Oil-immersed transformer with explosion-proof protection structure

Abstract

The invention belongs to the technical field of oil-immersed transformers, and discloses an oil-immersed transformer with an explosion-proof protection structure, the oil-immersed transformer comprises a transformer main body and a protection seat, the transformer main body is installed in the protection seat, and the inner wall of the protection seat is provided with a heat dissipation assembly; an air inlet, a ventilation cavity, a first air outlet and a second air outlet are formed in the inner wall of the protection base, the air inlet, the first air outlet and the second air outlet are evenly distributed, a dehumidizer is installed in the ventilation cavity, and in the working process of the oil-immersed transformer, rotation of the cooling fan is controlled through the motor, so that the cooling effect of the oil-immersed transformer is improved. When the heat dissipation fan rotates, external air enters the protection base through the air inlet, then flows into the ventilation cavity to make contact with the dehumidizer, the air entering the ventilation cavity is dehumidified through the dehumidizer, then is exhausted into the protection base through the first air outlet and finally is exhausted out of the device through the second air outlet, dehumidification and heat dissipation are achieved, and the anti-explosion protection effect of the oil-immersed transformer is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil-immersed transformers, and in particular relates to an oil-immersed transformer with an explosion-proof protection structure. Background Art

[0002] Oil-immersed transformer is a common power transformer, whose core and winding are immersed in insulating oil. This design not only provides good insulation performance, but also effectively dissipates heat, and is suitable for high-voltage and large-capacity power systems;

[0003] In order to prevent explosions caused by internal faults of oil-immersed transformers and ensure the safety of the equipment and the surrounding environment, installing explosion-proof protection structures has become a common protective measure for oil-immersed transformers;

[0004] After searching, such as patent: CN117316583B, an oil-immersed transformer with explosion-proof protection structure, including a protection seat and a transformer, the top of the protection seat forms an opening, and the transformer is embedded and installed in the protection seat, and the inner wall of the protection seat is respectively installed with protection mechanisms, and the inner bottom of the protection seat forms a cooling chamber and the interior of the cooling chamber is filled with cooling oil, and the cooling chamber is also provided with an air guide frame, and the outer wall of the protection seat is installed with a ring pipe and a lower fan. The invention sets the transformer in the protection seat, and a protection mechanism with a certain buffering capacity is installed on the inner wall of the protection seat. When the transformer bursts and causes oil and heat sink to splash, the protection mechanism can play a certain buffering role, and cooperate with the protection seat to avoid fragments and liquid splashing, thereby improving its safety performance. The protection mechanism has a certain heat dissipation effect while protecting against explosion, reducing the temperature of the transformer, and can play an explosion-proof effect in cooperation with the automatic pressure relief valve and cooling cylinder on the top;

[0005] This is unavoidable given that there is usually a certain amount of humidity in the working environment of oil-immersed transformers (especially in humid areas or rainy seasons). The insulation system of oil-immersed transformers is mainly composed of oil and paper, which have a high adsorption capacity for moisture. When moisture in the air (i.e. water) enters the transformer through the heat dissipation holes, it will weaken the insulation performance, accelerate equipment aging, and may even trigger serious failures. Summary of the invention

[0006] The object of the present invention is to provide an oil-immersed transformer with an explosion-proof protection structure to solve the problems raised in the above background technology.

[0007] In order to achieve the above object, the present invention provides the following technical solution: an oil-immersed transformer with an explosion-proof protection structure, comprising a transformer body and a protection seat, wherein the transformer body is installed inside the protection seat, and a heat dissipation component is provided on the inner wall of the protection seat;

[0008] The heat dissipation component includes a cooling fan disposed inside the protection seat. One side of the cooling fan is fixedly connected to a first rotating shaft. A pulley group is installed on the outer wall of the first rotating shaft. A second rotating shaft is embedded inside the pulley group away from the first rotating shaft. A motor is installed at one end of the second rotating shaft.

[0009] The inner wall of the protection seat is provided with an air inlet, a ventilation cavity, a first air outlet and a second air outlet. The air inlet, the first air outlet and the second air outlet are all evenly distributed. A dehumidifying agent is installed inside the ventilation cavity.

