Write By Atika .M

2008-2009

.

# $% ) , . / 1 3 14 ) .

I thank God who to us in giving force and will to

accomplish this modest work.

This stain will have been possible succeed under the support of several persons to the which I express here every my recognition

and sympathy. I thank to my picture framer Mr. T.M, to have run this plan for this precious advice, who does not have hesitate to give advices

and especially his comments and his precious help. My sincere gratitude to the jury members who were kind enough

to honour with their presence. My gratitude also goes to all professors who taught me during

my university programme.

At the end I deeply let us thank all those who of meadows or from a distance, contributed in either way to the realisation of

this project.

M.Atika

Ddication Ddication Ddication Ddication

I dedicate this modest job to all persons who are expensive to me, my two dear parents for their support and their Encouragement, my sisters Nad, and

my brother. My best friends: Fati.

My group; kenza, Bilal, Amal, Zaki, Meriem, Hala.

To all the family M and k . Without forget all my friends.

And the first Promotion of LMD. M. Atika

General introduction...08

*Chapter I:

The phenomenon of lightning

I.1. The stormy cloud .................................................................................... 10

I.2. Electrical field ......................................................................................... 11

I.3. Effect of point .......................................................................................... 12

I.4. Leader by bound ..................................................................................... 12

I.5. The origin of lightning............................................................................ 13

I.6. Different type of lightning...................................................................... 13

I.6.1. Intra Cloud .............................................................................. 14

I.6.2. Inter Cloud .............................................................................. 15

I.6.3. cloud-ground ........................................................................... 15

I.7. Main types of lightning strokes ............................................................. 15

I.7.1. The downward lightning stroke ............................................ 16

I.7.1. 1) The negative ................................................................... 16

I.7.1. 2) The positive .................................................................... 16

I.7.2. The upward lightning stroke ................................................. 17

I.7.2. 1) The negative ................................................................... 17

I.7.2. 2) The positive .................................................................... 17

I.8. Mechanisms of the lightning.................................................................. 18

I.9. Effects of the lightning............................................................................ 18

Chapter II The risks of lightning

II.1. Artificial triggering of the lightning .................................................... 20

II.2. The Danger of the lightning ................................................................. 21

II.2.1. Keraunic level ........................................................................ 21

II.2.2 The density of striking by lightning ..................................... 22

II.2.3 Risks of the lightning ............................................................. 22

II.2.4 Damage of the lightning on the man .................................... 24

II.3 Prevention and detection of the lightning............................................ 26

II.3.1 Lightning detector in the space meteorology centre....26

II.3.2 Mill with field.......................................................................... 27

II.3.3 The directional antennas ....................................................... 27

II.3.4 The satellite ............................................................................. 28

Chapter III The protection against lightning

III.1. protection of the persons .................................................................... 30 III.2. protection of the installations electrical............................................. 30

III.2.1 The lightning rod with simple stem .................................... 30

III.2.2 the Faraday cage ................................................................... 31

III.2.3 The lightning rod with tense threads .................................. 32

III.2.4 the installation of lightning rod ........................................... 33

III.2.4 -1 The installation portrays ............................................. 33

III.2.4-2 Situation of Lightning rods .......................................... 33

III.2.4-3 The Mast......................................................................... 34

III.2.4-4 The descents ................................................................... 35 III.2.4-5 Earth plug ...................................................................... 35 A. Value ohmic earth plug...................................................... 35

B. equipotentiality ................................................................... 36

C. Look of visit......................................................................... 36 D. Improvement of earth plug................................................ 36 III.2.4-6 crow's foot ...................................................................... 36 III.2.4-7 pickets............................................................................. 37 III.2.4-8 Mixed .............................................................................. 38 III.2.5 lightning arrester .............................................................. 38 III.2.5.1 Lightning conductor medium tension (HTA) .............................. 39 A. Constitution.............................................................................. 39 B. Functioning principle .............................................................. 40 III.2.5.2 Lightning conductor of high voltage (HTB)................................. 42 A. Constitution.............................................................................. 42 B. Functioning principle .............................................................. 43

General Conclusion ...................................................................... 45

Bibliography .................................................................................... 47

The lightning is a natural phenomenon of discharge disruptive electrostatics which occurs

plasma during the discharge, causing an explosive expansion of air by clearing of heat. By

dissipating, this plasma creates a flash of lightning of light and a thunder.

It is a disruptive phenomenon mattering on all electrical installations, in several titles:

- She can be at the origin of disturbance momentary in service continuity, therefore of

degradation of the quality of feeding,

- She can cause destruction of equipment, and as a result of lengthy outages of installations,

- She constitutes a danger for the persons (of step tension, elevation of potential of masses and

of earth circuit).

Unfortunately, the disruptions of natural origin, it is in general impossible to have any

influence on the source. The only recourse is therefore the protection of the threatened

systems. It is the reason for which it is necessary to know precisely the characteristics of

disruption (physical mechanisms, characteristic sizes) to be possible to protect systems

efficiently victims.

Suchin the particular case of the lightning, mechanisms and generated electromagnetic

radiation did not change in the course of time but the incidents caused by this natural

phenomenon go by augmenting due to the more and more important use of systems by which

vulnerability also grows. Even if she remains an extremely dangerous instrument of the anger

of the sky (she is the reason of many deaths of humans and animals, of fires of forests,

industrial buildings), the current study of this phenomenon has as objective the precise

knowledge of its effects on the sensitive equipments, mainly on installations, the knowledge

of physical phenomenon in itself is far from being improved and more fundamental studies

are makes easier has understand the general mechanism.

For our part, our objective is not to elucidate how the protection is put into play in the course

of explaining complex physical phenomena and the risks due to the lightning, to provide

protection perfectly safe.

