NZ212409A

NZ212409A - Switchgear arc extinction plate construction

Info

Publication number: NZ212409A
Application number: NZ212409A
Authority: NZ
Inventors: K Greete; R Kommert; R Sellner; E Muders
Original assignee: Bbc Brown Boveri & Cie
Priority date: 1984-06-13
Filing date: 1985-06-13
Publication date: 1988-05-30
Also published as: EP0164632A2; EP0164632B1; EP0164632A3; DE3583459D1; DE3421876A1

Description

II 2 12409 Priority Dat8(s) WIA..UUKM : ../.Zr.brM CQmplete Specification Filed: Class: ftO/riJ3//& Publication Pdta: .... ? 3. Journal, Nc: .... ?! N.Z.No.

NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION " V \ % "ARC EXTINCTION DEVICE" We, BROWN, BOVERI & CIE AKTIENGESELLSCHATT, of D 6800 Mannheira-Kafertal, Kallstadter StraBe 1, "ernany, a German body corporate, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : - - 1 - (followed by 1A) The invention relates to an arc extinction device.

Arc extinction devices have an arc extinction plate bundle surrounded by a cover which normally covers the two extinction plates that are at the outer ends of the arc extinction plate bundle and also the rear edges of the extinction plates; and there are holes in the closing-off wall covering the rear edges to permit the arc gases to escape from the extinction plate bundle.

These covers essentially prevent reignition of the arc at the sides and rear of the arc extinction plate bundle. In one known arrangement the upper and lower covering plates, that is, the plates on the upper and lower extinction plates, also have a hole in them so that the arc cannot migrate frontwards to the contact point and thus cannot be reignited at the front part of the arc extinction plate bundle. These known covers do not in themselves have any effect of speeding up the arrival of the arc at the arc extinction plate bundle.

The object of this invention is to speed up as much as possible the arc travel away from the contact points and the formation of a higher arc voltage.

According to a broad aspect the invention provides an arc extinction device for electrical switch gear, having: a contact point at which, upon separation of the contact pieces during the switching-off process, an arc is formed; an arc extinction plate 2 I 24 bundle between two arc guide bars into which the arc runs, along the guide bars, and in which it is extinguished; and a cover for the extinction plates, which covers, with side walls, the two sides of the arc extinction plate bundle running transverse to the extinction plates and which covers, with a closing-off wall, the rear side of the arc extinction plate bundle; characterized in that the side walls protrude beyond the extinction plate bundle in an area facing the contact point and, in a rear area, have together with the closing-off wall approximately the same height as the extinction plate bundle.

Due to the cutaways in the rear part, that is, the reduced height of the cover, which is made of arc-resistant material -preferably fibre paper - the speed of arrival of the arc roots at the guide bars is measurably increased at the rear of the extinction plate bundle, because the pressure can drop more rapidly owing to the resultant increased exhaust air openings between the guide bars and the first and last plates respectively. This greatly speeds up the arc roots on the guide bars, which all leads to more rapid arc arrival. As a result, the build-up of a current-limiting voltage occurs more rapidly than with the known covers, whereby the current-limiting effect of the switch-gear is improved.

It is particularly beneficial to use this cover with arc extinction plate bundles used in automatic cutout switches. In this case the cover can also hold additional arc extinction plates at a distance. Thus the cover performs two functions at the same time.

The shortening of the guide bars serves essentially to prevent shortening of the arc behind the chamber and to increase the size of the exhaust air openings, with the result that heat-buildup effects, which drive the arc forwards in the direction of the contact point, are prevented.

In one preferred arrangement, an arc extinction device for use with electrical switch gear mounted in a housing and having on electromagnetic trigger with a magnet yoke, has at least an arc guide bar adjacent to the magnet yoke shorter than the arc extinction plate bundle. Desirably, the arc guide bar adjacent to the magnetic yoke ends in the area in which the front end of the cutaways occurs.

Preferably an arc guide bar contiguous with one wall of the housing is partially overlapped at its lower region by a projection integral with the housing wall to hold the arc guide bar.

Further beneficial improvements and advantages of the invention will be explained and described in more detail with reference to the accompanying drawings which shows one embodiment of the invention, and in which: Figure 1 shows a side view of an arc extinction chamber.

Figure 2 shows a section through Figure 1 in accordance with line 11 — 11. and Figure 3 shows a view in the direction of arrow A in Figure •MMMli 1;: i A normal commercially available electrical automatic cutout switch has a contact point 12 consisting of a movable contact piece 10 and a fixed contact piece 11. between which an arc 13 is formed during switching off. The movable contact piece 10 is mounted on a contact lever 14 (shown here as integral with it), which is activated by a switch latch on the basis of a short-circuit or an overload current. The overload current trigger can be an electromagnetic trigger.

