FIELD OF THE INVENTION

[0001] The invention relates to an arc-quenching device of electrical switching apparatus and, more particularly, to the improvement of the existing arc-quenching device of SF6 insulated switch. The invention can be further applied to electrical switching apparatus or switchgear with such an arc-quenching device with different interruption medium, e.g. different gases and oils at different voltage levels.

BACKGROUND OF THE INVENTION [0002] SF6 insulated medium voltage secondary switch is a kind of electric apparatus which breaks current in a closed enclosure. The arc-quenching device of this switch is usually with simple structure, because of the small size and low rated current. While the breaking capacity, especially transfer current has been a bottle neck for the switches and switchgears so far.

[0003] As shown in figure 1 , the arc chute assembly is widely used currently. Arc chute consists of several pieces of metal plates 12, which are fixed on the support frame 11 in parallel with defined intervals. As shown in figure 2, the metal plate 12, made of ferromagnetic material, is a flat plate with a cutting at the low position which is for the moveable contact 14 to pass though. The remaining parts at the low position on the metal plate 12 are symmetrical. There is a horizontal groove above the cutting, and also a small cutting with two spurs for fixing on support frame 11 at the upper position of metal plate 12. As shown in figure 3, upon initial separation of the moveable contact rotating away from the fixed contact 13, the electric arc is ignited between the contacts. As the moveable contact 14 move through or past the arc chute, the electric arc will be attracted into the metal plates 12 due to the electromagnetic force, as shown in figure 4, and then separated and cooled by the plates of arc chute, which facilities the arc extinguished after the current passes through zero. Arc chute assemblies are widely used because of the simple structure, easy production and low cost. But the switch with the existing arc chute assembly has a limited breaking capacity, for example, at 12kV the transfer current is about from 1400A to 1750A. The main reason for the failure of breaking transfer current is the arc chute cannot keep the electric arc within the arc chute. If the arc stays in the arc chute, after current zero, multiple gaps of recovery of cathode voltage drop will assist the interruption of the current. If the arc escape from the arc chute, this recovery will not exist and also the electric arc will escape from the metal plates 12 of arc chute to cause short-circuit fault of phase to earth or between phases.

[0004] Not only in SF6 medium voltage switches, arc chute assemblies are also used in other kind of gas-insulated, air-insulated and other kind of interruption medium e.g. oil, electric switching apparatus as well as some low and high-voltage switches. But the working principle and structure of those arc chute assemblies are the same or similar.

[0005] Therefore, there is a need for improving the breaking capacity of switch without adding cost. SUMMARY OF THE INVENTION

[0006] To improve the breaking capacity of switches, the present invention provides an arc-quenching device of electrical switching apparatus, and is implemented for the SF6 switch with such an arc-quenching device.

[0007] According to one aspect of the invention, an arc-quenching device of switch is provided. It comprises multiple metal plates which are fixed on a supporting frame. Each of the metal plate comprises at least one groove and the groove is U-shaped or L-shaped. The function of the groove is as follows: the groove will be deep enough, after placing all the plates parallel together, there should be some overlapping or at the same level of the groove in the deep area to the normal flat area in such a way that the arc plasma will not be able to go out of the chute into the surroundings. In another word, the arc chute is not "transparent" for the arc plasma to go out directly. As a result the arc chute will keep the arc between the plates for longer time.

[0008] According to a preferred embodiment of the present invention, the metal plate of the arc-quenching device comprises at least one U-shaped groove or at least one L-shaped groove.

[0009] According to a preferred embodiment of the present invention, the metal plate of the arc-quenching device comprises at least one U-shaped groove and at least one L-shaped groove. The metal plate of the arc-quenching device may comprise two or more U-shaped grooves and/or two or more L-shaped groove.

[0010] According to a preferred embodiment of the present invention, the profile of the U-shaped groove and the L-shaped groove is semicircle or arc.

[0011] According to a preferred embodiment of the present invention, the profile of the

U-shaped groove and the L-shaped groove can be made with different shapes as shown in figure 10A-D.

