lightning discharge
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Lightning Discharge. 1 Introduction 2 Physical Phenomena 3 Effects and Typical Parameters 4 Lightning protection 5 Conclusions. Lightning Discharges. 1 Introduction 2 Physical Phenomena 3 Effects and Typical Parameters 4 Lightning protection 5 Conclusions. since at ancient times - PowerPoint PPT PresentationTRANSCRIPT
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Lightning Discharge
1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions
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Lightning Discharges
1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions
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since at ancient times the lightning phenomena have impressed the mankind ** often explained by ** mystical reasions
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from the Bibles history up to the weapon of Thor Moses at the announcement of the gods law on Sinai
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and to Benjamin Franklin (1752) and his experiments, in which were demonstrated the electrical nature of lightning
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such dangerous experiments were stopped after the tragical death of Prof. Richmann (1753) serious explanations of lightning phenomena exist until the 19th/ 20th century
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Lightning Discharges
1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions
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Atmospheric effectsfine- weather- field ( )global current (air ions, ~ 2pA/m2)lightnings lead mostly to a negative charge on earth global exchange of charge by conductivity of soil and middle atmosphere (charge generator)
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Statistics of lightning (northern hemisphere) during a year during a day
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Lightning- distribution along Europe 1-7 / (akm2) north- south- gradient Maxima on alps, Italy and Adrialightning- location- systems (BLIDS, EUCLID, )lightnings per year (a) and area (km2)
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Lightning- distribution along Europeactually at 21th april, 11hwww.euclid.org
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Global distribution (NASA Satellite 1996-2000) 50 flashes per second (in 1000 aktive thunderstorms) Maximum about tropical areas (shore)
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Generation of lightning moisture in air & (vertical) wind--> intensive soil heating by sun--> cold weather front under warm air- sheet separation of charges into a cloud polarization friction gravitation
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Electrical structure of a thunderstorm- cloudpositive charge in upper part (T < -25C)negative charge in lower part (T > -25C)(small) positive charge near the rain areainfluenced (positive) charge on the earth + + +++ + + + +
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for direct breakdown between cloud and earth an (average) value of E = 3000 kV/m would be necessary ---> impossible increased values of E on the top of space charge channel lead to ionisation processesionization processes into the cloud
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Generation of lightning (neg. CG) charge channel moves in direction to the ground ~ 10 m, high ionized core ~ 1 cm -> LEADER velocity ~ 3 105 m/s, stepwise 10 .. 60 m, ~ 10 s --> stepped leader
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Generation of lightning (neg. CG)the most important part for the target point is the last step (before ground) final striking distance
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Generation of lightning (neg. CG)This behaviour can be used for evaluation of target point(rolling sphere model)
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Types of lightningCloud- Ground (95%)Ground- Cloud (5%)Classifikation of CG- strokes is determined by the direction of stepped leader Intra- Cloud(s) (IC) Cloud- Ground (CG) IC/ CG = 7/ 3 (50th latitude) positive/ negative polarity
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Types of lightning negative/ positive CG- stroke(positive CG 5 .. 10%)negative/ positive GC- stroke
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Generation of lightning (neg. CG)After the meeting of catching discharge with the stepped leader a main discharge will be initiated imax ~ 10 100 kA , T ~ (10 30) 103 K (!) W ~ (109 1010) J Q ~ (1 60) nC of charge channel ~ 15 cm p ~ 100 bar time duration ~ (10 .. 100) s
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spossible current types single current multiple currents
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Generation of multiple lightning (flash)stepped leadermain discharge(return stroke)dart leadervelocity: ~ 108 m/s (c/3)
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Lightning Discharges
1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions
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Effects of lightning lightning effects can be distinguished into: indirect effects ---> overvoltages
direct effects ---> electrical, thermal, chemical, biological
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Indirect Effects Overvoltages on overhead lines caused by liberation of influenced charges or as back- flashover from tower to phases
Overvoltages in loops (installation, equipment) by inducing effects of lightning current
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Generation of overvoltages on overhead lines1 2 31 - influenced charged on overhead lines (o.l.) at thunderstorm2 - due to admittance of lines remains positive charge only on o.l.3 - occuring a stroke the charge is not further fixed --> travelling overvoltage wave along the line
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lightning overvoltages can damage electrical equipment for power transmission which connected on overhead lines e.g power transformers, switch- gears,
--> all equipments for power transmission must be tested before going in operation (test against atmospheric overvoltages)
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Lightning Impulse Testing (LI)Test parameter: --> front time - 1.2 (+ - 30%) s LI - 1.2/ 50 s --> half-to-value time - 50 (+ - 20%) s
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Parameter for LI- testingtesting voltage (1.2/50) s/ phase- ground- insulation
