Utilization of Line Surge Arresters in Transmission Lines
Hetal Pranlal
Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
Abstract – Surges generated by lightning strokes can
lead to failures in the supply of electricity, therefore they
have brought several concerns in the design and operation
of transmission lines due to the consequences of these for
the various components. This dissertation presents the
results of the work performed with the aim of studying the
use of line surge arresters on transmission lines, using the
simulation program ATPDraw. The physical phenomenon
associated to lightning is explained, as well as the
characterization of the discharge waveforms and the
establishment of an equivalent electric model for its
representation. The models of the components of the
electrical system that are considered relevant to the study of
the electromagnetic transients generated by the incidence of
lighting strokes were also analysed. Assuming that the
stroke hits the top of the transmission tower and
considering discharge currents with different peak values
and different characteristic times, several simulations were
performed with the aim of studying the influence of ground
resistance and the adjacent towers in the evolution of the
voltages in the phase conductors and in the insulators,
analyzing the backflashovers as well. It is also performed
the study of the voltages in the insulators when line surge
arresters are installed. Finally, the installation of line surge
arresters in uniform and non-uniform lines was simulated,
performing the analysis of the backflashovers that occurs
and studying the strategy of the installation of this devices
that leads to the reduction of backflashovers. It was found
that the installation of line surge arresters in three phases of
one of the circuits when uniform lines are considered leads
to best results. In non-uniform lines, the installation of
arresters in the transmission towers that have the highest
grounding resistances and in the adjacent towers presents a
significant reduction in backflashovers, eliminating
backflashovers in one of the line circuit.
Keywords: Lightning Stroke, Transmission Line,
Backflashover, Grounding Resistance, Line Surge
Arresters, ATPDraw
I. Introduction
A transmission line is designed to ensure an insulation
level higher than the maximum instantaneous voltage. The
insulation level is selected based on surges that are
predictable to occur, whether their source are internal or
external. Internal origin surges refer to those produced by
switching or disconnecting operations. On other hand, the
external surges are generally caused by lightning flashes.
When a lightning strikes a component of the power
system a current of high amplitude and short duration is
injected to that power system, caused by the establishment
of an electric arc through an ionized channel formed
between a thundercloud and the point of impact, called arc
of return. The current previously mentioned produces
waves that travel through the conductor “paths” near the
impact point, which is associated with characteristic
impedance, called surge impedance. This phenomenon
produces overvoltages which amplitude corresponds to the
product of surge impedance with the instantaneous value of
the discharge current.
Lightning discharges are responsible for a significant
number of interruptions in electricity supply, because when
a lightning stroke hits a transmission tower, the overvoltage
generated can lead to the backflashover of the insulators,
leading to line operation failure. Therefore, lightning
induced overvoltages assume a high importance for
dimensioning the insulation of high voltage electrical
installations.
To minimize the effects of discharges, ground wires are
strategically placed in the transmission lines. The ground
wires are normally connected to earth at all towers creating
a preferential path for the discharge of the lightning current.
However, the existence of this wires do not exclude the
possibility of direct discharges on the phase conductors, by
shielding failure, or the appearance of electric arcs at
insulator strings, causing problems in the continuity of
service.
The use of line surge arresters on transmission lines to
prevent backflashovers of the insulator strings has been
studied over the years. The arresters prevent backflashovers
by maintaining the voltage at the insulators below their
maximum capability. In general, for lines without ground
wires, the placement of line surge arresters in all towers is
an alternative. For lines protected with ground wires, the
arresters are installed in remote locations where
maintenance is difficult or where there is a high soil
resistivity (sand, rocky terrain).
Currently, the surge arresters are used in transmission
lines to improve reliability of service. However, due to
economic reasons, it is not possible to equip all towers with
these devices. Therefore, it is necessary to study the best
strategy for placement of surge arresters to ensure a certain
level of protection against lightning. Thus, it is primordial
the understanding of the phenomenon that are associated
with backflashover, as well as with their installation. Since,
in case of a double circuit line, it is not desirable to have
both circuits operation failure, the surge arresters can have
a very important role in preventing this situation, because a
proper installation of arresters can lead to a significant
reduction of backflashovers, eliminating them in one of the
line circuits.
