Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
PROTECTION PERFORMANCE OF LIGHTNING PROTECTION
SYSTEMS UNDER SWITCHING SURGE VOLTAGES
Z. Faydalı1, A. Ozdemir1*, S. lhan1
Separtment of Electrical Engineering,
Istanbul Technical University, Maslak-Istanbul 34469, Turkey
*Email: ozdemir@elk.itu.edu.tr
1
Abstract: Using (Franklin) Air Terminals to control and divert lightning discharges is still
indispensable method after 200 years of usage. Still, there are several uncertainties regarding the
discharge mechanism of the lightning phenomena that lead to variety of lightning protection
systems. Early Streamer Emission (ESE) Air Terminals and Charge Transfer Systems (CTS) have
evolved from these uncertainties.
This study presents the experimental performance of CTS against ordinary Franklin Air Terminal
based protection systems under the same electrogeometric conditions. Their comparative
advantages and disadvantages are illustrated according to the results of corona emission current
tests, comparative tests under the same electrogeometrical conditions and critical switching
impulse flashover voltage tests. These tests are conducted at High Voltage Laboratory of Istanbul
Technical University for several different electrode spacing at different DC polarization
conditions.
1.
There are still several uncertainties regarding the
discharge mechanism of the lightning phenomena that
lead to variety of lightning protection systems.
Therefore, experimental and observational researches
performed to solve the lightning protection problem are
still ongoing [5].
INTRODUCTION
Lightning protection systems are used to eliminate or
minimize the direct and indirect effects of lightning
strikes. The effects of lightning that were taken into
consideration when designing a protection system were
limited with fire and life risk at old times. However,
technological developments and improved life
standards require an expanded scope of protection.
The objective of this paper is to compare and illustrate
the advantages and disadvantages of the Charge
Transfer Systems and ordinary Franklin Air Terminal
based protection systems with respect to the results of
several experimental studies; namely, critical flashover
(CFO) voltage tests, comparative tests under the same
electrogeometrical conditions and corona emission
current tests. The tests are chosen similar those
presented in previous studies in order to make fair
comparisons. It is obvious that the comparisons and the
derived conclusions are limited with the scope of the
tests.
The first commonly used Lightning Protection System
(LPS) is the capturing rod (which is also known as
Franklin rod named after Benjamin Franklin) which
aims to capture the lightning and to direct it to the
ground through the conductors and grounding system
[1]. After long and detailed analysis of the protection
system performances, Franklin rods have taken their
final forms today. Their performances are improved by
using them together with Faraday Cage structures [2].
2.
Early Streamer Emission (ESE) systems are later
developed and are claimed to improve the capturing
performance of ordinary Franklin rods by using
different types of triggering mechanisms. It is claimed
that the triggering mechanism increases the efficiency
of lightning attraction and extends the range of
protection [3]. However, scientific and technical basis
of the system is open to some questions and they are
still not accepted by most of the authorities.
CRITICAL FLASHOVER VOLTAGE
TESTS
Charge transfer systems consist of multi point
discharge paths assigned to neutralize the thundercloud
and minimize the risk of charge transfer between the
cloud and the earth [4]. The charges emitted by these
multi point paths are also assumed to shield the area
over the air terminal and to prevent lightning strike
nearby objects and areas [5]. CFO voltage tests are
performed in order to investigate and to compare the
differences due to the emitted charges.
Charge Transfer Systems (CTS) are one of the last
approaches in Lightning Protection. Their operating
principle is based on multi point discharges that are
created by means of many sharp electrodes. By the
charge created in opposite polarity to the charges in the
thundercloud, the thundercloud is claimed to be
neutralized and the specified region is prevented from
direct lightning strikes [4].
Two types of CTSs and a Franklin rod (standard
lightning rod) given in Figure 1 are tested. A plane
electrode of 5m x 3.5m is used to simulate the cloud.
Air terminals are installed at four different heights
under the plane electrode; namely, 2 m, 3 m, 3.5 m and
4 m. The negative standard switching impulse test
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Paper G-32
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
voltages (300/2500 µs) are applied between the plane
electrode and the air terminals for all electrode
configurations and spacing (Figure 2). The critical
flashover voltages (CFO) of air terminals are
determined by up-down method described in IEC
60060.
