JPH056330B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-core reactor with an electromagnetic shield.

For example, an AC filter used in a power system is composed of a reactor, a capacitor, and a resistor. In these configurations, not only the inductance but also the resistance of the reactor itself may be used as the resistance for the filter described above, and therefore, the reactor may be designated with an effective resistance.

A conventional air-core reactor of this type is shown in FIGS. 1 and 2. That is, 1 is an air-core coil, 2
is an electrically conductive shield made of copper, aluminum, etc., and is configured, for example, in the shape of a pipe, and is placed around the coil 1. This is usually stored in a steel tank.

Therefore, when designing this type of reactor,
In the case of a filter, first determine the minimum dimensions of the shield 2, such as its height and diameter, from the standpoint of insulation, and then set the coil 1 to a predetermined inductance within the range of the size that can fit into the shield 2. Determine the coil dimensions and number of turns that will yield the desired result. When the effective resistance is specified here, the eddy current loss of coil 1 determined as above,
Find the DC resistance loss. The shortfall in effective resistance due to these factors is considered to occur as a shielding loss of the shield 2.

However, there is a drawback that the effective resistance of the shielding loss of the shield 2 depends on the frequency. That is, when the shield loss of the shield 2 is examined in detail, the shield 2 surrounds the outer periphery of the coil 1 and has an electrically short-circuited structure of one turn, and an electromagnetic induction effect acts between the coil 1 and the shield 2. One of the losses caused by this effect is that the magnetic flux generated by the coil 1 is confined inside the shield 2, and the current due to the electromagnetic coupling between the coil 1 and the shield 2 and one turn in the circumferential direction of the shield are This loss is caused by the resistance of the coil 1, and is similar to the DC resistance of the coil 1. This shield resistance loss
P _R is given by P _R = I ² R ……(1). Here, I is an induced current and R is a shield resistance.

The second loss is an eddy current loss inside the shield caused by the inflow of magnetic flux into the inside of the shield 2 from the inner surface of the shield 2, which is unavoidable. The eddy current loss P _e in this shield is given by P _e =π ² /6ρf ² B ² d ³ (2). Here, ρ is the conductor resistivity, f is the frequency, B is the magnetic flux density, and d is the conductor thickness (Fig. 3: width a and depth b are assumed to be 1).

Among these losses in the shield 2, the seal resistance loss P _R is independent of frequency, but it can be seen that the in-shield eddy current loss P _e is proportional to the square of the frequency.

As a characteristic of the filter reactor, it is desirable that the effective resistance be constant regardless of frequency. Therefore, it is necessary to keep the eddy current loss in the shield low. In actual design examples, when the shield thickness is several mm, the shield resistance loss is the dominant shield loss up to around several hundred Hz, but at even higher frequencies (above several hundred Hz), eddy current in the shield The frequency dependence of loss causes a sudden increase in loss, and the undesirable frequency dependence of the reactor's effective resistance becomes conspicuous.

Therefore, an object of the present invention is to provide an air-core reactor that can improve the frequency characteristics of effective resistance.

A first embodiment of the invention is shown in FIGS. 4 and 5. In other words, this air-core reactor is constructed by stacking a plurality of short-circuited coils 3, which are formed by short-circuiting both ends of a coil wound in two or more turns to form multiple turns, in the axial direction around an air-core coil 1 to form a cylindrical electromagnetic shield. It is composed of 4. Each short-circuit coil 3 has four turns of disc-shaped coils 5a to 5d stacked in four stages and connected to each other in series, and both ends are short-circuited by a lead wire 6, making a total of 16 turns. Fifth
The symbols "1", "2", etc. shown in each conductor in the figure indicate the number of turns of the conductor in ascending order.

