SHARED SHUNT REACTOR TYPE TRANSFORMER

Abstract: In a shared shunt reactor type transformer according to this invention in which a transformer and a shunt reactor are constructed as a unitary assembly, the transformer has diminished and bypass yokes serving as yokes for the reactor, too. The shared shunt reactor type transformer, therefore, includes a smaller amount of yoke material, has a smaller overall size and a smaller weight, and can be manufactured at a lower cost.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a shared shunt reactor type transformer used in a power transmission or distribution system. Description of the Prior Art There is known a shared shunt reactor type three-phase transformer, as disclosed in Japanese Patent Application laid open under No. 30112/1985. Its construction is schematically shown in FIGURE 1. It comprises a transformer 1, a shunt reactor 2, and a tank 3 in which the transformer and the shunt reactor are installed. The transformer 1 has a limb core 1 a , an upper and a lower yoke 1 b and 1 c and a coil 1 d . The excitation of the transformer 1 causes main magnetic flux to pass as shown at 1 e . The shunt reactor 2 has an upper yoke 2 b a gap core 2 a , and a coil 2 d . The excitation of the reactor 2 causes magnetic flux to pass as shown at 2 e . The coils 1 d and 2 d are so wound respectively that the main magnetic flux passing through the limb core 1 a of the transformer 1 may be of the same polarity as that passing through the gap core 2 a of the shunt reactor 2, as shown in FIGURE 1. FIGURE 2 shows a case that a transformer 1 and a shunt reactor 2 are separate from each other. The transformer 1 is installed in a tank 4, and the shunt reactor 2 in another tank 5. The reactor 2 includes a lower yoke 2 c . The transformer 1 and the reactor 2 are otherwise of the same construction as those which have been described with reference to FIGURE 1. If the reactor 2 is connected to the top of the transformer 1 in a common tank 3 so that the upper yoke 1 b of the transformer 1 may serve as the lower yoke 2 c of the reactor 2, too, a shared shunt reactor type transformer as shown in FIGURE 1 is obtained. Referring again to FIGURE 1, the modes in which magnetic flux passes through the upper yoke 1 b of the transformer 1 consist of three cases, i.e.: Case 1 - The main magnetic flux 1 e of the transformer passes if only the transformer is excited; Case 2 - The magnetic flux 2 e of the shunt reactor 2 passes if only the shunt reactor is excited; and Case 3 - The magnetic flux passing through it corresponds to the difference between the magnetic flux 1 e and 2 e if the transformer and the shunt reactor are both excited. Therefore, the assembly of FIGURE 1 exhibits the same performance as the separate type shown in FIGURE 2, and yet calls for a smaller space for installation, if the upper yoke 1 b of the transformer 1 has so large a cross-sectional area that it may not be magnetically saturated in any of the three cases. It is, however, usual that the maximum magnetic flux passes through the upper yoke 1 b of the transformer 1 in Case 1, as the magnitude of the flux 1 e is usually greater than that of the flux 2 e . This requires the upper yoke 1 b to have the same cross-sectional area as the lower yoke 1 c . This requirement has hitherto disabled any desirable reduction in weight of the core of the transformer. SUMMARY OF THE INVENTION Under these circumstances, it is an object of this invention to provide an improved shared shunt reactor type transformer in which a transformer and a shunt reactor are constructed as a unitary assembly having a reduced transformer core weight. This object is essentially attained by the features disclosed in claim 1. This arrangement enables a reduction in the cross-sectional area of the yoke of the transformer, and yet the shared shunt reactor type transformer according to this invention is satisfactory for use in any case where the transformer or the shunt reactor is operated alone, or where they are operated together. These and other objects, features and advantages of this invention will become more apparent from the following description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic sectional view of a known shared shunt reactor type transformer; FIGURE 2 is a schematic sectional view illustrating the operation of the apparatus shown in FIGURE 1; FIGURE 3 is a schematic sectional view of a shared shunt reactor type transformer embodying this invention; FIGURES 4 and 5 are views similar to FIGURE 3, but showing the operation of the apparatus shown in FIGURE 3; FIGURE 6 is a schematic sectional view of another embodiment of this invention; and FIGURE 7 is a schematic sectional view of still another embodiment of this invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of this invention will now be described with reference to the drawings which are merely illustrative of this invention and are not intended for limiting the scope thereof. Reference is first made to FIGURE 3 showing a shared shunt reactor type transformer of a single-phase shell-type. The transformer 1 has a limb core 1 a , a yoke 1 c , and a coil 1 d . The yoke 1 c has a diminished yoke X and a bypass yoke Y. The apparatus also includes a shunt reactor 2. The reactor 2 has a gap core 2 a , and a coil 2 d which is surrounded by the diminished yoke X of the transformer 1 and the bypass yoke Y. The diminished yoke X and the bypass yoke Y form a yoke for the reactor 2, too. The excitation of the transformer 1 causes a main magnetic flux to pass as shown at 1 e , while the excitation of the shunt reactor 2 causes magnetic flux to pass as shown at 2 e . The coils 1 d and 2 d are wound in such a way that the magnetic flux 1 e and 2 e passing through the diminished yoke X may cancel each other. Attention is drawn to FIGURE 4 showing a case that a shell type transformer 1 and a shell type shunt reactor 2 are so positioned that the respective yokes 1 c and 2 b thereof may stay apart from each other, but in a mutually closely adjacent relation. The main magnetic flux 1 e and the magnetic flux 2 e are designed for passing in opposite directions through the yoke 1 c of the transformer 1 and the yoke 2 b of the reactor 2, respectively. The apparatus shown in FIGURE 3 is obtained if the transformer 1 and the shunt reactor 2 which are shown in FIGURE 4 are so combined that the yoke 1 c of the transformer 1 may serve as the yoke 2 b of the reactor 2, too. Insofar as the magnetic fluxes 1 e and 2 e pass in the opposite directions, they cancel each other when passing through the diminished yoke X in the apparatus shown in FIGURE 3. It is, therefore, sufficient for the diminished yoke X to have a cross-sectional area which allows for the passage of the amount of magnetic flux equal to the difference between 1 e and 2 e , and which is smaller than the original cross-sectional area of the yoke 1 c . Attention is also drawn to FIGURE 5 showing the magnetic flux distribution which occurs when only the transformer 1 is excited. As is obvious from the figure, the main magnetic flux of the transformer 1 is distributed through the diminished yoke X and the bypass yoke Y. Therefore, it is sufficient for the diminished yoke X and the bypass yoke Y to have a sum of cross-sectional areas of yokes X and Y which is equal to the original cross-sectional area of the yoke 1 c . Therefore, the apparatus shown in FIGURE 3 enables a reduction in the cross-sectional area of the yoke of the transformer 1 by an amount equal to the difference between that of 1 c as shown in FIGURE 4 or 5 and that of X, and thereby a smaller space for installation. Although the invention has been described as a single-phase apparatus, similar results can be obtained from a three-phase apparatus as shown by way of example in FIGURE 6. Although the invention has been described as a shell type apparatus, similar results can be attained from a core type apparatus as shown by way of example in FIGURE 7.

