© Prof.Dr.R.Haller Lightning Discharge 1 Introduction 2 Physical Phenomena 3 Effects and Typical...
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Transcript of © Prof.Dr.R.Haller Lightning Discharge 1 Introduction 2 Physical Phenomena 3 Effects and Typical...
© Prof.Dr.R.Haller
© 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
2 Physical Phenomena
3 Effects and Typical Parameters
4 Lightning protection
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
© Prof.Dr.R.Haller
… 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
Lightning Discharges
1 Introduction
2 Physical Phenomena
3 Effects and Typical Parameters
4 Lightning protection
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
© Prof.Dr.R.Haller
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
© Prof.Dr.R.Haller
Global distributionGlobal distribution
(NASA Satellite 1996-2000)• 50 flashes per second (in 1000 aktive thunderstorms)• Maximum about tropical areas (shore)
© Prof.Dr.R.Haller
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
© Prof.Dr.R.Haller
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
+ + +++ + + + +
© Prof.Dr.R.Haller
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
© Prof.Dr.R.Haller
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
Generation of lightning (neg. CG)Generation of lightning (neg. CG)
the most important part for the target point is the last step (before ground)
final striking distance
© Prof.Dr.R.Haller
Generation of lightning (neg. CG)Generation of lightning (neg. CG)
This behaviour can be used for evaluation of target point
(rolling sphere model)
© Prof.Dr.R.Haller
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
© Prof.Dr.R.Haller
Types of lightning Types of lightning
negative/ positive CG- stroke(positive CG 5 .. 10%)
negative/ positive GC- stroke
© Prof.Dr.R.Haller
Generation of lightning (neg. CG)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 ~ (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
© Prof.Dr.R.Haller
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
Lightning Discharges
1 Introduction
2 Physical Phenomena
3 Effects and Typical Parameters
4 Lightning protection
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
© Prof.Dr.R.Haller
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
© Prof.Dr.R.Haller
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)
© Prof.Dr.R.Haller
Damages in nature (trees)Damages in nature (trees)
typical spiral- structure
exploded, broken by vaporized water
© Prof.Dr.R.Haller
Damages in airplanesDamages in airplanes
hole by melting
stroke in radar
Space-shuttle
© Prof.Dr.R.Haller
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
© Prof.Dr.R.Haller
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
© Prof.Dr.R.Haller
U = imax ·RE
Effects by maximal current
© Prof.Dr.R.Haller
© Prof.Dr.R.Haller
© Prof.Dr.R.Haller
U = M · Δi/ Δt
Effects by current gradient
© Prof.Dr.R.Haller
© Prof.Dr.R.Haller
Q = ∫ i dt
W = Q · UA,K
Effects by charge (of lightning)
© Prof.Dr.R.Haller
© 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
© Prof.Dr.R.Haller
Lightning Discharges
1 Introduction
2 Physical Phenomena
3 Effects and Typical Parameters
4 Lightning protection
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
© Prof.Dr.R.Haller
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
© Prof.Dr.R.Haller
Standardized lightning currents
© Prof.Dr.R.Haller
External lightning protection
© Prof.Dr.R.Haller
“rolling sphere“
External lightning protection
© Prof.Dr.R.Haller
Protection against lightning
© Prof.Dr.R.Haller
External lightning protection
© Prof.Dr.R.Haller
External lightning protection
© Prof.Dr.R.Haller
protection model of the cathedral of Aachen
(protection class II, III)
External lightning protection
© Prof.Dr.R.Haller
Lightning Protection System
© Prof.Dr.R.Haller
Lightning Protection System
© Prof.Dr.R.Haller
Lightning Protection System
© Prof.Dr.R.Haller
Internal lightning protection
protection by environmental zones [Vance, 1980]
Lightning Protection Zones (LPZ)
© Prof.Dr.R.Haller
Internal lightning protection
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
Internal lightning protection
© Prof.Dr.R.Haller
Internal lightning protection
example for zone- concept in LV- installation
© Prof.Dr.R.Haller
Internal lightning protection
© Prof.Dr.R.Haller
Lightning Discharges
1 Introduction
2 Physical Phenomena
3 Effects and Typical Parameters
4 Lightning protection
5 Conclusions
© 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
Thank you
Questions ?
& Answers !
© Prof.Dr.R.Haller
Impressions about lightnings
© Prof.Dr.R.Haller
© Prof.Dr.R.Haller
© Prof.Dr.R.Haller
© Prof.Dr.R.Haller
© Prof.Dr.R.Haller
© Prof.Dr.R.Haller
© Prof.Dr.R.Haller
Ball lightningBall lightning
© Prof.Dr.R.Haller
© Prof.Dr.R.Haller
Ball lightningBall lightning
© 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
© 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