higher pollution performance when compared to ceramic equivalents. Irrespective of insulator material, however, the likelihood of flashover increases significantly once the bottom surface of suspension insulator watersheds become contaminated in wet ash.
The thesis investigates the vulnerability (hazard intensity/damage ratio) of electric power systems to volcanic ashfall hazards. Identification, analysis, and reduction of the risk of ashfall impacts to power networks is explored as a part of holistic volcanic risk assessment. The findings of the thesis contribute to the readiness, response and recovery protocols for large electric power systems in volcanic disasters; which directly affects the functional operation and economics of industrial and commercial society.
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Cortés, Daniel. "Modelado y simulación para la predicción de explosiones en espacios confinados." Doctoral thesis, Universidad de Alicante, 2021. http://hdl.handle.net/10045/115293.
Abstract:
Los incendios en recintos confinados son un tipo de emergencia que involucra a bomberos cuyas vidas a veces se ponen en peligro. En cualquier incendio confinado, el equipo de emergencia puede encontrar dos tipos de ambientes de combustión, ventilados o infra-ventilados. El comportamiento cambiante de este escenario depende de múltiples factores como el tamaño del recinto, la ventilación o el combustible involucrado, entre otros. Sin embargo, la dificultad de manejar este tipo de situaciones junto con el potencial error humano sigue siendo un desafío sin resolver para los bomberos en la actualidad. En ocasiones si se dan las condiciones adecuadas, pueden aparecer los fenómenos, extremadamente peligrosos, que son estudio de este trabajo (flashover y backdraft). Por lo tanto, existe una gran demanda de nuevas técnicas y tecnologías para abordar este tipo de emergencias que amenazan la vida y puede causar graves daños estructurales. A lo anterior hay que añadir que la incorporación de cámaras térmicas en los servicios de extinción de incendios y salvamentos, supone un gran avance que puede ayudar a prevenir estos tipos de fenómenos en tiempo real utilizando técnicas de inteligencia artificial.
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Slama, Mohammed El-Amine. "Etude expérimentale et modélisation de l'influence de la constitution chimique et de la répartition de la pollution sur le contournement des isolateurs haute tension." Thesis, Ecully, Ecole centrale de Lyon, 2011. http://www.theses.fr/2011ECDL0023/document.
Abstract:
Ce travail porte sur la caractérisation optique et électrique ainsi que la modélisation mathématique du contournement d’isolateurs pollués en tenant compte de la forme de tension appliquée, de la répartition ainsi que de la constitution chimique du dépôt polluant. Sous tension de choc de foudre (1,2/50μs), la morphologie des décharges ainsi que les courants associés dépendent de la tension (forme, amplitude, polarité),de la répartition de la pollution et de sa conductivité. Les vitesses moyennes de la décharge mesurées dépendent de la polarité appliquée à la pointe et de la conductivité de la pollution. Le temps critique correspondant aux conditions critiques est de l’ordre de 9/10 du temps total de contournement quelles que soient la polarité de la tension et la conductivité de la pollution. La constitution chimique de la couche de pollution a peu d’effet sur la tension critique contrairement aux courants critiques. Les valeurs des constantes caractéristiques n et N sont fonction de la nature chimique des dépôts et de la polarité de la tension. Le modèle élaboré montre que les constantes caractéristiques de la décharge n et N sont des paramètres dynamiques et dépendent des éléments du circuit électrique équivalent du système et des paramètres thermiques de la décharge. Les relations des conditions critiques du contournement développé relient les paramètres électriques et thermiques du circuit équivalent et la condition de propagation de la décharge. L’application de ce modèle, pour différentes formes de tension et pour plusieurs types de pollution, donne des résultats satisfaisants. L’hypothèse selon laquelle la colonne de la décharge ne contient que de la vapeur d’eau et de l’air constitue une bonne approximation des grandeurs critiques. Sous tension de choc de foudre, les courants et les tensions critiques dépendent de la configuration de la pollution et de la polarité de la tension. Le courant circule à travers une section effective de la pollution. L’introduction de la notion d’épaisseur critique effective et son application au calcul des grandeurs critiques donne de bons résultats pour les cas de figures étudiés. L’épaisseur effective du dépôt est proportionnelle la résistivité de la pollution et dépend dela configuration de la pollution et de la polarité de la pointe. Dans le cas de dépôt de pollution discontinue et/ou non uniforme, les conditions de propagation des décharges sont locales et leurs paramètres caractéristiques varient selon la configuration et la conductivité du dépôt ainsi que la polarité de la tension appliquée. Le modèle développé pour ce cas de figure donne de bons résultatsThis work aimed on optical and electrical characterization and mathematical modeling of flashover of polluted insulators, taking into account the applied voltage waveform, the distribution and chemical composition of pollutant deposit. Under lightning impulse voltage (1.2 /50μs), the morphology of the discharge and the associated currents depend on voltage (shape, amplitude, polarity), the distribution ofpollution and its conductivity. The measured average velocity of the discharge depends on the polarity applied to the tip and the pollution conductivity. The critical time corresponding to the critical conditions is about 9/10 of total flashover duration regardless of the polarity of the voltage and the pollution conductivity. The chemical composition of the pollution layer has little effect on the critical voltage unlike the critical currents. The values of the characteristic constants n and N depend on the chemical nature of the deposits and the voltage polarity.The developed model shows that the discharge constant characteristics n and N are dynamic parameters and depend on the elements of the equivalent electrical circuit system and thermal parameters of the discharge. The developed relationships of critical conditions of flashoverlink the electrical parameters and thermal equivalent circuit and the propagation condition of the discharge. This approach allows us tounderstand the effect of the chemical constitution of pollution on the values of n and N. The application of this model for various voltage waveforms and for several types of pollution, gives satisfactory results. The assumption that the column of the discharge contains only watervapor and air is a good approximation of the critical conditions. Under lightning impulse voltage, the current circulate into a effective section of the pollution surface. The introduction of the concept of critical effective thickness of pollution and its application to the calculation ofcritical parameters gives good results compared with the experimental values. We have also shown that the effective thickness of the depositis proportional to the resistivity of the pollution and depends on voltage polarity and pollution configuration. In the case of discontinuous deposit of pollution and / or non-uniform propagation conditions of discharges are local and their characteristic parameters vary dependingon the configuration and the conductivity of the deposit and the polarity of the applied voltage. The developed model gives good results
29
Parkes, Anthony Richard. "The impact of size and location of pool fires on compartment fire behaviour." Thesis, University of Canterbury. Civil and Natural Resources Engineering, 2009. http://hdl.handle.net/10092/3444.