To these ends, our work was dividing into three parts which we are going to introduce in the

course of this report.

Firstly, we wanted to describe everything about the phenomenology of the lightning. We

present so the electrical field and the effect of point, the formation of the stormy clouds and

various forms of lightning stroke. Then, a quick description of the characteristics of

discharges which occur between the cloud and the soil is followed by the presentation of the

mechanism of the lightning. Finally, we finish this first part by the effects of the lightning.

Our study of the lightning followed by the creation of this last in laboratory, and to explain

the principle of triggering artificial, and also to identify the prevention devices and to analyze

risks dregs has the lightning. And in the last part we present different methods and devices for

protection against the lightning in the whole of cases (person, installation electrical and

electronic, building), and just like that danger owed of this phenomenon was avoided.

I. The phenomenon of lightning:

I.1 The stormy cloud: [07]

The stormy cloud is of huge mass generally of type cumulonimbus (fig.I.1); it is

originally from the production of lightning. that it holds up to several tens of square kilo, its

base is located about 2 to 3 km above the sole and expands at altitude up to 10 km, born from

the combined effect of moisture and of local warming of the soil; he forms a bubble of hot and

humid air, and a deference of temperature mattering between the low and the high of cloud

leading to violent currents of ascendants and descendants air cause the collision of the different

hydrometeors (water surfondue, ice crystals, snow, hailstones). The rubbing between these

hydrometeors creates an electrification followed by a separation of charges.

The ascending air current draws away the lighter particles that rise in form of crystals

of ice and take a positive charge while the heavier particles descendants who are down are

loaded negatively falling under the action of their weight, there is often a small positive charge

at the bottom of the cloud is in greenhouses in the negative ground.

The cloud searched has evacuated this load by "exploding "; he off-loads by exchange of

charges either with the soil (lightning stroke), or with other clouds or cloud zones, there are

two types of flashes of lightning, the intra or inter cloud; the discharge occurs has the inside of

the cloud or between two clouds.

Fig.I.1: Schema of stormy cloud

With the approach of a stormy cloud, and under the influence of negatives charges

finding in the bottom of the cloud, the atmospheric electrical field on the soil habitually in the

order of the hundred of volts per metre per good weather is reversed and attained by stocks in

the order of 15 has 20 KV / m; the difference of potential between the cloud and the soil is

such as discharge is imminent. Negative sign results from the convention of sense chosen, for

the field on the soil: the field is negative when atmospheric electrical charges are negative.

I.2 Electrical field: (fig.I.2)

Per good weather, the electrical field at ground level is about 100 is 120 V/m in the

direction of the Earth. With the arrival of the cloud charged electrically, it is reversed and can

attain 15 has 20 kV / m. In the right of the cloud (under the cloud), this electrical field is of in

fact that the high layers of the atmosphere are loaded positively while the Earth is loaded

negatively. The module of the field attains maximum value E max=20 kV / m. [07]

Fig.I.2: The electrical field at ground.

I.3 Effect of point: (fig.I.3)

Effect of point comes due to the fact that the electrical field is stronger near a peak

conductive loaded. All ionisation phenomena (ionisation due to the intense field) are therefore

most important in the vicinity of a point.

The effect of the electrical field is sufficient, but this gives its appearance of

progress to the lightning under form of branches or of bounds. Indeed, this translates also the

fact that the lightning seeks the best way, that is to say the quickest and the least resistant in

the breast of the atmosphere and the electrical field. In measure that the leader gets closer to

the Earth by bounds, the electrical field between the soil and the leader augments. In

particular, in the area around the pointed objects, the field is then sufficient to cause the

ionisation of air: he is therefore better driver of electricity in the vicinity of a point charge in

the vicinity of a surface charge of the greater ray of curvature. It is the reason for which the

lightning hits a point of preference. But things are not also simple because they realise that the

lightning does not always hit of a favoured way the very pointed drivers. [07]

Fig.I.3: Effect of point.

I.4 Leader by bound: [07]

We have seen that electric charges are naturally present in the air are speeded up by

the electric field. In the vicinity of a point the electric field can be increased locally

sufficiently to trigger an avalanche phenomenon. The way followed by these electrons creates

a slightly luminous ionised channel, called the leader: it is pre-discharge. Between each

bound, the tracer takes a pause about 50 microseconds.

As they move away from the point, the electrical field goes down. When he becomes

lower in 26 kV / cm, the energy of the electron becomes insufficient to continue the

phenomenon of avalanche: the avalanche stops and the leader stops during a length from 40 to

100 s. The charges of the leader are going to migrate under the influence of the electrical

field and the ionised channel becomes a point. A new avalanche of some dozens metres can

then develop at the end of the first one. The leader continues its path but not necessarily in the

same direction until the instant when the field will go back down once again below 26 kV /

cm. the field underneath 26 kV / cm. The same phenomenon will take place up to the

triggering of the lightning. That is why they say that the leader spreads by bound. This pre-

discharge its origin is in the cloud and progresses toward the ground.

I.5 The origin of the lightning: [02]

The lightning is defined as an electrical discharge associated to an impulse of

transient current of very strong amplitude.

The atmosphere is passed by a permanent current, said good weather current, under

the influence of a potential difference in the order of 300Kv between the atmosphere

positively load and the ground, the charges move through this current are offset by various

transfers of charge towards the ground of which the most important is the lightning stroke,

and lightning current is a current of complex form, he occurs a separation of electrical charges

in the breast the cloud.

I.6. Different types of the lightning [07]

It exists three kinds of the lightning are possible:

Inter clouds (between clouds) and intra clouds (inside the cloud) and between cloud and

ground (lightning stroke), Les figures here against the three types of lightning.

