A temperature rise control method and system for offshore wind power transformer under harmonic working condition

Abstract

The present application relates to offshore wind power transformer temperature rise control technical field, disclose a kind of offshore wind power transformer harmonic operating condition under temperature rise control method and system.The present application is first obtained operating load, harmonic operating condition, transformer measured temperature, current cooling level and target winding temperature rise sensitive area, reference area measured temperature;When harmonic operating condition meets trigger condition and basic cooling operating state meets degradation condition, according to load interval and current cooling level, the reference temperature difference formed by the temperature rise test data of target model transformer under reference harmonic condition is obtained, the local temperature difference deviation is calculated;When not meeting release condition, maintain current cooling level, when meeting, reduce cooling level.The present application can reduce the situation of reducing cooling level in advance when local temperature difference is still in deviation state.

Description

Technical Field

[0001] This invention relates to the field of temperature rise control technology for offshore wind power transformers, and in particular to a method and system for temperature rise control under harmonic conditions of offshore wind power transformers. Background Technology

[0002] Offshore wind turbines use power electronic converters to convert electrical energy. During operation, the step-up transformer may be subjected to load currents containing harmonic components. Besides increasing ohmic losses in the windings, harmonic currents also alter the spatial distribution of eddy current losses, causing different temperature rises at different coil sections and radial locations. The paper "The Influence of Harmonic Currents on the Winding Losses and Temperature Distribution Characteristics of Converter Transformers," published in the *Journal of Electrical Engineering*, Vol. 38, No. 2, 2023, studied the winding losses and temperature distribution under the influence of harmonic currents. The results show that harmonic currents exacerbate local winding losses and cause the winding temperature to exhibit a non-uniform distribution along the radial direction. Therefore, using a single overall temperature to characterize the thermal state of the transformer under harmonic conditions is insufficient to fully reflect the temperature rise differences at different locations within the windings.

[0003] Regarding transformer internal temperature monitoring, Chinese invention patent application CN109781264A discloses a transformer fiber optic temperature measurement system and method. This system collects real-time temperatures at sampling points using multiple fiber optic temperature sensors placed at different locations inside the transformer and processes the temperature data from different locations. Regarding cooling control of oil-immersed transformers, Chinese invention patent application CN108037780A discloses a cooling control method for oil-immersed transformers based on temperature rise and load rate. This method assesses the transformer's thermal state based on the top oil temperature, winding hot spot temperature, and load rate, and adjusts the cooler's operation according to different heat dissipation requirements. Existing technologies are already capable of acquiring temperatures at different locations inside the transformer and adjusting the cooling system's operating status based on load and temperature parameters.

[0004] However, after a harmonic condition occurs, when the transformer's basic temperature parameters have reached the conditions for reducing the cooling level, the existing cooling control method lacks further judgment on the recovery state of the local temperature distribution of the target winding. It is difficult to determine whether the local temperature distribution has recovered to the normal level under the corresponding operating load and cooling operation state based on the current temperature difference between different temperature measurement areas of the target winding. There is a situation where the cooling level is reduced when the local temperature difference is still in a deviated state. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for controlling temperature rise under harmonic conditions of offshore wind power transformers. This method can solve the problem of prematurely reducing the cooling level when the local temperature difference is still in a deviated state when the basic cooling operation meets the degradation conditions. It can achieve the constraint of cooling degradation based on the recovery state of the local temperature difference of the target winding.

[0006] To achieve the above objectives, the present invention provides the following solution: A method for controlling temperature rise of offshore wind power transformers under harmonic operating conditions includes: Obtain the operating load, harmonic conditions, measured transformer temperature, current cooling level, and measured temperatures of the target winding's temperature rise sensitive area and reference area for the offshore wind power transformer; Determine the foundation cooling operation status based on the actual measured temperature of the transformer; After the preset triggering conditions are met under harmonic conditions, when the basic cooling operation meets the conditions for reducing the cooling level, the load range is determined according to the operating load. The reference temperature difference is obtained based on the load range and the current cooling level. The reference temperature difference is determined by the temperature rise test data of the target model transformer under the load range, the current cooling level and the reference harmonic conditions. The current temperature difference is determined based on the measured temperatures of the temperature rise sensitive area and the reference area, and the local temperature difference deviation is determined based on the degree of deviation of the current temperature difference from the reference temperature difference. When the local temperature difference deviation does not meet the release conditions, maintain the current cooling level; when the local temperature difference deviation meets the release conditions, reduce the current cooling level.

[0007] Preferably, the temperature rise sensitive area and the reference area are determined in the following way: Acquire temperature rise test data at multiple temperature measurement locations in the target winding of the target transformer under multiple preset load ranges and multiple cooling levels, respectively, when under reference harmonic conditions and test harmonic conditions that meet preset triggering conditions; For each temperature measurement location, the difference between the test temperature rise corresponding to the test harmonic conditions and the test temperature rise corresponding to the reference harmonic conditions under the same preset load range and the same cooling level is determined, and the average value of multiple differences is determined. The area corresponding to the temperature measurement location with the largest average value is determined as the temperature rise sensitive area, and the area corresponding to the temperature measurement location with the smallest average value is determined as the reference area. After determining the temperature rise sensitive area and the reference area, the measured temperature of the temperature rise sensitive area and the reference area is obtained.

[0008] Preferably, the preset triggering conditions for harmonic operation are determined according to the content of each harmonic current, including: Obtain the current content of each harmonic order within a preset harmonic order range; The content of each harmonic current is compared with the corresponding trigger threshold. When the content of at least one harmonic current reaches the corresponding trigger threshold, it is determined that the harmonic operating condition meets the preset trigger condition. After the harmonic operating condition meets the preset triggering conditions, when the basic cooling operating state meets the conditions for reducing the cooling level, the load range is determined according to the preset load range to which the operating load belongs.

[0009] Preferably, after the harmonic operating condition meets the preset triggering conditions and the basic cooling operating state meets the conditions for reducing the cooling level, the load range can also be determined based on the operating load within a preset observation period, including: After the harmonic operating condition meets the preset triggering conditions, when the basic cooling operating state meets the conditions for reducing the cooling level, the operating load within the preset observation period is obtained; Determine the maximum and minimum values ​​of the operating load within the preset observation period; When the maximum and minimum values ​​are within the same preset load range, the corresponding preset load range is determined as the load range. Maintain the current cooling level when the maximum and minimum values ​​are not within the same preset load range.

