Field of the invention

The present invention relates to an arcing chamber for use in a safety switch, comprising a cavity in a housing where an arc can be produced when contacts of the safety switch are broken, a blow-out opening that is in communication with the cavity for discharging the increase in gas and/or pressure caused by the arc, and an extinguishing element for splitting the arc into sub-arcs, wherein the extinguishing element is positioned between the contacts and the blow-out opening in the cavity.

State of the art

The object of arcing chambers is to suppress as much as possible the effects, i.e. the heat, the ionising effect of the hot gases generated and the pressure wave created by these gases, of an electric arc caused when the contacts of a safety switch are opened and thus to contribute to rapid extinguishing of the electric arc.

Such arcing chambers are described, for example, in German Patent DE 10038642, which describes an arcing chamber for a safety switch. The arcing chamber comprises an extinguishing element consisting of a number of conductive plates positioned parallel to one another. An arc between contacts generated when the safety switch is switched off is split by the extinguishing element into separate sub-arcs which extinguish faster and more easily. A particular feature of this known arcing chamber is the attachment of the lid to the arcing chamber, whereby the arcing chamber is suitable for being mounted as a separate component on a safety switch or is incorporated in a separate shaft in the safety switch. The disadvantage of the known provision is that it is less suitable for use in small so-called MCBs (miniature circuit breakers). A further disadvantage is that this is only suitable for one particular design; in other words, it works in optimum fashion for a particular rated current and break power of one type of switch. A different type of arcing chamber will therefore also be required for a different rated current and break power.

Summary of the invention

The present invention seeks to provide an arcing chamber for a safety switch which is easily (for example, when fitting the safety switch) adaptable to the type of safety switch and which is particularly suitable for use in safety switches of very small dimensions.

According to the invention, an arcing chamber of the type defined in the preamble is provided wherein the arcing chamber is made up of an extinguishing element installed in the cavity and constructed as an independent unit, side walls of the housing and a closure plate which, without separate fixing elements, can be fixed to the extinguishing element, wherein the closure plate is provided with a predefined pattern of openings, and the extinguishing element and the closure plate are integrated in the housing such that they can be removed. Ih a preferred embodiment the closure plate is mounted on the side of the extinguishing element facing the blow-out opening of the arcing chamber. However, the closure plate can also be positioned on the side of the extinguishing element that is upstream in the discharge direction for gases generated in the event of an arc. hi contrast to the arcing chamber known from the abovementioned German patent, the closure plate can be adapted separately by selecting a suitable pattern of openings, as a result of which the blow-out characteristic of the arcing chamber, and thus the characteristic manner in which an arc is extinguished, can be adjusted by means of the properties of the closure plate. hi one embodiment the extinguishing element consists of a multiplicity of conductive plates positioned parallel to one another and the openings in the closure plate are arranged in locations that correspond to the gaps between the plates. This type of extinguishing element is often used in the state of the art. As a result of the outlined measures relating to the closure plate, the unit is simple to install in a switch without the need for special alignment of the extinguishing element and closure plate.

Ih a further embodiment the plates of the extinguishing element are provided with a potential booster layer. This enables a small number of plates to be sufficient to extinguish an arc with a particular characteristic (voltage, energy). In turn, this consequently takes up even less space, as a result of which this arcing chamber is easier to use in miniature circuit breakers. hi yet another embodiment the present arcing chamber comprises two conductive elements which are electrically at a potential that corresponds to the potential of the respective contacts for guiding the arc towards the extinguishing element. Consequently, the arc in the arcing chamber is routed automatically, as it were, to the extinguishing element

In a further embodiment the safety switch has a neutral side and a phase side that are mechanically and electrically separated from each other by a support element. The arcing chamber is on the phase side of the support element, and the support element is provided at

the location of the cavity with an opening that enables the increase in gas and/or pressure caused by the arc to be discharged towards the neutral side of the safety switch. This enables the inside of the switch to be used for discharge, possibly via further discharge openings in the switch housing. In yet another embodiment the closure plate has a flap which acts as a valve to close off an opening to the interior of the housing, as a result of which the internal cavity can be used as an expansion vessel. This embodiment can also be used if the switch is a single- pole switch. Because the flap which is acting as a valve is positioned downstream of the extinguishing element, the flow characteristic of the combination of arcing chamber and extinguishing element is not impaired.

Brief description of the drawings

The present invention will now be discussed in greater detail on the basis of an illustrative embodiment, with reference to the appended drawings, in which Fig. 1 shows a detailed view of an arcing chamber according to one embodiment of the present invention, used in a switch; and

Fig.2 shows a front view of a closure plate as used in the arcing chamber according to Fig. 1.

Detailed description of illustrative embodiments

Fig. 1 shows an enlarged detail view of the arcing chamber in one example of a switch in which the present arcing chamber can be used.