I.6.1 Intra-cloud: (fig.I.4-1)

The cloudy intra is an electrical discharge of altitude inside a storm cloud and whose

the graphics does not appear. The observer receives that a light diffuses and vague, more or

less intense light. It is estimated that 70 - 80 % of flashes of lightning are of this type

particularly in tropical zones. Discharge intra clouds uninterrupted. [07]

I.6.2 Inter-cloud: (fig.I.4-2)

The cloudy inter is an air electrical discharge whose the graphics appears distinctly.

Some of these flashes of lightning can measure several tens of kilometres (particularly at the

back of frontals storms). [07]

I.6.3 Cloud-ground: (fig.I.4-3)

The lightning stroke is an electrical discharge between the cloud and the soil, There

are two types of lightning cloud-ground: downward (summit of the cloud towards the soil), or

upward (soil towards base of the cloud). The downward type is the most frequent but a swing

of this type towards the upward type is often indicative of violent time because the cloud is

then particularly developed. Upward type occurs often at the front of the cloud as such,

because he leaves the anvil what can surprise people who think in the shelter by seeing the

storm in the distance. Upward type is the most frequent in the case of lightning stroke on

structures of big height (turn, pylon). [07]

Fig.I.4: Different type of the lightning

I.7 Main types of lightning strokes: [02]

The lightning stroke is classified according to:

- The positive or negative part of the cloud which off-loads.

- The sense of training of the leader who develops between the cloud and the ground.

This leader creates a channel in which ionise the arch circles. According to the Origin

of the leader, the lightning strokes will be descending or ascending.

I.7.1 The downward lightning stroke: (fig.I.5)

The lightning strokes begins inside the storm cloud, and towards the ground, there are two

categories positive and negative down. [02]

1-The negative downward lightning strokes, which is the most common, is initiated

by a negative leader spreading since the main negative charge towards the ground (fig.I.7-1).

At the end of course, the leader leads to the appearance of a return stroke to the positive cloud

and a transfer of negative charges to the ground. In the plains and low mountainous country, it

is estimated that more than 90 % of lightning strokes are of this type. [02]

2-The positive downward lightning stroke is initiated by a positive leader spreading

generally since the upper positive load towards the soil (fig.I.7-2). The arch back which

follows, presents a negative polarity and a transfer of positive charges of the cloud towards

the ground, often very important. This lightning stroke is rather rare. [02]

Fig.I.5: The downward lightning stroke.

I.7.2 The upward lightning stroke: (fig.I.6)

In that case the tracer develops from a prominence important for the soil. The phenomenon is

noticed in mountain or on big buildings. [02]

3-The negative upward lightning stroke is initiated by the spread of a positive tracer

developing since the soil towards the negative cloud (fig.I.7-3). It is followed by an arch back

positive and by a transfer of negative load of the cloud towards the soil. This lightning stroke

is spread enough in High Mountain. [02]

4-The positive upward lightning stroke is initiated by the spread of a negative leader

developing since the soil towards the positive cloud (fig.I.7-4). It is followed by an arch back

negative and by a generally very important load transfer positive. This lightning stroke is also

rather rare. [02]

Fig.I.6: The upward lightning stroke.

Fig.I.7: Upward and downward (negative and positive).

I.8 Mechanisms of the lightning: [02]

The air is finding between the cloud and the soil. And he is not a perfect insulator:

en effect the cosmic rays endowed with a big energy and a radioactivity of the Earth cause an

ionization of the molecules of air. The molecule which lost an electron becomes a positive

ion.

The released electron is captured by a molecule, giving a negative ion, However the

number of ions in atmospheric pressure is too weak (between 100 and 1000 by cm) for to

make the air conductor enough and therefore for to create flashes of lightning.

It is the avalanche phenomenon that will make the air conductor. During a storm, an

electrical field results from charges compared between the cloud and the earth, in effect of the

stormy cloud form with the earth a huge capacitor. The electron created by the ionization of

air is speeded up by the electrical field. When the energy of the electron is sufficient, he may,

by entering collision with an atom, tear from it off another electron. These two electrons

continue this process: it is avalanche phenomenon! There is a multiplication of electrons in

the gas thanks to this phenomenon.

I.9 Effects of the lightning: [07] & [02]

The main effects of the lightning are the following:

Thermal Effects (Joule effect):

- The fusion of elements at the point of impact of the lightning stroke.

- Crushing of the cable a cause of the producing by the vaporization of the water in the humid

soil.

-Dissipation of energy in form of heat.

Mechanical Effect:

- When the current of the lightning circulates in parallel drivers, they cause the force of

attraction or of repulsion could lead to mechanical distortions and breaks.

- Degradation of material in a violent way as the straining dielectric by surge or by premature

ageing because of pressures of structures.

Electrical Effects:

- Come from very strong potentials caused by to two reasons.

- The circulation of the current of the lightning (1KA in 100KA); by far the most important.

- Surges by conduction: when a lightning stroke hits a power line, the electrical wave

propagates along the conductor, generating a very strong current in the additional power line,

who causes a surge in its turn. This phenomenon almost loads always a short circuit.

Electromagnetic Effects:

- The lightning generating of the electromagnetic waves a broad specter of frequency (KHZ in

MHZ) causes radio disruptive.

- The impact of lightning is accompanied with an electromagnetic radiance, if this last attains

a conductor (a power line for example), the electromagnetic flux is generative of tensions

induced high.

II. The risks of lightning:

II.1 Artificial triggering of the lightning: [7]

To simulate the lightning, the scientists recreate in laboratory of similar discharges

as the lightning, and then guide them with the aid of a laser emitted by a device called

Teramobile.

