2. 2
caused by lightning; some of the 40% of failures are
temporary and caused by other reasons such as birds,
contamination, trees, etc., as shown in Fig. 2.
It can be observed in Fig. 5, that the 2005 has been the year
with highest lightning activity, with an average of 2.446
atmospheric events in the latest 5 years.
2004/2005 Failures_
mm
Lightning Birds
11 5 7 3
Vegetation thirds
6k17
Unkwnon
5 5
Contam
Fig. 2. Distribution network growth in Campo Boscan
Most of the failures are located on distribution lines (62%)
and about 33% are related to Load Immunity. (Fig. 3)
Fig. 3. Failures distribution
The biggest problem is induced sag, in either a single or
two phases faults which -a root causes are: Flash over from
lightning, Grounding failures, Birds strikes and very sensitive
load
C. Strategy to solve the problems
Fig. 4 shows the strategy of problem solving was focused
on the process analysis, regarding the source, distribution
lines and load.
520 km 24kV
Distribution Lines
DISTRIBUTION LOAD
Fig. 4. Solving strategy
After analyzing the different options, we arrived to the
conclusion that the definite actions to improve the reliability
of the Electric System in Campo Boscan are the following:
1) Distribution Lines. Related to lightning (poorlmissing
path grounding), bird strikes, insulator contamination (birds),
over voltage to low voltage equipment, singlephasefaults
2) Load. Related to load immunity
IV. ACTIONS RELATED TO LIGHTNING
As evidenced in the statistics, there is an intense
isokeraunic activity in the area of Campo Boscan. This
lightning activity is confirmed against the database available
on the NASA WEB which through the project satellites
Lightning Image Sensor (LIS) [1] it is possible to obtain, with
a high degree of reliability, the amount of lightning cloud-
cloud, cloud-earth within a specific geographical area.
Fig. 5. Statistics for atmospheric events in Campo Boscan during the 2004-
2005
Another source of information available is the statistics
kept by EDELCA Company [2], which reveals that the
lightning discharge density in the area of Campo Boscan
averages 8 lightning/km2/year.
A. GroundFlash Density
The Ground Flash Density (GFD) indicates the number of
lightning that fall on a specific area and it is expressed as
follows [3]:
Ng=0,04*TD 1,25
where TD are the storm days per year.
Ng=GFD=0,04*75 1,25 = 8,8 rays/km2/year
(1)
Also we can calculate the flashes to a Distribution lines by
the number of lightning towards a line is determined by means
ofthe following equation:
(2)N =
Ng28 1 ±b]
Iwhere h is the height of the overhead ground conductor and b
is the separation between the overhead ground conductors, in
this case is zero because we have only one overhead ground
conductor.
N = Ng L 28 h + b 8128
*
1 1.706±0+
= 10 10
=8,8*12,25= 108 rays/100 km/year
B. Lightning strikes on Distribution Lines
The lightning can affect a distribution line in two ways, as
a direct impact or induced flashover Fig. 6.
83100
80
60
40
20
0
4000.
203
10 V
S/E km 48
S/E Z-9
SOURCE
E.4r.
3. 3
descarga
Retroactiv.
descarga
Inducida
Fig. 6. How a lightning affects a distribution lines
The direct impact on the distribution line causes a
phenomenon known as Back Flashover which drains the
current of the ray to ground through the pole's ground down
conductor. The induced discharge is a result of lightning
impact over objects located near the lines.
C. Back Flashover
We have calculated that failures due to induced over
voltages, and found that these are to very low in Boscan Field,
so most of the failures are due to back flashover
phenomenon. In order to analyze this phenomenon, we will
consider the most unfavourable case which is when the
lightning falls just on top of the pole, in this case 60% [12] of
the current of the lightning will be drain to ground through
down conductor.
