AU2018217779B2

AU2018217779B2 - Arc splitter plate

Info

Publication number: AU2018217779B2
Application number: AU2018217779A
Authority: AU
Inventors: Balazs NOVAK; S. Ramesh; Rahul SONAR
Original assignee: Lucy Electric Ems Ltd
Current assignee: Lucy Electric (ems) Ltd
Priority date: 2017-02-09
Filing date: 2018-01-31
Publication date: 2022-06-16
Anticipated expiration: 2038-01-31
Also published as: GB2560300A; GB201702172D0; GB2560300B; WO2018145969A1; AU2018217779A1; ZA201905265B

Abstract

An arc splitter plate, for a switch having a fixed contact and dual movable contacts, comprises a body having a length being a distance between a first set of two parallel planes defined at a proximal end and a distal end respectively with reference to the dual movable contacts, and a width being a distance between a second set of two parallel planes defined at sides of the body, each plane of the second set being perpendicular to the planes of the first set, the body defining a substantially U-shaped recess in the proximal end of the body with reference to the dual movable contacts, the recess having side walls, a projection at the vertex of the recess extending into the recess and a notch either side of the projection.

Description

Arc Splitter Plate

FIELD OF THE INVENTION

The present invention relates to electrical current interruption devices. In particular, this invention relates to an arc splitter plate and designs for such devices, especially for switchgear with dual moving contacts.

BACKGROUND

Electrical switchgear is provided in an electric power distribution system (or grid) and consists of electrical current interruption devices including fuses and/or circuit breakers which are used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow maintenance work to be carried out, and to clear downstream faults.

Current interruption devices, such as over-current protection circuit breakers, rely on the separation of two electrical contacts to break an electric current. As these two electrical contacts separate, an electrical arc strikes between them. Electric current still flows until this arc is extinguished even though the two contacts are mechanically separated.

A number of different ways to reduce the amount of time required for the arc to extinguish have been developed. Generally, they involve creating conditions in which the voltage required to sustain the arc increases quickly to a point where its value is above that which can be provided by the circuit. When this occurs, the arc extinguishes. One known way is a mechanical switch mechanism having two contacts wherein, when a high current condition occurs and the two contacts separate, the gap distance between them increases as quickly as possible. This exploits the fact that the voltage required to sustain an arc increases with the gap distance.

Originally, switchgear was insulated by appropriate air gaps between the contacts. However, as voltage and power levels have increased, and the size of equipment has decreased, the dielectric strength of air has proved to be inadequate. To address this, oil- insulated equipment became common with a bank of conductors and switches housed within an open oil bath. As switches opened or closed, any arc that formed would be quenched and extinguished by the oil. However, frequently and after switching, it would be necessary to drain the oil from the bath to allow for maintenance of any individual switch, following which the switch contacts would have to be cleaned or replaced, and the oil replenished; this was inconvenient and the presence of large volumes of oil near to electrical arcing was an obvious fire hazard.

Vacuum interrupters were later employed. An example of a vacuum interrupter 10 is shown in figure 1, and has a pair of contacts 12, 14 held in a vacuum 16 which could be brought together to make a contact or separated in order to isolate a circuit. The contacts are mounted within a vacuum flask, usually consisting of a ceramic cylinder 18 with metallic end caps 20, 22 sealed to the ceramic. Conductive rods 24, 26 set in each of the end caps 20, 22 both support a respective contact 12, 14 and allow an electrical connection to be made with it. A set of bellows 28 within one end cap 22 allows the associated rod 26 to move back and forth relative to the end cap 22 and, indeed, the remainder of the interrupter 10, so as to bring the contacts 12, 14 into and out of physical and electrical contact without harming the vacuum 16.

Vacuum interrupters have minimal arcing, as there is essentially nothing to ionise other than the contact material. As a result, the arc is extinguished when it is stretched by a very small amount (say 6-8 mm) whilst being controlled by a magnetic field. Vacuum interrupters have therefore been used in modern medium-voltage switchgear to 36,000 volts. As an alternative to a vacuum, an insulating gas with a high dielectric strength can be employed, Sulphur Hexafluoride (SF6) being the most common. SF6 has been used in medium- and high-voltage (from 1000V up to 36kV and above) interrupters, switchgear, and other electrical equipment. SF6 gas has a much higher dielectric strength than air or dry nitrogen, making it possible to significantly reduce the size of electrical switchgear and making such switchgear more suitable for certain purposes such as indoor placement. SF6 gas also has arc-quenching properties not found in other gasses. Gas-insulated electrical gear is also more resistant to the effects of pollution and climate, as well as being more reliable in long-term operation because of its controlled operating environment.