[0010] As a further technical solution of the present invention, a first baffle is evenly arranged on one side of the air inlet. Each of the first baffles is fixedly connected by a connecting plate. A rack plate is fixedly installed at the top of the connecting plate. A gear is meshed at the top of the rack plate. The gear is fixedly installed at one end of the second rotating shaft.

[0011] Both sides of the rack plate are fixedly connected with fixing seats. Connecting shafts are slidably installed inside the inner walls of the two fixing seats. First springs are installed on the outer walls of the two connecting shafts. The far ends of the two connecting shafts are fixedly installed on one side of a tooth block. The tooth block is arranged at the bottom of the gear.

[0012] As a further technical solution of the present invention, the rack plate is slidably installed inside the protection seat. A second spring is installed between the rack plate and the protection seat.

[0013] As a further technical solution of the present invention, a second baffle is arranged on one side of the second air outlet. The second baffle is fixedly connected to the connecting plate.

[0014] As a further technical solution of the present invention, a third air outlet is opened inside the protection seat. The third air outlet is arranged on one side of the dehumidifying agent. A third baffle is arranged on one side of the third air outlet. The bottom end of the third baffle is fixedly connected to the second baffle. One end of the second baffle is arranged on one side of the connecting plate.

[0015] As a further technical solution of the present invention, a slider is fixedly connected to one side of the second baffle. The slider is slidably installed inside the protection seat. A third spring is installed between the slider and the protection seat.

[0016] As a further technical solution of the present invention, the air inlet is arranged to slope downward.

[0017] As a further technical solution of the present invention, a mounting plate is fixedly installed on the inner wall of the air inlet. One side of the mounting plate is connected to a connecting head through a fifth spring. A convex block is arranged on one side of the end of the connecting head. The convex block is installed inside the first baffle.

[0018] As a further technical solution of the present invention, the bump is slidably installed inside the first baffle, and a fourth spring is installed between the bump and the first baffle.

[0019] As a further technical solution of the present invention, a knocking rod is fixedly installed on the outer wall of the connecting head, and the knocking rods are evenly distributed in an annular array.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. Through the setting of the heat dissipation component, during the operation of the oil-immersed transformer, the second rotating shaft is controlled by the motor to rotate. When the second rotating shaft rotates, the first rotating shaft is driven to rotate through the transmission of the pulley group. The rotation of the first rotating shaft drives the rotation of the heat dissipation fan. When the heat dissipation fan rotates, external gas enters the protection seat through the air inlet, then flows into the ventilation cavity and contacts the dehumidifying agent. After the entering gas is dehumidified by the dehumidifying agent, it is discharged into the protection seat from the first air outlet, and finally discharged from the second air outlet of the device, realizing dehumidification and heat dissipation, and improving the explosion-proof protection effect of the oil-immersed transformer.

[0022] 2. When the first baffle moves to close the air inlet, when the humidity sensor monitors that the humidity is too high, the motor is controlled by the PLC to turn off. When the motor turns off, the second rotating shaft stops rotating. The elastic potential energy of the second spring is released to drive the connecting plate to move. The movement of the connecting plate drives the first baffle to move to close the air inlet, preventing external gas from entering the protection seat under the condition of high humidity and having a negative impact on the transformer body, and further improving the protection effect of the device.

[0023] 3. Through the setting of the connecting head, when the first baffle moves to close the air inlet, the movement of the first baffle drives the movement of the bump. After the bump moves and contacts the connecting head, the connecting head is forced to swing to one side, and the elasticity of the fifth spring enables the connecting head to swing after separating from the bump, facilitating knocking on the inner wall of the air inlet and helping to discharge the dust attached to the inner wall of the air inlet to improve the heat dissipation effect of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic diagram of the overall structure of the present invention;

[0025] Figure 2 is a schematic cross-sectional view of the overall structure of the present invention;

[0026] Figure 3 is the present invention Figure 2 is an enlarged schematic view of the structure at A in;

[0027] Figure 4 is a schematic cross-sectional view of the structure at the protection seat of the present invention;

[0028] Figure 5Schematic diagram of the structure at the second baffle and the third baffle of the present invention;

[0029] Figure 6 For the present invention Figure 5 Enlarged schematic diagram of the structure at position B in the present invention;

[0030] Figure 7 For the present invention Figure 5 Enlarged schematic diagram of the structure at position C in the present invention;

[0031] Figure 8 Schematic cross-sectional view of the structure at the gear of the present invention.

