WO2017059912A1

WO2017059912A1 - An arc extinguishing chamber for a switching device

Info

Publication number: WO2017059912A1
Application number: PCT/EP2015/073223
Authority: WO
Inventors: Gunnar Johansson; Mats Henning JOHANSSON; Erik Johansson
Original assignee: Abb Schweiz Ag
Priority date: 2015-10-08
Filing date: 2015-10-08
Publication date: 2017-04-13

Abstract

The present disclosure relates to an arc extinguishing chamber (170) for a switching device (100) comprising an arcing contact unit (160, 150, 140) and a main contact unit (165, 130, 120), each of the contact units including a movable contact (150, 130) and a stationary contact (140, 120), the arc extinguishing chamber (170) comprising a plurality of arc splitters (172) disposed with a distance to each other, each of the arc splitters (172) including a pair of arms and the plurality of arc splitters is arranged to form a passage (P) for the movable arcing contact, wherein the passage has a height. The height of the passage is adapted such that, when a current is switched off/ interrupted, the separation distance (h) of the arc contacts is longer than the one (H) of the main contacts and the movable arcing contact moves within the passage during the most part of the separation distance (h).

Description

AN ARC EXTINGUISHING CHAMBER FOR A SWITCHING DEVICE

TECHNICAL FIELD

The present disclosure generally relates to an arc distinguishing chamber for a switching device for breaking an electric current. In particular it relates to an arc distinguishing chamber of a switching device that includes a stationary main contact and a stationary arcing contact arranged in parallel with the stationary main contact.

BACKGROUND

Switching devices are used for interrupting a current or protecting an electric circuit in the event of an electrical failure for example due to a short circuit. Switching devices may comprise contacts including a stationary and a movable contact, which during a normal operation are in mechanical and electrical connection. When the contacts are separated from each other a current breaking operation is achieved. In addition to separating the contacts, a current breaking/interrupting operation involves extinguishing an arc between the contacts, and to force the current to decrease to zero.

When breaking a current without any natural zero-crossings, it is necessary to force the current down to zero. One common practice is to create a voltage across the breaking point that is higher than the system voltage thus forcing the current to decrease to zero. In order to achieve such a voltage across the breaking point it is desired to stretch the breaking arc over a long distance since the length of the arc increases the arc voltage and a long arc is also easily cooled and split into several shorter arcs that further increase the arc voltage.

An arc may be prolonged by either separating the contacts to a desired length so that the arc is stretched out or enabling the originally short arc to move along a path that stretches the short arc. When the contacts separate from each other at a limited distance, the arc must leave contact points quickly to avoid erosion of contact materials. To this end, an arc distinguishing chamber/chute is provided so that the arc moves away from the contacts into it, which further increases the arc voltage. It is desired that the arc moves along the desired path in a correct direction and with sufficient speed so that the arc voltage increases to a sufficient high value to break the current.

It is also known in the art that a so-called parallel make-and break contact system may be used, wherein the system comprises a main contact assembly including a movable main contact and a stationary main contact and an arcing contact assembly including a movable arcing contact and a stationary arcing contact coupled in parallel with the main contact assembly. Different characteristics that are required for different modes of operations are thus optimized. In such a system, the main contacts normally only conduct the current and is not involved in the switching operations that create arcs. The material in the main contact is optimized for a good conductivity thus reducing the generated power when current is flowing. On the other hand, the arcing contacts are arranged to handle switching operations and are not meant for continuously conducting the current.

EP2037472A2 describes a switching system including main contacts and arcing contacts, wherein during a switching operation there is a timing between the main contacts and the arcing contacts so that all switching (opening or closing) are handled by the arcing contacts while the main contacts conducts an electric current when the circuit is closed and are not damaged by any switching operations, wherein an arc-extinguishing chamber is arranged in a contact region for distinguishing an arc caused when interrupting a current.

SUMMARY

An object of the present disclosure is to provide an arc distinguishing chamber for a switching device of type of parallel make-and-break. The arc distinguishing chamber facilitates the switching device to break a high current at a sufficient speed.

