FR2848352A1 - Lightning arrester with capture device polarized as a function of the sign of the descending tracer, uses sensing of polarity of storm cloud and synchronization with descending tracer to create opposite polarity charge at tip of arrester - Google Patents

Abstract

The lightning arrester has a point (1) isolated from ground by break-over devices (2) and connected to a high voltage source (3). A detector (5) senses polarity of a storm cloud and a controller (4) ensures the polarity of the point is opposite to the polarity of the descending tracer, and delivers a trigger command to synchronize the high voltage source with arrival of the descending tracer.

Description

The present invention relates to a lightning conductor and more

  particularly a lightning rod with polarized capture device.

  The systems making it possible to protect oneself from the risks of lightning in the event of a thunderstorm do not only consist of lightning rods 5 with single rod (PTS). There is also a whole range of lightning conductors, qualified as active, in the sense that they implement physical phenomena making it possible to increase the protection radius of the lightning rod compared to a PTS whose tip would have the same geometry. Lightning rods with a priming device are known which ionize the air in the immediate vicinity of the point of the lightning rod. The document published by the National Institute for the Industrial Environment and Risks in October 2001 and entitled "Study of the lightning conductors with priming device" by Mr. P. Gruet, presents an investigation concerning 15 such devices. This ionization can be achieved, for example, by an electrical discharge in the air separating two electrodes placed near the tip electrically connected to the ground. In another embodiment, one of the electrodes is formed by the tip itself.

  In order to increase their efficiency, certain lightning conductors have sensors capable of detecting the approach of a descending tracer coming from the base of the storm cloud, which announces the fall of lightning. These lightning conductors trigger, in a synchronized manner, the ionization of the air in the vicinity of the tip, in order to create the conditions necessary for generation and propagation of an upward tracer capable of intercepting the detected downward tracer.

  Furthermore, document EP 0 192 000 describes a lightning rod whose tip is electrically isolated from the ground by a spark gap and connected to one of the terminals of a voltage generator. Under these conditions, the point is brought periodically to a high potential. 30 The voltage generator delivers a potential in the form of a highly damped sine wave train. The wave trains are emitted periodically and are identical from one period to another. It should be noted that the lightning conductor described in this document is autonomous since it can include a source of electrical power 35 constituted, for example, by solar panels supplying an accumulator.

  Depending on the particular geometry of the lightning rod tip, and in particular the radius of curvature of the tip itself, there is a threshold potential beyond which the electric field generated in the vicinity of the tip causes the ionization of the air. surrounding the tip. When a thunderstorm approaches, the electric field increases.

  The point of the lightning rod having a certain impedance and crossing several field lines is naturally brought to one.

  potential due to the ambient electric field. The potential of the tip 10 is offset by a constant relative to the potential applied by the voltage generator due to the amplification due to the ambient electric field. When the cloud is negative, the potential shift is made by a positive constant. When the cloud is positive, the potential shift is made of a negative constant. If the potential across the voltage generator is such that under non-stormy conditions the maximum amplitude of the tip potential is less than the threshold ionization potential, said offset of the tip potential of a constant can allow the maximum amplitude of the tip potential to cross the threshold potential and ionize the air.

  In the lightning conductor described in document EP 0 192 000, the sign of the potential to which the point is subjected is not chosen as a function of the nature of the storm. In addition, the tip feeder is controlled to turn on when thunderstorm conditions are detected. Once the tip supply device in operation, the latter periodically brings the tip of the lightning rod to a potential, without correlation with the arrival of a descending tracer. The present invention aims to provide a lightning rod with polarized tip not having the aforementioned disadvantages.

  The present invention has for first object a lightning rod with polarized capture device, comprising a tip electrically isolated from the ground and polarized by means of a high voltage bias circuit, the base of said tip being connected to the ground by spark gap means. , said lightning rod being able to produce an ionization of the ambient atmosphere, characterized in that it comprises detection means making it possible to detect the polarity of the base of a storm cloud and control means able to emit a signal bias towards said high voltage bias circuit so that the latter, when triggered, brings said tip to a potential whose sign is correlated with the detected polarity.

