GB1599040A

GB1599040A - Circuit breaker accessory

Info

Publication number: GB1599040A
Application number: GB2430877A
Authority: GB
Original assignee: Dorman Smith Switchgear Ltd
Current assignee: Dorman Smith Switchgear Ltd
Priority date: 1978-05-12
Filing date: 1978-05-12
Publication date: 1981-09-30

Description

(54) CIRCUIT BREAKER ACCESSORY (71) We, DORMAN SMITH SWITCHGEAR LIMITED, a British Company, of Atherton Works, Blackpool Road, Presto, 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 accessories for circuit breakers, and has for its object to provide a novel construction of actuating accessory providing for circuit-breaker tripping operation upon occurrence of phenomena other than those commonly sensed in and by the circuit breaker itself (i.e. overload, that is to say sustained passage of current in excess of the dated current of the circuit breaker; and short circuit, that is to say passage of excessively high currents due to breakdown of or bypassing of operative impedance(s) in the circuit protected by the breaker), in which adjustment of the mechanism is achieved in a very simple and convenient way.

With this object in view, the present invention provides an actuating accessory, for use with a moulded-case circuit breaker or breakers, the accessory comprising a casing which is separately formed with respect to the moulded case(s) of the circuit breaker(s) with which it is to be used and which is adapted to be mounted side-byside with said circuit breaker(s), and an intertrip component adapted to be operatively coupled to a movable element of the circuit breaker, which movable element serves, upon movement from a rest position, to trip the circuit breaker, the accessory also comprising an actuating mechanism supported by a bracket so as to be adjustable relative to and co-operative with the intertrip component, means being provided for effecting displacement of said bracket relative to said intertrip component.

The means for effecting displacement of said bracket preferably comprises an adjusting screw which engages the bracket and whose head faces an abutment surface within the casing, the bracket being loaded by a spring to retain the screw head in engagement with the abutment surface.

Preferably, the actuating mechanism in dudes an intertrip lever connected to and swingably mounted by the intertrip component, and a solenoid having an armature or plunger whose movement serves to swing the intertrip lever.

It will readily be understood that the arrangement can be adapted for the intertrip lever to be swung, for causing circuit breaker tripping, either by energisation of the solenoid or by de-energisation of the solenoid. In the case where energisation of the solenoid serves to cause swinging of the intertrip lever of the accessory and consequential circuit breaker tripping movement, the device of the invention may be a shunt trip device the practical function of which, when the accessory is connected to a circuit breaker, is to enable the circuit-breaker tripping to be effected by command, e.g. by providing an appropriate signal to a relay to close and to supply power to the solenoid for energising the latter. Such an arrangement can be used, for example, to ensure that circuits protected by the circuit breaker(s) are switched off when sensing means senses deviation of a parameter, in an industrial process, of an unacceptable magnitude, and supplies a corresponding signal to the relay.

In the case where de-energisation of the solenoid is effective to cause circuit-breaker operation, the device of the invention is conveniently constructed as an undervoltage release device arranged to receive current supply from the same source as the circuit breaker(s), so that in the event of cessation of passage of current therethrough, or upon supply of only a reletively low voltage thereto, the circuit breakers will be tripped.

The invention will now be described further, by way of example, with reference to the accompanying drawing, in which: Fig. 1 is a side elevation illustrating a commercially-available moulded-case electrical circuit breaker; Fig. 2 is a side elevation illustrating a first embodiment of the actuating accessory of the invention, this accessory being de signed for use in conjunction with the circuit breaker of Fig. 1, and being illustrated with its cover removed to reveal its internal construction, and with its components in the tripped" positions; Fig. 3 is a plan view of the actuating accessory of Fig. 2; Fig. 4 is a side elevation illustrating a second embodiment of the actuating accessory of the invention this accessory also being designed for use in conjunction with the circuit breaker of Fig. 1, and also being illustrated with its cover removed to reveal its internal construction but being shown with its solenoid energised so that the accessory is in its non-tripped condition; and Fig. 5 is a plan view of the actuating accessory of Fig. 4.

