Lightning stroke anti-bursting device for offshore wind turbine blade

Abstract

The invention discloses an offshore wind turbine blade lightning stroke anti-bursting device, and relates to the field of lightning protection. The lightning stroke anti-bursting device for the fan blade is composed of a fan blade with a micro exhaust channel of a layered structure, a detection device, a control device and an exhaust device. According to the fan blade with the layered structure and the micro-exhaust channels, the layered structure and the micro-exhaust channels are adopted, and gas generated in a sandwich layer of the blade after lightning stroke is exhausted into a cavity of the blade; the detection device comprises an induction metal sheet, an operational amplifier, a comparator and a transistor, predicts thunder and lightning and is matched with the control system to open the exhaust device in advance; the control system controls the work of the detection device and the exhaust device through a normally open relay; the air exhausting device is composed of an electromagnetic valve, a filtering cover, an auxiliary channel and an external power source, and the fan blade lightning stroke anti-bursting device can effectively prevent air bursting of the fan blade during lightning stroke.

Description

Technical Field

[0001] The present invention relates to the field of protection of new energy devices, and more specifically, to a lightning strike explosion-proof device for an offshore wind turbine blade. Background Art

[0002] Wind power generation has become the most technically mature, large-scale developable and commercially promising renewable energy power generation method in the world at present. Vigorously developing wind power has important strategic significance in aspects such as energy security, diversified energy supply, response to climate change, energy conservation and emission reduction.

[0003] At present, the lightning strike protection of wind turbine blades mainly relies on the lightning arrester downlead system, which is composed of tip and blade body lightning arresters connected to the grounding wire arranged inside the blade cavity. When a lightning strike occurs, the tip and blade body lightning arresters initiate upward leaders to intercept the downward leader of the lightning. After the upward and downward leaders are connected, the lightning current energy is discharged to the ground through the downlead, thereby protecting the blade and even the entire unit from lightning damage. However, according to statistics, the success rate of lightning strike interception by the current lightning arrester downlead system is only 90%. When the lightning arrester downlead system fails to intercept the downward leader of the lightning, the lightning impact high voltage will directly break through the blade body material and form a lightning strike arc connected to the downlead. The multi-field coupling effect of heat-magnetism-flow of the lightning strike arc will cause the blade material to burn, tear, and even crack and break in a large area. To solve the problem of lightning strike faults of wind turbine blades, in addition to the existing lightning arresters, the mechanical defense ability of the wind turbine blades themselves should also be strengthened.

[0004] After the lightning strikes the blade, the lightning current conducts to the middle of the composite material layer. Since there is still air in the interlayer water vapor or the bubble defects of the composite material itself, the huge energy released by the lightning causes the temperature inside the blade structure to rise sharply. The decomposed gas expands at high temperature, and the pressure rises, causing bursting damage. Due to the possible different distributions of water vapor at different materials and different parts inside the blade, this imbalance inside the material, under the action of high temperature and internal arc during the lightning process, causes rapid and unbalanced expansion, resulting in blade bursting or tearing damage to the blade surface along the leading and trailing edges and the blade load-carrying beam (from small cracks on the blade surface to complete fragmentation of the blade). In severe cases, the pressure wave will be conducted through the hub to the blades that have not been struck by lightning, causing chain damage. During a lightning strike, an arc is formed in the cavity or on the inner surface inside the blade, and a pressure shock wave is formed around the arc. The intense high temperature during the arc ignition process will also cause serious damage to the blade.

[0005] Aiming at the deficiencies of the current lightning strike explosion-proof and protection technology for offshore wind turbine blades, the present invention proposes a lightning strike explosion-proof device for offshore wind turbine blades. It can predict lightning before the lightning strike and open the exhaust device, and close the exhaust device after the lightning strike is completed, which can effectively adjust the air pressure on both sides of the blade and effectively protect the blade from gas bursting caused by lightning strikes. Summary of the Invention

[0006] The object of the present invention is to provide a lightning strike explosion-proof device for an offshore wind turbine blade. It can predict lightning before the lightning strike, open the exhaust device, and close the exhaust device after the lightning strike is completed, which can effectively adjust the air pressure on both sides of the blade and effectively protect the blade from gas explosion caused by lightning strikes.

