JP7481276B2 - Switchgear - Google Patents

Description

This application relates to switchgear.

In a switchgear in which a DC circuit breaker is installed, a ventilation port is provided in the ceiling plate of the switchgear panel to exhaust heat generated in the DC circuit breaker to the outside of the switchgear panel, and a ventilation tower with a ventilation port is provided to cover the ventilation port. Heat generated in the DC circuit breaker is exhausted to the outside of the switchgear panel from the ventilation port of the ventilation tower. (See Patent Document 1)

When a DC circuit breaker interrupts current, an arc occurs between the contacts and is extinguished in the arc extinguishing chamber, generating high-temperature, high-pressure hot gas and high-temperature metal particles. The high-temperature, high-pressure hot gas and high-temperature metal particles are released from the arc extinguishing chamber into an arc space frame located between the top of the arc extinguishing chamber and the ventilation opening in the ceiling plate of the switchgear panel. This arc space frame prevents metal particles from scattering into the switchgear panel.

The high-temperature, high-pressure hot gas released into the arc space frame is exhausted through a ventilation connection in the ceiling plate of the switchgear panel and out of the switchgear panel through the ventilation tower's ventilation port. As the high-temperature, high-pressure hot gas is exhausted, some of the high-temperature metal particles are also exhausted out of the switchgear panel through the ventilation tower's ventilation port.

Japanese Patent Application Laid-Open No. 62-206723

In the conventional switchgear described above, the arc space frame is filled with high-temperature, high-pressure hot gas and high-temperature metal particles that are released from the arc extinguishing chamber into the arc space frame. It is necessary to efficiently exhaust the hot gas outside the panel while preventing the metal particles from being released outside the panel.

However, conventional switchgears have problems in that it is difficult to increase the efficiency of exhausting the hot gas that fills the arc space frame, and it is also difficult to prevent metal particles from being released outside the panel.

As DC circuit breakers become smaller, efforts are being made to reduce the size of the arc space frame, which further reduces the efficiency of hot gas exhaust and increases the amount of metal particles released outside the panel.

This application discloses technology to solve the problems described above, and its purpose is to provide a switchgear that improves the efficiency of hot gas exhaust and suppresses the release of metal particles outside the panel.

The switchgear disclosed in this application is a switchgear having a DC circuit breaker, an arc extinguishing chamber arranged above the DC circuit breaker, a ventilation duct formed in the panel ceiling plate, a ventilation tower communicating with the ventilation duct, and an arc space frame arranged between the arc extinguishing chamber and the ventilation duct, and is provided with a shielding structure attached to the arc space frame, the shielding structure being composed of a plurality of shielding plates arranged at an angle, a shielding plate mounting frame to which the shielding plates are attached, and a panel mounting frame to which the shielding plate mounting frame is fixed and which is attached to the arc space frame.

The switchgear disclosed in the present application is a switchgear having a DC circuit breaker, an arc extinguishing chamber arranged above the DC circuit breaker, a ventilation duct formed in a panel ceiling plate, a ventilation tower communicating with the ventilation duct, and an arc space frame arranged between the arc extinguishing chamber and the ventilation duct, and is provided with a first shielding structure attached to the arc space frame, and a second shielding structure attached to the arc space frame and arranged downstream of the first shielding structure, the first shielding structure being composed of a plurality of first shielding plates arranged at an incline, a first shielding plate mounting frame to which the first shielding plates are attached, and a first panel mounting frame to which the first shielding plate mounting frame is fixed and attached to the arc space frame, and the second shielding structure being composed of a plurality of second shielding plates arranged at an incline, a second shielding plate mounting frame to which the second shielding plates are attached, and a second panel mounting frame to which the second shielding plate mounting frame is fixed and attached to the arc space frame.

The switchgear disclosed in this application can increase the efficiency of hot gas exhaust and suppress the release of metal particles outside the panel.

