Description

The invention is related to a switchgear, comprising a frame and at least a bus bar to transmit electrical current.

A potential risk of failure exists for a bare bus bar system during internal arc fault tests, especially at 400 V and 100 kA and at 690 V and 65 kA.

Internal arc faults in switchgears are usually avoided either by insulations or man- aged by either providing dedicated arc-escape routes, e.g. pressure relief flaps.

Additionally or as an alternative the switchgear can be made mechanically and ther- mally robust to withstand an arc.

The insulating components are usually rigid or solid. This makes it difficult, to install them in tight spaces, which are usually present in compact switchgears.

The currently existing assemblies or procedures make use of solid parts and/or moulded insulating parts.

They provoke difficulties as follows: mounting of the parts in the available space, challenges to use the parts or components at the required area or surface, which needs to be protected, expensive requirements for molds, no readily available off- the-shelf components etc.

Further, one of the existing methods of construction is to completely insulate bus bar systems, which are classified as arc-ignition protected zones. In other current as- semblies active arc fault protections are used. By using current constructions, there is a high probability of the arc finding metal parts of the frame or enclosure, hence burning and causing damage.

The internal arc usually runs along a main bus bar in the direction of energy flow and usually burns at the ends of the bus bar. The insulating angle, which covers the final few millimeters of the bus bar is providing a semi-enclosed area for the arc to burn. The partitions within the insulating angle are helping in arc-elongation.

However, with higher rating of the arc faults, namely higher kA ratings, the arc has a tendency to jump from the dedicated arc-burning region to the neighboring frames, enclosures and to burn causing holes, which could endanger the switchgear safety.

Additionally, in spite of the insulating angle, there could be radiative heat effects on the enclosures and on the adjacent regions.

The object of the invention therefore is to control and localize arc damages and to create a switchgear, which provides arc-fault containment.

The object of the invention is achieved by means of the features of claim 1.

According to this claim in the switchgear an arc attractor and/ or at least a flexible insulation are arranged.

According to the invention it has been found, that present constructions or arrange- ments of swichgears do not use any dedicated arc attraction mechanism, neither is there any flexible protection mechanism for the metal and cladding.

According to the invention it further has been found that an arc attractor, preferably a sacrificial electrode, along with flexible insulation material either individually or in con- junction with solid insulation materials can be utilized to increase the arc quenching as well as the thermal withstand capability of the switchgear, thus making it arc- resistant. According to the invention a dedicated arc attractor provides a dedicated arc-burning location. The protection can be increased by means of a flexible insulation.

The main concept of the invention is to provide a dedicated and safe arc-burning zone together with an arc attracting mechanism, and a flexible protection mecha- nism. A switchgear, in which this concept is realized, is safer than those of the state of the art, because a damage due to an arc is contained and localized. The arc is guided into dedicated locations for localized burning. The arc attractor also leads to a continuous arc-fault current, which results in a more consistent current value and in cases of presence of an up stream protection, helps in current detection and tripping.

Advantageously the arc attractor is an electrode and/ or is a sacrificial electrode. A sacrificial electrode can be made of cost-efficient materials. The switchgear has po- tential to be cheaper than switchgears of the state of the art.

Further, advantageously, the arc attractor is embodied as a sacrificial metallic struc- ture and/ or is a sacrificial metal structure. Such a structure may be positioned in such a way that it provides a safe region for the burning of the arc. The damage caused by the arc is minimized. The safety of the switchgear is increased.

Advantageously the arc attractor is in the form of metal strips or metal bars. Such an arc attractor can be made of metal strips or metal bars and therefore can easily be manufactured.

Further advantageously, the flexible insulation is, preferably reversibly, attachable or attached to a frame, enclosure or cladding of the switchgear. Advantageously the invention deals with providing a flexible protection for frames, enclosures and clad- ding of the switchgear, possibly without the already existing solid insulating angles. The normally exposed frames and enclosures are most vulnerable parts, which can be damaged due to the arc, thus compromising on the switchgear and operator safe- ty-

Advantageously, the flexible insulation is a protective layer. Materials for the flexible insulation may have suitable properties to be applied into existing assemblies to pro- tect the most vulnerable parts of the assembly, destruction of which could compro- mise on safety aspects of the switchgear. Metallic frames or regions of them can be protected by the flexible insulation.

Further, advantageously the flexible insulation is not a solid or rigid insulating materi- al. Preferably, the flexible insulation is an elastomer or comprises an elastomer. With the flexible insulation, sufficient protection is provided for the materials of the enclo- sure or the frame. The dedicated flexible insulating material with required properties is convenient to be installed in tight spaces, in which typically solid insulating materi- als cannot be used. The flexibility also helps to realize an effective installation as a first line of protection on the frames and enclosures without the already existing solid insulating angles.

Preferably, the bus bars are not completely insulated and/ or solid insulating angles are not provided, but flexible insulations are arranged.

A passive protection mechanism for arc fault protection in switchgears is presented by this invention. The passive protection mechanism uses a combination of flexible insulation and an attraction electrode for arc fault protection in switchgears.

This invention is used most preferably in industrial installations such as switchgears, low or medium voltage switchboards.

