A cooling control method for oil-immersed transformers

Abstract

This invention relates to the field of oil-immersed transformer cooling control technology and discloses an oil-immersed transformer cooling control method to solve the problem of bypass flow of cooling oil caused by rapid winding temperature rise and lag in insulating oil response in traditional methods. The method first collects load status information, top insulating oil temperature, bottom insulating oil temperature, and ambient temperature as the basis for determining the operating status. When the load is high, the operating frequency limit of the submersible pump is set according to the insulating oil response status and bottom insulating oil temperature to control the limited operation of the submersible pump and the activation of cooling equipment. The operating frequency of the submersible pump, oil flow anomaly adjustment, and load fallback control are adjusted according to the insulating oil temperature to improve the effectiveness of winding cooling and the stability of cooling control.

Description

Technical Field

[0001] This invention relates to the field of oil-immersed transformer cooling control technology, specifically to a cooling control method for oil-immersed transformers. Background Technology

[0002] Oil-immersed transformers often experience short-term surges in load under conditions of concentrated high-power fast charging station access and fluctuating new energy demand. For such conditions, existing cooling control technologies typically rely on top oil temperature, hot spot temperature, or load rate as the primary control basis, adjusting the operation of coolers or the start / stop of fans accordingly. For example, patent application CN108037780B discloses a cooling control method for oil-immersed transformers based on temperature rise and load rate. This method assesses the transformer's thermal state using top oil temperature, hot spot temperature, and load rate, and determines the appropriate cooler operation ratio. Furthermore, patent application CN103779059B discloses a dynamic capacity expansion method for oil-immersed transformers. This method predicts internal temperature based on a thermal circuit model and issues a warning and activates cooling fans when the temperature may exceed limits. Therefore, existing technologies primarily rely on temperature prediction or temperature rise results to drive the cooling devices to perform corresponding controls. However, existing technologies still struggle to effectively cool the transformer windings during the initial stages of a sudden load surge. This is because the windings heat up rapidly after a load impact, while the insulating oil heats up more slowly due to thermal inertia, especially since the bottom insulating oil is typically still in a low-temperature, high-viscosity state during this phase. In this situation, if the operating intensity of the submersible pump or cooling device is directly increased using existing control methods, the high-viscosity cold oil cannot overcome the flow resistance of the narrow oil channels inside the windings and tends to flow along the less resistant gaps around the windings, resulting in insufficient cooling oil entering the winding's internal channels. Consequently, even though external cooling equipment operates under high load, the hot spots in the windings cannot be effectively cooled, leading to heat accumulation, localized overheating, accelerated insulation aging, and in severe cases, even insulation failure. Therefore, there is an urgent need to provide a transformer cooling control method to address the problem of bypass flow of cooling oil caused by the rapid temperature rise of the windings and the lag in the response of the insulating oil, thereby improving the winding cooling effect, reducing ineffective cooling energy consumption, and extending the service life of the transformer insulation system. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a cooling control method for oil-immersed transformers, which solves the problem of bypass flow of cooling oil caused by rapid winding temperature rise and lag in insulating oil response in traditional methods.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A cooling control method for an oil-immersed transformer includes: S1. Collect transformer load status information, top layer insulating oil temperature, bottom layer insulating oil temperature and ambient temperature, and establish a basis for determining the operating status based on the time correspondence of each piece of information; S2. When the load status information meets the load surge condition, determine that the transformer has entered the operating state where the winding temperature rises faster than the insulating oil response, and determine the operating frequency limit of the submersible pump based on the bottom insulating oil temperature. S3. Control the submersible pump to start according to the operating frequency limit, and control the cooling device to start operation; S4. Gradually adjust the operating frequency of the submersible pump according to the temperature change of the insulating oil. If an abnormal oil flow occurs, pause the frequency increase and perform adjustment control. After the oil flow is restored, continue to adjust the frequency. After the load drops, reduce the operating intensity of the cooling device.

[0005] Furthermore, information on transformer load status, top insulating oil temperature, bottom insulating oil temperature, and ambient temperature is collected, including: The load status information consists of the effective values ​​of the three-phase operating load current and the change information of active power on the high-voltage side and the low-voltage side. The temperature of the top insulating oil, the temperature of the bottom insulating oil and the ambient temperature are collected by the corresponding detection points according to the preset sampling period. Boundary checks, rate of change checks, and anomaly flags are performed on each collected value; When abnormal temperature data changes, the abnormal temperature data is compensated with a substitute value.

[0006] Furthermore, a basis for determining the operational status is established based on the time correspondence of various pieces of information, including: The basis for determining the operational status includes the original time sequence record table, the current cycle's operational input group, and the historical input sequence; According to a unified timestamp, load status information, top insulating oil temperature, bottom insulating oil temperature and ambient temperature are periodically merged and nearest neighbor matched, and the current cycle operation input group is generated within the allowable time deviation range. When temperature data is abnormal, the basic compensation value is determined based on the historical stable range, and then corrected in conjunction with the current load deviation before being written into the current cycle operation input group.

[0007] Furthermore, when the load status information meets the conditions for a sudden load increase, it is determined that the transformer has entered an operating state where the winding temperature rises faster than the insulating oil response, including: The control terminal forms a short-window judgment sequence based on the current cycle operation input group and the previous cycle operation input group, and determines the load impact judgment quantity by combining the stable reference cycle in the historical input sequence; When the load impact judgment quantity meets the joint triggering condition, the temperature sequence of the top insulating oil and the temperature sequence of the bottom insulating oil are extracted. Based on the continuous change of the top insulating oil temperature, the temperature range of the bottom insulating oil, and the relative hysteresis relationship between the two, the current working condition is judged.

[0008] Furthermore, the operating frequency limit of the submersible pump is determined based on the temperature of the bottom insulating oil, including: The control terminal determines the operating frequency limit range of the submersible pump based on the temperature range of the bottom insulating oil, and adjusts the upper limit of the frequency limit range in combination with the ambient temperature. When temperature data is abnormal, temperature jumps out of bounds, or abnormal signs appear in the submersible pump drive link, maintain a conservative frequency boundary, increase the frozen frequency, or switch to an abnormal recovery pending state, and generate a status result record that includes at least a status number, temperature zone number, frequency limit value, and abnormal marker.

[0009] Furthermore, controlling the submersible pump start-up according to the operating frequency limit includes: The control terminal forms a start-up execution input group based on the status result record and the self-test result of the actuator, and determines the target start-up frequency, frequency rise time and holding time of the submersible pump according to the current status number, the bottom insulating oil temperature zone number and the frequency limit boundary; During the startup process of a submersible pump, pre-start checks, in-start monitoring, and post-start confirmation are performed. When abnormal current, speed, torque, or driver code occurs, the frequency freeze control is activated, and the system switches to delayed retry control or micro-drainage recovery control.

[0010] Furthermore, the cooling device is put into operation, including: The control terminal performs tiered pre-activation control of the external cooling device based on the load impact level and the availability of the external cooling device, and observes and confirms the activation based on the operation feedback after activation. After the submersible oil pump enters restricted operation, it continuously acquires the temperature of the top insulating oil, the temperature of the bottom insulating oil, the ambient temperature, and the operating status of the external cooling device. It confirms the status switch based on the temperature change trend and the environmental correlation, and generates a startup result output record. The startup result output record should include at least the operating frequency, the target intensity of the cooling device, the temperature change trend marker, and the frequency adjustment permission marker.

[0011] Furthermore, the operating frequency of the submersible pump is gradually adjusted according to the temperature change of the insulating oil, including: The control terminal forms a phase adjustment input set based on the startup result output record and the current cycle acquisition data, and judges the internal heat exchange link status based on the continuous change relationship between the top layer insulating oil temperature and the bottom layer insulating oil temperature. When the temperature of the top insulating oil rises continuously and the temperature of the bottom insulating oil changes synchronously, the control terminal enters the frequency release state, determines the release step size according to the range of the current operating frequency of the submersible pump, and sets an observation window after each frequency increase. The control terminal combines current feedback, torque feedback, speed feedback, and the correlation changes between the top insulating oil temperature, the bottom insulating oil temperature, and the ambient temperature to confirm the next level of frequency release permission and generate a stage adjustment output record. The stage adjustment output record includes at least a frequency level mark and a release permission mark.

[0012] Furthermore, when an abnormal oil flow occurs, frequency adjustment is paused and adjustment control is implemented. Frequency adjustment resumes after oil flow recovers. After the load decreases, the operating intensity of the cooling system is reduced, including: When the control terminal detects abnormal current fluctuations, abnormal torque fluctuations, abnormal speed tracking, or abnormal temperature relationships, it maintains the current frequency or reverts to a lower frequency depending on the severity of the abnormality, and performs fixed frequency holding, slow frequency reduction recovery, or micro-oscillation adjustment. After continuous observation and meeting the recovery conditions, continue to adjust according to the frequency level at which no abnormality occurred last time. If the recovery is still not achieved after continuous adjustment, switch to release and termination control. After the load enters the fallback judgment, the heat accumulation status is judged by combining the temperature of the top layer insulating oil, the temperature of the bottom layer insulating oil and the temperature difference between the two. First, the frequency of the submersible pump is gradually reduced, then the intensity of the external cooling device is reduced in stages, and the reduction is stopped when the load rises again and restored to the most recent stable operation level.

