AU684051B2

AU684051B2 - A lightning conductor having an initiator device using a sliding electrical discharge along a dielectric

Info

Publication number: AU684051B2
Application number: AU50302/93A
Authority: AU
Inventors: Gerard Berger; Nicolas Floret
Original assignee: HELITA SA
Current assignee: HELITA SA
Priority date: 1992-10-28
Filing date: 1993-10-26
Publication date: 1997-12-04
Anticipated expiration: 2013-10-26
Also published as: EP0596775A1; DE69304654D1; TR28592A; MY110348A; ATE142823T1; EP0596775B1; FR2697379B1; ES2092262T3; CN1036965C; FR2697379A1; MX9306743A; SG48340A1; JP2886062B2; JPH07142188A; GR3021709T3; AU5030293A; CA2109365A1; CN1090433A; ZA937989B; CA2109365C

Abstract

Lightening protector (100) with an arcing device comprising a central electrode (110) having a free end (111) and an end (112) connected to earth, an insulating piece (121) surrounding the central electrode and having an outer surface (121a) which is connected in a continuous manner to the free end, and an electrically conducting outer electrode (122) partially covering the said outer surface of the insulating piece in such a way that a non-covered part (121'a), connected to the free end of the central electrode, of the outer surface of the insulating piece defines an insulating bridge between the said outer electrode and the free end of the central electrode, the said outer-surface part forming the bridge making it possible to guide a spark between the outer electrode, electrically charged under suitable atmospheric conditions, and the free end of the central electrode during the discharging of the said outer electrode. <IMAGE>

Description

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AUSTRALIA

Patents Aci 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

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Name of Applicant: Actual Inventor: Address for service in Australia: Invention Title: HELITA S.A.

Nicolas FLORET CARTER SMITH BEADLE 2 Railway Parade Camberwell Victoria 3124 Australia A Lightning Conductor having an Initiator Deivice using a Sliding Electrical Discharge along a Dielectric The following statement is a full description of ths invention, including thc best method of performing it known to us I I I~ I~ ~_I A LIGHTNING CONDUCTOR HAVING AN INITIATOR DEVICE USING A SLIDING ELECTRICAL DISCHARGE ALONG A DIELECTRIC The present invention relates in general to systems for providing protection against lightning, and more particularly to a novel lightning conductor having an initiator device that uses a sliding electrical discharge along a dielectric.

A particularly advantageous application of the invention lies in providing protection against lightning strikes to buildings, private houses, blocks of flats, factories, and in general any zone, any person, any structure or any equipment which it is desired to provide with such protection.

In addition, a particularly advantageous application of the invention lies in providing direct protection against lightning for equipment disposed on conducting metal structures, e.g. telecommunications antennas. It reinforces protection of high tension and medium tension cables on electricity pylons by reinforcing the effectiveness of guard cables and by improving the capture of lightning strikes by the pylons themselves.

S"A conventional lightning conductor of the Franklin rod or Franklin spike type comprises a metal rod having one end connected to ground and having its other end in the form of a sharp point.

Such a lightning conductor operates as follows.

When a storm cloud forms, the atmospheric electric field over the ground increases up to values of about 3 kilovolts per meter A corona effect then occurs at the point of the Franklin rod. Subsequently, a lightning strike begins by a descending leader forming Sinside the storm cloud and leaping towards the ground.

Simultaneously with the cloud leader moving down towards the ground, the ionization of the air in the vicinity of the Franklin point due to the corona effect continues to increase. When the downward-travelling leader reaches an altitude of about 100 meters above the Franklin point, I MCEQIPM the electric field that it develops in a broad area around the rod exceeds a minimum value of the order of a few hundreds of kilovolts per meter. The corona effect discharge, hitherto localized close to the point suddenly transforms into a rising leader or discharge that is characterized by a succession of waves of ionization separated by rest periods or "dark periods". This phenomenon is also called the "random corona effect".

