EP0845843B1 - Protection device for telephone lines - Google Patents

Description

The present invention relates to the field of devices for protection of telephone lines.

Telephone lines, even when they are not exposed directly, can carry dangerous overvoltages for terminal equipment connected to these lines.

The origin of these disturbances is generally linked to the lightning.

It is therefore common to limit these overvoltages, to use devices called "lightning arresters" connected on the lines deriving the lightning currents to earth.

Surge arresters for telephone lines are generally made from three-pole gas spark gaps to allow protection of the two line wires relative to the earth. Most of the time, these components end up short-circuiting report the unavailability of the line on the one hand, and ensure the protection of the terminal on the other hand. This end of life is ensured by an external device on the spark gap.

The short-circuiting devices used on the commercial surge arresters, generally consist of devices thermal which, from a determined temperature, remove the insulation between two of the spark gap electrodes.

Illustrated in Figure 1 attached, the structure of a device for protection known from the prior art.

In this figure 1, there is shown under reference 10 a spark gap conventional gas pipe with three output electrodes 11, 12, 13, and 20 a leaf spring of electrically conductive material connected in permanence at the central electrode 12, but isolated at the origin of the electrodes 11, 13 terminated by respective washers 21, 22 made of material electrically insulating. Heating of the device at the end of its life causes the fusion of the washers 21, 22 of insulation and consequently the contact of the blade 20 with the electrodes 11, 13 to ensure the complete short circuit of the device between the three electrodes 11, 12 and 13.

The known device illustrated in FIG. 1 gives overall satisfaction with the protection of telephone lines. However, it has a major drawback: it does not allow the formal visualization of the fault.

Other examples of line protection devices telephone calls can be found for example in documents: FR-2409616, FR-2466854, FR-2560457, FR-2560458, FR-2659504, FR-2696581, FR-2710793 and FR-2692738.

The document EP-A-0312729 describes a protection device for telephone line comprising a lightning arrester placed in a main housing of a housing made of thermoplastic material and which comprises in an auxiliary housing separated from the main housing by a fusible membrane, an elastic rider-shaped blade, made of material electrically conductive. In the event of overheating, the fusible membrane is broken and the elastic blade in jumper is likely to short-circuit the surge arrester cell.

Document FR-A-2696588 describes a surge limiter with medium fault indicator. According to this document, the overvoltage comprises in a box, in series between two terminals of connection, a varistor and a fusible element with, under dependence of the fuse element an indicating means which, mounted movable between a operating position and a fault position, is continuously requested by elastic means towards its defect position. More again precisely, the indicating means consists of a tape which, while whole housed in the housing, is slidably mounted longitudinally in this one with on this box, a window thanks to which this ribbon is at least partially visible.

The present invention now aims to meet the aforementioned problems by proposing a new surge arrester device protection of telephone lines with an end-of-life indicator.

An important goal is in particular to propose such an adapted device to support the normative tests in force.

These objects are achieved in the context of the present invention by to a protection device for telephone lines of the type defined in the claim 1 appended.

According to another preferred characteristic of the invention, the blade elastic is made of electrically conductive material and is suitable to view the end of life of the device.

• la figure 1 précédemment décrite représente un dispositif de protection classique conforme à l'état de la technique,
• la figure 2 représente une vue latérale d'un dispositif de protection conforme à la présente invention,
• les figures 3A et 3B illustrent deux variantes de réalisation de cellules de protection conformes à la présente invention,
• la figure 4 représente schématiquement la visualisation de fin de vie,
• la figure 5 représente schématiquement un dispositif de protection conforme à la présente invention, partiellement éclatée, et
• la figure 6 représente schématiquement une membrane fusible conforme à la présente invention.

Other characteristics, objects and advantages of the invention will appear on reading the detailed description which follows, and with reference to the appended drawings, given by way of nonlimiting example and in which:

• FIG. 1 previously described represents a conventional protection device in accordance with the state of the art,
• FIG. 2 represents a side view of a protection device according to the present invention,
• FIGS. 3A and 3B illustrate two alternative embodiments of protection cells in accordance with the present invention,
• FIG. 4 schematically represents the end-of-life display,
• FIG. 5 schematically represents a protection device in accordance with the present invention, partially exploded, and
• FIG. 6 schematically represents a fusible membrane in accordance with the present invention.

• non fonctionnement du dispositif de mise en court-circuit lors de séquences d'application d'une tension secteur alternative 50Hz sous forme d'une répétition, cinq fois de suite d'un courant de 5A pendant une seconde, suivi d'un repos de 3mn (simulant les fermetures/ouvertures des contacts de lignes),
• fonctionnement du dispositif de mise en court-circuit pour une application prolongée accidentelle d'une tension secteur alternative 50Hz avec un courant compris entre 500mA et 10A.

