A method, system, and equipment for assessing the lifespan of cryogenic cables for LNG carriers.

Abstract

A method, system, and equipment for assessing the lifespan of cryogenic cables for LNG carriers include: acquiring operating condition data of cable samples; conducting multiple progressive voltage breakdown tests on the cables to obtain the duration and breakdown voltage of the final voltage stage in each test; calculating the lifespan index of the cable samples; establishing a voltage-duration equivalent model to calculate electrical aging test parameters based on operating voltage, annual operating time, and lifespan index; establishing a temperature cycle screening model to calculate thermomechanical aging test parameters based on ambient temperature change data; and aging a set number of cable samples based on the electrical aging test parameters and thermomechanical aging test parameters, verifying whether the insulation resistance of each cable sample exceeds a set resistance threshold through multiple checks to determine if the cable lifespan meets the requirements. This invention can quickly and accurately assess the lifespan of cryogenic cables for LNG carriers under complex and extreme operating conditions.

Description

Technical Field

[0001] This invention belongs to the field of special cable insulation technology, and in particular relates to a method, system and equipment for assessing the life of cryogenic cables for LNG carriers. Background Technology

[0002] With the widespread use of clean energy liquefied natural gas (LNG), cryogenic cables for large LNG carriers have seen significant development. Assessing the service life of cryogenic cables in cryogenic environments is crucial for ensuring the safe transport and storage of LNG.

[0003] Under the long-term combined effects of electric fields, ultra-low temperatures, temperature changes, and mechanical vibration, the insulation performance of cryogenic cables gradually declines, affecting their safe operation. The unique operating conditions of cryogenic cables complicate their multi-factor aging mechanisms. Research on aging assessment of cryogenic cables, both domestically and internationally, is insufficient. Existing aging models are not suitable for predicting the service life of cryogenic cables under complex and extreme conditions, leading to difficulties in lifespan assessment. Cryogenic cables for LNG carriers are required to have a service life of no less than 40 years; however, there is currently no standard method for lifespan assessment, becoming a significant factor restricting the domestic production of cryogenic cables for LNG carriers. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method, system, and equipment for assessing the lifespan of cryogenic cables for LNG carriers.

[0005] The present invention adopts the following technical solution.

[0006] The first aspect of this invention proposes a method for assessing the lifespan of cryogenic cables for LNG carriers, specifically comprising: The data is used to obtain the operating condition data of the cable sample, including the cable's operating voltage, annual operating time, and ambient temperature variation data; and to conduct multiple cable step-by-step voltage increase breakdown tests when the ambient temperature is below a set low temperature threshold, to obtain the duration of the last stage of voltage increase and the breakdown voltage of each test; and to calculate the life index of the cable sample based on the duration of the last stage of voltage increase and the breakdown voltage. A voltage-duration equivalent model is established, and the electrical aging test parameters are calculated using the operating voltage, annual operating time, and life index. The electrical aging test parameters include the test voltage and test duration. A temperature cycle screening model is established, and the thermomechanical aging test parameters are calculated based on ambient temperature change data. The thermomechanical aging test parameters include the temperature change range during the test, the temperature change rate during the test, and the number of temperature cycles during the test. A set number of cable samples are subjected to two cycles of aging based on electrical aging test parameters and thermomechanical aging test parameters. At the end of the second cycle, the insulation resistance of each cable sample is checked to see if it is greater than the set resistance threshold. If not, it means that the cable service life has not met the requirements. If yes, the aging process continues for two more cycles. If the insulation resistance of each cable sample is greater than the set resistance threshold and all pass the AC withstand voltage test of the set standard after aging, it means that the cable service life has met the requirements. Otherwise, it has not been met.

[0007] Preferably, the acquisition of the operating condition data of the cable sample specifically includes: The ambient temperature change data includes the range of ambient temperature change in the cargo tanks of an LNG carrier when it is fully empty, the rate of temperature change, and the number of temperature cycles during operation. Obtain the annual LNG loading / unloading frequency and the duration of each power-on session. The product of the annual LNG loading / unloading frequency and the duration of each power-on session is the annual working time.

