Judgment method of unequal-diameter submarine cable conductor connection quality

Abstract

The invention discloses an unequal-diameter submarine cable conductor connection quality judgment method, and relates to the field of submarine cable detection. The objective of the invention is to solve the problem that dynamic resistance characteristics and thermal stability of unequal-diameter joints cannot be accurately evaluated in the prior art. The method comprises the following steps: preparing unequal-diameter submarine cable conductor samples, large-section conductor samples and small-section conductor samples, respectively measuring resistance values of the samples in an initial state, a load state and a recovery state, and converting the resistance values into resistance values at a standard temperature; applying a load current through a series loop to simulate an actual working condition, and calculating an equivalent resistance value of an unequal-diameter section; and based on the resistance limit values of the large and small cross-section conductors, in combination with a dynamic resistance change rule, performing criterion verification. According to the technical scheme, all-dimensional evaluation of thermal stability, interface resistance characteristics and the like of unequal-diameter joints is realized, and the detection precision is remarkably improved; and the connection reliability is guaranteed, and key technical guarantee is provided for intelligent upgrading, cost reduction and benefit improvement of submarine cable lines.

Description

Technical Field

[0001] The present invention relates to the field of submarine cable detection, and particularly to a method for judging the connection quality of non-uniform diameter submarine cable conductors. Background Art

[0002] In recent years, with the rapid development of offshore wind power and island power supply projects, submarine cables (hereinafter referred to as "submarine cables"), as the core carrier of electric energy transmission, have seen a significant expansion in their construction scale. The length of a typical submarine cable line can reach dozens of kilometers and is mainly composed of an underwater section and a landing section: The underwater section is immersed in seawater for a long time or buried under the seabed, with relatively stable environmental temperature and excellent heat dissipation conditions; while the landing section extends from the coastline to the land, covering the intertidal zone (periodically submerged and exposed) and the onshore area, facing complex environmental challenges. Measured research shows that the landing section is affected by the double fluctuations of air and seawater temperatures, and the environmental temperature is significantly higher than that of the underwater section. Coupled with limited heat dissipation conditions (such as soil thermal resistance, changes in the covering layer caused by tidal scouring, etc.), this section has become the bottleneck area for the current-carrying capacity of the entire line. According to statistics, under the same cross-section, the steady-state temperature rise of the landing section submarine cable is higher than that of the underwater section, directly restricting the overall transmission capacity of the line.

[0003] Currently, the industry generally adopts the "short board matching" design principle, that is, determining the conductor cross-section of the entire submarine cable according to the current-carrying capacity limit of the landing section. Although this method can ensure safe operation, it results in redundant current-carrying capacity of the conductors in the underwater section of dozens of kilometers, increasing material costs and seriously reducing the economic efficiency of the project. Existing improvement schemes focus on optimizing the heat dissipation conditions of the landing section. For example, removing the armor layer on the onshore section to enhance convective heat dissipation, but the actual effect of increasing the current-carrying capacity is insufficient, and it may sacrifice mechanical protection performance. At the same time, with the breakthrough of laying technology (such as the shipborne 500 kV soft joint process), the non-uniform diameter connection technology has been gradually applied to the landing section. By differentiating the conductor cross-sections of the underwater section and the landing section, precise matching of the current-carrying capacity is achieved. However, this technology faces two core problems: The current standards only formulate resistance and temperature rise test methods for the connection of equal-diameter conductors, and cannot effectively evaluate the interface resistance stability at the non-uniform diameter connection and the thermoelectric coupling effect in the cross-section transition area; due to material heterogeneity and geometric mutations at the non-uniform diameter connection, local overheating is likely to occur under load fluctuations and environmental temperature changes, and existing static resistance detection means are difficult to capture such time-varying characteristics.

