WO1996030924A1

WO1996030924A1 - Circuit breaker

Info

Publication number: WO1996030924A1
Application number: PCT/GB1996/000722
Authority: WO
Inventors: John Stevens
Original assignee: Delta Circuit Protection & Controls Limited
Priority date: 1995-03-29
Filing date: 1996-03-27
Publication date: 1996-10-03
Also published as: AU5154296A; GB9506399D0

Abstract

A miniature circuit breaker having a fixed contact (19), a movable contact (27) movable between an operative position in which it engages the fixed contact (19) and a rest position in which it is spaced from the fixed contact (19), latch means (32, 33, 42) for latching the moving contact (27) in its operative position, and a solenoid (16) operable to trip said latch means to release said movable contact (27) for movement towards its rest position; said solenoid (16) when operated, assisting the movement of said movable contact (27) from its operative position in addition to tripping said latch means.

Description

CIRCUIT BREAKER

Technical Field

This invention relates to a miniature circuit breaker.

The term miniature circuit breaker is abbreviated hereinafter as MCB and is herein intended to denote an electrical circuit breaker the dimensions of which satisfy DIN standard 43880 and circuit breakers of a similar shape and size which are so designed as to be interchangeable with circuit breakers satisfying DIN standard 43880.

Background Art

MCBs are commonly used in the United Kingdom in electrical consumer units of domestic dwellings and small industrial premises to protect and control the electrical supply to predetermined circuits of the dwelling or industrial premises. MCBs generally include a manually operable lever for operating the contacts of the MCB to make or break the supply to the respective circuit and a trip mechanism which can be operated by any one of a number of different sensors to open the contacts in a predetermined fault condition. The number of different fault conditions which can be accommodated is of course determined by the number of different sensors incorporated in or associated with the MCB, but it is usual for the MCB to include a solenoid for operating the trip mechanism to open the contacts in response to a rapid rise in the current flowing through the contacts. The speed at which the contacts are opened, and thus the speed at which the circuit through the MCB is broken, when the solenoid is operated by a rapid current rise above a predetermined level is an important parameter of the MCB, and it is an object of the present invention to provide an MCB in which opening of the contacts, in response to solenoid operation of the trip mechanism, is augmented.

Disclosure of Invention

In accordance with the present invention there is provided an MCB having a fixed contact, a movable contact movable between an operative position in which it engages the fixed contact and a rest position in which it is spaced from the fixed contact, latch means for latching the moving contact in its operative position, and a solenoid operable to trip said latch means to release said movable contact for movement towards said rest position; said solenoid when operated, assisting the movement of said movable contact from its operative position in addition to tripping said latch means.

Preferably the movable contact is mounted such that in being moved from its rest position to its operative position it pivots firstly about a first pivot axis against the action of resilient means, until it engages the fixed contact and thereafter is pivoted about its point of engagement with the fixed contact further stressing said resilient means, whereby the resilient means, in the operative position of the movable contact, loads the movable contact against the fixed contact.

The movement of the movable contact between engaging the fixed contact and reaching the operation position in which it is latched, can conveniently be referred to as movable contact overtravel.

Preferably said solenoid includes a plunger which is moved against a resilient bias, by energisation of a winding of the solenoid, to move a release member of said latch means to trip the latch means, said member bearing against the movable contact to assist its movement away from the operative position.

Conveniently the MCB includes a fixed pivot pin extending through an elongate slot in the movable contact, said initial movement of the movable contact about said first pivot axis being movement about the axis of said pivot pin with one end of said slot engaging said pin, and said overtravel pivotal movement of the movable contact being accommodated by the elongation of said slot, said release member being pivoted on said pivot pin.

Desirably said release member, after tripping of said latch means, translates movement of said plunger firstly to assist said resilient means to collapse said overtravel and then to assist said resilient means to pivot said movable contact away from said fixed contact.

Brief Description of the Drawings

One example of the invention as illustrated in the accompanying drawings wherein:

Figure 1 is a diagrammatic plan view of an MCB in an "OFF" condition;

Figure 2 is a view similar to Figure 2 but illustrating the parts of the MCB in the "ON" position;

Figure 3 is an enlarged diagrammatic representation of the moving contact and part of the trip mechanism of the MCB; Figures 4 to 8 inclusive are diagrammatic representations of the operation of the moving contact and the solenoid release of the MCB; and

Figures 9 to 12 are views similar to Figures 4 through 8 but illustrating the moving contacts and the trip mechanism of the MCB in more detail.

