WO1991002370A2

WO1991002370A2 - Miniature circuit breakers

Info

Publication number: WO1991002370A2
Application number: PCT/GB1990/001157
Authority: WO
Inventors: William Henry Anquetil
Original assignee: Federal Pioneer Limited; Federal Electric Limited
Priority date: 1989-07-28
Filing date: 1990-07-26
Publication date: 1991-02-21
Also published as: GB8917283D0; CA2065031A1; WO1991002370A3; AU6068790A

Abstract

A miniature circuit breaker for domestic and like electricity supply circuits has a double break design featuring a contact carrier (28) mounted on a plastic sliding carriage (60) directly connected to a coiled tension spring (108) and controlled by a latch mechanism which releases it for completely independent breaking movement on overload. Major parts of the latch mechanism are moulded in a plastics material. An anti-bounce stop (120) is provided for the carriage. Simple adjustement of the trip point is provided by a threaded adjuster which moves a thermal trip lever (88). Leaf springs(114, 134) position the movable contacts and the plunger (126) of the overload-detecting solenoid (24).

Description

MINIATURE CIRCUIT BREAKERS

This invention relates to miniature circuit breakers of the kind for providing overload protection and selective manual circuit breaking for domestic and like electricity supply circuits, including installations for use in business and commercial situations, but is to be distinguished from industrial and other heavy duty circuit breakers. An example of an embodiment of the invention provides not only instantaneous circuit breaking in the event of a massive overload, but also a circuit breaking response in the event of a creeping current rise above a predetermined maximum. The invention also provides a current sensing flux shifting device per se .

Many proposals have been made for miniature circuit breakers of the above kind, particularly in recent years. Many of these can meet the practical requirement of a relatively rapid current trip upon massive overload. However, for circuit breakers applicable to the particular field with which the present invention is concerned (miniature circuit breakers for domestic and the like situations) there is a further requirement concerning dimensions. In short, there is a need for an absolute minimum space requirement so that, if possible, a cassette¬ like construction can be adopted so that a series of minature circuit breakers can be assembled side-by-side in a bank the width of each being preferably no greater than half an inch (12.7 millimetres).

There are additional requirements raised by prior proposals including a need for improved ease of manufacture and assembly arising from the somewhat complex and muddled layout adopted in certain cases.

We have determined that, surprisingly, in the low-duty application with which the present invention is concerned, the use of a double break circuit breaker leads to significant advantages in terms of rapidity of current interruption while permitting a simplicity of layout and construction leading to advantages in manufacture and assembly.

In EP A 0 270 158 there is disclosed a circuit breaker as defined in the pre-characterising portion of claim 1 hereof.

Other requirements and shortcomings in relation to the above prior application and other prior art known to the applicants include the following. Firstly, an improved and simplified means for adjusting the operation of a solenoid used for sensing current overload and tripping a contact breaker mechanism. Secondly, improvements in relation to the mounting of one or more movable contacts in relation to maintenance of adequate contact pressure during use. Thirdly, improvements in runner design in order to achieve rapid transfer of arc and thus minimise energy let-through and contact wear. Fourthly, provision of a design permitting the use of a large number of arc plates without the need for large contact separation whereby rapid and large increases in arc voltage can be obtained. Fifthly, there is a need for a particularly low moment of inertia for the movable contact assembly, whereby delays in contact opening are minimised. Sixthly, the provision of improved means for adjusting the setting of the trip mechanism as a whole and of the thermal trip in particular, particularly having regard to manufacturing simplicity and ease of calibration.

An object of the present invention is to provide__a miniature circuit breaker offering improvements in relation to one or more of the matters discussed above, and elsewhere herein, or generally.

According to the invention there is provided a miniature circuit breaker as defined in the accompanying claims.