[0007] To achieve the above object, the technical solution of the present invention is:

[0008] A lightning strike explosion-proof device for an offshore wind turbine blade, comprising a layered structure micro-exhaust channel wind turbine blade, a detection device, a control device and an exhaust device;

[0009] The layered structure micro-exhaust channel wind turbine blade adopts a layered structure and a micro-exhaust channel to discharge the gas generated in the blade sandwich layer after a lightning strike into the blade cavity; the layered structure micro-exhaust channel wind turbine blade adopts a three-layer structure, the outermost layer is the outer skin, the middle layer is the sandwich layer, and the innermost layer is the inner skin; its thickness distribution is optimized according to functional requirements and load characteristics; the outer skin accounts for 30%-40% of the total thickness, mainly providing rigidity, aerodynamic performance and external protection, usually made of carbon fiber or glass fiber reinforced composite materials; the sandwich layer accounts for 50%-60%, mainly made of lightweight foam or honeycomb materials, providing heat insulation, weight reduction and impact resistance, and can integrate micro-channels to relieve gas explosion after lightning strikes; the inner skin accounts for 10%-20%, enhancing the overall structural rigidity and protecting the sandwich layer; there are differences in the thickness distribution of different regions of the blade: the root region of the blade is thicker to withstand greater bending moment and torque, the middle region emphasizes the balance between lightweight and structural strength, and the tip region mainly minimizes the weight;

[0010] The root region of the blade withstands greater bending moment and torque, and the thickness needs to be increased. The thickness ratio is: outer skin: sandwich layer: inner skin = 4:5:1; the load in the middle region is medium, and the structure is mainly lightweight. The thickness ratio is: outer skin: sandwich layer: inner skin = 3.5:5.5:1; the load in the tip region is small for aerodynamic load, and the weight needs to be minimized. The thickness ratio is: outer skin: sandwich layer: inner skin = 3:6:1;

[0011] The micro-exhaust channels are mainly distributed in the sandwich layer, and the channel outlets are connected to the wind turbine blade cavity through the inner skin; the micro-exhaust channels are mainly distributed in the sandwich layer, and their distribution characteristics are in the form of a multi-layer network, and the channel diameter is about 3-5 mm. The specific value can be determined through experiments according to different materials; the channel outlets are connected to the wind turbine blade cavity through the inner skin;

[0012] The detection device includes an induction metal sheet, an operational amplifier, a comparator, and a transistor. It predicts lightning and is connected to the control system to open the exhaust device in advance. The induction metal sheet is placed 0.1 m away from the hub box at the top of the fan hub. The operational amplifier, comparator, and transistor are packaged and placed inside the fan hub. Preferably, the induction metal sheet is made of copper or aluminum material, which not only has good electrical conductivity but also helps to quickly sense the change of the electric field. Under anodizing treatment or with coating protection, it has good corrosion resistance. Preferably, the surface area of the induction metal sheet is 100 cm 2 (0.01 m 2 ) or so. The induction metal sheet is in the shape of a disc and parallel to the horizontal plane. When a thundercloud approaches, the induction metal sheet induces a voltage (the induced voltage is generally very small and cannot directly drive the relay). Through the operational amplifier, the signal is amplified so that it is sufficient to trigger the relay. According to the amplitude of the induction signal and the required relay control voltage, the gain is set by adjusting the feedback resistance of the operational amplifier. The gain should be large enough to ensure that the amplified voltage can drive the relay. To avoid the relay being triggered by each small electric field fluctuation, a threshold voltage is set through the comparator, and the relay is only triggered when the voltage exceeds this threshold. An NPN transistor is used as a switch. The output of the comparator is connected to the base of the transistor, and the switching of the transistor is controlled through an appropriate current-limiting resistor. The collector of the transistor is connected to one end of the relay, and the other end is connected to the power supply. When the transistor conducts, the relay is attracted. The relay power supply is usually independent of the signal circuit, and an appropriate power supply (such as 5V, 12V, or 24V) is required to provide sufficient current;

[0013] The control device controls the operation of the detection device and the exhaust device through a normally open relay. One end is connected to the detection device, and the other end is connected to the exhaust device. When the detection device is started, the normally open relay closes, the control circuit conducts, and the exhaust device is opened. The normally open relay is placed inside the fan blade hub. One end of its switch is connected to the detection device, and the other end is connected to the exhaust device. Preferably, the normally open relay selects relays with voltage levels such as 5V, 12V, 24V, etc.;

[0014] The exhaust device consists of an electromagnetic valve, a filter cover, a sub-channel, and a power supply. One end is connected to the control circuit. When the detection device and the control device are started, the series circuit of the power supply and the electromagnetic valve conducts, and the electromagnetic valve opens. The exhaust devices are distributed on the leeward side of the blades and are densely arranged at positions adjacent to the lightning arrester and sparsely arranged at positions far from the lightning arrester;

