Current transformer for a gas insulated switchgear

Abstract: A gas insulated switching device including a series of pressure containers 1 and 4 mutually connected, in which a conductor 2 is positioned in an inside center, and an insulating and arc-extinguishing gas is filled in a space around the conductor 2, and a current transformer fabricated by Rogowskii coils for detecting a current passing through the conductor 2, the current transformer is attached to flanges of the pressure containers 1 and 4 via a metallic adaptor 5, wherein the current transformer is accommodated in a groove formed toward an inside of the metallic adaptor 5 and uses the metallic adaptor 5 to obtain an earth potential, whereby the gas insulated switching device having the current transformer with high accuracy can be miniaturized.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a gas insulated switching device transforming an electrical energy in a power system, particularly to installation of a current transformer. DISCUSSION OF BACKGROUND A gas insulated switching device, used in a field of generating and transforming an electric power in a power system, is constructed by a switching device, a conductor, a current transformer, a surging arrester, and so on, which are accommodated in a metallic pressure container, filled with an arc-extinguishing gas such as a sulfur hexafluoride (hereinbelow referred to as SF 6 gas) having excellent insulating capability and excellent arc-extinguishing capability. The switching device, the conductor, the current transformer, the surging arrester, and so on are mutually connected, whereby the gas insulated switching device has been small-sized. A similar installation is described in US-A-5,939,876. However, further improvement in economy is required by reducing a space occupied by the gas insulated switching device by virtue of miniaturization and improvement in reliability of component obtained as a result of a recent technology development. Figure 7 is a cross-sectional view illustrating a conventional current transformer. In Figure 7, numerical references 1, 4 designate a pressure container, in which a conductor 2 is accommodated in a center thereof and which is SF 6 gas filled. Numerical reference 3 designates an insulating spacer for supporting the conductor 2 and separating the gas in the pressure container 1 from the gas in the other pressure container 4, connected to the pressure container 1. Numerical reference 6 designates a current transformer holder attached to flanges of the pressure containers 1 and 4 via the insulating spacer 3, the current transformer holder includes a cylindrical portion having grooves like a ring and an attaching flange corresponding to the flanges of the pressure containers 1 and 4. Numerical reference 7 designates a plurality of Rogowskii coils, positioned in the groove like the ring in the current transformer holder 6 via a spacer 8 in an axial direction of the pressure container 1. Numerical reference 9 designates a fixing plate for fixing the Rogowskii coils 7 inside the groove. A current transforming portion is constructed by the current transformer holder 6, the Rogowskii coils 7, the spacer 8, and the fixing plate 9 for detecting a current applied to the conductor 2. The Rogowskii coils 7 is formed by uniformly winding a coil around a high molecular member, being flexible and having a circular cross sectional view or the like by many turns, wherein the Rogowskii coils work as a current sensor, from which a current signal is obtainable in proportion to a current value flowing inside the Rogowskii coils 7. However, since the Rogowskii coils 7 forming the current transformer are flexible, hollow portions of the Rogowskii coils are deformed by a pressure applied to surfaces of the Rogowskii coils when attaching these to the current transformer holder 6, whereby the accuracy of detecting a current is deteriorated. Further, since the Rogowskii coils 7 are attached to the current transformer holder 6 having protrusions in the axial directions of the pressure container 1, for example, in case that a breaker container containing a breaker and so on are connected, the protrusion of the current transformer holder 6 insufficiently protrudes inside the breaker container, whereby the length of the pressure container 1 should be increased, and a miniaturization of an entirety of the switching device is difficult. Further, although it is necessary to sufficiently keep an insulating distance between the Rogowskii coils and the conductor 2, the current transformer holder 6 also protrudes in a radial direction of the pressure container 1, whereby the diameter of the pressure container is increased, miniaturization of the entire switching device is difficult. