TELKOMNIKA Indonesian Journal of Electrical Engineering
Vol. 13, No. 1, January 2015, pp. 42 ~ 56
DOI: 10.11591/telkomnika.v13i1.6844
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42
Effective Factors on the Generated Transient Voltage in
the Wind Farm due to Lightning
M. A. Abd-Allah, Mahmoud N. Ali, A. Said*
Faculty of Engineering at Shoubra, Benha University, Egypt
*Corresponding author, e-mail: abdelrahman.ghoniem@feng.bu.edu.eg
Abstract
According to reports that had been published in many papers, wind turbines (WTs) fault due to
lightning is one of the most difficult challenges. Lightning overvoltage lead to malfunction in the wind farm
equipments. These improper functioning contain of malfunction electronic equipments and deformation of
transformer winding and Surge arrester failures. The travelling waves which are generated due to high
ground potential rise under lightning struck turbine cause these problems. To evaluate these cases, it must
be performed an accurate analysis on the wave shape and level of the Lightning overvoltage and ground
potential rise. This paper investigates the effective factors on the wave shape and level of the overvoltage,
GPR and surge arrester burnout. These factors are included impulse Current-second characteristics,
position of lightning, inception angle, multiple lightning strokes and chopped current. ATP-EMTP simulation
program is applied to analyze the lightning over-voltage of onshore wind farm. This paper provides a
practical procedure of lightning protection.
Keywords: WTs, current-second characteristics, lightning overvoltage, GPR, ATP/EMTP
Copyright © 2015 Institute of Advanced Engineering and Science. All rights reserved.
1. Introduction
With a rapid growth in wind power generation, lightning hazard to wind turbines (WTs)
has come to be regarded with more attention. Due to their great height, distinctive shape, and
exposed location, WTs are extremely vulnerable to lightning stroke. After a WT is struck by
lightning, high lightning current flows through the WT and causes considerable damage to
electrical equipment inside the WT structure and wind turbine nacelle results stop of the
generator operation and probably expensive repairs [1].
In order to decrease downtime, repairs and blade damaged. Protecting the blade is very
important and well-designed lightning protection is a necessity for this equipment so Modern
wind turbine blades are made of insulating materials such as glass fiber reinforced plastic
(GFRP) as a common material or wood epoxy. The lightning protection of wind turbine blades
can be classified as receptor, metallic cap, mesh wire, and metallic conductor as reported in
IEC-61400-24 standards.
In general, the problem of lightning protection of wind turbine blades is to conduct the
lightning current safely from the attachment point on the blade to the hub and then to the
ground.
However another serious problem known as "back-flow surge" which not only causes
damages to the wind turbine that has been struck but also the other turbines that have not. The
back-flow surge phenomenon has been defined as the surge flowing from a customer’s
structure such as a communication tower into the distribution line. High resistivity soil often
makes Surge Arresters (SAs) at tower grounding systems operate in reverse and allow backflow
of surge current to the grid. The phenomenon of surge invasion from a wind turbine that is
struck by lightning to the distribution line in a wind farm is quite similar to the case of “back-flow
surge” [2].
Due to significant influence on the wind farm behavior under lightning, the transient
response must be either accurately analyzed. So in this paper wind farm component model is
implemented using ATP_EMTP. Characteristics and hazards of back-flow surge in onshore
wind farm are analyzed and discussed. Effective Factors on the Transient Voltage Generated in
the Wind Farm due to Lightning are analyzed. These factors are included impulse Current-
Received October 14, 2014; Revised November 10, 2014; Accepted November 28, 2014
TELKOMNIKA
ISSN: 2302-4046
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second characteristics, position of lightning, inception angle, multiple lightning strokes and
chopped current. This paper provides a practical procedure of lightning protection.
2. Description and Modeling of the Onshore Wind Farm
Figure 1 shows layout of onshore wind farm composed of two identical wind power
generators. Boost transformers for the generators are installed in vicinity of the wind turbine
towers. All boost transformers are connected to the grid via grid-interactive transformer by
overhead distribution line. Surge arresters are inserted to the primary and secondary sides of
the boost and grid-interactive transformers.