[0008] Preferably, the step of performing multiple cable voltage-increase breakdown tests when the ambient temperature is below a set low-temperature threshold specifically includes: The cable test was conducted under liquid nitrogen immersion, with the ambient temperature always below the set low temperature threshold. Multiple cable samples were divided into multiple groups, with each group containing the same number of cable samples. For different samples in each group, a step-up voltage breakdown test was performed. For cable samples in the same group, the duration of each voltage increase was the same except for the last voltage increase. The breakdown voltage of different cable samples in the same group was different. The duration of each voltage increase was different between different groups. The starting voltage and voltage increase ratio of all cable samples in all groups were the same, which were all set values. Obtain the breakdown voltage and the duration of the final stage of the step-up breakdown test for all cable samples in each group.

[0009] Preferably, the calculation of the cable sample's life index based on the final stage pressurization duration and breakdown voltage specifically involves: The cumulative damage of each cable sample is calculated based on the life index, breakdown voltage and the duration of the last stage of pressurization, and a cumulative damage matrix is ​​established. The element in the i-th row and j-th column of the cumulative damage matrix is ​​the cumulative damage of the j-th sample in the i-th group. The difference between the average cumulative damage of the i-th row and the average cumulative damage of the entire cumulative damage matrix is ​​divided by the average cumulative damage of the cumulative damage matrix. The square of the result of the division is the square difference of the i-th group. The square differences of all groups are summed and then divided by the difference between the number of cable samples and 1 to obtain the variance of the cumulative damage matrix. The optimal lifetime index is obtained by solving the objective function by minimizing the variance of the cumulative damage matrix.

[0010] Preferably, the calculation of cumulative damage for each cable sample based on the life index, breakdown voltage, and duration of the final pressurization stage specifically involves: The cumulative damage formula for each cable sample is:

[0011] in, The cumulative damage is for the j-th sample in the i-th group. Where is the starting voltage, and r is the lifetime exponent. Breakdown voltage For boost ratio, This indicates the m-th voltage boost; k is the number of boost stages. The duration of each pressurization stage in the i-th group. The duration of the final pressurization stage for the j-th sample in the i-th group.

[0012] Preferably, the establishment of the voltage-duration equivalent model, which calculates the electrical aging test parameters using operating voltage, annual operating time, and lifespan index, specifically involves: The ratio of the cable's working voltage to the test voltage is a set value. Using this ratio as the base, the life index is used as the exponent for exponential calculation. The result is multiplied by the cable's annual working time to obtain the test duration.

[0013] Preferably, the step of establishing a temperature cycling screening model and calculating thermomechanical aging test parameters based on ambient temperature change data specifically involves: The formula for calculating the parameters of the thermomechanical aging test is as follows:

[0014] Among them, R s R represents the temperature variation range of the LNG carrier's cargo tanks when it is fully empty. t V represents the temperature range during the experiment. s V represents the rate of temperature change of an LNG carrier when it is fully empty. t N represents the rate of temperature change during the experiment. s N represents the number of temperature cycles during operation. t The number of temperature cycles during the experiment is given, where e is the natural constant; the temperature range during the experiment is given by R. t and the rate of temperature change V during the experiment t This is the set value.

[0015] Preferably, the aging based on electro-aging test parameters and thermomechanical aging test parameters specifically includes: Each cycle begins with annual electrical aging using electrical aging test parameters equivalent to one-quarter of the cable's design life, followed by thermomechanical aging using thermomechanical aging test parameters equivalent to one-quarter of the cable's design life, and finally, mechanical vibration aging using the set mechanical vibration aging test parameters.

