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C4_301_2012
CIGRE 2012
Lightning Transient Analysis of a 69kV Transmission Line with Externally
Gapped Line Surge Arrester under Normal Open Circuit Breaker System
S.J Hsiao*
Taiwan Power Company
J.F Chen
National Cheng Kung
University
M.T Chen
National Kaohsiung
University of Applied Sciences
Taiwan
SUMMARY
Determining the optimum location for installation of the transmission line arrester to achieve the
desired outage rate of the power line system is really not a simple task. If no externally gapped line
surge arrester (EGLA) is installed on the transmission line, it is well known that a lightning stroke
direct to a phase conductor usually causes insulator flashover. It is also a fact that EGLA installed on
every phase of every tower will effectively protect insulator from flashover when a lightning directly
strikes to the ground wire or phase conductor. Therefore EGLA is a effective solution to improve
lightning protection performance of overhead transmission lines.
The lightning overvoltage is the main reason which causes the overhead transmission line outage.
Usually, the Air-Breaker Switch (ABS) or Gas Circuit Breaker (GCB) is designed with normal open
due to system power flow conditions, where a lightning strikes overhead transmission lines at the
outlet of substation, even EGLAs are installed on every phase of every tower of the transmission line,
flashover may still occurs at the arc horn of post insulator of ABS, or even a burning accident of GCB
occurs. So there were several times that transmission line outage happened in Taiwan Power Company
(TPC) till now and caused system voltage sag, which influenced the power supply quality, especially
in the Science Park. This paper presents the analysis of lightning surges transient overvoltage in a
69kV transmission line regarding the above conditions. Based on the actual system information, the
distributed parameter model is adopted to build a 69kV transmission network by EMTP-ATP for
simulations, where the major criteria suggested by IEEE and IEC standards are used to assess the level
of insulation coordination of a 69kV circuit breaker with normal open condition.
KEYWORDS
distributed parameter, EGLA, insulation coordination, lightning Transient overvoltage.
*u897746@taipower.com.tw
1. INTRODUCTION
The transmission network usually exposes to the atmosphere and is subject to a lightning stroke.
According to IEC 60071-1, 1.2 x 50μs is just a standard voltage shape for lightning impulse test
instead of a lightning current shape [1-2]. Generally, 2 x 70μs is applied as lightning current shape for
simulations.
The common lightning damage investigation is usually focused on the lightning strength and the other
possible reasons such as grounding resistance. Some internal literatures of TPC stated the lightning
strength by calculation of the related data. In order to prevent the lightning fault, TPC has already
installed about 4888 sets [4] of EGLAs on the 69kV transmission lines from 1988 to 2011, which take
32% of towers of the 69kV system of the company [3]. Even this, when the GCB in the substation is
under normal open condition, the lightning surges striking on the substation outlet tower or overhead
transmission lines still caused the overvoltage, and the energy of flashover was induced into the
transmission network. Then the EGLA on the tower operates. This condition happened several times in
2011 that the flashover appeared at the arc horn of ABS post insulator or caused GCB burned-down
accident which happened twice in this year in power system of TPC. As shown in Fig. 1 [3], the
flashover caused the power shutdown and the voltage sag of system in the Science Park. In order to
prevent the damage of equipment caused by lightning overvoltage or network voltage dips, the study
on ABS and GCB with normal open condition has become more and more important. In this study, the
actual system parameters offer the necessary data to EMTP-ATP model for simulating on system
insulation coordination. The followings will present the major task of the said conditions when violent
lightning surge occurs.
burned- down
(a) ABS arc horn flashover
(b) GCB burned-down of S phase
Fig. 1 ABS arc horn flashover and GCB burned-down caused by lightning stroke to the overhead
transmission line
2. LIGHTNING CHARACTERISTICS OF TAIWAN
TPC has set up and operated a Lightning Location System (LLS) since June, 1989, and upgraded the
system to a Total Lightning Detection System (TLDS) in November 2002. The TLDS consist of seven
lightning detection stations, which could detect total cloud discharge phenomenon, including cloud to
cloud discharge and cloud to ground discharge. About two million lightning flash data have been
recorded since the system was installed. Based on the cloudy to ground discharge data collected,
several research projects for lightning have been carried out to investigate system impact of the
voltage sag. The average probability density and cumulative probability of lightning current is shown
in Fig. 2.
