US3735075A

US3735075A - Electric circuit breaker having an arcing contact with larger pivot notch than parallel movable contacts

Info

Publication number: US3735075A
Application number: US00184799A
Authority: US
Inventors: A Kidd
Original assignee: SMITH D SWITCHGEAR Ltd
Current assignee: SMITH D SWITCHGEAR Ltd
Priority date: 1970-10-29
Filing date: 1971-09-29
Publication date: 1973-05-22
Anticipated expiration: 1990-05-22
Also published as: IT940999B; GB1312156A; DE2152643B2; DE2152643A1; FR2110155A5

Abstract

An electrical circuit breaker or isolator, for switching currents of the order of 100,000 amperes, has for each pole thereof, a respective moving contact assembly comprising a plurality of parallel-connected movable contact arms each carrying a respective movable contact engageable with a fixed contact, said arms being of strip metal resiliently mounted sideby-side and substantially parallel to each other in a carrier, each said arm having a V-shaped notch adjacent one end whereby it locates onto an arcuate surface provided by a fixed hinge contact block to which the carrier is hingedly connected, whereby electrical continuity is provided between the arms and the block by direct contact therebetween. An arcing contact arm present in the assembly has the angle of the V-shaped notch in the arcing contact different from that in the other arms to take account of the larger blow-off force occurring between the arcing contact arm and the arcuate surface.

Description

United States Patent [191 Kidd [451 May 22,1973

[75] Inventor: Alan Lister Kidd, Southport, En-

gland [73] Assignee: Dorman Smith Switchgear Limited,

Preston, PR2 2DQ, England [22] Filed: Sept. 29, 1971 [21] Appl. No.: 184,799

[58] Field of Search ..200/l46 R, 166 F, 200/170 A, 170 R; 335/15, 16, 195

[56] References Cited UNITED STATES PATENTS 3,402,274 9/1968 Bould ..200/l46 R 2,821,594 l/l958 Latour ..335/l95 3,560,683 2/1971 Maier et al.... ..200/146 R 3,041,431 6/1962 Mills ..200/170 A 3,365,561 l/1968 Jencks et al. ..200/170 A X FOREIGN PATENTS OR APPLICATIONS 1,552,452 11/1968 France ..200/l46 R Primary ExaminerRobert K. Schaefer Assistant Examiner-Robert A. Vanderhye Attorney-Kenwood Ross and Chester E. F lavin [57] ABSTRACT An electrical circuit breaker or isolator, for switching currents of the order of 100,000 amperes, has for each pole thereof, a respective moving contact assembly comprising a plurality of parallel-connected movable contact arms each carrying a respective movable contact engageable with a fixed contact, said arms being of strip metal resiliently mounted side-by-side and substantially parallel to each other in a carrier, each said arm having a V-shaped notch adjacent one end whereby it locates onto an arcuate surface provided by a fixed hinge contact block to which the carrier is hingedly connected, whereby electrical continuity is provided between the arms and the block by direct contact therebetween. An arcing contact arm present in the assembly has the angle of the V-shaped notch in the arcing contact different from that in the other arms to take account of the larger blow-off force occurring between the arcing contact arm and the arcuate surface.

7 Claims, 4 Drawing Figures PATENTEU HLYZZ I975 SHEET 1 BF 3 mvsuroa; ALAN LISTER moo WwwziQon Mn/167 M ATTORNEYS.

PATENTEL MAY 2 21975 SHEET 3 OF 3 mm 9 mv k @v I Nm mv mm @v QN mm Gum QM 1 mm W F Q 2 I I. h n 9 N a OQL m N w x Q if wm mm mm mm 9v mv mm 9 mm @w v I av mv mm Gm) \m 9 vVv/ z/ INVENTOR:

ALAN LISTER moo ATTOR NEYS.

ELECTRIC CIRCUIT BREAKER HAVING AN ARCING CONTACT WITH LARGER PIVOT NOTCH THAN PARALLEL MOVABLE CONTACTS This invention concerns electric circuit breakers and isolators and more particularly contact arrangements thereof.

lt is well known, in relation to electric switchgear, such as circuit breakers, that a socalled blowoff force occurs at the abutting surfaces of successive conductors, e.g. abutting contacts, when current is passing therethrough, tending to separate such surfaces, and this force is proportional to the square of the current passing. Accordingly, with circuit breakers of large short circuit currant capacity, e.g. of the order of one hundred thousand peak amperes, provision has to be made to counteract very substantial blow-off forces to keep the movable contacts thereof properly in engagement with their stationary contacts.

