DISTRIBUTION AND INDUSTRIAL NETWORKS
LIGHTING PROTECTION
Sebastian Szyluk
Table of contests
1.
Introduction ..................................................................................................................................... 4
2.
Basic characteristic of lighting ......................................................................................................... 4
3.
4
2.1
Atmospheric discharges .......................................................................................................... 4
2.2
Thunderstorm.......................................................................................................................... 4
2.3
Lighting strikes ......................................................................................................................... 6
2.4
Why we see the lightning? ...................................................................................................... 7
2.4
Thunder ................................................................................................................................... 8
2.5
Types of Lighting...................................................................................................................... 8
The consequences of lighting ........................................................................................................ 10
3.1
IEC BS EN 62305 – Standard .................................................................................................. 10
3.2
Lighting Protection Levels (LPL) ............................................................................................. 11
3.3
Impact on people and building .............................................................................................. 11
3.4
Lighting Protection Zones (LPZ) ............................................................................................. 13
3.5
Risk management .................................................................................................................. 14
3.6
Risk assessment ..................................................................................................................... 16
How to protect distribution system from lighting......................................................................... 17
4.1
Lighting Protection System ................................................................................................... 17
4.2
External Lighting protection system ...................................................................................... 18
4.2.1
Air Termination System ................................................................................................. 18
4.2.2
Down Conductor System ............................................................................................... 19
4.2.3
Earth Termination System ............................................................................................. 21
4.3
Internal lighting protection system ...................................................................................... 23
4.3.1
Lightning equipotential bonding ................................................................................... 23
4.3.2 Surge Protection Device ........................................................................................................... 24
4.3
5
Lighting Arrester .................................................................................................................... 25
How to plan lighting protection .................................................................................................... 26
5.2
Design of external lighting protection ................................................................................... 26
5.2.1
Air Termination System - The Roling sphere method ....................................................... 26
5.2.2
Air Termination System - The Protective Angle method ................................................... 28
5.2.3
The Mesh Method ............................................................................................................. 29
5.3
Separation Distance for lighting protection system .............................................................. 30
5.4
Design of internal lighting protection ................................................................................... 31
5.3.1
Equipotential Bonding ................................................................................................... 32
5.3.2
5.5
Surge Protection Device .................................................................................................... 32
Lighting Protection of Power Lines........................................................................................ 33
5.5.1
Lightin Protection in MV Power Lines ........................................................................... 33
5.4.2 Lighting Protection in HV Power Lines ..................................................................................... 34
5.6
Lighting Protection of Transformers ..................................................................................... 35
Questions............................................................................................................................................... 36
Homework ............................................................................................................................................. 39
Bibliography........................................................................................................................................... 41
1. Introduction
Lightning is fascinating and amazing phenomenon. Greeks, Romans and Germans saw
it as a whim of Zeus, Jupiter or Donar (Thor). In 1752 the American statesman and inventor Benjamin Franklin - proved in a dangerous experiment with a kite that lightning is an
electrical discharge.
Every student in Engineering has to be aware of lighting system protection.
Lightning strikes or surges in the electrical system can cause considerable damage - the
damage to electronic devices to the fire house. To prevent this, we can create lightning
protection system to protect against harmful effects of lightning.
2. Basic characteristic of lighting
2.1 Atmospheric discharges
Atmospheric discharges produce disturbances of atmospheric circulation that appear
depending on the time of year and location on the globe, with more or less frequency. The
huge size of storm clouds is caused by rapid condensation accumulated in steam. In these
clouds collide currents of warm and cold air, which are a sign of gusty winds, heavy rain,
thunder, lightning and even hail. In the old days, while scientists and observers have not
discovered the mechanisms of formation of storms and lightning, people saw it as
supernatural. Today we know that lightning its grandeur and often destructive forces, but also
a source of great energy. If we learn to capture it and use, it will be huge discovery and bring
immeasurable energy benefits.
2.2 Thunderstorm
Across the globe, at any time there are 44 thousand storms, and in addition, there are
relationships between them, which mean that if one storm fades , the next is born in a distance
of 1500 km. The same phenomenon lasts from a few minutes to approx. 2.5 hours, and often
arises over land than over water. Storm can be anticipate by fast create of huge black storm
clouds, gusty, chilly and damp wind.
Thunderstorm Cycle:

Cumulus stage – The sun heats the Earth's surface during the day. Since warm air is
lighter than cool air, it starts to rise (updraft). If the air is moist, then the warm air
condenses into a cumulus cloud.