In a preferred embodiment, a minature circuit breaker comprises spaced connectors for connection to the circuit to be cont olled/protected. The circuit breaker interconnecting the connectors comprises overload detection means and contact breaker means actuable thereby, and having arc extinguishing means. Manual operating means for the contact breaker means is provided. The contact breaker means comprises a pair of movable contacts and a pair of relatively fixed contacts. Actuation means for the movable contacts is provided to effect separation thereof. Each contact of the pair of contacts is spaced apart from the other thereof, one at each side of a central contact carrier mounted for lengthwise movement about a longitudinal carrier axis, to open and close the contacts. The actuation means comprises a releasable latching mechanism engageable with the contact carrier to hold same in a latched "circuit closed" condition, and energy storage means (for example in the form of a coiled tension spring directly connected to the contact carrier means) to releasably store energy for opening the contacts when the latching mechanism releases the contact carrier. A housing is provided for the circuit breaker. The contact carrier is mounted for guided sliding movement in the housing, entirely independently of the latching mechanism, and under the action of a tension spring generally aligned with the longitudinal carrier axis. The tension spring acts between the housing and one end of the contact carrier. The latching mechanism is disposed to make latching engagement with the other end of the carrier member. The arrangement is such that after release of the contact carrier by the latching mechanism, the contact carrier is free to move under the sole action of the spring in the contact-opening direction.

A pair of arc chutes are located one on each side of the contact carrier, and each one is connected at one end by an arc runner to its own one of said contacts. The arc chutes are interconnected at their other ends by a bottom arc runner. The tension spring for the contact carrier extends through an opening in the bottom arc runner. Stop means is provided for the contact carrier to arrest movement of same in the contact opening direction. The stop means comprises at least one pair of mutually engageable fixed and movable complementary stop surfaces on the contact carrier and on a relatively fixed structure carried by the housing. The stop surfaces are disposed so that they face in a direction inclined with respect to the carrier axis, whereby rebound of the carrier on tripping is minimised.

Further in the preferred embodiment, the movable contacts are mounted on the contact carrier by means of a lateral contact support, carrying the contacts, and which can angularly adjust itself with respect to the contact carrier under the bias of a leaf spring engaging the contact support on the convex surface of the spring, to promote proper alignment of the fixed contacts.

The overload detection means comprises a solenoid having a plunger extendable upon detection of an overload to actuate- the contact breaker means. The plunger is^ positioned to engage a leaf spring mounted externally of the solenoid and operative to return the plunger after extension on overload.

The latching mechanism comprises main and secondary latch levers pivotally mounted for mutual engagement in a position in which they co-operate to hold a main latch lever in a position in which it retains the contact carrier in its contact closed position. Said latch levers are pivotally mounted on a bell crank lever. Said latch levers and said bell crank and said contact carrier are all formed of a synthetic polymeric material, preferably by moulding techniques.

The overload detection means comprises thermal trip means to cause the contacts to be opened. The thermal trip means is electrically connected in series with said contacts and positioned to act mechanically on a pivotally mounted thermal trip lever itself positioned to act on said latch mechanism. The arrangement is such that the latch mechanism can be tripped by said thermal trip lever upon detection of a progressive overload. The thermal trip lever is position-adjustable under the control of a screw- threaded adjuster to vary the position at which the latch mechanism trips.

In the preferred embodiment, a large spring is utilised to achieve rapid movement of the contact carrier assembly. The magnetic and thermal forces required to trip the breaker are minimised by the mechanical advantage provided by a secondary latch lever. Re-latch of the breaker after tripping is accomplished by rotation of the linkage on the bell crank lever by means of the manually- operable handle to the re-latch position. A plastic guide in the case forces the latch to reset. Previous proposals in this respect rely on a spring for re-latching of the mechanism.

Fibre barriers placed in the throat of the arc chamber serve to accelerate the movement of the arc along the runners and to provide the necessary dielectric strength of the arc chamber. The bimetals used in the thermal trip are such that the temperature rise requirement for the necessary thermal force and thermal deflection are approximately equal. This ensures efficient use of bimetal material and minimises the effects of variability of force and deflection requirements on the calibration of the breake .

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which :-

Fig 1 shows a minature circuit breaker in side elevation and in the contact- closed position, and surrounding the assembly are individual drawings of the main parts thereof, some shown in perspective, for purposes of illustration;

Fig 2 shows the minature circuit breaker of Fig 1 in its tripped position; and

Fig 3 shows, on a larger scale, a flux shifter which can be incorporated in the circuit breaker of Figs 1 and 2 in place of the solenoid there-used for tripping the contact-opening mechanism.

