EP3338289B1

EP3338289B1 - Electrical switching device and process for cooling a switching medium in an electrical switching device

Info

Publication number: EP3338289B1
Application number: EP16753384.3A
Authority: EP
Inventors: Mahesh DHOTRE; Javier MANTILLA FLOREZ; Jean-Claude Mauroux; Oliver Cossalter; Sami Kotilainen; Xiangyang Ye; Stephan Grob
Original assignee: Hitachi Energy Ltd
Current assignee: Hitachi Energy Ltd
Priority date: 2015-08-21
Filing date: 2016-08-17
Publication date: 2025-10-01
Anticipated expiration: 2036-08-17
Also published as: WO2017032667A1; CN108140501A; CN108140501B; EP3338289A1

Description

The present invention relates to an electrical switching device comprising at least one switching chamber, according to the preamble of claim 1, specifically to a circuit breaker or a generator circuit breaker. The present invention further relates to a process for cooling a switching medium in an electrical switching device, specifically a circuit breaker or a generator circuit breaker.
In conventional circuit breakers, the arc formed during a current breaking operation is extinguished using a switching gas (also referred to as "arc-quenching gas"). For this purpose, the circuit-breaker comprises one or more series-connected switching chambers, which are filled with the switching gas and operate on one of the conventional principles for extinguishing the arc generated in the arcing region, e.g. by way of e.g. a self-blasting mechanism or conventional puffer-assisted mechanism. The hot gas created during arc extinction flows from the arcing region in direction to an exhaust volume whereby it needs to be cooled down sufficiently before entering the tank volume.
EP 0 836 209 , e.g., discloses a circuit breaker comprising a switching chamber which is filled with e.g. SF₆ as the arc-quenching gas. According to EP 0 836 209 , an arc is generated between the two main contacts during the breaking operation and is quenched by the arc-quenching gas. The hot and ionized gases which are produced in the arcing region are transported downstream, i.e. in direction to an exhaust volume, with a portion of the hot gases being stored in a self-blast volume and being used later in a known manner to assist the quenching process. The remaining hot gases are transported through the tubular main arcing contacts into an exhaust volume.
Aiming at an improvement in the interruption performance, EP 1 403 891 discloses a circuit-breaker having a switching chamber, which is filled with a switching gas, contains an arcing region and has at least two arcing contacts. At least one of the arcing contacts is in the form of a hollow tubular contact, which is provided for transporting hot gases out of the arcing region into an exhaust volume connected to the switching chamber volume.
As mentioned, SF₆ is typically used as arc-quenching gas. This is also the case for the circuit breakers according to EP 0 836 209 and EP 1 403 891 .
Aiming at improved interruption capability and at the same time simple and economic construction and operation of the circuit breaker, a switching medium comprising an organofluorine compound selected from the group consisting of a fluoroether, a fluoroamine, a fluoroketone and mixtures thereof has been suggested in WO 2013/087687 . These alternative "non-SF₆" switching media allow for a good dielectric strength and at the same time exhibit a very low Global Warming Potential (GWP) and an Ozone Depletion Potential of about 0. Despite of the environmental-friendliness of the alternative switching media according to WO 2013/087687 , issues might occur due the organofluorine compound decomposing when being subjected to the high temperatures present during burning of the arc. Contrary to SF₆, which after decomposition readily recombines again, the decomposition of the organofluorine compounds of interest, in particular the fluoroketones, is an irreversible process. In order to maintain a high interruption performance and a long lifetime of the circuit breaker, decomposition of organofluorine compound shall be minimized.
EP 0 042 456 A1 describes a high voltage power switch having a stationary contact and an axially displaceable contact, with a nozzle-like orifice through which quenching gas flows during the disconnecting process from a quenching chamber to an expansion chamber, and a coil through which the disconnect current flows after the commutation of the disconnect arc to an annular contact.
EP 1 895 558 A1 describes an equipment having a metallic container and an exhaust constituted of an arcing contact support tube and a metallic case surrounding the support tube and defining an annular volume with the support tube.
DE 198 32 709 A1 describes a high-voltage power breaker having an interrupter unit which is enclosed, with a gap, by a gas-tight housing filled with quenching gas, the interrupter unit has two arcing contacts between which an arc produced during disconnection is blown by means of a blowing device with a quenching gas which afterwards at least partially flows away in the axial direction of the arcing contacts.
Apart from this and irrespective of the switching medium used, there is an ongoing need to minimize the size of the exhaust volume to allow for a compact design and, ultimately, for a reduction in costs.
The object of the present invention is thus to provide a circuit breaker and cooling method which allows for a high interruption performance also when choosing a very compact design. In particular, the circuit breaker shall allow for a high interruption performance and a prolonged lifetime also when using a non-SF₆ switching medium. The problem is solved by the electrical switching device and method or process of the independent claims. Embodiments of the invention are defined in the dependent claims.
According to embodiments of the process, heat is transferred at least partially by heat radiation. Additionally, also other heat transfer mechanisms can take effect, in particular heat transfer by heat conduction.
The invention is further illustrated by means of the attached figures of which:

