A bottom-exhaust traction transformer cooling structure

Abstract

This utility model provides a down-draft traction transformer cooling structure, belonging to the field of traction transformer technology. The down-draft traction transformer cooling structure includes an annular groove fixed to the wall of the duct outlet, a flexible air duct housed within the groove, a rotatable hinge connecting one edge of the air duct to the bottom of the groove, fusible alloy pins spaced circumferentially along the groove opening, and elastic reset ribs located at the free edge of the air duct. When in the retracted state, the air duct is constrained by the pins and completely folded into the groove. After the pins melt, the air duct flips outwards due to the self-opening force of the elastic reset ribs, transforming the air duct from a folded state to a cylindrical extended state. This increases the effective exhaust area of ​​the duct outlet, solving the technical problem that the down-draft traction transformer cooling structure cannot expand its exhaust area during transient overheating due to a fault, leading to a sudden accumulation of heat and gas, endangering the safety of the oil tank.

Description

Technical Field

[0001] This utility model belongs to the field of traction transformer technology, and specifically relates to a cooling structure for a downdraft traction transformer. Background Technology

[0002] Downdraft traction transformer cooling structures are a crucial heat dissipation component of rail vehicle power systems. The core idea is to guide the heat generated by the transformer's hot oil circulation to the space beneath the vehicle via bottom air ducts. Utilizing the negative pressure created by train movement or fan operation, hot air is expelled downwards, achieving oil-air heat exchange. Compared to traditional side or top exhaust systems, downdraft systems leverage high-speed airflow under the vehicle to enhance heat exchange, preventing hot air from directly blowing onto electrical equipment on the roof and reducing the probability of rain, snow, and dust entering the oil tank. Therefore, they are widely used in mainline locomotives and urban rail vehicles. A typical structure involves installing finned tube or corrugated wall radiators below the oil tank, with rigid air ducts connected to the radiator outlets. The duct openings are usually equipped with fixed louvers or protective nets to guide airflow and block foreign objects. The entire cooling path relies on the external negative pressure created by continuous vehicle operation. Once the train stops or operates at low speeds, axial flow fans are used to maintain the necessary exhaust volume.

[0003] The drawbacks of traditional structures are mainly reflected in three aspects: rigidity, lack of adjustability, and lack of emergency response. First, the duct outlet area is designed based on the maximum continuous load. During normal operation at low loads, this leads to excessive cooling, increased oil viscosity, and increased pumping losses. In case of overload or short-circuit faults, the fixed cross-section cannot provide additional exhaust capacity, and the heat dissipation rate is far lower than the heat generation rate, resulting in temperature spikes. Second, the narrow space under the vehicle and the interference of components such as bogies, brake lines, and cable supports prevent the expansion of the exhaust area by connecting temporary external ducts. In the event of abnormal temperature rise, maintenance personnel can only reduce power output or stop the vehicle to allow it to cool down, disrupting traffic flow. Third, traditional louvers or grilles are static components, lacking effective means of separating high-speed oil mist. After long-term operation, oil droplets are carried by the airflow to the underside of the vehicle, polluting the environment and causing a hidden drop in oil level. More importantly, when an arcing fault occurs inside the transformer, the insulating oil decomposes rapidly, generating a large amount of gas, causing a sudden increase in tank pressure. The fixed exhaust cross-section cannot form a rapid pressure relief channel, and the pressure wave may tear the tank seals, even causing a fire. Existing technologies have attempted to add electrically controlled louvers or rupture membranes inside the air duct, but the electrical control scheme relies on sensors and power supplies, and its reliability is limited by electromagnetic interference and maintenance cycles; once the rupture membrane is activated, it needs to be replaced as a whole and cannot be reused, and there is a risk that fragments may enter the fan and damage the blades. Utility Model Content

[0004] In view of this, the present invention provides a bottom-exhaust traction transformer cooling structure, which solves the technical problem that the bottom-exhaust traction transformer cooling structure has a fixed exhaust area that cannot be expanded in an emergency during transient overheating due to a fault, resulting in a sudden accumulation of heat and gas, endangering the safety of the oil tank.

