The triggered lightning experiments using a rocket have been carried out on a winter mountain in Japan since 1986. For the four years from 1986 to 1989, 39 rockets were launched and 19 of them triggered lightning strikes. The emphasis here is on the methodology for triggering lightning to the transmission system. Completed experiments are discussed. The failure of lightning protection and the striking distance are noted

Horii, Kenji

Nakamura, Koichi

Wada, Atsushi

English

NASA Technical Reports Server

N 9 1 - 3 2 6 5 4  
DISCUSSIONS ON A LONG GAP DISCHARGE TO AN EHV TRANSMISSION TOWER 
BY A ROCKET TRIGGERED LIGHTNING EXPERIMENT 
Ko i ch i NAKAJvlURA 
Nagoya Institute of Technology, Nagoya, Japan 
Atsushi WADA 
Nagoya University, Nagoya, Japan 
Kenji HORII 
Toyoda College of Technology 
ABSTRACT 
The triggered lightning experiments using a rocket have been 
carried out on a winter mountain in Japan since 1986. The 
lightning stuck, nineteen times, the EHV test transmission line 
and tower. This paper emphasizes the methodology for triggering 
lightning to the transmission system and presents the record of 
experiments carried out. Based on the results of these 
experiments, the failure of lightning protection and the striking 
distance of lightning have been discussed. 
INTRODUCTION 
The rocket triggered lightning experiments have been carried 
out in the several countries [1,2,3,4]. In Japan such 
experiments have been performed in the northern region for the 
winter thunderclouds since 1977 [ 5 , 6 , 7 ] .  From 1986, the 
experiment site was shifted to mountainous range of about 1000 m 
altitude [ 8 ] .  The lightning struck, nineteen times, thc EIIV test 
transmission line and tower. The artificial method for triggering 
lightning involves a rocket and a bobbin fixed together. The 
bottom of the rocket system is connected to a 200 m l o n g  s t e e l  
wire which in turn is connected to a 70 - 120 m long nylon line. 
Both steel wire and nylon line are wounded on a bobbin. The free 
end on the nylon line is held to the ground and thus acts a s  a 
insulator for a rocket steel wire. During the shootjng operation 
of the rocket, the nylon line gets unwound first, followed by 
unwinding of the steel wire. 
Most of the lightning strokes occurred on the ground wire 
and the peak or the arm end of tower. However, a few lightning 
strokes occurred on the phase conductors. This indicates the 
inadequate lightning protection for the transmission line. 
The current was measured by a Hogowski coil unit placed on 
the tower. The sampling time and memory capacity of the unit 
were one micro-seconds and 256 kilo-words respectively. The peak 
current was measured by a magnetic tape placed on the t o p  of 
rocket . 
In order to obtain the triggered lightning discharge on a 
62- 1 
https://ntrs.nasa.gov/search.jsp?R=19910023340 2020-03-17T15:03:28+00:00Z
high tower artificially but similar to the natural one, a two- 
stage rocket was used to initiate lightning as well as to carry 
the current measuring system (Rogowski coil - for the measurement 
of lightning discharge in the air). 
The striking distance was estimated from the photograph or 
the reconstructed channel by an acoustic analysis method. In the 
measurement of the acoustic analysis, three microphones were 
used, each separated by a 10 m distance amongst them. This 
analysis was quite useful to estimate the discharge channel 
within the cloud or under the invisible conditjon such as 
snowfall, etc. This analysis method and its accuracy have been 
discussed i n  the literature 19,101. The striking distance versus 
the peak current characteristics were thus obtained. The results 
were comparatively close to the characteristics reported by Golde 
and Chan [11 .121 .  
This paper primarily emphasizes the methodology for 
triggering lightning to the transmission system and presents the 
record of experiments carried out in the four years. Finally, 
based on the results of these experiments, the failure of 
lightning protection and the striking distance of lightning have 
been discussed. 
THTCCERING METHOD 
The experiment site was chosen on the peak of the 
Okushishiku mountain with the altitude of 930 m above sea level 
and IKI,(Iso Keraunics L e v e l )  of about. forty. A test trans- 
m i s s i o n  line of 275 kV of about 2 km length running over sevcn 
transmission towers is located near the site. Fig. 1 indicates 
1 1 1  
Fig. 1 Experiment site 
: thundercloud 
rocket second 
rocket 
bobbin 
steel  wire 
part f l r s t  
rocket 
iylon line 
tower 
( a )  ( b )  
