Method for predicting residual life in middle and later periods of cable operation

Abstract

The invention discloses a method for predicting the residual life in the middle and later periods of cable operation, and relates to the technical field of power equipment state prediction. Comprising the following steps: S1, constructing sample groups A, B and C under the same aging condition; s2, performing a short-time breakdown experiment on the sample group A and the sample group C in the S1; s3, carrying out a constant stress accelerated life test on the sample C to obtain withstand voltage time under each field intensity; S4, simultaneously taking logarithms of an inverse power model expression in the S3 to obtain a life curve equation; s5, acquiring a voltage tolerance index n of the sample C; s6, calculating the residual insulation damage amount through the residual insulation damage model RID; s7, calculating the residual life of the sample group B; s8, verifying the prediction accuracy of the RID model; according to the method for predicting the residual life in the middle and later periods of cable operation, the problem that only the initial time of cable use can be obtained and the residual life in the later periods cannot be obtained in operation and maintenance work is solved through the RID model and the matched experiment process.

Description

Technical Field

[0001] The invention relates to the technical field of power equipment state prediction, and in particular to a method for predicting the remaining service life of a cable in the middle and late stages of operation. Background Art

[0002] In urban distribution networks, power cables are the carrier of power supply and the core equipment in power supply and distribution. Their high reliability and long life operation have become important goals of power grid companies. From the perspective of operation failure rate and operation time, Figure 1 As shown in the figure, cables with a service time of more than 15 years have reached the middle and late stages of their operation. The cause of insulation failure has gradually shifted from accidental failure to insulation aging, and the failure rate has increased with time, becoming a key object in determining the reliability of urban power supply. At the same time, the middle and late stages of service are also the most critical period for the remaining insulation life in cable operation and maintenance work.

[0003] At present, the reason why the insulation life of cables is difficult to predict online is that the relevant parameters in the life model cannot be obtained through online detection or calculation. Since the characterization parameters cannot be obtained online, the online prediction of the cable insulation life is still restricted and has long endangered the safety of cables in the later stages of operation. Summary of the invention

[0004] The purpose of the present invention is to provide a method for predicting the remaining service life of a cable in the later stages of operation. Through the residual insulation damage model RID and its supporting experimental process, the problem that only the initial time of cable use can be obtained but the remaining service life in the later stages cannot be obtained in operation and maintenance work is solved.

[0005] To achieve the above object, the present invention provides a method for predicting the remaining service life of a cable in the later period of operation, comprising the following steps:

[0006] S1. Construct retired sample group A, service sample group B and new cable sample group C of the same factory batch model under the same aging conditions;

[0007] S2, the sample group A and sample group C in S1 were subjected to a short-time breakdown test with a voltage increase rate v of 1 kV / s and the breakdown field strength threshold E b Analyze and process to obtain the breakdown field strength E of sample group A b-A The breakdown field strength E of sample group C b-C ;

[0008] S3, according to E in S3 b-C Set the external field strength E i (i=1,2,3…) Perform a constant stress accelerated life test on sample C, and obtain the withstand time t under each field strength based on the inverse power model.

[0009] S4, taking the logarithm of the inverse power model expression in S6 to obtain the life curve equation;

[0010] S5, according to the life curve equation and data in S6 (E i , t) performing linear fitting to obtain the voltage tolerance index n of sample C;

[0011] S6, the above voltage increase rate v, the breakdown field strength E of sample group A are converted into b-A Substitute the values ​​of the voltage withstand index n into the calculation to calculate the value of the remaining insulation damage ΔD;

[0012] S7, using the value of ΔD described in S6 to calculate the remaining life L of sample group B with an operating field strength of E0 through an inverse power model remainder ;

[0013] S8. Verify the accuracy of the RID model in predicting the remaining life of sample group B through the life curve equation.

[0014] Preferably, the calculation formula of Eb in S2 is as follows:

[0015] E b =vt (1);

[0016] Among them, E b is the breakdown field strength threshold, v is the voltage rise rate, and t is the withstand time.

[0017] Preferably, the calculation formula of the inverse power model in S3 is as follows:

[0018] t=D c ·E -n (2);

[0019] Among them, t is the withstand time, E is the external field strength, D c It is the cumulative amount of damage required for the cable insulation to fail.

