JPH0216560B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to lightning protection devices, in particular to ionizing lightning rods. The principle of this type of device consists in forming a column of ionized air above the end of the lightning rod. It has been demonstrated primarily through laboratory measurements that ion sources reduce the breakdown voltage of the atmosphere by increasing the conductivity of the outside air, i.e., reducing the voltage threshold at which discharge begins. There is. In this way, the generation of an electrical discharge is facilitated, and the energy released by the lightning strike is guided to the ground by the lead-in conductor of the lightning rod.

The large area of protection of ionizing lightning rods and the effectiveness of their protection are therefore superior to that of simple lightning rods, also referred to as "Franklin lightning rods".

However, this solution is not without its disadvantages, as to date the ion source consists of a radioactive pellet placed around the tip of the needle, and an alpha beam from which the pellet is produced is required. This is because it performs ionization. However, the use of radioactive sources requires special care in their construction, storage, and installation.

In order to preserve the advantages of ionizing lightning rods while eliminating the disadvantages due to radioactive sources, in particular French patent no. 907037 in the name of CLEMENT
It is proposed to supply electricity to the needle end of a lightning rod by means of a high voltage generator connected at one end to the needle end and at the other end to earth in such a way as to release a charge into the surrounding atmosphere. However, this charge either discharges the thundercloud by recombining with the charge held by the thundercloud, or
A sufficient amount shall be created to sufficiently change the ionization of the outside air to create a conductive atmosphere. A spark gap device is installed in parallel with the generator to shunt the lightning strike.

The device described above, however, is powered by a fairly large amount of electrical power, on the order of about 40 KW, which is required to generate a fairly large amount of ions. This power and the extremely high voltage (400KV) required will introduce a number of insulation and safety issues that have not been previously encountered in order to achieve the objective.

In contrast, the present invention uses a so-called "corona effect" to ionize the air around the end of a lightning rod, which is a very strong local deformation of the electric field. arises from the existence of This is the case, for example, in the electric field in the atmosphere near a very sharp conductive element. When positive or negative ions are ejected by means of a conductive element at a high voltage, these ions are accelerated by the external electric field and themselves cause secondary ionization of gas molecules. The increase in the number of ions can be observed in the form of a luminescent corona on the tip of the needle. The ions thus produced are then diffused into the space surrounding the needle end of the lightning rod and accelerated by the external electric field to form the ionized air corona described above.

This multiplication phenomenon is caused by low power consumption (several tens to several tens of
(of the order of 100 mW), insulation and protection techniques enable the amplification of the natural action of the Franklin needle tip by corona discharges occurring at the tip of the needle, which is sufficient under voltages (several tens of KV) that are readily available under the prior art. .

It is absolutely essential that there is a local distortion of the electric field, which is a condition for the appearance of a corona discharge, and that this is very localized. To this end, the present invention proposes the adoption of a pointed needle end that has an outer circumferential surface consisting of a rotating concave surface inscribed in a coaxial virtual enveloping conical surface with the needle end apex as its apex and concave toward the axis. , the apex angle of the needle end can be reduced considerably compared to the apex angle of the surrounding cone while retaining good mechanical strength for a given needle end base diameter and height. Preferably, the apex angle of this needle end is on the order of 10 degrees. According to a comparative example, this type of needle tip with a base diameter/height ratio of 0.45 has an apex angle of 25 degrees.

Since the needle end is not connected to the ground (unlike a simple Franklin needle end), but is connected to a high-voltage power source, it is necessary to install a device to divert lightning that reaches the needle end to the ground. Preferably, the device comprises a lightning arrester, one electrode of which is constituted by the lower part of the needle end itself, and the other electrode of which is grounded by the drop conductor of the lightning rod. In the event of a lightning strike, the arrester becomes a conductor, electrically connecting the needle end to the ground.

Preferably, the bottom portion of the needle end constituting the upper electrode of the discharge gap of the lightning arrester has a round shape with the convex portion facing downward and facing the lower electrode. The latter or lower electrode may, for example, consist of a conductive ring having a diameter close to that of the base of the needle end, which is connected to the lead-in conductor of the lightning rod, the upper surface of which is flat and faces the rounded base of the needle end. It is arranged separately from this. This rounding of the needle end avoids edge effects between the electrodes and eliminates protruding corners where parasitic corona discharges can occur, since the discharge at the bottom of the needle end as described above prevents ions from diffusing. First, since the annular portion, which is at ground potential, is nearby, it is immediately neutralized and is therefore not effective. Furthermore, these parasitic discharges can reduce the firing voltage of the arrester to a value lower than the high voltage charging the needle tip, and the energy of the generator is therefore reduced instead of causing a corona discharge at the tip of the needle. It is consumed inside the lightning arrester.

