US3564176A

US3564176A - Magnetic electric arcing extinction device

Info

Publication number: US3564176A
Application number: US754818A
Authority: US
Inventors: Louis J M Fechant
Original assignee: La Telemecanique Electrique SA
Current assignee: Telemecanique SA
Priority date: 1967-09-01
Filing date: 1968-08-23
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16
Also published as: BE720186A; DE1765946B1; PL80761B1; NO127132B; SE348314B; AT278956B; GB1221573A; ES357575A1; DK121964B; BR6801707D0; CH489884A; NL6812269A; FR1543338A

Abstract

An arc extinction device has a U-shaped magnetic member formed of flat strip folded about lines parallel to the width of the strip, and each limb is slotted along its length to provide second limb portions reversely directed towards the base of the U without meeting the latter.

Description

Inventor Appl. No.

Filed Patented Assignee Priority Louis J. M. Fechant Chatou, Yvelines, France 754,818 Aug. 23, 1968 Feb. 16, 1971 La Telemecanique Electrique Haute de Seine, France Sept. 1, 1967 France 119,683

MAGNETIC ELECTRIC ARCING EXTINCTION DEVICE 10 Claims, 7 Drawing Figs.

[511 mu H0lh9/34 so FieldofSearch 200/144, 147, 147 (A), 148.3

[56] References Cited UNITED STATES PATENTS 2,428,254 9/1947 Walle 200/ 147(A) 2,898,427 8/1959 Nadeau 200/147 Primary Examiner-Robert S. Macon Artorney- Karl W. F locks as E E 5 F20 j 122;? 6.22 g

PATENTED F-EB 1 s IBYI sum 2 OF '2 forming betweenthe two contacts. of a circuit breaker at the moment of their'separation by means of a ferromagnetic plate of u-shape'd formation which symmetrically surrounds the contact elementsand the cheek and bottom portions of which are parallel with the direction in which the contacts separate, in other words parallel with the are at the moment it appears between them.

This plate channels the magnetic induction generated by the current, i.e'., partly by the arc itself except between the legs of theU,ort the side opposite the bottom of the U, and the magnetic field present between the legs pushes the arc towards the bottom of the U-shaped plate. This may be sufficient to extinguis'h the are, simply by elongation orby breaking it up in a suitable device.

Howeverfithis is only true if the arc is produced in the plane of symmetry of the U-shaped plate because, otherwise, the arc will be pushed towards the nearest cheek for the same reason as previously stated, thatis to say. because of the channeling effect of the plate as a result of the magnetic induction generated by the current. What happens is that the arc is attracted by its mirror image," the reflecting surface of the mirror being the internalsurface of the check. The force attracting the arc towards the cheek grows as the arc approaches the latter,and when current finally passes through the cheek there appears a portion of the arc perpendicular to the said cheek with every contact.

If an insulating'box is interposed between the U-shaped plate and the contacts, this attractive 'force-is'a well-known 1 cause for the deterioration of the insulating material of which this are extinction box consists. The arc is in fact flattened violently against the wall of the box and the parts of the are which stand substantiallyperpendicular on the cheek are no longer subject to the magnetic force pushing them towards the bottom portion.

' When the U-shaped plate is situated inside the box the are which is thrown against this plate is allowed to become divided, and only the two arc portions perpendicular on the cheek remain which, for the same reason, cannot move towards the bottom portion so that theycan still cause the box to deteriorate; it is even possible that the arc subsists and the circuit is not broken. a a

It is also known that, in order to favor the extinction of an are which shifts while remaining substantially parallel to itself, it is possible to break up this are by transverse extinction ele ments,.consisting of insulating material, or preferably, of conductive and ferromagnetic material, which stand in the way of the arc.

The present invention has for its object an improved are extinction device which, in order to ensurethe shifting of the arc, comprises a substantially U-shaped element of ferromagnetic material, without the above-mentioned disadvantages.

During the separation of the contact elements, this .U-

shaped piece brings the arc into contact with extinction means extending in a direction perpendicular to the displacement of the are.

According to the present invention there is provided an arc extinction'device which comprises a fixed and a moving contact member; a substantially U-shaped member of fiat-section ferromagnetic material arranged withits width parallel to the direction of movement of the moving contact, the member having a base portion and a pair of limbs each formed to define'a corresponding first limb portion, which first limb portions together with the base portion surround the moving contact throughout its range of movement, and second limb portion each of which is coplanar with its associated first limb portion and extends from the free end of the latter towards the base portion, which second limb portions are arranged at the level of the fixed contact; a'horn on the fixed contact extend-- ing towards the base portion of the U-shaped member, and at least one extinction element located between the moving contact and the base of the U-shaped member, parallelv to the latter.