1
In this work is pretended to understand the phenomena
that are associated to backflashover, as well as the
influence of line surge arrester utilization. For the
simulation performed in the study it was used the
application ATP, which have a graphic processor,
ATPDraw.
II. Line Surge Arresters
A. State of Art
The literature suggests that the line surge arresters should
be installed at the towers which have higher ground
resistances [2], as well as at towers that are installed at
local peaks or high altitude locations [3]. In [4] is proposed
to install line surge arresters at towers that combine high
exposure to lightning with high ground resistance.
According to [2], depending on the value of the ground
resistance, the arresters should be installed in more than
one phase, as it is shown in Table I. It is also proposed that
the configuration of the arresters placement to be uniform
along the section of the line, even if the ground resistance is
different in some towers.
Table I
Line Surge Arresters Placement Configuration [2]
Ground Resistance, RT (Ω)
Surge Arresters Placement
RT ≤ 10
No arresters
10 < RT ≤ 20
One phase
20 < RT ≤ 40
Two phases
RT > 40
Three phases
Currently in Portugal there are two transmission lines
which are protected with line surge arresters, Sines-Tunes
and Recarei-Canelas. Arresters are installed in five towers
of Sines-Tunes line. Despite having studies done, there
isn’t a large utilization of these devices.
B. ZnO Surge Arresters
The line surge arrester should act as an open circuit at
power system frequency, limit overvoltages below the
insulation level of the transmission line and return the
system to its normal operating mode so that transients
overvoltages are suppressed. Consequently, a surge arrester
should have a very high resistance when the system is in
normal operating mode and a relatively low resistance
during transient overvoltages. Based on this it can be
concluded that its V-I characteristic must be non-linear.
These devices are essentially made of one or more sparks
connected in series with one or more non-linear resistors.
Usually there are incorporated resistant and capacitive
voltage dividers to ensure a proper distribution of the
voltage applied to the various elements. In normal
operation, the sparks inserted between the non-linear
resistors are not disrupted and a reduced intensity current
determined by the voltage dividers go through the surge
arrester connected between the phase conductor and earth.
The modern surge arresters use metal oxide varistors
(MO) with a highly non-linear V-I characteristic. The
varistors are constituted by a powder of zinc oxide (ZnO)
and traces of other metals oxides united in a ceramic mold.
Its characteristics do not require the use of sparks. Thus, the
electrical behaviour of these devices is only determined by
the blocks of MO.
There are two types of zinc oxide arresters (ZnO) for
surge protection. The first type does not include sparks in
its constitution, which is directly connected to the phase
conductor. This type of surge arrester has the advantage of
not having delays in absorbing the overvoltage energy. The
other type presents sparks in its composition, which are
inserted between the arrester and the phase conductor, also
functioning as an insulator between them. The spark
arresters only operate when lightning strikes the
transmission line or tower, being out of service in every
other situation, including switching overvoltages. This
means that there is a current going through the arrester
during a very small period of time, corresponding to the
discharge time. This type of surge arresters has a bigger
lifetime and a more reliable operation then the other type.
The non-linear characteristic of the surge arrester is
formed by exponential segments and each segment can be
approximated by equation (1).
(1)
Where i and v represents the surge current and voltage,
respectively, and p, q and Vref are the component constants.
III. Study Data and Modelling
A. Study Data
Base Case
In this work is performed a study of the 150 kV SinesTunes line, which is a double circuit line with the
configuration presented in Fig. 1, called cross
configuration.
Fig. 1 - Sines-Tunes 150 kV line phases configuration - cross
configuration.
The grounding resistances of the line under study are
represented in Fig. 2.