Abstract:
An understanding of compartment fire behaviour is important for fire protection
engineers. For design purposes, whether to use a prescriptive code or performance
based design, life safety and property protection issues are required to be assessed. The
use of design fires in computer modelling is the general method to determine fire safety.
However these computer models are generally limited to the input of one design fire,
with consideration of the complex interaction between fuel packages and the
compartment environment being simplified. Of particular interest is the Heat Release
Rate, HRR, as this is the commonly prescribed design parameter for fire modelling. If
the HRR is not accurate then it can be subsequently argued that the design scenario may
be flawed. Therefore the selection of the most appropriate fire design scenario is
critical, and an increased level of understanding of compartment behaviour is an
invaluable aid to fire engineering assumptions.
This thesis details an experimental study to enhance the understanding of the impact and
interaction that the size and location of pool fires within an enclosure have upon the
compartment fire behaviour. Thirty four experiments were conducted in a reduced scale
compartment (½ height) with dimensions of 3.6m long by 2.4m wide by 1.2m high
using five typical ventilation geometries (fully open, soffit, door, window and small
window). Heptane pool fires were used, located in permutations of three evenly
distributed locations within the compartment (rear, centre and front) as well as larger
equivalent area pans located only in the centre. This thesis describes the experimental
development, setup and results of the experimental study. To assist in the classification
of compartment fire behaviour during the experiments, a ‘phi’ meter was developed to
measure the time dependent equivalence ratio. The phi meter was developed and
configured to measure O₂, CO₂ and CO. The background development, calibration, and
experimental results are reported. A review of compartment fire modelling using Fire
Dynamics Simulator, has also been completed and the results discussed.
The results of this experimental study were found to have significant implications for
Fire Safety Engineering in that the size of the fire is not as significant as the location of
the fire. The effect of a fire near the vent opening was found to have a significant impact
on compartment fire behaviour with the vent located fuel source increasing the total
compartment heat release rate by a factor of 1.7 to that of a centrally placed pool fire of
the same total fuel area. The assumption that a fire located in the centre of the room
provides for the highest heat release rate is not valid for post-flashover compartment
fires. The phi meter was found to provide good agreement with the equivalence ratio
calculated from total compartment mass loss rates, and the results of FDS modelling
indicate that the use of the model in its current form can not be applied to complex pool
fire geometries.
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Douar, Adnane. "Recherche de matériaux isolants pour la conception d'une nouvelle génération de connecteurs électriques haute tension : influence de la pollution sur les phénomènes de décharges partielles du contournement et de claquage." Thesis, Ecully, Ecole centrale de Lyon, 2014. http://www.theses.fr/2014ECDL0046/document.
Abstract:
Dans le présent travail, nous abordons une problématique essentielle liée aux accessoires des lignes électriques et plus particulièrement au connecteur à perforation d’isolant (TTDC 45501 FA), commercialisé par la société Sicame située à Arnac-Pompadour (Corrèze). Ce produit permet d’effectuer des dérivations de courant en moyenne tension gainé HTA entre 15 et 25kV. Cependant, il devient nécessaire de concevoir une nouvelle génération de connecteurs capable de fonctionner à une tension de 52 kV en raison de la constante augmentation des besoins en électricité. En réalité, le principal souci concernant ces produits réside dans l’apparition de décharges partielles dans le volume constitué par la matière isolante (polyamide 6 chargée à 50% en poids de fibres de verre). Ces décharges engendrent un vieillissement prématuré du produit sous l’action conjuguée d’une atmosphère corrosive (brouillard salin) et d’un champ électrique. Ainsi, l’objectif de la présente thèse est de faire, dans un premier temps, un choix approprié de matériaux isolants parmi des polymères thermoplastiques, thermodurcissables époxydes ou élastomères en EPDM, capables de résister à plusieurs contraintes : thermique, électrique, mécanique, chimique et climatique. La partie expérimentale concerne, tout d’abord, la mesure de la tension de contournement, de l’activité des décharges partielles se propageant à la surface des matériaux isolants et de la tension de claquage, en tension alternative (A.C.). Pour cela, des échantillons polymères qui comportent des surfaces planes ou des surfaces pourvues de protubérances ont été moulés en vue de comparer leur comportement diélectrique en présence d’atmosphères polluées de type brouillard salin; ces mesures sont nécessaires pour effectuer un choix approprié du matériau à intégrer dans le connecteur. Par la suite, l’étude et la caractérisation optique et électrique de décharges glissantes, se propageant en surface de divers matériaux polymères, en tension impulsionnelle (L.I.) pour les deux polarités (positive et négative) et pour deux types de champ électrique (normal et tangentiel) sont présentées pour le cas d’une interface solide/air. La mesure de la longueur finale des décharges glissantes et la visualisation de l’onde de courant sont les deux paramètres principaux pour différencier les caractéristiques des matériaux utilisés. L’ensemble des résultats de mesures a permis de sélectionner les résines époxydes cyclo-aliphatiques (CEP) comme candidates potentielles pour la conception d’une nouvelle génération de connecteurs. De plus, la simulation du champ électrique, à l’aide du logiciel Flux 2D/3D, sur le connecteur électrique (TTDC 45501FA) a permis d’aboutir à la proposition d’un prototype de connecteur présentant une nouvelle géométrie et pouvant fonctionner à 52kVIn the present study, we deal with an essential problem related to electrical lines accessories and more particularly to piercing connectors (TTDC 45501FA) commercialized by a private company named Sicame and which is located in Arnac-Pompadour (Corrèze, France). This product/accessory is designed to provide power diversions on medium voltage live lines HVA operating between 15 and 25kV. However, it becomes required to design a new generation of piercing connectors able to operate on 52kV live lines because of the electrical power demands that are steadily increasing. Actually, the main concerns about these products are the occurrence of partial discharges