A cold leg split multi-phase transformer

Abstract

This invention discloses a multiphase transformer with a separate cooling circuit, comprising a dry-type transformer body and a cooling system. The cooling system includes a first cooling circuit located outside each phase's high-voltage coil and a second cooling circuit located within the main air passage between the high- and low-voltage coils. The second cooling circuit includes an insulating air duct frame and an axially extending cooling air duct inside, an air duct adjustment mechanism, and an independent air supply system. The independent air supply system is physically isolated from the first cooling circuit. A temperature detection system collects the temperature of each phase coil in real time, and a control unit performs differentiated control of the air duct adjustment mechanism based on the temperature data. This invention achieves precise differentiated cooling of the relatively high-temperature phases through a dual-circuit separate architecture of external air cooling and built-in controllable internal cooling air ducts, effectively suppressing inter-phase temperature differences.

Description

Technical Field

[0001] This invention relates to the field of power transformer technology, specifically to a dry-type multiphase transformer, and more particularly to a transformer that actively suppresses interphase temperature difference through a dual-path separate cooling architecture consisting of external air cooling and a built-in controllable internal cooling duct. Background Technology

[0002] Multiphase transformers (especially three-phase transformers) are widely used in power systems. During operation, temperature differences arise between phases due to factors such as unbalanced three-phase loads, asymmetrical magnetic circuits, differences in cooling environments for each phase, and harmonic distortion. When the interphase temperature difference exceeds the allowable limit (usually 15-20K), the following risks may occur: accelerated thermal aging of the insulation material in the high-temperature phase windings, leading to a significant reduction in insulation life; thermal stress causing winding deformation or epoxy resin cracking; the transformer being forced to operate at the highest temperature phase with limited capacity, reducing equipment utilization; and in severe cases, insulation breakdown accidents may occur.

[0003] In existing transformer cooling solutions, the most common approach is to arrange independent cooling air paths outside the high-voltage coils of each phase, equipped with fans to blow air onto each phase for cooling. However, although each phase has its own independent air path, from a thermodynamic perspective, multiple air paths exist in the same spatial environment, essentially cooling the entire transformer. Regardless of how the airflow speed of each path is adjusted independently, it cannot effectively suppress the steady-state interphase temperature difference caused by the difference in heat generation power between phases—because external air cooling can only change the thermal resistance, not the difference in heat source power. When the heat generation power of one phase is significantly higher than that of other phases, external airflow cannot specifically address the heat accumulated inside that phase.

[0004] In existing technology, Chinese patent CN202352463U discloses a heat pipe-heat-conducting dry-type three-phase power transformer. This transformer uses heat pipes embedded within epoxy resin cylinders of the high and low voltage windings to conduct heat to the heat dissipation fins, which are then cooled by a fan. While this solution improves winding heat dissipation efficiency using heat pipes, heat pipes are passive heat transfer elements. The amount of heat transferred depends on the temperature difference; when the temperature difference is small, the driving force is insufficient, and the transformer cannot actively adjust according to changes in operating conditions, making it difficult to cope with dynamically changing load imbalances.

[0005] Another approach attempts to incorporate cooling ducts between the high- and low-voltage coils, but existing designs lack selective and proactive adjustment mechanisms to address phase-to-phase temperature differences. The ducts within each phase either open or close simultaneously, failing to provide precise, differentiated cooling for the relatively warmer phases. Furthermore, transformer thermal systems exhibit high inertia, nonlinearity, and pure time lag. Traditional temperature control relies primarily on simple threshold triggering, failing to adequately consider heat conduction lag and measurement delays, which can easily lead to untimely control response or oscillations in the control system. Summary of the Invention

[0006] To address the problems mentioned in the background art, the present invention provides a transformer capable of actively suppressing interphase temperature difference through a dual-path separate cooling architecture consisting of external air cooling and a built-in controllable internal cooling duct.