  Preferably, the lightning conductor according to the invention comprises a time base allowing said control means to trigger, at regular intervals, said high voltage bias circuit. Preferably, the lightning rod comprises a time base 10 and said detection means are further capable of detecting the arrival of a descending tracer and of transmitting a detection signal to said control means, and said control means are capable of triggering said high voltage bias circuit in response to receipt of said detection signal so as to synchronize the polarization of the tip with said detected descending tracer.

  According to one embodiment, said high voltage bias circuit comprises a bistable element and a low voltage / high voltage transformer, and said bias signal emitted by said control means in the direction of said high voltage bias circuit, is capable of modifying a state of said bistable element so as to modify the direction of current flow in the primary of said transformer, said tip being connected to the secondary of said transformer so that the polarization of the tip is in correlation with the detected polarity.

  Preferably, the control means are capable of emitting a triggering signal intended to close an electronic switch to trigger said polarization circuit of the tip.

  Preferably, the lightning rod comprises at least one source of electrical power and means for storing said electrical power generated by said at least one source.

  In one embodiment of the invention, said at least one source of electrical power is constituted by a panel comprising photovoltaic cells, and said means for storing electrical power are constituted by an accumulator.

  The invention will be better understood, and other objects, details, characteristics and advantages thereof will appear more clearly during the following description of a particular embodiment of the invention, given solely by way of illustration and not limiting, with reference to the accompanying drawings. In these drawings: - Figure 1 is a block diagram of the polarized lightning rod according to the invention; and, - Figure 2 is an electronic diagram of the voltage / voltage converter and the high voltage bias circuit of the lightning rod tip according to the invention.

  Before describing the operation of the polarized lightning rod 10 according to the invention, the currently preferred modeling of the lightning phenomenon will be described.

  During the formation of a thunderstorm, large quantities of electrical charges are produced in a cloud. These charges are distributed, depending on their sign, at the base of the cloud or at its top. The base of the cloud can either group negative charges, and we speak of a negative cloud, or group positive charges, and we speak of a positive cloud. It should be noted that in more than 90% of cases, the cloud base carries negative charges. The base of the cloud thus charged influences an electrical charge on the surface of the ground. The surface of the ground then carries a charge, the sign of which is opposite to the sign of the charge carried by the base of the storm cloud. The presence of these charges creates very large potential differences between the base of the cloud and the ground.

  Above a certain threshold of potential difference, the air, which was hitherto an insulator, undergoes an abrupt variation in its dielectric properties and becomes conductive of the electric current. An electric arc between the base of the cloud and the ground is formed which makes it possible to neutralize part of the charges carried by the ground and by the base of the cloud. More precisely, just before the effective fall of the lightning, the negative charges, in the lower part of the cloud, move towards the ground according to a sinuous path. These charges form a descending tracer. In addition to the approach of a descending tracer, the electric field increases strongly and rapidly at ground level.

  Upward discharges are created at the ends of objects on the ground. When the electric field at ground level exceeds a certain threshold, said discharges form an ascending tracer which develops and goes against the descending tracer. Several ascending tracers can be emitted simultaneously, but only one of them comes into contact with the descending tracer in order to form a conductive channel between the base of the cloud and the point of the ground from which the ascending tracer was emitted. The conductive channel then allows the flow of charges from the cloud to the ground.

  The power of the tips of a conductor to accumulate electrical charges is known in electrostatic. In particular, the smaller the radius of curvature of said tip, the greater the quantity of charges accumulated. The electric field in the vicinity of the tip is then intense, it is able to partially ionize the air: this is the Corona effect. This is why the tip of a conductor connected to the ground constitutes a privileged point from which ascending tracers can be emitted. As a result, lightning strikes favorably on conductive objects having a tip. It is this principle which is the basis of the operation of lightning rods. Lightning falling in a privileged manner on the tip of the lightning rod, the surface of the ground surrounding the lightning rod is protected.