1
Following the format of equation as Eq. (1) proposed by Anderson-Erikson[5], the cumulative
probability of stroke current I0 exceeding i0 in Taiwan is derived as Eq. (2)
1
1 + (i0 / 31) 2.6
1
P ( I 0 ≥ i0 ) =
1 + (i0 / 29.5)3.15
Anderson-Erikson P ( I 0 ≥ i0 ) =
Taiwan
(1)
(2)
In Taiwan, the difference between these two models is that there is about 10 % of lightning current has
magnitude greater than 59kA which is lower than that of Anderson (72kA). From the lightning data
recorded, the statistical results can be summarized as follows:
－ Most of the lightning occurred during the period of months from June to September, especially in
the summer.
－ The average magnitude of the lightning current was 32.48 kA. The rate of negative lightning
current was about 94% of the total strokes.
－ The probability of lightning current with magnitude larger than 59kA was about 10 %. There was a
rate of 47% of the total lightning current with magnitude ranged from 15kA to 35kA.
Fig. 2 Average stroke current probability density and cumulative probability of Taiwan
3. EMTP-ATP Model and Simulation
The main purpose of the transient analysis on electric power system is for multi-aspect application by
choosing an accurate model on actual electric power system. The distributed parameter is usually
adopted on the electric power system and EMTP- ATP is adopted as the simulation tool [6] to build
the simulation model, such as transmission tower model, transmission line model, line arrester model
etc [7-13].
In addition to building the distributed parameter of tower, JMarti model by EMTP-ATP is employed
by referring to the actual system structures such as the diameter and layout of conductors, the span and
grounding resistance of tower, and other factors such as switch equipment in the substation. The
EMTP-ATP model [6] is built as Fig. 3. The system parameters are as following:
－ Conductor：795MCM(45/7)ACSR；Diameter: 27mm；DC resistance: 0.0695Ω/km.
－ Ground wire: 7NO.8ACW；Diameter: 9.78mm；DC resistance: 1.4626Ω/km.
－ Insulator string：6 pieces in one string.
2
－ 50% Impulse flashover voltage of EGLA arc horn gap(320- 350mm): 240kV[4].
－ 50% Impulse flashover voltage of ABS arc horn gap( 380mm): 250kV。
－ BIL for ABS : 350kV [13]
－ BIL for GCB : 350kV [13]
Fig. 3 The EMTP-ATP model of transmission system by lightning stroke under a 69kV GCB with
normal open condition
When substation GCB is in normal open position,we presumes the worst situation that lightning stroke
point is on the conductor between substation export tower No.1 and steel structure or the top of Tower
No.1 or overhead ground wires, it will cause the EGLA or ABS arc horn flashover as shown on Fig. 4.
And the flashover lightning surge overvoltage will be accessed into 69kV substation through
transmission system.
EGLA
(a) 69kV EGLA
(b) Simulation sketch
Fig. 4 Simulation sketch of the flashover occurring at the EGLA and ABS additional arc horn when
lightning is striking to the conductor between substation export tower No.1 and steel structure
or the top of Tower No.1 or overhead ground wires.
3.1 lightning Directly strikes on conductor
When EGLA is installed on transmission steel tower, according to the lightning currents (2 x 70μs)
and lightning channel 400Ω under different conditions which are listed on Table 1, the transient
simulation of each case will be proceed with the lightning srtoke direct to the upper conductor between
substation structure and outlet tower No.1. Those simulation cases include ABS with or without arc
horn, ABS closes or not, GCB open or not, GCB installed with arrester or not respectively. The results
are shown as the Table 2 :
3
Table 1 The simulation conditions of lightning stroke direct to the conductor
Simulation Parameter
ABS closes and has no arc horn,GCB opens. Using lightning current 20kA (2 x
70μs) directly strikes to the upper conductor between the substation outlet tower
Case 1
No. 1 and structure.
Condition
Case 2
Case 3
Case 4
ABS closes and has arc horn, GCB opens. Using lightning current 45kA (2 x 70μs)
directly strikes to the upper conductor between the substation outlet tower No. 1
and structure.
ABS closes and has arc horn, GCB opens and arrester installed. Using lightning
current 70kA (2 x 70μs) directly strikes to the upper conductor between the
substation outlet tower No. 1 and structure.
ABS open and has no arc horn, arrester installed. Using lightning current 100kA (2
x 70μs) directly strikes to the upper conductor between the substation outlet tower
No. 1 and structure.
Case1：When lightning current is over 20kA and the maximum PM values of simulation lightning
transient overvoltage on ABS and GCB are both lower than 1％, ABS and GCB will be
damaged with power outage.
Case2：If ABS closes and has arc horn, and GCB opens, when lightning current is over 45kA, the
flashover occurs at ABS arc horn. The lightning transient overvoltage on ABS is restrained
under 250kV and PM value of ABS is over 40%. But the PM value of GCB is less than 1%,
so that GCB will still be damaged with power outage.