[0007] The technical solution of this invention is as follows: A cold-circuit separated multiphase transformer includes a dry-type transformer body and a cooling system. The dry-type transformer body includes an iron core and high-voltage coils and low-voltage coils wound on the iron core columns of each phase. The cooling system comprises: The first cooling path is located on the outside of each phase high-voltage coil and includes an independent fan installed on the outside of each phase high-voltage coil for blowing air to cool the outer surface of each phase high-voltage coil. The second cooling path is located within the main channel between the high-voltage and low-voltage coils of each phase. It includes an insulating air duct frame, cooling air ducts, an air duct adjustment mechanism, and an independent air supply system. The insulating air duct frame is fixedly installed in the main channel between the high-voltage and low-voltage coils, and the interior of the insulating air duct frame has a pre-reserved cooling air duct that runs through the axis. The air duct adjustment mechanism is used to independently control the opening, closing, and opening degree of the corresponding cooling air duct. The independent air supply system is physically isolated from the fan of the first cooling path and includes a supply fan and a supply duct. The supply fan is connected to each cooling air duct through the supply duct. The temperature detection system includes multiple temperature sensors installed on each phase coil to collect temperature data of each phase coil in real time. The control unit is electrically connected to the temperature sensor, the fan of the first cooling path, the air supply fan of the second cooling path, and the air duct adjustment mechanism.

[0008] Preferably, in the cold-circuit-separated multiphase transformer as described above, the air duct adjustment mechanism is located at the inlet front end of each cooling air duct, and the air supply fan is connected to the air duct adjustment mechanism at the inlet front end of each cooling air duct through the air supply pipeline.

[0009] Preferably, in the cold-circuit-separated multiphase transformer described above, the air duct adjustment mechanism is any one of an electric air valve, a rotatable guide vane, or a retractable baffle.

[0010] Preferably, in the cold-circuit-separated multiphase transformer described above, the opening degree of the air duct adjustment mechanism is independently and continuously adjusted by the control unit.

[0011] Preferably, in the multiphase transformer with separate cooling circuit as described above, an air filter and a dehumidifier are provided at the air inlet of the independent air supply system of the second cooling circuit.

[0012] Preferably, in the cold-circuit-separated multiphase transformer described above, the air filtration device is a three-stage filtration structure comprising a G4-level primary filter, an F7-level medium-efficiency filter, and an H10-level sub-high-efficiency filter.

[0013] Preferably, in the cold-circuit-separated multiphase transformer described above, an online dew point meter is installed on the outlet duct of the independent air supply system.

[0014] Preferably, in the cold-circuit separated multiphase transformer as described above, the temperature sensor is a fiber optic temperature probe, with at least three probes provided for each phase, respectively arranged in the upper, middle, and lower regions of the phase coil.

[0015] Preferably, in the cold-circuit separated multiphase transformer as described above, the control unit calculates the effective temperature value of each phase and the temperature difference between phases based on the collected values ​​from the temperature sensors of each phase.

[0016] Preferably, in the cold-circuit-separated multiphase transformer described above, the control unit further performs graded regulation of cooling by calculating the predicted temperature difference.

[0017] The beneficial effects of this invention are as follows: This invention adopts a two-stage cooling circuit separation architecture. The first cooling circuit is responsible for overall temperature rise control, and the second cooling circuit is responsible for phase-to-phase temperature equalization. The two circuits are physically isolated, have independent air paths, and decoupled control, resulting in high system reliability. The second cooling circuit uses an air duct adjustment mechanism and an independent air supply system to independently switch and adjust the opening of the cooling air ducts in each phase, thereby achieving precise differentiated cooling for phases with relatively high temperatures.