(a)
(b)
3.
COMPERATIVE TESTS UNDER THE
SAME ELECTROGEOMETRICAL
CONDITIONS
The three protective devices are subjected to
comparative tests under the same electrogeometrical
conditions. The aim of this test is to strengthen of the
conclusions derived from flashover voltages as well as
to derive final conclusions with the aim of supporting
test results.
Three protective devices are placed under a plane
electrode of 3.5*5 m. They are placed symmetrically
and equidistant from the centre of the plane electrode
(Figure 3) to provide the same electrogeometrical
conditions. 100 standard switching impulse voltages of
negative polarity are applied to the plane electrode for
each of three different electrode spacing. The test
voltages are chosen to be higher than the CFO voltages
of the protective systems.
(c)
Figure 1: Photographs of the air terminals tested.
a – Franklin rod
b – CTS 1
c – CTS 2
The CFO voltages of air terminals for all electrode
spacing are shown in Table 1. A quick check of the
table shows that there are not significant differences
between the CFO voltages of the Franklin rod and of
the CTS 2, while CFO voltages of CTS 1 are
noticeably higher than those of the others’.
Table 1: CFO voltages for switching impulse voltages.
Figure 3: Positioning of the air terminals under the
plane electrode.
CFO (kVpeak)
Electrode
Franklin
Spacing (m)
CTS 1 CTS 2
rod
2
-838
-1036 -914
3
-1370 -1559 -1400
3.5
-1659 -1765 -1676
4
-1874 -2103 -1915
The tests are carried out for several test voltages. The
results are approximately the same. Therefore, the
results of only one test voltage is illustrated for each
spacing in Table 2. Photographs of the flashovers are
given in Figure 4.
Table 2: Number of flashovers between the plane
electrode and the protective systems.
Number of Discharges
Gap [m] / Applied Voltage [kVpeak]
2 / 1200
3 / 1750
4 / 2200
Franklin rod
86
92
87
CTS 2
14
8
13
CTS 1
0
0
0
Figure. 2: Negative switching impulse test voltage (300 /
2500 µs).
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Paper G-32
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
(a)
(a)
(b)
(b)
Figure 4: Photographs of the comparative tests under
the same electrogeometrical conditions.
(a) Flashover to CTS 2
(b) Flashover to Franklin rod
As it can easily be realized from the table, all the
flashovers from the plane electrode occurred either to
the CTS 2 or to the Franklin rod. The ratio of the
discharges to CTS 2 and to Franklin rod does not
significantly differ for different electrode spacing.
4.
(c)
CORONA EMISSION CURRENT TESTS
Corona emission current is thought to block the
formation of upward discharge by causing a delay for
the attachment process of lightning [5]. Therefore, it is
generally accepted as an index of the protective
effectiveness of a CTS.
(d)
Standard switching impulse test voltages (300 / 2500
µs) of both the positive and the negative polarity are
individually applied between the plane electrode and
air termination system. The tests are repeated for
several different amplitudes of the test voltages for 2
m, 3 m and 4 m electrode spacings. For the sake of
higher accuracy, each test voltage is applied three
times and their average is recorded as a result. The
results are shown graphically in Figure 4.
(e)
The corona emission currents of CTS 1 and CTS 2 are
found to be close to each other and also seem to be
considerably higher than the emission currents
recorded for Franklin rod.
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Paper G-32
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
(f)
The results of these tests can be stated as DC
polarization has no significant effect on the number of
discharges attracted by CTS 1.
Figure 5: Corona Emission Currents for switching
impulse voltages.
(a)
(b)
(c)
(d)
(e)
(f)
5.
3.1 Corona emission current tests with DC
polarization
Electrode spacing: 2 m, Polarity of voltage: +
Electrode spacing: 2 m, Polarity of voltage: Electrode spacing: 3 m, Polarity of voltage: +
Electrode spacing: 2 m, Polarity of voltage: Electrode spacing: 2 m, Polarity of voltage: +
Electrode spacing: 2 m, Polarity of voltage: -)
DC part of the test setup is used alone and corona
emission currents are measured for 2 m, 3 m and 4 m
of electrode spacings. DC voltages providing a
constant electric field strength around 15 kV/m are
applied between the plane electrode and the air
terminals.
