01 rakov cigre lightning parameters

7/26/2019 01 Rakov CIGRE Lightning Parameters

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CIGRE Technical Brochure onLightning Parameters for

Engineering Applications

Department of Electrical and Computer Engineering

University of Florida, Gainesville, Florida

IV International Conference on Lightning Protection

t! Peters"urg, #ussia, $ay %&'%(, %)*+

Vladimir A. Rako

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CIGRE (G C).)"* has completed its 'ork on theTechnical Brochure in 0a/ !"14. This Brochure%CIGRE TB 5)6$ !"14& can 2e ie'ed as anupdate on preious CIGRE documents on thesu27ect pu2lished in Electra more than threedecades ago8 Berger et al. %16*5& and Andersonand Eriksson %16#"&.

This lecture is largel/ a presentation of theE9ecutie ummar/ of CIGRE TB 5)6 %!"14&$e9panded to include some illustrations.

Anderson, R.B., and Eriksson, A.J. 198. Lightning parameters for engineeringapplication. Electra, No. 69, pp. 65-102.

Berger, !., Anderson, R.B., and !roninger, ". 19#$. Parameters of lightningashes. Electra, No. 41, pp. 2-!.

CI%RE &B $'9, Lightning Parameters for Engineering "pplications, #$ %4.40!,&.". 'a(o), %on)enor *+, ". orghetti, ecretar/ *, %. o3egnea *E, #.".


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General Characteri:ation of Lightning

About 80%or more of negative cloud-to-ground

lightning ashes are composed of two or morestrokes. This percentage is appreciably higher than%previously estimated by Anderson and !riksson"#$80& based on a variety of less accurate records.

'oughly one-third to one-half of lightning ashescreate two or more terminations on ground separatedby up to several kilometers.

(n order to account for multiple channel terminationson ground& a correction factor of #.-#.)"considerably larger than #.#previously estimated byAnderson and !riksson "#$80 for the ground ash

density is needed. *ou+uegneau et al. ",0#,suggested a conservative value of ,for lightning risk


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Histogram of the distances between the multiple terminations of 22 individual ground flashesin Florida. The distances were determined using optical triangulation and thunder ranging.

Adapted from Thottappillil et al. (1992).

ultiple !hannel Terminations on "round

$in )!- .m

$a/ &!- .m

G$ *!& .m


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Return;troke Parameters 3eried fromCurrent 0easurements

/irect current measurements by . *erger and co-workers in wit1erlandremain the primaryreference for both lightning research and lightningprotection studies. *erger2s peak currentdistributions are generally con3rmed by recent

direct current measurements& particularly by thosewith larger sample si1es obtained in4apan "56#,0&Austria "567#& and lorida "56#7.

rom direct current measurements& the medianreturn-stroke peak current is about 90 kA fornegative 3rst strokes and typically #0-# kA forsubse+uent strokes. Additional measurements areneeded to determine more reliably the tails of thestatistical distributions. As of today& there is no


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!umulative statistical distributions of lightning pea# currents$ giving percent ofcases e%ceeding abscissa value$ from direct measurements in &wit'erland(erger et al. 19*). The distributions are assumed to be lognormal and given for(1) negative first stro#es(+,1-1)$ (2) positive first stro#es (+,2)$ and (/)negative subse0uent stro#es (+,1/*).

ightning pea# currents forfirst stro#esvar b a

factor of *- or more$ fromabout* to 2*- #A.

The probabilit ofoccurrence of a givenvalue rapidl increases up

to2* #Aor so and thenslowl decreases.&tatistical distributions ofthis tpe are oftenassumed to be lognormal.

Lightning Pea. Current 0 1erger2s Distri"utions

+egative first stro#es

+egativesubse0uent stro#es

3ositive first stro#es


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!umulative statistical distributions ofpea# currents for negative first stro#esadopted b 4555 and !4"65 (+ , 7-8).Ta#en from !4"65 6eport / (1991).

For the CIG#E distri"ution, (34 of pea.

currents e/ceed + .5, 3)4 e/ceed %)

.5, and 64 e/ceed () .5!

For the IEEE distri"ution, the

7pro"a"ility to e/ceed8 values are given

"y the follo9ing e:uation

9here ;Iis in per unit, and I is in .5!


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Return;troke Parameters 3eried from Current0easurements

/irect lightning current measurements oninstrumented towers should be continued.urrently& direct current measurements areperformed on instrumented towers in

; Austria %%ais(erg &o)er, 1 m&$; Bra:il %*orro do Cac+im(o &o)er, m&$; Canada %C- &o)er, $$ m&$

; German/ %/eissen(erg &o)er, 1 m&$;


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Return;troke Parameters 3eried fromCurrent 0easurements

'ecommended lightning current waveshapeparameters are still based on *erger et al.2s"#$) data& although the current rate-of-riseparameters estimated by Anderson and!riksson "#$80 from *erger et al.=soscillograms are likely to be signi3cantlyunderestimated& due to limitations of the

instrumentation used by *erger et al.

