GB2114371A - An electric circuit breaker - Google Patents

Abstract

In a miniature electric circuit breaker, the electromagnetic device which, on passage of a short circuit current, initiates the tripping operation, comprises a stationary yoke 11 with a planar surface and an associated conductor 16 inter-connected between the breaker terminals, a flat magnetisable flapper armature 25 pivotable about an axis parallel to the conductor between a first position and a second position in which it is inter-facial contact with the planar surface of the yoke, a spring 26 urging the flapper to the first position, and a trip mechanism 27, 28 operatively coupled to the flapper. On passage of a short circuit current, magnetisation of the yoke 11 causes the flapper armature 25 to pivot against the action of the spring 26 into inter-facial contact with the yoke and thereby to effect disengagement of the trip mechanism 27, 28 and initiate operation of the breaker. <IMAGE>

Description

SPECIFICATION An improved electric circuit breaker This invention relates to electric circuit breakers of the kind which include an electromagnetic device which, on passage of a short circuit current through the circuit breaker, initiates the tripping operation of the circuit breaker and which also include a thermal element which becomes heated upon passage of a current through the circuit breaker and which, upon occurrence of sustained overload (i.e. sustained passage of current in excess of the rated capacity of the breaker) initiates the tripping operation of the circuit breaker. Electric circuit breakers of this kind.

will hereinafter, for convenience, be referred to as "electric circuit breakers of the kind described".

The 15th Edition of the l.E.E. Wiring Regulations requires that Type 3 electric circuit breakers of the kind described in accordance with British Standard Specification No. 3871, Part 1, 1965 shall trip electromagnetically on passage of a short circuit current that is seven to ten times the rated current of the circuit breaker.

It is an object of the present invention to provide an improved electric circuit breaker of the kind described which meets the requirements of the 15th Edition of the l.E.E. Wiring Regulations.

According to the invention, in the improved electric circuit breaker, the electromagnetic device comprises a stationary yoke which has a planar surface and an associated electric conductor interconnected between the terminals of the circuit breaker; a substantially flat magnetisable flapper which is pivotable about an axis laying in a plane substantially parallel to said planar surface of the yoke between a first position and a second position in which the flapper is in inter-facial contact with said planar surface of the yoke; spring means urging the flapper to said first position; and a trip mechanism operatively coupled to the flapper, the arrangement being such that, in the event of passage of a current of at least a predetermined value, resultant magnetisation of the stationary yoke causes the flapper to pivot against the action of said spring means into interfacial contact with the yoke and thereby to effect disengagement of said trip mechanism and initiate operation of the circuit breaker.

Preferably, the pivotal axis of the magnetisable flapper is substantially normal to the pivotal axis of the dolly of the circuit breaker.

The short circuit current at which operation of the circuit breaker will be initiated by the electromagnetic device is in part determined by the cross-sectional area of the magnetisable flapper, the larger the area of the flapper the lower the short circuit current at which the circuit breaker will trip electromagnetically; thus, the rating of an improved circuit breaker can be arranged to be of any value within a limited range by employing a flapper of an appropriate area.

In its preferred form, the stationary yoke is substantially rectangular in shape and comprises two transversely spaced substantially rigid elongate side portions which are arranged with planar surfaces of the side portions lying in a substantially common plane and which define between them a channelled portion which is integral with the side portions and along which extends the associated electric conductor.

The trip mechanism preferably comprises a trip gate which is pivotable about an axis substantially normal to the pivotal axis of the flapper and parallel to the pivotal axis of the dolly between a first position in which the trip gate is retained by a trip catch engaging the trip gate and a second position in which the trip catch is disengaged from the trip gate against the action of the main spring of the circuit breaker to initiate operation of the circuit breaker.

Preferably, the spring means urging the flapper to said first position is a leaf spring secured to the trip gate and bearing against a part of the flapper, the arrangement being such that when the flapper is caused to pivot to said second position in the event of passage of a current of at least a predetermined value, the flapper, in pivoting against the action of said leaf spring, causes the trip gate to pivot about its pivotal axis to disengage from the trip catch and thereby initiate operation of the circuit breaker.

Operative coupling between the flapper and the trip gate is preferably provided by arranging for a shuttle, carried by the trip gate, to overlie an edge of the flapper and to have a recess in which loosely engages a lug projecting from the flapper, the looseness of the engagement being such that, during initial pivotal movement of the flapper, no consequential pivotal movement of the trip gate occurs and that, during further pivotal movement of the flapper to bring it into interfacial contact with the yoke, the lug projecting from the flapper pulls the shuttle towards the yoke thereby causing the trip gate to pivot about its pivotal axis and actuate the trip mechanism.