For this reason, as well as others, it is advantageous to provide, for each pole of such a circuit breaker, a moving contact assembly comprising a plurality of parallel-connected movable contact arms or fingers each carrying a respective movable contact engageable with a fixed contact, so that the current in each pole is split according to the number of arms. The total blowoff force then arising at the abutting contacts for any particular current is reduced in inverse proportion to the number of such arms, as compared with the case where only a single contact arm is present, and consequently the actuating mechanism and structure of the circuit breaker needs only to apply a substantially smaller force to retain the movable contacts in their closed positions, without blow-off occurring. However, the mounting of such plural parallel-connected movable contact arms or fingers in such an assembly, in itself, involves certain difficulties, particularly in relation to making provision for current continuity from a fixed conductor to the arms whilst enabling them to move relative to such fixed conductor so that their movable contacts can engage with and disengage from the fixed contacts.

The fixed conductor can, if desired, be formed with slots for accommodating the ends of respective ones of the contact arms or fingers, with a pivot rod extending through the fixed conductor and the ends of the arms or fingers so as to provide hinged connections therewith. Such an arrangement involves a considerable number of machining operations and is therefore expensive.

lt is also known to provide a fixed conductor in the form of a hinge contact block which has a V-sectioned channel extending transversely thereof, each of the arms or fingers having on one end thereof an arcuate lobe which locates in the channel, so that the arms each contact the hinge contact block at two opposed locations and are pivotable relative to such block. In such an arrangement, the hinge contact block can, if desired, be made by extrusion, as also may be stock from which the movable arms or fingers are made.

In the known moving contact assemblies, it is usual to provide a so-called arcing contact". This contact, which is carried upon its own contact arm, is arranged so that it disengages from its respective fixed contact after opening of the contacts of the other arms or fingers of the assembly, so that any arcing which may occur upon opening of the contacts is drawn to such arching contact and burning of the other contacts is minimized. Accordingly, it will be appreciated that the entire current passing through the contact assembly is momentarily diverted through the arcing contact arm or finger, upon opening movement of the contact assembly. Therefore, where such an arcing contact arm is formed with an arcuate lobe engaging into a V- sectioned channel in a hinge contact block arrangement, as discussed in the preceding paragraph, the blow-off forces occurring at the contact surfaces between the arcuate lobe of the arcing contact arm and the hinge contact block, upon opening movement of the contact assembly, is substantially higher than that which occurss between the other contact arms and the hinge contact block when current is passing normally through such other contact arms. From this, it will be appreciated that in practice advantages can arise if provision is made for the possibility that the geometry of the contact surfaces between the arcing contact arm and the hinge contact block can be different from that of the other contact arms. This, of course, is not readily possible with the above-discussed known V-sectioned channel and lobe arrangement, and an object of this invention is to provide a parallel-connected novable contact arm arrangement which is suitable for use in electric circuit breakers or in electric isolators wherein such difference can be provided if desired, and which enables the contact arms to be produced simply and inexpensively.

With this object in view, the present invention provides an electric circuit breaker or isolator which has, for the or each pole thereof, a respective moving contact assembly comprising a plurality of parallelconnected movable contact arms each carrying a respective movable contact engageable with a fixed contact, characterized in that said arms are of strip metal resiliently mounted side-by-side and substantially parallel to one another in a carrier, each said arm having a V-shaped notch adjacent one end whereby it locates onto an arcuate surface provided by a fixed hinge contact block to which the carrier is hingedly connected,

whereby electrical continuity is provided between the arms and the block by direct contact therebetween.

With such a construction, if an arcing contact arm is present in the assembly, the angle of the .V-shaped notch in such arcing contact arm may be different from that of the other arms, so that the geometry thereof is such as to take into account the fact that the blow-off force occuring between the arcing contact arm and the arcuate surface, upon contact-opening movement of the assembly is considerably higher than that occurring between the other contact arms and said surface.

Each movable contact arm is conveniently in the form of a metal pressing, the respective movable contact being secured adjacent the other end thereof, e.g. by high speed brazing which can be effected without softening the contact arms.

In the arrangement of the invention, each of the arms may be mounted in the carrier by a respective locator spring which is shaped, as discussed in our copending Patent application No. 184,800 to provide a loading portion which engages one longitudinal edge of the arm and a pair of limbs extending across the arm one adjacent each side thereof and which locates on a cross member, extending transversely of the arms, of the carrier, adjacent the other longitudinal edge of the arm.

