JP2017103348A - Damping structure of stationary induction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vibration damping structure for stationary induction device that can contribute not only to vibration and noise but also to miniaturization of stationary induction device.SOLUTION: A structure includes a vibration damping support portion 5 that extends from the bottom wall 11 of the container 1 to the inside of the container 1 and supports the contents 2 using a container 1 of the stationary induction device capable of accommodating contents 2 of the stationary induction device and an insulating medium 3. The damping support portion 5 has a spring function capable of elastically expanding and contracting in the direction between the bottom wall 11 and the contents 2 and a damper function for attenuating the elastic expansion and contraction of the spring function. The bottom wall 11 has a base portion in which a bottomed tubular peripheral wall 40 recessed at a position facing the contents 2 on the bottom wall inner side surface 11a is formed, and a bottom portion outer side surface 11b of the peripheral wall 40 contacts an installation surface 1a of the stationary induction device.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a vibration damping structure for a stationary induction device such as a transformer or a reactor that is applied to various power facilities.

  As static induction devices such as transformers and reactors applied to electric power facilities, the contents of static induction devices having an iron core and windings attached to the iron core (hereinafter simply referred to as “contents” as appropriate) are used as insulating media. A configuration is known in which a stationary induction device container (hereinafter simply referred to as a container) is housed together with (insulating oil, insulating gas, etc.) and the contents are placed in an insulating medium (for example, impregnated in insulating oil). .

  When such a stationary induction device is operated, the electromagnetic force generated when a current flows through the windings causes the contents to vibrate (winding vibrations and iron core excitation vibrations), and the vibrations are transmitted to the container to generate noise. Can cause. Examples of the propagation of this vibration include propagation through an insulating medium (propagation in oil, etc.), solid propagation (transmission through a content support stand that supports the contents), and the like.

  As a method for suppressing vibration and noise of the stationary induction device, for example, a soundproof wall 82 is installed on the outer peripheral side of the container 81 that houses the contents 2 and the insulating medium 3 as in the stationary induction device 8 shown in FIGS. It is conventionally known to attach the soundproof panel 83 to the outer surface of the container 81. Furthermore, as shown in Patent Document 1, a method of obtaining vibration damping properties by interposing a spring mechanism (such as a helical isolator or a leaf spring) between the inner side surface of the bottom wall of the container and the contents (or a support base for the contents). Is also known.

JP-A-8-316061

  If the spring mechanism as described above is simply interposed between the inner surface of the bottom wall of the container and the contents (or the support base for the contents) to suppress vibration and noise, the container becomes large (for example, the direction between them) May increase the size of the stationary induction device.

  The present invention has been made in view of such technical problems, and it is an object of the present invention to provide a damping structure for a stationary induction device that can contribute to downsizing of the stationary guidance device as well as suppression of vibration and noise. It is said.

  The vibration suppression structure for a stationary induction device according to the present invention is a creation that can solve the above-described problems, and one aspect thereof includes an iron core and the contents of the stationary induction device having a winding wound around the iron core, and a bottom. A stationary induction device container including a wall and a side wall erected from the peripheral edge of the inner surface of the bottom wall, and containing the contents together with an insulating medium; and a vibration damping support portion extending from the bottom wall to the inside of the container to support the contents; The vibration damping support portion has a spring function that can be elastically expanded and contracted in the direction between the bottom wall and the contents, and a damper function that attenuates the elastic expansion and contraction of the spring function.

  In such an aspect, the bottom wall is formed with a bottomed cylindrical peripheral wall that is recessed at a position facing the contents on the inner surface of the bottom wall, and the bottom outer surface of the peripheral wall is in contact with the installation surface of the stationary induction device. The vibration suppression support portion may include a base portion and may have a shape extending from the inner surface of the bottom portion of the peripheral wall to the inside of the container. Further, the vibration damping support portion supports the contents via a support stand provided on the base portion side of the contents, and the support stand extends in a direction intersecting the direction between the two and is larger than the opening portion of the peripheral wall. It may be a shape and located between the opening and the contents. Further, the vibration damping support part supports the contents through a support base provided on the base part side of the contents, the peripheral wall has a reduced diameter part formed on the inner peripheral surface of the side part, and the support base is in the direction between both The shape may be a shape that extends in a direction intersecting with the diameter and is smaller than the opening and larger than the inner diameter side shape of the reduced diameter portion, and is located between the opening and the reduced diameter portion.