Preferably, the trip mechanism is also operatively coupled to the thermal element of the circuit breaker, which thermal element upon occurrence of a sustained overload of a predetermined value in excess of the rated capacity of the circuit breaker, effects disengagement of the trip mechanism and initiates operation of the circuit breaker.The thermal element preferably comprises a bimetallic elongate member which is secured at or near one of its ends to the trip gate and which, at the other of its ends, is urged towards an adjustable stop under the action of the leaf spring, the arrangement being such that, in the event of a a sustained overload of a predetermined value in excess of the rated capacity of the circuit breaker, the elongate thermal element deflects and causes the trip gate to pivot about its pivotal axis to disengage from the trip catch against the action of the main spring and thereby initiate operation of the circuit breaker.

Preferably, also, the trip catch engages in a window in, and is electrically insulated from, the trip gate. To effect electrical isolation of the trip catch with respect to the trip gate, at least the boundary wall of the window in the trip gate may be made of or may be coated with electrically insulating material but, with a view to reducing wear of the trip gate arising from operation of the circuit breaker, preferably a bushing of resilient metal having a coating of electrically insulating material on one or each of its faces, or of plastics insulating material, is detachably engaged in the window in the trip gate.

The trip gate preferably has at or near its pivotal axis a projection which protrudes through a hole in one side wall of the housing of the circuit breaker, and the shuttle, carried by the trip gate, is accessible through a hole in the other side wall of the housing and has a recess for reception of the protruding projection on the trip gate of an adjacent circuit breaker, the arrangement being such that two or more circuit breakers mounted side by side can be so operatively interconnected by means of interengagement of the protruding projection of the trip gate and the recess of the shuttle, that operation of one circuit breaker will initiate operation of the adjacent circuit breaker or circuit breakers.

The circuit breaker may also include, adjacent the fixed and moving contacts, supplementary sacrificial plates which are so shaped as to encourage formation of an arc between the sacrificial plates when operation of the circuit breaker effects disengagement of the moving contact from the fixed contact, thereby reducing wear of the fixed moving contacts.

The sacrificial plate associated with the moving contact is preferably electrically connected to the conductor associated with the stationary yoke via a low resistance current path.

The invention is further illustrated by a description, by way of example, of a preferred form of the improved circuit breaker with reference to the accompanying drawings, in which: Figure 1 is a side view of the circuit breaker with a sidewall of the circuit breaker omitted, the circuit breaker being shown in the tripped position; Figure2 is a fragmental sectional view of the circuit breaker taken on the line II - II in Figure 1 and showing the circuit breaker in inter-engagement with an adjacent circuit breaker; Figure 3 is a fragmental sectional view of the circuit breaker taken on the line III - III in Figure 1;; Figure 4 is a sectional view of the circuit breaker taken on the line IV - IV in Figure 1 but with the circuit breaker in the "on" position with the trip gate lying parallel to the stationary yoke, and Figure 5 is a sectional view of the circuit breaker taken on the line IV - IV in Figure 1 but with the trip gate and flapper omitted.

Referring to the drawings, the circuit breaker comprises a housing 1 of electrically insulating material in which is mounted a fixed contact 7, which is electrically connected to a terminal 6 protruding from one end of the housing, and a moving contact 8 operatively coupled to a link 4 having an associated main spring 5. The link4 is inter-connected by a link pin 3 to a dolly 2 which protrudes from a minor side wall of the housing 1. A dolly re-set spring 9 engages between the arm of the moving contact 8 and the inner end of the dolly 2.Positioned in the housing 1 remote from the fixed and moving contacts 7 and 8 is a stationary yoke 11 which is substantially rectangular in shape and which comprises two transversely spaced rigid elongate side portions 12 arranged with planar surfaces of the portions lying in a common plane and defining between them a channelled portion 13 which is integral with the side portions.Asupplementarysacrificial plate 17 is associated with the fixed contact 7 and a supplementary sacrificial plate 18 is associated with the moving contact 8 and is electrically connected to a low resistance path 15 of which an elongate member 16 lying in the channelled portion 13 between the side portions 12 of the yoke 11 constitutes a conductor associated with the yoke, the elongate member 16 being electrically connected to a terminal 10 protruding from the other end of the housing 1.

Aflat magnetisable flapper 25 is pivotable about an axis which is normal to the pivotal axis of the dolly 2 and which lies in a plane parallel to the common plane of the planar surfaces of the side portions 12 of the yoke 11. Pivotal mounting of the flapper 25 is effected by a lug 22, integral with one of the side portions 12 of the yoke 11 engaging in a hole 23 in the flapper and a clevis 24, at one end of the flapper, engaging with a bracket 36 integral with the side portion. The flapper 25 is pivotable between a first position and a second position in which the flapper is in inter-facial contact with the planar surfaces of the yoke 11 to form a closed magnetisable loop.A leaf spring 26 secured at one of its ends to a trip gate 27 urges the flapper 25 towards the first position, the free end of the leaf spring bearing against, and being electrically insulated with respect to the flapper by, a layer 20 of electrically insulating material.

