EP0782753B1 - Lightning arrester device - Google Patents

Description

The present invention relates to a device low voltage surge arrester of the type used in particular to protect equipment electronic.

We know that the phenomenon of lightning generates instantaneous currents which can be extremely important and can reach in some cases 10,000 to 100,000 amps with voltages that can reach 10 to 20 million volts for extremely short times. In order to ensure lightning protection of devices electronic, we insert in the circuit supply of these surge protective devices made up of components which normally behave like neutral elements, but which, in violent overvoltage due to lightning, become conductive and thus provide insulation of the device by diverting the current to the ground generated by lightning.

A good arrester designed to protect against electronic devices must have three qualities essential. On the one hand it must have great current rise speed in order to divert quickly towards the ground the lightning energy which, without it, would destroy electronic equipment. The current rise speed will be all the more high as the inductance of the arrester will be low. he must then be able to keep enough long its effectiveness so that the diversion to the energy ground lasts long enough to allow the implementation of conventional means of logout. This period of effectiveness is all the more stronger than mechanical strength, in all directions, surge arrester is high. He must finally be able to be put in place and removed quickly of its support.

Usually used to ensure such functions, gas spark gaps. These spark gaps have significant drawbacks, and especially that of being seriously delayed, so that in some cases, and particularly in the particularly violent lightning strikes and rapid deterioration of electronic devices occurs before grounding the lightning by the spark gap.

We also know devices surge arresters made up of tubular elements cylindrical containing varistors and / or zener diodes, embedded in an insulating resin. Of such devices, must, in a volume particularly reduced, be able to flow to earth very high impulse currents while maintaining acceptable tensions at their terminals. We can see that the powers developed in such lightning arresters can reach excessively high values. So, a varistor has the possibility of running out currents of the order of 5,000 amperes for time on the order of 10 microseconds, while now the voltage across its terminals to a value of around 1,500 volts. The power thus developed in such a varistor is around 7.5 megawatts. Such powers developed during extremely short times, also in volumes are extremely difficult to channel, if although the SPDs behave sometimes like real miniature "bombs", with as a consequence, in addition to the destruction of the device arrester itself, that of electronic elements that they are meant to protect.

We also know surge arresters which are used in high voltage power lines used for the distribution of electric current. In these energy lines, following the impedance of the power supply transformer placed upstream of the arrester, the currents developed can reach peak values of 6 to 25 kiloamperes for periods of the order of 100 milliseconds. In order to ensure the protection of installations it is essential that surge arresters used maintain grounding, as long as disconnecting devices, such as circuit breakers, did not themselves ensure breaking of the line. It is therefore particularly important at least delay the destruction of such surge arresters, until the devices are actuated disconnectors. The components used in the constitution of lightning arresters are usually coated in housings resins which are mainly chosen for their insulating qualities. We know that, unfortunately the best insulating materials are with particularly mechanical qualities mediocre.

The manufacturers of this type of device have therefore been faced with the need to strengthen the mechanical strength of the enclosures containing the components by stiffening them and drowning the whole in insulating curable resins.

These solutions are not satisfactory in because on the one hand, they turn out dangerous, and that on the other hand they turn out not very effective, both in terms of resistance mechanical and in terms of characteristics the appliance.

These solutions are dangerous because the resin that surrounds the area where the significant instantaneous power cracks, which promotes the birth of an electric arc causing the carbonization of this resin. Carbon as well product ensures the conductivity of electricity, and the current from the overvoltage, or from a network of energy goes into it, heating up quickly the area concerned, which increases carbonization of it and, by cumulative effect, we are thus leads to rapid destruction of the arrester, destruction can even set fire to the environment.

These solutions are also not very effective, since the mass of resin, between where generated instantaneous power and the area where locates the rigid enclosure, constitutes a mattress malleable and / or elastic promoting the appearance of cracks thus creating incipient fractures reducing the mechanical characteristics of the surge arrester.