[0010] Preferably, a reference temperature difference is obtained based on the load range and the current cooling level. The reference temperature difference is determined by temperature rise test data of the target model transformer under load range, current cooling level, and reference harmonic conditions, including: The test condition in which the content rate of each harmonic current within the preset harmonic order range is not higher than the corresponding benchmark limit is determined as the benchmark harmonic condition. Under reference harmonic conditions, the target model transformer is operated in combinations of each preset load range and each cooling level. After the temperature rise corresponding to each combination reaches stability, multiple sets of test temperatures in the temperature rise sensitive area and reference area are obtained simultaneously. The test temperature difference is determined based on the test temperature of each group, and the average value of multiple test temperature differences corresponding to the same combination is determined as the reference temperature difference corresponding to the combination. The corresponding reference temperature difference is obtained based on the load range and the current cooling level.

[0011] Preferably, the current temperature difference is determined based on the measured temperatures of the temperature-sensitive area and the reference area, and the local temperature difference deviation is determined based on the degree of deviation of the current temperature difference from the reference temperature difference, including: Obtain the measured temperatures of the temperature rise sensitive area and the reference area at the same sampling time; The difference between the measured temperature of the temperature rise sensitive area and the measured temperature of the reference area is determined as the current temperature difference; When the current temperature difference is greater than the reference temperature difference, the difference between the current temperature difference and the reference temperature difference is determined as the local temperature difference deviation. When the current temperature difference is not greater than the reference temperature difference, the local temperature difference deviation is set to zero.

[0012] Preferably, the release threshold and release conditions are determined in the following manner: Determine the differences between multiple test temperature differences corresponding to the same combination and the reference temperature difference, and determine the maximum value among the multiple differences as the release threshold; Multiple local temperature difference deviations are continuously determined within a preset judgment period; When the deviation of multiple local temperature differences is not greater than the release threshold, the local temperature difference deviation is determined to meet the release condition. When there is a local temperature difference deviation among multiple local temperature difference deviations that exceeds the release threshold, it is determined that the local temperature difference deviation does not meet the release conditions.

[0013] Preferably, the cooling level control after the harmonic operating condition no longer meets the preset triggering conditions includes: After the harmonic operating condition no longer meets the preset triggering conditions, continue to determine the local temperature difference deviation. When the local temperature difference deviation does not meet the release conditions, the current cooling level is maintained; When the local temperature difference deviation meets the release condition, the basic cooling operation status is re-determined based on the current measured temperature of the transformer. If the redefined basic cooling operating conditions meet the conditions for reducing the cooling level, the current cooling level is reduced; if the redefined basic cooling operating conditions do not meet the conditions for reducing the cooling level, the current cooling level is maintained.

[0014] Preferably, when the local temperature difference deviation meets the release conditions, the current cooling level is reduced, including: Perform a cooldown reduction and update the reduced cooldown level to the current cooldown level; After the current cooling level is updated, the load range is redefined based on the operating load. The baseline temperature difference and release threshold are re-established based on the redefined load range and the updated current cooling level; When the basic cooling operation condition meets the conditions for reducing the cooling level again, the local temperature difference deviation is determined based on the newly obtained reference temperature difference, and the current cooling level is determined based on the local temperature difference deviation and the newly obtained release threshold.

[0015] A temperature rise control system for offshore wind power transformers under harmonic operating conditions includes: The data acquisition unit is used to acquire the operating load, harmonic conditions, measured temperature of the transformer, current cooling level, and measured temperature of the target winding's temperature rise sensitive area and reference area of ​​the offshore wind power transformer. The basic cooling operation status determination unit is used to determine the basic cooling operation status based on the actual measured temperature of the transformer. The load range determination unit is used to determine the load range based on the operating load after the preset triggering conditions are met under harmonic conditions and the basic cooling operating state meets the conditions for reducing the cooling level. The reference temperature difference acquisition unit is used to obtain the reference temperature difference based on the load range and the current cooling level. The reference temperature difference is determined by the temperature rise test data of the target model transformer under the load range, the current cooling level, and the reference harmonic conditions. The local temperature difference deviation determination unit is used to determine the current temperature difference based on the measured temperatures of the temperature rise sensitive area and the reference area, and to determine the local temperature difference deviation based on the degree of deviation of the current temperature difference from the reference temperature difference. The cooling level control unit is used to maintain the current cooling level when the local temperature difference deviation does not meet the release conditions, and to reduce the current cooling level when the local temperature difference deviation meets the release conditions.

[0016] The present invention discloses the following beneficial effects: (1) The present invention determines the basic cooling operation status by measuring the transformer temperature, and after the harmonic operation condition meets the preset triggering conditions, it further performs local temperature difference judgment only when the basic cooling operation status meets the conditions for reducing the cooling level. This adds local temperature difference constraint to the cooling degradation under the harmonic operation condition in addition to the basic cooling operation status judgment, and reduces the situation of directly reducing the cooling level based solely on the basic cooling operation status.

[0017] (2) The present invention determines the load range based on the operating load and obtains the reference temperature difference in combination with the current cooling level. The reference temperature difference is determined by the temperature rise test data of the target model transformer under the corresponding load range, corresponding cooling level and reference harmonic conditions, so that the current temperature difference can be compared with the reference temperature difference according to the corresponding load range and current cooling level, reducing the impact of changes in load level and cooling level on the judgment of local temperature difference.

[0018] (3) The present invention determines the current temperature difference based on the measured temperature of the temperature rise sensitive area and the reference area, and determines the local temperature difference deviation based on the degree of deviation of the current temperature difference from the reference temperature difference, so that the cooling degradation judgment further considers the degree of deviation of the temperature difference between the two areas of the target winding from the reference state, thereby judging whether the local temperature difference deviation has met the release condition when the basic cooling operation state meets the conditions for reducing the cooling level.

