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(11) | EP 0 367 436 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Electric isolator switch |
| (57) An electrical isolator switch having a moving contact member (20) in the form of
a link bridging spaced stationary contacts (22, 24) in which the moving contact has
a preference for breaking its electrical contact with one (24) of the stationary controls
rather than the other (normal break action) but can be broken at the other, and wherein
means (x) is provided to limit movement of the moving contact member away from said
other stationary contact to force breaking at said one contact. |
[0001] This invention relates to electric switches applicable to mains electrical customers' units for isolation purposes.
[0002] It is commonplace to find isolator switches between incoming mains and sub-circuit fuses or circuit breakers. Such isolator switches may be of knife-action type, typically double knife-action for live and neutral lines, or of biased cantilever type. Moreover, it is increasingly the case that such isolator switches are being made available in a modular form, typically a slim casing with the switch lever or dolly protruding from one edge. It is an object of this invention to provide a viable alternative switching mechanism suitable for isolator switches.
[0003] We have proposed, see British patent specification No. 2180404 an electrical isolator switch having a moving contact member in the form of a link bridging between spaced stationary contacts in its make position, the moving contact member being both biased towards make and associated with break-forcing means so that operation of the latter results in preference for the moving contact member to break its electrical contact with one of the stationary contacts rather than the other.
[0004] Normal break action results where the moving contact member effectively pivots against its bias and about its engagement of said other stationary contact, but can be broken at the latter if the moving contact member is reluctant to break from the said one stationary contact, such as can occur at contact welding usually due to sparking at operation and thus more likely at the one stationary contact concerned in normal break action.
[0005] It is the case that breaking at said other stationary contact will most often lead to breaking of any such weld at said one stationary contact, but it is an object of the present invention to improve prospects of that occurring.
[0006] Accordingly, one aspect of the present invention further provides means for limiting movement of the moving contact member away from said other stationary contact before full movement of the moving contact member normal for break purposes is complete. Preferably, at such breaking, and after freeing from said one stationary contact, the moving contact member will go automatically, due to the bias, to its normal position after break action.
[0007] Then, other than for normal break action, and where movement of the moving contact involves its pivotting against its bias, there will be first pivotting about said one stationary contact then second pivotting about the means for limiting movement, which may be a simple abutment.
[0008] As with our previous proposal, the biasing applied to the moving contact member can be by a spring acting at a position between the stationary contacts but closer to said other than to said one thereof, or at least to one side of a moving contact engager of the break-forcing means which serves to act on the moving contact member between its bias spring position and said one stationary contact.
[0009] Also, preferred break-forcing means is of toggle action in continual engagement between a switch dolly or handle and the moving contact member, preferably with positive retaining relation between the link and the moving contact member. A link or lever of the break-forcing means may be hinged or pivotted to the switch dolly or handle.
[0010] However, another aspect of the invention further provides that the aforesaid hinged or pivotted construction provides slack in the pivotted contact of its link or lever with the switch dolly or handle when the switch dolly is in the contacts closed position to ensure that the contacts are always made (i.e. that the opeing mechanism does not hold the contacts apart). This is a particularly preferred and advantageous construction.
[0011] The connection nevertheless provides for positive opening of the contatcts by push action in cooperation of the link pivot with the switch dolly, and positive movement of the closing contact member in the closing direction by a pulling action with spring assistance.
[0012] That slack is readily provided by an elongate generally oval or elipse-like slot in one of the switch dolly/handle or the link, preferably the former having opposite end parts preferably circular to act as abutments for a cooperating engagement with an end pivot axle of the cooperating part preferably the link - conveniently cicular to match the end parts on which hinging takes place. The spacing of the end parts provides for slack in the connection between the link and the switch dolly. The aforedescribed elongate slot is open to one side permitting insertion of the end part into the slot.
[0013] A convenient construction of link provides the end pivot axle to opposite sides of a central strut, giving a T-shaped end of which the two pivot axles are received in respective transversely spaced elongate slots arranged as claw-like projections to the switch dolly.
[0014] Such a link should at least bear on the moving contact member if not be further hinged or pivotted thereto. A suitable link can be entrant via an end into a relieved location of the moving contact member, and a suitable relieved location is a through-hole into or through which enters an end portion of the link or lever that is shouldered or pinned to engage on the moving contact member, preferably further pinned or spread beyond the latter for positive retraction of the moving contact member back into its make state.
[0015] Continual engagement for toggle action effectively sets a range of forced movement of the moving contat member, thereby aiding the two-stage pivotting referred to above for contact break action first at said other stationary contact followed by weld break action at said one stationary contact.