Best Mode for Carrying Out the Invention

Referring to the drawings, the MCB includes first and second moulded synthetic resin casing halves which, in use, are rivetted together to form the housing of the MCB and support between them the MCB components. Items pivotally mounted in the MCB housing are movable about axes extending between the housing halves, only one of the casing halves, 1 1 , being indicated in the drawings. In effect Figures 1 and 2 show the casing half 1 1 as the lower half, the upper half having been removed to reveal the components of the MCB.

One edge of the MCB casing, hereinafter referred to as the rear edge, includes a re-entrant recess 12 for receiving a mounting rail provided within a domestic consumer unit or the like. One wall of the recess is formed with a tongue or rail clip 13 which is movable between a retracted position in which an end of the tongue is housed substantially within a slot provided in the casing of the MCB, and an exposed position in which the end of the tongue 13 protrudes into the recess 12 by an amount such that when the MCB is mounted on a mounting rail the tongue 13 engages behind the edge of the rail preventing removal of the MCB therefrom. Conveniently a spring or other resilient device urges the tongue 13 to its operative position. Housed within the casing adjacent one end thereof is a first screw clamp electrical terminal 14, a second similar screw clamp terminal 15 being housed within the casing at its opposite end. The end walls of the casing are apertured to allow the bared ends of electrical leads to be introduced into the terminals 14, 15 and the front edge of the casing of the MCB is apertured to provide access to the screws of the terminals 14, 15.

A solenoid 16 has its winding connected to the terminal 14, the terminal 14 being electrically connected to one end of a heavy gauge copper wire wound to form the helical solenoid winding 1 7 through which extends a hollow, cylindrical, moulded synthetic resin former 18. The end of the winding 17 remote from the terminal 14 is physically and electrically connected to a shaped copper strip defining the fixed contact 19 of the MCB. The strip defining the fixed contact is welded to one limb of an L- shaped, copper-plated, mild steel strip frame 21 , said one limb extending across the innermost axial end of the winding 1 7 and former 18, and the other limb extending parallel to the axis of the winding and former. Said other limb of the frame 21 is presented towards the rear edge of the casing and housed within the casing between the rear edge and the frame 21 is an arc stack 22 oi generally conventional form comprising a plurality of spaced parallel mild steel plates for receiving and quenching, in known manner, an arc struck between the fixed and movable contacts of the MCB when the contacts open.

Electrically connected to the terminal 15 by means of a flexible copper braid 23 is a shaped elongate copper-plated, mild steel strip defining an arc runner 24. The arc runner 24 extends from the region of the terminal 15, from adjacent the rear edge of the casing towards the front edge. However, at approximately the level of the fixed contact the arc runner 24 is bent back on itself so as to extend obliquely towards the inner surface of the rear edge of the casing. As it reaches the rear edge of the casing it is bent again to lie along the inner surface of the rear edge of the casing and to pass between the arc stack 22 and the rear edge of the casing where it terminates. The intermediate region of the arc runner 24 is trapped firmly in position within the casing when the two casing halves are ri vetted together. However, the end of the arc runner 24 adjacent the terminal 15 lies within a void in the casing and thus can be flexed relative to the casing. Welded to the arc runner 24, at its commencement adjacent the rear edge of the casing is an elongate bimetallic strip 25 which, when heated, will bend towards the terminal 15. A screw adjuster 26 is carried by the casing and coacts with the junction of the bimetallic strip 25 and arc runner 24 to provide the facility for adjusting the orientation of the bimetallic strip 25 within the casing by moving the bimetallic strip and arc runner as permitted by flexure of the arc runner.

