Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
A CALCULATION OF SWITCHING TRANSIENT OVERVOLTAGE ON
COMBINED TRANSMISSION SYSTEMS
C.K. Jung*1 J.W. Kang1, K.S. Lim2 and J.B. Lee2
1
Transmission and Distribution Research Lab.
KEPRI(Korea Electric Power Research Institute), 103-16 Munji-dong , Daejeon, South Korea
2
Department of Electrical, Electronic and Information Engineering
Wonkwang University, 344-2 Shinyong-dong , Iksan, South Korea
*Email: chekyun@kepri.re.kr
Abstract: Switching overvoltage may cause the breakdown of power cable or joint box on
combined transmission systems. This paper describes the characteristic of switching transient
overvoltage on 154[kV] combined transmission systems. The switching transient is analysed by
various fault conditions including fault resistance, the amplitude of trapped charge and
underground power cable rate using statistical approach. This paper is also analysed the reduction
effects of switching transient by surge arrester installation.
1.
combined transmission systems, and 3-phase reclosing
has been considered. The switching transient is
evaluated by various fault conditions including fault
resistance of 1[Ω] to 50[Ω], trapped charge of 100[%]
and 110[%]. This paper also considers the underground
power cable rate, and analyses the reduction effects by
surge arrester.
INTRODUCTION
Some kinds of overvoltage are generally generated by
lightning surge, switching surge and ground fault, etc.
on combined transmission systems[1-2]. Accurate
analysis of these overvoltages is also very important to
the reliable estimation of power system operation
because it has effect on the insulation design of
underground cable and various power devices.
Switching overvoltages caused by line energization, 3phase reclosing under various fault conditions have
been investigated by statistical approach. The
calculations are only performed by computer
simulation of EMTP/ATP, the results can contribute to
the insulation co-ordination redesign on 154[kV]
combined transmission systems.
Switching impulse withstand level of extra high
voltage transmission line insulators are also generally
lower than the lightning impulse withstand level[3-4].
Therefore, some measurements are needed to protect
the transmission line against switching overvoltages.
Moreover, the study on effect of the switching
overvoltage needs in special transmission systems such
as combined transmission systems. The combined
transmission system means the system which is mixed
overhead transmission with underground cables. The
transient characteristics are different between the
combined transmission system and just overhead
transmission or just underground power cables.
After brief review of the combined transmission model
system and fault conditions in second section, the
switching overvoltages will be evaluated by statistical
approach in section 3. The last section concludes the
paper.
2.
MODEL SYSTEM
The diagram of combined transmission system to be
This paper discusses the characteristic of switching
transient overvoltage performance on 154[kV]
154kV
ACSR 330㎟
3 phase
reclosing
......
XLPE 2000㎟
Overhead line section(1km, 3km, 5km)
Underground power cable section(5km, 10km, 15km, 20km)
Figure 1: 154kV combined transmission system
modelling.
Pg. 1
Paper G-27
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
discussed in the paper is shown in figure 1. It consists
of the overhead transmission system of ACSR 330[㎟]
and the single core cable of XLPE 2000[㎟] with the
voltage of 154[kV]. Each length of overhead
transmission line section and underground power cable
section is 5[km] to 20[km] and 1[km] to 5[km],
respectively.
For the 100 operation study, the closing angle of the
circuit breaker contact has normal distribution and its
standard deviation is 1[ms], the open time is 0.02[s]
and the reclosing time is 0.05[s]. The circuit breaker
model accommodates variations in the pole closing
speed according to a normal distribution with a
specified standard variation and limited ±2σ .
In this paper, the single line to ground fault of phase A
is supposed to occur at 1[km] from cable head,
EMTP/ATP program is used for system modelling and
simulation. The calculation frequency is 1[kHz]. Fault
resistance is assumed to be 1[Ω], 10[Ω], 30[Ω] and
50[Ω], the trapped charges of 100[%] and 110[%] are
also considered.
3.1.
Cases
12 cases assumed in this paper are expressed in table 1.
As shown in table 1, cases are divided by underground
power cable rate. The underground power cable rate is
4.76[%] to 50[%].
Table 1: Cases description
The V-I characteristic curve of applied 154[kV] surge
arrester is shown in figure 2, they can be installed at
termination of overhead line and underground power
cable and cable head, respectively.
