JP7593733B2 - Gapped core for static induction machines - Google Patents

Description

An embodiment of the present invention relates to a gapped core for a stationary induction machine.

The core of a three-phase transformer used in stationary induction equipment, such as a semiconductor power conversion device, is composed of three legs around which the windings of each phase are wound, and upper and lower yokes that connect them from top to bottom. Each of these legs and yokes is made by laminating multiple electromagnetic steel sheets. In addition, a gap is provided between the upper end of each leg and the underside of the upper yoke, and an insulator made of a non-magnetic material is placed in the gap to improve magnetic saturation characteristics, etc.

Japanese Patent Application Publication No. 6-283351

In a transformer with a gap as described above, leakage flux is generated, spreading across the gap between the upper end of the legs of the core and the upper yoke. However, the spread of the leakage flux varies in distribution, with the center leg being larger than the left and right legs. Such variation in distribution of leakage flux changes the coil impedance of each phase, which may cause fluctuations in the characteristics of the transformer. In this case, it is possible to shift the position of the gap further down the legs, but if the gap is hidden inside the winding, the manufacturing process becomes complicated, the width of the gap cannot be made uniform due to the weight of the core, and the leakage flux may have an effect such as local heating of the winding and other structural components, so it is preferable to provide the gap at the top of the legs.

Therefore, we provide a gapped core for stationary induction equipment that has gaps at the upper ends of the legs and can reduce the variation in the distribution of leakage magnetic flux in each phase.

The gapped core for stationary induction equipment according to the embodiment comprises a plurality of legs around which windings are wound, and upper and lower yoke portions to which the plurality of legs are joined, with a gap provided at the butt joint between the upper end of each leg and the upper yoke portion, and the side surface of the upper end of each leg is configured as an inclined surface that narrows toward the gap .

FIG. 1 is a perspective view illustrating a schematic configuration of a transformer according to a first embodiment. Front view showing the top of the transformer A diagram showing the test results of the fluctuation rate of the excitation current in the eaves of various sizes. FIG. 1A is a front view of the right end of the upper yoke part for explaining the length dimension S from the side of the leg part of the eaves part, FIG. 1B is a plan view of the right end of the upper yoke part, and FIG. 1C is a plan view of the upper yoke part removed FIG. 1A is a front view of the right end of the upper yoke part to explain various dimensions a to d of the eaves part, and FIG. 1B is a plan view of the right end of the upper yoke part. FIG. 13 is a front view showing a schematic configuration of a transformer according to a second embodiment. FIG. 13 is a front view showing a schematic configuration of a transformer according to a third embodiment. FIG. 13 is a front view showing a schematic configuration of a transformer according to a fourth embodiment. A perspective view of the upper end portion of one leg FIG. 13 is a perspective view illustrating a schematic configuration of a transformer according to a fifth embodiment. Side view of the transformer Plan view of one leg FIG. 13 is a perspective view illustrating a schematic configuration of a transformer according to a sixth embodiment. Transformer front view Side view of the upper part

Below, several embodiments applied to, for example, a three-phase transformer for power electronics will be described with reference to the drawings. Note that the same parts are given the same reference numerals between the multiple embodiments, and repeated explanations will be omitted.

(1) First embodiment The first embodiment will be described with reference to Fig. 1 to Fig. 5. Fig. 1 shows a schematic diagram of a main configuration of a three-phase transformer 1 as a stationary induction device of this embodiment. This transformer 1 is configured by mounting three windings 3 on a gapped core 2 (hereinafter simply referred to as "core 2") according to this embodiment.

The iron core 2 has an upper yoke section 4 and a lower yoke section 5 that extend in the left-right direction in the figure, as well as three legs 6 that connect the yoke sections 4, 5 vertically. These yoke sections 4, 5 and each leg section 6 are formed by stacking multiple electromagnetic steel sheets, for example made of silicon steel sheets, in the front-to-back direction (thickness direction) in the figure. The entire iron core 2 is formed by butt-joining the yoke sections 4, 5 and each leg section 6. The lower yoke section 5 and the three legs 6 may be provided integrally, that is, a configuration in which E-shaped electromagnetic steel sheets are stacked. Furthermore, the electromagnetic steel sheets may be, for example, grain-oriented electromagnetic steel sheets.