[0018] Furthermore, this invention employs a prefabricated insulated duct frame to physically shape the duct, ensuring a safe insulation distance between the high and low voltage coils. The duct is enclosed and the airflow is directional, preventing disturbance to the main insulation and eliminating the risk of introducing foreign objects into the coil. A three-stage filtration and dehumidification device is installed, along with online dew point monitoring, ensuring that the air entering the internal duct is clean and dry, preventing insulation performance degradation caused by moisture or particulate matter. By introducing feedforward compensation based on the rate of change of temperature difference, the system acts in advance before the actual temperature difference reaches the threshold, overcoming the response delay caused by thermal conduction hysteresis and sensor measurement delay, resulting in more timely and stable control. By eliminating the bottleneck effect of the relatively high-temperature phase, the transformer as a whole can withstand a higher load rate, extending the overall service life of the equipment. Attached Figure Description

[0019] The solutions and advantages of this application will become clear to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0020] In the attached diagram: Figure 1This is a schematic diagram illustrating the structural principle of the present invention; Figure 2 This is an example of the second cooling path arrangement of the present invention.

[0021] The components represented by the various reference numerals in the diagram are: 1. Dry-type transformer body; 2. Independent fan; 3. Independent air supply system; 4. Support pads. Detailed Implementation

[0022] Example 1 This embodiment provides a cold-circuit-separated multiphase transformer, such as... Figure 1 As shown, it includes a dry-type transformer body 1 and a cooling system. The dry-type transformer body 1 includes an iron core and high-voltage coils and low-voltage coils wound on the iron core columns of each phase. Its structure is no different from that of the existing dry-type multiphase transformer.

[0023] The cooling system includes: The first cooling path is located on the outside of each phase high-voltage coil and includes an independent fan 2 installed on the outside of each phase high-voltage coil for blowing air to cool the outer surface of each phase high-voltage coil. This cooling method is also existing technology.

[0024] The second cooling path is located in the main air duct between the high-voltage coil and the low-voltage coil of each phase, and includes an insulating air duct frame, a cooling air duct, an air duct adjustment mechanism, and an independent air supply system 3.

[0025] The insulating air duct frame is a cylindrical structure made of prefabricated insulating material, which is fixedly installed in the main air duct between the high and low voltage coils. The interior of the insulating air duct frame has multiple cooling air ducts that run through the axis.

[0026] The above-mentioned construction of cooling ducts through an insulated duct frame is also an existing approach. In specific arrangements, the wall thickness of the insulated duct frame should be controlled to be no less than 5mm, so that the cooling ducts are evenly distributed along the circumference of the frame. Each cooling duct is independent of the others and not connected to them. A safe insulation distance is maintained between the outer wall of the insulated duct frame and the inner surface of the high-voltage coil, and between the inner wall of the frame and the outer surface of the low-voltage coil.

[0027] The air duct adjustment mechanism of the present invention is set at the inlet front end of each cooling air duct and is used to independently control the opening, closing and opening degree of the corresponding cooling air duct. It can be selected as any one of electric air valve, rotatable guide vane or telescopic baffle, and its opening degree is independently and continuously adjusted by the control unit mentioned later.

[0028] The independent air supply system 3 is physically isolated from the fan of the first cooling path, and includes an air supply fan and an air supply pipeline. The air supply fan is connected to the air duct adjustment mechanism at the front end of each cooling air duct inlet through the air supply pipeline.

[0029] Due to the special nature of the cooling space, the air inlet of the independent air supply system 3 of the second cooling path of the present invention is equipped with an air filtration device and a dehumidification device. The air filtration device is a three-stage filtration structure including a G4-level primary filter, an F7-level medium-efficiency filter and an H10-level sub-high-efficiency filter. An online dew point meter is installed on the air outlet duct of the air supply system.

[0030] The temperature detection system includes multiple temperature sensors installed on each phase coil for real-time acquisition of temperature data of each phase coil. In this invention, the temperature sensors are fiber optic temperature probes, with at least three sensors installed on each phase, respectively arranged in the upper, middle, and lower regions of the phase coil; the sampling period of the temperature sensors is no more than 1 second.

[0031] The control unit is electrically connected to the temperature sensor, the fan of the first cooling path, the air supply fan of the second cooling path, and the air duct adjustment mechanism.

