Lightning Discharge

1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions

Lightning Discharges

1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions

since at ancient times the lightning phenomena have impressed the mankind ** often explained by ** mystical reasions

from the Bibles history up to the weapon of Thor Moses at the announcement of the gods law on Sinai

and to Benjamin Franklin (1752) and his experiments, in which were demonstrated the electrical nature of lightning

such dangerous experiments were stopped after the tragical death of Prof. Richmann (1753) serious explanations of lightning phenomena exist until the 19th/ 20th century

Lightning Discharges

1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions

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)

Statistics of lightning (northern hemisphere) during a year during a day

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)

Lightning- distribution along Europeactually at 21th april, 11hwww.euclid.org

Global distribution (NASA Satellite 1996-2000) 50 flashes per second (in 1000 aktive thunderstorms) Maximum about tropical areas (shore)

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

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 + + +++ + + + +

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

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

Generation of lightning (neg. CG)the most important part for the target point is the last step (before ground) final striking distance

Generation of lightning (neg. CG)This behaviour can be used for evaluation of target point(rolling sphere model)

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

Types of lightning negative/ positive CG- stroke(positive CG 5 .. 10%)negative/ positive GC- stroke

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

spossible current types single current multiple currents

Generation of multiple lightning (flash)stepped leadermain discharge(return stroke)dart leadervelocity: ~ 108 m/s (c/3)

Lightning Discharges

1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions

Effects of lightning lightning effects can be distinguished into: indirect effects ---> overvoltages

direct effects ---> electrical, thermal, chemical, biological

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

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

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)

Lightning Impulse Testing (LI)Test parameter: --> front time - 1.2 (+ - 30%) s LI - 1.2/ 50 s --> half-to-value time - 50 (+ - 20%) s

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

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)

Damages in nature (trees)typical spiral- structureexploded, broken by vaporized water

Damages in airplaneshole by meltingstroke in radarSpace-shuttle

Damages in human beings or animalsDamage by direct stroke, over-step or induced step- voltage burning, overheating bio- electrical disturbance heart- interruption

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

U = imax REEffects by maximal current

U = M i/ t Effects by current gradient

Q = i dtW = Q UA,KEffects by charge (of lightning)

W = R i2 dt

W/ R = i2 dtEffects by specific energy (of lightning)

temperature risingT (in K)

Lightning Discharges

1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions

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)

Protection against lightning current ligthning conductor screening (Faraday Cage)Ligthning protection by

historical overview1752 B.Franklin1754 P.Divis

Protection against lightningdefinition of Lightning Protection Levels (LPL) and related current parameters (shape, time, max)

Components of a Lightning Protection System

recent lightning protection can be separated into external lightning protection internal lightning protectionLPS

Standardized lightning currents

External lightning protection

rolling sphereExternal lightning protection

Protection against lightning

External lightning protection

External lightning protection

protection model of the cathedral of Aachen (protection class II, III) External lightning protection

Lightning Protection System

Lightning Protection System

Lightning Protection System

Internal lightning protectionprotection by environmental zones [Vance, 1980] Lightning Protection Zones (LPZ)

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

Internal lightning protection

Internal lightning protectionexample for zone- concept in LV- installation

Internal lightning protection

Lightning Discharges

1 Introduction2 Physical Phenomena3 Effects and Typical Parameters4 Lightning protection5 Conclusions

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

Thank youQuestions ?& Answers !

Impressions about lightnings

Ball lightning

Ball lightning

Lightnings into StratosphereRed Spriteslenght up tos 95 kmwidth 5-30 kmduration 100 ms single or synchronized in groups

Lightnings into StratosphereBlue Jets length up to 50 km blue duration 200 ms single

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)

Luftionen (Lebenszyklus)10-6 s10-3 s10-2 sPrimre IonisierungKleinionen durch ClusterbildungUmwandlung in Groionen

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