Dynamic cooperative calculation method for freezing maintenance temperature and freezing length of oil-filled cable

Abstract

The invention relates to the technical field of high-voltage submarine cable maintenance, and discloses an oil-filled cable freezing maintenance temperature and freezing length dynamic cooperative calculation method, which comprises the following steps of: acquiring parameters of a cable pipeline, a working condition and a freezing condition; executing a cooperative calculation model, establishing a quantitative relation between the freezing length and the maintaining temperature, and performing safe temperature constraint evaluation based on the brittle transition temperature of the material and oil plug strength constraint calculation based on the oil pressure difference to determine the minimum freezing length; and a dynamic temperature adjustment control strategy is executed, and through staged temperature adjustment and real-time monitoring feedback, it is ensured that the actual freezing length meets the constraint condition, and the temperature is controlled to be above a safety threshold value. According to the method, a multi-parameter coupling calculation framework is established, the problems that in the prior art, freezing parameter synergy is poor, embrittlement risks exist, and the oil plug strength is insufficient are effectively solved, and construction safety and adaptability are improved.

Description

Technical Field

[0001] This invention relates to the field of high-voltage submarine cable maintenance technology, specifically a method for dynamically calculating the freezing maintenance temperature and freezing length of oil-filled cables. Background Technology

[0002] Currently, in the maintenance of oil-filled cables, especially high-voltage oil-filled cables, it is essential to seal the internal insulating oil. Using liquid nitrogen to freeze the outside of the cable conduit, causing the internal insulating oil to solidify and form an oil plug, is a common technique for temporary on-site sealing.

[0003] Regarding the above-mentioned issues, existing freezing methods are typically implemented based on a predetermined construction plan. Operators focus on the physical span of the freezing chamber and the total freezing time. They control the supply of a cooling medium (such as liquid nitrogen) to apply low temperatures to the pipeline for a predetermined period of time until the oil flow stops, thus determining that an oil plug has formed.

[0004] Existing freezing methods have shortcomings: they lack an optimization mechanism for maintaining the freezing temperature, and operators often prioritize rapid sealing by using lower temperatures, neglecting the brittle transition characteristics of steel pipe materials. This leads to the safety hazard of low-temperature brittle fracture. Traditional operations fail to establish a quantitative relationship between the frozen length and the pressure-bearing capacity of the oil plug. In scenarios with high drops and high oil pressures, the strength of the oil plug obtained solely based on experience is insufficient, making it susceptible to being punctured or displaced by high-pressure oil flow, resulting in sealing failure. Existing technologies mostly employ static temperature control, which cannot adapt to dynamic thermal disturbances during construction. For example, the heat generated by welding operations can cause the oil plug tip to retract, and static freezing strategies cannot compensate for this, posing a risk of oil plug failure. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a dynamic collaborative calculation method for the freezing maintenance temperature and freezing length of oil-filled cables. This method solves the problems in existing oil-filled cable freezing and plugging technologies, which lack a temperature and length coordination mechanism, leading to risks such as brittle fracture of steel pipes at low temperatures, insufficient oil plug strength under high oil pressure, and inability to effectively cope with construction thermal disturbances that cause unstable plugging.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for dynamically co-calculating the freezing maintenance temperature and freezing length of oil-filled cables, comprising the following steps:

[0007] S1. Input parameter definition and acquisition parameters, including acquisition cable and pipe parameters, operating condition parameters and refrigeration condition parameters;

[0008] S2. Based on the collected parameters, execute the joint calculation model of freezing length and holding temperature, wherein the joint calculation model of freezing length and holding temperature includes:

[0009] Execute the core calculation model for freezing length and establish a quantitative relationship between freezing length and freezing maintenance temperature;

[0010] Perform a safety temperature constraint assessment to determine the safe threshold for maintaining the freezing temperature;

[0011] Perform oil plug strength constraint calculations to determine the minimum freezing length;

[0012] S3. Execute a dynamic temperature control strategy, which includes staged temperature regulation and, based on real-time monitored temperature data, calculates and adjusts according to the quantitative relationship between freezing length and freezing maintenance temperature to ensure that the actual freezing length always meets the constraint condition of the minimum freezing length and controls the freezing maintenance temperature above the safety threshold.