Case
Case 1
Case 2
400000
350000
Case 3
Voltage[V]
300000
250000
200000
OV[km] : UG[km]
Rate[%]
5:1
10 : 1
15 : 1
20 : 1
5:3
10 : 3
15 : 3
20 : 3
5:5
10 : 5
15 : 5
20 : 5
16.7
9.09
6.25
4.76
37.5
23.1
16.7
13
50
33.3
25
20
Case 1-1
Case 1-2
Case 1-3
Case 1-4
Case 2-1
Case 2-2
Case 2-3
Case 2-4
Case 3-1
Case 3-2
Case 3-3
Case 3-4
OV : Overhead transmission line, UV : underground power
cable, Rate : underground power cable rate
150000
100000
3.2.
50000
0
0
5000
10000
15000
20000
Figure 4 shows the switching overvoltage of each case
in case of fault resistance of 1[Ω], the measurement
points are sending end of overhead line section, cable
head, middle and receiving end of underground power
cable section, respectively.
25000
Current[A]
Figure 2: V-I characteristic curve of 154[kV] arrester
3.
Switching overvoltage according to
underground power cable rate
As shown in figure 4, the overvoltage of each case at
sending end of overhead line section shows less than
1.6[p.u.], but it is increasing at the underground power
cable section. The overvoltage is also increasing at the
high underground power cable rate.
SWITCHING OVERVOLTAGE
CALCULATION
In this paper, in order to verify the influence of fault
initiation angle, 100 shots of uniform distribution are
used for the fault switch using ATP statistical approach
as shown in figure 3.
2.4
switching overvoltage[p.u
2.2
AIMING POINT
CLOSING TIME
2
1.8
1.6
case 1-1(16.7%)
1.4
case 1-2(9.09%)
case 1-3(6.25%)
1.2
case 1-4(4.76%)
1
OVERHEAD
t0
tA
μ
tC
tB
t
MIDDLE
RECEIVING
point
(a) Case 1
POLE SPAN
− 2σ
CABLE HEAD
+ 2σ
Figure 3: Uniform distribution
Pg. 2
Paper G-27
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
2.6
2.6
2.4
2.4
2.2
2.2
overvoltage[p.u.]
overvoltage[p.u.]
ISBN 978-0-620-44584-9
2
1.8
case 2-1(37.5%)
case 2-2(23.1%)
case 2-3(16.7%)
case 2-4(13%)
case 3-1(50%)
case 3-2(33.3%)
case 3-3(25%)
case 3-4(20%)
1.6
1.4
1.2
2
case 1-1(16.7%)
case 1-2(9.09%)
case 1-3(6.25%)
case 1-4(4.76%)
case 2-1(37.5%)
case 2-2(23.1%)
case 2-3(16.7%)
case 2-4(13%)
case 3-1(50%)
case 3-2(33.3%)
case 3-3(25%)
case 3-4(20%)
1.8
1.6
1.4
1.2
1
1
OVERHEAD
CABLE HEAD
MIDDLE
OVERHEAD
RECEIVING
CABLE HEAD
point
MIDDLE
RECEIVING
point
(b) Case 2 and case 3
Figure 6: Switching overvoltage according to
underground power cable rate(fault resistance : 50[Ω])
Figure 4: Switching overvoltage according to
underground power cable rate(fault resistance : 1[Ω])
2.6
2.4
In figure 4(a), in case of fault resistance of 1[Ω], case
1-1(16.7%) which is the highest cable rate shows the
maximum overvoltage value of 2.2208[p.u.] compare
to other case 1. In case 2-1(37.5%) and case 3-1(50%),
the trend is almost similar, and each maximum
overvoltage is 2.3001[p.u.] and 2.3429[p.u.]. The
overvoltage is also more increasing at receiving end
compare to cable head and middle of cable section.
overvoltage[p.u.]
2.2
2
case 1-1(16.7%)
case 1-2(9.09%)
case 1-3(6.25%)
case 1-4(4.76%)
case 2-1(37.5%)
case 2-2(23.1%)
case 2-3(16.7%)
case 2-4(13%)
case 3-1(50%)
case 3-2(33.3%)
case 3-3(25%)
case 3-4(20%)
1.8
1.6
1.4
1.2
1
OVERHEAD
CABLE HEAD
MIDDLE
RECEIVING
point
2.4
2.2
Figure 7: Switching overvoltage according to
underground power cable rate(trapped charge :
100[%])
overvoltage[p.u.]