nominal voltage (grid) [kV]test voltage(LI) [kV]7.2 (6)4012 (10)7524 (20)125123 (110)450
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Direct Effects Lightning current effects by current flows through the object voltage drop on the ground thermal action into the object (overheating, radiation, melting, explosion)
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Damages in nature (trees)typical spiral- structureexploded, broken by vaporized water
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Damages in airplaneshole by meltingstroke in radarSpace-shuttle
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Damages in human beings or animalsDamage by direct stroke, over-step or induced step- voltage burning, overheating bio- electrical disturbance heart- interruption
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maximal current imax 25 ... 100 kA time- gradient di/dt 10 ... 200 kA/s charge i dt 3 ... 100 As specific energy i2 dt 2.5 ... 10 (kA)2sTypical parameters of lightning
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U = imax REEffects by maximal current
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U = M i/ t Effects by current gradient
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Q = i dtW = Q UA,KEffects by charge (of lightning)
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W = R i2 dt
W/ R = i2 dtEffects by specific energy (of lightning)
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temperature risingT (in K)
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Lightning Discharges
1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions
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Protection against lightning overvoltagesInsulation design for withstanding to LI (electrical strength of insulation > LI- strength)Limiting of overvoltages by lightning arresters (Ventil-, MOA- type) Surge Protection Devices (SPD)
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Protection against lightning current ligthning conductor screening (Faraday Cage)Ligthning protection by
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historical overview1752 B.Franklin1754 P.Divis
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Protection against lightningdefinition of Lightning Protection Levels (LPL) and related current parameters (shape, time, max)
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Components of a Lightning Protection System
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recent lightning protection can be separated into external lightning protection internal lightning protectionLPS
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Standardized lightning currents
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External lightning protection
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rolling sphereExternal lightning protection
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Protection against lightning
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External lightning protection
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External lightning protection
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protection model of the cathedral of Aachen (protection class II, III) External lightning protection
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Lightning Protection System
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Lightning Protection System
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Lightning Protection System
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Internal lightning protectionprotection by environmental zones [Vance, 1980] Lightning Protection Zones (LPZ)
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Internal lightning protectionZone- prinziple was developed for protecting against NEMP (USA) and could be successfully used even against LEMP In each zone are defined elektromagnetic conditions which were guarantied by screening, SPD , equipotential bonding
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Internal lightning protection
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Internal lightning protectionexample for zone- concept in LV- installation
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Internal lightning protection
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Lightning Discharges
1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions
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lightning phenomena are very important even in recent times and are well- known lightning effects could be very dangerous for human beings, animals and could be lead to essential damages lightning protection is therefore necessary for everyone
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Thank youQuestions ?& Answers !
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Impressions about lightnings
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Ball lightning
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Ball lightning
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Lightnings into StratosphereRed Spriteslenght up tos 95 kmwidth 5-30 kmduration 100 ms single or synchronized in groups
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Lightnings into StratosphereBlue Jets length up to 50 km blue duration 200 ms single
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LuftionenKleinionenCluster aus 10-20 Moleklen (meist H2O) um ein zentrales IonGre aus Gleichgewicht zw. Stoenergie und el. Potential am Clusterrandtragen eine ElementarladungAnzahl-Dichte: 500 cm-3Geschwindigkeit: 1-3 cm/sLebensdauer: 10 s - 300 s Luft ist kein Isolator es existieren Ladungstrger (bipolar): die LuftionenEntstehung der Luftionen:1. Primre Ionisierung eines Gasatoms in Elektron und Ion2. Anlagerung des Elektrons an Gasatom zu Molekl-Ion3. Clusterbildung durch Anlagerung von Liganden (Wasser)
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Luftionen (Lebenszyklus)10-6 s10-3 s10-2 sPrimre IonisierungKleinionen durch ClusterbildungUmwandlung in Groionen
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Beweglichkeit der IonenBewegung im Gas elektrisches Feld beschleunigtabgebremst durch Ste mit Gasmoleklenneuer Geschwindigkeitsvektor nach jedem StoParabelbahn zwischen 2 StenMittlere Geschwindigkeit ist gleichfrmig in Richtung des Feldes:mit k - Beweglichkeit (Mobilitt)Bewegung eines Kleinions im Gas unter Einflu eines elektrischen Feldes