To improve the effectiveness of lightning arresters, it is useful to divide at least one electrode into a plurality of conductive channels separated by a dielectric. This can be achieved in particular by drilling a plurality of longitudinal grooves through the entire thickness of the annular part mentioned above.

In fact, in the event of a lightning strike, a very strong current flows through the arrester within the gap separating these two electrodes.
This current occurs at a very localized point, usually one point, in this gap. Therefore, a voltage is generated between both terminals of the lightning arrester due to the resistance (small but not zero) that exists between the two electrodes during discharge (this resistance is hereinafter referred to as "discharge resistance").

This lightning voltage may damage the high voltage generator not only in the case of exceptional energy lightning strikes, but also after repeated lightning strikes over a long period of time.

If, instead of electric discharge at one point, lightning strikes occur simultaneously,
If it can be divided into discharges, the discharge resistance will be divided into this number n, and the lightning voltage will also be divided at the same ratio. In this way the protection of the high voltage generator is considerably improved.

The division results in n discharge gaps connected in parallel. In order for these discharge gaps to be able to operate simultaneously during a lightning strike, it is necessary to provide an inductive coupler for each conductive channel between them; in fact, without the gap, the discharge currents would flow into one electrical path. Only one discharge gap, rather than n in series, will therefore be effective.

The required inductance value is obtained by providing the gap, and therefore the groove, with a length such that a sufficiently long electrical path can be created between the electrodes of two adjacent discharge gaps.

Other features and advantages of the invention will become apparent from a reading of the following detailed description, taken in conjunction with the accompanying drawings.

The curve of FIG. 1 shows the amount of ions produced by the apparatus according to the invention, which is schematically illustrated in FIG. 1A. A voltage generator 10 is connected at one end to the ground 20 and at the other end via a cable 40 to a conductive member 30 of a lightning rod. The generator creates a potential difference V _p between these terminals and causes a current I _p to flow. When the voltage V _p is low, the circuit is open and the current I _p is zero. Voltage
As V _p increases, a current I _p is generated due to ion generation near the needle tip based on corona discharge. The magnitude of the current flowing in the generator, which is a charge current, is
Therefore, it shows the ionic current generated at the top of the needle end. 1st
In the figure, the horizontal mark is the voltage expressed in kilovolts.
V _p , the ordinate is the current magnitude I _p expressed in microamperes. Curve 60 is for a needle end having a positive potential with respect to ground, and curve 61 is for a needle end having a negative potential with respect to ground. 10KV
For voltages below, the current is zero except for dielectric loss. Corona phenomenon occurs from about 10KV,
A current flows due to the generation of ions.
This phenomenon increases as the voltage V _p increases. The results are almost the same regardless of whether the potential at the needle end is positive or negative. However, thunderclouds are in most cases carriers of negative electrostatic charges, which positively charge the ground by induction. Therefore, it is advantageous to connect the needle end to the positive pole of the voltage generator and the negative electrode to earth. In this way, the needle end becomes at a positive potential with respect to the ground, and the "Franklin needle end" effect is enhanced.

It can also be seen that the power consumption is greatly reduced due to the corona discharge multiplication effect. 25KV voltage
The current I _p is on the order of 1 to 2 μA with respect to V _p and the power is 25 to 50 mW.

FIG. 2 shows a pointed needle end 100, the end 1
Corona discharge occurs at 01. Ions 102 generated in region 102 may diffuse into the air surrounding the needle tip. The lower part 104 is an annular part 1 connected to the ground 410 via a conductive shaft part 111 that supports a lightning rod.
Located near 10. The lower needle end 104, the annular portion 110 and the air gap located therebetween constitute a lightning arrester. The width of the gap 120 is such that the lightning falling on the needle end is guided to the ground by the appearance of an electrical discharge in the gap 120, but the spark gap is determined by the operating voltage value at which the needle end is charged by the high voltage generator. (The discharge starting voltage is, for example, 30 KV for an operating voltage of 25 KV at average external humidity.)

