GB2152299A - High current switching devices - Google Patents

Abstract

The switching device comprises at least one pair of parallel, transversely spaced contact surfaces 21 resiliently urged towards one another by springs 23 and movably attached to a common base 29 so as to make a pressurised contact with a cooperatively sized knife blade 22 inserted between them. <IMAGE>

Description

SPECIFICATION High current switching devices The present invention relates to mechanical electric switching devices and in particular to these devices as applied to disconnectors, switches and fuse-holders used in high current power supplies.

Mechanical electric switching devices will include at least two components which at alternative times are in pressured physical contact with one another or distant from one another. When the components are in the pressured contact mode, the actual contact area, on the microscopic scale, is considerably less than the actual surface area which appears to be in contact. In known devices in this field this reduced contact area is aggravated by the fact that there is often at least some misalignment between the contacting surfaces, meaning thatthe pressured contact is really only along a line ratherthan a surface. When high currents flowconsiderable heat is produced attheseconnections, the heattending to deteriorate the components.

The problem of heat is exaggerated when one considers that high current usage is generally in the daytime when ambient temperatures are considerably higherthan at night when only a minimal current is flowing. Thus the metal components are subjected to considerable deterioration caused bythetemperature cycle. Many components used in this field may have a life expectancy as low as four to five years.

When one considers that there are many thousands of such devices in use in electricity distribution networks, it becomes obvious thatthe cost in material and time for replacing defective items is considerable.

It is therefore an object of the present invention to ameliorate the disadvantages ofthe priorart or at least to provide a suitable alternative choice to the market.

In one broad form the present invention may be said to provide a switching device adapted for use in a high current circuit, said device comprising at least two approximately parallell, transversely spaced apart contact surfaces resiliently urged toward one another and movabiy attached to a common base so asto make a pressured floating contact with a cooperatively sized knife blade connection introduced therebetween.

In another form the present invention may be said to provide a switching apparatus adapted for use in a high current circuit, said apparatus comprising: a body adapted to slide between two busbars arranged parallel and transversely spaced apart; and at least one pair of conducting members resiliently urged one of each pair toward the other, said pair(s) being attached to said body so that upon placement of said body between said busbars said members of each pair are moved apart by interaction with edges of said busbars so as to make pressured contact with each said busbar.

The switching apparatus described immediately above may best be used in a disconnector in a secondary circuit of an electricity supply authority distribution transformer. The switching device firstly described herein above is well suited for use in a fuse in a sub-circuitofthe low voltage supply.

By way of example only, two preferred embodiments of the present invention will now be described with reference to the drawings in which: Fig. is a perspective view of a disconnector; Fig. 2 is a perspective view of a portion of a fuse-holder of a fuse disconnector; Fig.3 is a perspective view of a disconnector suitable for disconnecting a power service from a distribution transformer and a busbar system; and Fig. 4 is a perspective view of a feeder circuit fuse-disconnector.

In Fig. 1 busbars 1 and 2 are seen to be parallel and transversely removed from one another buy a distance 3 as required by the length of break in the circuit.

Busbar 1 might be the main linktothelowvoltage secondary of a distribution transformer while busbar 2 leads off to the low voltage sub-circuits. When busbars 1 and 2 are not electrically connected then the circuit supplied by that transformer will visibly be broken and safe to work on.

To make the circuit the body or carrier 9 is inserted in between busbars 1 and 2. Edges 5 and 6 of the busbars 1 and 2 include chamfers 13 at their lead points. Upon insertion of carrier 9 chamfers 1 3force apart the insulating guide blocks 8which ultimately sit within notches 12 so as to lock carrier 9 in working position.

Chamfers 13 also move apart opposing copper conductors 4 of each successive pair. Each conductor 4 of a common pair is resiliently urged toward the other conductor 4 of the respective pair by springs 17.

When carriers is fully home ail conductors 4will be in pressured contact with edges 5 and 6 of both busbars 2 and 1 so as to complete the circuit of the low voltage supply. In orderto release carrier9 and therefore ensure that the circuit is safe to work on, release lever 10 within handle 11 is compressed thereby forcing apart guide blocks 8.

An important feature ofthis apparatus is that it is easy to accommodate different current requirements.

Different sized transformers in common use will range in being able to deliverfrom 200 amps to 2,000 amps.

The abovedescribed disconnectorcan easily be used throughoutthis range by selecting the required numberof conductor pairs 4 and busbars 1 and 2 can be different cross sectional areas. Thus tooling costs are kept to a minimum and devices can easily be changed from one current rating to another when load changes demand.

In Fig. 2 can be seen one contact from a fuse-holder of a fused disconnector. A pair of contacts 21 are adapted to engage with a fuse-link blade 22 when the fuse-link is inserted into the circuit. Contact pressure between the contacts 21 and the blade 22 is maintained by the springs 23.

The contacts 21 arefreetohingeslightlyonthe curved surface 24, formed across the widih of contacts 21, curved surface 24 being in rocking contact with base plate 29. Pressuring screws 25 pass through elongated holes (not shown) in the base 27 of each contact 21. The screws 25 together with cooperative springs 28 maintain contact pressure between the curved surface 24 and the base plate 29 so as to form electrical connection therebetween. The springs 28, while maintaining adequate contact pressure, allow a small rocking action of the contacts 21 while the elongated holes (described above) allow a sliding action of contacts 21 toward and away from one another.The rocking and sliding actions com bine to make the contact faces 30 of the respective contacts 21 self aligning against the contact surface of the fuse-link blade 22.

