Explosion-proof protection structure for power transformer

Abstract

The anti-explosion protection structure for the power transformer is applied to the related technical field of transformers, through the arrangement of an external cylinder, in the working process of an oil-immersed transformer, insulating oil in the oil-immersed transformer can be continuously subjected to internal and external circulation, so that the insulating oil absorbing a large amount of heat inside can directly carry heat to the outside for heat dissipation, and the heat dissipation efficiency is improved. Compared with a heat dissipation mode through heat dissipation fins and an external fan in the prior art, the cooling speed and the heat dissipation efficiency of the insulating oil are greatly improved, so that the potential safety hazard of explosion caused by overheating gasification of the insulating oil of the transformer is reduced; and meanwhile, when the insulating oil is overheated, the split-flow cooling unit in the external cylinder can be self-adaptively changed in space, and more refrigerants dissipate heat of less insulating oil in unit time, so that the cooling speed is remarkably increased, and the risk that the temperature of the insulating oil continues to rise is reduced.

Description

Technical Field

[0001] The present invention relates to a protection structure, and in particular to an explosion-proof protection structure for a power transformer applied in the technical field related to transformers. Background Art

[0002] Transformers generally include oil-immersed transformers and dry-type transformers. In comparison, oil-immersed transformers are filled with a large amount of insulating oil (usually mineral oil), which is mainly used for insulation and heat dissipation.

[0003] Currently, almost all explosions of oil-immersed transformers are caused by internal pressure imbalance. The most direct cause of pressure imbalance is that the insulating oil changes from liquid to gas, greatly increasing the pressure inside the transformer. When the pressure exceeds the structural strength, structural damage occurs, leading to leakage and spraying of the insulating oil, followed by fire, combustion, and explosion. A large part of the reason for the evaporation of the insulating oil from liquid to gas is the abnormal increase in the oil temperature of the insulating oil, which, when it rises to a critical point, leads to vaporization. The heat dissipation method in the existing technology is often through cooling fins combined with an external fan to accelerate heat dissipation through forced convection. For example, Chinese patent specification No. CN115370613B discloses a transformer with a low-noise cooling fan, and Chinese patent specification No. CN111667981A discloses a transformer heat dissipation device. However, when the oil temperature rises abnormally, this heat dissipation method is insufficient to suppress the further increase in oil temperature, resulting in a greater risk of explosion.

[0004] Therefore, a protective structure with explosion-proof function for an oil-immersed transformer is proposed. Summary of the Invention

[0005] In view of the above-mentioned prior art, the technical problem to be solved by the present invention is that the insulating oil in the oil-immersed transformer will gasify due to high temperature during use, resulting in an increase in the pressure value in the transformer and causing fire and explosion.

[0006] In order to solve the above problems, the present invention provides an explosion-proof protection structure for a power transformer, comprising a transformer body, an oil pipe fixedly connected to the upper left end of the transformer body, the oil pipe communicating with the interior of the transformer body, an external cylinder further provided at the upper left end of the transformer body, two upper support rods and a side support rod fixedly connected between the outer end of the external cylinder and the left end and the upper end of the transformer body, a return pipe and a circulation pipe fixedly connected between the front and rear ends of the external cylinder and the upper end of the transformer body, a discharge pipe and an inlet pipe fixedly connected to the front and rear ends of the external cylinder, a water pump installed on the inlet pipe, and a discharge pipe fixedly connected to the upper end of the transformer body. Below the return pipe, the inlet pipe is located above the circulation pipe. A shunt cooling unit is also fixedly connected to the inside of the external cylinder. The shunt cooling unit includes a double-pass baffle fixedly connected to the front and rear inner walls of the external cylinder, a plurality of heat exchange combs fixedly connected to the lower ends of the double-pass baffles, and a plurality of connecting pipes fixedly connected between two adjacent heat exchange combs. The frontmost heat exchange comb is also fixedly connected to the inner wall of the external cylinder with a connecting pipe. The discharge pipe, the connecting pipe and the heat exchange comb are connected to each other. A plurality of evenly distributed holes are opened on the upper end of the double-pass baffle, and a plurality of holes are connected to a plurality of heat exchange combs respectively.

[0007] A heat regulating unit is also fixedly connected to the upper end of the double-pass partition. The inlet pipe is connected to the space between the double-pass partition and the heat regulating unit. The circulation pipe and the return pipe are both connected to the space below the double-pass partition. An oil sensing unit is installed on the discharge pipe.

