© prof.dr.r.haller lightning discharge 1 introduction 2 physical phenomena 3 effects and typical...

© Prof.Dr.R.Haller

Lightning Discharge

1 Introduction

2 Physical Phenomena

3 Effects and Typical Parameters

4 Lightning protection

5 Conclusions

© Prof.Dr.R.Haller

Lightning Discharges

1 Introduction




5 Conclusions

© Prof.Dr.R.Haller

since at ancient times

the lightning phenomena

have impressed the mankind

** often explained by **

mystical reasions

© Prof.Dr.R.Haller

from the Bible´s history up to the weapon of Thor …

Moses at the announcement of the god´s law on Sinai

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

© Prof.Dr.R.Haller

… such dangerous experiments were stopped after the tragical death of Prof. Richmann (1753) …

serious explanations of lightning phenomena exist

until the 19th/ 20th century

© Prof.Dr.R.Haller


1 Introduction




5 Conclusions

© Prof.Dr.R.Haller

Atmospheric effects

• fine- weather- field ( )fine- weather- field ( )• global current global current (air ions, ~ 2pA/m(air ions, ~ 2pA/m22))• lightnings lead mostly lightnings lead mostly

to a negative charge on to a negative charge on earth earth

• global exchange of global exchange of charge by conductivity charge by conductivity of soil and middle of soil and middle atmosphereatmosphere

(„charge generator“)(„charge generator“)

© Prof.Dr.R.Haller

Statistics of lightning (northern Statistics of lightning (northern hemisphere)hemisphere)

during a year

during a day

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Lightning- distribution along Lightning- distribution along EuropeEurope

• 1-7 / (a⋅km2)

• north- south- gradient

• Maxima on alps, Italy

and Adria

lightning- location- systems (BLIDS, EUCLID, …)

lightnings per year (a) and area (km2)

© Prof.Dr.R.Haller

Lightning- distribution along Lightning- distribution along EuropeEurope

actually at 21th april, 11h

www.euclid.org

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Global distributionGlobal 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 Electrical structure of a thunderstorm- cloudthunderstorm- cloud

•positive charge in positive charge in upper upper

part (part (T <T < -25°C) -25°C)•negative charge in negative charge in lower part (lower part (T T > -> -25°C)25°C)

•(small) positive (small) positive charge near the rain charge near the rain areaarea

•influenced (positive) influenced (positive) charge on the earthcharge 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 processes

ionization processes into the cloud

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Generation of lightning (neg. CG)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

© Prof.Dr.R.Haller


the most important part for the target point is the last step (before ground)

final striking distance

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This behaviour can be used for evaluation of target point

(rolling sphere model)

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Types of lightningTypes of lightning

Cloud- 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 Types of lightning

negative/ positive CG- stroke(positive CG 5 .. 10%)

negative/ positive GC- stroke

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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 ~ (101099 … 10 … 101010) J) J

Q ~ (1 … 60) nC

of charge channel ~ 15 cm

p ~ 100 bar

time duration ~ (10 .. 100) s

© Prof.Dr.R.Haller

μs

possible current types

single current

multiple currents

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Generation of multiple Generation of multiple lightning (flash)lightning (flash)

stepped leader

main discharge

(return stroke)

dart leader

velocity: ~ 108 m/s (c/3)

© Prof.Dr.R.Haller


1 Introduction




5 Conclusions

© Prof.Dr.R.Haller

Effects of lightning

lightning effects can be distinguished into:

indirect effects ---> overvoltages

direct effects ---> electrical, thermal,

chemical, biological

© Prof.Dr.R.Haller

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

3

1 - influenced charged on overhead lines (o.l.) at thunderstorm

2 - 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

© Prof.Dr.R.Haller

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“)

© Prof.Dr.R.Haller

Lightning Impulse Testing (LI)

Test parameter: --> front time - 1.2 (+ - 30%) s

LI - 1.2/ 50 s --> half-to-value time - 50 (+ - 20%) s

© Prof.Dr.R.Haller

Parameter for LI- testing

nominal nominal voltage voltage

(grid) [kV](grid) [kV]

test voltagetest voltage

(LI) [kV](LI) [kV]

7.2 (6)7.2 (6) 4040

12 (10)12 (10) 7575

24 (20)24 (20) 125125

123 (110)123 (110) 450450

testing voltage (1.2/50) (1.2/50) s/ phase- ground- s/ phase- ground- insulationinsulation

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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)Damages in nature (trees)

typical spiral- structure

exploded, broken by vaporized water

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Damages in airplanesDamages in airplanes

hole by melting

stroke in radar

Space-shuttle

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Damages in human beings or Damages in human beings or animalsanimals

Damage by direct stroke, over-step or induced step- voltage

burning, overheating

bio- electrical disturbance

heart- interruption

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maximal current imaximal current imax max 25 ... 25 ... 100 kA100 kA

time- gradient di/dt time- gradient di/dt 10 ... 10 ... 200 kA/200 kA/ss

charge charge i i dt dt 3 ... 3 ... 100 As100 As

specific energy specific energy i i22 dt dt 2.5 ... 2.5 ...