Figure 1. Wind farm model [2]
Table 1 gives the required data for modeling the generators of the wind turbines,
transmission line and transformers.
Table 1. Wind Turbines, Transformers Data and connected line data [2]
Wind Turbine Model(Synchronous Generator- Y connected)
Voltage (line rms)
0.660 [kV]
Rated power
Leakage reactance
Frequency
1.0 [MVA]
0.1 [H]
60.0 [Hz]
Transformer Model (Boost, Grid-Interactive)
Connection method
Voltage (line rms)
Rated power
Leakage reactance
Copper losses
No-load losses
Line Model (values at 60 Hz)
positive / zero phase resistance [Ω/Km]
Positive / zero phase inductance [mH/Km]
Positive / zero phase capacitance [nF/Km]
Y / ∆, Y / ∆
0.660/6.6 [kV], 66.0/6.6 [kV]
1.0 [MVA], 10.0 [MVA]
0.15 [p.u]
0.005 [p.u]
neglected
0.00105/0.021
0.83556/2.50067
12.9445/6.4723
A current function model called Heidler is now used widely to model a lightning current
[3-5]. Equation (1) represents the lightning current. A 400 Ω lightning path resistance was
connected shunt to the simulated natural lightning as shown in Figure 2.
Effective Factors on the Generated Transient Voltage in the Wind Farm… (M. A. Abd-Allah)
44
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i (t )  I o
(t /  1 ) 2
e t /  2
2
[( t /  1 )  1]
(1)
Where I0: the peak of current, τ1, τ2: time constants of current rising and dropping.
Figure 2. Lightning current model
The down conductor in the blade and the wind turbine tower have been considered as a
lossless transmission line and they were estimated according to following experimental equation
[4-7], Equation (2), where the down conductor and the tower often were treated as a cylindrical
conductor.
Z  60 (ln
2
2
r
h  2)
(2)
Where, Z is the surge impedance, r and h are the radius and height of the cylinder,
respectively. The wind tower is taken as an iron vertical conductor of 60 m height and 3.0 m
radius.
The overhead lines are considered and represented by single-phase positive wave
impedance (i.e. Surge impedance) with the light velocity.
Z0 
v 
L /C 
1
LC
(3)
m/s
(4)
Where, C and L are the capacitance and inductance of line, respectively, Z0 is the surge
impedance and v is the propagation velocity [3, 8].
A simplified model of surge arrester was derived from IEEE model [9, 10]. The model
circuit is shown in Figure 3. This model is composed by two sections of nonlinear resistances
usually designated by A0 and A1 which are separated by inductance L1 and L0. A parallel
resistance Rp (about 1 MΩ) is added to avoid the numerical instability of the combination of the
current source and nonlinear elements.
Figure 3. Pinceti and Giannettoni model
TELKOMNIKA Vol. 13, No. 1, January 2015 : 42 – 56
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In case medium and high voltage levels the inductances L1 and L0 in the model are in
μH and calculated using:
L1 
1 Ur 1 / T 2  Ur 8 / 20
Un
4
Ur 8 / 20
(5)
L0 
1 Ur 1 / T 2  Ur 8 / 20
Un
Ur 8 / 20
12
(6)
In case low voltage levels the inductances L1 and L0 in the model are in μH and
calculated using:
L1=0.03Un
(7)
L0=0.01Un
(8)
Where Un is the arrester rated voltage in kV, Ur1/T2 is the residual voltage at 10 kA fast
front current surge (1/T2 μs). Ur8/20 is the residual voltage at 10 kA current surge with 8/20 μs
time parameters.
The nonlinear characteristics of the two elements A0 and A1 are based on the pu data
published in [11]. In this paper Ground system model is based on the nonlinear performance of
the grounding resistance with high currents i.e. high voltage, high frequency model [13]. The
nonlinearity nature of the ground resistance can be represented by a nonlinear resistance, RT,
whose value is given as [12];
 Rt  R 0  For ( i  Ig )

R0

 For ( i  Ig )
 Rt 
i

1

Ig
(9)
Where, i is the current through the rod (kA), and Ig is the critical current for soil
ionization (kA) which is given by:
Ig 
E0  
2 R 0
(10)
2
Where, E0 is the critical soil ionization gradient and R0 constant resistance and given
by:
R0 

2 l
{ln
4l
 1}
a
(11)
Where, ρ is the soil resistivity (Ω.m), L is the electrode length (m) and a is the electrode
radius (m).