The tests required by the standards in force for telephone lines are as follows:

• non-functioning of the short-circuiting device during sequences of application of an AC mains voltage 50Hz in the form of a repetition, five times in succession of a current of 5A for one second, followed by a rest of 3 mins (simulating closings / openings of line contacts),
• operation of the short-circuiting device for accidental prolonged application of an AC mains voltage 50Hz with a current between 500mA and 10A.

Such specifications cannot be kept with a device calibrated weld type fusion. According to the tests and studies of the Applicant, this results from the fact that such calibrated welds do not allow to take into account that the only temperature parameter.

On the other hand, the device according to the present invention according to which the means for retaining under stress the elastic blade is formed of a calibrated fuse membrane, makes it possible to hold the two aforementioned tests. This results in particular from the fact that the dimensioning of the membrane fuse allows to play on the two parameters temperature and time.

Is illustrated in Figure 2 attached, a protective device according to the present invention comprising a housing or cradle 30 which houses a protection cell 10 and supports an elastic blade 40 thus a fusible membrane 50, as indicated previously.

The cradle 30 can be the subject of numerous variants of production. It preferably corresponds to a classic geometry (by example of width equal to 17.5 mm) standardized to allow sound combination in cabinets and on conventional rails such as rails DIN.

The lightning protection cell 10 is preferably also classic in itself. It may for example be a gas spark gap tripolar as previously indicated.

The elastic blade 40 is preferably made of electrically material driver to participate, in combination with contacts 42, 44 electrically conductive carried by the housing 30, has a visualization distance from end of life of the device.

The elastic blade 40 is held under stress, at rest by the fuse membrane 50.

To this end preferably, the elastic blade 40 is embedded or fixed by other means, to a first of its ends 41 on the case 30. The elastic blade 40 is moreover retained at its second end 43 by the fusible membrane 50.

The latter is fixed by a first end 51 on the lightning protection cell 10, and by a second end 52 on said second end 43 of the elastic blade 40.

Thus, the stress of the elastic blade 40 exerts a force on the traction on the fuse membrane 50.

When the protective cell 10 and consequently the membrane fuse 50 reach a determined temperature for a defined time, the fusible membrane 50 releases the elastic blade 40. The elastic blade 40 then occupies a second position as illustrated in broken lines on Figure 2. In this second position, the elastic blade 40 abuts on the aforementioned contacts 42, 44, previously isolated, which allow ensure the end of electrical life of the arrester.

Depending on the connection of points 42, 44 it is possible to ensure end of life in short circuit, open circuit or insert another circuit electrical including other components (resistance, fuse, other spark gaps, CTP ...). The elastic blade 40 can also be associated, by its second end 43 has a display piece 60 mounted at displacement, for example in translation on the housing 30. Such a piece of display 60 is more particularly visible in FIG. 5. It can be the subject of numerous embodiments.

Where appropriate, the display part 60 can be associated with two protection cells 10 placed in parallel and each associated with an elastic blade 40 and a fusible membrane 50 respectively. In this case, preferably, the display part 60 is provided with two stages of training finger, illustrated under the general reference 62 in the figure 5, some rigid, others flexible to elastically cross the end 43 of a blade 40. Such an arrangement makes it possible to distinguish the cases where 1) the two cells 10 are in service, 2) one of the two cells 10 is disconnected and 3) the two cells 10 are disconnected. Indeed, the amplitude of movement of the display part 60 depends on the number of cells 10 in service. More specifically, at rest, when the two cells 10 are in service, the ends 43 of the blades 40 take support on the rigid stages of the drive fingers of the part 60 of viewing. When one of the fusible membranes 50 is broken, the end 43 of the corresponding blade 40 moves and drives the part 60 of display on a first amplitude. During this displacement, the flexible stage of the other drive finger of the part 60 elastically crosses the end 43 of the blade 40 associated with the second cell 10 so that this end 43 of this blade 40 is placed in abutment against said flexible stage. So when the second fuse membrane 50 is broken in turn, in the event of deficiency of the second cell 10, the end 43 of the blade 40 in question moves the part 60 on a second amplitude, by requesting the flexible drive stage placed opposite. The display part 60 illustrated in FIG. 5 is broadly in accordance with the provisions described in the patent application FR-94 14586 of 5/12/94.

For this reason, the structure of this display part 60 does not will not be described in detail later. However, it should be noted that preferably, this part 60 is provided with a flap 64 designed to be moved next to a window formed in the housing 60 during the release of the elastic blade 40.

Where appropriate, the device according to the present invention can further include an optical barrier detection system for order a fault display by remote monitoring.

To do this, the elastic blade 40 may include an opaque flap 45 positioned to modify the state of an optical curtain according to whether the blade 40 occupies the original position maintained by the fusible diaphragm 50 or is moved after rupture of the membrane 50. Preferably, the flap 45 is formed by folding a portion of the elastic blade 40 at 90 ° from its plane way. For example, the flap 45 can be adapted to release the curtain optical in the original position of the elastic blade 40, but on the contrary obscure it when the membrane 50 releases the elastic blade 40. The optical curtain can be defined by a channel 31 formed in the housing 30 or a series of boxes 30 attached, between an optical transmitter and a receiver associated optics.