The trip gate 27 is pivotable about an axis normal to the pivotal axis of the flapper 25 and parallel to the pivotal axis of the dolly 2 by means of lugs 33 engaging in recesses 34 in the side walls of the housing 1, between a first position in which the trip gate is retained by a trip catch 28 engaging in a window 29 in the trip gate and in which the link 4 rests on a shoulder 21 on the trip catch and a second position in which the trip catch is disengaged from the window 29 against the action of the spring.5 to initiate operation of the circuit breaker. The part of the trip catch 28 engaging in the window 29 in the trip gate 27 is electrically insulated from the trip gate by a bushing 39 of plastics insulating material detachably engaged in the window.

Operative coupling between the flapper 25 and the trip gate 27 is provided by a shuttle 30, carried by the trip gate, which overlies an edge of the flapper and has a recess 31 in which loosely engages a lug 32 projecting from the flapper. The looseness of the engagement of the lug 32 in the recess 31 is such that, during initial pivotal movement of the flapper 25, no consequential pivotal movement of the trip gate 27 occurs and that, during further pivotal movement of the flapper to bring it into inter-facial contact with the yoke 11, the lug 32 pulls the shuttle 30 towards the yoke thereby causing the trip gate 27 to pivot about its pivotal axis, disengage from the trip catch 28 and actuate the trip mechanism.

The trip mechanism is also operatively coupled to the thermal element of the circuit breaker, which thermal element comprises a bi-metallic elongate member 35 which is secured at one of its ends to the trip gate 27 and which, at the other of its ends is urged under the action of the leaf spring 26 towards an adjustable stop 37 carried by the bracket 36. In the event of a sustained overload of a predetermined value in excess of the rated capacity of the circuit breaker, the elongate thermal element 35 deflects and causes the trip gate 27 to pivot about its pivotal axis to disengage from the trip catch 28 and thereby initiate operation of the circuit breaker.

Near its pivotal axis, the trip gate 27 has a projection 41 which protrudes through a hole 40 in one side wall of the housing 1 and the shuttle 30, carried by the trip gate, is accessible through a hole 43 in the other side wall of the housing and has a recess 44 for reception of the protruding projection 41 on the trip gate of an adjacent circuit breaker. In this way, two or more circuit breakers mounted side by side can be so operatively inter-connected by means of inter-engagement of the protruding projection 41 of the trip gate 27 and the recess 44 of the shuttle 30, that operation of one circuit breaker will initiate operation of the adjacent circuit breaker or circuit breakers.

In the event of passage of a current of at least a predetermined value, the flapper 25 is caused to pivot to its second position and, in pivoting against the action of the leaf spring 26, it causes the trip gate 27 to pivot about its pivotal axis to disengage from the trip catch 28 and thereby initiate operation of the circuit breaker.

The supplementary sacrificial plates 17 and 18 encourage formation of an arc between the sacrificial plates when operation of the circuit breaker effects disengagement of the moving contact 8 from the fixed contact 7, thereby reducing wear of the fixed and moving contacts.

The improved circuit breaker of the present invention has the further important advantage that it is assembled from substantially fewer component parts than comparable circuit breakers hitherto proposed and used.

Claims (15)

1. An electric circuit breaker of the kind described, wherein the electromagnetic device comprises a stationary yoke which has a planar surface and an associated electrical conductor interconnected between the terminals of the circuit breaker; a substantially flat magnetisable flapper which is pivotable about an axis lying in a plane substantially parallel to said planar surface of the yoke between a first position and a second position in which the flapper is in inter-facial contact with said planar surface of the yoke; spring means urging the flapper to said first position; and a trip mechanism operatively coupled to the flapper, the arrangement being such that, in the event of passage of a current of at least a predetermined value, resultant magnetisation of the stationary yoke causes the flapper to pivot against the action of said spring means into inter-facial contact with the yoke and thereby to effect disengagement of said trip mechanism and initiate operation of the circuit breaker.