Mature stage – When the cumulus cloud becomes very large, the water in it becomes
large and heavy. Raindrops start to fall through the cloud when the rising air can no
longer hold them up. Meanwhile, cool dry air starts to enter the cloud. Because cool
air is heavier than warm air, it starts to descend in the cloud (downdraft). The
downdraft pulls the heavy water downward, making rain.

Dissipating stage - After about 30 minutes, the thunderstorm begins to dissipate. This
occurs when the downdrafts in the cloud begins to dominate over the updraft. Since
warm moist air can no longer rise, cloud droplets can no longer form. The storm dies
out with light rain as the cloud disappears from bottom to top.
Figure 1. Storm Cycle
Storms generally lead to negative impacts on lives and property such as storm surge,
heavy rain or snow (causing flooding or road impassibility), lightning, wildfires, and vertical
wind shear.
2.3 Lighting strikes
Storm clouds bring a huge amount of electric charge. These charges are fragmented and
divided into group of positive and negative charges. Positive charges are accumulated mostly
in the upper layers of clouds, and negative in the lower parts. In this way, its create a voltage
electric field between both fragments of clouds, and the clouds and the surface of the Earth.
Tensions inside the clouds are unloaded by sparks - called lightning flat, while between the
clouds and the Earth in the form of lightning. Inevitably accompanied by the roar and crackle
we called thunder.
The stages of the formation of lightning:

Negative charges accumulated at the bottom of the clouds are have the positive
charges, which induce a buildup of positive charge on the Earth’s surface directly
below;

Negative charges move from the bottom of the cloud to the ground, ionizing the air
and forming “step leader” or invisible conductive paths.

In the same time, streamers of positive charge move upward from the ground toward
the cloud

When a “step leader “ connects to a streamer, negative charges pour down, visible to
as a lighting bolt

Repeated strikes occur until the negative charge is drained from the cloud.
Figure 2. This drawing shows the position of positively and negatively charged particles
(ions) before, during and after the lightning strike occurs. Notice that there are charged
particles in the cloud and on the Earth.
2.4
Why we see the lightning?
Lightning are colorless, but we can see them. This is possible because lighting heats
the air, and like other substances heated to a temperature exceeding 800 C emit red light,
which further temperature rise goes into white color. The temperature of lightning sometimes
can be even exceeds 25 000 K - four times more than the temperature on the surface of the
sun. Others properties of the lighting are:

the average length is approx. 1 km, but the lightning was seeing with a length of more
than 20km;

the voltage difference between the clouds and the ground can even exceed the value of
millions of volts (approximately several hundred million) - it depends also on the
impurities, the temperature and air pressure, as well as rainfall;

Lightning power ranges from 1000 to 2000 kWh;

every day in every 1s in the ground 100 lightning strikes;

the number of storms during the year largely depends on the location of the region on
the globe, for example in Poland approx. 36 and in California only about 8 days.
2.4 Thunder
The temperature inside the lightning is typically approx. 4 - 5 times higher than the
temperature of the sun. This causes a rapid heating of the air along the lightning bolt. When
the air temperature rises, the air expands its volume, and wanting to re-align the pressure
spreads out in all directions with supersonic speed. It produces vibrations, which we perceive
as thunder (rumbling). When lightning strikes relatively close to us, thunder is like the sound
of the explosion, but from a distance propagates is in the form of characteristic sound.
The light is greater than the velocity of sound, it allows us to determine our distance from the
lightning strike. This distance expressed in kilometers we get by dividing the number of
seconds elapsing between the flash and the thunder by 3.
2.5 Types of Lighting

Cloud-to-Ground Lightning – Negative - A lightning discharge between cloud and
ground initiated by a downward-moving, negatively-charged stepped leader;

Cloud-to-Ground Lightning – Positive - A lightning discharge between cloud and
ground initiated by a downward-moving, positively-charged leader;

Ground-to-Cloud Lightning - Ground-to-Cloud lightning (sometimes called Upwardmoving lightning) is a discharge between cloud and ground initiated by an upwardmoving leader originating from an object on the ground;

Intracloud Lightning - The most common type of discharge - lightning inside a single
storm cloud, jumping between different charge regions in the cloud;

Anvil Crawlers - Anvil Crawlers are horizontal, tree-like, in-cloud lightning
discharges whos leader propagation is resolvable to the human eye;