[0032] In the figure: 1. Transformer main body; 2. Protection seat; 3. Heat dissipation fan; 4. First rotating shaft; 5. Pulley group; 6. Second rotating shaft; 7. Motor; 8. Air inlet; 9. Ventilation cavity; 10. First air outlet; 11. Second air outlet; 12. Desiccant; 13. Third air outlet; 14. First baffle; 15. Connecting plate; 16. Rack plate; 17. Gear; 18. Tooth block; 19. Connecting shaft; 20. Fixed seat; 21. First spring; 22. Second spring; 23. Second baffle; 24. Third baffle; 25. Slide block; 26. Third spring; 27. Convex block; 28. Fourth spring; 29. Connecting head; 30. Fifth spring; 31. Mounting plate; 32. Knocking rod. Detailed implementation manners

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] As Figures 1 to 8 shown, in the embodiment of the present invention, an oil-immersed transformer with an explosion-proof protection structure includes a transformer main body 1 and a protection seat 2. The transformer main body 1 is installed inside the protection seat 2, and a heat dissipation component is arranged on the inner wall of the protection seat 2;

[0035] The heat dissipation component includes a heat dissipation fan 3 arranged inside the protection seat 2. One side of the heat dissipation fan 3 is fixedly connected to a first rotating shaft 4. A pulley group 5 is installed on the outer wall of the first rotating shaft 4. The inner part of the pulley group 5 far from the first rotating shaft 4 is embedded with a second rotating shaft 6, and one end of the second rotating shaft 6 is installed with a motor 7;

[0036] The inner wall of the protection seat 2 is provided with an air inlet 8, a ventilation cavity 9, a first air outlet 10 and a second air outlet 11. The air inlet 8, the first air outlet 10 and the second air outlet 11 are all evenly distributed, and a desiccant 12 is installed inside the ventilation cavity 9.

[0037] Existing: CN117316583B discloses an oil-immersed transformer with an explosion-proof protection structure. The transformer body 1 proposed in this application document is disclosed in this patent, and the technical means will not be elaborated here one by one;

[0038] During the operation of the oil-immersed transformer, the second rotating shaft 6 is controlled by the motor 7 to rotate. When the second rotating shaft 6 rotates, the first rotating shaft 4 is driven to rotate through the pulley group 5. The rotation of the first rotating shaft 4 drives the rotation of the radiator fan 3. When the radiator fan 3 rotates, external gas enters the protection seat 2 through the air inlet 8, then flows into the ventilation cavity 9 and contacts the dehumidifying agent 12. After the entering gas is dehumidified by the dehumidifying agent 12, it is discharged into the protection seat 2 from the first air outlet 10 and finally discharged from the second air outlet 11, realizing dehumidification and heat dissipation;

[0039] This device dehumidifies the heat dissipation gas entering the protection seat 2, preventing moisture from being carried in the heat dissipation gas, thereby avoiding the safety risks of moisture weakening the insulation performance, accelerating equipment aging, and possibly causing serious failures, and improving the explosion-proof protection effect of the oil-immersed transformer.

[0040] As Figures 1 to 7 shown, a first baffle 14 is evenly arranged on one side of the air inlet 8. Each first baffle 14 is fixedly connected through a connecting plate 15. The top of the connecting plate 15 is fixedly installed with a rack plate 16. The top of the rack plate 16 is meshed with a gear 17. The gear 17 is fixedly installed at one end of the second rotating shaft 6;

[0041] Both sides of the rack plate 16 are fixedly connected with fixing seats 20. The inner walls of the two fixing seats 20 are both slidably installed with connecting shafts 19. First springs 21 are installed on the outer walls of the two connecting shafts 19. The far ends of the two connecting shafts 19 are fixedly installed on one side of the tooth block 18. The tooth block 18 is arranged at the bottom of the gear 17.