A high pressure generator, indicated schematically at 400, is connected to needle end 100 by conductor 105. Preferably, the conducting wire 105 constitutes the core of a coaxial cable, and the shield 111 connected to the ground 410 forms the shaft portion of the lightning rod near the end of the rod. 2
The conductors are separated by an insulator 130.

The needle end has a slightly concave side surface 106, in other words, this surface of rotation is created by a curved meridian whose convexity is directed towards the axis of rotation. The apex angle α of this surface is the cone 107 surrounding the needle end.
is therefore smaller than the apex angle β. This needle end shape allows a good compromise between the two points: a large base diameter D/needle end height H ratio (excellent mechanical strength) and a small apex angle (enhanced corona effect).

The lower part of the needle end has a curve 108 with no sharp edges and therefore no risk of parasitic corona discharge.

Surface 108 constitutes the upper electrode of the discharge gap of the lightning arrester and is located adjacent to the upper surface 112 of the annulus, where the annulus forms the lower electrode. This surface 112 is preferably planar. Due to this shape of the spark gap, there is no edge effect between the electrodes, and it is possible to accurately determine the firing voltage.

The annular part 110 has, for example, four cuts 113 (seen in FIGS. 2 to 4) dividing it over its entire thickness. These splits create an equal number of conductive channels 114,
There is insulation between them.

In order to increase the length of these conductive channels, the cuts can be made longer on the conductive shafts 111, which cuts are of course drilled through the entire thickness of these shafts.

Even if the cracks are left as they are, for example, an insulating layer (not shown) made of the same material as that of the insulating part 130
May be filled with In this case, the dielectric separating the conductive channels is no longer air, but a solid dielectric. Furthermore, the degree of weathering is improved by preventing water from entering the lightning rod shaft.

Furthermore, this degree of weathering is improved by drainage holes 115, which prevent liquid from accumulating in the gap 120 separating the electrodes of the arrester discharge gap and prevent corrosion from penetrating inside the annulus. Additionally, the presence of water in this area prevents changes in the operating characteristics of the arrester and sometimes its firing voltage.

The needle end, annulus and shank are made of a material with good electrical conductivity, resistance to atmospheric corrosion and good mechanical properties, such as brass or rust-free steel.
Preferably, the selected materials are the same for each part, primarily to avoid electrochemical corrosion phenomena between the electrodes of the arrester discharge gap.

Of course, the slotted annular part made as one piece may be replaced by a combination of multiple parts that are electrically connected at the bottom, and the slot filling layer serves as a spacer in this case. do.

FIG. 5 shows the power supply circuit of the device according to the invention.
The outside air electric field trap 401 is a DC-AC converter 40
3 is operated via the control circuit 402. This converter is powered by a DC power source composed of a buffer storage battery 404 charged by a solar cell 405. At the output of the converter 403 the alternating voltage is rectified in a circuit 406 which simultaneously triples the voltage. The rectified current is finally supplied to the conductive member 407 of the lightning rod, but a protection circuit 408 is inserted between the rectifier and the conductive member to prevent lightning that may strike the lightning rod from damaging the power supply circuit. There is.

The use of an external electric field trap in combination with a high voltage generator causes the device to operate only when the external electric field reaches a predetermined value corresponding to the probability of a large lightning strike. In other words, it is possible to supply electric potential to the conductive elements of the lightning rod. Below this value, the converter is not powered and therefore the storage battery is not discharged unnecessarily.

FIG. 6a is an equivalent circuit illustrating the operation of a single-spark gap lightning rod when a lightning strike occurs.

Lightning strikes the terminals of the spark gap, i.e. point 407 and ground 4.
10 may be equivalent to a very strong (more than 10,000 amps) current source 500 connected between the A lightning arrester discharge gap has a specific resistance Re and a specific inductance Le.

When a discharge occurs, the larger the discharge current, the higher the potential difference generated between the arrester discharge gap terminals. This potential difference, in the case of discharges of exceptional intensity, can become prohibitive and can damage the DC voltage generator, or at least damage it due to repeated shock effects.

