CN102175936B - Unrestrictive expected operation life assessment method for distribution network lightning arrester under given confidence level - Google Patents

Abstract

The invention discloses an unrestrictive expected operation life assessment method for a distribution network lightning arrester under a given confidence level. The method comprises the following steps of: 1, monitoring the lightning overvoltage amplitudes at the installation position of the lightning arrester in one year, and counting the amplitude distribution; 2, calculating the statistical distribution of lightning impact discharge capacity resource consumption of the lightning arrester in one year; and 3, calculating the unrestrictive/restrictive lightning overvoltage expected life of the lightning arrester under the given confidence level. According to the method, the lightning overvoltage serving as a decisive factor of the service life of the lightning arrester for a distribution network is analyzed, a route and a method for calculating lightning discharge capacity resource of the lightning arrester for the distribution network and one-time lightning arrester lightning discharge capacity resource consumed by overhead circuit overvoltage due to lightning are further introduced, and finally, the expected operation life of the lightning arrester for the distribution network is calculated by adopting simplified parameters and the method.

Description

Non-limiting expection operation life appraisal procedure under the given confidence level of a kind of distribution lightning arrester

Technical field

Be the pith of electric system asset management the serviceable life of judgement electrical equipment, is also one of criterion of assessment electric system safety work.Yet the life termination of electrical equipment is the subjective judgement of electric system often, because breaking down, probably by a lot of accidentalia, caused equipment.The function of distribution lightning arrester is in order to protect other equipment, if it loses in protection, its application is valueless at all so, can cause the damage of the protected equipment that cost is higher simultaneously.Therefore, the reliability of assessment lightning arrester,, under a given confidence level, the long-term non-fault expection of assessment lightning arrester operation life is significant.

Background technology

Calculating distribution and expect operation life with lightning arrester, is when verifying that distribution limits lightning surge with lightning arrester in certain concrete distribution network systems, the reliability of its work.If having the distribution of certain confidence level P is N by lightning arrester expection operation life, N value should be not less than the setting of technical conditions, and distribution is reliable by protection of arrester distribution system.

Also do not set up relevant criterion the serviceable life of the relevant electrical equipment of China at present, not yet this is made any regulation yet.This method judges that by monitoring analysis distribution is lightning surge by the deciding factor in lightning arrester serviceable life, then introduces calculated route, step and method that thunder discharge capability resource that distribution has with lightning arrester and thunder and lightning cause the lightning arrester thunder discharge capability resource that overhead transmission line superpotential consumes.

So far there is not under a given confidence level appraisal procedure comparatively accurately of the long-term non-fault expection of assessment lightning arrester operation life.

Summary of the invention

Object of the present invention, be just to provide a kind of under given confidence level, comparatively believable distribution lightning arrester expection operation life appraisal procedure.

This appraisal procedure, comprises following steps:

Step 1: monitor the non-limiting lightning surge amplitude at lightning arrester mounting points place in a year, add up its minute

Cloth;

Step 2: the statistical distribution of calculating lightning arrester lightning impulse discharge capability resource consumption in a year;

Step 3: the expected life of calculating lightning arrester restriction lightning surge.

Further embodiment is shown in embodiment.

Beneficial effect: the function of distribution lightning arrester is in order to protect other equipment, if it loses in protection, its application is valueless at all so, can cause the damage of the protected equipment that cost is higher simultaneously.Therefore, the reliability of assessment lightning arrester,, under a given confidence level, the long-term non-fault expection of assessment lightning arrester operation life is significant.

Accompanying drawing explanation

Fig. 1 is the current wave-when thunder is attacked directly in the A of endless wire point of thunderbolt endless wire, the direct lightning strike superpotential calculating schematic diagram that A is ordered;

Fig. 2 is that the current amplitude schematic diagram of lightning arrester is passed through in the thunderbolt of Graphical Method overhead transmission line;

Fig. 3 is that current integration is asked electric charge value schematic diagram.

Embodiment

Below in conjunction with specific embodiment, the present invention is described in further detail.

This appraisal procedure, comprises following steps:

Step 1: monitor the non-limiting lightning surge amplitude at lightning arrester mounting points place in a year, add up its distribution;

Step 2: the statistical distribution of calculating lightning arrester lightning impulse discharge capability resource consumption in a year;

Step 3: the expected life of calculating lightning arrester restriction lightning surge.

