Rachid i Slides

8/10/2019 Rachid i Slides

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1. Aim of Presentation

To give some answers to the questions that are

most commonly raised by engineers and

scientific researchers dealing with the problem of

protection against lightning-induced voltages.


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2. What causes induced voltages ?

Electromagnetic coupling between the field radiated

by a lightning stroke and the line conductors

Incident field Scattered field

TOTAL FIELD


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2. What causes induced voltages ? Cont.

Essentially the return-stroke phaseis responsible of

the induced voltage

However, when lightning strikes the ground nearbythe line at close distance from the line, also the

preceding leader phasecan results in a significant

induced voltage


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Return-Stroke Current

i (0,t) RSC i (z,t)

Lightning ElectroMagnetic Pulse (appr. expr. for E horiz.)

i (z,t) LEMP E, B

ElectroMagnetic Coupling

E, B EMC V, I

3. How to evaluate them?


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A review of the various return-stroke models has been

recently made by Rakov and Uman on

IEEE EMC Transactions, Special Issue on Lightning,

1998where they have discussed, among others, the

following engineering models

Bruce-Golde (BG)

Transmission Line (TL)Uman, McLain, Krider

Traveling Current Source (TCS) Heidler

Modified Transm. Line - Linear (MTLL) Rakov and Dulzon

Modified Transm. Line - Exponential (MTLE) Nucci et al.

Diendorfer-Uman (DU)

Return-stroke current models

3. How to evaluate them? Cont.


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Experimental validation

Given a channel-base current ==>

the RSC model must reproduce the

corresponding Electromagnetic field

For Natural lightning:

PROBLEM: practically no existing data sets of

simultaneously measured current and fields

Data of this kind have been collected using

the Triggered lightningtechnique




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nn TRIGGERED LIGHTNING:TRIGGERED LIGHTNING:

Lightning is artificiallyLightning is artificially

initiated firing small rocketsinitiated firing small rockets

trailing grounded wirestrailing grounded wiresupwardupwardaafew hundredfew hundred

metersmetersunderunder

thunderstormsthunderstorms..




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Triggered lightning: A sequence of frames




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TCS

a) b)

microseconds microseconds

V/m TCS MTL

Validation by means of triggered lightning




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Reduced scale model at the University Of So Paulo - Brazil

The Agrawal model: Experimental validation



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0 2 4 6 8 10 12

Time in s

0

20

40

60

80

100

120

140

CALCULATED

MEASURED

Using reduced-scale line model

Experimental data: by A. Piantini, Univ. Of So Paulo

70 m

130 m 40 m 100 m

OBSERVATION POINT




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0 0.5 1 1.5 2 2.5 3 3.5 4Time in us

-60

-40

-20

0

20

4060

80

100

120

140

160Calculated dV/dt

Measured dV/dt

Measured dV/dt (filtered)


Using reduced-scale line model

Experimental data: by A. Piantini, Univ. Of So Paulo



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Using NEMP simulators


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Using NEMP simulators


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0

u (x)

i(x) L'dx

x x+dx

+-

i(x+dx)

+

-

+

-

L

us(x+dx)

-u i (0)

R 0

-u i (L)

R L

u i(x)

iE x dx

sC'dx

Agrawal et al.



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0

u (x)

i(x) L'dx

x x+dx

+-

i(x+dx)

+

-

+

-

L

us (x+dx)-u i (0)

R 0

-u i (L)

R L

u i(x)

iE x dx

sC'dx

Agrawal et al.



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-20

0

20

40

60

80

0 2 4 6 8

Time (s)

E contribution

E contribution

Total

X

Z

0

u (x)

i(x) L'dx

x x+dx

+-

i(x+dx)

+

-

+

-

L

us(x+dx)-ui(0,t)

R0

-u i(L)

RL

ui(x)

iEx dx

s

C'dx



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+=h

iz

ix

h

iy dztzxE

xthxEdztzxB

t00

),,(),,(),,(

Nucci and Rachidi, IEEE Trans. on EMC,

Vol. 37, No. 4, November 1995.

z

xy

E i, B i



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0

u (x)

i(x) L'dx

x x+dx

+-

i(x+dx)

L

u (x+dx)

R0

R L

i(By(x,z) dz)dx

C'dx

ddt

i(Ez (x,z) dz)dx

d

dt

-C

Taylor et al.



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-

-40

-20

0

20

40

60

80

B contribution

E contribution

Total

z

y

0

u (x)

i(x) L'dx

x x+dx

+-

i(x+dx)

L

u(x+dx)R

0RL

i(B

y(x,z) dz)dx

C'dx

ddt

i(Ez

(x,z) dz)dxddt

-C



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0

iB y (x,L)

1

L-

h

dz

0

u (x)

i(x) L'dx

0R L

C'dxiB x(x,z)

y

1

L0

-

h

dz[ ]

0

iB y (x,0)

1

L-

h

dz

Rachidi



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-20

0

20

40

60

80

0 2 4 6 8Time (s)

B contribution

B contribution

Total

X

y

0

iBy(x,0)

1

L-

h

dz

0

u (x)

i(x) L'dx

x x+dx

i(x+dx)

L

u (x+dx)

R0 RL

C'dx

iBy(x,0)

1

L-

h

dz

iBx (x,z)

y

1

L0

-

h

dz[ ]dx

3. How to evaluate them? Cont


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The contribution of a given electromagnetic field

component in the coupling mechanism depends

strongly on the used model.