  In addition, a rocking restricting material that restricts rocking of the contents in the direction intersecting the direction between the two is provided on the inner surface of the bottom wall, and the rocking restricting material is interposed between the contents and the inner surface of the bottom wall. It may be located opposite to the direction between the two. Alternatively, a rocking restricting material for restricting the rocking of the contents in the direction intersecting the direction between the two is provided on the support base, and the rocking restricting material is interposed between the support base and the inner peripheral surface of the side portion and is disposed in the side portion. It may be positioned facing the peripheral surface.

  Further, the vibration damping support portion may include a spring that is elastically stretchable in the direction between the two and a damper (for example, a piston-type damper) having a damper function that attenuates the elastic expansion and contraction of the spring. Alternatively, the vibration damping support portion may be provided with an anti-vibration rubber that is elastically stretchable in the direction between the two and attenuates the elastic expansion and contraction.

  As described above, according to the present invention, it is possible to contribute to downsizing of a static induction device and suppression of vibration and noise related to the static induction device.

FIG. 3 is a schematic cross-sectional view illustrating the transformer 1 </ b> A of the present embodiment, with the container 1 and the like taken along the line XX in FIG. 2 and facing the inside. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view illustrating a transformer 1A according to the present embodiment, in which a container 1 and the like are cut along a line YY in FIG. The schematic sectional drawing which expands and demonstrates the base part 4 grade | etc., Of FIG. The schematic explanatory drawing explaining the example of fixation with the spring 51 and the support stand 6. FIG. The schematic sectional drawing at the time of applying anti-vibration rubber 50 in transformer 1A (schematic sectional drawing similar to Drawing 1). The schematic sectional drawing at the time of forming the reduced diameter part 43 in the base part 4 of 1 A of transformers (The schematic sectional drawing similar to FIG. 2, the figure which expanded the principal part). The schematic sectional drawing at the time of applying the rocking | fluctuation control material 7 in 1 A of transformers ((A) is a schematic sectional drawing similar to FIG. 1, (B) is a schematic sectional drawing similar to FIG. 2). Schematic explanatory drawing of a general stationary induction device. Schematic explanatory drawing of a general stationary induction device. Schematic explanatory drawing of a general stationary induction device.

  The vibration suppression structure of the stationary induction device according to the embodiment of the present invention is different from a configuration in which a spring mechanism using a simple spring is interposed between the bottom wall and the contents of the container, and the direction between the two It is the structure provided with the damping support part which has a spring function which can be elastically expanded and contracted, and a damper function which attenuates elastic expansion and contraction of the spring function concerned.

  For example, as shown in FIG. 10, a simple coil-shaped spring 84 is interposed between the bottom wall 81a of the container 81 and the contents 2 (the support base 6 in the figure). In this case, even if the desired vibration damping property is obtained and vibration and noise can be suppressed, the stationary induction device 8 may be increased in size (for example, increased in size due to the shape of the spring). Further, there is a possibility that vibration and noise cannot be sufficiently suppressed due to the reason that the elastic expansion and contraction is difficult to attenuate (for example, the periodic vibration of the spring 84 is difficult to converge).

  On the other hand, according to the configuration in which the vibration damping support portion using both the spring function and the damper function is applied as in the present embodiment, the damper function has an effect of easily reducing the elastic expansion and contraction of the spring function. Similarly, the elastic force can be given, and the natural frequency is small and the desired vibration damping property (damping performance or the like) is obtained. Obtaining the desired vibration damping performance by the vibration damping support portion of this embodiment itself can be sufficiently realized by, for example, designing appropriately in consideration of the excitation frequency and natural frequency based on the well-known vibration isolation design theory. It is.

  Therefore, according to this embodiment, it is possible to support the contents while efficiently and sufficiently suppressing the vibration and noise of the stationary induction device as compared with the configuration using the spring mechanism using a simple spring as described above. Thus, it is possible to contribute to downsizing of the stationary induction device.