As shown in Fig 1 a miniature circuit breaker 10 comprises a casing 12 having connectors 14, 16 for connection to a circuit to be controlled. Interconnecting the connectors 14, 16 is a circuit breaker circuit 18 comprising a lug plate 20, a solenoid coil 22 of a solenoid 24, a left arc runner 26, a contact carrier 28, associated pairs of fixed and movable contacts 30, 32 and 34, 36, a right arc runner 38, a bimetal strip 40, and a length of flexible braid 42.

Solenoid 24 constitutes overload detection means and is arranged to actuate contact breaker means 44 including the contacts 30, 32 and 34, 36 together with actuation means for the movable contacts, which will be described below.

Arc extinguishing means 46 is provided for the contact breaker means 44 in the form of a pair of arc chutes 48, 50 located one each side of the contact carrier 28 and interconnected by a bottom arc runner 52.

Manual operating means for the contact breaker comprises a handle 54 pivotally mounted on casing 12 and connected by a link 56 to a latch mechanism 58 to be more fully described below.

The movable contacts 32, 36, mounted on contact carrier 28 are located one at each side of a carriage member 60 which is mounted for lengthwise movement about a longitudinal carrier axis 62, to open and close the contacts. Carriage 60 is guided for sliding movement by guides 64, 66. As shown in the perspective view of the carriage, it is formed as a moulding of polymeric material. A recess 68 is provided at one end of the carrier to receive one end 70 of a main latch lever 72, which is pivoted at 74 and has a notch 76 at its other end for engagement with a complementary formation 78 on a secondary latch lever 80, pivotally mounted at 82 on a bell crank lever 84 which is itself pivotally mounted on housing 12 at 86. Main latch lever 72 is likewise pivotally mounted on bell crank 84. The bell crank itself is connected by link 56 to handle 54, for re-latching purposes.

A thermal trip lever 88 is pivotally mounted at 90 on a pin 92 of a calibration bracket 94 which is position- adjustable by means of an calibration screw 96 having a threaded stem 98 engaging an internal threaded bore 100 in bracket 94. Thermal trip lever 88 has an in-turned end 102 for engagement with bimetal strip 40. Its other end 104 engages a recess 106 formed in secondary latch 80, whereby position-adjustment of calibration bracket 94 varies the sensitivity of the latch mechanism 58.

Carriage 60 has a spigot 106 to which is directly connected a coiled tension spring 108. The other end of spring 108 is connected at 110 to housing 12, whereby the spring force is applied directly to carriage 60 and contact carrier 28, directly in-line with same, and without any intermediary structure.

Contact carrier 28 is connected to carriage 60 by being inserted through an opening 112 therein, in which it is a relativley loose fit, so as to be pivotable about an axis generally parallel to spigot 106. A convex leaf spring 114 has its ends located in lips at the ends of lateral brackets 116, 118 formed integrally with carriage 60. The spring's convex surface engages contact carrier 28 and biases same in a contact-closing direction.

Stop means 120 is provided for carriage 60 to arrest movement of same in the contact-opening direction. The stop means comprises two pairs of mutually engageable fixed and movable stop surfaces, one pair 122 at the underside of the brackets 116, 118, and another pair 124 provided on a fixed structure mounted via bottom runner 52 on housing 12. The stop surfaces are disposed so that they face in directions inclined with respect to the carrier axis 62 so as to minimise rebound on contact-opening. This fixed structure may likewise be moulded from a polymeric material, likewise carriage 60, levers 72 and 80 and handle 54.

Solenoid 24 comprises coil 22, a casing 124, and plunger 126, an insulator tube 128 and an actuator pin 130 positioned to actuate the end 132 of secondary latch lever 80. A generally L-shaped leaf spring 134 is fixed to a mounting 136 and has its end 138 positioned to engage pin 130 so as to be resiliently deflected thereby and to provide a return function therefor. By virtue of the location of spring 134 externally of solenoid 24 and its accessibility for manipulation, it permits manual adjustment (by deflection) , of its return function.

In use, with the circuit breaker in the condition shown in Fig 1, the contacts 30 to 36 are closed and the circuit is made between connectors 14, 16.

In the event of a progressive slight overload, bimetal 40 progressively heats, deflects, and causes thermal trip lever 88 to pivot clockwise as seen in Fig 1 and, at a predetermined deflection of the bimetal, secondary latch lever 80 is pivoted anti-clockwise as seen in Fig 1, thereby releasing main latch lever 72 and thus likewise releasing carriage 60 under the action of spring 108, which retracts the carriage and opens the contacts. Stop means 120 inhibits carriage bounce.