The overvoltage on the insulator see Fig. 7 can be
expressed in [4] by
U=k*(R*i+L*di/dt)+Vpeak, (3)
Where:
k= 0,6 (was previously considered)
R= is the dynamic resistance ofthe footing resistance
I= is the lightning current
L= is the inductance of the ground down conductor from
the overhead to ground.
di/dt= is the rate of growth of the tension wave, which
according to IEEE [6] is 20 kA/ Ls
Vpeak= <23*24kV=19,6 KV aprox= 20 kV
[R +
Fig. 7. Insulator Withstand Voltage
The inductance of the copperweld conductor is calculated
from its inductive reactance of 0,629 X/mile:
XL 1 mile 0,629 Q 1 mile 04 pHL = x~ 1,O4jt m (4)
2 1609 m 2;r60 1609 m
The average height of the phase conductors is 11,7 m, and
for a measured static resistance of 5 OHM it corresponds to a
dynamic resistance of 3 OHM, and assuming a current of the
ray of 20 kA, we find that the overvoltage over insulator is
using (3):
U=k*(R*i+L*di/dt)+ Vpico,
U=0,6*(3 *20 kA+1,04 ptH/m*11,7 m*20 kA/ Ls)+ 20 kV
U= 36kV+ 146kV+20kV =202kV
In this particular case, the overvoltage is slightly higher
than the insulator's BIL, so there will be a flashover, but for
currents over 20 kA or static resistances over 5 X, there will
be a more severe flashover.
Notice that approximately 70% of the contribution made by
the overvoltage is a result ofthe L di/dt factor and the other 30
% is due to the R*I factor. Controlling this overvoltage is a
commitment between these two factors.
In old poles, when there is a high factor of resistance in
grounding and they only have one solid copper No. 4 ground
down conductor [6] (L= 1,3 [tH/m), it is evident that any
small value of current resulted in flashover since the
overvoltage to be on insulator was always over 200 kV, no
matter the magnitude of the lightning. The only contribution
ofthe L di/dt factor is around 200kV.
The action of installing the grounding with a lower or
equal value to 5 X is quite right since a low impedance path is
supplied for the drainage of the current of the ray, and in
addition to the installation of a copperweld 7/7 ground down
conductor, the overvoltage as a result of the L di/dt. is
reduced.
The original network consists of 45 feet concrete pole with
a solid copper No. 4 conductor. The average grounding was in
the best case 30 X and we will assume a current with a 2 kA
of amplitude being 99, 9% , according with (5):
P(° >i) 1= (io 31)2,6 (5)
According with (3), Overvoltage is expressed by:
U=k*(R*i+L*di/dt)+ Vpeak,
U=0,6*(30 E*2 kA+1,3 tH/m 11,5 m *20 kA/[ts)+ 20 kV
U= 36kV+ 179kV+20kV =235kV
Notice that all lightning practically resulted in flashover in
the insulators and as a consequence, in failures of the line. If
there was no solid copper ground down conductor or it was
disconnected, the overvoltage would be even more severe.
D. New design in poles
In the year 2003 a 4/0 AWG strand copper ground down
conductor was installed, whose inductance was relatively low;
but in the field the majority of these conductors were stolen,
4. which in turn led to the use of Copperweld-type conductors
which are difficult to steal because oftheir hardness.
The Copperweld 7/7 conductor has an inductive reactance
of XL= 0,629 X/mile, the previously calculated inductance
was 1,04 [tH/m. The minimum lightning current without the
occurrence of flashover was formerly calculated and it is
around 20 kA.
The installation of additional conductors and different
calibres results in a variety of options and percentages of
protection which are summarized as follows:
TABLE I
GROUND DowN CONDUCTOR PROTECTION RANGE
Wire Protection Range
Copper solid No. 4 0%
Copper strand 4/0 AWG 76%
One Copper weld 7 No 7 40%
Two Copper weld 7 No 7 80%
Two Copper strand 4/0 AWG 94%
E. NGR (Neutral Grounding Resistor)
We are studying this option to decrease short circuit
current level in all distribution lines. The study result
showed that installing an NGR could produce overvoltages
in non faulty phases, so the insulation level of this
conductor should be greater. In Boscan field, as the
transformers and substation equipment are already installed
it is not economical option to installed this NGR in the
main substation.