For even greater values of the electric field, the rising leader begins to propagate without discontinuity and subsequently meets the descending leader. The sooner a continuous rising leader is developed, the further the junction point between the two opposite leaders from the Franklin rod.

The main drawback of a lightning conductor of the Franklin rod type lies in the long duration of the startup period during which the random corona effect takes place. As a result, the continuous rising leader develops late and so the encounter between the two 20 leaders takes place close to the Franklin rod.

A technical solution to this problem is to fit the Franklin rod with an initiator device that is capable of contributing to eliminating the rest periods or dark periods during the development of the rising leader, thereby artificially reducing the length of time required for starting the continuous rising leader.

To this end, Document EP-0 228 984 discloses an air spark-gap lightning conductor comprising a metal rod connected to ground and surrounded by a hollow shell likewise made of metal. The rod has one of its ends connected to ground and has a point at its opposite end that emerges to the outside through a circular opening *4O.

provided in the hollow shell. The shell is insulated from the metal rod by air, such that an air gap is defined between the circular opening in the shell and the point of the rod. Furthermore, it is necessary for the shell to be connected to the central rod by an isolating ~ra M I ~O -I resistance of high impedance.

Thus, when a storm cloud is to be found near the above-mentioned lightning conductor and a descending leader comes near to said lightning conductor, the metal shell charges electrically so as to reach a critical potential above which a spark forms from the shell and propagates across the air gap to the point of the rod.

This spark discharges the metal shell.

The operation of the electrical initiator device in that lightning conductor is random. The spark that forms across the gap between the rod and the metal shell arises randomly in time and in space and in "premature manner" at the point of the rod.

Document FR-2 620 581 teaches a lightning conductor installation that includes a hollow rod connected to ground, wiith an electrical conductor disposed therein and electrically isolated from the rod, the conductor projecting beyond one of the ends thereof for connection to complex means adapted to take up atmospheric potential 20 so as to give rise to spark-over phenomena between the conductor and the rod.

C. Co In addition, Document EP-0 096 655 teaches a lightning conductor installation that comprises a rod connected to ground and an electrically conductive member including a first portion that extends radially relative co the rod and that terminates in points that make it easy to take up atmospheric electrical potential, and a second portion forming an electrode that extends away from the first portion towards the rod along a curved 30 path that is disposed at a short distance from the rod so .:ee.i S"that, in stormy weather, an electrical discharge is established between said electrode and the rod.

Finally, Document FR-2 043 220 discloses a lightning conductor installation that includes a rod connected to ground and a radioactive source of beta radiation that is carried by the rod close to its end.

Those three lightning conductor installations are I-L~ -LRI~L1- i-- I_ 4 complex and do not operate in satisfactory manner.

The present invention proposes a novel lightning conductor having an electrical initiator device that seeks to solve the above-mentioned problems of the prior art.

More particularly, the present invention provides a lightning conductor having an electric discharge initiator device, the conductor including: a central electrode having a free end and an end connected to ground; a part made of insulating material, surrounding the central electrode, and having an outer surface that touches the free end of the central electrode continuously; and an electrically conductive outer electrode partially covering said outer surface of the insulating part in such a manner that a non-covered portion of said outer surface that connects to the free end of the central electrode defines a bridge of insulating material between said outer electrode and the free end of the central electrode, said bridge being capable, during discharged of said outer 20 electrode, of guiding a spark between the electrically conductive outer electrode that is electrically charged under appropriate atmospheric conditions, and the free end of the central electrode.

'Thus, when a descending leader coming from a storm cloud approaches the lightning conductor of the invention, the electrically conductive outer eiectrode charges by electrical induction until its electrical potential reaches a critical value I above which a spark forms between the electrically conductive outer electrode and the free end of the central electrode which is advantageously in the form of a point, thereby enabling plasma to be created in the vicinity of the point of the central electrode.