According to a first aspect of the present disclosure, an arc distinguishing chamber is provided for such a switching device as defined in the preamble of claim 1 . The arc distinguishing chamber is further characterized in that the height of the passage is adapted such that, when a current is switched off/interrupted, the separation distance of the arc contacts is longer than the one of the main contacts and the movable arcing contact moves within the passage during the most part of the separation distance. This provides an advantage that the arc is well cooled in the passage formed by the arc splitters as it is stretched out and, the arc is easily split into several small arcs that enter between the arc splitters to be finally distinguished. According to one embodiment, the arms of the splitters enclose the passage for the movable arcing contact.

According to one embodiment, the passage formed by the arc splitters has a dimension with a width and a height and the height of the passage is adapted so that the separation distance of the arc contacts is at least twice times than the one of the main contacts.

Preferably, the passage formed by the arc splitters has a dimension include a width that is less than twice times than the width of the movable arcing contact.

According to a second aspect of the present disclosure, a switching device is provided for breaking a current comprising a main contact unit including a main contact carrier, a movable main contact and a stationary main contact, an arcing contact unit including an arcing contact carrier, a movable arcing contact and a stationary arcing contact, and an arc distinguishing chamber of claim 1 .

According to one embodiment, the switching device further comprises a first rack and a first gear for actuating the arcing contact carrier so that, when interrupting the current, a separation distance between the arcing contacts is longer than a separation distance between the main contacts.

According to one embodiment, the arcing contact carrier is attached to either the first gear or the first rack. According to another embodiment, the switching device further includes a second rack and a second gear, wherein the first and second gears are co- mounted on a shaft and the radius of the first gear is bigger than the radius of the second gear. The second rack may be attached to the main contact carrier.

Thus, when a current is switched off/interrupted, the separation speed of the arc contacts is faster than the one of the main contacts.

According to a further embodiment, the movable main contact is displaced outside the passage formed for the movable arcing contact. Furthermore, the switching device is a parallel double break and make switching device.

BRIEF DESCRIPTION OF THE DRAWINGS

The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

Figs. 1 a-c show an isometric and a cross-section views of an arc distinguishing chamber for a switching device for breaking a current; Figs. 2a-b show various views including isometric, cross-section view of a switching device for breaking a current comprising an arc distinguishing chamber according to the example of Figs.1 a-c. DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

A number of variations of a switching system for breaking a current will be described herein. Figures 1 a-c show a cross-section and top views of an arc distinguishing chamber 170 for a switching device 100 for breaking a current. The switching device comprises a stationary arcing contact 140, a movable arcing contact 150 and an arcing contact carrier 160 for actuating the movable arcing contact 150. It further comprises a stationary main contact 120, a movable main contact 130 and a main contact carrier 165. The movable main contact 130 is attached to the main contact carrier 165. An actuating unit 1 10 is provided for actuating the main and arcing contact carriers 165, 160 from an open position to close position or vice versa at an actuating distance. The arc distinguishing chamber 170 encloses the stationary arcing contacts 140 and movable arcing contacts 150 and comprises a plurality of U-shaped arc splitters 172 disposed in parallel to each other and, during a switching operation, the U-shape splitters 172 forms a narrow passage for a movable arcing contact 150 so that it moves alongside/adjacently to the edges of the U- shaped parts of the arc splitters 172. Furthermore, each of the U-shaped splitters 172 extended with two arms 173, 173' that further enclose the passage. The height of the passage is adapted so that, when a current is switched off/interrupted, the separation distance h of the arc contacts is longer than the one H of the main contacts and during the most part of the separation distance h, the movable arcing contact moves within the passage.

As indicated in Figure 1 c, the passage P formed by the arc splitters has a dimension with a height that is adapted so that the separation distance h of the arc contacts is at least twice times than the one H of the main contacts. In this the arc to be distinguished is stretched longer so that the arc voltage is increased in a sufficient speed. Consequently, a higher current will be interrupted in a sufficient speed.

It should be understood that the arc splitters 172 may have other shapes like Y- or V-shaped and may displaced at a distance not necessarily in parallel to each other. For example, they may be displaced as a fan-shape.

The passage formed by the arc splitters has a dimension include a width w and the width of the passage is less than twice times than the width of the movable arcing contact so that the movable arcing contacts is moving adjacently to the edge of the U-, Y- or V-shaped splitters during a switching operation. This enables the size of a switching device even impact.