It has also been proposed in patent FR-A-2 678 765 a surge arrester intended for the protection of overhead power lines which consists of a envelope containing a tube provided with lights longitudinal inside which are arranged varistors. A silicone elastomer fills the empty parts of the envelope, between the periphery varistors and the inner face of the tube. The electrical contact is made at each ends of the tube.

Such a device, if it is satisfactory in protection of power lines is not when it comes to ensuring the protection of electronic devices. Indeed, from share the reaction time is too high due connection lengths and inductances too resulting, and on the other hand, the physical explosion protection is not sufficiently efficiently, and in in some cases it is even sought to achieve end-of-life indicators for the arrester.

The solutions proposed by the previous state of the technique is also ineffective in terms of of the speed of current surge arrester. In Indeed, we know that to maintain its effectiveness, a surge arrester must have the property of putting itself in conduction quickly, so that its inductance must be particularly weak, so as not to delay unduly its conduction. In the devices of the prior art, the presence of a rigid carcass requires manufacturers to carry out complex connections at the same time increasing the length of the connections and therefore the inductance of the arrester, which causes the this its conduction characteristics fast.

The object of the present invention is to provide a lightning arrester having a high speed of current rise, and which has a resistance sufficient mechanics allowing it to delay its destruction until means of cutting off current such as disconnectors, etc. time to take action, this device being easier and faster to connect and disconnect.

The subject of the present invention is therefore a surge arrester device consisting of a housing, comprising two electrical contact terminals, formed at least one housing element, containing at least a protective element whose terminals are connected electrically at the contact terminals, this element being embedded in an insulating material contained in said housing element, characterized in that at less a mechanically resistant sleeve is interposed in the insulating material between the element of housing and the protective element and in that the housing consists of two housing elements electrically insulated from each other which constitute the two terminals of contact.

In one embodiment of the invention, the housing consists of two housing elements and at least one of these has a bottom, or transverse wall, come in one piece with him, the electrical contact between the protective element and the housing element being made by said bottom. In a variant of this embodiment of the invention, the other housing element comprises also a bottom, or transverse wall, which is mechanically and electrically secured to it, the second terminal of the protective element being in electrical contact with said bottom. Such a mode of implementation allows for a connection particularly easy and fast of the surge arrester on its support.

In another embodiment of the invention, the sleeve is made of fibers of glass or carbon fiber, woven.

It should be noted that the bodies of surge arrester which constitute one of the terminals of electrical connection can only have a homogeneous mechanical resistance over their entire periphery, since the body being conductive of the electric current it must necessarily include an insulating zone allowing passage to the second connection terminal. This discontinuity has the effect to weaken the body and thus decrease its explosion resistance.

The present invention makes it possible to compensate for the weakened area of the body of the arrester, making thus possible the realization of surge arresters having both the three qualities mentioned previously.

We will describe below, by way of example not limiting, an embodiment of this invention, with reference to the attached drawing in which:

Figures 1 and la are schematic views representing two modes of use of a device arrester according to the invention in circuits that they are intended to protect.

FIG. 2 is a view in axial section and longitudinal of a first mode of implementation of a lightning arrester according to the invention.

Figures 3a to 3d are views showing schematically the different stages of a process of a lightning arrester device of the type of the one shown in figure 2.

FIG. 4 is a view in axial section and longitudinal of another embodiment of the lightning arrester according to the invention.

As shown in Figure 1, when we want to provide lightning protection an electronic device 1 supplied with current by a power line 2, one has between earth 3 and power line 2 a device arrester 4 and, on the other hand, between line 2 and the lightning protection device 4 a circuit breaker device 5.

During normal operation, the surge arrester 4 has an impedance sufficient to behave like a neutral element, so that it does not interfere with the functioning of the device 1. On the other hand, under the effect of a violent overvoltage due to lightning or a fault "medium voltage" (10 to 30 KV) in the circuit, the surge arrester then behaves like an element conductor so that it grounds 3 the current arriving via power line 2, short-circuiting thus the device 1, which ensures its protection.