Laser Tramobile the most powerful in the world, This laser is a mobile device which

produces flashes extremely powerful ultra powerful (terawatts 4, that is to say 4000 thousand

million Watts, the equivalent of 1000 power stations) during a very brief instant ultra-short

(100 femtoseconds, or 1 hundredth of a billionth of a billionth of a second).

Teramobile weighs 9 tons and holds in a classical container of 6 metres long. It is

the first time in the world where they manage to construct an instrument of this power in a so

reduced volume. This technological prowess allows transporting the laser easily on different

sites of experiments.

They use a generator of high voltage (fig.II.1) which allows collecting negative

expenses in an electrode similarly than negative expenses regroup at the root of a

cumulonimbus during a storm. The generative employee is unique; he allows attaining a

tension of 2 million volts. Facing the electrode cloud, a second electrode plays the role of the

soil of the Earth.

Fig.II.1: Generator of high voltage.

When tension between the base of a stormy cloud and the dry land becomes too

important, the lightning hits the soil. In the same way, in the laboratory, when the potential

difference between two electrodes attains some threshold, a flash of lightning forms between

them. But until now, it was not possible for the scientists neither to envisage, nor to decide on

the trajectory borrowed by the flash of lightning.

The first discharge is between the electrodes, without laser (fig.II.2-B). We noticed

that the track is not straight. The lightning spreads here, as in the natural state, borrowing a

random ionised path: it can leave any place of the cloud and can touch any point of the Earth.

The second is the same experience with a guidance laser (fig.II.2-A).

Fig.II.2: The discharge with and without laser

II.2 The Danger of the lightning: [8]

The lightning is the lethal meteorological danger to which all inhabitants of the planet are

most often displayed.

Where is the lightning the most present?

The lightning is the most present at the mountain climates then continental. There are two

principles:

II.2.1 Keraunic level: [8]

This is the number of days per year where we hear the thunder. We noticed a certain

similarity between the level keraunic of a region and density of lightning strikes in the

territory, proving so their link (this one being that flashes of lightning are the shutter releases

of the thunder) and showing more important risk in regions more propitious for storms.

II.2.2 The density of striking by lightning: [8]

A much more interesting parameter is the density of striking by lightning on the soil,

she expresses herself in number of impact on the soil by km and a year.

II.2.3 Risks of the lightning: [8]

Risks of the lightning are habitually classified in two categories:

Direct risks occur when the lightning touches an object directly (fig.II.3), the electric

current passing up to the soil across attained structure (deflagration of all types: tree, house,

fence, power line, living being, etc. ).

Fig.II.3: Direct risks

They are due to the passage of the lightning current circulating in elements attained

directly. Indeed the elevation of temperature can go up to fusion and perforation of metallic

objects, virifiction of the sand, explosion of materials of various natures or the blast-off of

flammable products. Under the effect of electric current, this humidity is instantly and

violently transformed into water steam and reacts under the form of violent explosion that can

cause the rupture or destruction of the insulating object.

Indirect risks are the most frequent. They are felt with hindsight, without the object

or the person's being directly touched by the flash of lightning and can be seen are possible be

received at relatively important distance of the point of impact, sometimes even without that

the thunder is heard. Indeed due to the resistively of the soil, the passage of electric current is

translated by a rise in tension of the local earth. This one can attain very high values close to

an impact of lightning, 300.000 volts for a current of lightning of 30.000 In and resistance of

10 ohm soil (Ohm law). The electrocution by step tension, which is rather frequent, is one of

the consequences of the elevation of the potential of the earth: when the lightning touches the

soil, a current wave spreads in surface and beams all around the point of impact (as when you

throw a stone into a water expanse, a kind of phenomenon of waves) on distance which can be

relatively important. If a person or an animal in contact with the soil is close to impact, it is

the striking by lightning by tension of step that explains the massive electrocution of the stock

in fields that is why we should be strongly dissuaded to run or to walk to big strides by time

of storm.

Moreover the surges of lightning on networks are create by the direct striking by

lightning of a power line or telephone, by electromagnetic radiance or by rise in potential of

the local earth (of current return by the soil).

To finish there are other risks of the lightning, less known but also dangerous, as

electromagnetic radiance produces by the lightning channel and which acts on apparatus

containing electronic components. It is therefore possible to sum up material damage caused

by to the lightning in several points:

- Fires and resultant accidents of defects in the earth or of contacts between high and low

tension.

- Surges by conduction, by induction or by elevation of the potential of earth produce

- Lightning current leads on one hand to a tension of common mode (U = R I+ L dI/dt) and an

electromagnetic field of an exceptional intensity. He follows the generation of very powerful

parasitic electrical impulses, which indeed are to degrade sensitive electronic equipments

(television sets, computers, etc.) even if the flash of lightning is moved away. If the flash of

lightning is closer, the parasite can also destroy more resistant equipments (lamps, engines,

ovens).

- Destruction of buildings and of equipments by fires or explosions.

- Accidents linked to the manipulation of flammable products.

- Deterioration of electronic components and other elements.

- Dysfunction of automatic machines and computer equipment.

- Premature ageing of the electronic components (but also insulating materials etc).

- Break of production chain in industrial middle, or computer and all that can with a

production loss due to the deflagration of the equipment.

II.2.4 Damage of the lightning on the man: [8]

The lightning, according to its theoretical aspect, has all characteristics of an

extremely lethal weapon. She can indeed act on many objects of our daily but also on our

environment. As fires are owed to the lightning, these fires are not without trace on our

environment and leave a deep scar in our forests. The general increase in temperatures is not

to lower the fear of seeing our forests disappearing. They so noted that because of lightning,

of dryness and of human factor of deforestation (always ask higher of wood), fires of forests

are caused by in discharge of clouds. Nevertheless these thunderbolts also have a big impact

on the Man. Damage of mechanical nature can be caused without his resulting from it of fire.