3. Results and Discussion
In this study, the lightning stroke is taken as striking wind turbine (WT#1) as shown in
Figure 4. Lightning current waveform of 51kA-2/631μs is used in this study.
Effective Factors on the Generated Transient Voltage in the Wind Farm… (M. A. Abd-Allah)
46
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Figure 4. lightning hit WT#1 [3]
In this case, voltages at four different locations (at Generator terminal with lightning hit,
6.6 kV sides of the boost transformers and the grid-interactive transformer) are taken for
analysis.
Figure 5 shows the voltage waveforms and its peak value at different locations of the
wind farm. It is observed that the peak magnitude of the generated overvoltage at WT#1
generator terminal can be as high as 125kV, at (WT#1) boost transformer secondary side reach
to 111kV, at (WT#2) boost transformer secondary side reach to 25kV and at grid reach to 27kV.
Also these wave forms oscillate with high frequency. It is clear that the surge hitting WT#1,
which was struck by lightning, was propagated to the adjacent turbine and the grid through
collecting point.
140
[kV]
120
120
100
[kV]
100
80
80
60
60
40
40
20
20
0
0
-20
0.0
0.2
0.4
0.6
0.8
1.0
[ms]
1.2
-20
0.0
0.2
0.4
0.6
0.8
1.0
[ms]
1.2
(f ile modelwind11.pl4; x-v ar t) v :X0002A
(f ile modelwind11.pl4; x-v ar t) v :X0001A
(a) Voltage on Generator WT#1
(b) Voltage at boost transformer voltage
(WT#1)
30.0
30
[kV]
[kV]
22.5
20
15.0
10
7.5
0
0.0
-10
-7.5
-20
0.0
0.2
0.4
0.6
0.8
1.0
[ms]
1.2
(f ile modelwind11.pl4; x-v ar t) v :X0004A
-15.0
0.0
0.2
0.4
0.6
0.8
1.0
(f ile modelwind11.pl4; x-v ar t) v :X0005A
(d) Voltage at primary grid voltage
(c) Voltage at boost transformer voltage
(WT#2)
125kV
120
111kV
Voltage(kV)
100
80
60
40
25kV
27kV
@ W T#2
@ G r id
20
0
@ G e n e ra to r
@ W T #1
N ode
(e) Peak value of voltage at different location in wind farm
Figure 5. Voltage waveforms through phase (a)
TELKOMNIKA Vol. 13, No. 1, January 2015 : 42 – 56
[ms]
1.2
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Figure 6 shows the GPR wave form at WT#1 and its peak value at different locations of
the wind farm. It is observed that the peak magnitude of the GPR at WT#1 reach to 126kV , at
(WT#2) reach to 8kV and at grid reach to 10kV. It is clear that the GPR is enough high to cause
Back flow current.