[0013] Compared with the prior art, the present invention provides a cooling control method for oil-immersed transformers, which has the following beneficial effects: 1. This invention collects and processes transformer load status information, top insulating oil temperature, bottom insulating oil temperature, and ambient temperature in a unified manner, and determines whether the transformer has entered an operating state where the winding temperature rises faster than the insulating oil response when the load suddenly increases. Then, based on the bottom insulating oil temperature, it determines the operating frequency limit boundary of the submersible pump. This allows the submersible pump to establish internal oil circulation in a restricted manner at the beginning of the sudden load increase. Combined with the activation of the cooling device, subsequent gradual frequency adjustment, oil flow anomaly adjustment, and phased retreat control after the load falls, this invention can reduce the flow of cooling oil along the low-resistance gaps around the windings and promote the entry of cooling oil into the internal oil channels of the windings. This alleviates the problems of insufficient internal effective cooling caused by rapid winding temperature rise, delayed insulating oil response, and high viscosity of bottom cold oil. This results in improved cooling capacity in the hot areas of the windings, reduced ineffective cooling energy consumption, and improved operational reliability of the transformer insulation system.

[0014] 2. This invention establishes a phased back-off mechanism during frequency adjustment, including continuous observation, abnormal pause, resumption of subsequent adjustments, and load reduction (from inside to outside). It integrates load status information, top-layer insulating oil temperature, bottom-layer insulating oil temperature, and execution feedback into a unified control link. This enables continuous linkage between submersible pump frequency release, abnormal handling, and cooling device intensity adjustment based on internal heat exchange status and external load changes. This avoids blindly increasing the frequency before the oil flow stabilizes and prematurely reducing the cooling intensity before sufficient heat dissipation. It reduces frequent fluctuations, repeated switching, and abnormal interruptions during the control process, thereby improving the stability of the transformer cooling control process, enhancing control continuity, and improving the traceability of the operating status. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the cooling control method for an oil-immersed transformer according to the present invention; Figure 2 This is a diagram showing the relationship between the cooling control object and information interaction in this invention; Figure 3 This is the load surge and thermal response hysteresis determination and frequency limiting decision diagram of the present invention; Figure 4 This is a diagram showing the frequency release, abnormal handling, and load reduction / retreat states of the submersible pump in this invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: Figures 1-4 A cooling control method for oil-immersed transformers is presented, including: S1. Collect transformer load status information, top layer insulating oil temperature, bottom layer insulating oil temperature and ambient temperature, and establish a basis for determining the operating status based on the time correspondence of each piece of information; S2. When the load status information meets the load surge condition, determine that the transformer has entered the operating state where the winding temperature rises faster than the insulating oil response, and determine the operating frequency limit of the submersible pump based on the bottom insulating oil temperature. S3. Control the submersible pump to start according to the operating frequency limit, and control the cooling device to start operation; S4. Gradually adjust the operating frequency of the submersible pump according to the temperature change of the insulating oil. When an abnormal oil flow occurs, stop the frequency increase and perform adjustment control. After the oil flow is restored, continue to adjust the frequency. After the load falls back, reduce the operating intensity of the cooling device. Specifically, such as Figure 2 As shown: After the transformer is put into operation, the control terminal establishes the basis for determining the operating status for subsequent status judgments. The basis for determining the operating status is formed by hierarchical recording and unified time correspondence, and may include the original time sequence record table, the current cycle operation input group, and the historical input sequence. The original time sequence record table is used to continuously receive and store load status information, top layer insulating oil temperature, bottom layer insulating oil temperature, and ambient temperature. The current cycle operation input group is used to form the formal judgment unit for the current control cycle. The historical input sequence is used to support cross-cycle status comparison and abnormal compensation calls. This processing method is adopted because load status information is a fast-changing quantity, insulating oil temperature is a slow-changing quantity, and ambient temperature changes even slower. If a single refresh frequency is used for mixed processing, it is easy to cause distortion of the time correspondence between different variables, affecting the continuous judgment of load surges, thermal response lag, and bottom layer cold oil status. The original time-series record table can be divided into a load status record area, a temperature status record area, and an environmental status record area. The load status record area is used to record the effective values ​​of the three-phase operating load current on the high-voltage and low-voltage sides, as well as the active power change information. The temperature status record area is used to record the temperature of the top and bottom insulating oils. The environmental status record area is used to record the ambient temperature. Each record area includes at least a unified timestamp field, a data validity marker field, a data source field, and an anomaly marker field. The unified timestamp field is used to establish the time correspondence between variables. The data validity marker field is used to identify whether the data has entered the formal judgment process. The data source field is used to distinguish between real-time sampled values ​​and alternative compensation values. The anomaly marker field is used to record out-of-bounds, jumps, link interruptions, or communication anomalies. Through the above record structure, multiple source inputs can be incorporated into the same control cycle for unified processing while maintaining the original sampling rhythm of each variable. Regarding parameter settings, the effective values ​​of the three-phase operating load current on both the high-voltage and low-voltage sides can be recorded using a 32-bit floating-point system, with the upper limit of the record set to four times the transformer's rated current. This setting takes into account that under conditions such as concentrated startup of high-power fast charging and grid connection of new energy sources, the transformer may experience a surge current significantly higher than the normal operating value in a short period of time. Setting the upper limit of the record to four times the rated current can cover the short-term surge sampling range and reserve a range margin for abnormal surge identification, avoiding the loss of effective information due to insufficient range during critical periods. The sampling update cycle for load status information can be selected as 10ms. This setting takes into account that load surges are a rapid change process, and it is necessary to capture the source of the surge before heat accumulates significantly. At the same time, the 10ms sampling cycle can provide at least 10 effective samples within the 100ms control cycle described later, which facilitates the merging of the load change amplitude and change slope within a single cycle. The temperatures of the top and bottom insulating oils can be recorded using floating-point data, with a data validity threshold of -50℃ to 150℃. The data validity threshold for ambient temperature can be selected as -40℃ to 70℃. Using -50℃ to 150℃ as the data validity threshold for insulating oil temperature is to cover data verification needs under cold start, normal operation, heavy load heating, and abnormally high temperature sampling scenarios in cold regions. This threshold is used to identify unreasonable temperature sampling values ​​and does not represent the long-term safe operating temperature range of the equipment. Using -40℃ to 70℃ as the data validity threshold for ambient temperature is... The temperature variation range covers common outdoor environments and local heat accumulation conditions near equipment. The top insulating oil temperature reflects the trend of oil temperature change in the upper part of the body, the bottom insulating oil temperature reflects the actual thermal state of the oil near the inlet of the submersible pump, and the ambient temperature reflects the external cold end boundary corresponding to the radiator. The sampling update period for the top and bottom insulating oil temperatures can be selected as 1000ms. This setting is based on the fact that oil temperature is a slow variable with thermal inertia that is significantly greater than load change. A 