The measured corona emission currents are in the order
of µA and are smaller than one thousandth of the
previous ones for switching impulses. Therefore,
switching impulses superimposed on DC voltages are
not used to perform another comparative test.
TESTS WITH DC POLARIZATION
Since there is a constant electric field between the
cloud and the earth during the formation of real
lightning phenomena, all the previous tests are repeated
for DC polarization between the plane electrode and
the air terminal. The value of the field strength is
chosen in the range of 10 - 25 kV/m as in similar
studies [5].
6.
CONCLUSIONS
CFO voltage tests with DC polarization show that there
are no significant differences between CFO voltages
without DC polarization. Therefore they will not be
reproduced here.
In order to compare the protective performance of CTS
systems and ordinary Franklin Air Terminal based
protection systems several experiments have been
conducted.
3.1
The results of the CFO voltage and comparative tests,
with and without DC polarization, showed that CTS 1
provided better protection performance than the
Franklin rod under the same electrogeometric
conditions. However, CFO voltages of CTS1 are not
much higher than of the Franklin rod to claim that
CTS1 will effectively eliminate direct strikes on it. On
the other hand, no distinction could be made for the
Franklin rod and CTS 2 as they showed similar
performances during the experiments.
Comparative
tests
under
electrogeometrical conditions
the
same
100 negative standard switching impulse voltages are
applied to the plane electrode which is polarized with a
DC voltage to provide a constant electric field of 17.5
kV/m. Flashovers to the three protection systems which
are placed symmetrically under the plane electrode
(Figure 3) are recorded for an electrode spacing of 2 m.
(Table 3).
Table 3: The number of discharges occurred for the air
terminals.
Since the corona emission currents of CTS 1 and CTS
2 were close to each other and were noticeably higher
than of the Franklin rod, protection performance of
CTS1 and CTS 2 were expected to be similar and also
much better than of the Franklin rod. However, this
contradicted with the results of previous CFO voltage
test and comparative tests. This contradictory behavior
of CTS 2 brought out two important facts:
Number of Discharges
Gap [m] / Applied Voltage [kVpeak]
2 m / 1200 kVpeak
Franklin rod
56
CTS 2
44
CTS 1
0


Although the tests are also carried out for several
different spacing as well as for several different test
voltage magnitudes, only a representative one will be
given here.
Corona emission current was not a reliable
index itself to determine the effectiveness of a
LPS.
CTSs based on the same technical and physical
laws behaved differently at similar tests.
It can be concluded from the test results that the charge
transfer systems are not reliable protective systems
from the point of eliminating the direct lightning
strikes yet. In addition, their construction and shape
affect their protection performance.
If the number of discharges given for a spacing of 2 m
and a test voltage of 1200 kVpeak is compared with the
test results without DC polarization, at a first glance an
increase in the number of strikes to CTS 2 can be seen.
However, all the discharges are still shared between the
Franklin rod and CTS 2. None of the test voltages have
resulted a flashover to CTS1.
An appropriate design that combines Franklin rods and
CTS seems to provide better performance to protect a
region against lightning. A CTS placed at an elevated
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Paper G-32
ISBN 978-0-620-44584-9
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
position of the protective area will reduce the
likelihood of direct lightning strikes onto the region.
Additional Franklin rods installed at elevated positions
surrounding the protective region captures the lightning
strikes and therefore provides additional protection for
the protective region.
7.
ACKNOWLEDGMENTS
The authors would like to thank to Fuat Kulunk High
Voltage Laboratory staff for their patient supports
during the tests.
8.
REFERENCES
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lightning
protection
systems”,
IEEE
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[2] D.W. Zipse, “Lightning protection systems:
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and Electronics Engineers Incorporated.
Industry Applications Society, 40th Annual
13-15 Sept. 1993, pp.51 - 64.
[3] R.J. Van Brunt, T.L. Nelson, K.L. Stricklett,
“Early streamer emission lightning protection
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Insulation Magazine, Volume 16, No. 1, Jan.Feb. 2000, pp. 5 – 24.
[4] D.W. Zipse, “Lightning protection methods:
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[5] J.B. Lee, S.H. Myung, Y.G. Cho, S.H. Chang,
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