[0012] According to the preferred embodiment, the depth of the groove is equal to or bigger than the interval between two metal plates in the arc-quenching device.

[0013] According to a preferred embodiment, the metal plates are fixed in parallel and are made of ferromagnetic material e.g. carbon steel.

[0014] According to a preferred embodiment, the horizontal position of the vertical part of the L-shaped groove depends on the direction of the horizontal component of the electromagnetic force on the electric arc.

[0015] According to a preferred embodiment, the arc-quenching device further comprises an insulation plate between each two near phases of the switch.

[0016] According to a preferred embodiment, the material of the insulation plate is polycarbonate.

[0017] According to another aspect of the present invention, a SF6 switch or switchgear is provided. The SF6 switch or switchgear comprises an arc-quenching device of anyone of above.

[0018] The SF6 switch or switchgear with the arc-quenching device of the present invention is able to break higher current. It can pass the transfer current test of more than 2200A successfully at 12kV.

[0019] According to a preferred embodiment, any other kind of interruption medium can be used, e.g. air, N2 and oils.

[0020] The arc-quenching device could be also used for low, medium and high voltage applications. All possible constructions of chute with some kind of groove construction which could make the arc chute not " transparent" for the arc to move out of the arc chute into the surroundings in all directions except the area facing the moving contact. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The embodiments of the invention that are presented in the sense of examples and their advantages are explained in greater detail below with reference to the accompanying drawings, in which:

[0022] Figure 1A and 1 B show a prior art arc chute assembly, wherein, figure 1A is the 3D perspective view; figure 1 B is the view of the metal plate;

[0023] Figure 2 shows the open position of the switch; The electric arc is ignited between the contacts upon initial separation of the moveable contact 14 rotating away from the fixed contact;

[0024] Figure 3 shows the electric arc being attracted into the metal plates due to the electromagnetic force;

[0025] Figure 4 shows the arc quenching device according to a preferred embodiment of the present invention;

[0026] Figure 5 shows the structure of the metal plate with U-shaped groove according to a preferred embodiment of the present invention;

[0027] Figure 6 shows the working principle of the arc quenching device.

[0028] Figure 7A and 7B show the structure of the metal plate with L-shaped groove according to the other preferred embodiments of the present invention; wherein, figure 7A and figure 7B show the vertical part of the L-shaped groove on left or right side separately;

[0029] Figure 8A, 8B and 8C show the metal plate with more than one grooves, wherein figure 8A shows the metal plate with two U-shaped grooves; figure 8B shows the metal plate with two L-shaped grooves of which vertical part in on the left; and figure 8C shows the metal plate with two L-shaped grooves of which vertical part in on the right;

[0030] Figure 9A and 9B show the metal plate with one U-shaped groove and one L-shaped groove, figure 9A and figure 9B show the vertical part of the L-shaped groove on left or right side separately;

[0031] Figure 10A, 10B, 10C and 10D show more other possible alternatives of the groove shapes.

DETAILED DESCRIPTION OF EMBODIMENTS

[0032] Hereinafter, the principle of the present invention will be described with reference to the illustrative embodiments. It should be understood, all these embodiments are given merely for the skilled in the art to better understand and further practice the present invention, but not for limiting the scope of the present invention.

[0033] To improve the breaking capacity of switches, the present invention provides an arc-quenching device of electrical switching apparatus and not only for the SF6 switch with such an arc-quenching device but also valid for other kind of interruption medium.

[0034] As shown in figure 4, the arc-quenching device of SF6 switch is also called arc chute which comprises a plurality of metal plates 22. The metal plates 22 are fixed on a supporting frame 21 in parallel. Each of the metal plate 22 comprises at least one groove, and the groove is U-shaped 221 or L-shaped 221 '.

[0035] According to a preferred embodiment, the arc-quenching device further comprises an insulation plate 25 between each two near phases of the switch. The material of said insulation plate 25 is polycarbonate.

[0036] According to a preferred embodiment, the arc-quenching device further comprises an insulation plate 25 between each two near phases of the switch. The material of said insulation plate 25 could be all possible insulation materials.