[0019] (4) The present invention maintains the current cooling level when the local temperature difference deviation does not meet the release conditions, and reduces the current cooling level when the local temperature difference deviation meets the release conditions. This makes the cooling level reduction after the harmonic condition is triggered subject to the constraints of both the basic cooling operation state and the local temperature difference deviation, thereby reducing the situation where the cooling level is reduced prematurely when the local temperature difference is still in a deviation state. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart of a method for controlling temperature rise under harmonic conditions of offshore wind power transformers provided in an embodiment of the present invention; Figure 2 This is a diagram showing the arrangement of the target winding temperature measurement positions according to an embodiment of the present invention. Figure 3 This is a curve for determining the local temperature difference deviation provided in an embodiment of the present invention; Figure 4 This is a logic diagram for adjusting the cooling level step by step, provided in an embodiment of the present invention. Figure 5 A schematic diagram of the temperature rise control system for offshore wind power transformers under harmonic conditions provided in an embodiment of the present invention. Detailed Implementation

[0022] 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.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 The method flowchart provided in the embodiments of the present invention is as follows: Figure 1 As shown in the figure, this embodiment provides a method for controlling temperature rise of offshore wind power transformers under harmonic operating conditions, including: Step 100: Obtain the operating load, harmonic conditions, measured temperature of the transformer, current cooling level, and measured temperature of the target winding's temperature rise sensitive area and reference area for the offshore wind power transformer; Step 200: Determine the foundation cooling operation status based on the actual measured temperature of the transformer; Step 300: After the preset triggering conditions are met under harmonic conditions, when the basic cooling operation status meets the conditions for reducing the cooling level, determine the load range based on the operating load. Step 400: Obtain the reference temperature difference based on the load range and the current cooling level; the reference temperature difference is determined by the temperature rise test data of the target model transformer under the load range, the current cooling level, and the reference harmonic conditions; Step 500: Determine the current temperature difference based on the measured temperatures of the temperature rise sensitive area and the reference area, and determine the local temperature difference deviation based on the degree of deviation of the current temperature difference from the reference temperature difference; Step 600: When the local temperature difference deviation does not meet the release conditions, maintain the current cooling level; when the local temperature difference deviation meets the release conditions, reduce the current cooling level.

[0025] In one specific embodiment, the offshore wind power transformer is located at an offshore substation and is an oil-immersed main transformer with forced oil circulation air cooling. The main transformer model is SFZ-640000 kVA, with a rated capacity of 640 / 320-320 MVA, a rated voltage of 525±8×1.25% / 66 kV-66 kV, OFAF cooling, and a connection group of YN,d11-d11. The main transformer adopts a split winding structure, with two low-voltage branches each having corresponding rated capacity and operating electrical quantities. The target winding is determined based on the winding for which temperature rise monitoring is performed. The rated capacity, voltage level, winding structure, oil duct layout, and cooler configuration of the target winding adopt the technical parameters of the target model transformer. Table 1 shows the main transformer equipment parameters used in this embodiment, specifically: Table 1 Parameters of the Target Transformer Model

[0026] In Table 1, the 640 / 320-320 MVA main transformer has two 320 MVA low-voltage branches. When the target winding is selected from one of the 66 kV low-voltage branches, the operating load is determined according to the electrical quantities of the corresponding branch; when the target winding is selected from the high-voltage winding, the operating load is determined according to the electrical quantities on the high-voltage side. The operating load thus corresponds to the target winding where the local temperature difference is determined.

[0027] The OFAF cooling system comprises multiple cooler groups. The cooler groups are equipped with oil pumps and cooling fans according to the combination determined by the main transformer manufacturer. The main transformer control cabinet or cooling control PLC stores the operating status of each cooler group. Cooling levels are determined according to the cooling operation modes configured by the target transformer manufacturer. When the rated cooling capacity of each cooler group is the same, the cooling levels are determined from low to high according to the number of cooler groups in operation; when the rated cooling capacity of each cooler group differs, the cooling levels are determined according to the order of the cooling operation modes configured by the manufacturer. The cooling level range of the target transformer model consists of the various cooling operation modes configured by the manufacturer.

[0028] The current cooling level directly reads the operating mode status in the cooling control PLC. The control program uses the current cooling level to select the reference temperature difference established under the same cooling boundary conditions. In this embodiment, the same cooling boundary conditions refer to the same load range and the same cooling level under the reference harmonic conditions. For each load range and cooling level combination, after the temperature rise reaches a stable state, the corresponding reference temperature difference is determined according to equations (18) and (19), and the load range, cooling level, and corresponding reference temperature difference are saved in the test parameter table. During operation, the corresponding reference temperature difference is obtained according to the current load range and the current cooling level. The changes in oil flow and heat exchange conditions caused by the switching of the cooler group thus enter the reference temperature difference matching process.

[0029] The offshore substation monitoring system provides the main transformer's active power, reactive power, operating temperature, and cooler group status. Power quality monitoring equipment provides fundamental current and harmonic current data. The fiber optic temperature sensor inside the windings provides the temperature at each measurement location within the target winding. A unified clock within the station adds sampling time to all types of data, and the control program generates data records for the same operating moment based on the sampling time.

[0030] The active power of the corresponding branch of the target winding is denoted as Reactive power is denoted as The three-phase apparent power is determined according to the following formula: (1) The rated capacity corresponding to the target winding is denoted as The operating load is based on the load rate. express: (2) In equation (1), This represents the three-phase apparent power. The active and reactive power in Equation (1) are obtained from the telemetry measurements of the corresponding electrical branches of the station control system. The rated capacity in Equation (2) is obtained from the main transformer nameplate or the target model technical agreement. Both capacities use the same unit, and the load factor is a dimensionless quantity.

[0031] For the 640 / 320-320 MVA main transformers in Table 1, when the target winding is located on a 66 kV low-voltage branch, the rated capacity is 320 MVA for the corresponding branch; when the target winding is located on the high-voltage side, the rated capacity is the corresponding capacity on the high-voltage side. For other offshore wind power main transformers, normalization is performed according to the rated capacity corresponding to the target winding. GB / T1094.7-2024 "Power Transformers Part 7: Load Guidelines for Oil-Immersed Power Transformers" has been implemented, and the load rate can be used as the basic operating quantity for the thermal state of oil-immersed transformers.

[0032] The power quality monitoring equipment is installed on the corresponding electrical side of the target winding and can be online monitoring equipment that conforms to GB / T 19862-2025 "General Requirements for Power Quality Monitoring Equipment". The monitoring equipment obtains the fundamental current and harmonic current according to the target site configuration and sends the monitoring results to the controller.

[0033] The effective value of the fundamental current is denoted as , No. The effective value of the second harmonic current is denoted as... , No. The content of subharmonic current is: (3) In equation (3), Indicates the harmonic order. Indicates the first The harmonic current content rate is determined based on the grid connection test report of the target offshore wind farm, harmonic calculation data, and long-term power quality monitoring records. Each monitored harmonic number has a corresponding trigger threshold stored in the controller. During operation, the current harmonic current content rate is compared with the corresponding trigger threshold sequentially. When any monitored harmonic number reaches its corresponding trigger threshold, the current harmonic operating condition meets the preset trigger condition.

