This application claims priority under 35 U.S.C. §119 to German Application No. 10 2006 054 030.1 filed in Germany on Nov. 16, 2006, the entire contents of which are hereby incorporated by reference in their entireties.
An electrical switching device is disclosed.
Electrical switches of this kind are line-protection circuit breakers, motor protection circuit breakers and the like, which serve to disconnect electrical lines, which are loaded with overcurrents of high current strength (short-circuit currents), from the supplying network in the event of a fault. For this purpose, line-protection circuit breakers have a contact point with a fixed and a moving contact piece, whereas with motor protection circuit breakers a double contact point is often provided having two fixed and two moving contact pieces, the latter being fitted to a contact bridge by means of which the two fixed contact pieces can be bridged.
When the contact points open, that is to say when the moving contact pieces are lifted from the fixed contact pieces, a switching arc, which is extinguished in an extinguishing device provided for the purpose, occurs at each contact point. The arc, which occurs immediately on switching off, commutates onto arc conducting rails and enters a stack of arc-extinguishing plates in which the arc is divided into shorter partial arcs, as a result of which a high arc voltage is produced to limit the current so that the arc extinguishes. The higher the number of plates in the arc-extinguishing stack, the larger the arc voltage becomes.
The stacks of arc-extinguishing plates generally consist of a defined number of extinguishing plates made from ferromagnetic steel, which are held spaced apart from one another by an insulating holding element or by insulating holding elements.
It is of no importance for the disclosure that the arc-extinguishing plates have entry slots designed in a particular manner.
Particle board strips, or, in the case of an elaborate embodiment, a 3-layer material combination made from a synthetic aromatic polyamide polymer and Akadur, are used as holding elements with which the arc-extinguishing plates are held spaced apart from one another.
Furthermore, there is also the possibility of coating the stack of arc-extinguishing plates itself with a plastic material, as a result of which the base of the arc is stabilised in the stack of extinguishing plates.
Furthermore, stacks of arc-extinguishing plates, which are held by means of side strips made from the above-mentioned materials, are also to be found; in addition, a so-called exhaust air mask, that is a cover with slots arranged on the rear of the stack of arc-extinguishing plates, can also be provided, and furthermore completely encased stacks of arc-extinguishing plates can also be found.
The use of particle board, in particular the type encased by a particle board film, is the most economic construction with regard to the manufacture of the arc-extinguishing chamber and assembly in a line-protection circuit breaker or a motor protection circuit breaker. On account of the inexpensive particle board material, the material costs are correspondingly low. As the individual components of the stack of extinguishing plates are very robust, the insertion and assembly of the parts can be categorised as being unproblematic. The quality of the device is also correspondingly reproducible.
In some embodiments of antechambers, which lie between the contact point and the actual stack of arc-extinguishing plates, materials are provided, which on the occurrence of the arc partially gasify due to the arc, as a result of which the gas pressure on the arc is increased and entry into the arc-extinguishing chamber is accelerated.
As particle board is not a gasifying material, the use of a stack of arc-extinguishing plates held together with particle board is limited with regard to the switch-off power and rated current range.
Systems, which are subject to high thermal loading, can resort to designs with side strip material made from Akadur and the synthetic aromatic polyamide polymer (which is marketed under the brand name “Nomex”), although this material combination of Akadur, Nomex and Akadur in the form of 3-layer strips is very cost intensive.
Furthermore, it must be stated that, with this material, the plastic strip for is manufacturing a plastic plate, which can be fitted to one or more of the arc-extinguishing plates, deforms into a sword-like shape, which makes manufacturing problematic. The joining process between the side strips and the plastic plate is likewise difficult, as the necessary forces encountered in the joining process cannot be absorbed by the unstable plastic plate. This then leads to stacks of arc-extinguishing plates sometimes finding their way into final assembly without secured plates or with inadequately secured plates.