[0042] During heat dissipation, the rotation of the second rotating shaft 6 drives the rotation of the gear 17. The rotation of the gear 17 drives the movement of the rack plate 16. The movement of the rack plate 16 drives the movement of the tooth block 18. When the tooth block 18 is driven to mesh with the gear 17, the elastic potential energy of the first spring 21 makes the tooth block 18 located at the bottom of the gear 17, so that the rack plate 16 no longer moves. Thus, during the heat dissipation process of the device, the first baffle 14 is located on one side of the air inlet 8, keeping the air inlet 8 open.

[0043] As Figure 6 and Figure 7 shown, the rack plate 16 is slidably installed inside the protection seat 2, and a second spring 22 is installed between the rack plate 16 and the protection seat 2.

[0044] A humidity sensor is installed on the outer wall of the protection seat 2 for monitoring the humidity of the working environment around the transformer main body 1;

[0045] When the humidity sensor detects that the humidity is too high, the PLC is used to control the motor 7 to close. When the motor 7 closes, the second rotating shaft 6 stops rotating. The elastic potential energy is released by the second spring 22 to drive the connecting plate 15 to move. The movement of the connecting plate 15 drives the first baffle 14 to move to close the air inlet 8, preventing external gas from entering the protection seat 2 under the condition of high humidity, which has a negative impact on the transformer main body 1 and further improves the protection effect of the device;

[0046] A plurality of tooth blocks 18 are installed in the gear 17 in an annular array, and a chute for its rotation is provided inside the gear 17;

[0047] Each tooth block 18 inside the gear 17 is rotationally connected to it through a rotating shaft, and a torsion spring is installed on the outer wall of the rotating shaft, so that the rack plate 16 does not rotate the gear 17 when moving.

[0048] As Figure 5 and Figure 7 shown, a second baffle 23 is provided on one side of the second air outlet 11, and the second baffle 23 is fixedly connected to the connecting plate 15.

[0049] When the air inlet 8 is closed, the movement of the connecting plate 15 drives the second baffle 23 to move to close the second air outlet 11, so that external gas cannot enter the device from the air inlet 8 and the second air outlet 11.

[0050] As Figures 1 to 7 shown, a third air outlet 13 is provided inside the protection seat 2. The third air outlet 13 is provided on one side of the dehumidifying agent 12. A third baffle 24 is provided on one side of the third air outlet 13. The bottom end of the third baffle 24 is fixedly connected to the second baffle 23, and one end of the second baffle 23 is provided on one side of the connecting plate 15.

[0051] One side of the connecting plate 15 facing the second baffle 23 is inclined;

[0052] When the connecting plate 15 moves to drive the first baffle 14 to close the air inlet 8, the inclined surface of the connecting plate 15 contacts the second baffle 23 to drive the second baffle 23 to move away from the connecting plate 15. The movement of the second baffle 23 drives the third baffle 24 to move to open the third air outlet 13, increasing the contact area between the gas in the protection seat 2 and the dehumidifying agent 12, and preventing some gas with high humidity from entering the protection seat 2 before the air inlet 8 and the second air outlet 11 are closed.

[0053] As Figure 5 and Figure 7As shown, one side of the second baffle 23 is fixedly connected with a slider 25. The slider 25 is slidably installed inside the protection seat 2, and a third spring 26 is installed between the slider 25 and the protection seat 2.

[0054] When the movement of the second baffle 23 drives the movement of the third baffle 24 to open the third air outlet 13, the movement of the second baffle 23 drives the movement of the slider 25, and the movement of the slider 25 deforms the third spring 26 to store elastic potential energy.

[0055] When the connecting plate 15 moves away from the second baffle 23, the elastic potential energy is released through the third spring 26 to reset the slider 25, so that the third baffle 24 closes the third air outlet 13, and the device is closed during ventilation, so as to improve the service life of the dehumidifying agent 12 and reduce the replacement frequency.

[0056] As shown in FIGS. 3 Figure 5 and Figure 6 shown, the air inlet 8 is arranged to slope downwards.