FIG. 1 is a cross-sectional view showing a switchgear according to a first embodiment. FIG. 2 is a cross-sectional view showing a shielding structure in the switchgear according to the first embodiment. FIG. 2 is a perspective view showing a shielding structure in the switchgear according to the first embodiment. FIG. 11 is a cross-sectional view showing a shielding structure in a switchgear according to a second embodiment. FIG. 11 is a perspective view showing a shielding structure in a switchgear according to a second embodiment. FIG. 11 is a cross-sectional view showing a shielding structure in a switchgear according to a third embodiment. FIG. 11 is a cross-sectional view showing a shielding structure in a switchgear according to a fourth embodiment. FIG. 13 is a cross-sectional view showing a shielding structure in a switchgear according to a fifth embodiment. FIG. 13 is a perspective view showing a shielding structure in a switchgear according to a fifth embodiment. FIG. 13 is a front view showing a shielding structure in a switchgear according to a sixth embodiment. FIG. 13 is a perspective view showing a shielding structure in a switchgear according to a sixth embodiment.

Embodiment 1.
A first embodiment of the present invention will be described below with reference to Figures 1 to 3, in which the same or corresponding members and parts are denoted by the same reference numerals. Figure 1 is a cross-sectional view of a switchgear according to the first embodiment, showing a state in which a contact in a DC circuit breaker is in an opening operation. Figure 2 is a cross-sectional view of a shielding structure in the switchgear according to the first embodiment. Figure 3 is a perspective view of a shielding structure in the switchgear according to the first embodiment.

First, the configuration of the DC circuit breaker 101 will be described with reference to Figure 1. When a current is passed through the DC circuit breaker 101, an upper conductor 103 is arranged at the bottom of an arc-extinguishing chamber 102 in which an arc-extinguishing space is formed, and a lower conductor 104 is arranged below the upper conductor 103. The fixed side main contact 105 connected to the upper conductor 103 comes into contact with a movable side main contact 107 connected to a movable element 106 connected to the lower conductor 104, and the movable element 106 passes a current through the upper conductor 103 and the lower conductor 104.

When a fault current flows during current interruption, the overcurrent detector 108 located on the lower conductor 104 detects the overcurrent and operates, and when current is passed through, the latch 109 that holds the movable member 106 is released, causing the movable member 106 to rotate clockwise around the rotating shaft 110 and perform an opening operation. The fixed main contact 105 and the movable main contact 107 are stored inside the arc extinguishing chamber 102, and above the fixed main contact 105 and the movable main contact 107, arc contacts that generate an arc K during interruption are located, and are composed of a fixed arc contact 111 and a movable arc contact 112.

During the opening operation, the fixed side arc contact 111 and the movable side arc contact 112 open with a delay after the fixed side main contact 105 and the movable side main contact 107 open, thereby preventing arc K from occurring in the fixed side main contact 105 and the movable side main contact 107 and causing melting, and protecting the fixed side main contact 105 and the movable side main contact 107.

Arc horns are arranged above the fixed arc contact 111 and the movable arc contact 112 to divert the generated arc K and guide it to the top of the arc extinguishing chamber 102, and the arc horns are composed of a fixed arc horn 113 and a movable arc horn 114.

A number of grids 115a made of thin magnetic plate-like material are arranged on the upper side of the arc extinguishing chamber 102, and the grid assembly 115 of the grids 115a has an exhaust port 116 on the upper side for exhausting the arc gas to the outside of the arc extinguishing chamber 102 by increasing the arc voltage and limiting the current by extending the electrode drop voltage and the arc length.

A circuit breaker upper opening 130 is provided on the upper side of the exhaust port 116 of the arc extinguishing chamber 102, and a ventilation communication port 140, for example of a rectangular shape, is provided in the panel ceiling plate 100a of the switch gear 100 above the circuit breaker upper opening 130, and an arc space frame body 120 is provided between the circuit breaker upper opening 130 and the ventilation communication port 140.

A ventilation opening 140 is formed in the panel ceiling plate 100a of the switch gear 100, and a ventilation tower 150 is provided above the ventilation opening 140, and the ventilation tower 150 is provided so as to cover the ventilation opening 140.

Next, the shielding structure 200 attached to the arc space frame 120 will be described. The shielding structure 200 is configured as follows. A plurality of shielding plates 201a, 201b, 201c, and 201d are arranged at an incline with respect to the emission direction HM of the high-temperature, high-pressure hot gas and high-temperature metal particles. Both sides of the plurality of shielding plates 201a, 201b, 201c, and 201d are formed with bent mounting portions 201a1, 201b1, 201c1, and 201d1, respectively. The inclination angle of the plurality of shielding plates 201a, 201b, 201c, and 201d is arranged at an angle of about 45 degrees, for example, with an upward slope to the right, but is not limited to this inclination angle.