Features of the embodiments illustrated in Figs. 2 to 5 are the subjects of our copending Patent Applications Nos.

24305/77 (Serial No. 1 599 037), 24306/77 (Serial No. 1 599 037) and 24307/77 (Serial No. 1 599 037).

Dealing firstly with Fig. 1 this illustrates a form of moulded case electrical circuit breaker already on the market. This circuit breaker comprises a moulded plastics casing 10 recessed at each end at 11 and 12 for respective terminals (not visible) for connecting the circuit breaker into a circuit intended to be protected against overload and short circuit by the circuit breaker. A tripping mechanism (not visible) within the casing 10 is operative, upon occurrence of sustained overload or short circuit conditions, to interrupt the continuity between the two teminals of the circuit breaker, for example by causing a movable contact, carried by a movable contact arm, to move away from a fixed contact. This tripping mechanism includes a dolly 13 which is shown in its "off" position. In this, the movable contact is separated from the fixed contact, and the circuit through the circuit breaker is interruped. Movement of the dolly 13 to its "on" position (which is not illustrated in the drawing) actuates the mechanism within the casing 10 to close the movable contact into engagement with the fixed contact.

The mechanism of the circuit breaker also includes a movable element, in the form of a rotatable member 14, accessible from outside the casing 10. The rotatable member 14 is formed with a diametrically-disposed slot 15 in each of its ends for reception of coupling slips (not shown) so that when two circuit breakers are disposed side-by-side in register with one another the rotatable members 14 thereof are coupled together in such a manner that rotational change of the orientation of the rotatable member 14, in one of the breakers, which occurs upon tripping of said breaker, results in corresponding rotational movement of the rotatable member 14 of the other breaker and causes that breaker to trip also. The same occurs for all breakers, however many may be coupled together.

Turning now to Figs. 2 and 3, the actuating accessory here illustrated is a shunt trip device. It will be appreciated that this accessory comprises a respective casing 16 which is separately formed with respect to, and corresponds in configuration to that of, the casing 10 of the circuit breaker of Fig. 1, so that the accessory can be mounted side-by-side with the circuit breaker and secured together therewith, e.g.

by bolts or rivets (not shown) through holes 17, 18, 19, and corresponding holes 20, 21, 22 in the circuit breaker. In practice, as many as four of the circuit breakers of Fig.

1 can be assembled together to form a multi-pole circuit breaker assembly, with their mechanisms coupled by way of their rotatable members 14, so that all of the circuit breakers will trip in unison. It will be seen from Fig. 2 that the actuating accessory has a corresponding intertrip component in the form of a rotatable intertrip member 23, with a slot 24 therein appropriately disposed for it to be coupled to the rotatable member(s) 14 of the circuit breaker(s). The intertrip member 23 is pivotally located by its ends in the casing 16 and its cover (which is removed in Fig.

2).

An actuating mechanism within the casing 16 is carried by a U-shaped mounting bracket 25 providing a web 26 along the opposite edges of which are flanges 27 and 28. The flange 27 has mounted thereon a coil 29 of a solenoid 30 having an armature or plunger 31, the coil 29 abutting by one end against the flange 27 (to which it is secured) and locating at its other end on a protrusion 32 within the casing 16. This protrusion 32 is formed integrally with an abutment wall 33 facing the respective end of the coil 29 so as to be spaced slightly away from said end of the coil 29. Thus, there is a possibility of adjusting the cpil 29 to a small extent towards the abutment wall 33, by corresponding movement of the mounting bracket 26.

This adjusting movement is provided for by means of a bracket-loading spring 34 disposed between the flange 28 of the bracket 25 and an adjacent abutment wall 35 of the casing 16, said spring 34 loading the bracket 25 towards the abutment wall 33, in combination with an adjusting screw 36 which threadedly engages into a hole in the flange 27 of the bracket 25 and which locates by its head 37 within the protrusion 32, the head 37 facing a corresponding abutment surface of the casing 16. An adjust ing hole 38 is provided in the abutment wall 33 to permit access to the head 37 of the screw 36 for adjusting purposes, and it will be understood that the hole 38 is smaller than the head 37 so that the latter cannot enter the hole 38 and that the hole 38 is sealed up with an appropriate compounded (not shown) after adjustment has been effected pursuant to assembly of the accessory in the factory.