  In the stationary induction device, the outer surface of the bottom wall of the container is not directly attached to the installation surface 1a such as a concrete foundation, but is installed outside the bottom wall 81a of the container 81 as shown in FIGS. A configuration is known in which installation is performed via an installation base member 85 (for example, H steel as shown in FIG. 10) provided on the side surface 81ab. However, the configuration in which the base member 85 is provided tends to increase the stationary induction device 90 and the installation space in the installation height direction and the like, and a configuration in which a spring 84 or the like is interposed between the bottom wall 81a and the contents 2. There is a possibility that the tendency becomes remarkable.

  Assuming such a tendency, in this embodiment, instead of applying the base material 85 as described above, for example, in the inner surface 11a of the bottom wall 11 as in a container 1 shown in FIGS. By forming the bottomed cylindrical peripheral wall 40 that is depressed at a position facing the contents 2, the bottom outer surface 41 b of the peripheral wall 40 constitutes the base portion 4 in contact with the installation surface 1 a, and the peripheral wall of the base portion 4 The damping support 5 may be provided on the bottom inner side surface 41a of 40. According to the configuration including the base portion 4, not only the base material 85 is unnecessary, but also the configuration in which the base portion 4 is effectively used (configuration in which the installation space for the vibration damping support portion 5 and the base material 85 are shared). It becomes. Therefore, according to the present embodiment, it is possible to reduce the cost of the stationary induction device and contribute to the downsizing of the stationary induction device and the installation space.

  If the vibration suppression structure of the stationary induction device according to the present embodiment is configured to apply the vibration suppression support portion having the spring function and the damper function as described above, it is modified by appropriately applying technical common sense in various fields. Examples of which are shown below.

≪Example of damping structure of stationary induction device≫
The schematic explanatory diagrams of FIGS. 1 to 7 illustrate the vibration damping structure of the transformer 1A according to the present embodiment. In addition, the detailed description is abbreviate | omitted suitably by attaching | subjecting the same code | symbol etc. to the thing similar to FIGS.

  1 to 7 is a container that can be formed using a metal material such as a normal steel plate, for example, and has a substantially flat bottom wall (for example, a disk shape, an elliptical shape, a rectangular shape, etc.). 11 and a cylindrical side wall (a part of the bottom wall 11 in FIG. 1 (the bottom wall 11 side) is reduced in diameter from a peripheral edge of one end surface of the bottom wall 11 (an inner surface 11a described later in FIG. 1). ) 12 and can accommodate the contents 2 and the insulating medium 3. An opening 12a that allows the contents 2 and the insulating medium 3 to be taken in and out of the container 1 is formed at one end of the side wall 12, and a lid 13 that can open and close the opening 12a is provided in the opening 12a. It has been.

  The contents 2 includes an iron core 21 made of, for example, a silicon steel plate or an amorphous magnetic material, and a winding 22 wound around the iron core 21, and is accommodated in the container 1 through the opening 12a, which will be described later. It is supported on the bottom wall 11 via the vibration damping support 5. The core 2 of the contents 2 shown in FIG. 1 to FIG. 3 is provided with three core legs 21a standing in parallel so as to extend in the vertical direction, and provided on the upper end side and the lower end side of each core leg 21a, respectively. The upper end side yoke 21b and the lower end side yoke 21c that extend in the horizontal direction, and the clamping plates 21bb and 21cc that fasten the upper end side yoke 21b and the lower end side yoke 21c are provided. The structure is wound to form a three-phase three-legged structure.

  Then, by filling the container 1 with the insulating medium 3 through the opening 12a, the contents 2 accommodated in the container 1 are immersed in the insulating medium 3. It is possible to connect between the contents 2 and the outer peripheral side of the container 1 (for example, a control panel, etc., not shown) via an extraction terminal (not shown) provided on the lid 13, for example.

  Reference numeral 4 denotes a base portion formed on the bottom wall 11, which has a bottomed cylindrical peripheral wall 40 that is recessed at a position facing the contents 2 on the inner surface 11 a of the bottom wall 11, and a bottom portion of the peripheral wall 40. The outer surface 41b of 41 is in contact with the installation surface (for example, the surface of a concrete foundation or the like) 1a of the transformer 1A. The base part 4 can also be fixed to the installation surface 1a, for example, with a foundation bolt or the like not shown.