In such arrangement, the locator springs serve yieldingly and resiliently to mount the movable contact arms in the carrier, and the space between adjacent pairs of the contact arms has one limb of the locator spring of each of said arms extending therethrough, so that these limbs serve effectively to locate the arms relative to one another.

As described in our aforementioned copending application, each locator spring is conveniently substantially rectangular in configuration, with its shorter sides constituting the limbs, one of the longer sides being the loading portion of the spring, and the other longer side incorporating a formation whereby it locates on thev cross member.

Said formation whereby the spring locates on the cross member may be an eye; and such eye can be formed by oppositely-directed hooks provided on the two ends of a single spring-wire length forming the locator spring.

The said one of the longer sides of the locator spring which provides the loading portion of the spring is conveniently shaped so that only a short central portion engages with the respective edge of the respective contact arm.

The end of each movable contact arm adjacent which the respective movable contact is provided is conveniently shaped to provide a protrusion beneath which engages a lip of the carrier whereby to limit possible movement of the arms under the loading of their springs.

The invention will be described further, by way of example, with reference to the accompanying drawings which illustrate a preferred embodiment thereof, as applied to an electric circuit breaker, it being understood that the following description is illustrative, and not [imitative of the scope of the invention.

In the drawings:

FIG. 1 is a cross-section through a preferred embodiment of electric circuit breaker conforming to the invention showing one contact breaker assembly thereof;

FIG. 2 is a plan view of the contact breaker assembly of FIG. 1;

FIG. 3 is a cross-section on the line 3-3 of FIG. 2; and

FIG. 4 is a cross-section on the line 4-4 of FIG. 2.

The preferred embodiment of the circuit breaker conforming to the invention is a three pole breaker and comprises a generally, rectangular casing (indicated generally at moulded from a suitable electricallyinsulating plastics material the interior of which is divided by appropriate partitions (not shown) to provide three channels (not shown) each of which accommodates a respective contact assembly 1 1. A manual operating mechanism (not shown) of the breaker includes a pivoted lever projecting through a top cover of the casing 10 and connected to the contact assemblies 11 by way of a toggle linkage 12 incorporating a member (not shown) which is supported by a pivoted trip bar (not shown) extending transversely across the three channels. A respective bimetal and electromagnet arrangement (not shown) associated with each contact assembly cooperates with the trip bar to pivot the latter, upon occurrence of a sustained overload (i.e., a sustained passage of current in excess of the rated current of the circuit breaker) or upon occurrence of short circuit conditions (i.e. the passage of a current substantially in excess of the rated current), to release its support and permit collapse of the toggle linkage 12 and thereby trip the breaker.

The contact assemblies 11 in each of the three channels are substantially identical, and therefore it is only necessary to describe on of them in detail.

Such contact assembly 11 comprises, at one end of the channel, a fixed contact block 13 having a fixed contact strip 14 secured to its upper surface so as to extend transversely across the channel. In the other end of the channel is mounted a hinge contact block 15 whose end 16 closest to the fixed contact block 13 has bores 17 at each side thereof each being about three quarters of an inch long and extending transversely of the channel and is shaped on its upper surface to provide a substantially semi-cylindrical upwardly-directed bearing surface 18 disposed so that its axis extends transversely of the channel substantially concentrically of the bores 17.

The bores accommodate respective hinge pins 19 the ends 20, 21 of which protrude from the hinged contact block 15 and serve pivotally to connect, to said hinge contact block 15, an inverted-U-sectioned or invertedchannel-sectioned movable contact arm carrier 22, with the ends 20, 21 of the rod 19 engaging into apertures 23, 24 in

respective side walls

25, 26 of said carrier 22.

The carrier 22, which is connected to the toggle linkage 12, serves to carry a plurality of parallel movable contact arms 27 which, in the closed condition of the breaker illustrated in FIG. 1, extend from the hinge contact block 15 to just above the fixed contact block 13, so that movable contacts 28 carried by each of said arms 27 engage with a respective location on the fixed contact strip 14 on the fixed contact block 13.