[0004] Therefore, there is an urgent need to establish a set of non-uniform diameter connection quality evaluation methods covering multi-physical field coupling analysis to solve key technical problems such as cross-section difference limit determination, dynamic resistance characteristic characterization, and spatial heat distribution verification, and provide theoretical support for the refined design and safe operation of submarine cable lines. Summary of the Invention

[0005] The technical problems to be solved and the technical tasks proposed by the present invention are to improve and refine the existing technical solutions, and provide a method for judging the connection quality of unequal-diameter submarine cable conductors, so as to achieve the purpose of evaluating the limit value and reliability of the connection of unequal-diameter submarine cable conductors. For this reason, the present invention adopts the following technical solutions.

[0006] A method for judging the connection quality of unequal-diameter submarine cable conductors, comprising the following steps: 1) Prepare three straight conductor samples of equal length, including an unequal-diameter submarine cable conductor sample, a large cross-section conductor sample, and a small cross-section conductor sample; the unequal-diameter submarine cable conductor sample has an unequal-diameter section located in the middle of the sample, and large cross-section sections of the same diameter as the large cross-section conductor sample and small cross-section sections of the same diameter as the small cross-section conductor sample are respectively connected at both ends of the unequal-diameter section; measure the length of the unequal-diameter section; 2) Measure the initial state resistance values A1, B1, and C1 of the three samples respectively at room temperature, and convert them into resistance values a1, b1, and c1 at the standard temperature; 3) Connect the three samples in series to form a loop, and continuously apply a predetermined load current. When the temperature of the small cross-section conductor sample exceeds the set threshold, synchronously measure the temperatures of the three samples and the corresponding load state resistance values A2, B2, and C2, and convert them into resistance values a2, b2, and c2 at the standard temperature; 4) After the samples are cooled to room temperature, measure the restored state resistance values A3, B3, and C3, and convert them into resistance values a3, b3, and c3 at the standard temperature; 5) Calculate the equivalent resistance values d1, d2, and d3 of the unequal-diameter section in the initial state, load state, and restored state according to the resistance values converted to the standard temperature; perform a second criterion verification according to the maximum resistance limits at the standard temperature of the large and small cross-section conductors and the equivalent resistance values d1, d2, and d3; Judge the connection quality through the criterion results. When the criterion is met, judge that the connection quality of the unequal-diameter section is qualified.

[0007] This technical solution effectively evaluates the thermal stability by applying a continuous load current to simulate the long-term current-carrying condition during the actual operation of the submarine cable and capturing the resistance change at the unequal-diameter connection under thermal cycling. Measuring the resistance after cooling (A3 / B3 / C3) verifies whether there is irreversible damage (such as plastic deformation, oxide layer formation) at the connection, avoiding missed detection of hidden defects. Converting the measured resistance values to the standard temperature uniformly eliminates the interference of ambient temperature fluctuations on the test results and ensures data comparability. It can effectively improve the accuracy and provide a key technical guarantee for the intelligent upgrade and cost reduction and efficiency increase of the submarine cable line.

[0008] As a preferred technical means: Step 5) further includes: calculating the equivalent resistance values D1, D2, and D3 of the unequal-diameter segments in the initial state, load state, and recovery state according to the directly measured resistance values; performing a first criterion verification based on the maximum resistance limits of the large and small cross-section conductors and the equivalent resistance values D1, D2, and D3.

[0009] The first criterion can be verified prior to the second criterion to determine the similarity of the resistance value distribution laws of the large, unequal-diameter segments, and small diameters in the initial state, load state, and recovery state. The first criterion verification is preferentially executed to quickly screen abnormal samples. If the first criterion is not passed, it can directly prompt that there is an abnormality in the unequal-diameter segment to improve efficiency.

[0010] As a preferred technical means: When measuring the resistance value, the distance between the two measurement ends is 1 meter.

