KR102522618B1 - Vibration isolation assembly for switchboard and switchboard having the same - Google Patents

Abstract

Disclosed are a vibration isolation assembly for a distribution board and a distribution board comprising the same, which may buffer vertical vibration and horizontal vibration applied to a distribution board. To this end, the vibration isolation assembly for a distribution board comprises: a lower fixing member which has an upward accommodating unit upwardly protruding, and is fixed on the ground surface; an upper fixing member which has a downward protrusion unit which downwardly protrudes and is inserted into the central space of the upward accommodating unit, and is fixed at the lower portion of the distribution board; a plurality of lower plate springs which are arranged by being stacked to surround the upward accommodating unit, and buffer the horizontal vibration and vertical vibration applied to the lower portion of the distribution board from the ground surface; a plurality of upper plate springs which are arranged by being stacked to surround the downward protrusion unit, and buffer the horizontal vibration and vertical vibration applied to the lower portion of the distribution board from the ground surface; a horizontal balance plate which is arranged between the uppermost portion of the lower plate springs and the lowermost portion of the upper plate springs; and a spherical bearing which is arranged to be inserted into a hole formed at the central area of the horizontal balance plate, and to which the downward protrusion unit is inserted to buffer the horizontal vibration applied to the lower portion of the distribution board from the ground surface. Therefore, the present invention can be simply installed.

Description

Seismic isolation assembly for switchboard and switchboard including the same {VIBRATION ISOLATION ASSEMBLY FOR SWITCHBOARD AND SWITCHBOARD HAVING THE SAME}

The present invention relates to a seismic isolation assembly for a switchboard and a switchboard including the same, and more particularly, to a seismic isolation assembly for a switchboard for buffering vertical and horizontal vibrations applied to the switchboard and a switchboard including the same.

In general, switchgear facilities have enclosures installed on the ground, so when vibrations or shocks caused by external forces, including earthquakes and explosions, occur, the shock waves are transmitted to the switchgear installed inside the enclosure and damage the electrical equipment installed inside the switchgear. Stable power supply cannot be provided where power is needed, and electric shock accidents may occur due to short circuits.

2. Description of the Related Art In recent years, in Korea, structural collapse accidents and resulting economic losses are increasing due to frequent natural disasters such as earthquakes, so securing the stability of building structures is being treated as important. In particular, in the case of important structures such as power plants or large buildings such as high-rise buildings as well as switchgear facilities installed in various places in various structures, the seismic design standards for earthquakes are being strengthened more than in the past.

However, conventional seismic devices for switchboards have a complicated structure, so the process of installing them on switchboards and maintenance and repair are not easy.

In addition, in terms of seismic performance, conventional earthquake-resistant devices mainly employ coil-shaped springs, and relatively smoothly perform the vibration damping function for vertical vibration. However, components constituting the earthquake-resistant device for horizontal vibration There is a problem in that the vibration damping efficiency is significantly reduced due to separation, damage, and the like.

Therefore, there is a need for a new means capable of securing durability with a simple configuration and stably damping vertical and horizontal vibrations generated by an earthquake to protect switchgear.

Korean Patent Registration No. 10-1768031 (2017. 08. 14.) (seismic unit for switchgear using a dish spring) Korean Patent Registration No. 10-1724102 (2017. 04. 06.) (seismic switchboard that damps seismic force and controls vertical displacement) Korean Patent Registration No. 10-2230259 (2021. 03. 19.) (Earthquake-resistant system and earthquake-resistant device for switchgear providing horizontal and vertical earthquake-resistant force) Korean Utility Model Publication No. 20-2011-0001697 (2011. 02. 18.) (disc spring assembly)

Therefore, the technical problem of the present invention is to focus on this point, and the object of the present invention is to primarily dampen the vibration of the disc spring for vertical vibration caused by external forces such as earthquakes, and for the left and right vibration, the disc spring and the spherical bearing. Together, vibration can be absorbed and shock can be alleviated. In particular, for left and right vibration, slip occurs between dish springs and vibration is damped to improve the seismic performance of facilities including switchboards. An object of the present invention is to provide a seismic isolation assembly for switchgear that can be easily installed in a facility requiring a device.