In order to protect this generator under all circumstances, the invention proposes to divide the arrester discharge gap into n individual discharge gaps separated from each other by a connecting inductance in the manner described above. , each discharge gap has the same individual resistance Re as in the case of a single gap (this resistance is effectively determined by the gap existing between the two electrodes), and the inductance Le of each discharge gap is equal to the length of the conducting channel. (and thus approximately equal to the length of the etched separation gap), and as mentioned above, these inductance values are adjusted so that simultaneous discharge initiation is observed in all of the individual discharge gaps. The value must be such that it allows effective splitting of the conductive channels.

In this way, the discharge current can be distributed to a plurality of discharge gaps, the overall resistance of which is reduced by a factor of n, and thus the potential difference appearing at the terminals of the DC voltage generator by a factor of n.

Preferably, a second protective circuit is inserted between the lightning arrester and the high voltage generator, which consists of a series resistor 43 installed in front of the lightning rod pull-side coaxial cable 111.
0 and a discharge tube 420 connected in parallel to the generator.

This protection circuit has an auxiliary role: if the voltage across the arrester terminals becomes very large, the discharge tube becomes conductive and thus protects the voltage generator.
The discharge tube itself is similarly protected by a series resistor 430 for limiting the discharge current.

Needless to say, the present invention is not limited to the embodiments described above, but extends to all modifications consistent with the spirit thereof, and the above-mentioned examples are preferred embodiments and are not limiting.

[Brief explanation of drawings]

Figure 1 is a curve showing the amount of ion generation measured as a function of the potential at the needle end made with the experimental apparatus shown in Figure 1A, and Figure 2 is a cross-sectional view of the needle end and lightning arrester, with the left half showing the split. The right half is a half plane that passes through one of the cracks, and the right half is a half plane that does not pass through the crack.
corresponds to the cross section of FIG. 2, FIG. 4 is an elevational view corresponding to FIG. 3, and FIG. 5 is a block diagram of a device for applying an electric potential to the needle end. Figures 6a and 6b are equivalent electrical circuits of the protection circuit with and without discharge gap division, respectively. FIG. 1A is an explanatory diagram of the apparatus of the present invention. 100... Needle end, 104... Lower needle end, 104, 112, 120... Lightning arrester, 106
... Needle end side surface, 107 ... Virtual enveloping cone, 110
... lower electrode, conductive annular part, 111 ... shaft part,
113...Crack, 114...Conductive channel, 1
15... Drain hole, 10,400... High pressure generator,
20,410...Earth, 420...Discharge tube, 43
0...Series resistance.

Claims (1)

[Scope of Claims] 1. A lightning rod end 100 that can be electrically connected to the ground through a lightning arrester having a discharge gap consisting of upper and lower electrodes when exposed to lightning discharge or other overvoltage; In a lightning rod equipped with an ionization device that generates an electric potential, the outer circumferential surface 106 of the needle end is a rotating concave surface inscribed in a coaxial virtual envelope conical surface 107 having the apex of the needle end and concave toward the axis. A lightning rod that is ionized by corona action, characterized in that the bottom surface 104 of the needle end has a downwardly bulging curved surface 108 and forms an upper electrode of a discharge gap of the lightning arrester. 2. The lightning rod according to claim 1, wherein the apex angle α of the apex of the needle end is about 10 degrees. 3. The lightning rod according to claim 1 or 2, wherein the potential of the needle end is set to a positive potential with respect to the ground. 4. The lightning rod according to any one of claims 1 to 3, wherein the lightning arrester is divided into a plurality of conductive channels 114 separated by a dielectric material. 5. The lower electrode of the lightning arrester has a conductive annular portion 110 placed at ground potential facing the bottom of the needle end with a gap, and the annular portion has at least two The lightning rod according to claim 4, characterized in that it has vertical slits (113), and these slits form a dielectric material that separates the conductive channels of the annular portion. 6. The lightning rod according to claim 5, wherein the annular portion is coupled to the vertical shaft portion 111 of the lightning rod, and the slit extends downward along the vertical shaft portion. 7. The lightning rod according to claim 5, wherein a strip made of a material with high dielectric strength is disposed within the slit. 8. The lightning rod according to any one of claims 5 to 7, wherein the annular portion has a drainage hole 115. 9. An additional protection circuit is inserted between the needle end and the high voltage generator 400 of the ionization device, the protection circuit including a resistor 430 in series with the line connecting the needle end to the high voltage generator. , and a discharge tube 420 connected in parallel to both terminals of the high voltage generator.
A lightning rod as described in any of Item 8.