Fig. 1: shows a longitudinal section of a circuit breaker according to a first embodiment of the present invention during a current breaking operation,
Fig. 2: shows a longitudinal section of a circuit breaker according to a second embodiment of the present invention during a current breaking operation,
Fig. 3: shows a longitudinal section of a circuit breaker according to a third embodiment of the present invention during a current breaking operation,
Fig. 4a-d: show the temperature development in the nozzle (Fig. 4a), the intermediate chamber (Fig. 4b), the exhaust volume (Fig. 4c) and the tank volume (Fig. 4d) (in this order) of a test device following a switching operation, both for the case where the inner surface of the exhaust volume is covered by a porous layer according to the present invention in comparison to the case where there is no porous layer, said temperature development having been determined by numerical experiments using a simulation model,
Fig. 5: the pressure development measured in the intermediate chamber of the test device following a switching operation, both for the case where the inner surface of the exhaust volume is covered by a porous layer according to the present invention in comparison to the case where there is no porous layer.

As shown in Fig. 1 to 3, the circuit breaker of the present invention comprises a switching chamber 10, which in the embodiments shown is rotationally symmetrical and extends along a longitudinal axis L. The switching chamber comprises a tank wall 11 which delimits a tank volume 13.
The switching chamber 10 comprises two nominal contacts 12 movable in relation to each other in the axial direction, specifically a main contact as a first nominal contact 121 and a contact cylinder as second nominal contact 122. The second nominal contact 122 surrounds a concentrically disposed nozzle arrangement 14 comprising a nozzle 16 and further surrounds a conducting portion 18 forming the wall of a self-blast volume 17. The nozzle arrangement 14 further surrounds two concentrically disposed arcing contacts 19, one in the form of a hollow tubular contact 191 and the other in the form of a pin contact 192.
In the embodiment shown, the second nominal contact 122 is exemplarily designed as a movable contact, whereas the first nominal contact 121 is designed as a stationary contact. This may also be vice versa or both contacts 122, 121 may be moveable.
During a current breaking operation, the second nominal contact 122 is moved in axial direction L away from the first nominal contact 121 from a connected (or closed) state to a disconnected (or open) state.
Thereby, also the hollow tubular contact 191 is moved in axial direction L away from the pin contact 192 and eventually disconnected, whereby an arc 20 is formed in the arcing region 22 located between the arcing contacts 191, 192. An actuating rod 24 is linked to the nozzle arrangement 14, said actuating rod 24 being connected to the pin contact 192 by means of an angular lever 26, adapted such to pull the pin contact 192 in a direction away from the hollow tubular contact 191 during current breaking, thereby increasing the speed of disconnecting the arcing contacts 191, 192.
The arc 20 formed is quenched by means of a self-blasting mechanism blowing the heated switching gas into the arcing region 22 and outwards through the nozzle 16. Thereupon, some of the heated and pressurized switching gas flows out of the arcing region 22 through the hollow tubular contact 191, whereas some switching gas flows out of the arcing region 22 in the opposite direction trough a nozzle channel 28 arranged concentrically to and extending along the pin contact 192. The flow direction of the hot switching medium away from the arcing region 22 is depicted with respective arrows.
On the side of the hollow tubular contact 191, a first intermediate chamber 30 is optionally present. It is disposed concentrically relative to the hollow tubular contact 191 and at a distance from the arcing region 22. The first intermediate chamber 30 is fluidically connected with the hollow tubular 191 contact by openings 32 provided in the wall 34 of the hollow tubular contact 191. Specifically, a row of e.g. four openings 32 having same cross section and being radially disposed over the circumference of the hollow tubular contact 191 are provided in the embodiment shown.
The first intermediate chamber 30 is delimited by a first intermediate chamber wall 36 comprising a proximal side wall 361 facing the arcing region 22, a distal side wall 362 arranged opposite to said proximal side wall 361 and a circumferential wall 363. The first intermediate chamber wall 36 is preferably made of metal, for example steel or copper, although it may also be composed of a comparatively highly thermally conductive plastic. In the specific embodiment shown, two rows of circumferentially disposed radial openings 38 of same cross-section are arranged in the first intermediate chamber wall 36, one in direct proximity to the proximal side wall 361 and one in direct proximity to the distal side wall 362. The openings 38 open into a first exhaust volume 40 arranged concentrically with respect to the first intermediate chamber 30.