But, on other results showed in Fig. 8 with the grill
substation resistance of 1 OHM , we have overvoltage
between 125% and 140% ( 18,3 kV and 20,3 kV phase to
ground) when a fault to ground occurs. This is the
explanation of arrester failures detected no longer than 5
km from substation, because the distribution lines had
installed 21 kV Rating (17 MCOV) arrester.
180,00
170,00
160,00
150,00
140,00
130,00-
(p 120,00-
110,00-
100,00
90,00
80,00
70,00
60,00
'In nnrl
SE (0 km)
6000
5500
5000
4500
4000
3500 i
3000
--
2500
2000
1500
1000
I 'Inn500
BN-28 (5 km) BN-390 (10,7 km) BN-535 (13,7 km)
Failed Bar
-V(%)R (%)R
*I(kA)R=l I(kA)R= 14
0,01 0,1 10 100 1000
PVR PDV VARIGAP, U-SIL
10000
Time in Secs.
AZE
Fig. 9. TOV in Arrester
F. Line Reclosers
Using of line Reclosing is well known, in our case, every
circuit will be divided in two or three parts to avoid that a
failure at the end of line can affect the whole circuit.
Actually, single phase tripping is being analyzing, because
it has been determined the more that 90 % of distribution
failures [7] are phase to ground, and according with
manufacturer data we have the opportunity to improve up to
9% the failure time respect a three phase tripping (Fig. 10).
Hrs[Yr %* vs%*Y
*1" . Case 1 Substation reclosing
3
3 phase only
-W- Case 2 - Line Recloser 2.6 21%
me
Case 3 Loop with Manual 2.3 30%
Switch
Fig. 10. Recloser Statistic
Single phase
.3 30%
.0 39%
V. ACTIONS RELATED TO BIRDS.
A. Birds problems
As showed in Fig. 2, the second most important cause of
failures, after lightning, is due to birds of the region. (See Fig.
11). Birds cause the interruption of electric flow in three
different ways:
Direct contact between line to earth and line to line.
J(%)R= 14 so66l(kA)R= 0
Fig. 8. Overvoltage due single phase fault.
The best arresters to be installed are those that can
withstand more time (TOV) without failure during a fault
to ground. (Fig. 9)
4
2,2
2
1,8
._
0
m
1,6
O 1,4
1,2
190Y,00 1 , 6500
DU,UU
I
I Z. 1- 1,
" , :z ,
0 9 -
a -
0 6 0 --
5. 5
Fig. 11: Examples of electrocuted birds
Bird excrement causes a flashover over the insulators, as
well as nests on the cross arms
During 2004, 11 deaths of birds with circuit opening and
24 failures caused by excrement contamination were reported.
In June 2004, approaches were made with different entities in
CHEVRON in order to look for alternative solutions.
During the June/November term of 2004, different
solutions were applied, among all, the metallic cone was the
most successful.
In January 2005, 250 cones were installed as a pilot test,
which turned out to be successful as birds were prevented
from perching on cones see Fig. 12 and 13:
Fig. 12: Cones installed
Also, and in order to provide birds a spot where birds could
perch, the installation of a lmt-rod so they can still have a site
for watching:
Fig. 13: Perching installed
The cone installation plan started in March 2005, installing
250 units.
By October 2005, 1250 units have been installed and by
the end of this year, 2500 units will have been completed.
The preliminary results of cone installation demonstrate
that failures due to birds have been decreasing.
B. Special Ornithology study
Since a serious study on environment impact on the
wildlife of the area was required, and in order to reduce the
failures due to bird excrement, electrocution by contact, etc, a
decision was made on contracting Biologists, experts in
Ornithology (Bird Study), so an assessment of the behavior of
these animals could be carried out and then alternative
proposals of solution could be developed.
