GB1564412A

GB1564412A - Electric circuit breakers

Info

Publication number: GB1564412A
Application number: GB3992476A
Authority: GB
Original assignee: Dorman Smith Switchgear Ltd
Current assignee: Dorman Smith Switchgear Ltd
Priority date: 1977-09-15
Filing date: 1977-09-15
Publication date: 1980-04-10

Description

(54) ELECTRIC CIRCUIT BREAKERS (71) We, DORMAN SMITH SWITCHGEAR LIMITED, a British Company, of Atherton Works, Blackpool Road, Preston, Lancashire, 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: This invention concerns electric circuit breakers, which may be single-pole breakers or multi-pole breakers, of the type (hereinafter referred to as "of the type described") comprising, for the or each pole, only a single movable contact arm, the arm or the arms being coupled to a pivoted trip arm by a toggle linkage which is connected, by way of a spring, with a pivoted dolly for movement of the latter in one direction (i.e. the "on" direction) to straighten the toggle linkage and cause contact-closing movement of the movable contact arm or arms, for respective movable contacts carried by the latter to engage with respective fixed contacts, and movement of the dolly in the other direction (i.e. the "off" direction) to collapse the movement of the movable contact arm or toggle linkage to cause contact-opening arms, the trip arm being adapted, upon trip ping of the circuit breaker, to be released from a latched position and to move to an unlatched tripped position wherein the spring collapses the toggle linkage.

It is well known that upon occurrence of very high short-circuit currents in electric circuit breakers, substantial electromagnetic blow-back forces arise in the vicinity of the movable contact arm through which the short-circuit current passes. These forces can be arranged to cause contact-opening movement of the movable contact arm, and various proposals have already been put forward enabling the movable contact arm to move, at least to a limited extent, relative to its mounting, thereby to utilise the blowback phenomenom to ensure rapid contact opening upon tripping of the circuit breaker under short-circuit conditions.

An object of the present invention is to provide a novel movable contact arm mounting arrangement which permits movement of the movable contact arm under the influence of these electromagnetic blow-back forces in a particularly simple and effective manner.

With this object in view the present invention provides an electric circuit breaker of the type described where in the or each movable contact arm is movable, independently of the toggle linkage, between a first or operative stable position relative to said linkage, in which it is relatively displaced towards and resiliently-loaded towards the fixed contact, and a second or blow-back stable position in which it is relatively displaced away from and resiliently-loaded away from the fixed contact, characterised in that said movable contact arm is pivotally carried by a member which carries also a spring which loads said movable contact arm to the one or the other of its said stable positions.

Conveniently the spring is mounted in a recess in the said member and is disposed to act on the movable contact arm in such a disposition that upon swinging of the movable contact arm between its two stable positions, the line of action of the spring passes through an intermediate dead centre position in which it extends through the axis of the pivotal connection of the movable contact arm to the said member.

The pivot connecting the movable contact arm to the said member conveniently also connects the said movable arm to the toggle linkage.

The invention will be described further, by way of example, with reference to the accompanying drawings, which illustrate a preferred embodiment of the circuit breaker, it being understood that the following description is illustrative, and not restrictive, of the scope of the invention. In the drawings:-- Fig. 1 is a fragmentary part-sectional side elevation illustrating those parts of the said preferred embodiment necessary for understanding the invention, the movable contact arm being shown in the "off" or "contacts open" position; Fig. 2 is a view of certain of the parts of the embodiment of Fig. 1, but showing the movable contact arm in the "on" or "contacts closed" position; and Fig. 3 is a view comparable with Fig. 2 but showing the movable contact arm blown back from the Fig. 1 position as a result of passage of a short-circuit current, in the very short period of time which elapses between commencement of said short-circuit current and collapse of the toggle linkage of the circuit breaker as a result of tripping thereof by the short-circuit current.

The drawings illustrate a three-pole circuit breaker, but show only the middle pole thereof. The circuit breaker comprises a moulded plastics casing 10 having a removable cover 11 and shaped internally to define three substantially parallel channels, one for each pole of the breaker, the drawings illustrating only the middle channel. The individual components accommodated in each said channel are substantially similar, and accordingly it will be understood that, except where otherwise explained, the illus- trated components are repeated in each of the channels.

