lightning activity

7/29/2019 Lightning Activity

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FachgebietHochspannungstechnik

High Voltage Technology / Chapter 11 - 1 -

Lightning Activity


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Lightning Activity

Worldwide about 2000 thunderstorms at any time

Worldwide about 2000 thunderstorms at any time

Estimation: 100 lightning strokes every second

Estimation: 100 lightning strokes every second

Strong local differences in lightning activities

Strong local differences in lightning activities

But for each region constant average lightning activity

But for each region constant average lightning activity

Lightning maps can be produced

Lightning maps can be produced

Keraunic level TD = number of thunderstorm days per year

Keraunic level TD = number of thunderstorm days per year


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Lightning Activity

Keraunic levels worldwide

Keraunic levels worldwide

Middle Europe: TD = 10 ... 25

in equator regions: TD = 100 ... 180




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Lightning Activity

Keraunic levels worldwideKeraunic levels worldwide

TD = 20 ... 80




in equator regions: TD = 100 ... 180TD = 80 ... 180


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Lightning Activity

Keraunic level GermanyKeraunic level Germany

Mean values

Lightning ground flash density Ng = number of lightning ground flashes per km2 and year

= N T1.25g d

0.04Empirical relation: Ng in (km

2

a)-1


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Lightning Activity


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Lightning Activity

Lightning ground flash detection and tracking systemsLightning ground flash detection and tracking systems


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Lightning Activity

Thunderstorms in Germany 29.6.2005, recorded by BLIDSThunderstorms in Germany 29.6.2005, recorded by BLIDS

http://www.blids.de


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Lightning Activity


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Lightning Activity

http://www.aldis.at/


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Lightning Activity

http://www.meteorage.fr/meteorage.fr/index.php


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Formation of Thunderstorms

Pre-conditions: strong upwinds and high humidity

Thermal thunderstormThermal thunderstorm

Ground temperatures > 30 C; warm air is raising up, cold air comes down in turnand flows back sideways

Front thunderstormFront thunderstorm

Mass ofcold air slides underhumid and warm mass of air

Warm and humid air raises up condensation of contained humidity:clouds of thunderstorms contain rain, snow and ice crystals

Warm and humid air raises up

condensation of contained humidity:clouds of thunderstorms contain rain, snow and ice crystals


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Tropopause

propagation

prevailingwind direction

wind direction on ground

rain

snow

ice crystals

rain


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propagation

prevailing

wind direction

wind direction on ground

rain

snow

ice crystals

rain

Generation mechanism of electricity not yetfully understood; contribution of scattering of water droplets fragmentation of ice crystals

freezing of polarized water droplets

Typical charge distribution: positive charge on top

negative charge at the bottom small positive area at the bottom

Thunderstorm cloud = dipole chargedto 25 As (in average)

Thunderstorm cloud = dipole charged

to 25 As (in average)


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Lebenszyklus einer Gewitterwolke: Startphase, Entwicklungsphase, Reifestadium, Abbauphase

maximum external activitymaximum external activity

maximum internal activitymaximum internal activity

Life cycle of a thunderstorm cloud: initial phase, development phase, mature phase, decay phase

Average life time: ca. 1 h


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Lightning Discharge

When the breakdown electric field strength at the cloudsedge has been reached:Streamerdischarge starting in the cloudPropogation of a first leader10 m to 200 m long

Development of a stepped leaderDevelopment of a stepped leader

Charge tube: several 10 mCharge tube: several 10 m

Plasma core: ca. 2 mmPlasma core: ca. 2 mm

Center ofnegative charges

Influencedpositive charges


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Lightning Discharge




After a time interval of 10 s to 100 s(during this time additional charge flowswithin and from the cloud):Formation of a new leader


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Lightning Discharge

etc. etc.propagation of the

stepped leader

Direction of individual leadersnot uniform; depends on field

distribution and ionizationconditions.

Increase of groundelectric field strength!

Approximation to ground up toseveral 10 meters

v 300 km/s (1/1000 c0)




Steppedleader withplasma coreand chargetube


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Lightning Discharge

Connecting leader

(developing from streamers)propagates towards thestepped leader

After unification:

Return strokeReturn stroke

propagates upwards light flash rolling thunder v 30 000 km/s (1/10 c0) up to 200 kA time duration only few 10 s






Connecting leader


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Lightning Discharge

Return stroke emptiesthe charge tube

Plasma core ofstepped leader

Charge tubeof steppedleader

Return stroke

Current flow of returnstroke caused by

discharge of thecharge tube, not ofthe cloud!

Current flow of returnstroke caused bydischarge of the

charge tube, not ofthe cloud!