There are 13 of said movable contact arms 27 of which the middle one 27a (see FIG. 4) is an arcing contact arm which is longer than the rest, has its own movable arcingcontact 29 offset relative to the others, and is spring loaded downwards relative to the carrier 22 by an independent helical spring 30 set into the carrier 22. Each of such movable contact arms 27 is in the form of a metal pressing, of copper strip, for example of approximately three-sixteenths of an inch in thickness, generally rectangular in configuration, and having the respective movable contact 28 secured to one edge thereof, adjacent to one end, e.g. by high speed brazing. Adjacent to the other end, each such strip has a V- shaped notch 31 cut therein, from the same edge, whereby the arm 27 locates on and makes electrical contact with the bearing surface 18 of the hinge contact block 15. The fact that the movable contacts 28 can be secured to their respective arms 27 by high speed brazing has the advantage that it can be effected without causing the material of the arm 27 to anneal and become soft. Any softening of the movable contact arms 27 is to be avoided, of course, since impacts of substantial force occur in the operation of the breaker, and this would cause distortion of the arms 27.

About midway along the length of the carrier 22 a cross member 32 thereof extends transversely across the carrier 22 between the

side walls

25, 26 thereof at a level below the lower edges of the contact arms 27, which lower edges are, of course, the edges in which the V-shaped notches 31 are provided and on which the fixed contacts 28 are secured. The arms 27 are mounted in the carrier 22 by way of respective locator springs 33 which engage with the upper edges of the respective contact arms 27 and locate on the cross member 32.

Each such locator spring 33 (FIGS. 3 and 4) is made from a length of strong spring wire bent to a substantially rectangular configuration. One of the longer sides thereof is a loading portion 34 which is slightly bowed along its length and provides a linear middle section 35 which abuts against a part of the upper edge of the respective contact arm 27. The two shorter sides of the spring constitute

guide limbs

36, 37 which extends across the respective contact arm 27, one against each side of the contact arm 27 and join with the other longitudinal side of the spring which is provided with a formation 39 is provided by the ends of the length of wire, which ends are curved to form oppositely directed hooks 40, ill which together form an eye around the cross member 32.

Each said one end of each contact arm 27 is formed with a protrusion 42 which engages with a lip 43 on the carrier 22 to limit movement of the arm 27 under the influence of its spring 33.

It will be appreciated that the circuit breaker effectively operates in the same way as prior known comparable constructions of breaker. With the operating handle in the on position, the toggle linkage 12 is extended to press the carriers 22 downwards, so that the movable contacts 28 all engage the fixed contact strip 14 and are loaded thereagainst by their respective locator springs 33.

The moving contact arms 27 in the contact assembly of each pole serve to divide the current passing in said pole, with the consequent advantage of reduced blowoff force (as already discussed herein) at the contacts so that the force necessary to hold the moving contacts 29 in adequate engagement with the fixed contact strip 14 is substantially less than in the case where each pole has a smaller number of contact arms 27 and respective movable contacts 28, and the components of the circuit breaker can be of lesser dimensions and strength than in the latter instance.

Upon occurrence of a sustained overload or short circuit (as above explained) the toggle 12 is broken, the carriers 27 are displaced away from the fixed contacts 14 to open the circuits through the circuit breaker, and the handle is moved to the tripped position.

Because the arms each locate by their respective V- shaped notches 31 on the bearing surface 18 of the hinge contact block 15, there are two contact surfaces between each said arm 27 and the bearing surface 18, and blow-off forces acting upon the arm 27 at said contact surfaces are at an angle to one another corresponding to the angle between the sides of the vees of the notches 31. The horizontal components of such forces, of course, substantially counteract one another. The vertical components thereof, however, combine and tend to lift the arm 27 from the bearing surface 18, and the magnitude thereof is a function of the angle between the sides of the vee of the notch 31. Since the arcing contact arm 27a is subject to substantially greater blow-off forces at its contact surfaces than the other contact arms 27, the angle of the walls of its notch 31 can be made sufficiently greater than that of the other arms 17 so that the combined vertical components of the blow-off force tending to lift such arcing contact arm 27a from the bearing surface 18 either approximates to that which occurs on the other arms 27 or is sufficiently small to enable actual lifting of the arm 27a to be resisted by the spring loading of the arm 27a.

Each contact arm 27 has a braid 45 welded thereto adjacent its said other end and a loop 46 of the braid 45 is attached to the hinge contact block by means of a screw 47. Screws 47 also fasten a length of L-section angle iron 48 to the hinge contact block 15. This angle iron has its longer free ends 49 extending beneath the arms 27. The braid 45 diverts some current from the edges of the notches 31 and so reduces the blow-off force at surface 18. The angle iron 48 tends to attract the contact arms 27 when current is flowing therein and so tends to oppose the blow-off forces. These features enable lower strength spring loading of the contact arms.