[0011] A 1-meter distance is consistent with the standard recommended method for measuring the resistance of conductors, ensuring that the test results are comparable, facilitating the conversion of the measurement results to the resistance per unit length, eliminating the influence of sample length differences, being convenient for engineering design and performance benchmarking, and a 1-meter standard distance is compatible with conventional laboratory equipment without the need for custom fixtures, reducing the cost of each test. It can ensure that the conditions of each measurement are consistent, reduce errors caused by different measurement lengths, make the measurement results more comparable and accurate, and can more accurately reflect the resistance characteristics of the unequal-diameter segments. A unified measurement length standard is conducive to forming a standardized measurement process and specification, facilitating different operators to follow the same standard when measuring at different times and places, improving the repeatability and reliability of the measurement, and being convenient for comparing and analyzing the measurement results of different samples. 1 meter is the standard probe distance of the resistance tester, without the need for custom fixtures or equipment adjustment, improving the test efficiency.

[0012] The distance between the two measurement ends is 1 meter, so the sample length can be 1.2 - 2.0 meters. It ensures the representativeness of the unequal-diameter segments, the feasibility of laboratory operations, measurement accuracy, cost-effectiveness, and compatibility with the measurement equipment. Limiting the sample length to 1.2 - 2.0 meters achieves Pareto optimality among the electromagnetic characteristic simulation accuracy, experimental cost, and defect detection sensitivity, providing a cost-effective standardized solution for the quality evaluation of unequal-diameter connections.

[0013] As a preferred technical means: In step 5), the calculation formulas for the equivalent resistance values D1, D2, and D3 of the unequal-diameter segments in the initial state, load state, and recovery state are: , where n = 1, 2, 3, corresponding to different test stages; is the length of the small cross-section segment between the two measurement ends, is the length of the large cross-section segment between the two measurement ends; is the length of the unequal-diameter segment.

[0014] Through the formula: , the total resistance A n is decomposed into the contributions of large cross-section segments ( ), small cross-section segments ( ), and unequal-diameter segments ( ). The equivalent resistance characteristics at the connection are accurately isolated. By separating the resistances of each segment, the quality of the connection can be evaluated more precisely. For the initial, load, and recovery three states (n = 1, 2, 3), D n is calculated respectively, reflecting the resistance change law of the unequal-diameter segment under thermal cycling (such as reversible expansion, irreversible oxidation). It is beneficial to improve the defect detection rate and economy.

[0015] As a preferred technical means: In step 5), the calculation formulas for the equivalent resistances d1, d2, and d3 of the unequal-diameter segment at standard temperature are: . The resistance values in each state are uniformly converted to the standard temperature to eliminate the influence of ambient temperature fluctuations on the test results, making the data measured at different times and locations directly comparable. By calculating the standardized resistance contributions of the large and small cross-section segments and accurately deducting their influences, the remaining resistance fully characterizes the true characteristics of the unequal-diameter segment, avoiding the "signal drowning" problem of the traditional overall measurement method, and providing a high-sensitivity, low-cost, and standardized quality control tool for submarine cable engineering.

[0016] As a preferred technical means: Step 5) also includes: performing multi-point resistance measurement on the unequal-diameter submarine cable conductor sample in the length direction, calculating the average equivalent resistance value y of the unequal-diameter segment through the multi-point resistance measurement values, calculating the average resistance value d through the equivalent resistances d1, d2, and d3, and performing the third criterion verification based on the average resistance value y and the average resistance value d.

[0017] By measuring the resistances at different positions of the unequal-diameter segment (such as near the large cross-section end, middle, near the small cross-section end), it is beneficial to identify spatial distribution defects such as local poor contact, material inclusions, or geometric deformations. The mean value of the multi-point measurement effectively suppresses random errors.

[0018] d is the average equivalent resistance based on the dynamic load experiment (initial, load, recovery three states), reflecting the comprehensive performance of the unequal-diameter segment under thermal cycling; y is the spatial equivalent resistance mean value of the multi-point measurement at normal temperature, reflecting the static distribution characteristics; comparing y and d can reflect the difference between dynamic and static, prevent performance deviation caused by thermal damage (such as oxidation, creep) or process fluctuations, and achieve a full-dimensional verification of the quality of the unequal-diameter connection, providing key support for the safe operation and full-life cycle management of submarine cables.