Fig. 2 Rocket triggering methods 
62-2 
the arrangement of the site. The height of one of the towers, 
tower N o .  30, is about 60 m. The rocket launchers were placed at 
a distance of 10 - 15 m from the tower. In order to get the 
lightning OR the towers one-stage and two-stage rocket methods 
were applied. 
One-stage rocket system 
This method has been applied since 1986. One of the rockets 
launched employing this method is shown in Fig. 2 ( a ) .  The 
length, the diameter and the weight of rocket were 170 mm, 40 mm 
and 0 .5  kg respectively. During launching of rocket, initially 
the nylon line was pulled out by about 70 to 120 m from the 
ground followed by unwinding of the steel wire of 0 . 2  mm 
diameter. With such a long nylon line, the steel wire gets well 
insulated from the ground. This paves the way for triggering of 
the lightning discharge to the nearest transmission line and 
tower making a long gap discharge of length 10 - 60 m. Hence the 
change in the starting point of the downward leader, (i.e. the 
distance from the ground), can be achieved simply by selecting 
the different lengths of nylon line. Fig. 3 shows one example of 
the triggered lightning to the top of tower. 
Two-stage rocket system 
In the one-stage rocket system the comparatively long 
partial discharges were often observed along the surface of the 
nylon line in the beginning of triggering of the lighting 
discharge [8]; To eliminate these discharges, the two-stage 
rocket system was then developed completely dispensing with the 
nylon line. 
As shown in Fig. 2(b), the two-stage rocket was launched by 
firing the first rocket and within two seconds the second rocket 
got automatically fired to separate each other in the air and 
then the steel wire was unreeled connecting them. On the top of 
the second rocket a magnetic tape and on the bottom side of the 
first rocket a compact Rogowski coil with a memory unit were 
equipped to measure the lightning current peak and waveform 
respectively. The diameter of Rogowski coil was 70 mm. The 
current signal was directly written into a compact memory card 
with memory of 256 kilo-words. As the magnetic tape used  was 
pre-magnetized with 1 kHz signal and so the peak current was 
estimated from the demagnetized distance on the tape. The 
triggered lightning by the two-stage rocket system was obtained 
two times in 1989, but unfortunately the current measurement 
could not be successfully recorded. 
EXPERIMENTED RESULTS 
General 
The table 1 depicts the results of the triggered lightning 
strokes occurred on the ground wire, phase conductors and tower. 
In the table, the nylon length indicated i s  that of the nylon 
62-3 
line wound on the bobbin for the one-stage rocket system. The 
results shown against the experiment No.89-16 and No.89-21 have 
been evaluated using the two-stage rocket system. The striking 
points were estimated either using the camera photograph or the 
lightning channel reconstruction by an acoustic analyzing method. 
Several points were identified and confirmed through the visual 
inspection after the end of experiment as well as other 
measurements such as the induced voltage on the insulator 
strings. The peak currents were obtained by Rogowskl coil 
measurement except i n  case of experiment No.89-16 and 89-21 in 
which relevant observation were taken by the magnetic tape 
measurement. The triggering tlme means the time lapse after the 
rocket launching till the occurrence of lightning. 
Striking distance here is defined as the distance between 
the striking point on the transmission system and the nearest 
bending point of the channel. According to the streak 
photograph, the downward leader began from the tip of the partial 
discharge appeared along the surface of the nylon line, and 
propagated towards the transmission system. The local return 
stroke run up from the transmission system to meet the leader 
within several hundred microseconds before the vaporization of 
wire. The main discharge occurred after the upward leader 
reached t h e  nearest cloud [8]. 
‘Fable 1 Experimental Results 
N o .  
86-11 
86-13 
87-05 
87-07 
87-08 
87-10 
87-18 
87-21 
87-22 
88-12 
88-04 
88-16 
89-04 
89-05 
89-07 
89-09 
89-10 
89-16 
89-21 
Lightning 
The 
nylon striking 
length points 
current 
peak (kA) 
70 m upper arm end of tower >+50 
70 ground 
100 peak of tower +23.0 
100 upper arm end of tower -8.5 
100 ground wire -11.0 
100 rocket launcher negative 
100 upper arm end of tower +14.0 
100 middle phase conductor negative 
100 upper arm end of tower (-5.5) 
100 ground wire - 
120 upper phase conductor - 