But this damage unsettles electricity networks and these incidents drive to electrical

breakdowns. More thunderbolts also attain planes (On average, a civil aircraft is subjected to

about a thunderbolt per year). And it is indeed on the man that she makes most damage. A

person hit by the lightning can be burnt to different degrees, but especially die. Indeed the

tension which crosses the human body and its intensity is such as the person is grilled on

place.

It is therefore possible to determine several types of striking by lightning on the

men, who can include as direct striking by lightning, death of the victim. First of all the

striking by lightning by step tension (fig.II.4) can prove to be lethal. When the lightning hits

the soil, current spreads across the earth, and as explained higher because of a potential

difference, a person or an animal getting into contact with the soil will be driver of the current

which will pass by points touching the soil. Often die therefore because of this type of striking

by lightning. The men too if they walk to big step have big risks of dying.

Fig.II.4: The striking by lightning by step tension

Then comes the striking by lightning by tension of touch (fig.II.5), which occurs

when a person touches a metallic object itself touched by the lightning, where quite other

strongly electrified object. Current is therefore going to go down across the body to join the

earth. Difference of potentials is then murderer but if you balance the potential of each side.

Fig.II.5: The striking by lightning by tension of touch

Of more striking by lightning by lateral flash of lightning also is much known.

Indeed it is the striking by lightning which is felt when a tree is struck down and that they are

in side. So the current of the lightning takes driver down by an element slightly then chosen

an element of lesser resistance which can be a person located nearby. It is therefore very

dangerous to shelter under a tree during a storm.

The striking by lightning of vehicles is also an important question of the danger of

the lightning on the man. The car is indeed isolated enough from a thunderbolt thanks to its

tyres which serve as insulating to avoid striking by lightning by step tension, and of more the

Faraday cage a role is which the metallic bodywork of the car plays well enough. A Faraday

cage is a surrounding wall used to protect electrical nuisances but also external

electromagnetic, or conversely, to prevent an equipment from polluting its environment. On

the contrary, tyres introduce certain obstacle to the flow of common towards the soil. Of such

kind, as one or several electrical arches are going inevitably to occur between the rocker panel

and the soil, these arches that can in a small number of cases draw away the fire of the vehicle

(burning of tyres, explosion by piercing the fuel tank). It is therefore necessary to pull down

the aerial of the car radio to avoid that these rare cases occur. However, a convertible vehicle

or composite material as a caravan or a camper gives no protection against direct striking by

lightning.

Danger and damage of the lightning on the man, as on his environment or his daily,

are therefore real, but the lightning can be envisaged, so that this one could get ready for not

have to make for the lightning, whatever ways it is.

II.3 Prevention and detection of the lightning: [8]

First of all radars are jointly used with the lightning detectors. Indeed these first are

the widely used to detect the formation, position and potential of threat of storms. Weather

radar captures the formation of a cumulonimbus, and everything that follows. They will

therefore follow the evolution of precipitation aloft and near the ground, but will not be able

to say if there is a presence of the lightning, it is at this moment there that intervene the

detectors.

It is therefore possible to determine the electrification of a cloud and to provide the lightning

that results from it thanks to several detectors:

II.3.1 Lightning detector in the space meteorology centre: (fig.II.6) [8]

A lightning detector is an apparatus which allows picking up the electromagnetic wave

generated by a flash of lightning coming from a storm.

To detect or to provide an imminent lightning they have several mechanical tools.

Fig.II.6: Meteorology

II.3.1 Mill with field: (fig.II.7) [8]

A field mill is an instrument which measures a field of static electricity. In

meteorology, this instrument allows, thanks to the analysis of the field electrostatics above

him, to signal the presence of an electrically loaded cloud translating the imminence of the

lightning.

Fig.II.7: Mill with field

II.3.2 The directional antennas: [8]

The most sophisticated lightning detectors are the directional antennas. It is found in

the weather stations of big wingspans for the antennas of big importance and very efficient

and in small structures for the smallest antennas.

There are several types of directional antennas, the very efficient parabolic (fig.II.8-

B) on long distance but more sensitive to problems of environments (wind, storm, rain) and

the directional antennas of type Yagi (fig.II.8-A) which are antennas protected well but

having a benefit between 7 and 19 dBi (isotropic decibel) while parabolic have a higher

benefit from 16 to 28 dBi what is more used for measures at long distance.

The benefit of decibel isotropic defines the angle of radiance of the aerial (therefore

defines the angle of vision of the aerial). The more this benefit is high, the more the radiance

angle is small, and therefore more the location of electrical discharges will be definite.

Consequently the parabolic antenna is more subject to physical and mechanical

disturbances; a parabolic antenna is a good choice to locate in a cloud, an intense

electrification that lets to provide the lightning. However, its not a good choice for short

distance (

only 5 - 10 minutes, what is rather long for some users who need to know the location of the

lightning times by minute. The satellite is therefore suitable rather for prevention

They have therefore the satellites METEOSAT which were to the number of 5 in the

seventies, and are now no more than 3 (Mtosat 5 who notices India, Mtosat 6 and 7

notices Europe, in case or one two would break down) and are aimed at being geostationary

(they keep the same position in comparison with the Earth) and allow so the continuous

observation of a definite zone of the globe.

The satellite is therefore an additional advantage in lightning detection, because he

allows to prevent storms and therefore to orientate then the directional aerials. However these

satellites also spot thanks to their many sensors, the luminous flashes caused by to flashes of

lightning and therefore can locate the location of the lightning thanks to degrees of latitude

and degrees of longitude, by paying however attention to the parallax introduces leaving

towards poles. (The parallax is the impact of the change of position of the observer on the

observation of an object.)

