Disconnector and surge arrester including such disconnector

Abstract

A disconnector and related surge arrester include first and second connection terminals connecting to active electrical leads, between which a protection element is inserted, having electrodes electrically connected to the connection terminals, a disconnector between the first terminal and an electrode of the protection element including a metal plate having a base end electrically connected to the first terminal and a distal end maintained electrically connected to the electrode, the plate being able to sublimate in the presence of short-circuit currents above a preset threshold, an intercepting slider, mounted longitudinally slidable along a longitudinal direction which lies between the base end of the lamina and the electrode of the protection element to intersect development of an electric arc, a sliding guide for the intercepting slider, the slider being biased in the longitudinal direction, through a preloaded elastic unit, towards an intercepting position abutting a portion of the plate.

Claims

1. Surge arrester, comprising a first and a second connection terminals (1, 2) for connection to the active leads of an electric plant, between which a protection element (3) is inserted, provided with a pair of electrodes (4) electrically connected to said connection terminals, a disconnector arranged between said first terminal (1) and an electrode (4) of the protection element (3) comprising a metal plate (5) having a base end (5a) electrically connected to said first terminal (1) and a distal end maintained electrically connected to said electrode (4), said lamina (5) being made of a material and section suited to cause it to sublimate in the presence of short-circuit currents above a preset threshold, an intercepting slider (7), mounted longitudinally slidable along a longitudinal direction which lies between said base end (5a) of the plate (5) and said electrode (4) of the protection element (3) to intersect development of an electric arc, a sliding guide (6) for said intercepting slider (7), the slider being biased in said longitudinal direction, through preloaded elastic means (8), towards an intercepting position abutting a portion of said plate (5), wherein said slider (7) is in the shape of a hollow, elongated body, open at a back end and closed at a front end, and partly houses said preloaded elastic means (8), and wherein said slider (7) is provided with at least one opening (10), on the side wall of said hollow body, which runs through the thickness thereof and puts in communication the outside with the inside of said hollow, elongated body of the slider (7).

2. Surge arrester as in claim 1, wherein said opening (10) is in the shape of a narrow, longitudinally elongated opening.

3. Surge arrester as in claim 2, wherein said opening (10) is obtained in a longitudinal groove (7a) of said slider (7) with which a guiding rib (9) of said sliding guide (6) is apt to engage.

4. Surge arrester as in claim 3, wherein a valve body (11) is provided between a rear end of said elastic means (8) and a fixed abutment integral with said sliding guide (6) provided with a gas discharge nozzle (6a).

5. Surge arrester as in claim 3, wherein said slider (7) has a quadrilateral crosswise section and said openings (10) are only on sides of the slider (6) substantially parallel to a connecting path of said metal plate (5).

6. Surge arrester as in claim 2, wherein a valve body (11) is provided between a rear end of said elastic means (8) and a fixed abutment integral with said sliding guide (6) provided with a gas discharge nozzle (6a).

7. Surge arrester as in claim 2, wherein said slider (7) has a quadrilateral crosswise section and said openings (10) are only on sides of the slider (6) substantially parallel to a connecting path of said metal plate (5).

8. Surge arrester as in claim 1, wherein a valve body (11) is provided between a rear end of said elastic means (8) and a fixed abutment integral with said sliding guide (6) provided with a gas discharge nozzle (6a).

9. Surge arrester as in claim 8, wherein said slider (7) has a quadrilateral crosswise section and said openings (10) are only on sides of the slider (6) substantially parallel to a connecting path of said metal plate (5).

10. Surge arrester as in claim 1, wherein said slider (7) has a quadrilateral crosswise section and said openings (10) are only on sides of the slider (6) substantially parallel to a connecting path of said metal plate (5).