[0013] By adopting the above technical solution, a coupled calculation framework between freezing length, maintenance temperature, and oil plug strength is established. Furthermore, a safety temperature constraint based on fracture mechanics and a dynamic, phased temperature adjustment strategy for construction thermal disturbances are introduced. Therefore, the problem of the inability to coordinate the optimization of freezing maintenance temperature and freezing length in existing technologies is solved. This method can prevent low-temperature brittle fracture of the steel pipe while ensuring sufficient strength and length of the oil plug under high oil pressure and high drop conditions. This effectively avoids oil leakage accidents and pipeline crack propagation, improving the safety and adaptability of oil-filled cable maintenance construction.

[0014] Preferably, the cable and pipe parameters collected in step S1 include the inner diameter of the steel pipe, the equivalent cable conductor radius, the equivalent cable core radius, the outer radius of the steel pipe, the thermal conductivity of the oil, the thermal conductivity of the conductor, the oil density, the conductor density, the specific heat capacity of the oil, the specific heat capacity of the conductor, the latent heat of solidification of the oil, and the solidification point of the oil.

[0015] By adopting the above technical solution, the physical boundary conditions required for heat conduction calculation and stress analysis were clarified, ensuring the accuracy of the subsequent collaborative calculation model.

[0016] Preferably, the operating parameters collected in step S1 include initial oil temperature, initial oil flow rate, oil pressure difference, and ambient temperature; the collected refrigeration condition parameters include target surface temperature of the refrigeration chamber, radial thermal resistance correction coefficient, and oil flow heat loss correction coefficient.

[0017] By adopting the above technical solution, the influence of environmental thermodynamic state on the freezing process is fully considered, and the deviation between the theoretical model and the actual engineering equipment is eliminated by the correction coefficient.

[0018] Preferably, the process of performing the safety temperature constraint assessment in step S2 is as follows: First, the basic safety temperature threshold is determined based on the brittle transition temperature of the main metallic material of the cable; second, a crack state assessment is performed. When a crack is detected, the basic safety temperature threshold is calculated and corrected using correction logic that includes a logarithmic term of the crack length, resulting in a corrected threshold; third, a working stress calibration is performed, calculating the actual thermal stress generated by the temperature difference between the ambient temperature and the freezing maintenance temperature, and determining whether to compensate for the increase of the basic safety temperature threshold based on the comparison between the actual thermal stress and the material yield strength; based on the corrected threshold and the judgment result of the working stress calibration, the final operating safety temperature is confirmed.

[0019] By adopting the above technical solution, a quantitative assessment of the risk of cold brittleness is achieved based on the principle of fracture mechanics. The lower limit of the temperature can be dynamically adjusted according to the actual crack state and thermal stress level of the pipeline, thus avoiding equipment damage caused by excessively low temperature.

[0020] Preferably, the process of performing the oil plug strength constraint calculation in step S2 is as follows: calculate the oil pressure difference based on the drop height and pump pressure; determine the compressive strength of the frozen oil; and calculate the minimum freezing length based on the calculation logic of dividing the product of the oil pressure difference and the outer radius of the steel pipe by the compressive strength of the frozen oil.

[0021] By adopting the above technical solution, clear mechanical constraints are established for high drop and high oil pressure scenarios to ensure that the formed frozen oil plug can resist the oil pressure in the pipe and prevent the oil plug from being punctured or slipped.

[0022] Preferably, the phased temperature control in step S3 specifically includes: in the initial freezing stage, controlling the freezing maintenance temperature below the set value of the final safe operating temperature to quickly form the oil plug; in the welding construction stage, to avoid the oil plug shrinking due to thermal shock, raising the freezing maintenance temperature above the safe operating temperature; in the pressure holding stage, dynamically adjusting the freezing maintenance temperature according to the real-time oil pressure difference feedback to ensure that the actual freezing length always meets the minimum freezing length constraint.

[0023] By adopting the above technical solutions and adjusting the control targets according to different physical requirements in the construction process, the sealing efficiency is guaranteed, the risk of cold brittleness is avoided in key links such as welding, and the mechanical stability of the oil plug is maintained during the pressure holding period.

[0024] Preferably, the initial freezing stage maintains the freezing temperature within the range of -120 degrees Celsius to -140 degrees Celsius.

[0025] Preferably, during the welding construction stage, the freezing maintenance temperature is adjusted to be greater than or equal to -100 degrees Celsius.

