GB2059159A

GB2059159A - Electric circuit breaker

Info

Publication number: GB2059159A
Application number: GB7931886A
Authority: GB
Original assignee: Dorman Smith Switchgear Ltd; Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Current assignee: Dorman Smith Switchgear Ltd; Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Priority date: 1979-09-14
Filing date: 1979-09-14
Publication date: 1981-04-15
Also published as: GB2059159B

Abstract

The electromagnetic tripping arrangement of an circuit breaker comprises, for each pole, a yoke 60, through which the conductor strip 20 extends, and an armature 63 whose end cooperates with a trip bar 47 to trip the breaker upon pivoting of said armature 63 on the passage of short-circuit current. The armature 63 is loaded by a spring 68 one end of which is connected to the armature 63 at a point offset from the armature pivot 64 and the other end of which is hooked over a setting screw 76 in a cradle 73 movably carried by a setting adjustment lever 70 whose pivotal axis coincides with the point of connection of the spring 68 with the armature 63. The lever 70 may be adjusted about its pivot by rotation of a spindle 87. The high setting is set by the spacing of the cradle 73 from the pivotal axis of the lever 70 and the low setting is adjusted by turning the screw 76. <IMAGE>

Description

SPECIFICATION Electric circuit breaker This invention concerns electric circuit breakers of the type comprising an electromagnetic armature adapted, upon passage of a short-circuit current, to be swung against the bias of a spring, out of a rest position to initiate tripping of the circuit breaker, thereby to result in an opening of contacts of the circuit breaker of all of the poles of the circuit breaker.

Constructions of circuit breaker of this type are already known and it is general in such known circuit breakers to provide for the possibility of varying the action of the spring by increasing and decreasing the stress of the spring, thereby to adjust the magnitude of the spring bias which has to be overcome to achieve tripping and consequently to set the current at which the circuit breaker will trip. Hitherto, it has not been possible in known constructions of multipole circuit breakers, to adjust the settings of the poles simultaneously in a simple manner and it is an object of the present invention to provide an improved circuit breaker wherein provision is made for adjusting the bias of the spring in a simple manner and, when the circuit breaker includes a plurality of poles, for adjusting the settings of the poles simultaneously.

With this object in view the present invention provides an electric circuit breaker including an electromagnetic armature adapted, upon passage of short-circuit current, to pivot against the bias of a spring out of a rest position to initiate tripping of the circuit breaker, characterised in that one end of the spring is connected to the armature at a point offset from the pivotal axis of the armature and the other end of the spring is connected to an adjustment member which is so pivotally mounted that the line of action of the spring relative to the pivotal axis of the armature can be adjusted, the pivotal axis of said adjustment member being coincident with said point at which the said one of the spring is connected to the armature.

The arrangement is such that the spring bias can be varied by swinging the adjustment member, thereby to adjust the perpendicular distance between the line of action of the spring and the pivotal axis of the armature and consequently to set the magnitude of the turning moment which has to be applied to the armature to cause it to pivot against the action of the spring. Accordingly, the adjustment can be achieved without varying the overall length of the spring in any way whatsoever.

The circuit breaker of the present invention has the important advantages that the limits of its range of magnetic element tripping current can be acuratly set in the factory enabling the circuit breaker after installation to be set to trip at any current lying within an accurately defined range and that when the circuit breaker includes a plurality of poles, the settings of the poles can be adjusted simultaneously.

Preferably the adjustment member comprises a lever which is pivotally mounted at one end and which has, at its other end, means to which the spring is anchored.

Variation of the stress imposed by the spring.can be effected by varying its effective length and for this purpose preferably the anchoring means of the spring comprises a cradle so carried by the lever at or adjacent its free end that the cradle is adjustable towards and away from the pivotal axis of the lever.

As will later be appreciated, such an arrangement can provide for a particularly simple and convenient way of adjusting the high limit of the spring bias on the armature.