[0034] Let the first The trigger threshold corresponding to the subharmonic is The triggering relationship is represented as: (4) The trigger threshold directly corresponds to the harmonic level of the target power station. During the initial commissioning phase, initial parameters can be established using the harmonic measurement results from the grid connection test report. The controller is configured according to the harmonic order. Save the corresponding trigger thresholds respectively After long-term monitoring records are established, when the approved operating parameters of the target site specify a new trigger threshold corresponding to a certain monitored harmonic number, the controller will trigger the controller according to the harmonic number. Original Replace it with the approved trigger threshold, and use the updated threshold in subsequent harmonic condition judgments. .

[0035] During the temperature rise test design phase, the influence of selected harmonic frequencies on the winding eddy current loss and harmonic loss factor can be evaluated. The harmonic loss factor is determined using the square relationship of the order harmonics, which is commonly used in the analysis of non-sinusoidal load transformers.

[0036] (5)

[0037] In equation (5), This represents the winding eddy current loss and harmonic loss factor. This represents the highest harmonic order included in the calculation. Equation (5) is used for thermal effect verification of the test harmonic spectrum. In actual testing, the effective value of each harmonic current is obtained from the power quality measurement equipment of the test circuit. The cooling level release during operation is still based on the local temperature difference deviation formed by the measured temperature inside the winding.

[0038] Table 2 lists the main data that the controller needs to read during operation and their sources, specifically: Table 2 Temperature rise control operation data and data sources

[0039] The data in Table 2 are correlated using a unified sampling time within the controller. Operating load, harmonic conditions, measured transformer temperature, and local winding temperature form the data basis for the same judgment period. The cooling control PLC provides the current cooling level, allowing the operating temperature difference to reference a test baseline established under the same cooling conditions.

[0040] The local temperature of the target winding is measured directly using internal optical fiber. Multiple candidate temperature measurement locations are set during the winding manufacturing stage, denoted sequentially as P1, P2, to Pm. These candidate locations are distributed along the axial direction of the target winding, covering the winding region with high additional losses in leakage magnetic field and load loss calculations, while also covering the winding region with relatively low temperature rise response. The number of candidate locations is determined based on the target winding structure and the manufacturer's temperature rise design.

[0041] One installation method uses a dedicated insulating pad with a temperature probe. The insulating pad is placed between adjacent coils, and the optical fiber extends along the winding support bars and insulating supports, connecting to an external optical fiber temperature measurement unit via an optical fiber through-hole component on the oil tank. Another installation method involves pre-installing an insulating conduit along the support bars during the winding manufacturing stage. After the coil body is dried, the optical fiber temperature probe is delivered to the predetermined temperature measurement position along the insulating conduit. Both installation methods ensure that the temperature probe is located inside the target winding and maintains the flow conditions corresponding to the designed oil passage.

[0042] The fiber optic temperature measurement host stores the measurement location number, temperature value, and sampling time. During the testing phase, the same location number is used to record data for each candidate measurement point. During the operational phase, continuous temperature measurement is performed using the already determined temperature rise sensitive area and reference area.

[0043] The temperature rise sensitive zone and reference zone are determined using grouped temperature rise test data of the target transformer model. Each group of data corresponds to the same load range and the same cooling level. The m-th data group includes one reference harmonic test section and one harmonic test section. The two test sections record the corresponding load range and cooling level, respectively. Valid paired data satisfy: (6) (7) In equations (6) and (7), , They represent the first The load range and cooling level of the reference harmonic test section. , They represent the first The load range and cooling level of the group harmonic test section, superscript , These represent the reference harmonic test section and the harmonic test section, respectively. Equations (6) and (7) ensure that the same set of comparative data is under the same load range and the same cooling condition. Variations in harmonic conditions become the main operational differences that need to be compared between the two test sections.

[0044] No. The candidate temperature measurement location is at the The measured temperature of the group harmonic test section is denoted as The corresponding ambient reference temperature is denoted as The temperature rise is: (8) The corresponding temperature rise in the reference harmonic test section was determined using the same method: (9) The harmonic temperature rise response at the same candidate temperature measurement location in the same group of tests is: (10) After completing M sets of valid paired data, calculate the average harmonic temperature rise response at the candidate temperature measurement locations: (11) The region corresponding to the candidate temperature measurement location with the largest average harmonic temperature rise response is designated as the temperature rise sensitive area, while the region corresponding to the candidate temperature measurement location with the smallest average harmonic temperature rise response is designated as the reference area.

[0045] (12) (13) In equation (8), Indicates the first The candidate temperature measurement location is at the Temperature rise of the group harmonic test section; in formula (9), , and They represent the first The candidate temperature measurement location is at the The measured temperature, corresponding ambient reference temperature, and temperature rise of the reference harmonic test section; in equation (10), Indicates the first The candidate temperature measurement location is at the The harmonic temperature rise response in the group test; in equation (11), Indicates the first The average harmonic temperature rise response of each candidate temperature measurement location; in equations (12) and (13), and These represent the candidate temperature measurement location numbers corresponding to the temperature rise sensitive area and the reference area, respectively. The temperature rise sensitive area represents the winding region of the target model that exhibits a large temperature rise response to harmonic conditions under the covered test conditions. The reference area represents the region within the same target winding with a relatively small temperature rise response. Both areas are derived from actual temperature measurement data. When the average harmonic temperature rise responses of multiple candidate temperature measurement locations are similar, the location with smaller temperature fluctuations and stable fiber optic measurement status in the reference harmonic test is preferred.

[0046] like Figure 2 As shown, the target winding forms multiple coils along the axial direction, with axial oil channels formed between adjacent coils; multiple candidate temperature measurement positions are distributed along the axial direction of the target winding, arranged from bottom to top in the figure. , , … express. This indicates the candidate temperature measurement locations corresponding to the aforementioned temperature rise sensitive area. This indicates the candidate temperature measurement locations corresponding to the aforementioned reference area; both belong to the candidate temperature measurement location sequence. The ellipsis in the figure indicates... and Other candidate temperature measurement locations are distributed in between, and the arrow on the right indicates the axial direction of the target winding.