Case3：If ABS closes and has arc horn, GCB opens and arrester installed, when lightning current is
over 70kA then flashover still occurs at ABS arc horn. The lightning transient overvoltage on
ABS is restrained under 250kV, and PM value of ABS and GCB is over 3%. The ABS and
GCB will not be damaged because the flashover still occurs on ABS arc horn.
Case4：If ABS has no arc horn and opens but is installed with arrester as shown in Fig. 7, when
lightning current is over 100kA, the PM value of ABS and GCB is over 27%, the ABS and
GCB will not be damaged with no outage. Discharge voltage of arrester by GCB side higher
than ABS side are shown as Fig. 5. So that ABS installed with arrester of three phases is the
best way.
Case
Case1
Case2
Table 2 The PR and PM of max. Transient overvoltage
Lightning current
Locatiion
Vmax(kV)
PR
GCB
392.24
0.892
20kA
ABS
382.26
0.915
GCB
362.81
0.964
45kA
ABS
249.87
1.40
Case3
70kA
Case4
100kA
PM
＜1％
＜1％
＜1％
40％
GCB
ABS
339.63
249.85
1.03
1.40
3％
40％
ABS
275.19
1.271
27.1％
Remarks : PR represents Protective Ratio; PM = (PR-1) multiplied by 100% represents Protective
Margin
4
Discharge voltage (kV)
△: GCB open and arrester installed
□: GCB open, ABS close and arrester installed
○: ABS open and arrester installed
time
Fig. 5 Discharge voltage of arester for CB open or ABS open
3.2 Lightning Directly Strikes toTower Top or Overhead Ground Wire
When EGLA is installed on the transmission steel tower, according to the lightning currents (2 x 70μs)
and lightning channel 400Ω [10-12] under different conditions which are listed on Table 3, the
transient simulation of each case will be proceed with the lightning stroke direct to tower top or
ground wires in different conditions respectively, such as ABS with or without arc horn, ABS closes
or not and arrester installed or not, GCB opens or not. The results are shown as Table 4.
Table 3 The simulation conditions of lightning strike direct to tower top or ground wire
Condition
Simulation Parameter
Case 5
Case 6
Case 7
ABS closes and has no arc horn, and GCB opens. Using lightning current 70kA (2 x
70μs), directly strikes to the substation export tower No. 1 top or overhead ground
wires.
ABS closes and has arc horn, and GCB opens. Using different lightning current 100kA
(2 x 70μs), directly strikes to top or ground wires between the substation export tower
No. 1 and No. 2.
ABS opens and has no arc horn, and arrester installed. Using different lightning current
100kA (2 x 70μs), directly strikes to top or ground wires between the substation export
tower No. 1 and No. 2.
Case 5：ABS closes and has no arc horn, and GCB opens, when lightning current is over 70kA, PM
value of the lightning transient overvoltage in middle phase is less than 1%, the system will
be outage because the post insulator of ABS is damaged in middle phase.
Case 6：If ABS closes with arc horn and GCB opens, when lightning current is over 100kA, PM
value of the lightning transient overvoltage in upper phase is less than 1%. The system will be
outage because of ABS arc horn flashover and insulator is damaged in upper phase. The
flashover transient surge current of upper phase is the highest through ABS arc horn, which is
shown as Fig. 6.
Case 7：If ABS opens and has no arc horn but arrester is installed, when lightning current is over
100kA and directly strikes on substation outlet tower top or overhead grounding line, the PM
value of ABS is over 23%. The post insulaor will not be damaged and the system will not be
outage either. Therefore, ABS installed with arrester of three phases is the best way,which is
shown as Fig. 7.
5
Case
Case 5
Case 6
Case 7
Remarks :
Table 4 PR and PM of Max. Transient overvoltage
Lighting Current
Locatiion
Vmax(kV)
PR
PM
Upper Phase
255.95
1.367
36.7％
261.96
1.336
33.6％
GCB Middle Phase
Lower Phase
210.64
1.661
66.1％
70kA
Upper Phase
248.57
1.408
40.8％
370.28
0.945
＜1％
ABS Middle Phase
Lower Phase
271.10
1.291
29.1％
Upper Phase
374.94
0.933
＜1％
131.23
2.667
166.7％
GCB Middle Phase
Lower Phase
116.71
2.998
199.8％
100kA
Upper Phase
250.1
1.399
40％
Middle
Phase
312.26
1.120
12％
ABS
Lower Phase
250.22
1.398
39.8％
Upper Phase
246.55
1.419
41.9％
Middle
Phase
259.48
1.348
34.8％
100kA
ABS
Lower Phase
282.85
1.237
23.7％
PR represents Protective Ratio; PM = (PR-1) multiplied by 100% represents Protective
Margin
350kV
GCB upper phase exceed BIL
ABS with arc horn flashover
Transient surge voltage(kV)
250kV
250kV
ABS with arc horn flashover
－ :ABS of upper phase
－ :ABS of middle phase
－ :ABS of lower phase
Fig. 6 The transient surge voltage ABS arc horn and GCB upper phase in Case 6
time
arrester
sec
arrester
ABS open without arc horn
ABS open without arc horn
(a) This arrester is installed on the steel frame (b) This arrester is installed on the structure
Fig. 7 ABS opens and without arc horn, and with arrester.