The circuit can then be re-made by actuating handle 154. The point at which the mechanism trips can be adjusted by means of calibration screw 96 which is readily manually adjustable after removing calibration cover 140.

As regards instantanous tripping under massive overload, the function is as follows. Solenoid 24 detects the overload, and pin 130 deflects spring 134 and engages end 132 of secondary latch lever 80, thereby pivoting it anti-clockwise and releasing main latch lever 72, which likewise releases carriage 60, as described previously. As the contacts open, an arc is struck and transferred to the arc chutes 48, 50, which rapidly extinguish same.

In the embodiment of Fig 3 there is shown a flux shifter which can be substituted for the solenoid 24 in the above-described embodiment.

As shown in Fig 3, flux shifter 140 comprises a casing 142, a conductor 144, a shunt 145, a magnet 146, legs 147 and 151, an insulator 148, an armature 150, and a return spring 152 acting between casing 142 and a pin head 154. The magnetic flux from the magnet 146 flows through the magnetic circuit formed by legs 147 and 151, armature 150 and shunt 145. The magnetic circuit elements should be made from high permeability materials. As air gap (not shown) between shunt 145 and legs 147 and 151 is introduced to bias the magnetic circuit so that most of- the flux passes through the armature 150. The resulting magnetic force between the legs 147 and 151 and the armature 150 holds said armature in place against the force from spring 152. Holes (not shown) in legs 147 and 151, placed in the region of said legs that lies between the magnet 146 and the armature 150, reduce the cross-section of material in said region. The magnet 146 and magnetic circuit cross- sectional areas are chosen so that in this region the material is at the knee in the hysteresis curve, just below saturation.

When current passes through the conductor 144 the magnetic field intensity is increased on one side of each hole and decreased on the other. Because of the nonlinearity of the hysteresis curve, the side of the hole with the increase in magnetic field intensity has a small increase in flux, while the other side has a much larger decrease in flux. The net result is a shifting of some of the flux from the armature 150 to the shunt 145. Should sufficient current pass through the conductor the magnetic force holding the armature 150 will be exceeded by the force of the spring 152. The armature 150 is then forced away from the legs 147 and 151 which increases the reluctance of the magnetic circuit through the armature 150. Most of the flux is shifted through the shunt 145 since it is now the low reluctance path and as a result the magnetic force on the armature 150 decreases rapidly. The loss of magnetic force allows rapid motion of the armature 150 and pin 154 through the action of the spring 152. Resetting of the trip unit 140 is accomplished by pushing the armature 150 back to its position next to the legs 147 and 151.

Amongst the advantages provided by the above embodiment are the following. Firstly, by the use of a double-break contact assembly, the more stringent modern requirements for rapidity of current interruption are more readily met. By arranging for the carriage 60 and contact carrier 28 to be mounted entirely independently of the latching mechanism 58, none of the structure of the latter is carried on the carriage, and the latter is thus quite free to retract rapidly under the action of spring 108. The latter has nothing else to move.

The calibration arrangement for the trip mechanism is less prone to mis-adjustment than previous proposals due to the direct and simple way in which adjustment is achieved.

By adoption of plastic materials (synthetic polymers) for a significant number of the major components of the circuit breaker, a low coefficent of friction is provided for the trip mechanism, whereby a lower trip point can be achieved.

The anti-bounce arrangement for the carriage and contact carrier provides the significant advantage of avoiding any tendency for the arc to re-strike after contact opening due to rebound of the contact carrier in the direction of the stationary contacts.