[0016] The second aspect of this invention proposes a system for assessing the lifespan of cryogenic cables for LNG carriers based on the method described in the first aspect of this invention, comprising: a cable sample testing module, a cable lifespan index calculation module, a cable electro-aging and thermomechanical aging test parameter calculation module, and a cable lifespan assessment module, specifically: Cable Sample Testing Module: Used to acquire operating condition data of cable samples, including cable operating voltage, annual operating time and ambient temperature variation data; and to conduct multiple cable step-by-step voltage increase breakdown tests when the ambient temperature is below the set low temperature threshold, to obtain the duration of the last stage of voltage increase and the breakdown voltage of each test. Cable Life Index Calculation Module: Calculates the life index of a cable sample based on the duration of the final stage of pressurization and the breakdown voltage; Cable electro-aging and thermomechanical aging test parameter calculation module: Establish a voltage-duration equivalent model to calculate electro-aging test parameters through working voltage, annual working time, and life index. The electro-aging test parameters include test voltage and test duration. Establish a temperature cycle screening model to calculate thermomechanical aging test parameters based on ambient temperature change data. The thermomechanical aging test parameters include the temperature change range during the test, the temperature change rate during the test, and the number of temperature cycles during the test. Cable life assessment module: A set number of cable samples are subjected to two cycles of aging based on electrical aging test parameters and thermomechanical aging test parameters. At the end of the second cycle, the insulation resistance of each cable sample is checked to see if it is greater than the set resistance threshold. If not, it means that the cable life has not met the requirements. If yes, the aging continues for two more cycles. If the insulation resistance of each cable sample is greater than the set resistance threshold and all pass the AC withstand voltage test of the set standard after aging, it means that the cable life has met the requirements. Otherwise, it has not. A third aspect of the present invention provides a device for assessing the lifespan of cryogenic cables for LNG carriers. Specifically, the device includes a processor and a memory. The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the method for assessing the lifespan of cryogenic cables for LNG carriers according to the instructions in the program code, as described in the first aspect of the present invention.

[0017] The beneficial effects of this invention are as follows: Compared with the prior art, it describes the life index of the cable sample under the combined action of electric field and cryogenic temperature by calculating the life index of the cable sample based on the step-by-step voltage-breakdown data of the cable sample and the duration of the last stage of pressure application in each test; it establishes a voltage-duration equivalent model based on operating condition data and life index to calculate the electrical aging test parameters by working voltage, annual operating time, and life index; it calculates the thermomechanical aging test parameters using a temperature cycle screening model based on ambient temperature change data; and it establishes a life assessment test procedure for cryogenic cables of LNG carriers based on the electrical aging and thermomechanical aging test parameters. The life assessment test procedure can quickly and accurately assess the life of cryogenic cables of LNG carriers under complex and extreme operating conditions. Attached Figure Description

[0018] Figure 1 Flowchart for the life assessment method of cryogenic cables for LNG carriers; Figure 2 This is the cumulative damage matrix variance-lifetime exponent curve of an embodiment of the present invention; Figure 3 This is a flowchart of the cable life assessment test according to an embodiment of the present invention; Figure 4 Diagram of a system for assessing the lifespan of cryogenic cables for LNG carriers. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0020] like Figure 1 As shown, Embodiment 1 of the present invention proposes a method for assessing the lifespan of cryogenic cables for LNG carriers, comprising: S1. Obtain the operating condition data of the cable sample, including the cable's operating voltage, annual operating time, and ambient temperature change data; and conduct multiple cable step-by-step voltage increase breakdown tests when the ambient temperature is below the set low temperature threshold to obtain the duration of the last stage of voltage increase and the breakdown voltage of each test. In this preferred embodiment, the acquisition of the cable sample's operating condition data specifically involves: The ambient temperature change data includes the range of ambient temperature changes in the cargo tanks of the LNG carrier when it is fully empty, the rate of temperature change, and the number of temperature cycles during operation; the number of temperature cycles during operation is determined by the frequency of LNG loading and unloading.

[0021] It's important to note that "empty" means the cargo tank contains no LNG, while "full" means it's filled with LNG. Loading involves transitioning from an empty to a full load state, while unloading involves returning from a full load to an empty state. The ambient temperature is higher when the tank is empty and lower when it's full. Therefore, temperature changes occur during loading and unloading.

[0022] Obtain the annual LNG loading / unloading frequency and the duration of each power-on session. The product of the annual LNG loading / unloading frequency and the duration of each power-on session is the annual working time.

[0023] In this preferred embodiment, the step of performing multiple cable voltage-increase breakdown tests when the ambient temperature is below a set low-temperature threshold specifically includes: Multiple cable samples were divided into multiple groups, with each group containing the same number of cable samples. For different samples in each group, a step-up voltage breakdown test was performed. For cable samples in the same group, the duration of each voltage increase was the same except for the last voltage increase. The breakdown voltage of different cable samples in the same group was different. The duration of each voltage increase was different between different groups. The starting voltage and voltage increase ratio of all cable samples in all groups were the same, which were all set values. Obtain the breakdown voltage and the duration of the final stage of the step-up breakdown test for all cable samples in each group.