The openings 32 in the hollow tubular contact 191 are arranged offset with regard to the openings 38 in the first intermediate chamber wall 36 so that the swirled gases flowing in the radial direction cannot flow further directly through the openings 38 into the first exhaust volume 40. However, it can also be feasible for at least one of the openings 32 in the hollow tubular contact wall 34 to be provided such that it is entirely or partially coincident with a respective opening 38 in the intermediate chamber wall 36, in order to deliberately ensure a direct partial or complete flow from the hollow tubular contact 191 into the first exhaust volume 40. The shape, size, arrangement and number of the openings 32 and 38, respectively, are optimally configured, and are matched to the respectively operational requirements.
The first exhaust volume 40 is delimited by an exhaust volume wall 42. In the embodiment shown, the exhaust volume wall comprises a proximal sidewall 421, a distal sidewall 422, an outer circumferential wall 423 and an inner circumferential wall 424, the circumferential walls 423, 424 being displaced axially from each other.
Specifically, the inner circumferential wall 424 extends from the distal side wall 422 leaving a gap 44 between its free end and the proximal side wall 421, whereas the outer circumferential wall 423 extends from the proximal side wall 421 in a manner such that it overlaps with the inner circumferential wall 424. Thereby, an annular channel 46 is formed between the circumferential walls 423, 424, said channel 46 opening into the tank volume 13 delimited by the tank wall 11 and being filled with switching gas of relatively low temperature. The tank wall 11 is designed in a gas-tight manner and is made of a metal.
Following the heating of the gas caused by the current breaking operation, a portion of the heated pressurized switching gas flows out of the arcing region through the hollow tubular contact 191, as mentioned above. The gas flow indicated by the arrow A10 is deflected by an approximately conical deflection device (not shown), as indicated by radially deflecting arrows, into a predominantly radial direction. The gas flow passes through the openings 38 into the first intermediate chamber 30, in which the switching gas is swirled.
The swirled switching gas is then allowed to pass through the openings 38 in the first intermediate chamber wall 36 in the radial direction into the first exhaust volume 40, as also indicated by arrows.
The switching gas that has entered the first exhaust volume 40 then flows through the gap 44 or first gap volume 44 and the annular channel 46 formed by the circumferential walls 423, 424 into the tank volume 13.
On the side of the pin arcing contact 192, a second intermediate chamber 52 is arranged, with the distal end 54 of the pin contact 192 and the angular lever 26 being arranged in the interior of the second intermediate chamber 52 being delimited by a second intermediate chamber wall 60. One row of circumferentially disposed radial openings 58 is arranged in the circumferential wall 603 of the second intermediate chamber 52 in direct proximity to its distal sidewall 602. These openings 58 open into the second exhaust volume 62.
Like the first exhaust volume 40, also the second exhaust volume 62 is delimited by an exhaust volume wall 64 comprising a proximal sidewall 641, a distal sidewall 642, an outer circumferential wall 643 and an inner circumferential wall 644, the circumferential walls 643, 644 being displaced axially from each other. Also with regard to the second exhaust volume 62, the inner circumferential wall 644 extends from the distal side wall 642 leaving a gap 66 or second gap volume 66 between its free end and the proximal side wall 641, whereas the outer circumferential wall 643 extends from the proximal side wall 641 in a manner such that it overlaps with the inner circumferential wall 644. Thereby, an annular channel 68 is formed between the circumferential walls, said annular channel 68 opening into the tank volume 13, as described above for the first exhaust volume 40.
During the current breaking operation, a second portion of the heated and pressurized switching gas flows through the nozzle channel 28 extending along the pin contact 192, as illustrated by arrows A20. This second portion of pressurized switching gas flows partly directly into the second exhaust volume 62 by passing openings 70 and partly into the second intermediate chamber 52 and from there into the second exhaust volume 62 by passing openings 58. Thereby, the portion flowing out of the second intermediary chamber 52 is deflected in the second exhaust volume 62 by means of the inner circumferential wall 644, before flowing out into the tank volume 13 containing switching gas of relatively low temperature, as described above for the first exhaust volume 40. Like the inner circumferential wall 424 of the first exhaust volume wall 40, also the inner circumferential wall 644 of the second exhaust volume wall 64 thus functions as an exhaust volume baffle.
