Figure 2.1: Shielding factor by objects near the overhead line [6]
Tải bản đầy đủ - 0trang
components that are calculated in detail for the types of structure taking into the different
construction materials and the number of service connection lines.
IEEE 1410 standard [6] is the standard of the American Association of Electrical
and Electronic Engineers, when calculating the number of lightning strikes on the power
line, the characteristics of the power line (the height of the pole, the distance between the
two outer phase wires), the object shielding around the line.
With the above analysis, it is found that the method of risk assessment of damages
due to lightning according to IEC 62305-2 [1] is more popular, international in comparison
with the other two standards. Therefore, the IEC 62305-2 standard was chosen as the basis
for the study to propose methods to improve the calculation and risk assessment of damages
due to lightning.
2.2.2 Determine the value of coefficients with the detailed calculation level which are
referenced and proposed from the AS/NZS 1768 and IEEE 1410 standard.
2.2.2.1. The probability of a dangerous discharge based on structure material types when
calculating the probability of PA for the risk component of RA
In standard [1], when calculating risk components related to human life's damage
by electric shock due to lightning strikes on structure RA. The probability of injury to living
beings by electric shock by step and touch voltages due to lightning strikes on structure P A
only consider two components:
- PTA is the probability depends on additional protection measures against touch and
step voltages, Table 2 - Annex 1.
- Pb is the probability depends on the lightning protection level, Table 3 - Annex 1.
The probability PA is calculated according to the expression (2.9).
In the standard [3], when calculating a risk component by touch and step voltages
to living beings outside the building due to lightning strikes on structure Rh (Rh equivalent
to the risk component of RA in the standard [1]). The value of probability by touch and step
voltages due to lightning strikes on structure Ph (Ph is equivalent to PA in standard [1]) but
takes into account three components (in addition to 2 components equivalent to calculating
PA [1], consider Ps component, specifically:
Ph Probability that lightning will cause a shock to animals or human beings outside
the structure due to dangerous step and touch potentials (Ph = PTA in standard [1]);
- k1 is the coefficient that depends on lightning protection system level when lightning
strike on structure (coefficient k1 = PB in standard [1]) with k1=1- E and E is efficiency of
lightning protection system on the structure, Table 1 - Annex 2;
- Ps is the probability of a dangerous discharge based on structure type, Table 2 Annex 2. The probability value Ph is defined as in the expression (2.49).
Through specific analysis of the standard [1] and [3], when lightning strikes on the
structure, the construction material of the structure is also one of the important factors that
directly affect the level of risk causing damage to human life inside the building, the
calculation of the PA probability for the risk of RA component in the standard [1] needs to
be further elaborated the probability of a dangerous discharge based on structure type P s is
referenced from the standard [3]. The probability value of P A is determined by the
following expression:
PA = PTA x PB x Ps
(2.92)
In the expression (2.92) the P TA value is determined according to Table 2 - Annex
1, the PB value is determined, Table 3 - Annex 1, the determined Ps value, Table 2 - Annex
2.
2.2.2.2. The shielding factor when calculating the number of lightning strikes directly and
indirectly on the service line connecting to the structure
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16
In the standard [1], when calculating the number of direct lightning strikes, such as
in the expression (2.19) and the number of indirect lightning strikes Nl as in the expression
(2.27) for the overhead power lines mentioned the installation factor of the line C l, line
type factor CT and environment factor CE are retrieved from the lookup table (Table 8 Appendix 1) depending on the line installed in rural or suburban , urban or urban areas with
surrounding structures higher than 20m.
In the IEEE 1410 standard [6], when calculating the number of lightning strikes
directly on the service line which is determined by the expression (2.90) taking into account
the lightning density, the way to install the power line and the shielding objects near the
power line. In which, Cf is the factor of how to install the power line and shielding objects
near the power line determined by the expression (2.91).
