ISEE2015 - Nguyen Nhat Nam
ISEE2015 - Nguyen Nhat Nam
ISEE2015 - Nguyen Nhat Nam
ABSTRACT:
In this paper, a model of nonuniform
transmission line is applied to estimate
the effective length of vertical grounding
electrodes under lightning strikes. The
estimated results in some typical cases
are then validated and compared with
1. INTRODUCTION
Grounding system is generally a network of
horizontal and vertical electrodes buried under the
ground. Its function is to disperse lightning
currents and fault ones quickly into surrounding
soil. Hence, this system is one of the most
important part in lightning protection. In case a
lightning protection system is installed in a small
area, simple vertical grounding electrodes can be
used. In areas with high resistivity of soil, these
grounding rods can even be longer than 20 m.
In lightning current dissipation, when the
length of a grounding electrode increases beyond
an critical limitation, the maximum ground
potential rise (GPR) does not decrease [1]. This
limitation, which is named effective length, is a
very important quantity for the lightning transient
analysis of grounding systems. From a
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Subsequence stroke
current
LPL I: 200
LPL I: 50
LPL III-IV: 25
0.930
0.993
1(s)
19
0.454
2(s)
485
143
10
10
Imax
(kA)
2. FUNDAMENTAL BACKGROUND
2.1 Nonuniform transmission line model
In the nonuniform transmission line model
proposed in [6], the distribution equations of
voltage v(x,t) and current i(x,t) on a grounding
electrode are displayed as (1) and (2).
v x, t
i x, t
rei x, t L x, t
x
t
(1)
i x, t
v x, t
(2)
G x, t v x, t C x, t
x
t
RLF
V
, where V is the voltage difference
I
formula [5].
I max t / 1
exp(t / 2 )
k 1 t / 1 n
RLF
i(t )
(3)
4l
ln 1
2 l a
(4)
V peak
(5)
I peak
Z
RLF
(6)
(m)
Subsequence stroke
current
10
6.9
7.4
4.6
2.1
1.3
3.6
100
22.2
23.8
12.3
7.4
7.4
7.6
500
49.3
32.0
31.0
17.3
18.1
16.2
1000
69.6
32.9
49.2
25.5
23.7
24
: soil resistivity
a: from nonuniform transmission line model in this study
b: from electromagnetic field based model in [5]
c: from hybrid electromagnetic model in [11]
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current
(m)
First stroke current
Subsequent stroke
current
10
10.2
1.5
100
32.2
5.2
500
70.9
12.7
1000
99.8
19.9
: soil resistivity
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