[0005] This utility model is implemented as follows:

[0006] This utility model provides a cooling structure for a downdraft traction transformer, used at the end of the cooling duct of a downdraft traction transformer, wherein:

[0007] It includes an annular groove fixed to the wall of the air duct outlet, a flexible air duct housed in the groove, a foldable hinge that forms a rotatable connection between one edge of the air duct and the bottom of the groove, fusible alloy pins arranged circumferentially along the opening of the groove, and elastic reset ribs provided at the free edge of the air duct.

[0008] When the duct is in the retracted state, it is completely folded and embedded in the groove by the pin. After the pin melts, it flips outward by the self-developing opening force of the elastic reset rib, so that the duct changes from the folded state to the cylindrical extension state, thereby increasing the effective exhaust area of ​​the duct outlet.

[0009] The technical effects of the down-draft traction transformer cooling structure provided by this utility model are as follows: By combining an annular groove, a flexible air duct, a foldable hinge, a fusible pin, and an elastic reset rib, a "passive trigger-self-expanding" exhaust expansion mechanism is formed. When the transformer is working normally, the air duct is hidden in the groove and does not increase the wind resistance. Once the inside is overheated, the pin melts, and the elastic rib instantly releases the preload force to flip the air duct out, which greatly increases the outlet area of ​​the cooling air duct and quickly dissipates the sudden increase in heat. After the fault is cleared, the air duct can be manually pressed back into the groove and the pin can be replaced to restore the structure. This realizes the emergency cooling function of one-time trigger and repeated use.

[0010] Based on the above technical solution, the cooling structure of the down-draft traction transformer of this utility model can be further improved as follows:

[0011] The groove is formed by recessing outward from the outlet end wall of the air duct. The groove depth is sufficient to accommodate the thickness of the fully folded air duct and its hinge. The outer peripheral surface of the groove smoothly transitions with the outer wall of the air duct to avoid airflow vortices.

[0012] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: the groove depth is limited to accommodate the folding air duct and hinge, and the outer periphery of the groove is smoothly transitioned to the outer wall of the air duct, avoiding the generation of vortices by the protrusion. Thus, without changing the original aerodynamic shape of the air duct, a compact storage space is provided for the concealed air duct, ensuring low resistance and low noise during daily operation.

[0013] Furthermore, the duct material is glass fiber cloth coated with high-temperature resistant silicone. Its base is truncated cone-shaped, with the small end connected to the bottom of the groove via a foldable hinge, and the large end being a free edge. The angle between the generatrix of the cone and the axis of the duct remains acute in the unfolded state, so as to form an outwardly expanding guide tube.

[0014] The beneficial effects of adopting the above-mentioned improved scheme are as follows: using a truncated conical silicone-coated fiberglass cloth as the air duct, with its small end fixed and its large end free, it naturally forms an outward-expanding guide cone after unfolding, which can guide the high-speed hot flow away from the equipment and prevent the hot air from flowing back at the outlet. At the same time, the silicone layer isolates oil mist and extends the life of the cloth base.

[0015] Furthermore, the foldable hinge is made of stainless steel sheet continuously stamped into V-shaped folds, the root of the fold is riveted to the bottom of the groove, and the fold wings are vulcanized into one piece with the small end edge of the air duct, so that the air duct always maintains symmetrical movement around the air duct outlet axis during unfolding and folding.

[0016] The beneficial effects of adopting the above-mentioned improved scheme are as follows: using continuous V-shaped stainless steel folds as hinges, with the root of the folds riveted to the grooves and the wings vulcanized into one piece with the air duct, the air duct always opens and closes symmetrically along the folds during unfolding or folding, the movement trajectory is determined and there is no jamming, ensuring that each trigger action is reliable and the reset is smooth.