The voltage magnitude of described step 1 is by monitoring below and calculating:

1, the statistical distribution of the non-limiting lightning surge amplitude in lightning arrester mounting points place for distribution

Calculate the statistical distribution of the non-limiting lightning surge in lightning arrester mounting points place, should be included in the statistics of amplitude, waveform and the annual lightning surge number of times of the non-limiting lightning surge in lightning arrester mounting points place, be i.e. mathematical expectation separately

and standard deviation (σ _k).

The landform that the factor of considering should comprise Thunderstorm Day level, thunderbolt density, line thunder protection design, the inlet wire section lightning Protection Design of the non-limiting lightning surge of circuit location, equipment layout, the method for operation and the transformer station of transformer station are of living in etc.

1.1 distribution overhead transmission line direct lightning strike Overvoltage Amplitude statistics

(1) calculating of distribution overhead transmission line direct lightning strike Overvoltage Amplitude

Because how unshielded distribution pole line is, the likelihood ratio that thunder is attacked wire directly is larger, and amplitude is also higher.When thunder is attacked directly in the A of endless wire point (as shown in Figure 1), the direct lightning strike superpotential that A is ordered is:

$U_A=\frac{i}{2}\frac{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HDA0000044407120000012.png"\; state="\{\{state\}\}">Z</figure-callout>}}{2}=\frac{i\&times;Z}{4}\left(\mathrm{kV}\right)$ --------------------------------------------------------(formula 1)

Wherein: i---lightning channel main discharge current amplitude (kA);

Z---surge impedance of a line (Ω).

(2) annual each the hundred kilometers average number of lightning strokes of attacking directly of distribution overhead transmission line calculate

Annual each the hundred kilometers average thunderbolt times N of attacking directly of the general height of distribution overhead transmission line ₁for

$\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA0000044407120000012.png,HDA0000044407120000021.png"\; state="\{\{state\}\}">N</figure-callout>}1=\mathrm{\&gamma;}\&times;\frac{10h}{1000}\&times;100\&times;T=\mathrm{\&gamma;}\&times;h\&times;T$ ---------------------------------------(formula 2)

The on average thunderbolt number of times over the ground of every square kilometre of wherein, γ---every Thunderstorm Day.

The equivalence of 10h---circuit is subject to thunder width, the average height that h is circuit, the m of unit;

T---local annual thunder and lightning number of days.

(3) thunder is attacked the lightning withstand level of aerial condutor directly

The flashover voltage of distribution line insulator is not high, as the lightning impulse flashover voltage of 10kV line insulator is approximately 75kV, if get critical value U _a=75kV, during wave impedance Z=300 Ω, when through type 1 obtains overhead transmission line direct lightning strike, the lightning withstand level I of overhead transmission line ₁=1kA.

Lightning induced voltage statistics during 1.2 distribution overhead transmission line thunderbolt circuit tower top on wire

When thunderbolt overhead transmission line tower top or near ground, can on the three-phase conducting wire of overhead transmission line, there is induced overvoltage, induced overvoltage comprises electrostatic induction component and electromagnetic induction component, conventionally due to main discharge passage and wire orthogonal, so electromagnetic induction component is little, electrostatic component plays a major role.

(1), while being struck by lightning overhead transmission line tower top, on aerial condutor, thunder and lightning induction voltage calculates

During thunderbolt overhead transmission line tower top, on aerial condutor, thunder and lightning induction voltage computing formula is:

$U_C=\frac{I\&times;h_d}{2.6}$ -------------------------------------------------------------------(formula 3)

Wherein, I---lightning channel main discharge current amplitude (kA);

H _d---overhead line conductor height (m);

(2) annual each the hundred kilometers average tower top number of lightning strokes of distribution overhead transmission line calculate

Annual each the hundred kilometers average tower top number of lightning strokes N of distribution overhead transmission line ₂for:

N ₂=γ * T * g * h=g * N ₁----------------------------------------------------(formula 4)

The average height of wherein, h---circuit (m);

G---hit number of times/thunderbolt circuit total degree of bar rate=thunderbolt head of mast (and the lightning conducter directly).