  The purpose of lightning conductors with a polarized capture device, and in general of priming lightning conductors, is to promote the emission of an ascending tracer capable of coming into contact with the descending tracer, and this in fact imposing a path preferential lightning flow. Thus, the radius of the ground surface which will be protected by said lightning rod with polarized capture device will be greater than the radius of the surface protected by a lightning rod lightning rod having an identical geometry.

  The end of the lightning rod capture device is, in general, constituted by a point but can sometimes be constituted by a sphere, a disc, etc. Thus, when the term "tip" is used in this document, it is necessary to understand all the equivalent means which can constitute the device for capturing said lightning rod.

  The preferred embodiment of the polarized lightning rod according to the invention is shown in FIG. 1.

  The lightning conductor according to the invention is distinguished from a conventional lightning rod with a single rod, in that the point 1 of the lightning rod is electrically isolated from the ground by a spark gap 2.

  The spark gap 2 can consist of two half-spheres spaced from each other by an interval of 4 cm containing air. When lightning falls on tip 1, the electric field between the two half-spheres of spark gap 2 is greater than the threshold electric field of 27 kV / cm beyond which the air is ionized and becomes current conductor. Thus, when lightning falls on the tip 1 of the lightning rod, the spark gap 2 being conductive, the current reaches the earth without passing through the various electronic devices.

  The polarized lightning rod has a high voltage polarization circuit 3 making it possible to bring the potential of the tip 1 to high values of the order of several tens of thousands of volts. The high voltage bias circuit 3 is controlled by a control circuit 4 to which at least one sensor is connected 5. Furthermore, the high voltage bias circuit 5 is connected to a voltage / voltage converter 6.

  The lightning rod also includes a time base 7 making it possible to supply a time signal to the various lightning rod devices. The time base 7 comprises, among other things, an oscillator capable of delivering square signals, between 0 and 5 V at a frequency 50 kHz. Finally, the lightning conductor according to the invention comprises an accumulator 8. The accumulator 8 is supplied, for example, by solar panels 9a-c comprising photovoltaic cells.

  The accumulator delivers a voltage of 6V to the various electronic devices of the lightning conductor. The latter is therefore self-sufficient in energy. However, the amount of electrical energy available remains low. This constitutes, for the moment, the main limiting factor, and the solutions adopted in the lightning rod according to the invention take this parameter into account.

  In detail, the sensor 5 includes a plate 30 capable of carrying loads influenced by the loads carried by the base of the cloud. The charges carried by said sensor 5 are therefore of opposite sign to the charges of the base of the cloud. The significant variation in the load carried by the sensor 5 during the progression of a descending tracer leads to the appearance of a current. When the intensity of this current 35 exceeds a predefined threshold, it constitutes a detection signal giving the indication of the arrival of a descending tracer. In addition, the sign of this current is correlated with the sign of the descending tracer.

  The detection signal is emitted by the sensor 5 to an input of the control circuit 4. From this detection signal, the 5 control circuit 4 generates a polarization signal and a synchronization signal in the direction of the high polarization circuit. voltage.

  The detection signal is applied to one of the terminals of a synchronous mono-stable belonging to the control circuit.

  Said mono-stable generates, in turn, the synchronization signal by giving it time characteristics capable of closing an electronic switch belonging to the high-voltage bias circuit 3 as will be described below with reference to FIG. 2. In particular the synchronization signal has a duration of 400 ps.

  It should be noted that the duration of the time interval separating the detection of the descending tracer and the triggering of the polarization of the lightning rod tip can be adjusted. This can be achieved either by adapting the threshold of the detection current or by adding to the control card 4 a component introducing a time delay between the detection signal and the emission of the synchronization signal. Indeed, increasing the threshold of the detection current beyond which the synchronization signal will be transmitted corresponds to waiting for the descending tracer to approach the lightning rod with polarized tip.

  On the other hand, as a function of the sign of the current of the detection signal and therefore of the sign of the descending tracer, the control card 25 4 transmits in the direction of either input A or input B of the high voltage bias circuit THT a signal capable of switching a bistable element from one position to another as will be described below.

  FIG. 2 describes the voltage / voltage converter 6 and the polarization circuit of the tip 3 in more detail.