[0008] In the above-mentioned explosion-proof protective structure for a power transformer, the provision of an external cylinder allows the insulating oil within the oil-immersed transformer to be continuously circulated internally and externally during operation. This allows the insulating oil, which has absorbed a large amount of heat, to be rapidly cooled when it circulates to the external cylinder. Compared with the heat dissipation method using heat dissipation fins and an external fan in the prior art, the cooling speed and heat dissipation efficiency of the insulating oil are greatly improved, thereby reducing the safety hazard of explosion of the transformer due to overheating and gasification of the insulating oil.

[0009] As a further improvement of the present application, the double-pass partition is located above the center line of the external cylinder, and the multiple connecting pipes are close to the lower edge of the heat exchange comb.

[0010] As a further improvement of the present application, the heat regulating unit includes a plurality of connecting pipes fixedly connected to the upper ends of the double-pass partitions and a spring-loaded pocket fixedly connected to the upper ends of the plurality of connecting pipes. The edges of the spring-loaded pocket are fixedly connected to the corresponding inner walls of the external cylinder. The spring-loaded pocket is an elastic sealing structure. The plurality of connecting pipes are spaced apart from the plurality of communicating pipes, and the connecting pipes are fixedly passed through the double-pass partitions and communicated with the space below the double-pass partitions.

[0011] As a further improvement of the present application, the oil sensing unit includes a reinforcing tube fixedly connected to the outer end of the drainage pipe and a pressure sensor installed on the inner wall of the reinforcing tube. An annular groove is opened on the drainage pipe, a protective ring is fixedly connected to the inner wall of the annular groove, and a flow sensor is installed on the inner wall of the drainage pipe near the external cylinder.

[0012] As a further improvement of the present application, the return pipe is close to the double-pass partition, the circulation pipe is close to the bottom of the external cylinder, the liquid level of the insulating oil in the oil pipe and the external cylinder is the same, and the liquid level is located between the double-pass partition and the center line of the external cylinder.

[0013] As a further improvement of the present application, the connecting pipe is a straight pipe and the heat exchange comb is an integrated structure.

[0014] As another improved supplement to the present application, the connecting pipe is a corrugated pipe, and the heat exchange comb is a split structure. The heat exchange comb includes an upper connecting section fixedly connected to the double-pass partition, a lower isolation section fixedly connected to the lower end of the upper connecting section, two outer expansion pieces respectively adsorbed on the outer surface of the lower isolation section, and two outer connecting pieces respectively fixedly connected between the upper outer surface of the outer expansion piece and the outer surface of the upper connecting section, and between the lower outer surface of the outer expansion piece and the lower end of the lower isolation section.

[0015] As another improved supplement to the present application, the outer expansion piece and the lower isolation section are both made of magnetic materials, and both have D-shaped cross-sections. The cross-sectional area of ​​the outer expansion piece is larger than the cross-sectional area of ​​the lower isolation section, and the outer connecting piece is made of elastic sealing material.

[0016] In summary, by setting up the external cylinder, during the operation of the oil-immersed transformer, the insulating oil therein can be continuously circulated inside and outside, so that the insulating oil that has absorbed a large amount of heat inside can be quickly dissipated when it circulates to the external cylinder. Compared with the heat dissipation method through heat dissipation fins and external fans in the prior art, the cooling speed and heat dissipation efficiency of the insulating oil are greatly improved, thereby reducing the safety hazard of explosion caused by overheating and gasification of the insulating oil in the transformer; at the same time, when the insulating oil is overheated, the shunt cooling unit in the external cylinder can adaptively change the space, so that more refrigerant can dissipate less insulating oil per unit time, thereby significantly accelerating the cooling speed, thereby reducing the risk of continued temperature increase of the insulating oil; at the same time, under the action of the oil sensing unit, the instantaneous change amplitude of the insulating oil can be sensed in real time, which is convenient for timely corresponding pressure relief operation, further reducing the risk of explosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a perspective view from the right side of the first embodiment of the present application;

[0018] Figure 2 This is a left-side perspective view of the first embodiment of the present application;

[0019] Figure 3This is a cross-sectional view of the external cylinder according to the first embodiment of the present application;

