FIELD OF THE INVENTION

This invention relates to a dropout fuse assembly and to a fuse holder forming a part thereof whereby a repeater fuse characteristic may be imparted to an installation having conventional dropout fuse elements with the result that electrical continuity can be automatically restored in the event of at least a first fuse of the assembly blowing.

More particularly, but not exclusively, the invention relates to a dropout repeater fuse of the general type described in published international patent application WO2008068575 of which applicant is now the proprietor. The content of that publication is incorporated herein by reference.

BACKGROUND TO THE INVENTION As stated in the earlier published patent application identified above, prior art repeater fuse assemblies suffer from the disadvantage that there is an inadequate time delay from the time that one fuse blows and the time that the other becomes connected. The time delay is provided in order to enable an arc created by the blown fuse to clear adequately before the circuit is reconnected.

The solution to this problem put forward in the earlier published patent application is an arrangement in which a tubular fuse element drops out of its operative position in consequence of its fuse becoming blown and a reset arm in the form of a leaf spring that is held in a somewhat flexed condition initially straightens out and in so doing urges the blown fuse out of its over centre but generally upright position. After an initial movement of the blown fuse in a downward arcuate path, a separately spring biased bridging member rotates under its own spring loading to its operative position in which it bridges first and second switch contacts in order to complete a circuit through the replacement fuse wire that passes through a passage in the tubular fuse element. The arrangement is such that there is an adequate time delay from the instant that the fuse blows for any arc generated to subside before the bridging member restores the connection. The time period has been determined to be preferably of the order of about 1 .2 seconds.

Whilst the arrangement described in the earlier published patent application will operate effectively, it has been determined that a more cost-effective arrangement is available and such an arrangement forms the subject matter of the present patent application. Other and additional improvements have also been made to the fuse holder assembly described in the earlier patent application and are described herein.

SUMMARY OF THE INVENTION In accordance with one aspect of this invention there is provided a fuse holder comprising an elongate electrically insulating body providing at least one electrically insulated elongate fuse housing in the form of a passage associated with the body and adapted to receive a fuse wire held under tension therein, first contact means at one end of the body and second contact means at the other end of the body wherein the first contact means and second contact means are configured for cooperation, in use, with co- operant first and second mating contacts of an insulator unit of a dropout fuse assembly, wherein the first contact means is electrically connected to first co- operant mating contact means on the fuse holder body and the second contact means is electrically connected to second mating contact means on the fuse holder body such that a dropout fuse element can be installed on the fuse holder body between said first and second co-operant mating contact means on the fuse holder body, wherein electrical conductors are provided in or on the body for defining an electrical circuit between the first and second contact means that operatively includes a fuse installed in said passage and switch means that is held open whilst a dropout fuse element is installed between said first and second co-operant mating contact means on the body and wherein such switch means is adapted to automatically close, in use, when such dropout fuse element drops out in consequence of its fuse being blown and wherein the switch means is biased to its closed position and is held in its open position against such bias by a catch associated with a release arm located to be moved to disengage the catch by motion of a dropout fuse element dropping out of its operative position in consequence of its fuse having blown.

Further features of the invention provide for the release arm to be directed generally downwards in the operative position so that its lower free end is moved by the dropout fuse element only once it reaches a position in the vicinity of its terminal dropped out position in which it hangs from the fuse holder; for the release arm to be pivotally mounted to the fuse holder so as to be rotatable about the pivotal mounting that is positioned between the catch and a lower free end of the release arm; and for the catch to be constituted by the upper free end of the release arm.

Still further features of the invention provide for the electrical conductors defining the circuit that includes a fuse installed in said passage to include a first electrical conductor in electrical contact with the first contact means and that extends through the body to terminate in a first switch contact on one side of the body and a second electrical conductor extending through the body from a second switch contact on an opposite side of the body to operatively electrically connect with a fuse wire installed in said passage, wherein the fuse is associated with an articulated contact assembly forming said second contact means on the body; and for a generally U-shaped bridging member that forms part of the switch means to be rotatable about an axis extending across the U-shaped bridging member at generally right angles to the arms thereof with the U-shaped bridging member being resiliently angularly biased towards an operative terminal closed position in which its arms are in electrical contact with the first and second switch contacts to close a circuit between the first contact means and second contact means by way of a fuse wire in the passage.