Another object of the present invention is to provide a switchboard having the above-described seismic isolation assembly for switchboard.

In order to realize the above object of the present invention, a seismic isolation assembly for switchgear according to an embodiment includes a lower fixing member having an upwardly protruding accommodating portion and fixed to the ground; an upper fixing member that protrudes downward and has a downward protrusion inserted into the central space of the upward receiving portion and is fixed to the lower portion of the switchboard; a plurality of lower dish springs that are stacked and disposed to surround the upward receiving portion and absorb left and right vibration and up and down vibration applied to the lower portion of the switchboard from the ground; a plurality of upper dish springs stacked and disposed to surround the lower protrusion and to absorb left and right vibration and up and down vibration applied to the lower portion of the switchgear from the ground; a number average platen disposed between uppermost portions of the lower disc springs and lowermost portions of the upper disc springs; and a spherical bearing disposed so as to be inserted into a hole formed in a central region of the number average template and having the downward protrusion inserted therein to absorb left and right vibration applied to a lower portion of the switchgear from the ground.

In one embodiment, the spherical bearing has a cylindrical shape and includes an outer ring bush inserted into a hole formed in a central region of the number average template; and an inner ring bush having a ball shape having a hollow hole formed therein and disposed on an inner region of the outer ring bush and rotating in the inner region of the outer ring bush in a state where the downward protrusion is inserted.

In one embodiment, the maximum diameter of the downward protrusion may be greater than or equal to the outer diameter of the upward receiving part.

In one embodiment, the downward protrusion has a shape in which the diameter becomes narrower toward the lower end, and may be accommodated in the upwardly receiving portion.

In one embodiment, a first hole is formed in the center of the upward receiving portion, a second hole is formed in the center of the downward protrusion, and the seismic isolation assembly for switchboard is fastened to the first hole through the second hole. A fastening member may be further included.

In one embodiment, each of the lower dish springs may be stacked such that an upwardly-curved dish spring and a downwardly-curved dish spring face each other.

In one embodiment, each of the upper dish springs may be stacked such that an upwardly-curved dish spring and a downwardly-curved dish spring face each other.

In order to realize another object of the present invention described above, a switchgear according to an embodiment includes an enclosure body; and a seismic isolation assembly for a switchgear supporting a lower portion of the enclosure body, wherein the seismic isolation assembly for a switchgear includes: a lower fixing member having an upwardly protruding accommodating portion and fixed to the ground; an upper fixing member that protrudes downward and has a downward protrusion inserted into the central space of the upward receiving portion and is fixed to the lower portion of the enclosure body; a plurality of lower dish springs stacked and arranged to surround the upward receiving portion, and absorbing left and right vibration and up and down vibration applied to the lower portion of the enclosure body from the ground; a plurality of upper dish springs stacked and disposed to surround the lower protrusion and to absorb left and right vibration and up and down vibration applied to the lower portion of the enclosure body from the ground; a number average platen disposed between uppermost portions of the lower disc springs and lowermost portions of the upper disc springs; and a spherical bearing disposed so as to be inserted into a hole formed in a central region of the number average template and having the downward protrusion inserted therein to absorb left and right vibration applied to a lower portion of the switchgear from the ground.

According to the seismic isolation assembly for a switchboard and the switchboard including the same, the lower plate springs and the upper plate springs are arranged in a stacked manner between a lower fixing member fixed to the ground and an upper fixing member fixed to the lower part of the switchboard, so that the left and right by earthquake Vibration and vertical vibration can be dampened, and left and right vibration can be dampened by disposing a spherical bearing in a hole formed in the central region of the number average platen disposed between the uppermost parts of the lower disc springs and the lowermost parts of the upper disc springs.