[0032] It should be noted that the temperature of each phase coil is a crucial parameter for assessing the operating status of a transformer. When there are temperature differences among the phase coils, the insulation material of the phase with a relatively higher temperature ages more rapidly, becoming a bottleneck restricting the overall lifespan and load capacity of the transformer. Actively adjusting the cooling intensity of the relatively higher-temperature phase to bring its temperature closer to that of the other phases can effectively alleviate this problem. This invention is based on this understanding. A temperature detection system acquires the temperature distribution of each phase coil in real time, and a control unit performs differentiated control of the airflow adjustment mechanisms in the second cooling path for each phase. This alters the flow state of the cooling medium within the cooling airflow channels of each phase, thereby adjusting the heat dissipation intensity of each phase coil as needed.

[0033] To achieve the objectives of this invention, the control unit calculates the effective temperature value of each phase and the current temperature difference between phases based on the data collected by the temperature sensors of each phase, calculates the rate of change of temperature difference, and calculates the predicted temperature difference value using a feedforward compensation formula based on the current temperature difference value and the rate of change of temperature difference. Furthermore, the control unit can further perform graded adjustment of cooling based on the magnitude of the predicted temperature difference value, for example: When the predicted temperature difference does not exceed the first preset threshold, each cooling duct remains closed. When the predicted temperature difference exceeds the first preset threshold, the control unit opens the corresponding cooling duct with a relatively higher temperature and sets the opening degree of the corresponding duct adjustment mechanism and the air supply speed according to the different ranges of the predicted temperature difference.

[0034] In addition, when the control unit opens the corresponding cooling duct with a relatively high temperature, it can also simultaneously reduce the speed of the corresponding first cooling duct fan.

[0035] Preferably, after the temperature difference prediction value falls below the second preset threshold and remains below it for a preset time, the control unit gradually reduces the cooling level until all cooling air ducts are completely shut down, and the cooling air ducts are allowed to operate at the current cooling level for at least a preset time after being opened before downgrading is allowed.

[0036] The control unit also monitors the airflow temperature at the outlet of each phase cooling duct. When the difference between the outlet temperature of any phase cooling duct and the inlet temperature of that phase cooling duct exceeds a third preset threshold, the control unit opens the cooling duct of that phase.

[0037] Example 2 This embodiment uses a 10kV / 0.4kV, 1250kVA three-phase dry-type transformer as an example to illustrate the specific implementation of the present invention in detail.

[0038] The transformer body is an epoxy resin cast dry-type three-phase transformer, comprising three core columns, with low-voltage and high-voltage coils arranged sequentially from the inside out on each core column. A ring-shaped main channel area is formed between the high-voltage and low-voltage coils. The first cooling path is located outside each phase high-voltage coil and includes independent fans installed outside each phase high-voltage coil for blowing air to cool the outer surface of each phase high-voltage coil. In this embodiment, two cross-flow cooling fans are installed outside each phase high-voltage coil, two for each phase, for a total of six fans across the three phases, installed on both sides of the bottom of the coil, with the airflow directed towards the outer surface of the high-voltage coil, blowing air from bottom to top.

[0039] The second cooling path is located within the main channel between the high-voltage and low-voltage coils of each phase, and includes an insulating duct frame, cooling ducts, a duct adjustment mechanism, and an independent air supply system. The insulating duct frame is a cylindrical structure made of prefabricated insulating material, fixedly installed in the main channel between the high- and low-voltage coils. Multiple axially continuous cooling ducts are pre-installed inside the insulating duct frame. The wall thickness of the insulating duct frame is not less than 5mm to prevent damage and deformation, and the cooling ducts are evenly distributed along the circumference of the frame, with their positions corresponding to the pads. Each cooling duct is independent of the others; a safe insulating distance is maintained between the outer wall of the insulating duct frame and the inner surface of the high-voltage coil, and between the inner wall of the frame and the outer surface of the low-voltage coil. The independent air supply system includes a supply fan and supply pipes, and is isolated from the fan of the first cooling path. The supply fan is connected to the duct adjustment mechanism at the inlet of each cooling duct via the supply pipes. Figure 2As shown, in order to achieve reliable airflow guidance for the second cooling path and adapt to the compact space at the bottom of the transformer, this embodiment cleverly modifies and utilizes the support pad 4 at the bottom of the transformer. The original epoxy material support pad 4 is changed to a composite structure with an epoxy layer transition at the top and a rigid hollow frame at the bottom. Thus, the support pad 4 serves as a bridge for cold air to enter each cooling air duct. The inward side of the support pad 4 is connected to the cooling air duct of the insulated air duct frame through a connector, and the outward side is adapted to the connection port of the air duct adjustment mechanism. Thus, the air duct adjustment mechanism is reliably installed at the inlet front end of each cooling air duct for independently controlling the opening, closing and opening degree of the corresponding cooling air duct.