Bolt from the Blue - A bolt from the blue (sometimes called 'anvil lightning' or 'anvilto- ground' lightning) is a name given to a cloud-to-ground lightning discharge that
strikes far away from its parent thunderstorm;

Cloud-to-Air Lightning - Referring to a discharge (or a portion of a discharge)
jumping from a cloud into clear air;

Bead Lightning - Bead Lightning is a name given to the decaying stage of a lightning
channel in which the luminosity of the channel breaks up into segments

Ribbon Lightning - Ribbon Lightning refers to the visual appearance of a
photographed lightning flash's individual return strokes being
separated by visible gaps on the final exposure;

Sheet Lightning - Sheet Lightning is a term used to describe clouds illuminated by a
lightning discharge where the actual lightning channel is either inside the clouds or
below the horizon (not visible to the observer) .
Figure 3. Four Types of Lighting Strike. 1 – Negative Ground to Ground Lighting, 2 -Cloudto-Ground Lightning – Positive, 3 - Bead Lighting, 4 - Anvil Crawles
3. The consequences of lighting
3.1
IEC BS EN 62305 – Standard
Standard IEC BS EN 62305 classifies the sources and types of damage to be evaluated
and introduces the risks or types of loss to be anticipated as a result of lighting activity. The
standard present the relationship between damage and loss. The parameters describes by:
Main Source damage :

S1 – Flashes to the structure;

S2 - Flashes near to structure;

S3 – Flashes to the lines connected to the structure;

S4 – Flashes near the lines connected to the structure.
Each source damage may result in one or more three types of damage:

D1 – Injury of living beings by electric shock

D2 – Physical damage ( fire, explosion, mechanical destruction, chemical release) due
to lighting current effect including sparking;

D3 – Failure of internal system due to Lighting Electromagnetic Impulse (LEMP).
The following types of loss may result from damage due to lighting:

L1 – Loss of human life (including permanent injury);

L2 – Loss of service to the public;

L3 – Loss of cultural heritage;

L4 – Loss of economic value
Figure 4. Damage and loss in a structure according to point of lighting strike *Only for
structure with risk of explosion and for hospitals or other structures where failures of internal
systems immediately endangers life; **Only for properties where animals may be lost
3.2
Lighting Protection Levels (LPL)
Lighting Protection levels determined four protection levels. Each level has a
minimum and maximum lighting current parameters. Te maximum values have been used to
design products like a lighting protection components and Surge Protection Devices. The
minimum values have been used to derive rolling sphere radius for each level.
Figure 5. Lighting current for each LPL based on 10/350 µs wave form
3.3
Impact on people and building
A lightning strike can result in a cardiac arrest (heart stopping) at the time of the
injury, although some victims may appear to have a delayed death a few days later if they are
resuscitated but have suffered irreversible brain damage.
How lightning causes injury:

Direct strike - occurs when the person is outside holding or wearing a metal object;

Flash discharge - can occur from being in close contact to the lightning current as it
strucks or something else. This can happen if a person is standing under a tree that is
struck by lightning;

Ground current - when lightning strikes a tree or other object, much of the energy
travels outward from the strike in and along the ground surface;

Conductions - Lightning can travel long distances in wires or other metal surfaces.
Metal does not attract lightning, but it provides a path for the lightning to follow.
Figure 6. The types of damage and loss resulting from a lighting strike on or near structure
A lightning bolt's main objective is to find the path of least resistance from the cloud
to deep into the ground. Most houses are filled with many potential routes for lightning to
follow in.
One of the most dramatic effects of the lightning strike is fire - usually by direct
discharge in the building. Lighting is a powerful electrical discharge, because it is dangerous
not only its immediate impact, as well as those that took place at a distance, even a 1.5 km
away. This applies both to discharge towards the ground and between the clouds. They
created the so-called surge waves, which move at a speed close to the speed of light. Before
you hear thunder, devices connected to the network can be destroyed.
We can divide the damage to three groups: fire, power surge and shock wave damage
When the electrical system in the house and within it the device does not have adequate
safeguards against surges may occur:

Damage to the insulation of cables in the electrical installation;

Damage to the motors, coils, transformers in electrical equipment (due to insulation
breakdown);

Destruction
of
the
electronics:
televisions,
computers,
telephones,
heating
programmers, as well as household appliances;