1000ms update period is sufficient to meet the trend recognition requirements and can reduce the processing burden caused by invalid high-frequency sampling. The control terminal performs input processing cyclically with a fixed control cycle, which can be selected as 100ms. This setting is to complete the merging of 10ms-level load sampling results, time alignment, validity checks, anomaly handling, and generation of the current cycle's operating input group within a single cycle, while reserving processing margin for subsequent status judgment and control execution. Within each control cycle, the control terminal first reads the most recent valid load status information from the load status recording area, and then reads the top insulating oil temperature, bottom insulating oil temperature, and ambient temperature from the temperature status recording area and the environmental status recording area, which are closest to the timestamp of the load status and within the allowable time deviation range. Time alignment can be selected using the nearest neighbor matching rule, and the allowable time deviation range can be selected to not exceed one control cycle, i.e., not exceed 100ms. This setting is because the load status information is the benchmark input for the current cycle's judgment, and the oil temperature and ambient temperature change relatively slowly within this time scale. Selecting the most recent valid value within a range not exceeding one control cycle can balance time consistency and processing efficiency. If it exceeds this range, it is marked as a time mismatch and will not directly enter the current cycle's formal judgment. After time alignment is completed, the control terminal generates the current cycle operation input group. The current cycle operation input group includes at least the cycle number, reference timestamp, effective value of three-phase current on the high-voltage side, effective value of three-phase current on the low-voltage side, active power change information, top insulating oil temperature, bottom insulating oil temperature, ambient temperature, data validity flag, and abnormal flag. Among them, the active power change information can be selected as the active power difference or change gradient between adjacent sampling cycles, which is used to characterize the rate of load change. The current cycle operation input group serves as the formal determination unit for the current control cycle and is called upon for subsequent status judgment. To ensure the continuity and reliability of the current cycle's input group, the control terminal performs boundary checks and anomaly handling on each input before writing it into the formal input group. The boundary check first verifies the validity of each input. When the temperature of the top or bottom insulating oil exceeds -50℃ to 150℃, the ambient temperature exceeds -40℃ to 70℃, or the effective value of the load current exceeds four times the rated current, the corresponding value is marked as an out-of-bounds value and prohibited from directly entering the current cycle's input group. For temperature data that is not out of bounds but has a risk of abnormal fluctuations, a rate of change check is further performed. The rate of change check is based on a 100ms detection window within the control terminal and does not change the original 1000ms oil temperature sampling period. The bottom insulating oil temperature... The criteria for judging abnormal change rate can be selected as follows: if the calculated change rate of the bottom insulating oil temperature continuously exceeds 10℃ / s within 5 consecutive detection windows, it is determined that there is an abnormality in the bottom insulating oil temperature measurement link. Using 10℃ / s as the abnormal screening boundary is because the bottom insulating oil is constrained by the overall oil body heat capacity and should not experience continuous rapid jumps during normal operation and the initial stage of a sudden load increase. This value is higher than the upper limit of the actual change rate of the bottom insulating oil temperature under normal operating conditions, therefore it is suitable for identifying measurement abnormalities rather than as a process control boundary. Using 5 consecutive detection windows as a continuous condition is to filter out single-pulse interference, short-term communication jitter, and instantaneous sampling errors, improving the stability of abnormality judgment. The top insulating oil temperature can also be checked for change rate in the same way. After the temperature anomaly judgment condition is triggered, the control terminal does not directly interrupt the process, but instead starts the alternative value compensation process. The alternative value compensation process can be performed first on the bottom insulating oil temperature, because the bottom insulating oil temperature is directly related to the subsequent operation status judgment and the submersible pump operation constraints. The control terminal first determines the historical stable range. The historical stable range can be selected as a continuous time period in which the load change amplitude is less than 5% of the rated load and the bottom insulating oil temperature change rate is less than 1℃ / min. The rated load of 5% and 1℃ / min are used as the stable range judgment conditions because this range can characterize the transformer operation in a state without obvious external impact and slow temperature evolution, which is suitable as a compensation reference basis. The historical stable range can be selected as the first 30 minutes, or it can be 20 minutes to 60 minutes according to the transformer capacity level and thermal inertia characteristics. 30 minutes is taken as the commonly used value because this time span can cover the stable evolution process of the slow variable of the insulating oil, while avoiding the introduction of outdated operating condition information. After determining the historical stable range, the control terminal extracts the average bottom insulating oil temperature corresponding to the current load range from this range as the basic compensation value. When the current load changes relative to the average load of the historical stable range, a correction is performed on the basic compensation value according to the current load deviation to obtain a replacement bottom insulating oil temperature value. The load correction rule can be selected as follows: when the deviation of the current load from the average load of the historical stable range does not exceed 10% of the rated load, the basic compensation value is directly adopted; when the deviation exceeds 10% of the rated load, the basic compensation value is finely adjusted in the same direction according to the deviation direction, and the fine adjustment amplitude does not exceed 2℃. The correction amplitude is controlled. Within 2℃, the overall thermal inertia of the bottom insulating oil is relatively large, and the actual temperature should not change drastically with load changes in a short period of time. Therefore, the replacement value correction should remain conservative and continuous. When the replacement bottom oil temperature value is written into the current cycle operation input group, it is marked as the replacement compensation source in the data source field, and the corresponding abnormality reason is recorded in the abnormality mark field. After the effective temperature input is restored for three consecutive formal sampling cycles, the replacement value compensation process is exited, and the real-time sampling value is resumed. Through this processing method, the control link can be maintained continuously when a local abnormality is detected, and the replacement value generation process has clear rules and reproducibility. Regarding time resource constraints, load merging, time alignment, boundary checks, anomaly detection, substitution value compensation, and current cycle operation input group writing are all completed within a single 100ms control cycle; the duration of a single core processing cycle can be selected to be no more than 20ms; keeping the core processing duration within 20ms is to reserve sufficient processing margin within a single control cycle for the generation of subsequent state judgment results, the issuance of execution signals, and the response of actuators, thereby meeting the real-time control requirements under sudden load increases; to meet this time constraint, the current processing adopts a rule-based approach, without introducing complex non-real-time calculations; The control terminal can retain at least 30 minutes of historical input sequence and store it using a circular buffer; each historical record is indexed in chronological order and can use the same field structure as the input group of the current cycle; the historical input sequence is used for both substitution value compensation processing and to support subsequent comparisons between the current cycle and the previous cycle of load change relationship, top insulating oil temperature change relationship, bottom insulating oil temperature change relationship and ambient temperature trend; After processing, the control terminal generates the current cycle operation input group and the historical input of the current cycle. If the current cycle operation input group meets the subsequent state determination conditions, the current cycle operation input group and the historical input of the current cycle are given to the subsequent processing process for operation state identification and submersible pump operation frequency constraint.

