Laminated iron core for transformer and laminated iron core transformer

Abstract

The present invention reduces noise generated from a transformer. This laminated core for a transformer comprises a leg part and a yoke part. The rigidity ratio obtained by dividing the average rigidity of the leg part by the average rigidity of the yoke part is between 0.70 and 0.95 both inclusive, or between 1.05 and 1.30 both inclusive.

Description

Stacked cores for transformers and stacked core transformers

[0001] The present invention relates to a stacked core for a transformer, and also to a stacked core transformer including the stacked core for a transformer.

[0002] Various technologies have been studied to reduce noise generated by transformers. In particular, because the iron core is a source of noise even when no load is applied, numerous technological developments have been made regarding the iron core and the electromagnetic steel sheets used therein, and efforts have been made to reduce noise. For example, Patent Documents 1 and 2 propose technologies for reducing noise by reducing the magnetostriction of grain-oriented electromagnetic steel sheets. Patent Documents 3 and 4 propose technologies for suppressing vibration of the iron core by sandwiching resin or vibration-damping steel sheets between grain-oriented electromagnetic steel sheets.

[0003] JP 2013-87305 A JP 2012-177149 A JP 8-250339 A JP 2006-14555 A

[0004] It is possible to reduce noise to a certain extent by applying the techniques proposed in Patent Documents 1 to 4. However, techniques for further noise reduction are desired.

[0005] The present invention has been made in view of the above-mentioned circumstances, and has an object to reduce noise generated from a transformer.

[0006] As a result of investigations into solving the above problems, the inventors discovered that vibration can be suppressed by controlling the natural vibration characteristics of the stacked core, which is a factor that affects vibration. The present invention was completed based on this discovery and further investigations. The gist of the present invention is as follows.

[0007] 1. A stacked core for a transformer having leg portions and a yoke portion, wherein a rigidity ratio obtained by dividing the average rigidity of the legs by the average rigidity of the yoke portion is 0.70 or more and 0.95 or less, or 1.05 or more and 1.30 or less.

[0008] 2. The transformer stack core according to 1 above, wherein the rigidity ratio is 0.70 or more and 0.95 or less.

[0009] 3. The transformer stack core according to 1 or 2 above, wherein the average modulus of rigidity of the yoke portion is more than 0.01 GPa and not more than 1.0 GPa.

[0010] 4. A stacked core transformer comprising the stacked core for a transformer according to any one of 1 to 3 above.

[0011] According to the present invention, noise generated from a transformer can be reduced.

[0012] 1 is a perspective view showing an example of a stacked core according to the present invention; FIG. 2 is a graph showing the relationship between an average clamping pressure and an average rigidity; FIG. 3 is a graph showing the relationship between a rigidity ratio and a noise level; and FIG. 4 is a graph showing the relationship between the average rigidity of a yoke portion and a noise level.

[0013] [Transformer stack core] The transformer stack core according to the present invention includes legs and a yoke, and a rigidity ratio obtained by dividing the average rigidity of the legs by the average rigidity of the yoke is 0.70 or more and 0.95 or less, or 1.05 or more and 1.30 or less.

[0014] First, the shape of the stacked core according to the present invention will be described. FIG. 1 is a perspective view showing an example of a stacked core according to the present invention. The stacked core 10 has a structure in which an upper yoke portion 1a and a lower yoke portion 1b are connected by a central leg 2a and side legs 2b and 2c. The yoke portion is usually composed of an upper yoke portion and a lower yoke portion. The number of legs is not limited to three and may be, for example, three or more. The stacked core 10 may be fixed by any method. For example, a clamping jig (not shown) may be provided to clamp and fix the stacked electromagnetic steel sheets, or the stacked electromagnetic steel sheets may be bonded together with an adhesive or the like.

[0015] [Rigidity Ratio] The stacked core according to the present invention has a rigidity ratio of 0.70 to 0.95 or 1.05 to 1.30. The rigidity ratio is the average rigidity of the legs divided by the average rigidity of the yoke. By making the average rigidity of the yoke and the legs different, the yoke and the legs have different vibration modes. Furthermore, because both ends of the yoke are adjacent to the legs and both ends of the legs are adjacent to the yoke, the interaction of the vibration modes of the yoke and the legs prevents the same vibration from occurring throughout the core. This reduces vibration and is believed to improve noise generated by the transformer. On the other hand, if the rigidity ratio is greater than 0.95 and less than 1.05, noise is not sufficiently reduced. Therefore, the stacked core according to the present invention has a rigidity ratio of 0.95 or less or 1.05 or more. Furthermore, a rigidity ratio of 0.90 or less or 1.10 or more can further improve noise. Therefore, the rigidity ratio is preferably 0.90 or less or 1.10 or more. On the other hand, if the rigidity ratio is less than 0.70 or more than 1.30, not only will the above-mentioned effect saturate, but the portion that deforms will tend to be limited, increasing the amplitude of vibration and failing to sufficiently reduce noise. Therefore, the rigidity ratio should be 0.70 or more when the rigidity ratio is 0.95 or less, and 1.30 or less when the rigidity ratio is 1.05 or more.

