Electric switchgear panel with improved arc protection assembly

A switchgear panel comprises an enclosure having an internal volume suitable to accommodate corresponding electrical or electronic equipment, and an arc protection assembly which is operatively associated to a wall of the enclosure. The arc assembly comprises at least a first barrier element having a first surface which is provided with one or more first through openings defining each a respective same first venting area, and a second barrier element which comprises a second surface provided with one or more second through openings defining each a respective same second venting area. The first venting area of each first through opening is different from the second venting area of the second through openings.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(a)-(d) to European Patent Application Serial Number 10163878.1, filed on May 26, 2010, the entire contents of which are hereby incorporated by reference.

FIELD OF INVENTION

The present invention relates to an electric switchgear panel with an improved arc protection assembly.

BACKGROUND

As is well known in electrical energy distribution systems, switchgear panels are electrical components used as node points, while cables and overhead lines represent the conjunction of the various nodes.

From a structural point of view, known switchgear panels, which can be also indicated with the equivalent terms of electric switchboards, or simply switchgear or electric panels, or similar definitions, usually comprise a metallic enclosure that is internally divided into several compartments or cells housing various apparatuses and equipment. For example, one compartment houses a switching unit, such as a circuit breaker; a second compartment houses main cables, such as bus-bars, feeding power from an electrical source; a further compartment houses a system of cables suitable to be connected to a load, for example an electrical motor. Depending on the application, switchgear panels may comprise other components that include but are not limited to current transformers, fuses, and voltage transformers.

During the working life of a switchgear panel, electrical faults or malfunctions may occur, such as short circuits, current overloads, and in particular, arcing events. Arcing events, e.g. arcing faults or flashes, occur when electric current arcs strike between two conductors inside the switchgear cabinet, e.g. between phase conductors, phase and neutral conductors, between the contacts of the circuit breaker used, between a conductor and ground, or another situation. When arcing faults occur, in particular in medium- to high-voltage power applications wherein the levels of energy involved are quite significant, the ionized gas associated with them may be released at significant pressures and temperatures sufficient to severely damage or destroy the switchgear panel, and/or the devices and equipment housed inside. An arcing fault may also be dangerous for operating personnel or equipment outside the enclosure. In particular, the materials involved in or exposed to the arc produce hot decomposition products, both gaseous and particulate either plastic and/or metallic, which may be discharged to the outside of the enclosure together with or in addition to hot gases and flames.

Due to the aforementioned problems, safety standards and related tests have been introduced. For example, one typical standard test utilizes highly flammable indicators, such as pieces of cotton or equivalent material, which are placed outside the switchgear enclosure around the perimeter of the enclosure at a certain distance from some or all of the lateral walls of the enclosure. During the test and more particularly, when an internal arc is caused to strike, these flammable indicators must not ignite.

Hence, such standards have imposed onto switchgear manufacturers the adoption of protection systems suitable to prevent and/or mitigate the effect of possible electrical arcs. In particular, many known solutions are focused on early detection of an occurring electric arc with a consequent fast intervention devoted to prevent or mitigate the undesired effects of an electric arc at an early stage.

For example, a first solution foresees the evaluation of current perturbations in a conductor which are indicative of an arcing event; however, this solution may require onerous processing demands resulting in an undesirably long reaction time for identifying an arcing event. Another solution uses pressure sensors to monitor the increase in pressure indicative of an arcing event; also this solution may require significant time before pressure increases to detectable levels, resulting in long reaction times before mitigating an arcing event.

One of the most used solutions for detecting arcing events involves the use of optical detectors, such as optical fibers, to detect visible light and thereby to sense the arc flash associated with an arcing event. However, this solution may result in erroneous detections as the light sensors may detect light from sources independent from electric arcs. This may further result in unwarranted tripping of protection units which would put out of service the whole switchgear panel or parts thereof.

In some cases, a combination of different types of arc protection systems has been used. For example, undesired interventions have been partially limited by combining the detection of light possibly linked to an occurring electric arc with monitoring of the current levels flowing into the part of the electric system being monitored.

Other solutions are instead focused on limiting the resulting effects of an electric arc. For example, arc-resistant switchgear cabinets are widely used and able to mechanically withstand the pressure waves and temperatures of the hot gases associated with an arcing fault; in some other cases there are provided specific parts of the enclosure which may blow up due to an electric arc occurring inside the enclosure.