[0017] Furthermore, the elastic reset rib is a spiral spring steel strip embedded in the free edge of the air duct. The spring steel strip is closed into a loop in the circumferential direction, and its two ends are bent in opposite directions in the air duct unfolding direction to form pre-tightening hooks, so as to store and release the torque that causes the air duct to unfold.

[0018] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: a spiral spring steel strip is embedded in the free edge of the air duct. The steel strip closes into a ring and bends in the opposite direction at both ends to form a pre-tightening hook. Torque can be stored in the folded state and released instantaneously after the pin melts. The flexible fabric edge is supported as a whole to form a rigid ring, ensuring that the air duct is fully unfolded and maintains its cylindrical shape, thereby improving the ventilation.

[0019] Furthermore, one end of the pin is inserted into the countersunk hole at the outer edge of the groove, and the other end abuts against the outward folded edge of the free edge of the air duct. The pin body extends radially along the air duct and completely detaches from the groove after melting, thereby releasing the mechanical constraint on the air duct.

[0020] The beneficial effects of adopting the above-mentioned improved scheme are as follows: the fusible pin is arranged radially, with one end sinking into the groove and the other end pressing against the outward folded edge of the air duct. After melting, the pin falls off as a whole, releasing the point-to-line circumferential constraint, allowing the air duct to be released synchronously in all directions, and avoiding incomplete unfolding caused by local lag.

[0021] Furthermore, the melting point of the pin is lower than the temperature at which the transformer oil cracks and produces gas, but higher than the highest oil temperature during normal operation, so that the pin only melts when there is a fault and overheating, thereby ensuring that the duct remains sealed during normal operation.

[0022] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: by limiting the melting point of the pin to between the normal maximum oil temperature and the oil cracking gas production temperature, the pin melts only when the fault temperature rises, which not only prevents daily thermal aging from causing false activation, but also ensures timely response when there is real overheating, realizing a one-to-one pure thermal triggering logic of "temperature threshold-mechanical action".

[0023] Furthermore, the outer side of the free edge of the air duct is provided with a surrounding flange. After the air duct is unfolded, the surrounding flange overlaps the outer wall of the air duct outlet to prevent external rainwater from entering the air duct in reverse. When the air duct is folded, it is embedded in the annular groove of the groove opening to form a sealing lip.

[0024] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: a surrounding flange is set on the outside of the free edge of the air duct. When unfolded, the flange overlaps the outer wall of the air duct to form a rainproof lip. When folded, it is pressed into the groove and ring groove to serve as a seal. The same part plays the roles of waterproofing and dust sealing in the two states respectively, without the need for additional sealing elements.

[0025] Furthermore, a pressure relief notch is provided at the bottom of the groove, which communicates with the interior of the air duct. The area of ​​the pressure relief notch is smaller than the minimum flow area after the air duct is deployed. This is used to quickly release the hot air accumulated in the groove during the initial deployment of the air duct and reduce the deployment resistance.

[0026] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: a pressure relief gap is opened at the bottom of the groove and communicates with the inside of the air duct. The area of ​​the gap is smaller than the minimum flow area of ​​the unfolded air duct. This allows the high-pressure hot air in the groove to be released before the air duct is fully opened, reducing the unfolding resistance. Once the air duct forms a complete cylindrical channel, the main airflow still passes through the inside of the cylinder. The gap will not become an exhaust bottleneck, thus taking into account both the dual requirements of "assisting unfolding" and "ensuring flow".

[0027] Furthermore, the pressure relief gap is a fan-shaped hole evenly distributed on the bottom surface of the annular groove. Its total area is set to 30% to 50% of the minimum cross-sectional area of ​​the cylindrical channel formed by the flexible air duct in the fully deployed state. This allows the gap to release the hot air accumulated in the groove before the air duct is deployed. After the air duct is deployed, the flow area of ​​the cylindrical channel is kept to be more than twice the area of ​​the gap.