In the embodiment shown in Fig. 1, the inner surface of the first intermediate chamber wall 36 and the second intermediate chamber wall 60, which function as a metal component for absorbing heat, is covered by a porous layer 72, particularly of a porous insulating or a porous metal material made of copper, aluminum, steel, brass or a nickel alloy. Specifically, this includes the inner surface of both sidewalls 361, 362 and the circumferential wall 363 of the first intermediate chamber 30 and the inner surface of the distal sidewall 602 and circumferential wall 603 of the second intermediate chamber 52.
Also, the inner surface of the first exhaust volume wall 42 and the second exhaust volume wall 64, which also function as a metal component for absorbing heat, is covered by the porous layer 72, preferably by the same porous insulating or porous metal material covering the inner surface of the intermediate chamber walls 36, 60.
Thus, the embodiment shown in Fig. 1 is specifically designed for augmenting heat transfer from the hot switching gas during its flowing out after a current breaking operation. During its passage through the intermediate chambers 30, 52 and exhaust volumes 40, 62, heat radiation emitted from the outflowing hot switching gas is efficiently absorbed by the porous layer 72, resulting in an overall increase in the cooling of the switching gas during its passage from the arcing region 22 into the tank volume 13. Due to the porous material 72 being made of a metal material, a particularly efficient heat absorption is achieved which is required for cooling the hot switching gas under the required threshold value.
In the embodiment shown in Fig. 2, the inner surface of the tank wall is covered by a porous layer 72, 72', particularly by a ceramic porous material 72'.
The embodiment shown in Fig. 2 is specifically designed for augmenting absorption of heat generated under normal conditions by ohmic heating under nominal current. This is achieved by the porous ceramic layer 72' of relatively great area applied on the tank wall 11. Specifically, the heat of the gas in the tank volume 13 is efficiently absorbed and transferred to the tank wall 11, from which it is emitted to the surrounding.
A further embodiment designed for augmenting absorption of heat generated under normal conditions by ohmic heating under nominal current is shown in Fig. 3, according to which the outer surface of the nominal contacts 12, specifically the first nominal contact 121 and the second nominal contact 122, is covered by a ceramic porous layer 72'. This embodiment allows ohmic heating of the nominal contacts 12 to be efficiently absorbed and, thus, to be dissipated. Of course, the layer arrangement according to Figs. 1 and/or 2 and/or 3 can be combined in order to achieve a particularly efficient dissipation of heat generated.
The concept of the present invention illustrated by Fig. 1 to 3 has further been evaluated by means of a test device. In the test device, the temperature of the switching gas as well as the pressure present in the respective compartment has been determined by numerical experiments using a simulation model and by running a test in which the temperature and pressure were actually measured after a switching operation.
The test device used encompasses a test device nozzle arrangement directly connected to a test device hollow tube opening into a test device intermediate chamber. In the downstream direction, the test device intermediate chamber is fluidically connected to a test device exhaust volume which opens into a test device tank volume. The interior of the test device nozzle arrangement, the test device hollow tube, the test device intermediate chamber, the test device exhaust volume and the test device tank volume is in each case subdivided into two compartments, of which a first compartment of the test device intermediate chamber, the test device exhaust volume and the test device tank volume comprises a porous layer according to the present invention, whereas the second compartment of said components is devoid of the porous layer.
According to Fig. 4a-d, the temperature measurement shows that whereas the temperature measured in the nozzle arrangement (Fig. 4a) is identical, there is a substantial temperature drop of the switching gas of about 22% in the test device intermediate chamber (Fig. 4b) comprising the porous layer in comparison to the one devoid of it. The effect is even more pronounced in the test device exhaust volume (Fig. 4c) and the test device tank volume (Fig. 4d), in which the temperature drops by 67% and 55%, respectively.
As further shown in Fig. 5, the concept of the present invention is further confirmed by the pressure development measured in the intermediate chamber:
According to Fig. 5, a significantly reduced pressure is measured for the case where the inner surface of the exhaust volume is covered by a porous layer (continuous line) according to the present invention compared to the case where there is no porous layer (dashed line). Specifically, a 40% lower maximum pressure increase when the exhaust volume is covered with the porous layer confirms a substantial enhancement of heat absorption by application of the porous layer(s).