The ornithology study was developed in Campo Boscan, it
covered a 30.000 ha, was done in 90 days, 10 observation
cycles were defined that includes 100 observations.
The study was completed in December 2005, with the
following results:
* 41,221 birds observed
* 128 species detected
* 33 species affected electric lines
The study gave 14 possible solutions within 6 are being
evaluated. These seven solutions are:
* Anti perching (cones)
* Bird repellents
* Ultrasonic devices
* Bird Scare
* Insulate conductors
* Artificial trees
VI. ACTIONS RELATED TO LOAD IMMUNITY
A. "Back Spin " control in PCP Wells
The Variables Speed Drive (VSD) used in Progressive
Cavity Pumping (B.C.P.) , is a production method used in the
majority of wells in the north area of Campo Boscan. It is very
susceptible to temporary interruptions of the electrical fluid,
shorter than 500 milliseconds. Once the well operation is
interrupted, it can not be re-started until four hours later, due
to the inverse rotation of the pump as a consequence of the
crude column descending from the surface to the reservoir. If
the well was started under this circumstance, the torque
exerted could break the axis and burn the engine, leaving the
well stopped.
In order to search for a solution to the problem, a
multidisciplinary team was formed, so that a solution could be
found and applied. The solution found included the
modification of the software, the installation of a drainage
resistance and the use of magnetic breaking as a regenerating
equipment, so an absolute control of the back spin could be
achieved. In March 2005, the solution was applied; the results
were successful. [8]
For instance, in Fig. 14 it is showed the results of the test
and the explanation below:
6. 6
700-
600 -
500
400 -
300 -
200 -
-100 -
951 42'36" 9:52 18'34" 952 4 44" 9:53 13'47"
Tinie (Houts inutes seconds'cente")
9:53 43'30
Fig, 14 Back spin filed test
P1: All equipment is working normally. Rpm BCP = 250
P2: A fault is induced, turn off main broker. Volt = 0 volt.
Interruption time> 300ms
P2-P3: Drive remains active running the software and
controlling back spin.
P3: Drive is energized again turning the main breaker ON.
Incoming voltage: 460 volt.
P3-P4: Drive accelerates lineally drive until motor reaches
normal speed.
P4: Drive and motor are in normal condition.
Actually, more that 78 wells have the back spin control
already installed.
B. Ride thru in ESP andPCP Wells
The electro-submergible pumping (E.S.P.) wells are also
susceptible to temporary interruptions, shorter than 500
milliseconds, producing a delay of 1 to 2 hours on the well
restart, as a product of the "back spin". The operation
philosophy of these wells is different, because the descent of
the crude column is very fast, so that the best way to prevent
the "back spin" from happening is guaranteeing the continuity
of service for temporary interruption of 500 milliseconds or
shorter.
In the ESP industry, the VSD design philosophy has
always been conceived to protect the down-hole equipment,
when the system was subjected to adverse conditions
CENTRILIFT Company opened a project and hereon it
will be referred to as the ride-thru project. After successful
testing in the test well and Gary 1 (CENTRILIFT field well),
Chevron was invited for a customer witness test. In addition to
testing, math model was developed with Chevron well data.
This model is accurate enough to provide information about
the required storage capacitors.
Fig.s 15 through 17 display the actual waveforms for 100%
of sag, that were captured on the PortoSag while conducting
the customer witness test.
750
-25
-750;
0D oo 00 300 400 500 000 700
Tie (mns)
Fig. 15 Input Volts with 1000 SAG for 30 cycles
Time (ms)
Fig. 16 Bus Volts with 100 % SAG for 30 cycles
For PCP wells, a test in EPRI laboratory was performed in
June 2005 [10], with a Drive loaded to 30 HP.