[0028] Compared with existing technologies, the beneficial effects of the down-draft traction transformer cooling structure provided by this utility model are as follows: While maintaining the original advantages of down-draft cooling, this utility model provides a new technical path for transformer cooling systems through the combination of a concealed, foldable air duct and a heat-triggered mechanical release, offering low resistance under normal conditions, emergency response in case of abnormalities, and post-event recovery. Its core lies in folding and storing the flexible, high-temperature resistant air duct within an annular groove on the outlet wall of the air duct. During normal operation, it does not change the aerodynamic shape of the air duct, does not increase additional resistance, and does not introduce new noise sources. When the internal oil temperature rises sharply to a set threshold due to a short circuit or overload, the fusible alloy pin melts, and the air duct, driven by its own elastic ribs, instantly folds outward, forming an outwardly expanding guide tube. The exhaust area then expands, and the hot airflow is rapidly discharged within a larger cross-section, simultaneously alleviating the pressure and temperature rise within the oil tank and preventing the continuous accumulation of oil cracking gases. After the fault is cleared, maintenance personnel only need to manually press the air duct back into the groove and replace the pin to restore it to its original state. The entire process requires no power, air supply, or special tools, and the maintenance workload is comparable to that of traditional filter replacement, achieving the convenience of "one-time trigger, unlimited cycles". Since the unfolding action is purely driven by a temperature-driven mechanical mechanism, the system is not affected by electromagnetic interference, vibration, or dust, and its reliability is higher than that of electronic control schemes. At the same time, the air duct material is made of silicone-coated fiberglass cloth, which combines flexibility, high temperature resistance, and resistance to oil mist corrosion. Long-term folding will not cause permanent deformation, ensuring the reliability of repeated unfolding. In addition, the conical airflow channel formed after the air duct is folded outward can guide hot air away from the equipment under the vehicle, reducing the probability of secondary heat backflow and also reducing the thermal aging effect of high-temperature gas on nearby cables and brake hoses. The surrounding flange of the free edge of the air duct overlaps with the outer wall of the air duct after unfolding, which also has the functions of rain protection and dust protection. When folded, it is pressed into the groove to form a seal, preventing dust from accumulating in the groove during operation. The pressure relief notch allows the high-pressure hot air in the groove to be discharged before the duct is fully opened, reducing the resistance to deployment and ensuring rapid and reliable operation. The notch area is smaller than the minimum flow area of ​​the deployed duct, ensuring that the main airflow is still discharged through the cylindrical channel and that the emergency ventilation capacity is not weakened due to the notch diversion. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments of this utility model will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is an example diagram of a bottom-exhaust traction transformer cooling structure.

[0031] Figure 2This is a side view of a bottom-exhaust traction transformer cooling structure;

[0032] Figure 3 A perspective view of a bottom-exhaust traction transformer cooling structure;

[0033] The attached diagram lists the components represented by each number as follows:

[0034] 10. Groove; 20. Air duct; 30. Foldable hinge; 40. Pin; 50. Flexible return rib. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings.

[0036] like Figures 1-3 The diagram shown is an example of a cooling structure for a downdraft traction transformer provided by this utility model, used at the end of the cooling duct of a downdraft traction transformer, wherein:

[0037] It includes an annular groove 10 fixed to the wall of the air duct outlet, a flexible air duct 20 housed in the groove 10, a foldable hinge 30 that forms a rotatable connection between one edge of the air duct 20 and the bottom of the groove 10, fusible alloy pins 40 arranged circumferentially along the opening of the groove 10, and elastic reset ribs 50 provided on the free edge of the air duct 20.

[0038] When the duct 20 is in the storage state, it is constrained by the pin 40 and completely folded into the groove 10. After the pin 40 melts, it flips outward by the self-developing opening force of the elastic reset rib 50, so that the duct 20 changes from the folded state to the cylindrical extended state, thereby increasing the effective exhaust area of ​​the duct outlet.

[0039] In the above technical solution, the groove 10 is formed by recessing outward from the outlet end wall of the air duct. The depth of the groove 10 is sufficient to accommodate the thickness of the fully folded air duct 20 and its hinge. The outer peripheral surface of the groove 10 smoothly transitions with the outer wall of the air duct to avoid airflow vortices.