2
1.8
1.6
2.6
case 1-1(16.7%)
1.4
case 1-2(9.09%)
1.2
2.4
case 1-3(6.25%)
2.2
case 1-4(4.76%)
OVERHEAD
CABLE HEAD
MIDDLE
overvoltage[p.u.]
1
RECEIVING
point
(a) Case 1
2
case 1-1(16.7%)
case 1-2(9.09%)
case 1-3(6.25%)
case 1-4(4.76%)
case 2-1(37.5%)
case 2-2(23.1%)
case 2-3(16.7%)
case 2-4(13%)
case 3-1(50%)
case 3-2(33.3%)
case 3-3(25%)
case 3-4(20%)
1.8
1.6
1.4
1.2
1
2.6
OVERHEAD
CABLE HEAD
MIDDLE
RECEIVING
point
2.4
overvoltage[p.u.
2.2
2
1.8
Figure 8: Switching overvoltage according to
underground power cable rate(trapped charge :
110[%])
case 2-1(37.5%)
case 2-2(23.1%)
case 2-3(16.7%)
case 2-4(13%)
case 3-1(50%)
case 3-2(33.3%)
case 3-3(25%)
case 3-4(20%)
1.6
1.4
1.2
Figure 5 to figure 8 show the switching overvoltage in
case of the fault resistance of 10[Ω ] and 50[Ω] as well
as trapped charge 100[%] and 110[%], respectively. As
shown these 4 graphs, the trend of overvoltage is very
similar to figure 4. The maximum overvoltage shows
2.4954[p.u.] at the highest cable rate of case 3-1 with
trapped charge of 110%.
1
OVERHEAD
CABLE HEAD
MIDDLE
RECEIVING
point
(b) Case 2 and case 3
Figure 5: Switching overvoltage according to
underground power cable rate(fault resistance : 10[Ω])
This paper also analyses the switching overvoltage by
just underground power cable rate regardless of case
orders. Examination orders rearranged by cable rate are
as follows;
Pg. 3
Paper G-27
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
In analysis by fault conditions, the overvoltage is some
higher at the trapped charge of 110% and 100%
compare to fault resistance from 1[Ω] to 50[Ω]. As the
fault resistance increases, overvoltage is also little
increasing, but the difference is not big.
Case 1-4( 4.76%) – case 1-3(6.25%) – case 1-2(9.09%)
– case 2-4(13%) – case 1-1(16.7%) – case 2-3(16.7%)
– case 3-4(20%) – case 2-2(23.1%) – case 3-3(25%) –
case 3-2(33.3%) – case 2-1(37.5%) – case 3-1(50%)
Each trend of switching overvoltage at cable head,
middle and receiving end of cable section is also
analysed by only underground power cable rate order
in figure 9 to figure 11. As the cable rate increases
from 4.76[%] to 50[%], the overvoltage is gradually
increasing regardless of the amplitude of fault
resistance and trapped charge.
3.3.
Effects of surge arrester
In this section, the reduction effects are discussed by
surge arrester installation. V-I curve of 154[kV] surge
arrester is expressed in figure 2.
Table 2: Switching overvoltage without surge
arrester(fault resistance : 50[Ω])
3
Fault resistance : 50Ω
2.5
Case
overvoltage[p.u.
2
Cable head
Mean
p.u.
1.5
1
1 ohm
10 ohm
30 ohm
50 ohm
100%
110%
0.5
0
case 1-4
case 1-3
case 1-2
case 2-4
case 1-1
case 2-3
case 3-4
case 2-2
case 3-3
case 3-2
case 2-1
SD
(σ)
Middle
(M+2σ)
p.u
Mean
p.u.
SD
(σ)
Receiving
(M+2σ)
p.u
Mean
p.u.
SD
(σ)
(M+2σ)
p.u
Case 1-2
2.225 0.5571 3.3392 2.2395 0.5638 3.3671 2.269 0.5757 3.4204
Case 2-2
2.028 0.5355 3.099 2.034 0.5413 3.1166 2.0875 0.5567 3.2009
Case 3-1
1.9215 0.481 2.8835 1.9955 0.5172 3.0299 2.0635 0.5505 3.1645
Case 3-2
2.0755 0.5121 3.0997 2.075 0.4978 3.0706 2.1385 0.5271 3.1928
case 3-1
Case
4.76%
50%
30%
10%
Figure 9: Switching overvoltage according
underground power cable rate(cable head)
to
Table 3: Switching overvoltage without surge
arrester(trapped charge : 110[%])
3
Trapped charge : 110%
2.5
Case
2
overvoltage[p.u.
