JPH04103109A - Gapped core for transformer - Google Patents

Abstract

PURPOSE:To facilitate adjustment of gap length, and to miniaturize the transformer for a converter by a method wherein gaps of magnetic insulator are provided between the V-shaped junction parts of the main leg and the upper yoke, and lap-junction joint parts are provided between the main legs of the upper yoke, the main legs and side legs. CONSTITUTION:The junction parts between side leg parts 4 and the yokes 5 and the upper yokes 6 are lap-jointed in a picture-frame shape, the main leg 3 and the side leg are coupled by the lower yokes 5, the upper yokes 6 are assembled, and the size G of a gap 7 is adjusted in such a manner that exciting impedance satisfies the value of specification. Even when the total height of the main leg 3 and the gap 7 is different between other legs, they are relatively moved in vertical direction. The magnetic flux generated on one main leg is not permitted to flow to the other main legs, it is allowed to flow passing the side legs 4, the lower yokes 5, and the upper yokes 6, and as a result, the magnetic coupling can be neglected between the main legs, several sets of DC-side windings and AC-side windings can be wound on a polycore as a transformer for a converter, it can be miniaturized, and gap length can also easily be adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a gapped core for a transformer used in a large-capacity semiconductor power conversion device.

(Prior art) A converter transformer used in a semiconductor power conversion device is composed of several unit transformers in which a DC side winding and an AC side winding are wound around a single core, and the DC side winding is There is a so-called series multiple voltage type inverter or converter in which several thyristors are connected in parallel and the AC side winding is connected in series to the power supply or load. , its operation has good properties in terms of fast dissolution, power factor on the power supply side and high frequency.

In a normal transformer, the iron core is made by reducing the gap between the blanked silicon steel plates to reduce magnetic resistance and reduce iron loss.
In order to reduce the excitation current and vibration noise, it is necessary to increase the magnetic resistance to a certain extent by providing a gap in the core of the converter transformer described above for the following two reasons.

■ DC component current is generated due to slight deviations in the on-timing of the thyristor, deviations in control, and differences in impedance characteristics of circuits including transformers. When this DC current flows through the transformer winding, DC bias magnetization occurs in the iron core, causing the iron core to become saturated, increasing the exciting current and deteriorating the characteristics of the power converter. vibration noise increases.

It is difficult to completely prevent this DC bias phenomenon, so even if a DC current of about 1% of the rated current flows, the magnetic resistance of the iron core is increased by providing a gap in the iron core.
Reduce the amount of biased magnetism to prevent iron core saturation.

Therefore, the gap in the iron core must be designed and constructed so as to satisfy the relationship between DC current and the amount of biased magnetism.

(2) Good operation as a power converter cannot be maintained unless the shared voltages of the AC side windings connected in series are made uniform, so the excitation impedance, that is, the magnetic resistance of the iron core, is the same between unit transformers. It is necessary to

Normally, it is difficult to make the magnetic resistance the same due to variations in magnetic properties due to the material of the core and irregularities in the gaps at the joints of the punched plates, but it is necessary to create a gap and measure the gap length for each transformer. By controlling the production so that they are exactly equal, the variation in excitation impedance can be kept within a few percent.

(Problem to be solved by the invention) In conventional power converters, the capacity of the unit transformers required was small and the number of units connected in series was small, so there were problems even with a method in which the core was made independent for each unit transformer. There was no.

However, magnetic levitation railway power converters and stationary non-active power generators that use self-excited inverters for the purpose of stabilizing power systems have large capacities.
The capacity of the unit transformer is large, and the number of units connected in series becomes large, resulting in a large scale.

If the equipment becomes large-scale, the iron core will be large, making it difficult to perform work such as adjusting the gap length, and converters for converters will have large external dimensions and be heavy, making them expensive.

The present invention has been made to solve the above problems,
We provide an iron core with a gap for transformers that allows the gap length to be easily adjusted to match the magnetic resistance of the iron core to the specified value, and that allows multiple unit transformer cores to be configured with one core, making the converter transformer more compact. The purpose is to

[Structure of the invention]

CM problem) In order to achieve the above object, the present invention has a plurality of main legs around which DC side windings and AC side windings are wound. Consists of side legs and a lower yoke and an upper yoke that are joined to the main legs through a V-shaped joint, with a gap of magnetic insulator between the V-shaped joint of the main leg and the upper yoke. The main leg portion of the upper yoke and the lap joint between the main leg and the side leg are provided.