1 is a side view illustrating a switchgear using a seismic isolation assembly for switchgear according to an embodiment of the present invention.
2 is a perspective view for explaining a seismic isolation assembly for switchgear according to an embodiment of the present invention.
FIG. 3 is an exploded perspective view for explaining the seismic isolation assembly for switchgear shown in FIG. 2;
4 is a cross-sectional view for explaining the seismic isolation assembly for switchgear shown in FIG. 2;
5 is a plan view and a cross-sectional view for explaining the upper fixing member shown in FIG. 2;
FIG. 6 is a plan view and a cross-sectional view for explaining the lower disc spring shown in FIG. 2 .
7 is a perspective view and a cross-sectional view for explaining the spherical bearing shown in FIG. 2;
8 is a plan view and a cross-sectional view for explaining the lower fixing member shown in FIG. 2;

Hereinafter, with reference to the accompanying drawings, the present invention will be described in more detail. Since the present invention may have various changes and various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Like reference numerals have been used for like elements throughout the description of each figure. In the accompanying drawings, the dimensions of the structures are shown enlarged than actual for clarity of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this application, terms such as "comprise" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

In addition, unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

1 is a side view illustrating a switchgear using a seismic isolation assembly for switchgear according to an embodiment of the present invention.

Referring to FIG. 1, a switchgear, distributing board 1 according to the present invention includes an inverter module (not shown), a power receiving and distribution module (not shown), and a transformer (not shown) inside the enclosure body ( 10) and a seismic isolation assembly 100 for switchgear supporting a lower portion of the enclosure body 10.

In the present specification, the switchboard 1 has a low voltage to meet the ratings of various facilities that actually use extra-high voltage electricity supplied from the Korea Electric Power Corporation to monitor, control, and protect the power system so that electrical facilities can be safely used. and equipment that converts to rating. The switchgear 1 is composed of a meter that measures the amount of power, a relay that detects abnormal conditions, and a circuit breaker that cuts off power due to signals from these relays, serving as a safety device for the stable supply of power. It is installed in various forms everywhere that uses electricity, such as commercial or residential buildings, factories, roads, railways, airports, ports, and infrastructure such as water and sewage facilities.

The main power devices built into the switchgear 1 include ALTS (Automatic Load Transfer Switch), ASS (Automatic Section Switch), LBS (Load Breaker Switch), TR(Transformer), VCB(Vacuum Circuit Breaker), ACB(Air Circuit Breaker), MOF(Metering Out Fit; instrument transformer), CT(Current Transformer), PT( Potential Transformer; Instrument Transformer), LA (Lightening Arrester; Lightning Arrester), PF (Power Fuse; Power Fuse), MCCB (Molded Case Circuit Breaker; Circuit Breaker), COS (Cut Out Switch; COS). For safety, these components are installed in a metal enclosure.

In this embodiment, the switchboard 1 is composed of a high voltage switchboard (high voltage/extra high voltage), a low voltage switchboard, a motor control panel, and a distribution panel, and these products can be connected as one system.

The extra high voltage switchgear is a switchgear in which a main circuit is composed of a voltage system exceeding 7000V, and receiving facilities for receiving extra high voltage power supplied from a power plant, substation, etc. to a transmission line are embedded. The extra-high voltage switchboard uses extra-high voltage power devices such as LBS, LA, MOF, PF, CT, VCB, ACB, and TR.

The high voltage switchgear has a main circuit composed of a voltage system with an AC voltage of 7000V or less, and is a switchgear that smoothly supplies the high voltage power transformed from the TR panel of the extra high voltage switchgear to the power load.

The low voltage switchgear is a switchgear that supplies power supplied from the high voltage switchgear to a motor control panel and a distribution panel, and is a power system having an AC rated voltage of 1000V or less and a frequency of 1000Hz or less or a DC rated voltage of 750V or less. used in

The motor control center (MCC) is a switchboard that supplies power supplied from the low voltage switchboard to electric motors installed in water supply pumps, drain pumps, fire water pumps, etc. It is composed of , load half, and auxiliary equipment.

The distribution panel (DP) is a panel used to directly supply power supplied from the low-voltage distribution panel to load facilities such as lighting, air conditioners, computers, and electric heaters in buildings, and includes switches, fuses, cut-out switches, and circuit breakers. It is a switchboard in which power parts such as lights are assembled.