Adjacent one end of the channel, and located so as to be disposed beneath an assembly of arc-quenching plates 12 is a fixed contact 13 of the circuit breaker, this fixed contact 13 being connected by a conductor 14 with a respective terminal 15 to enable it to be connected into a circuit to be protected, by way of a respective electric lead (not shown).

Cooperating with the fixed contact 13 is a movable contact 16 carried at one end of a movable contact arm 17, the other end of which. projects into and is pivotally connected, by a pivot 18, to an approximatelysquare pivoted member 19 which is shaped to define an internal recess 20 into which an extension 21 of the movable contact arm 16 projects. This extension 21 is formed with an arcuate indent 22 into which locates the curved end of a plunger 23 which is surrounded by and loaded by a helical spring 24 the other end of which is located in the recess 20 at a diagonally-opposite corner of the square. It will- thus be understood that the movable contact arm 17 can be swung between a first or .operative stable position disposed towards the fixed contact 13, as shown in Figs. 1 and 2, into which it is loaded resiliently by the spring 24, and a second or blown-back stable position, shown in Fig. 3, shifted relatively away from the fixed contact 13, and into which it is loaded resiliently by the spring 24 (the latter having been swung through a dead centre position, in which its line of action extends directly through the axis of the pivot 18, of the movable contact arm 17) independently of the pivoted member 19, that is to say without the latter moving.

In the operative position of the movable contact arm 17 shown in Figs. 1 and 2, the limit of movement of the arm 17 relative to the pivoted member 19 under the action of the spring 24 is defined by abutment of a lobe 25, integral with the arm 17, with the confronting exterior of the pivoted member 19. Conversely, the limit of movement of the arm 17 into the blown-back position is defined by abutment of an edge of the extension 21 of the arm 17 against the interior of the wall of the pivoted member 19.

The moving contact arm 17 is connected, by a flexible braid 26, to a thermal (or bimetal) trip mechanism (not shown) in which in turn is connected an electromagnetic trip mechanishm (also not shown) and a second thermal (not shown) for connection to a respective electric lead.

The illustrated middle pivoted member 19 of the circuit breaker is formed, at each side, with integral discs 27 located in respective apertures in the walls 28 dividing the interior of the casing 10 into channels as previously described. The pivoted members 19 in the outer channels are connected to the respective discs of the middle channel, so that all the three pivoted members 19 are able to rotate in unison.

The pivoted member 19 in the middle one of the three channels is connected, by its pivot 18 by which its respective moving contact arm is attached, to lower link 29 of a toggle linkage the upper end of the upper link 30 of which is connected by a pivot 31 to a pivoted trip arm (not shown), and centre pivot 32 of which is connected, by a dolly spring 33, to a manually-pivotable dolly (not shown) of the circuit breaker, which dolly projects through a slot in the cover 11 of the casing 10.

The non-illustrated pivoted trip arm is latched into a set position by engaging by its free end under a trip tongue (not shown) projecting from a trip bar (not shown) which extends transversely across the circuit breaker channels and which is adapted, under operation of any of the thermal trip mechanisms (upon passage of sustained overload through the respective pole of the breaker) or of any of the electromagnetic trip mechanism (upon passage of a short-circuit current to pivot so as to withdraw the trip tongue and release the trip arm, as a result of which the toggle linkage is caused to collapse and the movable contact arms 17 are all moved away from their fixed contacts 13 by the dolly spring 33 acting through the link 29 on the pivoted members 19.

The mode of operation of the circuit breaker will readily be understood from the foregoing description. When, as shown in Fig. 2, the dolly is in its "on" position with the dolly spring 33 having caused the toggle linkage 29, 30 to straighten, the toggle linkage 29, 30 holds all of the three movable contact arms 17 resiliently in their "contact closed" positions wherein their moving contacts 16 engage with their fixed contacts 13.

Currents up to the operative rating of the circuit breaker can, then, pass through each of the poles of the circuit breaker uninterruptedly.