(Function) With this configuration, the core is not independent for each unit transformer, but one unit transformer can be configured with one main leg, so multiple unit transformers can be integrated into one core. It can be made possible by Since a gap is formed in the main leg, the magnetic resistance of the core can be increased, and since the gap is installed above the transformer winding, the magnetic resistance can be adjusted to the specified value simply by removing the upper yoke. The gap length can be easily adjusted. Furthermore, since the shape of the gap is provided to match the V-shaped joint between the main leg and the upper yoke, overheating of the core that tends to occur at this joint can be suppressed.

(Example) An embodiment of the present invention will be described below with reference to FIG.

Figure 1 shows the main landing gear 3 wrapped with DC side winding 1 and AC side winding 2.
There are three side legs 4 on both sides, and these legs are connected to the lower yoke 5 and the upper yoke 6 via a V-shaped joint, and the V-shaped joint between the main leg 3 and the upper yoke 6 is formed. A magnetic insulator gap 7 is provided between the shaped joints, and a lap joint seam 8 is provided between the main leg and between the main and side legs of the upper yoke 6, respectively. Although not shown, a backing plate is attached to each of the main leg 3 and side leg 4, and clamps are attached to the lower yoke 5 and upper yoke 6, and pin tightening is performed using bolts or glass tape.

An enlarged view of the seam 8 seen from above is shown in FIG.

The upper yoke 6 is made by stacking punched silicon steel plates, and the joint 8 is a lap joint between the punched sheets with dimension A, and the left and right upper yokes 6 are magnetically coupled, but the vertical direction is It is constructed so that it can be moved relative to the other.

In a core with a gap, due to the magnetic flux passing through the gap,
The upper yoke 6 and the gap 7 are not shown in the figure because a magnetic attraction force acts between the upper and lower surfaces of the gap and generates vibration noise.
, the main leg 3 and the lower yoke 5 are firmly tightened vertically using tightening studs.

If the upper yoke 6 is a single piece without a seam 8,
By tightening the lower yoke 5 and upper yoke 6 vertically, compressive force is applied to the main leg 3 and side leg 4, but due to manufacturing dimensional tolerances and assembly errors, gaps may occur at the joints or the upper and lower yokes may protrude. If the main leg 3 and the side leg 4 have uneven dimensions in the vertical direction, the gap 7 may not be tightened with an appropriate pressure and vibration noise may increase.

However, in this embodiment, the upper yoke 6 has a seam 8 and is divided for each leg, allowing for relative movement in the vertical direction, absorbing the above-mentioned errors and making the tightening force uniform. This makes it possible to suppress an increase in vibration noise.

Next, a method of adjusting the gap length using this configuration will be explained.

The main leg 3 and the side leg 4 are connected by a lower yoke 5, and the windings are assembled by inserting the DC side winding 1 and the AC side winding 2 from the upper part.
Attach the gap 7 to the upper part of the main leg 3, incorporate the upper yoke 6, and tighten the clamp and upper and lower tightening studs.

Then, an AC power source is connected to the DC side winding 1 or the AC side winding 2, and the excitation impedance of each leg is measured. If the measured excitation impedance does not satisfy the specification value, remove the assembled upper yoke 6, adjust the dimension G of the gap 7, reassemble the upper yoke 6, and adjust the excitation impedance so that it satisfies the specification value. . By adjusting the dimension G of the gap 7 in this way, even if the total height of the main leg 3 and the gap 7 differs between the other legs, the upper yoke 6 has a seam 8, so the upper yoke 6 can be adjusted in the vertical direction. All you have to do is move relative to .

When the temperature of the iron core increases during operation, a difference in elongation due to thermal expansion occurs between the main legs and side legs due to various conditions, which may push and bend the upper yoke 6 or cause excessive bending stress or compressive stress. occurs, magnetostriction increases, and vibration noise due to magnetostriction increases. However, in this embodiment, no unreasonable force is generated due to the action of the joint 8 of the upper yoke 6, so it is possible to suppress the increase in vibration noise due to magnetostriction.