Claims: A shared shunt reactor type transformer comprising: a bypass yoke (Y) of a transformer (1) for serving as a yoke of a shunt reactor as well as a part of a yoke of the transformer (1), characterised in that said yoke of the transformer (1) is partially divided into two parts of a diminished yoke (X) and said bypass yoke (Y); a gap core (2a) of the shunt reactor (2) provided to an open space formed between said diminished and bypass yokes (X,Y) of the transformer (1); and a coil (2d) of the shunt reactor (2) wound around said gap core (2a) of the shunt reactor (2), for producing magnetic flux (2e) in a direction reducing magnetic flux of the transformer produced in said diminished yoke (X) of the transformer (1). A shared shunt reactor type transformer as set forth in claim 1, wherein said transformer (1) and said shunt reactor (2) are respectively of a shell type. A shared shunt reactor type transformer as set forth in claim 1, wherein said transformer (1) and said shunt reactor (2) are respectively of a core type. A shared shunt reactor type transformer as set forth in claim 1, 2 or 3, wherein said transformer (1) and said shunt reactor (2) are respectively of a single-phase type. A shared shunt reactor type transformer as set forth in claim 1, 2 or 3, wherein said transformer (1) and said shunt reactor (2) are respectively of a three-phase type.

Inventors: NAKATSUKA, SYOJI, SOKAI, KATSUJI, TANINOUCHI, KENTARO, NAKATSUKA, SYOJI, C/O MITSUBISHI DENKI K.K., SOKAI, KATSUJI, C/O MITSUBISHI DENKI K.K., TANINOUCHI, KENTARO, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1990
Main classification: H01F31
IPC codes: H01F27, H01F30, H01F37