In the event of a sustained overload current passing through one or another of the poles of the breaker, such current causes actuation of the thermal tripping mechanism, with the result that the trip lever is unlatched, the toggle linkage 29, 30 collapses, and all of the moving contact arms 17 are swung, by the dolly spring 33 acting through the toggle linkage 29, 30 and the pivoted members 19, to the contact-open positions as shown in Fig. 1. The dolly is simultaneously moved to an intermediate or tripped position by the dolly spring 33.

Resetting is effected by moving the dolly manually into its "off" position to cause the trip lever to be relatched, whereafter movement of the dolly back to the "on" position straightens the toggle linkage 29, 30 as in Fig. 2 and causes the movable contact arms 17 to close their moving contacts 16 against the fixed contacts 13.

In the event, during passage of current through the circuit breaker in the Fig. 2 condition, of passage of a short-circuit current through one of the poles of the breaker, the corresponding electromagnetic tripping mechanism operates to trip the circuit breaker and cause contact-opening movement of the movable contact arms 17, in the same way as has just been described, and resetting is effected similarly, it being understood, of course, that if the fault which caused the short-circuit current (or overload current, as the case may be) has not been rectified, the circuit breaker will trip again as soon as the dolly is moved to the "on" position, or shortly thereafter.

Upon the occurrence of a short-circuit current, not only is the electromagnetic trip mechanism actuated as just described, but also the electromagnetic forces generated in the vicinity of the movable contact arm 17 apply an instantaneous blow-back force to such movable contact arm 17, tending to cause it to perform contact-opening movement even before actuation of the electromagnetic tripping mechanism. Accordingly, with the arrangement as described, the shortcircuit current blows the respective movable contact arm 17 away from its corresponding fixed contact 13 and into the second or blown-back position, as shown in Fig. 3, independently of the toggle linkage, 29, 30, thereby interrupting the flow of such shortcircuit current in the shortest possible time and protecting both the load circuit and the components of the breaker (particularly the u-Jal bimetal strip(s) of the thermal tripping mechanism(s) and the contacts 13, 16 themselves) against damage from such shortcircuit current.

This movement of the respective movable contact arm 17 into the blown-back position occurs, as will be understood, just in advance of the tripping of the breaker. When such tripping occurs, the contact-opening movement of the respective pivoted member 19 will, of course, attempt to swing the blownback moving contact arm past its blown-back position. As shown in the drawings, an appropriate abutment 34 is provided, for each of the movable contact arm 17, so that when the tripping occurs the movable contact arm 17 is arrested whilst the pivoted member 19 moves, thereby restoring the movable contact arm to its first position relative to the pivot member, as illustrated in Fig. 1, ready for resetting the circuit breaker.

It is to be understood that the preceding description serves only to illustrate one form the arrangement of the present invention may take, and that variations may be made to the described details, without departing from the scope of the following claims.

WHAT WE CLAIM IS:- 1. An electric circuit breaker of the type described wherein the or each movable contact arm is movable, independently of the toggle linkage, between a first or operative stable position relative to said linkage, in which it is relatively displaced towards and resiliently-loaded towards the fixed contact, and a second or blown-back stable position in which it is relatively displaced away from and resiliently-loaded away from the fixed contact, characterised in that said movable contact arm is pivotally carried by a member which carries also a spring which loads said movable contact arm to the one or the other of its said stable positions.

2. An electric circuit breaker as claimed in claim 1 wherein the spring is mounted in a recess in the said member and is disposed to act on the movable contact arm in such a disposition that upon swinging of the movable contact arm between its two stable positions, the line of action of the spring passes through an intermediate dead centre position in which it extends through the axis of the pivotal connection of the movable contact arm to the said member.

3. An electric circuit breaker as claimed in claim 2 wherein the spring acts upon an extension of the movable contact arm, which extension projects into the recess.