[0018] Specifically, such as Figure 3 As shown: The control terminal calls the current cycle operation input group and corresponding historical input sequence in the aforementioned operation status determination basis, and completes the identification of load surge, the judgment of operation status when the winding temperature rises faster than the insulating oil response, and the generation of submersible pump operation frequency limits within the status determination cycle; the status determination cycle can be selected as 100ms; the reason for taking the status determination cycle as 100ms is that this cycle can directly receive the aforementioned input processing results and can complete continuous status judgment within a second range, meeting the real-time requirements of sudden load increase identification and frequency constraint generation; the control terminal can optionally read the current 1 operation input group and 10 consecutive previous operation input groups to form a short window judgment sequence of about 1 second, and combine it with the long-term background information in the historical input sequence for status judgment; the short window is used to identify rapid load changes, and the long-term background information is used to provide a load stability baseline and a temperature gradual change baseline; The control terminal first determines the load surge. To do this, the control terminal extracts the effective values ​​of the three-phase operating load current on the high-voltage and low-voltage sides from the current cycle and the previous cycle, and combines them with active power change information to form a load surge determination quantity. The load surge determination quantity includes at least indicators such as relative increment and absolute increment. The relative increment can be taken as the difference between the total load of the current cycle and the total load of the stable reference cycle divided by the total load of the stable reference cycle. The absolute increment can be taken as the difference between the total load of the current cycle and the total load of the stable reference cycle. The stable reference cycle can be selected from long-term background information, choosing a period with small load fluctuation amplitude and continuous stability. To accommodate transformers of different capacity levels, the control terminal can employ a dual-threshold joint triggering rule: when the relative increment is not less than 20%, or the absolute increment is not less than 10% of the rated load, and this condition remains true for three consecutive state judgment cycles, the current operating condition is determined to enter the sudden load increase monitoring state. The reason for setting the relative increment to 20% is that load changes below this level are generally considered normal operating fluctuations, with relatively limited impact on transient winding heating. Setting the absolute increment to 10% of the rated load is to cover situations where the relative change is small but the absolute thermal shock is significant under high load conditions; this change is sufficient to cause identifiable changes in winding heating. Using three consecutive state judgment cycles as a continuous condition, corresponding to a duration of approximately 300ms, serves to filter out single-cycle communication jitter, short-term measurement spikes, and pulse interference, improving the stability of sudden load increase identification. If neither the relative nor absolute increment meets the above conditions, the control terminal maintains a stable monitoring state; if the above conditions are met, it enters the sudden load increase monitoring state. After entering the sudden load monitoring state, the control terminal does not directly increase the operating frequency of the submersible oil pump, but further determines whether the transformer has entered an operating state where the winding temperature rises faster than the insulating oil response. This judgment is not based on direct measurement of the winding internal temperature, but on a comprehensive judgment based on the load change sequence, the temperature change of the top insulating oil, the temperature change of the bottom insulating oil, and the relative hysteresis relationship between the two. The control terminal can optionally extract the current cycle load impact judgment quantity, the current top insulating oil temperature, the current bottom insulating oil temperature, as well as the top insulating oil temperature sequence and the bottom insulating oil temperature sequence in the short window judgment sequence. If the current operating condition has entered a state of sudden load increase monitoring, and the temperature of the bottom insulating oil is still in the low temperature range, while the temperature of the top insulating oil has not formed a recognizable continuous rise within a short window of about 1 second, and shows a lag in response to load changes, then the transformer is determined to have entered an operating state where the winding temperature rises faster than the insulating oil response. The low temperature range of the bottom insulating oil temperature can be selected as 10℃ to 30℃. The reason for selecting this range as the low temperature range is that the viscosity of the bottom insulating oil is high when it is in this temperature range, and the flow resistance in the narrow oil channels inside the winding increases significantly, which can easily lead to the risk of bypass flow in the peripheral gap. The minimum recognizable response amplitude of the top insulating oil temperature can be selected as 0.2℃. The reason for selecting 0.2℃ as the minimum response amplitude is that this value is higher than the fluctuation range after smoothing of common industrial temperature acquisition links, and lower than the continuous temperature rise amplitude that can be observed when the normal thermal response is established. Therefore, it can be used as the minimum judgment boundary for the top insulating oil temperature to enter the recognizable response state. To improve the reproducibility of the judgment, the control terminal can also adopt the following rules: If the cumulative increase in the top insulating oil temperature within three consecutive state judgment cycles is less than 0.2℃, or the rate of change of the top insulating oil temperature is less than the preset response rate of change threshold, then it is determined that the top insulating oil temperature has not yet formed an effective response matching the load increase; if the above conditions are met, the control terminal marks the current operating condition as a high viscosity anti-bypass constraint state; if the bottom insulating oil temperature is higher than 30℃, or the top insulating oil temperature has formed a continuous rise matching the load increase, then the control terminal marks the current operating condition as a non-misaligned thermal response state and enters a more relaxed internal cooling constraint branch; the more relaxed internal cooling constraint branch still generates the submersible pump operating frequency boundary, but its boundary is wider than the frequency boundary under the high viscosity anti-bypass constraint state, so as to maintain a consistent calling method with the subsequent restricted start-up and frequency adjustment process; Under high viscosity bypass constraint conditions, the control terminal uses the bottom insulating oil temperature as the core criterion for limiting the operating frequency of the submersible pump, and generates the upper limit of the operating frequency of the submersible pump based on the temperature zone of the bottom insulating oil. The bottom insulating oil temperature can characterize the thermal state of the oil near the pump inlet, and the magnitude of the driving force applied by the submersible pump in the low temperature and high viscosity stage will affect whether the oil preferentially enters the narrow oil channel inside the winding or forms a bypass flow along the gap with less resistance on the outside. Therefore, the control terminal can divide the bottom insulating oil temperature into at least three temperature zones and set corresponding frequency limit intervals for each zone. When the temperature of the bottom insulating oil is between 10℃ and 30℃, the frequency limit range of the submersible pump can be 10Hz to 18Hz, with the starting reference frequency being 12Hz. When the temperature of the bottom insulating oil is above 30℃ but not above 45℃, the frequency limit range of the submersible pump can be 18Hz to 26Hz. When the temperature of the bottom insulating oil is above 45℃, the frequency limit range of the submersible pump can be relaxed to 26Hz to 35Hz. 12Hz is chosen as the starting reference frequency for the low-temperature, high-viscosity region because the hydraulic pressure corresponding to this frequency band is sufficient to overcome the static viscous resistance of the cold oil at the bottom, causing controllable displacement of the oil, but it is not enough to cause the oil to largely bypass the interior. The oil flows rapidly along the outer gap under high dynamic pressure conditions; 18Hz, 26Hz, and 35Hz are set as the upper limits of each temperature zone, which are determined according to three control levels: conservative pumping in the low temperature and high viscosity stage, transitional pumping in the intermediate temperature zone, and controlled relaxation after leaving the main risk zone; among them, below 18Hz is mainly used to limit the internal driving force in the low temperature and high viscosity stage, below 26Hz is mainly used for transitional release after the flow resistance is improved, and below 35Hz is mainly used for controlled relaxation after the bottom insulating oil has significantly increased in temperature; through temperature zone division and frequency interval mapping, the control terminal forms a constraint mechanism based on the thermal state of the bottom insulating oil rather than simply based on load changes; To improve environmental adaptability, the control terminal can also perform environmental temperature correction on the upper limit of the submersible pump's operating frequency. The environmental temperature can be taken from the effective environmental temperature field in the aforementioned operating status determination basis, and its effective boundary follows the aforementioned -40℃ to 70℃. When the environmental temperature is below 0℃, the control terminal can lower the upper limit of the current frequency restriction range by 2Hz. When the environmental temperature is between 0℃ and 15℃, the original frequency restriction range can be maintained unchanged. When the environmental temperature is above 35℃, the upper limit of the current frequency restriction range can be raised by 1Hz to 2Hz. The reason for adopting the above correction rules is that when the environmental temperature is low, the radiator and external cold end are more likely to maintain a low return oil temperature, and the bottom insulating oil is usually in a high viscosity state for a longer period of time. Therefore, the upper limit of the submersible pump's operating frequency should be appropriately conservative. When the environmental temperature is high, the cold end temperature difference effect is weakened, and the viscosity barrier of the bottom insulating oil decays faster. The upper limit of the frequency can be appropriately relaxed. The above correction amount is a boundary fine-tuning amount. Its value is smaller than the frequency range of the main temperature zone. It is used to improve environmental adaptability without changing the mapping relationship of the main temperature zone. After generating the frequency limit boundary, the control terminal creates a status result record. The status result record includes at least the following fields: current status number, status entry time, sudden load increase flag, thermal response status flag, bottom insulating oil temperature zone number, submersible pump operating frequency limit lower limit, submersible pump operating frequency limit upper limit, ambient temperature correction value, frequency lock flag, and anomaly flag. The status number can optionally include stable monitoring status, sudden load increase monitoring status, high viscosity bypass constraint status, relatively relaxed internal cooling constraint status, and anomaly recovery pending status. The frequency lock flag indicates that subsequent execution processes must not exceed the current frequency upper limit, and the anomaly flag indicates whether to enter a conservative start branch or an anomaly recovery branch. To ensure the continuity of the frequency limit generation process under extreme conditions, the control terminal also sets anomaly and boundary handling rules. If the current value of the bottom insulating oil temperature comes from the substitute compensation value rather than the real-time effective sample value, the control terminal automatically adopts a more conservative frequency limit strategy, that is, it lowers the frequency limit by 2Hz based on the upper limit of the corresponding temperature zone and prohibits entering the relaxed branch in the current cycle. The lowering value is set to 2Hz because this value can improve the conservatism without significantly disrupting the control continuity. If the load surge condition has been met, but the top or bottom insulating oil temperature exceeds the limit or has an abnormal jump, the control terminal maintains a high viscosity anti-bypass constraint state and uses the lowest frequency limit range as a temporary boundary until the temperature sampling returns to stability. If, during the frequency limit generation period, a stall precursor, abnormal spike, or overload pressure characteristic is detected in the current or torque feedback corresponding to the submersible pump drive link, the control terminal freezes any upwardly relaxed frequency adjustment and switches the current state to an abnormal recovery pending state, so that the low-frequency micro-pulsation recovery path can be called subsequently. The frequency range of the low-frequency micro-pulsation recovery path can be 3Hz to 6Hz. This frequency range is used as the recovery entry point because this frequency band can alleviate local stagnation under extreme stagnation conditions through alternating ultra-low frequency slight pulsations and start-stop cycles, while avoiding the introduction of new hydraulic shocks. In the abnormal recovery pending state, the control terminal can also output a conservative frequency limit boundary for subsequent recovery control to call. After the abnormal recovery is completed, the frequency limit generation process will be re-entered according to the current operating conditions. The control terminal can complete load surge identification, thermal response status judgment, temperature zone mapping, ambient temperature correction, and status result writing within a single 100ms status judgment cycle. The formal judgment and result writing time can be no more than 20ms. The reason for controlling the formal judgment and result writing time within 20ms is that the initial stage of the sudden impact load is a critical period for limiting the blind acceleration of the submersible pump. It is necessary to complete the status judgment and frequency boundary freezing as early as possible to reserve sufficient time for subsequent control execution. To meet this time requirement, the control terminal can use a regularized temperature zone mapping and threshold judgment method to complete the status recognition and frequency limit generation. After the above processing, the control terminal generates a record of the submersible pump operating frequency limit boundary and status result corresponding to the current operating condition, and transmits it to the subsequent processing process for the control of limited start-up of the submersible pump and activation of the cooling device.