[0016] Isolator switch mechanisms hereof may be of single, or more, phase action. It is readily installed in a slim housing of the type mentioned above, one for each phase if preferred, say then with its switch dollys or other operating means engaged. Typically, a preferred insulator switch mechanism has its fixed spaced contacts to be bridged by the moving contact member located between spaced plates, and its moving contact member guided between such plates, preferably, at least for one end, say its unfavoured break end (but possibily for both ends), via cooperating formations, for example involving grooves or other indentation of those side plates.
[0017] Specific implementation of this invention is now described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a section through an incomplete isolator switch;
Figure 2 is a fragmental transverse sectional view of its slim casing;
Figures 3 and 4 show alternative moving contacts;
Figures 5 and 6 show normal break action diagramatically;
Figures 7, 8, 9 and 10 show stages of other break action, and
Figures 11 and 12 illustrate a preferred toggle link construction in contacts closed and contacts open positions respectively.
[0018] In Figures 1 and 2, a slim housing 10 is shown with a pivot position 12 for a switch dolly or handle indicated only by lines 14 for the ON position and 14′ for the OFF position, and shown angled at the pivot position to present a toe 14T itself pivotted or hinged, see 16, (preferably with controlled float or slack as described further hereafter) to a link or lever 18 that acts on a moving contact member 20 shown bridging a space between two fixed contact members 22, 24 and electrically interconnecting same in the ON statem and with the normal OFF and alternative OFF positions indicated by dashed lines 20X and 20Y, respectively.
[0019] Electrical connection is indicated in Figure 1 as being made by mating contacts 22A, 22B and 24A, 24B formed in or on or suitably secured to end-adjacent positions on the contact members, say in the well-known rivetted manner in holes through those members. A variant shown in Figures 3 has a domed contact 22B′ at the normally pivotting end of the moving contact member, and Figure 4 shows no contact at the other end of the moving contact member, say where reliance is made simply on suitable facing of at least that end. However, any suitable contact system may be used, in like manner as can any switch dolly or handle that can be linked to the moving contact member to achieve desired breaking action relative thereto.
[0020] The moving contact member 20 is in a well 26 of the housing 10 and is shown biased by a compression spring 28 suitably located in the wel 26 and on the contact member 20, say by seating recess 28A and a pip 28B as shown, or vice versa, or some other suitable system. The position of the spring 28 is between end positions of the moving contact member 20 and closer to one end, shown to the left hand side of Figure 1 and carrying the contact 22B.
[0021] Accordingly, when the switch dolly or handle is moved to the OFF position a toggle action via the link will force a displacement of the moving contact member 20 into the well 26 against the compression spring 28. However, the position of the latter will obviously favour breaking of contact at the end of the moving contact member 20 most remote from the spring 28, i.e. to the other side of the position at which the toggle link 18 engages the member 20 and shown to its right hand side in Figure 1 carrying the contact 24B.
[0022] Both of the assymmetric location of the spring 28 relative to the moving contact member 29 and the oppositely assymmetric location of engagement of the toggle link also relative to the length of the moving contact member 20 contribute to favouring break (20X) at the contact 24B, but a disinclination so to do does not preclude alternative breaking (20Y) at the contact 22B, say where there is a contact weld at the contact 24B. Such alternative contact breaking (22Y) will encourage breaking of such wed.
[0023] Figures 5 and 6 demonstrate the principles of normal break action at the contacts 24A and 24B.
[0024] Figures 7 to 10 similarly demonstrate the principle of abnormal break action, i.e. when the contacts 24A and 24B are seized together. Figures 7 and 10 are as Figures 5 and 6, respectively. However, Figure 8 shows pivotting first about those seized contacts 24A and 24B to open the contacts 22A and 22B and until the moving contact member 20 meets the abutment X shown as part of a moulding at the side of a seat for the bias 28, (conveniently as a side wall part of the seat). Figure 9 shows later pivotting of the moving contact member 20 about the abutment X resulting in freeing of the contacts 24A and 24B. Thereafter, the bias 28 assures achievement of the condition shown in Figure 10, i.e. equivalent to normal break action with contacts 22A and 22B closed but contacts 24A and 24B open. It will be appreciated that the illustrated action is presented as it is for illustrative purposes only, i.e. in practice there should never be a position truly corresponding to Figure 8 (due to bias action). If desired, of course, the rigid abutment X could be replaced by a limit device offering resisted compliance to the moving contact member 20, thereby not completely obstructing switch dolly operation if the weld at contacts 24A and 24B will not break easily.
[0025] The moving contact member 20 is conveniently guided between spaced parallel locating plates 30A, 30B and 32A, 32B with at least one pair thereof preferably providing further guidance/location for the moving contact member 20, say via grooves, slots or other recesses (33A, 33B) therein or protrusions 34 from sides of the moving contact member 20, though an opposite arrangement of ribs on the locating plates and indents of the moving contact is feasible.