within the insulating material volume (polyamide 6 containing 50%wt of glass fibers). Most of the time, these discharges induce an early ageing process of the accessory under the combined effects of a corrosive environment (as salt fog) and an electric field threshold. Thus, the main objective of the present Ph.D. thesis is to carry out an appropriate choice of insulating materials among several tested polymers such as thermoplastics and thermosetting epoxy resins and EPDM elastomers that are capable of withstanding several constraints: thermal and electrical and mechanical and chemical conditions. The experimental section is focusing on the measurements of flashover voltage and partial discharges activity propagating on polymeric surfaces and breakdown voltage within material bulks under A.C voltage. That is why polymeric samples with plane surfaces and textured surfaces are molded to compare their resistance to partial discharges when being subjected to polluted environments such as salt fog; these measurements are necessary to choose the suitable materials for the required application to be integrated in the new generation of connectors. Then, the optical and electrical characterization results of creeping discharges propagating on several polymeric surfaces under lightning impulse (L.I.) voltage with its both polarities (positive and negative) and for two kinds of applied electric field (normal and tangential) are presented in the case of solid/air interfaces. Final length measurements of creepage discharges are the main parameter for distinguishing material properties. The whole obtained results (under AC and LI voltages) allow us to point out the cycloaliphatic epoxy resins as potential candidates to the conception of a new generation of piercing connectors. In addition, the electric field simulation and modelling of the TTDC 45501FA connector by using the Flux 2D/3D software seems to be helpful to design a connector prototype which exhibits a new geometry and is able to reach a voltage level that equals 52kV
31
"Three dimensional flame reconstruction towards the study of fire-induced transmission line flashovers." Thesis, 2007. http://hdl.handle.net/10413/2076.
Abstract:
The work presented in this thesis focuses on the problem of reconstructing threedimensional models of fire from real images. The intended application of the reconstructions is for use in research into the phenomenon of fire-induced high voltage flashover, which, while a common problem, is not fully understood. As such the reconstruction must estimate not only the geometry of the flame but also the internal density structure, using only a set of a few synchronised images. Current flame reconstruction techniques are investigated, revealing that relatively little work has been done on the subject, and that most techniques follow either an exclusively geometric or tomographic direction. A novel method, termed the 3D Fuzzy Hull method, is proposed, incorporating aspects of tomography, statistical image segmentation and traditional object reconstruction techniques. By using physically based principles the flame images are related to the relative flame density, allowing the problem to be tackled from a tomographic perspective. A variation of algebraic tomography is then used to estimate the internal density field of the flame. This is done within a geometric framework by integrating the fuzzy c-means image segmentation technique and the visual hull concept into the process. Results are presented using synthetic and real flame image sets.Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.
32
Taheri, Ledari Shamsodin. "Two-arc dynamic modeling of AC and DC flashovers of EHV post station insulators covered with ice based on laboratory experiments." Thèse, 2014. http://constellation.uqac.ca/2786/1/030620915.pdf.
Abstract:
L'accumulation de glace et de neige sur les isolateurs a été reconnue comme l'un facteur de risque les plus importants dans la fiabilité des lignes de transmission aériennes et des postes électriques. La glace accumulée sur les isolateurs peut amorcer des décharges électriques le long des zones exempts de glace, souvent appelés espaces d'air. En présence d'un film d'eau très conducteur à la surface de la glace, sous une tension appliquée suffisamment élevée, des décharges partielles peuvent être initiées et se développer en arcs partiels. Sous certaines conditions, ces arcs partiels peuvent entraîner le contournement total de la chaîne d'isolateurs et provoquer des pannes d'électricité.
L'objectif général de cette recherche est d'étudier le phénomène du contournement électrique des isolateurs de poste extra-haute tension (THT) recouverts de glace. Ainsi, des modèles dynamiques à deux arc, basées sur des modèles mathématiques existants a été proposé pour prédire les paramètres du contournement en courant continu (CC) et alternatif (CA). Le modèle considère l'arc comme une impédance dépendant du temps, constituée d'une résistance en série avec une inductance. La couche de glace résiduelle est définie en termes de résistance équivalente, où la conductivité surfacique équivalente est calculée en tenant compte du film d'eau coulant à la surface de la glace. La présente contribution propose une nouvelle approche permettant de déterminer la conductivité surfacique équivalente. Cette approche est basée sur des concepts de mécanique des fluides incluant les équations de Navier-Stokes, ainsi que sur une série d'expériences menées pour quantifier le débit du film d'eau et la conductivité surfacique équivalente.
De plus, les mécanismes à l'origine de l'amorçage des décharges et du développement de l'arc sur la surface de la glace accumulée sur les isolateurs ont été étudiés. Une attention particulière a été accordée à l'évaluation de l'effet de la conductivité volumique de la surface de la glace sur la vitesse de propagation de l'arc pour différentes conductivités de l'eau de congélation, en utilisant des techniques d'enregistrement par caméras vidéo à haute vitesse.
Les modèles proposés ont été validés avec succès en laboratoire sur des isolateurs de poste - généralement utilisés dans Hydro-Québec 735 kV - sous tensions CA et CC. La tension de tenue maximale en CC et CA ont été déterminées expérimentalement basés sur la norme IEEE Std 1783. En outre, l'influence du nombre et la position des intervalles d'air sur le contournement des isolateurs recouverts de glace a été étudiée expérimentalement. Les résultats expérimentaux ont montré que la configuration des espaces d'air affecte significativement la tension de tenue maximale. Les principales caractéristiques de contournement, comprenant la tension minimale de contournement et le courant de fuite, prédits par le modèle dynamique à deux arc proposé, concordent à la variation des principaux paramètres, à savoir, la longueur de 'isolateur et la conductivité de l'eau de congélation.