If, in addition, the slotted cover is used on the rear side of the stack of extinguishing plates, then an additional component, which must be appropriately manufactured and fitted manually before the stack of arc-extinguishing plates can be fitted, must be processed during assembly, because such an exhaust air mask cannot be processed in a vibrator during assembly, so that in this case an intermediate manual step is necessary, which makes the stack of arc-extinguishing plates more expensive.
An electrical switching device is disclosed of the kind mentioned in the introduction with which the manufacture of the stack of arc-extinguishing plates is simplified and can also be mechanised.
According to the disclosure, this object is achieved in that the holding elements are manufactured from a thermoplastic, which is radiation cross-linked after assembly.
Radiation cross-linked thermoplastics as such are known, see PTS-Technik, PTS-Marketing, Strahlenvernetzung, May 2002 published by the company PTS (Plastic Technology Service), Hautschenmühle 3, 91587 Adelshofen. According to this, thermoplastic materials are cross-linked by means of electron beams or cobalt 60 (gamma radiation) regardless of the shaping process, wherein the cross-linking can be adjusted by means of the radiation dose. In many cases, a cross-linking booster can also be used. Certain main characteristics can be improved by means of radiation cross-linking, see stated publication, Page 4, Item 2.
As a result of this, the thermal usage limits of inexpensive standard and engineering thermoplastics, for example DE, PT, PA 6, PA 6.6, TBT, are extended, and the resistance to media highly increased. In particular, the amorphous portions of partially crystalline thermoplastics are cross-linked by means of electron beams, which leads to a change in the molecular structure and an increase in the degree of cross-linking. This results in increased resistance to distortion when exposed to heat, improved strength and creepage characteristics, and a reduced thermal expansion. The resistance to wear and the resistance to stress cracking are also significantly increased. Furthermore, a fibre-matrix adhesion and a plastic-plastic bonding strength are also improved.
Because of the radiation cross-linking, the material is no longer able to melt; the resistance to distortion guarantees a more consistent behaviour during short-circuit switch-off and, in addition, the gas pressure and therefore also the arc voltage between the individual extinguishing plates is increased due to the out-gassing of the thermoplastic.
When a so-called exhaust air mask or a complete encasing of the stack of arc-extinguishing plates is provided, cross-linked thermoplastics can also be used for this purpose in that the stack of arc-extinguishing plates is first encased with the thermoplastic and the arc-extinguishing plates fixed, and then the thermoplastic, to which an additive for increasing the radiation cross-linking has been added if necessary, is cross-linked by irradiating with gamma rays or electron beams.
Further advantageous embodiments of the invention can be seen from the further dependent claims.
The invention and further advantageous embodiments and improvements of the invention are explained and described in more detail with reference to the drawing, in which 7 exemplary embodiments of the invention are shown.
In the drawing
How an arc-extinguishing stack is fitted into a line-protection circuit breaker or motor protection circuit breaker is disclosed. It is also disclosed that the stack of arc-extinguishing plates is constructed in a particular manner.
According to the disclosure, these holding strips are made from thermoplastic with radiation cross-linking; it is the simplest embodiment in which particle board strips have also been used in the prior art.
The central area 32 or central section is connected to a holding section 40, 41 in each case at the point where the longitudinal edges of the arc-extinguishing plate 33 run, by means of a film hinge 38, 39 respectively, holes 42 in which lugs (not shown) engage in a similar way to the extinguishing plate 11 in
In the embodiment according to
The extinguishing plates 109 are fixed by means of the holding sections 104 and 105; the plate 101 is arranged at a distance from the top extinguishing plate 109, which corresponds to the distance of the individual arc-extinguishing plates from one another.
In the exemplary embodiment according to
A cover section 167 is moulded on to the edge of the cover plate 161 opposite the slot 166 by means of a film hinge 168. As can be seen from
When all these casings are assembled, that is to say fixed to the stack of extinguishing plates, so that the extinguishing plates are also held to one another, then the thermoplastic plastic is subjected to radiation cross-linking as mentioned in the introduction.
It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
Number | Date | Country | Kind |
---|---|---|---|
10 2006 054 030.1 | Nov 2006 | DE | national |