JPH03190112A - Composite core - Google Patents

Abstract

PURPOSE:To obtain a small type electric machine core having reduced magnetostriction vibration by a method wherein a first electromagnetic steel plate layer having high magnetic flux density characteristics and a second electromagnetic steel plate layer having low magnetostriction characteristics are laminated, the second electromagnetic steel plate layer is formed in the thickness thinner than the first electromagnetic steel plate layer, and a slit is provided on a part of the second electromagnetic steel plate layer. CONSTITUTION:When the voltage, in which high harmonics are superposed on commercial frequency, is applied to a coil 4, the magnetic flux corresponding to the change of voltage is allowed to flow to the composite core consisting of a high magnetic flux density electromagnetic steel plate 1 and a low magnetostriction thin band 2. The high harmonic of the magnetic flux flows to the low magnetostriction thin band easier than flowing to the high magnetic flux density electromagnetic steel plate 1. On the other hand, the greater part of the magnetic flux component of commercial frequency is allowed to flow to the high magnetic flux density electromagnetic steel plate 1. The reason is that the flow of magnetic flux is prevented by a cavity 3. Accordingly, core noise can be reduced sharply by the high harmonic, which gives substantial effect on the core noise, flowing to the low magnetostriction thin band. Also, it is unnecessary to have the core totally composed of the low magnetostriction thin band, the quantity of the low magnetostriction thin band may be one over several integers, and as a result, the core can be formed small in size.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an iron core used as a component of electrical equipment such as transformers and electric motors.

(Prior Art) Iron cores used in electrical equipment such as transformers and electric motors are generally constructed by laminating electromagnetic steel sheets in the shape of an iron core. Ferromagnetic materials such as electrical steel sheets have a phenomenon called magnetostriction.
It is known that its dimensions change when magnetized. Therefore, if the iron core is magnetized with alternating current, the dimensions change due to magnetostriction and the iron core vibrates, resulting in noise.

On the other hand, recently, it has become common to drive electrical equipment using inverters. The output current or voltage of an inverter includes harmonics caused by turning on and off semiconductor elements. Therefore, harmonics are included in the magnetostrictive vibration of the iron core and the resulting noise.
Moreover, since the frequency is within a range that is uncomfortable for the human body, there is a strong desire to reduce the noise.

As a method to reduce such magnetostrictive vibrations,
By selecting the chemical composition of the alloy, we create a steel plate with low magnetostriction.
There is a method of configuring an iron core using this. However, such materials generally have a low saturation magnetic flux density, resulting in an unavoidable increase in core size.

(Problems to be Solved by the Invention) Therefore, there has been a need for a technology that reduces magnetostrictive vibration and noise without increasing the size of the iron core.

The present invention aims to improve the above-mentioned drawbacks of the prior art, and aims to provide an electrical equipment iron core that reduces magnetostrictive vibration and is also advantageous in terms of size reduction. There is.

[Structure of the invention]

(Means for Solving the Problems) A composite core according to the present invention has a first core having high magnetic flux density characteristics.
An electromagnetic steel sheet layer and a second electromagnetic steel sheet layer having low magnetostriction characteristics are laminated in the shape of an iron core, the thickness of the second electromagnetic steel sheet layer being thinner than the thickness of the first electromagnetic steel sheet layer, and It is characterized in that a slit is provided in at least a part of the 21st magnetic steel sheet layer.

In the present invention, the first electromagnetic steel sheet layer itself can also be constructed by laminating a plurality of electromagnetic steel sheets by step stacking.

The iron core of the present invention is made of an electromagnetic steel sheet that has a reduced saturation magnetic flux density by reducing the amount of added alloy elements such as pure iron or Si, and a low magnetostrictive magnetic material such as a 6.5% 5i-Fe alloy. By combining these two methods, the aim is to produce an iron core for electrical equipment that is suitable for reducing the size of the iron core and has low noise characteristics.

FIG. 1 shows the basic configuration of the present invention. The iron core is composed of a high magnetic flux density electrical steel sheet 1 and a low magnetostriction ribbon 2.
This is linked to coil 4.

Furthermore, a gap (slit) 3 is provided in the magnetic path formed by the low magnetostriction ribbon 2.

