FIELD OF THE INVENTION

The present invention relates to an electrical disconnector.

BACKGROUND ART

Electrical disconnectors are required in a wide range of situations in order to isolate an electrical circuit. This is necessary so that the circuit can safely be worked on, for example.

The design of disconnectors presents particular difficulties in respect of high current-carrying circuits, such as in the l-2kA range, as currents of this order are "reluctant" to cease flowing. If sufficient precautions are not taken then they may establish an arc across the nominally separate contacts of the disconnector, enabling the current to continue, leaving the circuit still "live", and causing damage to the disconnector.

SUMMARY OF THE INVENTION

The present invention therefore provides an electrical disconnector comprising a pair of contacts electrically isolated from each other, a bridge contact moveable between a first position in which the bridge contact is in electrical connection with the pair of contacts and a second position which the bridge contact is spaced from the pair of contacts, and a spring operative to urge the bridge contact towards the first or the second position, the spring comprising an elongate elastically deformable member seated at either end thereof in a pair of recesses, the recesses being spaced apart from each other by a distance less than the length of the member.

Such a spring provides the disconnector with an action that is suited to handling high current flows. It will initially resist movement of the bridge contact until a sufficient force is applied, at which point the spring will be deformed to a mid-position. Beyond this point, the energy stored in the spring will be released suddenly and, in combination with the applied force, will propel the bridge contact to its new position swiftly. This allows for a sudden making or breaking of electrical contact.

The spring can be a section of steel sheet. Suitably, it is connected to the bridge contact at an approximate midpoint of the spring.

The pair of contacts are ideally fixed in place within the disconnector. A space is preferably provided between the pair of contacts, with the bridge contact occupying that space when in its first position, thereby to contact one contact of the pair of contacts on each side of the bridge contact.

A housing will usually be needed for the electrical disconnector. A tab whose position is correlated with the bridge contact can protrude from the housing when in the second position, to give a clear visible indication of the status of the device. The tab can have a through-aperture located in the part which projects from the housing, to allow for a padlock or similar device to be fitted so as to prevent the circuit from being made live. This could be done, for example, while an engineer is working on the circuit at a location remote from the disconnector. By taking the key with him, the engineer can ensure that no- one accidentally operates the disconnector.

The bridge contact can be driven between the first and second positions by a cam mounted on a rotateable member. The rotateable member can then be made accessible from the exterior of the disconnector, such as by allowing a part to extend through an aperture in a housing of the disconnector. That part can include a handle or a socket for a removable handle.

A non-conductive shield can be provided in the disconnector, moveable when the bridge contact is in the second position to a position in which it lies between the bridge contact and at least one contact of the pair of contacts. Thus, when the disconnector is "open" (i.e. no current allowed to flow) the shield will reduce the likelihood of an arc developing. The shield is preferably biased towards the said position, and also shaped so as to be urged away from the said position by the bridge contact as it moves from the second to the first position.

In a second aspect, the present invention relates to an electrical disconnector comprising a pair of contacts electrically isolated from each other, a bridge contact moveable between a first position in which the bridge contact is in electrical connection with the pair of contacts and a second position which the bridge contact is spaced from the pair of contacts, and a non-conductive shield moveable with the bridge contact so as to lie between the pair of contacts when the bridge contact is in the second position.

Each of the pair of contacts can comprise two resilient fingers arranged to sit either side of the bridge contact (in the first position). The bridge contact (and the fingers) can then be sized so that the fingers are urged apart by the . bridge contact, to maintain a secure electrical contact between them. The non- conductive shield can be similarly sized to urge apart the resilient fingers when the bridge contact is in the second position, thereby reducing fatigue damage to the fingers as a result of repeated operation.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which;

Figure 1 is a perspective view from the front and one side of the disconnector module according to the present invention;

Figure 2 is a partially exploded view corresponding to figure 1; -A-

Figure 3 is a more fully exploded view;

Figure 4 is a perspective view of the cartridge unit;

Figure 5 is a view from one side; and

Figures 6 to 8 show sequential stages of deformation of the spring.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 shows the general layout of the manually independent switch disconnector according to the present invention. The disconnector assembly consists of a rear assembly 10, and a front cover 12, and a disconnector cartridge 14, not visible in figure 1 but contained within the rear assembly 10 and the front cover 12. An operating lever 16 projects from the disconnector cartridge 14 through a slot 18 in the front cover 12, to allow the disconnector to be changed from a closed (connected) state shown in figure 1 to an open (isolated) state by moving the operating lever 16 downwards (as illustrated). An interlock 20 is provided to prevent unintentional operation, and will be described later.