In more recent times, however, vacuum interrupters have been beginning to displace the known SF6 breakers for a number of reasons. Although most of the decomposition products of SF6 tend to quickly re-form the original gas, some highly toxic by-products are produced during arcing. SF6 is also believed to be a greenhouse gas, the Intergovernmental Panel on Climate Change reporting that it was the most potent greenhouse gas so far evaluated as of 2007, with a global warming potential of 22,800 times that of C02.

Vacuum interrupters do present technical challenges, however. The space around the interrupter will be subject to a high electrical stress, and this can give rise to severe potential gradients that ultimately cause electrical discharge and flashover, resulting in failure of the equipment. This, in turn, causes long-term reliability problems and short-term noise pollution. In addition, it is difficult to inspect a vacuum interrupter (such as during routine maintenance) to confirm that the vacuum still exists.

Despite the use of interrupters described above, it has not been possible to entirely eliminate the arc formed when switch gear contacts are open and efforts have been made to increase the speed and efficiency with which the arc can be extinguished.

One known way, which is sometimes used together with a switch mechanism described above, makes use of an arc chute, which provides a path for the arc to jump from the region between the two opening contacts to a plurality of metal arc splitter plates. The function of the arc splitter plates is to split the arc into a series of smaller arcs. Arc splitter plates take advantage of the fact that there is minimum voltage, typically of about 30 to 80 volts, necessary to sustain any single arc. Thus, splitting an arc into a series of arcs can rapidly increase the voltage required to sustain the whole series. Additionally, arc splitter plates have been found to cool the arcs, which further increases the voltage required to sustain them.

One problem with the use of splitter plates is that it is difficult to ensure that the arc is positioned in the middle of the plate. In this regard, the arc can start anywhere and it must be repositioned to the centre of the plate.

The operation of known arc splitter plates is shown in FIGS. 1 and 2. In FIG. 1, a contact arm 14 of circuit breaker 13 is rotating counter-clockwise, causing a movable contact 15 to separate from fixed contact 17. An arc 18 forms between movable and fixed contacts 15, 17 as they separate. Adjacent to movable and fixed contacts 15, 17, are a series of arc splitter plates 21. Arc splitter plates 21 are supported by electrically insulating side plates or one or more electrically insulating posts. As the contacts continue to separate, the arc 18 moves to the arc splitter plates 21 as shown in FIG. 2.

FIG. 3 shows an example of a prior art circuit breaker 13 having arc splitter plates 21. Here, a series of metal arc splitter plates 21 are positioned between two electrically insulating side supports 19 as shown in FIGS. 4 and 5. Side supports 19 are typically formed from a ceramic or other material that can withstand high temperatures. Arc splitter plates 21 commonly include tabs 27 that fit in to slots 29 formed in side supports 19 to hold arc splitter plates 21 in the desired position.

Conventional arc splitter plate designs found in electrical switching devices use various profiles to increase the pull force on the arc, assuming the arc generates at the center of the arc splitter plate assembly. Hence providing a notch at the center greatly adds to the pull force experienced by the arc. As a result the arc is attracted toward the arc splitter plates and is split into a series of smaller arc roots.

But in case of switches with dual moving contacts per pole (for example shown in Figure 5 of the accompanying drawings), during switching, the arc doesn't generate at the center of the arc splitter plate assembly but the arc is offset by a slight distance which makes it difficult for the arc splitter plates to steer it back toward the center and consequently the arc ends up traveling sideways on the arc splitter plates or slipping out entirely.

Although the known arc splitter plates significantly reduce the time before an arc is extinguished, it would be desirable to further reduce the time between a trip event and complete cessation of current.

The invention addresses at least this issue. In this regard, it has now been found that the shape of the splitter plate is important and a new splitter plate has now been developed.

Remarkably, it has been found that a splitter plate according to the invention steers an initially displaced arc toward the center.

SUMMARY OF THE INVENTION

In accordance with a first aspect, the invention provides an arc splitter plate for a switch having a fixed contact and dual movable contacts, the plate comprising a body having a length being a distance between a first set of two parallel planes defined at a proximal end and a distal end respectively with reference to the dual movable contacts, and a width being a distance between a second set of two parallel planes defined at sides of the body, each plane of the second set being perpendicular to the planes of the first set, the body defining a substantially U-shaped recess in the proximal end of the body with reference to the dual movable contacts, the recess having side walls, a projection at the vertex of the recess extending into the recess and a notch either side of the projection.