Enfin, pour interpréter la performance des isolateurs sous différentes positions des espaces d'air, les distributions de champ électrique et tension le long de l'isolateur recouvert de glace ont été simulés numériquement au cours de la période de fonte, en utilisant la méthode des éléments finis (MEF). Les résultats de simulations confirment que l'augmentation du nombre d'espace d'air améliore la tension de tenue maximale ainsi que l'uniformité de la distribution de tension le long des isolateurs de poste THT. Selon les résultats obtenus, l'utilisation des jupes d'appoint (booster sheds) et anneaux de garde pour améliorer les performances d'isolation des isolateurs de poste dans des conditions de givrage est recommandé.
Cette recherche peut être considérée comme une base importante pour le développement de modèles multi-arc et un outil puissant pour la conception et le choix des isolateurs THT soumis à l'accumulation de glace.
-
Ice and snow accretion on insulators has been recognized as a significant risk factor in the reliability of overhead transmission lines and substations. Accumulated ice on insulators can initiate corona discharge along ice-free zones, often called air gaps. In the presence of a highly conductive water film on the surface of the ice, while applied voltage is sufficiently high, corona discharge activity may be initiated and developed into partial arcs. Under certain conditions, these partial arcs may result in complete flashover.
The general objective of this research is to study the flashover phenomenon on icecovered extra-high-voltage (EHV) post insulators. Hence, a two-arc dynamic model based on the existing mathematical models was proposed to predict the parameters of AC and DC flashovers. The model considers the arc as time-dependent impedance constituted of a resistance in series with an inductance. The residual ice layer is defined in terms of an equivalent resistance, where the equivalent surface conductivity is calculated by taking into account the water film flowing along the ice surface. The present contribution proposes a novel approach to determine the equivalent surface conductivity, based on fluid mechanics and the Navier-Stokes equations, as well as on a series of experiments carried out to measure the water film flow rate and conductivity.
Moreover, the mechanisms of discharge initiation and arc development on the surface of the ice accumulated on the insulators were studied. Special attention was paid to evaluate the effect of the volume conductivity of the ice surface on the arc propagation velocity for different freezing water conductivities, using high-speed video camera techniques.
The proposed models were successfully validated in laboratory using station post insulators - typically used in Hydro-Quebec 735 kV substations - under AC and DC voltages. The maximum AC and DC withstand voltages were experimentally determined based on IEEE Std 1783. Furthermore, the influence of the number and position of air gaps on the flashover performance of ice-covered insulators was investigated experimentally. Experimental results revealed that the air gap configuration affects the maximum withstand voltage significantly. The main characteristics of flashover, including minimum flashover voltage and leakage current, derived from the proposed two-arc dynamic model, respond properly to the variation of major parameters, namely, insulator length and freezing water conductivity.
Finally, in order to interpret the performance of insulators under different air gap positions, the voltage and electric field distributions along the ice-covered insulator were simulated numerically during the melting period, using the Finite Element Method (FEM). Simulations results confirm that increasing the number of air gaps improves the maximum withstand voltage and uniformity of voltage distribution of EHV post insulators. Based on the results, the use of booster sheds and grading rings to improve the insulating performance of post insulators under icing conditions is recommended.
This research may be regarded as an important basis for the development of multi-arc models and a powerful tool for the design and selection of EHV insulators subjected to ice accretion.
33
Reske, Dean. "Modeling of High Voltage Pollution Discharge to Investigate Hot Stick Flashover." 2013. http://hdl.handle.net/1993/18487.
Abstract:
Electric “flashover” or insulation breakdown has occurred on “hot stick” safety tools used on live AC transmission lines at Manitoba Hydro in 1997 and 2002. Investigations showed pollution flashover as the cause, whereby leakage currents cascade into flashover. Prior to reinstating live-line work with mitigation procedures, DC voltage experiments suggested an atypical flashover uncharacteristic of pollution flashover without leakage currents, which may require a different mitigation strategy. In this thesis, statistical analysis shows that relative humidity has a greater correlation than voltage with the type of flashover. Labeled a “fast flashover”, it seems to be distinct from pollution flashover, although not statistically significant. A time-stepping computer model was developed to calculate a critical voltage for flashover as a function of relative humidity. However, lack of data prevents the model from making firm
conclusions. A list of recommended research is proposed to remedy these deficiencies to allow future model refinement.
34
CHEN, LU SO, and 盧守謙. "A Study on Catastrophe Model of Flashover." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/hk33bb.
Abstract:
碩士中央警察大學
消防科學研究所
88
The last decade has seen a substantial increase in the mathematical modeling of fire growth within buildings. In particular, a number of deterministic models have been developed to characterize the dynamical behavior of compartment fires within buildings. Meanwhile in the mathematics field, arguably the most exciting development is the discovery of chaos and catastrophe, introducing a shift away from the Newtonian paradigm. This has led to a mushrooming of activities in the theoretical and computationally experimental fields of nonlinear dynamical systems, resulting in a greater understanding of jumps and other complex nonlinear behavior. It is through this qualitative approach of nonlinear dynamics that we are beginning to understand the physics of basic fire phenomena. Armed with this knowledge, we can investigate models for fire growth with a view to verifying their predictive powers. The large fire simulation models can then build upon this sound framework of knowledge of fundamental physical events. Flashover is a phenomenon whereby a room fire undergoes a rapid increase in size and intensity. Such a transition is suggestive of a nonlinear process. In order to investigate the internal mechanism of flashover, we will apply the catastrophe theory to analyze the event. Flashover itself as a final stage of development is analyzed using heat balance considerations for the developed hot layer on the basis of a zone model and classic thermal ignition theory. The systematic model of the project will refer to the governing equations developed by Center for Nonlinear Dynamics and its Applications and University of Edinburgh, U.K. and will be solved using the MATLAB computational software to analyze the catastrophe behavior of flashover. A model with a single state-variable corresponding to temperature in terms of ordinary differential equations is visualized in both transient simulations and quasi-steady evolution manifolds, for variations in controlling parameters. Besides, we will apply the wall-lining characteristics of the R.C./brick generally used in domestic residential buildings, the combinations constructions used in the 921 Chi-Chi earthquake for disaster area, the iron-sheet constructions generally used in domestic plants and recreation room of KTV for fire experimental dynamical simulations. Findings show, Flashover criteria are then determined from the resultant heat gain and loss curves plotted against room temperature, the heat gain curve depends on the room temperature at an early stage of the fire which is fuel-controlled, it then becomes independent of room temperature at the developed stage. The heat loss curve is almost linearly related to the room temperature through the total heat transfer coefficient; -Gas layer temperature are therefore governed by the forms of gain and loss that are functions of its; RIt is being associated with a jumping which a fuel-controlled state becomes unstable and a transition to a ventilation-controlled state would be expected. In particular, the concept of eigenvalue has been employed in order to find the conditions, which cause a system to lose stability and to explore transient jump line. This research comes after earlier work by Tang Yun-ming that constructed a catastrophe model of flashover and Drysdale et al which identified non-linear dynamics of flashover in compartment fires.