[0016] Furthermore, noise can be further reduced by increasing the rigidity of the yoke section relative to the rigidity of the legs. While the exact reason is unclear, it is believed to be as follows: Noise is generated when vibrations from the core propagate through oil, a tank, etc. Because stacked cores are typically installed upright, the yoke section contacts the tank. Since noise is more likely to propagate through the tank, increasing the rigidity of the yoke section that contacts the tank is believed to suppress vibrations transmitted through the tank, resulting in more effective noise reduction. Therefore, the rigidity ratio is preferably 0.95 or less, and more preferably 0.90 or less.

[0017] [Average Rigidity Modulus of the Yoke Section] The average rigidity modulus of the yoke section is not limited. However, when the average rigidity modulus is high, noise caused by vibration as a rigid body becomes a major component rather than noise caused by magnetostriction, and therefore, controlling the rigidity ratio further improves noise reduction. Furthermore, controlling the average rigidity modulus of the yoke section provides vibration reduction effects regardless of the frequency band. Therefore, the average rigidity modulus of the yoke section is preferably greater than 0.01 GPa. Furthermore, the average rigidity modulus of the yoke section is more preferably 0.05 GPa or greater. The average rigidity modulus of the yoke section may be greater than 0.010 GPa or may be 0.050 GPa or greater. From the standpoint of manufacturability, the average rigidity modulus of the yoke section is preferably 1.0 GPa or less. The average rigidity modulus of the yoke section may be 1.000 GPa or less.

[0018] In the present invention, the average rigidity modulus of the yoke is the average of the rigidity moduli of all the yokes (the average of the rigidity moduli of the upper yoke and the lower yoke), and the average rigidity modulus of the legs is the average of the rigidity moduli of all the legs (for example, in the case of a three-legged structure, the average of the rigidity moduli of the right leg, the center leg, and the left leg).

[0019] The modulus of rigidity is the modulus of transverse elasticity G (= Gxz = Gyz) in two planes including the lamination direction. The modulus of rigidity can be determined by determining in advance the relationship between the average clamping pressure in the lamination direction and the modulus of transverse elasticity G, and then substituting the average clamping pressure in the lamination direction at each part of the stacked core to be evaluated into this relationship. Here, the average clamping pressure is the value obtained by averaging the clamping pressure at a target part of the stacked core over the area of ​​the electromagnetic steel sheets used at that part.

[0020] Specifically, it can be determined as follows. First, a vibration test is performed on a test stack core while changing the average clamping pressure in the lamination direction, and the natural frequency of a specific vibration mode is measured to determine the relationship between the natural frequency and the average clamping pressure. A test stack core configured to allow adjustment of the average clamping pressure in the lamination direction can be used as the test stack core. Next, a structural analysis of the test stack core is performed using structural analysis software to estimate the relationship between the natural frequency and the modulus of transverse elasticity G. Next, the modulus of transverse elasticity G, i.e., the rigidity modulus, of each part is determined from the average clamping pressure at each part of the stack core to be evaluated, the relationship between the natural frequency and the average clamping pressure, and the relationship between the natural frequency and the modulus of transverse elasticity G. More specifically, the modulus of transverse elasticity G can be determined using the method described in Japanese Patent No. 6729837.

[0021] [Method for manufacturing stacked iron core] The method for manufacturing the stacked iron core is not particularly limited, and the stacked iron core can be manufactured by stacking a plurality of electromagnetic steel sheets. The electromagnetic steel sheets to be stacked may be oblique angle steel sheets that have been subjected to oblique shearing.

[0022] In the manufacturing method of the stacked core, the rigidity modulus of the legs and yoke must be controlled to achieve a rigidity ratio of 0.70 to 0.95 or 1.05 to 1.30. The method for controlling the rigidity modulus of the legs and yoke is not particularly limited. For example, the shape of the core may be changed. However, changing the core shape affects the size of the transformer, which limits the scope of possible adaptation due to installation area restrictions. Therefore, the rigidity modulus of the yoke and legs may be controlled by controlling the average clamping pressure using a clamping jig or the like. For example, the torque of the clamping members, such as bolts, used for clamping in the clamping jig may be controlled. Furthermore, if the stacked magnetic steel sheets are bonded to each other, the bonding method may be controlled. For example, the rigidity modulus may be controlled by adjusting the bonding area. Alternatively, the rigidity modulus may be controlled by providing layers that bond the magnetic steel sheets to each other and layers that do not, and changing the ratio of the number of the two layers. This allows the rigidity modulus to be controlled and also makes it easy to increase the difference between the rigidity modulus of the yoke and the rigidity modulus of the legs.

[0023] In the present invention, the electromagnetic steel sheet used as the material for the stacked core is not particularly limited. Grain-oriented electromagnetic steel sheet, non-oriented electromagnetic steel sheet, or amorphous strip may be used as the electromagnetic steel sheet, but grain-oriented electromagnetic steel sheet is preferred. The thickness of the electromagnetic steel sheet may be appropriately selected depending on the application, and may be, for example, 0.10 mm or more, or 0.18 mm or more. It may also be, for example, 0.35 mm or less, or 0.27 mm or less.