In the drawings:

Fig. 1 schematically shows on the left side a side view of a bus bar assembly in a switchgear, for a particular arrangement, and on the right side a back view of the bus bar assembly, for a particular arrangement, wherein the curved lines show the arc-burning on copper and the dashed arrows show the potential burning regions of the arc on neighboring frame and enclo- sure material,

Fig. 2 shows a three dimensional front view of a busbar assembly and Fig. 3 shows a three dimensional rear view of the assembly of Fig. 2.

Fig. 1 on the left side schematically illustrates an assembly of a switchgear, in par- ticular a low voltage or medium voltage switchgear, comprising a frame 1 , an insulat- ing angle 2, which may be solid or solid and flexible, and several bus bars 3 to transmit electrical current. The bus bars 3 are made of copper, aluminum or made of another metal.

The insulating angle 2 has the potential to be removed and to be replaced by other kinds of insulating materials. The bus bars 3 are aligned above each other and are oriented in parallel way.

The frame 1 comprises at least one unprotected surface 1 a or area, where flexible insulations 6 may be arranged, to protect it. On the right side of Fig. 1 there is shown an internal electric arc 4 occurring in a possible region 1 b of the frame 1.

The switchgear comprises at least a frame 1 and at least a bus bar 3 to transmit elec- trical current, wherein an arc attractor and at least a flexible insulation 6 are ar- ranged.

The arc attractor is an electrode 5, namely a sacrificial electrode. In the example shown, six flexible insulations 6 are arranged to protect a previous unprotected sur- face 1 a of the frame 1 from the arc 4.

In the region 1 b an attraction to the electrode 5 occurs. This causes heat effects to an enclosure or the frame 1. Flexible insulations 6 therefore are used at the frame 1 or enclosure to protect it.

The electrode 5 or the arc attractor is also arranged. This electrode 5 is a protective cathode. The dashed arrows on the right side of Fig. 1 show the possible areas of arc spreading. An arc spreading in all dimensions may be possible.

In the illustrated embodiment according to Fig. 1 , the additional electrode 5 is in the form of metal strips or metal bars or of a sort of a metallic structure, like a metal fin structure. This electrode 5 is provided as means of an attraction for the arc 4.

Fig. 1 shows the electrode 5 placed within a dedicated insulating angle 2. The posi- tion of the electrode 5 itself may be made flexible and can be changed into another position than the one illustrated in Fig. 1.

The selection of the position of the electrode 5 is made based on the potential of the arc-voltage and the smallest distance required for the arc 4 to make a suitable bridge to the grounded electrode 5.

Based on an analysis of material properties of the flexible insulation material, it is possible to replace the insulating angle 2 by a flexible insulating material of similar properties, which additionally has advantages of encompassing a bigger area and easier installation.

The arc attracting mechanism by virtue of its position and structure is providing a safe region 1 b for the burning of the arc. With a flexible insulation 6, a protective layer, preferably optionally, is provided for the frame 1 and enclosure materials, potentially without the solid insulating angles 2.

The flexibility of the flexible insulation 6 also helps to effectively install it either as a first line of protection on the frame 1 or enclosure or as an additional line potentially without the requirement of any solid insulating angle 2.

In Fig. 1 , the flexible insulation 6 is attached to the frame 1 of the switchgear. The flexible insulation 6 is a protective layer and is not a solid or rigid insulating material.

The flexible insulation 6 is an elastomer. The longitudinal ends of the bus bars 3 are nearby the flexible insulations 6.

Fig. 2 and 3 show a perspective front view and rear view respectively of a switch- gear, in particular a low voltage or medium voltage switchgear, comprising a frame 1 , an insulating angle 2, which may be solid or solid and flexible, and several bus bars 3 to transmit electrical current. The bus bars 3 are made of copper, aluminum or made of another metal.

The insulating angle 2 has the potential to be removed and to be replaced by other kinds of insulating materials. The bus bars 3 are aligned above each other and are oriented in a parallel way.

The frame 1 comprises at least one unprotected surface 1 a or area, where flexible insulations 6 are arranged, to protect it. The switchgear comprises at least a frame 1 and at least a bus bar 3 to transmit electrical current, wherein an arc attractor and at least a flexible insulation 6 are arranged.

The arc attractor is an electrode 5, namely a sacrificial electrode. In the example shown, four flexible insulations 6 are arranged to protect a previous unprotected sur- face 1 a of the frame 1 from the arc.

In the region 1 b an attraction to the electrode 5 occurs. This causes heat effects to an enclosure or the frame 1. Flexible insulations 6 therefore are used at the frame 1 or enclosure to protect it.

The electrode 5 or the arc attractor is also arranged. This electrode 5 is a protective cathode.

In the illustrated embodiment according to Fig. 2 and 3, the additional electrode 5 is in the form of a metal strip or metal bar. This electrode 5 is provided as means of an attraction for the arc.

Fig. 3 shows the electrode 5 placed within a flexible insulation 6. The flexible insula- tion 6 is attached on a rear side of the arc attractor, namely the electrode 5. The front side of the electrode 5 is bare. The position of the electrode 5 itself may be made flexible and can be changed into another position than the one illustrated in Fig. 3.

In Fig. 2 and 3, the flexible insulation 6 is attached to the frame 1 of the switchgear. The flexible insulation 6 is an elastomer. The longitudinal ends of the bus bars 3 are nearby the flexible insulations 6. Reference numbers