[0057] As shown in FIGS. 3 Figure 5 and Figure 6 shown, an installation plate 31 is fixedly installed on the inner wall of the air inlet 8. One side of the installation plate 31 is connected with a connector 29 through a fifth spring 30. One side of the end of the connector 29 is provided with a convex block 27, and the convex block 27 is installed inside the first baffle 14.

[0058] When the first baffle 14 moves to close the air inlet 8, the movement of the first baffle 14 drives the movement of the convex block 27. After the convex block 27 moves and contacts the connector 29, it forces the connector 29 to swing to one side, and the elasticity of the fifth spring 30 enables the connector 29 to swing after separating from the convex block 27, which is convenient for knocking the inner wall of the air inlet 8 and helps to discharge the dust adhering to the inner wall of the air inlet 8, so as to improve the heat dissipation effect of the device.

[0059] As shown in FIGS. 3 Figure 5 and Figure 6 shown, the convex block 27 is slidably installed inside the first baffle 14, and a fourth spring 28 is installed between the convex block 27 and the first baffle 14.

[0060] One end of the convex block 27 is an arc surface;

[0061] When the first baffle 14 moves to open the air inlet 8, the convex block 27 contacts the inner wall of the protection seat 2 and slides into the first baffle 14 under force. At the same time, the fourth spring 28 deforms to store elastic potential energy.

[0062] When the first baffle 14 moves to close the air inlet 8, the elastic potential energy is released through the fourth spring 28 to make the convex

[0063] block 27 move outwards to facilitate contact with the connector 29.

[0064] As shown Figure 6 As shown, a knocking rod 32 is fixedly installed on the outer wall of the connector head 29, and the knocking rods 32 are evenly distributed in an annular array.

[0065] The knocking rod 32 is elastically arranged;

[0066] When the connector head 29 shakes on the inner wall of the air inlet 8, the connector head 29 drives the knocking rod 32 to shake, so that the knocking rod 32 contacts the inner wall of the air inlet 8, further improving the knocking effect on the inner wall of the air inlet 8.

[0067] Working principle and usage process:

[0068] During the operation of the oil-immersed transformer, the motor 7 controls the rotation of the second rotating shaft 6. When the second rotating shaft 6 rotates, it drives the first rotating shaft 4 to rotate through the belt pulley group 5. The rotation of the first rotating shaft 4 drives the rotation of the cooling fan 3. When the cooling fan 3 rotates, the external gas enters the protection seat 2 through the air inlet 8, and then flows into the ventilation cavity 9 and contacts the dehumidifying agent 12. After the entering gas is dehumidified by the dehumidifying agent 12, it is discharged into the protection seat 2 from the first air outlet 10, and finally discharged from the second air outlet 11 of the device, realizing dehumidification and heat dissipation;

[0069] At the same time, the rotation of the second rotating shaft 6 drives the rotation of the gear 17. The rotation of the gear 17 drives the movement of the rack plate 16. The movement of the rack plate 16 drives the movement of the tooth block 18. When the tooth block 18 meshes with the gear 17, the elastic potential energy of the first spring 21 makes the tooth block 18 located at the bottom of the gear 17, so that the rack plate 16 stops moving. Thus, during the heat dissipation process of the device, the first baffle 14 is located on one side of the air inlet 8, keeping the air inlet 8 open for ventilation;

[0070] When the humidity sensor detects that the humidity is too high, the PLC controls the motor 7 to turn off. When the motor 7 turns off, the second rotating shaft 6 stops rotating. The elastic potential energy of the second spring 22 is released to drive the movement of the connecting plate 15. The movement of the connecting plate 15 drives the movement of the first baffle 14 to close the air inlet 8. At the same time, the movement of the connecting plate 15 drives the movement of the second baffle 23 to close the second air outlet 11, preventing external gas from entering the device through the air inlet 8 and the second air outlet 11;

[0071] At the same time, the contact between the connecting plate 15 and the second baffle 23 drives the second baffle 23 to move away from the connecting plate 15. The movement of the second baffle 23 drives the movement of the third baffle 24 to open the third air outlet 13, dehumidifying the gas in the protection seat 2;

[0072] Meanwhile, the movement of the first baffle 14 drives the movement of the convex block 27. After the convex block 27 moves and contacts the connecting head 29, it forces the connecting head 29 to swing to one side, and the elasticity of the fifth spring 30 enables the connecting head 29 to swing after separating from the convex block 27, which is convenient for knocking the inner wall of the air inlet 8 and helps to discharge the dust adhering to the inner wall of the air inlet 8.