[0020] Figure 4 This is a three-dimensional diagram of the external cylinder according to the first embodiment of the present application;

[0021] Figure 5 A perspective view of a heat regulating unit according to a first embodiment of the present application;

[0022] Figure 6 This is a cross-sectional view of the oil sensing unit according to the first embodiment of the present application;

[0023] Figure 7 This is a cross-sectional view of the external cylinder according to the second embodiment of the present application;

[0024] Figure 8 This is a cross-sectional view of a heat exchange comb according to a second embodiment of the present application;

[0025] Figure 9 This is a schematic diagram of the heat exchange combs of the second embodiment of the present application after being horizontally expanded;

[0026] Figure 10 This is a front view of the heat exchange comb of the second embodiment of the present application after removing the outer expansion plate;

[0027] Figure 11 This is a front view of the heat exchange comb according to the second embodiment of the present application;

[0028] Figure 12 This is a cross-sectional view of the external cylinder after the heat exchange combs of the second embodiment of the present application are laterally expanded.

[0029] Description of the numbers in the figure:

[0030] 1 Transformer body, 101 upper support rod, 102 side support rod, 2 external cylinder, 21 circulation pipe, 22 return pipe, 201 inlet pipe, 202 discharge pipe, 3 oil pipe, 41 double-pass partition, 42 heat exchange comb, 43 connecting pipe, 421 upper connecting section, 422 lower isolation section, 423 external connecting piece, 424 external expansion piece, 51 pressure pocket, 52 connecting pipe, 61 reinforcement pipe, 62 protection ring, 63 flow sensor, 601 pressure sensor. DETAILED DESCRIPTION

[0031] Two implementation modes of the present application are described in detail below with reference to the accompanying drawings.

[0032] The first implementation method:

[0033] Figure 1-2As shown, an explosion-proof protection structure for a power transformer includes a transformer body 1, an oil pipe 3 is fixedly connected to the upper left end of the transformer body 1, and the oil pipe 3 is communicated with the interior of the transformer body 1. An external cylinder 2 is also provided at the upper left end of the transformer body 1, and two upper support rods 101 and side support rods 102 are fixedly connected between the outer end of the external cylinder 2 and the left end and the upper end of the transformer body 1, respectively. Figure 3 The front and rear ends of the external cylinder 2 are fixedly connected to the upper end of the transformer body 1 with a return pipe 22 and a circulation pipe 21 respectively. The front and rear ends of the external cylinder 2 are fixedly connected to the discharge pipe 202 and the inlet pipe 201 respectively. A water pump is installed on the inlet pipe 201. The discharge pipe 202 is located below the return pipe 22, and the inlet pipe 201 is located above the circulation pipe 21. The external cylinder 2 is also fixedly connected to a shunt cooling unit. Through the arrangement of the external cylinder 2, the insulating oil in the transformer body 1 can circulate inside and outside the transformer body 1, so that the insulating oil with more heat adsorbed can be directly circulated from the transformer body 1 to the outside, and then circulated back to the transformer body 1 after fully contacting with the refrigerant in the shunt cooling unit for heat dissipation. Compared with the forced convection heat dissipation method of the heat sink fins and the external fan, it greatly accelerates the heat dissipation. Under abnormal circumstances, it can effectively suppress the temperature rise rate, effectively prevent the occurrence of explosion, and reduce safety hazards.

[0034] Among them, a temperature sensor can be installed on the circulation pipe 21 to detect the temperature of the insulating oil that has just circulated to the outside world in the transformer body, so as to facilitate the regulation of the heat dissipation effect at the external cylinder according to different temperatures. For example, when the temperature is too high, the air intake speed of the refrigerant is increased or the temperature of the refrigerant is lowered.