[0040] Furthermore, in the above technical solution, the air duct 20 is made of glass fiber cloth coated with high-temperature resistant silicone. Its cloth base is truncated cone-shaped. The small end is connected to the bottom of the groove 10 through a foldable hinge 30, and the large end is a free edge. The angle between the cone generatrix and the air duct axis remains acute in the unfolded state to form an outwardly expanding guide tube.

[0041] Furthermore, in the above technical solution, the foldable hinge 30 is continuously stamped into a V-shaped fold from a thin stainless steel sheet. The root of the fold is riveted to the bottom of the groove 10, and the fold wing is vulcanized into one piece with the small end edge of the air duct 20, so that the air duct 20 always maintains symmetrical movement around the air duct outlet axis during the unfolding and folding process.

[0042] Furthermore, in the above technical solution, the elastic reset rib 50 is a spiral spring steel strip embedded in the free edge of the air duct 20. The spring steel strip is closed into a ring in the circumferential direction, and its two ends are bent in opposite directions in the unfolding direction of the air duct 20 to form pre-tightening hooks, so as to store and release the torque that causes the air duct 20 to unfold.

[0043] Furthermore, in the above technical solution, one end of the pin 40 is inserted into the countersunk hole on the outer edge of the groove 10, and the other end presses against the outward folded edge of the free edge of the air duct 20. The body of the pin 40 extends radially along the air duct and completely detaches from the groove 10 after melting, so as to release the mechanical constraint on the air duct 20.

[0044] Furthermore, in the above technical solution, the melting point of the pin 40 is lower than the temperature at which the transformer oil cracks and produces gas, but higher than the highest oil temperature during normal operation, so that the pin 40 only melts when there is a fault and overheating, thereby ensuring that the duct 20 remains sealed during normal operation.

[0045] Furthermore, in the above technical solution, the outer side of the free edge of the air duct 20 is provided with a surrounding flange. After the air duct 20 is unfolded, the surrounding flange overlaps with the outer wall of the air duct outlet to prevent external rainwater from entering the air duct in reverse. When the air duct 20 is folded, it is embedded in the annular groove of the groove 10 opening to form a sealing lip.

[0046] Furthermore, in the above technical solution, a pressure relief notch is provided at the bottom of the groove 10, which is connected to the inside of the air duct. The area of ​​the pressure relief notch is smaller than the minimum flow area after the air duct 20 is deployed. This is used to quickly release the hot air accumulated in the groove 10 in the early stage of the deployment of the air duct 20, thereby reducing the deployment resistance.

[0047] Furthermore, in the above technical solution, the pressure relief gap is a fan-shaped hole evenly distributed on the bottom surface of the annular groove 10. Its total area is set to 30% to 50% of the minimum cross-sectional area of ​​the cylindrical channel formed by the flexible air duct 20 in the fully deployed state. This allows the gap to release the hot air accumulated in the groove 10 before the air duct 20 is deployed. After the air duct 20 is deployed, the flow area of ​​the cylindrical channel is maintained at more than twice the area of ​​the gap.