The bent mounting portions 201a1, 201b1, 201c1, and 201d1 of the shielding plates 201a, 201b, 201c, and 201d, respectively, are attached to the shielding plate mounting frame 202. The shielding plate mounting frame 202 is fixed to the board mounting frame 203. The board mounting frame 203 is then attached to the arc space frame 120, forming the shielding structure 200.

In addition, U-shaped reinforcing bodies 204a, 204b, 204c, and 204d are provided on the upper surfaces of the shielding plates 201a, 201b, 201c, and 201d to reinforce the shielding plates 201a, 201b, 201c, and 201d. The shape of the reinforcing bodies 204a, 204b, 204c, and 204d is not limited to a U-shape. In addition, if the shielding plates 201a, 201b, 201c, and 201d can withstand the high pressure of hot gas and metal particles, it is not necessarily necessary to provide the reinforcing bodies 204a, 204b, 204c, and 204d.

2, when viewed from the panel ceiling panel 100a side of the switch gear 100, the shielding plates 201a and 201b, and the shielding plates 201c and 201d are arranged in an overlapping state, so that high-temperature and high-pressure hot gas and high-temperature metal particles are not directly released into the ventilation communication port 140 of the switch gear 100. Also, when viewed from the panel ceiling panel 100a side of the switch gear 100, the shielding plates 201b and 201c are arranged in a non-overlapping state, but the shielding plates 201b and 201c may be arranged in an overlapping state.

Next, the ventilation direction will be described. When the fixed main contact 105 and the movable main contact 107 are separated during the opening operation of the fixed arc contact 111 and the movable arc contact 112, an arc K is generated between the fixed main contact 105 and the movable main contact 107, and the arc gas fills the arc extinguishing chamber 102 and is ejected from the exhaust port 116 toward the upper circuit breaker opening 130.

When the arc gas is ejected upward from the exhaust port 116, it is ejected as a high-temperature, high-pressure hot gas, and high-temperature metal particles are also ejected at the same time. An arc space frame 120 is provided to prevent the metal particles from scattering onto the equipment inside the switchgear 100.

The action of the shielding structure 200 attached to the arc space frame 120 will be explained. The high-temperature, high-pressure hot gas and high-temperature metal particles ejected into the arc space frame 120 collide with the undersides of the shielding plates 201a, 201b, 201c, and 201d, and the high-temperature, high-pressure hot gas flows smoothly along the inclination direction of the undersides of the shielding plates 201a, 201b, 201c, and 201d, circulates to the ventilation communication port 140 side at the top of the arc space frame 120, and is released outside the board from the ventilation tower 150.

By arranging the shielding plates 201a, 201b, 201c, and 201d at an angle, the cross-sectional area of the ventilation flow path can be increased, improving the efficiency of exhausting the hot gas filling the arc space frame 120.

Since the hot gas can be smoothly exhausted outside the panel of the switchgear 100, the pressure load on the DC circuit breaker 101 during current interruption can be reduced, and damage to the panel structure of the switchgear 100 or the DC circuit breaker 101 can be prevented.

In addition, the high-temperature metal particles collide with the lower surfaces of the shielding plates 201a, 201b, 201c, and 201d, stopping their upward ascent, and thus significantly suppressing the release of the high-temperature metal particles outside the plate. Note that, in the direction HM of the release of the high-temperature, high-pressure hot gas and high-temperature metal particles, the high-temperature metal particles attempt to rise in the small space between the shielding plates 201b and 201c, but the rise of the metal particles is stopped by the collision with the lower surface of the shielding plate 201b, but some of the metal particles are collided with by some of the metal particles flowing along the inclined surface of the lower surface of the shielding plate 201b, and the rise is stopped.

Embodiment 2.
Fig. 4 is a cross-sectional view showing a shielding structure in a switchgear according to embodiment 2. Fig. 5 is a perspective view showing a shielding structure in a switchgear according to embodiment 2.