3.4
Destruction systems, fire alarms, burglar and signaling devices.
Lighting Protection Zones (LPZ)
Lighting Protection Zones was introduced to assist in determining the protection
measures required to establish protection measures to counter Lighting Electromagnetic
Impulse (LEMP) within a structure. LPZ determine three LPZ level where 2 and 3 are for the
lower electromagnetic effects expected and 0 for the higher. Any sensitive device should be
placed in higher number LPZs and be protected by relevant Surge Protection Measures.
Figure 7. The LPZ Concept
3.5
Risk management
Risk management is a procedure for the evaluation of risk. Once an upper tolerable limit for
the risk has been selected, this procedure allows the selection of appropriate protection measures to be
adopted to reduce the risk to or below the tolerable limit. The first step is to identify which of the four
types of loss the structure and its contents can incur. The Risk management are describe by losses and
have to be quantify and if necessary reduce:

R1 – risk of loss of human life;

R2 – risk of loss of service to the public;

R3 - risk of loss of cultural heritage;

R4 – risk of loss of economic value.
For each of the first three primary risks, a tolerable risk (RT) is set. Each primary risk (Rn) is
determined through a long series of calculations as defined within the standard. If the actual risk (R n)
is less than or equal to the tolerable risk (RT), then no protection measures are needed. If the actual risk
(Rn) is greater than its corresponding tolerable risk (RT), then protection measures must be instigated.
The above process is repeated (using new values that relate to the chosen protection measures) until Rn
is less than or equal to its corresponding RT. It is this iterative process as shown in figure 3 that
decides the choice or indeed Lightning Protection Level (LPL) of Lightning Protection System (LPS)
and Lightning Electro-magnetic Impulse (LEMP) Protection Measures System (LPMS)
Figure 8. Procedure for deciding the need for protection
3.6
Risk assessment
Lightning Risk assessment Study is actually the measure of risk of a lightning strike
and probability of damages. It assesses the lightening risks to the facility according to
international standards requirements. Risk assessment follow the Standard IEC BS EN 62305.
To determine the need for protection against lightning for a given building or structure, the
following variables are to be considered:
1. Lightning Flash Density – Ng It is the measure of lightning strikes per kilometer
square per year in the particular area. Higher the lighting strike density, higher the
probability of lightning strike which needs higher level of lightning protection level. If
we have a number of storm days in year Td we can calculate Ng
Ng = 0,04 * Td1,25
2. Structures Collective Area - For a rectangular shape :
Ae = LW + 6H(L+W)+π9H2
For structure where a prominent part encompasses all portions of the lower part of the
structure:
Ae = π9H2;
Where: L – lenght, W – width, H – height of the building
3. Relative Structure Location C1 - It is the risk reduction factor with respect to the
location and surrounding of the building / installation. For example, chance of lighting
strike is minimized if the building is near to a high tower.
4. Type of Construction C2 - type of construction is divided into roof and structure and
the material nonflammable, common, flammable
5. Structure Contents C3 - The structure contents range from low value, nonflammable
contents to those of exceptional value, irreplaceable items.
6. Occupancy C4 - The occupancy of the structure is the third parameter that is
determined. The definition of structure occupancies are: unoccupied; normally
occupied; or difficult to evacuate . Loss due to lighting strike is higher in hospital as
compared to a store warehouse
7. Lightning Consequence C5 - The definitions are: continuity of service is not required,
no environmental impact; the continuity of service is required, no environmental
impact; or the there are consequences to the environment.
Expended Lightning Frequency Nd = Ng * Ae *C1 *10-6
Accepted Lightning Frequency NC =
If Nd ≤ NC – optional protection
If Nd > NC - protection required
The effectiveness of lightning protection systems
E≥ 1 - NC/ Nd
4 How to protect distribution system from lighting
4.1
Lighting Protection System
To protect our device in house we have to design Lighting protection system. It is a
system to protect a structure or building and contents from damage caused by the intensely
high voltage currents of a lightning strike. A lightning protection system offers a lightning
strike a low resistance path to ground where the enormous energy is then safely dispersed.
Standard IEC/BS EN 62305 has defined four Lighting Protection Levels based on
probable maximum and minimum lighting currents. Lighting Protection Level (LPL) is equate
classes of Lighting Protection System (LPS) and is showed below. The greater level of LPL
need greater level of LPS.
Figure 9. Relation between Lighting Protection Level and Lighting Protection System
4.2
External Lighting protection system
The function of an external lightning protection system is to protect buildings from
direct lightning strikes, potential fire as well as the effects of injected lightning currents (nonincentive flash). Depending on the consequence the designer have to choose either of the
isolated or non-isolated types of external LPS. External LPS is chosen when the structure is
constructed of combustible materials or presents a risk of explosion.
LPS has a three
individual elements which should be connected together using appropriate lighting protection
components (LPC).
An external Lighting protection system consists of :