[0019] Specifically, such as Figure 4 As shown: After receiving the aforementioned status result record, the control terminal generates the start-up control information for the current cycle based on the submersible pump operating frequency limit boundary, thermal response status mark, bottom insulating oil temperature zone number, ambient temperature correction value, and abnormal mark corresponding to the current operating condition, and respectively forms submersible pump control command and external cooling device control command; the two types of control commands are generated and issued separately, but are both constrained by the current start-up control status. Based on the aforementioned status result records, the control terminal can form a start-up execution input group by combining the current cycle actuator self-test results. The start-up execution input group includes at least the following fields: cycle number, reference timestamp, current status number, thermal response status flag, bottom insulating oil temperature zone number, lower limit of submersible pump operating frequency limit, upper limit of submersible pump operating frequency limit, ambient temperature correction value, submersible pump startable flag, submersible pump driver health flag, external cooling device activatable flag, external cooling device health flag, and abnormal flag. The submersible pump startable flag indicates whether the submersible pump currently meets the start-up conditions, and the submersible pump driver health flag is also considered. The markings are used to indicate whether the frequency converter has normal output capability; the external cooling device can be engaged markings are used to indicate whether the fan unit or oil cooling unit is in a permissible engagement state; and the external cooling device health markings are used to indicate whether the fan, motor, contactor, or frequency converter corresponding to the external cooling device is normal. At the beginning of each execution cycle, the control terminal first reads the start execution input group and then enters the start control process. Through this processing method, the aforementioned operating status judgment results and the available status of the actuator can be associated within the same cycle, avoiding control mismatch caused by the actuator not having the start conditions when the frequency limit boundary has been generated. The control terminal can execute startup control using a state switching method. The startup control process includes at least the following states: waiting execution state, external cooling pre-activation state, internal low-frequency restricted startup state, internal and external synchronization establishment state, startup anomaly protection state, and stage switching confirmation state. If the submersible pump operating frequency limit boundary in the startup execution input group is empty, or the current state does not allow entry into startup control, the control terminal maintains the waiting execution state. If the frequency limit boundary is valid and the execution conditions are met, the startup control branch is entered. When the external cooling device is available and in normal health, the control terminal prioritizes entering the external cooling pre-activation state. When the external cooling device is temporarily unavailable but the submersible pump meets the startup conditions, the control terminal can directly enter the internal low-frequency restricted startup state. When neither the external cooling device nor the submersible pump meets the activation conditions, the control terminal enters the startup anomaly protection state and records the current fault cause. Through the above state switching rules, the control path is triggered by explicit conditions and does not rely on manual experience judgment. In the pre-activation state of external cooling, the control terminal first sends control commands to the external cooling device. The external cooling device can be a radiator fan unit, an independent oil cooling unit, or a heat exchange device formed by a combination of the two. The target operating intensity of the external cooling device can be set in layers according to the current load impact level. When the load impact is in the general surge range, the target frequency of the external fan can be 35Hz to 45Hz; when the load impact is in the higher surge range, the target frequency of the external fan can be 45Hz to 50Hz; when the bottom insulating oil temperature is in the lowest temperature range and the active power impact reaches a high proportion of the rated power, the target frequency of the external fan can be directly set to 50Hz. For example, when the active power surge reaches more than 35% of the rated power, 50Hz can be directly used. 50Hz is used as the upper limit because the rated power frequency of common industrial variable frequency fans is 50Hz. Directly using full frequency operation can quickly establish external forced convection capability without exceeding the conventional capacity boundary of the equipment. 35% of the rated power is used as a reference value for a higher surge ratio because this power level can characterize the high surge range that requires the rapid establishment of full-load cold end capability. If the external cooling device is not a variable frequency fan, but a staged cooling unit, then the equivalent high-intensity input can be achieved by first inputting the main heat dissipation branch and then the auxiliary heat dissipation branch. The control terminal continuously monitors the fan current feedback, speed feedback, and contactor engagement status in the external cooling pre-activation state, with an observation time of 0.5s to 2s. The observation time is set to 0.5s to 2s because this time range is sufficient to cover the stabilization process of the current, speed, and contact status after the external cooling device starts. If the external cooling device operates stably within the observation window, the control terminal switches to the internal low-frequency restricted start state. If a start failure, overcurrent, phase loss, or feedback failure occurs, the external cooling link abnormality is recorded, and a decision is made based on the health status of the cooling link to continue performing submersible pump restricted start under a more conservative frequency boundary. Under internal low-frequency restricted start-up conditions, the control terminal generates submersible pump control commands based on the aforementioned submersible pump operating frequency limit boundaries. These commands include at least the target start-up frequency, frequency ramp-up time, hold time, start-up direction, abnormal interruption flag, and feedback sampling period. The initial start-up frequency of the submersible pump is selected according to the temperature range of the bottom insulating oil. When the bottom insulating oil temperature is between 10℃ and 30℃, the initial start-up frequency can be between 10Hz and 14Hz, preferably 12Hz. When the bottom insulating oil temperature is between 30℃ and 45℃, the initial start-up frequency can be between 14Hz and 20Hz. When the bottom insulating oil temperature is above 45℃ and the current operating condition is still under restricted conditions... Under constrained conditions, the initial starting frequency of the submersible pump can be set to 18Hz to 24Hz; these frequencies correspond to the restricted starting ranges in the low-temperature, intermediate-temperature, and high-temperature zones, respectively; the starting frequency ramp-up time can be set to 1s to 3s, and the holding time can be set to 10s to 60s; the frequency ramp-up time is set to 1s to 3s because the starting resistance of low-temperature, high-viscosity oil is relatively large, and a slow frequency ramp-up helps to reduce transient shocks to the motor and sudden hydraulic changes; the holding time is set to 10s to 60s because this time range can cover the observation process of establishing low-speed oil circulation and the initial formation of temperature feedback; during the holding period, the control terminal does not perform upward relaxation operations, but only monitors whether the submersible pump has stably established low-speed oil circulation; To ensure the reproducibility of the low-frequency restricted start-up process, the control terminal sets conditions for pre-start checks, in-start monitoring, and post-start confirmation. Pre-start checks include at least: whether the submersible pump shutdown time exceeds the minimum restart interval, whether the submersible pump driver is currently in a protected locked state, whether a severe mechanical stall precursor was recorded in the previous cycle, and whether the bottom insulating oil temperature data is valid or has been replaced by a replacement compensation value. The minimum restart interval can be no less than 5 seconds, set to avoid repeated starts before the driver protection has fully reset or the motor's mechanical inertia has decayed. In-start monitoring includes at least three-phase stator current feedback, real-time speed feedback, driver output torque feedback, and a stable operation marker. The feedback sampling period can be 5ms to 20ms, set because in the initial stage of low-frequency start-up, millisecond-level sampling is needed to continuously monitor the current waveform and torque pulsation to promptly identify abnormal spikes, overload voltage buildup, or stall precursors. If the three-phase current waveform remains within the rated start-up allowable range for 500ms after start-up, and the real-time speed reaches more than 90% of the target start-up frequency with fluctuations not exceeding ± If the output torque of the driver does not continuously exceed the preset resistance threshold, the submersible pump is considered to have successfully started at low frequency, and the system transitions from the internal low-frequency restricted start state to the internal and external synchronization establishment state. A 500ms interval is used as the confirmation duration because this duration characterizes the formation of a stable operating segment after low-frequency start, rather than an instantaneous attainment of the target state. If any of the following occurs after startup, it is considered a startup abnormality: any phase of the three-phase current exceeds 1.8 times the rated starting current for more than 100ms; the real-time speed is lower than 50% of the target starting frequency for more than 300ms; the output torque exhibits a spike pulsation that does not subside within three consecutive sampling windows; or the driver indicates overcurrent, stall, or overvoltage. Using 1.8 times the rated starting current as the abnormal threshold is to distinguish between normal startup impact and abnormal overload trends. The aforementioned rated starting allowable range can be taken from the rated starting parameter range of the driver, and the preset resistance threshold can be taken from the rated output torque allowable range, or from the range value after the average torque of the unrestrained stable start segment is increased by a preset percentage. After triggering a startup abnormality, the control terminal enters the startup abnormality protection state. When the abnormal protection state is activated, the control terminal first freezes the current submersible pump target frequency increase command and maintains the current external cooling device in an engaged or safe engaged state to prevent the external cooling link from being simultaneously canceled before the internal oil circulation is established. Subsequently, the control terminal executes corresponding recovery control according to the type of abnormality. For electrical transient abnormalities, such as current feedback jitter, short-term code, or slow speed establishment but not reaching the stall condition, the control terminal can execute a delayed retry. The delay time can be 3s to 10s, and the retry frequency can be reduced by 1Hz to 2Hz compared to the previous target frequency. This setting is to reduce the resistance to restarting while waiting for the transient abnormality to subside. For suspected mechanical jamming, such as continuous overload pressure buildup, spike pulsation, or obvious blockage, the control terminal can perform a delayed retry. When the pre-recovery signal appears, the control terminal can enter the micro-dredging recovery branch; the micro-dredging recovery branch can execute low-frequency pulsation control of 3Hz to 6Hz, with a single duration of 2s to 5s and a round-trip switching cycle of 0.5s to 1s; the above parameters are used to provide sufficient mechanical disturbance and fluid pulsation without causing significant hydraulic shock, so as to alleviate local obstruction; if the pumping resistance torque fed back by the driver after recovery falls back to the safe range, the control terminal returns to the internal low-frequency restricted start state and re-executes the start; if micro-dredging still fails to recover after 3 consecutive attempts, the start abnormal protection state is maintained and a serious obstruction abnormality is reported; the aforementioned safe range can be the driver output torque recovering to the rated operating torque allowable range, or recovering to within the preset proportion of the average torque floating above the unobstructed stable start section; After the submersible pump successfully starts at low frequency, the control terminal enters the internal and external synchronization establishment state. In this state, the external cooling device has been put into operation or simultaneously activated, and the submersible pump establishes internal low-speed oil circulation at a limited frequency. The control terminal enters the observation and confirmation process and continuously acquires temperature feedback and environmental information. The observation input includes at least the top insulating oil temperature, bottom insulating oil temperature, ambient temperature, submersible pump current, submersible pump speed, and the operating status of the external cooling device. The observation window can be set from 10s to 120s. The observation window is set from 10s to 120s because the time for establishing internal oil circulation and forming heat exchange response varies for transformers of different capacity levels and under different oil circuit conditions. If the bottom insulating oil temperature remains low and the top insulating oil temperature has not changed continuously within the observation window, it is determined that the current stage is still in the slow entry of cold oil into the internal oil channel, and the control terminal continues to maintain the submersible pump operating at the current limited frequency. If the top insulating oil temperature begins to rise continuously within the observation window, and the cumulative change over three consecutive state judgment cycles is not less than 0.2℃, and the temperature difference between the bottom insulating oil temperature and the ambient temperature changes (e.g., the difference between the bottom insulating oil temperature and the ambient temperature decreases or a stable deviation occurs), it is determined that the internal heat exchange link has begun to be established, and the cold end resources have been actually brought into the transformer. At this time, the control terminal transitions from the internal and external synchronous establishment state to the stage switching confirmation state, and outputs the current temperature change trend, pumping feedback, and external cooling device operating status as an output record, which is then transmitted to the subsequent processing process. The control terminal generates a startup result output record; the startup result output record includes at least the following fields: cycle number, status number, current operating frequency of the submersible pump, current target intensity of the external cooling device, successful startup marker for the submersible pump, successful activation marker for the external cooling device, temperature change trend marker for the top insulating oil, temperature change trend marker for the bottom insulating oil, environmental correlation change marker, whether the frequency adjustment phase is allowed marker, and anomaly marker; subsequent processing determines whether to enter the frequency adjustment process based on the whether the frequency adjustment phase is allowed marker.