[0035] like Figure 4-5 The split cooling unit includes a double-pass partition 41 fixedly connected to the front and rear inner walls of the external tube 2, a plurality of heat exchange combs 42 fixedly connected to the lower ends of the double-pass partition 41, and a plurality of connecting pipes 43 fixedly connected between two adjacent heat exchange combs 42. The front heat exchange comb 42 is also fixedly connected to the inner wall of the external tube 2 with a connecting pipe 43. The discharge pipe 202, the connecting pipe 43 and the heat exchange comb 42 are connected to each other. The upper end of the double-pass partition 41 is opened with a plurality of evenly distributed 401, and the plurality of 401 are respectively connected to the plurality of heat exchange combs 42. The return pipe 22 is close to the double-pass partition 41, and the circulation pipe 21 is close to the bottom of the external cylinder 2, so that the insulating oil pumped out of the transformer body 1 enters from the low position of the external cylinder 2 and exits from the high position, so that the insulating oil can evenly contact the refrigerant in the heat exchange comb 42, so that it can return to the transformer body 1 after uniform cooling. The liquid levels of the insulating oil in the oil pipe 3 and the external cylinder 2 are the same, and the liquid level is located between the double-pass partition 41 and the center line of the external cylinder 2. The oil pipe 3 is still used for oil replenishment and observation of the liquid level in the transformer body 1. The setting of the external cylinder 2 leaves part of its internal space vacant, which can provide a certain space for the thermal expansion of the insulating oil, effectively alleviating the safety hazards caused by overheating.

[0036] The upper end of the double-pass partition 41 is also fixedly connected to a heat regulating unit, which includes a plurality of connecting pipes 52 fixedly connected to the upper ends of the double-pass partition 41 and a spring-pressing pocket 51 fixedly connected to the upper ends of the plurality of connecting pipes 52. The edges of the spring-pressing pocket 51 are fixedly connected to the corresponding inner walls of the external cylinder 2. The spring-pressing pocket 51 is an elastic sealing structure. The plurality of connecting pipes 52 are respectively spaced apart from the plurality of connecting pipes 43, and the connecting pipes 52 are fixedly passed through the double-pass partition 41 and communicated with the space below the double-pass partition 41. When the insulating oil expands and vaporizes due to heat, part of the vaporized insulating oil can enter the space above the spring-pressing pocket 51 along the connecting pipe 52. This space can provide a certain space for its expansion, and at the same time facilitate the insulating oil to adapt to the thermal expansion and contraction caused by the environment.

[0037] The double-pass partition 41 is located above the center line of the external tube 2, and the multiple connecting pipes 43 are close to the lower edge of the heat exchange comb 42. The connecting pipes 43 are straight pipes, and the heat exchange comb 42 is an integrated structure.

[0038] like Figure 3 and Figure 6 The inlet pipe 201 is communicated with the space between the double-pass partition 41 and the heat regulating unit, the circulation pipe 21 and the return pipe 22 are both communicated with the space below the double-pass partition 41, and an oil sensing unit is installed on the discharge pipe 202. The oil sensing unit includes a reinforcement pipe 61 fixedly connected to the outer end of the discharge pipe 202 and a pressure sensor 601 installed on the inner wall of the reinforcement pipe 61. An annular groove is cut on the discharge pipe 202, and a protective ring sheet 62 is fixedly connected to the inner wall of the annular groove. A flow sensor 63 is installed on the inner wall of the discharge pipe 202 near the external cylinder 2. At the same time, under the action of the oil sensing unit, when thermal expansion occurs, especially when the amplitude of instantaneous gasification is large, the spring pocket 51 will be forced to expand downward, thereby squeezing the refrigerant to accelerate it into the heat exchange comb 42, thereby causing the heat exchange to The refrigerant in the comb 42 is accelerated and discharged from the drain pipe 202. At this time, the gas thrust on the protective ring 62 in the drain pipe 202 increases, causing the pressure sensor 601 to be triggered, causing the pressure sensor 601 data to fluctuate significantly. At the same time, within a unit time, when the refrigerant intake at the inlet pipe 201 remains unchanged, the data obtained by the flow sensor 63 also increases synchronously. The greater the fluctuation amplitude of the two, the greater the amplitude of the gasification of the insulating oil. The mutual verification of the two data can effectively avoid false alarms, thereby promptly determining the abnormality of the insulating oil in the transformer body 1, facilitating the timely implementation of relevant pressure relief operations, effectively reducing the occurrence of explosions, reducing safety hazards, and being able to sense the gasification of the insulating oil in real time, facilitating the timely implementation of corresponding pressure relief operations, and further reducing the risk of explosions. In addition, the oil sensing unit does not directly contact the insulating oil, making it less susceptible to damage and easier to maintain.

[0039] It is worth noting that power transformers are generally equipped with a pressure relief valve. After sensing the vaporization of the insulating oil, the pressure can be relieved through the existing pressure relief valve. This part is existing technology, so it will not be elaborated on in detail.

