High-voltage circuit breaker

Abstract: High-voltage circuit breaker comprising an elongated casing filled with a gaseous arc-extinguishing medium, said casing comprising two cooperating arcing contacts and two cooperating main contacts (10), which during an opening operation separate earlier than the arcing contacts. According to the invention one of the main contacts (10) consists of one end portion of a metal tube (12) which is secured to the casing. This end portion is formed by pressing (bulging) and slotted in such a way as to form a plurality of contact fingers (14) integral with the tube. The contact fingers may be surrounded by a tubular metal sleeve (15) serving as a field-equalizing shield. This sleeve may also serve as a holder and counter-support for one or more auxiliary springs (17) arranged between the sleeve and the contact fingers. By allowing the free end portion of the sleeve (15) to surround the end portions of the contact fingers, the contact fingers are furthermore prevented from being bent too far inwards.

Description: TECHNICAL FIELD The present invention relates to a high-voltage circuit breaker according to the precharacterising part of claim 1. The invention is primarily intended for circuit breakers with rated operating voltages of the order of magnitude of 100-300 kV, but it may be used to advantage also in circuit breakers for voltages both above and below this range, for example in medium voltage circuit breakers. BACKGROUND ART Circuit breakers of the above-mentioned kind are previously known, for example from EP-A-0 475 270. Such circuit breakers must be capable of carrying very high operating currents, for example 4000 A, and it is therefore important for the resistance across each breaker pole to be as low as possible. In circuit breakers of this kind, the stationary main contact of the circuit breaker is usually arranged at the free end portion of a hollow-cylindrical current path section which is fixed in the circuit breaker casing and which, for example, may consist of a copper tube. A known design of such a main contact consists of a plurality of separate contact pieces which together with associated contact springs are movably mounted around the end portion of the current path section. In such a design, there are two series-connected current transition points at each contact piece, which entails a relatively high total contact resistance. Another drawback in this design is that the mounting of the plurality of contact pieces is time-demanding and hence costly. From DE-B-1 913 969, a circuit breaker of the above-mentioned kind is previously known, in which the stationary main contact consists of a plurality of contact fingers which are formed by slotting of one end portion of a hollow-cylindrical metal body. At each such contact finger, only one current transition point is obtained between the fixed and the movable current path section. However, it is not clear from the described designs how to obtain the necessary contact pressure or how to avoid local field concentrations at the free end surface of the metal body. In addition, in view of the design of the metal body and the thickness of the material thereof, it cannot in a simple manner be formed by pressing (bulging) but must be machined by metal-cutting tools, which is expensive. Also US-A-3 839 613 shows a circuit breaker of the above-mentioned kind, which is provided with a tubular stationary main contact with contact fingers formed by slotting. Also in case of this contact, in view of its design and the material thickness thereof, it cannot be formed in a simple manner by pressing (bulging). In addition, it is provided, at the free end portion of the contact, with a field-equalizing shield which projects in the radial direction and thus causes a considerable increase of the diameter of the stationary contact assembly. In addition, in this design there may also be a risk that one or more of the contact fingers are bent too far inwards, by mechanical or electromagnetic influence, thus causing operational disturbances. SUMMARY OF THE INVENTION The main object of the present invention is to provide a circuit breaker of the above-mentioned kind which does not suffer from the above-mentioned disadvantages of comparable prior art breakers. To achieve this object the invention suggests a high-voltage circuit breaker according to the introductory part of claim 1, which is characterized by the features of the characterizing part of claim 1 or claim 2. Further developments of the invention are characterized by the features of the additional claims. By pressure forming (bulging) and slotting of the end portion of the metal tube, a main contact according to the invention is provided which consists of a large number of contact fingers which are integral with the tube. With this embodiment, a larger number of parallel transition points is obtained than in the known contact arrangement with separately mounted contact pieces described above, since a tube with a given circumference may accommodate a larger number of the contact fingers integrated in the tube, since these contact fingers require less space in the lateral direction than separate contact pieces. This contributes to reduce the contact resistance. BRIEF DESCRIPTION OF THE DRAWINGS By way of example, the invention will now be described in greater detail with reference to the accompanying drawings showing in Figure 1 in an axial section the central part of a prior art high-voltage circuit breaker, in which the invention may be used, Figure 2 in an axial section a first embodiment of a section of a current path, designed according to the