GB1599039A - Circuit breaker accessory - Google Patents

Description

(54) CIRCUIT BREAKER ACCESSORY (71) We, DOLMAN SWITCHGEAR LIMI'ED, a British Company of Atherton Works, Blackpool Road, Preston, Lancashire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns accessories for circuit breakers, and has for its object to provide a construction of actuating accessory which serves to initiate circuitbreaker tripping operation upon occurrence of an "under-voltage" that is to say upon diminution of or cessation of the electrical power supply to the circuit(s) protected by the circuit breaker(s) with which the accessory is used, and which will reset automatically without the need for any manual intervention.

With this object in view, the present invention provides an actuating accessory for use with a moulded-case circuit breaker or breakers, said accessory being in the form of an under-voltage release device comprising a casing adapted to be secured to the circuit breaker(s) with a pivotable intertrip component of the accessory coupled with a corresponding pivotable intertrip element of the circuit breaker(s) so that tripping movement of the intertrip component of the accessory initiates tripping of the circuit breaker(s), characterised in that the accessory comprises an intertrip lever secured to and swingable about an axis provided by the intertrip component, an actuating lever co-operating with the intertrip lever so that swinging movement of the actuating lever causes or permits corresponding swinging of the intertrip lever, a spring loading the actuating lever in a direction to cause tripping movement of the intertrip lever, and a solenoid having an armature or plunger which, in the energised condition of the solenoid, retains the actuating lever in a non-tripping position against the action of the spring, and further characterised in that the spring is disposed to act upon the actuating lever with a line of action whose distance from the pivotal axis of the actuating lever varies with a winging of said lever so as to approximate the resistance offered by the spring/lever combination to the solenoid to the maximum force the solenoid can provide at each point of its travel.

tt will readily be understood that in use of the accessory of the invention deenergisation of the solenoid is effective to cause circuit-breaker operation, so that the device will be connected so as to receive current supply from the same source as the circuit breaker(s); then, in the event of cessation of passage of current through the breaker(s), or upon supply of only a relatively low voltage thereto, the circuit breaker(s) will be tripped.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: - Fig. 1 is a side elevation illustrating a commePcially-available moulded-case electrical circuit breaker; Fig. 2 is a side elevation illustrating a preferred embodiment of the actuating accessory of the invention, this accessory being designed 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 "nontripped" position; and Fig. 3 is a plan view of the actuating accessory of Fig. 2.

Features of the embodiments shown in Figures 2 and 3 are the subjects of our copending Patent Application Nos. 24305/77 (Serial No. 1599037), 24306/77 (Serial No.

1599037) and 24308/77 (Serial No. 1599037).

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 interupt the continuity between the two terminals 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 separted from the fixed contact and the circuit through the circuit breaker is interrupted. Movement of the dolly 13 to its "on" position (which is not illusraed 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 pivotable element, in the form of a rotatable member 14, accessible from outside the casing 10. This member 14 is formed with a diametricallydisposed slot 15 in each of its ends for reception of respective coupling slips (not shown) so that when two of the 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 illustrated therein is an under-voltage release 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 accesory can be mounted side-by-side with the circuit breaker and secured together therewith, e.g. by bolts or rivets (not shown 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, this 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 this coil 29. Thus, there is a possibility of adjusting the coil 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. An adjusting 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 compound (not shown) after adjustment has been effected pursuant to assembly of the accessory in the factory.

A pivot pin 50 is fixed to the web 26 of the bracket 25 and this provides a pivot axis near to 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 Fig. 2.

Because the pivot pin 50 is positioned away from the adjacent end of the actuating lever 40 it forms the actuating lever 40 into a two-armed 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.

Fixed to the intertrip member 23 is an intertrip lever 44 from which projects a peg 53 disposed so as to be engageable by the actuating lever 40. The peg 53 is positioned close to the extreme end of the lever 44.

The mode of operation of this actuating accessory will readily be understood from the foregoing description.

So long as the coil 29 of the solenoid is energised, the armature or 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 becames correspondingly de-energised, and the armature or plunger 31 is able to move to the left towards the rest position, indicated at 31a in Fig. 2, 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 to cause tripping of the circuit breaker(s) to which the accessory is coupled.

One of the problems in achieving reliability in the illustrated accessory 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 under-voltage 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 illustrated accessory which is designed to achieve resetting 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 characteristics of the spring 51 used to store this energy approximates so far as possible to the force/distance curve of the coil 29. This cannot always be achieved by adjustment of the spring force and rate alone, so in the illustrated arrangement the geometry has been so arranged that the distance between the axis (or line of action) 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 com pressed but, in addition, its access is rela tively much further from the pivot 50 so that 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 characten-stics of the coil 29 and the effect of the spring 51, thereby obtaining an arrangement which will reset efficiently under the action of the solenoid 30, and yet the spring 51 will store sufficient energy to ensure reliable tripping action when the coil 29 is de-energised.

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 inter trip member 23.

The invention is, of course, not re stricted to the precise details of the illustrated embodiment of the actuating accessory, and modificaions may be made thereto within the scope of the following

Claims (7)

claims. WHAT WE CLAIM IS: -

1. An acuating accessory, for use with a moulded-case circuit breaker or breakers, said accessory being in the form of an under-voltage release device comprising a casing adapted to be secured to the circuit breaker(s) with a pivotable intertrip component of the accessory coupled together with a corresponding pivotable intertrip element of the circuit breaker(s) so that the tripping movement of the inter trip component of the accessory initiates tripping of the circuit breaker(s), characterised in that the accessory com prises an intertrip lever secured to and swingable about an axis provided by the intertrip component, an actuating lever co-operating with the intertrip lever so that swinging movement of the actuating lever causes or permits corresponding swinging of the intertrip lever, a spring loading the actuating lever in a direction to cause tripping movement of the intertrip lever, and a solenoid having an aramture or plunger which, in the energised condition of the solenoid, retains the actuating lever in a non-tripping position against the action of the spring, and further characterised in that the spring is disposed to act upon the actuating lever with a line of action whose distance from the pivotal axis of the actuating lever varies with swinging of said lever so as to approximate the resistance offered by the spring/lever combination to the solenoid to the maximum force the solenoid can provide at each point of its travel.

2. An acuating accessory as claimed in Claim 1 wherein the actuating lever is a two-armed lever having a longer arm acted upon by the armature or plunger and a shorter arm actuated upon by the spring.

3. An actuating accessory as claimed in Claim 2 wherein the longer arm is abutted by an extension of the armature or plunger.

4. An acuating accessory as claimed in Claim 2 or 3 wherein the spring is provided upon a guide rod pivotally connected to the shorter arm of the actuating lever.

5. An actuating accessory as claimed in Claim 4 wherein the guide rod extends through a hole in a member against which one end of the spring abuts.

6. An actuating accessory as claimed in any preceding claim wherein the solenoid and the actuating lever are mounted upon a bracket adapted to be adjusted relative to the intertrip lever, so as to permit adjustment of the instant of tripping.

7. 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.