[0026] Preferably, the real-time temperature data is acquired through a temperature monitoring and feedback system, which deploys a thermocouple array along the pipeline to monitor the temperature distribution in real time. The controller receives the temperature distribution data and dynamically adjusts the flow rate of the cooling medium based on the freezing length and maintenance temperature model established in step S2 and the minimum freezing length constraint to maintain the cable surface temperature in the freezer chamber.

[0027] By adopting the above technical solution, a distributed sensing and closed-loop control loop along the pipeline axis is constructed, which can accurately capture and compensate for thermal disturbances caused by construction operations.

[0028] Preferably, the temperature monitoring and feedback system maintains the cable surface temperature in the freezer compartment within a safe and functional range, the boundary of which is defined by the operating safe temperature determined in step S2 and the freezer maintenance temperature used to maintain the current required frozen length.

[0029] By adopting the above technical solutions, refined management of control objectives has been achieved, ensuring that the system always operates within the intersection of the dual constraints of material safety and effective sealing, thus eliminating the safety hazards caused by blind temperature adjustment.

[0030] This invention provides a method for dynamically co-calculating the freezing maintenance temperature and freezing length of oil-filled cables. It has the following beneficial effects:

[0031] 1. This invention establishes a coupled calculation framework between freezing maintenance temperature, freezing length, and oil plug strength. By performing oil plug strength constraint calculations, the oil pressure difference under high drop conditions is quantitatively correlated with the required minimum freezing length, solving the problem of insufficient oil plug strength caused by traditional experience-based operations. This ensures that the frozen oil plug is not punctured or slipped under high oil pressure, guaranteeing the sealing effectiveness of maintenance work.

[0032] 2. This invention introduces a safe temperature constraint assessment. This assessment is based on the brittle transition temperature of the cable's main metallic materials and is calibrated in conjunction with crack state and operating stress to determine the final safe operating temperature. This overcomes the shortcomings of traditional methods that do not consider the risk of brittle fracture in steel pipes, effectively preventing brittle fracture of pipelines due to excessively low freezing temperatures, and improving equipment safety during construction.

[0033] 3. This invention employs a dynamic temperature control strategy. Through staged temperature regulation and a real-time temperature monitoring and feedback system, this method can dynamically adjust the cooling medium flow rate according to thermal disturbances introduced at different stages of welding construction. This overcomes the limitations of traditional static temperature control, which cannot cope with changes in working conditions, and achieves precise and stable control of the freezing length, improving the method's adaptability to complex construction environments. Attached Figure Description

[0034] Figure 1This is a flowchart illustrating the overall method of this embodiment;

[0035] Figure 2 This is a flowchart illustrating the input parameter definition and acquisition process for step S1 in this embodiment.

[0036] Figure 3 This is a flowchart of the collaborative computing model for step S2 in this embodiment;

[0037] Figure 4 This is a flowchart of the dynamic temperature control strategy in step S3 of this embodiment. Detailed Implementation

[0038] See attached document Figure 1 This embodiment provides a method for dynamically co-calculating the freezing maintenance temperature and freezing length of oil-filled cables.

[0039] This method is applicable to cable repair and construction under high oil pressure conditions, and aims to solve the problems in the existing technology, such as the inability to optimize the freezing maintenance temperature and freezing length in a coordinated manner, the risk of steel pipe brittleness, insufficient oil plug strength under high oil pressure, and poor adaptability to dynamic working conditions.

[0040] The calculation method provided by this invention establishes the freezing length ( ), maintain temperature ( ), oil plug strength ( The coupled computational framework between the two systems was proposed, and a safety temperature constraint based on fracture mechanics and a dynamic phased temperature adjustment strategy for construction thermal disturbances were introduced.

[0041] The method may specifically include step S1: defining and acquiring input parameters.

[0042] In step S1, the parameters of the cable and pipe are first collected, including: the inner diameter of the steel pipe. Equivalent cable conductor radius Equivalent cable core radius Outer radius of steel pipe Thermal conductivity of oil Thermal conductivity of conductor (copper) Oil density Conductor (copper) density Oil specific heat capacity Specific heat capacity of conductor (copper) Latent heat of oil solidification and oil pour point .

[0043] In step S1, operating parameters are also collected, including: initial oil temperature. Initial oil flow rate Oil pressure difference and ambient temperature .

[0044] In step S1, freezing condition parameters are simultaneously acquired, including: the target temperature of the freezing chamber surface. Radial thermal resistance correction factor And the oil flow heat loss correction factor .

