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LIGHTNING PROTECTION
G/E Ardhra, JET1(BIOG-P)
Information Classification: Internal
CONTENT
• INTRODUCTION
• WHAT IS LIGHTNING…
• EFFECTS OF LIGTNING STROKE
• CONSIDERATION FOR PROTECTION
- Is lightning protection needed ?
- Zone of protection
• COMPONETS IN LIGTNING PROTECTION
• SYSTEM DESIGN
• AIR TERMINATION FOR DIFFERENT LEVELS
• CONCLUSION
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INTRODUCTION
Benjamin Franklin, an American scientist, conducted an
experiment with a kite and a conductor.
He flew the kite on a stormy day. The conductor hanging
on the kite detected the ambient charge in the
atmosphere.
Lightning is a giant spark of electricity in the atmosphere
between clouds, the air, or the ground.
So to protect buildings, aircraft, other structures and
most importantly people from Lightning lightning
protection system were introduced.
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WHAT IS LIGHTNING…
• Lightning is a natural phenomenon
• Electric charges travel from one point to the other within the clouds or between a cloud and the
earth.
• Lightning frequently happens as the weather cools and begins to rain.
• When the temperature drops, the water droplets that are held in the clouds begin to become ice
crystls.
• These rubs each other and charges are produced on clouds .
• The Earth's surface, on the other hand, behaves like a big positive-charged surface.
• Positive and negative charges (opposite charges) attract one another. This massive charge flow
generates heat and light.
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EFFECTS OF
LIGTNING STROKE
• Physical damage : Fire explosion,
mechanical explosion
• Injuries/ death to living beings
• High flow of current through the
resistance of earth electrode.
• Side flashing : point of strike on the
protective system raised to high
potential respect to adjacent metals.
• Thermal effect : Temperature rises of
the conductor as current passes
through it .
[It is negligible as high current
passes for a short time]
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CONSIDERATION FOR PROTECTION
• Mainly there are two types of consideration:
IS LIGHTNING PROTECTION
NEEDED ?
ZONE OF PROTECTION
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CONSIDERATION FOR PROTECTION
1. Is lightning protection needed ?
Factors for calculation :
 Length
 Width
 Height
 Flashes/km²/year (Ng)
 Weighting factor classified into:
A : USE OF STRUCTURE
B : TYPE OF CONSTRUCTION
C : CONTENTS
D : DEGREE OF ISOLATION
E : TYPE OF COUNTRY
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• Flashes/km²/year – mean value of thunderstorm
days/year
a) Collection area –
Ao= (L*W) + 2(L*H) + 2(W*H) + π*H²
b) Probability of being struck –
P = Ao*Ng*10^-6
c) Applying weighting factor = P*[A*B*C*D*E]
d) Overall risk factor is obtained.
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HOW to Know protection is required or not !
If the overall risk factor is :
less than 10^-6
greater than 10^-6
protection is not required
protection is required
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2. Zone of protection
Positioning of air termination inline with 3 methods :
PROTECTIVE
ANGLE
MESH
METHOD
ROLLING
SPHERE
METHOD
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1. PROTECTIVE ANGLE
• Depends upon severity of stroke.
CLASS OF LPS
PROTECTIVE ANGLE FOR 2M AIR
TERMINATION ROD
1
70
2
72
3
76
4
79
* LPS : Lightning Protection System.
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CONE SHAPE FOR SINGLE VERTICAL/HORIZONTAL AIR TERMINATION
• In general, the protective angle is considered;
∝ = 45 ̊ – single horizontal / vertical conductor
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TENT SHAPE FOR TWO OR MORE AIR
TERIMATIONS
 ∝ = 60 ̊ – between two or more
vertical conductors
 S = Min 2 m [ with max sag ]
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2. MESH METHOD
• Suitable for structures with flat surfaces.
• Also used for buildings with small slope.
• Conductors placed on the roof in the form of mesh.
CLASS OF LPS
MESH SIZE
1
5*5
2
10*10
3
15*15
4
20*20
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3. ROLLING SPHERE METHOD
• A sphere is rolled across the building.