Included in the base of contacts 21 are heat radiating fins 31. By effectively dissipating heat from the contacts 21 the tempersture of the unit is kept within reasonable operating limits.

Springs 23 are retained in position by a metal "U" shaped bracket 32. The top of the contacts 21 are provided with nipples 33 that engage with the side of bracket 32 so thatwhen the fuse-link blade is withdrawn the jaws formed by the two contacts 21 do not fully close. This reducces the force required to insertthe fuse-link without reducing the pressured contact when it is in place.

The structure of the fuse disconnector of Fig. 2 can easily be modified to work in a knife switch where a knife blade is pivoted at one end with one handle at the other and a conducting section in between. The conducting section corresponds to blade 22 and when the switch is closed extends between two contacts sirn'larto the one illustrated in Fig. 2.

Dlsclosed are mechanical electric switching devices app. ;cable to disconnectors, switches a nd fuse-hol- ders used in high current power supplies. Disclosed is d disconnector and including a body adapted to slide between two busbars arranged parallel and trans rsely spaced apart. The body includes at least one pair ot conducting members resiliently urged toward each other, with the two conducting members of each pair positioned in opposing slots in respective opposing sides of the body and being urged towards one another by a spring located in an internal opening of the body.The edges of the busbars between which the bod . may be inserted have leading chamfered corners so thatwhen the body is pushed in between the busbars and the chamfered section pushes the conducting members apart before they slide down the edges of the busbars. The load of the springs urging the two conducting members of each pair together maintains the conducting members in electrical contact with both busbars. The bodyfurther includes insulating guide blocks held to the body similarly to the conducting members. Cooperative slots are included in the edges of the busbars so that upon insertion ofthedisconnectorfully home, the guide blocks lock into these slots preventing removal of the disconnector. Removal can only be accomplished by actuating a handle which forces the guide blocks apart sufficiently to be clear of the slots.

A knife blade connection for a fuse disconnector or knife switch includes two parallel spaced apart contact surfaces resiliently urged towards one another and attached in pressured floating contact to a common base. The attachment to the common base is such as to allow a pivotal movement of the contact surfaces toward and away from one another as well as translational movement in the same directions. The contact surfaces are prevented from contacting one another so as t 3 always provide a space therebetween which is somewhat less than the width of the blade designed to cooperate the unit. This ensures easy insertion ofthe blade while maintaining desired pressured contact over a large surface area.

Claims (10)

1. A switching device adapted for use in a high current circuit, said device comprising at least approximately parallel, transversely spaced apart contact surfaces resiliently urged toward one another and movably attached to a common base so asto make a pressured floating contact with a cooperatively sized knife blade connection introduced therebetween.

2. A switching device as defined in claim 1 wherein said contact surfaces are contiguous with respective floating contact bars, each said contact bar held in spring loaded electrical contact with a base plate wherein the electrical contact between contact bars and the base plate allows for rocking movement of said contact bars relative to said base plate about an access parallel to both said base plate and said contact surfaces and also allowing limited sliding action between said contact bars and said base plate in a direction parallel to the plane of said base plate and at right angles to the plane of said contact surfaces.

3. A switching device as defined in either claim 1 or 2 further comprising a U-shaped bracket at least partially surrounding said contact surfaces and bias means between each respective contact surface and a respective arm of said U-shaped bracketwherein said bias means resiliently urge said contact surfaces toward one another.

4. Aswitching device as defined in claim 3 wherein said contact surfaces include nipples sized and shaped so as to extend from each respective contact surface overthe respective arm of said U-shaped bracket preventing said contactsurfacesfrom being urged toward one another into mutual contact.

5. A switching device as defined in any one of the preceding claims further comprising radiating fins contiguous with said contact surfaces.

6. A switching apparatus adapted for use in a high current circuit, said apparatus comprising: a body adapted to slide between two busbars arranged parallel and transversely spaced apart; and at least one pair of conducting members resiliently urged one of each pairtoward the other, said pair(s) being attached to said body so that upon placement of said body between said busbars said members of each pair are moved apart by interaction with edges of said busbars so asto make pressured contact with each said busbar.

7. Apparatus as defined in claim 6 wherein said body is a generally rectangular plate like structure with a central approximately rectangular hole therein, conducting members of each pair of conducting members being positioned in opposing slots in respective opposing sides of said body and being urged towards one another by resilient springs positioned in said approximate rectangular hole and held in tension between respective ones of each respective pair of conducting members.

8. Apparatus as defined in claim 6 or7 further comprising insulating guide blocks held within said body and transversely movable toward and away from one another and spring bias means resiliently urging said guide blocks toward one another with a release lever operable so as to urge said guide blocks away from one another.

9. A switching apparatus as defined in claim 8 wherein said busbars include chamfered corner edges at one end thereof and notches in said edges positioned of a distance from said chamfered corners and cooperative with said guide blocks so asto lock said body in between said two busbars.

10. Apparatus as described with reference to Fig.

1,2,3or4.