2. What is Lightning?
Lightning is a natural electrical discharge that occurs within a
thunderstorm. It happens due to the buildup of electrical charges within
the storm clouds and between the clouds and the ground.
Typical Cloud to Ground
Lightning between ground
and negative charges
Inter-cloud Strike
(cloud to cloud)
Discharge within cloud
between negative base and
positive top (intra-cloud)
Typical Cloud to Ground
Lightning between ground
and negative charges
3. How Lightning Occurs?
Charge Separation:
Inside a thunderstorm, water droplets, ice crystals, and other particles collide
and interact, causing the different materials to gain or lose electrons. This
results in the separation of positive and negative charges within the cloud.
Electric Fields:
As the charges separate, an electric field forms between the positively and
negatively charged regions within the cloud. This electric field intensifies as
more charge separation occurs.
Breakdown and Ionization:
When the electric field becomes strong enough, it can ionize the air molecules
along its path. This means that it strips electrons from some of the atoms,
creating a conductive path through the air.
5. Lightning Discharge:
Once the ionized path, known as a stepped leader, extends from the cloud
toward the ground, it creates a channel of ionized air. Simultaneously, a
positively charged region on the ground, called a streamer, reaches upward.
When these two paths meet, a highly conductive channel is established, and a
lightning bolt travels along this channel. This current flow is termed the return
stroke and may carry currents as high as 200 kA, although the average current is
about 20 kA.
Lightning Bolt:
The actual lightning bolt consists of a rapid series of electrical discharges that
travel along the ionized path, creating a visible flash of light and releasing a
tremendous amount of energy. The movement of the electrons generates
intense heat and causes the air to expand rapidly, creating the characteristic
thunderclap.
How Lightning Occurs?
(Cont.)
6. Return Stroke:
The primary, initial discharge of the lightning bolt is called the "return stroke." It
travels from the ground to the cloud and is what we see as a lightning flash.
This return stroke happens extremely quickly, typically in a fraction of a second.
Aftereffects:
After the initial return stroke, subsequent strokes can follow the same path,
creating a flickering effect that we perceive as lightning. The process can repeat
multiple times along the same channel, creating a jagged appearance.
How Lightning Occurs?
(Cont.)
7. Necessity of a Lightning Protection System
The purpose of a lightning protection
system is to protect all living beings,
buildings and structures from lightning
strikes and possible fire, or from the
consequences of the load independent
active lightning current.
8. • The science of lightning protection is best attributed to Benjamin Franklin.
• The first mention of the traditional lightning rod was published by Benjamin
Franklin in 1750 in Gentleman’s Magazine and then later in his treatises on the
subject published in 1751.
• In this he recommends the use of lightning rods to “Secure houses, etc, from
lightning”
Introduction to Protection Methods and Risks
9. Damage
Damage to structure
•Including all incoming electrical overhead
and buried lines connected to the
structure
Damage to a service
Service in this instance being part of
telecommunication, data, power, water,
gas and fuel distribution networks.
Damages:
• Sources of damage (S)
• Types of damage (D)
Damage due to Lightning
10. Sources of Damage
S1 – Lightning flash to the
structure
S2 – Lightning flash near
the structure
S3 – Lightning flash to the
services
S4 – Lightning flash near
to the services
11. Types of Loss
L1 – Loss of human life.
L2 – Loss of essential service to the public.
L3 – Loss of cultural heritage.
L4 – Economic loss (structure and its contents, service and loss of
activity).
12. Types of Damage
D1 – Injury of living beings (humans and animals) due to touch
and step potential.
D2 – Physical damage (fire, explosion, mechanical destruction,
chemical release).
D3 – Failure of internal electrical/electronic systems due to
lightning electromagnetic impulse.
13. The relationship between source of damage, type
of damage and loss
Point of Strike Source of damage Type of Damage Type of Loss
Structure S1
D1
D2
D3
L1,L4a,L1
L2,L3,L4
L1b,L2,L4
Near a structure S2 D3 L1b,L2,l4
Line connected to
the structure
S3
D1
D2
D3
L1,L4a,L1
L2,L3,L4
L1b,L2,L4
Near a Line S4 D3 L1b,L2,l4
14. Types of Risks Associated with Losses
Risk R: is the value of probable average annual loss (humans or goods) due to lightning,
relative to the total value (humans or goods) of the structure to be protected.
15. Requirements for lightning protection
• The need for the lightning protection of a structure to be protected in order to reduce
the loss of social values L1, L2 and L3 shall be evaluated.
• In order to evaluate whether or not lightning protection of a structure is needed, a risk
assessment in accordance with the procedures contained in IEC 62305 shall be made.
The following risks shall be taken into account, corresponding to the types of loss.