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Lightning Discharge

Further discharge of the cloud by subsequent strokes (multiple strokes) in timeintervals of 10 ms to 100 ms, utilizing the pre-ionized discharge channel

Single (not stepped) leaders (dart leaders) at v 3000 km/s (1/100 c0)

higher front steepness lower amplitude up to 54 follow strokes reported --> flashing of a lightning flash

often: dc component(in ca. 50% of all cases)11 current impulses of 7 kAup to 63 kA peak value

dc component

scale of dccomponent


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Lightning Discharge

Multiple strokes of a negative cloud-to-ground lightning flash

discharge channels separated by wind

branches of first stroke directed downwards indicate cloud-to-earth flash

subsequent strokes do not have branches dart leaders time interval between first and second stroke so long that the

flash finds a new point of strike

veil of last stroke indicates a dc component


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Types of Lightning Flashes

> 90%> 90%

fromexposedpoints suchas aerials,tv towers

no subsequentstrokes,highestreportedcurrent peakvalues andcharges

Seldom!

downward flash

upward flash

cloud-to-cloud flash

negative cloud-to-ground positive cloud-to-ground

negative ground-to-cloud positive ground-to-cloud


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Lightning Activity


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Lightning Current Parameters

Lightning currents are imposed currents!Lightning currents are imposed currents!

Surge impedance of discharge channels: 900 (@ 50 kA) 2000 (@ 10 kA)

Surge impedance overhead line:

300

Grounding surge impedance: < 10 up to several 10


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Four important lightning current parameters:Four important lightning current parameters:

peak value peak value

maximum steepness Smax (also: di/dtmax)maximum steepness Smax (also: di/dtmax)

charge idt(current-time integral)charge idt(current-time integral)

i-squared-time integral i2dt(action integral)

i-squared-time integral i2dt(action integral)

Impulse current of acloud-to-ground stroke

several 100 micro-seconds

h P


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Peak value Peak value = 5 kA ... 100 kA (250 kA as an extreme)

Resistive voltage drops at grounding structures overvoltages, flashovers

Resistive voltage drops at grounding structures overvoltages, flashovers

Amplitude of overvoltages propagating as traveling waves along lines(= Z)

Amplitude of overvoltages propagating as traveling waves along lines(= Z)

Grounding impedance should be < 10 !Grounding impedance should be < 10 !

Kind of ground in m

Humid soil 30

Humid sand 200

Dry gravel 1000

Rocks 3000

Li h i C P


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Hufigkeit der Blitzstromscheitelwerte (1: erste negative Teilblitze; 2: negative Folgeblitze; 3: positive Blitze)

Peak value Peak value = 5 kA ... 100 kA (250 kA as an extreme)50%-value 30 kA

= 5 kA ... 100 kA (250 kA as an extreme)50%-value 30 kA

Relative occurrence of lightni es)ng current peak values (1: 1st negative stroke; 2: negative subsequent strokes; 3: positive strok

Relativeoccurrence

Lightning current peak value

Li ht i C t P t


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Maximum steepness Smax (also: di/dtmax)Maximum steepness Smax (also: di/dtmax)

Electromagnetically induced voltages in conductor loopsElectromagnetically induced voltages in conductor loops

Smax Most relevant for electromagneticinterference of lines, electronic circuits etc.

Most relevant for electromagneticinterference of lines, electronic circuits etc.

In Schleifen induzierte Spannungen innerhalb eines durch einen Blitzableiter geschtzten Gebudes1: Eigenschleife des Blitzableiters mit mglicher berschlagstrecke s12: Schleife aus Blitzableiter und Installationsleitung mit mglicher berschlagstrecke s2

3: Vom Blitzableiter isolierte Installationsschleife mit mglicher berschlagstrecke s3

Voltages induced to conductor loops in a building protected by a Franklin rod

1: intrinsic current loop of the lightning conductor with possible flashover distance s12: loop formed by lightning conductor and power installation with possible flashoverdistance s23: completely isolated loop (e.g. of power supply system) with possible flashover

distance s3

Building

Lightning conductor

Li ht i C t P t


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Maximum steepness Smax (also: di/dtmax)Maximum steepness Smax (also: di/dtmax)

Hufigkeit der maximalen Stromsteilheiten (beide Polaritten)

Smax = 1 kA/s ... 100 kA/s50%-value 20 kA/s

Smax = 1 kA/s ... 100 kA/s50%-value 20 kA/s

Relative occurrence of maximum steepness (both polarities)

Relativeoccurrence

Maximum steepness di/dt

Li ht i C t P m t s


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Charge idt(current-time-integral)Charge idt(current-time-integral)

Energy dissipation in foot point of the arc (due to u const.)

melting effects at point of strike points of flashovers

Energy dissipation in foot point of the arc (due to u const.) melting effects at point of strike points of flashovers