Based on the content of the CE factor analysis of the standard [1] and the Cf factor
of the standard [6], the meaning of the two factors is the same but the value of C f in the
standard [6] detailed calculation and compliance with the actual conditions of the power
line than the CE value from the lookup table. Therefore, in order to calculate the number of
lightning strikes directly and indirectly on the power line in accordance with the actual
conditions at the place where the line is installed, the CE factors are proposed by the Cf
factor with the calculated level details in the expression (3.91) are referenced from standard
[6] to replace expressions (3.19) and (3.27) to calculate:
The number of the lightning strikes directly on the overhead line is determined by
the expression (2.93):
NL = NG x AL x Cl x Cf x CT x 10-6 (times/km2/year)
(2.93)
The number of the lightning strikes indirectly on the overhead line is determined by
the expression (2.94):
Nl = NG x Al x Cl x Cf x CT x 10-6 (times /km2/year)
(2.94)
2.2.2.3. Number of service lines when calculating probability related to lightning strikes
directly and indirectly on service lines connecting to the structure
In the standard [1], when calculating the risk related injury to living beings due to
electric shock when lightning strikes directly on service lines connecting to the structure
for the RU risk component. The value of the probability of lightning strike to the service
lines directly causes the surge into the structure causing damage to human life P U, the PU
probability value is calculated by the expression (2.21).
When calculating risks related to physical damage when lightning strikes directly
on service lines connecting to structure risk component RV. In the standard [1], the value
of the probability of lightning strike to the service lines directly causes material damage
PV, the PV probability value is calculated according to the expression (2.23).
Similarly, when calculating risks associated with damage to internal systems when
lightning strikes directly on service lines connecting to risk component RW. The probability
value of lightning strikes directly on service lines causes damage to the systems inside P W,
PW probability value is calculated according to the expression (2.25).
And when calculating risks associated with damage to internal systems while
lightning strikes near service lines connecting to the structure with risk component R Z, the
probability value of lightning near service lines causes failed systems inside the structure
PZ, PZ probability values are calculated according to the expression (2.29).
Meanwhile, in the standard [3], when calculating the risk factors caused by lightning
strikes directly or indirectly on service lines causing overvoltage on service lines entering
the structure: Rg component risk related to damage to life (Rg is equivalent to risk
component R U in standard [1]); Rc component risks related to physical damage (Rc is
equivalent to the P V risk component in the standard [1]); Re component risks involve
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17
internal system failures due to direct lightning strikes on service lines (Re equivalent to RW
risk components in the standard [1]); The risk of Rl component relates to the failure of
internal systems due to indirect lightning strikes on service lines (Rl is equivalent to the RZ
risk component in the standard [1]). The probabilities of lightning hitting directly or
indirectly on service lines cause overvoltage on service lines entering the building
considering the number of overhead lines noh or the number or underground lines nug that
connect to the structure as in the expression (2.70), (2.71), (2.72), (2.73).
Therefore, if there are many service lines connecting to the structure on separate
lines, the probability of lightning strike directly or indirectly to the service lines will cause
overvoltage on the service lines go into the structure and the risk of damage due to lightning
will be different. In order to calculate in more detail according to actual conditions, the
calculated values of P U, PV, PW and PZ for component risks in the standard [1] need to
consider the number of connecting service lines connected to the structure [3] and the
proposed calculation is as follows:
PU/oh = PTU x PEB x PLD x CLD x noh
(2.95)
PV/oh = PEB x PLD x CLD x noh
(2.96)
PW/oh = PSPD x PLD x CLD x noh
(2.97)
Pz/oh = PSPD x PLI x CLI x noh
(2.98)
Expressions for the probability of P U, PV, PW and PZ for underground lines are as
follows:
PU/ug = PTU x PEB x PLD x CLD x nug
(2.99)
PV/ug = PEB x PLD x CLD x nug
(2.100)
PW/ug = PSPD x PLD x CLD x nug
(2.111)
Pz/ug= PSPD x PLI x CLI x nug
(2.102)
The factors of PTU, PEB, PLD and CLD are defined as in the standard [1]; Noh is the
number of overhead service lines and nug is the number of underground service lines
connected to a specified building in the standard [3].
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18
2.2.2.4. Table of improved factors
Table 2.1: Table of improved factors
No.