In the above-mentioned embodiment 1, the multiple shielding plates 201a, 201b, 201c, and 201d are arranged with an inclination angle that rises to the right, but in this embodiment 2, they are arranged with an inclination angle that is opposite to the inclination angle of the above-mentioned embodiment 1, that is, an inclination angle that rises to the left. In this embodiment 2, the operation is the same as in the above-mentioned embodiment 1, and the same effect is achieved.

Embodiment 3.
FIG. 6 is a cross-sectional view showing a shielding structure in a switchgear according to a third embodiment.

In this third embodiment, the inclination angles of the shielding plates 201a and 201b and the inclination angles of the shielding plates 201c and 201d are arranged in opposite directions. That is, the shielding plates 201a and 201b are inclined to the right, and the shielding plates 201c and 201d are inclined to the left. Alternatively, the shielding plates 201a and 201b may be inclined to the left, and the shielding plates 201c and 201d may be inclined to the right.

In this embodiment 3, the operation is the same as in the above-mentioned embodiments 1 and 2, and the same effects are achieved. In addition, by arranging the shielding plate 201b and the shielding plate 201c at inclination angles in opposite directions, it is possible to cause some of the metal particles rising along the lower surface of the shielding plate 201b to collide with some of the metal particles rising along the lower surface of the shielding plate 201c, thereby further suppressing the rise of the metal particles.

Embodiment 4.
FIG. 7 is a cross-sectional view showing a shielding structure in a switchgear according to a fourth embodiment.

In this fourth embodiment, the inclination angles of the shielding plates 201a and 201c and the inclination angles of the shielding plates 201b and 201d are arranged in the opposite directions. That is, the shielding plates 201a and 201c are inclined to the right, and the shielding plates 201b and 201d are inclined to the left. Alternatively, the shielding plates 201a and 201c may be inclined to the left, and the shielding plates 201b and 201d may be inclined to the right.

In this embodiment 4, the operation is the same as in the above-mentioned embodiments 1 to 3, and the same effect is achieved. In addition, by arranging the shielding plate 201a and the shielding plate 201b and the shielding plate 201c and the shielding plate 201d at an inclination angle in the opposite direction, it is possible to collide a part of the metal particles rising along the lower surface of the shielding plate 201a with a part of the metal particles rising along the lower surface of the shielding plate 201b, and it is possible to collide a part of the metal particles rising along the lower surface of the shielding plate 201c with a part of the metal particles rising along the lower surface of the shielding plate 201d, and it is possible to further suppress the rise of the metal particles. In addition, since the shielding plate 201b and the shielding plate 201c are installed so that there is substantially no space between them, it is possible to prevent the release of high-temperature and high-pressure hot gas and high-temperature metal particles from between the shielding plate 201b and the shielding plate 201c.

Embodiment 5.
Fig. 8 is a cross-sectional view showing a shielding structure in a switchgear according to embodiment 5. Fig. 9 is a perspective view showing a shielding structure in a switchgear according to embodiment 5.

A first shielding structure 300 is attached to the arc space frame 120, and a second shielding structure 400 is attached to the arc space frame 120 downstream of the first shielding structure 300. The first shielding structure 300 is configured as follows.

The multiple first shielding plates 301a, 301b, 301c are arranged at an incline with respect to the release direction HM of the high-temperature, high-pressure hot gas and high-temperature metal particles. Both sides of the multiple first shielding plates 301a, 301b, 301c are formed with first mounting portions 301a1, 301b1, 301c1 that are bent. The inclination angle of the multiple first shielding plates 301a, 301b, 301c is arranged at an angle of approximately 45 degrees, for example, with a left-shouldered upward slope, but is not limited to this inclination angle.

The first mounting portions 301a1, 301b1, and 301c1 bent on the first shielding plates 301a, 301b, and 301c, respectively, are attached to the first shielding plate mounting frame 302. The first shielding plate mounting frame 302 is fixed to the first panel mounting frame 303. The first panel mounting frame 303 is then attached to the arc space frame 120, forming the first shielding structure 300.

In addition, first reinforcing bodies 304a, 304b, 304c, which are U-shaped, are provided on the upper surfaces of the first shielding plates 301a, 301b, 301c to reinforce the first shielding plates 301a, 301b, 301c. The shape of the first reinforcing bodies 304a, 304b, 304c is not limited to a U-shape. Note that if the first shielding plates 301a, 301b, 301c can withstand the high pressure of hot gas and metal particles, it is not necessarily necessary to provide the first reinforcing bodies 304a, 304b, 304c.

