lightining and its effects

7/28/2019 Lightining and its effects

1/42

IMPACT OF LIGHTNING ON BUILDINGS AND ITS REMEDIAL

MEASURES

1. INTRODUCTION

1.1. The Phenomenon of Lightning

Thunderstorms develop when ground heat creates a hot rising

current of air. This air gradually cools until it condenses into

small cumulus clouds. The cumulus continues to grow vertically

until it eventually becomes a storm cloud or cumulonimbus.

These atmospheric conditions lead to the creation of electric

charges resulting from collisions between water, hail and ice

particles of different sizes. There are charges separation inside

the cloud, with a negative charge at the bottom of the cloud

and a positive charge at the top.

The centre of the negative charges is usually at the base of the

cloud due to the movement of electrons through the heavier

droplets and hailstones, whilst the centre of the positive

charges moves up to the top of the cloud carried by convection

currents, which can easily lift the light positively charged

particles. The effect produces a similar change at the earth's

surface due to the charge repulsion, of about the same

magnitude but opposite polarity.


2/42

The potential inside the cloud is usually of the order of several

million volts and electric field may exceed 5 kV/m at ground

level, which gives the creation of the upwards leaders rising

from surface irregularities or metallic structures. (Fig.2 a).

Electrical field is so strong that small discharges are produced

from the cloud, known as step leaders. As these step leaders

get closer to ground level, the upward leaders rise up to meetthem. When the step leader and the upward leader meet, the

circuit is completed creating a short circuit, the lightning strike,

with discharges current from 10 to 200 kA (Fig. 2c).

The energy carried by a lightning strike can easily reach 20

GW.

The most common lightning strikes are from the cloud to

ground (in 80% of cases), and are named negative discharges,

but when the discharge is positive in the downward direction,

the intensity is extremely high.

1.2. Statistics


3/42


4/42


5/42

were damaged. The copper circuits between building became a

path for the equalisation current. The correct application of

surge protection could have prevented the resulting damage.

This is why an effective lightning protection system will include

protection against the direct strike (i.e. an external lightning

protection system), and protection against the indirect strike

(i.e. an internal lightning protection system using Surge

Protection).


6/42

2. LIGHTNING PROTECTION AND ITS WORKING

Lightning protection creates a preferred point for lightning to

strike (avoiding strikes to sensitive rooftop equipment) using

an air termination network, then conducts the energy to ground

using down conductor(s) and injects the energy into a purpose

designed earthing system.

In some cases, existing structure materials can be used as part

of the lightning protection system, such as using reinforcingsteel as down conductors. The items are referred to as natural

components. The use of existing structure items is most

applicable to situations where the lightning protection is

included in the initial design and construction. For buildings

where lightning protection is retrofitted, it is often difficult to

use natural components.


7/42

There are many possible designs for air termination networks,

and final selection is based on efficiency of performance, ease

of installation/maintenance, cost, visual impact and

compatibility with existing building materials. While the

traditional lightning rod is well known, horizontal conductors,

handrails, parapet flashings and conductive roofing materials

may also be used.

Down conductors are selected to route the energy to ground

and reduce the risk of side-flashing to nearby items. Routes areselected to reduce electromagnetic radiation and control risk of

dangerous touch potentials being developed. The size and

interconnection method of down conductors reduces the risk of

heating and resultant structure fire during a lightning strike.

For new concrete construction, the reinforcing steel within the

building may be utilised.

The earthing system is designed to inject the energy into

ground and reduce the risk of voltage-ground-potential-rise

(step and touch potentials). Various positioning and layout

options are evaluated to select the best choice.

Lightning protection systems are designed to:

Reduce the presence of dangerous voltages (reduce step

and touch potentials)

Reduce the risk of flash-overs (reducing the risk of the

building catching fire)


8/42

Reduce physical damage to buildings (stop holes being

punctured in roofs, stop chucks of building materials being

knocked out)

Reduce the risk of equipment damage

2.1. Protection zone


9/42


10/42

To aid in the design of the lightning and surge protection

system, the concepts of zones is used. For example zones

are classified based on:

Is the area vulnerable to a direct strike?

Is the area exposed to the full or partial lightning current?

