Electrical apparatus

Abstract: An electrical apparatus comprising an electrical apparatus main body 1 e.g. a transformer, a tank 2 containing the electrical apparatus main body, and a plurality of bushings 3, 4 extending through the tank. The apparatus further comprises an enclosure member 11 having a good electrical conductivity and connectable to a phase-separated bus conductor outer sheath 7B surrounding each of the bushings 4 at the portion located outside of the tank and coaxially surrounding each of the bushings at the portion located inside of the tank, and an enclosure member shorting plate 12 having a good electrical conductivity and connecting the enclosure members 11 to each other.

Description: BACKGROUND OF THE INVENTION This invention relates to an electrical apparatus such as a high-power electrical transformer. Fig. 1 is a sectional view illustrating a conventional three-phase transformer as an example of an electrical apparatus used in a power plant or the like, in which 1 is a transformer main body which comprises an iron core 101 and a winding 102. 2 is a tank for containing the transformer main body 1 therein and is filled with an electrically insulating oil. Fig. 2 is a front view of the upper portion of the tank 2, which is a view of the transformer shown in Fig. 1 as viewed from the right in the figure. 201 and 202 are high-voltage bushing mounting seats and low-voltage bushing mounting seats formed on the tank 2, respectively, and 3 are high-voltage bushings mounted to the high-voltage bushing mounting seats 201 and is connected to a high-voltage side of the winding 102. 203 are bus conductor outer sheath mounting flanges formed in the low-voltage mounting seats 202, 204 are low-voltage bushing mounting flanges formed in the bus conductor outer sheath mounting flanges 203, and 4 are low-voltage bushings mounted to low-voltage bushing mounting flanges 204 and are connected to the low-voltage side of the winding 102, the detail of which is shown in Fig. 3. In the figure, 401 is an insulator tube, 402 is a circular rod-shaped central conductor inserted into the insulator tube 401, 403 and 404 are an upper terminal and a lower terminal disposed at the opposite ends of the central conductor 402, 405 is a mounting unit disposed about the outer circumference of the central portion of the insulator tube 401 and secured thereto by cement 406. By attaching this to the low-voltage bushing mounting flange 204 by bolts 5A, the low-voltage bushing 4 is mounted so that it extends through the tank 2. As partly shown in Fig. 2, there are three of the high-voltage and low-voltage bushings 3 and 4 and their mounting seats 201 and 202 for three phases. In Figs. 1 and 2, 6 are three-phase separated bus conductors connecting the low-voltage bushings 4 and a generator (not shown), 7A are transformer-side three-phase separated bus conductor outer sheaths surrounding the low-voltage bushings 4 at the portion located outside of the tank 2, 8A and 8B are outer sheath shorting plates in common to three phases and disposed at the opposite ends of the transformer-side three-phase separated bus conductor outer sheaths 7A, one of the shorting plates 8A being mounted to the bus conductor outer sheath mounting flanges 203. 7B are generator-side three-phase separated bus conductor outer sheaths surrounding the three-phase separated bus conductors 6, 8C is an outer sheath shorting plate in common to three phases and disposed at one ends of the generator-side three-phase separated bus conductor outer sheaths 7B, a similar outer sheath shorting plate (not shown) being provided at the other ends. 9 are expansion joints made of an electrically insulating material and disposed between the transformer-side and the generator-side three-phase separated outer sheaths 7A and 7B. The operation will now be described. An electric current which flows from the unillustrated generator through the three-phase separated bus conductors 6 and the low-voltage bushings 4 flows into the winding 102 of the transformer main body 1 and is boostered to be supplied to an external circuit. By the way, since the current from the generator is a large current, a massive magnetic flux is generated around the three-phase separated bus conductors 6, so that a stray loss is increased and the metal of the adjacent structural members (not shown) is overheated. Therefore, the so-called mini-flux structure is adapted, in which a three-phase closed circuit is formed by the three-phase separated bus conductor outer sheaths 7B on the generator-side, the outer sheath shorting plate 8C on one ends of the outer sheaths and the unillustrated outer sheath shorting plate on the other ends of the outer sheaths so that the magnetic flux crosses the closed circuit and generates a current flowing in the direction opposite to the three-phase separated bus conductors 6 thereby generating a magnetic flux which offsets the magnetic flux generated by the current flowing through the three-phase separated bus conductors 6. Similarly, the transformer-side three-phase separated bus conductor outer sheaths 7A and the shorting plates 8A and 8B form a three-phase closed circuit in the mini-flux structure. Further, the expansion joint 9 absorbs the dimentional difference between both of the three-phase separated bus conductor outer sheaths 7A and 7B, and an insulating material is selected for the joint to electrically isolate the generator side and the transformer side so that they do not electrically influence each other. Since the conventional electrical apparatus is constructed as above described and the mini-flux structure by the phase separated bus conductors and the outer sheath shorting plates is employed at the outside of the tank, the magnetic fluxes generated by the current flowing through the phase separated bus conductors are cancelled out. However, since the mini-flux structure is not adapted at the