The arcing chamber comprises a cavity 15, a specially shaped connector 61 located in the cavity 15, and an extinguishing element 33. The extinguishing element 33 comprises a number of conductive plates 66 with a special shape which are positioned parallel to one another and are held together by means of insulating side plates and thus form a mechanical entity. However, the extinguishing element 33 is still open on all sides. The housing 31 is shaped such that, after fitting of the extinguishing element 33, the arcing chamber is closed on both sides by the walls of the housing 31. Furthermore, the extinguishing element 33 is closed at the rear by means of a removable closure plate 34 which is shaped such that it, in conjunction with the extinguishing element 33 and the housing, forms the arcing chamber, without any further fastenings. Since the arcing chamber is open at the front, an arc will form between the moving phase contact 7 and the

fixed phase contact 35 in the first instance in the event of the circuit being broken. A conductor 45, which is electrically connected to the moving phase contact 7, ensures that the arc jumps and is then between the conductor 45 and connector 61. As a consequence of the increase in hot gases and pressure in the cavity 15 caused by the electric arc, the arc is forced into the arcing chamber. From the connector 61 the arc moves to the extinguishing element 33 where, moving to the right in the drawing, it will split into a number of sub-arcs between the plates 66 of the extinguishing element 33, after which the sub-arcs will extinguish.

Because the extinguishing element 33 is provided at the rear with the closure plate 34 which is in turn provided with one or more escape openings 67, as shown in the front view of the closure plate 34 in Fig.2, the hot gases will be able to escape from the arcing chamber. The closure plate 34 is advantageously provided with corrugations 68 in which the openings 67 are located. The openings 67 of the closure plate 34 can then easily be aligned with the openings between the plates 66 of the extinguishing element 33. The housing 31 incorporates a blow-out opening 44 which permits the hot gases flowing from the cavity 15 to be discharged from the housing 31 via the extinguishing element 33. Depending on the rated current of the safety switch 50, the electric arc will produce a larger or smaller volume of hot gases with a corresponding pressure, and a larger or smaller volume of gases will therefore have to be discharged to guarantee optimum operation. Because the closure plate 34 does not form a fixed element of the arcing chamber or the housing 31, it can be adapted to different rated currents and is easily fitted in the appropriate place in the housing 31, as a result of which the switch 50 is easy to assemble for different types of rated current.

The flow properties of the hot gases generated by the arc are influenced by the number of openings 67 in the closure plate 34, the shape of the openings 67, and the location of the openings 67. If the safety switch 50 is fitted with a short-circuit safety device with a higher rated current (for example, 32 A), any arc occurring between the contacts 7, 35 will have a higher energy than in the case of a lower rated current (for example, 6 A). To ensure that the arc moves sufficiently quickly through the arcing chamber towards the extinguishing element 33 in that case, the gas flow caused by the arc must be discharged more quickly. This can be achieved, for example, by increasing the number of openings 67 or the size of the openings 67. In addition to the closure plate 34, it is alternatively possible to influence the arc movement by means of a small closure plate

that is fitted at the place where the arc enters the arcing chamber from the cavity 15. This method permits the arc movement to be further optimised.

In a further embodiment, the small closure plate 68 is provided on one side with a flap 69 (see Figs 1 and 2) which is designed to act like a valve into an internal cavity of the housing 3 i of the switch 50. In the event of a sudden, very marked increase in pressure in the section between the cavity 15 and the blow-out opening 44, this enables the internal cavity in the switch 50 to be used as a kind of expansion vessel via the flap 69. This will improve the operation of the arcing chamber, particularly in the case of a switch 50 of small dimensions, in which the size of the arcing chamber with its related elements 33, 34, 44 cannot be optimally sized.

In the illustrative embodiment shown in Fig. 1 the arcing chamber is further provided with an opening 70 in the support element 32, as a result of which a third option for optimising the arc movement and extinguishing is created in that, by this means, any surplus gases generated by the arc can also be discharged via the neutral side of the switch 50. The opening 70 can be adapted to influence the flow in the arcing chamber such that the arc is rapidly extinguished.

The characteristics of the arcing chamber, comprising the assembly of the cavity 15, extinguishing element 33, side walls of the housing 31 and closure plate 34, are very easy to adapt by changing the pattern of escape openings 67 in the closure plate 34. Thus, for example, it is possible to provide a larger number of escape openings 67 or a number of larger escape openings 67 on one side of the closure plate 34, as a result of which more gas is discharged to that side. Depending on the geometry of the cavity 15 and the arcing chamber, therefore, this provides a simple means of extinguishing the arc in an optimum manner. hi a further advantageous embodiment of the extinguishing element 33, the plates 66 are provided with a (potential) booster layer on their surface. Fewer plates are consequently required in the extinguishing element 33, enabling the latter to be made smaller. A booster layer on the plates 66 can be achieved, for example, by treating the surface structure of the (metal) plates 66, for example by rolling. Alternatively, a separate booster layer can be applied to the plates 66, for example using plastics known to those skilled in the art.