2
Table II
Distribution parameters [1]
Grounding Resistance (Ω)
400
350
Parameter
300
250
200
150
100
50
1
10
19
28
37
46
55
64
73
82
91
100
109
118
127
136
145
154
163
172
181
190
199
208
217
226
235
244
253
0
Tower
Fig. 2 - Sines-Tunes line grounding resistances.
(2)
√2
Where M corresponds to the average value and β to the
logarithmic standard deviation.
The expression of the probability distribution is given
by the equation (3).
/
(3)
√2
To calculate the distribution parameters that allow
obtaining the discharge current, that are the peak value,
rise time, half-wave time and growth rate, it is necessary
to transform the log-normal distribution in a normal
distribution, using a change of variables.
1
/
√2
Being the change of variables given by (5).
ln /
β
Peak Value
61 kA
1.33 kA
Rise Time
4.7 µs
0.49 µs
Growth Rate
29.4 µs
0.55 µs
Half-wave Time
30.2 µs
0.93 µs
The characteristic parameters of the discharge currents
obtained for 80, 60, 40, 20, 10 e 5% probability of being
exceed is presented in Table III.
Table III
Based on the figure presented it was decided to study one
section of the line that has very high grounding resistance:
towers 69-81.
The next step consists in determining the discharge
currents to carry out the studies. [1] proposes a concave
waveform for the discharge current representation, which
parameters follows a log-normal distribution whose
probability density is given by equation (2).
/
1
1
M
(4)
(5)
Setting the value of P(X’) the calculation of X’ is done
by using the inverse function of error, being implemented
using a mathematical program (MATLAB), and then
obtain X.
The parameters of the probability distribution to
calculate the parameters that characterize the discharge
current are presented in Table II, calculated according [1].
Discharge currents parameters
Probability
Peak
(%)
Value
Rise Time
Growth
Rate
Halfwave
Time
80
20.0129
2.0483
12.5809
13.7716
60
28.5679
3.1706
19.9236
23.8425
40
38.8160
4.6192
29.6031
38.2527
20
55.4088
7.1499
46.8805
66.2261
10
72.3052
9.9127
66.1152
99.8361
5
90.0796
12.9828
87.8220
140.119
In the simulations only line sections are represented. The
remaining line is implemented using infinite length line
connected to power sources intended to impose the line
voltage. The most significant parameter of these sources is
the voltage angle, because it influences the value of the
voltage that will be at the insulator strings, which is given
by (6).
(6)
Based on the above equation, the worst case corresponds
to the lower phases because they have the lower coupling
factor with the ground wire. It is considered that de R’S’T’
circuit has the worst case scenario. The values of the
voltages angles in both circuits at the moment of the
discharge are presented in the Table IV.
Table IV
Voltages angle at the moment of discharge.
Phase
Voltage Angle
S
-60º
R
60º
T
180º
T’
180º
R’
60º
S’
-60º
The study cases of the 150 kV Sines-Tunes line presented
in this work are represented in Table V.
3
Table V
Table VII
Case studied for non-uniform line
Cases studied for uniform line
Case
Ipeak (kA)
1
Tower Hit by
Lightning
39 74 Case
Ipeak (kA)
Grounding
Phases that
Resistance (Ω)
Flashover
1
39 80
T, T’ 2
55 80
T, T', S' Uniform Line
The same discharge currents presented in Table III are
used to perform the study of a uniform line. However, it is
necessary to establish a criterion for the selection of the
grounding resistances to be simulated.
Fig. 3 shows the probability of the grounding resistance
of Sines-Tines line being exceeded.
90
Lightning Current
Once the characteristic parameters of the discharge
current are calculated, it is possible to reconstruct that
current wave in ATPDraw, by using a current source with a
parallel resistance, which has the purpose to represent the
lightning path impedance as shown is Fig. 4. This
resistance value is taken to be 400 Ω.
80
70
60
50
40
30
20
10
Fig. 4 - Lightning stoke model used in ATPDraw.