[0047] Once the candidate temperature measurement location is determined, the same winding structure and probe installation location are used in transformers of the same model. If the winding structure, oil passage layout, or cooler configuration of the target model changes, the temperature rise sensitive area and reference area are re-established according to the changed model.

[0048] The reference temperature difference data for the target transformer model is established during the temperature rise test in the manufacturing stage. The temperature rise test for liquid-immersed transformers can be performed according to GB / T 1094.2-2013 "Power Transformers Part 2: Temperature Rise of Liquid-Immersed Transformers". The test wiring, current combination, and cooler operation status of multi-winding or split-winding main transformers are determined according to the temperature rise test outline for the target model.

[0049] The reference harmonic conditions correspond to the low-harmonic reference state in the temperature rise test of the target model. When all monitored harmonic orders are within the reference limit range specified in the test plan for the target model, the data from the stabilization phase are included in the reference temperature difference calculation. The harmonic test section needs to generate specified harmonic current components. When the test platform has the corresponding capacity, the main test power supply bears the fundamental short-circuit test power, and the harmonic current source provides the harmonic components to be examined. The power quality measurement equipment of the test circuit records the actual fundamental current and each harmonic current.

[0050] When an offshore substation is already equipped with a winding fiber optic temperature measurement system, grouped data can also be generated during commissioning or special thermal tests. Select the low-harmonic operating segment and harmonic operating segment under the same load range and the same cooling level, and determine the temperature rise response of the corresponding temperature measurement location according to equations (8) to (13). The test data during the manufacturing stage and the field special test data use the same data fields and calculation relationships.

[0051] After the test reaches the thermal stability conditions required for the target model, it enters a stable sampling period. During the test, the liquid temperature and cooling medium temperature are continuously acquired to determine the thermal stability. The liquid temperature rise is expressed by the following formula: (14) During the continuous observation period t1 to t2, the rate of change of liquid temperature is calculated according to the following formula: (15) In equation (14), Indicates the time of the experiment. , and Representing the test time The liquid temperature, cooling medium temperature, and liquid temperature rise; in equation (15), , These represent the start and end times of the continuous observation period, respectively. This indicates the rate of temperature change of the liquid. Thermal stability conditions are performed according to the applicable temperature rise test procedure and test outline for the target model. After entering the stable sampling range, the fiber optic temperature sensor synchronously records the temperatures of the temperature-sensitive area and the reference area. The local temperature difference formed during the stabilization phase is used to establish the reference temperature difference and the release threshold.

[0052] During operation, continuous load data is used to determine the effective load range. The controller acquires p load rates during a preset observation period. The minimum and maximum load rates for each observation period are as follows: (16) (17) In equations (16) and (17), Indicates the first observation within the preset observation period Each sampling time, and These represent the minimum and maximum load rates within the preset observation period, respectively. The controller stores multiple preset load ranges. When both the minimum and maximum load rates fall within the same preset load range, that range becomes the current effective load range. When the observation period crosses the boundary of a load range, the controller enters a new observation period and continues to collect operating load data. After an effective load range is established, the corresponding reference temperature difference is then retrieved.

[0053] After establishing a load range through observation periods, a correlation is formed between the winding temperature, which has thermal inertia, and the continuously existing load state. Single-point load changes caused by short-term fluctuations in wind power output will not immediately switch the reference temperature difference.

[0054] The reference temperature difference is established separately according to the load range and cooling level. Let the load range currently under investigation be numbered k, and the cooling level be numbered c. After the reference harmonic conditions reach thermal stability, N sets of synchronous temperatures for the temperature rise sensitive area and the reference area are obtained in the stable sampling range. The temperature difference of the qth test group is: (18) The reference temperature difference for the corresponding load range and cooling level is: (19) In equation (18), , These represent the load interval numbers respectively. Cooling level number is Time Synchronous test temperatures of the temperature rise sensitive area and the reference area of ​​the group. Indicates the first Temperature difference in group test; in formula (19), The load range number is Cooling level number is The reference temperature difference at that time. The two temperatures in Equation (18) come from the same sampling time and the same target winding. The two temperature measurement positions experience the same external environmental changes, and the spatial temperature difference can be directly compared with the test spatial temperature difference under the same conditions. The temperature rise is used when determining the temperature rise sensitive area because the reference harmonic test section and the harmonic test section may occur at different times, and it is necessary to use the environmental reference temperature to correct the environmental differences between the test sections.

[0055] The controller maintains the parameter correspondence between load range, cooling level, and reference temperature difference. When a load range corresponds to multiple cooling levels, a reference temperature difference is maintained for each cooling level. After the cooler group status changes, the controller switches to the reference temperature difference corresponding to the new cooling level.

[0056] The same set of stable test data that forms the reference temperature difference is used to determine the release conditions. The positive deviation of the q-th test temperature difference relative to the reference temperature difference is: (20) The release threshold corresponding to the same load range and cooling level is taken as the maximum positive deviation in the stable sampling data: (twenty one) Since the reference temperature difference is the average of multiple test temperature differences in the same combination, the maximum value of the difference between the multiple test temperature differences and the reference temperature difference is equal to the maximum value of the positive deviation, and is used as the release threshold.

[0057] In equation (20), Indicates the first The positive deviation of the test temperature difference from the reference temperature difference; in equation (21), The load range number is Cooling level number is The release threshold is determined by the stable temperature difference fluctuations that the target model has already exhibited under reference harmonic conditions. The reference temperature difference describes the average spatial temperature difference during the stable phase, while the release threshold describes the allowable positive fluctuation range during the stable phase. Both parameters are derived from the same set of synchronized temperature measurements.

[0058] During operation, the fiber optic temperature measurement unit synchronously reads the temperature of the temperature rise-sensitive area and the temperature of the reference area at sampling time t. The current temperature difference is: (twenty two) Based on the current effective load range and current cooling level, the corresponding reference temperature difference is obtained, and the local temperature difference deviation is: (twenty three) In equation (22), , They represent the sampling times respectively. Temperature of the temperature-sensitive area and the reference area, Indicates the current temperature difference; in equation (23), Indicates the sampling time The local temperature difference deviation is calculated as follows: When the current temperature difference equals the corresponding reference temperature difference, the local temperature difference deviation is zero; when the current temperature difference is higher than the corresponding reference temperature difference, the excess portion directly constitutes the local temperature difference deviation. The calculation process uses two real-time temperatures and one target model test parameter. The local temperature difference deviation describes the degree of deviation of the spatial temperature difference between two fixed regions of the target winding relative to the corresponding reference state.