Further, for permitting minor variation of the stress imposed by the spring, the angle at which the line of action of the spring is inclined to the effective centre line of the lever may be adjustable and for this purpose preferably, the end of the spring connected to the cradle carried by the lever conveniently hooks over a screw which is rotatable in the cradle to permit progression along the screw of the point of engagement of the spring on the screw.

The arrangement is preferably such that adjustment of the rating of the circuit breaker can be effected from outside the breaker. This may be achieved, for instance, by means of a linkage or other drive means connected to the lever, the drive means being activated, for example, by rotation of a rod to which access can be had through a hole in a casing of the circuit breaker.

As applied to a multipole circuit breaker (e.g. a three-pole circuit breaker) the arrangement is preferably such that each pole of the breaker has its respective armature, spring and adjustment member, the adjustment members being coupled together to swing in unison. This enables the circuit breaker to be factory set with the range of adjustment of the poles to be identical, so that subsequent rating adjustment can be effected by a single operation which simultaneously adjusts all of the poles.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which Figure 1 is a cross-sectional side elevation illustrating a preferred embodiment of the circuit breaker of the invention, this circuit breaker being a threepole breaker, and the cross-section being taken to show the components present in the middle one of the three poles; and Figure 2 is a plan view, with the cover removed and certain parts cut away, of the circuit breaker of Figure 1.

The illustrated embodiment of the electric circuit breaker of the invention comprises a casing, indicated generally by the reference numeral 10, composed of a base 11 and a cover 12, the latter being removed in the view shown in Figure 2. As will be evident from Figure 2, the interior space of the casing 10 is divided longitudinally by parallel partitions 13 and 14 to define three separate compartments 15, 16 and 17, one for each of the poles of the breaker.

The middle component 16 accommodates a manually-movable toggle 18 and associated operating mechanism which will be described in detail later. Apart from this, each of the compartments 15, 16 and 17 accommodates similar components for carrying its respective current. Thus, each such compartment comprises a respective first terminal 19 from which extends a conductor strip, indicated generally by the numeral 20, which strip 20 serves also as a heater element in the operation of a breaker under certain circumstances, and is of inverted-U form providing limbs 21 and 22.The limb 22 extends into a clamping section 23 which is clamped to the bottom of the base 11 by a bolt 24 and connects buy a flexible braid 25 to a respective moving contact arm 26 having a contacttip 27 which cooperates with a respective fixed contact 28 of a contact bar 29 extending to a respective second terminal 30. Each moving contact arm 26 is mounted by a tongue 31 thereof projecting into a respective mounting capsule 32 and a respective pivot 33, secured in the capsule 32, extending through the tongue 31. A respective spring 34 within the capsule 32 engages the tongue 31 in such a way as to make the moving contact arm 26 bistable.This is achieved by the line of action of the spring 34 being such as to act to one side of the axis of the pivot 33 in the one pivoted position of the arm 26 shown in Figure 1, and to act to the other side of the axis of the pivot 33 upon the arm 26 being pivoted in a ciockwise direction about the pivot 33 to its second pivoted position in which edge 35 of the tongue 31 abuts confronting inner surface 36 of the capsule 32.

The three capsules 32 are coupled with one another through the partitions 13, 14so asto move in unison, and the middle capsule 32 is coupled with a toggle arrangement comprising a lower link 37 which is pivoted at one end to the pivot 33 and which is pivotally connected at 50 by its upper end to an upper link plate 38, the pivotal connection between the lower link 37 and the upper link plate 38 coinciding with an anchor pin 39 by which a dolly spring 40 connects with the toggle arrangement 37, 38. At an upper position thereof, the upper link plate 38 is pivotally secured to a latch plate 41, pivoted at 42 and having a latch nose 43 engaging into a recess 44 in a retainerarm 45 which is pivotally mounted at 46.A common trip bar 47 extends transversely of the circuit breaker, through the partitions 13 and 14, and this has, within the middle compartment 16, an inset retainer plate 48 which serves to tend to retain the retainer arm 45 in its illustrated position with the latch nose 43 located in the recess 44 and the latch plate 41 thereby prevented from pivoting in the anti-clockwise direction, about its pivot 42, from the illustrated position.