At this time, as shown in part in Figure 4(c), each leg 6 is configured with the front, rear, left and right edges chamfered so that it forms an approximately octagonal shape when viewed from above. Specifically, as shown in part in Figure 4(c), it consists of three parts of approximately equal thickness in the front-to-rear direction (stacking direction), and in the center of these, electromagnetic steel sheets of equal width are stacked. In the front part in the thickness direction, the electromagnetic steel sheets are stacked in a form that gradually narrows toward the front, and in the rear part, the electromagnetic steel sheets are stacked in a form that gradually narrows toward the rear.

The winding 3, which is not shown in detail, is configured to have an inner circumferential winding 3a on the low voltage side and an outer circumferential winding 3b on the high voltage side. As shown in FIG. 1, three windings 3 for three phases are wound around the outer periphery of each leg 6. In this case, the edges of the front, rear, left and right of each leg 6 are chamfered, so that the outer shape of each leg 6 is close to a circle, and the gap between the inner circumferential surface of the winding 3 and the leg 6 is small when the winding 3 is wound.

Now, in the core 2 of this embodiment, as shown in Figures 1 and 2, a gap 7 is formed at the butt joint between the upper end of each leg 6 and the lower surface of the upper yoke portion 4. This gap 7 is located at the upper part exposed from the upper end of the winding 3. Although not shown, an insulator made of a non-magnetic material such as insulating paper of a predetermined thickness is inserted in this gap 7 part. Also, at both ends of the upper yoke portion 4, eaves portions 8, 8 are integrally provided which protrude laterally beyond the legs 6 located at both ends.

In this embodiment, the eaves portions 8, 8 have the same cross section as the upper yoke portion 4, i.e., the same thickness and height dimensions, and are provided so as to extend to both the left and right sides in the figure. Here, Figures 4 and 5 show the right-side eaves portion 8 as a representative, and the protruding length dimension S of the eaves portion 8 from the side of the leg extension 6 extends to at least the extent that it covers the inner circumferential winding 3a in a plan view, and at the same time, extends at least to the extent that it does not exceed the outer peripheral edge of the outer circumferential winding 3b in a plan view. The left-side eaves portion 8 is also provided symmetrically to the right-side portion.

Next, the action and effect of the above configuration will be described with reference to Figs. 3 to 5. In the transformer 1 configured as above, a gap 7 is provided between the upper end of each leg 6 of the core 2 and the upper yoke portion 4, so that leakage flux is generated, spreading across the gap 7 between the upper end of the leg 6 and the upper yoke portion 4 and leaking into the space. In this case, if there is variation in the distribution of leakage flux between the three legs 6, the magnetic flux interlinked with the winding 3 will differ, changing the coil impedance of each phase and possibly causing fluctuations in the characteristics of the transformer 1.

However, in this embodiment, the upper yoke portion 4 is provided with a visor portion 8 at both ends that protrudes out to the side beyond the legs 6 at both ends. This allows the legs 6, 6 at both the left and right ends and the leg 6 at the center to face the upper yoke portion 4 across the gap 7, i.e., the positional relationship and shape with the upper yoke portion 4, to be the same for all legs 6. As a result, even if leakage flux spreads into the space at the gap 7, the distribution of the leakage flux - that is, the shape of the space between the legs 6 and the upper yoke portion 4 - is uniform for each leg 6, i.e., each phase, and this prevents problems caused by variations in the distribution of leakage flux.