Next, the second shielding structure 400, which is disposed downstream of the first shielding structure 300, is configured as follows. A plurality of second shielding plates 401a, 401b are disposed at an incline with respect to the release direction HM of the high-temperature, high-pressure hot gas and high-temperature metal particles. A bent second mounting portion 401a1, 401b1 is formed on both sides of the plurality of second shielding plates 401a, 401b. The inclination angle of the plurality of second shielding plates 401a, 401b is, for example, approximately 45 degrees upward to the right, but is not limited to this inclination angle.

The second mounting portions 401a1, 401b1 bent on the second shielding plates 401a, 401b are attached to a second shielding plate mounting frame 402. The second shielding plate mounting frame 402 is fixed to a second board mounting frame 403. The second board mounting frame 403 is then attached to the arc space frame 120, forming the second shielding structure 400.

In addition, second reinforcing bodies 404a, 404b, for example U-shaped, are provided on the upper surfaces of the second shielding plates 401a, 401b to reinforce the second shielding plates 401a, 401b. The shape of the second reinforcing bodies 404a, 404b is not limited to a U-shape. Note that if the second shielding plates 401a, 401b can withstand the high pressure of hot gas and metal particles, it is not necessarily necessary to provide the second reinforcing bodies 404a, 404b.

As shown in FIG. 8, in this embodiment 5, the first shielding structure 300 has three first shielding plates 301a, 301b, and 301c arranged at an inclination angle that rises to the left, and the second shielding structure 400 has two second shielding plates 401a and 401b arranged at an inclination angle that rises to the right in the opposite direction to the first shielding plates 301a, 301b, and 301c, with the second shielding plate 401a being arranged so as to be located between the first shielding plate 301a and the first shielding plate 301b, and the second shielding plate 401b being arranged so as to be located between the first shielding plate 301b and the first shielding plate 301c.

In this way, by arranging the first shielding plates 301a, 301b, 301c of the first shielding structure 300 and the second shielding plates 401a, 401b of the second shielding structure 400, when viewed from the panel ceiling plate 100a side of the switchgear 100, the first shielding plates 301a, 301b, 301c and the second shielding plates 401a, 401b are arranged in an overlapping state, and this arrangement prevents high-temperature and high-pressure hot gas and high-temperature metal particles from being directly released into the ventilation communication port 140 of the switchgear 100.

The action of the first shielding structure 300 and the second shielding structure 400 attached to the arc space frame 120 will be explained. The high-temperature, high-pressure hot gas and high-temperature metal particles ejected into the arc space frame 120 collide with the bottom surface of the first shielding plates 301a, 301b, and 301c on the upstream side, stopping the rise of the metal particles, and the high-temperature, high-pressure hot gas flows smoothly and rises along the inclined direction of the bottom surface of the first shielding plates 301a, 301b, and 301c.

The high-temperature, high-pressure hot gas and high-temperature metal particles that pass between the first shielding plate 301a and the first shielding plate 301b, and between the first shielding plate 301b and the first shielding plate 301c collide with the lower surface of the downstream second shielding plate 401a, 401b, stopping the metal particles from rising, and the high-temperature, high-pressure hot gas flows smoothly and rises along the inclination of the lower surface of the second shielding plate 401a, 401b. It then flows to the ventilation communication port 140 side at the top of the arc space frame 120 and is released outside the panel from the ventilation tower 150.

By arranging the first shielding plates 301a, 301b, and 301c on the upstream side and the second shielding plates 401a and 401b on the downstream side with inclinations in opposite directions, the cross-sectional area of the ventilation flow path can be increased, thereby further improving the efficiency of exhausting the hot gas filling the arc space frame 120.

The two-stage structure allows hot gas to be smoothly exhausted outside the panel of the switchgear 100, reducing the pressure load on the DC circuit breaker 101 when current is interrupted and preventing damage to the panel structure of the switchgear 100 or the DC circuit breaker 101.

In addition, the high-temperature metal particles collide with the undersides of the first shielding plates 301a, 301b, and 301c arranged on the upstream side and the second shielding plates 401a and 401b arranged on the downstream side, and the two-stage structure stops the upward rise, further preventing the release of high-temperature metal particles outside the plate.