[0040] In the above-mentioned explosion-proof protective structure for a power transformer, by providing the external cylinder 2, the insulating oil therein can be continuously circulated inside and outside the oil-immersed transformer during operation, so that the insulating oil that has absorbed a large amount of heat inside can be quickly dissipated when it circulates to the external cylinder 2. Compared with the heat dissipation method through heat dissipation fins and external fans in the prior art, the cooling speed and heat dissipation efficiency of the insulating oil are greatly improved, thereby reducing the safety hazard of explosion of the transformer due to overheating and gasification of the insulating oil.

[0041] The second implementation method:

[0042] Based on the first embodiment, this embodiment changes the specific designs of the heat exchange combs 42 and the connecting pipes 43, while the rest of the parts remain the same as the first embodiment.

[0043] Figure 7-Figure 8 As shown, the connecting pipe 43 is a bellows, and the heat exchange comb 42 is a split structure. Figure 8 The heat exchange comb 42 includes an upper connecting section 421 fixedly connected to the double-pass partition 41, a lower isolation section 422 fixedly connected to the lower end of the upper connecting section 421, two outer expansion pieces 424 respectively adsorbed on the outer surface of the lower isolation section 422, and two outer connecting pieces 423 respectively fixedly connected between the upper outer surface of the outer expansion piece 424 and the outer surface of the upper connecting section 421, and between the lower outer surface of the outer expansion piece 424 and the lower end of the lower isolation section 422. The outer expansion piece 424 and the lower isolation section 422 are both made of magnetic material, so that they can be adsorbed to each other when they are close to each other, so that they are relatively stable with the lower isolation section 422. At the same time, when the temperature inside the transformer body 1 is reduced to an appropriate temperature and the refrigerant introduction speed is reduced, the outer expansion piece 424 can be adsorbed and positioned with the lower isolation section 422 after it is reset, thereby maintaining a certain stability. Figure 10-11 , and both cross sections are D-shaped, the cross-sectional area of ​​the outer expansion piece 424 is larger than the cross-sectional area of ​​the lower isolation section 422, so that when the outer expansion piece 424 changes position, when the distance between the two outer expansion pieces 424 is the smallest, the two outer expansion pieces 424 can conflict with the outer surface of the lower isolation section 422, thereby effectively maintaining the internal space of the heat exchange comb 42, allowing the refrigerant to enter the heat exchange comb 42, and then cool the insulating oil. The outer connecting piece 423 is made of elastic sealing material, such as Figure 9 and Figure 12When the transformer body 1 is abnormally heated, the refrigerant introduction speed at the inlet pipe 201 can be controlled to be accelerated, while the discharge speed at the discharge pipe 202 remains unchanged. At this time, after the refrigerant enters the large heat exchange comb 42, a pushing force can be generated on the heat exchange comb 42 from the inside to the outside, thereby causing it to expand laterally, so that it can accommodate more refrigerant. The space for accommodating insulating oil at the lower part of the double-pass partition 41 is correspondingly reduced, thereby achieving more refrigerant to dissipate heat from less insulating oil, thereby significantly accelerating the cooling speed, reducing the risk of continued heating of the insulating oil, thereby reducing the risk of explosion and achieving an explosion-proof effect.

[0044] Compared with the first embodiment, the cooling speed of the external circulating insulating oil in this embodiment can be adjusted, and it will be faster and more effective. During specific implementation, a suitable embodiment can be selected according to actual needs.

[0045] In view of current actual needs, the protection scope of the above-mentioned implementation mode adopted in this application is not limited to this. Various changes made within the knowledge scope of technical personnel in this field without departing from the concept of this application still fall within the protection scope of the present invention.