Fig. 3 is a diagram showing the magnetic equivalent circuit of the iron core in Fig. 1, and the power display Ea, Eb, and Ec are the excitation current for causing magnetic flux to flow through the main leg and the winding through which the excitation current flows. This is the magnetomotive force determined by the product of the number of turns. Resistance display Ryu, R
2, R3, R, is the magnetic resistance of each magnetic path, R1 is the magnetic circuit of the main landing gear including the gap 7, R2, R is the magnetic resistance of the lower yoke 5
, R4 is a magnetic circuit corresponding to the upper yoke 6 between the main legs, and R4 is a magnetic circuit corresponding to the lower yoke 5, the upper yoke 6, and the side legs 4 between the main and side legs.

Since the resistor R1 has the gap 7, its value is much larger than the resistors R, , R, , R, which have no gap.

If the resistances R2, R3, and R4 are small and can be ignored compared to the resistance R1, then in Fig. 3, for example, consider the case where the magnetomotive force Ea is generated only in the left main landing gear 3 and the magnetic flux φa flows. , magnetic flux φ1. flowing through the side legs 4 on both sides. φ,
increases, and the magnetic flux φ2. flows through the center and right main landing gears 3.
φ3 is small and can be ignored. The flow of magnetic flux is the same for other main landing gears, and the following can be said.

In other words, the magnetic flux generated in one main landing gear does not flow to the other main landing gear, but instead flows through the side landing gear 4, lower yoke 5, and upper yoke 6, so the magnetic coupling between the main landing gears can be ignored, and the conventional This is equivalent to using a separate iron core for each unit transformer, and there is no problem even if the windings for each main leg are controlled separately, that is, using a pulse width modulation method.

As a means to further reduce the values of the resistors R2, R3, and R4, (a) the side legs 4, the lower yoke 5, and the upper yoke 6 are made of highly oriented materials with high magnetic permeability and better characteristics.

(b) The cross-sectional area of the lower yoke 5 and the upper yoke 6 may be half the cross-sectional area of the main leg in the case of a normal transformer core, but it should be made somewhat larger to lower the magnetic flux density.

(c) Side legs 4 and lower yoke 5. The joint with the upper yoke 6 may be a frame-shaped lap joint, and if necessary, it may be a so-called step-lap structure in which the blanks are joined by shifting them in a stepwise manner.

These joining means are employed in an optimal combination depending on the specifications of the iron core.

FIG. 4 is a diagram showing the flow of magnetic flux at the V-shaped joint between the upper yoke 6 and the main leg 3. The direction indicated by arrow 9 is the rolling direction of the grain-oriented silicon steel sheet.

Magnetic flux flows in that direction to reduce loss. Also, regarding the magnetic flux flowing from the main landing gear 3 through the gap 7 to the upper yoke 6, the upper yoke 6 and the main landing gear 3 are joined in a figure 7 shape with an angle of 45 degrees. , there is no component flowing in the direction perpendicular to the rolling direction, and the loss generated in that part can be kept small and there is no risk of local overheating.

The present invention is not limited to the above-described embodiments, and the number of main landing gears can be changed as desired, and can be applied without changing the gist of the invention.

〔Effect of the invention〕

As explained above, according to the present invention, several sets of DC side windings and AC side windings can be wound around one multiphase core, and the converter transformer can be made compact.
In addition, the external dimensions, weight, and price can be reduced, and the gap length can be easily adjusted, resulting in a rational tightening method that makes the tightening force uniform. It is possible to provide an iron core with a gap for a transformer that can suppress vibration noise caused by magnetostriction of a steel plate.

[Brief explanation of the drawing]

FIG. 1 is a side view of an embodiment of the present invention, FIG. 2 is an enlarged view of the joint shown in FIG. 1, and FIG. 3 is a magnetic equivalent circuit diagram of FIG. 1.
FIG. 4 is an explanatory diagram showing the flow of magnetic flux at the V-shaped joint between the upper yoke and the main leg in FIG. 1. 1.2...DC side winding, AC side winding 3...Main leg 4...Side leg 5.6...
Lower and upper yokes 7... Gap 8... Seam 9... Rolling direction agent Patent attorney Noriyuki Chika

Claims (1)

[Claims] A transformer core comprising an arbitrary number of main legs wrapped with transformer windings, side legs placed on both sides of the main legs, and a lower yoke and an upper yoke that connect these legs, A gap of magnetic insulator is installed between the V-shaped joint between the main landing gear and the upper yoke, and a lap joint is provided between the main landing gear and between the main landing gear and the side landing gear of the upper yoke. An iron core with a gap for transformers featuring the following.