Energy absorption capability of distribution surge arresters

and line arresters

Energy absorption capability of distribution surge arresters

and line arresters



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Charge idt(current-time-integral)Charge idt(current-time-integral)

Hufigkeit der Ladungen (1: alle Blitze aus 119 Messungen; 2: negative Blitze; 3: positive Blitze;4: erste negative Teilblitze; 5: Stokomponenten der ersten negativen Teilblitze)

idt= 1 As ... 100 As (350 As as an extreme50%-value 10 As

idt= 1 As ... 100 As (350 As as an extreme50%-value 10 As

Relative occurrence of charges (1: all flashes out of 119 measurements; 2: negative flashes;3: positive flashes; 4: 1st negative strokes

Relativeoccurre

nce

Charge



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i-squared-time integral i2dti-squared-time integral i2dt ("action integral")

Thermal heating of conductors R i2dtThermal heating of conductors R i2dt

Mechanical impulse FdtMechanical impulse Fdt

electro thermal

electro dynamiceffects

Heating

Mechan

icalimpulse

Lightning conductor



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Hufigkeit der Stromquadrat-Zeitintegrale (1: alle Blitze aus 206 Messungen; 2: negativeTeilblitze; 3: positive Teilblitze)

i2dt= 103A2s ... 107A2s50%-value 2104A2s

i2dt= 103A2s ... 107A2s50%-value 2104A2s

i-squared-time integral i2dti-squared-time integral i2dt

Relative occurrence of i-squared-time integrals (1: all flashes out of 206 measurements; 2: negative flashes;3: positive flashes

Relativeoccurrence

i-squared-time integral



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Basic difference of negative / positive lightning discharges with regard to course in time occurrence of subsequent strokes peak value

Basic difference ofnegative / positive lightning discharges with regard to course in time occurrence of subsequent strokes peak value

1st stroke

2nd stroke

3rd stroke

Time

Time

Current

Current

Countermeasures against lightning flash


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Providing pre-defined points of strikeProviding pre-defined points of strike

Shield wire foroverhead linesShield wire foroverhead lines

Lightning rods, meshes, wires, ropes forbuildingsLightning rods, meshes, wires, ropes forbuildings

Lightning current arrestersLightning current arresters

Surge

arrestersSurge

arresters external protection onlyexternal protection only

Concept oflightningprotection zones (LPZ)

Concept oflightningprotection zones (LPZ)

IEC 61024-1



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LPZ 0A: Direct lightning strikes and high electromagnetic fieldsLPZ 0B: No direct lightning strikes, but high electromagnetic fieldsLPZ 0C: Threat by contact or step voltages for living beings (3 m height /

3 m depth around the building)LPZ 1: Protected electrical system, weakened electromagnetic fields

(typically 30 dB)LPZ 2: Centrally protected terminal equipment, considerably weakened

electromagnetic fields

LPZ 3: Protected area within a terminal equipment. Protected by thisconcept, electronic equipment can also work at direct or closelightning strikes without interference.

HAK = Main connection boxB = B arrester (lightning current arrester)C = C arrester (surge arrester, high energy)D = D arrester (surge arrester, low energy)

Recommendation: for more info see http://www.dehn.de/www_DE/frameset_E.html



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Theory of protection zone by the electro-geometrical modelTheory of protection zone by the electro-geometrical model (former CIGR SC 33)

Hypothesis:

Once the head of the stepped leader has approached any object on ground bya certain distance (the final breakdown distance), the connecting leader willbridge this distance along the shortest possible path.

Once the head of the stepped leader has approached any object on ground bya certain distance (the final breakdown distance), the connecting leader willbridge this distance along the shortest possible path.

Following dependence of the final breakdown distance hB from the peakvalue of the first stroke

= +

h 6.8B

2 30 (1 e ) hB

in m; in kA

The higher the peak value of the first stroke, the higher is hB.

Lightning Discharge


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Lightning Discharge


Influenced

positive charges

Stepped

leader with

plasma core

and charge

tube

Development of stepped leaderDevelopment of stepped leader

increase ofground fieldstrength!

The higher the ground fieldstrength, the higher is thedistance which can be bridged

by a breakdown.

The more charge is containedin the charge tube, the higheris the ground field strength.

The more charge is containedin the charge tube, the higheris the current peak value of

the first stroke.

The higher the lightning

current peak value, the higher

the final breakdown distance!

The higher the lightning

current peak value, the higher

the final breakdown distance!



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Protected space of a lightning rodProtected space of a lightning rod

Lightning rod Protected space

Protected space of a lightning rod of height h< hB



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unt rm a ur aga n t g tn ng f a

Protected space cannot

become larger thanthat of a lightning rod ofheight h= hB!