The enclosure body 10 has a rectangular parallelepiped shape, and one or more partition walls (not shown) are provided therein so that the inverter module, the power receiving/distribution module, and the transformer unit can be located, and a plurality of spaces are provided to separate or combine in the horizontal or vertical direction. A section (not shown) is formed. In addition, although not shown in the drawings, basic components such as a PCB, a circuit breaker, a lightning arrester, a fuse, and a switch, and a configuration according to heat radiation and moisture protection are additionally provided inside the space.

A door part 12 is provided on one side of the enclosure body 10 to selectively open the space part. One or a plurality of door units 12 are provided to fully or partially open and close the space, and installation and maintenance of the inverter module, the power receiving/distribution module, and the transformer unit are performed through the door unit 12 .

The door part 12 may be formed in a casement or sliding structure, and an example in which the door part 12 is installed in a casement structure in the switchboard 1 according to the present invention will be described. At this time, a viewing window (not shown) may be provided on the door part 12 so that the operator can check the inside of the enclosure body 10 . The see-through window is made of transparent glass or synthetic plastic material so that the inside of the enclosure body 10 can be checked, and the see-through window can be opened and closed so that a worker's hand or part of the upper body can come in and out. .

In addition, the enclosure main body 10 includes a display unit 13 that indicates generation information of electricity input and output from the inverter module and the power reception/distribution module and whether or not there is an abnormality. The display unit 13 displays the current diagnosis status of the inverter module and the power receiving and distributing module, power generation amount, solar radiation amount, network environment setting, power generation efficiency, and the like, and is preferably disposed on the door unit 12 .

The seismic isolation assembly 100 for switchgear has a function of preventing transmission of vibration generated from one side of the enclosure body 10 or the installation surface to the other side, and a detailed description thereof will be described later.

2 is a perspective view for explaining a seismic isolation assembly for switchgear according to an embodiment of the present invention. FIG. 3 is an exploded perspective view for explaining the seismic isolation assembly for switchgear shown in FIG. 2; 4 is a cross-sectional view for explaining the seismic isolation assembly for switchgear shown in FIG. 2; 5 is a plan view and a cross-sectional view for explaining the upper fixing member shown in FIG. 2; FIG. 6 is a plan view and a cross-sectional view for explaining the lower disc spring shown in FIG. 2 . 7 is a perspective view and a cross-sectional view for explaining the spherical bearing shown in FIG. 2; 8 is a plan view and a cross-sectional view for explaining the lower fixing member shown in FIG. 2;

2 to 8, the seismic isolation assembly 100 for switchgear according to an embodiment of the present invention includes a lower fixing member 110, an upper fixing member 120, a plurality of lower disc springs 130, a plurality of It includes upper conical springs 140, number average platen 150 and spherical bearing 160.

The lower fixing member 110 includes a first square plate part 112 and an upward receiving part 114 protruding upward from the first square plate part 112, and is fixed to the ground. Fastening holes for fixing to the ground are formed in each of the four corner regions of the first square plate part 112 . The upward receiving portion 114 has a cylindrical shape with an open top.

The upper fixing member 120 has a downward protrusion 124 that protrudes downward from the second square play part 122 and the second square plate part 124 and is inserted into the central space of the upward receiving part 114. and is fixed to the lower part of the switchboard (1, shown in FIG. 1). Fastening holes for fixing with the switchgear are formed in each of the four corner regions of the second square plate part 122 . A maximum diameter of the downward protruding portion 124 may be greater than or equal to an outer diameter of the upward receiving portion 114 . In addition, the downward protrusion 124 has a shape in which the diameter becomes narrower toward the lower end, and is accommodated in the upward receiving portion 114 . Accordingly, the downward protruding portion 124 is partially accommodated in the upward receiving portion 114 but not completely accommodated.

The lower dish springs 130 are stacked and disposed to surround the upward receiving portion 114, and absorb horizontal and vertical vibrations applied to the lower portion of the switchgear from the ground. In this embodiment, it is shown that four lower disc springs 130 are disposed, but three or less lower disc springs 130 may be disposed, and five or more lower disc springs 130 may be disposed. It could be. In this embodiment, a dish spring having an upward convex center is disposed at the lowermost part, a dish spring having a downward convex center is disposed at the upper portion, and a dish spring having an upward convex center is disposed at the upper portion thereof. A dish spring having a downward convex center is disposed on the upper portion.