  The voltage / voltage converter 6 is located between the input terminals C and D on the one hand and the output terminal F and the ground on the other hand.

  Between terminal C and ground, a square wave signal between 0 and 5 V is applied, the frequency of which is half the frequency of the signal output from the time base, ie 25 kHz. In the same way, an identical signal is applied to terminal D but with a shift of half a period with respect to the signal applied to terminal C. These signals are respectively and alternately applied to transistors Tc and Td. Consequently, an impulse is emitted respectively and alternately in the mesh Mc and in the mesh Md. Each of these meshes comprises the primary of a transformer voltage / voltage T. Thus, for 5 each half period a pulse is transmitted to the secondary of the transformer T. Typically said pulse generated at the secondary has an amplitude of 300V, in absolute value. The primary of the mesh Mc and the mesh Md being wound in an opposite direction, the pulses induced in the secondary are of opposite sign. At the terminal of the secondary of the voltage / voltage transformer T, for a first half period the signal is at -300 V and for a second half period the signal is at 300V. The capacitor C3 and the diode D2 allow an alignment of the induced pulses to 0 V in order to create a zero pulse during the first half period and equal to 600 V during the second half period.

  The tip bias circuit is located between the input terminals A, B, E and F and the secondary of a low voltage / high voltage transformer THT. The secondary of this THT transformer is connected by a terminal to the tip 1 of the lightning conductor and by the other terminal to ground, itself connected to earth. The presence of the resistor RI and of the capacitor Cl ensures that only a small current flows through the secondary of the transformer THT when lightning strikes the tip 1. In this way, the various electronic circuits are not damaged by lightning.

  When the electronic switch constituted by the triac 15 is not conducting, the mesh M is open. The pulse generated by the secondary of the voltage / voltage transformer T arriving at the input F of the bias circuit 3 makes it possible to charge a capacitor C2. In the presently preferred embodiment, C2 is about 3 µF.

  The control circuit 4 emits a synchronization signal on the input E of the high voltage bias circuit 3.

  Said synchronization signal is able to circulate a current in the transistor TE so as to create a current making the triac 15 passing in both directions. The mesh M is then closed on the ground and the capacitor C2 is placed in a closed circuit. The direction of the current in the mesh M is such that the diode Dl is blocking what forces the capacitor C2 to discharge in the primary of the transformer THT. While the capacitor C2 discharges in the primary, a large voltage, of the order of several tens of thousands of Volts, is created at the secondary of the transformer THT ,.

  The way of imposing a particular direction of current flow in the primary of the THT transformer in order to bring the point 1 of the lightning conductor to a positive or negative potential with respect to the ground potential will now be described.

  The high-voltage bias circuit 3 of the tip 10 comprises a bistable relay 20 composed of two windings 16 and 17 wound around a rod 18 with paddles 19a and 19b so as to constitute an electromechanical switch with two positions.

  In the first position, illustrated in FIG. 2, the node G is connected to the terminal K of the primary of the transformer THT, and the node H (connected furthermore to ground) is connected to the terminal L of the transformer THT.

  In the second position, the node G is, on the other hand, connected to the terminal L of the primary of the transformer THT, and the node H (connected moreover to ground) is connected to the terminal K of the transformer THT.

  To activate said bistable relay 20, two control transistors Ta and Tb are provided in order to control the windings 16 and 17 respectively. When the control circuit 4 emits a positive bias control signal on the input terminal A of the 25 high voltage polarization 3, the transistor TA emits a current in the winding 16 which forces the rod 18 out of the winding 16. The blades l9a and l9b rock so as to be in the second position. This position is maintained by the presence of a return spring on the winding 17. Consequently, the current necessary to actuate the bistable consists just of a pulse when it is necessary to change the position of the bistable. This solution makes it possible to consume only a very small amount of electrical energy.

  Likewise, when the control circuit emits a negative polarization control signal on the input terminal B of the high voltage polarization circuit 3, the transistor TB emits a current in the winding 17 which forces the rod 18 to come out of the winding 17. The pallets l9a and l9b tilt so as to be in the first position.