  Reference numeral 5 denotes a vibration damping support portion that extends from the bottom wall 11 (an inner side surface 41a, which will be described later in FIGS. 1 to 3) to the inside of the container 1 and supports the contents 2. The bottom wall 11, the contents 2, This has a spring function that can be elastically expanded and contracted in the direction between the two (hereinafter, simply referred to as the direction between the two as appropriate) and a damper function that attenuates the elastic expansion and contraction of the spring function. The contents 2 are supported by such a vibration suppression support portion 5 in a state of being biased in a direction away from the bottom wall 11.

  In the case of the vibration damping support 5 of FIGS. 1 to 3, the end provided on the inner side 41 a of the bottom 41 of the peripheral wall 40 extends from the inner side 41 a to the inside of the container 1, and the end on the side facing the contents 2 is the peripheral wall. 40, which protrudes from the opening 4a of the 40 and supports the contents 2 (a support base 6 which will be described later in FIGS. 1 to 3) in a state of being urged away from the inner side surface 41a of the bottom 41 (for example, as shown in FIG. 3). It is configured to support the gap S with the bottom wall 11.

  According to the transformer 1A as shown in FIGS. 1 to 3, in a situation where the contents 2 vibrate and can be transmitted to the container 1 due to electromagnetic force generated by energizing the winding 22, the vibration is suppressed. It is attenuated by the vibration support part 5. That is, vibration and noise related to the transformer 1 </ b> A are suppressed by the vibration suppression support unit 5.

≪Example of vibration control support part≫
As described above, the vibration damping support portion 5 extends from the bottom wall 11 to the inside of the container 1 and urges the contents 2 in a direction away from the bottom wall 11 (inner surface 41a of the bottom portion 41 in the drawing). As long as the configuration can be supported, various forms can be applied. Further, the vibration damping support unit 5 is based on, for example, a vibration damping design theory. The vibration damping support unit 5 has a vibration damping property (reduction of vibration transmission due to the low natural frequency of the spring and vibration damping rubber and the damping function Vibration properties) and the shape (size, mass, etc.) of the contents 2 can be provided as appropriate, and a plurality of them may be provided instead of just one. In the case of FIGS. 1 to 3, base portions 4 are respectively formed at positions in the extending direction of the respective core legs 21 a on the bottom wall 11, and three restraints are respectively formed on the inner side surfaces 41 a of the bottom portions 41 of the respective base portions 4. The vibration support 5 is arranged in parallel.

  As a specific example of the vibration damping support portion 5, for example, as shown in FIGS. 1 to 3, a spring 51 that is elastically expandable / contractible in the direction between them, and a damper 52 having a damper function that attenuates elastic expansion / contraction of the spring 51, (Hereinafter, referred to as a mechanical configuration as appropriate). As a specific example of the spring 51, for example, as shown in FIG. 4, it is a coil-type spring extending in a coil shape in the direction between the two, and is fixed to the support base 6 via fastening means (bolts or the like) 51a. Possible ones.

  Examples of the damper 52 include a cylinder filled with a fluid and a shock absorber (a piston type damper such as a single cylinder type or a double cylinder type) provided with a piston rod extending and contracting from the cylinder. Various fluids such as oil, gas, and air can be applied as the fluid filled in the cylinder. When the insulating medium in the container 1 is insulating oil, the insulating oil can be used. Is possible. A configuration in which the coiled spring 51 as described above extends concentrically on the outer peripheral side of the shock absorber is also applicable.

  In addition to the mechanical configuration, for example, as shown in FIG. 5, an anti-vibration rubber configuration including an anti-vibration rubber 50 made of a rubber material or the like and having a spring function or a damper function may be applied. As the anti-vibration rubber 50 applied to this anti-vibration rubber configuration, various forms can be applied, for example, an application that is often applied to structures (such as buildings) that require an earthquake-resistant function is applied. Is mentioned.

≪Example of support base and base part≫
The contents 2 may not be directly supported directly by the vibration suppression support part 5 but may be indirectly supported via a support base (iron core base) 6. As the support base, for example, as shown in FIGS. 1 to 5, a flat plate shape that can be interposed between the contents 2 and the vibration suppression support portion 5 and extends in a direction crossing the direction between the two is applied. Is mentioned.