120 ground wire - 
120 peak of tower +25.6 
120 upper phase conductor positive 
120 upper phase conductor positive 
120 ground wire -4.3 
120 peak of tower -18.1 
ground wire +13.0 
middle arm end of towe + 5 . 0  
Discharges 
length of nylon line applied in the 1986 
remarks 
(protection) 
failure 
failure 
failure 
failure 
(two-stage) 
(two-stage) 
was 70 m. The 
62-4 
I 
I 
I 
F i g .  5 R e c o n s t r u c t i o n  of l i g h t n i n g  f l a s h  87-21 ( m i d d l e  p h a s e )  
62-5 
Fig. 4 shows the lightning flash of experiment No.87-10 on 
the launcher. The lightning discharge came down straight from 
the air, and jumped to one of the six launchers on the ground 
after flashing over along the nylon surface for about 20 m 
length. Fig. 5 shows the reconstruction of the lightning 
experiment No.87-21. The striking point was estimated to be on 
the middle phase conductor 20 m at a distance from the tower. 
Fig. 6 shows a photograph and a current through the ground 
wire measured by a Rogowski coil unit in the lightning experiment 
No.87-08. The lightning experiments viz, No.87-21 and No.87-10 
was the negatively charged clouds. 
3RlGINP.L PAGE 
WHITE PHOTOGRAPti 
. - .  - , n  .... . 1 L. , 
F i g .  1 1  (:ur-rcrit through thr  ground w ~ r v  
Fig. 6 Lightning flash and current through the ground wire 87-08 
In case of experiments conducted during 1988, two nylon 
lines of 100 m and 120 m length were applied. Two lightning 
occurred on the ground wire and one occurred on the upper phase 
conductor. Fig. 7 shows the reconstruction of the lightning 
flash of 88-04.  Fig. 7-a , 7-b and 7-c are the front, the side 
and the plane views, respectively. The striking point were 
estimated to  be 60 m away from the tower. 
In the year 1989, such experiments were conducted using 
nylon line of length 120 m. Seven triggered lightning including 
the two initiated by the two-stage rocket system were obtained. 
The triggering lightning strokes as recorded in the experiments 
No.89-05 and No.89~07 occurred directly on the upper phase 
conductor which indicates the insufficient shielding against 
lightning. Clear photographs could not be obtained for any of 
lightning discharges because of the heavy snowfall. Fig. 8 
62-6 
indicates the seven striking 
points of the lightning 
est imated by the 
The 
locations of these points 
were evaluated by another 
methods and found to be in 
good agreement. 
- f i f i - m o t v ~ ~ n t i n n  m n t h n A  I LL"I*J t,I UL l..Lw., 11.b b I I W U .  
I-. 
DISCUSSIONS 
I 
0 
8 
8 
8 
. 
0 
I! 
A s  shown in Table 1 .  
two 1 ightning strokes 
occurred separately on the 
tower or the ground without 
the failure of s h i e l d i n g  
against lightning in the 
case of 70 rn nylon line. 
However, out of seven 
lightning strokes triggered 
using nylon line of 100 m 
length, only one struck the 
middle phases conductor, 
whereas one of same number 
of strokes triggered using 
nylon line of 120 m length. 
three struck the upper p h a s e  
conductor. On evaluating of 
this date, it was obscrvcd 
that the failure rate of the 
lightning protection was 14 
% in the case of 100 m nylon 
line and 43 % in the case of  
120 m nylon line. 
These results suggest 
that the longer the nylon 
line, the higher is tho 
failure rate of the 
2 hJ ,,i 
8 
a 
I 
! 
'9- 
. I  -7 
I. I I' r (0 )  -I. - - 
62-7 
lightning. It was also 
observed that in the cvent 
striking the tower, the 
downward leader began near 
the junction of the nylon 
line and the steel wire [ 8 1 .  
Thus the starting location 
of the leader may depend on 
the length of nylon line. 
If the length of the nylon 
of t r i ggered 1 i gh tn i ng 
Y h, 
I 1  
_ a  .,. m I In 1- 
microphone - .am ?a -.a1 
n e  
n 0 
8 
0 
5 Y- 
Y (IU) 
area of the tower, the lightning can occur on the tower. If the 
length of the nylon line is comparatively long, the leader can 
begin outside from the attracting area and then the lightning can 
take place on somewhere the nearest point from the leader. 
8 9 - 0 7  
- 8 9 - 0 5  
P - 7  1 
P a -  - -  - a =  
microphone microphone 
Fig.8 Striking points identified by the reconstruction 
[ G O  
0 posit ive cloud 
II) 
b120 - 
(d 
u 
.A a 
80 - 
0 10 20 30 40 50 
peak current I (kA) 
Love 
Brown and 
Arms t rong 
Golde and 
Wagner 
Vh i tehead 
and Whitehead 
Chan 
Fig. 9 Striking distance and peak current 
Fig. 9 shows the characteristics of thestriking distance 
versus the current peak. Several theoretical curves are 
documented together. The characteristics curve of the triggered 
lightning becomes close to or comparatively below the curve 
