English

I.- INTRODUCTION

II.- WHY IS LIGHTNING PRODUCED?

II.1 Lightning's electrical charge

II.2 Lighting discharge processes

III.- CAN WE PROTECT OURSELVES?

IV.- INHIBITION SYSTEM VERSUS PROVOCATION SYSTEM

IV.1 Important aspects

IV.2 Basic concepts: transparency of the apparatus

IV.3 Activation potential

IV.4 Maximum potential accepted by the filter

IV.5 Operating times

V.- STUDY OF THE SAF Nuevas Tecnologías LIGHTNING INHIBITOR

V.1 Structural description

V.2 Operational possibilities

V.3 True operation of the inhibitor

V.4 Capacitor discharge

VI.- CONCLUSIONS

VI.1 With respect to the aerial head

VI.2 With respect to the capacitor discharge

Vll.- SYNTHESIS OF THE SAF Nuevas Tecnologías SYSTEM

VII.1 A quick summary and overview for the reader

The natural atmospheric phenomena, such as electrical discharges, the most well-known effects of which are thunder and lightning, are capable of causing serious injury to persons and damage to property. The most common that occur to buildings or to their contents are normally fire, the breakage of structures and the heavy losses due to the interruption of business activities.

All this is extremely worrying to all those in positions of responsibility and produces a pressing need to find the most suitable, optimum solution that eliminates this type of problem as far as is possible.

SAF Nuevas Tecnologías is fully aware of this need, and proposes an innovating global system of protection that is fruit of a thorough investigation into the problem and based on the most advanced multidisciplinary knowledge that intervenes in atmospheric electrical discharge and their collateral effects.

By starting out from the true fact that preventing the cause will eliminate the problem, all its effort was concentrated in this path of research, because practically, since Franklin's experiments, there have not been any real innovations in this field.

PREVENTION IS THE MAXIMUM PROTECTION This learned principle has guided all SAF Nuevas Tecnologías efforts in its developments and products. More than one million lightning strikes are produced in Spain every year (see Figure 1), causing damages and losses to the tune of several million Euros. A lightning strike basically produces three types of problems:

Figura 1: Niveles de tormenta en España.

Firstly, If it directly strikes a building without any protection it can cause accidents such as electrocution of the people inside, fires, damage to the building itself, destruction of electrical installations and the equipment that is connected to it, motors, machinery, computer and communications systems, together with interruption of business activities.

Secondly, If it strikes an overhead electricity power supply cable, it will cause a heavy over-voltage condition that is distributed to the electrical installations provoking destruction of the electrical and electronic equipment connected to them.

Thirdly, The actual lightning conductor itself may be considered as an immense antenna that connects the cloud to the ground, emitting strong electromagnetic radiation that is captured by any electric power conductors and electronic equipment that is located within the radius of action of the antenna, transforming the received radiation into a conducted power over-voltage. All this contributes to both damage and destruction.

Since the signals used in electronic apparatus are quite small, any electromagnetic interference, however small it is, will affect the correct operation, and may even cause irreparable damage to security, fire-fighting and data-processing systems etc.

All this makes the requirement for protection against this atmospheric phenomenon quite evident, making use of the most efficient protection system in existence, since it will have direct repercussions on personnel and the correct operation of all types of installations and equipment.

The lightning formation inhibition system is based on certain solid theoretical and practical physics fundamentals that guarantee the efficiency and reliability of the system.

Due to the newness of the system, it is not easy to locate any literature on it, so that in order to facilitate its understanding, SAF Nuevas Tecnologías provides a description of the basic operational principles of the innovating Inhibition System in a simplified manner, and with the intention that is be as simple as possible since the intervening phenomena are very complex.

This description is divided into six sections:

II. Why is lightning produced?

III. Can we protect ourselves?

IV. Inhibition system versus provocation system

V. Study of the SAF Nuevas Tecnologías lightning inhibitor

VI. Conclusions

II.1 Lightning's electrical charge

The electrical gradient in the atmosphere with a clear sky is around 100V/metre, and is due to the electrical field produced by the negative charges that normally exist of the earth's surface. In a storm situation, the variations in pressure and temperature in the atmosphere give rise to the formation of cumulonimbus cloud formations, where the central column may reach beyond 15,000 metres. The higher the cloud's core column, the more frequent will be the lightning. In order to be capable of generating a lightning bolt, this internal column has to exceed 3,000 metres in height.