invention, with the stationary main contact for a circuit breaker of, for example, the type shown in Figure 1, Figures 3a and 3b separately the central part of the current path section in axial section and an end view, respectively, Figures 4a and 4b in plane view and in side view, respectively, a first embodiment of an auxiliary spring intended for the main contact according to Figure 2, Figure 5 in perspective view a second embodiment of an auxiliary spring intended for the main contact according to Figure 2, Figure 6 in an axial section a second embodiment of a current path section with the stationary main contact for a circuit breaker according to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit breaker shown in Figure 1 has been described in the above-mentioned patent specification EP-A-0 475 270 and is only an example of the type of circuit breaker in which the present invention may advantageously be used. The circuit breaker has a gas-tight casing 1 which comprises a stationary plug-shaped arcing contact 2 and an axially movable sleeve-shaped arcing contact 3. The movable contact 3 is connected to an operating device via a tubular contact rod 4 and an insulating operating rod (the latter not shown). With the aid of the operating device, the movable contact may be displaced between the closed position shown on the lefthand side in the figure and the open position shown on the righthand side in the figure. The movable contact 3 supports a hollow metal cylinder 5 which encloses a pressure-collecting space 6, the volume of which is constant, a compression space 7, and an electrically insulating blast nozzle 8 with an annular channel 9, which connects the pressure-collecting space 6 to the region where the arc is burning during an opening operation. The hollow cylinder 5 constitutes the movable main contact of the circuit breaker, which contact cooperates with a stationary main contact 10. The stationary contacts 2 and 10 of the circuit breaker are electrically and mechanically fixedly connected with each other, as are also the movable contacts 3 and 5. During a breaking operation, the contact rod 4 is pulled downward with the aid of the operating device, whereby the main contacts 5 and 10 are first separated. The current thereby commutates to the arcing contacts 2, 3 which upon their separation form an arc between them. The arc heats the gas in the arc region whereby the gas pressure increases which starts a gas flow through the channel 9 into the pressure-collecting space 6. As a result of this flow, the pressure in the pressure-collecting 6 space increases. The arc current follows the power frequency sine curve, and when the current approaches the zero crossing, the pressure in the arc region starts to decrease. The contact movement has now proceeded so far that the plug contact 2 has exposed the nozzle outlet, where the pressure is now lower than in the pressure-collecting space 6. This gives rise to a gas flow from the pressure-collecting space 6 through the channel 9 and the nozzle 8 to the surrounding expansion space 11. The arc is cooled by this flow and is extinguished during the zero-crossing of the current. Figure 2 shows an upper current path section 12, designed according to the invention, with the stationary main contact 10 for a circuit breaker of, for example, the design shown in Figure 1. The current path section 12 is shown separately in Figures 3a and 3b. It consists of a copper tube with a thickness of one or a few millimetres. The upper end portion of the tube consists of a flange 13, formed by pressing (bulging), for fixing the tube against the upper end flange (not shown) of the circuit breaker, which end flange at the same time constitutes one of the two connection terminals of the circuit breaker. The lower end portion of the tube is formed by pressing (bulging) and slotted such that a large number of contact fingers 14, integral with the tube, are formed. As will be clear from Figure 2, the lower end portion of the tube is surrounded by a tubular metal sleeve 15, fixed to the tube, with approximately the same diameter as the non-pressure-formed part of the copper tube 12. This sleeve has several different functions. Besides serving as a field-equalizing shield, it constitutes both holder and counter-support for spring elements 17, which are arranged between the metal sleeve 15 and the contact fingers 14. The metal sleeve 15 also prevents the contact fingers from being bent too far inwards by providing the free end portion of the sleeve with an inwardly flanged portion 16, which is made with a substantially circular contour and which surrounds the end portions of the contact fingers. The above-mentioned spring elements 17 may, for example, consist of a plurality of separate leaf springs of, for example, the embodiment shown in Figures 4a and 4b. Alternatively, these spring elements may consist of a ring 18 arranged around the contact fingers of, for example, the embodiment shown in Figure 5. This ring is formed from a resilient wire which is bent in a large number of meander-shaped loops and in such a way that the diameter of the ring decreases in an axial direction away from the mid-portion of the ring towards the ends. If the metal tube 12 with the integrated contact fingers 14 is made of a self-resilient material, for example beryllium copper, the metal sleeve 15 and the spring elements 17 may be omitted. Figure 6 shows an example of such a current path section with an integrated main contact of a self-resilient material. The invention is not limited to the embodiments shown, but several modifications are possible within the scope of the following claims.