This plasma associated with the intense electric field that extends in the vicinity of WINWCRIlOR NEMOR NODEiLrT wfIIpG tOC I -eE I Y~ the end of the central electrode constitutes the first step in developing a rising leader. The discharge spark from the outer electrode is intense and vigorous since it slides along the outside surface of the insulating part, and more particularly over the bridge between the outer electrode and the point of the central electrode, said bridge forming a springboard for the spark between the outer electrode and the free end of the central electrode.

In the lightning conductor of the invention, the value of the electric field required for self-propagation of the trigger spark can be as little as ten times smaller than the corresponding field value in the lightning conductors of the above-mentioned prior art techniques.

Preferably, according to the invention, said outer surface of the insulating part includes at least one portion whose shape is essentially convex towards the outside, and the electrically conductive outer electrode 20 rests on said convex portion of the outer surface.

It should be specified that it is advantageous for 4. 4e* S said outer electrode to have no projecting portions that could favor the formation of parasitic sparks at locations other than between the free end of the central electrode and the outer electrode. The shape and the disposition of the insulating part and of the S° electrically conductive outer electrode are designed so that the spark forms from the edge of said outer electrode, adjacent to the springboard-forming bridge of e 30 insulating material, to the free end of the central S"electrode, and propagates over said bridge to the central electrode.

c oc In a preferred embodiment of the lightning conductor 4 of the invention, the insulating part is in the form of a henisphere whose outer surface is essentially convex towards the outside and which supports the electrically conductive outer electrode, and the portion of the outer b_ IILIU-~MIL____y_ ~I~Hds~~ gL1 _I C surface that is not covered by the outer electrode and that forms the bridge between said electrode and the central electrode is in the form of a ramp that is generally concave towards the outs 4 de.

In addition, in the above specified embodiment, said outer electrode is in the form of a hollow spherical cap.

In an embodiment of the invention, the outer electrode and/or the central electrode is/are made of copper or of a copper-based alloy.

In a second embodiment of the invention, the outer electrode and/or the central electrode is/are made of iron or of an iron-based alloy.

In a third embodiment of the invention, the outer electrode and/or the central electrode is/are made of aluminum or an aluminum-based alloy.

In another embodiment of the invention, the outer electrode is a metal deposit on a fraction of the outer surface of the insulating part.

In an embodiment of the invention, the insulating 20 part is a dielectric constituted by a polymer material.

.In another embodiment of the invention, the 9. *9 insulating part is a dielectric constituted by a ceramic material.

The following description made with reference to the accompanying drawings relates to non-limiting embodiments of the invention and serves to show clearly what the *5 invention consists in and how it may be implemented. In the drawings: Figure 1 is a vertical section view through a first 30 embodiment of a lightning conductor of the invention; eoooa Figure 2 is a vertical section view through a second embodiment of a lightning conductor of the invention; Figure 3 is vertical section view through a third 9 Sto embodiment of a lightning conductor of the invention; Figure 4 is a vertical Section view through a fourth embodiment of a lightning conductor of the invention; Figure 5 is a vertical section view through a fifth -rms a~,,ll I, I ~R-~sl ~A I embodiment of a lightning conductor of the invention; Figure 6 is a curve showing variations in predischarge current as a function of time for a conventional Franklin rod type lightning conductor put under electrical conditions appropri3te for being struck by lightning; Figure 7 is a curve showing variations in predischarge current as a function of time for a lightning conductor aving an air spark-gap and subjected to conditions identical to those of Figure 6; and Figure 8 is a curve showing variations in predischarge current as a function of time for a lightning conductor of the invention subjected to the same electrical conditions as Figure 6.

As a preliminary point, it should be observed that from one figure to another, elements that are identical or similar are designated, whenever possible, by the same reference symbols, and they are not described again every time.