A pivot pin 39 is fixed to the web 26 of the bracket 25 and this provides a pivot axis for one end of an -actuating lever 40 the other end of which is abutted by an extension 41 of the armature or plunger 31.

This armature or plunger 31 is shown in Fig. 2 in its extended condition, corresponding to the coil 29 having been energised, and can return by shifting to the left (considered as in the drawing) from the position shown in Fi. 2. A resetting spring 43 is connected by one end to the flange 27 and by its other end to the actuating lever 40 to load the latter and the plunger 31 from the illustrated position and back into an initial rest position indicated at 31a.

Fixed to the intertrip member 23 is an intertrip element in the form of a lever 44 from which projects a peg 45 disposed so as to be engageable by the actuating lever 40.

The mode of operation of this actuating accessory will readily be understood from the foregoing description. The accessory is mounted side-by-side with, and is operatively coupled to, one or more circuit breakers as described, and the solenoid coil 29 is connected by way of appropriate leads 46, 47 and terminals 48 and leads (not shown) to means (such as a control device which senses one or more parameters in an industrial process) which will supply current to the coil 29 when tripping of the circuit breakers is required. Normally, the armature or plunger 31 is in a rest position projecting as indicated in dotted lines at 31a. Upon the coil 29 being energised, the armature or plunger 31 is shifted to the right into the tripping position shown in Fig. 2, causing pivoting of the actuating lever 40 in a clockwise direction, thereby to cause corresponding pivoting of the intertrip lever 44 in an anticlockwise direction.

This latter pivoting causes corresponding pivoting of the intertrip member 23 and consequential tripping of the circuit breakers.

Upon the coil 29 being de-energised, the accessory is reset by the force of the spring 43 acting upon the actuating lever 40 thus disengaging it from the pin 45 on the intertrip lever 44.

It will be appreciated, of course, that adjustment of the screw 36 serves to adjust the instant of tripping of the circuit breakers, since this adjusts the bracket 26 and actuating lever 40 relative to the intertrip member 23.

Turning now to Figs. 4 and 5, these figures illustrate a second embodiment of the accessory of the invention, which is an under voltage release device. It will readily be appreciated, from comparison of the figures, that this accessory comprises a large number of components similar to those already described with reference to Figs. 2 and 3. Accordingly, similar reference numerals have been allocated to these parts, which do not have to be described in detail again. In Fig. 4, the accessory is shown in its condition corresponding to the solenoid coil 29 being energised so that the accessory is in its non-tripped condition.

In this embodiment, the actuating lever 40 is pivotally mounted upon a respective pivot pin 50 which is differently positioned compared with the pivot pin 39 of Fig. 2, so as to form the actuating lever 40 into a twoarmed lever of which the longer arm is abutted by the extension 41 of the solenoid's armature or plunger 31 and the shorter arm is abutted by an actuating spring 51 carried by a guide rod 52 pivotally connected to said shorter arm and slidably located in a hole in the flange 27 of the bracket 26.

Peg 53 secured to the intertrip lever 44 for abutment by the shorter arm of the actuating lever 40 is positioned closer to the extreme end of the intertrip lever 44 as compared with the peg 45 in Fig. 2.

With this embodiment, so long as the coil 29 of the solenoid is energised, the armature of plunger 31 is retained in the extended position illustrated, with the extension 41 abutting the longer arm of the actuating lever 40 and thereby holding the shorter arm thereof away from engagement with the peg 53. Accordingly, assuming the solenoid 30 to be connected so as to be energised by the same current supply as is supplied to the circuit breaker(s), the actuating accessory will remain in its illustrated non-tripping condition. Should, however, there be a failure of the power supply or a significant reduction in the voltage thereof, the solenoid 29 becomes correspondingly de-energised, and the armature or plunger 31 is able to move to the left towards and rest position indicated at 312 under the influence of the actuating spring 51 acting on the actuating lever 40.