The dolly 18 is swingable about a pivot axis (not visible) whose position is near to the axis of the anchor pin 39, and the dolly spring 40 is connected, by its end remote from the anchor pin 39, to the dolly 18.

In the condition of the operating mechanism shown in Figure 1, with the dolly 18 in the "on" position, the toggle composed of the upper link plate 38 and the lower link 37 is effectively in a "straightened" condition with the pivots 50 and 33 and the anchor pin 39 substantially in a straight line. The toggle, under the influence of the dolly spring 40, is accordingly forcing the moving contact arm 26 downwards to ensure firm engagement of the contact tip 27 with the fixed contact 28 to provide electrical continuity between the first and secured terminals 19 and 30.It will be readily understood that if the latch plate 41 should be released from its illustrated position (by the latch nose 43 being allowed to disengage from the recess 44 in the retainer arm 45 upon tripping of the breaker as will later be described), the upper link plate 38 will be caused to move, with swinging of the latch plate 41, under the stress of the dolly spring 40, in an anticlockwise direction. The toggle accordingly collapses, the pivot 50 moving to the other side of the line of action of the dolly spring 40 so that the spring 40 then acts to swing the moving contact arm 26 upwards away from the fixed contact 28 to open the circuit between the terminals 19 and 30. In so swinging, the arm 26 moves through slots in a bank of arc-quenching plates 51.Since all of the moving contact arms 26 are coupled, by way of their capsules 32 to move in unison, they are all pressed against their respective fixed contacts 28 in the illustrated condition ofthe breaker and are all swung away from their respective fixed contacts 28 to open their respective circuits upon the breaker being tripped.

Similar opening of the circuits into which the circuit breaker is connected can be achieved by swinging the dolly 18 in a clockwise direction from the "on" position of Figure 1 towards an "off" position. During this movement, the line of action of the dolly spring 40 passes the pivot 50 and thereupon causes collapse of the toggle, again to cause upward swinging of the moving contact arms 26.

For providing for the circuit breaker to trip upon the passage of a sustained overload (i.e. continued passage of a current in excess of its rated current) through any of its poles, each conductor strip 20 has one end of a respective thermally responsive element, in the form of a bimetal strip 52, fastened to the limb 21 in heat conducting contact therewith.

The other end of each said bimetal strip 52 has therethrough an adjusting screw 53 on the inner end of which is a flexible coupling 54 which serves flexibly to connect a respective push rod 55 to the screw 53. Each such push rod 55 extends through a respective hole 56 in the respective conductor strip 20 and through a respective guide bracket 57 to face a respective thrust surface 58 on a respective tongue 59 for the respective pole, which tongues 59 are integral with the trip bar 47. Accordingly, upon any one of the three bimetal strips 52 becoming heated by a sustained overload passing through its respective conductor strip 20, such bimetal strip 52 deflects to cause the respective push rod 55 to engage the respective tongues 59 and pivot the trip bar 47. This pivoting movement of the trip bar 47 causes the retainer plate 48 to move so as to permit the retainer arm 45 to release the latch plate 41, thereby causing tripping of the breaker as already discussed in detail above.

To provide for the circuit breaker to be caused to trip substantially instantaneously, upon passage of short-circuit current through any one of its poles, each said pole has, associated with its respective conductor strip 20, a respective fixed magnetic circuit provided by a U-shaped soft iron magnetic member 60, the conductor strip 20 extending between the limbs 61,62 of the U. Pacing each said magnetic member 60 is a respective armature 63 which is pivoted at 64 and has respective limbs 65, 66 corresponding to the limbs of the U of the member 60.At its side remote from the limbs 65, 66, the armature 63 is formed as a closed loop and is provided with a respective fastening lug 67 which provides for one end of a respective biassing spring 68 to be connected to the armature 63 at a point offset relative to the swinging axis, provided by the pivot 64, of the armature 63. The three biassing springs 68 are each connected, at their other ends, to respective adjustment members in the form of levers 69,70 and 71 each of which has a respective dovetail sectioned slot 72 extending longitudinally thereof for a short distance from its free end. These slots 72 accommodate respective cradles 73 having respective complementary tongues 74 located within the respective slots 72 and adjustable up and down the respective levers 69, 70, 71 by respective high setting adjustment screws 75.Each cradle 73 has extending thereacross a respective spring anchoring screw 76 over which the respective biassing spring 68 hooks, the arrangement being such that upon rotation of each of said screws 76, the threads thereof cause the hooked-over part of the respective spring 68 to be progressed therealong for low-setting adjustment purposes as will later be described in detail.