(3) lightning withstand level of thunderbolt circuit tower top

When thunderbolt circuit tower top, tower top current potential is

$U_T=I(R_E+\frac{L_T}{2.6})$ --------------------------------------------------------(formula 5)

Wherein, R _e---Tower Impulse Grounding Resistance, Ω;

L _t---shaft tower inductance, μ H;

Induced voltage on aerial condutor is (formula 3);

Voltage on line insulator is

$U_i=I(R_E+\frac{L_T}{2.6}-\frac{h_d}{2.6})$ ---------------------------------------------------(formula 6)

Lightning induced voltage on wire in the time of outside 1.3 thunderbolt distribution overhead transmission lines

(1), when thunderbolt distribution overhead transmission line is outer, on wire, lightning induced voltage amplitude is calculated

During the ground of thunderbolt outside overhead transmission line, can on the three-phase conducting wire of overhead transmission line, there is induced overvoltage.Thunder and lightning induction voltage computing formula:

$U_i=25\frac{I\&times;h_d}{l}$ -----------------------------------------------------------------(formula 7)

Wherein, I---lightning channel main discharge current amplitude (kA);

H _d---overhead line conductor height (m);

1---the vertical range (m) of lightning strike spot and wire.

(2) distribution overhead transmission line annual each hundred kilometers because occurring on thunderbolt overhead transmission line outer conductor that the number of times of lightning induced voltage calculates

Distribution overhead transmission line annual each hundred kilometers because there is the times N of lightning induced voltage on thunderbolt overhead transmission line outer conductor ₃, dodging hypothetically number of times is N, N ₃=k * N, k ∈ (0,1) wherein, N=n * S, wherein n dodges density with representing, inferior/km ²year, S represents the area of zoning, km ².

1.4 amplitude of lightning current probability statistics (the non-limiting lightning surge amplitude at lightning arrester mounting points place)

By amplitude of lightning current cumulative probability data, with least square fitting, go out the expression formula of the amplitude of lightning current cumulative probability of positive and negative polarity thunder after comprehensive:

$P(>I)=\frac{1}{1+{(I/35.6)}^{3.0}}$ -------------------------------------------------------(formula 8)

Wherein, P (> I)---amplitude of lightning current surpasses the probability of I;

I---amplitude of lightning current (kA);

What parameter 35.6 reflected is intermediate value electric current, and amplitude of lightning current is 50% over the probability of 35.6kA.

In step 2 described in 21 year, distribution comprises by the statistics of lightning arrester thunder discharge capability resource consumption:

The lightning impulse discharge capability of 1 year internal consumption of distribution lightning arrester (energy value and electric charge value) resource equals

${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="HDA0000044407120000021.png"\; state="\{\{state\}\}">T</figure-callout>}}_0=\underset{S=1}{\overset{3}{\mathrm{\&Sigma;}}}\stackrel{\&OverBar;}{N_S}\stackrel{\&OverBar;}{T}$ -----------------------------------------------------------------(formula 9)

Wherein,

---the expection useful effect number of times of lightning arrester operation lightning surge during a year for distribution;

---the mathematical expectation of the lightning impulse discharge capability resource (energy value or electric charge value) of a lightning surge consumption.

The lightning impulse discharge capability resource that 2.1 distributions consume by lightning surge of lightning arrester

(1) lightning surge is by the calculating of lightning arrester amplitude of lightning current mathematical expectation

If while only considering Lightning Incoming Wave that circuit distant place thunderbolt causes, because the wave propagation time has surpassed duration of lightning current wave, need not consider the repeatedly catadioptric synergistic effect of ripple, therefore the lightning current by lightning arrester is only single afferent echo.Can simply estimate by lightning arrester thunder and lightning streaming 10, and there is suitable accuracy.

$I=\frac{2U_{\mathrm{in}}-U_{\mathrm{res}}}{Z}$ -------------------------------------------------------------------(formula 10)

Wherein, I---by the thunder discharge electric current estimated value of lightning arrester;

U _res---lightning arrester coordinates the residual voltage under electric current;

Z---the single-phase shock wave impedance of overhead transmission line (single-phase shock wave impedance 300 Ω of 10kV overhead transmission line);

U _in---be the lightning impulse tolerance intensity (the lightning impulse tolerance intensity of the overhead transmission line insulation of 10kV isolated neutral system is 75kV) of overhead transmission line insulation.