[0015] The filter covers are distributed at the notch of the concave-shaped housing, and one side is aligned with the outer skin on the leeward side of the fan; the filter covers have the function of filtering external moisture and salts, preventing external moisture and salt spray from entering the blade cavity; the inner surface of the filter covers is filled with materials such as polyvinyl alcohol, polyurethane, calcium chloride, and magnesium chloride, which have strong hygroscopicity and can absorb moisture and salt spray in the air;

[0016] The auxiliary channel is used to balance the air pressure inside and outside the blade cavity after lightning strikes; the auxiliary channel is distributed at the sunken wall at the notch of the concave-shaped housing, connecting the inner cavity of the fan blade and the notch of the concave-shaped housing; low-quality and low-density balls are placed inside the auxiliary channel. When the internal and external air pressures are balanced, the balls block the auxiliary channel. When the external air pressure is greater than the internal air pressure, the external gas bounces the balls open to connect the internal and external spaces, thus balancing the air pressure inside and outside the blade cavity after lightning strikes; multiple auxiliary channels are distributed around the sunken wall at the notch of the concave-shaped housing, connecting the inner cavity of the fan blade and the notch of the concave-shaped housing; the inlet and outlet of the auxiliary channel are circular, and the diameter is smaller than the diameter of the balls; the inner wall of the auxiliary channel is inclined to ensure that the balls bounced open after the air pressure inside and outside the blade cavity is balanced can block the inlet of the auxiliary channel. There should be a baffle at the outlet of the auxiliary channel to prevent the bounced balls from flying out of the auxiliary channel;

[0017] The electromagnetic valve consists of an electromagnetic chuck, a metal disc, a concave-shaped housing, a spring, a rubber patch, and an external power supply; after the control device is started, the external power supply is connected to the electromagnetic chuck circuit; at this time, the electromagnetic chuck generates magnetic force to attract the metal disc, and the metal disc separates from the concave-shaped housing, and the inner and outer spaces of the blade are connected; the spring connects the metal disc and the concave-shaped housing; in the normal closed state, the spring is in a stretched state to ensure that the spring connects the metal disc and the concave-shaped housing to fit tightly; rubber patches are respectively placed at the fitting positions of the metal disc and the concave-shaped housing to ensure that the metal disc and the concave-shaped housing fit tightly and play a buffering role when opening and closing;

[0018] The beneficial effects of the present invention: After lightning strikes the blade, the lightning current conducts to the middle of the composite material layer. Due to the air in the interlayer water vapor or the bubble defects of the composite material itself, the huge energy released by the lightning causes the temperature inside the blade structure to rise sharply. The decomposed gas expands at high temperature, and the pressure rises, causing bursting damage. In addition, an electric arc is formed in the cavity inside the blade during lightning strikes, and a pressure shock wave is formed around the electric arc. Intensely high-temperature and high-pressure gas is also generated during the arcing process, causing serious damage to the blade. There are few devices for preventing the explosion and cracking of offshore wind turbine blades during lightning strikes to reduce or avoid blade damage caused by gas explosion. The present invention provides a solution to the above problems, providing an offshore wind turbine blade lightning strike explosion prevention device. By predicting lightning before the lightning strike occurs and opening the exhaust device, and closing the exhaust device after the lightning strike is completed, the air pressure inside and outside the blade cavity can be effectively adjusted, and the gas explosion of the blade caused by lightning strikes can be effectively protected. Description of the Drawings

[0019] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

[0020] Figure 1 Structural diagram of a lightning strike explosion-proof device for an offshore wind turbine blade of the present invention;

[0021] Figure 2 Structural diagram of a layered structure micro-exhaust channel wind turbine blade of a lightning strike explosion-proof device for an offshore wind turbine of the present invention;

[0022] Figure 3 Structural diagram of a detection device of a lightning strike explosion-proof device for an offshore wind turbine blade of the present invention;

[0023] Figure 4 Control circuit diagram of a lightning strike explosion-proof device for an offshore wind turbine blade of the present invention;

[0024] Figure 5 Structural diagram of an exhaust device of a lightning strike explosion-proof device for an offshore wind turbine blade of the present invention;

[0025] Figure 6 Structural diagram of a secondary channel of a lightning strike explosion-proof device for an offshore wind turbine blade of the present invention;