[0024] S2. Calculate the life index of the cable sample using the duration of the final stage of pressurization and the breakdown voltage, specifically: The cumulative damage of each cable sample is calculated based on the life index, breakdown voltage and the duration of the last stage of pressurization, and a cumulative damage matrix is ​​established. The element in the i-th row and j-th column of the cumulative damage matrix is ​​the cumulative damage of the j-th sample in the i-th group. The cumulative damage formula for each cable sample is:

[0025] in, The cumulative damage is for the j-th sample in the i-th group. Where is the starting voltage, and r is the lifetime exponent. Breakdown voltage For boost ratio, This indicates the m-th voltage boost; k is the number of boost stages, which can be calculated based on the breakdown voltage and the boost ratio. The duration of each pressurization stage in the i-th group. The duration of the final pressurization stage for the j-th sample in the i-th group.

[0026] Establish a cumulative damage matrix, wherein the element in the i-th row and j-th column of the cumulative damage matrix is ​​the cumulative damage of the j-th sample in the i-th group; The cumulative damage matrix is:

[0027] Where u is the number of sample groups, v is the number of samples in each group, u is an integer not less than 2, and v is an integer not less than 7.

[0028] The difference between the average cumulative damage of the i-th row and the average cumulative damage of the entire cumulative damage matrix is ​​divided by the average cumulative damage of the cumulative damage matrix. The square of the result of the division is the square difference of the i-th group. The square differences of all groups are summed and then divided by the difference between the number of cable samples and 1 to obtain the variance of the cumulative damage matrix. The variance of the cumulative damage matrix is:

[0029] Among them, S 2 For variance, The average value of the cumulative damage matrix. This represents the average cumulative damage of the i-th row (i.e., the average value of all elements in the i-th row).

[0030] The optimal lifetime index is obtained by solving the objective function by minimizing the variance of the cumulative damage matrix.

[0031] S3. Establish a voltage-duration equivalent model and calculate the electrical aging test parameters using the working voltage, annual working time, and life index. The electrical aging test parameters include the test voltage and test duration. Establish a temperature cycle screening model and calculate the thermomechanical aging test parameters based on ambient temperature change data. The thermomechanical aging test parameters include the temperature change range during the test, the temperature change rate during the test, and the number of temperature cycles during the test. In this preferred embodiment, the establishment of the voltage-duration equivalent model calculates the electrical aging test parameters using the operating voltage, annual operating time, and lifespan index, specifically as follows: The ratio of the cable's working voltage to the test voltage is a set value. Using the ratio of the cable's working voltage to the test voltage as the base, the life index is used as the exponent for exponential calculation. The result of the calculation is multiplied by the annual working time of the cable to obtain the test time, which is specifically set to 2.5.

[0032] The formula is:

[0033] Where r is the lifespan index, U s The operating voltage is t. s For total working hours, U t For the test voltage, t t This refers to the duration of the experiment.

[0034] In this preferred embodiment, the establishment of the temperature cycling screening model and the calculation of thermomechanical aging test parameters based on ambient temperature change data specifically involve: The formula for calculating the parameters of the thermomechanical aging test is as follows:

[0035] Among them, R s R represents the temperature variation range of the LNG carrier's cargo tanks when it is fully empty. t V represents the temperature range during the experiment. s V represents the rate of temperature change of an LNG carrier when it is fully empty. t N represents the rate of temperature change during the experiment. s N represents the number of temperature cycles during operation. t The number of temperature cycles during the experiment is given, where e is the natural constant; the temperature range during the experiment is given by R. t and the rate of temperature change V during the experiment t For the set value, specifically, the rate of temperature change V during the test. t Set to 1-3℃ / min.