The latter engages, of course, with the peg 53, so that the intertrip lever 44 is pivoted in the same way as described with reference to the arrangement of Figs. 2 and 3 to cause tripping of the circuit breaker(s) to which the accessory is coupled.

It will he appreciated from the foregoing description that the two described accessories, although operating under different circumstances, are constructed largely with identical components, it being necessary only to modify only a minimum of the common components, and to employ a minimum of alternative components to achieve the two differently-operating arrangements.

Insofaras concerns the embodiment of Figs. 4 and 5 of the drawings, one of the problems is to ensure that the mechanical work output of the coil, having a short stroke and being continuously-rated, is adequate to store sufficient energy in the spring 51 to ensure an adequate safety margin over the work required to trip the circuit breaker(s).

Comparable problems, in the past, have been overcome in circuit breakers embodying undervoltage release devices by providing resilient mechanical reset means for the coil, driven by the operating dolly of the circuit breaker. Since, the holding force of a coil is very much greater than that which it can pull in against, a much stronger spring can be used to provide the necessary margin of trip energy. However, these mechanical reset means present problems which are avoided in the accessory of Figs.

4 and 5 which is designed to achieve re setting, purely electrically.

For a given coil of small size suitable for this application with a given maximum dissipation, it is possible to obtain more mechanical work output if it is energised by A.C. rather than D.C. Since the work output is proportional to the area under the force/distance curve, it is also important to ensure that the characteristic of the spring used to store this energy closely matches the coil's forceldistance curve in shape.

This cannot always be achieved by adjustment of the spring force and rate alone, so in the arrangement of Figs. 4 and 5 the geometry has been so arranged that the distance between the axis of the spring 51 and the pivot 50 alters appreciably due to the relatively large angle of movement of the actuating lever 40. Thus, when the armature or plunger 31 is withdrawn to its position indicated at 31a, the spring 51 is extended and producing low force and, in addition, its axis extends close to the pivot 50 thereby giving low torque and, in turn, low initial resistance to travel of the armature or plunger 31. Towards the end of the travel of the armature or plunger 31 when the available force of the coil 29 is approaching its maximum, the spring 51 is more compressed but, in addition, its axis is relatively much further from the pivot 50 so that the effect on the resistance which the coil 29 must overcome increases disproportionately.

By careful arrangement of these several parameters, it is possible to achieve a very close degree of matching between the characteristics of the coil 29 and the spring 51, thereby obtaining an arrangement which will reset efficiently under the action of the spring 51, and yet store sufficient energy to ensure reliable tripping action when the coil is de-energised.

The invention is not confined to the precise details of the foregoing examples and variations may be made thereto.

WHAT WE CLAIM IS:- 1. An actuating accessory, for use with a moulded-case circuit breaker or breakers, the accessory comprising a casing which is separately formed with respect to the moulded case(s) of the circuit breaker(s) with which it is to be used and which is adapted to be mounted side-by-side with said circuit breaker(s) and an intertrip component adapted to be operatively coupled to a movable element of the circuit breaker, which movable element serves, upon movement from a rest position, to trip the circuit breaker, the accessory also comprising an actuating mechanism supported by a bracket so as to be adjustable relative to and co-operative with the intertrip component, means being provided for effecting displacement of said bracket relative to said intertrip component.

2. An actuating accessory as claimed in Claim 1, in which the means for effecting displacement of said bracket comprise an adjusting screw which engages the bracket and whose head faces an abutment surface within the casing, the bracket being loaded by a spring to retain the screw head in engagement with the abutment surface.

3. An actuating accessory as claimed in Claim 1 or 2 in which the actuating mechanism includes an intertrip lever connected to and swingably mounted by the intertrip component, and a solenoid having an armature or plunger whose movement serves to swing an intertrip lever.

4. An actuating accessory as claimed in Claim 3, in which energisation of the solenoid serves to cause circuit breaker tripping movement or swinging, the accessory being a shunt trip device, the practical function of which, when the accessory is connected to a circuit breaker, is to enable the circuit-breaker tripping to be effected by command.