The circuit breaker may be constructed with components of lesser dimensions and/or strength than has hitherto been necessary and also has other advantages. Thus, the arrangement of springs 33 providing for one

limb

36, 37 thereof alongside each side of the respective contact arm 27 achieves proper location of the contact arms 27 relative to one another, so that they lie side-by-side in parallel disposition in a very simple and convenient manner which is easy to assemble. Furthermore, the form of the contact arm 27 is such that they can be manufactured readily and relatively inexpensively by simple pressing operations as compared with the expensive castings or extruded sections which have hitherto been conventionally employed for movable contact arms.

it is to be understood that the invention is not confined to the precise details of the foregoing example, and variations may be made to these details without dcparting from the scope of the invention. Thus, for example, the contact arrangement 1 l of the invention can be employed in an electrical isolator, the construction being such as to provide two opposed carriers 22 with their contact arms 27 facing one another to provide therebetween a gap for accommodating a withdrawable conductor leading, for example, to an electrical component, the arrangement being such that relative movement between the contact arms 27 and the conductor is possible for withdrawing the latter to isolate the electrical component.

What we claim is:

1. An electric circuit breaker or isolator which has, for the or each pole thereof, a respective moving contact assembly comprising: a plurality of parallelconnected movable contact arms each carrying a respective movable contact engageable with a fixed contact, the contact arms being of strip metal and being resiliently mounted side-by-side and substantially parallel to each other in a carrier, each contact arm having a V-shaped notch adjacent one end for locating onto an arcuate surface provided by a fixed hinge contact block to which the carrier is hingedly connected, electrical continuity being provided between the contact arms and the contact block by direct contact therebetween, one of the contact arms being an arcing contact arm, the angle of the V-shaped notch therein being different from that of the other arms.

2. A circuit breaker as claimed in claim 1, each of the contact arms being mounted in the carrier by a respective locator spring shaped to provide a loading portion which engages one longitudinal edge of the contact arm and a pair of limbs extending across the contact arm one adjacent each side thereof and which locates on a cross member, extending transversely of the arms, of

the carrier, adjacent the other longitudinal edge of the contact arm.

3. A circuit breaker as claimed in claim 2, each locator spring being substantially rectangular in configuration, with its shorter sides constituting the limbs, one of spective contact arm. it}.

6. A circuit breaker as claimed in claim 1, a length of L-section angle iron being attached to the hinge contact block and one web thereof extending below the contact arms so that when current is passing through the arms a magnetic attractive force is set up tending to draw the arms towards the one web and thus the notches into better contact with the arcuate surface.

7. A circuit breaker as claimed in claim 6, the angle iron being attached to the hinge block by screws, braid being sandwiched between the other web of the angle iron and the hinge contact block so as also to be attached thereto by the screws.

Claims

1. An electric circuit breaker or isolator which has, for the or each pole thereof, a respective moving contact assembly comprising: a plurality of parallel-connected movable contact arms each carrying a respective movable contact engageable with a fixed contact, the contact arms being of strip metal and being resiliently mounted side-by-side and substantially parallel to each other in a carrier, each contact arm having a V-shaped notch adjacent one end for locating onto an arcuate surface provided by a fixed hinge contact block to which the carrier is hingedly connected, electrical continuity being provided between the contact arms and the contact block by direct contact therebetween, one of the contact arms being an arcing contact arm, the angle of the V-shaped notch therein being different from that of the other arms.

2. A circuit breaker as claimed in claim 1, each of the contact arms being mounted in the carrier by a respective locator spring shaped to provide a loading portion which engages one longitudinal edge of the contact arm and a pair of limbs extending across the contact arm one adjacent each side thereof and which locates on a cross member, extending transversely of the arms, of the carrier, adjacent the other longitudinal edge of the contact arm.

3. A circuit breaker as claimed in claim 2, each locator spring being substantially rectangular in configuration, with its shorter sides constituting the limbs, one of the longer sides being the loading portion of the spring, and the other longer side incorporating a formation whereby it locates on the cross member.

4. A circuit breaker as claimed in claim 3, the formation being an eye formed by oppositely-directed hooks provided on the two ends of a single spring wire length forming the locator spring.

5. A circuit breaker as claimed in claim 3, the said one longer side being shaped so that only a short central portion engages with the respective edge of the respective contact arm.