In the instance that the U-shaped bridging member is rotatable about a generally horizontal axis that is remote from the ends of the arms that contact the contacts in the closed position of the switch, in use, it is preferably provided with a reset arm that is rotatable in unison with the U-shaped bridging member and that can be rotated from a remote position by means of a suitable manually operated rod or pole in order to reset the switch to an inoperative position from a remote position when a replacement dropout fuse is installed in the fuse holder. In such an instance it is preferred that the reset arm extend transversely, typically at right angles, to a plane in which the U-shaped bridging member is orientated and it is further preferred that the reset arm be of low electrical conductivity or at least have a suitable electrically insulating cover or coating in order to obviate stray arcs that could otherwise occur. The U-shaped bridging member may also be electrically insulated as may be required. Are

Other structural details of the fuse holder will become more apparent from what follows in which one embodiment of the invention will be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-

Figure 1 is a schematic side elevation of one embodiment of dropout fuse holder according to the invention without any dropout fuse installed therein; Figure 2 is a schematic front view thereof;

Figure 3 is a schematic side elevation of an assembly of the embodiment of fuse holder illustrated in Figures 1 and 2 in an installed condition in an electrical insulator and having a dropout fuse element installed therein; Figure 4 is the same as Figure 3 but illustrating the fuse element in a dropped out condition following on blowing of the fuse therein and where the dropout fuse element is approaching the lower free end of the release arm; is the same as Figure 4 but showing the dropout fuse element having moved the release arm to disengage the catch defined by the upper free end of the release arm;

Figure 6 is the same view but illustrating the fuse holder itself in a dropped out condition relative to the electrical insulator following on blowing of the fuse contained in its passage;

Figure 7 is a detailed schematic side view showing the reset arm and U-shaped bridging member held in their inoperative spring biased positions by the upper free end of the reset arm;

Figure 8 is the same as Figure 7 but showing the end of the reset arm disengaged from the U-shaped bridging member;

Figure 9 is the same as Figure 8 but showing the U-shaped bridging member engaging and interconnecting the contacts of the circuit; and,

Figure 10 is a front view of the U-shaped bridging member and contacts in their inter-engaged condition.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

In the event that the practical implementation of the embodiment of the invention described below is in any way unclear, reference may be had, as may be necessary, to the published international patent application identified above.

Turning now to the embodiment of the present invention that is illustrated in the drawings, an elongate fuse holder (20) is made of electrically insulating material and has an electrically insulated elongate fuse housing in the form of a passage (21 ) associated with the body and adapted to receive a fuse wire

(22) held under tension therein by means of an articulated contact assembly

(23) , that includes a tensioning flap (24), the articulated contact assembly forming the second contact means defined above. The fuse holder body also has first contact means in the form of a domed nut (25) at its other end.

The arrangement is thus such that the fuse holder itself can be installed between a first mating contact (3) of an insulator unit (1 ) and the second mating contact or cradle (7) in exactly the same manner as the dropout fuse element itself, and as a replacement therefor.

The first contact means or domed nut (25) is electrically connected to first co- operant mating contact means (26) on the fuse holder body that is substantially identical to the first mating contact (3) on the insulator unit. The articulated contact assembly (23), being the second contact means, is electrically connected to a second mating contact means on the body of the fuse holder that assumes the form of a substantially identical cradle (27). This arrangement is such that a dropout fuse element (5) having a domed contact nut (4) at its upper end and a relatively rotatable articulated contact assembly (8) at its opposite end can be installed on the fuse holder body between said first and second co-operant mating contact means in substantially conventional manner, the only difference being that it is in this instance carried by the fuse holder rather than directly by the insulator unit.

The tubular dropout fuse element (5) with the fuse therein intact, closes the circuit from the first contact means or domed nut (25) to the articulated contact assembly (23).

In this condition the circuit through the fuse wire (22) in the passage (21 ) of the fuse holder is electrically isolated. Electrical connections for this fuse wire include a first electrical conductor (28) provided in the body in electrical contact with the first contact means or domed nut (25) and this first electrical conductor terminates in a first switch contact (29) on one side of the body. A second electrical conductor (30) extends through the body from a second switch contact (31 ) on an opposite side of the body to electrically connect with the fuse wire (22) installed in said passage, and thence with the substantially identical cradle (27) (for the arrangement of contacts see in particular Figures 2 and 10).