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems inherent in the conventional technique and to provide a gas insulated switching device, in which a highly accurate current transformer is equipped for miniaturizing the gas insulated switching device. According to a first aspect of the present invention, there is provided a gas insulated switching device comprising: a series of mutually connected pressure containers within the center of which a conductor is positioned and within which an insulating and arc-extinguishing gas fills a space around the conductor; and a current transformer fabricated by Rogowskii coils for detecting a current passing through the conductor and being accommodated in a groove formed within the body of an annular adaptor attached to the pressure containers; characterised in that the annular adaptor is metallic and located between flanges of the pressure containers, and the current transformer is attached to the pressure containers via the annular metallic adaptor and uses the metallic adaptor to obtain an earth potential, the groove being open to the space purged with the insulating and arc-extinguishing gas. Preferably, the Rogowskii coils of the current transformer are formed by uniformly winding a coil with a plurality of turns around an inflexible insulating member. Preferably also, the metallic adaptor is attached to one of the pressure containers via an insulating spacer that separates the gas in the series of containers, and the metallic adaptor defines a rounded portion in an inner peripheral surface on a side in contact with the insulating spacer to relax an electric field in a triple junction, formed by the insulating and arc-extinguishing gas filled in the pressure containers, the insulating spacer, and the metallic adaptor. Preferably also, a flange of one of the pressure containers is the metallic adaptor. Preferably also, a current detector for measuring the current detected by the current transformer is located on an outer periphery of the metallic adaptor. Preferably also, a breaker is located inside a breaker container, which is closely joined to the series of pressure containers; a second current transformer is fabricated by Rogowskii coils for detecting the current passing through a second conductor connected to the breaker by attaching a second annular metallic adaptor located in an outer periphery of the conductor to a breaker container; and the second current transformer is accommodated in a groove formed within the body of the second metallic adaptor and uses the second metallic adaptor to obtain an earth potential. Preferably also, a plurality of Rogowskii coils of the same dimensions is concentrically arranged in the metallic adaptor in an axial direction with respect to the pressure containers. Preferably also, a plurality of the Rogowskii coils of the same dimensions in an axial direction with respect to a cross section of the coils and of different dimensions in a radial direction with respect to the coils are concentrically arranged in a radial direction with respect to the pressure containers. Preferably also, the Rogowskii coils are monolithically molded by a flexible resin inside the metallic adaptor. BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Figure 1a is a cross-sectional view of a current transformer of a gas insulated switching device according to Embodiment 1 of the present invention; Figure 1b is an enlarged view illustrating the current transformer of the gas insulated switching device according to Embodiment 1 of the present invention; Figure 2 is a cross-sectional view illustrating a current transformer of a gas insulated switching device according to Embodiment 2 of the present invention; Figure 3 is a cross-sectional view of a current transformer of a gas insulated switching device according to Embodiment 3 of the present invention; Figure 4 is a cross-sectional view illustrating a current transformer of a gas insulated switching device according to Embodiment 4 of the present invention; Figure 5 is a cross-sectional view illustrating a current transformer of a gas insulated switching device according to Embodiment 5 of the present invention; Figure 6a is a cross-sectional view of a breaker container of a gas insulated switching device according to Embodiment 6 of the present invention; Figure 6b is an enlarged view of the breaker container of the gas insulated switching device according to Embodiment 6 of the present invention; and Figure 7 is a cross-sectional view illustrating a current transformer of a conventional gas insulated switching device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A detailed explanation will be given of preferred embodiments of the present invention in reference to Figures 1 through 6b as follows, wherein the same numerical references are used for the same or similar portions and description of these portions is omitted. EMBODIMENT 