Download - Lightning Activity
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High Voltage Technology / Chapter 11 - 1 -
Lightning Activity
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High Voltage Technology / Chapter 11 - 2 -
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
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
Middle Europe: TD = 10 ... 25
in equator regions: TD = 100 ... 180
Middle Europe: TD = 10 ... 25
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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High Voltage Technology / Chapter 11 - 10 -
Lightning Activity
http://www.aldis.at/
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High Voltage Technology / Chapter 11 - 11 -
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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Formation of Thunderstorms
Tropopause
propagation
prevailingwind direction
wind direction on ground
rain
snow
ice crystals
rain
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High Voltage Technology / Chapter 11 - 14 -
Formation of Thunderstorms
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High Voltage Technology / Chapter 11 - 15 -
Formation of Thunderstorms
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High Voltage Technology / Chapter 11 - 16 -
Formation of Thunderstorms
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High Voltage Technology / Chapter 11 - 17 -
Formation of Thunderstorms
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High Voltage Technology / Chapter 11 - 18 -
Formation of Thunderstorms
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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Formation of Thunderstorms
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
Center ofnegative charges
Influencedpositive charges
Development of a stepped leaderDevelopment of a stepped leader
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)
Center ofnegative charges
Influencedpositive charges
Development of a stepped leaderDevelopment of a stepped leader
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
Center ofnegative charges
Influencedpositive charges
Development of a stepped leaderDevelopment of a stepped leader
Steppedleader withplasma coreand chargetube
Steppedleader withplasma coreand chargetube
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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Lightning Current Parameters
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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Lightning Current Parameters
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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Lightning Current Parameters
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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Lightning Current Parameters
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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Lightning Current Parameters
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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Lightning Current Parameters
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
Lightning Current Parameters
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Lightning Current Parameters
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
Lightning Current Parameters
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Lightning Current Parameters
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
Lightning Current Parameters
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Lightning Current Parameters
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
Lightning Current Parameters
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Lightning Current Parameters
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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Countermeasures against lightning flash
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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Countermeasures against lightning flash
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
Countermeasures against lightning flash
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Countermeasures against lightning flash
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
Center ofnegative charges
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!
Countermeasures against lightning flash
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Countermeasures against lightning flash
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 of a shield wireProtected space of a shield wire
Protected space
Protected space of a shield wire of elevationh
>h
B
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g g g
Protected space of a shield wireProtected space of a shield wire
hB
h = hB
hB
h = hB
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g g g
Protected space of a shield wireProtected space of a shield wire
hB
h > hB
hBhB
h > hB
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Protected space of a shield wireProtected space of a shield wire
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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Rolling sphere methodRolling sphere method
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 methodRolling sphere method
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!
Lightning Protection of Overhead Lines
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hB
Application of the rolling sphere methodApplication of the rolling sphere method
i > ilimit
Line conductors protected!Line conductors protected!
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 not protected!Line conductors not protected!
Lightning Protection of Overhead Lines
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Application of the rolling sphere methodApplication of the rolling sphere method
hB i < ilimit
Higher elevationof shield wire
Line conductors not protected!Line conductors not protected!
Lightning Protection of Overhead Lines
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Application of the rolling sphere methodApplication of the rolling sphere method
hB
i < ilimit
Double shield wire
Line conductors protected!Line conductors protected!
Lightning Protection of Overhead Lines
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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)
Lightning Protection of Overhead Lines
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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
Lightning Protection of Overhead Lines
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Relative occurrence of direct lightning strokes to overhead linesRelative occurrence of direct lightning strokes to overhead lines
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=26 to 52 strokes/100 kma
Line strokes/system:0.7 to 1.4/100 kma
Flashovers/system:0.4 to 0.8/100 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=35 to 70 strokes/100 kma
Line strokes/system:3.0 to 6.0/100 kma
Flashovers/system:1.7 to 3.4/100 kma
N=30 to 60 strokes/100 kma
Line strokes/system:1.4 to 2.8/100 kma
Flashovers/system:1.0 to 2.0/100 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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Relative occurrence of direct lightning strokes to overhead linesRelative occurrence of direct lightning strokes to overhead lines
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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Back flashoverBack flashover
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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High Voltage Technology / Chapter 11 - 68 -
Back flashoverBack flashover
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)