Now, consider a case where a voltage in which harmonics are superimposed on a commercial frequency is applied to the coil 4. Magnetic flux corresponding to this voltage change flows through a composite core consisting of two high magnetic flux density electrical steel sheets (first electrical steel sheet layer) 1 and low magnetostrictive ribbons (second electrical steel sheet layer) 2. It is easier for harmonic components of the magnetic flux to flow through the low magnetostriction ribbon 2 than through the high magnetic flux density electrical steel sheet 1. This is because the current induced in the steel plate by the flow of harmonic magnetic flux obstructs the flow of magnetic flux, but since the low magnetostrictive thin ribbon 2 has a thin plate thickness, the current induced within the steel plate is reduced. This is because the current is small (as a result, the magnetic permeability to harmonic magnetic flux becomes relatively high with respect to the high magnetic flux density electrical steel sheet 1).

On the other hand, the commercial frequency magnetic flux component flows more into the high magnetic flux density electrical steel sheet 1. This is because the frequency of commercial frequency magnetic flux is not high, so the influence of eddy currents that hinder magnetization is small. (slit) 3 is
This is to block the flow of magnetic flux. The fact that the commercial frequency magnetic flux component is difficult to flow into the low magnetostrictive thin ribbon 2 means that it is difficult to be saturated, and the permeability of the low magnetostrictive thin ribbon 2 to harmonic magnetic flux is prevented from decreasing due to saturation.

As a result, a large amount of commercial frequency magnetic flux flows through the high magnetic flux density electrical steel sheet 1, while a large amount of harmonic magnetic flux flows through the low magnetostriction ribbon 2.

Therefore, the harmonic magnetic flux, which has a large effect on iron core noise, flows through the low magnetostriction ribbon, thereby significantly reducing noise.

In addition, the present invention is superior in that it is not necessary to make all of the core's constituent materials from low magnetostrictive thin ribbons, and this can usually be made by a few fractions of the total amount, so the core can be made smaller. .

(Example) Hereinafter, the present invention will be explained with reference to Examples.

FIG. 2 shows an example in which the present invention is applied to a transformer.

This core is a wound core consisting of an outer core (first magnetic steel sheet layer) 5 and an inner core (second m magnetic steel sheet layer) 6. of steel plate,
The inner core 6 has a wound structure of a 6.5% silicon steel ribbon having a thickness of 0.35 mm, for example. In this example, the ratio of the inner core to the total cross-sectional area of the core was 25%.

The transformer is assembled by inserting the annealed core into the coil 8, which has been prepared in advance, in multiple pieces.
Both silicon steel ribbons have a cut section at the upper yoke position of the iron core, and during assembly, this section can be opened once, inserted into the coil, and then rejoined.

The inner core 6 is joined at the upper yoke position by a butt joint, but an insulating paper 7 is sandwiched therebetween as a magnetic gap.

FIG. 3 shows an enlarged side view of the outer core 5 at the upper yoke position. The joints of the pure iron electromagnetic steel sheets 9 constituting the outer core have a step-overlap joint structure, thereby reducing the influence of the voids 10 at the butt portions of the steel plates, which cannot be completely reduced to zero in practice. .

The electrical resistance of electrical steel sheets increases depending on the amount of St, which is a main additive element. For example, the electrical resistivity when containing 6.5% Si is about 80×10-8 Ω・m, whereas the electrical resistivity of pure iron-based or low-Si electrical steel sheets containing 0 to 0.5% Si is less than 20×10′Ω·m.

Therefore, the outer core made of pure iron-based electrical steel sheet has a small amount of added elements, so while it has a high saturation magnetic flux density, it has a low electrical resistance and allows eddy current to easily flow, as shown in Figure 4. As the frequency increases, the magnetic permeability decreases.

On the other hand, the inner core made of 6.5% silicon steel ribbon has a thin plate thickness and high electrical resistance, so it produces less eddy current and less decreases in magnetic permeability when the frequency increases.

If the magnetic gap created by sandwiching insulating paper between the inner core is too long, the magnetic permeability will decrease not only for commercial frequencies but also for harmonics, and on the other hand, if it is too short, the commercial frequency magnetic flux will decrease. It flows a lot and approaches saturation, resulting in a decrease in magnetic permeability to harmonics. In order to avoid this, the effective air gap length should be set to 0.1 per meter of iron core magnetic path.
It is preferable to set it as the range of -11I11. Note that the lower limit of this gap length of 0.1 m+s can be further reduced by using a material with higher magnetic permeability as the material of the outer core.