There are several varied and complicated theories in existence that attempt to explain the true mechanism for charge separation, but none provides an exact explanation of what pushes the charges inside the storm cloud. Within the central column of a cumulonimbus core exist ascending air currents with speeds in excess of 120 km/hour which separate the electrical charges that originate the lightning discharge. Studies on rainfall have revealed that fine precipitation acquires a positive electrical charge, whereas larger raindrops gain a negative charge. The strong movement of air within the interior column of the cumulonimbus separates these charges by driving the finer drops (positive) up towards the higher zones. The heavier negative charge remains at the base of the cloud. As the charges are separated, the various cloud zones are charged to such a degree that the electrical forces produce more and more charged fragments (Figure 2).

Figure 2: Inside a storm cloud, the electrical charges separate. The warm winds drag the positive charges downwards, leaving the base of the cloud negatively charged. The attraction between the ground and the negative charges at the base of the cloud create the lightning bolt, a brief current of negative charges that travel from the cloud to the ground.

Since the cloud base has a great many more negative charges than the earth below, an attraction is generated between both charges. Therefore, the electrons that are liberated close to the cloud are attracted towards the earth. As these electrons move, they collide with molecules in the air that exist in their path, their bonds are broken (they become ionised) and in this way further charged fragments are created. These new fragments are dragged towards the lower section, together with the original electrons, creating and electrical avalanche effect. The positive ions that are left behind create further attraction towards the cloud for the collection of electrons. In turn, more and more electrons continue to be freed inside the cloud, dragging those that are trying to rise, down towards the base. This process of acceleration and braking is continually repeated, causing the initial group of electrons to follow a zigzag path, with advances of some 50 metres in 50 µS from the cloud towards the earth, which is known as the "stepped leader" (Figure 3).

Figure 3: A diagrammatic representation of the lightning formation mechanism.

As it approaches the ground, the descending stepped leader discharge produces, by induction, a fast increase in the electrical gradient on the earth's surface, which adds to the continuous component that already exists as a consequence to the static distribution of charges within the cloud.

II.2 Lightning discharge phases.

This is divided into four phases:

1st phase: PREDISCHARGE or descending discharge, the appearance of descending stepped leader discharge, that extend from the cloud in direction of the earth.

2nd phase: The APPEARANCE OF ASCENDING ELECTRICAL DISCHARGE, when the descending stepped leader head approaches the earth. In the majority of cases, these discharges arise from elements that protrude from the earth's surface, such as trees, chimneys, antennas and lightning arresters etc. as a consequence of the tip effect.

3rd phase: The CREATION OF AN IONISED CHANNEL between the cloud and the ground when the stepped leader head unites with the ascending discharge. A short-circuit is created between the cloud and the earth which allows the flow of a high intensity electrical current. This is the so-called "return stroke".

4th phase: A HIGHLY-LUMINOUS STEPPED LEADER between the cloud and the earth. The electrons that are located close to the ground are usually the first to feel the connection and they accelerate downwards. Then the successive upper groups do likewise. Therefore, although the negative charges move from the cloud towards the earth, the luminous flash travels from the earth towards the cloud in a time of 100 µS. At the very same time, during their journey towards the earth, the negative particles collide with the air and cause it to heat up, this results in a sudden expansion that is propagated in the form of sound shock wave known as thunder.

Current peaks vary from 1 kA to 400 kA, with an internationally agreed mean value of 30 kA.

It is possible to observe that a single lightning bolt is not produced, quite on the contrary, by taking advantage of the same ionised channel, the discharges may be multiple, at time up to forty have been counted. The energy freed by the discharge in produced within a time of 100 to 300 µS, and the maximum peak duration of the discharge is only of the order of 1 or 2 microseconds.

More than 90% of the discharges from the cloud towards the earth take place between the negatively charged cloud and the positively charged earth as has been explained, however, the inverse can also occur.

Three basic levels of protection should be considered when designing an installation.

1) Primary protection level against a direct lightning bolt strike. This traditionally includes the arrester, the down-lead and the ground connection.