[0045] The method may specifically include step S2: performing a freeze length ( ) and maintaining temperature ( Collaborative computing model.

[0046] In step S2, the core calculation model for the freeze length is first executed. This model is used to establish the freeze length. Maintaining temperature with freezing The quantitative relationship between them, the calculation input includes the data collected in step S1. , (Right now Frozen span Inner diameter of steel pipe and experimental correction factor .

[0047] In step S2, a safety temperature constraint assessment is further performed. This assessment is used to determine... The safety threshold is set to ensure that the steel pipe does not undergo brittle fracture during low-temperature construction.

[0048] The safety temperature constraint assessment includes determining the basic safety temperature threshold based on the brittle transition temperature (DBTT) of the cable's main metallic material. .

[0049] The safety temperature constraint assessment also includes: conducting a crack state assessment, when a crack with a length of... When cracks appear, Perform calculations to correct the threshold value. .

[0050] The safety temperature constraint assessment also includes: performing operating condition stress calibration and calculating the stress caused by ambient temperature. Maintaining temperature with freezing The actual thermal stress generated by the temperature difference between them and according to With material yield strength The comparison relationship determines whether it is necessary to... To make a compensatory increase;

[0051] Finally, based on the above assessment results, the final safe operating temperature was confirmed.

[0052] In step S2, the oil plug strength constraint calculation is further performed. This calculation is for scenarios with high drop and high oil pressure, and is used to determine the minimum freezing length to ensure the oil plug strength. .

[0053] Oil plug strength constraint calculation based on oil pressure difference Outer radius of steel pipe and compressive strength of frozen oil , deduced .in, Based on the height difference and pump pressure Calculations show that Determine through experiments or by consulting tables.

[0054] Specifically, the method may include step S3: executing a dynamic temperature control strategy.

[0055] In step S3, a phased temperature control is first implemented. This control strategy includes:

[0056] Phase 1 (Initial Freeze): Control Lower the temperature (e.g., -130°C) to quickly form the oil plug.

[0057] Phase 2 (Welding Construction): To prevent the oil plug from retracting due to thermal shock, Heat to above the safe operating temperature (e.g.) .

[0058] Phase 3 (Pressure Holding Phase): Based on real-time oil pressure Feedback, dynamic adjustment Ensure the actual length of freezing Always satisfied Constraints.

[0059] Step S3 also includes a temperature monitoring and feedback system. This system deploys a thermocouple array along the pipeline for real-time monitoring of temperature distribution. The controller is based on the data established in step S2. Model and By constraining and dynamically adjusting the liquid nitrogen flow rate, the surface temperature of the cables in the freezing chamber is maintained between the safe operating temperature and the required freezing maintenance temperature, thereby achieving stable control of the freezing length.

[0060] See attached document Figure 2 In step S1, the input parameters are first defined and collected. The first type of parameters collected are cable and pipe parameters, which form the physical basis for subsequent heat conduction and stress calculations.

[0061] Cable and conduit parameters specifically include geometric dimensions: inner diameter of steel pipe. Unit is mm; equivalent cable conductor radius Unit is mm; equivalent cable core radius The unit is mm, and this radius is defined including the conductor and insulation layer; outer radius of the steel pipe. The unit is mm. This parameter is used for subsequent calculations of oil plug strength constraints.

[0062] Cable and pipe parameters also include material thermophysical properties: the thermal conductivity of oil. The unit is W / m·℃; thermal conductivity of the conductor (copper). The unit is W / m·℃; oil density The unit is g / cm³ 3 Conductor (copper) density The unit is g / cm³ 3 Oil specific heat capacity The unit is J / g·℃; specific heat capacity of conductor (copper) The unit is J / g·℃. Cable and pipe parameters further include material phase transformation parameters: latent heat of solidification of oil. Units are J / g; oil pour point The unit is ℃. This parameter Specifically defined as the temperature at which oil can withstand a pressure of 0.6 MPa without flowing.

[0063] In step S1, the second type of parameters collected are operating condition parameters, which are used to characterize the initial thermodynamic state and external environmental conditions of the cable.

[0064] Operating parameters include: initial oil temperature The unit is ℃. This parameter This characterizes the temperature of the insulating oil inside the cable before the start of the freezing construction.

[0065] Initial oil flow rate The unit is L / h. This parameter Used to describe the flow of oil inside a cable, when the cable is in a static oil condition. The value of is 0.