130
126kV
[kV]
120
110
100
GPR peak(kV)
90
70
50
80
60
40
30
20
10
8kV
@ W T#1
-10
0.0
10kV
0
0.2
0.4
0.6
0.8
1.0
[ms]
@ W T#2
@ G r id
N ode
1.2
(f ile modelwind11.pl4; x-v ar t) v :XX0080
(b) Peak value of GPR at different location in
wind farm
Figure 6. GPR at different locations of the wind farm
(a) GPR waveform at WT#1
The Surge Arrester (SA) burnout depends on the heat produced by the current flowing
through the arrester exceeds its thermal limit. The absorbed energy can be obtained in watthour [14]:
T
w 

P ( t ) dt / 3600
(12)
0
Where, P(t) is the instantaneous power in watt. The absorbed energy in kJ is calculated
as:
Energy = 3,6 x W
(13)
(a) Thermal limit of SA
(b) Energy consumption of SA @ WT#1
T h e m a l lim it 1 5 k J
Consumption energy (KJ)
1 ,0
0 ,8
0 ,6
0 ,4
0 ,2
0 ,0
@ W T#1
@ W T#2
@ G r id
N ode
(c) SAs consumption energy at different location in wind farm
Figure 7. Energy consumption of surge arrester at different locations of the wind farm
Effective Factors on the Generated Transient Voltage in the Wind Farm… (M. A. Abd-Allah)
48
ISSN: 2302-4046
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Figure 7 shows the energy consumption of surge arrester through phase (a) located at
6.6 kV side of boost transformers at WTs#1, 2 and at the primary side of grid. It is observed that
the SA in phase a at the wind turbine that was actually struck consumed the largest energy,
then SA at WT#2 and Grid consume less energy. The result shows that the absorbed energy of
surge arresters at turbines and grid are higher but within limits.
4. Effective Factor on Generated Transient Voltages.
4.1. Effect of Lightning Type
Three lightning surges are used in this investigation [15, 16]. Table 2 gives the
characteristics of each lightning surge.
Table 2. Lightning Surges Characteristics (Standard for Lightning Protection and Lightning
Strength in Japan)
Japan
Lightning type
Summer #1
Peak value [kA]
30.0
Front time [μs]
2.0
Tail time [μs]
70.0
Winter #2
51.0
2.0
631.0
200.0
10.0
350.0
Case #3
5
x 10
2.5
30kA-2/70us
200kA-10/350us
51kA-2/631us
2 0 0 k A 1 0 /3 5 0 u s
200
5 1 k A 2 /6 3 1 u s
1.5
3 0 k A 2 /7 0 u s
150
voltage (kV)
Voltage @WT#1 in (kV)
2
1
100
0.5
50
0
0
@ W T#1
-0.5
0
0.2
0.4
0.6
Time in Sec
0.8
1
@ W T#2
@ G r id
N ode
1.2
-3
(a) Voltage waveforms @WT#1
x 10
(b) Comparison between peak values of voltage
at each node
5
3
x 10
2
GP R @ WT#1 in (V )
250
200kA10/350us51kA-2/631us
30kA-2/70us
2.5
2 0 0 k A 1 0 /3 5 0 u s
5 1 k A 2 /6 3 1 u s
200
3 0 k A 2 /7 0 u s
GPR(kV)
1.5
1
0.5
150
100
50
0
0
@ W T#1
-0.5
0
0.2
0.4
0.6
Time in Sec
0.8
1
1.2
@ W T #2
@ G rid
N ode
-3
(c) GPR waveforms @WT#1
x 10
(d) GPR at different locations of the wind farm
4
x 10
SA Consumption energy in (j)
25
51kA-2/631us
200kA-10/350us
30kA-2/70us
2.5
Arrester absorbation energy (kJ)
3
2
1.5
1
0.5
0
2 0 0 k A 1 0 /3 5 0 u s
20
t h e r m a l L im it( 1 5 k J )
15
5 1 k A 2 /6 3 1 u s
10
5
0
@ W T#1
-0.5
0
0.2
0.4
0.6
Time in sec
0.8
1
1.2
@ W T#2
@ G r id
NODE
-3
x 10
(f) comparison of SA energy consumption at
(e) SA consumption energy waveforms
different location
@WT#1
Figure 8. overvoltages, GPR and arrester absorption energy at different locations of the wind
farm under different type of lightning
TELKOMNIKA Vol. 13, No. 1, January 2015 : 42 – 56
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Figure 8 shows the overvoltage, GPR and consumption energy of arrester through
phase a located at 6.6 kV side of boost transformers at WTs#1, 2 and at the primary side of grid
comparison with varying the lightning peak value. It is observed that the peak value of the
overvoltage and GPR at WT#1 reach to 231kV and 250kV respectively, also the energy
consumption of the SA surpassed their thermal limitation only at the WT#1 under lightning surge
#3. This is due to high peak value of lightning surge #3. It is clear that the lightning surge strikes
the wind tower is more significant under high crest lightning surge #3.
