JPH10261536A - Method for clamping yoke of three-phase transformer laminated core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce noise and iron loss by arranging a plate that is applied to a yoke and clamps it, dividing the plate into two parts in the longer direction so that it does not contact the T junction part of a core, and using a connection bolt or a spring for generating a force for attracting two plates each other. SOLUTION: Plates 8 and 9 are yoke-clamping plates being divided into two parts. A bolt 11 where the plates are arranged properly is connected to a plate being located on a reverse side, and the bolt 11 is clamped to give a clamping force to the yoke. After the bolt 11 is clamped, a bolt 10 for connecting the plates 8 and 9 is clamped, thus applying a compression stress in rolling direction for the yoke part of the T junction part. The compression stress can be controlled by the clamping torque of the bolt 10. Also, by adding a spring 16 to a bolt 15 for connecting plates 13 and 14, the stress can also be transferred via the spring 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for tightening a yoke for reducing noise and iron loss in an iron core of a transformer, particularly in a laminated iron core.

[0002]

2. Description of the Related Art The major technical issues in transformer cores are:
Noise and iron loss are reduced. One of the causes of noise is magnetostriction of an electromagnetic steel sheet. The magnetostriction is such that when the magnetization of the magnetic steel sheet changes, the shape of the magnetic steel sheet changes accordingly. Due to this phenomenon, when the iron core is AC-excited, the iron core vibrates with it, thereby generating noise. On the other hand, iron loss is energy loss generated in an electromagnetic steel sheet. Since the noise and the iron loss change depending on the magnetic characteristics determined by the structure of the magnetic steel sheet and the shape and structure of the iron core, improvement by technology development is always desired.

[0003] A structure often used in a transformer core is to form a closed magnetic circuit by cutting a grain-oriented electrical steel sheet into a predetermined width and length, and joining a plurality of parts formed by laminating them. , Called the stacked iron core. Of these, the iron core used for three-phase alternating current has a structure in which three legs 1 and two yokes 2 are combined as shown in FIG.
As shown in (b), a structure in which five legs 3 and two yokes 4 are combined is adopted. The former is called a three-phase three-legged core, and the latter is called a three-phase five-legged core.

In a three-phase three-legged core, the coil is wound around three legs, and in a three-phase five-legged core, the coil is wound around three legs excluding the outer legs. Since the iron core is in a state where only the electromagnetic steel sheets are laminated, it is unstable as it is, and needs to be fixed by some method. For this purpose, the method shown in FIG. 3 is often used. Since the coil is wound around the leg portion as described above, a method of applying a surface pressure by winding the iron core while applying tension to the band 5 is used for fixing the portion. On the other hand, since no coil is provided on the yoke, a method is used in which a highly rigid plate 6 large enough to cover the entire length of the yoke is applied and tightened with bolts or the like.

In general, it is said that a three-phase transformer has higher noise and iron loss when compared with a single-phase transformer having the same weight. One of the causes is considered as described in the document “Progress of Silicon Steel Sheet and Various Problems in Use” (IEEE Technical Report II, No. 85, 1979). Rotational magnetization generated at the T junction. The position of the T junction is shown in FIG.

The three-phase AC consists of three components whose phases are shifted by 120 °, respectively, and the magnetic flux generated by these components passes through the T junction of the iron core. The phase shift causes T
At the junction, the point where the magnetic flux density becomes 0 does not occur, and when the magnetization vector is observed at that point, an ellipse is drawn in one cycle of excitation. This is rotational magnetization.

[0007] When rotational magnetization is generated in the grain-oriented electrical steel sheet, it is also magnetized in directions other than the [001] direction, which is the rolling direction. As a result, the literature "Dynamic rotational magnetostriction of silicon steel sheet" (Journal of the Japan Society of Applied Magnetics, Vol. 15, No. 2,
P261-264, 1991)
Magnetostriction is a value much larger than that caused by alternating magnetization in the rolling direction. Therefore, it is conceivable that noise is greatly increased due to vibration generated in the iron core due to the magnetostriction. In addition, as shown in the document “Progress of Silicon Steel Sheets and Problems in Use” (Technical Report II of the Institute of Electrical Engineers of Japan, No. 85, 1979), iron loss is also higher in rotational magnetization than in alternating magnetization. Then take a large value. Thereby, it is considered that the iron loss of the three-phase iron core is larger than the iron loss of the single-phase iron core and the material.

Japanese Patent Application Laid-Open No. Sho 54-842 discloses a method aimed at suppressing the characteristic deterioration of a three-phase laminated iron core due to the above-mentioned causes.
No. 29 discloses this. This method is to mechanically or chemically remove the coating on the electromagnetic steel sheet at the T-joint. The cause of the effect is described in the document "Effects of G
lass-film on Magnetic Properties and Domain Struct
ures under Two-dimensional Magnetization in 3% Si-
Fe with Orientationnear (110) [001] ”(Proceedings
of Third International Workshop on the Magnetic P
roperties of Electrical Steel Sheets under Two-dim
Extension Excitation, P117-130, 1993). That is, the coating of the unidirectional magnetic steel sheet imparts surface tension to the steel sheet, and as a result, magnetic domains whose magnetization direction is in the rolling direction, that is, the [001] direction are dominant. On the other hand, when the film is removed, the tension effect disappears, and an auxiliary magnetic domain appears which contributes to magnetization in a direction at 90 ° to the rolling direction. It is considered that this improves the magnetic properties in directions other than the rolling direction, and exhibits the same effect under the condition of rotational magnetization.