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4. CONCLUSION
EGLAs being installed on 69kV overhead transmission lines cannot fully prevent ABS from being
damaged by the lightning transient voltage. This paper demostrates the analysis of lightning strike
transient overvoltage which is based on actual distributed parameter and the JMarti model by EMTPATP. For considering the insulation coordination of system, the important conclusions by simulation
results are as follows.
－ ABS closes and has arc horn, GCB opens and arrester installed. Using lightning current 70kA (2 x
70μs) directly strikes on the upper conductor between the substation outlet tower No. 1 and str., it
will still cause the flashover at ABS arc horn. Though PM values of ABS and GCB are over 3% at
this moment, the insulation will not be damaged. However, it will still cause the transmission
network outage and the voltage sag on proximal systems.
－ ABS closes and has arc horn, and GCB opens. Using different lightning current 100kA (2 x 70μs)
directly strikes on the top or ground wire between the substation outlet tower No. 1 and No. 2. The
result shows that the lightning transient will exceed BIL value and cause the flashover at ABS arc
horn on three phases and equipment damage because the max. PM value of lightning transient
overvoltage on GCB upper phase is lower than 1% .
－ According to the simulation results of various cases, to solve the GCB fault problem on normal
open demarcation point of transmission system, the only solution is to install arrester on the line
side of ABS with normal open condition which is shown as Fig. 7. Even the lightning current is
over 100kA, which will not damage the insulation and cause system outage because the PM values
of ABS and GCB are over 23%. So this is the best way of insulation coordination and can
eliminate the blind spot of EGLA installation on the transmission network.
5. BIBLIOGRAPHY
[1] Insulation co-ordination –, Part 1: Definitions, principles and rules. ( IEC Std. 60071-1-2006)
[2] IEC 60071-2, Insulation co-ordination – Part 2: Application Guide. ( Third Edition, 1996)
[3] Taiwan Power Company, Event Statistics of Mechanic and Electric Equipments in Taiwan Power
System. (Taiwan Power Company 2011)
[4] NGK Insulators. LTD, External Gap Type Transmission Line Arrester For Advanced Lighting
Protection, ( NGK Release No.105 2002).
[5] Eriksson, A. J., “The Incidence of Lightning Strikes to Power Lines”, (IEEE Transactions on
Power Delivery, vol. 2, pp. 859-870, July 1987).
[6] H. K. Hoidalen, ATPDraw for Windows version 5.5, 2010.
[7] IEEE Design Guide for Improving the Lightning Performance of Transmission Lines, (IEEE Std.
1243-1997)
[8] Surge arresters - Part 8: Metal-oxide surge arresters with external series gap (EGLA) for overhead
transmission and distribution lines of a.c. systems above 1 kV, ( IEC 60099-8 Ed. 1.0, 2009).
[9] T. Ito, T. Ueda, H. Watanabe, T. Funabashi, “Lightning Flashovers on 77-kV Systems: Observed
Voltage Bias Effects and Analysis”, (IEEE Trans. on Power Delivery, vol. 18, pp. 545-550 ,April
2003).
[10] M. Ishii, T. Kawamura, T. Kouno, E. Ohsaki, K. Shiokawa, K. Murotani, and T. Higuchi,
“Multistory transmission tower model for lightning surge analysis”, ( IEEE Trans. Power
Delivery, vol. 6, pp. 1327–1335, July 1991).
[11] J. A. Martinez, B. Gustavsen, D. Durbak, “Parameter Determination for Modeling System
Transients—Part I: Overhead Lines”, ( IEEE Trans. Power Delivery, vol. 20, pp 2038-2044, July
2005).
[12] J. A. Martinez and F. C. Aranda, "Tower Modeling for Lightning Analysis of Overhead
Transmission Line," ( Proceedings of 2005 IEEE Power Engineering Society General Meeting,
Vol. 2, June 12-16, 2005, p.p.1212- 1217).
[13] IEEE Standard for Insulation Coordination—Definitions, Principles, and Rules, ( IEEE Std.
1313.1-1996).
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