• R1: risk of loss or permanent injury of human life
• R2: risk of loss of services to the public
• R3: risk of loss of cultural heritage
• Protection against lightning is needed if the risk R (R1 to R3) is higher than the
tolerable level RT
R > RT
• Risk R4: risk of loss of economic values, should be assessed whenever the economic
justification of lightning protection is considered
16. International Standard
The IEC 62305 standard covers the regulations required for the protection of equipment
and structures from the effects of both direct and indirect lightning strikes
Protection against
lightning
IEC 62305
Part 1
General principles
Part 2
Risk management
Part 3
Physical damage
to structures and
the hazard
Part 4
Electrical and
electronic systems
within structures
17. Connection between the parts of IEC 62305
SPM - System Protection Measures
LPS - Lightning Protection System
18. Protection measures
• Protection is achieved by the lightning protection system (LPS) which includes the following features:
• Air-termination system
• Down-conductor system
• Earth-termination system
• Lightning equipotential bonding (EB)
• Electrical insulation (and hence separation distance) against the external LPS
• Possible System protection measures (SPM) to reduce failure of electrical and electronic systems include
• Earthing and bonding measures
• Magnetic shielding
• Line routing
• Isolating interfaces
• Coordinated SPD system
• These measures may be used alone or in combination.
19. Protection measures selection
• Selection of the most suitable protection measures shall be made by the designer of the
protection measures and the owner of the structure to be protected according to the
type and the amount of each kind of damage, the technical and economic aspects of
the different protection measures and the results of risk assessment.
• The criteria for risk assessment and for selection of the most suitable protection
measures are given in IEC 62305-2.
• Protection measures, adopted to reduce damages and relevant consequential loss, shall
be designed for the defined set of lightning current parameters against which
protection is required (lightning protection level)
20. Lightning protection levels (LPL)
• For the purposes of IEC 62305, four lightning protection levels (I to IV)
are introduced.
• For each LPL, a set of maximum and minimum lightning current
parameters is fixed
22. Lightning protection zones (LPZ)
• Lightning protection zone LPZ are used to define the lightning
electromagnetic environment. The zone boundaries of an LPZ are not
necessarily physical boundaries (e.g. walls, floor and ceiling). The zones
are areas characterized according to threat of direct or indirect lightning
flashes and full or partial electromagnetic field. Protection measures
such as LPS, shielding wires, magnetic shields and SPD determine
lightning protection zones (LPZ).
24. Lightning protection zones (LPZ)
With respect to the threat of lightning, the following LPZs are defined
• LPZ 0A zone where the threat is due to the direct lightning flash and the full lightning
electromagnetic field. The internal systems may be subjected to full or partial lightning
surge current;
• LPZ 0B zone protected against direct lightning flashes but where the threat is the full
lightning electromagnetic field. The internal systems may be subjected to partial
lightning surge currents;
• LPZ 1 zone where the surge current is limited by current sharing and by isolating
interfaces and/or SPDs at the boundary. Spatial shielding may attenuate the lightning
electromagnetic field;
• LPZ 2, ..., n zone where the surge current may be further limited by current sharing
and by isolating interfaces and/or additional SPDs at the boundary. Additional spatial
shielding may be used to further attenuate the lightning electromagnetic field.
25. Protection of structures
The structure to be protected shall be inside an LPZ 0B or higher. This is achieved by
means of a lightning protection system (LPS).
An LPS consists of both external and internal lightning protection systems.
The functions of the external LPS are
• Air termination system - to intercept a lightning flash to the structure
• Down conductor system - to conduct the lightning current safely to earth
• Earth termination system - to disperse it into the earth
26. External LPS Design Considerations
Air Termination Network
Down Conductors
Earth Termination
27. Air Termination System
The three basic methods recommended for determining the
position of the air termination systems:
1. The rolling sphere method
2. The protective angle method
3. The mesh method
28. Rolling Sphere Method
• The Rolling Sphere method is a
simple means of identifying areas
that need protection, taking into
account the possibility of side
strikes to the structures.
• Different radii of the rolling sphere
correspond to relevant class of LPS.
29. Rolling Sphere Method
• The distance of the last step is striking
distance and determine by the
amplitude of the lightning current.
• This striking distance can be represent
by a sphere with a radius equal to the
striking distance.
(Cont.)
30. Application of Rolling Sphere Method
• It can be clearly seen that the corners
are exposed to a quarter of the circular
path of the sphere.
• This means that if the last step falls
within this part of the circular path it
will terminate on the corner of the
building.
• Corners of structures are vulnerable to
lightning strikes.
31. Protective angle method
• Protective angle method is a
mathematical simplification of
rolling sphere method.
• Only for simple shaped buildings.