Claims

1. An explosion-proof protective structure for a power transformer, characterized in that: The invention comprises a transformer body (1), wherein the upper left end of the transformer body (1) is fixedly connected to an oil pipe (3), the oil pipe (3) is communicated with the interior of the transformer body (1), the upper left end of the transformer body (1) is further provided with an external cylinder (2), two upper support rods (101) and side support rods (102) are fixedly connected between the outer end of the external cylinder (2) and the left end and the upper end of the transformer body (1), respectively, a return pipe (22) and a circulation pipe (21) are fixedly connected between the front and rear ends of the external cylinder (2) and the upper end of the transformer body (1), a discharge pipe (202) and an inlet pipe (201) are fixedly connected between the front and rear ends of the external cylinder (2), respectively, a water pump is installed on the inlet pipe (201), the discharge pipe (202) is located below the return pipe (22), and the inlet pipe ( 201) is located above the circulation pipe (21), and the external cylinder (2) is also fixedly connected to a shunt cooling unit, and the shunt cooling unit includes a double-pass partition (41) fixedly connected to the front and rear inner walls of the external cylinder (2), a plurality of heat exchange combs (42) fixedly connected to the lower ends of the double-pass partition (41), and a plurality of connecting pipes (43) fixedly connected between two adjacent heat exchange combs (42). The frontmost heat exchange comb (42) is also fixedly connected to the inner wall of the external cylinder (2) with a connecting pipe (43). The discharge pipe (202), the connecting pipe (43) and the heat exchange comb (42) are connected to each other. The upper end of the double-pass partition (41) is opened with a plurality of evenly distributed (401), and the plurality of (401) are respectively connected to the plurality of heat exchange combs (42); The upper end of the double-pass partition (41) is also fixedly connected to a heat regulating unit. The inlet pipe (201) is in communication with the space between the double-pass partition (41) and the heat regulating unit. The circulation pipe (21) and the return pipe (22) are both in communication with the space below the double-pass partition (41). An oil sensing unit is installed on the discharge pipe (202).

2. The explosion-proof protective structure for a power transformer according to claim 1, characterized in that: The double-pass partition (41) is located above the center line of the external cylinder (2), and the plurality of connecting pipes (43) are all close to the lower edge of the heat exchange comb (42).

3. The explosion-proof protective structure for a power transformer according to claim 1, characterized in that: The heat regulating unit comprises a plurality of connecting pipes (52) respectively fixedly connected to the upper ends of the double-pass partitions (41) and a spring-loaded pocket (51) fixedly connected to the upper ends of the plurality of connecting pipes (52). The edges of the spring-loaded pocket (51) are all fixedly connected to the corresponding inner walls of the external cylinder (2). The spring-loaded pocket (51) is an elastic sealing structure. The plurality of connecting pipes (52) are respectively spaced apart from the plurality of communicating pipes (43). The connecting pipes (52) are fixedly passed through the double-pass partitions (41) and communicate with the space below the double-pass partitions (41).

4. The explosion-proof protective structure for a power transformer according to claim 3, characterized in that: The oil sensing unit comprises a reinforcement tube (61) fixedly connected to the outer end of the discharge tube (202) and a pressure sensor (601) mounted on the inner wall of the reinforcement tube (61); an annular groove is bored on the discharge tube (202); a protective ring sheet (62) is fixedly connected to the inner wall of the annular groove; and a flow sensor (63) is mounted on the inner wall of the discharge tube (202) close to the outer cylinder (2).

5. The explosion-proof protective structure for a power transformer according to claim 1, characterized in that: The return pipe (22) is close to the double-pass partition (41), the circulation pipe (21) is close to the bottom of the external cylinder (2), the liquid levels of the insulating oil in the oil pipe (3) and the external cylinder (2) are the same, and the liquid level is located between the double-pass partition (41) and the center line of the external cylinder (2).

6. The explosion-proof protective structure for a power transformer according to claim 5, characterized in that: The connecting pipe (43) is a corrugated pipe, and the heat exchange comb (42) is a split structure.

7. The explosion-proof protective structure for a power transformer according to claim 6, characterized in that: The heat exchange comb (42) comprises an upper connecting section (421) fixedly connected to the double-pass partition (41), a lower isolating section (422) fixedly connected to the lower end of the upper connecting section (421), two outer expansion pieces (424) respectively adsorbed on the outer surface of the lower isolating section (422), and two outer connecting pieces (423) respectively fixedly connected between the upper outer surface of the outer expansion piece (424) and the outer surface of the upper connecting section (421), and between the lower outer surface of the outer expansion piece (424) and the lower end of the lower isolating section (422).

8. The explosion-proof protective structure for a power transformer according to claim 7, characterized in that: The outer expansion piece (424) and the lower isolation section (422) are both made of magnetic material, and both have D-shaped cross-sections. The cross-sectional area of ​​the outer expansion piece (424) is larger than the cross-sectional area of ​​the lower isolation section (422). The outer connecting piece (423) is made of elastic sealing material.

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