Air Termination System;

Down Conductor system;

Earth Termination System.
4.2.1
Air Termination System
Air Termination system is a metal elements arranged in the highest points of the roof,
which are the first point of the lightning protection. Their task is to take the impact energy and
transfer it to the next element of the installation.
Standard IEC/BS EN 62305 describe three elements, in any combination for the
design of the air termination:

Air rods (or finals) - 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 conductors networks – may lie in direct contact with the roof or be suspended
above it.
Standard describe this elements very clear. All elements have to meet the positing
requirements laid down in the body of the standard. Should be installed on corners, exposed
points and edges of the structures. The three methods recommended for installing the air
termination systems :

The rolling sphere method;

The protective angle method;

The mesh method.
When metallic roofs are constructed by natural air termination arrangement we have to
follow standard where is a guidance about minimum thickness and type of material. Standard
gave also additional information if the roof has to be considered puncture proof from a
lightning discharge.
Figure 10. Minimum thickness of metal sheets or metal pipes in air termination system. (1) –
prevent puncture, hot spot or ignition problems. (2) – only for metal sheets if it is not
important to prevent puncture, hot spot or ignition problem.
4.2.2
Down Conductor System
The purpose of the down conductor is to provide the low impedance path from the air
termination system to the earth system. The greater the number of down conductors the better
the lighting current is shared between them. They should be routed as directly as possible
from the air termination network to the earth termination network to avoid risks of side
flashing. Conductors System should always have a minimum of two down conductors
distributed around the perimeter of the structure. Each exposed corner should have a down
conductors because can carry the major part of the lighting current.
Figure 11. Typical values of the distance between down conductors according to the
class of LPS
Down Conductor should use a fortuitous metal parts on or within the structure to be
incorporated into the LPS. The standard allows to use of natural conductors such as rebars
and structural steelwork, provided that they are electrically continuous and adequately
earthed. The Natural components can be used provided there is electrical continuity, where
the joints are tightly bolted they can be considered as electrically continuous
Figure 12. Down Conductor
4.2.3 Earth Termination System
The earth-termination system is the next point of the air-termination systems and
down conductors installed on top of or on a building. In each building with lightning
protection system must be mounted at least two such conductors located in the corners of the
roof diagonal line. Its functions are discharge of lightning current to earth, equipotential
bonding between the down conductors and potential control. Each down conductor must have
a separate earth termination. A good earth connection should posses the following
characteristics:

Low electrical resistance between the electrode and the earth. The lower the earth
electrode resistance the more likely the lightning current will choose to flow down that
path in preference to any other, allowing the current to be conducted safely to and
dissipated in the earth;

Good corrosion resistance. The choice of material for the earth electrode and its
connections is of vital importance. It will be buried in soil for many years so has to be
totally dependable
Earth Termination system can be divided into three type of arrangement:

Type A arrangement - consists of horizontally star-type earth electrodes or vertical
earth electrodes installed outside the structure footprint. There must be earth
electrodes installed at the base of each down-conductor fixed on the outside of the
structure. A minimum of two electrodes must be used.
Figure 13. Type A arrangement

Type B arrangement - a ring earth electrode or natural elements within the
foundation that is sited around the periphery of the structure and is in contact with
the surrounding soil for a minimum 80% of its total length
Figure 14.Type B arrangement