In the case of the above example, the effective length of the air gap provided in the inner core was 0.4 mm per 1 m of the core magnetic path. As a result, the average relative magnetic permeability of the inner core can be set to about 2000 for both commercial frequencies and harmonics. This value is
It is significantly lower than the magnetic permeability of the outer core for commercial frequencies.
It is also much higher than the magnetic permeability to harmonics. Therefore, a large amount of the commercial frequency magnetic flux component flows to the outer core, and a large amount of the harmonic magnetic flux component flows to the inner core.

The magnetostriction of silicon steel is usually shown in Figure 5 (I?, M, Bozo
-rth, according to Ferron+agnetisn+), it decreases with the amount of Si, and 6 to 7 wt% S
It is known that it is the lowest among i. The 6.5% silicon steel ribbon used as the inner core in this example was
The core material has extremely low magnetostriction, so the magnetostrictive vibration of the inner core is extremely small.

FIG. 6 shows the proportion of the total harmonic magnetic flux that flows through the inner core when the harmonic frequencies are IKHz and 2KHz. The cross-sectional area of the inner core is 25% of the total core cross-sectional area.
Approximately 7096 of the harmonic magnetic flux flows through the inner iron core even though it is only .

As a result, the harmonic magnetostrictive vibration of the iron core is significantly reduced, making it possible to obtain a low-noise transformer.

In the above embodiments, the present invention was applied to a transformer core. However, similar effects can be obtained by applying this to a rotating machine core. Harmonic vibrations in an inverter-driven motor are not only caused by electromagnetic force based on harmonic current components flowing through the coils, but also magnetostrictive vibrations of the iron core cannot be ignored. However, by combining two types of core materials to form a composite core, a low magnetostrictive motor core can be obtained.

FIG. 7 shows a motor stator core punched plate 11 made of a high magnetic flux density electromagnetic steel sheet and has no joints.

On the other hand, FIG. 8 shows a core punched plate using a low magnetostrictive electromagnetic steel sheet, which is divided into four segments 12. A slight air gap 13 is created at the joint between the segments. As a result of assembling the motor stator core by laminating these core punched plates 11 and 12, noise could be reduced.

In the above two examples, a 6.5% silicon steel ribbon was used as the low magnetostriction electrical steel sheet, but if a Co-based low magnetostriction amorphous alloy is used, the harmonic frequency will further increase. Even if the price is higher, the same effect can be obtained.

In addition, although a pure iron electrical steel sheet was used as the high magnetic flux density electrical steel sheet, the same effect can be obtained even with ordinary silicon steel ribbon if it can be operated at a higher magnetic flux density than low magnetostrictive material. be able to.

〔Effect of the invention〕

In the composite core according to the present invention, a first electromagnetic steel sheet layer having a high magnetic flux density characteristic and a second electromagnetic steel sheet layer having a low magnetostriction characteristic are laminated in the shape of an iron core, and the thickness of the second electromagnetic steel sheet layer is set to be the same as that of the first electromagnetic steel sheet layer. Since it is formed thinner than the thickness of the electromagnetic steel sheet layer, it has an excellent effect in reducing magnetostrictive vibrations, and is also advantageous in that it can be made smaller in size.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the basic configuration of the present invention, and FIG. 2 is an explanatory diagram showing the basic configuration of the present invention.
FIG. 3 is a partially enlarged view of the yoke core, FIG. 4 is a graph showing the relative magnetic permeability of pure iron electrical steel sheets, and FIG. 5 is a graph showing the relative permeability of a silicon-iron alloy. FIG. 6 is a graph showing the magnetostriction, and FIG. 6 is a graph showing the ratio of core harmonic magnetic flux flowing to the inner core in the example. FIG. 7 is a plan view of the core punched plate of the high magnetic flux density electrical steel sheet in the example. The figure is a plan view showing the shape of a core punched plate of a low magnetostrictive ribbon. 1... High magnetic flux density electrical steel sheet, 2... Low magnetostrictive ribbon, 3
．． 10.13... air gap, 4.8... coil.

Claims (1)

[Claims] A first electromagnetic steel sheet layer having high magnetic flux density characteristics and a second electromagnetic steel sheet layer having low magnetostriction characteristics are laminated in the shape of an iron core,
A composite core characterized in that the thickness of the second electromagnetic steel sheet layer is thinner than the thickness of the first electromagnetic steel sheet layer, and a slit is provided in at least a part of the second electromagnetic steel sheet layer. .