0
1
14
27
40
53
66
79
92
105
118
131
144
157
170
183
196
209
222
235
248
261
274
287
300
313
326
339
352
Prtobability of the value be
exceeded (%)
100
B. Modelling
Grounding Resistance (Ω)
Transmission Line
Fig. 3 - Probability of the value of the grounding resistance being
exceeded.
The criterion established for selecting the grounding
resistance is based in the previous figure. The resistances
that have 30, 20, 15, 10, 5, 2 e 1 % probability of being
exceeded were selected, presented in Table VI. For this
simulation it was considered that the section of the line has
17 towers, 16 spans of 446.9 meters each, connected to 20
km lines at its end that subsequently connects to voltage
sources of 150 kV with the angles described in Table IV.
Table VI
Grounding resistances values used for uniform line study
Probability (%)
Grounding Resistance (Ω)
30
22
20
31
15
40
10
54
5
80
2
136
1
338
The cases that were studied in this work are presented in
Table VII.
The line parameters vary with frequency and ATPDraw
offers possibility to use various frequency dependent line
models to represent overhead transmission lines. In this
study JMarti model was selected. The ground wire is
represented as a phase wire connected to the top of the
towers.
Tower
For simplification purposes and since the study of the
different tower models are not the aim of the study, the
towers were represented by short-circuits.
Grounding Resistance
The grounding resistance is represented by a linear
resistance.
Insulators
The insulator strings were represented by a high value
resistance in parallel with a low value resistance that is
connected in series with a voltage controlled switch, which
only conduct when the voltage across its terminals exceeds
the value presented in equation (7).
4
·
(7)
Where ld corresponds to the insulators electrodes, E0 to
the electric field, which value is taken to be 750 V/km and
V(t) to the instantaneous voltage value.
Fig. 5 presents the model used in ATPDraw.
900
[kV]
T
680
S
460
240
R
20
-200
Fig. 5 - Insulator string model used in ATPDraw.
0
10
20
30
(f ile contornamentoinv erso.pl4; x-v ar t) v :TOP
-S
v :TOP
40
-R
v :TOP
50
[us]
60
-T
Fig. 7 - Insulators voltages of RST circuit in the tower hit by the
discharge.
Line Surge Arresters
The selection of the appropriate line surge arrester is done
based on the arrester Maximum Continuous Operating
Voltage (MCOV), which is calculated by the equation (7).
1.1
(1)
√3
Where Vm represents the line voltage level. The
multiplicative factor derives from the fact that during the
line operation the voltage of the line can get a value 10%
above of the line voltage level.
The surge arresters are represented in ATPDraw by a
MOV block, Fig. 6, modelled by a current dependent
exponential resistance, which follows equation (1).
12
[kA]
10
T
8
6
4
R
2
0
S
-2
-4
0
10
20
30
(f ile contornamentoinv erso.pl4; x-v ar t) c:TOP -S
c:TOP
40
-R
c:TOP
50
[us]
60
-T
Fig. 8 - Insulators currents of RST circuit in the tower hit by the
discharge.
900
[kV]
S’
680
Fig. 6 - Surge arrester model used in ATPDraw.
460
For the simulations, ABB PEXLIM R surge arresters
were used, which characteristic is presented in Table VIII.
Table VIII
R’
240
T’
20
Surge arrester characteristic
Rated
Voltage,
Ur (kV)
120
TOV
Max. Residual Voltage (kV)
MCOV
(kV)
with Current Wave 8/20 µs
(kV)
for 1
sec
98
138
5kA
10kA
20kA
40kA
294
311
349
398
-200
0
10
20
(f ile contornamentoinv erso.pl4; x-v ar t) v :TOP
30
-T'
v :TOP -R'
40
50
[us]
60
v :TOP -S'
Fig. 9 – Insulators voltages of R'S'T' circuit in the tower hit by the
discharge.