The inventors also conducted a test to determine how much the eaves 8 should extend laterally from the side of the leg 6 to suppress the excitation current fluctuation. The test results are shown in Figure 3. Here, the extension length dimension of the eaves 8 from the side of the leg 6 is S, and as shown in Figure 5, the maximum excitation current fluctuation rate was examined for six samples with length S values of -10 mm, 0 mm, a (40) mm, b (85) mm, c (130) mm, and d (175) mm. The test results in Figure 3 show the distance (mm) from the side of the leg 6 on the horizontal axis and the maximum excitation current fluctuation rate on the vertical axis.

These results show that when the dimension S was -10 mm or 0 mm, i.e. when the eaves 8 was not provided, the maximum rate of fluctuation of the excitation current was relatively large. In contrast, with the eaves 8 of a length of about 40 mm from the side of the leg 6, i.e. long enough to cover the inner circumferential winding 3a in plan view, the maximum rate of fluctuation of the excitation current could be made relatively small. Similarly, similar test results were obtained for b and c. Furthermore, with d, which was made longer so that it exceeded the outer circumferential end of the outer circumferential winding 3b in plan view, the effect was not much different from that of shorter lengths.

As described above, according to the core 2 of this embodiment, a gap 7 is provided at the upper end of the leg 6, and the eaves 8 are provided at both ends of the upper yoke 4, which provides the excellent effect of suppressing the variation in the distribution of leakage magnetic flux in each phase. In particular, in this embodiment, the length of the eaves 8 is set to at least cover the inner circumferential winding 3a in a plan view, which provides a sufficient effect of equalizing the distribution of leakage magnetic flux in the gap 7. Furthermore, in this embodiment, the length of the eaves 8 is set to not exceed the outer circumferential winding 3b, which provides a sufficient effect without unnecessarily making the eaves 8 large.

(2) Second embodiment Fig. 6 shows a transformer 11 according to a second embodiment. The core 12 of this transformer 11 is also made of a laminated core, and includes an upper yoke portion 14 and a lower yoke portion 15, as well as three legs 16 that vertically connect the yoke portions 14, 15. At this time, a gap 17 is provided below the upper portion of each leg portion 16, with a part 16a of the upper end of the leg portion 16 joined to the upper yoke portion 14. Note that no eaves are provided on either end of the upper yoke portion 14, and the ends of the upper yoke portion 14 approximately coincide with the side surfaces of the legs 16 in a plan view.

In this second embodiment, the position of the gap 17 is not directly below the underside of the upper yoke portion 14, but slightly below it. Therefore, the gap 17 is present halfway through the leg 16, and the vertical distance to the upper yoke portion 14 when the leakage flux flows becomes large. As a result, in all legs 16, the leakage flux is distributed so that it flows by expanding the space between both sides of the gap 17, and the distribution of the leakage flux is uniform in each leg. Therefore, even with this embodiment, it is possible to obtain the effect of suppressing the variation in the distribution of the leakage flux in each phase when the gap 17 is provided at the upper end of the leg 16.

(3) Third embodiment Fig. 7 shows a transformer 21 according to a third embodiment. The core 22 of the transformer 21 is also a laminated core, and includes an upper yoke portion 24 and a lower yoke portion 25, as well as three legs 26 that vertically connect the yoke portions 24, 25. A gap 27 is provided between the upper end surface of each leg 26 and the lower surface of the upper yoke portion 24. In this embodiment, a grain-oriented electromagnetic steel sheet with a vertical rolling direction is used for a portion 26a of each leg 26 located below the gap 27. In the other portions of the core 22, a non-grain-oriented electromagnetic steel sheet is used. Note that no eaves are provided at both ends of the upper yoke portion 24, and in a plan view, the ends are substantially aligned with the side surfaces of the legs 26.

In this third embodiment, in the portion 26a of the leg 26 below the gap 27, magnetic flux flows more easily in the vertical direction, and leakage magnetic flux is less likely to occur in the direction of spreading into space. Therefore, according to this embodiment, the generation of leakage magnetic flux itself can be suppressed, and the effect of suppressing the variation in the distribution of leakage magnetic flux in each phase can be obtained by providing the gap 27 at the upper end of the leg 26.