[0040] In this embodiment, the insulating air duct frame is a prefabricated cylindrical frame made of SMC composite material, with a wall thickness of 8mm and a height of 1200mm, matching the coil height. The outer diameter of the cylinder is fitted with a 12mm gap to the inner diameter of the high-voltage coil, and the inner diameter is fitted with a 10mm gap to the outer diameter of the low-voltage coil. Four axially continuous circular cooling air ducts are pre-reserved within the frame wall, evenly distributed along the circumference of the frame, and each cooling air duct is independent of the others. The frame is fitted onto the outside of the low-voltage coil after the low-voltage coil is wound and before the high-voltage coil is wound. The bottom and top of the frame are fixed by insulating end rings.

[0041] The air duct adjustment mechanism is an electric air valve, whose opening degree is independently and continuously adjusted by the control unit. In this embodiment, a freely adjustable miniature electric air valve is installed on the outward-facing side of the support pad 4. The number of electric air valves is the same as that of the support pad 4 for each phase, for a total of 4. The control cables of each air valve are centrally connected to the control cabinet and are independently controlled by the control unit.

[0042] The independent air supply system is equipped with an air filter and a dehumidifier at its air inlet. The air filter is a three-stage filtration system consisting of a G4-level pre-filter, an F7-level medium-efficiency filter, and an H10-level sub-high-efficiency filter. An online dew point meter is installed on the air outlet duct of the air supply system. In this embodiment, an air supply fan is installed at the bottom of the transformer cabinet, and the fan outlet is connected to branch ducts corresponding to each phase via a main duct. These branch ducts are then connected to the inlet air collection chambers at the bottom of the A, B, and C phase frames, respectively. Based on this, the air supply is adjusted and an alarm is triggered according to the alarm status of the online dew point meter.

[0043] The temperature detection system then includes temperature sensors positioned between the coils of each phase to collect temperature data in real time. Furthermore, to obtain more accurate values, multiple temperature sensors can be used, and a weighted average temperature value can be calculated to adjust the airflow.

[0044] The control unit uses a Siemens S7-1200 PLC, which is equipped with an analog input module to collect temperature and dew point signals, an analog output module to control the opening of the electric damper and the frequency of the frequency converter, and a digital output module to control the start and stop of the fan.

[0045] The thermal time constant of the transformer was calibrated by step response test. Under rated load, the load on phase A was suddenly increased by 30%, and the time required for the temperature of phase A to rise from the initial steady state to the final steady state was recorded. The measured thermal time constant was obtained, and the feedforward advance time ΔT_pred was set accordingly.

[0046] Furthermore, in the above process, the safe temperature threshold is set to 120℃, and the temperature difference action threshold is set to 5K.

[0047] The control unit calculates the effective temperature value of each phase and the current temperature difference between phases based on the collected values ​​of each phase temperature sensor, and calculates the temperature difference change rate with a preset step size Δt. Then, based on the current temperature difference value and the temperature difference change rate, the feedforward compensation formula is used to calculate the predicted temperature difference value. The formula is: ΔT_pred(t+τ)=ΔT(t)+τ×d(ΔT) / dt.