[0009]

In order to realize the above-mentioned method, an electromagnetic steel sheet is sheared in accordance with the shape of an iron core, and thereafter, a work for removing a film on both sides of a sheet corresponding to a T-joint one by one. Is required. However, since the film is in close contact with the steel sheet and the removal operation is not easy, it is extremely difficult to commercialize this method. The present invention solves this problem and provides an easily realizable means for eliminating the effect of the film tension at the T-joint.

[0010]

SUMMARY OF THE INVENTION According to the present invention, there is provided a plate which is applied to a yoke of a three-phase transformer core using a grain-oriented electrical steel sheet and tightens a portion of the yoke. It is characterized in that it is divided into two parts, arranged so that it does not hit the T joint of the iron core, and further using a connecting bolt or a spring for generating a force for attracting the two plates to each other.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. As described in the section of the prior art, if the tension generated by the coating of the grain-oriented electrical steel sheet is eliminated only at the T-joint, the core characteristics can be improved. As a specific method, in the prior art, this effect was obtained by removing the film, but in the present invention, a compressive stress is applied in the rolling direction to the steel sheet at the yoke portion of the T joint, and the film in the rolling direction is applied. The same effect is obtained by reducing or eliminating the tension.

FIG. 1 shows an apparatus to which the present invention is applied. FIG.
The plate 8 and the plate 9 in (a) are yoke fastening plates divided into two. These plates are connected to the plate located on the back side by appropriately arranged bolts 11, and a tightening force is applied to the yoke by tightening the bolts 11. After the bolt 11 is tightened, the bolt 1 connecting the plate 8 and the plate 9
By tightening 0, compressive stress in the rolling direction is applied to the yoke portion of the T joint. This compressive stress is
It can be controlled by the tightening torque of the bolt 10.

As shown in FIG. 1 (b), a spring 1 is attached to a bolt 15 connecting the plate 13 and the plate 14.
There is also a method in which the stress is transmitted through this spring 16 by adding 6. In this method, the compressive stress applied to the T-joint can be known from the contraction length of the spring 16.

After applying a compressive stress to the T-joint, there is a possibility that the steel sheet in this portion is bent and deformed. In order to prevent the deformation, there is a method in which an auxiliary plate that does not give a tightening force is applied to the T joint, and then the bolt 10 or the bolt 15 is tightened.

Incidentally, in this device, stress is also applied to the leg portion of the T-joint. Compressive stress acts on this portion in a direction perpendicular to the rolling direction, and a problem arises in that the characteristics in rotational magnetization cannot be improved. However, in practice, this region does not pose a problem because the area where the rotational magnetization occurs is relatively small in area.

[0016]

Embodiments of the present invention will be described below.
1 shows an example in which the device shown in FIG. 1B is used for a three-phase three-legged iron core. The compressive stress applied to the T-joint was calculated from the spring constant of the spring 16 and the contraction length. Table 1 shows the result of comparing the core loss and the noise in the state where the bolt 15 is not tightened and in the state where the bolt 15 is tightened. Here, the compressive stress applied to the T-joint with the bolt 15 tightened was 0.5 kg / mm ² .
The electromagnetic steel sheet used for the iron core had a thickness of 0.23 mm and B8
Was 1.91 T, and the excitation conditions were 1.7 T and 50 Hz. The noise was measured at eight locations around the iron core in accordance with the Japan Electrical Manufacturers' Association Standard JEM1117. From Table 1, it can be seen that the use of the method according to the present invention improves the noise and iron loss of the iron core.

[0017]

[Table 1]

[0018]

By using the yoke tightening method of the present invention, it has become possible to reduce the noise and iron loss of the transformer core used conventionally.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment when the method of the present invention is applied to a three-phase three-legged iron core.

FIG. 2A is a structural view of a general three-phase three-legged transformer core. (B) is a structural diagram of a general three-phase five-leg transformer core.

FIG. 3 is a view showing a general fixing method of a three-phase tripod transformer core.

FIG. 4 is a diagram showing a position of a T junction of a three-phase three-legged transformer core.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Three-phase three-legged iron core 2 Three-phase three-legged iron core 3 Three-phase five-legged iron core 4 Three-phase five-leg iron core 5 Band for tightening legs 6 Plate for tightening yoke 7 T Joints 8, 9, 13, 14 Plates for tightening the yoke 10, 15 Bolts for applying a force to attract the plates 11, 17 Bolts for applying a tightening force to the yoke 12, 18 Iron core body 16 Attract the plates to each other Spring to give force

Claims (3)

[Claims] 1. A method for tightening a yoke of a three-phase transformer product iron core using a unidirectional magnetic steel sheet, wherein a yoke main body is tightened by applying a plate to both side surfaces of the yoke. How to tighten the yoke of the iron core. 2. The yoke tightening method for a three-phase transformer core according to claim 1, wherein the plate to be tightened is divided into two parts in the longitudinal direction and is arranged so as not to contact the T joint of the iron core. 3. The yoke tightening method for a three-phase transformer core according to claim 2, further comprising a connecting bolt or a spring for generating a pulling force between the two plates divided into two in the longitudinal direction.