Claims

CLAIMS : -

1 A miniature circuit breaker of the kind for providing overload protection and selective manual circuit breaking for domestic and like electricity supply circuits, the circuit breaker comprising :- a) spaced connectors for connection to the circuit to be controlled/protected; b) a circuit breaker circuit interconnecting said connectors; c) said circuit breaker circuit comprising overload detection means and contact breaker means actuable thereby and having arc extinguishing means; d) manual operating means for said contact breaker means; e) said contact breaker means comprising a pair of movable contacts and a pair of relatively fixed contacts, and actuation means for said movable contacts to effect separation thereof; f) each contact of said pairs of contacts being spaced apart from the other thereof, one at each side of a central contact carrier mounted for lengthwise movement about a longitudinal carrier axis to open and close said contacts ; g) said actuation means comprising a releasable latching mechanism engageable with said contact carrier to hold same in a latched circuit closed condition, and energy storage means to releasably store energy for opening said contacts when said latching mechanism releases said contact carrier; and h) a housing for said circuit breaker; characterised in that i) said contact carrier is mounted for guided sliding movement in said housing entirely independently of said latching mechanism under the action of a tension spring generally aligned with said axis and acting between said housing and one end of said contact carrier, and said latching mechanism being disposed to make latching engagement with the other end of said carrier member, whereby after release thereof by said latching mechanism said contact carrier is free to move under the sole action of said spring in the contact-opening direction.

2 A miniature circuit breaker comprising overload detection means and contact breaker means actuable thereby, characterised by a contact carrier mounted for independent movement in the contact opening direction.

3 A miniature circuit breaker according to claim 1 or claim 2 characterised by a pair of arc chutes located one on each side of said contact carrier and each connected at one end by an arc runner to its own one of said contacts, and said arc chutes being interconnected at their other ends by a bottom arc runner.

4 A minature circuit breaker according to claim 3 characterised in that said tension spring for said contact carrier extends through an opening in said bottom arc runner.

5 A miniature circuit breaker according to any one of claims 1 to 4 characterised by stop means for said carrier to arrest movement of same in the contact-opening direction, said stop means comprising at least one pair of mutually engageable fixed and movable complementary stop surfaces on said contact carrier and on a relatively fixed structure carried by said housing, said stop surfaces being disposed so that they face in a direction inclined with respect to said carrier axis.

6 A miniature circuit breaker according to any one of claims 1 to 5 characterised by said movable contacts being mounted on said contact carrier by means of a lateral contact support member carrying the contacts and which can angularly adjust itself with respect to the carrier under the bias of a leaf spring engaging the contact support on its outer convex surface to promote proper alignment with the fixed contacts.

7 A miniature circuit breaker according to any one of claims 1 to 6 characterised by said overload detection means comprising solenoid means having a plunger extendable upon detection of an overload, to actuate said contact breaker means, said plunger being positioned to engage a leaf spring mounted externally of the solenoid and operative to return said plunger after extension on overload.

8 A miniature circuit breaker according to any one of claims 1 to 7 characterised by the latching mechanism comprising main and secondary latch levers pivotally mounted for mutual engagement in a position in which they co-operate to hold the main latch lever in a position in which it retains the contact carriage in its contact-closed position.

9 A miniature circuit breaker according to claim 8 characterised by said latch levers being pivotally mounted on a bell crank lever, both said latch lever and said bell crank and said contact carrier being formed of a synthetic polymeric material.

10 A miniature circuit breaker according to any one of claims 1 to 9 characterised by said overload detection means comprising thermal trip means to cause said contacts to be opened, said thermal trip means being electrically connected in series with said contacts and positioned to act mechanically on a pivotally mounted thermal trip lever positioned to act on said latch mechanism, whereby said latch mechanism can be tripped upon overload, said thermal latch lever being position-adjustable under the control of a screw threaded adjuster to vary the point at which the latch mechanism trips.

11 A miniature circuit breaker according to any one of claims 1 to 6 characterised in that said overload detection means comprises a magnetic flux shifting device in which the magnetic effect of a current overload shifts magnetic flux from a movable armature to magnetic shunt means.

12 A minature circuit breaker according to claim 11 characterised in that said magnetic effect is produced by a single conductor carrying a current.

13 A miniature circuit breaker according to claim 11 or claim 12 characterised in that spring means biases said flux shifting device to its tripped position.

14 Current sensing means suitable for use, for example, in a miniature circuit breaker, comprising a magnetic flux shifting device in which the magnetic effect of a current shifts magnetic flux from a movable armature to magnetic shunt means.

15 A miniature circuit breaker or a current sensing device according to either of claims 11 or 14 characterised in that said flux shift serves to reduce magnetic attraction between said armature and a relatively fixed structure.

16 A current sensing device according to claim 14 or 15 characterised in that said magnetic effect is produced by a single conductor carrying a current.

17 Current sensing means according to any one of claims 14 to 16 characte ised in that spring means biases said armature to a tripped position.