11
[kA]
9
IV. Study of Backflashovers in Uniform Line without Line
7
S’
5
Surge Arresters
3
T’
1
In Fig. 7 to Fig. 10 are represented the voltages and
currents in the insulators for both RST and R’S’T’ circuits
for the simulation of the case from Table VII.
-1
R’
-3
0
10
20
(f ile contornamentoinv erso.pl4; x-v ar t) c:TOP -T'
30
c:TOP -R'
40
50
[us]
60
c:TOP -S'
Fig. 10 – Insulators currents of R'S'T' circuit in the tower hit by the
discharge.
When a lightning hits a tower, its potential increases
because a big portion of discharge current is conduct by the
grounding resistance of that tower, being the remaining
5
current transmitted by the ground wires to the adjacent
towers and subsequent spans.
After the discharge incidence, the voltage of the
insulators increases as a result of the tower and the phase’s
potential increases (because of ground wire coupling).
When backflashover occurs the voltage across the
insulators decreases to approximately zero and a current
circulates across the air gap, as shown in Fig. 8 and Fig. 10.
A phase flashover implies the decrease of the tower
potential and the increase of the phase’s potential. Tower
potential decreases because a new path of conduction is
inserted, the phase wires. Phase conductor’s potential
increase as result of phases coupling. It is observed in the
presented waves that the phases that don’t flashover have a
decrease in their insulator voltages when other phase
flashover. This occurs because the tower potential decrease
is bigger than the phase’s potential increase. If the
discharge current has not reached its peak, the tower and
phases potential increases again, as well as the voltage
across the insulators, as shown in Fig. 7 and Fig. 9. After
the backflashover, the potential of phase is approximately
equal to the tower potential.
In the figures presented it is possible to visualize that the
waves have two oscillations with different period, one with
3 µs and other with 12 µs. The first oscillation is justified
by the reflections of the adjacent towers (the span has 446.9
meters, corresponding to a propagation time of 1.5 µs) as a
result of the portion of the current that is transmitted by the
ground wire to those towers. The second oscillation is
explained by the flashovers that occur in neighbouring
towers. To understand this phenomenon it is presented
Table IX. This table represent the flashover in the tower
and in the phase. The shaded column represents the tower
hit by the lightning
is the phenomenon that is observed in Fig. 10, at 25 µs the
current of the insulators in phase T’ increases, that
corresponds the flashover in the tower N-4, which occurs at
19 µs, plus the propagation time of the 4 spans. After 12 µs
the current increases again, being this increase smaller.
This phenomenon is observed because the reflection travels
again through the phase conductor to the phase that has
suffered a flashover and comes back. Since the flashover in
the phases T and T’ occurs in the immediately adjacent
towers, the travel time is much lower, so it is only observed
the current growth, followed by its decrease.
To a better understanding of the neighboring towers
effect the values of the maximum potential of the tower that
is hit by the lightning are presented in Table X.
Table X
Maximum voltage values in the tower hit by the discharge
in one tower case and in uniform line case
Maximum Voltage in the
Tower Hit by the Discharge
Ipeak (kA)
(MV)
One Tower
Maximum
Voltage in the
Tower Hit by
Uniform Line
the Discharge
Reduction (%)
20 1.02 1.01 0.98 29 1.26 1.24 1.59 39 1.66 1.47 11.4 55 2.28 1.99 12.7 72 2.84 2.38 16.2 90 3.50 2.80 20.0 In Table X it is possible to observe that the tower
potential decrease, which is explained by the new
conducting path provided by the ground wire and the
reflections of the adjacent towers, which does not exist in
the situation of only one tower.