Preferably, the recess, the projection and the two notches are symmetrical about a plane equidistant from the second set of two parallel planes.

Preferably, each notch is defined by a smoothly curved surface.

Preferably, the vertex of the recess is located at a distance from the proximal end of the body with reference to the dual movable contacts being in the range of about 25% to about 50% of the length of the body.

Preferably, the projection extends from the vertex of the U-shaped recess towards the proximal end of the body with reference to the dual movable contacts. Preferably, the projection has a length from the notch on each side parallel to the length of the body being in the range of about 10% to about 40% of the length of the body, more preferably about 10% to about 30% of the length of the body, even more preferably about 10% to about 20% of the length of the body, most preferably about 10% to about 15% of the length of the body. Preferably, the projection has a width between the two notches being in the range of about 20% to about 40%, more preferably about 25% to 35%, even more preferably about 30% the width of the body.

This provides the advantage that there are dual notches spaced apart in a way such that they appear closest to the arcing paths and the body has a shape which resembles a shape defined by the letter M. In this regard, the shape has a top, a bottom and sides and between the sides a projection which projects downwardly from the top. The dual notches are defined at the inside angles at the junctions between the sides and the top. In addition, the projection projecting downwardly from the top has a length parallel to the sides of about 10% to about 40%, more preferably 10% to about 30%, more preferably about 10% to about 20%, most preferably about 10% to about 15% of the length of the body.

Preferably, in a first section of the side walls of the recess, the side walls are substantially parallel to the sides of the body for a length being in the range of about 20% to about 30%, more preferably about 25% the length of the body. Preferably, in a second section of the side walls, the side walls taper inwardly from the first section to a notch on each side of the projection. Preferably, the side walls of the recess meet the proximal end of the body with reference to the dual movable contacts in a first curve. Preferably, the curve is smooth and has a radius of about 40% to about 60%, more preferably about 50% the width between each first section of the side wails of the recess and the proximal side of the body.

Preferably, the proximal end of the body with reference to the dual movable contacts meets each side of the body in a second curve having a radius significantly smaller than the radius of the first curve. In this regard, the second curve is preferably provided by a rounded corner.

Preferably, an indent is provided in each side of the body adjacent to the second curve proximal to the proximal end of the body with reference to the dual movable contacts. In this regard, preferably, each indent is defined by a first wall proximal to the proximal end of the body with reference to the dual movable contacts which is substantially perpendicular to the second set of two parallel planes and a second wall which adjoins the first wall and tapers outwardly therefrom to join the side of the body distal to the proximal end of the body with reference to the dual movable contacts.

Preferably, the plate is provided with a projection on each side at the distal end of the body with reference to the dual movable contacts. In this regard, preferably, the width of the body is increased at its distal end with reference to the dual movable contacts. Preferably, each projection has a length parallel to the length of the body being in the range of about 5% to about 15%, more preferably about 10% of the length of the body. In addition, preferably, each projection has a width parallel to the width of the body being in the range of about 10% to about 20%, more preferably about 15% of the length of the body.

Preferably, the movable contacts of the switch are displaceable through the substantially U-shaped recess without contacting the side walls of the recess.

In accordance with another aspect of the present invention, an arc chute comprises an assembly of at least one stack of splitter plates, each profiled splitter plate as disclosed herein above.

Preferably, each stack comprises at least about 5 plates, more preferably about 5 to about 20 plates. In an embodiment, the stack preferably comprises about 6 to about 10 plates. More preferably, it comprises about 8 plates.

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;

Figures 1 and 2 show the typical structure of known arc splitter plates.

Figure 3 shows an example of a prior art circuit breaker having arc splitter plates;

Figure 4 shows an arc splitter plate in accordance with the invention having two notches; Figure 5 shows multiple arc splitter plates in accordance with the invention in an assembly;

Figure 6 shows an arc splitter assembly having current carrying contacts; and Figure 7 shows a switch assembly having arc splitters and current carrying contacts. DETAILED DESCRIPTION

It will be appreciated that aspects, embodiments and preferred features of the invention have been described herein in a way that allows the specification to be written in a clear and concise way. However, unless circumstances clearly dictate otherwise, aspects, embodiments and preferred features can be variously combined or separated in accordance with the invention. Thus, preferably, the invention provides a device having features of a combination of two or more, three or more, or four or more of the aspects described herein. In a preferred embodiment, a device in accordance with the invention comprises all aspects of the invention.