  Thus, in the first position, the current d at the discharge of the capacitor C2 flows through the primary of the THT transformer 5 in the counterclockwise direction (with reference to FIG. 2). On the other hand, in the second position, the current d at the discharge of the capacitor C2 flows through the primary of the transformer THT clockwise.

  Under these conditions, although the amplitude of the potential induced in the secondary is identical in the two positions of the bistable relay 10 20, the sign of this potential changes from one position to another. If the potential at point F is 600 V higher than the potential for ground, when the triac 15 becomes conducting, the potential for point G is 600 V below the potential for ground.

  In the first position of the bistable, the point K is therefore at a potential lower than the potential of the mass. Provided that the transformer THT does not reverse the current induced at the secondary, the potential of the point 1 of the lightning conductor is therefore lower than the potential of the ground. By identical reasoning, in the second position of the bistable, the point 1 of the lightning conductor is brought to a potential greater than the potential of the earth.

  If the tip 1 is at a potential lower than the ground potential, during the ionization of the air located above the top of the tip, the positive charges are attracted by the tip. An excess of negative charges is therefore produced, capable of generating a negative ascending tracer. 25 It is this type of ascending tracer that the lightning rod with polarized tip must emit when a positive descending tracer has been detected.

  Similarly, if the tip 1 is at a potential greater than the ground potential, when the air surrounding the tip is ionized, the negative charges are attracted to the tip. An excess of positive charges is therefore produced, capable of generating a positive ascending tracer.

  It is this type of ascending tracer that the polarized lightning rod must emit when a negative descending tracer has been detected.

  It therefore suffices to switch the bistable relay to the second position, if it was not already there, when a negative descending tracer 35 has been detected by the sensor 5 by emitting a positive bias signal on the input A ; and towards the first position, if it was not already there, when a positive descending tracer has been detected by the sensor 5 by emitting a negative bias signal on input B. Although the invention has been described in connection with a particular embodiment, it is obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these fall within the scope of the 'invention.

Claims (7)

  1. Lightning rod with polarized capture device, comprising a tip (1) electrically isolated from the ground and polarized by means of a high voltage bias circuit (3), the base of said tip being connected to the ground by means spark gaps (2), said lightning rod being able to produce an ionization of the ambient atmosphere, characterized in that it comprises detection means (5) making it possible to detect the polarity of the base of a stormy cloud and means for control (4) capable of emitting a polarization signal in the direction of said high voltage bias circuit so that the latter, when it is triggered, brings said tip to a potential whose sign is correlated with the detected polarity.   2. Lightning conductor according to claim 1, characterized in that it comprises a time base (7) allowing said control means (4) to trigger, at regular intervals, said high voltage bias circuit (3).   3. Lightning conductor according to claim 1, characterized in that it comprises a time base (7) and that said detection means (5) are, moreover, capable of detecting the arrival of a descending tracer and at 20 transmitting a detection signal to said control means (4), and that said control means are capable of triggering said high voltage bias circuit (3) in response to the reception of said detection signal so as to synchronize the polarization of the tip (1) with said descending tracer detected.   4. Lightning conductor according to one of claims 1 to 3, characterized in that said high voltage bias circuit (3) comprises a bistable element (20) and a low voltage / high voltage transformer (THT), and that said signal polarization emitted by said control means (4) towards said high voltage polarization circuit (3), is capable of modifying a state of said bistable element so as to modify the direction of current flow in the primary of said transformer, said tip being connected to the secondary of said transformer so that the polarization of the tip is correlated with the detected polarity.   5. Lightning conductor according to one of claims 1 to 4, characterized in that the control means (4) are capable of emitting a trigger signal intended to close an electronic switch (15) to trigger said high voltage bias circuit ( 3).   6. Lightning conductor according to one of claims 1 to 5, characterized in that it comprises at least one source of electrical power (9a-c) and storage means (8) of said electrical power generated by said at least a source.   7. Lightning conductor according to claim 6, characterized in that said at least one source of electrical power is constituted by a panel (9a-c) comprising photovoltaic cells, and that said means for storing electrical power are constituted by a accumulator (8).