Thus, when speaking about the contribution of a

given electromagnetic field component to the

induced voltages, one has to specify the coupling.

3. ? Cont.


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Induced voltage magnitude and shape significantly

depend on

lightning return stroke parameters (channel-base

current parameters, return stroke velocity),

distance and relative position with respect to the

transmission line,

line configuration and terminations.

Induced overvoltages can reach magnitudes up to few

hundreds of kV and can therefore cause line flashover.

4. are

for lightning induced


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1 2 3 4 5 6 7

12I in kA

Time in us

10

8

6

4

2

0

-20

-10

1020

30

40

50

60

0 1 2 3 4 5 6 7

Time in us

UA

in kV

1 km

Shape

4. What magnitudes and shape are typical

for lightning-induced overvoltages ? Cont.

However ...


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1 2 3 4 5 6 7

12IinkA

Timeinus

10

8

6

4

2

0

-20

-10

10

20

30

40

50

60

0 1 2 3 4 5 6 7

Time in us

UA

in kV




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Magnitude

1 km



However ...


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For perfectly conducting grounds and for an

infinitely long wire



the simplified Rusck formula allows for a

satisfactory estimation

d

hIZU maxmax 0=

== 30/4/1 00 oZ where

HOWEVER


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5.How far away can lightning strokes be that

cause an induced voltage flashover ?

Generally within 200 m

However it depends on many parameters

(=> computer code)

Lightning strokes occurring beyond a few

hundred meters from the line can cause a line

flashover for poor conducting soils (De La

Rosa et al., IEEE Trans. on PWDR, 1988)


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6.How does the induced voltage drop as a

function of distance from the line ?

-20

-10

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7

Time in us

UAin kV

30m

60m

90m

Perfectly conducting ground and stroke location equidistant to the

line termination => nearly proportionally to 1/d

HOWEVER ...

1 km

d


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7.What BIL is needed to prevent induced

flashovers ?

50 100 150 200 250 300

Basic Insulation Level kV

0.01

0.10

1.00

10.00

100.00

1000.00

No.ofeventshavingamplitudesexceeding

theBIL/(100km

year)

perfect ground

ground conductivity = 0.01 S/m

ground conductivity = 0.001 S/m


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8.What arrester spacing is needed to prevent

flashover?

X0 X1 X2 X3 X4 X50

20

40

60

80

100

120

Transf.Transf. + Surge arr.Matched

Stroke location: B1


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8.What arrester spacing is needed to prevent

flashover?

X0 X1 X2 X3 X4 X5

Observation Point Along the Line

0

50

100

150

200

250

300

350

400

Transf.Transf. + Surge arr.Matched

Stroke location: H1

c)


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a)

1

2

3

10 m

3.7 m

3.7 m

3.7 m

4

1 2 3

3.7 m 3.7 m

10 m

4 5

3.7 m

3.7 m

b)

9.Will a shield wire help ?


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9.Will a shield wire help ? Cont.

Shield wires help in reducing the magnitude of

induced voltages by a factor of about 20 to 40 %.

This implies about the same reduction of the fault

frequency.

wireProtective

RatioVerticalConfig.

HorizontalConfig.

1

2

3

PR1

PR2

PR3

0.81

0.78

0.72

0.67

0.60

0.67


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10. Is horizontal or vertical construction

best ?

a)

1

2

3

10 m

3.7 m

3.7 m

3.7 m

4

1 2 3

3.7 m 3.7 m

10 m

4 5

3.7 m

3.7 m

b)


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best ? Cont.

a)

Voltage

Ratio

Vertical

Configuration

Horizontal

Configuration

V1/V(h1)

V2/V(h2)

V3/V(h3)

0.75

0.79

0.89

0.85

0.81

0.85

Ratio between peak values of the induced voltages on a line

conductor Viand those corresponding

to a single-conductor line of the same height V(hi).


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The induced voltage magnitude for typical distribution

lines is virtually proportional to the line height.

As a consequence, an important factor determining the

magnitude of lightning-induced voltage is the line

height above ground, rather than the type of

construction.

In general, a construction allowing a shorter height for

the conductors is epected to experience lower induced

overvoltages.


best ? Cont.


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11. What effect does pole grounding and

ground resistivity have ?

Pole grounding affects the performance of the ground

wire in reducing the induced overvoltages.

In general, lower the pole ground impedance, betterthe performance of the ground wire.

Influence of pole grounding


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The ground resistivity affects:

1. electromagnetic field

2. propagation of the surges

Influence of ground resistivity

11.What effect does pole grounding and

ground resistivity have ? Cont.