Adjacent its end remote from the adjuster 26, the bimetallic strip 25 is electrically connected, by means of a further copper braid (not shown) to a moving contact member 27 of the MCB. The moving contact member 27 is movable by a toggle lever 28, and when engaged with the fixed contact 19 completes an electrical circuit between the terminals 14, 15 by way of the winding 1 7 and the bimetallic strip 25. A latching/tripping mechanism (to be described hereinafter in more detail) is associated with the moving contact member 27 and can be tripped to release the moving contact member 27 for movement to an open position away from the fixed contact, by bending of the bimetallic strip 25 or by movement of a plunger 29 of the solenoid 16, slidable within the former 18 against the action of a light return spring. It will be recognised therefore that with the MCB contacts closed, should there be a sudden rise in the current flowing through the contacts, above a predetermined level, then that same current flowing through the winding 1 7 will energise the solenoid 16 to cause the plunger 29 to trip the mechanism associated with the movable contact releasing the movable contact for return to an open position breaking the circuit through the MCB. Similarly, should a current in excess of a predetermined value flow for a predetermined length of time, then that current flowing through the bimetallic strip 25 will cause bending of the bimetallic strip and consequent actuation, by means of a mechanical linkage 31 , of the mechanism again to release the moving contact for movement to its open position. The adjustment mechanism 26 provides for adjustability in the amount of bending of the bimetallic strip 25 which must be present before the mechanism is tripped.

The general concept of thermal and electromagnetic tripping of an MCB is known, and it is believed that no further detailed disclosure of these aspects is necessary.

The arrangement of the moving contact, the latching/tripping mechanism, and its actuation will now be described in more detail.

The toggle lever 28 is pivotally mounted in the casing and its operating lever protrudes through an aperture in the front edge of the casing so as to be manually accessible. The aperture in the front edge of the casing restricts angular movement of the toggle lever about its pivotal axis to approximately 100°, clockwise movement from the position shown in Figure 1 to the position shown in Figure 2 moving the lever from its OFF position to its ON position. Although not illustrated in the drawings there is a light torsion spring associated with the toggle lever 28 and cooperating with the lever 28 and the casing, to urge the toggle lever to pivot to its OFF position. Throughout the remaining description a number of axes of pivotal movement and pivotal interconnection are described in relation to the moving contact assembly and its latching and tripping mechanism. For the avoidance of doubt it is to be recognised that these axes of pivotal movement are parallel and spaced from one another unless otherwise indicated.

A rigid wire link 32 is pivotally connected at one end to the toggle lever 28 for movement about an axis spaced from the rotational axis of the toggle lever. The opposite end of the link 32 is pivotally connected to a moulded synthetic resin latch piece 33 adjacent one end thereof, the opposite end of the latch piece 33 being pivotally connected to one end of the moving contact member 27. The moving contact member 27 is an elongate component stamped from a thick copper sheet and is best seen in Figure 3 of the accompanying drawings. The member 27 is arranged to be received, at one end, between parallel limbs of the latch piece 33 and is pierced with an aperture 34 to receive a pivot pin interconnecting the member 27 and the latch piece 33. At its opposite end the moving contact member 27 has a thickened region 35 defining the contact region for engagement with the fixed contact 19. Intermediate its ends the member 27 is formed with an elongate slot 36 for receiving a pivot pin 37 and between the elongate slot 36 and the piercing 34 the member 27 is formed with a further, larger, elongate slot 38 extending generally parallel to the slot 36. A fixed abutment pin 39 extends through the slot 38, being received at its ends in the opposite casing halves. An helically wound tension spring 41 is anchored at one end to the casing and at its opposite end is hooked through the slot 38 the spring being stressed so as to urge the moving contact member 27 to the left as shown in the drawings. The pin 39 abuts the end of the slot 38 remote from the spring 41 to limit movement of the member 27 under the action of the spring 41.

The pivot pin 37 is also anchored at its ends in the casing halves but by virtue of the elongate slot 36 the moving contact member 27 has a degree of freedom for bodily movement relative to the pin 37 although it can also pivot about the pin 37.

The moving contact member 27 seats within a trip lever moulding 42 of complex shape also pivotally mounted on the pin 37. The trip lever moulding 42 does not have freedom for bodily movement on the pin 37, and can thus simply pivot about the axis of the pin. Although the moving contact member 27 lies partially within the moulding 42 there is a limited degree of freedom for pivotal movement and bodily movement of the member 27 relative to the moulding 42 as permitted by the interaction oi the pin 37 and elongate slot 36. Additionally within the range of movement of the moulding 42 the moulding 42 abuts the contact member 27 and thereafter the two move as a unit about the axis of the pin 37.