35
TSE, CHIU HAN, and 邱翰澤. "The Study of Fire Flashover Training Simulation Cabinet." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/48902343277044445920.
Abstract:
碩士中華科技大學
土木防災工程研究所在職專班
102
It is a common phenomenon in disaster rescue a "flashover" and " deflagration " as the process of building fire developing. "Flashover" and " deflagration " are also the biggest killer in the rescue of fire. In order to reduce firefighter injuries, New Taipei City Fire Department imported the fire simulation training equipment in 1997 from the Republic of Germany. Fire simulation training equipment, with high-quality materials and superb group of instructors trained firefighters. This fire simulation training devices used powerful computing capability to simulate a fire in a variety of scenarios. In this study, by using literature review, case studies, interviews with experts, found the need to improve deficiencies for the curriculum, presented sophisticated fire simulation training equipment suggestion. After making completely full advantage of this training equipment, new experience firefighter can use this device to get hands-on experience in the fire. Firefighter took this fire simulation training equipment by constantly training, tempered into a steel. This study proposed waterjet fire extinguishing equipment in the factory fire, using its features to punch through wall and cool inside method. After the "flashover" and "deflagration" had occurred, then firefighter broke into the room and distinguished fire, thereby reduced the firefighters casualties in the fire scene.
36
Tang, Liang. "Modelling of HVDC wall bushing flashover due to uneven wetting." 2002. http://hdl.handle.net/1993/19778.
37
Yeh, Chia Nan, and 葉家男. "Effectiveness Analysis of Mobile Water Spray System in Flashover Scenario." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/31041145350224143591.
Abstract:
碩士長榮大學
職業安全與衛生研究所
97
The heat flux gauge is used to measure the heat flux from a fire source but it is affected by the wind strength around the gauge. A correlation is developed to predict the wind effect for a heat flux measurement. A fire simulator with 12m*2.6m*2.5m dimension is developed to simulate industrial fire scenarios. The heat flux is measured with 4.1 , 3.3 , 2.1 , and 1.1 at 1m , 2 m, 3m, and 4m distance from the opening of the simulator respectively. A trainer standing at 1 m wearing fire fighting clothing would not be hurt in the training activity. Another 3m*1.8m*1.9m fire simulator is used to evaluate the cooling effect of water system in flashover scenarios. The water mist has better cooling effect than water stream in this test. The water entered with air and a water mist with a higher pressure is found to be a better cooling effect. The water mist provides a better cooling effect if it is applied to a smaller fire spot and a water stream has a better cooling effect when it is applied to a lager fire location.
38
Su, Mo-jie, and 蘇莫捷. "The study of menace to firemen of flashover and backdraft." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/28709003259513993352.
Abstract:
碩士國立雲林科技大學
環境與安全工程系碩士班
95
The death of firemen in the flash over and backdraft scenes are still happened nowadays. According to statistical data, the percentage of habitation buildings is the highest. Therefore, the blaze of habitation buildings is the most case that firemen need to face it. It is necessary to the advanced researches. The most two killer of blaze scene to the firemen are flash over and back draft. When the flash over happened, it full all the space of a room suddenly. Not only the suffering people but also the firemen can not be survived. On the other hand, backdraft is a harm because of the destroy of the firemen. This research is going to use fire dynamics simulator---- FDS to analysis the blaze of the one house of an apartment. Compare and contrast the result of simulation and the time firemen come in to rescue. By this researching, it is hope to understand the boundary of flash over and back draft and have the solution and the suggestion of the range of flash over and back draft to provide some ideas and future study for fire officers and fire researchers. Key words: Fire-fighting, Flash over, Backdraft, Fire dynamic simulate
39
Chen, San-Mu, and 陳三木. "Preventive Strategies of the Lightning Flashover in Overhead Transmission Line." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/73536812197473992577.
Abstract:
碩士國立成功大學
電機工程學系碩博士班
94
This thesis proposes a method to analyze the lightning flashover in overhead transmission line. During this study, three kinds of tower models are used to discuss the phenomenon of lightning flashovers. To obtain a more general inference for flashover, the variables, including tower footing resistance, lightning current, the front of the current surge, are also weighed in to research into the causes of tower’s voltage rise. Moreover, in order to prove these contentions, the 161kV overhead transmission line between the Nanke E/S and the San-Chu D/S in Tainan Science Park was used as simulating example, according to theory and simulations by EMTP, besides fitting the overhead ground wire and the line arrester, reducing the footing resistance of the tower can also decrease the probability of lightning accident. Furthermore, installing parallel capacitors with multistory tower are effectively for reducing the incidents of the lightning flashover.
40
"Source Strength Impact Analysis on Insulator Flashover under Contaminated Conditions." Doctoral diss., 2016. http://hdl.handle.net/2286/R.I.39422.