[0066] oil pressure difference The unit is MPa. This parameter It is a key input for calculating the oil plug strength constraint, especially in the case of a high drop of S.

[0067] Ambient temperature The unit is ℃. This parameter The temperature characterizing the external environment in which the cable is located is usually taken as... The value of .

[0068] In step S1, the third type of parameters collected are freezing condition parameters. These parameters are used to define the working state of the freezing equipment and to calibrate specific correction terms in the subsequent calculation model.

[0069] The specific parameters for freezing conditions include:

[0070] target temperature of the freezing chamber surface The unit is ℃. This parameter Typically, this is the temperature of liquid nitrogen, for example -196°C.

[0071] Radial thermal resistance correction factor This coefficient This was obtained through experimental calibration. In one embodiment of the present invention, .

[0072] Oil flow heat loss correction factor This coefficient Similarly, this was obtained through experimental calibration. In one embodiment of the present invention, .

[0073] In step S2, the freeze length is executed. With maintaining temperature Collaborative computing model. This model primarily includes a core computing model for frozen length.

[0074] This core calculation model is used to determine the freeze length. Maintaining temperature with freezing The quantitative relationship between them.

[0075] Freeze length The calculation is performed using the following formula:

[0076] ;

[0077] in:

[0078] The calculated frozen length;

[0079] The inner diameter of the steel pipe defined in step S1 is in mm;

[0080] This is an experimental correction coefficient. In one embodiment of the invention, this coefficient... ;

[0081] This is the oil's freezing point temperature, which corresponds to the temperature defined in step S1. (The temperature at which the oil can withstand a pressure of 0.6 MPa without flowing), in °C;

[0082] This refers to the temperature maintained during freezing, measured in °C. This parameter... These are the variables that need to be optimized and solved.

[0083] The initial oil temperature defined in step S1, in °C;

[0084] The freezing span is defined as the effective length of the freezing equipment, and its unit is meters (m).

[0085] See attached document Figure 3 In step S2, the collaborative computing model further includes a safety temperature constraint assessment.

[0086] The purpose of this assessment is to determine the cryogenic maintenance temperature. The safety threshold is determined to ensure that the steel pipe does not fracture brittlely during low-temperature construction. This assessment process focuses on the material's brittle transition temperature (DBTT) and crack sensitivity coefficient (CSC). ) and thermal shrinkage stress rate ( ).

[0087] The safety temperature constraint assessment first includes determining the safety temperature threshold. The steps involve classifying the main metallic materials in the cable, looking up their brittle transition temperature (DBTT), and thus determining a basic safe temperature threshold. .

[0088] The safety temperature constraint assessment is followed by a crack condition assessment step.

[0089] In this step, if non-destructive testing confirms the absence of cracks, then proceed as follows: implement.

[0090] If a crack is detected, assuming the crack length is... The corrected safety threshold is then calculated using the following formula. :

[0091] ;

[0092] in, The unit is ℃.

[0093] For example, when a 2mm crack is found in stainless steel armor, and its At -80℃, its The calculation is as follows:

[0094] ;

[0095] The safety temperature constraint assessment also includes a working condition stress calibration step. This step calculates the actual thermal stress generated by temperature differences during construction using the following formula. :

[0096] ;

[0097] in, The elastic modulus of the material (e.g., copper = 110 GPa, stainless steel = 200 GPa); The coefficient of thermal expansion of the material (e.g., , ; The ambient temperature defined in step S1; To maintain the temperature for freezing.

[0098] In the working condition stress calibration step, if the calculated Greater than the material yield strength 0.5 times (i.e.) This indicates that the material has entered the plastic deformation zone, increasing the risk of crack propagation. The temperature needs to be increased by 5°C.

[0099] The safety temperature constraint assessment culminates in determining the final safe operating temperature. This step is based on the material's safe temperature threshold. Crack condition assessment ( The final safe operating temperature is determined by combining the results of the operating condition stress calibration with those of the operating stress calibration.

[0100] In step S2, the collaborative calculation model further includes an oil plug strength constraint formula. This constraint is designed for high-drop scenarios to ensure that the strength of the frozen oil plug is sufficient to withstand high oil pressure differentials, and calculates the minimum freezing length that meets the strength requirements. .