2. An electric circuit breaker of the kind described, wherein the electromagnetic device comprises a stationary yoke and an associated electric conductor inter-connected between the terminals of the circuit breaker, which yoke is substantially rectangular in shape and comprises two transversely spaced substantially rigid elongate side portions which are arranged with planar surfaces of the side portions lying in a substantially common plane and which define between them a channelled portion which is integral with the side portions and along which extends the associated electric conductor; a substantially flat magnetisable flapper which is pivotable about an axis lying in a plane substantially parallel to said common plane between a first position and a second position in which the flapper is in inter-facial contact with said planar surface of the yoke to form a closed magnetisable loop; spring means urging the flapper to said first position; and a trip mechanism operatively coupled to the flapper, the arrangement being such that, in the event of passage of a current of at least a predetermined value, resultant magnetisation of the stationary yoke causes the flapper to pivot against the action of said spring means into inter-facial contact with the yoke and thereby to effect disengagement of said trip mechanism and initiate operation of the circuit breaker.

3. An electric circuit breaker as claimed in Claim 1 or 2, wherein the pivotal axis of the magnetisable flapper is substantially normal to the pivotal axis of the dolly of the circuit breaker.

4. An electric circuit breaker as claimed in Claim 3, wherein the trip mechanism comprises a trip gate which is pivotable about an axis substantially normal to the pivotal axis of the flapper and parallel to the pivotal axis of the dolly between a first position in which the trip gate is retained by a trip catch engaging the trip gate and a second position in which the trip catch is disengaged from the trip gate against the action of the main spring of the circuit breaker to initiate operation of the circuit breaker.

5. An electric circuit breaker as claimed in Claim 4, wherein the spring means urging the flapper to said first position is a leaf spring secured to the trip gate and bearing against a part of the flapper, the arrangement being such that when the flapper is caused to pivot to said second position in the event of passage of a current of at least a predetermined value, the flapper, in pivoting against the action of said leaf spring, causes the trip gate to pivot about its pivotal axis to disengage from the trip catch and thereby initiate operation of the circuit breaker.

6. An electric circuit breaker as claimed in Claim 4 or 5, wherein operative coupling between the flapper and the trip gate is provided by arranging for a shuttle, carried by the trip gate, to overlie an edge of the flapper and to have a recess in which loosely engages a lug projecting from the flapper, the looseness of the engagement being such that, during initial pivotal movement of the flapper, no consequential pivotal movement of the trip gate occurs and that, during further pivotal movement of the flapper to bring it into interfacial contact with the yoke, the lug projecting from the flapper pulls the shuttle towards the yoke thereby causing the trip gate to pivot about its pivotal axis and actuate the trip mechanism.

7. An electric circuit breaker as claimed in Claim 6, wherein the trip gate has at or near its pivotal axis a projection which protrudes through a hole in one side wall of the housing of the circuit breaker, and the shuttle, carried by the trip gate, is accessible through a hole in the other side wall of the housing and has a recess for reception of the protruding projection on the trip gate of an adjacent circuit breaker, the arrangement being such that two or more circuit breakers mounted side by side can be so operatively inter-connected by means of interengagement of the protruding projection of the trip gate and the recess of the shuttle, that operation of one circuit breaker will initiate operation of the adjacent circuit breaker or circuit breakers.

8. An electric circuit breaker as claimed in any one of Claims 4 to 7, wherein the trip catch engages in a window in, and is electrically insulated from, the trip gate.

9. An electric circuit breaker as claimed in Claim 8, wherein at least the boundary wall of the window in the trip gate is made of or is coated with electrically insulating material.

10. An electric circuit breaker as claimed in Claim 8, wherein a bushing of resilient metal having a coating of electrically insulating material on one or each of its faces, or a bushing of plastics insulating material, is detachably engaged in the window of the trip gate.

11. An electric circuit breaker as claimed in any one of the preceding Claims, wherein the trip mechanism is also operatively coupled to the thermal element of the circuit breaker, which thermal element upon occurrence of a sustained overload of a predetermined value in excess of the rated capacity of the circuit breaker, effects disengagement of the trip mechanism and initiates operation of the circuit breaker.

12. An electric circuit breaker as claimed in Claim 5, wherein the thermal element of the circuit breaker comprises a bi-metallic elongate member which is secured at or near one of its ends to the trip gate and which, at the other of its ends, is urged towards and adjustable stop under the action of the leaf spring trip gate, the arrangement being such that, in the event of a sustained overload of a predetermined value in excess of the rated capacity of the circuit breaker, the elongate thermal element deflects and causes the trip gate to pivot about pivotabl axis to disengage frdm the trip catch and thereby initiate operation of the circuit breaker.

13. An electrica circuit breaker as claimed in any one of the preceding Claims, wherein supplementary sacrificial plates adjacent the fixed and moving contacts are so shaped as to encourage formation of an arc between the sacrificial plates when operation of the circuit breaker effects disengagement of the moving contact from the fixed contact.

14. An electric circuit breaker as claimed in Claim 13, wherein the sacrificial plate associated with the moving contact is electrically connected to the conductor associated with the stationary yoke via a low resistance current path.

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