A torsion spring 43 coacts with the moulding 42 and the pin 39 to urge the moulding 42 to pivot about the pin 37 in a clockwise direction (as viewed in the drawings).

For the purposes of the further consideration of the MCB latching/tripping mechanism it is convenient to consider the moulding 42 as a letter "H" with the pivot axis defined by the pin 37 passing through the cross-bar of the H adjacent the left hand upright of the H.

The inner wall of the top end of the left hand upright of the moulding 42 is formed with an abutment face 44 terminating, part way along the moulding in a notch and shoulder 45. The opposite end of the left hand upright is pierced at 46 pivotally to receive the end of the link 31 remote from the bimetal strip 25.

Referring now particularly to Figures 4 to 8 and 9 to 12 the OFF position of the MCB in which the components are in rest positions is illustrated in Figures 4 and 9; the toggle lever 28 is in its extreme counter-clockwise position; the moving contact member 27 is spaced from the fixed contact 19; the pin 39 is at the right hand end of the slot 38 remote from the spring 41 and the pin 37 engages the right hand end of the slot 36. Initial angular movement of the toggle lever 28 about its pivot axis relative to the casing drives the latch piece 33, by way of the link 32, in a counter-clockwise direction about its pivotal connection with the moving contact member 27 until its end face and lower corner abut the face 44 and shoulder 45 respectively of the moulding 42 (the position shown in Figure 10).

Continued clockwise movement of the toggle lever 28 cannot move the latch piece 33 further relative to the moulding 42 and thus the moulding 42, the latch piece 33 and the moving contact 27 pivot clockwise as a unit about the pivot pin 37 and against the action of the tension spring 41 , the moulding 42 in effect following the movement of the latch piece 33 and contact member 27 by virtue of the spring 43. Such pivoting movement brings the contact region 35 of the member 27 towards the fixed contact 19, and shortly before the toggle lever 28 reaches its clockwise limit position the contact region 35 engages the fixed contact 19. At this point in the movement of the member 27, by virtue of the engagement of the end of the slot 36 with the pivot pin 37, the spring 41 is acting to oppose movement of the contact region 35 towards the fixed contact 19. Thereafter, continued movement of the toggle lever 28 drives the upper end of the contact member 27 further to the right but since the contact region 35 is abutting the fixed contact 19 then the member 27 cannot pivot further about the pin 37 and thus pivots about the point of engagement of the contact area 35 with the fixed contact 19, moving bodily on the pin 37 and relative to the moulding 42 as permitted by the elongation of the slot 36. It will be recognised that such a movement of the member 27 which, for convenience can be referred to as overtravel, further stresses the spring 41 but since the member 27 is no longer pivoting about the pin 37 the action of the spring 41 is now loading the moving contact 35 against the fixed contact 19 to achieve a predetermined desired contact pressure. During overtravel of the member 27 after its curved region 35 has engaged the fixed contact 19, the region 35 performs a rolling action on the contact 19 so achieving a contact cleaning effect.

At a point in the movement of the toggle lever 28 during the movable contact member overtravel and fractionally before the limit of movement of the toggle lever 28 to its ON position is reached, the linkage defined by the toggle lever 28, the link 32, and the latch piece 33 moves "over- centre" that is to say the point of connection of the toggle lever 28 and the link 32 passes through an imaginary line intersecting the axis of rotation of the toggle lever 28 and the axis of pivotal connection of the link 32 and the latch piece 33. Prior to passing "over-centre" it will be recognised that should the lever 28 be released then the spring 41 in conjunction with the return spring of the lever 28 will return the lever 28 and all of the components to their rest position. However, after passing "over-centre" the force of the spring 41 is driving the toggle lever 28 towards its ON position and overcoming the effect of the toggle lever return spring. The toggle lever cannot rotate further in the ON direction because oi abutment with the end of the aperture in the casing through which the lever projects. It will be recognised therefore that in the ON position the toggle lever 28 is limited by abutment with the casing the pin 37 is part way along the slot 36, the pin 39 is part way along the slot 38 and the moving contact region 35 is loaded against the fixed contact 19 with a predetermined contact pressure. Current thus flows between the terminals 14, 15 through the winding 17, the fixed contact 19, the moving contact member 27, the braid connecting the member 27 to the bimetallic strip 25, the strip 25 itself, the braid connecting the strip 25 to the terminal 15.