The lever 69 is carried on a boss 79 extending through and journalled in the partition 14, the boss 79 connecting with an upwardly projecting adjusting arm 80 disposed within the middle compartment 16.

This arm 80 is connected, by a crosspiece 81, with the lever 70 which in turn is carried on a respective boss 82 extending through and journalled in the partition 13. This boss 82 also has the lever 71 mounted thereon, so that the three levers 69,70,71 swing in unison. The pivotal axes of the bosses 79 and 82 are in alignment and are coincident with the points of connection of the biassing springs 68 with the respective fastening lugs 67 of their respective armatures 63. Thus, rotation of the assembly of levers 69,70,71 about their common pivotal axis does not result in an extension of the springs 68 and there is no tendency for the levers to return to a particular angular position under spring action when rotationally displaced.The adjusting arm 80 is connected buy a pivot 83 to a coupling link 84 which in turn is connected by a pivot 85 to a radial arm 86 provided on an upright adjusting spindle 87 which is mounted in place by a bridge piece 88 extending across the middle compartment 16 and which has a slotted head 89 accessible through a hole 90 in the cover 12 at a position away from an escutcheon 91, through which the dolly 18 projects, formed on the cover. Rotation of the adjusting spindle 87 enables the levers 69,70 and 71 to be swung through an angle of approximately 90 from the position illustrated in full lines in Figure 1, to that shown in dotted lines in the same figure.

Upon passage of short-circuit current through one or the other of the conductor strips 20, the respective magnetic member 60 is energised. As a result, the corresponding armature 63 is attracted thereby and is caused to pivot into the position shown in dotted lines in Figure 1. Upon the occurrence of this movement, the extremity of the loop of the armature engages a respective complementary protrusion 92 on the trip bar 47 to cause breaker-tripping pivotal movement of the trip bar 47, the tripping occurring as has already been described in detail.

For initial factory setting of the circuit breaker, firstly the adjusting spindle 87 is rotated to swing the levers 69,70,71 to the dotted line disposition shown in Figure 1. As this is done, the lengths of the springs 68 do not alter in any way, because the swinging axes of the levers 69,70,71 are coincident with the axes of the points of connection of the springs 68 with their respective armatures 63, so the only work required to be done is that necessary to overcome friction. However, the bias of the springs 68 is at a maximum, because they have been brought into dispositions wherein the perpendicular distance between the lines of action of said springs 68 and the axes of the pivots 64 of the armatures 63 is a maximum.The lengths of the springs 68 are then set by means of the high setting adjusting screws 75 on each of the levers 69,70 and 71 in turn, so that in each case tripping occurs at a desired high current value.

The adjusting spindle 87 is now rotated to swing the levers 69, 70 and 71 back to the illustrated full line position in Figure 1, in which the perpendicular distance between the lines of action of the springs 68 and the axes of the pivots 64 is minimum. Thereupon, the low value at which the breaker is to trip is set, in each pole, by means of the spring anchoring screws 76 rotation of which serves to cause slight variation of the angular orientations of the lines of action of the springs. It will readily be understood that this adjustment does not significantly affect the previously-set high adjustment.

The invention is not confined to the precise details of the foregoing example, and variations may be made thereto. Thus, for instance, in the illustrated case the circuit breaker is a three-pole breaker, but the invention can equally well be applied to a single-pole breaker which will, then, correspond generally to that described for the middle pole of the illustrated construction.