List of reference numerals

10: switching chamber
11: tank wall
12: nominal contacts
121; 122: first nominal contact (main contact); second nominal contact (contact cylinder)
13: tank volume
14: nozzle arrangement
16: nozzle
18: conducting portion
17: self-blast volume
19: arcing contacts
191; 192: hollow tubular (arcing) contact; pin (arcing) contact
20: arc
22: arcing region
24: actuating rod
26: angular lever
28: nozzle channel, nozzle throat and diffusor
30: first intermediate chamber
32: openings in wall of tubular hollow contact
34: wall of tubular hollow contact
36: first intermediate chamber wall
361, 362, 363: proximal side wall, distal side wall, circumferential wall (of first intermediate chamber wall)
38: openings in the first intermediate chamber wall
40: first exhaust volume
42: first exhaust volume wall
421; 422; 423; 424: proximal sidewall; distal sidewall; outer circumferential wall; inner circumferential wall (of first exhaust volume wall)
44: gap, first gap volume
46: annular channel
52: second intermediate chamber
54: distal end of pin contact
58: openings in second intermediate chamber wall
60: second intermediate chamber wall
602; 603: distal side wall; circumferential wall of second intermediate chamber
62: second exhaust volume
64: second exhaust volume wall
641; 642; 643; 644: proximal sidewall; distal sidewall; outer circumferential wall; inner circumferential wall of second exhaust volume wall
66: gap, second gap volume
68: annular channel formed by circumferential walls of second exhaust volume
70: openings from nozzle channel into second exhaust volume
72, 72': porous layer(s).