[0048] The control unit performs tiered adjustments based on the predicted temperature difference. When the predicted temperature difference does not exceed a first preset threshold, all cooling ducts remain closed. When the predicted temperature difference exceeds the first preset threshold, the control unit opens the corresponding cooling duct with the relatively higher temperature and sets the opening degree of the corresponding duct adjustment mechanism and the air supply speed according to the different ranges of the predicted temperature difference. In this embodiment, multiple preset thresholds can be set, and the duct opening degree and air speed can be adjusted based on these thresholds.

[0049] When the control unit opens the corresponding cooling duct with a relatively high temperature, it simultaneously reduces the speed of the corresponding first cooling duct fan by 20%-30% of the fan's current speed. In this embodiment, the reduction is 25%.

[0050] After the predicted temperature difference falls below the second preset threshold and remains below it for a preset time, the control unit gradually reduces the cooling level until all cooling air ducts are completely shut down. Furthermore, after the cooling air ducts are opened, the current cooling level must be maintained for at least a preset time before downgrading is allowed. In this embodiment, the second preset threshold is 3K, the duration is 30 seconds, and the downgrading process involves reducing the cooling level by one every 30 seconds, with a minimum holding time of 60 seconds.

[0051] The control unit also monitors the airflow temperature at the outlet of each phase cooling duct. When the difference between the outlet temperature and the inlet temperature of any phase cooling duct exceeds a third preset threshold, the control unit opens the cooling duct for that phase. In this embodiment, the third preset threshold is 8K.

[0052] The following is a specific operational example of this transformer. In this example, the feedforward advance time Δt_pred is set to 10 seconds, and the temperature difference grading thresholds are 5K, 10K, and 15K. Initially, the three-phase load is balanced, with phase A temperatures at 86℃, phase B at 87℃, and phase C at 85.5℃. The maximum temperature difference between phases is 1.5K. All cooling ducts are closed, and the external fans are all running at 60% speed. At second 0, the load on phase A suddenly increases by 40%.

[0053] At the 60th second, the temperature of phase A rises to 92℃, phase B to 87.5℃, and phase C to 86℃. The current temperature difference ΔT(t) = 5.5K, and the rate of change of temperature difference d(ΔT) / dt = 0.13K / s. The control unit calculates the predicted temperature difference 10 seconds later using the feedforward compensation formula ΔT_pred(t + Δt_pred) = ΔT(t) + Δt_pred × d(ΔT) / dt: ΔT_pred = 5.5 + 10 × 0.13 = 6.8K. Since the predicted value exceeds the 5K threshold, the control unit opens the phase A cooling damper to 35% of its opening at the 60th second, supplying an air velocity of 4m / s. Simultaneously, it reduces the speed of the phase A external fan from 60% to 45%.

[0054] At the 120th second, the temperature of phase A is 96℃, phase B is 88℃, and phase C is 86.5℃. The current temperature difference is 8K, the temperature difference change rate is 0.07K / s, and the feedforward prediction value ΔT_pred=8+10×0.07=8.7K. It enters the 5-10K range. The control unit increases the opening of the phase A air valve to 60% and increases the wind speed to 8m / s.

[0055] At 180 seconds, the temperature of phase A reached a peak of 98.5℃ and then began to drop, with phase B at 89℃ and phase C at 87℃. The current temperature difference is 9.5K, and the rate of change of temperature difference is -0.05K / s. The feedforward prediction value ΔT_pred=9.5+10×(-0.05)=9.0K, which is still in the 5-10K range, maintaining the current cooling level.

[0056] At the 240th second, the temperature of phase A is 96℃, phase B is 89.5℃, and phase C is 87.5℃. The current temperature difference is 6.5K, the temperature difference change rate is -0.04K / s, and the feedforward prediction value ΔT_pred=6.5+10×(-0.04)=6.1K. The prediction value drops, and the control unit reduces the opening of the air valve to 30%, and the wind speed drops to 4m / s.