[0048] Example 1: On a high-altitude trunk line at 3,000 meters above sea level with a continuous 20-kilometer gradient of 20 per thousand, the locomotive traction transformer needs to operate at full power for extended periods, in an environment with thin air and large diurnal temperature variations. This example directly embeds the structure described in the claim into the outlet end of the existing rectangular steel air duct under the train: a 25-millimeter-deep annular groove with a width matching the folded thickness of the air duct is machined in the center of a 4-millimeter-thick low-carbon steel end plate; six fan-shaped pressure relief notches are formed on the bottom surface of the groove through punching, with a total area approximately 40% of the minimum flow area of ​​the unfolded conical air duct, ensuring both pressure relief and no weakening of the main exhaust capacity. The flexible air duct uses fiberglass cloth coated with high-temperature resistant silicone, with the cloth base cut into a truncated cone shape. The diameter of the small end is equal to the inner diameter of the air duct, and the diameter of the large end is 1.3 times larger than the small end, forming an outwardly expanding guide cone after unfolding; the edge of the small end is vulcanized integrally with a continuous "V"-shaped stainless steel hinge, and the root of the hinge is fixed to the bottom surface of the groove with rivets evenly distributed in a circular pattern to ensure uniform turning force. The elastic reset rib is made of stainless steel spring steel with a rectangular cross-section. After being coiled into a complete circle, both ends are bent in the opposite direction to form pre-tightening hooks, which are pressed into the groove to store torque when the air duct is folded. The fusible alloy pin is made of bismuth-tin alloy with a melting point of 120 degrees Celsius, and is made into a cylindrical pin with a diameter of 5 mm. One end is tightly fitted into the countersunk hole on the outer edge of the groove, and the other end presses against the outward folded edge of the air duct, providing circumferential constraint for the air duct. During daily operation, the locomotive passes through long slopes at a speed of 60 km / h. The external negative pressure is sufficient, and the air duct is hidden in the groove, with the air duct resistance consistent with the original. When the traction winding experiences a surge in oil temperature due to continuous high current, the heat is conducted through the air duct wall to the pin, which melts rapidly. The elastic rib releases the torque, and the air duct flips outward within 0.5 seconds, instantly expanding the exhaust area. The gas and heat generated by the decomposition of hot oil are quickly discharged to the outside of the sleeper through the expanded conical channel, preventing gas from accumulating in the oil tank. After the fault is cleared, the locomotive is put into the depot for maintenance. The maintenance personnel only need to press the air duct to fold it back into the groove and insert a new pin to complete the reset. There is no need to disassemble the air duct or add oil. The whole process does not change the car body structure and does not add daily maintenance points. It is especially suitable for plateau railways with limited space and short maintenance windows.

[0049] Example 2: Subway trains operate in underground sections with short station intervals and frequent starts and stops. Transformer loads experience periodic peaks, and the tunnels are dusty and humid, with the ventilation duct outlet only 300 mm from the rail surface. This example integrates the claimed structure into the end of a cylindrical ventilation duct cast in aluminum alloy: an annular groove is directly cast around the outer periphery of the ventilation duct outlet flange, with a depth sufficient to accommodate three layers of folded ventilation ducts. An annular sealing lip is provided along the outer edge of the groove, flush with the rainproof side beam of the car body underframe, preventing backflow of water during tunnel cleaning. The flexible ventilation duct uses a 0.5 mm thick silicone fiberglass composite cloth with an anti-mildew treatment. It is cut into a cylindrical shape rather than a truncated cone, allowing it to extend straight when unfolded, directly discharging hot air towards the center of the track and preventing heat flow from eroding the tunnel sidewall cables. The hinges are replaced with six sets of spaced stainless steel hinges. One end of each hinge is pre-embedded in the bottom of the cast aluminum groove, and the other end is riveted to the inside of the ventilation duct, allowing the ventilation duct to extend axially as a whole when unfolded, with a straight movement trajectory suitable for low-ceilinged spaces. The elastic reset rib is made of two semi-circular spring steel bars joined together, with quick-release clips at the joint for easy replacement inside the tunnel. The rib is wrapped with an insulating sleeve to prevent electrochemical corrosion caused by contact between the steel bars and the aluminum alloy groove wall. The melting point of the fusible alloy pin remains at 120 degrees Celsius, but its shape has been changed to a stepped pin with a flange head. The flange head is recessed into the outer wall of the groove, and the pin body passes through the reinforcing webbing on the free edge of the ventilation duct. After melting, the flange head remains in the countersunk hole for easy collection, preventing small parts from falling onto the track. The pressure relief notch has been adjusted to four elongated oval holes, with the total area controlled at 35% of the flow area of ​​the unfolded straight ventilation duct, to accommodate the relatively low external negative pressure inside the subway tunnel. When the train is running at full speed inside the tunnel, the external air pressure fluctuates violently. The concealed state of the ventilation duct ensures the integrity of the aerodynamic shape of the ventilation duct. When the traction transformer load suddenly increases during the acceleration phase after leaving the station, the oil temperature rises rapidly. After the pin melts, the ventilation duct extends straight along the hinge track, forming a straight-cylinder emergency exhaust channel. Hot air is directly discharged downwards to the track area, quickly reducing the internal pressure of the oil tank. Since subway nighttime maintenance time is only two hours, this embodiment uses a quick-release structure for the pin and elastic ribs, allowing maintenance personnel to complete the replacement in five minutes. The ventilation duct fabric can be washed and then folded back to its original position, meeting the high-frequency, short-window maintenance needs of underground lines. Both embodiments are within the scope of the claims. By changing the shape of the ventilation duct, the hinge form, and the pin structure, they adapt to the different spaces, climates, and maintenance conditions of plateau railways and underground urban rail transit, respectively, verifying the versatility and reliability of this utility model in various operating environments.