The following definitions shall apply throughout the specification and the appended claims.

Within the context of this specification, the word "about" means preferably plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%.

Within the context of this specification, the word "comprises" means "includes, among other things" and should not be construed to mean "consists of only".

Within the context of this specification, the word "substantially" means preferably at least 90%, more preferably 95%, even more preferably 98%, most preferably 99%.

It has surprisingly been found that providing an arc splitter plate having two notches can be used to quickly attract an initially displaced arc to the centre. In addition, it has been found that the special profile of the notches described herein increases the concentration of magnetic field which in turn increases the pull force on the arc. Accordingly, the special profile on the arc splitter plate described herein has two notches adapted to appear directly above an off-centre arc to attract it toward the arc splitter plate assembly. Remarkably, it has been found that the arrangement attracts the arc from either side irrespective of its initial displacement and pulls it toward the centre.

Figures 1 to 3 show known and generally conventional arc splitter plates, and have been described already.

Referring to figures 4 to 7, an arc splitter plate (1) according to the present invention is suited for a switch having a fixed contact (2) and dual movable contacts (3). The plate (1) comprises a body (4) having a length being a distance between a first set of two parallel planes defined at a proximal end and a distal end respectively with reference to the dual movable contacts (3), and a width being a distance between a second set of two parallel planes defined at sides of the body (4), each plane of the second set being perpendicular to the planes of the first set, the body (4) defining a substantially U-shaped recess (5) in the proximal end of the body (4) with reference to the dual movable contacts (3), the recess (5) having side walls (6), a projection (7) at the vertex of the recess (5) extending into the recess (5) and a notch (8) either side of the projection (7).

The recess (5), the projection (7) and the two notches (8) are symmetrical about a plane equidistant from the second set of two parallel planes.

Each notch (8) is defined by a smoothly curved surface.

The vertex of the recess (5) is located at a distance from the proximal end of the body (4) with reference to the dual movable contacts (3) being in the range of about 25% to about 50% of the length of the body (4).

The projection (7) extends from the vertex of the U-shaped recess (5) towards the proximal end of the body (4) with reference to the dual movable contacts (3). The projection (7) has a length from the notch (8) on each side parallel to the length of the body (4) being in the range of about 5% to about 15% of the length of the body (4). The projection (7) has a width between the two notches (8) being in the range of about 20% to about 40% the width of the body (4).

In a first section of the side walls (6) of the recess (5), the side walls (6) are substantially parallel to the sides of the body (4) for a length being in the range of about 20% to about 30% the length of the body (4). In a second section of the side walls (6), the side walls (6) taper inwardly from the first section to a notch (8) on each side of the projection (7). The side walls (6) of the recess (5) meet the proximal end of the body (4) with reference to the dual movable contacts (3) in a first curve (9). The curve (9) is smooth and has a radius of about 40% to about 60% the width between each first section of the side walls (6) of the recess (5) and the proximal side of the body (4).

The proximal end of the body (4) with reference to the dual movable contacts (3) meets each side of the body (4) in a second curve (29) having a radius significantly smaller than the radius of the first curve (9). In this regard, the second curve (29) is provided by a rounded corner.

An indent (30) is provided in each side of the body (4) adjacent to the second curve. In this regard, preferably, each indent (30) is defined by a first wall proximal to the proximal end of the body (4) with reference to the dual movable contacts (3) which is substantially perpendicular to the second set of two parallel planes and a second wall which adjoins the first wall and tapers outwardly therefrom to join the side of the body (4) distal to the proximal end of the body (4) with reference to the dual movable contacts (3).

The plate (1) is provided with a projection (31) on each side at the distal end of the body (4) with reference to the dual movable contacts (3). In this regard, the width of the body (4) is increased at its distal end with reference to the dual movable contacts (3). Each projection (31) has a length parallel to the length of the body (4) being in the range of about 5% to about 15% of the length of the body (4). In addition, each projection (31) has a width parallel to the width of the body (4) being in the range of about 10% to about 20% of the length of the body (4).

The movable contacts (3) of the switch are displaceable through the substantially U- shaped recess (5) without contacting the side walls (6) of the recess (5).

The location of the notches (8) is important. Advantageously, in use, the notches (8) are provided equidistant from a plane equidistant form the second set of two parallel planes and they are located in a position corresponding to the distance by which the initial arc is displaced from the centre so that either notch (8) is nearly above the arc at all times irrespective of the direction the arc is displaced from the centre. Remarkably, in use, this can help increase the pull force on the arc and keep it from slipping away from the arc splitter plate assembly (100), consequently steering the arc toward the centre of the arc splitter plates (1) to extinguish the arc effectively.