11. Disconnector for short-circuit overcurrents, comprising a first and a second terminal (1, 2) for connection to the active conductors of an electric system, a metal plate (5) having a base end (5a) electrically connected to said first terminal (1) and a distal end maintained electrically connected to said second terminal (2), said plate (5) being made of a material and section suited to cause it to sublimate in the presence of short-circuit cur-rents above a preset threshold, an intercepting slider (7), longitudinally slidably mounted along a longitudinal direction which lies between said base end (5a) of the plate (5) and said second terminal (2) to intersect development of an electric arc, a sliding guide (6) for said intercepting slider (7), the slider being biased in said longitudinal direction, through preloaded elastic means (8), to-wards an intercepting position abutting a portion of said plate (5), wherein said slider (7) is in the shape of a hollow, elongated body, open at a rear end and closed at a front end, and partly houses said preloaded elastic means (8), and wherein said slider (7) is provided with at least one opening (10), on the side wall of said hollow body, which runs through the thickness thereof and puts in communication the outside with the inside of said hollow elongated body of the slider (7).

12. Disconnector as in claim 11, wherein said opening (10) is in the shape of a narrow, longitudinally elongated slot.

13. Disconnector as in claim 12, wherein a valve body (11) is provided between a rear end of said elastic means (8) and a fixed abutment integral with said sliding guide (6) provided with a gas discharge nozzle (6a).

14. Disconnector as in claim 12, wherein said slider (7) has a quadrilateral crosswise section and said openings (10) are only on sides of the slider (6) substantially parallel to the connecting path of said plate (5).

15. Disconnector as in claim 11, wherein said opening (10) is obtained in a longitudinal groove (7a) of said slider (7) with which a guiding rib (9) of said sliding guide (6) is apt to engage.

16. Disconnector as in claim 15, wherein a valve body (11) is provided between a rear end of said elastic means (8) and a fixed abutment integral with said sliding guide (6) provided with a gas discharge nozzle (6a).

17. Disconnector as in claim 15, wherein said slider (7) has a quadrilateral crosswise section and said openings (10) are only on sides of the slider (6) substantially parallel to the connecting path of said plate (5).

18. Disconnector as in claim 11, wherein a valve body (11) is provided between a rear end of said elastic means (8) and a fixed abutment integral with said sliding guide (6) provided with a gas discharge nozzle (6a).

19. Disconnector as in claim 18, wherein said slider (7) has a quadrilateral crosswise section and said openings (10) are only on sides of the slider (6) substantially parallel to the connecting path of said plate (5).

20. Disconnector as in claim 11, wherein said slider (7) has a quadrilateral crosswise section and said openings (10) are only on sides of the slider (6) substantially parallel to the connecting path of said plate (5).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will anyhow be more evident from the following detailed description of a preferred embodiment, given as a non-limiting example and illustrated in the accompanying drawings, wherein:

(2) FIG. 1A is a schematic side elevation view, with parts cut away, of a surge arrester in an armed condition and with disconnector at rest;

(3) FIG. 1B is a cross-section view taken along line B-B of FIG. 1A; and,

(4) FIG. 2 is a view similar to that of FIG. 1, of a surge arrester according to the invention, in a state in which the disconnector has reached the end of stroke and completed the opening of the circuit.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(5) In FIG. 1 there is shown a configuration of a surge arrester known per se from EP2790192, which here is considered included as reference.

(6) A surge arrester is housed in a box-shaped body or housing, referenced as module C, with dimensions such as to be housed in a single standard module and wired inside a switchboard for electrical plants. In this housing C, in a per se known manner, two opposing terminals are accommodateda first terminal 1 for the connection of the phase lead and a second terminal 2 for the connection of the protective, or neutral, leadbetween which a protection element (typically a varistor) is arranged, here schematized by a plate 3, on whose opposing surfaces the respective conducting electrodes are arranged (in the figures only an electrode 4 is illustrated, the other being on the opposite side is not visible in the drawing).

(7) The electrode 4 is electrically connected to the phase terminal 1, while the opposed electrode is connected to the ground or neutral terminal 2. The connection between the electrode 4 (FIG. 1A) and terminal 1 is realized by a conductor constituting an element of the disconnector. In particular, this conductor of the disconnector is in the form of a flexible lamina or plate 5, which is elastically preloaded and joined to the electrode 4 by a suitable low-melting solder dot at the point marked with 5d.