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Lossy ground

Perfect ground

microseconds 0.5 km 0.5 km

Lossy ground:

= 0.001 S/m

Influence of ground resistivity Cont.




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b)

Ideal field

Ideal line

Lossy ground

Lossy ground

( = 0.001 S/m)

Ideal field:ground resisitivity only inthe expression of the

ground impedance

Ideal line:ground resistivity only inthe expression of the

incident field





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How does the ground resistivity affect

magnitude and shape of the induced

voltages?

Influence of ground resistivity




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0.5 km 0.5 km


0 200 400 600 800 1,000

Obs. point along the line in m

30

50

70

90

110

infinite

=0.01 S/m




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1 km


0 200 400 600 800 1000

Obs. point along the line in m

-40

-20

0

20

40

infinite

= 0.01 S/m




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The ground resistivity can increase or

decrease the magnitude of the induced

voltages depending on the stroke location

and the observation point along the line

=> the calculation is not trivial





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- Lightning electromagnetic field characterization

using natural and artificially-initiated lightning

- Experimental validation of field-to-transmission line

coupling models- Development of engineering tools for the protection

of power networks against lightning-induced

overvoltages

- Leader-induction effect

- Effect of ground conductivity on lightning-induced

overvoltages

12.Some of the current researches which are

being done on induced voltages


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The LIOV-EMTP code

The LIOVLIOVcode calculates:

LEMP (using the MTL model and Cooray-Rubinstein expr.)

Couplingusing the Agrawal model.

The EMTPEMTP:

calculates the boundary conditions

makes available a large library of power components

0

LIOV-line

n-port

Overhead

Distribution Line


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The LIOV-EMTP code Contd

LIOV has been developped within the framework

of an international collaboration involving

University of Bologna

Swiss federal Institute of Technology (EPFL, Lausanne)University of Roma La Sapienza

Its link with EMTP has been realized in collaboration with

ENEL-CESI (Univ. Bologna)

Other methods have been proposed

EdF (EPFL )


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0

u (x,t)

i(x,t) L'dx

C'dx

x x+dx

+-i(x+dx,t)

u (x+dx,t)

ui(x,t)

E

i

x (x,h,t)dx

ss

+

-

0

i0 u 0

-ui(0,t)

u u u u E x t dz t s i s zi

h

= + = ( , )0

i2i1

i0

u 1 u 2

linea Bergeron linea LIOV

+

-

0

u 1'

i0'

-u i(0,t)

Bergeron LIOV line

i0

Z

+

-

u 1

V

+

-

+

-

i2i1

u 2

V11'

0 Z cc

u1 '

'i0

-ui(0,t)

Link between LIOV and EMTP



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u x t

xL

i x t

tE x h t

s

xi( , ) ( , ) ( , , )+ =

i x t

xC

u x t

t

s( , ) ( , )

+ = 0

( )u t u t i t E z t dz s o zih( , ) ( ) ( , ) ( , , )0 0 01

0

= = +

[ ]u t Z i t u t t Z i t t

Z i t V t t

c c

c

1 0 1 0

0 1

( ) ( ) ( ) ( )

( ) ( )

' '= + +

= +

[ ]u t Z i t u t t Z i t t

Z i t V t t

c c

c

1 0 1 0

0 1

' '

' '

( ) ( ) ( ) ( )

( ) ( )

= +

= +



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Validation using data from a more complex systemData: courtesy of Dr. A. Piantini, Univ. Sa Paulo


being done on induced voltages Cont.


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0 1 2 3 4 5 6 7 8Time in us

-100

-50

0

50

100

150

200 Calculated voltageMeasured voltage

Validation using data from a more complex systemData: courtesy of Dr. A. Piantini, Univ. Of Sa Paulo




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0 1 2 3 4 5 6 7 8

Time in us

0

10

20

30

40

50

60 calculated voltageMeasured voltage

Validation using data from a more complex systemData: courtesy of Dr. A. Piantini, Univ. Of Sa Paulo




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13.What is the CIGRE working group doing on

induced voltages ?

Within the framework of

CIGRE working group WG 33.01 "Lightning",

Task Force 33.01.01 "Lightning induced voltages"

established some years ago.

C.A. Nucci(responsible member), P. Chowdhuri, G. V.

Cooray, M.T. Correia de Barros, M. Darveniza, F. De la Rosa,

G. Diendorfer, F. Heidler, M. Ishii, W. Janischewskyj, T.

Kawamura, C. Mazzetti, P. Pettersson, F. Rachidi, V. Rakov,

M. Rubinstein, T. Short, J.V. Shostak, M.A. Uman, S.

Yokoyama


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13.What is the CIGRE working group doing on

induced voltages ?

TF 33.01.01 has already produced two papers

published in Electra dealing respectively with

lightning return stroke models (August 95) and

lightning electromagnetic field-to-transmission linecoupling models (October 95).

A third paper, dealing with a sensitivity analysis and

aimed at providing ranges of overvoltage values to

be expected in the different typical line

configurations, is in preparation.

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