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Title:
ELECTRICAL SWITCH INCORPORATING AN ARC SPLITTER ARRANGEMENT
Document Type and Number:
WIPO Patent Application WO/2017/141197
Kind Code:
A1
Abstract:
This invention relates to an electrical switch incorporating an arc suppressing arrangement. The switch includes an electrical contact set comprising a first, stationary contact and a second, displaceable contact, the displaceable contact being displaceable between a connected position in which the contacts abut, and a disconnected position in which the contacts are spaced apart. The switch furthermore includes first and second arc splitting arrangements, each comprising a plurality of spaced apart arc splitting plates forming an arc splitting stack. The first arc splitting arrangement and the second arc splitting arrangement are configured in order for an arc that, in use, develops between the stationary contact and the displaceable contact to be divided up into at least two discrete arcs, with each such divided arc then being displaced to its own splitting arrangement.

Inventors:
LIEBENBERG MICHAEL WILLIAM (ZA)
NATORP PAUL (ZA)
Application Number:
PCT/IB2017/050899
Publication Date:
August 24, 2017
Filing Date:
February 17, 2017
Export Citation:
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Assignee:
CIRCUIT BREAKER IND (ZA)
International Classes:
H01H9/36; H01H73/18
Foreign References:
DE1160922B1964-01-09
GB1068436A1967-05-10
EP2743950A12014-06-18
Other References:
None
Attorney, Agent or Firm:
SPOOR & FISHER et al. (ZA)
Download PDF:
Claims:
CLAIMS:

1. An electrical switch including:

an electrical contact set comprising a first, stationary contact and a second, displaceable contact, the displaceable contact being displaceable between a connected position in which the contacts abut, and a disconnected position in which the contacts are spaced apart;

a first arc splitting arrangement comprising a plurality of spaced apart arc splitting plates that form an arc splitting stack; and

a second arc splitting arrangement comprising a plurality of spaced apart arc splitting plates that form an arc splitting stack;

the first arc splitting arrangement and the second arc splitting arrangement being configured in order for an arc that, in use, develops between the stationary contact and the displaceable contact to be divided up into at least two discrete arcs, with each such divided arc then being displaced to its own splitting arrangement.

2. The electrical switch of claim 1 in which the first arc splitting arrangement and the second arc splitting arrangement are configured electrically in series.

3. The electrical switch of claim 1 or claim 2 in which the electrical switch includes a primary arc blowout channel extending from the contact set, and first and second secondary arc blowout channels extending from the primary arc blowout channel. The electrical switch of any claim 3 in which the first arc splitting arrangement is located towards an end of the first secondary arc blowout channel. The electrical switch of claim 3 or 4 in which the second arc splitting arrangement is located towards an end of the second secondary arc blowout channel. The electrical switch of any one of claims 3 to 5 in which the primary arc blowout channel branches out into the first and second secondary arc blowout channels. The electrical switch of any one of claims 3 to 6 in which the primary arc blowout channel is defined between a first conductor or runner extending from the first, stationary contact, and a second conductor or runner that is located adjacent the second, displaceable contact, and which is electrically connected to the second contact. The electrical switch of any one of claims 3 to 7 in which the first secondary arc blowout channel is defined between an extended part of the first conductor or runner, and an opposing intermediate conductor or runner. The electrical switch of claim 8 in which the second secondary arc blowout channel is defined between the intermediate conductor or runner, and the second contact or runner, in order for the intermediate conductor or runner to be common to both arc splitter arrangements. . The electrical switch of any one of the preceding claims in which the arc splitting stacks of the first and second arc splitting arrangements are spaced apart but in the same plane.

11. The electrical switch of any one of claims 1 to 9 in which the arc splitting stacks of the first and second arc splitting arrangements overlie one another, and are in different planes with an insulator provided between the two overlying arc splitting stacks.

12. The electrical switch of claim 1 substantially as herein described with reference to Figures 4 to 8.

13. A method of suppressing an arc in an electrical switch, the method including the steps of:

displacing an arc formed between two contacts of a contact set away from the contact set;

dividing the arc into two discrete arcs; and

displacing each discrete arc towards an independent arc splitting arrangement.