[0059] Local temperature deviation triggers a cooling degradation release judgment. If n local temperature deviations are continuously acquired within a judgment period, the maximum local temperature deviation within that period is: (twenty four) The local temperature difference deviation meets the release condition when the following formula is satisfied: (25) In equation (24), Indicates the first time period within the judgment period Each sampling time, This indicates the maximum local temperature difference deviation within the judgment period. If the maximum local temperature difference deviation within the judgment period exceeds the release threshold, the current cooling level will remain unchanged. The release condition is met once all local temperature difference deviations within the complete judgment period fall within the allowable fluctuation range established by the target model's stability test. A short-term drop at a single sampling point will not trigger a cooling degradation on its own.

[0060] like Figure 3 As shown, the horizontal axis represents the sampling time. The unit is min, and the vertical axis represents the local temperature difference deviation. The unit is K; black dots and connecting lines represent continuously obtained data during the judgment process. The red horizontal dashed line represents the current load range. Current cooling level Corresponding release threshold The release threshold is formed by the stable temperature rise test data of the target model transformer under the corresponding load range, corresponding cooling level, and reference harmonic conditions; the two vertical dashed lines define a judgment period, with the right boundary time... This indicates the moment when the judgment period ends and a release judgment is made. The diagram shows the continuous sampling record. K, the judgment period is from 80 min to 160 min; within the judgment period, each All not higher than Therefore, the maximum local temperature difference deviation during this period satisfy The release conditions have been met.

[0061] The judgment period can be coordinated with the minimum operating hold time or minimum switching interval of the cooler used in the original cooling program of the target model. If the original cooling program already has a minimum operating hold time, the controller directly uses the same time scale to form the judgment period, so that the local temperature difference judgment corresponds with the cooler control timing.

[0062] The measured temperature of the transformer uses the temperature value used by the original cooling control system of the target model for determining the activation and deactivation of the cooler. When the target model uses the top oil temperature for cooling control, the controller reads the top oil temperature; when the original cooling control also uses the winding temperature indication value or other temperature values ​​specified by the manufacturer, the controller reads the measured temperature corresponding to the original control logic. The basic cooling operation status follows the original cooling control conditions of the target model.

[0063] After the original cooling control logic establishes the conditions for reducing the current cooling level, the controller reads the maximum local temperature difference deviation during the most recent judgment period. If the maximum local temperature difference deviation exceeds the release threshold, the current cooling level remains unchanged. Once the maximum local temperature difference deviation falls within the release threshold range, the controller reads the current measured transformer temperature again and reconfirms the basic cooling operation status. If the basic cooling operation status still meets the conditions for reducing the cooling level, the cooling control PLC receives a permission instruction to reduce the cooling level by one level.

[0064] Once a harmonic condition reaches the preset trigger condition, the controller saves the trigger time and continuously collects the harmonic current and winding temperature for each harmonic. After changes in wind power output or grid connection mode, the harmonic current content may decrease before the local temperature difference in the winding. The winding temperature continues to generate the current temperature difference and local temperature difference deviation based on the current sampled value. After the basic cooling operation meets the degradation conditions, if the local temperature difference deviation is still higher than the release threshold, the existing cooling capacity will continue to be maintained.

[0065] This control process involves both basic cooling conditions and local temperature difference conditions in cooling degradation. When the basic temperature has reached the exit range of the original cooling program, but the spatial temperature difference between the two regions of the target winding is still higher than the stable range of the corresponding operating state of the target model, the cooling level remains at the current state; after the spatial temperature difference enters the stable range, the degradation action corresponding to the original cooling program is executed.

[0066] When the current cooling level is reduced from one level to the next, the cooler combination and oil flow conditions are updated accordingly. The controller updates the current cooling level and restarts load observation. The new observation period forms a new minimum load rate and a new maximum load rate according to equations (16) and (17), and then determines a new effective load range.

[0067] Once the new effective load range is determined, the reduced cooling level becomes the new current cooling level. The controller calls upon the reference temperature difference and release threshold corresponding to the new load range and new cooling level, and recalculates the local temperature difference deviation when the degradation conditions are met in the next basic cooling operation. Each level adjustment uses the thermal state parameters corresponding to the current load range and current cooling level.

[0068] After employing a step-by-step judgment process, the new oil flow and heat exchange state resulting from the cooler group switching can be observed for the corresponding time. The controller re-determines the load range under the new operating state, obtains the corresponding reference temperature difference and release threshold, and then proceeds to the next cooling level judgment.

[0069] like Figure 4 As shown, the controller first obtains the current operating data in the current operating state to determine the current load range. and call the current cooldown level. Corresponding reference temperature difference and release threshold Then calculate the local temperature difference deviation. And obtain the maximum local temperature difference deviation within the judgment period. ;when Higher than At the same time, maintain the current cooling level. ;when Not higher than When this happens, the cooling level is reduced, and the reduced cooling level is used as the new current cooling level. Continue to observe under the new operating conditions and redetermine the load range. and call the corresponding and Then, it proceeds to the next cooling level assessment. The zigzag arrows in the diagram represent the cyclical relationship of re-entering the next round of load range determination, thermal state parameter retrieval, and local temperature difference deviation assessment after the cooling level is adjusted.

[0070] The judgment period can be coordinated with the minimum operating hold time of the cooler used in the original cooling program of the target model. If the controller already has the minimum switching interval parameter for the cooler, the judgment period can be directly established using the same time scale. This allows the newly added local temperature difference judgment to be integrated with the existing cooler control timing.

[0071] In one specific implementation, when the target model has two 66 kV low-voltage branches and the two branches share an OFAF cooling system, a temperature rise sensitive area and a reference area can be established in the windings of each branch respectively. Local temperature difference deviations are generated in each branch. The common cooling system uses the larger local temperature difference deviation between the two branches to trigger a release judgment. (26) In equation (26), , They represent the sampling times respectively. The local temperature difference deviation between the two low-pressure branches, This represents the larger of the local temperature difference deviations between the two low-pressure branches. When there is a difference in load distribution between the two branches, equation (26) makes the branch with the higher degree of local temperature difference deviation participate in the common cooling level judgment. Each branch uses the reference temperature difference corresponding to its own load range to calculate the local temperature difference deviation.