2) Secondary protection level, against the over-voltages produced by a nearby lightning strike. This includes voltage-limiting systems.

3) Tertiary protection level, specific protection of equipment against inductive coupling, which is difficult to achieve with traditional lightning arresters used for primary protection due to the close proximity of the strike zone which produces very strong electromagnetic interference.

We shall concentrate our study on the first level of protection, where SAF Nuevas Tecnologías introduces the innovating concept of the inhibitor, which prevents the formation of the path along which the lightning bolt is produced, thus eliminating the possibility of a strike. We shall then refer to the Induc-Control earth filter, which covers the second and third levels, or the protection of the earth connections against atmospheric electrical interference that storms cause via the earth, avoiding its passage and propagation in both directions.

The fundamental operating principle of the classic lightning arrester is that of provoking and providing the descending stepped leader with a predetermined path to earth that allows maximum discharge of the heavy lightning current, thus diminishing the destructive effects on buildings and its direct consequences. There are several lightning arrester systems and various techniques.

The first system is based on Faraday's Laws. This is limited to surrounding the building to be protected with a dense metallic cage through which the lightning, if it strikes the building, is dissipated to earth, causing minimum damage to structures, however, it does not prevent and in fact, increases the destructive, so-called secondary effects, cause by inherent and powerful electromagnetic induction in electric and electronic equipment.

The other systems are intended to be more active, since they actually provoke the lightning strike through the ionisation of the lightning arrester tip and producing the appearance of ascending discharges. These active systems are based on the so-called electro-geometric model.

This models starts out from the experimental fact that the advance of the lightning stepped leader is not produces in a continuous manner, but that it is formed by pulses, which advance a certain distance then halt, advance once again and stop repeatedly.

According to this model, the lightning strike point is the first point on the earth that is located at the descending stepped leader's limiting distance. This limiting distance, R, separates the descending electrical discharge head from the strike point, and partly depends on the maximum lightning current intensity. It is therefore possible to suppose that the stepped leader tip is surrounded by an imaginary sphere, having a radius R that accompanies it along its path. As it nears the earth, the first point that comes into contact with the imaginary sphere will determine the lightning bolt's strike point (Figures 4 and 5).

Figure 4: The "switching" distance or limit, and the area protected by a conventional lightning arrester in accordance with this model.

Figure 5: Screening distances in accordance with the required type of protection.

The activated tip system is based on the following considerations: the electrical field gradient increases around the lightning arrester because of its geometric design (tip effect). When a descending discharge approaches during the 1st phase, the electrical field gradient around the vertex takes on a value that exceeds the minimum required to produce the discharge. This, therefore, commences from the tip, producing an ascending discharge that moves out to meet up with the descending discharge (2nd phase). The end-result is the union between both and the draining of the lightning current (3rd and 4th phases) through the earthing system.

The electrical field influences the lightning bolt development by means of two simultaneous components.

· By the slow growth of the field in function of the spatial charge located inside the cloud.

· By the fast growth of the field associated with the descending discharge that is moving towards the ground.

Since it is not possible to control the descending discharge, one method of improving the efficiency of these systems is to encourage the creation and propagation of the ascending discharge.

The first lightning arrester of this type to be used was the Franklin arrester, consisting of a tip surrounded by ridges that increased the ionisation of the air around this central tip. The protection radius for the arrester can be approximately calculated by multiplying its height by 1.7.

A currently forbidden lightning arrester because of its contaminating effects is the radioactive type, whereby the ionisation is obtained through the emission of particles from a radioactive element fitted to the extreme end of the arrester, an effect, which in practice is nil.

The ionising lightning arrester is another type that is employed, which basically operates by increasing the voltage at the tip when the environment is charged so that an increase is produced in the "corona effect" (the formation of ions in the form of a corona around the tip), which tends to increase the formation of the ascending discharge.

IV.1 Important aspects of the SAF Nuevas Tecnologías system.

There are two extremely important aspects that advise the fitting of SAF Nuevas Tecnologías protection in all types of installations:

1.- The use of SAF Nuevas Tecnologías protection elements in any installation does not interfere with, neutralise nor reduce any already existing protection, with the obvious exception of conventional lightning arresters, which, because they are "lightning provocation capture devices" should be removed, because they are in contradiction to the Inhibition System in which the fundamental characteristic is precisely that of preventing the formation of lightning, together with its consequent strikes.

