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Proteccin ContraTormentas Elctricas en
el Centro EspacialKennedy
Pedro J. Medelius, Ph.D.
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Lightning Protection at Pad 39B
Lightning protection is primarily provided by the tall mast on top of the
FSS, the RSS, and the catenary wire running in a North/South direction
to ground points 1000 ft. away on each side of the mast
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Ground Flash Density
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Central Florida Is Lightning Alle
TampaTitusvil
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Lightning Initiation
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Lightning Initiation
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Lightning Initiation
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Lightning Initiation
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Lightning Initiation
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Considerations
The Kennedy Space Center is located in a region withsignificant lightning activity. The possibility of a lightningstrike at the surface or aloft is a hazard that must beavoided during launches and during ground activities.
Lightning activity at the Space Shuttle launch pads ismonitored in several ways. Local instrumentation andremote measurements provide an indication of lightningstrike locations and induced voltages or currents into
conductors.
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Lightning Locator
A network of magnetic direction finder antennas is used
to locate ground strikes in the KSC area. Individual
antennas provide an azimuth angle to a particular
lightning strike, and the location is determined by the
intersection of the azimuth lines from different antennas.The accuracy of the system is in the order of a few
hundred meters within the KSC area.
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LDAR
The Lightning Detection andRanging (LDAR) system has shownto be highly useful to the spacecraftlaunch community in reducing thehazards associated with lightningactivity, through a combination of
effective detection and displaytechnologies.
The system was designed to mapthe location of intracloud and cloud-to-ground lightning based on the
time of arrival of theelectromagnetic radiation. Thelocation system consists of 7 VHFradio receivers centered at 66MHz., and displays intracloudlightning activity in real-time.
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LDAR
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Cameras
A lightning strike location method currently in use at the
pads involves the use of a set of video cameras pointing
at different locations within the Pad. If a lightning strike
occurs within the field of view of three or more cameras,
the location of the strike can be determined. However, ifthe cameras are not pointing in the correct direction, or
their field of view is obscured by either the Pad structure
or by a heavy downpour, the determination of the striking
point becomes difficult, and in some cases impossible.There is often an uncertainty as far as the location of the
exact point of contact to the ground.
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SOLLO
The Sonic Lightning Location (SOLLO) system is basedon the use of both electric field and thundermeasurements, and can achieve 5-meter accuracy forlightning strikes within the pad perimeter. The SOLLO
System will enable the users to accurately determine theattachment point of a lightning strike. This will provideimportant information that can be used to determine ifany equipment and/or instrumentation
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L l C l ti Di t ib ti
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Lognormal Cumulative Distribution
Function of First Strokes Peak
Current
1st Stroke Median: 27.7kA, =0.461 [CIGRE, Uman 87]
0 10 20 30 40 50 60 70 80 90 1000
20
40
60
80
100
Current, kA
Percent
Lognormal Cumulative Distribution Function P(I > I0)
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Cone of Protection MethodNot applicable for tall structures
An angle of protection close to
39 would be required to
effectively protect the Space
Shuttle.
Although widely used in the past,the cone of protection approach is
not suitable for tall structures. A
tall structure is one whose height
is larger than the striking distance
of the lightning strike.
International Standards and the
NFPA code recommend the use of
the Rolling Sphere method for
determining areas at risk.
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Cone of Protection MethodNot applicable for tall structures
The use of the Cone of Protection approach was an accepted way of
protecting facilities against direct lightning strikes back through the
1970s. Further scientific studies have proven that the cone of
protection is not an effective way to provide protection for tall
structures, although it is still adequate for short structures whose
heights are less than the striking distance. The striking distance is thedistance between the tip of the lightning leader and the object being
struck.
Since the 1990s, the use of the Rolling Sphere method has been
recommended by international and U.S. standards as a preferred
method for designing lightning protection systems for tall and forcomplex structures.
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Cone of Protection MethodNot applicable for tall structures
The IEEE Standard 998-1996 recommends using a
protective angle of 40-45 degrees for heights up to 15
m, 30 degrees for heights between 15-25m, and less
than 20 degrees for heights up to 50 m.
It is important to realize that since the height of the
Space Shuttle and supporting structures (FSS, RSS,
lightning mast, catenary wires, etc.) is larger than 50
m, an alternate method such as the Rolling Spheremust be used to determine the regions where
lightning protection is lacking.
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Lightning Strike Frequency
This section describes two methods that can be used to estimate the
lightning strike frequency to a structure.