Is the area exposed to the full or partial electromagnetic

field?

ZoneLightning

FlashCurrent Field

LPZ 0a Yes Full Full

LPZ 0b No Partial Full

LPZ 1 No Limited Partial

LPZ 2 No Reduced Reduced

By identifying the various zones around and within a structure,

protection can be applied appropriately. For example, electrical

services passing through a LPZ 0 zone will require surge

protection where they enter into a LPZ 1 zone. Note that zones

may not necessarily be physical boundaries of the structure

2.2. Isolated lightning protection system


11/42

Lightning protection systems may be isolated or non-isolated.

Non-isolated systems electrically bond all conductive building

materials together so they rise and fall at the same potential,

eliminating potential differences and the risk of flash-overs.

This is the traditional lightning protection method.

However, with modern facilities containing a large amount of

electronic equipment, and more critically, rooftop equipment

(air handling units, lift motors, TV aerials and communication

equipment), non-isolated systems can be difficult and costly to

implement.

Isolated systems use special methods to capture the lightningstrike and conduct this to ground without it contacting the

structure. Isolated conductors are the main methods to achieve

this. Isolated systems are ideal for:

Highly flammable structures (grass/straw roofs)

Locations with a high concentration of electronic

equipment (communication towers)


12/42

Structures where the cost of bonding all metallic items

would be prohibitive

Isolated systems are ideal to keep the dangerous lightningenergy away from:

Rooftop communication equipment

Solar cells and other electrical/electronic equipment

Explosion or gas hazard areas

2.3. Surge protection and its working

Surge protection devices are non-linear voltage dependent

devices that transition from high impedance state to low

impedance state to divert over voltages and over current safely


13/42

to ground. They are similar to a safety pressure value that

stops dangerous pressures being built up in pressure vessels.

The correct selection and installation of surge protection isessential for reliable performance. Unfortunately there are a

number of people selling these products with little knowledge

of these issues. HV Power have specialist application

knowledge to guide you.

It is important that:

The right ratings are installed at the right locations

That electrical safety is maintained by having the correct

backup over current protection

That devices are installed in such a manner to ease

inspection and replacement

That the location and wiring to the SPDs does notcompromise the possible protection

That surge protection is properly coordinate

2.4. Coordinated protection


14/42

With surge protection designs, the normal approach to apply a

large lightning rated surge protection device on the main

service entrance. This stops energy entering the facility via the

Z0/Z1 boundary. These are referred to as Lightning Current

Arrestors (IEC 61643-11 Type 1).

Secondary coordinated protection is then installed closer to the

sensitive equipment to be protected. According to IEC 61643-

11 these SPDs are Type II devices, or Surge Arrestors. You

cannot rely on a Surge Protection Device (SPD) mounted in the

main switchboard to protect equipment 10-100s of metres

away, especially when other loads in your facility may also be

generating transient voltages. Having two SPDs ensures the

massive lightning current/voltage is suitably reduced so as not

to damage sensitive equipment. The term "coordinated-


15/42

protection" is used as these two devices must be selected to

work in a coordinated fashion.

This first of this two-pronged approach diverts the bulk of theenergy away from the point-of-entry to the facility, thus:

Stopping energy from entering into building and

radiating/coupling into nearby low voltage

data/communication circuits

Stopping damage to electrical distribution boards (so

power is not disrupted!)

Providing effective protection to robust downstream

equipment such as heating and lights

The second of this two pronged approach, provides fine

protection to the sensitive electronic equipment, thus:

Protecting sensitive equipment to a suitable low voltage

Providing backup if the point-of-entry protection is

damaged

Protecting equipment from internally generated transients


16/42


17/42

electronic equipment that it might contain. It is common for

lightning strikes several kilometers away to cause damaging

electrical surges. And even in Newport, Rhode Island, where

there are only about 20 thunderstorms a year, each square

kilometer is struck an average of twice a year. This is enough

to be of concern to facilities where damage can result in

expensive downtime, the loss of important data or the potential

to lose control over hazardous processes - not to mention the

actual damage to costly electronic hardware.

3.2. lightning effect on a building

Direct and indirect effects are the two broad categories. Direct

effects include the physical damage produced by lightning.