Typically, in accordance with the present disclosure, the location of the projection (7) and accordingly the location of the notches (8) is adapted to increase effective magnetic material in the vicinity of the arc of the switch and provide predetermined clearance between the plate (1) and the movable contacts (3).

Typically, in accordance with the present disclosure, the plate (1) has a profile corresponding to the shape and geometry of the profile of at least one of an arc runner, movable contacts (3) and tips of the movable contacts (3).

As shown in Figures 5 and 7, an arc chute comprises an assembly (100) of at least one stack of eight splitter plates (1), each profiled splitter plate (1) as disclosed herein above.

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.

Claims

1. An arc splitter plate for a switch having a fixed contact and dual movable contacts, the plate comprising a body having a length being a distance between a first set of two parallel planes defined at a proximal end and a distal end respectively with reference to the dual movable contacts, and a width being a distance between a second set of two parallel planes defined at sides of the body, each plane of the second set being perpendicular to the planes of the first set, the body defining a substantially U-shaped recess in the proximal end of the body with reference to the dual movable contacts, the recess having side walls, a projection at the vertex of the recess extending into the recess and a notch either side of the projection.

2. An arc splitter plate according to claim 1, wherein the recess, the projection and the two notches are symmetrical about a plane equidistant from the second set of two parallel planes.

3. An arc splitter plate according to claim 1 or claim 2, wherein each notch is defined by a smoothly curved surface.

4. An arc splitter plate according to any one of the preceding claims, wherein the vertex of the recess is located at a distance from the proximal end of the body with reference to the dual movable contacts being in the range of about 25% to about 50% of the length of the body.

5. An arc splitter plate according to any one of the preceding claims, wherein the projection extends from the vertex of the U-shaped recess towards the proximal end of the body with reference to the dual movable contacts.

6. An arc splitter plate according to any one of the preceding claims, wherein the projection has a length from the notch on each side parallel to the length of the body being in the range of about 10% to about 40% of the length of the body.

7. An arc splitter plate according to any one of the preceding claims, wherein in a first section of the side walls of the recess, the side walls are substantially parallel to the sides of the body for a length being in the range of about 20% to about 30% the length of the body.

8. An arc splitter plate according to claim 7, wherein in a second section of the side walls of the recess, the side walls taper inwardly from the first section of the recess to a notch on each side of the projection.

9. An arc splitter plate according to any one of the preceding claims, wherein the side walls of the recess meet the proximal end of the body with reference to the dual movable contacts in a first curve.

10. An arc splitter plate according to claim 9, wherein the first curve is smooth and has a radius of about 40% to about 60% the width between each first section of the side walls of the recess and the proximal side of the body.

11. An arc splitter plate according to any one of the preceding claims, wherein the proximal end of the body with reference to the dual movable contacts meets each side of the body in a second curve having a radius significantly smaller than the radius of the first curve.

12. An arc splitter plate according to claim 11, wherein an indent is provided in each side of the body adjacent to the second curve proximal to the proximal end of the body with reference to the dual movable contacts.

13. An arc splitter plate according to claim 12 wherein each indent is defined by a first wall proximal to the proximal end of the body with reference to the dual movable contacts which is substantially perpendicular to the second set of two parallel planes and a second wall which adjoins the first wall and tapers outwardly therefrom to join the side of the body distal to the proximal end of the body with reference to the dual movable contacts.

14. An arc splitter plate according to any one of the preceding claims, wherein a projection is provided on each side at the distal end of the body with reference to the dual movable contacts.

15. An arc splitter plate according to claim 14 wherein each projection has a length parallel to the length of the body being in the range of about 5% to about 15% the length of the body.

16. An arc splitter plate according to claim 14 or claim 15 claims, wherein each projection has a width parallel to the width of the body being in the range of about 10% to about 20% the length of the body.

17. An arc splitter plate according to any one of the preceding claims, wherein movable contacts of the switch are displaceable through the substantially U-shaped recess without contacting the side walls of the recess.

18. An arc chute which comprises an assembly of at least one stack of arc splitter plates, wherein each arc splitter plate is an arc splitter plate according to any one of the preceding claims.

19. An arc chute according to claim 18, wherein each stack comprises at least about 5 plates.

20. Electrical switchgear substantially as herein disclosed with reference to and/or as illustrated in the figures 4 to 7 of the accompanying drawings.