[0019] As a preferred technical means: The calculation formula for the average equivalent resistance value y is: , where: is the equivalent resistance value of the unequal-diameter section at the i-th position, and m is the total number of positions; , where: The measured resistance value at the position is converted into the total resistance value at the standard temperature; is the length of the small cross-section section between the two measurement ends at the position; is the length of the large cross-section section between the two measurement ends at the position.

[0020] Multi-point spatial averaging improves data stability and reliability. By calculating the average value of the equivalent resistance values of multiple measurement points, local random errors (such as poor contact and microscopic inhomogeneity of materials) are significantly suppressed, the data dispersion is reduced, and the overall evaluation result is ensured to be closer to the true value. All are converted to the standard temperature to eliminate the interference of environmental temperature fluctuations on the resistance value, so that the test results at different times, locations, and seasons can be directly compared. By dividing the total resistance value by the length L3 of the unequal-diameter section, the total resistance value is converted into the resistance per unit length (Ω / m), making the test results of different-sized samples directly comparable. This scheme realizes the high-precision and full-dimensional evaluation of the unequal-diameter connection quality through multi-point spatial averaging, dynamic parameter decoupling, and temperature-length double normalization.

[0021] As a preferred technical means: in step 5), three criteria are used to judge whether the connection quality of the unequal-diameter section is qualified: The first criterion: each D n value does not exceed 1.1 times the maximum value of the corresponding B n and C n ; The second criterion: each d n value does not exceed 1.05 times the maximum value of the corresponding b n and c n ; The third criterion: |y - d| ≤ 5%; When and only when all three criteria are met, it is determined that the connection quality of the unequal-diameter section is qualified.

[0022] Since the total length L is 1 meter, during the calculation, B n , C n can be directly used for calculation without dividing by L. Through the criterion D n ≤ 1.1×max(B n , C n ), it is mandatory that the equivalent resistance of the unequal-diameter section in the initial state, load state, and recovery state does not exceed 1.1 times the resistance of the large and small cross-section conductors, ensuring that the connection remains stable under thermal cycle shock and avoiding the out-of-control temperature rise caused by overload (such as the common thermal bottleneck problem in the submarine cable landing section). d n≤1.05×max(b n ,c n ), based on the resistance value at standard temperature, eliminates the interference of ambient temperature fluctuations and accurately evaluates the inherent resistance characteristics of the connection. It is stricter (1.05 times) than the dynamic criterion (1.1 times), ensuring that the conductor material still meets the design requirements after thermal expansion and contraction. ∣yd∣≤5%, local defects or uneven processes can be identified. Through the three-criteria joint mechanism of dynamic performance verification, temperature standardization control and spatial distribution verification, the full life cycle and multi-physical field coupling evaluation of the quality of unequal diameter connections is realized. The triple line of defense intercepts thermal damage, material defects and local anomalies, effectively improving the reliability of submarine cable projects and reducing full-cycle costs.

[0023] As the preferred technical means: the standard temperature is 20°C.

[0024] Direct use can avoid secondary conversion errors. In addition, 20℃ is close to the normal laboratory environment temperature, and no additional temperature control equipment is required to keep the measurement conditions stable, reducing test costs.

[0025] As a preferred technical means: in step 3), the predetermined load current is continuously applied for 24 hours before subsequent temperature measurement is performed.

[0026] The 24-hour continuous load current simulates the actual working conditions of the submarine cable in long-term operation, so that the temperature distribution inside the conductor reaches a stable state. Measuring the temperature in this steady state can accurately reflect the thermal characteristics of the conductor under continuous high load and avoid measurement errors caused by transient temperature fluctuations. Continuous load helps to expose potential defects that may not be discovered in short-term tests but are extremely harmful to long-term operation. By simulating long-term operation, it is helpful to discover design or process defects at the connection in advance, avoid submarine cable failures caused by thermal failure in actual applications, and reduce operation and maintenance costs.

