Tải bản đầy đủ - 0 (trang)
Figure 2.1: Shielding factor by objects near the overhead line 

# Figure 2.1: Shielding factor by objects near the overhead line 

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  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  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 , 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 , 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 ). The value of probability by touch and step

voltages due to lightning strikes on structure Ph (Ph is equivalent to PA in standard ) but

takes into account three components (in addition to 2 components equivalent to calculating

PA , 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 );

- k1 is the coefficient that depends on lightning protection system level when lightning

strike on structure (coefficient k1 = PB in standard ) 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  and , 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  needs to

be further elaborated the probability of a dangerous discharge based on structure type P s is

referenced from the standard . 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 , 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 , 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  and the Cf factor

of the standard , the meaning of the two factors is the same but the value of C f in the

standard  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

 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 , 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 , 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 , 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 ); Rc component risks related to physical damage (Rc is

equivalent to the P V risk component in the standard ); 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 ); 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 ). 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  need to

consider the number of connecting service lines connected to the structure  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 ; 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 .

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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 

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 :

Ph= k1 x Ph x Ps

Standard :

NL = NG x Cf x 10-6

Với: C f = (b + 28 x h0,6) x 10-1 (1 - Sf)

Standard :

Pc1p = nohp x k5 x Peo

Pc1 = noh x k5 x Pe1

Standard :

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  and the improved method of risk assessment are proposed, the calculation results

are shown in Table 2.2.

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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 

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

 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 :

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 :

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 .

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) :

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

NCS: Lê Quang Trung

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 8/20s-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

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Figure 2.1: Shielding factor by objects near the overhead line 

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