The results was successfully and it showed in Fig. 17
rig. i / 1NortdiaUnLer iouaue to jui1p A
Ride-Thru
C. TVSS (Transients Voltage Surge Suppressors) Installation
In this scenario the primary 480 volt three phase power
drop to the drive would be considered as our "service
entrance" in the cascade scheme (Fig. 18). The secondary
level of protection needed was at the critical junction of 480
volt -three phase feeder to the inverter -rectifier section of the
drive and the third level of protection would be the secondary
side of the 480/120 control transformer feeding
microprocessor drive controls.
--
~~~~~~~~~-BusVolage ------- ----
t------ -- -j-- -X-
__ --r---------r~~~~~~~~~~~~~~~~~~~~~~~--~~~~ jszed~~------
P. 2 _
>-jg ou.
-------- --- ---------j---------r--------- -----'----F--------- ---------->-------------------
j---'-F-'j --------
---'------ -----'------------
'------------
7. 3) Laboratory Cascade implementation
The experiment set up looked like this in Fig. 19:
24KV- 480V y
3X167.5KVA A
TVSS I
DV/480V
VARIATOR ELECTRONIC
24V
l 24V
V
12V
RADIO UNIT (RTU)
480 V - 2300 V
Fig 18. Typical diagram of a VSD in ESP
Three different brands of suppression devices utilizing
separate similar yet distinct designs were chosen in order to
evaluate the theory. The technology of Brand 1 was single
component design. The technology of Brand 2 was hybrid
network - fully encapsulated - type technology. The
technology of Brand 3 was hybrid network - conformal
encapsulant - board level current fusing and individual
component level thermal fusing. The objective desired in the
laboratory was to simulate as closely as possible the field set
up of a typical variable speed drive and RTU cabinet, utilizing
the industry accepted test criteria contained in the ANSI/IEEE
C62.41.2-2002 recommended practices standards. However, a
single Category C3 impulse was implemented into our
cascade approach test utilizing 3 levels of SPD's with
approximately 1.5 meters of wire between Level 1 and Level
2 and then approximately 20 feet of wire between Level 2 and
Level 3.
1) Laboratory Test
In order to certify the values provided by the manufacturers
regarding the Let Through Voltages, laboratory tests were
performed by Surge Suppression Incorporated, located in
Brooksville, USA. Tests were performed on October 12th and
13th, 2005. [11]
Tests to three TVSS manufacturers were performed:
* Brand 1, used in the CENTRILIFT VSD
* Brand 2, used in the TOSHIBA VSD
* Brand 3, new technology to be tested
2) Test results
Each unit was tested separately, applying every voltage
category, line to line and line to ground, and recording the
most significant data.
This test is between phase A and B (line to line). It can be
seen that the best equipment is the one manufactured by Brand
3 because it is the one with the lowest remaining voltage (Let
Through Voltage).
Fig. 19 Diagram in cascade set up in the laboratory
The result of the test is shown graphically in Fig. 20 which
shows that the remaining voltage at the end of the
implementation in cascade is 25 V (below 120 V, which is the
nominal tension at this level).
TVSS 1
Main Unit (External)
TVSS 2
Second Unit (Internal)
TVSSS 3
Third Unit (internal)
1 20 V20 kV 480 V 2300 V 480 V 133.
10 KA 3 feet Lead 20 feet
Category C
Fig. 20 Summary ofthe test in cascade in the laboratory
VII. CONCLUSIONS
* It has been demonstrated that the use of two ground
down conductor plus a grounding resistance less than 5
ohms in concrete poles are enough to drain a lightning
current to ground plus.
* The use of Neutral ground Resistor requires enough
insulation to avoid failures due overvoltages caused by
a fault to ground .
* Arrester located not far that 5 km from substation mus
be replaced from 17 MCOV to 21 MCOV to avoid
failures caused by single phase to ground.