[0026] The position of engagement for the toggle link 18 to the moving contact member 20 is conveniently provided via a recess in the latter to take the end of the link 18, conveniently a hole into or through which that end can pass, with a shoulder or cross pin (see dot 42 in Figure 1 and dashed in Figure 3) to push the moving contact member shown. Where, as can be particularly advantageous, the end of the toggle link end goes clear through the hole 40 a cross pin or further cross pin below the moving contact member can serve to assure positive action of the isolator switch relative to its moving contact member 20, see dashed in Figure 3 to 44. Any other suitable positive retaining engagement between the link 18 and the moving contact member 20 can be used, for example pivotting the former to an upstand of the latter.
[0028] Reference to Figures 11 and 12 show fragmentary views of a preferred embodiment of isolator switch with contacts closed and open respectively, actually showing in detail one embodiment of switch dolly 14 and cooperating link 18 for operating contact member 20. The basic operation of the switch corresponds to that described previously and corresponding parts are denoted by the same reference numerals. The switch dolly is pivotted about axis 16 and is slotted at 100, actually preferred as a pair of transversely spaced slots, to secure pivottably the end of link 18. That slot is elongate having opposite arcuate end parts (circular) 102, 104 for mating engagement with a cooperating end pivot axle 106 of the link in operation of the switch mechanism on movement of the contact member between its open and closed positions. The end pivot axle 106 is actually preferred as two coaxial parts projecting from opposite sides of the link giving a T-head configuration.
[0029] The slot 100 has a side opening 108 by which the end pivot axle of the link is introduced into the slot, thereby giving a claw-like configuration.
[0030] The link is secured to the contact member for pivotal movement about axis 142. That connection provides for positive pushing and pulling movement of the contact member according to the force exerted by way of the link 18.
[0031] It will be seen from Figure 11 that in the contacts closed position, the end pivot axle 100 is actually disposed between the end parts of the slot 100 so that spring biasing from spring 28 ensures contact engagement, with dolly actually having a limited degree of slot (see dotted outline for dolly in Figure 11) before the axle 106 contacts either of the end parts. On moving the switch from the on to off position the axle is first brought into engagement with the end part 104 then exerting a pushing force on the link to move the contact member in the opening direction. The switch goes over centre with the axle moving into engagement with the end part 102 so that the inks then physically holds the contact member in the off position.
[0032] It will be apparent from the above construction that the mechanism provides a positive off action and dolly float in the off position. The forced opening of the contact member is as previously described.
[0033] Figures 11 and 12 show how the spring 28 can be accommodated in a well formation 128 whose open end is formed at an angle or has an extension which provides an abutment 129 acting as the means for limiting the movement of the moving contact member. Such a construction is applicable to the aforedescribed embodiment.
1. An electrical isolator switch having a moving contact member (20) in the form of
a link bridging between spaced stationary contacts (22, 24) in its make position,
the moving contact member being both biased towards make and associated with break-forcing
means so that operation of the latter results in preference for the moving contact
member to break its electrical contact with one (24) of the stationary contacts rather
than the other (22) by pivotting of the moving contact member against its bias and
about its engagement with said other stationary contact (normal break action), but
can be broken at the latter if the moving contact member is reluctant to break from
said one stationary contact, characterised by means (x) for limiting movement of the
moving contact member away from said other stationary contact before full movement
of the moving contact member normal for break purposes is complete.
2. An electrical isolator switch as claimed in claim 1 in which at such breaking,
and after freeing from said one stationary contact, the moving contact member is biased
to its position after normal break action.
3. An electrical isolator switch as claimed in claim 1 or 2 in which, other than for
normal break action, and where movement of the moving contact involves its pivotting
against its bias, there will be first pivotting about said one stationary contact,
then second pivotting about the means for limiting movement.
4. An electrical isolator switch as claimed in any one of claims 1, 2 or 3 in which
the means for limiting movement comprises a simple abutment.
5. An electrical isolator switch as claimed in any one of the preceding claims in
which the means for limiting movement is located closer to the other of the two stationary
contacts.
6. An electrical isolator switch as claimed in any one of the preceding claims in
which the biasing applied to the moving contact member is a spring (28) acting at
a position between the stationary contacts but closer to said other than said one
thereof.
7. An electrical isolator switch as claimed in claim 6 in which the spring is received
in a well whose open end provides said means ior limiting movement.
8. An electorical isolator switch as claimed in any one of the previous claims in
which the break-forcing means is of toggle action in continual engagement between
a switch dolly or handle and the moving contact member.
9. An electrical isolator switch as claimed in claim 8 in which there is positive
retaining relation between the link and the moving contact member and the link is
hinged or pivotted to the switch dolly or handle in a manner which provides slack
when the switch dolly is in the contacts made position.
10. An electrical isolator switch as claimed in claim 9 in which the slack is provided
by an elongate slot in one of the switch dolly/handle or the link and a pivot axle
of the other received therein, and wherein the slot is partially open to one side
to admit said pivot axle for assembly purposes.