Preferably, the fusible membrane 50 is made of a material thermoplatique.

By way of nonlimiting example, the fusible membrane 50 can be made of polycarbonate and have a width of the order of 3 to 5mm and a thickness of the order of 375 to 500 μm. Its length is for example of around 20mm.

Illustrated in Figure 6, an embodiment of the membrane fuse 50 according to the present invention. Note that this membrane 50 illustrated by way of nonlimiting example in FIG. 6 includes an orifice 53 at its first end 51 for engagement on the pin 14, and a oblong light 54 at its second end 52 for engagement on the elastic blade 40. Furthermore, this membrane 50 which has edges longitudinal straight is generally flared towards its second end 52.

Note that the device according to the present invention with an end-of-life indicator eliminates all power supply for display of end-of-life protection, even if the site's telecommunications equipment is no longer supplied. This represents a very important advantage compared to the devices existing classics that previously required an electrical protection test after finding the faulty telephone line among all the site lines.

The present invention may be applied to different protective cell variants 10. Thus, in FIG. 3A, a first variant according to the present invention comprising a spark gap with three-pole gas 10, the end 51 of the fusible membrane 50 being linked to a pin 14 placed on the central electrode 12.

It is indeed preferable to bond the membrane 50 to the electrode central 12 which is the one that heats the most in the event of a failure. However, as a variant, the end 51 of the membrane 50 could be linked to one of the end electrodes 11 or 13.

FIG. 3B illustrates another variant of the protection 10 according to the present invention formed by a gas spark gap 10 bipolar, with two electrodes 11, 12, the end 51 of the membrane fuse 50 being linked to a pin 14 placed on one of the electrodes 12.

The term "membrane" should not be understood in a sense limiting. In practice, the invention encompasses any equivalent means based on ribbon or link capable of initially keeping the elastic blade under stress 40.

According to yet another variant, the protection device according to the present invention can be completed by a blade 20 in electrically conductive material, conventional, of the type described previously with regard to FIG. 1 to connect the various poles of cell 10 in the event of failure, as shown diagrammatically in the figure 4.

Claims (11)

1. A device for protecting telephone lines, the device comprising a lightning arrestor cell (10), a spring blade (40) maintained under stress, and a fusible membrane (50) of a thermoplastic material adapted to keep said spring blade (40) under stress and to release it when the lightning arrestor cell (10) reaches a determined temperature, the device being characterized by the fact that the spring blade (40) is fixed via a first end (41) to a housing (30) and is retained at its second end (43) by the fusible membrane (50), the fusible membrane (50) working in traction to keep the spring blade (40) under stress and having a first end (51) fixed to the lightning arrestor cell (50) and a second end (52) fixed to the second end (43) of the spring blade (40), said spring blade (40) being adapted to activate end-of-life indicator means (42, 44; 60) whenever it is released by the fusible membrane (50).
2. A device according to claim 1, characterized by the fact that the spring blade (40) is made of an electrically conductive material and is placed facing electrical contacts (42, 44) so as to modify the connection states between them in the event of the spring blade (40) being released after the fusible membrane (50) has melted in order to display the end of the life of the device.
3. A device according to claim 1 or claim 2, characterized by the fact that the fusible membrane (50) is made of polycarbonate.
4. A device according to any one of claims 1 to 3, characterized by the fact that the fusible membrane (50) possesses a width of the order of 3 millimeters (mm) to 5 mm, and a thickness of the order of 375 micrometers (µm) to 500 µm.
5. A device according to any one of claims 1 to 4, characterized by the fact that the spring blade (40) co-operates with a moving display piece (60).
6. A device according to anyone of claims 1 to 5, characterized by the fact that the arrestor cell (10) is formed by a three-pole gas discharger.
7. A device according to claim 6, characterized by the fact that the fusible membrane (50) is placed against the central electrode (12) of the three-pole discharger (10).
8. A device according to any one of claims 1 to 5, characterized by the fact that the arrestor cell (10) is formed by a two-pole gas discharger.
9. A device according to any one of claims 1 to 8, characterized by the fact that the spring blade (40) posses an opaque flap (45) suitable for modifying the state of a light barrier depending on the position of said spring blade (40).
10. A device according to claim 5, characterized by the fact that it comprises two arrestor cells (10) placed in parallel and each associated with a respective spring blade (40) and fusible membrane (50), and associated with a moving display piece (60) adapted to distinguishes between the circumstances in which: 1) both cells (10) are in operation; 2) one of the two cells (10) is disconnected; and 3) both cells (10) are disconnected.
11. A device according to claim 10, characterized by the fact that the display piece (60) is provided with two drive finger stages (62), one being rigid and the other being flexible in order to go past the end (43) of a blade (40) elastically.

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