During lightning surge, the volt-ampere characteristic of distribution lightning arrester is as follows:

U _res=U _1mA+ AI ^a--------------------------------------------------------------(formula 11)

The 10kV distribution type lightning arrester (Φ 35 * 24mm) of take is example.

U _1mA>=25kV, gets U _1mA=25kV calculates.

A. when I=2.5kA, U=44kV;

B. when I=5kA, U=48kV;

By a, b substitution above formula, try to achieve A=13.8, a=0.28,

U=25+13.8 * I ^0.28-----------------------------------------------------------------(formula 12)

The lightning withstand level of association type (10) and formula (12) Graphical Method distribution overhead transmission line.When insulator arc-over, by the amplitude of lightning current I=0.38kA of lightning arrester.

(2) lightning surges choosing by lightning arrester lightning current wavelength

Current waveform is the key factor of examination lightning arrester lightning impulse discharge current, for the lightning arrester that is applied in shielding line circuit, the duration of electric current is tens microseconds, for being applied in the lightning arrester that there is no shielding line circuit, the duration of electric current is hundreds of microsecond, according in GB11032-2010 about the testing requirements of lightning impulse discharge capability, the wavelength of 200 μ s has been considered to the suitably compromise of typical case's application and multiple thunderbolt effect, rush of current waveform is roughly sine wave, the instantaneous value of dash current is greater than duration of rush of current peak value 5% should be between 200 μ s～230 μ s.

(3) lightning surges are by the calculating of the electric charge value mathematical expectation of lightning arrester lightning current

According to step (1) and step (2), obtain thunderbolt time during insulator arc-over by the amplitude of lightning current I=380A of lightning arrester, when current waveform is the near sinusoidal ripple of 200 μ s, quantity of electric charge mathematical expectation Q=48.4mC.The quantity of electric charge is obtained by current waveform integration, as shown in Figure 3.

Lightning surge useful effect number of times during 2.2 distributions move 1 year with lightning arrester

the lightning surge expection useful effect number of times of circuit is attacked in distribution directly because of thunder during 1 year with lightning arrester operation;

the lightning arrester operation induction lightening superpotential expection useful effect number of times because of thunderbolt tower top during a year for distribution;

distribution with lightning arrester operation during 1 year because of the induction lightening superpotential expection useful effect number of times outside thunderbolt circuit.

When considering useful effect number of times, can think and only take into account the superpotential number of times over line lightning resisting level, and for

should consider to be struck by lightning and effectively block distance outside circuit.Certainly, this can affect the confidence level of calculating.

3 determine the expection operation life under lightning arrester lightning surge for distribution

Distribution is determined by formula 13 by the expected life of lightning arrester lightning surge:

$\stackrel{\&OverBar;}{N}\left(P\right)=\frac{{\mathrm{<figure-callout\; id="0"\; label="T\; R\; T"\; filenames="HDA0000044407120000021.png"\; state="\{\{state\}\}">T</figure-callout>}}_R}{\stackrel{}{T_{}}}=\frac{T_R}{\underset{S}{\mathrm{\&Sigma;}}\stackrel{\&OverBar;}{N_S}\stackrel{\&OverBar;}{T}}$ ------------------------------------------------------------(formula 13)

Wherein, T _r---(disposable) lightning impulse discharge capability (energy value or electric charge value) resource that lightning arrester has;

T ₀---the lightning impulse discharge capability resource of 1 year internal consumption of lightning arrester;

---the mathematical expectation of lightning arrester consumption of natural resource under a lightning surge;

---the predictive role number of times of distribution lightning arrester operation lightning surge during a year;

P---confidence level.

utilize Fig. 2 diagram to determine.

The lightning impulse discharge capability Resource Calculation that 3.1 distributions have with lightning arrester

According to standard GB11032 to lightning arrester performance requirement, the lightning impulse discharge capability of 10kV distribution type, power station type and line type polymeric housed metal oxide arrester determines by energy and the quantity of electric charge of 20 5kA 8/20 μ s lightning waves and 2 large electric currents of 65kA4/10 μ s, and the lightning impulse discharge capability of strong thunder type lightning arrester is determined by energy and the quantity of electric charge of 20 20kA8/20 μ s lightning waves and 2 40kA30/80 μ s lightning waves.