In addition or in alternative, there are provided also suitable paths for channeling and venting the hot gases and flames generated by an arcing fault out from the internal compartments towards a desired area. For example, there are provided flaps or ducts which lead the hot gases, flames and particulate to the outside environment through the ceiling of the enclosure or in some cases even underground, i.e. toward zones far away from the possible presence of operating personnel.

Although known solutions perform satisfactorily, there is still room for further improvements in arc protection for switchgear. For example, the ceiling and wall of the room wherein the switchgear panel is located may deflect hot gasses, flames and particles, down onto personnel working near the panel thus being still potentially dangerous.

SUMMARY

The switchgear panel of the present invention comprises an enclosure having a plurality of walls which delimit an internal volume suitable to accommodate corresponding electrical or electronic equipment, and at least a first wall of the plurality of walls being provided with one or more openings. The switchgear panel according to the present invention comprises, in particular, an arc protection assembly which is operatively associated to at least the first wall and comprises at least a first barrier element having a first surface which is provided with one or more first through openings defining each a first venting area. The switchgear panel comprises a second barrier element which is operatively associated to the first barrier element comprises a second surface provided with one or more second through openings defining each a second venting area. The first venting area of each first through opening of the one or more first through openings is different from the second venting area of each second through opening of the one or more second through openings.

DETAILED DESCRIPTION

FIG. 1shows an example of an electric switchgear panel according to the invention, indicated by the overall numeral reference100which comprises, according to known solutions, an enclosure having a plurality of walls, namely a rear wall1, a front wall2, two lateral walls3,6, a top wall4and a bottom wall5, which all together define an internal volume suitable to accommodate various electrical or electronic equipment and/or devices including, but not limited to circuit breakers, bus-bars, cables, and electronic relays.

At least one of the walls of the enclosure, in the embodiment illustrated, preferably the rear wall1(hereinafter referred to as the “first wall”), is provided with one or more openings7, e.g. two as illustrated schematically inFIG. 1with dotted lines. The one or more opening(s)7are suitable to allow venting of the hot gases, flames, particulate, and the like, to the outside of the enclosure, all of which may be generated when an electric arc strikes inside the panel100.

Advantageously, the switchgear panel100according to the present invention comprises an arc protection assembly which is globally indicated by the reference number10and is operatively associated to the enclosure of the panel100. In the embodiment illustrated, the arc protection assembly10is positioned outside the enclosure and is operatively associated to at least the first wall1. As will result more clearly from the following description, the arc protection assembly10is devised to mitigate the effects resulting from any electric arc striking inside the enclosure, e.g. hot gases, flames, particulates.

The arc protection assembly10preferably comprises at least a first barrier element11and a second barrier element21, some exemplary embodiments of which are illustrated inFIGS. 2 and 3, respectively. As illustrated inFIG. 2, the first barrier element11comprises a first surface15which is provided with one or more first through openings12.

For the sake of simplicity and better illustration, inFIG. 2a portion (A) of the first surface15has been magnified. The magnified portion (A) extends over at least a predominant (i.e. more than about 50%) part of, if not almost all, the entire first surface15.

The perimeter of the rims of each first opening12delimit a through area13, i.e. a venting area13through which the hot gases, flames, and particulates, coming from the inside of the enclosure can pass through. The venting areas13defined by each of the first openings12are about equal to each other in area. Preferably, the one or more first through openings12, each of which delimit an equal venting area13, are randomly positioned on the first surface15.

In the embodiment illustrated, the first barrier element11is constituted by a metallic plate which, seen in section from a top or bottom plan view, is U-shaped. The central side of the U-shaped plate constitutes the first surface15and is suitably perforated so as to have the one or more, preferably a plurality of, first though openings12.

Preferably, as illustrated inFIG. 2, the first through openings12are constituted by circular through holes12, with the front area of each circle forming the respective venting area13(an exemplary one of which is marked with points in the magnified portion (A)). Alternatively, there may be first through openings of any shape that is compatible with the scope of the present invention, including but not limited to squared through openings or elliptical through openings, each delimiting the same venting area13, respectively. In addition, one or more first through openings12may also be provided on the two lateral sides16,17of the U-shaped plate11.

Further, in addition to the one or more first through openings12defining each a respective venting area13, with all venting areas13being equal to each other, the barrier element11can be provided with other openings having rim perimeters that may delimit a different through area. For example, some openings18,19may be used for receiving fixing screws, venting or both purposes at the same time.

The number of first through openings12defining each a respective same venting area13provided on the first surface15is preferably predominant, i.e. at least more than about half of the holes provided on the first surface15are constituted by the indicated first through openings12.