The MCB can be manually moved to its OFF position by moving the toggle lever 28 in a counter-clockwise direction, this movement, and the movements of the MCB components, being the reverse of the sequence of operation described above. In the drawings Figures 1 and 9 illustrate the components of the MCB in their rest position, Figure 10 illustrates initial movement of the toggle lever 28 towards the ON position to achieve abutment of the latch piece 33 with the moulding 42. Figure 5 illustrates the condition at which the moving contact region 35 has just engaged the fixed contact 19 and Figures 6 and 1 1 illustrate the ON position of the MCB in which the toggle lever 28 is in its extreme clockwise position and predetermined contact pressure is applied between the moving and fixed contacts. In the event that the current flowing through the bimetallic strip 25 exceeds a predetermined value, for a predetermined length of time then, as mentioned above, the bimetallic strip will bend towards the terminal 15. The bending movement is of course reflected most markedly at the upper, free end of the strip 25 and it is at this point that the strip 25 coacts with the link 31. The bending strip 25 pushes the link 31 towards the terminal 15, and in so doing pulls the lower end of the left hand limb of the moulding 42 thus pivoting the moulding 42 in a counter¬ clockwise direction against the action of the spring 43. Such pivoting movement of the moulding 42 takes place relative to the contact member 27 and latch piece 33 and the immediate effect is to disengage the abutment surface 44 and shoulder 45 of the moulding 42 from the end of the latch piece 33.

Immediately such disengagement occurs the latch piece 33 is free to pivot in a counter-clockwise direction relative to the contact member 27 and does so as a result of the upper end of the contact member 27 moving to the left as the contact member overtravel collapses under the action of the spring 41 . In effect the linkage defined by the link 32 and the latch piece 33 collapses with the point of pivotal interconnection of the link 32 and latch piece 33 tending to move downwardly. However, simultaneously the "over-centre" locking effect imposed upon the toggle lever 28 and linkage 32 is released and the toggle lever 28 is driven rapidly in a counter-clockwise direction by its return spring to its OFF position. Also taking place simultaneously is an opening movement of the moving contact member 27 relative to the fixed contact 19. It will be recalled that immediately the latching action of the latch piece 33 and moulding 42 is released by counter-clockwise movement of the moulding 42, the overtravel of the moving contact member 27 collapses under the action of the spring 41. The initial movement of the member 27 is pivoting movement about the point of interconnection of the moving contact region 35 and the fixed contact 19 but this movement is small and ceases as the right hand end of the slot 36 abuts the pin 37. At the completion of the overtravel collapse the movement of the member 27 is converted into counter-clockwise pivoting movement of the member 27 about the pin 37 thus moving the contact region 35 rapidly away from the fixed contact 19. The counter-clockwise pivoting of the member 27 is halted by the right hand end of the slot 38 abutting the pin 39 whereupon the toggle lever 28, the link 32, the latch piece 33, the moulding 42, and the contact member 27 are back in their OFF positions. Any arc struck between the moving contact region 35 and the fixed contact 19 as the contacts open is guided by the arc runner 24 and the shaping of the fixed contact 19, into the arc stack 22 where it is quenched.