(4) Fourth embodiment Figures 8 and 9 show a fourth embodiment. As shown in Figure 8, the core 32 of the transformer 31 according to this embodiment is also made of a laminated core, and includes an upper yoke portion 34 and a lower yoke portion 35, as well as three legs 36 that vertically connect the yoke portions 34, 35. A gap 37 is provided between the upper end surface of each leg 36 and the lower surface of the upper yoke portion 34. In this case, as also shown in Figure 9, the side surface of the upper end portion of each leg 36 is an inclined surface 36a that narrows toward the gap 37. Note that no eaves are provided at both ends of the upper yoke portion 34, and in a plan view, they are substantially aligned with the side surfaces of the legs 36.

In this fourth embodiment, the side surface of the upper end of the leg 36 is inclined surface 36a, which shortens the distance between the inclined surface 36a and the lower surface of the upper yoke portion 34, making it difficult for leakage flux to occur in the direction of expanding into space. Therefore, according to this embodiment, the generation of leakage flux itself, that is, the expansion into the lateral space, can be suppressed, and the effect of suppressing the variation in the distribution of leakage flux in each phase can be obtained by providing a gap 37 at the upper end of the leg 36.

(5) Fifth embodiment Next, a fifth embodiment will be described with reference to Figs. 10 to 12. Figs. 10 and 11 show an overall configuration of a transformer 41 according to a fifth embodiment. The core 42 of the transformer 41 is also a laminated core, and includes an upper yoke portion 44 and a lower yoke portion 45, as well as three legs 46 that vertically connect the yoke portions 44, 45. A gap 47 is provided between the upper end surface of each leg 46 and the lower surface of the upper yoke portion 44. As shown in Fig. 12, each leg 46 is configured to have so-called chamfered edges on the front, rear, left and right sides so as to form an approximately octagonal shape when viewed from above, as described in the first embodiment.

In this embodiment, as shown in Figures 10 and 11, the upper yoke portion 44 is made up of three parts of approximately equal thickness in the front-to-rear direction (stacking direction), of which the front and rear portions are made of laminated electromagnetic steel sheets of equal width (height), while the central portion 44a is made of laminated electromagnetic steel sheets of a larger width (height) than the front and rear portions. As a result, the upper yoke portion 44 is configured so that the central portion in the thickness direction has a larger cross-sectional area than the front and rear portions. As shown in Figure 11, the lower yoke portion 45 is also configured so that the central portion 45a is convex downward, symmetrically to the upper yoke portion 44.

In this fifth embodiment, the magnetic resistance of each leg 46 at the center in the thickness direction is smaller than the magnetic resistance at the front and rear, so that magnetic flux flows more easily at the center in the thickness direction and less easily at the front and rear. Also, in the upper yoke portion 44, the magnetic resistance at the center in the thickness direction 44a is smaller than the magnetic resistance at the front and rear, so that magnetic flux flows more easily at the center in the thickness direction 44a and less easily at the front and rear. This makes it less likely that leakage magnetic flux will occur in the direction that expands into the space at the gap 47.

According to this embodiment, the magnetic flux flows more easily in the center of the thickness direction of the iron core 42, and flows less easily in the front and rear parts in the thickness direction, so that the occurrence of leakage magnetic flux itself can be suppressed. As a result, it is possible to obtain the effect of suppressing the variation in the distribution of leakage magnetic flux in each phase.

(6) Sixth embodiment and other embodiments Figures 11 to 13 show a sixth embodiment, and the configuration different from the fifth embodiment will be described below. The iron core 52 of the transformer 51 according to the sixth embodiment is also made of a laminated iron core, and includes an upper yoke part 54 and a lower yoke part 55, as well as three legs 56 that vertically connect the yoke parts 54, 55. A gap 57 is provided between the upper end surface of each leg part 56 and the lower surface of the upper yoke part 54, as described later.