Ignition of fires is a clear example caused by contact of the

20,000C lightning channel. Other direct effects include

shattering of wood, windows, masonry and other poorly

conductive materials. Direct effects also include the burnout of

electrical power and distribution equipment caused when

lightning injects high currents and voltages into a power

distribution line. A common example of this is the explosion of

power distribution transformers.

Lightning also causes a variety of indirect effects. These result

from earth-voltage rises caused when the flash dumps

thousands of amperes into the earth and from the

electromagnetic fields generated by the lightning stroke

currents. These induce voltage and current surges in electric

power and signal circuits, which may, in turn, burn out

electrical equipment connected by these circuits. Solid-state


18/42

electronics are especially vulnerable to these surges unless

properly protected. Of particular concern are facilities with

several buildings or installations that are interconnected with

above or below ground cables. These cables can experience

significant induced transients. Power, telephone, data and even

underground plumbing have the potential to transfer damaging

lightning surges into a building. Even some fiber-optic cables

can be susceptible to damage from lightning. Although the

fiber-optic signal lines themselves are nonconductive, the

cables are often constructed with a conductive metal sheath

for strength purposes. Fiber-optic cable sheathes can attract

lightning and its blast pressures may crush optical fibers.

3.3. Protection of buildings from direct effects

Since the time of Ben Franklin, the lightning rod, or air

terminal, has been the front line of defense against lightning.

Its basic concept is to provide a preferential terminal for

lightning that would have otherwise hit a vulnerable part of the

structure. An air terminal only will protect a portion of a

building, so most structures will have several lightning

terminals. The spacing and position of air terminals has been

well understood for many years and the proper configuration

and installation of air terminals is detailed in well-known

standards, such as NFPA 780 (National Fire Protection

Association). Basic direct-effects protection also includes a

system of down conductors connecting the air terminals to the

grounding system.


19/42

The configuration of the grounding system is very important

and depends upon soil conditions, building construction and the

presence of other underground conductors. Grounding systems

can be created with driven ground rods, plates and possibly a

counterpoise, which is a buried cable encircling the site. A

counterpoise adds greatly to the protection from earth voltage

rises that may injure people standing on the ground.

The interconnection (bonding) of other metallic items in the

building is important to prevent sparkover from a lightningconductor to other conductive items, such as water pipes, roof

edgings, vent stacks or HVAC equipment, depending on their

locations.

3.4. Protection of buildings protected from indirect

effects

Lightning can cause damaging transient voltages and current

surges in equipment through a direct strike to a wire, through

earth voltage rise and through magnetic field and capacitive

coupling.

There are four engineering concepts that, when properly

applied, can comprise a total lightning protection plan, whether

for a single piece of equipment or a complex of buildings.

These concepts are grounding, bonding, shielding and surge

suppression.

There is no magic bullet for lightning protection. Protection is

achieved only through a careful investigation to identify allsensitive components and all possible paths for lightning


20/42

currents and voltages, followed by the design, specification,

installation and maintenance of a protection system.

Grounding and bonding improvements are made to provideadditional paths for lightning currents to flow to earth, thereby

minimizing surges. These improvements usually involve

interconecting adjacent conductors, such as structural steel,

conduits and ground conductors. Commonly overlooked

grounding problems include conduits, metal equipment

cabinets and individual components within computer rooms.

Shielding of cables helps to reduce surges by providing a

preferential path for lightning currents rather than the actual

circuits. To be most effective, shielding must be completely

continuous, and grounded or terminated to equipment

housings at both ends.

In some cases, grounding, bonding and shielding provide a

sufficient reduction in indirect effects. However, critical

sensitive equipment, and any equipment interconnected by

cables over long distances, requires the installation of surge

suppressers. There are many types and many manufacturers of

surge-suppression equipment. Care must be taken to select themost cost-effective device that will handle the currents and

voltages expected from a severe strike. Surge suppressors

should be installed where they readily can be inspected and

replaced when damaged by a severe strike. In many cases, the

most expensive surge suppressors turn out to be the least

effective or appropriate for a particular application.