Abstract:
abstract: Transmission voltages worldwide are increasing to accommodate higher power transfer from power generators to load centers. Insulator dimensions cannot increase linearly with the voltage, as supporting structures become too tall and heavy. Therefore, it is necessary to optimize the insulator design considering all operating conditions including dry, wet and contaminated. In order to design insulators suitably, a better understanding of the insulator flashover is required, as it is a serious issue regarding the safe operation of power systems. However, it is not always feasible to conduct field and laboratory studies due to limited time and money.
The desire to accurately predict the performance of insulator flashovers requires mathematical models. Dynamic models are more appropriate than static models in terms of the instantaneous variation of arc parameters. In this dissertation, a dynamic model including conditions for arc dynamics, arc re-ignition and arc motion with AC supply is first developed.
For an AC power source, it is important to consider the equivalent shunt capacitance in addition to the short circuit current when evaluating pollution test results. By including the power source in dynamic models, the effects of source parameters on the leakage current waveform, the voltage drop and the flashover voltage were systematically investigated. It has been observed that for the same insulator under the same pollution level, there is a large difference among these flashover performances in high voltage laboratories and real power systems. Source strength is believed to be responsible for this discrepancy. Investigations of test source strength were conducted in this work in order to study its impact on different types of insulators with a variety of geometries.
Traditional deterministic models which have been developed so far can only predict whether an insulator would flashover or withstand. In practice, insulator flashover is a statistical process, given that both pollution severity and flashover voltage are probabilistic variables. A probability approach to predict the insulator flashover likelihood is presented based on the newly developed dynamic model.Dissertation/Thesis
Doctoral Dissertation Electrical Engineering 2016
41
Wu, Kuan-Yi, and 吳冠億. "The Flashover Characteristics of Insulating Insulator of Overhead Transmission Systems." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/37328877131886719228.
Abstract:
碩士中原大學
電機工程研究所
90
Insulating insulators are used for insulation of overhead transmission lines and their supporting tower for power delivery. Due to Taiwan surrounded by sea, highly developed in industry, and major power delivery equipments located along coastal areas, the insulators are frequently subjected to pollution from NaCl-fog and dust-fog, and suspended solid particles. Electric arc and flashover often occur on the contaminated insulators. The failure of the insulators usually results in blackout of either local area or whole area along the power transmission. Therefore, to maintain the security and reliability of the power systems, performance of the insulators is vitally important. This thesis aims at development of measurement methods of equal salt deposit density (ESDD), leakage current experiment and flashover voltage experiment schemes. The environment of the insulators for the 69kV system is simulated to investigate the influences of vapor, temperature and pressure changes on the ESDD on the insulator. Accordingly, relationship of the flashover voltages to the leakage currents is discovered. All the experimental data are collected and analyzed to conclude an alert for possibility of flashover. Hence, the emergent measures to avoid flashover of the contaminated insulators can be taken. The quality and reliability of power supply can be ensured. The experimental results show that the possibility is indeed related to degrees of contamination of the insulators and the input rate of the vapor. Also, the variation of the flashover voltages can be predicted through the leakage current measurements.
42
Chagas, Fernando A. "Flashover mechanism and laboratory evaluation of polluted insulators under DC voltage." 1997. http://hdl.handle.net/1993/19399.
43
Chang, Han-Chan, and 張瀚展. "Effect of post-flashover flame emerging from opening on external wall." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/35732213235991055873.
Abstract:
碩士國立高雄第一科技大學
環境與安全衛生工程研究所
102
Fire spread in high rise buildings occurs if flames emerge and extend on the facade of the building to cause ignition in floors above the floor of fire origin. Considerable work has investigated the heat exposure onto the facade owing to flames emerging from a door-like opening in an enclosure. However, the heat exposure to the external facade from window-like opening locations has not been incorporated into current engineering fire design methods. In this study, experiments in small scale enclosures having various opening shapes and locations were underpinned for flames on facade emerging from ventilation controlled fire at the floor of fire origin. To limit uncertainties, a propane gas burner was used to produce controlled heat release rates (30, 40 and 50 kW) as fire source. The size of opening (in W×H) were 20×10 cm, 10×20 cm and 20×20 cm. Actual heat release rate, gas temperature inside the enclosure, heat flux on the facade wall, and flame contours were measured. Our experimental observations and data show that the shape of opening strongly influenced the combustion conditions, and two categories were found, giving combustion primarily outside the enclosure and combustion both inside and outside the enclosure. Two sets of correlations for the two categories were derived. For the category of combustion both inside and outside the enclosure, the heat flux on the facade from window-like openings was close to that from door-like openings. The external flame heights are very close in the experiments with the same opening geometry, and fuel supply rate. The highest heat flux always occurs with lower opening because the lintel barrier caused gas fuel to accumulate in the enclosure. When the gas fuel flowed out, the cool gas fuel temperature has been heated into hot gas fuel. Further, for the category of combustion outside the enclosure, a series of correlation was provided.
44
HE, SHI-NAN, and 何世南. "Study on influence of parameters for back flashover lightning surge analysis." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/27618284101806407688.
45
Chen, Shin-Hong, and 陳信宏. "The Effect of Smoke Production of Material on the Occurrence of Flashover." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/60484839952219573481.
Abstract:
碩士國立高雄第一科技大學
環境與安全衛生工程所
94
ABSTRACT Flashover is a very phenomena leading to high heat release during fire growth. From previous studies, it has been investigated that heat flux of 20 kW/m2, temperature of 600 ℃ and heat release rate of 1 MW are the criteria of flashover. However, the smoke production of materials is not considered but influences the radiant heat transfer in a compartment which is related to the occurrence of flashover. Thus, this study focuses on the effect of smoke production on the occurrence of flashover by small scale experiments. The size of the experimental compartment is 1/3 ISO 9705 room. Fuels used included gasoline, hexane, iso-propanol and methanol in the order of smoke production. Measurements made were heat flux on the floor, temperature at 100 mm below the ceiling, heat release rate. Flashover is determined when flame ran out of the compartment opening and paper on the floor ignited. Our data showed that the criteria of flashover in the small scale compartment are heat flux of 20 kW/m2, temperature of 700 ℃ and heat release rate of 60 kW. Among these values, temperature and heat release rate measured follow the scale law. In addition, the more smoke produced, the higher heat flux at flashover although no trend of temperature was found. Moreover, a correlation of �� 532.92 �{0.3466 fo t Q�t (R2=0.7743) is found. The correlation is not related to smoke production but all the time to flashover are shortest with methanol, and then iso-propanol, hexane and gasoline. However, this trend needs further research.