The second barrier element21is operatively associated to the first barrier element11and comprises, as illustrated inFIG. 3, a second surface25which is provided with one or more second through openings22. For the sake of simplicity and better illustration, a portion (B) of the second surface25has been magnified inFIG. 3. The magnified portion (B) extends over at least a predominant (i.e. more than about 50%) part of, if not almost all, the entire second surface25.

The perimeter of the rims of each second opening22delimit a through area23, i.e. a venting area23through which can pass the hot gases, flames, particulates, coming from the inside of the enclosure and having already passed the opening(s)7and the first openings12. The venting areas23defined by each of the second openings22are equal to each other. Preferably, also the one or more second through openings22which each delimit an equal venting area23are randomly positioned on the second surface25.

In the embodiment illustrated, the second barrier element21is constituted by a metallic plate which, seen in section from a top or bottom plan view, is substantially U-shaped. The central side of the U-shaped plate21comprises the second surface25and is suitably perforated so as to have the one or more, preferably a plurality of, second though openings22.

In the same embodiment and as depicted inFIG. 3, the second through openings22are constituted by circular through holes22, with the front area of each circle forming the respective venting area23(an exemplary one of which is marked with points in the magnified portion (B)).

Alternatively, the second barrier element21may be provided with through openings of another shape as indicated above for the first barrier element21, e.g. squared, elliptical, or another shape, each delimiting a respective equal area23. In addition, the one or more second through openings22can be also provided on the two lateral sides26,27of the U-shaped plate21. In the exemplary embodiment ofFIG. 3, the two sides26,27present an outwardly folded rim28suitable to allow fixing to corresponding walls of the enclosure, as will be described in detail hereinafter.

Also the second barrier element21may be provided with openings29additional to the one or more second through openings22defining all the same respective venting areas23, and the perimeter of the rims may delimit a different through area. For example, some openings29may be used for receiving fixing screws, venting, or both purposes at the same time.

The number of second through openings22defining each a respective same venting area23provided on the second surface25is preferably predominant, i.e. at least more than about half of the second surface25may be comprised of the indicated second through openings22.

Advantageously, in the switchgear panel100according to the invention, the first venting area13delimited by the rims of each first through opening12of the set of one or more first through openings12is different from the second venting area23delimited by the rims of each second through opening22of the set of one or more second through openings22. According to a particularly preferred embodiment, the first venting area13defined by each first through opening12of the set of one or more first through openings12is larger than the second venting area23of each second through opening22of the set of one or more second through openings22. In particular, the second venting area23of each second through opening22of the set of one or more second through openings22is between about 5% to about 50% of the size of the first venting area13defined by each first through opening12of the set of one or more first through openings12.

For instance, in the example illustrated, each circular first opening12has a diameter D1of 6 mm while each circular second opening22has a diameter D2of 2 mm. Therefore, each first venting area13is equal to 28.26 mm2, while each second venting area23is equal to 3.14 mm2.

In order to improve safety on all lateral walls1,2,3,6of the enclosure, the arc protection assembly10may be provided with a third barrier element31which is operatively associated to at least one of the first and second barrier elements11,12. Preferably, as illustrated inFIG. 4, the third barrier element31comprises a third surface35which is provided with one or more third through openings32. For the sake of simplicity and better illustration, inFIG. 4a portion (C) of the third surface35has been magnified. The magnified portion (C) extends over at least a predominant (i.e. more than 50%) part of, if not almost all, the entire third surface35.

The perimeter of the rims of each third opening32delimit a through area33, i.e. a venting area33through which the hot gases, flames, and particulates coming from the inside of the enclosure can pass through. The various venting areas33defined by each of the one or more third openings32are about equal to each other. Preferably, the one or more third through openings32which delimit about equal venting areas33, respectively, are randomly positioned on the third surface35.

In the embodiment illustrated, the third barrier element31is constituted by a metallic plate which has a central side35suitably perforated so as to have the one or more, preferably a plurality of, third though openings32, and a plurality of sides36,37.

Preferably, as illustrated inFIG. 4, the third through openings32are constituted by circular through holes32, with the front area of each circle forming the respective venting area33(an exemplary one of which is marked with points in the magnified portion (C)).

Alternatively, the third through openings32may be provided in another shape that is compatible with the scope of the present invention, e.g. there can be squared through openings, elliptical through openings, or other compatible through openings delimiting the same venting area33, respectively.