1
2
3
Additional
Standard [1]
considerations/changes
The probability of a dangerous
discharge based on structure
material types when calculating PA = PTA . PB
the probability of PA for the risk
component of RA
The shielding factor when
NL = NG x AL x Cl x CE x CT x 10-6
calculating the number of
lightning strikes directly and
indirectly on the service line Nl = NG x Al x C l x CE x CT x 10-6
connecting to the structure
PU = PTU x PEB x PLD x CLD
Number of service lines when PV = PEB x PLD x CLD
calculating probability related
(3.96)
to lightning strikes directly and PW = PSPD x PLD
x CLD
indirectly on service lines
connecting to the structure
Pz = PSPD x PLI x CLI
Reference standards
Standard [3]:
Ph= k1 x Ph x Ps
Standard [6]:
NL = NG x Cf x 10-6
Với: C f = (b + 28 x h0,6) x 10-1 (1 - Sf)
Standard [3]:
Pc1p = nohp x k5 x Peo
Pc1 = noh x k5 x Pe1
Standard [3]:
Pc2p = nugp x k5 x Peo
Pc2 = nug x k5 x Pe2
Suggestions for improvement (*)
PA = PTA x PB x Ps
NL = NG .AL .Cl. Cf .CT .10-6
Với: C f = (b + 28.h0,6) x10-1 (1 - Sf)
Nl = NG x Al x Cl x C f x CT x 10-6
Với: C f = (b + 28 x h0,6) x 10-1 (1 - Sf)
PU/oh = PTU x PEB x PLD x CLD x noh
PV/oh = PEB x PLD x C LD x noh
PW/oh = PSPD x PLD x CLD x noh
Pz/oh = PSPD x PLI x C LI x noh
PU/ug = PTU x PEB x PLD x CLD xnug
PV/ug = PEB x PLD x C LD x nug
PW/ug = PSPD x PLD x CLD x nug
Pz/ug = PSPD x PLI x C LI x nug
(*)
k1 is the reducing factor for lightning protection system level; Ph is the probability that lightning will cause a shock to animals or human beings outside the structure due
to dangerous step and touch potentials; Ps is the probability of a dangerous discharge based on structure type; Cf is the factor of how to install the power line and shielding
objects near the power line determined by the expression; Sf shielding factor; noh is the number of the overhead lines connected to the structure; nug noh is the number of the
undergound lines connected to the structure.
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19
2.2.3. Procedure for risk assessment
Identify the structure to be
protected
Identify the types of loss relevant to the structure
For each type of loss determine the tolerable risk RT
Identify and calculate the risk components R = RD + RI
R > RT
Yes
Yes
Structure is protected
No
No
Intall adequate protection measures to reduce R
Figure 2.2: Procedure for risk assessment
2.2.4. Calculation of the risk of damage due to lightning for the sample structure
2.2.4.1. Basic parameters of sample structure
Calculation of risk assessment of damage due to lightning for a commercial building in
Ho Chi Minh City; structure dimensions: 20×15×35m; lightning density: 12 (times/km2 /year),
no other buildings nearby; power line has a length of 200m, overhead; telecommunication
cable has a length of 1000m, underground .
H = 35m
ng dây đi n (trên không)
LP = 200m
W = 15m
ng dây vi n thông (đi ng m)
LT = 1000m
Figure 2.3: The structure need to assess the risk of damage due to lightning
2.2.4.2. The results of risk assessment
Steps to calculate the risk of damage due to lightning for the structure according to the
standard [1] and the improved method of risk assessment are proposed, the calculation results
are shown in Table 2.2.
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20
Table 2.2: The risks value of the structure
Type of risk of damage
Risk of loss of a human life R1
Risk of loss of economic value R 4
IEC – 62305 [1]
3,75.10-5
0,255
Improved method
3,256.10-5
0,227
Errors (%)
13%
11%
2.2.5. The program calculates the risk assessment of damage caused by lightning
The program calculates the risk assessment LIRISAS has the interface as shown in
Figure 4, based on the application of optimal parameters of risk assessment on a standard basis
[1] with improvement suggestions as shown in Table 2.1. The program allows users to enter
the necessary parameters related to the structure, the program will calculate the results of the
risk value of damage caused by lightning for the structure.
