Patent Application
20080087648
Other features and advantages of the present invention will become more apparent after reading the following description made with reference to the figures, given as purely illustrative and non-limiting, wherein:
The device according to the present invention for protecting an electrical installation against overvoltages, overloads or short circuits, is designed to protect an electrical piece of equipment or installation. The expression “electrical installation” refers to any type of apparatus or network subject to voltage perturbations, notably transient overvoltages due to lightning or even overloads, notably overload or short circuit currents. Such devices may consist of spark gap lightning arresters or surge suppressors provided with a follow current breaking device or circuit breakers fitted with a short circuit current breaking device.
In this description, we are more particularly interested in a spark gap type lightning arrester type device for protection against overvoltages, but the invention obviously applies to circuit breakers.
In the case of a circuit breaker, the electrodes are formed by two contacts, for example, a fixed contact and a mobile contact, held in physical contact with each other so as to provide the electrical connection. In this case, the electric arc is formed between both contacts when the mobile contact separates from the fixed contact to provide electrical disconnection.
According to the present invention and as illustrated in
In a particularly advantageous way, the breaker device 6 is formed by an assembly of splitting plates 7 made of electrically conducting material, for example, in metal, positioned in parallel and at a distance from each other. The splitting plates 7 are advantageously kept at a distance from each other by supporting strips 8 made of an electrically insulating material.
According to the present invention, the breaker device 6 extends, considering the direction of propagation F of the electric arc 5, between an upstream end 6A and a downstream end 6B. As shown in
According to one essential feature of the present invention, the breaker device 6 includes at its upstream end 6A, insulating means 10 against the return of the electric arc 5.
These insulating means 10 are structurally designed and arranged so as to allow the electric arc 5 to enter the breaker device 6 while forming an obstacle against the exit of the electric arc 5, in order to prevent the electric arc 5 from escaping from the breaker device 6 once the electric arc is inside the breaker device.
The insulating means 6 are adapted to prevent the electric arc 5 from returning backwards along a direction opposite to its normal direction of propagation F, in such a way that once the electric arc 5 has been broken down into a plurality of elementary arcs within the breaker device 6, the electric arc may no longer form again outside the breaker device 6, notably in the divergent space 9.
Therefore, the non-return insulating means 10 operate as a ground and are built and positioned relative to the splitting plates 7 on the one hand and to the electrodes 2, 3, on the other hand, so as to significantly reduce the likelihood that the electric arc 5 escapes from the breaker device 6. Therefore, the design of the protection device 1 according to the present invention may significantly improve its short circuit current breaking capacity.
The insulating means 10 according to the present invention must provide an answer to a new problem which is that of letting the electric arc 5 penetrate into the inside of the protection device 6 while limiting the likelihood that the electric arc escapes and forms again outside the breaker device 6.
Advantageously, the insulating means 10 are arranged so as to form a partial insulating barrier between the electrodes 2, 3 and the upstream end 6A of the breaker device 6. The expression “partial insulating barrier” refers not only to physical barriers made of electrically insulating material, but also to not necessarily physical barriers which may be electrically insulating barriers, capable of preventing the formation of an electric arc between the electrodes 2, 3 and the upstream end 6A of the breaker device 6.
Advantageously, the splitting plates 7 extend along the direction of propagation F of the electric arc 5, between a front end 7A and a distal end 7B. The front end 7A and the distal end 7B are located at substantially the same level as the upstream end 6A and the downstream end 6B of the breaker device 6. In a particularly advantageous way, the splitting plates 7 are each provided with a notch 11, at least partially separating each splitting plate 7 into two separate branches 7C, 7D. Thus, when the splitting plates 7 are assembled so as to form the breaker device 6, the notches 11 form a groove 12, the shape of which, for example a V-shape, is specifically designed to attract the electric arc 5 towards the inside of the breaker device 6. In this way, the entry area E for the electric arc 5 substantially coincides with the groove 12.
According to a first exemplary embodiment of the present invention, the insulating means 10 are arranged so as to at least partially physically close off the upstream end 6A of the breaker device 6, thus forming a physical insulating barrier between the electrodes 2, 3 and the upstream end 6A of the breaker device 6.
Even more preferably, the insulating means 10 are arranged so as to entirely cover the upstream end 6A of the breaker device located around the entry area E for the electric arc 5, for example, on either side of it. The insulating means 10 may be positioned on either side of the groove 12, as illustrated in
According to a another exemplary embodiment of the present invention, the insulating means 10 may be formed from one or several rigid strips (not shown), for example, positioned on either side of the groove 12 so as to cover the front end 7A of the splitting plates 7. The rigid strips then preferably extend along a plane approximately perpendicular to the direction of propagation F of the electric arc 5, and coplanar with the plane formed by the front ends 7A of the splitting plates 7.
The rigid strips may advantageously be perforated with a plurality of orifices so as to provide air flow between the divergent space 9 and the breaker device 6.
