rachid i slides
TRANSCRIPT
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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
Return-stroke current models
3. How to evaluate them? Cont.
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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..
Return-stroke current models
3. How to evaluate them? Cont.
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Triggered lightning: A sequence of frames
Return-stroke current models
3. How to evaluate them? Cont.
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TCS
a) b)
microseconds microseconds
V/m TCS MTL
Validation by means of triggered lightning
Return-stroke current models
3. How to evaluate them? Cont.
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Reduced scale model at the University Of So Paulo - Brazil
The Agrawal model: Experimental validation
3. How to evaluate them? Cont.
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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
The Agrawal model: Experimental validation
3. How to evaluate them? Cont.
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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)
The Agrawal model: Experimental validation
Using reduced-scale line model
Experimental data: by A. Piantini, Univ. Of So Paulo
3. How to evaluate them? Cont.
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The Agrawal model: Experimental validation
3. How to evaluate them? Cont.
Using NEMP simulators
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The Agrawal model: Experimental validation
3. How to evaluate them? Cont.
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.
3. How to evaluate them? Cont.
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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.
3. How to evaluate them? Cont.
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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
3. How to evaluate them? Cont.
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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
3. How to evaluate them? Cont.
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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.
3. How to evaluate them? Cont.
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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
3. How to evaluate them? Cont.
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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
3. How to evaluate them? Cont.
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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
4. What magnitudes and shape are typical
for lightning-induced overvoltages ? Cont.
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Magnitude
1 km
4. What magnitudes and shape are typical
for lightning-induced overvoltages ? Cont.
However ...
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For perfectly conducting grounds and for an
infinitely long wire
4. What magnitudes and shape are typical
for lightning-induced overvoltages ? Cont.
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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10. Is horizontal or vertical construction
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.
10. Is horizontal or vertical construction
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.
11.What effect does pole grounding and
ground resistivity have ? 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
Influence of ground resistivity Cont.
11.What effect does pole grounding and
ground resistivity have ? Cont.
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How does the ground resistivity affect
magnitude and shape of the induced
voltages?
Influence of ground resistivity
11.What effect does pole grounding and
ground resistivity have ? Cont.
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0.5 km 0.5 km
Influence of ground resistivity Cont.
0 200 400 600 800 1,000
Obs. point along the line in m
30
50
70
90
110
infinite
=0.01 S/m
11.What effect does pole grounding and
ground resistivity have ? Cont.
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1 km
Influence of ground resistivity Cont.
0 200 400 600 800 1000
Obs. point along the line in m
-40
-20
0
20
40
infinite
= 0.01 S/m
11.What effect does pole grounding and
ground resistivity have ? Cont.
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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
Influence of ground resistivity Cont.
11.What effect does pole grounding and
ground resistivity have ? Cont.
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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
The LIOV-EMTP code Contd
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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
' '
' '
( ) ( ) ( ) ( )
( ) ( )
= +
= +
The LIOV-EMTP code Contd
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Validation using data from a more complex systemData: courtesy of Dr. A. Piantini, Univ. Sa Paulo
12.Some of the current researches which are
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
12.Some of the current researches which are
being done on induced voltages Cont.
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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
12.Some of the current researches which are
being done on induced voltages Cont.
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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.