1 Figure 1a is a cross-sectional view illustrating a current transformer of a gas insulated switching device according to Embodiment 1 of the present invention. Figure 1b is an enlarged view of the current transformer. In Figures 1a and 1b, numerical references 1 and 4 designate pressure containers filled with a SF 6 gas, wherein a conductor 2 is accommodated in a center of the pressure containers. Numerical reference 3 designates an insulating spacer for supporting the conductor 2 and separating the gas in the pressure container 1 and the other pressure container 4 connected thereto. Numerical reference 5 designates an annular metallic adaptor attached to flanges of the pressure containers 1 and 4 via the insulating spacer 3. Numerical reference 7 designates a plurality of Rogowskii coils arranged in a groove formed in the metallic adaptor 5. Numerical reference 10 designates a current detector measuring a current detected by the current transformer including the Rogowskii coils. Numerical reference 11 designates a lead wire for connecting the Rogowskii coils 7 with the current detector 10. Numerical reference 12 designates a resin having flexibility, by which the metallic adaptor 5 and the Rogowskii coils 7 are monolithically molded. The current transformer is fabricated by the metallic adaptor 5, the Rogowskii coils 7, the current detector 10, and the lead wire 11 for detecting a current passing through the conductor 2. Differences between Embodiment 1 and the conventional technique are as follows. First, a current transformer holder in the conventional technique is changed to the metallic adaptor 5. The metallic adaptor 5 according to Embodiment 1 has the groove inside a body of the metallic adaptor 5. The Rogowskii coils 7 are accommodated in the groove, wherein a plurality of the Rogowskii coils 7 having same diameters are arranged side by side in an axial direction of the pressure container 1 around same axis centers, wherein two Rogowskii coils are exemplified in Figures 1a and 1b. The metallic adaptor 5 is attached to the flanges of the pressure containers 1 and 4 in a similar manner to that in the conventional technique. The current detector 10 is attached to an outer periphery of the metallic adaptor 5, which is connected to the Rogowskii coils 7 through a lead wire 11. Further, a rounded portion is formed in an inner diameter of the metallic adaptor 5 on a side in contact with the insulating spacer 3. The rounded portion is to relax an electric field in a triple junction among the insulating and arc-extinguishing gas filled in the pressure containers 1 and 4, the insulating spacer 3, and the metallic adaptor 5. Second, although in a conventional technique the coil having many turns is uniformly wound around an insulating member having flexibility, an inflexible insulating member is used for the Rogowskii coils 7 in Embodiment 1. A suitable material for the insulating member of the Rogowskii coils 7 is an epoxy laminating resin with a glass fabric base, a phenol laminating resin with a paper base, FRP and so on. On the other hand, the Rogowskii coils are monolithically molded by the resin 12 having flexibility inside the groove of the metallic adaptor 5. By monolithically molding the Rogowskii coils, it is possible to obtain the current transformer, which can be easily operated and simply installed, at a low cost. A method of monolithically molding the Rogowskii coils 7 is injection of a silicon system resin, an epoxy system resin, a butyl system resin, and so on respectively having excellent anti-arced gas property. Further, it is possible to apply a conventional method of producing the Rogowskii coils such that a resin is impregnated after winding an insulating tape. As described, according to Embodiment 1, since the Rogowskii coils 7 are arranged in the groove of the metallic adaptor 5 without protruding portions, it is possible to prevent sizes in the axial and radial directions of the pressure container 1 from increasing, and an entire size of the switching device can be miniaturized. Further, since the Rogowskii coils 7 is obtained by winding the coil around the insulating member without flexibility, it is possible to suppress deformation of hollow portions of the Rogowskii coils 7, and the current can be detected with high accuracy. EMBODIMENT 2 Figure 2 is a cross-sectional view illustrating a current transformer of a gas insulated switching device according to Embodiment 2 of the present invention. A difference from Embodiment 1 is that a flange of a pressure container 1 overlaps a groove accommodating the Rogowskii coil because the pressure container 1 and a pressure container 4 have same diameters. Therefore, a cut-out 15 is formed in the flange of the pressure container 1 so as not to clog an opening portion of the groove. Accordingly, it is