[0036] S4. A set number of cable samples are subjected to two cycles of aging based on electro-aging test parameters and thermomechanical aging test parameters. At the end of the second cycle, the insulation resistance of each cable sample is checked to see if it is greater than the set resistance threshold. If not, it indicates that the cable service life has not met the requirements. If yes, the aging process continues for two more cycles. If, after aging, the insulation resistance of each cable sample is greater than the set resistance threshold and all pass the AC withstand voltage test according to the set standard, it indicates that the cable service life has met the requirements; otherwise, it has not. Preferably, in this embodiment, the aging based on electro-aging test parameters and thermomechanical aging test parameters specifically includes: Each cycle begins with annual electrical aging using electrical aging test parameters equivalent to one-quarter of the cable's design life, followed by thermomechanical aging using thermomechanical aging test parameters equivalent to one-quarter of the cable's design life, and finally, mechanical vibration aging using the set mechanical vibration aging test parameters.

[0037] It should be noted that the mechanical vibration aging parameters in this embodiment are those specified in GB / T 7094, the insulation resistance test requirement is greater than 500MΩ, the AC withstand voltage test is the standard set by IEC 60092-350, the set number is an integer not less than 5, and the cable samples are of the same model.

[0038] In this embodiment, the specific implementation process of the LNG carrier cryogenic cable life assessment method is as follows: First, two groups of samples were subjected to a step-up voltage breakdown test under liquid nitrogen immersion conditions. Each group consisted of 7 samples, with an initial voltage of 35kV and a voltage increase ratio of 1.06. The duration of each pressure increase in the first group was 20 minutes, and the duration of each pressure increase in the second group was 40 minutes. The step-up voltage breakdown data are shown in Table 1.

[0039] Table 1. Breakdown data for step-up voltage boosting:

[0040] By analyzing the actual operating conditions of the cryogenic cables on LNG carriers, the following operating data were obtained: operating voltage is 10kV; LNG loading and unloading frequency is 52 times per year, with each power-on period lasting 16 hours; the ambient temperature range of the cargo tank when fully empty is -140 ℃ to -70 ℃, with a temperature change rate of 70 ℃ / 16h. The calculated annual operating time is 832 hours.

[0041] The cumulative damage matrix variance-life index curve was calculated based on data obtained from the step-up breakdown test, as shown below. Figure 2 As shown. Based on the minimum value of the variance of the cumulative damage matrix, the life index of the cryogenic cable for LNG carriers is 12.4.

[0042] In this embodiment, the design life of the cryogenic cable for the LNG carrier is 40 years. Substituting the operating voltage and annual operating time into the voltage-duration equivalent model, the equivalent 10-year electrical aging test parameters are obtained: test voltage 25 kV, test duration 6 minutes. Substituting the annual LNG loading / unloading frequency and temperature change data into the temperature cycle screening model, the equivalent 10-year thermomechanical aging test parameters are obtained: 55 cycles of alternating temperature from -140℃ to -70℃, with a heating / cooling rate of 60℃ / h.

[0043] In this embodiment, the test procedure for the life assessment of cryogenic cables for LNG carriers is as follows: Figure 3 As shown. Following the test procedure, five samples were evaluated. At the end of the second cycle, the insulation resistance of each sample was greater than 500 MΩ; at the end of the fourth cycle, the insulation resistance of each sample was also greater than 500 MΩ, and they passed the AC withstand voltage test. Based on the evaluation, the cryogenic cable for LNG carriers has a service life of no less than 40 years under operating conditions, meeting the design requirements.