[0026] Explanation of reference numerals: Layered structure micro-exhaust channel wind turbine blade (1), detection device (2), control device (3), exhaust device (4); Three-layer structure (101), outer skin (1011), sandwich layer (1012), inner skin (1013); Micro-exhaust channel (102); Blade cavity (103); Inductive metal sheet (201), operational amplifier (202), comparator (203), transistor (204); Normally open relay (301); Electromagnetic valve (401), electromagnetic chuck (4011), metal disc (4012), concave housing (4013), spring (4014), rubber patch (4015); Filter cover (402), secondary channel (403), ball (4031), secondary channel inlet (4032), secondary channel outlet (4033), secondary channel inner wall (4034); External power supply (404); Detailed implementation manners

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments; the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0028] The object of the present invention is to provide a lightning strike explosion-proof device for an offshore wind turbine blade. Lightning is predicted before the lightning strike, and the exhaust device (4) is opened. After the lightning strike is completed, the exhaust device (4) is closed, which can effectively adjust the air pressure on both sides of the blade and effectively prevent the blade gas explosion caused by lightning strikes.

[0029] To achieve the above object, the technical solution of the present invention is as follows:

[0030] First, in combination with Figure 1 、 Figure 2 and Figure 3 an offshore wind turbine blade lightning strike explosion-proof device provided by an embodiment of the present application is introduced. An offshore wind turbine blade lightning strike explosion-proof device includes a layered structure micro-exhaust channel wind turbine blade (1), a detection device (2), a control device (3), and an exhaust device (4); when a thundercloud comes and forms a leader discharge, charges will accumulate on the surface of the induction metal sheet (201) in the electric field. During the process of the thundercloud formation to discharge, the electric field will change, and an electromotive force (i.e., induced electromotive force) will appear on the induction metal sheet (201), which can be described by Faraday's law of electromagnetic induction. The magnitude of the induced electromotive force is related to the time change rate of the electric field. The specific formula is as follows: ε = -AdE(t) / dt A is the area of the induction metal sheet (201);

[0031] The induced electromotive force finally closes the normally open relay (301) through the operational amplifier (202), comparator (203) and transistor (204). Therefore, the detection device (2) is in the startup state during the period when the thundercloud comes and the leader discharge ends, ensuring that the control device (3) and the exhaust device (4) are in the operating state during lightning strikes. After the lightning strikes the blade, gas is generated under the coupling action of the strong electromagnetic and thermal fields on the blade. In addition, an arc is formed in the cavity inside the blade during lightning strikes, and a pressure shock wave is formed around the arc. Intense high-temperature and high-pressure gases are also generated during the arcing process. As shown in Figure 2, the gas generated under the coupling action of the strong electromagnetic and thermal fields on the blade enters the blade cavity (103) through the micro-exhaust channel (102) and is finally released to the external space through the exhaust device (4). After the lightning strike ends, the electric field around the induction metal sheet (201) is zero, the electromotive force induced in the changing electric field is zero, the output voltage of the detection device (2) is zero, the normally open relay (301) opens, and the control device (3) and the exhaust device (4) stop operating.

[0032] Figure 2 Figure 4 shows the structural diagram of the stratified micro-exhaust channel fan blade (1). The stratified micro-exhaust channel fan blade (1) designed in the present invention adopts a three-layer structure (101). The outermost layer is the outer skin (1011), the middle layer is the sandwich layer (1012), and the innermost layer is the inner skin (1013); the micro-exhaust channels (102) are mainly distributed in the sandwich layer (1012); its thickness distribution is optimized according to functional requirements and load characteristics; the outer skin (1011) accounts for 30%-40% of the total thickness, mainly providing rigidity, aerodynamic performance and external protection, and usually uses carbon fiber or glass fiber reinforced composite materials; the sandwich layer (1012) accounts for 50%-60%, mainly using lightweight foam or honeycomb materials, providing heat insulation, weight reduction and impact resistance, and can integrate micro-channels to relieve gas bursting after lightning strikes; the inner skin (1013) accounts for 10%-20%, enhancing the overall structural rigidity and protecting the sandwich layer (1012); there are differences in the thickness distribution of different regions of the blade: the root region of the blade is thicker to withstand greater bending moments and torques, the middle region emphasizes the balance between lightweight and structural strength, and the tip region mainly minimizes weight; the root region of the blade withstands greater bending moments and torques, and the thickness needs to be increased. The thickness ratio is: outer skin (1011): sandwich layer (1012): inner skin (1013) = 4:5:1; the load in the middle region is medium, and the structure is mainly lightweight. The thickness ratio is: outer skin (1011): sandwich layer (1012): inner skin (1013) = 3.5:5.5:1; the load in the tip region is relatively small for aerodynamic loads, and the weight needs to be minimized. The thickness ratio is: outer skin (1011): sandwich layer (1012): inner skin (1013) = 3:6:1;