20 Figure 1 shows a lightning conductor 100 having an initiator device using a sliding electrical discharge.

This lightning conductor 100 comprises a vertical central ooe electrode 110 made of metal having an end 112 for o.f connection to ground and a free end 111 that forms a point that points towards the sky. In addition, the lightning oonductor 100 comprises both an ineulating part C.e°°C •121 surrounding the central electrode 110 and having a circularly symmetrical outside surface 121a adjacent to the free end 111 of the central electrode 110, and also 30 an electrically conductive outer electrode 122 that covers a portion of the outer surface 121a of the insulating part 121.

:More precisely, the insulating part 121 is a solid dielectric that, in this case, is in the form of a hemisphere whose said outer surface 121a is essentially convex towards the outside and that includes a portion 121'a in the form of an outwardly concave ramp that L~Lsaa ~h~bP~ ~B~s~ IBR IW a ~I I- 8 touches said free end 111 of the central electrode 110 continuously, i.e. without leaving any gaps. This dielectric may advantageously be made of a polymer material or of a ceramic material, or even of a juxtaposition of both types of material. It should be specified that the dielectric material constituting the insulating part advantageously has very high electrical resistivity, good mechanical stiffness, and characteristics of non-wettability and of resistance to environmental conditions.

Furthermore, said convex outer surface 121a is partially covered by a hollow spherical cap made of metal that forms an electrically conductive outer electrode 122 fitting the convex shape of the outer surface 121a of the dielectric 121. The outer electrode 122 does not cover the ramp-shaped portion 121'a of the said outer surface 121. Said outer electrode 122 includes a circular top opening 122a such that said portion 121'a emerges through said opening 122a towards the outside, thus forming a 20 bridge of insulating material that extends between the *099 circular edge 122'a of the top circular opening 122a in o• o• the outer electrode 122 and the free end 111 of the central electrode 110. The outer electrode 122 may be made of iron, copper, or aluminum, or of an alloy based on iron, copper, or aluminum. In a variant embodiment, the outer electrode 122 is constituted by a deposit of 9* 09 metal formed directly on that portion of the outer surface 121a of the insulating part 121 that is to be covered.

99*9 In a typical example, the metal central electrode *999*9 S" 110 has a diameter of about 10 mm to 20 mm, the heinispherical insulating part 121 has a maximum diameter of 25 cm, and the bridge of insulating material 121'a has a length lying in the range 1 mm to 50 mm. It should be observed that the outer electrode 122 may be of several different thicknesses. Furthermore, it advantageously includes no projecting portions since that would impede e~-P W-b p~ -n C- Im~s~- proper operation of the lightning conductor as explained below.

Figure 2 shows a first variant embodiment of the Figure 1 lightning conductor. In this variant, the part 121 of insulating material is in the form of a body of revolution that flares away from the bottom of the central electrode 110 towards the top of said electrode and that then runs into the point 111. The insulating part 121 has a rounded top portion 121" whose outer surface is convex towards the outside. This top portion 121" extends to the point 111 by means of a frustoconical connection portion 121' whose outer surface 121'a is in the form of a ramp that is concave towards the outside.

The conductive outer electrode 122 in the form of a hollow spherical cap partially overlies the insulating part 121, bearing against the rounded portion 121" of the insulating part 121 so that a portion of the outer surface of said rounded portion 121" is the only contact surface between the outer electrode 122 and the 20 insulating part 121. The outer surface 121'a of the •e ".frustoconical portion 121' of the insulating part 121 is 99 99 not covered by the outer electrode, and it extends between said outer electrode and the point 111 of the o• :central electrode 110.

In a variant embodiment shown in Figure 3, the outer electrode 122 is in the form of a torus 124 that surrounds the insulating part 121. This torus has a connection skirt 124a that partially overlies the outer surface of the rounded top portion 121" of the part 121 9900 30 made of insulating material.

In another variant embodiment, as shown in Figure 4, the outer electrode 122 is a spherical zone that partially overlies the rounded top portion 121" of the b:insulating part 121. This spherical zone is connected by electrical wires 131 to metal spheres 130 that are secured to the insulating part 121. More precisely, the insulating part 121 has arms that project radially, with L I L I moml a metal sphere 130 being mounted at the end of each arm.