2.- Their actual operating characteristics render the SAF Nuevas Tecnologías protection equipment invulnerable. More specifically, the activation times of the protection elements are so rapid that they will never be found in a saturation situation.

IV.2 Basic concepts: equipment transparency (extremely low resistance path).

The SAF Nuevas Tecnologías aerial and earth filters have the same nature in concept, although they are dimensioned in various manners that are suitable according to both function and location.

These filters are "bridged". This means that in static atmospheric conditions, in other words, no electrical interference, the potential between the ends of the filter is zero, and the resistance is practically non-existent (hardly a few hundredths of an ohm, which is due to the resistance of the wire itself and the terminal connections). For this reason, the Induc-Control earth filter is completely transparent (R = almost 0W) to earth connection measurement checks, suitable operating as a shunt for any unwanted leakage currents to earth, all of which is established in the Low Voltage Electro-technique Legislation from the Ministry of Industry and Energy.

IV.3 Activation potential

Under transient conditions, in other words during electrical interference, it becomes activated after a certain potential, which constitutes the activation threshold. As from this moment in time, the filter is activated and presents an effect of super-conductivity or negative resistance, therefore the current intensity necessarily has to flow through the filter, and does not circulate through the cable, which, at this time presents a greater resistance or high impedance path.

In the case of the inhibitor, the filter is fitted with an aerial head that acts as a capacitor to the effects of the electrical field oscillations due to the environmental electromagnetic agitation caused by an incipient cloud. Among its several functions, this capacitive head guarantees reaching the activation threshold.

IV.4 Maximum potential accepted by the filter

As from this activation potential, although the interference or activating wave continues its progression, through inertia, the filter presents a small spike that exceeds the activation potential, reaching its maximum value in only 300 to 500 ns.

The filter response is simple. It consists of a damped sinusoidal waveform, the amplitude of which is reduced in an exponential manner.

IV.5 Operating times

The activation potentials in both of the two cases are reached in a very short time (the maximum time is 100ns and the minimum is negligible).

In order to verify the speed at which the SAF Nuevas Tecnologías protection begins to operate, we shall give a brief explanation of the standard tests as established by the most stringent legislation.

For any type of protection device, and specifically in our case of the Induc-Control earth connection filter, the standard isolation tests are carried out with the standard 1.25/50 voltage curve, for a direct or almost direct lightning strikes or its spurious residue. In fact, this value is nothing more than an extreme proposal of a difficult-to-quantify phenomenon, but where the first strike does not normally switch in lass than 2 to 3 ms (estimated by Lenz's Law in the case where the model consist of an arc between the two plates of a capacitor that represent the cloud and the earth's surface, together with a variable-humidity atmospheric dielectric).

Additionally, the residual induction (shunt currents, there is no sense in speaking of voltages) is considered to be damped for two reasons: both because of their induction nature (it is induction without direct contact depending on the coupling factor) and of the resistive elements of different natures (resistive, inductive and capacitive) that are encountered in their path. In summary, the current tests are modelled with the standard 8/20 , which has a waveform with a ramped peak, a less-pronounced ascending phase and a much reduced trailing edge and therefore much less energetic in the descending phase.

It should be emphasised that the Induc-Control earth connection filter operates in a bi-directional manner. This means that it is capable of absorbing the currents that are induced by the actual earth network itself (for example, by a lightning bolt that has struck 100 metres or 1 kilometre away causing interference in certain surface or subterranean layers with greater or lesser resistive quality and which are transmitted to the installation via the earth connection), or which may also be due to currents induced in the infrastructure of the installation itself.

The SAF Nuevas Tecnologías Inhibition System has proven that direct lightning strikes are now a thing of the past.

If any doubt exists as to the possibility of a fast cloud settling over our protected installation and its electrical field creation effect is faster than our activation potential (with the extreme hypothesis of a cloud charge to a maximum of 40 coulombs and that the electrical field does not suffer perturbations at 1 kilometre from our installation's vertex), we would have to state that the cloud speed would have to be 3.6 x 109 kilometres per hour, which in fact represents some 7 or 8 orders of magnitude above the maximum cloud speed.