46
Wang, Shih-Cheng, and 王士承. "Numerical Study of Flashover Phenomena and Fire Reconstruction in the Building Fire." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/68619564992850854750.
Abstract:
博士元智大學
機械工程學系
96
Accidental building fires present considerable valuable information on fire phenomena and behavior. However, fire and smoke movement quantitative data cannot be obtained directly from a building fire accident. Therefore, computational methods have been widely used to reestablish the fire scenario and obtain a great deal of information for fire study. This paper utilized two types of fire simulation software, CFAST (ver. 6.0.10) zone model and FDS (ver. 4.0.7) field model, and full-scale fire tests for motorcycles to reconstruct a motorcycle shop fire accident in Taiwan. Computational results reasonably agreed qualitatively with post-accident reports. Simulation analysis for backdraft phenomena demonstrated that window size in the limited-ventilation compartment fire greatly influenced smoke leaking from vents, deflagration induction time and fire intensity from a new opening. The impact of natural/forced ventilation on the fire was also studied. The results showed that the larger forced airflow gets into the building, the longer egress time is needed to evacuate to a safe place from the fire. In addition, flashover phenomena were studied. Flashover is an extremely important phenomenon whereby a compartment fire undergoes a rapid elevation in size and intensity. The mechanism that is near simultaneous ignition of all combustible material in an enclosed area is a nonlinear behavior. Therefore, an improved two-layer zone model was proposed for evaluating the transition from ignition to flashover during a compartment fire. The radiation feedback from hot smoke layer was identified utilizing the National Institute of Standard Technology (NIST) full-scale compartment fire tests. Time to flashover for various t-squared fires, wall materials, and ventilation conditions derived. Computational results demonstrated that height of vents and wall materials singinficatly affected flashover-induced time in low intensity fire development.
47
CHEN, YU-HUNG, and 陳禹宏. "Research on Design Scheme of flashover simulator for Training in Fire Department." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/anm5x4.
Abstract:
碩士吳鳳科技大學
消防研究所
106
When a fire grows in a confined space, it will enter a heyday after a short period of flashover. The flame and high temperature accompanying the flashover will cause loss of life and property, and often cause a fire to be variable, regardless of the fire. Or life-saving assistance, due to the accumulation of hot smoke layers and the development of fire, increase the difficulty of disaster relief personnel in rescue and reduce the survival opportunities of trapped people. In view of this, if training can be carried out through the flashover simulator, firefighters can understand and prevent the occurrence of flashover, which will effectively reduce casualties. The main purpose of this study is to explore the effectiveness of self-construction of flashover simulator for fire training. Through self-designed flashover simulator and fire training, combined with academic and practical services, all firefighters can understand the precursors of flashover and how to effectively prevent the occurrence of flashovers. Ensure the safety of new firefighters in the event of disaster relief.
48
Frost, Philip Edward. "Development of a Fire-induced Flashover Probability Index (FIFPI) for Eskom transmission lines." Thesis, 2012. http://hdl.handle.net/10210/4691.
Abstract:
M.Sc.The need for a fire-induced flashover (power line arcing to the ground) probability index for Eskom transmission (high voltage power) lines became evident soon after the installation the Advanced Fire Information System (AFIS) in 2004. AFIS is a satellite based fire detection system that utilizes polar and geostationary satellite sensors to detect fires as small as 50 m x 50 m in size. As soon as a fire is detected by either, the Terra, and Aqua Moderate Resolution Imaging Spectro-radiometer (MODIS) or Meteosat Second Generation (MSG) geostationary satellites close to any of the 28 000 km of Eskom transmission lines, a cell phone and email text warning is sent out to line managers responsible for the management of the particular section of line affected. Between 3000 - 6000 fires are recorded annually close to Eskom transmission lines with a fire-induced flashover rate of 100 - 150 transmission line trips per year. Fire-induced flashovers occur when the air around high voltage transmission lines are ionised due to a hot flame (> 500° C). As the air becomes conductive, electricity can move from the line to the ground in the form of a lightning flash. Studies have shown that one flashover can cause an average of three voltage depressions (dips) on the electrical transmission system, and each voltage depression can cause damage to a customer’s production ranging between R5000 and R150000 per dip. The aim of this study was to develop a prediction model with the ability to accurately predict fire-induced flashover occurrences on Eskom transmission lines in order to reduce the large amount of false alarms (SMS and email messages) produced annually by AFIS. The prediction model in the form of a probability index was derived from a combination of remote sensing satellite products as well as weather forecast variables. With the MODIS active fire product as base layer, weather forecast variables in the form of air temperature, relative humidity, wind speed and wind direction, as well as topographical elevation and a satellite derived vegetation condition product served as input to the predictor data set of the model, while flashover statistics for 2007 provided the target data set within a Classification and Regression Tree (CART) analysis. iii The prediction capabilities for each of the variables were evaluated based on their prediction accuracy and Receiver Operation Characteristic (ROC) value in terms of the validation data set. Wind speed, relative humidity, wind direction and air temperature were shown to have the highest predictor importance and were used to develop the probability index calculated from a logistic regression analysis. The Fire-induced Flashover Probability Index (FIFPI) was tested through simulations of predictor variables and was also compared to existing Fire Danger Indices (Willis et al. 2001). The FIFPI was able to outperform most of the standard Fire Danger Indices (FDI’s) with only the McArthur Grassland Index (MK 4) which demonstrated some prediction capability. The importance of wind direction as an environmental component in the prediction of flashovers became clear as it tended to decrease the misclassification rate from 4.45% when only wind speed, relative humidity and temperature were used to 3.87% when wind direction was added. The research has shown that wind speed, wind direction, relative humidity and temperature can be used as an indicator of possible fire-induced flashovers underneath Eskom transmission lines. However, additional research is needed to verify the results from 2007. Ideally at least 3 years of data should be used.