The disposable thunder discharge capability resource that table 1 lightning arrester has

Model	Distribution type	Power station type	Line type	Strong thunder type
					The energy that lightning arrester has (kJ)	218.4kJ	182.3kJ	174.6kJ	709.5kJ
The quantity of electric charge that lightning arrester has (C)	17.98C	14.73C	14.37C	27.44C

The lightning impulse discharge capability Resource Calculation that 3.2 distributions consume with lightning arrester for 1 year

Under given confidence level P, the mathematical expectation of lightning arrester operation life is obtained by formula 14.

$N\left(P\right)=\frac{T_R}{T_0\left(P\right)}=\frac{T_R}{\underset{S}{\mathrm{\&Sigma;}}{N}_{S}T\left(P\right)}$ ------------------------------------------------------(formula 14)

T (P) is given by the T value of corresponding confidence level P, and the quantity of electric charge Q value consuming while take a lightning surge is here example calculating.Before the mathematical expectation of the quantity of electric charge Q value that consumes while having obtained a lightning surge by integration be 48.4mC, obtain

$T_0\left(Q\right)=48.4\mathrm{mC}\&times;(\stackrel{\&OverBar;}{{\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA0000044407120000012.png,HDA0000044407120000021.png"\; state="\{\{state\}\}">N</figure-callout>}}_1}+\stackrel{\&OverBar;}{{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HDA0000044407120000012.png"\; state="\{\{state\}\}">N</figure-callout>}}_2}+\stackrel{\&OverBar;}{{\mathrm{<figure-callout\; id="3"\; label="N"\; filenames="HDA0000044407120000012.png,HDA0000044407120000021.png"\; state="\{\{state\}\}">N</figure-callout>}}_3})$ ------------------------------------------(formula 15)

Confidence level P represents that lightning surge surpasses the probability of lightning withstand level.

3.3 distributions are calculated by lightning arrester lightning surge expection operation life

The data of association list 1 and formula 15, substitution formula 14, can obtain distribution lightning arrester lightning surge expected life.

Conclusion

The thunder discharge capability resource having with lightning arrester by distribution and thunder and lightning cause the lightning arrester thunder discharge capability resource that overhead transmission line superpotential consumes, and through the calculating of this method, can show that distribution expects operation life with lightning arrester.

Claims (2)

1. a non-limiting expection operation life appraisal procedure under the given confidence level of distribution lightning arrester, comprises following steps:

Step 1: monitor the lightning surge amplitude at lightning arrester mounting points place in a year, add up its distribution;

Step 2: the statistical distribution of calculating lightning arrester lightning impulse discharge capability resource consumption in a year;

Step 3: the expected life of calculating non-limiting lightning surge under the given confidence level of lightning arrester:

Distribution is determined by formula 13 by the expected life of lightning arrester lightning surge:

$\stackrel{\&OverBar;}{N}\left(P\right)=\frac{T_R}{\stackrel{\&OverBar;}{T_0}\left(P\right)}=\frac{T_R}{\underset{S}{\mathrm{\&Sigma;}}\stackrel{\&OverBar;}{N_S}\stackrel{\&OverBar;}{T}}$ -----------------------------------------------(formula 13)

Wherein, Т _r---the disposable lightning impulse discharge capability resource that lightning arrester has;

T ₀---the lightning impulse discharge capability resource of 1 year internal consumption of lightning arrester;

---the mathematical expectation of lightning arrester consumption of natural resource under a lightning surge;

---the predictive role number of times of distribution lightning arrester operation lightning surge during a year;

P---confidence level.

2. according to expecting and it is characterized in that operation life appraisal procedure under the given confidence level of distribution lightning arrester described in right 1: the voltage magnitude of described step 1 obtains by following steps:

1) statistical distribution of the non-limiting lightning surge amplitude in lightning arrester mounting points place for distribution

1.1 distribution overhead transmission line direct lightning strike Overvoltage Amplitude statistics

(1) calculating of distribution overhead transmission line direct lightning strike Overvoltage Amplitude

When thunder is attacked directly in the A of endless wire point, the direct lightning strike superpotential that A is ordered is:

$U_A=\frac{i}{2}\frac{Z}{2}=\frac{i\&times;Z}{4}$ (kV)-------------------------------------------------------(formula 1)