Triggered-lightning data for current rates ofrise"ac+uired using modern instrumentation

can be applied to subse+uentstrokes in


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Parameter Description

I10 1- intercept along the stro#e current waveshapeI30 /- intercept along the stro#e current waveshapeI90 9- intercept along the stro#e current waveshape

I100= II 4nitial pea# of currentIF Final (global) pea# of current (same as pea# current without an ad:ective)

T10/90 Time between I10 and I90 intercepts on the wavefrontT30/90 Time between I30 and I90 intercepts on the wavefront

S10 4nstantaneous rate;of;rise of current at I10S10/90

Average steepness (through I10 and I90 intercepts)S30/90 Average steepness (through I30 and I90 intercepts)

Sm a%imum rate;of;rise of current along wavefront$ tpicall at I90td 10/90 50uivalent linear wavefront duration derived from IF / S10/90td 30/90 50uivalent linear wavefront duration derived from IF / S30/90

t m 50uivalent linear waveform duration derived from IF / SmQI 4mpulse charge (time integral of current)

/escription of lightning current waveform parameters. The waveformcorresponds to the typical negative 3rst return stroke. Adapted from(>'! /ocument 79 "#$$# and (!!! td #


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Parameters of log'normal distri"ution for negative do9n9ard flashes

Parameter

First stro.e u"se:uent stro.e

M, $edian

standarddeviation

F#?@<

td10/90

= T10/90

=-.8 6!B- -.* )!&6 -.921

td30/90

= T30/90

=-. -!3- -.**/ )!B& 1.-1/

tm=IF/ Sm *!%3 -.11 )!-)3 -.-8

Sm$ a%imum %+!- -.*99 -(!( -.8*2

S10

, at 1- %!B -.921 *3!( 1.7-7

S10/90

, 1-;9- 6!) -.7* *6!+ -.977

S30/90, /-;9- &!% -.22 %)!* -.9

PE5 =C#E CU##E@< =.5>

II, initial %&!& -.71 **!3 -.*/-

IF, final -*!* -.787 *%!- -.*/-

6atio$ II/IF )!( -.2/- )!( -.2-

Lightning current parameters %2ased on Berger=s data&recommend 2/ CIGR> 3ocument ?4 %1661& and IEEE td1)1";!"1"


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'elation between the peak value of "ma:imum current

rate of rise and peak current from triggered-lightninge:periments conducted at the 5AA ennedy paceenter& lorida& in #$8& #$8)& and #$88 and in rancein#$87. The regression line for each year is shown& and thesample si1e and the regression e+uation are given.

Adapted from ?eteinturier et al. "#$$#.


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Peak Current Inferred from 0easuredElectromagnetic ield

The 3eld-to-current conversion procedure employed bythe B.. 5ational ?ightning /etection 5etwork "5?/5and other similar lightning locating systems has beencalibrated& using rocket-triggered lightning data andtower-initiated lightning data& only for negativesubse+uent strokes& with the median absolute errorbeing #0 to ,0%.Ceak current estimation errors for negative 3rst strokesand for positive lightning are presently unknown.

*esides systems of 5?/5 type& there are other lightninglocating systems that are also reporting lightning peakcurrents inferred from measured 3elds& including ?(5!T

"mostly in !urope& BC?5"in the B..& but similarsystems operate in other countries& !5T?5"in the B..


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5?/5 reported peak currents vs. those directly measured at amp*landing& lorida& for ,78 negative strokes in lightning triggered in ,00


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Continuing Currents

The percentage of positive ashes or strokescontaining continuing currents " is muchhigher than that of negative ashes orstrokes. Cositive strokes tend to be followed

by longer and more intense than negativestrokes.

5egative strokes initiating long"F


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Ceak current "(p versus duration for 87

negative strokes and #


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Lightning Return troke Propagation peed

The lightning return-stroke speed is needed in

computing lightning electromagnetic 3elds thatcause induced overvoltages in power distributionlines. (t is also e:plicitly or implicitly assumed inprocedures to infer lightning currents from

measured 3elds.

The average propagation speed of a negativereturn stroke "3rst or subse+uent below the lowercloud boundary is typically between one-third andone-half of the speed of light.

(t appears that the return-stroke speed for 3rststrokes is lower than that for subse+uent strokes&

although the diGerence is not very large "$.7 H #0)8


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Euialent Impedance of the Lightning Channel

The e+uivalent impedance of the lightning channel&

Ich& is needed for specifying the source in studies ofeither direct-strike or induced lightning eGects.

The estimates of this impedance from limitede:perimental data suggest values ranging from

several hundred ohms to a few kiloohms. (n manypractical situations the impedance JseenK bylightning at the strike point is some tens of ohms orless& which allows one to assume in3nitely large

e+uivalent impedance of the lightning channel. (nother words& lightning in these situations can beviewed as an ideal current source.

'epresentation of lightning by a current source withinternal impedance of


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Positie and Bipolar Lightning 3ischarges

(n spite of the recent progress& our knowledge of thephysics of positive lightning remains considerably poorerthan that of negative lightning.