possible to obtain an effect of matching the diameter of the pressure container 1 with the diameter of the pressure container 4 and making the diameters of the pressure containers 1 and 4 small. Embodiment 3 Figure 3 is a cross-sectional view illustrating a current transformer of a gas insulated switching device according to Embodiment 3 of the present invention. In Embodiment 3, an opening portion of a groove in a metallic adaptor 5 is formed to face a side of an insulating spacer 3. Therefore, as in Embodiment 2, it is unnecessary to form a cut-out in a flange of a pressure container, and processing of the flange of the pressure container 1 is simplified, whereby an effect of producing at a low cost is obtainable. EMBODIMENT 4 Figure 4 is a cross-sectional view illustrating a current transformer of a gas insulated switching device according to Embodiment 4. In embodiment 4, flanges of a pressure container 1 and a metallic adaptor 5 are identical. Therefore, it is unnecessary to use the metallic adaptor 5, a dimension of the pressure container 1 in its axial direction is reduced, and a body of the switching device is miniaturized. EMBODIMENT 5 Figure 5 is a cross-sectional view illustrating a current transformer of a gas insulated switching device according to Embodiment 5 of the present invention. In Embodiment 5, two Rogowskii coils 7 having same dimensions in an axial direction of a pressure container 1 and different dimensions in radial directions are concentrically arranged in a groove of a metallic adaptor 5. Therefore, the width of the metallic adaptor 5 in the axial direction is shortened to make a dimension of an entirety of the gas insulated switching device in its axial direction short, whereby the device is miniaturized. Further, in Embodiment 5, a case that the Rogowskii coils having the same dimensions in the axial direction of the pressure container 1 and different dimensions in the radial direction are concentrically arranged in the groove of the metallic adaptor 5, such a structure can be respectively applied to the above-mentioned embodiments. EMBODIMENT 6 In Embodiment 6, a case that a structure of locating a current transformer in a connecting portion of pressure containers in the above-mentioned embodiments to an inside of a breaker container. Figure 6a is a cross-sectional view illustrating a breaker container of a gas insulated switching device according to Embodiment 6 of the present invention. Figure 6b is an enlarged view illustrating a current transformer located inside the breaker container. In Figures 6a and 6b, numerical reference 13 designates the breaker container; numerical reference 14 designates the breaker; and numerical reference 15 designates an inner conductor connected to the breaker 14. As illustrated in Figure 6a and 6b, an annular metallic adaptor having a groove is arranged in an outer periphery of the internal conductor 15 around an axis center thereof. In the groove of the metallic adaptor 5, two Rogowskii coils 7 having same diameters are arranged side by side in an axial direction of the metallic adaptor. Although a structure around the metallic adaptor 5 inside the breaker container is similar to that illustrated in Figure 1, structures respectively described in the above-mentioned embodiments can be applied to Embodiment 6. Further, in all of the above-mentioned embodiments, two Rogowskii coils 7 are used. However, the present invention is not limited to the use of two coils 7, and three or more Rogowskii coils 7 may be used. Further, in Figures 1a through 5, an inner diameter of the metallic adaptor 5 may be the same as an inner diameter of the pressure container 1 or less. Further, the gas insulated switching device may be a three-phase-bus and single-phase breaker type, a type that all three phases are simultaneously switched, and an isolated phase type. The breaker illustrated in Figure 6 is a vertically arranged type. However, the breaker may be a horizontally arranged type. Also, in all of the embodiments, the coils 7 forming the current transformer uses the metallic adaptor 5 to obtain an earth potential. The first advantage of the gas insulated switching device according to the present invention is that the dimensions of the pressure containers in the axial and radial directions are not increased, and an entire size of the switching device is miniaturized. The second advantage of the gas insulated switching device according to the present invention is that the hollow portion of the Rogowskii coils can be prevented from deforming, and a current can be detected with high accuracy. The third advantage of the gas insulated switching device according to the present invention is that an electric field around the triple junction can be relaxed. The fourth advantage of the gas insulated switching device according to the present invention is that an influence of a surge noise is suppressed, and it is possible to measure with high accuracy and high reliability. The fifth advantage of the gas insulated switching device according to the present invention is that the dimension of the pressure containers in the axial direction can be shortened, the dimension of the entire gas insulated switching device can be shortened, and therefore the gas insulated switching device is miniaturized. The sixth advantage of the gas insulated switching device according to the present invention is that the structure of attaching the Rogowskii coils to the metallic adaptor is simplified, and the Rogowskii coils can be produced at a low cost. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims: A gas insulated switching device comprising: a series of mutually connected pressure containers (1,4) within the center of which a conductor (2) is positioned and within which an insulating and arc-extinguishing gas fills a space around the conductor; and a current transformer fabricated by Rogowskii coils (7) for detecting a current passing through the conductor (2) and being accommodated in a groove formed within the body of an annular adaptor attached to the pressure containers (1,4); characterised in that the annular adaptor (5) is metallic and located between flanges of the pressure containers (1, 4), and the current transformer is attached to the pressure containers (1, 4) via the annular metallic adaptor (5) and uses the metallic adaptor (5) to obtain an earth potential, the groove being open to the space purged with the insulating and arc-extinguishing gas. The gas insulated switching device according to Claim 1, characterised in that the Rogowskii coils (7) of the current transformer are formed by uniformly winding a coil with a plurality of turns around an inflexible insulating member. The gas insulated switching device according to Claim 1 or Claim 2, characterised in that the metallic adaptor (5) is attached to one of the pressure containers (1, 4) via an insulating spacer (3) that separates the gas in the series of containers (1, 4), and in that the metallic adaptor defines a rounded portion in an inner peripheral surface on a side in contact with the insulating spacer (3) to relax an electric field in a triple junction, formed by the insulating and arc-extinguishing gas filled in the pressure containers (1, 4), the insulating spacer (3), and the metallic adaptor (5). The gas insulated switching device according to Claim 1 or 2, characterised in that a flange of one of the pressure containers (1,4) is the metallic adaptor (5). The gas insulated switching device according to Claim 1 or 2, characterised in that a current detector (10) for measuring the current detected by the current transformer is located on an outer periphery of the metallic adaptor (5). The gas insulated switching device according to Claim 1 or 2, characterised in that a breaker (14) is located inside a breaker container (13), which is closely joined to the series of pressure containers (1,4); in that a second current transformer is fabricated by Rogowskii coils (7) for detecting the current passing through a second conductor (15) connected to the breaker (14) by attaching a second annular metallic adaptor (5) located in an outer periphery of the conductor (15) to a breaker container (13); and in that the second current transformer is accommodated in a groove formed within the body of the second metallic adaptor (5) and uses the second metallic adaptor (5) to obtain an earth potential. The gas insulated switching device according to Claim 1 or 2, characterised in that a plurality of Rogowskii coils (7) of the same dimensions is concentrically arranged in the metallic adaptor (5) in an axial direction with respect to the pressure containers (1,4). The gas insulated switching device according Claim 1 or 2, characterised in that a plurality of the Rogowskii coils (7) of the same dimensions in an axial direction with respect to a cross section of the coils and of different dimensions in a radial direction with respect to the coils is concentrically arranged in a radial direction with respect to the pressure containers (1, 4). The gas insulated switching device according to Claim 1 or 2, characterised in that the Rogowskii coils (7) are monolithically molded by a flexible resin (12) inside the metallic adaptor (5). The gas insulated switching device according to claims 1 or 2, characterised in that an opening of the groove of the metallic adapter (5) faces to a side of the insulating spacer (3).

Inventors: AOKI HIROHIDE, HAMA HIROYUKI, MAEDA YASUHIRO, MATSUMOTO MITSUO, AOKI, HIROHIDE, HAMA, HIROYUKI, MAEDA, YASUHIRO, MATSUMOTO, MITSUO
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 2000
Main classification: H02B13
IPC codes: H02B13, H02G5