[0072] In another specific implementation, each of the three phases is provided with a temperature rise sensitive zone and a reference zone. When the three phases share a cooling system, each phase generates a local temperature difference deviation. The shared cooling system uses the maximum value among the three phases to determine the release condition. (27) In equation (27), , , These represent the local temperature difference deviations of phases A, B, and C, respectively. This represents the maximum value among the three-phase local temperature difference deviations. Equation (27) applies to the main transformer structure where the three-phase cooling capacity is adjusted together. When the local temperature difference of a single phase is at a high deviation, the shared cooling system maintains the current cooling level.

[0073] In another specific implementation, the preset load interval is established according to the temperature rise test arrangement and cooling control table of the target model transformer manufacturer. The load interval can be divided into equal-width segments, or different widths can be set according to the common load distribution of the target offshore wind farm. Each load interval entering the operation control has a corresponding reference temperature difference and release threshold.

[0074] The reference harmonic conditions are determined by the target model's temperature rise test scheme. The controller stores the reference harmonic limits and the operating trigger thresholds. The reference harmonic limits are used to establish a low-harmonic reference state, while the operating trigger thresholds are used to determine whether local temperature difference degradation verification has been initiated during operation. These two types of parameters have testing and operational uses, respectively.

[0075] In one system implementation, the temperature rise control system for offshore wind power transformers under harmonic conditions is installed in the industrial controller of the main transformer control cabinet, or it can be installed in the auxiliary control server of the offshore substation that is communicatively connected to the main transformer control cabinet. For example... Figure 5 As shown, the system includes a data acquisition unit, a basic cooling operation status determination unit, a load range determination unit, a reference temperature difference acquisition unit, a local temperature difference deviation determination unit, and a cooling level control unit.

[0076] The data acquisition unit is connected to the station control system, power quality monitoring equipment, fiber optic temperature measurement host, and cooling control PLC, respectively. The station control system provides the active power, reactive power, and measured transformer temperature of the corresponding branch of the target winding; the power quality monitoring equipment provides the fundamental current and harmonic current; the fiber optic temperature measurement host provides the temperature of the temperature rise sensitive area and the reference area; and the cooling control PLC provides the current cooling level.

[0077] The basic cooling operation status determination unit retrieves the original cooling control conditions for the target model and determines whether the current cooling level has reached the degradation condition based on the measured transformer temperature. The load range determination unit forms the effective load range based on the load rate corresponding to the target winding. The reference temperature difference acquisition unit accesses the test parameter table using the effective load range and the current cooling level.

[0078] The local temperature difference deviation determination unit synchronously reads the temperatures of the temperature rise sensitive area and the reference area, first forming the current temperature difference, and then calling the corresponding reference temperature difference to form the local temperature difference deviation. The cooling level control unit forms the maximum local temperature difference deviation within the judgment period and compares it with the corresponding release threshold.

[0079] Once the basic cooling operation status and the local temperature difference release condition are simultaneously met, the cooling level control unit sends a permission command to the original cooling control PLC to reduce the cooling level by one. After the cooling level is changed, the load observation is re-established, and a new reference temperature difference and release threshold are obtained according to the updated cooling level.

[0080] This embodiment determines the temperature rise sensitive area and reference area based on the grouped temperature rise test data of the target model transformer, so that the operating temperature measurement position corresponds to the actual temperature rise response of the target winding under harmonic conditions. Stable temperature rise test data are obtained under the same load range and the same cooling level. The temperature difference between the two synchronously measured areas is formed, and the release threshold is determined using the same set of stable test data, so that different load levels and different cooler operation states have corresponding reference temperature differences and release thresholds. During operation, the synchronously measured temperature of the temperature rise sensitive area and the reference area forms the current temperature difference. The part of the current temperature difference that exceeds the corresponding reference temperature difference forms the local temperature difference deviation. The maximum local temperature difference deviation within the judgment period is then compared with the release threshold to reduce the impact of short-term temperature difference drops at a single sampling moment on the cooling degradation judgment. Once the basic cooling operation meets the conditions for reducing the cooling level, the current cooling level is maintained if the maximum local temperature difference deviation during the judgment period is still higher than the release threshold. The cooling level is then allowed to be reduced only if the maximum local temperature difference deviation is not higher than the release threshold. After the cooling level changes, the load range is redefined, and the reference temperature difference and release threshold are obtained again according to the new cooling level. This allows the step-by-step cooling judgment to determine the new oil flow and heat exchange state formed after the corresponding cooler group is switched, thereby reducing the situation where the cooling level is reduced prematurely when the local temperature difference of the target winding is still in a deviated state.

[0081] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0082] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for controlling temperature rise under harmonic conditions in offshore wind power transformers, characterized in that, include: Obtain the operating load, harmonic conditions, measured transformer temperature, current cooling level, and measured temperatures of the target winding's temperature rise sensitive area and reference area for the offshore wind power transformer; The foundation cooling operation status is determined based on the measured temperature of the transformer. After the harmonic operating condition meets the preset triggering condition, when the basic cooling operating state meets the condition for reducing the cooling level, the load range is determined according to the operating load. A reference temperature difference is obtained based on the load range and the current cooling level. The reference temperature difference is determined by the temperature rise test data of the target model transformer under the load range, the current cooling level, and the reference harmonic conditions. The current temperature difference is determined based on the measured temperatures of the temperature rise sensitive area and the reference area, and the local temperature difference deviation is determined based on the degree of deviation of the current temperature difference from the reference temperature difference. When the local temperature difference deviation does not meet the release condition, the current cooling level is maintained; when the local temperature difference deviation meets the release condition, the current cooling level is reduced.

2. The method for controlling temperature rise under harmonic conditions of offshore wind power transformers according to claim 1, characterized in that, The temperature rise sensitive area and the reference area are determined in the following way: The temperature rise test data of multiple temperature measurement positions in the target winding of the target model transformer are obtained when they are under the reference harmonic conditions and the test harmonic conditions that meet the preset trigger conditions under multiple preset load ranges and multiple cooling levels. For each temperature measurement location, the difference between the test temperature rise corresponding to the test harmonic conditions and the test temperature rise corresponding to the reference harmonic conditions under the same preset load range and the same cooling level is determined, and the average value of multiple differences is determined. The area corresponding to the temperature measurement location with the largest average value is determined as the temperature rise sensitive area, and the area corresponding to the temperature measurement location with the smallest average value is determined as the reference area. After the temperature rise sensitive area and the reference area are determined, the measured temperatures of the temperature rise sensitive area and the reference area are obtained.