[0073] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An oil-immersed transformer with an explosion-proof protection structure, comprising a transformer main body (1) and a protection seat (2), characterized in that: The transformer body (1) is installed inside the protection seat (2), and a heat dissipation component is arranged on the inner wall of the protection seat (2). The heat dissipation component includes a heat dissipation fan (3) arranged inside the protection seat (2). One side of the heat dissipation fan (3) is fixedly connected with a first rotating shaft (4). A pulley group (5) is installed on the outer wall of the first rotating shaft (4). A second rotating shaft (6) is embedded inside the pulley group (5) away from the first rotating shaft (4). One end of the second rotating shaft (6) is installed with a motor (7). An air inlet (8), a ventilation cavity (9), a first air outlet (10) and a second air outlet (11) are formed on the inner wall of the protection seat (2). The air inlet (8), the first air outlet (10) and the second air outlet (11) are all evenly distributed. A dehumidifying agent (12) is installed inside the ventilation cavity (9).

2. The oil-immersed transformer with an explosion-proof protection structure according to claim 1, wherein: A first baffle (14) is evenly arranged on one side of the air inlet (8). Each of the first baffles (14) is fixedly connected through a connecting plate (15). A rack plate (16) is fixedly installed at the top of the connecting plate (15). The top of the rack plate (16) is meshed with a gear (17). The gear (17) is fixedly installed at one end of the second rotating shaft (6). Both sides of the rack plate (16) are fixedly connected with fixing seats (20). Connecting shafts (19) are slidably installed inside the inner walls of the two fixing seats (20). First springs (21) are installed on the outer walls of the two connecting shafts (19). The far ends of the two connecting shafts (19) are fixedly installed on one side of a tooth block (18). The tooth block (18) is arranged at the bottom end of the gear (17).

3. The oil-immersed transformer with an explosion-proof protection structure according to claim 2, characterized in that: The rack plate (16) is slidably installed inside the protection seat (2). A second spring (22) is installed between the rack plate (16) and the protection seat (2).

4. The oil-immersed transformer with an explosion-proof protection structure according to claim 1, wherein: A second baffle (23) is arranged on one side of the second air outlet (11). The second baffle (23) is fixedly connected with the connecting plate (15).

5. A oil-immersed transformer with an explosion-proof protection structure according to claim 1, characterized in that: A third air outlet (13) is formed inside the protection seat (2). The third air outlet (13) is arranged on one side of the dehumidifying agent (12). A third baffle (24) is arranged on one side of the third air outlet (13). The bottom end of the third baffle (24) is fixedly connected with the second baffle (23). One end of the second baffle (23) is arranged on one side of the connecting plate (15).

6. The oil-immersed transformer with an explosion-proof protection structure according to claim 5, wherein: One side of the second baffle (23) is fixedly connected with a slider (25). The slider (25) is slidably installed inside the protection seat (2). A third spring (26) is installed between the slider (25) and the protection seat (2).

7. The oil-immersed transformer with an explosion-proof protection structure according to claim 1, characterized in that: The air inlet (8) is arranged to incline downward.

8. The oil-immersed transformer with an explosion-proof protection structure according to claim 1, characterized in that: An installation plate (31) is fixedly installed on the inner wall of the air inlet (8). One side of the installation plate (31) is connected with a connecting head (29) through a fifth spring (30). A convex block (27) is arranged on one side of the end of the connecting head (29). The convex block (27) is installed inside the first baffle (14).

9. The oil-immersed transformer with an explosion-proof protection structure according to claim 8, characterized in that: The bump (27) is slidably installed inside the first baffle (14), and a fourth spring (28) is installed between the bump (27) and the first baffle (14).

10. The oil-immersed transformer with an explosion-proof protection structure according to claim 8, characterized in that: A knocking rod (32) is fixedly installed on the outer wall of the connector (29), and the knocking rods (32) are evenly distributed in an annular array.

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