[0050] Specifically, the principle of this invention is as follows: This invention utilizes the coupling of material phase transition temperature and elastic potential energy to achieve passive control of temperature threshold, mechanical action, and area abrupt change. The fusible alloy pin remains solid at room temperature, locking the free edge of the flexible duct within the annular groove. At this time, the duct is in a folded and retracted state, and the elastic ribs store torque due to bending. When an internal transformer fault causes a rapid increase in oil temperature, heat is conducted outward through the duct wall. After absorbing heat, the pin reaches its melting point and undergoes a solid-liquid phase transition, instantly losing strength. The circumferential constraint on the duct is then released, and the elastic ribs release the stored torque, pushing the flexible fabric edge outward. The duct rotates along a preset hinge trajectory, forming a continuous and smooth guide cone surface. The exhaust channel expands from its original fixed cross-section to an additional cylindrical cross-section. The hot airflow continues to expand and accelerate in a larger space. According to the continuity equation, the flow velocity decreases and the flow rate increases, rapidly drawing out the high-temperature gas in the oil tank, achieving transient heat and pressure relief. After the air duct is deployed, its conical generatrix forms an acute angle with the duct axis, utilizing the Coanda effect to guide airflow to adhere to the duct wall, reducing separation vortices and lowering exhaust noise. Simultaneously, the conical outlet directs hot air to the outside of the vehicle undercarriage, preventing hot air from swirling within the bogie cavity and suppressing secondary heating. Since the entire operation relies solely on the phase change of the pin and the energy release of the elastic ribs, no external signal or power is required. The response speed is limited only by the heat conduction path, theoretically achieving millisecond-level triggering, meeting the release requirements of rapidly generated gas in the early stages of an arc fault. During reset, the air duct is manually pressed back into the groove, the elastic ribs bend again to store energy, and replacing the pin allows for relocking, completing one full cycle of "energy storage-trigger-deployment-reset." The pressure relief gap utilizes a small-area bypass principle to provide a low-resistance short circuit for the high-pressure gas in the groove at the moment before the ventilation duct is fully opened and the cylindrical channel is formed, preventing the gas pressure in the groove from hindering the ventilation duct's rotation. Once the ventilation duct is fully opened, the area of ​​the main channel is much larger than the area of ​​the gap, and the main airflow is still guided out through the cylinder wall. The impact of the gap on the overall ventilation capacity is negligible, thus maintaining emergency ventilation efficiency while ensuring operational reliability. In terms of materials, the melting point of the fusible alloy can be adjusted according to the characteristics of different transformer oils to form a series of products; the silicone coating of the flexible ventilation duct remains inert at high temperatures, blocking oil mist penetration, and the fiberglass cloth matrix provides sufficient radial stiffness, allowing the ventilation duct to maintain its cylindrical shape without collapsing after being opened, ensuring continuous unobstructed ventilation.