3. The method for controlling temperature rise under harmonic conditions of offshore wind power transformers according to claim 1, characterized in that, After the harmonic operating condition meets the preset triggering conditions, when the basic cooling operating state meets the conditions for reducing the cooling level, the load range is determined according to the operating load, including: Obtain the current content of each harmonic order within a preset harmonic order range; The content of each harmonic current is compared with the corresponding trigger threshold. When the content of at least one harmonic current reaches the corresponding trigger threshold, it is determined that the harmonic condition meets the preset trigger condition. After the harmonic operating condition meets the preset triggering condition, when the basic cooling operating state meets the condition for reducing the cooling level, the load range is determined according to the preset load range to which the operating load belongs.

4. The method for controlling temperature rise under harmonic conditions of offshore wind power transformers according to claim 1, characterized in that, After the harmonic operating condition meets the preset triggering conditions, when the basic cooling operating state meets the conditions for reducing the cooling level, the load range is determined according to the operating load, including: After the harmonic operating condition meets the preset triggering condition, when the basic cooling operating state meets the condition for reducing the cooling level, the operating load within the preset observation period is obtained; Determine the maximum and minimum values ​​of the operating load within the preset observation period; When the maximum value and the minimum value are within the same preset load range, the corresponding preset load range is determined as the load range; When the maximum value and the minimum value are not within the same preset load range, the current cooling level is maintained.

5. The method for controlling temperature rise under harmonic conditions of offshore wind power transformers according to claim 1, characterized in that, A reference temperature difference is obtained based on the load range and the current cooling level. This reference temperature difference is determined by temperature rise test data of the target model transformer under the load range, the current cooling level, and reference harmonic conditions, including: The test condition in which the content rate of each harmonic current within the preset harmonic order range is not higher than the corresponding benchmark limit is determined as the benchmark harmonic condition. Under the reference harmonic conditions, the target model transformer is operated in combinations of each preset load range and each cooling level, and after the temperature rise corresponding to each combination reaches a stable level, multiple sets of test temperatures of the temperature rise sensitive area and the reference area are obtained simultaneously. The test temperature difference is determined based on the test temperature of each group, and the average value of the multiple test temperature differences corresponding to the same combination is determined as the reference temperature difference corresponding to the combination. The reference temperature difference is obtained based on the load range and the current cooling level.

6. The method for controlling temperature rise under harmonic conditions of offshore wind power transformers according to claim 5, characterized in that, The current temperature difference is determined based on the measured temperatures of the temperature rise sensitive area and the reference area, and the local temperature difference deviation is determined based on the degree of deviation of the current temperature difference from the reference temperature difference, including: Obtain the measured temperatures of the temperature rise sensitive area and the reference area at the same sampling time; The difference between the measured temperature of the temperature rise sensitive area and the measured temperature of the reference area is determined as the current temperature difference; When the current temperature difference is greater than the reference temperature difference, the difference between the current temperature difference and the reference temperature difference is determined as the local temperature difference deviation. When the current temperature difference is not greater than the reference temperature difference, the local temperature difference deviation is determined to be zero.

7. The method for controlling temperature rise under harmonic conditions of offshore wind power transformers according to claim 6, characterized in that, When the local temperature difference deviation does not meet the release conditions, the current cooling level is maintained; When the local temperature difference deviation meets the release condition, the current cooling level is reduced, including: Determine the differences between the multiple test temperature differences corresponding to the same combination and the reference temperature difference, and determine the maximum value among the multiple differences as the release threshold; Multiple local temperature difference deviations are continuously determined within a preset determination period; When all of the aforementioned local temperature difference deviations are not greater than the release threshold, it is determined that the local temperature difference deviations meet the release conditions. When one of the multiple local temperature difference deviations is greater than the release threshold, it is determined that the local temperature difference deviation does not meet the release condition.

8. The method for controlling temperature rise under harmonic conditions of offshore wind power transformers according to claim 7, characterized in that, When the local temperature difference deviation does not meet the release conditions, the current cooling level is maintained; When the local temperature difference deviation meets the release condition, the current cooling level is reduced, including: After the harmonic condition no longer meets the preset triggering condition, the local temperature difference deviation continues to be determined; When the local temperature difference deviation does not meet the release condition, the current cooling level is maintained; When the local temperature difference deviation meets the release condition, the basic cooling operation status is re-determined based on the current measured temperature of the transformer. When the redefined basic cooling operating state meets the conditions for reducing the cooling level, the current cooling level is reduced; when the redefined basic cooling operating state does not meet the conditions for reducing the cooling level, the current cooling level is maintained.

9. The method for controlling temperature rise under harmonic conditions of offshore wind power transformers according to claim 8, characterized in that, When the local temperature difference deviation meets the release condition, the current cooling level is reduced, including: Perform a cooling level reduction and update the reduced cooling level to the current cooling level; After the current cooling level is updated, the load range is redefined based on the operating load; The reference temperature difference and the release threshold are re-obtained based on the redefined load range and the updated current cooling level; When the basic cooling operation state meets the conditions for reducing the cooling level again, the local temperature difference deviation is determined based on the newly obtained reference temperature difference, and the current cooling level is determined based on the local temperature difference deviation and the newly obtained release threshold.

10. A temperature rise control system for offshore wind power transformers under harmonic operating conditions, characterized in that, include: The data acquisition unit is used to acquire the operating load, harmonic conditions, measured temperature of the transformer, current cooling level, and measured temperature of the target winding's temperature rise sensitive area and reference area of ​​the offshore wind power transformer. A basic cooling operation status determination unit is used to determine the basic cooling operation status based on the measured temperature of the transformer. The load range determination unit is used to determine the load range based on the operating load after the harmonic operating condition meets the preset triggering condition and the basic cooling operating state meets the condition for reducing the cooling level. The reference temperature difference acquisition unit is used to acquire a reference temperature difference based on the load range and the current cooling level. The reference temperature difference is determined by the temperature rise test data of the target model transformer under the load range, the current cooling level and the reference harmonic conditions. The local temperature difference deviation determination unit is used to determine the current temperature difference based on the measured temperatures of the temperature rise sensitive area and the reference area, and to determine the local temperature difference deviation based on the degree of deviation of the current temperature difference from the reference temperature difference. A cooling level control unit is configured to maintain the current cooling level when the local temperature difference deviation does not meet the release condition, and to reduce the current cooling level when the local temperature difference deviation meets the release condition.

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