Claims

Electrical switching device comprising at least one switching chamber (10), which comprises
at least two arcing contacts (191, 192) movable in relation to each other and defining an arcing region (22) in which an arc (20) is formed during a current breaking operation,

at least a portion of said switching chamber (10) being filled with a switching medium for quenching the arc (20) and for providing dielectrical insulation,

the switching chamber (10) further comprising an exhaust volume (40, 62), which is fluidically connected to the arcing region (22), to allow the switching medium heated by the arc (20) to flow out of the arcing region (22) in direction to the exhaust volume (40, 62), thereby transferring heat to a metal component of the switching chamber (10), wherein

at least a portion of a surface contained in the switching chamber (10) is covered with a porous layer (72, 72'),

characterised in that

the electrical switching device further comprises a self-blast volume (17) for building up pressure of the switching medium, at least a portion of the inner wall of said self-blast volume being covered with the porous layer.
Electrical switching device according any one of the claims, wherein at least a portion of the metal component is covered with the porous layer (72, 72'); and/or the porous layer is in contact with at least a portion of the heated switching medium; and/or the surface covered by the porous layer (72, 72') relates to an inner surface of a hollow body designed to be passed through by at least a portion of the heated switching medium; and/or the surface covered by the porous layer (72, 72') is a surface other than the surface of a nozzle arranged in the switching device.
Electrical switching device according to any one of the preceding claims, wherein it is a circuit breaker or a generator circuit breaker.
Electrical switching device according to any one of the preceding claims, wherein the porous layer (72, 72') contains or essentially consists of a porous insulating or porous metal material, particularly a metal foam, and/or a ceramic porous material; in particular the metal foam is made of aluminum, and/or the metal foam has gas-filled pores that are sealed to form a closed-cell metal foam or that are interconnected to form an open-cell metal foam.
Electrical switching device according to any one of the preceding claims, wherein the porous layer, in particular the metal foam, has been produced on the surface contained in the switching chamber (10) by metallic sintering, by electrodeposition, by chemical vapor deposition, or by metal deposition through evaporation.
Electrical switching device according to any one of the preceding claims, wherein the porous layer (72, 72') has a pore density ranging from 30 ppi to 60 ppi.
Electrical switching device according to any one of the preceding claims, wherein the heated switching medium has a temperature of 2000 K at most and the porous layer has a pore density of 50 ppi at most; or the heated switching medium has a temperature of 1500 K at most and the porous layer has a pore density of 30 ppi at most; or the heated switching medium has a temperature of higher than 000 K and the porous layer has a pore density of higher than 50 ppi.
Electrical switching device according to any one of the preceding claims, wherein the porous layer (72, 72') has a porosity of at least 65%, preferably at least 85%, and most preferably at least 95%.
Electrical switching device according to any one of the preceding claims, wherein the porous layer (72, 72') has a mean pore diameter in the range from 1 mm to 1.5 mm, preferably from 1.1 mm to 1.3 mm.
Electrical switching device according to any one of the preceding claims, wherein the exhaust volume (40, 62) is delimited by an exhaust volume wall (42, 64), at least a portion of the inner surface of the exhaust volume wall (42, 64) being covered with the porous layer (72, 72'); and/or in the exhaust volume (40, 62) an exhaust volume baffle is arranged, at least a portion of the surface of the exhaust volume baffle being covered with the porous layer (72, 72').
Electrical switching device according to any one of the preceding claims, in particular a circuit breaker, wherein it further comprises an intermediate chamber (30, 52), which, in direction of the outflow of the heated switching medium, is arranged between the arcing region (22) and the exhaust volume (40, 62), said intermediate chamber (30, 52) being delimited by an intermediate chamber wall (36, 60), at least a portion of the inner surface of the intermediate chamber wall (36, 60) being covered with the porous layer (72, 7 2'); in particular in the intermediate chamber (30, 52) an intermediate chamber baffle is arranged, at least a portion of the surface of said intermediate chamber baffle being covered with the porous layer (72, 72').