[0024] The method for manufacturing the electrical steel sheet is not particularly limited. For example, the grain-oriented electrical steel sheet can be manufactured by the following method. First, a steel slab having a predetermined chemical composition is obtained. The chemical composition of the steel slab is not limited, and steel slabs having known chemical compositions can be used. The steel slab is then heated at 1150 to 1450°C, further hot-rolled, and, if necessary, hot-rolled annealed at 900 to 1150°C. Subsequently, the steel slab is cold-rolled once or twice or more times with intermediate annealing in between, and then decarburized in a wet hydrogen atmosphere at 700 to 900°C, and, if necessary, further nitrided. An annealing separator is then applied, and the steel slab is finish-annealed at 1000 to 1200°C, and an insulating coating is formed at approximately 900°C (e.g., 850 to 950°C).

[0025] The grain-oriented electrical steel sheet may be subjected to a magnetic domain refining treatment. The method of the magnetic domain refining treatment is not limited, and known methods such as introducing distortions or grooves can be used.

[0026] [Stacked Core Transformer] The stacked core transformer according to the present invention includes the stacked core described above. Therefore, by using the stacked core transformer according to the present invention, it is possible to reduce generated noise.

[0027] The present invention will be specifically described below based on examples.

[0028] A steel slab containing 3.2% Si by mass was heated to 1200°C, further hot-rolled, and then hot-rolled at 900°C. The cold-rolled sheet was then cold-rolled twice to a final thickness of 0.22 mm, and decarburization annealed at 850°C in a wet hydrogen atmosphere. An annealing separator primarily composed of MgO was then applied, followed by a finish annealing at 1200°C, including a secondary recrystallization process and a purification process, to form a forsterite coating. A tension coat consisting of 50% colloidal silica and magnesium phosphate was then applied, followed by baking at 850°C to obtain a 0.23 mm-thick highly oriented electrical steel sheet. The resulting grain-oriented electrical steel sheet was then bevel-sheared to produce beveled bar. The produced beveled bar was stacked into the shape shown in Figure 1 to produce a transformer stack core. Here, the stacked core had 1,000 laminated sheets, an overall width of 890 mm, an overall height of 800 mm, a laminate thickness of 230 mm, a central leg width of 160 mm, a side leg width of 125 mm, and a height of 160 mm for the upper and lower yoke sections. The stacked core was provided with a tightening jig for tightening and fixing the laminated electromagnetic steel sheets, and the rigidity modulus of the yoke section and legs was varied by changing the torque of the bolts used for tightening in the tightening jig.

[0029] An excitation coil was wound around the resulting stacked core, and the core was excited with an AC current with a maximum magnetic flux density B of 1.7 T and a frequency of 50 Hz. The noise level was measured at six locations on the front and back of the three legs, at a height of 400 mm and a distance of 300 mm from the surface of the core. The measured values ​​were power-averaged to obtain an overall noise level. The noise level was calculated using the method described in JIS C 4306:2013. The average rigidity of the yoke and legs was also measured using the same method. The results are shown in Tables 1 to 4 and Figures 2 to 4.

[0030] The relationship between the average clamping pressure and the average rigidity is shown in Figure 2. As the average clamping pressure increases, the average rigidity tends to increase for both the yoke and the legs.

[0031] Tables 1 to 4 show the relationship between the average rigidity modulus of the yoke, the average rigidity modulus of the legs, the rigidity ratio, and noise level. Figure 3 also shows the relationship between the rigidity ratio and noise level when the average rigidity modulus of the yoke is 1.100 GPa. Comparing cases where the average rigidity of the yoke is the same, noise was reduced when the rigidity ratio was 0.70 or greater and 0.95 or less, or 1.05 or greater and 1.30 or less. Furthermore, when the rigidity ratio was 0.95 or less, i.e., when the average rigidity of the yoke was greater than the average rigidity of the legs, noise was further reduced.

[0032] Figure 4 shows the relationship between the average rigidity of the yoke and noise level when the rigidity ratio is 0.80, 1.00, or 1.20. When the average rigidity of the yoke was greater than 0.01 GPa, noise was further reduced.

[0033]

[0034]

[0035]

[0036]

[0037] 1a Upper yoke portion 1b Lower yoke portion 2a Central leg portion 2b, 2c Side legs 10 Stacked core

Claims

1. A stacked core for a transformer having legs and a yoke, wherein the rigidity ratio obtained by dividing the average rigidity of the legs by the average rigidity of the yoke is 0.70 or more and 0.95 or less, or 1.05 or more and 1.30 or less.

2. A transformer stack core according to claim 1, wherein the rigidity ratio is 0.70 or more and 0.95 or less.

3. A transformer stack core according to claim 1 or 2, wherein the average modulus of rigidity of the yoke portion is greater than 0.01 GPa and not greater than 1.0 GPa.

4. A stacked core transformer comprising the stacked core for a transformer according to any one of claims 1 to 3.

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