The fixed contact piece 11 is attached to an arc guide bar 15, there being another arc guide bar 16 opposite, between which there is an arc extinction plate bundle 17. The arc 13 arising during switching is expanded due to an electromagnetic blow-out field, formed for example by the arrangement of the movable contact level - 3a - \ - "■ > ' \ \ 0 NOV 1987 ■1 Te-yi-r - i ^ -5,1 & ; o 2 1 240 14 with contact piece 10 vis-a-yis the fixed contact piece 11 with the arc guide bar 15, and driven into the arc extinction plate bundle 17, where it is extinguished. The arc extinction plate bundle consists of a number of arc extinction plates 18 lying on one another and formed in a normal manner; the design of this is not material to the invention.

The arc extinction plates 18 of the arc extinction plate bundle 17 are kept apart by a cover 19. For this purpose there are two projections/bosses 20, 21, and 22, 23, on either side of the arc extinction plates 18 which are pushed into openings 24 and 25 in the side walls 19' and the cover 19' and conversely the openings 24 and 25 are pushed over the projections 20, 21, 22, and 23 in such a way that the projections engage the side walls \ 1 19• of the cover 19, The outer faces of the outer arc extinction plates are kept apart from each other at a distance of B. Figure 3 shows that the two side walls protrude from the arc extinction plate bundle at region C, both above and below (Co and Cu in fig. 3). The cover and particularly the side walls 19" have a downwards region D, downwards being the direction of exhaust gas flow, whose height H corresponds to the distance B between the two outer faces of the arc extinction plate bundle 17. The transition between region C and region D occurs via transition radii (27 above and 28 below).

The two side walls 19' are connected by means of a connecting plate 30 (back/closing-off wall), whereby an approximately U-shaped cover is formed, with the two arms forming the side walls 2 1 240 . 19' and the web forming the back wall 30. This cover does not just serve to prevent arcing back at the sides and back of the arc extinction plate bundle 17 - more importantly the side walls 19' serve at the same time to hold the arc extinction plates at a distance from one other. There are exhaust gas openings 31 in the closing-off wall 30, which are of customary design.

Fig. 1 shows that the arc guide bars 15 are directly contiguous with a housing wall 32. The housing wall 32 has, in this region, a groove 33 into which the arc guide bar 15 is set. In the rear area the housing also has a covering boss 34 which overlaps part of the arc guide bar 15, as can be seen in fig. 2, whereby the arc guide bar is attached to the housing 32. At the rear end the known cover is cut away to form transitions 27 and 28; in the region of the two guide bars 15 and 16 - the upper and lower regions and the front region - the cover 19, with its side walls 19', projects beyond the arc extinction plate bundle 17 both above and below.

Experiments have shown that such cutaways measurably improve the speed of travel of the arc roots on the guide bars.

As can be clearly seen from fig. 1, the cutaway at 28 is also beneficial in that it leaves space for the provision of a boss at housing-area 32 (see figure), which serves to attach the guide-bar. In order to enlarge the exhaust air openings on the one hand, and to prevent the arc from shorting behind the arc extinction plate on the other, the two guide bars end before the rear edge of the arc extinction plate bundle: guide bar 16 ends at the step area at 27 and guide bar 15 ends a little bit before the rear edge of the arc extinction plate bundle.

Claims

WHAT WE CLAIM IS:

1. An arc extinction device for electrical switch gear, having: a contact point at which, upon separation of the contact pieces during the switching-off process, an arc is formed; an arc extinction plate bundle between two arc guide bars into which the arc runs, along the guide bars, and in which it is extinguished: and a cover with side walls which cover two sides of the arc extinction plate bundle and with a closing-off wall which covers the rear of the arc extinction plate bundle; characterized in that the side walls protrude beyond the front and rear of the extinction plate bundle and, the closing-off wall is approximately the same height as the extinction plate bundle.

2. An arc extinction device in accordance with claim 1. characterized in that the side walls of the cover covering the sides of the arc extinction plate bundle hold a plurality of arc extinction plates in parallel planes perpendicular to the side walls.

3. An arc extinction device in accordance with claim 1 or 2, for electrical switch gear in a housing, with an electromagnetic trigger with a magnet yoke, characterized in that at least the arc guide bar adjacent to the magnet yoke is shorter than the arc extinction plate bundle.

4. An arc extinction device in accordance with claim^Kf characterized in that the arc guide bar adjacent to//the magnetta yoke ends in the area in which the front end ol the cutaways occurs.

5. An arc extinction device in accordance with any one of the preceding claims, characterized in that the arc guide bar contiguous with one wall of the housing is partially overlapped at its lower region by a projection integral with the housing wall to hold the arc guide bar.

6. An arc extinction device substantially as herein described with reference to the accompanying drawings. BROWN. BOVERI & CIE AKTIENGESELLSCHAFT By Their Attorneys HENRY HUGHES LIMITED 1 0 NOV 1987 Si) - 7 -