Preferably, the rigid strips, through one of their faces, come into contact with the front ends 7A of the splitting plates 7, and preferably bear on them in a sealed manner.
Even more preferably, the insulating means 10 are formed by caps 13 arranged so as to form a partial insulating barrier between the electrodes 2, 3 and the upstream end 6A positioned on either side of the groove 12 and designed in such a way that, in their functional position, they will also cover the front end 7A of one or several splitting plates 7.
Advantageously, the caps 13 are arranged so as to entirely cover the upstream end 6A of the breaker device 6 located around the entry area E for the arc.
As illustrated in
Preferably, the edge 15 of the cap 13 is adapted to substantially penetrate inside the groove 12 when the cap 13 is in its functional position (
Even more preferably, and as illustrated in
According to one exemplary embodiment illustrated in
According to one exemplary embodiment of the present invention (not shown in the figures), the insulating means 10 are advantageously made from the same material as the casing 20 of the protection device 1, the casing 20 including the main electrodes 2, 3 on the one hand and the breaker device 6 on the other hand.
In this case, the shape of the inner surface of the casing 20 is adapted, for example, at the time when the casing 20 is moulded, to exhibit structures in relief capable of forming the insulating means 10.
The insulating means 10 and/or the casing 20 may advantageously be made from a rigid material able to withstand the arc temperature, for example, injected plastic with good temperature resistance, and even more preferably an epoxy resin or ceramic.
According to another exemplary embodiment of the present invention illustrated in
Advantageously, the strips 17 are made in a high-temperature-resistant insulating material, and notably resistant to the temperature of the arc. Preferably, the strips 17 are made from fiberglass, coated on one of its faces with a thermosetting type silicone adhesive so as to provide excellent thermal and mechanical strength.
In a particularly advantageous way, the sticky portion of the strips 17 will conform to the upstream end 6A of the breaker device 6, so as to fix the ribbons 17 onto the latter end.
According to another exemplary embodiment of the present invention illustrated in
According to a first exemplary embodiment illustrated in
According to another exemplary embodiment of the present invention illustrated in
According to another more preferred exemplary embodiment of the present invention, the breaker device 6 includes, at its downstream end 6B, an insulating screen 30 positioned so as to at least partially cover the downstream end 6B of the breaker device 6 so as to prevent the electric arc 5 from escaping from the breaker device 6 after the electric arc has passed through the breaker device, for example once (
In this preferred exemplary embodiment, the insulating means 10 have a crucial role in that, after passing through the breaker device 6 along the direction of propagation F, the electric arc 5 “rebounds” on the insulating screen 30 and then continues in a direction substantially opposite the direction of propagation F, towards the upstream end 6A of the breaker device 6. In such a configuration, the applicant has observed that the electric arc 5 preferably returns along the branches 7C, 7D of the splitting plates 7 and much more rarely to the central portion 12B of the groove 12.
Consequently, in this exemplary embodiment, the insulating barrier formed by the insulating means 10 may notably reduce the likelihood that the electric arc escapes at the upstream end 6A of the breaker device 6, thereby preventing the electric arc 5 from forming again between the main electrodes 2, 3.
Operation of the protection device 1 according to the invention will now be described, with reference to
During operation, when an overvoltage exceeding a predetermined threshold value occurs, notably as a result of a lightning strike, an electric arc 5 is established between one of the two main electrodes 2, 3 allowing the lightning current to flow to ground. This electric arc 5 then moves up to the breaker device 6 into which the electric arc penetrates at the entry area E, located in approximately the same plane as the groove 12. The electric arc 5 is then broken down into a plurality of elementary arcs so as to increase the arc voltage of the current above the mains voltage and limit the intensity of the current drained by the protection device. The elementary electric arcs move towards the downstream end 6B of the breaker device 6 until they reach the insulating screen 30. A “rebound” phenomenon then occurs and the elementary electric arcs leave in the direction opposite to the initial direction of propagation F of the electric arc 5, towards the downstream end 6A of the breaker device 6. According to the most likely operating mode, the elementary electric arcs move towards the branches 7C, 7D and more specifically along these branches as far as their front end 7A.
They are then trapped by the insulating means 10 which prevent the electric arc 5 from forming again outside the breaker device 6.
Therefore, the protection device 1 according to the present invention has a better short circuit current or follow current breaking capacity than the current breaking capacity for devices according to the prior art, while limiting the likelihood that the electric arc, once inside the breaker device and broken down into a plurality of elementary arcs, escapes from the breaker device to form again outside the breaker device between the main electrodes.
By the presence of the insulating means 10, the protection device according to the present invention has a current-breaking power multiplied by at least two as compared with devices from the prior art.
The invention finds one aspect of its industrial application in the design, the manufacturing and the use of protection devices against overvoltages, overloads, or short circuits.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0408095 | Jul 2004 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR05/01888 | 7/21/2005 | WO | 00 | 10/9/2007 |