Table IX
Flashovers in uniform line for case 2
V. Study of Backflashovers in Uniform Line with Line
Case 2 ‐ R0 = 80 Ω, Ipico = 55 kA
F
a
s
e
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
-
8
7
6
5
4
3
2
1
N
Surge Arresters
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
-
1
2
3
4
5
6
7
8
S
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
R
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
T
-
-
-
-
-
-
-
-
-
-
T’
-
-
-
-
-
-
-
-
-
-
-
R’
-
-
-
-
-
-
-
-
-
-
S’
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
To understand the effect that surge arresters causes the
Fig. 11 is presented. It illustrates the voltage across the
phase S’ insulator when case 2 is simulated, with and
without arresters installed. In Fig. 12 the current that
circulates through the arresters in case 2 when these devices
are installed in all phases of the circuit R’S’T’ are
represented.
As it is possible to observe in the table above, in T’ phase
the flashover occurs in the tower that is hit by the lightning,
N, and in towers that are 4 spans apart, N-4. The flashover
of the same phase in other towers triggers a reflection that
propagates through the phase wire. When that reflection
reaches the tower N, the current suffers a big increase. That
6
900
Table XII
[kV]
Flashovers in uniform line for case 2, no arresters
680
With Arresters
Case 2 ‐ R0 = 80 Ω, Ipico = 55 kA
460
No Arresters Without Arresters
F
240
a
s
20
e
-200
0.00
0.02
(f ile Descarregadores.pl4; x-v ar t) v :TOP
0.04
-S'
0.06
0.08
[ms] 0.10
v :TOP3 -S'3
Fig. 11 - Phase S' insulator voltage with and without arresters for
case 2.
4000
[A]
3500
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
-
8
7
6
5
4
3
2
1
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
N
-
1
2
3
4
5
6
7
8
S
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
R
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
T
-
-
-
-
-
-
-
-
-
-
T’
-
-
-
-
-
-
-
-
-
-
-
-
R’
-
-
-
-
-
-
-
-
-
-
-
-
-
S’
-
-
-
-
-
-
-
-
-
-
-
N
-
-
-
-
-
-
-
3000
Table XIII
2500
Flashovers in uniform line for case 2, arresters in phase S’
S’
2000
1500
T’
Case 2 ‐ R0 = 80 Ω, Ipico = 55 kA
1000
500
0
0.00
Arrester in phase S’ R’
0.02
F
0.04
(f ile Descarregadores.pl4; x-v ar t) c:TOP3 -PHAC
0.06
c:TOP3 -PHAA
0.08
[ms] 0.10
c:TOP3 -PHAB
Fig. 12 - Currents in arresters installed in all phases of R'S'T'
circuit for case 2.
For the study of the backflashovers in uniform line with
installation of surge arresters the case 1 presented in Table
VII was simulated, for the configurations of arresters
placement given in Table XI. The arresters are installed in
every tower simulated, only in the circuit R’S’T’, because
this circuit has the best case scenario regarding the angles
of the line voltage.
a
s
e
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
-
8
7
6
5
4
3
2
1
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
-
1
2
3
4
5
6
7
8
S
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
R
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
T
-
-
-
-
T’
-
-
-
-
R’
-
-
-
-
-
S’
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
N
Table XIV
Flashovers in uniform line for case 2, arresters in phase S’
and R’
Table XI
Surge arresters placement configurations simulated
Case 2 ‐ R0 = 80 Ω, Ipico = 55 kA
Configuration 1
No arresters
Configuration 2
Arrester in phase S’
F
Configuration 3
Arresters in phase S’ and R’
a
Configuration 4
Arresters in phase S’, R’ and T’
Arresters in phase S’ and R’
s
e
Table XII to Table XV are presented for a better
visualization of the results. The shaded column represents
the tower hit by the lightning and the shaded lines
correspond to the phases that have arresters installed.
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
-
8
7
6
5
4
3
2
1
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
-
1
2
3
4
5
6
7
8
S
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
R
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
T
-
-
-
-
-
-
-
-
-
-
T’
-
-
-
-
-
-
R’
-
-
-
-
-
S’
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
7
Table XV
flashover caused by the potential of the phase being bigger
than the potential of the tower and, in this case, it can’t be
called backflashover. These phenomena are represented in
Fig. 13 and Fig. 14, where the first correspond to
backflashover and the second to the other type of flashover.