Protected space cannot

become larger thanthat of a lightning rod ofheight h= hB!

Protected space of a lightning rodProtected space of a lightning rod

Protected space of a lightning rod of height h> hB

Protected space



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g g g

Protected space of a shield wireProtected space of a shield wire

Protected space

Protected space of a shield wire of elevation h< hB



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g g g


Protected space

Protected space of a shield wire of elevationh

>h

B



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g g g


hB

h = hB

hB

h = hB



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g g g


hB

h > hB

hBhB

h > hB



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hB

h = hB

hB

h = hB



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Protected space of a shield wireProtected space of a shield wire Optimum forh= hBOptimum forh= hB

hB

h < hB

hBhB

h < hB



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Anwendung der Blitzkugel-Methode bei der Blitzschutzplanung von Gebuden

Alle schraffierten Flchen mssen durch

Fangeinrichtungen geschtzt werden.

Rolling sphere methodRolling sphere method

All hashed areas (i.e. all those which can betouched by the sphere) must be protected by

lightning rods/meshes/wires

Application of rolling sphere method for developing a lightning protection concept for buildings



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Shielding angleProtectionclass

Sphere

radius

(m)

Meshwidth

Efficiency E

Protected space

Height of lightning rod aboveground

Radius of lightning sphereShielding angle



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Rolling sphere

Application of the rolling sphere method: aslong as the sphere only touches the lightningrods but not the building, the degree ofprotection is sufficient



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Lightning Protection of Overhead Lines


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Application of the rolling sphere methodApplication of the rolling sphere method

hB

i = ilimit

Line conductors protected!Line conductors protected!



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hB


i > ilimit




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hB i < ilimit

Line conductors not protected!Line conductors not protected!



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hB i < ilimit

Higher elevationof shield wire

Line conductors not protected!Line conductors not protected!



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hB

i < ilimit

Double shield wire




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Max. current peak value of a direct lightning stroke to an overhead line conductorMax. current peak value of a direct lightning stroke to an overhead line conductor

E

L

S

a

b

hB

hB is the maximum final breakdowndistance for a direct stroke to theline conductor.

Thus the current peak value whichbelongs to hB is the maximumpossible current amplitude of adirect stroke to the line conductor.

hB is the maximum final breakdowndistance for a direct stroke to theline conductor.

Thus the current peak value which

belongs to hB is the maximumpossible current amplitude of adirect stroke to the line conductor.

a= location of allpoints of equi-distances to theline conductorof concern andto ground

"shielding angle"

Note: Cigr recommends a slightly

differing method see lecture"Insulation Coordination"; there furtherinformation is given on lightningprotection of overhead lines.

(One of several possible approaches)



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Relative occurrence of direct lightning strokes to overhead linesRelative occurrence of direct lightning strokes to overhead lines

i

ilimit

1

2

3

i1

hB,E,1

hB,L,1

Width of attraction for line conductor

bL,1Width of attraction for shield wirebE,1

Multiplication of total area of attractionwith ground flash density Ng: Relative occurence of direct strokes

for current of amplitude i1

Multiplication of width of attractionwith length of overhead line: total area of attraction of the line

Same procedure for other amplitudes:Relative occurrence of direct

strokes to the line in general



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Even terrain Hilly terrain

N=30 to 60 strokes/100 kma

Line strokes/system:1.6 to 3.2/100 kma

Flashovers/system:0.8 to 1.6/100 kma




N=20 to 40 strokes/100 kmaLine strokes/system:0.2 to 0.4/100 kmaFlashovers/system:0.2 to 0.4/100 kma







N=22 to 44 strokes/100 kmaLine strokes/system:0.35 to 0.7/100 kmaFlashovers/system:0.35 to 0.7/100 kma



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Bad! ("shielding failure")

Good!



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Back flashoverBack flashover

iB = 2iE + iM

uM = iMRMShield wire

Line conductor

RM ... Tower surge impedanceRM ... Tower surge impedance

uinsul. = uM - uL

At unfavorable phase relation:uinsul. = uM + |uL|

If

uinsul. > ud, LI



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Countermeasure: RM < 10 Countermeasure: RM < 10

Else: line arrestersElse: line arresters

Shield wire

Line conductor

gapless

gapped



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Line ArrestersLine Arresters



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Stromaufteilung auf benachbarte Masten nach einem Masteinschlag bzw. einem Einschlag in das Erdseilin Spannfeldmitte; gleiche Maststoerdungswiderstnde angenommenDistribution of lightning current fractions among neighboring towers after a stroke to a tower and after a mid

span stroke to the shield wire respectively (identical tower surge impedances assumed)

lightning activity

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