14. The method of claim 13 in which the electrical switch is an electrical switch according to any one of claims 1 to 12.

Description:
ELECTRICAL SWITCH INCORPORATING AN ARC SPLITTER

ARRANGEMENT

BACKGROUND TO THE INVENTION

THIS invention relates to an electrical switch incorporating an arc suppressing arrangement and more particularly, but not exclusively, to an electromagnetic circuit breaker incorporating an arc splitting arrangement.

In electrical engineering, an electrical switch is an electrical component that can break an electrical circuit by interrupting a current or by diverting it from one conductor to another. The most common form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. The or each set of contacts can be in one of two states. The set of contacts can be "closed", meaning the contacts are touching and electricity can flow between them, or "open", meaning the contacts are separated and the switch is nonconducting. The mechanism actuating the transition between these two states may take various forms, and can for example be toggle-type flip switch mechanism. A circuit breaker is a special kind of automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow. Unlike a fuse, which operates once and must then be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.

When a set of contact tips are opened, with the intention of interrupting the current flow, an electrical arc is formed between the contact tips. As the contact tips move apart, the surface area that remains in contact begins to decrease. Consequently, the resistance to current flow rises, and the temperature of the diminishing contact area of the contact tips also rises. When the melting point of the contacts is reached, only a thin bridge of molten material remains to carry the current between the two contacts. At this point the temperature of the metal rises so steeply that the metal evaporates, creating ideal conditions for initiation of a plasma arc. This arc damages the contact tips as well as other adjacent areas of the circuit breaker.

In order to quench or extinguish an arc it must be cooled to a point where the air sustaining the arc is no longer conductive. A common arc control scheme used in many circuit breaker designs is to force the arc into an arc baffle or splitter structure. Arc baffles act to break a single arc into several shorter arcs connected in series. Each time an arc is split the resistance across the device is increased, which in turn reduces the current flowing through the device.

An example of a circuit breaker including one embodiment of a conventional arc splitting structure known in the art is shown in Figures 1 and 2. The circuit breaker 10 comprises a plastic housing 11 which houses the contact set 20 and the switching arrangement 30. A line terminal 12 is provided, and in use an external electric conductor (not shown) is connected thereto. The line terminal 12 is an electrical contact with a first contact 21 of the contact set 20. The first contact 21 is a stationary contact. A load terminal 13 is provided in an opposite end of the housing 11, and in use an external electric conductor (not shown) is connected thereto. The load terminal 13 is in electric contact with a second contact 22 of the contact set via an electrical conductor 14 housed inside the housing 11.

A rigid and stationary carriage 15 is secured to the housing 11, and in use carries, inter alia, the switching arrangement 30 and the second contact 22. The second contact arrangement 20 includes a pivotable arm 22.1, with the contact tip 22.2 located on one end of the arm 21. An opposite end of the arm 21 is pivotably secured to the carriage 15 at a pivot point 22.3. The pivotable arm is therefore pivotably displaceable between a connected position (Figure 1) in which the first contact 21 and the second contact 22 abut, and a disconnected position (Figure 2) in which the first contact 21 and the second contact 22 are spaced apart. The arc referred to above will develop between the first contact 21 and the second contact 22 when the circuit breaker is displaced from the dosed position (Figure 1) to the open position (Figure 2).

The circuit breaker 10 also includes a conventional arc splitter 40 comprising a stack of spaced apart splitter plates 41 that are electrically insulated from one another. A first conductor 42 extends from the first contact 21 to the stack 41 , and a second conductor 43 extends from the second contact 22 to the stack 41. Functionally, the two conductors (42 and 43) are extensions of the two contacts (21 and 22), and the stack of splitter plates 41 are located between the ends of these conductors (42 and 43).