There is shown in Figure la a device arrester used to ensure the safety of a telephone line against overvoltages. In this type of use, the circuit breaker device 5 is replaced by a 5 'current limiting device, such as for example a CTP element (with a coefficient of positive temperature), i.e. a component whose the impedance increases with the heating which it undergoes due to the current flowing through it by the surge arrester 4. The action of such a limiter is slow (in the order of a few milliseconds, or even a few seconds).

The lightning arrester 4 is made up electronic elements, such as for example zener diodes or varistors that have speeds high current rise, which makes them suitable for react almost instantaneously to overvoltages, and in any case well before the activation of the devices 5 'disconnectors or limiters.

As mentioned earlier, the device lightning arrester being traversed, when the lightning phenomenon, by currents developing extremely high powers it is important that its mechanical strength is sufficient to allow it to resist these strong powers, at least for sufficient time to allow the devices disconnectors 5 or limiters 5 'to act.

In one embodiment of the invention shown in Figure 2, the lightning arrester 4 consists of a housing 7 formed of two elements cylindrical housing, namely a first element of lower case 7a and a second element of upper case 7b. These two housing elements are separated by a distance e. The housing element lower 7a comprises, in an area close to one of its ends, a bottom 9 which is formed of manufacturing. The bottom 9 is pierced in the center with a orifice 10 into which one of the two engages connection tabs 11a of a protective element 13, essentially consisting of a zener diode. This zener diode will most often consist of several silicon wafers 20, of dissipators 21 which are interposed between the silicon elements and an insulator of very high resistivity dielectric. The upper housing element 7b has a pad 15, forming the bottom, which is fixed, for example by welding, on its internal wall at a distance close to one of its ends, if although it is rigidly held on the housing element 7b and in excellent contact electric with him. The pad 15 is pierced in its center of an orifice 16 which receives the second leg of protection element llb connection 13. The connection lugs 11a and 11b are respectively fixed by welding, or by any other process ensuring both their maintenance mechanical and good electrical contact with the bottom 9 and the tablet 15. The internal volume delimited by the internal walls of the housing elements 7a, 7b, the bottom 9, the pad 15, and the external surface of the protective element 13 is filled with a resin 17, for example a thermosetting resin or epoxy.

The protective element 13 can of course be made of a component other than a diode zener, and we can thus call on a varistor. We can thus generally use so-called non-linear components, i.e. elements whose characteristic voltage / current ends with a plateau value.

The resin 17 is chosen on the one hand, for its qualities of insulation, but also on the other hand its qualities of adhesion with the elements of housing 7a, 7b as well as for its resistance qualities clean mechanics.

A tubular sleeve 19 is arranged in this volume, between the internal walls of the elements of housing 7a, 7b and the external wall of the element protection 13.

This sleeve 19 is made, for example, of glass fibers or carbon fibers which are of preferably braided.

The lightning protection device described above has a number of advantages over corresponding devices from the previous state of the technical, especially from the point of view of resistance mechanical explosion, from the point of view of connectivity, from the point of view of the manufacturing, and finally from the point of view of inductance.

With regard to mechanical strength, the sleeve 19 ensures, through the resin curable 17, maintaining the housing elements 7a, 7b against the efforts and constraints exercising in particular in the longitudinal direction, when the surge arrester is traversed by a lightning current such as the energy released at the level silicon wafers 20 brings it into a state close to the explosion.

The sleeve 19 also exerts a resistance action against the forces exerted in a transverse direction, that is to say a direction perpendicular to the longitudinal axis yy 'of the arrester device, in particular in its central part where the spacing e provided between the two housing elements 7a and 7b to isolate them electrically constitutes a weakening zone of the arrester.