[0101] Minimum freeze length The calculation is performed using the following formula:

[0102] ;

[0103] in, Minimum frozen length, in meters; This refers to the compressive strength of the refrigeration oil, a value determined experimentally, for example, an experimental value > 5 MPa; This represents the oil pressure difference, measured in MPa. In high-altitude scenarios, according to The pump is calculated, among which For oil density, It is the acceleration due to gravity. The height difference This refers to pump pressure. For example, at a drop of 90 meters, Up to 10.5 kgf / cm 2Approximately 1.03 MPa; The outer radius of the steel pipe is defined in step S1, in mm.

[0104] The calculation process for the oil plug strength constraint specifically includes the following steps:

[0105] First, calculate the oil pressure. .

[0106] Measure the drop height under actual working conditions (e.g., 90m), and substitute into the formula. Perform the calculation.

[0107] Next, determine the freezing oil strength. .

[0108] This parameter The pressure resistance of refrigeration oil is determined through laboratory crush tests or based on empirical data. Different types of oil... The experimental values ​​(MPa) are shown in the table below:

[0109] Table 1. Different types of oil Experimental reference values

[0110]

[0111] Finally, according to and Back-calculation of minimum freeze length For example: when MPa, mm, select When MPa, calculate .

[0112] See attached document Figure 4 In step S3, the phased temperature control strategy of dynamic temperature regulation is first executed. This regulation process divides the temperature control into three different stages according to the different needs of the construction process, in order to adapt to the thermal disturbance during construction and maintain the stability of the oil plug.

[0113] The phased temperature control process includes the following steps:

[0114] Phase 1 is the initial freezing phase. In this phase, the control objective is to rapidly form an oil plug capable of blocking oil flow. To achieve this, the system rapidly cools by controlling the liquid nitrogen flow rate, maintaining the freezing temperature. Controlled .

[0115] Phase 2 is the welding construction phase. The control objective in this phase is to prevent excessive retraction of the oil plug due to thermal shock from welding. To achieve this objective, the system performs a heating operation to maintain the freezing temperature. Adjust to During this stage of operation, due to the heat input from the welding process or the oil draining operation, the oil plug in the draining section or at the welding end will physically retract, with a retraction length of [length missing]. .

[0116] Phase 3 is the pressure holding phase. In this phase, the control objective is to maintain the minimum freeze length that can withstand the current oil pressure. To achieve this goal, the system uses real-time monitored oil pressure differentials. Feedback control is implemented to dynamically adjust the freezing maintenance temperature. To ensure the actual freezing length Always satisfied The constraints.

[0117] In step S3, the dynamic temperature control strategy further includes the execution of a temperature monitoring and feedback system. This system constructs a closed-loop control circuit designed to ensure the refrigeration temperature is maintained. Precise execution and freeze length Stability.

[0118] The temperature monitoring and feedback system specifically includes a thermocouple array deployed along the pipeline. This thermocouple array does not monitor only a single point of temperature but is deployed along the pipeline's axial direction, enabling real-time monitoring and feedback of the temperature distribution along the pipeline. This distributed monitoring configuration allows the system to accurately detect the conduction and distribution of thermal disturbances caused by external construction operations (such as welding) along the pipeline.

[0119] The temperature monitoring and feedback system further includes a controller and model-based regulation logic. The controller receives real-time temperature data from the thermocouple array and, based on the logic established in step S2... The model is used for calculation and analysis.

[0120] The controller's dynamic adjustment process is as follows: based on real-time monitored temperature distribution data, the controller dynamically adjusts the flow rate of the cooling medium (liquid nitrogen). The control objective of this adjustment is to ensure that the cable surface temperature in the freezer compartment is maintained within a specific safe and functional range. The boundary of this range is defined by the following two parameters:

[0121] One is the operating safety temperature determined through the safety temperature constraint assessment in step S2, to prevent material brittleness.

[0122] Secondly, based on The model calculates the required freeze length to maintain the current position. Freezing maintenance temperature .

[0123] Through the above-mentioned real-time feedback based on thermocouple array data and based on The system dynamically corrects the liquid nitrogen flow rate of the model, enabling precise control of the freezing length. In one embodiment of the invention, the system can maintain the control error of the freezing length within a certain range. Within the range.

[0124] To verify the feasibility and effectiveness of the technical solution of the present invention, the application scenarios of the method of the present invention will be described in detail below with reference to specific embodiments.