[0037] Figure 5 shows the structure of the metal plate with U-shaped groove according to a preferred embodiment of the present invention. According to the preferred embodiments, the profile 2211 of the groove is semicircle shape or other shapes. The depth or the height 2210 of the groove is equal to or more than the interval between two metal plates 22 in the arc chute. The number of grooves can be two or more. The grooves 22, 221 ' can be one single type or the combination of U-shape and L-shape. Figure 7A and 7B show the structure of the metal plate 22 with L-shaped groove according to the other preferred embodiments of the present invention; wherein, figure 7A and figure 7B show the vertical part of the L groove on left or right side separately. Figure 8A, 8B and 8C show the metal plate with more than one groove. The grooves can be the combination of U-shape one and L-shape one, such as shown in figure 9A and 9B. [0038] The working principle of the invention is illustrated with reference to figure 6. When the moveable contacts 24 going through or passing the arc chute assemblies, the ignited electric arc 27 is attracted by the metal plates 22. The electric arc 27 is a schematic diagram in figure 6. It is not a component of the device, but a highly ionized arc plasma. The currents flowing through the busbars 26 installed above the fixed contacts 23 and the other two phases of switchgear will also create the magnetic field and have the electromagnetic forces on the electric arc. Therefore, the generated electromagnetic force F on the electric arc is not vertical or upward. It has a horizontal component of force F1 . The magnitude and direction of generated electromagnetic force F can be got by simulation. There is only a horizontal groove in prior-art which can prevent the electric arc escaping upwards on the metal plate 22 only, so the electric arc can escape from the lateral side of the metal plate 22 easily. Based on the above analysis, the metal plate 22 with a U-shape groove 221 , as shown in figure 4 and figure 5, can solve the problem that the arc move out laterally driven by the electromagnetic force. In order to improve the performance of the arc chute, an extra flat area on the lateral side near the U-shape groove is also added to the chute where the electric arc intends to escape from. This will have an extra effect for delay the arc to escape and also provides better cooling for the arc moves to this area. The metal plate of the prior art arc-quenching device is symmetric in this area of cutting at the lower position without groove instead.

[0039] If the distribution of currents inside switchgear is known, the direction of electromagnetic force of electric arc can be determinate. Then the metal plate 22 with an L-shape groove 221 ' can prevent the electric arc escaping from arc chute. If the direction of horizontal component of electromagnetic force on electric arc is right, the vertical part of L-shaped groove is on right, as shown in figure 7A. If the direction of horizontal component is left, then the vertical part of L-shaped groove is on left, as shown in figure 7B. That means the horizontal or the left/right position of the vertical part of the L-shaped groove 221 ' depends on the direction of the horizontal component of the electromagnetic force on the electric arc.

[0040] As shown in figure 8A, 8B and 8C, if the number of grooves is increased, the ability of prevent the electric arc escaping from arc chute will be improved. This purpose can be achieved by adding number of single type grooves in the metal plates, such as two U-shape grooves 221 in figure 8A, or two L-shape grooves 221 ' in figure 8B and 8C, and also can be achieved by combining these two types grooves together as shown in figure 9A and 9B.

[0041] Figure 10A, 10B, 10C and 10D show more other possible alternatives of the groove shapes. The profile of the groove can be "V" shaped or convert "V" shaped or their combination or combination of lines and arcs.

[0042] The SF6 switch or switchgear with an arc-quenching device of the present invention can pass 2200A transfer current test successfully at 12kV which is still not the limit.

[0043] Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no means limit the scope of the present invention. There are many variations and modifications to the embodiments. For example, each of the metal plate may comprise three or more grooves. And the insulation plate may be made of other materials besides polycarbonate. The main functionality is that the structure of the arc chute is made in such a way that the arc plasma is not "transparent" to outside or in another word difficulty to move to outside. In this way the multiple gap recovery will works properly. As a result the interruption current will be increased and also the electric lifetime for the switchgear will also improved.

[0044] Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.