In Figure 5, there can be seen another variant embodiment of the lightning conductor of Figure i, which is more suitable for being installed on horizontal conductors, such as the guard cables of electricity lines or the horizontal conductors of mesh cages. In this variant, the insulating part 121 extends beneath the outer electrode 122 in the form of an insulating portion 123 which is generally in the form of a rectangular block in this case. This extension portion 123 may be added on to the insulating part 121 or it may be formed integrally therewith. In addition, as can be seen in Figure 5, the insulation extending portion 123 includes a horizontal passage 140 for receiving a horizontal conductor perpendicularly to the vertical central electrode 110.

It may be observed that the horizontal passage 140 is disposed at a distance d from the outer electrode 122 oe that is about twice as great as the distance between the edge 122'a of the outer electrode 122 and the point 111 20 of the central electrode 110. The central electrode 110 is connected to the conductor disposed inside the passage 140 by connection means 150 (in this case a metal tab).

The conductor is itself connected to ground.

It will be observed that in another variant (not 25 shown), it is possible to envisage the end 112 of the electrode projecting towards the inside of the passage 140 so that the horizontal conductor installed in said passage comes into contact with the vertical electrode.

In addition, it would also be observed that the outer 30 surface of the insulating extension portion 123 is not covered by the outer electrode.

The operation of the lightning conductor, e.g. as shown in Figure i, is now described.

When a descending leader comes close to a lightning conductor as shown in Figure 1 and having an initiator device, then the external electric field increases and the electrically conductive outer electrode 122 charges ~~~L~PBP~^low aft-lil9ft-MM4 _l I I electrically until it reaches a critical potential above which a spark forms going from the circular edge 122'a of the opening 122a of said outer electrode 122 and slides over the bridge of insulating material 121'a until it reaches the point 111 of the metal central electrode 110.

This spark makes it possible to create a plasma in the vicinity of the point 111 of the central electrode 110, and said plasma (which is associated with the intense electric field 'chat exists in the vicinity of the point 111 of the central electrode 110) causes a rising leader to be formed that travels to meet the descending leader. When the two opposite leaders meet, a conductive channel is established between the cloud and ground. The lightning current then flows to ground via the metal central electrode.

It should be specified that the bridge 121'a serves to guide the discharge spark between the outer electrode 122 and the central electrode 110, said spark then being 2 much more vigorous than in other lightning conductors of 20 the prior art that use an air spark-gap.

oth eIn addition, the electric field required for causing the trigger spark to propagate can be as little as ten times smaller than the field required in lightning conductors that use an air spark-gap.

25 Furthermore, the fact that the outer electrode 122 has no projecting portions advantageously serves to avoid parasitic sparks forming at locations other than the circular edge 122'a of said outer electrode.

Figures 6, 7, and 8 relate to three different S 30 lightning conductors put under identical electrical and lightning conditions, and they comprise, respectively, a conventional Franklin rod (not shown), a lightning conductor having an air spark-gap (not shown), and a lightning conductor having an initiator device of the invention, with the experimental curves reproducing variations in the predischarge current at the point of the various devices as a function of time.

More precisely, all three lightning conductors were tested in the laboratory using a test procedure that simulates lightning conditions. That is to say an ambient electric field was created simulating the fields produced by the distribution of charge in a storm cloud, and a pulse field was created representing the field induced by the approach of the descending leader in the vicinity of the ground. These two fields were superposed and applied to a plate (not shown in the figures) situated abovs the lightning conductor in question. The ambient field is represented by a DC field of the order of 10 kV/m to 20 kV/m between ground and the plate, and the pulse field was created by a Marx impulse generator that delivered a driving wave having a long rise time lying in the range 200 microseconds to 1,000 microseconds.