[0020] Preferably, the life curve equation in S4 is as follows:

[0021] lnt=-nlnE+lnD c (3).

[0022] Preferably, the calculation process of the voltage tolerance index n in S5 is as follows:

[0023]

[0024] Preferably, the RID model expression in S6 is as follows:

[0025]

[0026] Preferably, the remaining life L in S7remainder The expression is as follows:

[0027]

[0028] Among them, L remainder is the remaining lifetime, and E0 is the operating field strength of sample group B.

[0029] Preferably, sample groups A, B and C in S1 all use cable insulation layer slices as samples, and the cable insulation layer is cut along the circumference into rectangular long slices with a thickness of 0.15-0.20 mm, and the rectangular long slices are divided into several circular slices with a diameter of 4-6 mm.

[0030] Preferably, the temperature control device for the short-time breakdown experiment in S2 is a thermostat, the temperature of the thermostat is set to 30° C. during the experiment, and dimethyl silicone oil is selected as the medium around the electrode.

[0031] Preferably, in S8, the calculation result of the RID model is verified by the prediction result of the life curve equation, and the relative difference between the two ranges from 4.5 to 4.9%.

[0032] Therefore, the present invention adopts a method for predicting the remaining service life of a cable in the later period of operation with the above structure, which has the following beneficial effects compared with the prior art:

[0033] The residual insulation damage model RID and the inverse power model are used to achieve the goal of predicting the remaining insulation life of the online cable using only the short-time breakdown test results of offline samples. The method is simple and quick to apply, which solves the thorny problem of online prediction of cable insulation life, and solves the problem of only being able to obtain the initial time of cable use but not the time it can still be used normally during operation and maintenance work. It is of great significance to ensure the long-term and reliable operation of the cable system.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A typical cable operation failure curve diagram of the background technology of a method for predicting the remaining service life of a cable in the middle and late stages of operation according to the present invention;

[0036] Figure 2 It is a flow chart of an embodiment of a method for predicting the remaining service life of a cable in the later period of operation according to the present invention;

[0037] Figure 3 A sample group construction diagram of an embodiment of a method for predicting the remaining service life of a cable in the later period of operation according to the present invention;

[0038] Figure 4 A life curve principle diagram of an embodiment of a method for predicting the remaining life of a cable in the later period of operation according to the present invention;

[0039] Figure 5 A schematic diagram of accumulated damage amount of an embodiment of a method for predicting the remaining service life of a cable in the later period of operation according to the present invention;

[0040] Figure 6 This is a life curve diagram of sample group B of an embodiment of a method for predicting the remaining life of a cable in the later stage of operation according to the present invention. DETAILED DESCRIPTION

[0041] Example

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0043] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] like Figure 2-Figure 5 As shown, a method for predicting the remaining service life of a cable in the later period of operation of the present invention comprises the following steps:

[0045] S1, construct retired sample group A, in-service sample group B and new cable sample group C of the same factory batch model under the same aging conditions; sample groups A, B and C in S1 all use cable insulation layer slices as samples, and the cable insulation layer is cut along the circumference into rectangular long slices with a thickness of 0.15-0.20mm, and the rectangular long slices are divided into several circular slices with a diameter of 4-6mm;

[0046] S2, the sample group A and sample group C in S1 were subjected to a short-time breakdown test with a voltage increase rate v of 1 kV / s and the breakdown field strength threshold E b Analyze and process to obtain the breakdown field strength E of sample group A b-A The breakdown field strength E of sample group C b-C , E b The calculation formula is as follows:

[0047] E b =vt (1);

[0048] Among them, E bis the breakdown field strength threshold, v is the voltage rise rate, and t is the withstand time; the temperature control device for the short-time breakdown experiment in S2 is a constant temperature box, the temperature of the constant temperature box is set at 30°C during the experiment, and dimethyl silicone oil is used as the medium around the electrode;

[0049] S3, according to E in S3 b-C Set the external field strength E i (i=1,2,3…) A constant stress accelerated life test is performed on sample C, and the withstand time t under each field strength is obtained based on the inverse power model; the calculation formula of the inverse power model is as follows:

[0050] t=D c ·E -n (2);