(8) The material used to make the low-melting solder and the exact configuration of the flexible plate is not relevant in this context and not be described here in further detail.

(9) The flexible plate 5 is preferably made of a low thickness (in the order of a few tenths of a millimeter, for example 0.2-0.3 mm) and a reduced section, with a metallic material having conductive properties equal or lower to that of copper.

(10) In case it is used a material having lower conductive properties (=conductivity rate), the thickness can be increased for example up to 0.5-1 mm. An exemplary conductivity rate can be a IACS (International Annealed Copper Standard)<60; in this case, the material is preferably made from a copper alloy with elements such as to modify its conductivity (copper IACS <90) and confer elastic properties.

(11) Such a plate is advantageously conceived to sublimate rapidlynamely passing from solid to gaseous statewhen run by short-circuit currents above a preset amount of current, of the order of a few kArms, e.g. from 3 up to 16 (indicative but not binding values).

(12) Between the abutment rigid wall of the plate 5 (FIG. 1A) and an inner housing for accommodating the varistor 3, it is defined a guide 6 where a slider 7 is sliding accommodated for the interception and compression of the arc. In particular, the slider 7 is longitudinally guided by two parallel containment walls 11a and 11b. In addition, preferably, the slider 7 is provided with a pair of longitudinal grooves 7a, on the two opposite sides, intended to engage and slide on corresponding longitudinal ribs 9 arranged within the guide 6.

(13) The slider 7 is mounted to slide longitudinally within the guide 6 while being constrained in rest conditions (represented in FIG. 1A), on one side against a bottom wall 13 of the guide 6 and, on the other side, on a part of the flexible plate 5. The slider 7 is mounted being biased toward (arrow F) the plate 5 by means of an elastic element, such as a spring 8 (visible in FIG. 2), which is mounted pre-compressed between the bottom wall 13 and the body of the slider 7.

(14) In particular, to exploit the interior space of the device, the slider 7 has a longitudinal cavity, in which a major part of the spring 8 is inserted.

(15) Preferably, the slider 7 is made as a tubular body, closed at one front end (the lower end in the drawing) and opened at the other back end.

(16) With this construction, the slider 7 is retained by the plate portion 5, which is abutting on the front end and which is opposing to the thrust of the spring 8.

(17) Instead, when the retaining action of the plate 5 is released, as a result of its sublimation resulting from the short-circuit current, the slider 7 is released and pushed by the spring 8 in the direction of the arrow F, so as to perform its electric arc extinguishing function and ending its run in abutment against an end wall.

(18) Note that the slider 7 must have a significant length, for example of the order of some tens of mm, because it must ensure an adequate area of contact with the containment and guide walls 11a and 11b as well as a high creepage distance favourable to the arc extinguish function. Due to the necessary sliding clearance between the slider 7 and the walls 11a and 11b, if the creepage distance is not sufficiently extended, there would be a high risk that the electric arc can remain switched on between the slider 7 and the guide walls 11a and 11b, circulating around the slider which would be not more effective for the arc extinction. Therefore, it is appropriate that the side walls of the slider, those perpendicular to the direction of propagation of the electric arc, are extended as much as possible.

(19) This significant length of the slider causes in part the problems arising from the development of plasma, because the pressure front of the plasma has to travel a long way before reaching the back side of the slider and re-balancing the thrust that is generated on the front side opposing to the spring 8: as a result, the timing of the action of the slider are getting longer, and there is the risk of explosion of the device due to the greater energy developed inside the casing.

(20) According to the invention, this problem is solved by providing in either or both opposite walls of the tubular body of the slider 7 one or more openings 10 (visible in FIG. 2), which put in communication the environment outside the slider with the environment within its longitudinal cavity housing the spring 8.

(21) In this way, when the plasma diffuses into the arc chamber, the pressure front reaches and enters, through the openings 10, the longitudinal cavity of the slider 7 so as to automatically and immediately determine a re-balancing of the pressures acting on the front end surface of the slider 7: this is an advantageous condition in order that the potential elastic energy of the slider spring is no longer hampered by the plasma pressure and can perform in short time its effectiveness in moving the slider in the working direction F.