[0020] Specifically, such as Figure 2 and Figure 4 As shown: After the aforementioned restricted startup and internal / external synchronization establishment process is completed, the control terminal, based on the startup result output record and the top insulating oil temperature, bottom insulating oil temperature, ambient temperature, load status information, submersible pump operation feedback, and external cooling device operation status collected in the current cycle, executes the gradual release of the submersible pump operating frequency, abnormal pause adjustment, and cooling intensity rollback control. To this end, the control terminal forms a stage adjustment input set, which includes at least the cycle number, reference timestamp, current submersible pump operating frequency, top insulating oil temperature, bottom insulating oil temperature, load status information, submersible pump operation feedback, current external cooling device operation intensity, and corresponding control flags. The control terminal first determines whether the conditions for entering the frequency gradual release state are met. This determination is based on the continuous change relationship between the top and bottom insulating oil temperatures. The top insulating oil temperature change rate can be taken as the difference value after being updated in 1-second cycles and smoothed by 3 points, and the bottom insulating oil temperature change rate can also be taken in 1-second cycles. If the top insulating oil temperature change rate remains positive for three consecutive control cycles, and the cumulative increase in top insulating oil temperature is not less than 0.2℃, while the cumulative change in bottom insulating oil temperature relative to the initial reference value of restricted start-up is not less than 0.1℃, then it is determined that the internal heat exchange link has been established. The cumulative top insulating oil temperature of 0.2℃ is used as the confirmation threshold because the top insulating oil temperature is greatly affected by the overall thermal inertia. The temperature change is usually slow. 0.2℃ is higher than the smoothed sampling fluctuation range and can characterize a identifiable continuous temperature rise trend. The cumulative temperature of the bottom insulating oil is set at 0.1℃ as the confirmation threshold because the bottom insulating oil temperature is closer to the cold end of the suction inlet, and its change amplitude is usually smaller than that of the top insulating oil temperature. 0.1℃ can characterize that the bottom insulating oil temperature has shown a identifiable shift and is higher than the smoothed short-term fluctuation range. If only the top insulating oil temperature rises while the bottom insulating oil temperature does not change accordingly, it can be determined that the external heat exchange disturbance has a significant impact, and the release state will not be entered for the time being. If only the bottom insulating oil temperature changes while the top insulating oil temperature does not change continuously, it can be determined that the environmental fluctuation or perceived disturbance has a significant impact, and the release state will not be entered for the time being. During the gradual frequency release, the control terminal uses small steps and graded holding to increase the submersible pump's operating frequency. If the current frequency of the submersible pump is between 10Hz and 18Hz at the end of the restricted start-up, the single release step size can be 2Hz to 4Hz, preferably 3Hz. If the current frequency is between 18Hz and 26Hz, the single release step size can be 2Hz. If the current frequency is higher than 26Hz, the single release step size can be 1Hz to 2Hz. The step size for the low-frequency region is set to 2Hz to 4Hz because the hydraulic pressure changes in the low-frequency region have a more significant effect on improving the internal flow, but are still within the safety margin. The step size for the mid-frequency region is set to 2Hz to balance release efficiency and operational stability. Qualitative analysis: The step size in the high-frequency region is set to 1Hz to 2Hz because the high-frequency region is more prone to sudden increases in flow and changes in oil flow boundaries, so the step size should be smaller. After each frequency increase, the control terminal maintains an observation window. The observation window can be set to 10s to 30s, and 20s is preferred in the case of large-capacity transformers. This observation window is set because the fluid state changes after the submersible pump frequency increase will not be completely stable in milliseconds. Sufficient time needs to be allowed for the internal oil flow to redistribute and be reflected in the temperature changes of the top and bottom insulating oils. In large-capacity transformers, the time required for internal oil flow redistribution and heat transfer response establishment is usually longer. Therefore, 20s can be preferred as a trade-off between response speed and stability assessment. Within each observation window, the control terminal synchronously performs an oil flow stability check. This check includes at least current fluctuation checks, torque fluctuation checks, speed tracking checks, and temperature relationship checks. The reference benchmark for each of these checks can be the average of continuous stable sampling values ​​after the current stage frequency upsampling is completed and initial disturbances are removed. The current fluctuation check calculates the fluctuation amplitude based on the root mean square value of the three-phase current. If the deviation of any phase current from the average value of the stable frequency range of this stage exceeds 15% within the observation window and remains continuous for three sampling windows, then abnormal current fluctuations are considered to exist. 15% is used as the current deviation judgment value because this amplitude can distinguish... Acceptable fluctuations during normal release and persistent deviations caused by abnormal oil flow; torque fluctuation checks can be performed based on the torque feedback from the drive output. If the torque feedback deviates from the steady-state mean of this stage by more than 20% and is maintained for two consecutive sampling windows, then an abnormal torque change is identified. 20% is used as the torque deviation judgment value because this amplitude can distinguish between acceptable fluctuations during normal release and persistent torque deviations caused by abnormal flow resistance; speed tracking checks are used to identify whether the submersible pump is unable to reach the target frequency due to increased flow resistance. If the real-time speed is lower than 90% of the target frequency and lasts for more than 2 seconds, then a slow oil flow establishment is identified. Temperature relationship check is used to determine whether the internal heat exchange state after frequency increase is still consistent with the normal evolution law; if the temperature of the top insulating oil does not continue to maintain the expected change within the observation window, or if the difference between the temperature of the bottom insulating oil and the ambient temperature shows a significant abnormal change, such as rapidly dropping back to near the ambient temperature level, and at the same time the current or torque is abnormal, then it is determined that there is an abnormal temperature relationship; the aforementioned judgment values ​​are used to identify whether there are continuous rather than instantaneous signs of oil instability after the current stage frequency increase; if any of the above abnormalities occur, the control terminal will switch from the frequency gradual release state to the abnormal pause adjustment state; In an abnormal pause and adjustment state, the control terminal first freezes the current frequency upscaling link and determines whether to maintain the current frequency or revert to the previous frequency level based on the severity of the anomaly. If the anomaly is minor, such as the current deviation just exceeding the threshold and the torque not reaching the danger zone, the current frequency can be maintained, and a short-term observation and holding period can be entered, with a holding time of 5 to 15 seconds. If the anomaly is moderate, such as torque and current deviations occurring simultaneously but not triggering the drive protection, the frequency can be reverted to level 1. If the anomaly is severe, such as the real-time speed being significantly lower and accompanied by a persistently high torque, the frequency can be reverted to level 2, and re-upscaling is prohibited in the current stage. The above maintenance or reverting rules are used to restore oil flow stability without causing new hydraulic shocks. The adjustment control after the rollback can be implemented in one of the following ways: First, maintain the fixed frequency operation after the rollback to allow the oil flow to stabilize again; Second, reduce the frequency by 1Hz to 3Hz within 2s to 5s, maintain this for a period of time, and then slowly restore it to the rollback level; Third, perform low-amplitude oscillations of ±0.5Hz to ±1Hz near the current safe frequency for 3 to 5 cycles. All the above parameters are taken within a low-disturbance adjustment range to alleviate local blockage, suppress abnormal fluctuations, and restore oil flow stability without disrupting the current flow path establishment state. If, after adjustment, the current, torque, and rotation speed within two consecutive observation windows show no significant changes... Once the speed and temperature relationships return to normal, the control terminal releases the abnormal pause adjustment state and re-enters the frequency gradual release state, using the previous frequency level where no abnormality occurred as the new starting point for continued release. Two consecutive observation windows are used as the recovery condition because this condition characterizes the recovery as continuous rather than random fluctuations. If recovery is still not achieved after three consecutive adjustments, the control terminal maintains the current conservative frequency operation, no longer attempts to release upwards, and marks the current stage as the release termination state. Three consecutive adjustments are used as the termination condition to limit the number of abnormal handling loops and avoid ineffective repeated adjustments. In the latter half of the frequency release phase, the control terminal determines whether to enter the cooling intensity reduction process based on the load status information. The control terminal continuously reads the load status information and uses a combination of short-window and long-window methods to determine whether the impact load has weakened. The short window can take 10 control cycles, and the long window can take 60 control cycles, which are used to calculate the short-term average load and the average value of the phase trend, respectively. At the same time, the control terminal also determines whether the load decline trend lasts for no less than 30 seconds. If the short-window average load decreases by no less than 15% from the peak stage, and the load decline trend lasts for no less than 30 seconds, the control terminal initially determines that it has entered the load decline observation stage. The 15% is used as the load decline criterion because this magnitude can characterize that the external impact load has weakened significantly. The 30-second duration criterion is used to distinguish between short-term fluctuations and a continuous decline trend. After entering the load reduction observation phase, the control terminal does not immediately stop the submersible oil pump and external cooling device. Instead, it judges whether there is still heat accumulation inside the transformer by combining the temperature of the top and bottom insulating oil. If the temperature of the top insulating oil is still more than 2°C higher than the reference value before startup, or the temperature difference between the top and bottom insulating oil is still greater than 3°C, it is determined that the internal heat has not been fully released. At this time, only the frequency of the submersible oil pump is allowed to be gradually reduced without reducing the operating intensity of the external cooling device. 2°C is used as the continuous judgment value for the top temperature rise and 3°C is used as the continuous judgment value for the temperature difference between the top and bottom oils because these two values ​​can characterize that there is still significant heat accumulation inside the transformer, while not delaying the rollback time due to excessively high thresholds. If the temperature of the top insulating oil drops to the preset tolerance range near the reference value before startup and the temperature difference between the top and bottom oils shrinks to within 3°C, it is determined that the internal thermal state tends to be stable and enters the full rollback process. During the cooling intensity reduction phase, the control terminal adopts a phased reduction sequence, starting from the inside and moving outwards. The submersible pump frequency can be gradually reduced in discrete levels, the opposite of the release rate, with each reduction step being 2Hz to 3Hz and maintaining an observation time of 10s to 20s. The reduction step size of 2Hz to 3Hz is to smoothly reduce the internal driving force during the reduction phase. The observation time of 10s to 20s is to continuously confirm changes in the thermal state and avoid excessively rapid reduction. If the oil temperature continues to decrease during the reduction process without a new load increase, the next reduction continues. If the top insulating oil temperature rises again after the reduction, or the temperature difference between the upper and lower oils widens again, the reduction is paused, and the next reduction is initiated. The previous level is maintained; the reduction in the intensity of the external cooling device lags behind the frequency recovery of the submersible pump; only when the submersible pump has recovered to near the initial limited start-up frequency, and the temperatures of the top and bottom insulating oils remain stable, can the control terminal reduce the intensity of the external cooling device according to the preset recovery rules; for variable frequency fans, the intensity can be reduced step by step in increments of 5Hz to 10Hz; for staged cooling units, the auxiliary heat dissipation branches should be removed first, followed by the main heat dissipation branches; the external fan recovery step size is set to 5Hz to 10Hz because the change in the external forced convection capacity has a relatively small impact on the internal oil circuit, and an adjustment range greater than the submersible pump recovery step size can be used; During the rollback process, the control terminal continuously monitors the load status information, top layer insulating oil temperature, and bottom layer insulating oil temperature, and sets a rollback interruption branch. If, within any rollback observation window, the average load of the short window rises again to more than 10% of the rated load, or the increase relative to the previous observation window exceeds 8%, a new load increase is determined, and the current rollback process is terminated. 10% and 8% are used as rollback interruption criteria because a new round of load increase at this magnitude is sufficient to affect the current thermal balance. If the new load increase occurs during the submersible pump pullback phase, the frequency is restored to the previous level before the pullback. If it occurs during the external cooling device intensity reduction phase, the external cooling device intensity is immediately restored to the previous level, and the state confirmation process before frequency release is re-entered. If the load remains stable and the oil temperature continues to decrease, the control terminal sequentially completes the submersible pump frequency pullback and external cooling device intensity reduction, and finally switches back to the normal monitoring state. In the normal monitoring state, the aforementioned input update mechanism is maintained so that the corresponding control process can be re-entered when the next sudden load increase occurs. To ensure seamless integration with the aforementioned and subsequent processing procedures, the control terminal generates a stage adjustment output record at the end of each control cycle. This stage adjustment output record includes at least the following fields: cycle number, current status number, current submersible pump frequency level, next-level release permission flag, abnormal pause adjustment flag, current external cooling device operating intensity, load reduction flag, cooling intensity reduction permission flag, reduction interruption flag, and routine monitoring recovery flag. This output record can be used for the next cycle within the current control process and can also serve as a process record in the operation log for subsequent traceability and parameter verification. Through this structured output, the control terminal establishes a submersible pump frequency release, abnormal pause adjustment, and cooling intensity reduction control process based on the continuous change relationship between the top and bottom insulating oil temperatures.