21/42

3.5. Protection of home and small business computers

from lightning

By far the best way to protect your computer from lightning isto disconnect it from both the power line and telephone line at

the approach of a thunderstorm. Commonly available surge

strips do provide protection against some of the surges caused

by lightning, specifically voltages induced between the positive

and negative lines of the power supply. Surge strips do not

always protect against voltages that arise between the powerline and house, or system ground or the telephone lines. The

larger concern, at least for any one capable of reading this

FAQ, is the modem. Simply stated, your computer effectively

forms a circuit between your local power company and your

local telephone company. The interface between these two

widely distributed networks is your computer. Lightning

commonly causes serious voltages to arise between circuits at

different distances from the strike and/or referenced to earth

ground at different locations. These voltages appear at the

interfaces between these systems - your computer. It is a

misconception to think that the lightning voltages are carried

down the telephone lines to your computer. Rather, the

voltages appear between the components of your computer.

That is why a surge suppressor designed for a modem would be

ineffective in most cases. This effect can be mitigated by

providing a common ground reference for every device

connected to your computer. In such a system, everything that

is connected to the computer that has its own power or

telephone connection is first connected to a device that


22/42

provides a single ground path. This device is based on the

concept of an equipotential plane, commonly used for lightning

protection of aircraft and other advanced systems.

3.6. Lightning in golf courses

Because public safety is the highest concern in any lightning

protection program, the most important installation for a golf

course is an early warning system. Early warning systems can

include dedicated systems installed at the golf course or

connections to realtime lightning data from a commercial

network. In addition, strategically placed shelters should be

designed and constructed to withstand all lightning effects.

Please see our article on golf shelters available on this web

site.

Golf courses often have sophisticated irrigation systems withelectronic controls. Because these systems have power and

control cables distributed over many acres, they are highly

susceptible to lightning-induced surges. Careful grounding and

shielding and the installation of surge suppression devices can

protect these systems.

There are devices being marketed with claims that they

actually reduce the likelihood of a lightning strike and others

with claims to provide increased effectiveness as air terminals.

What are the merits of these devices?

Lightning Technologies, Inc. has no firsthand experience with

these devices. Most such items are not available for purchaseor installation other than directly through manufacturers and


23/42

their licensees, often making it difficult for independent

evaluation. Moreover, LTI has had very good success with

commonly available conventional parts and materials, and so

has not found it necessary or useful to use expensive,

unproven and sometimes controversial proprietary protection

devices. To our knowledge, no independent studies have

yielded any conclusive evidence of the effectiveness of many

of these devices. Total lightning protection can be achieved

with the proper planning and installation of conventional

lightning-protection hardware and improvements to grounding,

bonding, shielding, circuit design and surge suppression.

Conventional lightning-protection hardware is relatively

inexpensive.


24/42

4. LIGHTNING STROKE IMPACTS IN A BUILDING

Lightning strokes can affect the electrical (and/or electronic)

systems of a building in two ways:

by direct impact of the lightning stroke on the building

(seeFig. 5 a);

by indirect impact of the lightning stroke on the building:

- A lightning stroke can fall on an overhead electric

power line supplying a building (see Fig. 5 b). The

overcurrent and overvoltage can spread several

kilometres from the point of impact.

A lightning stroke can fall near an electric power line

(see Fig. 5 c). It is the electromagnetic radiation of the

lightning current that

produces a high current and an overvoltage on the

electric power supply network.

In the latter two cases, the hazardous currents and

voltages are transmitted by the power supply network.

A lightning stroke can fall near a building (see Fig. 5 d).

The earth potential around the point of impact rises

dangerously.


25/42

Fig. 5: Various types of lightning impact

In all cases, the consequences for electrical installations and

loads can be dramatic.

4.1. Lightning falls on an unprotected building.
http://www.electrical-installation.org/wiki/File:Fig_J06a_EN.jpghttp://www.electrical-installation.org/wiki/File:Fig_J05_EN.jpg


26/42

The lightning current flows to earth via the more or less

conductive structures of the building with very destructive

effects:

thermal effects: Very violent overheating of materials,

causing fire,

mechanical effects: Structural deformation,

thermal flashover: Extremely dangerous phenomenon in

the presence of flammable or explosive materials

(hydrocarbons, dust, etc.)