Because of this configuration, whereas the conventional pipe-shaped shield 2 was electromagnetically coupled to the reactor coil as a one-turn short-circuit coil, by having two or more turns, it is possible to confine the magnetic flux inside the shield 4. Since the required shield ampere-turns are constant, the current through the shield is reduced by a factor of the number of turns. Therefore, since the cross-sectional area per turn can be reduced, the conductor thickness d in equation (2) can be reduced, eddy current loss in the shield can be reduced, and the frequency dependence of the reactor's effective resistance can therefore be reduced. can be done. On the other hand, the current I in equation (1) is also 1/the number of turns, but the cross-sectional area is 1/the number of turns, and the conductor length is multiplied by the number of turns, so R is the square of the number of turns. After all, _PR is constant.

In addition, the reason why a plurality of such short circuit coils 3 are stacked in the axial direction is that the ampere turns of the shield required to confine the magnetic flux inside the shield change in the axial direction as shown in Figure 6. If short-circuiting coils 3 with a high axial height are used, the ampere-turns within one short-circuiting coil 3 will be constant, so there will be a difference in ampere-turns required as a shield, and magnetic flux will leak out of the shield. This is because it is necessary to avoid Therefore, it becomes necessary to use separate shorting coils for the parts where the ampere-turn curve changes sharply in Figure 6, and the number of shorting coils and the number of turns in each shorting coil should be selected appropriately depending on the specification conditions when designing the reactor. It turns out.

A second embodiment of the invention is shown in FIG. That is, this relates to the structure of the short-circuiting coil 3a constituting the electromagnetic shield, and includes the multilayer cylindrical coils 7a to 7.
The layers d are connected by lead wires 8 as shown in the figure. The symbols in the conductor indicate the increasing number of turns.
Further, its operation and effect are similar to those of the first embodiment.

A third embodiment of the invention is shown in FIG. That is, this relates to the structure of the short-circuiting coil 3b constituting the electromagnetic shield, which is formed by winding a foil-like conductor 9 multiple times in a concentric cylindrical shape, and short-circuiting the inner and outer ends with a lead wire 10 as shown in the figure. ing. Its operation and effect are similar to those of the first embodiment.

A fourth embodiment of the invention is shown in FIG. That is, this air-core reactor uses an electromagnetic shield 4' composed of a short-circuited coil only in a portion near the coil 1 where the amount of magnetic flux is large, and pipe-shaped shields 11a and 11b are used at both ends of the electromagnetic shield 4'.
The result is similar to the first example.

A fifth embodiment of the invention is shown in FIG. That is, in this air-core reactor, instead of the pipe-shaped shield of the fourth embodiment, an electromagnetic shield 3'' consisting of a short-circuited coil having the same structure as described above is surrounded by a pipe-shaped shield 12 having a large height.

As described above, the air core reactor of this invention is
The electromagnetic shield is constructed by stacking multiple short-circuited coils, which are formed by short-circuiting both ends of a coil wound with two or more turns to form multiple turns, around an air-core coil, so the current flowing through the electromagnetic shield is equal to the number of turns. Since the cross-sectional area per turn can be reduced to 1, it is possible to reduce the conductor thickness and reduce eddy current loss, thus improving the frequency dependence of the effective resistance. . Furthermore, since a plurality of short-circuited coils are stacked in the axial direction, leakage of magnetic flux to the outside of the shield can be avoided.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a conventional example, Fig. 2 is a plan view thereof, Fig. 3 is a perspective view of a conductor for explaining eddy current loss, and Fig. 4 is a sectional view of a first embodiment of the present invention. , FIG. 5 is an enlarged sectional view of the short-circuited coil, and FIG.
The figure is an ampere-turn curve diagram, Figure 7 is an enlarged sectional view of the short circuit coil of the second embodiment, Figure 8 is an enlarged sectional view of the short circuit coil of the third embodiment, and Figure 9 is an enlarged sectional view of the short circuit coil of the third embodiment.
FIG. 10 is a half-sectional view of the fifth embodiment. 1... air core coil, 3, 3a, 3b... short circuit coil, 4, 4'... electromagnetic shield.

Claims (1)

[Claims] 1. An air core equipped with an air core coil and an electromagnetic shield formed by stacking a plurality of short-circuited coils in which multiple turns are formed by short-circuiting both ends of a coil wound with two or more turns in the axial direction around the air core coil. reactor.