We can therefore to conclude that different means to detecting the lightning exist,

and are more or less effective. These means of detection are often centred on the detection of

important electrical discharges, as well as of electromagnetism. They allow so to determine

the location of an imminent lightning or who is under way, and also to tell the individuals by

various ways (Internet, television, daily newspapers etc.)

III. The protection against lightning:

III.1 Protection of the persons: [14]

All recommendations to protect the persons against the lightning are founded on two

principles: do not constitute a target for the lightning; not be situated in situations which risk

applying a potential difference between two parts of the body. In practice it is always

necessary to try to find the situation of lesser risk: it is indeed rare not to find a situation at

high risk in reports of accidents. Recommendations which follow aim all to respect principles

enunciated above.

These recommendations are logically deducted from the physical properties of the

lightning, from the mechanisms of striking by lightning, from the specific characteristics of

electric currents linked to the lightning, all these data known well, finally the physiopathology

of striking by lightning today.

Generally, they will avoid some external activities, of the domain of leisure, sports

or of job, known to be particularly dangerous by time of storm. Such is the case of following

activities: peach, bathing, boat, cycling, golf, mountaineering, as well as electrical jobs,

roofing repairing. Generally, all activities that exposes to striking by lightning direct.

What to make when they are surprised by a storm and that they are outside?

The best a car is to take refuge in a building or. And disconnect the cables of aerial

and of electrical feeding of any electrical device. If it is not possible, it is necessary to move

away from insulated trees, from summits or from bones, because the lightning hits most often

the highest point which she finds in the region. In forest, the highest trees constitute a bigger

danger than the babies, especially if they are in the edge. The discharge of the flash of

lightning spreads in the soil in all directions and produces tensions which ease progressively

only with distance. You should be therefore necessary lie down never on the soil when a

storm bursts, but to put on in squatted position, folded up, preferred arms and legs in a bowl

on the dry soil.

Avoid any contact with metallic objects A distance of security of 5 m at the very

least (behaviours of water, an umbrella, a bike), electrical devices;

Persons being in group have to move away one of others of at least 3 metres, to

avoid the risk of a lateral flash of lightning between two persons.

The risk of striking by lightning of a person can spread to her neighbours by a spark

crossing spacing out between persons too much brought closer: this phenomenon is called

"lateral flash of lightning ".

You should not forget that, in relation to natural phenomena, each has duty to notice

a level of security rather excessive than limits, and that, by time of storm, it is sometimes

reasonable to come back at home and to prepare candles and lamps storm!

III.2 Protection of the installations electrical:

III.2.1 The lightning rod with simple stem: [2] & [5]

This device is a metallic stem must be installed on the highest point of the building,

and connects to the drivers of descent (copper), perfectly isolated and whose lower end is

grounded. Who must be accomplished in crow's foot. The lightning rod allows to protect and

relieves her of the lightning in a security way. The functioning of the lightning rod is based on

the point effect. This method is named in norm NFC 17 100.

Choice of the lightning rod will be determined has leave the current of allowable

lightning maximum for the installation.

The functioning of the lightning rod exploits the distance of priming D, by the

method of the fictitious sphere (fig.III.1). For a leader who moves, the point of impact on the

soil is part of points of the soil located at distance D, and is therefore on a ray sphere D it is

centred on the end of the tracer which moves at the same time as to him. As a result the top of

the lightning rod, which is a point of the fictitious sphere, must be at a height H such as the

closest zones to be protected on the soil are located out of this sphere (see following fig).

Fig.III.1: Lightning rod with simple stem.

III.2.2 The Faraday cage or mesh cage: (fig.III.2) [2]

This principle is use for the very sensitive and important buildings (Electronics,

computer science, serviceman, control towers), sheltering from computer equipment or from

integrated circuits. The external armour plating protects against the waves of the lightning,

consisting in protecting structure by a metallic mesh size (belts, numerous descents towards

the earth).

It consists has multiply the straps of descent has the outside of the building in a

symmetrical way. Horizontal links are added if the building is high. The drivers of descent are

link up has the earth by crows' foots, and prolonged by vertical stems, in the right of knots,

which form lightning rods. Effect results in better equipotentiality of the building and the

division of lightning currents, reducing so strongly fields and electromagnetic induction.

Fig.III.2: The Faraday cage.

III.2.3 The lightning rod with tense threads: (fig.III.3) [2]

This lightning rod, in principle close to that of the Faraday cage, is constituted of a

conductive distant mesh size of structure to be protected for avoiding that lightning current is

in contact with this one.

This system is composed of one or of several threads tense drivers above

installations to be protected. The protection zone is determined by application of the electro-

geometric model.

The drivers must be connected to a ground to each of their extremity.

The installation of tense threads requires a particular study notably taking into

account the mechanical keeping, nature of the installation, the distance of isolation.

This technology is very used to protect stores of munitions and in general when it is

not possible to use the structure of the building as drivers' support that flows lightning

currents in the earth.

Fig.III.3: The lightning rod extended.

III.2.4 The installation of lightning rod: [5]

The installation is composed of one or several lands plugs, different electrical driver,

one or several lightning rods simple stem and indirect protection systems. Application norm

for the installation is NFC 17 100.

III.2.4 -1 The installation portrays: [5]

The installation must meet the criteria and needs established in prior study.

Establishment, The installation is composed: d 'one or several lands plugs, different electrical

driver, one or several lightning rods and indirect protection systems.

III.2.4-2 Situation of Lightning rods: [5]

The lightning rod will be located in the centre of the installation, in the highest point,

and at the very least, two metres above the zone to be protected, including aerials, turn of

cooling, roofs, of water reservoir etc.

Fig.III.4: The installation of lightning rod.