[0057] At the 300th second, the temperature of phase A is 94.5℃, phase B is 90℃, and phase C is 88℃, with a current temperature difference of 4.5K and a temperature difference change rate of -0.03K / s. The feedforward prediction value ΔT_pred = 4.5 + 10 × (-0.03) = 4.2K, which is below the 5K threshold. The control unit maintains the current cooling state for 60 seconds. After confirming that the temperature difference is stable, it initiates the degradation process at the 360th second, completely shutting down the phase A cooling duct and restoring the external fan to 60% speed.

[0058] Throughout the process, the peak temperature of phase A was 98.5℃, and the peak temperature difference was 9.5K, which did not exceed the 15K threshold. During the adjustment process, the control unit always predicted the temperature difference 10 seconds in advance based on the feedforward compensation formula and actively intervened at the 60th second, rather than waiting for the actual temperature difference to reach the action threshold. This effectively suppressed the expansion of the temperature difference, and the entire adjustment process was stable. The temperature difference eventually converged and fell back to the safe range.

Claims

1. A cold-circuit separated multiphase transformer, comprising a dry-type transformer body (1) and a cooling system, wherein the dry-type transformer body (1) comprises an iron core and high-voltage coils and low-voltage coils wound on the iron core columns of each phase, characterized in that, The cooling system includes: The first cooling path is located on the outside of each phase high voltage coil, including an independent fan (2) installed on the outside of each phase high voltage coil for blowing air to cool the outer surface of each phase high voltage coil; The second cooling path is located in the main channel between the high-voltage coil and the low-voltage coil of each phase, and includes an insulating air duct frame, a cooling air duct, an air duct adjustment mechanism and an independent air supply system (3); the insulating air duct frame is fixedly installed in the main channel between the high-voltage and low-voltage coils, and the interior of the insulating air duct frame is reserved with a cooling air duct that runs through the axis; the air duct adjustment mechanism is used to independently control the opening, closing and opening degree of the corresponding cooling air duct; the independent air supply system (3) is physically isolated from the fan of the first cooling path, and includes an air supply fan and an air supply pipeline, and the air supply fan is connected to each cooling air duct through the air supply pipeline; The temperature detection system includes multiple temperature sensors installed on each phase coil to collect temperature data of each phase coil in real time. The control unit is electrically connected to the temperature sensor, the fan of the first cooling path, the air supply fan of the second cooling path, and the air duct adjustment mechanism.

2. The cold-circuit separated multiphase transformer according to claim 1, characterized in that, The air duct adjustment mechanism is located at the inlet front end of each cooling air duct, and the air supply fan is connected to the air duct adjustment mechanism at the inlet front end of each cooling air duct through the air supply pipeline.

3. The cold-circuit separated multiphase transformer according to claim 1, characterized in that, The air duct adjustment mechanism is any one of an electric air valve, a rotatable guide vane, or a retractable baffle.

4. The cold-circuit separated multiphase transformer according to claim 3, characterized in that, The opening degree of the air duct adjustment mechanism is independently and continuously adjusted by the control unit.

5. The cold-circuit separated multiphase transformer according to claim 1, characterized in that, An air filter and a dehumidifier are installed at the air inlet of the independent air supply system (3) of the second cooling circuit.

6. The cold-circuit separated multiphase transformer according to claim 5, characterized in that, The air filtration device is a three-stage filtration structure comprising a G4-level pre-filter, an F7-level medium-efficiency filter, and an H10-level sub-high-efficiency filter.

7. The cold-circuit separated multiphase transformer according to claim 5 or 6, characterized in that, An online dew point meter is installed on the air outlet duct of the independent air supply system (3).

8. The cold-circuit separated multiphase transformer according to claim 1, characterized in that, The temperature sensor is a fiber optic temperature probe, with at least three probes installed in each phase, respectively located in the upper, middle, and lower regions of the phase coil.

9. The cold-circuit separated multiphase transformer according to any one of claims 1 to 8, characterized in that, The control unit calculates the effective temperature value of each phase and the temperature difference between phases based on the data collected by the temperature sensors of each phase.

10. The cold-circuit separated multiphase transformer according to claims 1-9, characterized in that, The control unit also performs graded adjustments to cooling by calculating predicted temperature differences.

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