The rear assembly 10 comprises a rear assembly housing 22 which supports a pair of copper conductors 24, 26 which are conveyed into the rear assembly 10 via insulating sleeves 28, 30. Figure 1 shows conductors 24, 26 with a conventional shape and pattern of bolt holes 32 to allow the disconnector unit to be fitted in place to a mounting structure. Alternative rear assemblies could be provided as necessary to conform to different designs of mounting structure.

It is also intended that the disconnector be available in 1000 Amp and 2000 Amp versions. This can be achieved by fitting one set of contacts 24, 26 and one link plate (to be described) in the IOOOA version illustrated, and two sets of contacts and two link plates in 2000A version. Thus, as well as allowing for different mounting arrangements, the rear assembly can be provided in multiple forms to allow for single or double conductors for the two ratings. Figure 2 shows the unit with the rear assembly 10 and the front cover 12 separated, to reveal the disconnector cartridge 14 within. The cartridge assembly 14 contains a gear mechanism, shuttle tray and spring to effect connection and disconnection of the electrical circuit as will be described. It is provided as a distinct cartridge within the overall unit so that it can be changed (if necessary) without stripping the whole unit, to enable replacement of disconnector working parts. The rear assembly and the front cover do however give additional mechanical support to the disconnector cartridge during operation.

Figure 2 also illustrates the tab 33 which projects from the front of the disconnector cartridge 14 and through a corresponding opening 34 in the front cover 12, when the circuit is "open". This has a through-hole 36 to allow the interlock 20 to be fitted, as shown in figure 1. This consists of a padlock 20 which can be locked in place onto the through-hole 36, preventing unintended connection of the circuit controlled by the disconnector. The padlock 20 is also sized and shaped so that, when fitted, it rests in the way of the lever 16. With the lever in the lower (disconnected) position, the padlock 20 is immediately above the lever thereby preventing any movement at all.

Figure 3 shows the disconnector cartridge 14 in an exploded form. Two external housings 38, 40 lie on either side, enclosing and supporting the parts within. A shuttle tray 42 is made up of left and right halves 42a, 42b and is able to slide forward and back within the cartridge 14. At its rear, an upper tab 44 and a lower tab 46 extend rearwardly; immediately forward of these are openings 48, 50 on either side of the shuttle tray 42. Within the shuttle tray 42 there is a vertically aligned copper conductor bar 52 rated to carry l,000A safely and located so that either side is exposed by the openings 48, 50.

An upper set of contacts 54 and a lower set of contacts 56 are located within the cartridge 14 and extend from the rear part thereof toward the shuttle tray 42. Each comprises a pair of resilient fingers between which can be sandwiched a suitable conductor to make electrical contact. When the cartridge 14 is fitted in place between the rear assembly 10 and the front cover 12, the upper and lower contacts 54, 56 fit over each of the copper conductors 26, 24 respectively. Thus, as the shuttle tray 42 moves forward and backwards, the conductor bar 52 moves into and out of electrical contact with the upper and lower contacts 54, 56. When it moves out of contact, it is replaced by the tabs 44, 46 which maintain the contacts 54, 56 at the correct spacing, preventing fatigue damage, and also interposing an insulative material between the contacts 54, 56 and the conductor bar 52. A suitably high dielectric strength material can be chosen to reduce the incidence of arcing.

To propel the shuttle tray 42, the lever 16 fits removably into a shaft 56 extending from a hub 58. The hub 58 is rotatably mounted on a shaft 60 that extends laterally to the external housings 38, 40, through slots 62 in the shuttle tray 42. Thus, as the lever 16 is moved through an operating arc, the hub 58 is rotated on the shaft 60.