At this time, each leg 56 is made up of three parts of approximately equal thickness in the front-to-rear direction (stacking direction), and the edges of the front, back, left and right sides of the front and rear parts are configured in a so-called chamfered shape so that they form an approximately octagonal shape when viewed from above. As shown in Figure 13, the central part of the three parts of each leg 56 is made of laminated electromagnetic steel sheets whose height dimension is slightly smaller than the other parts, and as a result, a concave groove part 56a is formed in the center of the thickness direction at the upper end of each leg 56.

In contrast, the underside of the upper yoke portion 54 is constructed by laminating electromagnetic steel sheets whose central portion in the thickness direction is longer in the height direction (longer downward) than the front and rear portions, and thus has a downwardly protruding convex portion 54a that engages with the concave groove portion 56a. As a result, the gap 57 formed between the upper end surface of each leg portion 56 and the underside of the upper yoke portion 54 is uneven when viewed from the side. Furthermore, eaves portions 58 are integrally formed on both ends of the upper yoke portion 54. The underside of the lower yoke portion 55 is flat.

According to the sixth embodiment, the provision of the eaves 58 at both ends of the upper yoke portion 54 makes it possible to suppress the variation in the distribution of leakage flux in each phase. As with the fifth embodiment, the core 52 as a whole allows magnetic flux to flow more easily in the center in the thickness direction, and less easily in the front and rear portions. This makes it difficult for leakage flux to occur in the direction of spreading into the space in the gap 57 portion. As a result, this embodiment provides a higher effect of suppressing the variation in the distribution of leakage flux in each phase, even when the gap 57 is provided at the upper end of the leg portion 56. In addition, it is possible to increase the cross-sectional area of the center portion of the upper yoke portion 54 without increasing its height.

In the sixth embodiment, the upper yoke portion 54 is provided with a eaves portion 58, but even without the eaves portion 58, the effect of suppressing the variation in the distribution of leakage magnetic flux in each phase can be obtained. In addition, although the above embodiments are applied to a three-phase transformer as a stationary induction device, it is also possible to apply the present invention to a four or more phase transformer as a stationary induction device. It is also possible to apply the present invention to a reactor. In addition, various modifications are possible regarding the joint structure between the yoke portion and the legs, etc.

The above-described embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims.

In the drawings, 1, 11, 21, 31, 41, and 51 are transformers (static induction devices), 2, 12, 22, 32, 42, and 52 are cores (gapped cores), 3 is windings, 4, 14, 24, 34, 44, and 54 are upper yoke parts, 5, 15, 25, 35, 45, and 55 are lower yoke parts, 6, 16, 26, 36, 46, and 56 are legs, 7, 17, 27, 37, 47, and 57 are gaps, and 8 and 58 are eaves parts.

Claims (2)

A plurality of legs around which a winding is wound;
The plurality of legs are joined to upper and lower yoke portions,
A gap is provided at a butt joint portion between the upper end portion of each leg portion and the upper yoke portion,
A gapped core for stationary induction equipment, wherein the side surfaces of the upper ends of the legs are configured as inclined surfaces that narrow toward the gap. A plurality of legs around which a winding is wound;
The plurality of legs are joined to upper and lower yoke portions,
A gap is provided at a butt joint portion between the upper end portion of each leg portion and the upper yoke portion,
At least the legs located at both ends of the leg portions are shaped to narrow forward at a front portion in a thickness direction of the side surface, and are shaped to narrow backward at a rear portion in a thickness direction of the side surface,
The upper yoke portion is configured so that a central portion in a thickness direction has a larger cross-sectional area than a front portion and a rear portion,
The upper end of each leg portion has a central portion in a thickness direction formed into a concave groove shape, and the lower surface of the upper yoke portion has a central portion in a thickness direction formed into a convex shape,
A gapped core for a stationary induction machine having said gap therebetween.

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