inside of the tank, a massive magnetic flux is generated by the current flowing through the bushings to increase the stray loss and overheats the adjacent structural members, the tank and the like. US-A-4 370 512 discloses an apparatus in which a necked portion of an outer sheath extends into a tank, but this arrangement is bulky. SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide an electrical apparatus free from the above problems of the conventional design. Another object of the present invention is to provide an electrical apparatus in which the stray loss is small. A further object of the present invention is to provide an electrical apparatus in which the structures around the bushing are not overheated. According to the invention there is provided an electrical apparatus comprising: an electrical device; a tank containing the electrical device; a plurality of bushings extending through the said tank; a plurality of electrically conducting outer sheaths, each surrounding a respective one of the said bushings in a region outside of the tank and a plurality of electrically conducting closure members each connected to a respective one of the outer sheaths, characterised in that each of the said closure members comprises a flange and a generally cylindrical tubular member, each said flange being situated outside of the said tank and supporting a respective one of the said outer sheaths to form a respective one of the said connections therewith, each said tubular member extending into the tank and surrounding a respective one of the said bushings within the tank; a shorting plate having good conductivity is provided within the said tank and comprises a plurality of connecting conductors which are connected to respective ones of the said tubular members. The effect of this arrangement is to cause a mini-flux structure to extend from the outside to the inside of the tank, whereby the magnetic flux inside of the tank due to the currents flowing through the bushings is cancelled out by the magnetic flux due to the current flowing through the enclosure member. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more readily apparent from the following detailed description of the preferred embodiment of the present invention taken in conjunction with the accompanying drawings, in which: Fig. 1 is a sectional view showing the conventional transformer; Fig. 2 is a front view showing the tank upper portion fo the transformer shown in Fig. 1; Fig. 3 is a front view showing the low-voltage bushing of the transformer shown in Fig. 1; Fig. 4 is a sectional view showing one embodiment of the transformer of the present invention; Fig. 5 is a front view showing the tank upper portion of the transformer shown in Fig. 4; Fig. 6 is a front view showing the low-voltage bushing and the enclosure member of the transformer shown in Fig. 4; and Fig. 7 is a perspective view showing the enclosure member shorting plate and the connecting conductors of the transformer shown in Fig. 4. PREFERRED EMBODIMENT OF THE INVENTION One embodiment of the present invention will now be described in conjunction with the accompanying drawings. Fig. 4 is a sectional view showing a three-phase transformer as an electrical apparatus according to one embodiment of the present invention, in which the transformer main body 1, the iron core 101, the winding 102, the tank 2, the high-voltage bushing mounting seats 201, the high-voltage bushings 3, the three-phase separated bus conductors 6, the generator-side three-phase separated bus conductor outer sheaths 7B, the outer sheath shorting plates 8B and 8C, and the expansion joint 9 are similar to those of the conventional design shown in Fig. 1, so that their explanation will be omitted. Fig. 5 is a front view of the upper portion of the tank 2 as viewed the transformer shown in Fig. 4 from the right in the figure. 202 is a low-voltage bushing mounting seat formed on the tank 2 and is common for three phases. 204 are low-voltage bushing mounting flanges formed on an upper plate 205 of the low-voltage bushing mounting seat 202, 4 are low-voltage bushings mounted to the low-voltage bushing mounting flanges 204 which are connected to the low voltage side of the winding 102. Fig. 6 is a front view of the low-voltage bushing and the enclosure member, in which the insulator tube 401, the central conductor 402, the upper and the lower terminals 403 and 404 are similar to those of the conventional design shown in Fig. 3, so that their explanation will be omitted. 11 is an enclosure member also serving as a mounting unit and is disposed at the outer circumference of the insulator tube 401 and is secured to the insulator tube by a cemenet 406. 111 is a flange, which mounts, by attaching this to the low-voltage bushing mounting flange 204 by the bolts 5A, the low-voltage bushing 4 is mounted in a manner in which the bushing extends through the low-voltage bushing mounting flange 204. 112 is a cylinder member having a general configuration of a circular cylinder, the bottom end (in the figure] of the member has a square cross section of which one side has a length equal to the diameter of the above-mentioned cylinder. This cylinder member 112 coaxially surrounds the low-voltage bushing 4 at its portion located inside of the tank 2. The flange 111 and the cylinder member 112 are made of a material having a good electrical conductivity such as copper or aluminium, these two constituting an enclosure member 11. 