The building and the installations inside the building are

generally destroyed

4.2. Lightning falls near an overhead line

The lightning current generates overvoltages through

electromagnetic induction in the distribution system. These

over voltages are propagated along the line to the electrical

equipment inside the buildings.
http://www.electrical-installation.org/wiki/File:Fig_J06b_EN.jpg


27/42

The electrical installations inside the building are

generally destroyed

4.3. Lightning falls near a building

The lightning stroke generates the same types of overvoltage

as those described opposite. In addition, the lightning currentrises back from the earth to the electrical installation, thus

causing equipment breakdown.
http://www.electrical-installation.org/wiki/File:Fig_J06d_EN.jpg


28/42

5. VARIOUS MODES OF PROPAGATION

5.1. Common mode

Common-mode over voltages appear between live conductors

and earth: phase-to-earth or neutral-to-earth (see Fig. 7). They

are dangerous especially for appliances whose frame is

connected to earth due to risks of dielectric breakdown.

Fig. 7: Common mode

5.2. Differential mode

Differential-mode over voltages appear between live

conductors:

phase-to-phase or phase-to-neutral (see Fig. 8). They are

especially dangerous for electronic equipment, sensitive

hardware such as computer systems, etc.
http://www.electrical-installation.org/wiki/File:Fig_J07_EN.jpg


29/42

Fig. 8: Differential mode


30/42

6. PROCEDURE TO PREVENT RISKS OF LIGHTNING STRIKE

The system for protecting a building against the effects of

lightning must include:

protection of structures against direct lightning strokes;

protection of electrical installations against direct and

indirect lightning strokes.

The basic principle for protection of an installation against the

risk of lightning strikes is to prevent the disturbing energy from

reaching sensitive equipment. To achieve this, it is necessary

to:

capture the lightning current and channel it to earth via

the most direct path (avoiding the vicinity of sensitive

equipment);

perform equipotential bonding of the installation;

This equipotential bonding is implemented by bonding

conductors, supplemented by Surge Protection Devices (SPDs)

or spark gaps (e.g., antenna mast spark gap). minimize

induced and indirect effects by installing SPDs and/or filters.

Two protection systems are used to eliminate or limit

overvoltages: they are known as the building protection system(for the outside of buildings) and the electrical installation

protection system (for the inside of buildings).


31/42

7. BUILDING PROTECTION SYSTEM

The role of the building protection system is to protect it

against direct lightning strokes.

The system consists of:

the capture device: the lightning protection system;

down-conductors designed to convey the lightning current

to earth;

"crow's foot" earth leads connected together;

links between all metallic frames (equipotential bonding)

and the earth leads.

When the lightning current flows in a conductor, if potential

differences appear between it and the frames connected to

earth that are located in the vicinity, the latter can cause

destructive flashovers.7.1. The 3 types of lightning protection system

Three types of building protection are used:

7.1.1. The simple lightning rod

The lightning rod is a metallic capture tip placed at the top of

the building. It is earthed by one or more conductors (often

copper strips) (see Fig. 12).


32/42

Fig. 12: Simple lightning rod

7.1.2. The lightning rod with taut wires

These wires are stretched above the structure to be protected.

They are used to protect special structures: rocket launching

areas, military applications and protection of high-voltage

overhead lines (see Fig. 13).


33/42

Fig. 13: Taut wires

7.1.3. The lightning conductor with meshed cage

(Faraday cage)

This protection involves placing numerous down

conductors/tapes symmetrically all around the building.

(see Fig. J14).

This type of lightning protection system is used for highly

exposed buildings housing very sensitive installations such as

computer rooms.


34/42

Fig. 14: Meshed cage (Faraday cage)

7.2. Consequences of building protection for the electrical

installation's equipment

As a consequence, the building protection system does not

protect the electrical installation: it is therefore compulsory to

provide for an electrical installation protection system.


35/42

50% of the lightning current discharged by the building

protection system rises back into the earthing networks of the

electrical installation (see Fig. 15): the potential rise of the

frames very frequently exceeds the insulation withstand

capability of the conductors in the various networks (LV,

telecommunications, video cable, etc.). Moreover, the flow of

current through the down-conductors generates induced

overvoltages in the electrical installation.