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Klopovic, Suzana. "Experimental and computational study of flames venting externally during full scale flashover fires." Thesis, 1999. https://vuir.vu.edu.au/15326/.
Abstract:
In this study, externally venting flames have been examined during two series of full scale flashover fires. The purpose of the work is to investigate the likelihood of
external fire spread from a burn room window with standard glass, when the external facade is non-combustible. The effects on externally venting flames of internal
ventilation conditions, burning rate, burn room size and wind have been studied in detail. Secondary fires and glass breakage have been examined.. Repeatable experimental data and reliable information on externally venting flames have been generated for numerical model validation and performance based design code development.
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Basappa, Subba Reddy. "A Novel Technique For Enhancing The Pollution Flashover Strength Of Ceramic Disc Insulators." Thesis, 2010. https://etd.iisc.ac.in/handle/2005/2114.
Abstract:
Pollution is the single largest cause of transmission/distribution line outages, next
to lightning, which result in expensive power outages. A major significance of the
problem is that it can repeatedly occur even at normal working voltages. As a result, it has become the most detrimental factor affecting the safe operation of extra and ultra high voltage (EHV/UHV) transmission lines and substations. In reality, the phenomenon of pollution-induced flashover is a very complex, and vexatious problem that continues to challenge high voltage engineers even today. In spite of knowing this phenomenon for the past several decades, a solution has remained still elusive.
Although there exist some remedial measures, there are associated limitations, which will become evident on long runs. The guaranteed solution seems to be the washing and cleaning of insulators for which utilities spend significant amount of money. Therefore, there is a need to develop a suitable mitigation technique which is cost effective and yield better performance in the field.
Motivated by this, the present study is undertaken and it essentially aims to seek
simple alternative solutions for the problem for strings with ceramic insulator discs. All the ten types (normal and anti fog) ceramic insulators, which are commonly employed in our country, are considered in the study. Amongst the several controllable and uncontrollable physical quantities leading to the pollution flashover phenomena, the maximum surface field identified as on of the major influencing factor. In fact, the field concentration near the pin can lead to early formation of dry band and scintillation/partial arcs. Considering this, it is intended to seek possible minimization of the maximum surface field occurring at the pin region. This is expected to yield enhanced pollution/contamination flashover strength and in addition, show an improvement in normal operation.
The intended study requires a detailed knowledge on field distribution. However, the required data is found to be rather scarce. In view of this a detailed study on field distribution is taken up for all the ten types of disc insulators used in our country.
For the problem under investigation, the governing equation has been identified for both clean and polluted conditions along with pertinent boundary conditions. Considering the open geometry nature of the problem along with presence of multiple dielectrics, Surface Charge Simulation (SCSM) methodology was found to be most suitable and hence adopted for the work. In particular, the Galerkin method with piecewise linear interpolation function is employed in the formulation. The method employed and the codes developed are verified with suitable examples.
First, a detailed quantification of the field distribution under clean conditions is made for all the ten types of discs in single disc and string configuration. Subsequently, the task of reducing the maximum surface field gradient, which occurs at the pin, is attempted. Several consideration lead to an artificial extension of pin as one of best feasible choice. However, any attempt to extend the pin would lead to some reduction in total creepage length, possible enhancement of bulk stress in air and enhancement of stress in triple junction. After a careful study, involving several experimental trials, a novel field control element (FCE) is developed both for normal and anti-fog types of insulator discs.
From the electric field simulation study, it is shown that the use of field control element for uniform pollution deposition prevailing under laboratory test conditions yields a significant reduction of maximum surface field for discs by about 47 to 54%. Similarly a reduction of about 37% to 55% in case of 3-disc string (for 33 kV class), 30% to 52% in case of 9-disc string (for 132 kV class), 27% to 52% in case of 14-disc string (220 kV class), 27% to 54% in case of 23/20 disc string (for 400 kV class) and 41% to 48% in case of 35/29 disc strings (for 765kV class) is achieved respectively for different strings. It is anticipated that this will lead to retardation in inception of scintillations/partial arcs, which in turn can reduce the risk of pollution induced flashover.
Subsequently, it was aimed to experimentally evaluate the impact of field control element on the performance of disc/string under normal and that during polluted conditions. For this a national level unique artificial pollution test facility as per the international standards has been established for conducting pollution studies on disc insulator/strings up to 132kV system voltage (The rating of test source: 150kV/2A,100kV/3A,50kV/6A of 300kVA).
Experimental investigations for the normal operation involving dry and wet power frequency flashover strengths, lightning impulse strength, radio interference level (RIV), visible discharge inception (Corona) level and voltage distribution along the string are carried out. The study showed that with the insertion of field control element, performance under normal condition is maintained and in fact noticeably improved in certain cases. Subsequently pollution flashover strength is evaluated using solid layer and cold fog methods. The pollution flashover strength exhibited an overall improvement 15 to 20% for all types of discs considered in the study. Similarly an improvement of 16 to 19% and 12-14% is observed for 3-disc string and 6-disc string respectively.
The reasons for relatively lower gain in the pollution flashover strength as compared to reduction in maximum surface field are investigated. In particular, the reduction in improvement with number of discs in a string is dealt with. The non-uniform wet-ting against highly non-uniform drying of insulator surface and discs in a string, are identified as the cause for deviation. For an experimental verification of the same, the pollution layer resistance of individual discs in a 3-disc string is measured prior to and immediately after flashover. It is shown that the resistances of the different units become grossly different even though initial values were substantially the same. The values measured immediately after flashover show that the resistance of the top unit develops voltage enough to result in its flashover and subsequently, the flashover of the whole string.
In summary, the main contribution of the present work is the development of novel field control element (FCE) for both normal and anti-fog type of ceramic disc insulators, which will enhance their pollution flashover strength. The actual cost of these elements is estimated to be about 1-2% of the cost of the disc, while the gain in strength is shown to be more than 12 - 20%.