An electrically conductive U-shaped bridging member (32) is pivotally mounted to the body by means of a pivot (33) and is spring loaded, by means of a double torsion spring (34), towards a position in which the arms of the U- shaped bridging member contact both of the first and second switch contacts (29, 31 ). That position closes the circuit to the fuse wire (22), that is, by movement in an anti-clockwise direction in the illustrated side views shown in Figures 3 and 4 of the drawings to the position illustrated in Figures 1 and 5 of the drawings. The bridging member is held against the spring loading thereof in an inoperative position by a catch formed by the upper free end (41 ) of a release arm (42) that is directed generally downwards in the operative position so that its lower free end (43) is in the line of terminal movement of the tubular fuse element (5) as it drops out. The bridging member may be electrically insulated as may be required. The release arm is pivotally attached to the body by means of a pivot (44) a short distance below the U-shaped bridging member so that it functions as a catch to hold the U-shaped bridging member in its inoperative position against its own spring loading. As will be appreciated from Figures 7 to 9 of the drawings, movement of the lower free end of the downwardly extending release arm in an anticlockwise direction will release the catch and enable the U-shaped bridging member to snap into its co-operating position with the contacts (29, 31 ) to close the circuit to the fuse wire (22) in the passage (21 ) of the fuse holder body. The arrangement is such that the upper free end of the release arm is only disengaged from the U-shaped bridging member when the lower end thereof is moved by the dropout fuse element once it reaches a position in the vicinity of its terminal dropped out position, as shown in Figures 4 and 5, in which it hangs from the fuse holder.

It is to be noted that one deviation from the fuse holder described in the earlier published international patent application is the fact that the configuration of the fuse holder is such that in a normal installed position the dropout fuse element is inclined somewhat in the direction in which it will move when its fuse blows and it drops out. This avoids any requirement that a leaf spring or the like needs to assist in initiating its movement once its fuse blows.

A rigid reset arm (46) is secured to the web of the U-shaped bridging member so as to extend out of the plane of the U-shaped bridging member whilst being rotatable in unison therewith. The reset arm can thus be used to rotate the U-shaped bridging member against its own spring loading to its inoperative position in which it is held in the spring loaded position by the catch formed by the upper free end of the release arm. Resetting of the U- shaped bridging member may thus be achieved remotely by using a pole or the like to move the reset arm against the spring loading of the U-shaped bridging member until such time as the catch engages.

The rigid reset arm is of low electrical conductivity or at least has a suitable electrically insulating cover or coating in order to obviate stray arcs that could otherwise occur. This reduces any chance of flash over occurring during the dropping out of the dropout tubular fuse element and restoring the circuit by way of the fuse wire (22) in the passage (21 ).

This arrangement is such that when the tubular fuse element (5) drops out of its operative position in consequence of its fuse becoming blown, the tubular fuse element swings downwards, as shown in Figure 4, and continues to swing to the point that it engages the lower free end of the release arm to cause the entire release arm to rotate about its pivot (44). This causes the catch to disengage the spring loaded U-shaped bridging member and allow it to rotate under its own spring loading to its operative position in which it bridges the first and second switch contacts and completes the circuit through the fuse wire (22) passing through the passage (21 ). The arrangement is such that there is an adequate time delay from the instant that the fuse blows until the bridging member restores the connection for the arc usually generated to subside. In this particular instance, the time period may be approximately 1 .2 seconds. The actual time delay will ultimately depend on the time that it actually takes for the flash to subside. It is presently accepted that the flash may take as little as 0.3 seconds to subside and time delays of the order of 0.6 seconds have proved to be satisfactory. It will be apparent from the foregoing, that the fuse holder provided by this invention may be installed in a suitable dropout insulator unit in place of a dropout fuse element, and the same dropout fuse element that has been removed from the insulator unit can then be installed in the fuse holder as indicated above.

The fuse element itself thus provides a first fuse circuit that operates normally, but in this case relative to the fuse holder, until such time as the relevant fuse becomes blown. At that stage it will drop out of the fuse holder to a position as illustrated in Figure 5. This will cause the U-shaped bridging element to be triggered to move to its operative position in which the fuse wire (22) in the passage through the body of the fuse holder is rendered operative and power is automatically restored to the circuit being supplied.

In the event that the fault causing the tubular dropout fuse to blow is not removed, that is to say it was not a transient fault, then the fuse in the fuse wire (22) will blow and the entire fuse holder of this invention will drop out of the insulator unit in the manner of a conventional dropout fuse and to a position that is illustrated in Figure 6.

Of course, in the event that the fault is a transient one, the fuse holder described above enables the blown fuse to be replaced without any appreciable interruption of the power supply.

It will therefore be appreciated that the invention provides an extremely simple yet highly effective fuse holder that can be simply installed in an existing insulator unit to replace a tubular fuse element and the same tubular fuse element can be installed in the fuse holder thereby providing a repeater fuse attribute where there was previously none. The fact that the same fuse element that has been removed to make way for the fuse holder of the invention is then installed in the fuse holder ensures that there are absolutely no redundant parts generated by fitting fuse holders of the invention.

Of course, it is fully within the scope of this invention that the entire assembly of insulator and fuse holder can be especially made for operating together. Numerous variations may be made to the embodiment of the invention described above without departing from the scope thereof.