If the circuit controlled by the MCB undergoes a fault condition such that the current flowing through the MCB rises rapidly beyond a predetermined threshold then the solenoid defined by the winding 1 7 and plunger 29 is energised to drive the plunger 29 rapidly, against the action of its light return spring, towards the terminal 15 (Figure 7). The plunger 29 thus strikes the lower part of the left hand limb of the moulding 42 pivoting the moulding 42 in a counter-clockwise direction (Figures 8 and 12). This movement of the moulding 42 generates exactly the same trip release action as described above in relation to the operation of the bimetallic strip 25, but with the addition that because the speed of operation of the plunger 29 is so much more rapid than the movement of the bimetallic strip 25 the upper end of the right hand limb of the moulding 42, together with the lower end of the left hand limb, are driven into contact with respective regions of the moving contact member 27 and thus physically drive the moving contact member towards its open position. A detailed analysis of the movements is as follows. In the contacts closed position clearance exists between the moulding 42 and the member 27 so that the moulding is not impeded by the member 27 in moving to generate the trip release action. This clearance is taken up almost instantaneously as the moulding 42 is moved by the plunger 29 with the result that the upper end of the right hand limb of the moulding 42 contacts the member 27 and assists the spring 41 in collapsing the movable contact member overtravel by moving the member 27 about its point of engagement with the fixed contact until the end of the slot 36 abuts the pin 37. During the overtravel collapse the member 27 is pivoting relative to the moulding 42 while the moulding is pivoting about the pin 37. As the end of the slot 36 reaches the pin 37 the lower left hand limb of the moulding 42 contacts the member 27 so that the plunger 29, through the moulding 42, drives the member 27 counterclockwise about the pin 37 in conjunction with the action of the spring 41 . In the event that through manufacturing tolerances or the like, the end of the slot 36 has not abutted the pin 37 when the lower left hand limb of the moulding engages the member 27, then the member 27 will be trapped between the upper right hand and lower left hand limbs of the moulding and so will be forced to pivot therewith about the axis of the pin 37. In effect the force generated by the solenoid, transmitted to the moving contact assembly by the plunger 29, assists the opening movement of the moving contact member 27 thus accelerating the entire sequence of contact opening movements. Naturally the speed at which contacts open in a fault condition is a crucial parameter of an MCB, and increasing the speed of operation is desirable. As with many known MCBs there can be a magnetic opening effect which augments the mechanical effect described above. Generally the fixed and movable contacts are so arranged that there are parallel limbs of each, in which the current flows in opposite directions thus generating mutually repulsive magnetic fields which assist the mechanical action in driving the movable contact away from the fixed contact.

The casing of the MCB is apertured adjacent the upper region of the right hand limb of the moulding 42 to provide access for a trip lever of an additional tripping module which may be clipped to the exterior of the casing. Normally the casing aperture is closed by a bezel. Other apertures may be provided in the casing for test purposes, and if desired the two casing halves can each be provided with an arcuate slot through which the mid-point of the right hand limb of the moulding 42 is exposed to allow mechanical ganging of the mouldings, and thus the trip actions, of two or more MCBs positioned side-by-side.

Although not described above it will be recognised that if desired a transparent window can be provided in the front edge of the casing to reveal a coloured flag, or other indica indicating the operative state of the MCB.

Claims

1. An MCB having a fixed contact (19), a movable contact (27) movable between an operative position in which it engages the fixed contact and a rest position in which it is spaced from the fixed contact, latch means (32, 33, 42) for latching the moving contact in its operative position, and a solenoid (16) operable to trip said latch means to release said movable contact for movement towards its rest position; the MCB being characterized in that said solenoid (16) when operated, assists the movement of said movable contact from its operative position in addition to tripping said latch means.

2. An MCB as claimed in Claim 1 , characterized in that said movable contact (27) is mounted such that in being moved from its rest position to its operative position it pivots firstly about a first pivot axis (37) against the action of resilient means (41 ), until it engages the fixed contact (19) and thereafter is pivoted about its point of engagement with the fixed contact (19) further stressing said resilient means (41 ), whereby the resilient means, in the operative position of the movable contact, loads the movable contact against the fixed contact.

3. An MCB as claimed in Claim 1 or Claim 2, characterized in that said solenoid (16) includes a plunger (29) which is moved against a resilient bias, by energisation of a winding (17) of the solenoid, to move a release member (42) of said latch means to trip the latch means, said member (42) bearing against the movable contact (27) to assist its movement away from the operative position.

4. An MCB as claimed in any one of Claims 1 to 3, characterized in that it includes a fixed pivot pin (37) extending through an elongate slot (36) in the movable contact (27), said initial movement of the movable contact (27) about said first pivot axis being movement about the axis of said pivot pin (37) with one end of said slot (36) engaging said pin, and the overtravel pivotal movement of the movable contact (27) about its point of engagement with the fixed contact (19) being accommodated by the elongation of said slot (36), said release member (42) being pivoted on said pivot pin (37).

5. An MCB as claimed in Claim 4, characterized in that said release member (42), after tripping of said latch means, translates movement of said plunger (29) firstly to assist said resilient means (41 ) to collapse said overtravel of said movable contact (27) and then to assist said resilient means (41 ) to pivot said movable contact (27) away from said fixed contact (19).