Claims: A high-voltage circuit breaker comprising an elongated casing (1) filled with a gaseous arc-extinguishing medium, said casing comprising two cooperating arcing contacts (2, 3), one of which (2) is stationary whereas the other (3) is adapted to be displaced axially in the casing with the aid of an operating device between a closed and an open position, and two cooperating main contacts (10, 5), which during an opening operation separate earlier than the arcing contacts, one of the main contacts (10) consisting of one end portion of a first metal tube (12) which is secured to the casing and which surrounds the stationary arcing contact, whereas the other main contact (5) consists of one end portion of a second metal tube arranged around the movable arcing contact and fixed to said contact, characterized in that the end portion of said first metal tube (12) is formed by pressing, in particular by bulging and slotted to form a plurality of contact fingers (14) integral with the tube (12), said end portion being surrounded by a tubular metal sleeve (15) serving as a field-equalizing shield, the free end portion of which has an inwardly-flanged portion (16) made with a substantially circular contour and surrounding the end portions of the contact fingers (14), thus limiting the inwards bending of the contact fingers. A high-voltage circuit breaker comprising an elongated casing (1) filled with a gaseous arc-extinguishing medium, said casing comprising two cooperating arcing contacts (2, 3), one of which (2) is stationary whereas the other (3) is adapted to be displaced axially in the casing with the aid of an operating device between a closed and an open position, and two cooperating main contacts (10, 5), which during an opening operation separate earlier than the arcing contacts, one of the main contacts (10) consisting of one end portion of a first metal tube (12) which is secured to the casing and which surrounds the stationary arcing contact, whereas the other main contact (5) consists of one end portion of a second metal tube arranged around the movable arcing contact and fixed to said contact, characterized in that said first metal tube (12) is made of a self-resilient material and that said end portion thereof is formed by pressing, in particular by bulging and slotted to form a plurality of contact fingers (14) integral with the tube (12), the free end portions of said contact fingers forming an inwardly-flanged collar with a substantially U-shaped contour serving as a contact and a field-equalizing shield. A circuit breaker according to claim 1, characterized in that between the metal sleeve (15) and the contact fingers (14), spring elements (17) are arranged for reinforcing the contact pressure. A circuit breaker according to claim 1 or 3, characterized in that the metal sleeve (15) has at least approximately the same diameter as the non-pressure-formed part of said first metal tube (12). A circuit breaker according to claim 3 or 4, characterized in that said spring elements (17) consist of a plurality of separate leaf springs. A circuit breaker according to claim 3 or 4, characterized in that said spring elements (17) consist of a ring (18) arranged around the contact fingers (14), said ring being formed from a resilient wire which is bent in a large number of meander-shaped loops and in such a way that the diameter of the ring decreases in the axial direction from the mid-portion of the ring towards the ends. A circuit breaker according to any of the preceding claims, characterized in that said first metal tube (12) consists of a tube of copper or copper alloy.

Inventors: AKESSON ULF, OTTERBERG TOMAS, STENGARD PETER, AKESSON, ULF, OTTERBERG, TOMAS, STENGARD, PETER
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1995
Main classification: H01H33
IPC codes: H01H1, H01H33