The exterior of the hub 58 is toothed, and engages with external teeth of a lower hub 64 mounted immediately below the hub 58 on a similarly mounted shaft. Thus, rotation of the hub 58 causes a corresponding and opposite rotation of the lower hub 64. The upper edge of the hub 58 and the lower edge of the lower hub 64 each carry a pair of cam pins 66 whish extend outwardly from either side and engage in four corresponding recesses 68 on the inner faces of the left and right halves 42a, 42b of the shuttle tray 42. Thus, as the handle is operated, the hubs rotate and drive the shuttle tray 42 forward and back, taking the conductor bar 52 into and out of contact with the contacts 54, 56.

Thus, when pulled the handle turns the two gears; the presence of two gears ensures a more uniform application of pressure to the shuttle tray. The pins on the gears then push the tray in the desired direction. This movement is (initially) resisted by a spring 70, a straight spring steel component which is inserted into two pockets (not visible) in the external housing 40 at either end of the spring. These pockets are spaced so that (at rest) the spring takes up a curved state as shown in figure 3. For clarity, figure 3 shows the spring 70 adjacent the gears; in practice it will sit outside the shuttle tray, between the tray and the 40. A second spring can be provided, if desired, on the opposite side of the shuttle tray between it and the external housing 38. The spring 70 is thus held at either end in pockets on the external housing 40 and at its midpoint is sandwiched in a channel 72 on the outside of the shuttle tray 42. As the handle is turned, the shuttle tray 42 pushes on the spring 70 and causes it to pass its centre point. From then on, the spring takes over and pushes the carrier until the spring reaches a second natural curve point, being a mirror image of the initial state.

Figure 4 shows the shuttle tray 42 and the spring 70, sandwiched in the channel 72. When the shuttle tray 42 is pushed past a centre point, the spring 70 will then fire the tray forward to make contact. The slots 62 in the tray allow the tray to move independently of the gears. Figure 4 also shows the tab 33, in position and attached to the shuttle tray 42. Thus, as the shuttle tray 42 moves back and forth, the tab 33 will move with it. With the tray 42 in its forward position and the supply disconnected, the tab 33 will project through the opening 34, allowing the padlock 20 to be fitted and preventing the shuttle tray from being withdrawn.

Figures 6 to 8 show the sequential steps in deformation of the spring 70 during operation of the disconnector. Initially, as shown in figure 6, the spring takes up a gently curved U-profile. As pressure is exerted on the spring at its midpoint 74 by the shuttle tray 42, it will initially begin to deform locally around its midpoint. Eventually, a position will be reached as shown in figure 7 at which the spring 70 takes over and drives itself to a second gently curved U-profile, opposite to the first. In doing so, the energy provided to the spring to deform it to the midway state of figure 7 is released as kinetic energy to the shuttle tray 42. This release is sudden, and propels the tray 42 into a connected or a disconnected state. The time that the disconnector spends in an intermediate state is therefore minimised, reducing the risk of arcing.

Figure 5 shows a partially sectional view of the disconnector from the side, illustrating the arrangement of the lever 16, the hubs 58, 64, and the cam pins 66. The disconnector of the present invention thus offers a number of advantages in use. When operating, the nose of the shuttle tray is always between the contacts, and the switch is made by the copper bar coming into contact with the contacts. The plastic front of the shuttle and the rib in the inner cassette achieve a useful degree of shielding in the open position. Pressure is kept on the contacts at all times by having a moulded nose on the tray. When disconnector is in the off position the indicator can be locked to stop the disconnector being turned back on, by placing a padlock through the indicator. An indication is however present to show an open or a closed state by projecting through the front cover to enable locking. Spacers can be added to reduce cost and achieve different ratings. The rear assembly and the front cover surround and support the inner cartridge to achieve strength required for the spring.

In particular, one unique feature of the invention is the use of a flat spring steel component to achieve manual independence. This and other aspects of the design of the disconnector allow manually independent switching.

It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.