Electrical switching device according to any one of the preceding claims, wherein at least one baffle that is covered with the porous layer (72, 72') , in particular the intermediate chamber baffle and/or the exhaust volume baffle, is arranged such that it functions as a filter for removing dust particles from the outflowing switching medium, specifically the switching gas.
Electrical switching device according to any one of the preceding claims, wherein the surface, which is covered with the porous layer (72, 72') , forms part of or corresponds to the surface of the switching chamber (10), and in particular forms part of or corresponds to a surface selected from the group consisting of: the inner surface of the exhaust volume wall (42, 64), the surface of the exhaust volume baffle, the inner surface of the intermediate chamber wall (36, 60), the surface of the intermediate chamber baffle, any portion thereof, and any combination thereof.
Electrical switching device according to any one of the preceding claims, wherein the porous layer (72, 72') contains or essentially consists of a porous insulating or porous metal material, in particular a porous metal material containing or essentially consisting of a metal, in particular selected from the group consisting of: copper and aluminum, a metal alloy, an iron/ carbon alloy, a steel, a copper/zinc alloy, a brass, a nickel alloy, and any combination thereof; with all these materials being in porous form.
Electrical switching device according to any of the preceding claims, wherein the exhaust volume (40, 62) opens out into a tank volume (13) delimited by a tank wall (11), at least a portion of the inner surface of the tank wall (11) is covered with the porous layer (72, 72') ; and/ or the electrical switching device further comprises a self-blast volume (17) for building up pressure of the switching medium, at least a portion of the inner wall of said self-blast volume being covered with the porous layer.
Electrical switching device according to any of the preceding claims, wherein the porous layer (72') contains or essentially consists of a ceramic porous material containing or consisting of alumina ceramic in porous form, in particular porous alumina ceramic having a porosity of at least 45%, preferably at least 65%, more preferably at least 85%, and most preferably at least 95%.
Electrical switching device according to any one of the preceding claims, wherein the porous layer (72, 72') has a thickness of more than 2 mm, preferably more than 3 mm, and most preferably more than 4 mm; and/ or the porous layer (72, 72') has a thickness of less than 40 mm, preferably less than 20 mm, more preferably less than 10 mm, and specifically of about 5 mm.
Electrical switching device according to any one of the preceding claims, wherein the switching medium is a switching gas; and/or the switching medium comprises or essentially consists of an organofluorine compound; in particular selected from the group consisting of: fluoroethers, in particular hydrofluoromonoethers, fluoroketones, in particular perfluoroketones, fluoroolefins, in particular hydrofluoroolefins, and fluoronitriles, in particular perfluoronitriles, and mixtures thereof.
Electrical switching device according to any one of the preceding claims, wherein the switching medium comprises or essentially consists of a fluoroketone containing from four to twelve carbon atoms, preferably containing exactly five carbon atoms or exactly six carbon atoms or mixtures thereof; and/or the switching medium comprises sulphur hexafluoride (SF6 ), air and/or at least one air component, in particular selected from the group consisting of: oxygen (02), ni trogen (N2), carbon dioxide (C02), and mixtures thereof.
Electrical switching device according to any one of the preceding claims, wherein the switching medium comprises a mixture of carbon dioxide and oxygen; in particular wherein the ratio of the amount of carbon dioxide to the amount of oxygen ranges from 50:50 to 100:1, preferably 25 from 80:20 to 95:5, more preferably from 85:15 to 92:8, even more preferably from 87:13 to less than 90:10, and in particular is about 89:11.
Process for cooling a switching medium in an electrical switching device of any one of the preceding claims, specifically a circuit breaker or a generator circuit breaker, wherein the switching medium after being heated by an arc (20) generated during a current breaking operation in an arcing region (22) flows out of the arcing region (22) in direction to an exhaust volume (40, 62)' wherein during flowing out, the switching medium transfers heat to a porous layer (72, 72') applied on a metal component of the switching device, wherein the porous layer (72, 72') has a characteristic property selected from the group consisting of: a porosity of at least 45%, a pore density ranging from 15 ppi to 70 ppi, a mean pore diameter in the range from 0.7 mm to 2.0 mm; a thickness of more than 1 mm; a thickness of less than 50 mm; and combinations thereof; in particular heat is transferred to the porous layer (72, 72') at least partially by heat radiation.