4.2. Effect of Lightning Parameter Front Time
4
14
x 10
12
10
120
2 u s fro n t
3 u s fro n t
100
8
Voltage (kV)
V oltage @ W T#1 in (V )
1 u s fro n t
5us
3us
2us
1us
6
5 u s fro n t
80
60
40
4
20
2
0
@ W T #1
0
1.05
1.1
1.15
1.2
1.25
Time in (Sec)
1.3
1.35
@ W T#2
@ G rid
N ode
1.4
-5
x 10
(a) Voltage waveforms @WT#1
(b) Comparison between peak values of
voltage at each node
4
16
x 10
12
140
2 u s fro n t
3 u s fro n t
120
10
100
8
80
GPR(kV)
G P R @ W T#1 in (V )
1 u s fro n t
5us
3us
2us
1us
14
6
5 u s fro n t
60
4
40
2
20
0
0
@ W T#1
-2
1.05
1.1
1.15
1.2
1.25
Time in Sec
1.3
1.35
@ G rid
-5
x 10
(d) GPR at different locations of the wind farm
(c) GPR waveforms @WT#1
2us
3us
5us
1us
950
1,0
1us front
2us front
0,8
Absorbation energy (kJ)
1000
SA consumption energy @WT#1 in (j)
@ W T#2
Node
1.4
900
850
800
3us front
5us front
0,6
0,4
0,2
750
0,0
700
@ W T#1
3
4
5
6
7
8
Time in sec
9
10
11
12
@ W T#2
@ Grid
Node
-5
x 10
(e) SA consumption energy waveforms
(f) comparison of SA energy consumption at
@WT#1
different location
Figure 9. Overvoltages, GPR and arrester absorption energy at different locations of the wind
farm under different lightning front time
Effective Factors on the Generated Transient Voltage in the Wind Farm… (M. A. Abd-Allah)
50
ISSN: 2302-4046
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The lightning strokes with different front time (1µs:5µs) [17] are studied to show the
effect of them. Figure 9 shows the comparison of voltage, GPR and arrester absorbing energy
with varying lightning front time. The results indicate that the maximum voltage and the GPR
located at turbines and grid are decreased with increasing front time of lightning. Also, the
absorbed energy by the arresters located at the non-thunderstruck turbines and grid decrease
with increasing front time of lightning.
This indicates that for the same current magnitude, the fast rising current dissipates to
ground more quickly than the slow rising current. The faster fronted current pulse results in
larger potential at feed point in the first moments because larger currents are forced to disperse
into the ground through small parts of the electrode.
4.3. Effect of Lightning Parameter Tail Time
4
x 10
600us
300us
20us
10
10 0
6
Voltage in (V)
80
Voltage(kV)
8
12 0
4
2 0 0 u s T a il
60
3 0 0 u s T a il
40
6 0 0 u s T a il
2
20
0
0
@ W T #1
-2
0.5
1
1.5
2
2.5
Time in sec
3
3.5
4
@ W T#2
@ G rid
N ode
4.5
-4
(a) Voltage waveforms @WT#1
x 10
(b) Comparison between peak values of
voltage at each node
4
x 10
100us
300us
200us
12
10
140
120
100
GPR (kV)
GPR in (V)
8
6
200us Tail
80
300us Tail
60
4
600us Tail
40
2
20
0
0
@ W T#1
0.2
0.4
0.6
0.8
1
1.2
1.4
Time in Sec
1.6
1.8
2
@ W T#2
@ G rid
N ode
2.2
-4
(c) GPR waveforms @WT#1
x 10
(d) GPR at different locations of the wind farm
1200
200us
600us
300us
1.0
Absorbation energy (kJ)
SA energy consumption in (j)
1000
800
600
400
200
200us Tail
300us Tail
0.8
600us Tail
0.6
0.4
0.2
0
0.0
-200
@WT#1
0
0.2
0.4
0.6
Time in sec
0.8
1
1.2
@WT#2
@Grid
Node
-3
x 10
(e) SA consumption energy waveforms
(f) comparison of SA energy consumption at
@WT#1
different location
Figure 10. Overvoltages, GPR and arrester absorption energy at different locations of the wind
farm under different lightning tail time
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The lightning strokes with different tail time (200µs:600µs) are studied to show the
effect of them. Figure 10 shows the comparison of voltage, GPR and arrester absorbing energy
with varying lightning front time. The results indicate that the maximum voltage and the GPR
located at turbines and grid are increased with increasing tail time of lightning. Also, the
absorbed energy by the arresters located at the non-thunderstruck turbines and grid increase
with increasing tail time of lightning.