Under the above-specified conditions, variation in eothe predischarge current at the point of each of the lightning conductors was observed as a function of time until a rising discharge was formed and caused to propagate from the point of the lightning conductor to the top plate.

When using a conventional Franklin rod, as can be V.0 seen in Figure 6, the curve shows changes in the 25 predischarge current as a function of time from the instants at which pulse voltages were applied at t=0 and *t=250 microseconds, in the rform of random pulses A corresponding to unsuccessful attempts at starting the rising discharge. The discharge leaves the point of the 30 Franklin rod at a time close to 250 microseconds and then travels through the space from the point towards the plate.

For a lightning conductor having an air spark-gap, as shown in Figure 7, the rising discharge propagates from the point at an instant lying in the range 250 microseconds to 300 microseconds, which is later than for the conventional Franklin rod (see Figure As in a Illa~ I~ -L i~" I Figure 6, it may be observed that random pulses of type A are recorded. The three observed fine B-type pulses correspond to initiation of the air spark-gap, with the first two corresponding to premature operation of the air spark-gap, too soon for starting the rising discharge.

In contrast, as shown in Figure 8, with a lightning conductor having an initiator device using a sliding electrical discharge along a dielectric of the invention (as shown in Figure discharge takes place much sooner, -etween 150 microseconds and 200 microseconds.

Firing of the initiator system as marked by a large fine pulse C at 160 microseconds enables a rising discharge to be started immediately. A statistical study of this lightning conductor has shown that the anticipated triggering of the rising discharge is regular and reliable compared with the Franklin rod type conductor or with the above-mentioned conductor having an air sparkgap.

By comparing Figures 6 and 8, it can be seen that S 20 there is a very significant reduction in the time Srequired for the capture discharge to be developed, due to its initiation being anticipated, said capture discharge taking place from a lightning conductor of the invention earlier than would the capture discharge from a 25 conventional Franklin type lightning conductor put under identical lighting conditions. The lightning conductor the invention thus makes it possible to trigger capture discharge for initiation field intensities that are much smaller than those which initiate a conventional iO Franklin type rod.

:It should be observed that the various embodiments shown in the figures described can be combined with one another.

Furthermore, the present invention is not limited in any way to the embodiments described and shown, and the person skilled in the art will be able to make variations on that theme within the spirit of the present invention.

-L IL~L_ Is PL 14 For example, it may be envisaged that the insulating part has a facetted outer surface that is partially covered by the outer electrode. Such an insulating part would also include an essentially frustoconical top portion that extends the facetted portion to the top end of the central electrode.

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Claims

1. A lightning ronductor having an electric discharge initiator device, for providing protection against lightning, the conductor including: a central electrode having a free end and an end connected to ground; a part made of insulating material, surrounding the central electrode, and having an outer surface that touches the free end of the central electrode continuously; and an electrically conductive outer electrode partially covering said outer surface of the insu'lating part in such a manner that a non-covered portion of said outer surface that connects to the free end of the central electrode defines a bridge of insulating material between said outer electrode and the free end of the central electrode, said bridge being capable, during discharge of said outer electrode, of guiding a spark between the electrically conductive outer electrode that is electrically charged under appropriate 20 atmospheric conditions, and the free end of the central electrode. V.

2. A lightning conductor according to claim I, wherein said outer surface of the insulating part includes at least one portion S. whose shape is essentially convex towards the outside, and wherein the electrically conductive outer electrode rests on said convex portion of the outer surface.