[0033] Since the sandwich layer (1012) is the main part that generates gas after being struck by lightning, the micro-exhaust channels (102) are mainly distributed in the sandwich layer (1012), and the channel outlets communicate with the blade cavity (103) through the inner skin (1013); their distribution characteristics are in a multi-layer mesh form, and the channel diameter is about 3-5 mm. The specific value can be determined through experiments according to different materials; the gas generated after the lightning strikes the blade overflows into the micro-exhaust channels (102) of the sandwich layer (1012); when the amount of overflowing gas reaches a certain level, it enters the blade cavity (103) through the connecting part of the inner skin (1013).

[0034] Figure 5 This is the structural diagram of the exhaust device of a lightning strike explosion-proof device for an offshore wind turbine blade of the present invention; the exhaust device (4) is distributed on the leeward side of the blade and is densely arranged at positions adjacent to the lightning arrester; it is sparsely arranged at positions far from the lightning arrester; the exhaust device (4) is composed of an electromagnetic valve (401), a filter cover (402), a sub-channel (403), and an external power supply (404); the electromagnetic valve (401) is composed of an electromagnetic chuck (4011), a metal disc (4012), a concave shell (4013), a spring (4014), and a rubber patch (4015); one end of the exhaust device (4) is connected to the control device (3). When the detection device (2) and the control device (3) are started, the series circuit of the external power supply (404) and the electromagnetic valve (401) is turned on. At this time, the electromagnetic chuck (4011) generates a magnetic force to attract the metal disc (4012), and the metal disc (4012) separates from the shaped shell (4013), and the internal and external spaces of the blade are connected, and the electromagnetic valve (401) is opened.

[0035] As Figure 5 shown, the spring (4014) connects the metal disc (4012) and the concave shell (4013); in the normal closed state, the spring (4014) is in a stretched state to ensure that the metal disc (4012) and the concave shell (4013) are closely attached.

[0036] The rubber patches are respectively placed at the joint of the metal disc (4012) and the concave shell (4013) to ensure that the metal disc (4012) and the concave shell (4013) are closely attached and play a buffering role when opening and closing; the filter cover (402) is located at the notch of the concave shell (4013), and one side is aligned with the outer skin on the leeward side of the fan.

[0037] As Figure 6As shown, low-quality and low-density small balls (4031) are placed inside the secondary channel (403). When the internal and external air pressures are balanced, the small balls (4031) block the secondary channel (403). When the external air pressure is greater than the internal air pressure, the external gas bounces the small balls (4031) away to connect the internal and external spaces, thus balancing the air pressures inside and outside the blade cavity (103) after lightning strikes. The secondary channels (403) are distributed at the sunken wall (4016) at the notch of the concave outer shell (4013), connecting the inner cavity of the fan blade with the notch of the concave outer shell (4013).

[0038] Before the thundercloud approaches and lightning strikes, the exhaust device opens in advance. During lightning strikes, the high-temperature and high-pressure gas generated is discharged through the exhaust device. After lightning strikes, the detection device (2) stops operating, the normally open relay (301) disconnects, and the series circuit of the external power supply (404) and the solenoid valve (401) is disconnected. At this time, the electromagnetic chuck (4011) separates from the metal disc (4012), and under the elastic force of the spring, the metal disc (4012) closes with the outer shell (4013), and the solenoid valve (401) closes. Although after lightning strikes, the air pressures inside and outside the exhaust device blades become the same, the inside of the blades is still filled with high-temperature gas at this time. As time passes, the temperature inside the blades gradually decreases. At this time, the external air pressure is greater than the internal air pressure of the blades. If the internal and external air pressures are not adjusted, it will cause damage to the blades. The secondary channel has the function of solving the above problems. When the external air pressure is greater than the internal air pressure, the external gas bounces the small balls (4031) away to connect the internal and external spaces, thus balancing the air pressures inside and outside the blade cavity (103) after lightning strikes.