5. An actuating accessory as claimed in Claim 3, in which de-energisation is

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

Claims

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

with identical components, it being necessary only to modify only a minimum of the common components, and to employ a minimum of alternative components to achieve the two differently-operating arrangements.

Insofaras concerns the embodiment of Figs. 4 and 5 of the drawings, one of the problems is to ensure that the mechanical work output of the coil, having a short stroke and being continuously-rated, is adequate to store sufficient energy in the spring 51 to ensure an adequate safety margin over the work required to trip the circuit breaker(s).

Comparable problems, in the past, have been overcome in circuit breakers embodying undervoltage release devices by providing resilient mechanical reset means for the coil, driven by the operating dolly of the circuit breaker. Since, the holding force of a coil is very much greater than that which it can pull in against, a much stronger spring can be used to provide the necessary margin of trip energy. However, these mechanical reset means present problems which are avoided in the accessory of Figs.

4 and 5 which is designed to achieve re setting, purely electrically.

For a given coil of small size suitable for this application with a given maximum dissipation, it is possible to obtain more mechanical work output if it is energised by A.C. rather than D.C. Since the work output is proportional to the area under the force/distance curve, it is also important to ensure that the characteristic of the spring used to store this energy closely matches the coil's forceldistance curve in shape.

This cannot always be achieved by adjustment of the spring force and rate alone, so in the arrangement of Figs. 4 and 5 the geometry has been so arranged that the distance between the axis of the spring 51 and the pivot 50 alters appreciably due to the relatively large angle of movement of the actuating lever 40. Thus, when the armature or plunger 31 is withdrawn to its position indicated at 31a, the spring 51 is extended and producing low force and, in addition, its axis extends close to the pivot 50 thereby giving low torque and, in turn, low initial resistance to travel of the armature or plunger 31. Towards the end of the travel of the armature or plunger 31 when the available force of the coil 29 is approaching its maximum, the spring 51 is more compressed but, in addition, its axis is relatively much further from the pivot 50 so that the effect on the resistance which the coil 29 must overcome increases disproportionately.

By careful arrangement of these several parameters, it is possible to achieve a very close degree of matching between the characteristics of the coil 29 and the spring 51, thereby obtaining an arrangement which will reset efficiently under the action of the spring 51, and yet store sufficient energy to ensure reliable tripping action when the coil is de-energised.

The invention is not confined to the precise details of the foregoing examples and variations may be made thereto.

WHAT WE CLAIM IS:- 1. An actuating accessory, for use with a moulded-case circuit breaker or breakers, the accessory comprising a casing which is separately formed with respect to the moulded case(s) of the circuit breaker(s) with which it is to be used and which is adapted to be mounted side-by-side with said circuit breaker(s) and an intertrip component adapted to be operatively coupled to a movable element of the circuit breaker, which movable element serves, upon movement from a rest position, to trip the circuit breaker, the accessory also comprising an actuating mechanism supported by a bracket so as to be adjustable relative to and co-operative with the intertrip component, means being provided for effecting displacement of said bracket relative to said intertrip component.
2. An actuating accessory as claimed in Claim 1, in which the means for effecting displacement of said bracket comprise an adjusting screw which engages the bracket and whose head faces an abutment surface within the casing, the bracket being loaded by a spring to retain the screw head in engagement with the abutment surface.
3. An actuating accessory as claimed in Claim 1 or 2 in which the actuating mechanism includes an intertrip lever connected to and swingably mounted by the intertrip component, and a solenoid having an armature or plunger whose movement serves to swing an intertrip lever.
4. An actuating accessory as claimed in Claim 3, in which energisation of the solenoid serves to cause circuit breaker tripping movement or swinging, the accessory being a shunt trip device, the practical function of which, when the accessory is connected to a circuit breaker, is to enable the circuit-breaker tripping to be effected by command.
5. An actuating accessory as claimed in Claim 3, in which de-energisation is

effective to cause circuit-breaker operation, the accessory being constructed as an undervoltage release device.
6. A moulded case circuit breaker and, mounted side-by-side with and operatively coupled to the circuit breaker, an actuating accessory as claimed in any one of the preceding claims.