[0027] Beneficial effects: This technical solution proposes a resistance measurement and evaluation method for unequal-diameter conductors based on comparative analysis, targeting the structural characteristics of unequal-diameter conductors. It realizes a full-dimensional evaluation of the thermal stability of unequal-diameter connections, interface resistance characteristics, etc., effectively improves accuracy, and solves the problem of difficulty in measuring the DC resistance of unequal-diameter submarine cable conductors. It can be used to guide related measurement and analysis work; it provides key technical guarantees for the intelligent upgrade of submarine cable lines and cost reduction and efficiency improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a sample diagram of the present invention.

[0029] Figure 2 It is a multi-point resistance measurement position diagram of the present invention.

[0030] In the figure: 1. Unequal-diameter submarine cable conductor sample; 101. Unequal-diameter section; 102. Large cross-section section; 103. Small cross-section section 103; 2. Large cross-section conductor sample; 3. Small cross-section conductor sample. Detailed implementation mode

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings of the specification.

[0032] The present invention includes the following steps: S1: First, conduct the preparation of conductor resistance samples. Equal-length samples are taken from the unequal-diameter submarine cable conductor, large cross-section conductor, and small cross-section conductor respectively. As Figure 1 shown, there are a total of 3 samples, namely unequal-diameter submarine cable conductor sample 1, large cross-section conductor sample 2, and small cross-section conductor sample 3; the length of each sample is 1.5 m, and the 3 samples are kept straight. Among them, for the unequal-diameter submarine cable conductor sample 1, it should be ensured that the unequal-diameter section 101 is in the middle position of the sample, that is, the lengths of the large cross-section sections 102 and small cross-section sections 103 at both ends of the unequal-diameter section 101 are equal.

[0033] S2: Measure the length of the unequal-diameter section 101 in the unequal-diameter submarine cable conductor sample 1; for example, if the length of the unequal-diameter section 101 is 0.2 m, and the lengths of the large and small cross-section sections 103 are 0.4 m respectively; the subsequent steps will be calculated based on the length of the unequal-diameter section 101 being 0.2 m.

[0034] The length of the unequal-diameter section 101 in the unequal-diameter submarine cable conductor sample 1 can be measured with a vernier caliper or a laser rangefinder, etc.

[0035] S3: After the 3 samples are left standing at room temperature, measure the conductor resistance according to relevant standards (select a 1 m distance for the conductor resistance measurement, and it should be ensured that the unequal-diameter section 101 of the unequal-diameter submarine cable conductor sample 1 is in the middle position of 1 m), and record them as A1, B1, C1 respectively, and convert to obtain the resistance values at 20 °C, and record them as a1, b1, c1 respectively.

[0036] S4: Connect the 3 samples into a loop, apply the same load current (select an appropriate current value according to the conductor cross-section) in the loop for 24 h, then measure the temperatures of the 3 samples respectively. The minimum conductor temperature among the 3 samples should be greater than 50 °C. For the unequal-diameter submarine cable conductor sample 1, select the unequal-diameter section 101 to measure the temperature. Immediately measure the conductor resistance according to relevant standards at the same time, and record them as A2, B2, C2 respectively, and convert to obtain the resistance values at 20 °C, and record them as a2, b2, c2 respectively.

[0037] S5: After cooling to room temperature, measure the conductor resistance according to relevant standards, and record them as A3, B3, C3 respectively, and convert to obtain the resistance values at 20 °C, and record them as a3, b3, c3 respectively.

[0038] Calculate (A1 - B1 0.4 - C1 0.4) / 0.2 = D1, (A2 - B2 0.4 - C2 0.4) / 0.2 = D2, (A3 - B3 0.4 - C3 0.4) / 0.2 = D3.