[0044] like Figure 4 As shown, Embodiment 2 of the present invention proposes a cryogenic cable life assessment system for LNG carriers based on the method described in Embodiment 1 of the present invention, including: a cable sample testing module, a cable life index calculation module, a cable electro-aging and thermomechanical aging test parameter calculation module, and a cable life assessment module, including: Cable Sample Testing Module: Used to acquire operating condition data of cable samples, including cable operating voltage, annual operating time and ambient temperature variation data; and to conduct multiple cable step-by-step voltage increase breakdown tests when the ambient temperature is below the set low temperature threshold, to obtain the duration of the last stage of voltage increase and the breakdown voltage of each test. Cable Life Index Calculation Module: Calculates the life index of a cable sample based on the duration of the final stage of pressurization and the breakdown voltage; Cable electro-aging and thermomechanical aging test parameter calculation module: Establishes a voltage-duration equivalent model to calculate electro-aging test parameters based on working voltage, annual working time, and life index. The electro-aging test parameters include test voltage and test duration. Establishes a temperature cycle screening model to calculate thermomechanical aging test parameters based on ambient temperature change data. The thermomechanical aging test parameters include the temperature change range during the test, the temperature change rate during the test, and the number of temperature cycles during the test. Cable life assessment module: A set number of cable samples are subjected to two cycles of aging based on electro-aging test parameters and thermomechanical aging test parameters. At the end of the second cycle, the insulation resistance of each cable sample is checked to see if it is greater than the set resistance threshold. If not, it indicates that the cable life has not met the requirements. If yes, two more cycles of aging are performed. If, after aging, the insulation resistance of each cable sample is greater than the set resistance threshold and all pass the AC withstand voltage test of the set standard, it indicates that the cable life has met the requirements. Otherwise, it has not met the requirements. Embodiment 3 of this invention proposes an ultra-low temperature cable life assessment device for LNG carriers. The device includes a processor and a memory. The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the method for assessing the lifespan of cryogenic cables for LNG carriers as described in Embodiment 1 of the present invention, according to the instructions in the program code.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for assessing the lifespan of cryogenic cables for LNG carriers, characterized in that, include: Obtain operating condition data for the cable sample, including the cable's operating voltage, annual operating time, and ambient temperature variation data. Multiple cable step-by-step voltage breakdown tests were conducted when the ambient temperature was below the set low temperature threshold to obtain the duration of the final voltage increase and the breakdown voltage of each test. The life index of the cable sample was calculated by the duration of the final stage of pressurization and the breakdown voltage. An equivalent voltage-duration model is established, and the electrical aging test parameters are calculated using the operating voltage, annual operating time, and lifespan index. These electrical aging test parameters include the test voltage and test duration. The ratio of the cable's working voltage to the test voltage is a set value. The ratio of the cable's working voltage to the test voltage is used as the base, and the life index is used as the exponent for exponential calculation. The result of the calculation is multiplied by the annual working time of the cable to obtain the test time. A temperature cycling screening model is established, and thermomechanical aging test parameters are calculated based on ambient temperature change data. These thermomechanical aging test parameters include the temperature change range, temperature change rate, and number of temperature cycles during the test. The formula for calculating the parameters of the thermomechanical aging test is as follows: Among them, R s R represents the temperature variation range of the LNG carrier's cargo tanks when it is fully empty. t V represents the temperature range during the experiment. s V represents the rate of temperature change of an LNG carrier when it is fully empty. t N represents the rate of temperature change during the experiment. s N represents the number of temperature cycles during operation. t The number of temperature cycles during the experiment is given, where e is the natural constant; the temperature range during the experiment is given by R. t and the rate of temperature change V during the experiment t Set value; A set number of cable samples are subjected to two cycles of aging based on electrical aging test parameters and thermomechanical aging test parameters. At the end of the second cycle, the insulation resistance of each cable sample is checked to see if it is greater than the set resistance threshold. If not, it means that the cable service life has not met the requirements. If yes, the aging process continues for two more cycles. If the insulation resistance of each cable sample is greater than the set resistance threshold and all pass the AC withstand voltage test of the set standard after aging, it means that the cable service life has met the requirements. Otherwise, it has not been met.

2. The method for evaluating the lifespan of cryogenic cables for LNG carriers according to claim 1, characterized in that: The acquisition of the operating condition data of the cable sample specifically includes: The ambient temperature change data includes the range of ambient temperature change in the cargo tanks of an LNG carrier when it is fully empty, the rate of temperature change, and the number of temperature cycles during operation. Obtain the annual LNG loading / unloading frequency and the duration of each power-on session. The product of the annual LNG loading / unloading frequency and the duration of each power-on session is the annual working time.

3. The method for evaluating the lifespan of cryogenic cables for LNG carriers according to claim 1, characterized in that: The procedure of conducting multiple cable voltage-increase breakdown tests under ambient temperatures below a set low-temperature threshold specifically involves: The cable was tested under liquid nitrogen immersion conditions, with the ambient temperature consistently below the set low-temperature threshold. Multiple cable samples were divided into multiple groups, with each group containing the same number of cable samples. For different samples in each group, a step-up voltage breakdown test was performed. For cable samples in the same group, the duration of each voltage increase was the same except for the last voltage increase. The breakdown voltage of different cable samples in the same group was different. The duration of each voltage increase was different between different groups. The starting voltage and voltage increase ratio of all cable samples in all groups were the same, which were all set values. Obtain the breakdown voltage and the duration of the final stage of the step-up breakdown test for all cable samples in each group.