4. An electric circuit breaker as claimed in claim 2 or 3 wherein the spring acts upon a plunger which engages in a com

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Fig. 2, the dolly is in its "on" position with the dolly spring 33 having caused the toggle linkage 29, 30 to straighten, the toggle linkage 29, 30 holds all of the three movable contact arms 17 resiliently in their "contact closed" positions wherein their moving contacts 16 engage with their fixed contacts 13. Currents up to the operative rating of the circuit breaker can, then, pass through each of the poles of the circuit breaker uninterruptedly. In the event of a sustained overload current passing through one or another of the poles of the breaker, such current causes actuation of the thermal tripping mechanism, with the result that the trip lever is unlatched, the toggle linkage 29, 30 collapses, and all of the moving contact arms 17 are swung, by the dolly spring 33 acting through the toggle linkage 29, 30 and the pivoted members 19, to the contact-open positions as shown in Fig. 1. The dolly is simultaneously moved to an intermediate or tripped position by the dolly spring 33. Resetting is effected by moving the dolly manually into its "off" position to cause the trip lever to be relatched, whereafter movement of the dolly back to the "on" position straightens the toggle linkage 29, 30 as in Fig. 2 and causes the movable contact arms 17 to close their moving contacts 16 against the fixed contacts 13. In the event, during passage of current through the circuit breaker in the Fig. 2 condition, of passage of a short-circuit current through one of the poles of the breaker, the corresponding electromagnetic tripping mechanism operates to trip the circuit breaker and cause contact-opening movement of the movable contact arms 17, in the same way as has just been described, and resetting is effected similarly, it being understood, of course, that if the fault which caused the short-circuit current (or overload current, as the case may be) has not been rectified, the circuit breaker will trip again as soon as the dolly is moved to the "on" position, or shortly thereafter. Upon the occurrence of a short-circuit current, not only is the electromagnetic trip mechanism actuated as just described, but also the electromagnetic forces generated in the vicinity of the movable contact arm 17 apply an instantaneous blow-back force to such movable contact arm 17, tending to cause it to perform contact-opening movement even before actuation of the electromagnetic tripping mechanism. Accordingly, with the arrangement as described, the shortcircuit current blows the respective movable contact arm 17 away from its corresponding fixed contact 13 and into the second or blown-back position, as shown in Fig. 3, independently of the toggle linkage, 29, 30, thereby interrupting the flow of such shortcircuit current in the shortest possible time and protecting both the load circuit and the components of the breaker (particularly the u-Jal bimetal strip(s) of the thermal tripping mechanism(s) and the contacts 13, 16 themselves) against damage from such shortcircuit current. This movement of the respective movable contact arm 17 into the blown-back position occurs, as will be understood, just in advance of the tripping of the breaker. When such tripping occurs, the contact-opening movement of the respective pivoted member 19 will, of course, attempt to swing the blownback moving contact arm past its blown-back position. As shown in the drawings, an appropriate abutment 34 is provided, for each of the movable contact arm 17, so that when the tripping occurs the movable contact arm 17 is arrested whilst the pivoted member 19 moves, thereby restoring the movable contact arm to its first position relative to the pivot member, as illustrated in Fig. 1, ready for resetting the circuit breaker. It is to be understood that the preceding description serves only to illustrate one form the arrangement of the present invention may take, and that variations may be made to the described details, without departing from the scope of the following claims. WHAT WE CLAIM IS:-

1. An electric circuit breaker of the type described wherein the or each movable contact arm is movable, independently of the toggle linkage, between a first or operative stable position relative to said linkage, in which it is relatively displaced towards and resiliently-loaded towards the fixed contact, and a second or blown-back stable position in which it is relatively displaced away from and resiliently-loaded away from the fixed contact, characterised in that said movable contact arm is pivotally carried by a member which carries also a spring which loads said movable contact arm to the one or the other of its said stable positions.

plementary niche in the movable contact arm, or its extension.

5. An electric circuit breaker as claimed in any preceding claim wherein the pivotal connection of the movable contact arm to the said member serves also to couple the toggle linkage to said member, which is thus displaceable by the toggle linkage.

6. An electric circuit breaker as claimed in claim 5 wherein the said member is rotatable.

7. An electric circuit breaker as claimed in any preceding claim wherein a lobe on the movable contact arm engages with the said member to define the limit of movement of the movable contact arm towards its first or operative position.

8. An electric circuit breaker as claimed in any preceding claim wherein an edge of the movable contact arm abuts the said member to define the limit of movement of the movable contact arm in the blown-back position.

9. An electric circuit breaker as claimed in any preceding claim further including an abutment disposed to be encountered by the movable contact arm, in its blown-back position, upon tripping operation of the circuit breaker and corresponding movement of the said member, to restore the movable contact arm to its first or operative position.

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