[0125] Example 1: Routine Maintenance Scenario

[0126] In this embodiment, the operation is performed under normal maintenance conditions for oil-filled cables. The characteristic parameter under this condition is: oil pressure difference. Maintain at normal levels, for example MPa. In this embodiment, step S1 is executed first. Physical and environmental parameters of the cable and pipe are collected to establish the calculation boundary conditions. Then, step S2 is executed. The frozen length core calculation model is used:

[0127] ;

[0128] Calculate at different freezing maintenance temperatures Theoretical freezing length below .

[0129] Simultaneously, a safety temperature constraint assessment was performed. Based on the brittle transition temperature (DBTT) of the cable's metallic sheath material and crack detection results, the following was determined: For example, determining the basic safe operating temperature when there are no cracks and the material is in good condition.

[0130] Under these normal operating conditions, due to The calculated oil plug strength constraint is relatively small. Relatively small, therefore The settings are mainly limited by construction efficiency and safe temperature thresholds.

[0131] Finally, step S3 is executed. A staged temperature control method is used:

[0132] In the initial freeze phase, set To quickly block it;

[0133] During the welding construction phase, Raise to above the safe temperature (e.g.) ), to prevent the risk of cold brittleness;

[0134] During the pressure holding stage, the temperature is maintained through thermocouple feedback to ensure that the freezing length meets the construction requirements.

[0135] Example 2: High-Drop Maintenance Scenario

[0136] In this embodiment, maintenance is carried out on cable lines with elevation differences. This operating condition is characterized by high oil pressure, which places stringent requirements on the strength of the oil plugs.

[0137] Parameter conditions and oil pressure calculation: In this embodiment, the cable maintenance point is located at the height difference of the line elevation. Based on the oil plug strength constraint formula in steps S1 and S2, first calculate the actual oil pressure difference acting on the oil plug at this time. :

[0138] ;

[0139] Calculation results show that at this 90-meter drop, the oil pressure difference... achieve Approximately At the same time, the outer radius of the steel pipe was collected. .

[0140] Minimum freeze length The reverse calculation: To ensure that the oil plug is not punctured or slipped under high pressure, the oil plug strength constraint calculation in step S2 must be strictly performed. The compressive strength of the refrigeration oil is selected. Based on experimental data or conservative values, set The minimum freezing length can be calculated by using the formula. :

[0141] ;

[0142] Substitute the values ​​into the calculation:

[0143] ;

[0144] Calculation results show that under this high drop condition, an effective freezing length of at least 25.8 cm must always be maintained.

[0145] Maintain temperature Constraint determination: Based on the core calculation model of freeze length in step S2 ( (Relationship), in order to ensure the actual frozen length Inverse kinematics calculation of the required cryogenic holding temperature .

[0146] Calculations show that, in order to maintain this length, it is necessary to control This temperature limit became a rigid constraint under this operating condition.

[0147] Execution of dynamic control strategy: During the execution of step S3, the following dynamic adjustments are made for this high-voltage operating condition:

[0148] In Phase 2 (welding), although heating is usually required to prevent brittle fracture, it is limited by... corresponding Constraints: The system must operate within a safe temperature threshold (e.g., ) and strength maintenance temperature ( Find the narrowest possible operation window between ( ).

[0149] If the welding heat input causes the oil plug tip to retract (such as the aforementioned 30cm retraction risk), the system will monitor in real time and detect it immediately. Approaching Immediately increase the liquid nitrogen flow rate to reduce This is to compensate for the shrinkage loss and ensure that the oil plug always meets the pressure requirement of 1.03MPa, thus preventing oil leakage accidents.

Claims

1. A method for dynamically co-calculating the freezing maintenance temperature and freezing length of oil-filled cables, characterized in that, Includes the following steps: S1. Input parameter definition and acquisition parameters, including acquisition cable and pipe parameters, operating condition parameters and refrigeration condition parameters; S2. Based on the collected parameters, execute the joint calculation model of freezing length and holding temperature, wherein the joint calculation model of freezing length and holding temperature includes: Execute the core calculation model for freezing length and establish a quantitative relationship between freezing length and freezing maintenance temperature; Perform a safety temperature constraint assessment to determine the safe threshold for maintaining the freezing temperature; Perform oil plug strength constraint calculations to determine the minimum freezing length; S3. Execute a dynamic temperature control strategy, which includes staged temperature regulation and, based on real-time monitored temperature data, calculates and adjusts according to the quantitative relationship between the freezing length and the freezing maintenance temperature to ensure that the actual freezing length always meets the constraint condition of the minimum freezing length and controls the freezing maintenance temperature above the safety threshold.