V.1 Description

The inhibitor consists of an aerial head supported on a mast to which a filter is coupled (Figure 6). The aerial head is a semi-spherical metal plate, that is separated from another semi-spherical metal plate by air, a special dynamic dielectric designed by SAF Nuevas Tecnologías and an organic, insulating separator piece, with a disk shape that is resistant to environmental atmospheric agents.

Figure 6: Inhibitor schematic.

V.2 Operational possibilities

Various operational hypotheses may be set forward about system operation. The two most typical are as follows:

1) The inhibitor is basically a capacitance in series with a resistance in parallel with an inductance. This very simple circuit behaves as a high-pass filter. Due to the fact that the capacitive impedance (Z=1/jwC) is in series, this is what places a limit on the entry of current into the circuit. Since this is inversely proportional to the frequency, it will only allow the high frequency component to pass.

2) In addition, since it consists of an aerial terminal, the system will be sensitive to differences in the surrounding electromagnetic field, and will behave as an antenna (Figure 7).

Figure 7: Wave captured by the head in the case where it behaves as an antenna.

Despite the fact that these two hypothesis appear to be certain, they do not correspond exactly to the inhibitor's basic operation.

The first may be directly eliminated as a solution to atmospheric discharge, since its operation is based on direct lightning strikes to the terminal's metal head. Taking into account the previous explanations about modern methods of lightning strike prevention, the semi-spherical shape of the head would not be a good attraction point for the stepped leader. Therefore, if a lightning bolt were to form around the inhibitor, it would be directly attracted to the structure of the building itself.

V.3 True operation of the inhibitor

The true functional basis for the lightning inhibitor is a great deal simpler than the possible solutions given in the previous section. It is based on fundamental electrostatic principles and corresponds to what is known as the third state in lightning bolt development.

The first state was described in previous sections. It corresponds to the attraction of the lightning bolt by means of the point effect. An intermediate evolution between this system and that proposed by SAF Nuevas Tecnologías would be the so-called second phase, which is based on an opposite proposal: the delay on the lightning bolt formation. Instead of employing a point (or a few points) as an ionising head, it is possible to construct a head consisting of a very large number of points which would distribute any charge due to the presence of a cloud. As the earth potential grew, the corona generated at a Franklin point increase and expands, permitting the formation of am ascending discharge that would meet up with the descending stepped leader. On the other hand, in the case of a dense distribution of points or a metal sphere or semi-sphere, the necessary potential to cause ionisation is mush greater, and when it is produced, it occurs suddenly and meets up with the stepped leader. The advantage of this system would be that in function of the energy accumulated in some cases, the cloud could pass over the installation without having sufficient time to form lightning (Figure 9).

The third state of development corresponds to the lightning Inhibitor developed by SAF Nuevas Tecnologías. Its operation is shown in a diagrammatic fashion in Figure 8

Figure 8: Inhibitor operation.

The operational stages are as follows:

1) The negative charge at the base of the cloud induces a positive charge on the ground which is transmitted via the inhibitor mast and charges the capacitor internal armour positively (with charge Q1).

2) The special complex dynamic dielectric developed by SAF Nuevas Tecnologías inside the capacitor enables the inside of the semi-spherical piece that surrounds it to induce an equal charge to that of the internal armour, but of opposite sign, -Q1 (charge induction).

3) Since the external armour conductor is initially neutral because it is not connected to any terminal, this internal negative charge produces an equal positive charge on the outside (charge separation) part which is in contact with the air. Q2=Q1.

4) The collision of charge particles (negative) in the surrounding atmosphere may influence the external charge Q2 without affecting the others. This is an effect which is similar to connecting a conductor to a voltage source and then disconnecting it, with the conductor remaining charged.

Thus, as the cloud charge increases, so does the image charge in the ground, and therefore that of the capacitor also increases, until it reaches a maximum value as determined by the capacitance value and the breakdown voltage of the special dynamic dielectric.

When the capacitor discharges, Q cancels -Q1 and only the semi-spherical piece remains charged with positive Q2. In an ideal situation, the atmospheric charge does not influence the external conductor and Q2 remains equal to Q1. We have, therefore, a positively charged conductor as the starting point for the previously described process. Therefore, after each capacitor discharge, the net positive charge is incremented by the same amount (Q1), and will successively increase in function of the cloud's charge (Figure 9).