It should be noted that it is known, for example as a result of the French Pat. No. 1,214,213, to provide slots extending across the path of the arc in U-shaped metal sheets serving for the extinction of such arcs. However, in the above-quoted specification the bottom .portion of the U-shaped piece is not interrupted between the branches limited by the slots, and these slots have for their sole purpose the fragmentation of the arc as well as the cooling and escape of the hot gases produced by this arc.

According to U.S. Pat. No. 2,356,039 it is also known to bend into U-shape the legs of a magnetic arc extinction piece which is itself U-shaped. However, contrary to the present invention, the three U's are bent within the same plane,.and this plane is parallel with the path of the arc, so that the effect obtained is entirely different.

The invention will now be described in greater detail with reference to the accompanying drawings, of which:

FIG. 1 is a longitudinal, partly diagrammatic sectional view of an arc extinction device according to the invention, the section corresponding to the line I-Iof FIG. 2;-

FIG. 2 in sectional view of this device along the line Il-Il of FIG. 1;

FIG. 3 is a diagrammatic view of the extinction of an arc appearing symmetrically between the contact elements;

FIG. 4 is a perspective diagrammatic view of the current path when the arc shifts laterally on the contact elements and is broken up into two portions;

FIG. 5a is a front view of the fixed contact and the portion of the magnetic element surrounding this contact;

FIG. 5b is a similar view of a modified embodiment; and

FIG. 6 is a front view (reversed in comparison with the two preceding views) of the moving contact and the portion of the magnetic element surrounding it.

The last three FIGS. are intended to show the path taken by the arc when the latter is produced to one side of the central plane of symmetry.

The deviceshown in FIGS. 1 and 2 is a bridge-type circuit breaker of which only one half and the central portion are illustrated in detail by FIG. 1.

This device is contained in an insulating chamber 1 comprising a guide 2 for the sliding support 3 of the contact bridge.

Each contact bridge consists ofa lightV-shaped conductor 4 bearing at each end a rare-metal contact element 5. At each end the edge of the conductor 4 is reinforced by a clamp 22 of refractory metal, for example stainless steel.

In its central part the conductor 4 rests in the V-shaped slot 3a of the support 3 and is stressed at its ends by a likewise V- shaped spring 6 the central portion of which applies itself to a wedge pushed by the spring 8 which latter, at its other end, bears on the support 3.

The fixed contacts cooperating with this bridge are two 0 shaped conductive elements 9 (only one of which is illustrated in FIG. 1.), these elements being fixed to the base 10 of the box l by means of the screw 11. The screw 12, accessible through the hole 13 of the element 9, ensures connection with the conductive lead 14.

The C-shaped element 9 comprises the rare-metal fixed contact 15 and a thickened horn portion 16, the surface of which, facing the moving contact 5, is in the same plane as the contact element 15. I

Both the fixed and the moving contact are surrounded by a plate 17 of ferromagnetic material of U-shape comprising a bottom portion 17a extending in a direction perpendicular on the longitudinal direction of the contact elements, and two cheeks each of which is divided by a slot 18 extending from the bottom portion towards the free end of the said cheeks. Thus, each of these checks is a flat U and, starting from the bottom portion 17a, can be imaginedas being returned on itself within its own plane (see FIG. 4), one leg 17!; starting from this bottom portion and one leg 17c returning towards it.

' moves along the horn 16.

' The legs 17c are situated substantially at the same level as the fixed contact element and the horn 16, whereas the legs 17b and the bottom portion l7a su rround the space within which the moving contact travels. The slot 18' preferably ascends towards the bottom portion 17a, see FIG. 1.

The space comprised between the end of the movingcontact and the bottom portion 17a is subdivided by fins 20 which extend parallel with each other and with the bottom portion 17a. These fins advantageously'consist of ferromagnetic conductive material and are notched at their edges in a manner known per se, see 20a in FIG. 2. The fins could be replaced by likewise known bucket-shaped members.

To each fin 20. is allocated a vent 21 in the box. These fins are fitted and held in position by means of screws 25 provided in the'box 1 (see FIG. 2) or by any other method known from arc chamber technology.