Furthermore, it was found that the sleeve 19 also performs another function, namely that of reducing (or even completely eliminating) the cracks that form in the resin, at small dimensions such as arc phenomena can no longer occur, thus avoiding rapid destruction of the arrester.

Regarding the connectors, we note that the present mode of implementation is interesting in that it uses connections particularly short electrical lengths, which promotes a high current rise speed. Furthermore, due to the cylindrical shape of the housing elements 7a and 7b, the electrical connection of the surge arrester element with the connection box in which it is mounted, is made so particularly effective. In addition, the shape cylindrical housing 7 allows a layout symmetrical active elements which contributes to further reduce the inductance.

Regarding the manufacturing process, the mode of implementation of the arrester described previously, an example showing the four steps of its implementation is illustrated on Figures 3a to 3d.

During the first step (FIG. 3a), we start from a tube 12, the length a of which is equal to that of the surge arrester element when it is finished, and which has a bottom 9. Next, a connection lug is introduced. 11a of the protective element 13 inside the orifice 10, then said tab 11a is fixed, by welding, to the bottom 9. During the second step (FIG. 3b), the sleeve is placed 19 around the protective element 13, then the resin is poured inside the tube 12. During the third step (FIG. 3c), the pellet 15 is put in place, by introducing the second tab of connection 11b of the protective element 13 in the orifice 16 thereof. Then fixed by welding, on the one hand the pad 15 on the tube 12 and on the other hand the connection tab 11b on the pad 15. During the fourth step (Figure 3d), a circular groove is made, by example by turning, in the center of the tube 12, so as to separate it into two housing elements 7a, 7b completely electrically isolated from each other.

The tests carried out by the applicant have established that such a surge arrester was in able to drift towards the earth, the energy coming lightning on the one hand quickly enough to prevent destruction of electronic devices, and on the other hand for a sufficiently long time, before destruction, so that means of cutting the conventional type have time to be activated.

It is of course, according to the invention, combine, inside the housing 7 several protective elements 13a and 13b arranged either in parallel, as shown in Figure 4, i.e. otherwise in series.

We can also interpose between the housing 7 and the protective element 13 several sleeves coaxial.

Claims (8)

1. Lightning arrester device constituted by a box (7), comprising two electrical contact terminals, formed by at least one box element (7a, 7b), containing at least one protection element (13), of which the terminals are electrically connected to the contact terminals, this element being embedded in an insulating material (17) contained in said box element (7), characterized in that the box is constituted by two box elements (7a, 7b), electrically insulated from each other, which constitute the two contact terminals and in that at least one mechanically resistant sleeve (19) is interposed in the insulating material (17) between the box elements (7) and the protection element (13).
2. Lightning arrester device according to Claim 1, characterized in that at least one (7a) of these box elements (7a, 7b) comprises a bottom (9), or transverse wall formed in one piece therewith, electrical contact between the protection element (13) and the box element (7a) being made via said bottom (9).
3. Lightning arrester device according to Claim 2, characterized in that the other box element (7b) also comprises a bottom (15) which is mechanically and electrically connected therewith, the second terminal (11b) of the protection element (13) being in electrical contact with said bottom (15).
4. Lightning arrester device according to any one of the preceding Claims, characterized in that the sleeve (19) is constituted by woven glass fibers.
5. Lightning arrester device according to any one of Claims 1 to 3, characterized in that the sleeve (19) is constituted by braided carbon fibers.
6. Lightning arrester device according to any one of the preceding Claims, characterized in that the protection element (13) is constituted by a plurality of nonlinear components arranged in series.
7. Lightning arrester according to any one of Claims 1 to 5, characterized in that the protection element (13) is constituted by a plurality of non-linear components arranged in parallel.
8. Lightning arrester according to any one of the preceding Claims, characterized in that it comprises a plurality of sleeves (19) coaxial to the longitudinal axis (yy') of the box (7).

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