In reference to Figures 2a-b, a switching device 200 is provided for breaking a current comprising a main contact unit including a main contact carrier 265, a movable main contact 230 and a stationary main contact 220, an arcing contact unit including an arcing contact carrier 260, a movable arcing contact 250 and a stationary arcing contact 240, and an arc distinguishing chamber 270 of examples shown in Figures 1 a-b. In this example, the switching device 200 is a two-pole DC contactor.

For each of the poles, there are provided with a movable arcing contact 250, and two stationary arcing contact 240, 240', and a movable main contact 230 and two stationary main contact 220, 220'. Furthermore, each of the stationary arcing contacts 240, 240' is attached to a corresponding stationary main contact 220 and is fornned as a U-shaped bar. The movable arcing contact 250 is formed as a thin bar with two ends. A contact tip 252 is placed at the each of the ends. The movable main contact 230 is formed as a wider bar with two ends as well. A contact tip 232 is placed at the each of the ends. As illustrated in the figures, the contact tips 252, 242 of the arcing contacts 250, 240 have much smaller dimensions/surfaces than the contact tips 232, 222 of the main contacts 230, 220. The main contact surface may be larger than the arcing contact. Furthermore, in this example, for both poles, a single arcing contact carrier 260 and a single main contact carrier 265 are provided for carrying the movable arcing contacts 250, 250' and the movable main contacts 230, 230' respectively. The main contact carrier 256 is further connected/attached to a magnet 210 acting as an actuating unit.

The switching device 200 further comprises a first rack 290 and a first gear 280 for actuating the arcing contact carrier 260. Rack 290 is provided on the arcing contact carrier 260 and to be meshed with gear 280. This first rack and gear unit enables a separation distance between the arcing contacts is longer than a separation distance between the main contacts when interrupting the current.

Furthermore, two second gears 285, 285' with a smaller radius are provided on a shaft 287, the first gear 280 with a bigger radius is mounted between the smaller gears 285, 285' on the same shaft 287. Two second racks 295, 295' are attached on the main contact carrier 265 to be engaged with gears 285, 285' respectively. Although this example shows two second gears and racks, it should be understood that it is possible to arrange a second gear and rack unit including one gear and one rack to achieve the same purpose.

Dual contact actions occur during a switching operation, i.e. either a closing or an opening operation. When the switch is separated/open, the main contacts open first then followed by opening of the arcing contacts. When the switch is closed, the arcing contacts close first followed by closure of the main contacts. This means that during the switching operation arcing contacts experience/confront arcs occurred while the main contacts can avoid arcs caused by the switching operation. During an interrupting/switching off operation, the actuating unit 210 actuates the main contact carrier 265 that in turn actuates the movable main contact 230 and the second rack 295. The main contacts 230 and 220 will be separated at a point of time. The second rack 295 and second gear 285 translate the liner movement of the actuation to a rotational movement of the gear 285. Since the first gear 280 and second gears 285, 285' are mounted on the same shaft 287, the rotation of the second gear 285 is transferred to a rotation of the first gear 280. With the meshed first rack 290, the rotation of the first gear 280 is translated to a liner movement of the first rack 290 thus actuates the arcing contact carrier 260. The arcing contacts 240, 250 will be separated later than the main contacts 220, 230. Due to the fact that the radius of the first gear 280 is bigger than the radius of the second gears 285, 285', the arcing contact carrier 260 moves longer and with a faster separation speed than the main contact carrier 265, which results in a bigger gap between the arcing contacts 240, 250 than the main contacts 220, 230. A proportion of the radiuses of the first gear and the second gear is in a range of 2:1 to 8:1 , which presents a gear ratio in relation to an actuating distance. Thus, with a gear ratio for the movable arcing contact in relation to the actuating unit 4:1 , if, during at least part of the movement of the actuating unit, the actuation unit 210 and the movable main contacts 230 move 10 mm, the movable arcing contacts 250 may move 40 mm thus allowing the arc to be stretched out longer.

The stationary arcing contacts 240, 240' are fixedly arranged just below the arc splitters while the movable arcing contact 250 is above the arc splitters when the arcing contacts are finally separated, which enables that the arc is well cooled and split into small arcs. The small arcs easily enter between the arc splitters and distinguished finally. The movable main contact is situated outside the passage/arc chamber formed for the movable arcing contact. Thus no further adaption for the main contacts is required.