Claims

1. An electric circuit breaker including an electromagnetic armature adapted, upon passage of shortcircuit current, to pivot against the bias of a spring out of a rest position to initiate tripping of the circuit breaker, characterised in that one end of the spring is connected to the armature at a point offset from the pivotal axis of the armature and the other end of the spring is connected to an adjustment member which is so pivotally mounted that the line of action of the spring relative to the pivotal axis of the armature can be adjusted, the pivotal axis of said adjustment member being coincident with the said point at which the said one end of the spring is connected to the armature.

2. An electric circuit breaker as claimed in Claim 1, wherein the said adjustment member comprises a lever which is pivoted at one end and which has, at its other end, means to which the spring is anchored.

3. An electric circuit breaker as claimed in Claim 2, wherein the anchoring means comprises a cradle so carried by the lever or at adjacent its free end that the cradle is adjustable towards and away from the pivotal axis of the lever.

4. An electric circuit breaker as claimed in Claim 3, wherein the end of the spring connected to the cradle hooks over a screw which is rotatable in the cradle to permit progression along the screw of the point of engagement of the spring on the screw.

5. An electric circuit breaker as claimed in Claim 2,3 or 4, wherein the lever is adjustable, from outside the breaker, by means of linkage or other drive means connected to the lever.

6. An electric circuit breaker as claimed in any preceding Claim, which is a multipole circuit breaker, each pole of the breaker having an associated armature, spring and adjustment member, the adjustment members ofthe poles being coupled together to pivot in unison.

7. An electric circuit breaker as claimed in Claim 6, comprising a common trip bar which is associated with all of the poles of the breaker and pivotal movement of which, from a respective rest position, initiates tripping of the breaker, each of the armatures being disposed to engage the trip bar and cause itto pivot.

8. An electric circuit breaker substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. An electric circuit breaker as claimed in Claim 7, wherein each pole of the circuit breaker comprises a conductor to which is connected a bimetal element which deflects upon passage of overload current, a push rod connected to the bimetal element extending through an opening in the conductor to cooperate with the trip bar.

9. An electric circuit breaker substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

New claims or amendments to claims filed on 16 September 1980 Superseded claims 1 to 9 New or amended claims:- 1 to 8 CLAIMS

1. A multipole electric circuit breaker including, for each pole, an electro-magnetic armature adapted, upon passage of short-circuit current through the respective pole, to pivot against the bias of a spring out of a rest position to initiate tripping of the circuit breaker, one end of the spring being connected to its armature at a point offset from the pivotal axis of the armature and the other end of the spring being connected to an adjustment member which is so pivotally mounted that the line of action of the spring relative to the pivotal axis of its armature can be adjusted, and the pivotal axis of said adjustment member being coincident with the said point at which the said one end of the spring is connected to its armature, the adjustment members associated with the poles being coupled together for movement in unison.

2. An electric circuit breaker as claimed in claim 1, wherein each said adjustment member comprises a lever which is pivoted at one end and which has, at its other end, means to which its spring is anchored.

3. An electric circuit breaker as claimed in claim 2, wherein the anchoring means comprises a credle so carried by the respective lever at or adjacent its free end that the cradle is adjustable towards and away from the pivotal axis of the lever.

5. An electric circuit breaker as claimed in claim 2,3 or 4, wherein the position of the lever is adjustable, from outside the breaker, by means of linkage of other drive means connected to the lever.

6. An electric circuit breaker as claimed in any preceding claim comprising a common trip bar which is associated with all of the poles of the breaker and pivotal movement of which, from a respective rest position, initiates tripping of the breaker, each of the armatures being disposed to engage the trip bar and cause it to pivot.

7. An electric circuit breaker as claimed in any preceding claim wherein each pole of the circuit breaker comprises a conductor to which is connected a bimetal element which deflects upon passage of overload current, a pack rod connected to the bimetal element extending through an opening in the conductor to cooperate with the trip bar.