[0039] The first criterion: When D1 should be within the resistance value range of B1 and C1, that is, the confidence interval. If it is not within the confidence interval, it should not be greater than 1.1 times the maximum value of B1 and C1. Similarly, D2 should be within the confidence interval of B2 and C2. If it is not within the confidence interval, it should not be greater than 1.1 times the maximum value of B2 and C2. D3 should be within the confidence interval of B3 and C3. If it is not within the confidence interval, it should not be greater than 1.1 times the maximum value of B3 and C3.

[0040] If the first criterion is met, d1, d2, and d3 can be calculated. If the criterion 1 is not met, the quality of the non-uniform diameter section 101 is suspected.

[0041] Calculate (a1 - b1 0.4 - c1 0.4) / 0.2 = d1, (a2 - b2 0.4 - c2 0.4) / 0.2 = d2, (a3 - b3 0.4 - c3 0.4) / 0.2 = d3.

[0042] The second criterion: When d1 should be within the confidence interval of b1 and c1, d2 should be within the confidence interval of b2 and c2, and d3 should be within the confidence interval of b3 and c3. If there is a situation where it is not within the confidence interval, it should not be greater than 1.05 times the maximum value.

[0043] If the second criterion is not met, the quality of the non-uniform diameter section 101 is suspected.

[0044] Based on comprehensively considering the overall characteristics of the submarine cable line, the connection structure and manufacturing characteristics of the non-uniform diameter conductor of the submarine cable, the conductor resistance value and its variation characteristics, combined with the technical requirements for the connection of the non-uniform diameter submarine cable conductor 1, and based on the data analysis of the variation characteristics of the conductor resistance value when connecting different conductor cross-sections, a method for evaluating the limit value and reliability of the connection of the non-uniform diameter submarine cable conductor 1 is realized to improve the operation reliability of the non-uniform diameter submarine cable line.

[0045] Embodiment 2: The same parts as in Embodiment 1 will not be repeated. The differences are that step S5 further includes: At room temperature, respectively pressFigure 2 Measure the DC resistance values of the unequal-diameter submarine cable conductor sample 1 at different positions, denoted as X1, X2, and X3 respectively, and convert them to the resistance values at 20°C, denoted as x1, x2, and x3 respectively.

[0046] Calculate y1 = x1 - 0.4b1 - 0.4c1, y2 = x2 - 0.2b1 - 0.6c1, y3 = x3 - 0.6b1 - 0.2c1 respectively; Y1 = y1 / 0.2, Y2 = y2 / 0.2, Y3 = y3 / 0.2; calculate the average value y of Y1, Y2, and Y3; calculate the average value d of d1, d2, and d3.

[0047] The third criterion: Compare y with d, and the difference is not greater than 5%. If the third criterion is not met, it is considered that the quality of the unequal-diameter section 101 is in doubt.

[0048] Based on Embodiment 1, this embodiment adds the measurement of the DC resistance value and the third criterion. Through more comprehensive data analysis, it further verifies the quality of the connection of the unequal-diameter submarine cable conductor and improves the operation reliability of the unequal-diameter submarine cable line.

[0049] The above-described method for judging the connection quality of an unequal-diameter submarine cable conductor is a specific embodiment of the present invention, which has already reflected the substantial features and progress of the present invention. According to actual usage needs, under the inspiration of the present invention, equivalent modifications can be made to it, and all are within the protection scope of this solution.