Further, in addition to the one or more third through openings32each defining about the same venting area33, respectively, the barrier element31may be provided with other openings whose rim perimeters may delimit a different through area. For example, some openings38,39may be used for receiving fixing screws, venting, or both purposes at the same time.

The number of third through openings32defining each a respective same venting area33provided on the third surface35is preferably predominant, i.e. at least more than about half of the third surface25may be comprised of the one or more third through openings22.

Preferably, the third venting area33delimited by the rims of each third through opening32of the one or more third through openings32is different from at least one of the first venting area13of each first through opening12of the one or more first through openings12and the second venting area23defined by each second through opening22of the one or more second through openings22.

According to a particularly preferred embodiment, the first venting area13defined by each first through opening12of the set of one or more first through openings12is larger than the third venting area33delimited by the rims of each third through opening32of the set of one or more third through openings32. More preferably, the third venting area33of each third through opening32of the one or more third through openings32is even smaller than the second venting area23defined by each second through opening22of the one or more second through openings22.

In particular, the third venting area33of each third through opening32of the set of one or more third through openings22should be between about 3% to about 30% of the first venting area13defined by each first through opening12of the set of one or more first through openings12. For instance, in the example illustrated, each circular third opening32has a diameter D3of 1.5 mm. Therefore, each first venting area33is equal to about 1.76 mm2.

Alternatively, the third barrier element31may be comprised of a plate that is not perforated (apart from possible holes required for connecting the third barrier element31to other components of the arc protection assembly10) in order to define one or more venting areas.

Finally, the arc protection assembly10may preferably further comprise a lower cover40and an upper cover50, exemplary embodiments of which are illustrated inFIGS. 5 and 6, respectively.

As shown inFIGS. 7-8, the first barrier element11is positioned with the first surface15facing the first wall1provided with the opening(s)7. Preferably, the central side which forms the first surface15of the first barrier element11is fixed to the first wall1with the lateral sides16,17of the first barrier element11protruding from the central side15away from the first wall1.

In the exemplary embodiment illustrated, the lower cover50is positioned close to the bottom end of the first barrier element11and is fixed to the rear wall1. The second barrier element21is positioned with the second surface25facing the first surface15so that the one or more second through openings22are at least partially off-set with respect to the one or more first through openings12. Preferably, the second barrier21is first connected to the upper cover50and is then positioned so as to surround the first barrier element11and with the central side of the second barrier element21forming the second surface25which faces the first surface15and with the lateral sides26,27of the second barrier element21protruding towards and being connected to the rear wall1of the enclosure, by means of the folded rims28.

When used, the third barrier element31is positioned with the third surface35facing the second surface25from the opposite side with respect to the first surface15and in such a way that the one or more third through openings32are at least partially off-set with respect to the one or more second through openings22. Preferably, the third barrier element31is operatively connected, e.g., screwed, to the other part of the assembly10from the opposite side with respect to the first barrier element11with reference to the second surface25, with the sides36,37substantially enclosing the corresponding parts of the barrier elements11,21and the upper cover50as well.

In this way the arc protection assembly10defines an overall, substantially confined, interior space which receives the byproducts of an electric arc struck in the enclosure.

The upper cover50and the lower cover40can be also used when the third barrier element31is not used, and therefore they may be likewise operatively connected to the first and second barrier elements11,21at the top and bottom ends thereof, respectively.

The switchgear panel100according to the present invention offers an improved arc protection system with advantages over the known prior art in a simple and effective manner. In particular, the assembly10defines, as a whole, a confined environment inside which the resulting effects of an electric arc are conveyed. The parts of each barrier element that are not perforated stop some of the arc-generated products, while the sets of first, second, and when used, third through openings, allow the passage of some other arc-generated products. By using different venting areas, and particularly through venting areas of decreasing size towards the direction of movement of the arc-generated products from the interior of the enclosure towards the open environment, the assembly10behaves like a suppressor. In acting as a suppressor, the assembly10extinguishes the hot gases and flames inside the assembly10, or outside the assembly10at a short distance compatible with relevant safety standard requirements and tests.

The electric switchgear panel100thus conceived may undergo numerous modifications and come in several variants, all falling within the scope of the inventive concept as defined by the appended claims. For example, the various barrier elements may be differently shaped, or they may be differently positioned with respect to each other and to the associated enclosure. The barrier elements may also be connected in a different configuration. Additionally, the assembly10can be connected to another wall of the enclosure, for instance the roof wall or any other wall of the enclosure. The component materials and dimensions of the switchgear may be of any type, according to needs and the state of the art and provided they are compatible with the scope of the invention as defined in the appended claims.