12 is a flat plate-shaped enclosure member shorting plate, and 13 are connecting conductors attached at their one end to the square bottom end of the cylinder member 112 of the enclosure member 11 by the bolt 5B and attached at their the other end to the enclosure member shorting plate 12 by the bolt 5C, whereby the three phase enclosure members 11 are connected to each other. The enclosure member shorting plate 12 and the connecting conductors 13 are also made of a material having a good electrical conductivity. Fig. 7 illustrates in a perspective view the enclosure member shorting plate 12 and the connecting conductors 13. The enclosure member shorting plate 12 has formed therein three circular holes 121 at a pitch equal to the mounting pitch of the low-voltage bushings 4 so that the connecting conductors from the low-voltage bushings 4 to the winding 102 may extend therethrough. Referring again to Figs. 4, 5 and 6, 7A are transformer-side three-phase separated bus conductor outer sheaths surrounding the low-voltage bushings 4 at the portion located outside of the tank 2 and attached to the flange portion 111 of the enclosure members 11 by bolts 5D. The operation will now be described. With respect to a large current flowing through the three phase separated bus conductors 6, the generator-side has the mini-flux structure constructed by the generator-side three-phase separated bus conductor outer sheaths 7B and the outer sheath shorting plate 8C similarly to the conventional example shown in Fig. 2 to cancel out the magnetic flux. On the transformer-side, a three-phase closed circuit extending into the inside of the tank 2 is formed by the transformer-side three-phase separated bus conductor outer sheaths 7A, the flange portion 111 and the cylindrical portion 112 of the enclosure members 11, the connecting conductors 13, the enclosure member shorting plate 12, and the outer sheath shorting plate 8B outside of the tank 2. Therefore, the magnetic flux inside of the tank 2 due to the current flowing through the low-voltage bushings 4 is cancelled out by the magnetic flux generated by the current flowing through the enclosure members 11. The enclosure members 11, the enclosure member shorting plate 12 and the connecting conductor 13 are made of copper or aluminium, and in this embodiment these elements are immersed within the insulation oil and cooled, so that these elements are not overheated even when a large current flows therethrough. As to the length of the cylindrical portion 112 of the enclosure members 11 and the position of the enclosure member shorting plate 12, since the area in which the magnetic flux offset effect of these members extends become larger when these elements are extended downwardly in the figure, it is preferable that they extend to the position lower than the low-voltage bushing mounting flanges 204 as well as the upper plate 205 of the low-voltage bushing mounting seat 202 which can be easily overheated because they are close to the low-voltage bushings 4. While the enclosure members 11 are indirectly connected to each other by the enclosure member shorting plate 12 through the connecting conductors 13 in the above-described embodiment, the enclosure members 11 may be directly connected to each other by the enclosure member shorting plate 12. Also, while a three-phase example has been shown, similar advantageous results can be obtained in case of a single phase. As has been described, according to the present invenion, each of the bushings is surrounded at the portion located inside of the tank by an enclosure member, and these enclosure members are connected to phase-separated bus conductor outer sheaths at the outside of the tank, and the enclosure members each is connected by an enclosure member shorting plate, so that the arrangement is such that the mini-flux structure extends to the inside of the tank, whereby the magnetic flux inside of the tank due to the currents flowing through the bushings is cancelled out by the magnetic flux due to the current flowing through the enclosure member, resulting in advantageous results that the stray loss is small and the structures around the bushing are not overheated.

Claims: An electrical apparatus comprising: an electrical device (102); a tank (2) containing the electrical device (102); a plurality of bushings (4) extending through the said tank (2); a plurality of electrically conducting outer sheaths (7A), each surrounding a respective one of the said bushings (4) in a region outside of the tank (2); and a plurality of electrically conducting closure members (11) each connected to a respective one of the outer sheaths (7A), characterised in that each of the said closure members (11) comprises a flange (111) and a generally cylindrical tubular member (112), each said flange (111) being situated outside of the said tank (2) and supporting a respective one of the said outer sheaths (7A) to form a respective one of the said connections therewith, each said tubular member (112) extending into the tank (2) and surrounding a respective one of the said bushings (4) within the tank (2); a shorting plate having good conductivity (12) is provided within the said tank (2) and comprises a plurality of connecting conductors (13) which are connected to respective ones of the said tubular members (112). An electrical apparatus according to claim 1, wherein the said tank (2) comprises a bushing mounting seat (202) which includes an upper plate (205), the upper plate having a plurality of openings formed therein, and a plurality of respective annular bushing mounting flanges (204), one bushing mounting flange (204) being situated around each said opening so as to form a neck; the flange (111) of each said closure member (11) being mounted upon a respective one of the said bushing mounting flanges (204). An electrical apparatus according to any preceding claim, wherein the said connecting conductors (13) provided on the said shorting plate are arranged in pairs, each pair being configured to connect within a respective single one of the said tubular members (112).

Inventors: SAKUMA TAKASHI C O AKO SEISAKU, SOKAI KATSUJI C O AKO SEISAKUS, SAKUMA, TAKASHI C/O AKO SEISAKUSHO, SOKAI, KATSUJI C/O AKO SEISAKUSHO
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1989
Main classification: H01F27
IPC codes: H01F27