This indicates that for the same current magnitude, the slow decay current dissipates to
ground more quickly than the fast decay current. The slower decayed current pulse results in
larger potential at feed point in the first moments because larger currents are forced to disperse
into the ground through small parts of the electrode.
4.4. Effect of Lightning Inception Angle
4
x 10
12
108kV 110kV 111kV
NP
ZC
PP
10
100
80
Voltage(kV)
V oltage in (V )
8
6
4
NP
ZC
60
PP
40
2
20
0
0
@ WT#1
-2
0
0.2
0.4
0.6
Time in sec
0.8
1
@ WT#2
@Grid
Node
1.2
-3
x 10
(b) Comparison between peak values of
voltage at each node
(a) Voltage waveforms @WT#1
4
14
x 10
NP
ZC
PP
120
10
100
8
80
GPR(kV)
G P R in (v )
12
6
NP
60
ZC
4
40
2
PP
20
0
0
-2
@ W T #1
0
0.2
0.4
0.6
Time in sec
0.8
1
1.2
@ W T #2
@ G rid
N o de
-3
x 10
(c) GPR waveforms @WT#1
(d) GPR at different locations of the wind farm
1,3
1020
NP
ZC
PP
980
1,2
NP
1,1
Absorbation energy (kJ)
S A c ons um ption energy (j)
1000
960
940
920
900
1,0
ZC
0,9
PP
0,8
0,7
0,6
0,5
0,4
0,3
880
0,2
860
0,1
840
0,0
@ W T#1
@ W T #2
@ G rid
820
4
4.5
5
5.5
Time in sec
6
6.5
7
N od e
-5
x 10
(d) SA consumption energy waveforms
(e) comparison of SA consumption energy at
@WT#1
different location
Figure 11. Overvoltages, GPR and arrester absorption energy at different locations of the wind
farm under different lightning inception angle
Effective Factors on the Generated Transient Voltage in the Wind Farm… (M. A. Abd-Allah)
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The impact of the inception angle is studied only with respect to phase a of voltage
waveform, this is because of the phase differences between the three phases. Three different
scenarios of lightning inception angle are studied. The first one is when the lightning hits the
wind turbine WT#1 at the negative peak (NP) of voltage waveform of phase a. The second case
is when the lightning hits it at the zero crossing (ZC). The third case is when the lightning hits at
the positive peak (PP). Figure 11 shows the overvoltage, GPR and consumption energy of
arrester through phase a located at 6.6 kV side of boost transformers at WTs#1, 2 and at the
primary side of grid with varying the inception instant.
Figure 11 shows the absorbed energy of phase a surge arrester located at the 6.6kV
side of boost transformers. The result shows that the absorbed energy of surge arresters at
negative peak inception instant is within limits but higher than those at zero crossing and
positive peak instants. This can be related to the fact that the lightning surge current in case of
negative peak is higher than that of the case of zero crossing and positive peak. The reason is
because the potential difference at the case of negative peak is higher than that in case of
positive peak and zero crossing. But the consumption energy of SA at the grid is negative
according to result at turbines. Also The GPR is independent of the inception instant on the
wave. Also the surge propagation magnitude is quite dependent on the inception instant when
the lightning hits the wind turbine.