Claims

1. A method for judging the connection quality of unequal diameter submarine cable conductors, characterized in that: The following steps are involved: 1) Prepare three straight conductor samples of equal length, including unequal diameter submarine cable conductor samples, large cross-section conductor samples and small cross-section conductor samples; The unequal diameter submarine cable conductor sample has an unequal diameter section located in the middle of the sample, and the two ends of the unequal diameter section are respectively connected to a large cross-section section with the same diameter as the large cross-section conductor sample and a small cross-section section with the same diameter as the small cross-section conductor sample; the length of the unequal diameter section is measured; 2) Measure the initial resistance values ​​A1, B1, and C1 of the three samples at room temperature and convert them into resistance values ​​a1, b1, and c1 at standard temperature; 3) Connect the three samples in series to form a loop, and continuously apply a predetermined load current. When the temperature of the small-section conductor sample exceeds the set threshold, synchronously measure the temperatures of the three samples and the corresponding load state resistance values ​​A2, B2, and C2, and convert them into resistance values ​​a2, b2, and c2 at the standard temperature; 4) After the sample cools to room temperature, measure the resistance values ​​A3, B3, and C3 in the recovery state and convert them into the resistance values ​​a3, b3, and c3 at the standard temperature; 5) Calculate the equivalent resistance values ​​d1, d2 and d3 of the unequal diameter sections in the initial state, load state and recovery state according to the resistance values ​​converted to the standard temperature; verify the second criterion according to the maximum resistance limit and equivalent resistance values ​​d1, d2 and d3 of the large and small cross-section conductors at the standard temperature; The connection quality is determined by the criterion results. When the criterion is met, the connection quality of the unequal diameter sections is determined to be qualified.

2. A method for judging the connection quality of unequal diameter submarine cable conductors according to claim 1, characterized in that: Step 5) also includes: calculating the equivalent resistance values ​​D1, D2 and D3 of the unequal diameter sections in the initial state, the load state and the recovery state according to the directly measured resistance values; and verifying the first criterion according to the maximum resistance limit values ​​and the equivalent resistance values ​​D1, D2 and D3 of the large and small cross-section conductors.

3. A method for judging the connection quality of unequal diameter submarine cable conductors according to claim 2, characterized in that: When measuring resistance, the distance between the two measuring ends is 1 meter.

4. A method for judging the connection quality of unequal diameter submarine cable conductors according to claim 3, characterized in that: In step 5), the calculation formulas for the equivalent resistance values ​​D1, D2, and D3 of the unequal diameter segments in the initial state, the load state, and the recovery state are: ,In the formula, n=1, 2, 3, corresponding to different test stages; is the length of the small cross-section between the two measuring ends, is the length of the large cross-section section between the two measuring ends; is the length of the unequal diameter segment.

5. A method for judging the connection quality of unequal diameter submarine cable conductors according to claim 4, characterized in that: In step 5), the calculation formula for the equivalent resistances d1, d2 and d3 of the unequal diameter segments at standard temperature is: .

6. A method for judging the connection quality of unequal diameter submarine cable conductors according to claim 5, characterized in that: Step 5) also includes: performing multi-point resistance measurement on the unequal diameter submarine cable conductor samples in the length direction, calculating the average equivalent resistance value y of the unequal diameter sections through the multi-point resistance measurement values, calculating the average resistance value d through the equivalent resistance values ​​d1, d2 and d3, and verifying the third criterion based on the average resistance value y and the average resistance value d.

7. A method for judging the connection quality of unequal diameter submarine cable conductors according to claim 6, characterized in that: The calculation formula for the average equivalent resistance value y is: , where: is the equivalent resistance value of the unequal diameter segment at the i-th position, and m is the total number of positions; , where: No. The resistance value measured at the position is converted into the total resistance value at standard temperature; For the The length of the small cross-section between the two measuring ends when in position; For the The length of the large cross-section segment between the two measuring ends when in position.

8. A method for judging the connection quality of unequal diameter submarine cable conductors according to claim 7, characterized in that: In step 5), the quality of the connection of the unequal diameter sections is judged based on the following three criteria: First criterion: Each D n The value does not exceed the corresponding B n With C n 1.1 times the maximum value; The second criterion: each d n The value does not exceed the corresponding b n With c n 1.05 times the maximum value; The third criterion: |yd|≤5%; The connection quality of unequal diameter sections is considered qualified if and only if the three criteria are met at the same time.

9. A method for judging the connection quality of unequal diameter submarine cable conductors according to claim 1, characterized in that: The standard temperature is 20℃.

10. A method for judging the connection quality of unequal diameter submarine cable conductors according to claim 1, characterized in that: In step 3), the predetermined load current is continuously applied for 24 hours before subsequent temperature measurements are performed.

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