In use, an arc 50.1 will develop between the first contact 21 and the second contact 22, as shown schematically in Figure 3. The arc will then be displaced in the direction of arrow F due to the Lorentz force resulting from the current in the arc itself. The movement of the arc, due to this self- induced magnetic force, is referred to as magnetic blow out of the arc. The arc 50.2 is therefore displaced to the conductors (42 and 43) or arc- runners, which are connected (directly or indirectly) to the contacts (21 and 22). Finally, the arc reaches the arc splitter plate stack 41 , where the arc is then divided up into a number of arcs 50.3 in series, resulting in a decrease in current and temperature, and eventually in the arc being extinguished. The provision of the arc splitter arrangement therefore reduces the damage caused by the arc.

Although the prior art arc splitting arrangements generally delivers satisfactory results, there is always room for improvement, because the quicker the arc can be extinguished, the less damage will be caused to the circuit breaker. However, due to the configuration and special requirements of a circuit breaker space is of the essence and it is therefore not that simple, for example, to enlarge the size of the arc splitting arrangement, or to increase the number of splitting plates in the stack without compromising force or space. As the distance between arc runners increases, so the Lorentz forces decreases. The result of increasing the number of arc splitting plates is weaker magnetic blow out forces due to an increased distance between line and load arc runners. It follows that one of the major disadvantages of existing electrical switches is that it is not that simple to increase the number of arc splitting plates while maintaining the magnetic forces and hence the arcing motion.

It is accordingly an object of the invention to provide an electrical switch incorporating an arc suppressing arrangement that will, at least partially, alleviate the above disadvantages.

It is also an object of the invention to provide an electrical switch that will incorporate a larger amount of arc splitting plates without loss of magnetic blow out forces. It is also an object of the invention to provide an electrical switch incorporating an arc suppressing arrangement that will, at least partially, alleviate space constraints associated with existing switches.

It is also an object of the invention to provide an electrical switch incorporating an arc suppressing arrangement which will be a useful alternative to existing electrical switches.

SUMMARY OF THE INVENTION

According to the invention there is provided an electrical switch including: an electrical contact set comprising a first, stationary contact and a second, dispiaceabie contact, the displaceable contact being displaceable between a connected position in which the contacts abut, and a disconnected position in which the contacts are spaced apart;

a first arc splitting arrangement comprising a plurality of spaced apart arc splitting plates forming an arc splitting stack; and a second arc splitting arrangement comprising a plurality of spaced apart arc splitting plates forming an arc splitting stack;

the first arc splitting arrangement and the second arc splitting arrangement being configured in order for an arc that, in use, develops between the stationary contact and the displaceable contact to be divided up into at least two discrete arcs, with each such divided arc then being displaced to its own splitting arrangement.

There is provided for the first arc splitting arrangement and the second arc splitting arrangement to be configured electrically in series. There is provided for the electrical switch to include a primary arc blowout channel extending from the contact set, and first and second secondary arc blowout channels extending from the primary arc blowout channel.

The first arc splitting arrangement is preferably located towards an end of the first secondary arc blowout channel.

The second arc splitting arrangement is preferably located towards an end of the second secondary arc blowout channel.

There is further provided for the primary arc blowout channel to branch out into the two secondary arc blowout channels.

In one embodiment, the primary arc blowout channel is defined between a first conductor or runner extending from the first, stationary contact, and a second conductor or runner that is located adjacent the second, displaceable contact, and which is electrically connected to the second contact.

There is provided for the first secondary arc blowout channel to be defined between an extended part of the first conductor or runner, and an opposing intermediate conductor or runner.

There is provided for the second secondary arc blowout channel to be defined between the intermediate conductor or runner, and the second contact or runner, in order for the intermediate conductor or runner to be common to both arc splitter arrangements.

A further feature of the invention provides for the arc splitting stacks of the arc splitting arrangements to be spaced apart but in the same plane. Alternatively, there is provided for the arc splitting stacks of the arc splitting arrangements to overlie one another, but to be in different planes with an insulator provided between the two overlying arc splitting stacks.

There is also provided for the electrical switch to include a switching mechanism for displacing the second contact between the connected and disconnected positions, the switching mechanism including a handle arrangement which is displaceable between an off position, in which the second contact is in the disconnected position, and an on position, in which the second contact is in the connected position.