III.2.4-3 The Mast: [5]

Will be iron galvanized or stainless steel (fig.III.4-B), fixed directly to structure or to

adapted support already prevented in the building.

III.2.4-4 The descents: [5]

One or several descents will be preferably realized in ribbon of red copper tinned by

30 mm wide and by 2 mm in thickness (fig. III.4-A). Will be fixed to the lightning rod by

means of final pods and will link to metallic structure and to equipotentailles links.

The lightning is a current high frequency which circulates on the periphery of the drivers.

III.2.4-5 Earth plug: [5]

Any descent of lightning rod must be linked up with an earth plug (fig. III.4-C). His

purpose is flow and dispersion of lightning current. This earth plug unites 3 indissociable

conditions:

A. Value ohmic earth plug: [5]

According to French and foreign norms as well as technical specifications of the

various administrations, value ohmic the resistance of earth plug must be less than 10 ohms.

This value must be measured on the earth plug isolated from quite other conductive

nature element.

If 10 ohm value is not attained, we consider the earth plug to conform if it is

constituted of at least 100 m of drivers or of electrodes, every element not exceeding 20 m.

B. Equipotentiality: [5]

Norms impose in equipotentiality of lightning rods earths plugs with the existent

earth plugs of protected structures, and the metallic doorframes of windows and of doors with

distance of lower separations in 1 m,

C. Look of visit: [5]

The look of visit sheltering the head of the stake and allowing verifying periodically

the connection is considered a necessary complement to a well-executed earth plug; the

elements of connection of an earth catch can be accessible in a look of visit (join crow's foot,

pickets, linked by control).

D. Improvement of earth plug: [5]

In the soil of high resistance, it is possible to improve conductivity chemically of the soil:

Salt addition: prefer a copper sulphate instead of a sodium chloride which can

corrode the electrode. Salts are deposited in a circular trench around the head of the picket

(depth 25 - 30 cm) then watered to impregnate the ground. This solution is not very

expensive, although requiring the use of several kilogramme of salt, but is necessary being

periodically renewed to compensate for the loss of the salt drawn away by infiltration waters.

Addition of metallic salt in form of insolvable frost: combination of two chemical

solutions forming a stable colloidal compound. This solution can last several years and is not

very sensitive to dryness. Necessary quantity is much weaker than for soluble salts.

III.2.4-6 Crow's foot: [5]

The plug of minimal earth is constituted by 25 metres of ribbon of tin-plated copper

30 x 2 mm, divided in 3 bites buried in 3 trenches from 60 to 80 cm deep, disposed to 45

degrees some of others, the dug fan-shaped forming crow's foot; the longest bite has an

extremity linked up with the joint of control, two other bites are linked up with it with the aid

of a special join called join crow's foot (fig.III.5).

Fig.III.5: Earth plug type crows foot.

III.2.4-7 Pickets: (fig.III.6) [5]

In case the topography of places does not allow the development of crows foot such

as describes above, it will be possible to realize an earth plug with the aid of at least 3 stakes

of length copper minimum of 2 m at least, buried vertically in the soil; these will be distant

some of others about 2 m; a distance of distance of the foundations of 1 m in 1,50 m will have

to be respected.

Fig.III.6: Earth plug type picket.

III.2.4-8 Mixed: (fig.III.7) [5]

In case the earth plug in crow's foot would be considered inadequate due to the

unfavourable nature of the soil, the combination of crows foot / pickets will allow getting

certain improvement. In that case, every extremity of the bites of crow's foot is linked up with

an earth picket.

fig.III.7: Earth plug type mixed.

III.2.5 Lightning arrester: [5]

The lightning arrester is a device intended to limit the transient surges of origin

atmospheric and to divert the current waves towards the earth, to limit the amplitude of this

surge in a not dangerous value for the installation electrical and the electrical equipment.

Different models of lightning conductors were conceived with the intention of assuring a

better protection of installations and good service continuity.

The lightning conductor serves for selling transitional surges across a link in the

earth capable of supporting currents of high intensity during very short length. This derivation

in the earth is made of two ways: by priming with the aid of a lightning conductor with spark

gap (almost left today) or by conduction with the aid of a lightning conductor in varistor.

Lightning arresters with variable resistance with spark gap are the most spreading in

installations HT and MT. the current of lightning .le is sold towards the earth by the priming

of spark gaps; variable resistor will limit the current of discharge and to make easier one the

redemption of the arch.

III.2.5.1 Lightning conductor medium tension (HTA): [10]

A. Constitution:

In this type of lightning arrester is constituted by one or several varistors (non linear

resistance) in the silicon carbide, puts together in series with one or several spark gaps

(fig.III.8). The whole is placed in sealed envelope insulation full of a dry gas (air or

nitrogen). Waterproof quality is primordial to avoid the corrosion of spark gaps, the bypasses

of the active part and the modification of characteristics. By subdividing the interval of

priming into several elementary spark gaps, they stabilise the characteristics of priming of the

lightning conductor.

Fig.III.8: Lightning arrester HTA in the silicon carbide and in spark gaps.

Spark gaps are constituted of brass discs smashed up, piled and separated by small

ceramic insulating rooms.

Variable resistor is constituted of grains of silicon carbide agglomerated by a

sociable and pressed under form of discs the parallel faces of which are mitallized and the

edge covered with an insulating coating intended to eliminate the skirting.

B. Functioning principle: [10]

In normal functioning in the absence of surge, spark gaps are not conductors, and the

resistance of the varistor is very high and prevents the passage of current. When remembrance

the upper surge at the level of priming (fig.III.9), spark gaps start and divert the current of

discharge through resistor, the current of the lightning chooses the way least resistor, that of

the resistor whose value is weak all the more as tension is high (non-linear characteristics),

what allows to limit surge.