The switching device shown in Figures 2a-b has a so called parallel double break and make switching structure, wherein the two stationary arcing contacts 240, 240' are positioned in parallel with the two stationary main contacts 220, 220'. Each of the stationary arcing and main contacts 240, 240'; 220, 220' are aligned with the corresponding movable arcing and main contacts 250, 230. Each of the movable main and arcing contacts 250, 230 includes two arms, wherein a contact tip 252, 252'; 232, 232' is displaced at each end of the arms facing the contact tips 242, 242'; 222, 222' of the corresponding stationary main and arcing contacts 240, 220, thus enable double contacting points connected in series for each of the arcing and main contacts when a contact is made. A contact tip may be also called as contact pad or contact surface on which a contact is made. It is advantageous to use a double break and make switching structure because this structure enables to reduce the separation length of the contacts to half of the length of a single break and make structure when generating a sufficient arc voltage. The structure thus enables a more compact switching device in respect to dimension.

It should be understood that a switching device based on the present invention may be used for interrupting either a DC or AC current and may be any of contactor, circuit breaker, or switch-disconnector. It should be also understood that the invention not only improve a capability of braking/interrupting a high current but also a capability of breaking a low current. Usually for a high current switching device, it is designed to break a high current. However, when it is used to break a low current it may result in severe damages of the device. This is because that, for a low current it is difficult to move a low current arc away from contact tips and stretch it out by itself due to low magnetic force, thus the arc will likely stay at the contact tips and not enter an arc distinguishing chamber. The present invention enables an arc to be stretched out at a long distance within a narrow passage inside the arc distinguishing chamber so that even when the current to be broken is low, the low current arc can be effectively cooled down and an arc voltage is increased at a sufficient speed and consequently the current is forced to zero. Thus, the invention is suitable for breaking a currents up to 5000A.

Claims

1 . An arc distinguishing chamber (170; 270) for a switching device (100, 200) comprising an arcing contact unit (160, 150, 140; 260, 250, 240) and a main contact unit (165, 130, 120; 265, 230, 220), each of the contact units including a movable contact (150, 130; 250, 230) and a stationary contact (140, 120; 240, 220), the arc distinguishing chamber (170, 270) comprising a plurality of arc splitters (172; 272) disposed with a distance to each other, each of the arc splitters (172; 272) including a pair of arms and the plurality of arc splitters is arranged to form a passage (P) for the movable arcing contact, wherein the passage has a height, characterized in that the height of the passage is adapted such that, when a current is switched off/interrupted, the separation distance (h) of the arc contacts is longer than the one (H) of the main contacts and the movable arcing contact moves within the passage during the most part of the separation distance (h).

2. Arc distinguishing chamber of claim 1 , wherein the arms of the splitters enclose the passage (P) for the movable arcing contact.

3. Arc distinguishing chamber of claim 1 , wherein the passage formed by the arc splitters has a dimension with a height and the height of the passage is adapted so that the separation distance (h) of the arc contacts is at least twice times than the one (H) of the main contacts.

4. A switching device (200) for breaking a current comprising:

a main contact unit including a main contact carrier (265), a movable main contact (230) attached to the main contact carrier and a stationary main contact (220),

an arcing contact unit including an arcing contact carrier (260), a movable arcing contact (250) attached to the arcing contact carrier and a stationary arcing contact (240) arranged in parallel with the stationary main contact (20, 120, 220), and

an arc distinguishing chamber (270) of claim 1 .

5. Switching device of claim 4 further comprising a first rack (290) and a first gear (280) for actuating the arcing contact carrier (260) so that, when interrupting the current, a separation distance between the arcing contacts (250, 240) is longer than a separation distance between the main contacts (230, 220).

6. Switching device of claim 4, wherein the arcing contact carrier (260) is attached to either the first rack (290) or the first gear (280).

7. Switching device of claim 4, wherein the switching device further includes a second rack (295) and a second gear (285), wherein the first and second gears (280, 285) are co-mounted on a shaft (287) and the radius of the first gear (280) is bigger than the radius of the second gear (285).

8. Switching device of claim 7, wherein the second rack (295) is attached to the main contact carrier (265).

9. Switching device of any of claims 5-8, wherein a separation speed of the arcing contacts is higher than the one of the main contacts.

10. Switching device of any of claims 4-9, wherein the movable main contact is situated outside the passage formed for the movable arcing contact.

1 1 . Switching device of any of claims 4-9, wherein the switching device is a parallel double break and make switching device.