According to a further aspect of the invention there is provided a method of suppressing an arc in an electrical switch, the method including the steps of:

- displacing an arc formed between two contacts of a contact set away from the contact set;

- dividing the arc into two discrete arcs; and

- displacing each discrete arc towards an independent arc splitting arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described by way of non-limiting examples, and with reference to the accompanying drawings in which: Figure 1 is a cross-sectional side view of a circuit breaker including a prior art arc splitting arrangement, with the circuit breaker being in a closed position;

Figure 2 is a cross-sectional side view of a circuit breaker including a prior art arc splitting arrangement, with the circuit breaker being in an open position; is a schematic representation of an arc splitting arrangement in accordance with a prior art arrangement;

Figure 4 is a schematic representation of a new arc splitting arrangement in accordance with the invention;

Figure 5 is a cross-sectional side view of a circuit breaker incorporating a new arc splitting arrangement based on the conceptual arc splitter arrangement of Figure 4;

Figure 6 is a top plan view of another embodiment of the new arc splitter arrangement;

Figure 7 is a cross-sectional top plan view of the arc splitter arrangement of Figure 6, showing the bottom half of the arc splitter arrangement of Figure 6;

Figure 8 is a side view of the arc splitter arrangement of Figure 6; and

Figures 9 to 14 is a sequence of photographs showing the electrical switch in use, and in particular showing how a single arc is separated into two arcs, and then quenched in two arc splitting arrangements. DET AILED DESCRIPTION OF INVENTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "Including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings and are thus intended to include direct connections between two members without any other members interposed there between and indirect connections between members in which one or more other members are interposed there between. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings. It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the," and any singular use of any word, include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term "include" and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

The prior art circuit breaker shown in Figures 1 to 3 has already been described above, and will not be described in detail again. It should be noted that the improvement brought about by the present invention relates to the re-design of the arc splitter arrangement 40 of the circuit breaker of Figures 1 to 3. The remainder of the circuit breaker, or any other electrical switch incorporating the new arc splitter arrangement, will conceptually remain the same, and is accordingly not described in detail.

Referring to the drawings, in which like numerals indicate like features, a non-limiting example of an electrical switch in accordance with the invention is generally indicated by reference numeral 100, and the arc splitting arrangement of this switch is generally indicated by reference numeral 60.

Reference is first made to Figure 5, showing an example of a circuit breaker including one embodiment of the new arc splitting structure 60. It should be noted that although a circuit breaker is shown, the concept can be applied to any electrical switch that incorporates an arc splitting arrangement. The circuit breaker 10 comprises a plastic housing 11 which houses the contact set 20 and the switching arrangement 30. A line terminal 12 is provided, and in use an external electric conductor (not shown) is connected thereto. The line terminal 12 is an electrical contact with a first contact 21 of the contact set 20. The first contact 21 is a stationary contact. A load terminal 13 is provided in an opposite end of the housing 11, and in use an external electric conductor (not shown) is connected thereto. The load terminal 13 is in electric contact with a second contact 22 of the contact set via an electrical conductor 14 housed inside the housing 11.

A rigid and stationary carriage 15 is secured to the housing 11, and in use carries, inter alia, the switching arrangement 30 and the second contact 22. The second contact arrangement 20 includes a pivotable arm 22.1, with the contact tip 22.2 located on one end of the arm 21. An opposite end of the arm 22 is pivotabiy secured to the carriage 15 at a pivot point 22.3. The pivotable arm is therefore pivotabiy displaceable between a connected position (not shown) in which the first contact 21 and the second contact 22 abut, and a disconnected position (Figure 5) in which the first contact 21 and the second contact 22 are spaced apart. The arc referred to above will develop between the first contact 21 and the second contact 22 when the circuit breaker is displaced from the closed position to the open position.

A new arc splitting arrangement is indicated by reference numeral 60, and is shown schematically in Figure 4, and is also shown as implemented in Figure 5.