The upper dish springs 140 are stacked on each other to surround the downward protrusion 124, and absorb horizontal and vertical vibrations applied to the lower portion of the switchgear from the ground. In this embodiment, it is shown that four upper disc springs 140 are disposed, but less than three upper disc springs 140 may be disposed, and five or more upper disc springs 140 may be disposed. It could be. In this embodiment, a dish spring having an upward convex center is disposed at the lowermost part, a dish spring having a downward convex center is disposed at the upper portion, and a dish spring having an upward convex center is disposed at the upper portion thereof. A dish spring having a downward convex center is disposed on the upper portion.

The number average template 150 has a square plate shape having a smaller area than the first square plate part 112 and a greater thickness than the first square plate part 112 while covering the lower plate springs 130 . It is disposed between the lower disc spring disposed at the uppermost part of the lower disc springs 130 and the upper disc spring disposed at the lowermost part among the upper disc springs 140. A hole having a larger diameter than the maximum diameter of the downward protrusion 124 of the upper fixing member 120 is formed in the central region of the number average template 150 .

The spherical bearing 160 is disposed to be inserted into a hole formed in the central region of the number average platen 150, and the downward protrusion 124 is inserted to absorb left and right vibration applied to the lower portion of the switchboard from the ground. That is, in a state in which the number average platen 150 is disposed between the lower plate springs 130 and the upper plate springs 140, the spherical bearing disposed in the central region of the number average platen 150 ( 160) can buffer left and right vibration by allowing the downward protrusion 124 of the upper fixing member 120 to smoothly perform the rolling motion.

Specifically, the spherical bearing 160 includes an outer ring bush 162 and an inner ring bush 164 . The outer ring bush 162 has a cylindrical shape and is inserted into a hole formed in the central region of the number average template 150 . The inner ring bush 164 has a ball shape with a hollow hole passing through the top and bottom, and is disposed in the inner region of the outer ring bush 162, and the inner ring bush 162 is in a state where the downward protrusion 124 is inserted. rotate in the area That is, the outer ring bush 162 is inserted into the number average template 150 to maintain a fixed state. In contrast, the inner ring bush 164 is disposed inside the outer ring bush 162 and moves left and right in conjunction with the left and right rotation of the downward protrusion 124 to absorb left and right vibration applied to the switchgear. In this embodiment, the reason for using the spherical bearing 160 is to withstand loads acting in various directions or to absorb shock and vibration by enabling rotation of the downward protrusion 124 inserted into the inner ring bush 164. Because.

The seismic isolation assembly 100 for switchgear according to an embodiment of the present invention may further include a fastening member 170 . Here, a first hole 116 is formed in the center of the upward receiving portion 114, and a second hole 126 is formed in the center of the downward protrusion 124, and the fastening member 170 is the first hole 116. It passes through the second hole 126 and is inserted into the first hole 116 .

As described above, according to the present invention, the lower dish springs and the upper dish springs are arranged in a stacked manner between the lower fixing member fixed to the ground and the upper fixing member fixed to the lower portion of the switchgear to prevent left and right vibration caused by earthquakes. and up-and-down vibration can be dampened, and left-right vibration can be dampened by arranging a spherical bearing in a hole formed in a central region of the number average platen disposed between the uppermost portions of the lower disc springs and the lowermost portions of the upper disc springs. That is, the dish spring primarily damps vibrations caused by external forces such as earthquakes, and the dish spring and spherical bearings absorb vibration together for left and right vibrations to mitigate the impact. For each other, slip occurs between the disc springs, and vibration is damped to improve the seismic performance of facilities including switchboards.

Although the above has been described with reference to examples, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention described in the claims below. You will understand.