Fig. 15: Direct lightning back current


36/42

7.3. Lightning protection - Electrical installation protection

system

The main objective of the electrical installation protection

system is to limit overvoltages to values that are acceptable for

the equipment.

The electrical installation protection system consists of:

one or more SPDs depending on the building

configuration;

the equipotential bonding: metallic mesh of exposed

conductive parts.

7.3.1. Implementation

The procedure to protect the electrical and electronic systems

of a building is as follows.

7.3.2. Search for information

Identify all sensitive loads and their location in the

building.

Identify the electrical and electronic systems and their

respective points of entry into the building.

Check whether a lightning protection system is present onthe building or in the vicinity.

Become acquainted with the regulations applicable to the

building's location.

Assess the risk of lightning strike according to the

geographic location, type of power supply, lightning strike

density, etc.


37/42

7.3.3. Solution implementation

Install bonding conductors on frames by a mesh.

Install a SPD in the LV incoming switchboard.

Install an additional SPD in each subdistribution board

located in the vicinity of sensitive equipment (see Fig.

16).


38/42


39/42


40/42

8. CONCLUSIONS

Thunderstorms and Lightning are climate related, highly

localized phenomena in nature known for devastating

consequences. Many scientific experiments have culminated in

inventions for lightning safety, yet the mystery behind lightning

is still unresolved and lightning as a phenomena is not

completely understood The technology of lightning protection

have registered steady improvements but even with all the

known precautions, complete safety is still beyond our grasp.

Creating awareness among the general people could go a long

way in mitigating lightning threats. The Asian countries like

India, Sri Lanka, Bangladesh, Nepal and Bhutan have started

Lightning Awareness Centres and one of their objectives is to

spread awareness among the people. The High Powered

Committee of the Government of India on Disaster

Management too has identified Thunderstorms and Lightning

as natural hazards of great concern. The Bureau of Indian

Standards purveys lightning protection guidance for structures

and the builders are advised to adhere to the prescribed code.

Research and Development programmes are being supported

on lightning protection and many leading Indian institutes and

Laboratories are working on lightning safety. The paper lays

stress on spreading the culture of safety against lightning. It

deals with the issues, Indian standards and methods of

lightning protection, and introduces on going awareness

programmes and research and development needs for

lightning safety in the Indian context.


41/42

Though lightning incidents are less, whenever they strike, they

cause severe damages to life and properties. Casualties due to

Lightning can be easily, efficiently and inexpensively avoided,

and lightning safety can be achieved mainly by creating public

awareness, technical education on Lightning Protections,

educating people on lightning and surge protection. Stringent

steps to ensure adherence of building standards and codes

wherever necessary and promoting research and development

on lightning protection are essential. There is a need to give

lightning its due attention as a natural disaster and give it a

priority in National Disaster Management Programmes.


42/42

9.REFERENCES

1. http://www.weighing-

systems.com/TechnologyCentre/Lightning1.pdf

2. http://www.kerenvis.nic.in/files/pubs/soe_2007/volume2/so

e_kerala_v2_chapter%205.pdf

3. http://www.cirprotec.com/products/lightning-

protection/Externa
http://www.weighing-systems.com/TechnologyCentre/Lightning1.pdfhttp://www.weighing-systems.com/TechnologyCentre/Lightning1.pdfhttp://www.kerenvis.nic.in/files/pubs/soe_2007/volume2/soe_kerala_v2_chapter%205.pdfhttp://www.kerenvis.nic.in/files/pubs/soe_2007/volume2/soe_kerala_v2_chapter%205.pdfhttp://www.cirprotec.com/products/lightning-protection/Externahttp://www.cirprotec.com/products/lightning-protection/Externahttp://www.weighing-systems.com/TechnologyCentre/Lightning1.pdfhttp://www.weighing-systems.com/TechnologyCentre/Lightning1.pdfhttp://www.kerenvis.nic.in/files/pubs/soe_2007/volume2/soe_kerala_v2_chapter%205.pdfhttp://www.kerenvis.nic.in/files/pubs/soe_2007/volume2/soe_kerala_v2_chapter%205.pdfhttp://www.cirprotec.com/products/lightning-protection/Externahttp://www.cirprotec.com/products/lightning-protection/Externa

lightining and its effects

Documents