Flashovers in uniform line for case 2, arresters in phase
S’, R’ and T’
Case 2 ‐ R0 = 80 Ω, Ipico = 55 kA
Arresters in phase S’, R’ ans T’ F
a
s
e
1.6
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
-
8
7
6
5
4
3
2
1
N
N
N
N
N
N
N
N
*10 6
-
-
-
-
-
-
-
-
1.3
1
2
3
4
5
6
7
8
N
S
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
R
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
T
-
-
-
-
-
-
-
-
-
-
T’
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
R’
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
S’
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tower
1.0
0.7
0.4
0.1
Phase
-0.2
0
10
20
(f ile Unif ormeResis80.pl4; x-v ar t) v :TOP_N
30
40
50
*10 -6
60
v :T_N
Fig. 13 - Tower and phase (T') potential in the tower N for the
simulation of the case 2 without arresters.
Based on the tables above, it is possible to conclude that
the installation of surge arresters improve the line
performance by reducing the flashovers. When these
devices are installed in more than one phase it is possible to
conclude that the improvement is bigger.
It is observed that the flashover in some phases do not
occur in the towers immediately adjacent to the tower hit
by the lightning. Due to the case 2 complexity, it was
simulated case 1 and the results are presented in Table XVI.
1.2
*10 6
1.0
Tower
0.8
0.6
0.4
0.2
Table XVI
0.0
Flashovers in uniform line for case 1, no arresters
Phase
-0.2
0
10
20
(f ile Unif ormeResis80.pl4; x-v ar t) v :TOP_N2
30
40
50
*10 -6
60
v :T_N2C
Fig. 14 - Tower and phase (T') potential in the tower N-2 for the
simulation of the case 2 without arresters.
Case 1 ‐ R0 = 80 Ω, Ipico = 39 kA
No Arresters F
a
s
e
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
-
8
7
6
5
4
3
2
1
N
N
N
N
N
N
N
N
N
-
-
-
-
-
-
-
-
1
2
3
4
5
6
7
8
S
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
R
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
T
-
-
-
-
-
-
-
-
-
-
-
-
-
-
T’
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
R’
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
S’
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
The phenomenon mentioned happens because when a
lightning hits a tower, the potential of every tower increase,
as well as of the phases. When a phase flashover, the
potential of that phase increases or decreases so it can
equate the potential of the tower. As we move away from
the tower where the flashover has occurred, the potential of
the phase maintains practically its value, but the tower
potential decreases. Therefore, in some cases, the potential
of the phase is bigger than the potential of the tower and it
causes the flashover of the insulators. Consequently, it is
concluded that exists two types of flashovers in uniform
line: flashover caused by the potential of the tower being
bigger than the potential of the phase, backflashover, or
VI. Study of Backflashovers in Non-uniform Line
In this section is wanted to study section of Sines-Tunes
line, considering it non-uniform, ie, considering the nonuniformity of the grounding resistances along the line. The
study was performed in the towers 69-81, for the case 1.
The surge arresters in this study are installed in all phases
of R’S’T’ circuit, but it is analysed de difference of
installing those devices only in the towers with high
grounding resistance and also in the adjacent towers.
Table XVII to Table XIX are presented as results, where
the shaded columns correspond to the tower where the
lightning hits and shaded towers represents where the
arresters are installed.