Figure 9: Comparison of the various systems of primary protection against lightning. The lines are concentrated at the Franklin point, ionising the air and favouring the attraction of the lightning bolt. With a spherical conductor connected to earth the field lines become dispersed and the ionisation is retarded. The inhibitor permits a lot of charge to be concentrated, which has an influence over a wider area. This variable charge permits a modification of the filed line density in function of the cloud charge.

For a distant negative ion, this charge acts as if it were a point having a value of Q2=n·Q1, (where n is the number of discharges that have taken place within the capacitor ) attracting it with a force proportional to Q2 and inversely proportional to the square of the distance.

Due to the semi-spherical shape of the head, the affected area would have a rounded form, just as shown diagrammatically in Figure 10.

Figure 10: Diagram of the inhibition process as described in the text.

Figure 11 shows a computer simulation of an inhibitor's area of influence, and in Figure 12 this area of influence of the same inhibitor supplemented with other aerial protection elements, we which shall call Field Correctors or Expanders. These simulations do not correspond to any specific scale.

Figure 11: Distribution of the electrical field.

Figure 12: Distribution of the electrical field.

Any particle that is within the area of influence of the head and the additional corrector elements will be attracted towards it.

Since the field lines do not converge at any point creating a point effect, but are in fact distributed throughout the entire head, an equal distribution of the descending charge is produced, without any formation of an ionised channel. In an extreme case, mini-discharges would occur distributed around the semi-spherical piece surface. In this way, the cloud is slowly discharged down to a low energy level, provided that the radius of action is sufficiently large. In practice, this devices possesses a charge-equalising nature.

In a situation whereby a stepped leader from a cloud were to form, and its radius of influence is within the area protected by the inhibitor, then a distribution of mini-discharges would take place across the entire surface. The process would be exactly the same as that previously described.

The process could be considered as the inverse: The head carries a certain charge that supplies the stepped leader in order to cancel the charge of the latter (inhibitor effect). This means that the return charge as from the ground never takes place and therefore neither does the high intensity that produces the lightning bolt.

The described situation corresponds to an ideal case where charge Q" is not affected by the surrounding atmosphere. In practice, a wet, windy environment could be favourable to the partial discharge of the external part of the head. In this case, Q2 would not increase so quickly and the Inhibitor would operate in exactly the same manner.

V.4 Capacitor discharge

It is during the capacitor discharge process when the special dynamic dielectric of the aerial head comes into play. This is fundamental, because the dielectric constant of the material determines capacity of the capacitor, and in turn, the charge that it is capable of holding.

In addition to maximum primary protection (preventing the cause), the SAF Nuevas Tecnologías system also proposes solutions for minimising and eliminating the secondary effects of the external discharges that are produced in trees, on high ground, unprotected buildings, metal structures reinforced concrete and nearby conventional lightning arresters etc, and which arrive via the various electricity power supply lines, earth networks, telephone lines, computer networks, metal piping and the earth connection itself.

Of course, the previous is a simplification of reality, since a detailed description of all the phenomena that accompany atmospheric discharges would be highly complex as has already been explained.

The purpose of this document is to provide understandable information in order to collaborate with the person who has to assume the important responsibility of selecting the most suitable and efficient protection system.

For this reason we place our Technical Department at your disposal to collaborate and orientate the installer in the main rules to follow in order to obtain maximum protection from the new SAF Nuevas Tecnologías system, since we firmly believe that those applied in conventional systems are now obsolete, whereas ours are based on highly innovating and completely different concepts.

It should be pointed out that each individual installation has its own particularities in function of the building shape, the location of the terrain, the type of material to be protected (it is not the same to provide protection for a ski station as for a wind-driven power plant), high voltage lines, transmitting towers or radio links, inflammable and/or explosive materials stores, communications centres and a large etc. In addition to this, the degrees of protection that is required or that have to be achieved will depend on the adoption of one type of installation or another.

SAF Nuevas Tecnologías places its Service and Design Centre at your disposal and at the service of installers and companies that require installation projects and the solutions to specific problems.