*ecause of the absence of other direct currentmeasurements for positive lightning return strokes& it is

still recommended to use the peak current distributionbased on the ,7 events recorded by . *erger& eventhough some of those ,7 events are likely to be not ofJclassicalK return-stroke type.

learly& additional measurements for positive lightningreturn strokes are needed to establish reliabledistributions of peak current and other parameters forthis type of lightning.


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ightning 3arameters ?erived from ?irect !urrent easurements


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ightning 3arameters ?erived from ?irect !urrent easurements

3arameters @nits&ample

&i'e

3ercent 5%ceeding Tabulated alue

9* *- *

3ea# current (minimum 2 #A)

First stro#es &ubse0uent stro#es #A

1-11/* 177. /-12 8-/-

!harge (total charge) First stro#es &ubse0uent stro#es !omplete flash

!

9/

12297

1.1-.21./

*.21.7.*

27117-

4mpulse charge (e%cluding

continuing current) First stro#es &ubse0uent stro#es

!

9-11

1.1-.22

7.*-.9*

2-7

Front duration (2 #A to pea#) First stro#es &ubse0uent stro#es

Bs89

1181.8-.22

*.*1.1

187.*

a%imum d4=dt First stro#es &ubse0uent stro#es #A Bs

;1 92122

*.*12

127-

/2

12-

&tro#e duration (2 #A to halfpea# value on the tail) First stro#es &ubse0uent stro#es

Bs9-11*

/-.*

*/2

2--17-

Action integral (C42dt) First stro#es

&ubse0uent stro#esA2s 91

88

.- % 1-/

*.* % 1-2

*.* % 1-7

.- % 1-/

*.* % 1-*

*.2 % 1-7

i ht i i d d lt h d li


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Tpical 4nduced oltage at a distance of 17* m and !orresponding &tro#e !urrent (9/;-*)

ightning;induced voltages on overhead power lines

, *- #

4 , ;22./ #A


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triking distance %! times the return;stroke initiation height& s.return;stroke peak current deried from luminosit/ for * strokesin the anomalous Fash %h 1" m& triggered at Camp Blanding in!"1!. The red cure is 2ased on data for 1) classical triggered;lightning strokes%'ith directl/ measured currents$ h 5 m&

Wang et al. (2014)


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Return;troke Parameters 3eried from Current0easurements

The JglobalK distributions of lightning peak currents for negative3rst strokes currently recommended by (>'!and (!!!are eachbased on a mi: of direct current measurements and lessaccurate indirect measurements& some of which are of+uestionable +uality.

Lowever& since the JglobalK distributions have been widely usedin lightning protection studies and are not much diGerent fromthat based on direct measurements only& continued use of theseJglobalK distributions for representing negative 3rst strokes is

recommended& along with *erger2s distribution having a medianof 90 kA& lg( 6 0.,7.

or negative subse+uent strokes and for positive lightningstrokes& *erger2s peak current distributions are stillrecommended. or negative subse+uent strokes& a log-normaldistribution with median 6 #, kA and lg( 6 0.,7 should be


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Lightning Return troke Propagation peed


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g g p g p

There e:ists some e:perimental evidence that the negativereturn stroke speed may vary non-monotonically along thelightning channel& initially increasing and then decreasing with

increasing height.

'eturn-stroke speeds "H#08m@s at diGerent heights for 3vestrokes in a triggered lightning ash. Adapted from Nlsen et al.",00


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!ngineering models of lightning strikes "a to lumpedgrounding impedance and "b to a tall grounded ob;ect& inwhich lightning is represented by the 5orton e+uivalentcircuit& labeled WWsource22. Adapted from *aba and 'akov

",00.


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Positie and Bipolar Lightning 3ischarges

Although positive lightning discharges account for

#0% or less of global cloud-to-ground lightningactivity& there are several situations& including& fore:ample& winter storms& that appear to be conduciveto the more fre+uent occurrence of positive lightning.

The highest directly measured lightning currents"near 900 kA vs. a ma:imum of about ,00 kA or lessfor negative lightning and the largest chargetransfers "hundreds of coulombs or more are

associated with positive lightning.

Cositive ashes are usually composed of a singlestroke& although up to four strokes per ash havebeen observed. ubse+uent strokes in positiveashes can occur either in a new "a more common


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!:amples of two types of positive lightning current waveforms

observed by . *ergerU "a microsecond-scale waveform& similar tothose produced by downward negative return strokes& and a sketchillustrating the lightning processes that might have led to theproduction of this waveform "b millisecond-scale waveform and asketch illustrating the lightning processes that might have led to

the production of this current waveform. Adapted from 'akov


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Geographical and easonal Variations inLightning Parameters

rom the information available in the literature at thepresent time& there is no evidence of a systematicdependence of negative cloud-to-ground lightningparameters on geographical location& e:cept maybefor 3rst and subse+uent return-stroke peak currents&for which relatively insigni3cant "less than 0%& fromthe engineering point of view& variations may e:ist.

(t is important to note& however& that it cannot be

ruled out that the observed diGerences in currentmeasurements are due to reasons other thanPgeographical locationJ& with the limited sample si1efor some observations being of particular concern.

imilarl no reliable information on seasonal


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01 rakov cigre lightning parameters

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