The calculations are based on the Equivalent Collection Method
described in the International Standard IEC 61024-1; and onErikssons equation, widely used for distribution and transmission
lines.
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Equivalent Collection AreaInternational Standard IEC 61024-1
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Lightning Strike FrequencyUsing the Equivalent Collection Area
H=347ft=105.8m
3H
Equivalent collection area Ae (as per IEC 61024-1):
222 316.03 kmHrAe
Lightning strike frequency Nd (as per IEC 61024-1):
116.31316.0102
21C
year
flashesCkm
yearkm
flashesCANN egd
Where Ng is the average flash density in the region where thestructure is located and C
1is the environmental coefficient
(equal to 1 for unshielded structures).
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Lightning Strike FrequencyUsing Erikssons Equation
Using the flash collection rate formula used for distributionand transmission lines (Erikssons equation):
yearkm
flashesbhNN g
10010
286.0
Where h is the height of the pole, b is the width of the line,and Ng is the flash ground density (flashes/km2/year).
Converting the the pad catenary system into an equivalenttransmission line (See figure on following page), and usingthe equivalent height and length we obtain:
year
f lashes
yearkm
flashesHN 85.1
10085.302
10
02/2810
6.0
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Lightning Strike FrequencyUsing Erikssons Equation
H
H/2
Equivalent Line
2000ft
Equivalent power line of the pad lightning protection system
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Rolling Sphere Method
The Rolling Sphere method is widely accepted by the scientific community,
and its use is recommended by International and National Standards:
NFPA 780
IEC 61024
IEEE Std 998-1996
Additional endorsement for the Rolling Sphere method will be included in
the IEC 62305 standard, soon to be released. IEC standards are based on
scientifically proven theories and technical experimentation worldwide
taking into account the international expertise in the matter.
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Rolling Sphere MethodUman and Rakov
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Rolling Sphere Method
Shaded area represents the protected region
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Rolling Sphere Method
Shaded area represents the protected region
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Rolling Sphere Method
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Rolling Sphere Method
The most accepted equation that relates dandI is:
d= 10 xI0.65 (1) [Golde, 1977; IEEE Std 998-1996]:
Where:
d = striking distance in meters
I = peak lightning current in kA
Rolling Sphere Method
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Rolling Sphere MethodStep length vs. peak lightning current (using
Eq. 1)Estimated Step Length (meters)
0.00
50.00
100.00
150.00
200.00
250.00
300.00
350.00
0 50 100 150 200 250
Peak lightning current (kA)
Step
length
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Rolling Sphere MethodNFPA 780
NFPA 780 code recommends using a sphere with a 46 m radius.
Where the sphere is tangent to earth and resting against a strike termination
device, all space in the vertical plane between the two points of contact and
under the sphere shall be considered to be in the zone of protection
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Rolling Sphere MethodInternational Standard IEC 61024-1
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Rolling Sphere MethodInternational Standard IEC 61024-1
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Rolling Sphere MethodInternational Standard IEC 61024-1
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Rolling Sphere MethodInternational Standard IEC 61024-1
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Rolling Sphere MethodInternational Standard IEC 61024-1
Monte Carlo Analysis
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Monte Carlo Analysis
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Monte Carlo Analysis
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References
Eriksson, A. J.: A Discussion on Lightning and Tall Structures. CSIR Special Report
ELEK 152, National Electrical Engineering Research Institute, Pretoria, South
Africa, July, 1978. See also, Lightning and Tall Structures. Trans. South Afr. Inst.
Electr. Eng., 69:2-16 (1978).
Golde, R. H.: The Lightning Conductor.InLightning, Vol. II, LightningProtection (R. H. Golde, ed.), pp. 545-576. Academic Press, New York, 1977.
Uman, M.A. and V.A. Rakov, A Critical Review of Nonconventional Approach to
Lightning Protection,Bulletin American Meteorological Society,pp 1809-1820,
December 2002.
Uman, M.A., The Lightning Discharge, Academic Press, Inc., 1987.
Working Group 01 (Lightning) of Study Committee 33 (Overvoltages and Insulation
Co-ordination), Guide to Procedures for Estimating the Lightning Performance of
Transmission Lines, CIGRE Brochure#63, Oct. 1991, Paris.
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Contact Information
Pedro J. Medelius
M/S ASRC-19
Kennedy Space Center, FL 32899
E-mail: [email protected]