[0021] Example 2: Based on Example 1, the specific application process of a cooling control method for an oil-immersed transformer is further explained: In one optional application scenario, an oil-immersed transformer is configured in a high-power fast charging station power supply system. The transformer body is electrically connected to the radiator fan unit, submersible oil pump, top insulating oil temperature sensor, bottom insulating oil temperature sensor, ambient temperature sensor, and control terminal. The control terminal continuously receives load status information, top insulating oil temperature, bottom insulating oil temperature, and ambient temperature from the high-voltage and low-voltage sides, and forms the basis for determining the operating status according to a unified time caliber. Assuming that during a certain period, the transformer operates stably at around 55% of the rated load, the ambient temperature is 8℃, the top insulating oil temperature is 46.3℃, and the bottom insulating oil temperature is 19.1℃, the control terminal generates the current cycle operating input group and historical input sequence according to a predetermined control cycle, and marks the current operating condition as a stable monitoring state. When multiple high-power charging terminals in a charging station are put into operation in a short period of time, the transformer load increases rapidly. After comparing the load status information of the current cycle with that of the previous cycle, the control terminal finds that the relative increase has exceeded 20%, and the absolute increase has reached more than 10% of the rated load. This condition has been maintained for three consecutive state judgment cycles. Therefore, the current operating condition is determined to enter the sudden load monitoring state. In this state, the control terminal does not immediately increase the operating frequency of the submersible oil pump. Instead, it continues to combine the continuous change relationship between the top and bottom insulating oil temperatures to determine whether the current operating condition has entered the state where the winding temperature rises faster than the insulating oil response. At this time, although the load has increased significantly, the bottom insulating oil temperature is still maintained at around 20°C, which is in the low temperature and high viscosity range. Moreover, the top insulating oil temperature has not yet formed a continuous increase that matches the load change in a short period of time. Therefore, the control terminal determines that the current operating condition meets the condition that the winding temperature rises faster than the insulating oil response and further switches to the high viscosity anti-bypass constraint state. Under high viscosity bypass constraint conditions, the control terminal generates the submersible pump operating frequency limit boundary based on the temperature range of the bottom insulating oil. Since the bottom insulating oil temperature is between 10℃ and 30℃, the control terminal determines the submersible pump frequency limit range to be 10Hz to 18Hz and sets the initial reference frequency to 12Hz. At the same time, the control terminal reads the ambient temperature as 8℃, which is within the range where no frequency boundary correction is required, so the submersible pump operating frequency limit boundary remains unchanged. After forming the status result record, the control terminal transmits information such as the current status number, the bottom insulating oil temperature range number, the upper limit of the submersible pump operating frequency limit, the frequency lock flag, and the abnormal flag to the subsequent start-up control process. Subsequently, the control terminal enters the startup control phase. After receiving the status result record, the control terminal first performs a self-check on the submersible pump driver, fan unit, and related actuators to confirm that the submersible pump meets the startup conditions, the driver is not in a protected locked state, and the external cooling device can be put into operation and is in a healthy state. On this basis, the control terminal prioritizes entering the external cooling pre-start state and first issues an operating command to the radiator fan unit. Since the current situation is a significant load impact condition and the bottom insulating oil temperature is in the lowest temperature range, the control terminal directly sets the target frequency of the external fan to 50Hz to quickly establish external forced convection capability. After the external fan unit starts, the control terminal continuously monitors the current feedback, speed feedback, and contactor engagement status within an observation period of 0.5s to 2s. If all feedback is detected to be normal, it is determined that the external cooling device has been stably put into operation, and the current state is switched to the internal low-frequency restricted startup state. In the internal low-frequency limited start-up state, the control terminal generates submersible pump control commands based on the previously determined frequency limit boundary, and sets the target start-up frequency to 12Hz, the frequency rise time to 2s, and the hold time to 20s. 12Hz is chosen as the start-up frequency because it is sufficient for high-viscosity cold oil to overcome static viscous resistance and begin to form controllable displacement, while avoiding excessive driving force that would cause a large amount of oil to bypass the winding gap. During submersible pump start-up, the control terminal continuously collects three-phase stator current feedback, speed feedback, and output torque feedback at a sampling period of 5ms to 20ms. If, within 500ms, the current of each phase is within the rated start-up allowable range, the real-time speed reaches more than 90% of the target start-up frequency and the fluctuation does not exceed the allowable range, and the output torque does not continuously exceed the resistance threshold, then the submersible pump is considered to have successfully started at low frequency. If a single-phase current is too high, the real-time speed is continuously too low, the output torque experiences continuous spikes, or the driver reports an abnormal code, then a start-up abnormality is detected, and the system switches to the start-up abnormality protection state. After the submersible pump successfully starts at low frequency, the control terminal switches from the internal low-frequency restricted start state to the internal and external synchronization establishment state. In this state, the external fan unit is already running at full frequency, and the submersible pump maintains low-speed oil circulation at 12Hz. The control terminal does not immediately increase the submersible pump frequency but instead enters the observation and confirmation process. During the observation process, the control terminal continuously acquires the top insulating oil temperature, bottom insulating oil temperature, ambient temperature, submersible pump current, submersible pump speed, and the operating status of the external cooling device. If, within the observation window, the bottom insulating oil temperature remains at a low level while the top insulating oil temperature has not yet shown continuous change, then it is judged that... If the current state is still in the stage of cold oil gradually entering the internal oil passage of the winding, and the submersible pump continues to operate at 12Hz; if in subsequent observations, the cumulative change of the top insulating oil temperature over three consecutive state judgment cycles reaches more than 0.2℃, and the cumulative change of the bottom insulating oil temperature relative to the initial reference value reaches more than 0.1℃, and the difference between the bottom insulating oil temperature and the ambient temperature shows a stable change, then it is determined that the internal heat exchange link has been established, the cold end heat exchange effect has been actually transferred to the inside of the transformer, and a startup result output record is formed, and the mark indicating whether the frequency adjustment stage is allowed is set to allowed; After entering the frequency gradual release phase, the control terminal does not directly increase the submersible pump to a high frequency, but releases it in small steps according to discrete levels. Since the current frequency is 12Hz, which is in the 10Hz to 18Hz range, the control terminal can increase the submersible pump frequency from 12Hz to 15Hz in 3Hz steps, and maintain a 20s observation window. Within the observation window, the control terminal simultaneously performs current fluctuation checks, torque fluctuation checks, speed tracking checks, and temperature relationship checks. If the deviation of any phase current from the average value of the current stable segment exceeds 15%, or the torque feedback deviation exceeds 20%, or the real-time speed is lower than the target frequency... If the oil flow rate remains above 90% for more than 2 seconds, or if the relationship between the top and bottom insulating oil temperatures and the ambient temperature becomes significantly abnormal, the oil flow is considered unstable at the current frequency, and the system switches to an abnormal pause adjustment state. If all feedback is normal, the oil continues to be released step by step according to a predetermined step size, for example, from 15Hz to 18Hz, and then from 18Hz into the release range corresponding to the intermediate temperature zone. After each release, an observation window is maintained for confirmation. By adopting the above step-by-step release method, the insulating oil that enters later can stably enter the deeper regions of the winding after the internal flow resistance gradually decreases, forming continuous internal scouring and heat exchange. If an oil flow anomaly occurs at a certain release level, the control terminal will perform different adjustment controls according to the severity of the anomaly. For a minor anomaly, the current frequency can be maintained for 5 to 15 seconds before continued observation. For a moderate anomaly, the frequency can be reduced by one level. For a severe anomaly, the frequency can be reduced by two levels, and further frequency increases at the current stage are prohibited. If necessary, the control terminal can also perform micro-oscillations of ±0.5Hz to ±1Hz near the current safe frequency to alleviate local blockage with low disturbance. If the flow returns to normal within two consecutive observation windows, the release will restart from the frequency level where no anomaly occurred last time. If the flow cannot be restored after three consecutive adjustments, the current conservative frequency will be maintained, and the current stage will be marked as a release termination state. As the load impact gradually weakens, the control terminal continuously reads the load status information within the short and long windows and determines whether to enter the cooling intensity reduction process. If the average load of the short window decreases by more than 15% from the peak stage, and the load decline trend continues for more than 30 seconds, the control terminal enters the load decline observation stage. After entering this stage, the control terminal does not immediately reduce the frequency of the submersible oil pump and the intensity of the external cooling device, but continues to determine whether there is still heat accumulation inside. Specifically, this can be determined by the temperature of the top insulating oil and the bottom insulating oil. If the temperature of the top insulating oil is still more than 2°C higher than the pre-start reference value, or the temperature difference between the top and bottom insulating oil is still greater than 3°C, it is determined that the internal heat has not been fully released. At this time, only the frequency of the submersible oil pump is allowed to be gradually reduced, and the current operating intensity of the external cooling device is maintained unchanged. If the temperature of the top insulating oil has dropped to near the pre-start reference value, and the temperature difference between the top and bottom oils has narrowed to within 3°C, it is determined that the internal thermal state has become stable, and the full reduction process begins. During the full rollback process, the control terminal reduces the cooling intensity in an inward-outward sequence; the submersible pump frequency is gradually reduced in discrete levels, opposite to the release rate, with each reduction ranging from 2Hz to 3Hz, and an observation period of 10s to 20s is maintained; if the oil temperature continues to drop during the rollback process without a new load increase, the next rollback continues; if the top insulating oil temperature rises again, or the temperature difference between the upper and lower oils widens again, the rollback is paused and maintained at the current level; only when the submersible pump has rolled back to near the initial restricted start frequency, and both the top and bottom insulating oil temperatures remain stable, does the control terminal begin to gradually reduce the intensity of the external cooling device; for For variable frequency fans, the pullback step size can be 5Hz to 10Hz. For staged cooling units, the auxiliary cooling branches can be withdrawn first, followed by the main cooling branches. If a new load increase occurs during the pullback process, such as the average load of the short window rising again to more than 10% of the rated load, or the increase relative to the previous observation window exceeding 8%, the control terminal will stop the current pullback process and restore to the most recent stable operating level. If the load increase occurs during the pullback phase of the submersible pump, the frequency will be restored to the previous level. If the increase occurs during the phase of reduced external cooling device intensity, the intensity of the previous level external cooling device will be restored, and the state confirmation process before frequency release will be re-entered. When the load remains stable and the oil temperature continues to decrease, and the submersible pump frequency and external cooling device intensity have both completed their pullback according to predetermined rules, the control terminal switches back to the normal monitoring state. In the normal monitoring state, the aforementioned input update and status judgment mechanism continues to be executed so that the corresponding control process can be re-entered when the next sudden increase in load occurs. At the same time, the control terminal continuously generates a stage adjustment output record at the end of each control cycle. The stage adjustment output record includes at least the following fields: cycle number, current status number, current submersible pump frequency level, next level release permission flag, abnormal pause adjustment flag, current external cooling device operating intensity, load drop flag, cooling intensity rollback permission flag, rollback interruption flag, and normal monitoring recovery flag. These fields are used for continuous recall of the current control process and subsequent operation traceability.