4.5. Effect of Different Lightning Location
5
x 10
2.5
220
Case#1
Case#2
Case#3
200
180
160
Voltage (kV)
2
Voltage (V)
1.5
1
140
120
C ase#3
100
C ase#2
80
C ase#1
60
0.5
40
20
0
0
@ W T#1
-0.5
0
0.2
0.4
0.6
Time sec
0.8
1
@ W T#2
@ G r id
N ode
1.2
-3
x 10
(b) Comparison between peak values of
overvoltage at each node
(a) Voltage wave form @WT#1
5
2.5
x 10
220
Case#1
Case#2
Case#3
2
200
180
160
140
GPR(kV)
GPR (V)
1.5
1
120
100
C ase#3
80
0.5
C ase#2
60
C ase#1
40
20
0
0
@ W T#1
-0.5
0
0.2
0.4
0.6
Time sec
0.8
1
@ W T#2
@ G r id
N ode
1.2
-3
x 10
(c) GPR @WT#1
(d) GPR at different locations of the wind farm
5
12
x 10
1 0 00 kJ
1 0 0 0 kJ
2 0
1 8
Case#1
Case#3
Case#2
8
6
1 6
th e r m a l L im it( 1 5 k J )
1 4
Absorbation energy (kJ)
SA consumption energy (J)
10
4
2
1 2
C a se # 3
1 0
C a se # 2
8
C a se # 1
6
4
2
0
0
@ W T #1
-2
0
0.2
0.4
0.6
Time sec
0.8
1
1.2
@ W T # 2
@ G r id
N o d e
-3
x 10
(f) comparison of SA energy consumption at
different location
Figure 12. Overvoltages, GPR and arrester absorption energy at different locations of the wind
farm under different lightning location
(e) SA consumption energy of SA @WT#1
TELKOMNIKA Vol. 13, No. 1, January 2015 : 42 – 56
ISSN: 2302-4046
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53
A different lightning strokes location is studied to show the effect of them. This
investigation is under three different cases. The first case is direct Stroke occurs when lightning
strike the boost transformer behind the wind turbine (Case#1). The second case is direct Stroke
occurs when lightning stroke hit the distance TL between the turbines (Case#2). The last case is
Backflow Current –Overvoltage when the lightning hits any part of wind turbine so lightning
reach the ground resistance via down conductor (Case#3). Figure 12 shows the comparison of
voltage, GPR and arrester absorbing energy at different turbine and grid with varying lightning
position. The results indicate that the maximum voltage and the GPR located at struck turbine
and grid are increased in case#1. Also, the absorbed energy by the arresters located at the
non-thunderstruck turbines and thunderstruck increase and exceed thermal limit in case
Case#2.
4.6. Effect of Multiple Lightning Strokes
Three selected of multiple lightning strokes, shown in Figure 13, with amplitudes of
18.6kA, 15kA and 12kA for the 1st, 2nd and 3rd strokes, with 1ms intervals were used [18].
Figure 14 gives the waveform of the single lightning stroke. Figure 15 to 19 shows waveform of
overvoltage at WT#1 and energy consumption of arrester at WT#1 also shows the voltage, GPR
and arrester absorbing energy at different turbine and grid under single and multi strikes. The
results show that multiple strikes don’t affect on peak value of overvoltage and GPR, but has a
great effect on energy consumption of SA. From the results obtained; multiple lightning strokes
which occur in real situations are much more severe than a single lightning stroke.