* It is an opportunity decrease impact of oil production
by implementing of single phase tripping in Line
Reclosers
* Implementing an antiperching system to birds and
doing a ornithology study, we are given more
opportunity to birds to live.
* Due of success of Back spin control is wide
recommended installing in all PCP oil wells.
* Ride Thru works in laboratory test, so next step is its
implementation in ESP wells and evaluate its behavior
with real failures.
* TVSS installation will reduce damage in electronic
components due to surges incoming from the network
after a lightning storm.
7
120 V
33 V
Xt Lead
25~
8. 8
VIII. ACKNOWLEDGMENT
The authors gratefully acknowledge the contributions of
Steven Mc Donnald, Donald Stelling, Peter Grootelard for
their work on the original version ofthis document.
IX. REFERENCES
[1] Miguel Martinez Lozano, "Atmospherics discharges in Venezuela"(in
Spanish). Laboratory ofhigh voltage, Simon Bolivar University.
[2] CVG-EDELCA. Annual map of density of discharges to ground
Management of gestion environmental. System of detention and
localization of discharge electrics atmospherics.
[3] IEEE Guide for Improving the Lightning Performance of Electric
PowerOverhead Distribution Lines. Standard IEEE 1410-2004. Feb-
2004
[4] Benoid de Metz-Noblat. "Lightning and electric installations in AT".
Technical book No. 168, Technical library of Schneider Electric.
[5] Anderson, J.G. 1975. Electric Power Research Institute. Transmission
Lines Reference Book 345 kVand above. Chapter 12
[6] IEEE Guide for the Application of Metal-Oxide Surge Arresters for
Alternating-Current System IEEE. Standar C22.22-1997, Dec. 1997
[7] ABB. OVR 3-PHRecloser & PCD Control. Oct 2004
[8] UNICO and Ep Solutions. Control ofefect Backspin Pozos BCP Campo
Boscan- Chevron Texaco. Jun. 2005
[9] BAKER HUGHES CENTRILIFT. Power Outage Ride-Thru Project
Customer Witness Test. Report. Dec. 2005
[10] EATON Electric. VFS Ride-Thru and sag correction Prototype testing.
ReportNumber TQS6015.1. Oct. 2005
[11] Energy Control System. SineTamer. TVSS test Report. Oct. 2005
[12] Siegert, Luis. 1996.High Voltage and Translation system.. Noriega
Editors.
Aidor Jacop Martinez was born in Barquisimeto, Lara state, Venezuela. He
graduated as Electrical Engineer in "Instituto Universitario politecnico de
Barquisiemto" in 1990. Since he graduated he has been working in Oil &
Gas Industrial Companies, starter as project engineer with the national oil
company PDVSA and during the past four years he has been working for
CHEVRON as senior supervisor, He co-authored a paper on the results of the
study and presented in the IEE 2003 Industrial and Commercial Power
Systems Technical conference. Also published in the IEE Industry
Application Magazzine, Vol. 11. He wrote a paper related to reliability plan
for distribution system for CHEVRON.
X. BIOGRAPHIES
Frank Bustamante was born in Tovar, Merida,
Venezuela. He is graduated as Electrical Engineer in
"Universidad de Los Andes" in 1989. In 1998, He
obtained a Master Degree in Power System at
UNEXPO, Venezuela. From 1989 has been working
in Oil & Gas Industrial Companies as a
Maintenance and Advisor Engineer. He had written
some technical documents and papers related to
Surges and Lightning, and has participated in several
congresses, seminars and Forums as a presenter.
Actually he works for Baker Energy of Venezuela in Chevron, Campo Boscan
since 2005. E-mail: frankbusta@gmail.com
Juan Biternas was born in CARACAS,
Venezuela. He i-s graduated as Electrical Engineer
in "Universidad RAFEL URDANETA" in 1989.