Cable head
Mean
p.u.
1.5
1
1 ohm
10 ohm
30 ohm
50 ohm
100%
110%
0.5
SD
(σ)
(M+2σ)
p.u
Middle
Mean
p.u.
SD
(σ)
Receiving
(M+2σ)
p.u
Mean
p.u.
SD
(σ)
(M+2σ)
p.u
Case 1-2
2.3365 0.6619 3.6603 2.3515 0.6703 3.6921 2.382 0.6760 3.7339
Case 2-2
2.202 0.6146 3.4313 2.209 0.6197 3.4484 2.2595 0.6355 3.5305
Case 3-1
2.0225 0.5629 3.1484 2.104 0.6064 3.3168 2.179 0.6499 3.4789
Case 3-2
2.137 0.6089 3.3548 2.139 0.6170 3.3730 2.205 0.6400 3.4851
0
case 1-4
case 1-3
case 1-2
case 2-4
case 1-1
case 2-3
case 3-4
case 2-2
case 3-3
case 3-2
case 2-1
case 3-1
Case
4.76%
50%
30%
10%
Figure 10: Switching overvoltage according to
underground power cable rate(middle)
3
2.5
Table 2 and 3 show the switching overvoltage of
underground cable section at fault resistance of 50[Ω]
and trapped charge of 110[%] in case of no surge
arrester condition. In fault resistance of 50[Ω], in case
that the surge arrester is not installed on the system, the
overvoltage is from 2.8835[p.u.] to 3.4204[p.u], it is
from 3.1448[p.u.] to 3.7339[p.u.] in trapped charge of
110[%].
overvoltage[p.u.
2
1.5
1
1 ohm
10 ohm
30 ohm
50 ohm
100%
110%
0.5
0
case 1-4
case 1-3
case 1-2
case 2-4
case 1-1
case 2-3
case 3-4
case 2-2
case 3-3
case 3-2
case 2-1
case 3-1
Figure 12 to figure 14 compare the overvoltage
according to with or without surge arrester installation.
As shown in these graphs, in case of no arrester, the
overvoltage is gradually increasing as underground
cable rate is decreasing. However, it is significantly
reduced by surge arrester. The average reduction rate is
expressed in figure 17.
Case
4.76%
10%
30%
50%
Figure 15 and figure 16 are the probability distribution
function of switching overvoltage of case 1-2 and case
3-1. The comparison of the curves in these 2 graphs
also indicates that surge arrester can reduce the
Figure 11: Switching overvoltage according to
underground power cable rate(receiving end)
Pg. 4
Paper G-27
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
switching overvoltage for the whole range of
accumulated frequency at all fault conditions.
conditions. The reduction rate range of case 1-2 is from
32.5% to 44.4% according to fault condition, and the
maximum reduction rate of case 2-2, case 3-2 and case
3-1 is 36.3%, 31.6% and 27.7%, respectively.
3.5
3
10 ohm(with arrester)
30 ohm(with arrester)
100
50 ohm(with arrester)
100%(with arrester)
2
probability of overvoltage[%
case 1-2(without arrester)
case 2-2(without arrester)
case 3-2(without arrester)
case 3-1(without arrester)
case 1-2(with arrester)
case 2-2(with arrester)
case 3-2(with arrester)
case 3-1(with arrester)
1.5
1
0.5
0
110%(with arrester)
10 ohm(without arrester)
80
30 ohm(without arrester)
50 ohm(without arrester)
100%(without arrester)
60
110%(without arrester)
40
20
MIDDLE
RECEIVING
point
3 .7 5
3 .6 5
3 .5 5
3 .4 5
3 .3 5
3 .2 5
3 .1 5
3 .0 5
2 .9 5
2 .8 5
2 .7 5
2 .6 5
2 .5 5
2 .4 5
2 .3 5
2 .2 5
2 .1 5
2 .0 5
1 .9 5
1 .8 5
1 .7 5
1 .6 5
1 .5 5
1 .4 5
1 .0 5
0
1 .3 5
CABLE HEAD
1 .2 5
OVERHEAD
1 .1 5
overvoltage[p.u.