  In the base portion 4, the vibration damping support portion 5 can be provided on the inner side surface 41 a of the bottom portion 41 of the bottomed cylindrical peripheral wall 40 as described above, and the outer side surface 41 b of the bottom portion 41 is installed on the installation surface 1 a. Various configurations are possible as long as they can be configured. For example, as shown in FIG. 3 (and FIG. 6 to be described later), the bottom 41 of the peripheral wall 40 may have a larger diameter than the side 42 to increase the contact area with the installation surface 1a.

  For example, the peripheral wall 40 may have a shape capable of providing the vibration damping support portion 5 (for example, a shape capable of receiving the lower end side (the side provided on the inner side surface 41a) of the vibration damping support portion 5). For example, as shown in FIGS. 1 to 5, in the case where the opening 4 a has a shape smaller than the support base 6 (for example, the opening diameter of the opening 4 a is larger than the support base 6), the vibration damping support section Even if 5 is damaged and cannot support the contents 2 (hereinafter referred to as a damaged state as appropriate), the support base 6 is supported in contact with the edge of the opening 4a, and the opening 4a is sealed. Will be. And the damage object (henceforth a damage object suitably) of the vibration suppression support part 5 is stopped by the area | region inside the surrounding wall 40, and scattering to the container 1 center part side from the said area | region is suppressed.

  Even if the size of the support base 6 is smaller than the opening 4a (even if it is smaller than the opening diameter of the opening 4a), the reduced diameter portion 43 is formed on the inner peripheral surface 42a of the side portion 42 of the peripheral wall 40 as shown in FIG. And the support base 6 is larger than the inner diameter side shape of the reduced diameter portion 43, the region between the reduced diameter portion 43 and the inner side surface 41a inside the peripheral wall 40 (hereinafter referred to as the reduced diameter portion 43 side). A damaged object is fastened to the region (appropriately referred to as a region), and scattering from the region on the reduced diameter portion 43 side to the center portion side of the container 1 is suppressed. In the reduced diameter part 43 of FIG. 6, it protrudes from the inner peripheral surface 42a (between the inner side surface 41a and the opening 4a) of the side part 42 of the peripheral wall 40 toward the axial center side of the peripheral wall 40, The shape extends along the direction and has a step surface 43a on the opening 4a side. With this configuration, in the case of a damage state, the support base 6 is supported in contact with the reduced diameter portion 43 (step surface 43a), and the reduced diameter portion 43 side region is sealed.

  The reduced diameter portion 43 has a shape that does not interfere with the vibration damping support portion 5 provided on the inner side surface 41a of the bottom portion 41, and is configured so that the support base 6 in contact with the damaged state contacts and the region on the reduced diameter portion 43 side is sealed. If it is good. Further, the reduced diameter portion 43 does not have a continuous shape extending along the inner peripheral surface 42a of the side portion 42 as shown in FIG. 6, but, for example, a shape extending intermittently along the inner peripheral surface 42a. Even so, it suffices if the reduced diameter portion 43 side region is sealed by the support base 6 in the damaged state as described above.

≪Others≫
When the transformer 1A as described above is moved (transported, installed, etc.), acceleration occurs in the transformer 1A, and in the contents 2, for example, a weight is applied to the direction intersecting the direction between the two to shake. There is a risk of causing the contents 2 to fall over or be displaced. Therefore, as a method for suppressing the swing of the contents 2, for example, as shown in FIGS. 1, 5, and 7 (A), a part of the side wall 12 (bottom wall 11 side) is reduced in diameter to form the side wall 12. In addition to reducing the gap between the contents 2 and the contents 2, it is possible to appropriately provide a rocking restricting material (so-called anti-swing material) 7 that restricts the rocking of the contents 2 in the direction intersecting the direction between the two.

  The swing restricting material 7 is not particularly limited as long as the swing of the contents 2 can be suppressed. In addition to a material made of the same material as the container 1 (such as one integrally formed with the container 1), For example, a material made of an elastic material such as a rubber material can be used, but a material having durability against the insulating medium 3 is preferably applied.