In 1993, He has graduated as mechanical Eng at
EMP, Greece. From 1989 has been working in Oil,
Textile, petrochemicals & Gas Industrial
Companies as a Design, Construction,
Maintenance, and Advisor Engineer. He has
participated in several congresses, seminars and
Forums as a presenter. Actually he works for
Chevron, Campo Boscan since 2001.
Jesus Borjas was born in Cabimas, Zulia Venezuela.
He is graduated as Electrical Engineer in
"Universidad Rafael Urdaneta" in 1996. Since 1989
he has been working in the Oil Industry holding
positions of increasing responsibility in the planning,
design, installation, commissioning, maintenance,
automation and development of Electrical Power
Systems, Turbo machinery and High Voltage Motor
Controls systems, combined with a solid background
in the operation and maintenance of 230, 115, 34.5,
12.4 and 6.9 kV Power Sub-stations and Transmission and Distribution Power
Lines. Actually he works for Chevron since 2003
![2
caused by lightning; some of the 40% of failures are
temporary and caused by other reasons such as birds,
contamination, trees, etc., as shown in Fig. 2.
It can be observed in Fig. 5, that the 2005 has been the year
with highest lightning activity, with an average of 2.446
atmospheric events in the latest 5 years.
2004/2005 Failures_
mm
Lightning Birds
11 5 7 3
Vegetation thirds
6k17
Unkwnon
5 5
Contam
Fig. 2. Distribution network growth in Campo Boscan
Most of the failures are located on distribution lines (62%)
and about 33% are related to Load Immunity. (Fig. 3)
Fig. 3. Failures distribution
The biggest problem is induced sag, in either a single or
two phases faults which -a root causes are: Flash over from
lightning, Grounding failures, Birds strikes and very sensitive
load
C. Strategy to solve the problems
Fig. 4 shows the strategy of problem solving was focused
on the process analysis, regarding the source, distribution
lines and load.
520 km 24kV
Distribution Lines
DISTRIBUTION LOAD
Fig. 4. Solving strategy
After analyzing the different options, we arrived to the
conclusion that the definite actions to improve the reliability
of the Electric System in Campo Boscan are the following:
1) Distribution Lines. Related to lightning (poorlmissing
path grounding), bird strikes, insulator contamination (birds),
over voltage to low voltage equipment, singlephasefaults
2) Load. Related to load immunity
IV. ACTIONS RELATED TO LIGHTNING
As evidenced in the statistics, there is an intense
isokeraunic activity in the area of Campo Boscan. This
lightning activity is confirmed against the database available
on the NASA WEB which through the project satellites
Lightning Image Sensor (LIS) [1] it is possible to obtain, with
a high degree of reliability, the amount of lightning cloud-
cloud, cloud-earth within a specific geographical area.
Fig. 5. Statistics for atmospheric events in Campo Boscan during the 2004-
2005
Another source of information available is the statistics
kept by EDELCA Company [2], which reveals that the
lightning discharge density in the area of Campo Boscan
averages 8 lightning/km2/year.
A. GroundFlash Density
The Ground Flash Density (GFD) indicates the number of
lightning that fall on a specific area and it is expressed as
follows [3]:
Ng=0,04*TD 1,25
where TD are the storm days per year.
Ng=GFD=0,04*75 1,25 = 8,8 rays/km2/year
(1)
Also we can calculate the flashes to a Distribution lines by
the number of lightning towards a line is determined by means
ofthe following equation:
(2)N =
Ng28 1 ±b]
Iwhere h is the height of the overhead ground conductor and b
is the separation between the overhead ground conductors, in
this case is zero because we have only one overhead ground
conductor.
N = Ng L 28 h + b 8128
*
1 1.706±0+
= 10 10
=8,8*12,25= 108 rays/100 km/year
B. Lightning strikes on Distribution Lines
The lightning can affect a distribution line in two ways, as
a direct impact or induced flashover Fig. 6.
83100
80
60
40
20
0
4000.
203
10 V
S/E km 48
S/E Z-9
SOURCE
E.4r.](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)