The device described here operates as follows:

upon the two

arcs

26A and 268 so as to push them towards the bottom portion 17a. This action will be the more efficient the flatter the current conductor (branches 17b, 17c) and the' nearer it is to the fixed and mobile contact elements through 1 which the incoming and outgoing lines of current pass.

' the bottom portion 170 is favored by the ascending direction As aresult of the reciprocatingrnovement of the support 3 in the direction of the double arrow (FIG. 1) the contacts open and close. I

When the contacts close, the pressure on the two contacts of one and the same bridge is equalized owing to the freedom of the wedge 7 at the end of the spring 8. Contact pressure is applied by the spring 8 and transmitted by the spring 6.

Because of the lightness of the moving assembly constituted by the conductor 4 and the spring 6 and because of the friction of the curved ends 6a of this spring on the outer surface of the conductor 4, the bouncing of the moving contact upon closure is considerably reduced.

When the contacts open the conductor 4 is removed from the fixed contact elements as soon as the hollow portion 3a of the support 3 which engages the central portion of the conductor 4 moves the latter. At that moment an arc appears between the fixed and the moving contact elements while they are being separated. t

It should benoted from the beginning that, due to the arrangement in the same direction and substantially parallel with each other of the fixed and moving contacts, even breaking is ensured and the arc has the'spontaneous tendency of escaping towards the bottom portion 17a.

If the arc'makes its appearance in the median plane corresponding to the sectioning, line H of FIG. 2, the U-shaped formation of the ferromagnetic element 17 enhances this tendency. The magnetic field produced around the arc by the current (and by the arc itself) is channeled on three sides by the ferromagnetic element 17; it therefore acts upon the arc only on the side opposite the bottom portion 17a and pushes it in thedirection towards this bottom portion whatever the direction ofthe'current. 1 i

What happens in this case is shown in FIG. 3. The are which has originated in 26a betweenythe contact elements 5 and 15. first shifts on the contact elements themselves (position 26b) and then, while clinging to the clamp 22 on one side, also Each time it approaches a ferromagnetic fin 20 it is attracted by thelatter (by the "mirror effect," i.e., as a result of. f the channeling of the magnetic field by the fin which only allows the field opposite it to remain operative).

The are thus clings consecutively to all fins 20, starting from ficult and therefore allow the metal of the element ISto form I 1 burrs on the horn 16. Theseburrs would in turn hinder the that nearest to the moving contact (positions 260 to 26) and,

finally, clings to the bottom portion 17a (position 26f), where it develops and is extinguished.

The original arc 26a may also start to one side of the median plane. In that case it will be attracted not only towards the bottom portion 17a but, with rising speed, by the nearest cheek.

This produces the situation shown by FIG. 4 in which, for

- reasons of clarity, the distances between elements have been exaggerated. The original arc isdivided (FIG. 4) into two arcs, one are (26A) between the fixed contact and the branch 17c of the cheek and the other arc (263) between the moving con- I tact and the branch 17b of the same cheek.'The roots of these arcs opposite the contact elements will be linked by a current loop 27 which circumvents the end of the slot 18 and acts the desired effect is obtained due to the fact that there is no electricalconnection between the two branches 17c. If such connection existed between the roots of the

arcs

26A and 268, a circuit would form on each cheek which would'obviously tend to nullify the effect obtained by the current loop 27. t

' But FIG. 5b shows that the ends of the branches 17c, instead of being parallel, may also be turned towards each other, as indicated by the numeral 30; in other words, the cutting of the plate forming the element 17 neednot eliminate the bottom portion between the branches 17c entirely, provided that this bottom portion is effectively interrupted in this location. Such interruption, if sufficient to break the electrical continuity,

may be very narrow so as to make for low reluctance and, conelement. It should also be noted that the bottom portion 17a of this U-shaped element could likewise be provided with a narrow interruption, without impairing operations. The l U- shaped element would then be constituted by two juxtaposed In the case of FIG. 5b, the arc 26A moves between

thepo'sitions

26A and 26 as shown in FIG. 5b.

In either case (FIG. 6) the original are 268, on the one hand, clings to the edge of the moving contact, then to the clamp 22 and, on the other hand, runs along the branch 17b so that, either due to repulsion or to rotation, the arc encounters successive fins 20, this time to one side and is extinguished after being cooled by them.