The new arc splitting arrangement 60 includes a first arc splitting arrangement 61 and a second arc splitting arrangement 62. The two arc splitting arrangements are electrically in series, but mechanically in parallel, and each arc splitting arrangement will in use receive and 'split' a discrete arc. Each arc splitting arrangement includes a plurality of isolated arc splitting plates (61.1 and 62.1) which are arranged in the form of stacks, as is known in the art.

As is the case in the prior art, an arc will typically form between the two contacts (21 and 22) when the contacts are moved apart. A first conductor or runner 42 extends from the first contact 21 , whereas a second conductor or runner is located adjacent the second contact 22. The second contact 22 and the second runner 43 are electrically coupled, even though they are not directly connected to one another in this particular example. A primary arc blowout channel or passage 63 is defined between the two conductors of runners (42 and 43), and the initial arc 50.1 is in use forced along this passage due to the Lorentz effect (indicated by force F). The displaced arc 50.2 travels along the primary arc blowout passage 63 away from the contacts (21 and 22).

In the prior art configuration, the passage 62 will terminate in a single arc splitter stack. However, in this embodiment, the passage 63 branches out into a first secondary blowout channel or passage 64 and a second secondary blowout channel or passage 65, with each of these passages terminating in its own, discrete arc splitter arrangement (61 and 62). The first secondary channel 64 is formed between an extension of the first conductor or runner 42, and an opposing intermediate conductor or runner 66. The second secondary channel 65 is in turn formed between the same intermediate conductor or runner 66 and an extension of the second conductor or runner 43. The intermediate runner 66 is therefore common to both arc splitter arrangements, and is essentially the element that divides the primary arc blowout channel up into two separate channels that are mechanically in parallel, but electrically in series. The intermediate runner is made from an elongate, flat metal strip.

In use the displaced arc 50.2 will move towards the two secondary channels (64 and 65) until it reaches the branch formed by the intermediate runner 66. Further displacement of the displaced arc 50.2 will result in the arc splitting up into two divided arcs 50.4, one located in each secondary arc blowout channel. The arcs will at the same time also energize the intermediate runner 66, which is an important aspect of this invention and new configuration. The divided arcs 50.4 will again be displaced along the secondary arc blowout channels due to the Lorentz effect, shown by forces F1 and F2. The divided arcs 50.4 will eventually reach the arc splitter plates (61.1 and 62.1) where the two divided arcs 50.4 will be broken up into a plurality of split arcs 50.3 as is known in the art. The mechanism stays the same as that which is known and used in the prior art, but the duplication of arc splitter stacks, and the concomitant division of the initial arc, result in much better arc suppressing capabilities.

It should be noted that the throat area of the secondary arc blowout channels are similar to that of the primary arc blowout channel. This geometry maintains the Lorentz forces while allowing for a greater number of splitter plates. By splitting a large current loop into two smaller loops, the force acting on each arc increases. Increasing the force on the arc in turn allows the arc to move into the grids much faster. As a result it is possible to increase the end arc resistance at a faster rate. A further embodiment of an arc splitter arrangement 60 is shown in Figures 6 to 8. This embodiment also includes a first arc splitting arrangement 61 and a second arc splitting arrangement 62, but in this case the two arc splitter stacks (61.1 and 62.1) overlies one another, but are located in different planes. The two stacks are separated by an insulating film 67, which essentially allows for the two stacks to operate independently, but without an increase in the cross-sectional area or footprint of the stacks. The operating principals remain exactly the same as described above for the spaced apart configuration of Figures 4 and 5.

Figures 9 to 14 is a sequence of the electrical switch of the invention in use, and particular show how the initial arc 50.1 is formed in Figure 9 between the two contacts (21 and 22) and then eventually extinguished in Figure 14. in Figures 10 and 11 the arc 50.2 has been displaced away from the contacts, and is displaced towards the two secondary channels (64 and 65) of the two splitter arrangements (61 and 62). In Figure 12 the arc has clearly been separated into two split arcs 50.4, each of which now enters its own splitting arrangement. The arcs are then again split into smaller arcs 50.3 in said splitting arrangements, and in Figure 14 the arcs are all but extinguished.

It will be appreciated that the above is only one embodiment of the invention and that there may be many variations without departing from the spirit and/or the scope of the invention.