10 (kA)10 (kA)22ss

Typical parameters of lightning

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U = imax ·RE

Effects by maximal current

© Prof.Dr.R.Haller

U = M · Δi/ Δt

Effects by current gradient

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Q = ∫ i dt

W = Q · UA,K

Effects by charge (of lightning)

© Prof.Dr.R.Haller

W = R · ∫ i2 dt

W/ R = ∫ i2 dt

Effects by specific energy (of lightning)

© Prof.Dr.R.Haller

temperature rising

ΔT (in K)

© Prof.Dr.R.Haller


1 Introduction




5 Conclusions

© Prof.Dr.R.Haller

Protection against lightning overvoltages

Insulation design for withstanding to LI

(electrical strength of insulation > LI- strength)Limiting of overvoltages by

lightning arresters (Ventil-, MOA- type)

Surge Protection Devices (SPD)

© Prof.Dr.R.Haller

Protection against lightning current

ligthning conductor

screening („Faraday Cage“)

Ligthning protection by

© Prof.Dr.R.Haller

historical overview

1752 B.Franklin

1754 P.Divis

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Protection against lightning

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

© Prof.Dr.R.Haller

Components of a Lightning Protection System

© Prof.Dr.R.Haller

recent lightning protection can be separated into external lightning

protection

internal lightning protection

LPS

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Internal lightning protection

protection by environmental zones [Vance, 1980]

Lightning Protection Zones (LPZ)

© Prof.Dr.R.Haller


Zone- 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

© Prof.Dr.R.Haller

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

© Prof.Dr.R.Haller

Lightnings into Lightnings into StratosphereStratosphere

Red Sprites•lenght up tos 95 km

•width 5-30 km

•duration 100 ms

• single or synchronized in groups

© Prof.Dr.R.Haller

Lightnings into Lightnings into StratosphereStratosphere

Blue Jets• length up to 50 km

• blue

• duration 200 ms

• single

© Prof.Dr.R.Haller

LuftionenLuftionen

KleinionenKleinionen• Cluster aus 10-20 Molekülen (meist Cluster aus 10-20 Molekülen (meist

HH22O) um ein zentrales IonO) um ein zentrales Ion

• Größe aus Gleichgewicht zw. Größe aus Gleichgewicht zw. Stoßenergie und el. Potential am Stoßenergie und el. Potential am ClusterrandClusterrand

• tragen tragen eineeine Elementarladung Elementarladung• Anzahl-Dichte: 500 cmAnzahl-Dichte: 500 cm-3-3

• Geschwindigkeit: 1-3 cm/sGeschwindigkeit: 1-3 cm/s• Lebensdauer: 10 s - 300 sLebensdauer: 10 s - 300 s

• Luft ist kein Isolator

• es existieren Ladungsträger (bipolar): die Luftionen

Entstehung der Luftionen:

1. Primäre Ionisierung eines Gasatoms in Elektron und Ion

2. Anlagerung des Elektrons an Gasatom zu Molekül-Ion

3. Clusterbildung durch Anlagerung von Liganden (Wasser)

© Prof.Dr.R.Haller

Luftionen (Lebenszyklus)Luftionen (Lebenszyklus)

10-6 s 10-3 s 10-2 s

Primäre IonisierungKleinionen durch Clusterbildung

Umwandlung in Großionen

© Prof.Dr.R.Haller

Beweglichkeit der IonenBeweglichkeit der IonenBewegung im Gas Bewegung im Gas

– elektrisches Feld elektrisches Feld beschleunigtbeschleunigt

– abgebremst durch abgebremst durch Stöße mit Stöße mit GasmolekülenGasmolekülen

– neuer neuer GeschwindigkeitsvektGeschwindigkeitsvektor nach jedem Stoßor nach jedem Stoß

– Parabelbahn Parabelbahn zwischen 2 Stößenzwischen 2 Stößen

Mittlere Geschwindigkeit ist gleichförmig in Richtung des Feldes:

Ekv

mit k - Beweglichkeit (Mobilität)

Bewegung eines Kleinions im Gas unter Einfluß eines elektrischen Feldes

© prof.dr.r.haller lightning discharge 1 introduction 2 physical phenomena 3 effects and typical...

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