Further, the swing restricting member 7 can be installed at various positions inside the container 1. As an example, as shown in FIG. 2, by providing a rocking restricting material 7 on the inner surface 11a of the bottom wall 11 (in FIG. 2, the edge surface of the opening 4a and the outer peripheral side of the support base 6). Further, there is a configuration in which the swing restricting material 7 is interposed between the contents 2 and the inner side surface 11a and is positioned opposite to the direction between the contents 2 as shown in FIG. 7B. By providing the swing restricting material 7 on the support base 6 (in FIG. 7B, the inner surface 41a side of the support base 6), the swing restricting material 7 is connected to the support base 6 and the inner peripheral surface 42a. It may be configured to be interposed between the inner peripheral surface 42a and the inner peripheral surface 42a.

  Although the present invention has been described in detail only for the specific examples described above, it is obvious to those skilled in the art that various modifications can be made within the scope of the technical idea of the present invention. It is natural that such changes and the like belong to the scope of the claims. For example, a specific example of the static induction device according to the present embodiment has been described with reference to the drawings and the like showing the transformer 1A. However, the present invention is not limited to the transformer, and may be applied to other static induction devices such as a reactor. It is possible to apply the same effects.

DESCRIPTION OF SYMBOLS 1 ... Container 1a ... Installation surface 1A ... Transformer 11 ... Bottom wall 11a ... Inner side surface of the bottom wall 11b ... Outer side surface of the bottom wall 11 ... Contents 3 ... Insulating medium 4 ... Base part 4a ... Opening part 40 ... Perimeter wall DESCRIPTION OF SYMBOLS 41 ... Bottom part 41a ... Inner side surface of bottom part 41b ... Outer side surface of bottom part 41 ... Side part 42a ... Inner peripheral surface 43 ... Reduced diameter part 5 ... Damping support part 50 ... Anti-vibration rubber 51 ... Spring 52 ... Damper 6 ... Support stand 7 ... Swing restricting material

Claims (8)

The contents of a stationary induction device having an iron core and a winding wound around the iron core;
A container of a stationary induction device having a bottom wall and a side wall erected from the peripheral edge of the inner surface of the bottom wall, and containing the contents together with an insulating medium;
A vibration damping support portion extending from the bottom wall to the inside of the container and supporting the contents,
The vibration damping support portion has a spring function that is elastically stretchable in the direction between the bottom wall and the contents, and a damper function that attenuates the elastic expansion and contraction of the spring function. Shaking structure. The bottom wall is formed with a bottomed cylindrical peripheral wall that is depressed at a position facing the contents on the inner side surface of the bottom wall, and includes a base portion that contacts the installation surface of the stationary induction device with the bottom outer surface of the peripheral wall,
2. The vibration suppression structure for a stationary induction device according to claim 1, wherein the vibration suppression support portion has a shape extending from the inner surface of the bottom portion of the peripheral wall to the inside of the container. The vibration suppression support part supports the contents via a support stand provided on the base part side of the contents,
3. The stationary guide according to claim 2, wherein the support base extends in a direction intersecting the direction between the two and has a shape larger than the opening portion of the peripheral wall, and is located between the opening portion and the contents. Device vibration control structure. The vibration suppression support part supports the contents via a support stand provided on the base part side of the contents,
The peripheral wall is formed with a reduced diameter part on the inner peripheral surface of the side part,
The support base extends in a direction intersecting the direction between the two and has a shape that is smaller than the opening and larger than the inner diameter side shape of the reduced diameter portion, and is located between the opening and the reduced diameter portion. The vibration suppression structure for a stationary induction device according to claim 2. A rocking regulation material for regulating rocking of the contents in the direction intersecting the direction between the two is provided on the inner surface of the bottom wall,
5. The stationary induction device according to claim 1, wherein the swing regulating member is interposed between the contents and the inner side surface of the bottom wall and is positioned to face the direction between the contents. Damping structure. A rocking regulation material for regulating rocking of the contents in the direction intersecting the direction between the two is provided on the support base,
5. The vibration damping structure for a stationary induction device according to claim 3, wherein the swing restricting member is interposed between the support base and the side inner peripheral surface and is positioned to face the side inner peripheral surface.   The vibration damping support portion includes a spring that is elastically expandable and contractable in a direction between the two and a damper having a damper function that attenuates the elastic expansion and contraction of the spring. Damping structure for stationary induction equipment.   The damping structure for a stationary induction device according to any one of claims 2 to 6, wherein the vibration damping support portion includes a vibration-proof rubber that is elastically stretchable in a direction between the two and that attenuates the elastic expansion and contraction. .

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