Claims

1. A cooling structure for a down-draft traction transformer, used at the end of the cooling duct of a down-draft traction transformer, characterized in that: It includes an annular groove fixed to the wall of the air duct outlet, a flexible air duct housed in the groove, a foldable hinge that forms a rotatable connection between one edge of the air duct and the bottom of the groove, fusible alloy pins arranged circumferentially along the opening of the groove, and elastic reset ribs provided at the free edge of the air duct. When the duct is in the retracted state, it is completely folded and embedded in the groove by the pin. After the pin melts, it flips outward by the self-developing opening force of the elastic reset rib, so that the duct changes from the folded state to the cylindrical extension state, thereby increasing the effective exhaust area of ​​the duct outlet.

2. The cooling structure for a down-draft traction transformer according to claim 1, characterized in that, The groove is formed by recessing outward from the outlet end wall of the air duct. The groove depth is sufficient to accommodate the thickness of the fully folded air duct and its hinge. The outer peripheral surface of the groove smoothly transitions with the outer wall of the air duct to avoid airflow vortices.

3. The cooling structure for a downdraft traction transformer according to claim 2, characterized in that, The duct is made of glass fiber cloth coated with high-temperature resistant silicone. Its base is truncated cone-shaped, with the small end connected to the bottom of the groove by a foldable hinge, and the large end being a free edge. The angle between the generatrix of the cone and the axis of the duct remains acute in the unfolded state to form an outwardly expanding guide tube.

4. The cooling structure for a down-draft traction transformer according to claim 3, characterized in that, The foldable hinge is made of stainless steel sheet continuously stamped into V-shaped folds. The root of the fold is riveted to the bottom of the groove, and the fold wings are vulcanized into one piece with the small end edge of the air duct, so that the air duct always maintains symmetrical movement around the air duct outlet axis during the unfolding and folding process.

5. The cooling structure for a down-draft traction transformer according to claim 4, characterized in that, The elastic reset rib is a spiral spring steel strip embedded in the free edge of the air duct. The spring steel strip is closed into a loop in the circumferential direction, and its two ends are bent in opposite directions in the air duct unfolding direction to form pre-tightening hooks, so as to store and release the torque that causes the air duct to unfold.

6. The cooling structure for a downdraft traction transformer according to claim 5, characterized in that, One end of the pin is inserted into the countersunk hole at the outer edge of the groove, and the other end presses against the outward folded edge of the free edge of the air duct. The pin body extends radially along the air duct and completely detaches from the groove after melting, thereby releasing the mechanical constraint on the air duct.

7. The cooling structure for a down-draft traction transformer according to claim 6, characterized in that, The melting point of the pin is lower than the temperature at which the transformer oil cracks and produces gas, but higher than the highest oil temperature during normal operation. This ensures that the pin only melts when there is a fault and overheating, thereby ensuring that the duct remains sealed during normal operation.

8. The cooling structure for a down-draft traction transformer according to claim 7, characterized in that, The outer side of the free edge of the air duct is provided with a surrounding flange. After the air duct is unfolded, the surrounding flange overlaps the outer wall of the air duct outlet to prevent external rainwater from entering the air duct in reverse. When the air duct is folded, it is embedded in the annular groove of the groove opening to form a sealing lip.

9. A cooling structure for a down-draft traction transformer according to claim 8, characterized in that, The bottom of the groove has a pressure relief notch that communicates with the inside of the air duct. The area of ​​the pressure relief notch is smaller than the minimum flow area after the air duct is deployed. This is used to quickly release the hot air accumulated in the groove during the initial deployment of the air duct and reduce the deployment resistance.

10. A cooling structure for a downdraft traction transformer according to claim 9, characterized in that, The pressure relief notch is a fan-shaped hole evenly distributed on the bottom surface of the annular groove. Its total area is set to 30% to 50% of the minimum cross-sectional area of ​​the cylindrical channel formed by the flexible air duct in the fully deployed state. This allows the notch to release the hot air accumulated in the groove before the air duct is deployed. After the air duct is deployed, the flow area of ​​the cylindrical channel is kept to be more than twice the area of ​​the notch.

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