10: enclosure body 13: display unit
12: door part 110: lower fixing member
120: upper fixing member 130: lower dish springs
140: upper disc springs 150: number average platen
160: ball bearing 162: outer ring bush
164: inner ring bush 170: fastening member

Claims (8)

a lower fixing member having a first square plate portion and an upward receiving portion protruding upward from the first square plate portion and fixed to the ground;
an upper fixing member having a second rectangular plate portion and a downward protruding portion protruding downward from the second rectangular plate portion and inserted into the central space of the upward receiving portion, and fixed to a lower portion of the switchboard;
a plurality of lower dish springs that are stacked and disposed to surround the upward receiving portion and absorb left and right vibration and up and down vibration applied to the lower portion of the switchboard from the ground;
a plurality of upper dish springs stacked and disposed to surround the lower protrusion and to absorb left and right vibration and up and down vibration applied to the lower portion of the switchgear from the ground;
It has a square plate shape covering the lower disc springs and having a smaller area than the first square plate portion and a greater thickness than the first square plate portion, and disposed between uppermost portions of the lower disc springs and lowermost portions of the upper disc springs. number averaged template; and
A spherical bearing disposed so as to be inserted into a hole formed in a central region of the number average template and having the downward protrusion inserted therein to absorb left and right vibration applied to the lower portion of the switchboard from the ground,
The spherical bearing,
an outer ring bush having a cylindrical shape and maintaining a fixed state by being inserted into a hole formed in a central region of the number average template; and
It has a ball shape with a hollow hole that penetrates vertically and is disposed in the inner region of the outer ring bush, moves left and right in conjunction with the left and right rotation of the downward projection in a state where the downward projection is inserted, Absorbing the left and right vibrations applied to the switchgear A seismic isolation assembly for switchgear, characterized in that. delete The seismic isolation assembly of claim 1, wherein the maximum diameter of the downward protrusion is greater than or equal to the outer diameter of the upward receiving part. The seismic isolation assembly according to claim 1, wherein the downward protrusion has a shape in which a diameter becomes narrower toward a lower end, and is accommodated in the upward receiving portion. The method of claim 4, wherein a first hole is formed in the center of the upward receiving portion,
A second hole is formed in the center of the downward protrusion,
The seismic isolation assembly for switchboard switchgear further comprises a fastening member that passes through the second hole and is fastened to the first hole. The seismic isolation assembly of claim 1, wherein each of the lower disc springs is stacked such that an upwardly curved disc spring and a downwardly curved disc spring face each other. The seismic isolation assembly of claim 1, wherein each of the upper dish springs is stacked such that a dish spring bent upward and a dish spring bent downward face each other. enclosure body; and
A seismic isolation assembly for switchgear supporting a lower portion of the enclosure body, wherein the seismic isolation assembly for switchgear,
a lower fixing member having a first square plate portion and an upward receiving portion protruding upward from the first square plate portion and fixed to the ground;
an upper fixing member having a second square plate part and a downward protrusion protruding downward from the second square plate part and being inserted into the center space of the upward receiving part, and fixed to the lower part of the enclosure body;
a plurality of lower dish springs stacked and arranged to surround the upward receiving portion, and absorbing left and right vibration and up and down vibration applied to the lower portion of the enclosure body from the ground;
a plurality of upper dish springs stacked and disposed to surround the lower protrusion and to absorb left and right vibration and up and down vibration applied to the lower portion of the enclosure body from the ground;
A hole is formed in a central region and has a square plate shape covering the lower disc springs and having a smaller area than the first square plate portion and a greater thickness than the first square plate portion, and the uppermost portion of the lower disc springs and the upper portion of the lower disc springs. a number average platen disposed between the lowermost portions of the upper disc springs; and
A spherical bearing disposed so as to be inserted into a hole formed in a central region of the number average template and having the downward protrusion inserted therein to absorb left and right vibration applied to the lower portion of the switchboard from the ground,
The spherical bearing,
an outer ring bush having a cylindrical shape and maintaining a fixed state by being inserted into a hole formed in a central region of the number average template; and
It has a ball shape with a hollow hole that penetrates vertically and is disposed in the inner region of the outer ring bush, moves left and right in conjunction with the left and right rotation of the downward projection in a state where the downward projection is inserted, Absorbing the left and right vibrations applied to the switchgear A switchboard characterized in that.

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