2. The method for dynamically calculating the freezing maintenance temperature and freezing length of oil-filled cables according to claim 1, characterized in that, The cable and pipe parameters collected in step S1 include: The inner diameter of the steel pipe, the equivalent cable conductor radius, the equivalent cable core radius, the outer radius of the steel pipe, the thermal conductivity of the oil, the thermal conductivity of the conductor, the oil density, the conductor density, the specific heat capacity of the oil, the specific heat capacity of the conductor, the latent heat of solidification of the oil, and the freezing point of the oil.

3. The method for dynamically calculating the freezing maintenance temperature and freezing length of oil-filled cables according to claim 1, characterized in that, The operating parameters collected in step S1 include: initial oil temperature, initial oil flow rate, oil pressure difference, and ambient temperature. The freezing condition parameters include: target surface temperature of the freezing chamber, radial thermal resistance correction factor, and oil flow heat loss correction factor.

4. The method for dynamically calculating the freezing maintenance temperature and freezing length of oil-filled cables according to claim 1, characterized in that, The safety temperature constraint assessment performed in step S2 specifically includes: The basic safe temperature threshold is determined based on the brittle transition temperature of the main metallic materials of the cable. A crack condition assessment is performed. When a crack is detected, the basic safe temperature threshold is calculated and corrected to obtain a corrected threshold. Perform working condition stress calibration, calculate the actual thermal stress generated by the temperature difference between the ambient temperature and the freezing maintenance temperature, and determine whether it is necessary to compensate for the increase of the basic safety temperature threshold based on the comparison between the actual thermal stress and the yield strength of the main metal material. Based on the correction threshold and the judgment result of the working condition stress calibration, the final safe operating temperature is confirmed.

5. The method for dynamically calculating the freezing maintenance temperature and freezing length of oil-filled cables according to claim 1, characterized in that, The oil plug strength constraint calculation performed in step S2 specifically includes: Calculate the oil pressure difference based on the drop height and pump pressure; determine the compressive strength of the refrigeration oil. The minimum freezing length is calculated based on the oil pressure difference, the outer radius of the steel pipe, and the compressive strength of the frozen oil.

6. The method for dynamically calculating the freezing maintenance temperature and freezing length of oil-filled cables according to claim 1, characterized in that, The staged temperature control in step S3 includes: Initial freezing stage: The freezing maintenance temperature is controlled below the set value of the final safe operating temperature to quickly form the oil plug; During the welding process: To prevent the oil plug from shrinking due to thermal shock, the freezing maintenance temperature is raised to above the safe operating temperature. Pressure holding stage: Based on real-time oil pressure difference feedback, the freezing maintenance temperature is dynamically adjusted to ensure that the actual freezing length always meets the minimum freezing length constraint.

7. The method for dynamically co-calculating the freezing maintenance temperature and freezing length of oil-filled cables according to claim 6, characterized in that, In the phased temperature control, the initial freezing stage maintains the freezing temperature within the range of -120 degrees Celsius to -140 degrees Celsius.

8. The method for dynamically calculating the freezing maintenance temperature and freezing length of oil-filled cables according to claim 6, characterized in that, In the phased temperature control, the freezing maintenance temperature is adjusted to be greater than or equal to minus 100 degrees Celsius during the welding construction stage.

9. The method for dynamically calculating the freezing maintenance temperature and freezing length of oil-filled cables according to claim 1, characterized in that, The real-time monitored temperature data is acquired through a temperature monitoring and feedback system, which includes: A thermocouple array is installed along the pipeline for real-time monitoring of temperature distribution; The controller receives the temperature distribution data and dynamically adjusts the flow rate of the cooling medium based on the freezing length and maintenance temperature model established in step S2 and the minimum freezing length constraint, so as to maintain the cable surface temperature in the freezer chamber.

10. The method for dynamically calculating the freezing maintenance temperature and freezing length of oil-filled cables according to claim 9, characterized in that, The temperature monitoring and feedback system maintains the cable surface temperature in the freezer compartment within a safe and functional range, the boundary of which is defined by the operating safe temperature determined in step S2 and the freeze maintenance temperature used to maintain the current required freezing length.

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