reported by Golde and Chan. According to the theory, the larger 
the total charge of the downward leader, the longer is the 
striking distance or the final jump because of the higher 
potential of the leader. And the return stroke current must be 
larger enough to cancel the corresponding charge the leader left 
62-8 
behind. 
On the other hand, the downward leader was forced to start 
from the bottom of wire and propagated only several tens meters 
twisrds  t he  transmission system in the triggered lightning. Then 
the return stroke did not reach the cloud at a dash, but ceased 
in the way. For this reason we named it as a partial return 
stroke. Within a few hundred microseconds the upward leader 
subsequently began to move towards the cloud to initiate the main 
lightning discharge. The peak current in Fig. 9 is not 
corresponding to the partial return stroke current, but the main 
discharge current. Therefore, the comparatively large currents 
the current during the partial return stroke can be measured by 
using the two-stage rocket, the more reasonable characteristics 
may be obtained. 
were obtained corresponding to the same striking distance. If 
CONCLUSIONS 
The results and the discussions on the triggered lightning 
experiments to the transmission line for four years from 1986 to 
1989 are summarized as follows. 
(1) Thirty nine rockets were launched and nineteen triggered 
lightning strokes were obtained on the transmission line and 
tower. and on the ground. The rate of success was 50 %.  Four 
times lightning strokes occurred on the phase conductor which 
meant the failure of lightning protection, and the twice struck 
the ground. 
(2 )  The nylon lines of 70 - 120 m length were used for the 
insulation of the steel wire. The longer the nylon line, the 
higher was the failure rate of the protection. 
( 3 )  The characteristics of the striking distance was close to or 
comparatively below the curve reported by Golde and Chan. 
( 4 )  The lightning using the two-stage rocket was successfully 
triggered. Unfortunately, the measurement of the discharge 
current could not be done succcssfully. 
The authors would like to thank the members involved in 
conducting the experiments and the students for their great help 
and assistance. The authors would also like to thank Hokuriku 
Electric Power Company and Chubu Electric Company for their great 
co-operation. We also gratefully acknowledge the financial 
support of the Ministry of Education, Science and Culture of 
Japan. 
REFERENCES 
[l] M.M.Newman et al., "Triggered Lightning Strokes at Very Close 
Range", Journal of Geophysical Research, vo1.72,pp.4761-4764, 
1967. 
121 R.P.Fieux et al., *'Research on Artificially Triggered 
Lightning in France", IEEE Transaction on Power Apparatus and 
Systems, vol.~~s-97,pp.725-733, 1978. 
131 W.Boeck et al., "Aktuelle Aufgaben und Methoden der 
62-9 
Blitzforschung", etz-a Bd.99,pp.652-654, 1978. 
[4] K.Horii et al., "Experiment of Rocket-Triggered Lightning in 
Indonesia", T.IEE Japan, vol.llO-B,No.l2,pp.l068-1069, 1990. 
[5] K.Horii et al., "Experiment of Long Gap Discharge by 
Artificially Triggered Lightning with Rocket", 3rd International 
Symposium on High Voltage Engineering, v01.51.10, 1979. 
[6] 1.Miyachi et al., "Five Years' Experiences on Artificially 
Triggered Lightning in Japan", 7th International Conference on 
Gas Discharge and their Applications, pp.468-471, 1982. 
[7] K.Horii et al., "Observation of Final Jump of the Discharge 
in the Experiment of Artificially Triggered Lightning", IEEE 
Transactions of Power Apparatus and Systems, vol.PAS-104. No.10, 
[8] K.Nakamura et al., "Artificially Triggered Lightning 
Experiments to an EHV Transmission Line",IEEE/PES Summer Meeting, 
191 H.Akiyama et al., "Channel Reconstruction of Triggered 
Lightning Flashes with Bipolar Currents from Thunder 
Measurements", J. of Geophysical Research, vo1.90.No.D6,pp.10674- 
10680, 1985. 
[lo] M.Wakamatsu and K.Horii, "Rocket-Triggered Lightning to 
Power Transmission Line Tower and Estimation of the Lightning 
Channel by Computer Graphics", Research Letters on Atmospheric 
Electricity, Vol.7,pp.17-20, 1987. 
[lll G.W.Brown and E.R.Whitehead, IEEE Transactions on Power 
Apparatus and Systems, vol.PAS-88.No.5, 1969. 
[121 M.A.Uman. "The Lightning Discharge", pp.101, Academic 
Press, New York, 1987. 
pp.2910-2917, 1985. 
90 SM 360-0 PWRD, 1990. 
62- 10 


Discussions on a long gap discharge to an EHV transmission tower by a rocket triggered lightning experiment

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