CHƯƠNG TRÌNH TÍNH TỐN ĐÁNH GIÁ RỦI RO THIỆT HẠI DO SÉT LIRISAS
Phương pháp cải tiến theo tiêu chuẩn IEC-62305
Kích thước cấu trúc và các yếu tố môi trường
Đường dây dịch vụ
Đường dây điện
Chiều dài (m)
20
Chiều rộng (m)
15
Chiều dài (m)
Chiều cao (m)
35
Số l ợng đ
Mật độ sét khu vực (l n/km2 /năm)
12
Cách lắp đặt
Môi tr
ng xung quanh cấu trúc
Cô lập
Các dạng rủi ro
Loại đ
ng dây
Thiệt hại về con người
200
Dạng cấu trúc thi t hại về con ng
1
Dạng cấu trúc thi t hại về vật chất
Công nghiệp
Dạng cấu trúc thi t hại h thống bên trong
Không xem xét
Trên không
Tất cả
i
Hạ thế/viễn thông
ng dây
Thiệt hại về dịch vụ
Bi n pháp nối đất, cách ly theo IEC 62305-4
Không có
Đặc điểm của cấu trúc và các biện pháp bảo vệ
Bảo v đ
Vật li u xây dựng cấu trúc
ng dây bên trong cấu trúc
Gạch ceramic
Rủi ro cháy
Thấp
Không xem xét
Dạng cấu trúc thi t hại h thống bên trong
Không xem xét
Không có che chắn
Bêtông cốt thé p
Vật li u sàn
Dạng cấu trúc thi t hại về vật chất
Đường dây viễn thông
Chiều dài (m)
Bi n pháp bảo v phòng cháy
Xác suất phóng đi n sét gây cháy
Mức thấp
H sớ suy giảm phòng cháy
Khơng có
ng dây
Thiệt hại về giá trị kinh tế
Loại đ
Đi ngầm
Bi n pháp nối đất, cách ly theo IEC 62305-4
Không có
Cấp độ SPD đ ợc thiết kế
Không có
Bảo v đ
SPD ở ngõ vào thiết bị
Dạng cấu trúc thi t hại về vật nuôi
Tất cả
Dạng cấu trúc thi t hại về vật chất
Thương mại
Dạng cấu trúc thi t hại h thống bên trong
Trường học, thương mại
Hạ thế/viễn thông
ng dây
Thấp
Cấp độ bảo v chống sét
ng dây dịch vụ
Không xem xét
1
Cách lắp đặt
SPD ở ngõ vào đ
Dạng cấu trúc thi t hại về vật chất
Không có
Số l ợng đ
Mức độ hoản sợ khi có sự cố
Thiệt hại về di sản văn hóa
1000
ng dây bên trong cấu trúc
Không có
Không có che chắn
Không có
Không có
Kết quả tính toán mức độ rủi ro
Giá trị rủi ro tính toán
Giá trị rủi ro chấp nhận đ ợc
Thiệt hại về con người
Thiệt hại về dịch vụ
3.25678E-05
0
0
0.2276893
0.00001
0.001
0.0001
0.001
Thiệt hại về di sản văn hóa
Thiệt hại về giá trị kinh tế
Figure 2.4: The interface of the program calculates the risk assessment of damage
caused by lightning LIRISAS
2.3. Conclusions
On the basis of the calculation method of risk assessment due to lightning according to
IEC 62305-2, the improved method has a more detailed level, taking into account the factor:
probability of a dangerous discharge based on structure type, the number of service lines
connected to the structure, considering the way to install the line and shielding objects along
the power lines connected to the structure. The calculation results with the sample structure
show that there is a significant difference in the value of risk of loss of a human life
R1 (about 13% lower), and the value of risk of loss of economic R4 (about 11% lower).
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21
Chapter 3
IMPROVED SURGE GENERATOR MODEL AND SURGE
PROTECTIVE DEVICE MODEL ON THE
LOW VOLTAGE POWER LINE
3.1. Surge generator model
3.1.1. The reasons for improving
Up to now, there are many domestic and international research projects on lightning
surge generator model but only focus on each type of lightning surge separately and have
relatively large errors compared to standard lightning surges. Meanwhile, the inspection of the
type of lightning protection devices on the low voltage power lines should be carried out with
many different types of lightning surges. Therefore, the study proposes an improved lightning
pulse model that produces many different types of lightning surges, which are highly accurate
compared to standard lightning surges to facilitate the use of equipment testing is necessary.
3.1.2. Mathematical model
3.1.2.1. Mathematical model of Heidler
The Heidler equation is used to describe lightning surges [57]:
i(t) =
(t/τ1 )10
I0
η
1+(t/τ1 )10
e(−t/τ2)
(3.1)
Where I0 is the value of peak current (kA), η is the correction factor for the peak current τ1 is
the front time constant, τ2 is the tail time constant.