3. A lightning conductor according to claim 1 or 2, wherein th> insulating part is in the form of a hemisphere whose outer surface is essentially convex towards the outside and which supports the electrically conductive outer electrode, and wherein the portion of the outer surface that is not covered by the outer electrode and that forms the bridge between said electrode and the central electrode is in the form of a ramp that is generally concave 5 towards the outside. C' >WINWORD NEM ORL 4ODE1.ET'lh2P1i DOC I ~~1191 p ~I Is~ I~b B3AIIICIILCI ~I~rr~ 16

4. A lightning conductor according to claim 3, wherein the insulating part is a hemisphere having a maximum diameter equal to about 25 centimetres, and wherein the bridge of insulating material has a length lying in the range 1mm to A lightning conductor according to claim 1 or 2, wherein the insulating part is of a shape that flares outwardly from the central electrode in an upwards direction, and that includes a rounded top portion having an outer surface that is convex towards the outside and that supports the conductive outer electrode, and a connection portion between the outer electrode and the free end of the central electrode, which connection portion is frustoconical in shape. o 6. A lightning conductor according to any one of claims 1 to wherein said outer electrode is in the form of a hollow spherical cap. 20 7. A lightning conductor according to claim 5, wherein the outer electrode is in the form of a spherical zone covering at least a portion of the outer surface of the rounded top portion of the S: insulating part, and is electrically associated with metal spheres secured to the insulating part.

8. A lightning conductor according to claim 5, wherein the ov.er electrode is in the form of a torus that surrounds the insulating part and that includes a connecting skirt which partially covers the outer surface of the rounded top portion of the part made of insulating material.

9. A lightning conductor according to any one of claims 1 to 8, wherein the part of insulating material extends beneath the outer electrode in the form of an insulating portion, said insulation 35 portion includes a horizontal passage for receiving a horizontal (C WINNORDFINIEMORPNODFLFTFIO2PG DOC II ilRpa~-~C-l conductor, and wherein it includes connection means between the central electrode and the horizontal conductor placed in said passage.

10. A lightning conductor according to any one of claims 1 to 9, wherein the outer electrode is made of copper or of a copper-based alloy.

11. A lightning conductor according to any one of claims 1 to 9, wherein the outer electrode is made of iron or of an iron-based alloy.

12. A lightning conductor according to any one of claims 1 to 9, wherein the outer electrode is made of aluminium or of an aluminium-based alloy.

13. A lightning conductor according to any one of claims 1 to 9, wherein the outer electrode is a metal deposit formed on a portion S of the outer surface of the insulating part. 14, A lightning conductor according to any one of claims 1 to 1l, wherein the central electrode is made of iron or of an iron-based alloy.

15. A lightning conductor according to any one of claims 1 to 13, S* wherein the central electrode is made of copper or of a copper- based alloy.

16. A lightning conductor according to any one uf claims 1 to 13, wherein the central electrode is made of aluminium or of an aluminium-based alloy.

17. A lightning conductor according to any one of claims 1 to 16, wherein the insulating part is made of a dielectric constituted by a polymer material. C \'WINWORD\FINMiORE\NOUELETIM~O02l DOt CC~ r-~ g~ ~-JI -J 18

18. A lightning conductor according to any one of claims 1 to 16, wherein the insulating part is made of a dielectric constituted by a ceramic material.

19. A lightning conductor substantially a- herein described with reference to any one of the embodiments illustrated in the accompanying drawings. DATED this 3rd day of SEPTEMBER, 1997 PHILLIPS ORMONDE FITZPATRICK Attorneys for: HELITA 3.A. 9* 9* S. S S 9~ a.. (C WINWVORD\FINE MORINODt-El-lo102PO DOC II -sl 117 -g I I~q3P- I ABSTRACT A lightning conductor (100) having an initiator device including a central electrode (110) having a free end (111) and an end connected to ground (112), an insulating part (121) surrounding the central electrode, having an outer surface (121a) that touches the free end continuously, and an electrically conductive outer electrode (122) partially covering said outer surface of the insulating part so that a non-covered portion (121'a) of the outer surface of the insulating part and touching the free end of the central electrode defines an insulating bridge between said outer electrode and the free end of the central electrode, said portion of the outer surface forming the bridge serving, during discharge of said outer electrode, to guide a spark between the outer electrode which is electrically charged under suitable atmospheric conditions and the free end of the central electrode. Soo* **0 *o *0e 0000 6 *00 *000 ~ra~a _Is