[0022] It should be noted that this invention can be deployed on the device itself to realize embedded applications, or it can run on a PC or other terminal with a user interface, thereby meeting various hardware environments and usage requirements.

[0023] The above embodiments can be implemented in whole or in part by software, hardware, firmware, or any other combination. When implemented in software, the above embodiments can be implemented in whole or in part by a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, the processes or functions of the embodiments of this application are implemented in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted wirelessly or wiredly from one website, computer, server, or data center to another website, computer, server, or data center. Wired methods include optical fiber, twisted pair, coaxial cable, etc. Wireless methods include infrared, microwave, etc. Available media include any available media that can be accessed by a computer or data storage devices such as servers and data centers that contain one or more sets of available media. Available media can be magnetic media (floppy disks, hard disks, magnetic tapes), optical media (DVDs), or semiconductor media. Semiconductor media can be solid-state drives.

[0024] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0025] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cooling control method for an oil-immersed transformer, characterized in that, include: S1. Collect transformer load status information, top layer insulating oil temperature, bottom layer insulating oil temperature and ambient temperature, and establish a basis for determining the operating status based on the time correspondence of each piece of information; S2. When the load status information meets the load surge condition, determine that the transformer has entered the operating state where the winding temperature rises faster than the insulating oil response, and determine the operating frequency limit of the submersible pump based on the bottom insulating oil temperature. S3. Control the submersible pump to start according to the operating frequency limit, and control the cooling device to start operation; S4. Gradually adjust the operating frequency of the submersible pump according to the temperature change of the insulating oil. If an abnormal oil flow occurs, pause the frequency increase and perform adjustment control. After the oil flow is restored, continue to adjust the frequency. After the load drops, reduce the operating intensity of the cooling device.

2. The cooling control method for an oil-immersed transformer according to claim 1, characterized in that, Collect transformer load status information, top insulating oil temperature, bottom insulating oil temperature, and ambient temperature, including: The load status information consists of the effective values ​​of the three-phase operating load current and the change information of active power on the high-voltage side and the low-voltage side. The temperature of the top insulating oil, the temperature of the bottom insulating oil and the ambient temperature are collected by the corresponding detection points according to the preset sampling period. Boundary checks, rate of change checks, and anomaly flags are performed on each collected value; When abnormal temperature data changes, the abnormal temperature data is compensated with a substitute value.

3. The cooling control method for an oil-immersed transformer according to claim 1, characterized in that, The operational status determination is based on the time correspondence of various information items, including: The basis for determining the operational status includes the original time sequence record table, the current cycle's operational input group, and the historical input sequence; According to a unified timestamp, load status information, top insulating oil temperature, bottom insulating oil temperature and ambient temperature are periodically merged and nearest neighbor matched, and the current cycle operation input group is generated within the allowable time deviation range. When temperature data is abnormal, the basic compensation value is determined based on the historical stable range, and then corrected in conjunction with the current load deviation before being written into the current cycle operation input group.

4. The cooling control method for an oil-immersed transformer according to claim 1, characterized in that, When the load status information meets the conditions for a sudden load increase, determine whether the transformer has entered an operating state where the winding temperature rises faster than the insulating oil response, including: The control terminal forms a short-window judgment sequence based on the current cycle operation input group and the previous cycle operation input group, and determines the load impact judgment quantity by combining the stable reference cycle in the historical input sequence; When the load impact judgment quantity meets the joint triggering condition, the temperature sequence of the top insulating oil and the temperature sequence of the bottom insulating oil are extracted. Based on the continuous change of the top insulating oil temperature, the temperature range of the bottom insulating oil, and the relative hysteresis relationship between the two, the current working condition is judged.

5. The cooling control method for an oil-immersed transformer according to claim 1, characterized in that, The operating frequency limit of the submersible pump is determined based on the temperature of the bottom insulating oil, including: The control terminal determines the operating frequency limit range of the submersible pump based on the temperature range of the bottom insulating oil, and adjusts the upper limit of the frequency limit range in combination with the ambient temperature. When temperature data is abnormal, temperature jumps out of bounds, or abnormal signs appear in the submersible pump drive link, maintain a conservative frequency boundary, increase the frozen frequency, or switch to an abnormal recovery pending state, and generate a status result record that includes at least a status number, temperature zone number, frequency limit value, and abnormal marker.

6. The cooling control method for an oil-immersed transformer according to claim 1, characterized in that, Controlling the submersible pump startup according to operating frequency limits includes: The control terminal forms a start-up execution input group based on the status result record and the self-test result of the actuator, and determines the target start-up frequency, frequency rise time and holding time of the submersible pump according to the current status number, the bottom insulating oil temperature zone number and the frequency limit boundary; During the startup process of a submersible pump, pre-start checks, in-start monitoring, and post-start confirmation are performed. When abnormal current, speed, torque, or driver code occurs, the frequency freeze control is activated, and the system switches to delayed retry control or micro-drainage recovery control.

7. The cooling control method for an oil-immersed transformer according to claim 1, characterized in that, Controlling the operation of the cooling system includes: The control terminal performs tiered pre-activation control of the external cooling device based on the load impact level and the availability of the external cooling device, and observes and confirms the activation based on the operation feedback after activation. After the submersible oil pump enters restricted operation, it continuously acquires the temperature of the top insulating oil, the temperature of the bottom insulating oil, the ambient temperature, and the operating status of the external cooling device. It confirms the status switch based on the temperature change trend and the environmental correlation, and generates a startup result output record. The startup result output record should include at least the operating frequency, the target intensity of the cooling device, the temperature change trend marker, and the frequency adjustment permission marker.

8. The cooling control method for an oil-immersed transformer according to claim 1, characterized in that, The operating frequency of the submersible pump is gradually adjusted according to the temperature change of the insulating oil, including: The control terminal forms a phase adjustment input set based on the startup result output record and the current cycle acquisition data, and judges the internal heat exchange link status based on the continuous change relationship between the top layer insulating oil temperature and the bottom layer insulating oil temperature. When the temperature of the top insulating oil rises continuously and the temperature of the bottom insulating oil changes synchronously, the control terminal enters the frequency release state, determines the release step size according to the range of the current operating frequency of the submersible pump, and sets an observation window after each frequency increase. The control terminal combines current feedback, torque feedback, speed feedback, and the correlation changes between the top insulating oil temperature, the bottom insulating oil temperature, and the ambient temperature to confirm the next level of frequency release permission and generate a stage adjustment output record. The stage adjustment output record includes at least a frequency level mark and a release permission mark.

9. The cooling control method for an oil-immersed transformer according to claim 1, characterized in that, When an abnormal oil flow occurs, frequency adjustment is paused and adjustment control is implemented. Frequency adjustment resumes after oil flow recovers. After the load decreases, the operating intensity of the cooling device is reduced, including: When the control terminal detects abnormal current fluctuations, abnormal torque fluctuations, abnormal speed tracking, or abnormal temperature relationships, it maintains the current frequency or reverts to a lower frequency depending on the severity of the abnormality, and performs fixed frequency holding, slow frequency reduction recovery, or micro-oscillation adjustment. After continuous observation and meeting the recovery conditions, continue to adjust according to the frequency level at which no abnormality occurred last time. If the recovery is still not achieved after continuous adjustment, switch to release and termination control. After the load enters the fallback judgment, the heat accumulation status is judged by combining the temperature of the top layer insulating oil, the temperature of the bottom layer insulating oil and the temperature difference between the two. First, the frequency of the submersible pump is gradually reduced, then the intensity of the external cooling device is reduced in stages, and the reduction is stopped when the load rises again and restored to the most recent stable operation level.

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