8
Table XVII
Flashovers in non-uniform line (tower 69-81) without
arresters
Case 1 – Ipeak = 55 kA
No Arresters
F
a
69
70
-
-
71
72
73
74
75
76
77
78
79
80
81
-
-
-
-
-
-
s
e
S
R
T
T’
R’
S’
-
-
-
-
-
-
-
-
-
Table XVIII
71
-
-
-
72
73
74
75
-
-
76
77
78
79
80
81
-
-
-
-
s
e
S
R
T
T’
R’
S’
-
-
-
-
-
Table XIX
Flashovers in non-uniform line (tower 69-81) with
arresters in towers 72-77
Case 1 – Ipeak = 55 kA
Arresters in Tower 72-77
F
a
69
70
-
-
71
72
73
-
-
74
75
76
-
-
-
77
78
79
80
81
-
-
-
-
s
e
S
R
T
T’
R’
S’
-
-
-
Resistance
Adjacent
of the
Towers
Tower Hit
Grounding
by
Resistance
Lightning
(Ω)
(Ω)
F
70
Grounding
(kA)
Case 1 – Ipeak = 55 kA
Arresters in Towers 73-76
69
Table XX
Grounding resistance values of the tower hit by lightning
that needs the installation of arresters in adjacent towers.
Ipeak
Flashovers in non-uniform line (tower 69-81) with
arresters in towers 73-76
a
Since these results are very complex, a simplified nonuniform line was simulated, where only one tower, the
tower that is hit by the lightning has a higher resistance,
while the other towers have grounding resistance of 22 Ω,
to understand when it is necessary to install arresters in the
adjacent towers to eliminate flashovers in R’S’T’ circuit.
In Table XX are presented the values of the grounding
resistances, for different lightning currents, which need the
installation of arresters in the adjacent towers, besides the
towers with high grounding resistances.
In these tables it is observed that the installation of
arresters in the towers with high grounding resistance and
in its adjacent towers, the flashovers in circuit R’S’T’ are
eliminated.
39
170
22
13%
55
77
22
29%
72
49
22
45%
90
37
22
59%
It is possible to conclude that the discharge current
increase causes an increase in the difference between the
grounding resistance of the tower hit by lightning and the
adjacent towers that needs the installation of arresters.
VII. Conclusions
- The evolution of the voltages and currents in insulators
present two type of oscillation. The first is justified by the
reflection of the adjacent towers. The second is explained
next. A phase flashover generates waves that propagate
through the phase wire. If the flashover occurs at a phase
located in the tower hit by lightning neighbourhood, the
wave generated propagates through the phase wire and
when it arrives at the tower, the current that circulate in the
air gap of the insulator that suffered the flashover increases.
- In the study of uniform line it was observed that
flashovers occur because two reasons: tower potential
higher than phase potential (backflashover) or phase
potential higher than tower potential.
- Line surge arresters installation leads to a limitation of
the peak of the insulators voltage, preventing its flashover.
- When arresters are installed in all phases of the circuit
having the best case scenario regarding the angle of the line
voltage, it is verified a reduction of flashovers.
- The installation of arresters in the three phases of the
circuit mentioned above, at the tower with higher
grounding resistance and at its adjacent leads to the
elimination of all flashovers in that circuit.
9
- In the study of the simplified non-uniform line it was
concluded that for higher discharge currents the value of
the grounding resistance of the tower hit by lightning
needing installation of arresters in adjacent towers to
eliminate flashovers in R’S’T’ circuit is lower.
REFERENCES
[1] CIGRÉ Working Group 33.01, Guide to Procedures for Estimating the
Lightning Performance of Transmission Lines, 1991.
[2] Oscar Kastrup, Luiz Cera Zanetta Jr., Lightning Performance Assessment
with Line Arresters, Transmission and Distribution Conference, pp: 288,
1996.
[3] Karthik Munukutla, Vijay Vittal, Gerald T. HEydt, Daryl Chipman, Brian
Keel, A Practical Evaluation of Surge Arrester Placement for
Transmission Line Lighntning Protection, IEEE Transactions on Power
Delivery, Vol. 25, pp: 1743, 2010.
[4] E. J. Tarasiewicz, F. Rimmer, A. S. Morched, Transmission Line Arrester
Energy, Cost, and Risk Analysis for Partially Shielded Transmission
Lines, IEEE Transactions on Power Delivery, Vol. 15, nº 3, pp. 919 –
924, 2000
10