Parameters τ1, τ2 and are determined by the time of increase of tds and the time of
reduction of ts of the lightning current surge.
The rise and fall time of lightning current surge form is specified as follows:
tds = 1,25(t2 – t1)
(3.2)
ts = t5 – t1+0.1tds
(3.3)
3.1.2.2. Determine parameters for Heidler's equation:
The current is considered to be the product of two time-response functions (increasing
time function x(t) and decrease time function y(t)). Establish the function of the current as
follows [64]:
i(t) = I0.x(t).y(t)
(3.4)
Where: x(t) =
(t/τ1 )10
1+(t/τ1 )10
y(t) = e(−t/τ2)
Applying the approximation method during increasing current surge, the value of
current function decreases y(t)=1. Similarly, when the current is reduced, the value of the
current function increases x(t)=1 [64].
In the process of increasing current (wave phase), equation (3.1) takes the form:
i(t)=
I0
η
(t/τ1 )10
1+(t/τ1 )10
e(−t/τ2)
(3.5)
At t = t1 the current value i(t) = 0,1I, inferred:
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22
t1 / τ1 10 0,1 0,9 t / τ 10 0,1
1 1
t1 / τ1 10 1
(3.6)
(3.7)
Hence:
t1 1 / 9.τ1
And at t = t2 the current value i(t) = 0,9I0, inferred:
10
t 2 / τ1 10 0,9 0,1 t / τ 10 0,9
2 1
t 2 / τ1 10 1
(3.8)
Hence: t 2 10 9.τ1
From there:
(3.9)
t 2 t1 0,8t ds (10 9 10 1 / 9).τ1
0,8.t
τ1 = 10 10ds
1,88t ds
( 9 - 1 / 9)
(3.10)
(3.11)
Similarly, in the process of current attenuation current, the current function is
determined approximately by the following expression:
t
(− )
i(t) = I0 e τ2
When t = t5 the current value i(t) = 0,5I0
Hence:
I0 e
t5
τ2
t
(− 5 )
τ2
(3.12)
= 0.5I0
(3.13)
= ln2
(3.14)
t5
τ2 =
(3.15)
ln2
When t > 0, x(t) < 1, the maximum current is lower than I0. Therefore, the peak current
correction factor η is determined by the value calculation formula (3.16) [57]:
η
1
τ1 / τ 2 .10 10τ 2 / τ1
e
(3.16)
Calculated results τ1, τ2, η according to the expressions (3.11), (3.15) and (3.16),
corresponding to the different types of lightning impulses presented, Table 3.1.
Table 3.1: Calculated parameter values with standard lightning current surge
tds(µs)
ts(µs)
𝛕𝟏(s)
η
𝛕𝟐(s)
ta(s)
tb(s)
e1(%) e2(%)
10
350
1.8800e-05 4.9052e-04 9.3533e-01 9.8750e-06 3.6039e-04 1.25
2.97
1
5
1.8800e-06 5.7708e-06 6.3204e-01 8.7500e-07 5.4875e-06 12.5
9.8
4
10
7.5200e-06 8.6562e-06 3.2983e-01 3.1250e-06 1.1013e-05 21.88 10,13
8
20
1.5040e-05 1.7312e-05 3.2983e-01 6.2500e-06 2.1825e-05 21.88 9.0
Where: ta is the front time calculation, tb is the tail time calculation, η is the correction factor, e1, e2 is
respectively error of front and tail time.
e1= 100% −
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𝑡𝑎∗100%
𝑡𝑑𝑠
e2= 100% −
𝑡𝑏 ∗100%
𝑡𝑠
23
Comment: lightning surge types of 1/5µs, 4/10µs, 8/20µs have the errors exceeding the
permissible value for the front and tail time error of the standard lightning surge.
With errors of 3 types of lightning surge in Table 3.1, the method of compensation for
error generated to perform the correction and use of the assumptions function
(t / τ )10
and y(t) = e(-t / τ ) 1 is used when calculating. Because of the functions
x(t)
2
1
=1
(t / τ1)10 +1
x(t) and y(t) both are smaller than 1 so the correction must be done so that values τ1 , τ2 make
the value of the functions x(t) and y(t) decreased.