32. Protective angle method
• Protective angle – Angle created
between the tip (A) of the vertical
rod and a line projected down to the
surface on which the rod sits.
38. Mesh Method
• A “meshed” air-termination system can be
used universally regardless of the height of
the structure and shape of the roof.
• This method is suitable where plain surfaces
require protection if the following conditions
are met:
• Air termination conductors must be
positioned at roof edges, on roof overhangs
and on the ridges of roofs with a pitch in
excess of 1 in 10 (5.7º)
• No metal installation protrudes above the
air termination system
40. Air Termination System (Summary)
• Air rods (or finials)
• Free standing masts or linked with conductors to
form a mesh on the roof.
• Catenary (or suspended) conductors,
• Supported by free standing masts or linked with
conductors to form a mesh on the roof.
• Meshed conductor network
• Lie in direct contact with the roof or be
suspended above it (in the event that it is of
paramount importance that the roof is not
exposed to a direct lightning discharge).
Example for air
rods (Finials)
Example for Catenary
air termination
Example for mesh
air termination
41. Types of External LPS
Non isolated Isolated
Air terminations
Meshed conductors
Only practical for specific
circumstances
Catenary Wires
S- Separation distance
requirement
44. Down Conductor System
• The lightning current is shared between the down
conductors
• The greater the number of down conductors, the
lesser the current that flows down each
• Typical values of the distance between down
conductors
45. Down Conductor Installation
• The down-conductors shall be installed so that, as far
as practicable, they form a direct continuation of the
air-termination conductors.
• Test links use to separate down conductors from earth
termination
• Down-conductors shall be installed straight and
vertical such that they provide the shortest and most
direct path to earth. The formation of loops shall be
avoided, but where this is not possible, the distance s,
measured across the gap between two points on the
conductor and the length, l, of the conductor between
those points shall comply Electrical insulation between
the air-termination or the down-conductor and the
structural metal parts
46. Down Conductor Installation
• It is encouraged to use of fortuitous metal parts on or
within the structure, to be incorporated into the LPS
• If the reinforcing bars are connected for equipotential
bonding or EMC purposes then wire lashing is deemed to
be suitable.
• Internal reinforcing bars are required to be connected
to external down conductors or earthing network
• If the reinforcing bars (or structural steel frames) are
to be used as down conductors then electrical
continuity should be ascertained from the air
termination system to the earthing system.
(Cont.)
48. Earth Termination System
• Effective Earthing System
• Providing a low impedance network to dissipate the fast-rising
lightning impulse
• Minimization of touch and step potential hazards
• Below 10 ohms
• Three basic earth electrode arrangements are used.
• Type A arrangement
• Type B arrangement
• Foundation earth
49. Type A arrangement
• Horizontal or vertical earth
electrodes, connected to each down
conductor fixed on the outside of the
structure.
• Each down conductor has an earth
electrode (rod) connected to it.
50. Type B arrangement
• Fully connected ring earth electrode
that is sited around the periphery of
the structure.
52. Earthing Connection
• The connection of the earthing
conductor to the earth electrode
must be suitably protected from
corrosion by applying grease or
paint.
• Material of earth electrode need
to be good corrosion resistance.
53. Internal LPS
• The function of the internal LPS
is to prevent dangerous sparking
within the structure, using
Equipotential Bonding or a
separation distance, s, (and
hence electrical isolation)
between the LPS components
and other electrically conducting
elements internal to the
structure.
54. Recommended Materials For Earth Termination
Material Configuration
Dimensions
Earth rod diameter mm Earth conductor mm 2 Earth plate mm
Copper/Tin plated copper
Stranded 50
Solid round 15 50
Solid tape 50
Pipe 20
Solid plate 500 X 500
Lattice plate 600 X 600
Hot dipped galvanized steel
Solid round 14 78
Pipe 25
Solid tape 90
Solid plate 500 X 500
Lattice plate 600 X 600
Profile d
Bare steel
Stranded 70
Solid round 78
Solid tape 75
Copper coated steel
Solid round 14 50
Solid tape 90
Stainless steel
Solid round 15 78
Solid tape 100
55. Lightning Protection System Components
Air Finial with Base
Copper Mesh
(2.5mm x 25mm)
Test Joint
Square Clamp
DC Clamp / Saddle
Earth rod
Earth plate
56. Substation Lightning Protection
• Lightning protection should be carried for open terminal substations to prevent the
followings:
• Damage to Substation Equipment
• Loss of Power to Public
• Equipment in a substation may be exposed to lightning in two ways.
• By voltage and current waves travelling along the exposed lines leading to the station.
• By direct lightning strokes to the station.
• Outdoor substations and switchyards are shielded against direct lightning strokes by:
• Earth Wires (Shield Wires)
• Masts
• Earth wires and Masts