Claims

1. A lightning strike explosion-proof device for an offshore wind turbine blade, characterized in that: It includes a layered structure micro-exhaust channel fan blade (1), a detection device (2), a control device (3), and an exhaust device (4); The layered structure micro-exhaust channel fan blade (1) adopts a three-layer structure (101) and micro-exhaust channels (102) to discharge the gas generated in the blade sandwich layer (1012) after lightning strikes into the blade cavity (103); The detection device (2) is composed of an induction metal sheet (201), an operational amplifier (202), a comparator (203), and a transistor (204). It predicts lightning and is connected to the control device (3) to open the exhaust device (4) in advance. The induction metal sheet (201) is placed at the top of the fan hub, 0.1 m away from the hub box. The operational amplifier (202), comparator (203), and transistor (204) are encapsulated and placed in the fan hub. The induction metal sheet (201) is disc-shaped and parallel to the horizontal plane; The control device (3) controls the operation of the detection device (2) and the exhaust device (4) through the opening and closing of a normally open relay (301). One end of it is connected to the detection device (2), and the other end is connected to the exhaust device (4). When the detection device (2) is activated, the normally open relay (301) closes, and the series circuit of the external power supply (404) and the solenoid valve (401) is turned on to open the exhaust device (4); The exhaust device (4) is composed of a solenoid valve (401), a filter cover (402), a secondary channel (403), and an external power supply (404). One end of it is connected to the control device (3). After the detection device (2) and the control device (3) are activated, the series circuit of the external power supply (404) and the solenoid valve (401) is turned on, and the solenoid valve (401) opens. The filter cover (402) has the function of filtering external moisture and salts. The secondary channel (403) functions to balance the air pressure inside and outside the blade cavity (103) after lightning strikes. The external power supply (404) functions to provide electrical energy for the solenoid valve (401).

2. The hierarchical micro-exhaust channel fan blade (1) according to claim 1, wherein: The fan blade adopts a three-layer structure (101), with the outermost layer being the outer skin (1011), the middle layer being the sandwich layer (1012), and the innermost layer being the inner skin (1013). The micro-exhaust channels (102) are mainly distributed in the sandwich layer (1012), and the channel outlets are connected to the fan blade cavity (103) through the inner skin (1013).

3. The control device (3) according to claim 1, characterized in that: The normally open relay (301) is placed inside the fan blade hub. One end of its switch is connected to the detection device (2), and the other end is connected to the exhaust device (4).

4. The exhaust device (4) according to claim 1, characterized in that: The exhaust device (4) is distributed on the leeward side of the blade and is densely arranged at positions adjacent to the lightning arrester and sparsely arranged at positions far from the lightning arrester.

5. The electromagnetic valve (401) according to claim 1, characterized in that: The solenoid valve (401) is composed of an electromagnetic chuck (4011), a metal disc (4012), a concave shell (4013), a spring (4014), and a rubber patch (4015).

6. The filter cover (402) according to claim 1, characterized in that: The filter cover (402) is distributed at the notch of the concave shell (4013), and one side is aligned with the outer skin on the leeward side of the fan.

7. The sub-channel (403) according to claim 1, characterized in that: Low-quality and low-density small balls (4031) are placed inside the auxiliary channel (403). When the internal and external air pressures are balanced, the small balls (4031) block the auxiliary channel (403). When the external air pressure is greater than the internal air pressure, the external gas bounces the small balls (4031) away to connect the internal and external spaces, thus balancing the air pressures inside and outside the blade cavity (103) after lightning strikes; Multiple auxiliary channels (403) are distributed around the recessed wall (4016) at the notch of the concave-shaped housing (4013), connecting the inner cavity of the fan blade with the notch of the concave-shaped housing (4013); the auxiliary channel inlet (4032) and the auxiliary channel outlet (4033) are circular, and their diameters are smaller than the diameter of the small balls (4031); the inner wall (4034) of the auxiliary channel is inclined to ensure that the small balls (4031) bounced away after the air pressures inside and outside the blade cavity (103) are balanced can block the auxiliary channel inlet (4032), and there should be a baffle at the auxiliary channel outlet (4033) to prevent the bounced small balls (4031) from flying out of the auxiliary channel (403).

8. The spring (4014) according to claim 5, characterized in that: The spring (4014) connects the metal disc (4012) and the concave-shaped housing (4013); in the normal closed state, the spring (4014) is in a stretched state to ensure that the spring (4014) connecting the metal disc (4012) and the concave-shaped housing (4013) fits tightly.

9. The rubber patch (4015) according to claim 5, characterized in that: The rubber patches (4015) are respectively placed at the fitting positions of the metal disc (4012) and the concave-shaped housing (4013) to ensure that the metal disc (4012) and the concave-shaped housing (4013) fit tightly and play a buffering role when opening and closing.

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