Fig.III.9: Lightning conductor HTA in the silicon carbide and in spark gaps.

After the passage of the current of discharge, the lightning arrester remains driver,

but the tension in its bounds diminishes and favour the non-linear resistors are decreasing

rapidly the current that can be easily interrupted by the gaps in its first zero crossing. So,

surge is levelled without causing, neither artificial defect, nor cut wave, since the presence of

serial resistor with spark gaps avoids the collapse of tension after priming.

III.2.5.2 Lightning conductor of high voltage (HTB): [10]

A. Constitution:

They try to improve in high voltage HTB and very of high voltage the level of

protection of lightning conductors. It means that it is necessary to reduce, on one hand,

priming tensions and, on the other hand, informed residual tension nominal of discharge.

To diminish, in complete safety, priming tensions, it is necessary to stabilise them

more. In order to do that, they add in the assemblage used in HTA (fig.III.10), Some lightning

arresters also include distributors systems of tension (divisors resistive or capacitive) and

systems of blowing of the arch (magnets or spools of magnetic blowing), These systems allow

to control the tension applied to every individual spark gap. In order to diminish priming

tensions, spark gaps (are constituted of electrodes two of copper) are changed and, placed in a

ceramic room of cylindrical form to make easier their stacking with non-linear resistor.

Fig.III.10: Lightning conductor HTB in the silicon carbide and in spark gaps.

Spark gaps to magnetic blowing use to diminish the residual tension nominal of

discharge. Arches are stretched in the ceramic room under the influence of a magnetic field

created by an induction coil covered by the current crossing the lightning arrester. The fluted

profile of the ceramic room favours the lengthening of the arch. So, arch tension being

augmented, the lightning arrester deactivates before passage by zero of the service tension,

limiting energy so to be dispelled by resistor non-linear and making easier the deionisation of

air in the ceramic rooms.

B. Functioning principle: [10]

In permanent regime, the lightning arrester is covered by very low-current (in the

order of the milliamp) drained by the system of tension sharing out.

The presence of the upper surge at the level of priming, spark gaps start and current

augments fast, which in front of a spool, the impedance of spool is high, the non-linear

resistor placed in parallel on the blowing spool, which allows passing current.

After the passage of a surge, the strongly ionised spark gaps do not deactivate.

Current crossing the lightning arrester then comes from network. Its amplitude and its

variations are weaker, and the impedance of the spool diminishes considerably and this one is

going to be, in its turn, covered by current. Under the influence of the magnetic field created

by this spool, the arch is stretched in the ceramic room. The arch tension augments.

When arch tension attains the tension applied to the lightning arrester, this one

deactivates (permanent area).

In this study of "protection against the lightning", we conclude that the man cannot control this phenomenon, and it is not possible to know the time and the place of effectiveness of this lightning stroke, consequences of the lightning are not a fate and modern researches allowed to include physical phenomena and these effects. Weve presented already cite protection methods. it is not mysterious or magical and can be concluded in only respecting the elementary rules of the installation and uses.

What has just been said concerns the traditional conception of the protection of buildings and of edifices by lightning rod or faraday cage, which has as function to avoid damage by direct lightning strokes, and that it was necessary to indicate by external protection .

But today, there is a very net tendency to stress, at the same time, the needs necessity to install an internal protection. Who protected electrical equipment, computer science, broadcasting, and telecommunications pervades against lightning strokes indirect, and all domains of the human activities, like industry, trade. The development speeded up by these techniques, equipment of which has an extreme vulnerability with the effects of the lightning. The equipotentiel is the guarantee of the good functioning of the modern electronic systems. Other many installations had since been protected by these methods and results are surprising so much got effectiveness is very good. Of course, the lightning being an impulsionnal phenomenon, no protection system will be able to guarantee a complete protection.

[01] : Philippe Dunand Protection des installations lecriques contre la foudre .

[02] : Mmoire: protection dun rseau lectrique [Thse de magister soutenu en juillet 2006] [03] : Mr.Bekri Abdelkader protection des rseaux lectriques contre la foudre [Thse de magister soutenu en juillet 1985]

[04] : Helita Protection foudre paratonnerre

[05] : Soule Protection contre la foudre et les surtension

[06] : Christian bouquegneau Doit- on craindre la foudre?

[07] : F.Rachidi la foudre et ses effets electromagnetique

[Site :http://lrewww.epfl.ch/dir-CEM/8_Foudre_2004.pdf]

[08] : Tramobile ATH-CNRS, la foudre dirige.

[Site:http://videotheque.cnrs.fr/media/doc_acc/g%C3%A9n%C3%A9riqueT%C3%A9ra.pdf]

[09] : TPE TPE consacr la foudre

[Site : http://tpefoudre.weegee.fr/]

[10] : Frdric MACIELA Parafoudres moyenne tension HTA et haute tension

HTB

[Site : http://www.techniques-ingenieur.fr/book/d4755/parafoudres-a-moyenne-tension-hta-et-

a-haute-tension-htb.html]

[11] : la protection contre la foudre

[Site : http://www.paratonnerre-pda.com/phenomene_foudre.htm]

[12] : Metz-Noblat la foudre et les installation lectriques HT N: 168

[Site: http://www.cret.fst.u-3mrs.fr/electronique/CT168_foudre.pdf ]

[13] : Projet de tramobile : Peut-on dompter la foudre ?

[Site : http://www.planete-energies.com/HtmlContents/fr-fr/Article/7_5_foudre/dossier.pdf]

[14] : Comprendre la foudre Protection de la personne

[ site : http://www.foudre.org/protection-prevention/protection-personne.html]

The BeSt WisHeS

AtiKa . M

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