(22) To avoid adverse effects on the creepage distance between the slider and guide walls, which has the effect indicated above, preferably said openings 10 are located on the upper and lower sides (i.e. those parallel to the lying plane of the annexed drawings) of the slider having a quadrilateral section. In other terms, the openings 10 are placed on the sides parallel to the extending path of the plate, which is the path on which the electric arc is propagated naturally.

(23) Still more preferably, the openings 10 are in the form of narrow slits located within the opposed grooves 7a, as clearly shown in FIG. 2.

(24) In this way, the plasma pressure front is directly channelled by the grooves 7a, enters within the cavity of the slider 7 through the openings 10 and, on one hand, it balances the pressure on the front surface of the slider 7 (allowing an effective action of the spring 8) and, on the other, by raising the pressure inside the slider 7, it creates an reaction effect with a direction according to the arrow F, being able only to escape towards the rear side, which further assists the desired propulsion of the slider 7.

(25) In fact, the hot gases generated by the electric arc conveyed through the feed channels into the inner chamber of the slider, tend to expand naturally according to a phenomenon similar to the expansion of the gases inside the cylinder of an internal combustion engine.

(26) The thrust generated by the expansion of the gases is suitably exploited to speed up the slider by means of a construction that suitably guides the escape of the gases. According to a further preferred feature of the invention, it is in fact provided a valve body 11, similar to a check valve, placed on the back of the slider and forming a support for the rear end of the spring 8. The valve 11 is maintained by the spring 8 in abutment on a nozzle 6a for venting the exhaust gases to the outside, formed on an abutment wall of the housing C, preventing the escape of the gases from the cavity of the slider 7 before they have completed their rebalancing and thrusting function on the slider itself.

(27) Preferably, the valve 11 is in the form of a poppet body, whose shank is inserted between the coils of the spring 8.

(28) The system thus conceived is therefore able to adequately convey the plasma under pressure and transform part of the problem (i.e. the huge plasma pressure energy) in the solution of the same.

(29) Compared to the spring 8, which is able to exert a force not variable with respect to the pressure, this adjuvant effect of the plasmaas long as it is within the limits of the mechanical strength of the whole systemis advantageously a function of the square of the current: the higher the short-circuit current and the resulting arc pressure, the greater the thrust exerted by hot gases on the slider in the direction that allows the arc extinction.

(30) In conclusion, the internal disconnection system on the arrester allows realizing the extinction of the short-circuit current through the combination of the following three principles: plasma thermodynamics in the inner chamber of the slider: the plasma entering the inner cavity or chamber of the slider allows the rebalancing of the pressures by creating the conditions for a timely intervention of the slider itself; furthermore, the hot gas expansion provides an additional thrust to that exerted by the preload spring; dynamics due to the shape of the slider: the slider movement stretches and compresses the electric arc, forcing it into a constrained path; electric arc electrodynamics: the elongation and the compression of the electric arc raise its electrical resistance and consequently its voltage up to match the voltage of the driving energy (i.e., mains voltage) resulting in a rapid decrease of the short-circuit current until its extinction.

(31) As is well understood from the above description, the configuration of the invention, despite its simplicity, is extremely effective for the safe shut-down of the arc by the disconnector apparatus, even in the presence of high short-circuit currents, which in turn develop an important amount of conductive plasma resulting from the sublimation of the conductive plate.

(32) It is understood, however, that the invention is not to be considered as limited by the particular arrangement illustrated above, which represents only an exemplary implementation of the same, but different variants are possible either inside or outside of the arrester, all within the reach of a person skilled in the art, without departing from the scope of the invention itself, as defined by the following claims.

(33) For example, the device above described is sized to be coordinated with any overcurrent limiters which should be required in the case the short-circuit current (Isc) of the plant is greater than the self-extinction capacity of the mains current (Ifi) of the disconnection device of the SPD.

(34) In addition, the disconnection device (disconnector) as described above can also be implemented in a special enclosure (housing) and used as an independent short-circuit switching device, regardless of the presence of a surge arrester.