• The edges which ever comes in contact with the
sphere needs the protection.
• We can determine the:
a) dimensions of the air termination
b) distance b/w air termination
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CLASS OF LPS
ROLLING SPHERE RADIUS
1
20m
2
30m
3
45m
4
60m
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COMPONETS IN LIGTNING PROTECTION
AIR TERMINATION : fixed points for likely
lightning strikes used to prevent the volume
to be protected from direct strikes.
DOWN CONDUCTORS : Conductor that
connects an air termination with an
earth termination.
EARTH TERMINATION : Disharges
lightning currents into general
mass of light.
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BOND : Provides electrical connection
between lightning protective
system and other metal works .
JOINTS : Mechanical or electrical
junction between two or more portions
of lightning protective system.
EARTH ELECTRODE : Part of earth
termination which makes direct contact
with earth.
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SYSTEM DESIGN
• Consultation should be taken before and during the design from :
a)
b)
c)
d)
e)
Architect
Public utilities
Fire/ safety officers
Television/ radio installers
Builders etc..
• Copper and aluminum are recommended for installations – For long life
• Galvanized steel of cross section as for copper – short term installations
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• AIR TERMINATION : They may contain vertical/ horizontal
conductor or combined of both.
MINIMUM DIMENSION OF COMPONENT PARTS
AREA
( mm²)
AIR TERMINATION
DIMENSIONS
(mm)
Aluminum, copper and
galvanized steel strip
20*3
60.00
Aluminum, aluminum
alloy or phosphor bronze
and galvanized steel rods
10.0 Dia
78.54
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• DOWN CONDUCTORS : Provides low impedence [path from air
termination to earth electrode.
MINIMUM DIMENSION FOR DOWN CONDUCTOR
MATERIAL
DOWN CONDUCTOR
( mm²)
Cu
16
Al
25
IMAGE
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AIR TERMINATION FOR DIFFERENT LEVELS
1. FLAT ROOF
2. FLAT ROOF AT DIFFERENT LEVEL
3. LARGE AREA OF ROOF OF VARIOUS PROFILES
4. TALL CONDUCTING STRUCTURES
5. STRUCTURE WITH HIGHLY EXPLOSIVE OR FLAMMABLE CONTENTS
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1. FLAT ROOF
• Horizontal conductors for
flat roof.
• Maximum spacing of 18m
– structures without
special inherent risk.
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2. FLAT ROOF AT DIFFERENT LEVEL
• Air termination along the outer
perimeter of the roof is required.
• No part should be more than 5m
from the nearest horizontal
conductor .
• A zone of protection of 60 ̊ is
provided by two adjacent
horizontal conductors for
structure less than 20m high
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3. LARGE AREA OF
ROOF OF VARIOUS
PROFILES
• If S > 10+2H , additional longitudinal
conductors are required; [ to not
exceed distance between conductors
more than 10 m].
• If the length of the roof exceeds 20 m
additional conductors are required.
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4. TALL CONDUCTING
STRUCTURES
• Horizontal conductors on roof
form 10m * 20m network.
• Bonds are there to steel work –
i.
at corners
ii. around periphery (20m interval)
iii. base of tower (0.5m above the
roof level)
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5. STRUCTURE WITH HIGHLY EXPLOSIVE OR
FLAMMABLE CONTENTS
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a) Air termination with
suspended horizontal
conductors
• If one horizontal conductor –
protective angle is 30 ̊
• If two or more parallel conductors
– protective angle is 45 ̊
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• Air termination should be
suspended at an adequate
height above the area to be
protected.
• Minimum clearance distance of
2m under maximum sag should
be maintained between
conductor and building.
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b) Air termination with horizontal conductors
• The horizontal conductor
mesh size should be
5m*10m or smaller.
• Each separate structure
protected in alternative
way should be equipped
with twice no of down
conductors.
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Conclusion
LIGHTNING PROTECTION SYSTEMS play a
crucial role in safeguarding buildings ,
structures, and their occupants from the
destructive forces of lightning strikes.
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