20
20
[kA]
[kA]
16
16
12
12
8
8
4
4
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5 [ms] 4.0
(f ile modelwind112222.pl4; x-v ar t) c:XX0004-X0003A
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5 [ms] 4.0
(f ile modelwind11.pl4; x-v ar t) c:XX0105-X0080A
Figure 13. Waveforms of the 1st, 2nd and 3rd
positive lightning strokes
60
Figure 14. Waveform of the 1st injected
lightning stroke
[kV]
60
[kV]
50
50
40
40
30
30
20
20
10
10
0
0
-10
0.0
-10
0.5
1.0
1.5
2.0
2.5
3.0
3.5 [ms] 4.0
(f ile modelwind11.pl4; x-v ar t) v :X0002A
Figure 15. Voltage Waveform at WT#1 under
single strike
-20
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5 [ms] 4.0
(f ile modelwind11.pl4; x-v ar t) v :X0002A
Figure 16. Voltage Waveform at WT#1 under
multiple strike
Effective Factors on the Generated Transient Voltage in the Wind Farm… (M. A. Abd-Allah)
54
ISSN: 2302-4046
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25
50
20
40
15
30
10
20
5
10
0
0.0
0.5
1.0
1.5
2.0
2.5
3.5 [ms] 4.0
3.0
0
0.0
0.5
1.0
1.5
2.0
2.5
3.5 [ms] 4.0
3.0
(f ile modelwind11.pl4; x-v ar t) t: XX0097
(f ile modelwind11.pl4; x-v ar t) t: XX0097
Figure 17. Consumption energy of arrester at
WT#1 under single strike
Figure 18. Consumption energy of arrester at
WT#1 under multiple strikes
70
50
60
40
50
Multi Strike
30
GPR(kV)
voltage (kV)
Single Strike
20
40
Single Strike
30
Multi Strike
20
10
10
0
0
@WT#1
@WT#2
@Grid
@WT#1
Node
@WT#2
@Grid
Node
(a) peak values of voltage at each node
(b) GPR at different locations of the wind farm
0,040
Single Strike
Consumption energy (kJ)
0,035
Multi Strike
0,030
0,025
0,020
0,015
0,010
0,005
0,000
@WT#1
@WT#2
@Grid
Node
(c) SA energy consumption at different location
Figure 19. Overvoltages, GPR and arrester absorption energy at different locations of the wind
farm under different lightning
4.7. Effect of Chopped Current
Lightning strokes chopped at tail wave 0.1, 0.3, 0.5ms waveform are used. Figure 20
gives the waveform of the lightning chopped tail time simulated. Figure 21 to 23 shows
waveform of overvoltage, GPR at WT#1 and energy consumption of arrester at WT#1, also
shows the comparison of voltage, GPR and arrester absorbing energy at different turbine and
TELKOMNIKA Vol. 13, No. 1, January 2015 : 42 – 56
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ISSN: 2302-4046
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55
grid under lightning chopped tail time. The results indicate that the maximum voltage and the
GPR located at turbines and grid were increased in case of chopped time near lightning peak
value. Also, the absorbed energy by the arresters located at the turbines and grid is increased.
Figure 20. Lightning 2/631 µs, chopped tail
time at 0.1, 0.3, 0.5 ms
Figure 21. Overvoltages @WT#1 under
Lightning 2/631 µs, chopped tail time at 0.1,
0.3, 0.5 ms
Figure 22. GPR @WT#1 under Lightning
2/631 µs, chopped tail time at 0.1, 0.3, 0.5 ms
Figure 23. SA consumption energy @WT#1
under Lightning 2/631 µs, chopped tail time at
0.1, 0.3, 0.5 ms
5. Conclusion
In this paper lightning surge analyses on a wind farm was performed using ATP/EMTP.
Lightning hits WTs creates an overvoltage at both HV and LV sides of the boost transformers.
The very high surge voltage would appear at struck turbine. Several factors may contribute to a
transformer failure and surge arrester burnout due to lightning overvoltage including, crest
lightning current, rise time, tail time, lightning inception angle, multiple lightning strike, chopped
lightning current and position of lightning. From the results of several analyses the following
conclusions were drawn, the result shows that impulse current crest, small front time and large
tail time may be the most serious. Also the absorbed energy of surge arresters at negative peak
inception instant is within limits but higher than those at zero crossing and positive peak
instants. Lightning hit current carrying conductor is more severe than lightning hit noncurrent
carrying conductor as tower and nacelle. Multiple strikes don’t affect on peak value of
overvoltage and GPR, but has a great effect on energy consumption of SA. The maximum
voltage and the GPR located at turbines and grid are increased in case of current chopped at
tail wave at time near lightning peak value. So this paper provides a practical procedure of
lightning protection i.e. lightning current-time characteristic and position of lightning and
Effective Factors on the Generated Transient Voltage in the Wind Farm… (M. A. Abd-Allah)
56
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ISSN: 2302-4046
chopped lightning current are the main parameters to select an appropriate protection measure
for the WT.
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