10
For function x(t) (t / τ1)
decreases when (t / τ1)10 decreases, τ1 increases, otherwise,
(t / τ1)10 +1
y(t) = e(-t / τ ) decreases when τ2 decreases.
The process for adjusting is according to 5 steps as follows:
2
Step 1: Find the value τ1 , τ2 according to the expression (3.11) and (3.15).
Step 2: Calculate the errors e1, e2
Step 3: Recalibrate τ1 , τ2 to increase τ1 and decrease τ2
Step 4: Recalculate the errors e1, e2
Step 5: Compare values of new errors e1, e2 and values of old e1 and e2 errors. If the
new e values are smaller than the old e values, stop, if the new e values are greater than
the old e values, go back to Step 3.
The correction algorithm is shown in Figure 3.1 and the calculation results are
presented in Table 3.2.
Find the value τ1, τ2 according to the
expression (3.11) and (3.15)
Calculate the errors τ1, τ2
Recalibrate to increase τ1 and decrease τ2
Recalculate the errors e1, e2
No
e1, e2 meet standard
errors
Yes
Exit
Figure 3.1: Flowchart for correcting errors
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24
Table 3.2: Error results after adjustment
tds(µs)
10
1
4
8
ts(µs)
350
5
10
20
𝝉𝟏
1.9740e-05
2.2800e-06
1.0032e-05
2.0064e-05
𝝉𝟐
4.6599e-04
4.6873e-06
6.3279e-06
1.2656e-05
ta(s)
1.0250e-05
1.0000e-06
4.0000e-06
8.0000e-06
tb(s)
e1 (%)
3.4402e-04
2.5
4.9000e-06
0
1.0500e-05
0
2.0900e-05
0
e2 (%)
1.7
2
5
4.5
Comment: When using the parameter correction algorithm, the calculated lightning
surge types according to Heidler's mathematical function have met the conditions of accuracy
according to the standard lightning surge. On that basis, the next step needs to build an
improved lightning surge generator model in the Mathlab, which integrates many different
types of lightning surge with the error of standard lightning surge conditions to serve the model
inspection Lightning protection device on low voltage power line.
3.1.3. Improved surge generator model in Matlab
Step 1: Identify the elements in the improved surge generator model according to Heidler's
mathematical equation.
Step 2: Constructing the diagram of improved lightning surge block.
After identifying the elements in the improved surge generator model according to Heidler's
mathematical equation, connecting the elements together is block diagramed as Figure 3.4.
Figure 3.2: Block diagram of the Improved surge generator model.
The resulting numeric value will be converted into a signal through the Control Current
Sources block
Step 3: Create Subsystem and create Mask for surge generator.
Figure 3.3: The dialog box for declaring the input parameters of the MOV model
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25
3.1.4. Evaluate simulation model of surge currents
The surge generator model after construction is in the form of Figure 3.4 (a) and the
simulation circuit evaluates the lightning current surge generator model as shown in Figure
3.4 (b).
(a)
(b)
Figure 3.4: Lightning current surge generator model and simulation circuit evaluate surge
generator model of surge current
(a) Surge generator model
(b) Simulation circuit evaluate surge generator model of surge current
Conducting simulation of lightning surge current in Figure 3.5, the results of estimating
errors of lightning surge current waveforms are presented in Table 3.3.
Figure 3.5. Lightning surge current waveforms simulated 8/20s-3kA
Table 3.3: Results of simulated lightning surge current waveforms
Input parameter
values of lightning The value is determined based on the simulated waveform
currents
tds(µs) ts(µs) Im(A) Ipeak(A)
t_10%
t_50%
t_90%
0.00001
tb(s)
Ipeak e1 e2
(%) (%) (%)
10
350
3000
2999
0.000016
0.000337 0.03
0
3.71
1
5
3000
3001
0.0000016 0.0000064 0.0000024 0.000001 0.0000049 0.03
0
2
4
10
3000
3000
0.0000072 0.0000168 0.0000104 0.000004
0.00001
0
0
0
8
20
3000
3000
0.0000144 0.0000336 0.0000208 0.000008
0.00002
0
0
0
NCS: Lê Quang Trung
0.000352 0.000024
ta(s)
Errors
26