Type C arrangement - It comprises conductors that are installed in the concrete
foundation of the structure
Figure 15. Type C arrangement
The standard also require a separation distance between the external LPS and the structural
metal parts. Separation minimize any chance of partial lighting current being introduced
internally in the structure. Separation can be achieved if we placing lighting conductors far
away from any conductive parts that have routes leading into the structure.
4.3
Internal lighting protection system
Internal Lighting Protection system is designer for electronic device. The increasing
pace of technological development has created the scenario where increasingly lightning
sensitive systems are essential to our society. The main role of internal LPS is avoid
dangerous sparking occurring within the structure to be protected. Lightning current flowing
in the external LPS or indeed other conductive parts of the structure. Internal Lighting
Protection system use a equipotential bonding measure or is a sufficient electrical insulation
distance between the metallic parts and Surge Protection Device.
4.3.1 Lightning equipotential bonding
Lighting equipotential bonding is a very important measure in reducing the risk of
equipment damage and personal injury. Bonding involves joining together all metalwork and
conductive items that are or may be earthed so that it is at the same potential (voltage)
everywhere. If a component failure occurs, all circuits and conductors in a bonded area will
have the same electrical potential, so that an occupant of the area cannot touch two objects
with significantly different potentials. Even if the connection to a distant earth ground is lost,
the occupant will be protected from dangerous potential differences resulting in injury or
death from electric shock. This electrical interconnection can be achieved by natural/
fortuitous bonding or by using specific bonding conductors that are sized according to IEC/BS
EN 62305-3. Bonding can also be accomplished by the use of surge protective devices (SPDs)
where the direct connection with bonding conductors is not suitable.
4.3.2 Surge Protection Device
Surge Protection devices are used in electrical systems for surge protection. When
lighting hit in the line which is connected to the building, part of the lightning current enters
the electrical system. This creates a risk of damage to electrical installation and receivers
device. Installing surge creates an alternative flow path for the lightning current. Stroke is
discharged through the PE wire to the ground.
Surge protection device have an important role in the electrical installations. It is
purpose to protect of electrical and electronic equipment. Surges can arise not only because
of lightning, but also as a result of failure of power networks.
SPD eliminates overvoltages:

in common mode, between phase and neutral or earth;

in differential mode, between phase and neutral.
In the event of an overvoltage exceeding the operating threshold, the SPD

conducts the energy to earth, in common mode;

distributes the energy to the other live conductors, in differential mode.
Surge Protection device is divided into three typesa;

Type 1 - protect against direct and close lightning strike, recommended in the
specific case of service-sector and industrial buildings, protected by a lightning
protection system or a meshed cage.

Type 2 - protect the electrical installation against overvoltages, resulting from
indirect lightning or switching processes in electrical network, installed in each
electrical switchboard;

Type 3 - protect sensitive loads from surges, reduced by the previous degree of
protection.
Figure 16. Surge Protection
4.3
Lighting Arrester
Lighting arrester is a device on an electric power or telecommunication system which
diverts power to ground when the system takes sees an extreme voltage spike. A lightning
protection arrester is placed where wires enter a structure, preventing damage to electronic
instruments within and ensuring the safety of individuals near them. Lightning protection
arresters, are devices that are connected between each electrical conductor in a power and
communications systems and the Earth. These provide a short circuit to the ground that is
interrupted by a non-conductor, over which lightning jumps. Its purpose is to limit the rise in
voltage when a communications or power line is struck by lightning.
Figure 17. Porcelain Lighting arrestor
5 How to plan lighting protection
5.2
Design of external lighting protection
The external LPS is designed to take over direct lightning discharges in the facility,
including the discharge side of the object, and discharge the lightning current from the point
of hitting the ground and disperse this current into the ground. It can be attached to the object
to be protected. Isolated external LPS should be taken into account when heat and explosive
effects at the point of impact or in the lines of the current lightning can cause damage to the
building or its contents.
5.2.1 Air Termination System - The Roling sphere method
When using the method of rolling sphere, arrangement is appropriate if no point of the
object to be protected is not in contact with a sphere of radius r, waged around and the upper
surface of the object in all directions, the radius r depends on the class of LPS
Figure 18. Application of the rolling sphere method
Figure 19. Maximum values of rolling sphere radius corresponding to the class of LPS
5.2.2 Air Termination System - The Protective Angle method
Space protected by a air terminal vertical has the shape of a cone with the vertex
placed on the axis of the air terminal. Specifies the angle of the protective α, equal to half the
apex angle of the cone and dependent on the class of LPS and the height of the air terminal
Figure 20. The protective angle method for a single air rod
Figure 21. Effect of the height of the reference plane on the protection angle
5.2.3 The Mesh Method
This protection involves placing numerous down conductors/tapes symmetrically all
around the building. Mesh method system is used for highly exposed buildings housing very
sensitive installations such as computer rooms. The mesh size is between 5 and 20 metres
depending upon the effectiveness required and its contained in standard. The top of the down
conductors fitted to the walls are connected to the roof mesh, and the bottom to dedicated
earthing systems
Figure 22. Maximum values of mesh size corresponding to the class of LPS
Figure 23. Lighting protection system with meshed cages
Figure Stretched wires have a several conductor wires above the protected installation.
The conductor must be earthed at each end. They are used to protect special structures: rocket
launching areas, military applications and protection of high-voltage overhead lines
Figure 24. Stretched wires
5.3
Separation Distance for lighting protection system
In case of direct lightning strike, dangerous sparking may occur between the external
LPS and metal installations inside the building. The function of the internal lightning
protection is to prevent such dangerous sparking either by lightning equipotential bonding or
by keeping the separation distance. The separation distance is the minimum clearance
required at the proximity of conductive parts inside the building and the external LPS
to avoid side flashes.
s
*L
ki – depends on the selected class of the LPS;
kc – depends on the lighting current flowing in the down-conductors (type of earth termination
arrangement);
km – depends on the electrical insulation material;
l – shortest length along the air-termination or the down – conductor, from the point where the
separation distance is to be considered, to the nearest equipotential bonding point.
Figure 25. Separation Distance
5.4
Design of internal lighting protection
The task of an internal lightning protection is to prevent dangerous sparks in the
protected object as well as within it. To the formation of sparks can occur when the result of
the flow of the lightning current through the lightning protection system comes to the creation
of large potential differences between metal parts of the building and parts of the electrical
system. Installation of potential equalization should be performed at the lowest level of the
building. Ground wires electrical and telecommunication installations of the building must be
connected to the potential equalization rail.
5.3.1 Equipotential Bonding
To prevent such undesirable phenomena it is necessary to make connections compensatory
following building elements:

Metal structural components of a building;

Metal sanitary installations;

The outer conductive parts;

Electrical power and information device.
Figure 26. Example of main equipotential bonding
5.3.2 Surge Protection Device
A direct lightning strike in lighting installation leads to high potential for electrical
and conductive inside the building. Surge protection device are part of the potential
equalization in the facility. Reduce the potential differences arising during the flow of the
lightning current in the electrical installation. Surge Protection device is connected in parallel
on the power supply circuit of the loads that it has to protect It can also be used at all levels of
the power supply network. This is the most commonly used and most efficient type of
overvoltage protection.
Figure 27. Surge Protection System
5.5
Lighting Protection of Power Lines
5.5.1
Lightin Protection in MV Power Lines
To protect MV power lines from lighting we can use a lighting arresters. It is
important to do it properly. The first way showed on the picture is incorrect. To the value of
the lowered voltage by the lighting arrester we have to add voltage drop at the connections
between A and B. The second way is correct. On the protection device exist only the value of
the lowered voltage by the lighting arrester without any drop voltage on u nnecessary
connections.
Figure Lighting Protection in MV Power Lines
5.4.2 Lighting Protection in HV Power Lines
Lightning surge in over head transmission line may be caused due to direct hits of
lightening strokes. It can be protected by providing a shield wire or earth wire at a suitable
height from the top conductor of transmission line. If the conducting shield wire is properly
connected to transmission tower body and the tower is properly earthed then direct lightning
strokes can be avoided from all the conductors come under the protective angle of earth wire.
The surge protection of these assets is critical to maintaining a healthy power delivery system.
Figure Lighting Protection in HV Power Line
5.6
Lighting Protection of Transformers
To protect Transformers from lighting we can use a lighting arrester. It is a three
method to do it. In first way the lighting arrester is mounted far away from the protection
device so the real value of the voltage lowered by the lighting arrester will be rise according
to drop voltage between lighting arrester – fuse base and the base of the transformer. In the
second way the lighting arrester is installed as the insulator, reduces the distance and increases
the level of protection. The voltage drop on the cable does not significantly reduce the
effectiveness of the limiter. The best way lighting arrester is installed near the equipment
protected provides the maximum level of protection for the simplification of the station for
dismantling fuse bases
Figure Lighting Protection of Transformers.
Questions
1. Does every building must have external lighting protection ?
The need for external protection shall be determined on the basis of the principles
contained in the standards, assessing the degree of risk of the building. It depends on: the roof
surface; its design and coverage; height of the building; its position on the ground and in
relation to other objects; the number of people staying in the building; of possible losses
caused by lightning. Free-standing building (ie, one that does not stand in a compact building)
with a height of over 15 meters and an area of over 500 m2 requires protection. Regardless of
the amount of protection is necessary even if it was built with combustible materials or
indicator threat of lightning, calculated according to the rules specified in the standard,
exceeds 10-4. Under the provisions of the security standards do not require buildings:

Situated in the protection zone adjacent buildings;

Flat a height not exceeding 25 m standing in the compact settlement;

Those for which the index threat of lightning is less than 10-5.
2. Calculate the distance from Lighting Strike if the number of seconds from
lightning to thunder is 18
Sound travels through air at
the speed 346 meters per second (depends on
temperature) but we can assume that the sound travels 1 kilometer in roughly 3 seconds
18/3 = 6 km
3. Why do we see the lighting flash before hearing the sound ?
The difference is related to the speed of the light wave and sound wave. Light wave
travels at the speed of about 300 000 000 m / s, while the sound wave with a speed of 343 m /
s.
4. Is it possible to have thunder without lightning?
No, it is not possible to have thunder without lightning. Thunder is a direct result of
lightning. However, it IS possible that you might see lightning and not hear the thunder
because it was too far away
5. Does every cloud causes lighting ?
No.
The only type of clouds, which may be accompanied by lightning are
Cumulonimbus. From a distance it resembles the shape of a very large anvil, a fungus or a
tower. It have in mind that the clouds can be hidden in the clouds of another type, eg.
Nimbostratus, which is a cloud layer and can completely cover the sky.
6. How to protect the antenna on the roof?
Situated on the rooftop antenna of the radio or television you need protection even
when the building itself does not have to install lightning protection. Antenna mast should be
connected to the earth electrode natural or artificial, while the satellite dish should unbutton
frame with high horizontal air terminals.
7. What elements of the building can be used as a natural part of the installation
of lightning protection?
Air terminals. In detached houses this function have sheet disposed on the nonflammable or hardly combustible substrate (if a thickness not less than 0.5 mm). Laying in
such a situation, the additional air terminals is not economically justified, unless on the top
floor there are valuable items. At the time of the lightning strike into a thin sheet may be
perforated. This may cause flooding rooms. As a natural feints can be used in addition:

Reinforcement concrete roof;

Metal parts protruding above the roof;

Reinforcement of concrete elements of walls and foundations;

Steel load-bearing columns.
Homework
According to Standard determine whether the house need the lighting protection. For
the IV level of protection calculate the separation distance. The house is situated in Poland
where the number of storm days is 23. House is surrounded by smaller structures. The house
is standard and nonflammable, occupied and continuity of service required (no environmental
impact). The dimensions of building is 150x150x30m and the coefficient km is 4.
Data from standard:
1. Relative Structure Location - surrounded by smaller sized structures = 0,5 C1
2. Type of Construction – common roof and structure = 0,5 C2
3. Structure Contents – standard value and non flammable = 0,5 C3
4. Occupancy – Normally occupied = 1 C4
5. Lightning Consequence – Continuity of services required, no environmental impact= 5
C5
Calculations:
Our building have a rectangular shape with dimensions: Length – 150m, Width – 150m and
Hight 30m. The collective area for a standard rectangular structure is calculated using
equation
Ae = LW + 6H(L+W)+π9H2 = 150*150+6*30(150+150)+3,14*9*302 = 101946.9005
Lightning Flash Density
Ng = 0,04 * Td1,25 = 0,04 * 231,25 = 2
Tolerable Lightning Frequency
NC =
= 0,0012
Lighting Strike Frequency (Nd)
ND = Ng * Ae *C1 *10-6 = 2*101946,9005 * 0,5 * 10-6 = 0,101947
ND > NC – Protection Required
The effectiveness of lightning protection systems
E ≥ NC / ND = 0,998
Separation Distance
Data:
c – 150m - Building length
h = 30m – Building height
Class of LPS – IV
n=4 – number of conductors
l = 30 m - length along the air-termination system
Earthing arrangement = type A
km =1 – air, electrical insulation material
Answer, according to standard :
ki = 0,04 – IV protection level
kc = 0,44 - partitioning coefficient
s
* l = 0,04 *
* 30 = 0,528m
Bibliography
[1]
Standard IEC BS EN 62305
[2]
http://www.edisontechcenter.org/LightningSuppression.html
[3]
http://www.lightningsafety.noaa.gov/struck.shtml
[4]
WALLIS, Consultant Handbook
[5]
Furse, Guide to IEC BS EN 62305
[6]
http/stormhighway.com/types.php
[7]
ABB, OPR Lighting Protection System
[8]
http://www.electricalinstallation.org/enwiki/The_Surge_Protection_Device_%28SPD