Whether starting directly towards the bottom of the box or starting laterally and being broken up, the arcs cling at one end to the edge of the moving. contact. Sincev the latter is lightweight, its cooling presents difficulties. The clamp 22 is of metal more highly resistant to heat than cuprous metals and is arranged so as to border the edge of the moving contact. It therefore avoids deterioration as a result of the passage of the arc. Moreover, its receding portion 22a'protects the brazed joint connecting the rare-metal element 5 to the conductor 4,

The mass of the fixed contact enables it to resist arc burns much better than the moving contact. Besides, the fact that the element 15 is embedded in the surface of the fixed contact avoidsobstruction of the passage of the arc from the contact element to the horn which would result in a slowing down of the arc movement and also make thermal dissipation more difshifting of the arc and cause local heating which would accentuate this effect. j

Finally, the boxes 1 may comprise 'a wall 32, as shown, which protects the contact springs 8 from overheating and fromlmetal splashes produced by the arc.

Ic aim: I

1. An arc extinction device which comprises a fixed and a moving contact member; a substantially U-shaped member of flat-section ferromagnetic material arranged with its width parallel to the direction of movement of the moving contact, the member having a base portion and a pair of limbs each formed to define a corresponding first limb portion, which first limb portions together with the base portion surround the moving contact throughout. its I range of movement, and second limb portion each of which is coplanar with its associated first limb portion and extends'from the free'end of the latter towards the base portion, which second limb portions are arranged at the level of the fixed contact; a horn on the fixed contact extending towards the base portion of the U- shaped member, and at least one extinction element located between the moving contact and the base of the U-shaped member, parallel to the latter.

2. An arc extinctiondevice as claimed in claim 1 in which said at least one extinction element is a ferromagnetic, electrically conductive fin with notched marginal regions.

3. An arc extinction device as claimed in claim 1 in which said U-shaped member comprises a cut and bent sheet-metal element in which each limb is of generally U-shaped configuration, said configuration being achieved by the provision of a common surface constituted by said fixed contact member and said horn is continuous.

6. An arc extinction device as claimed in claim 5 in which said surface is planar. i

7. An arc extinction device as claimed in claim 1 in which said moving contact member includes a free end portion facing said base portion of said U-shaped member and said free end portion is bordered by a clamp fabricated of refractory metal.

8. An arc extinction device as claimed in claim 7 in which said clamp comprises a receding portion which covers a joint between said moving contact member and a contact element carried thereon.

9. An arc extinction device as claimed in claim 7 in which said moving contact member is a bridge contact biased by a leaf spring and said clamp includes an edge portion raised above the level of a corresponding end of said leaf spring.

10. An arc extinction device as claimed in claim I in which said U-shaped member of flat-section ferromagnetic material is constituted by two substantially symmetrical, juxtaposed parts.

Claims

1. An arc extinction device which comprises a fixed and a moving contact member; a substantially U-shaped member of flat-section ferromagnetic material arranged with its width parallel to the direction of movement of the moving contact, the member having a base portion and a pair of limbs each formed to define a corresponding first limb portion, which first limb portions together with the base portion surround the moving contact throughout its range of movement, and second limb portion each of which is coplanar with its associated first limb portion and extends from the free end of the latter towards the base portion, which second limb portions are arranged at the level of the fixed contact; a horn on the fixed contact extending towards the base portion of the U-shaped member, and at least one extinction element located between the moving contact and the base of the Ushaped member, parallel to the latter.

2. An arc extinction device as claimed in claim 1 in which said at least one extinction element is a ferromagnetic, electrically conductive fin with notched marginal regions.

3. An arc extinction device as claimed in claim 1 in which said U-shaped member comprises a cut and bent sheet-metal element in which each limb is of generally U-shaped configuration, said configuration being achieved by the provision of a longitudinal slit in said limb and by omission of the corresponding portion of said base of said U-shaped member.

4. An arc extinction device as claimed in claim 3 in which said slit is oblique and extends towards an open end in the direction of operating movement of said moving contact away from said fixed contact.

5. An arc extinction device as claimed in claim 1 in which a common surface constituted by said fixed contact member and said horn is continuous.

6. An arc extinction device as claimed in claim 5 in which said surface is planar.

10. An arc extinction device as claimed in claim 1 in which said U-shaped member of flat-section ferromagnetic material is constituted by two substantially symmetrical, juxtaposed parts.