4. The method for evaluating the lifespan of cryogenic cables for LNG carriers according to claim 2, characterized in that: The calculation of the cable sample's life index based on the duration of the final stage of pressurization and the breakdown voltage is as follows: The cumulative damage of each cable sample is calculated based on the life index, breakdown voltage and the duration of the last stage of pressurization, and a cumulative damage matrix is ​​established. The element in the i-th row and j-th column of the cumulative damage matrix is ​​the cumulative damage of the j-th sample in the i-th group. The difference between the average cumulative damage of the i-th row and the average cumulative damage of the entire cumulative damage matrix is ​​divided by the average cumulative damage of the cumulative damage matrix. The square of the result of the division is the square difference of the i-th group. The square differences of all groups are summed and then divided by the difference between the number of cable samples and 1 to obtain the variance of the cumulative damage matrix. The optimal lifetime index is obtained by solving the objective function by minimizing the variance of the cumulative damage matrix.

5. The method for evaluating the lifespan of cryogenic cables for LNG carriers according to claim 4, characterized in that: The cumulative damage for each cable sample is calculated based on the life index, breakdown voltage, and duration of the final pressurization stage, specifically as follows: The cumulative damage formula for each cable sample is: in, The cumulative damage is for the j-th sample in the i-th group. Where is the starting voltage, and r is the lifetime exponent. Breakdown voltage For boost ratio, This indicates the m-th voltage boost; k is the number of boost stages. The duration of each pressurization stage in the i-th group. The duration of the final pressurization stage for the j-th sample in the i-th group.

6. The method for evaluating the lifespan of cryogenic cables for LNG carriers according to claim 1, characterized in that: The aging process based on electro-aging test parameters and thermomechanical aging test parameters specifically includes: Each cycle begins with annual electrical aging using electrical aging test parameters equivalent to one-quarter of the cable's design life, followed by thermomechanical aging using thermomechanical aging test parameters equivalent to one-quarter of the cable's design life, and finally, mechanical vibration aging using the set mechanical vibration aging test parameters.

7. A system for assessing the lifespan of cryogenic cables for LNG carriers based on the method of any one of claims 1-6, comprising: The cable sample testing module, cable life index calculation module, cable electro-aging and thermomechanical aging test parameter calculation module, and cable life assessment module are characterized by: Cable Sample Testing Module: Used to acquire operating condition data of cable samples, including cable operating voltage, annual operating time and ambient temperature variation data; and to conduct multiple cable step-by-step voltage increase breakdown tests when the ambient temperature is below the set low temperature threshold, to obtain the duration of the last stage of voltage increase and the breakdown voltage of each test. Cable Life Index Calculation Module: Calculates the life index of a cable sample based on the duration of the final stage of pressurization and the breakdown voltage; Cable electro-aging and thermomechanical aging test parameter calculation module: used to establish a voltage-duration equivalent model, calculate electro-aging test parameters through working voltage, annual working time and life index, the electro-aging test parameters include test voltage and test duration; establish a temperature cycle screening model, calculate thermomechanical aging test parameters based on ambient temperature change data, the thermomechanical aging test parameters include temperature change range during test, temperature change rate during test and number of temperature cycles during test; Cable life assessment module: This module is used to perform two cycles of aging on a set number of cable samples based on electrical aging test parameters and thermomechanical aging test parameters. At the end of the second cycle, it checks whether the insulation resistance of each cable sample is greater than the set resistance threshold. If not, it means that the cable life has not met the requirements. If yes, it continues for two more cycles of aging. If, after aging, the insulation resistance of each cable sample is greater than the set resistance threshold and all pass the AC withstand voltage test of the set standard, it means that the cable life has met the requirements. Otherwise, it has not.

8. A device for assessing the lifespan of cryogenic cables for LNG carriers, characterized in that, The device includes a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the method for assessing the lifespan of cryogenic cables for LNG carriers according to any one of claims 1-6, based on the instructions in the program code.

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