Wherein: i---lightning channel main discharge current amplitude (kA);

Z---surge impedance of a line (Ω);

(2) annual each the hundred kilometers average number of lightning strokes of attacking directly of distribution overhead transmission line calculate

Annual each the hundred kilometers average thunderbolt times N 1 of attacking directly of the general height of distribution overhead transmission line are

$N1=\mathrm{\&gamma;}\&times;\frac{10h}{1000}\&times;100\&times;T=\mathrm{\&gamma;}\&times;h\&times;T$ ---------------------------------------(formula 2)

The on average thunderbolt number of times over the ground of every square kilometre of wherein, γ---every Thunderstorm Day;

The equivalence of 10h---circuit is subject to thunder width, the average height that h is circuit, the m of unit;

T---local annual thunder and lightning number of days;

(3) thunder is attacked the lightning withstand level of aerial condutor directly

Get critical value U _a=75kV, wave impedance Z=300 Ω, while obtaining overhead transmission line direct lightning strike by (formula 1), built on stilts

The lightning withstand level I of circuit ₁=1kA;

Lightning induced voltage statistics during 1.2 distribution overhead transmission line thunderbolt circuit tower top on wire

(1), while being struck by lightning overhead transmission line tower top, on aerial condutor, thunder and lightning induction voltage calculates

During thunderbolt overhead transmission line tower top, on aerial condutor, thunder and lightning induction voltage computing formula is:

$U_C=\frac{I\&times;h_d}{2.6}$ -------------------------------------------------------------------(formula 3)

Wherein, I---lightning channel main discharge current amplitude (kA);

H _d---overhead line conductor height (m);

(2) annual each the hundred kilometers average tower top number of lightning strokes of distribution overhead transmission line calculate

Annual each the hundred kilometers average tower top number of lightning strokes N2 of distribution overhead transmission line are:

N2=γ * T * g * h=g * N1----------------------------------------------------(formula 4)

The average height of wherein, h---circuit (m);

G---hit number of times/thunderbolt circuit total degree of bar rate=thunderbolt head of mast and near direct lightning conducter thereof;

(3) lightning withstand level of thunderbolt circuit tower top

When thunderbolt circuit tower top, tower top current potential is

$U_T=I(R_E+\frac{L_T}{2.6})$ ---------------------------------------------------------(formula 5)

Wherein, R _e---Tower Impulse Grounding Resistance, Ω;

L _t---shaft tower inductance, μ H;

Induced voltage on aerial condutor is calculated by formula 3;

Voltage on line insulator is

$U_i=I(R_E+\frac{L_T}{2.6}-\frac{h_d}{2.6})$ --------------------------------------------------(formula 6)

Lightning induced voltage on wire in the time of outside 1.3 thunderbolt distribution overhead transmission lines

(1), when thunderbolt distribution overhead transmission line is outer, on wire, lightning induced voltage amplitude is calculated

Thunder and lightning induction voltage computing formula:

$U_i=25\frac{I\&times;h_d}{l}$ -----------------------------------------------------------------(formula 7)

Wherein, I---lightning channel main discharge current amplitude (kA);

H _d---overhead line conductor height (m);

The vertical range of l---lightning strike spot and wire (m);

(2) distribution overhead transmission line annual each hundred kilometers because occurring on thunderbolt overhead transmission line outer conductor that the number of times of lightning induced voltage calculates

Distribution overhead transmission line annual each hundred kilometers because there is the times N 3 of lightning induced voltage on thunderbolt overhead transmission line outer conductor, dodging hypothetically number of times is N, N3=k * N, k ∈ (0,1) wherein, N=n * S, wherein n dodges density with representing, inferior/km ²year, S represents the area of zoning, km ²;

1.4 amplitude of lightning current probability statistics

By amplitude of lightning current cumulative probability data, with least square fitting, go out the expression formula of the amplitude of lightning current cumulative probability of positive and negative polarity thunder after comprehensive:

$P(>I)=\frac{1}{1+{(I/35.6)}^{3.0}}$ -------------------------------------------------------(formula 8)

Wherein, P(>I)---amplitude of lightning current surpasses the probability of I;

I---amplitude of lightning current (kA);

What parameter 35.6 reflected is intermediate value electric current, and amplitude of lightning current is 50% over the probability of 35.6kA.

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