2.5
[PU]
Figure 12: Comparison of switching overvoltage
according to surge arrester installation(fault resistance :
10[Ω])
Figure 15: Probability distribution function of
switching overvoltage(case 1-2)
4
10 ohm(with arrester)
30 ohm(with arrester)
100
50 ohm(with arrester)
3.5
Probability of overvoltage[%
100%(with arrester)
2.5
2
case 1-2(without arrester)
case 2-2(without arrester)
case 3-2(without arrester)
case 3-1(without arrester)
case 1-2(with arrester)
case 2-2(with arrester)
case 3-2(with arrester)
case 3-1(with arrester)
50 ohm(without arrester)
CABLE HEAD
MIDDLE
110%(without arrester)
40
20
3 .7 5
3 .6 5
3 .5 5
3 .4 5
3 .3 5
3 .2 5
3 .1 5
3 .0 5
2 .9 5
2 .8 5
2 .7 5
2 .6 5
2 .5 5
2 .4 5
2 .3 5
2 .2 5
2 .1 5
2 .0 5
1 .9 5
1 .8 5
1 .7 5
1 .6 5
1 .5 5
1 .4 5
0
0
OVERHEAD
100%(without arrester)
60
1 .3 5
0.5
30 ohm(without arrester)
1 .2 5
1
10 ohm(without arrester)
1 .1 5
1.5
110%(with arrester)
80
1 .0 5
overvoltage[p.u.
3
[PU]
RECEIVING
point
Figure 16: Probability distribution function of
switching overvoltage(case 3-1)
Figure 13: Comparison of switching overvoltage
according to surge arrester installation(fault resistance :
30[Ω])
50
10 ohm
30 ohm
50 ohm
100%
110%
45
40
Reduction rate[%]
4
3.5
overvoltage[p.u.]
3
2.5
2
1
0.5
30
25
20
15
10
case 1-2(without arrester)
case 2-2(without arrester)
case 3-2(without arrester)
case 3-1(without arrester)
case 1-2(with arrester)
case 2-2(with arrester)
case 3-2(with arrester)
case 3-1(with arrester)
1.5
35
5
0
Case 1-2
Case 2-2
Case 3-2
Case 3-1
Case
0
OVERHEAD
CABLE HEAD
MIDDLE
RECEIVING
point
Figure 17: Average reduction rate for underground
cable section by surge arrester
Figure 14: Comparison of switching overvoltage
according to surge arrester installation(trapped charge :
100[%])
4.
In figure 17, the average overvoltage reduction rate of
underground cable section is expressed by surge
arrester installation at all fault conditions. As shown in
this graph, the average reduction rate is the highest in
case 1-2. According to analysis by fault conditions, in
trapped charge of 110%, it is higher than other
CONCLUSION
In this paper, the switching overvoltage has been
investigated by statistical approach on 154[kV]
combined transmission systems. The influence of fault
resistance, trapped charge and surge arrester is also
evaluated. The results can be summarized as follows;
Pg. 5
Paper G-27
ISBN 978-0-620-44584-9
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
1) The switching overvoltage of overhead line section
is lower than that of underground cable section, it is
increasing at the high underground power cable rate.
6) In trapped charge of 110[%], the average reduction
rate is higher than other conditions by surge arrester
installation, the maximum reduction rate is 44.4[%].
2) In underground cable section, the overvoltage is also
more increasing at receiving end compare to cable head
and middle of cable section
5.
REFERENCES
[1] J. B. Kim, W. B. Shim, J. W. Shim, “Switching
overvoltage analysis and air clearance design on
the KEPCO 765kV double circuit transmission
system”, IEEE Trans. on PWD. Vol. 15, N0. 1, Jan.
2001.
[2] KEPCO brochure, “Underground transmission
cable system”, Dec. 2002.
[3] A. Carvalho, M. Lacorte, O. Knudsen, “Improved
EHV line surge control by application of MOarresters and controlled switching, IEEE catalogue
No. 95TH8130, pp. 292 – 297, 1995
[4] D. A. Woodford, L.M. Wedepohl, “Transmission
line energization with breaker pre-strike”, IEEE
CAT. NO. 97CH36117, pp. 105-108, 1997
3) As the cable rate increases from 4.76[%] to 50[%],
the switching overvoltage is gradually increasing
regardless of the amplitude of fault resistance and
trapped charge.
4) The switching overvoltage is higher in the trapped
charge of 110[%] and 100[%] compare to fault
resistance, and it is also little increasing, but the
difference is not big.
5) In case of no arrester, the switching overvoltage is
gradually increasing as underground cable rate is
decreasing, but it is significantly reduced by surge
arrester.
Pg. 6
Paper G-27