Embodiment 6.
Fig. 10 is a cross-sectional view showing a shielding structure in a switchgear according to embodiment 6. Fig. 11 is a perspective view showing a shielding structure in a switchgear according to embodiment 6.

In the above-mentioned embodiment 5, the first shielding plates 301a, 301b, 301c are arranged at an inclination angle that rises to the left, and the second shielding plates 401a, 401b are arranged at an inclination angle that rises to the right. In this embodiment 6, however, the inclination angles are opposite to those in the above-mentioned embodiment 5, that is, the first shielding plates 301a, 301b, 301c are arranged at an inclination angle that rises to the right, and the second shielding plates 401a, 401b are arranged at an inclination angle that rises to the left. In this embodiment 6, the operation is the same as in the above-mentioned embodiment 5, and the same effect is achieved.

Although the present application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.
Therefore, countless modifications not exemplified are assumed within the scope of the technology disclosed in the present specification, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment.

This application is suitable for realizing a switchgear that can increase the efficiency of hot gas exhaust and suppress the release of metal particles outside the panel.

100 switch gear, 100a panel ceiling plate, 101 DC circuit breaker, 102 arc extinguishing chamber, 120 arc space frame, 140 ventilation communication port, 150 ventilation tower, 200 shielding structure, 201a shielding plate, 201b shielding plate, 201c shielding plate, 201d shielding plate, 202 shielding plate mounting frame, 203 panel mounting frame, 204a reinforcement body, 204b reinforcement body, 204c reinforcement body, 204d reinforcement body, 300 first shielding structure, 301a first shielding plate, 301b first shielding plate, 301c first shielding plate, 302 first shielding plate mounting frame, 303 first panel mounting frame, 304a first reinforcement body, 304b first reinforcement body, 304c first reinforcement body, 400 Second shielding structure, 401a Second shielding plate, 401b Second shielding plate, 402 Second shielding plate mounting frame, 403 Second panel mounting frame, 404a Second reinforcement body, 404b Second reinforcement body

Claims (7)

A switchgear having a DC circuit breaker, an arc extinguishing chamber arranged on an upper portion of the DC circuit breaker, a ventilation communication port formed in a panel ceiling plate, a ventilation tower communicating with the ventilation communication port, and an arc space frame body arranged between the arc extinguishing chamber and the ventilation communication port,
A switchgear comprising a shielding structure attached to the arc space frame body, the shielding structure being composed of a plurality of shielding plates arranged at an angle, a shielding plate mounting frame to which the shielding plates are attached, and a panel mounting frame to which the shielding plate mounting frame is fixed and which is attached to the arc space frame body. The switchgear according to claim 1, characterized in that the inclination directions of the multiple shielding plates are arranged in the same direction. The switchgear according to claim 1, characterized in that the inclination direction of one of the shielding plates is opposite to the inclination direction of the other of the shielding plates. The switchgear according to any one of claims 1 to 3, characterized in that a reinforcing body is provided on the shielding plate. A switchgear having a DC circuit breaker, an arc extinguishing chamber arranged on an upper portion of the DC circuit breaker, a ventilation communication port formed in a panel ceiling plate, a ventilation tower communicating with the ventilation communication port, and an arc space frame body arranged between the arc extinguishing chamber and the ventilation communication port,
A switchgear comprising: a first shielding structure attached to the arc space frame; and a second shielding structure attached to the arc space frame and arranged downstream of the first shielding structure, wherein the first shielding structure is composed of a plurality of first shielding plates arranged at an angle, a first shielding plate mounting frame to which the first shielding plates are attached, and a first panel mounting frame to which the first shielding plate mounting frame is fixed and attached to the arc space frame; and the second shielding structure is composed of a plurality of second shielding plates arranged at an angle, a second shielding plate mounting frame to which the second shielding plates are attached, and a second panel mounting frame to which the second shielding plate mounting frame is fixed and attached to the arc space frame. The switchgear according to claim 5, characterized in that the inclination direction of the first shielding plate and the inclination direction of the second shielding plate are arranged in opposite directions. The switchgear according to claim 5 or 6, characterized in that a first reinforcing body is provided on the first shielding plate, and a second reinforcing body is provided on the second shielding plate.

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