[0051] Among them, t is the withstand time, E is the external field strength, D c It is the cumulative damage required for cable insulation failure;

[0052] S4. Take the logarithm of the inverse power model expression in S6 to obtain the life curve equation; the life curve equation is as follows:

[0053] lnt=-nlnE+lnD c (3);

[0054] S5, according to the life curve equation and data in S6 (E i , t) perform linear fitting to obtain the voltage tolerance index n of sample C; the calculation process of the voltage tolerance index n is as follows:

[0055]

[0056] S6, the above voltage increase rate v, the breakdown field strength E of sample group A are converted into b-A Substitute the values ​​of the voltage withstand index n and calculate the value of the residual insulation damage ΔD; the RID model expression is as follows:

[0057]

[0058] S7, using the value of ΔD described in S6 to calculate the remaining life L of sample group B with an operating field strength of E0 through an inverse power model remainder ; Remaining life L remainder The expression is as follows:

[0059]

[0060] Among them, L remainder is the remaining lifetime, is the operating field strength of sample group B

[0061] S8. The accuracy of the RID model in predicting the remaining life of sample group B is verified by the life curve equation. The calculation results of the RID model are verified by the prediction results of the life curve equation. The relative difference between the two ranges from 4.5 to 4.9%.

[0062] The specific experimental process is as follows:

[0063] (1) Sample preparation

[0064] Cable insulation layer slicing was selected as the sample solution. Using XLPE power cables with a voltage level of 35kV, its insulation layer was cut into 0.17mm thick rectangular long slices along the circumference, and then the rectangular long slices were divided into several 5mm diameter circular slice samples. After the obtained multiple samples were divided into three groups of A, B, and C, the sample preparation was completed and the test was carried out.

[0065] (2) Test equipment

[0066] A high-voltage test transformer and an electrode device are required in the test. In order to control the environmental variables that affect the test results, a constant temperature box is selected as the temperature control device for the breakdown and aging tests. The temperature of the constant temperature box is set at 30°C in the test, and dimethyl silicone oil is used as the medium around the electrode.

[0067] (3) Short-time breakdown test of sample group C

[0068] Seven XLPE sheets from sample group C were selected and subjected to a short-time breakdown test at a voltage increase rate of v = 1000 V / s in a breakdown and aging test temperature control device and the test data were recorded. (4) Constant stress accelerated life test of sample group C

[0069] After obtaining the breakdown field strength of the unaged sample C, E b-C , 9 samples were selected from the sample group, each 3 samples were divided into a group, a total of 3 groups; each group of samples was placed in the electric field E i (i=1,2,3) to conduct a constant stress accelerated life test, record the sample failure time, and obtain the failure time of sample C at E after statistics. i Withstand voltage time t under (i=1,2,3). E i The selection of is related to the breakdown field strength of sample C. Three values ​​lower than the breakdown field strength can be selected in proportion based on relevant experience, such as selecting E1 = 46% E b-C , E2=42%E b-C , E3=38%E b-C .

[0070] (5) Electrical aging test of sample group A and sample group B

[0071] The cable working field strength is selected as the aging field strength for electrical aging for 20 days. Because the thickness of the selected cable insulation layer is 10mm, the aging external field strength is selected.

[0072] (6) Short-time breakdown test of sample A after aging test

[0073] After aging for 20 days, sample group A quits aging, and sample group B continues aging. Seven XLPE sheets from sample group A are selected and subjected to a short-time breakdown test at a voltage increase rate of v=1 kV / s in the device, and the test data are recorded.

[0074] (7) Using the above test results, calculate the remaining life of sample group B

[0075] The RID model is used to calculate the voltage rise rate v, the breakdown field strength E of sample group A, and the b-A The value of the remaining insulation damage ΔD is calculated by substituting the value of the voltage tolerance index n into the value, and then the remaining life of sample group B can be calculated through the inverse power model.

[0076] Calculation and verification of the remaining life of sample group B. Based on the parameter values ​​that have been obtained, including n, v, and Eb-A, the remaining insulation damage ΔD of sample group B that has not yet terminated the aging test can be calculated by RID model formula (5). The results are shown in Table 1.

[0077] Table 1 Calculation of ΔD using the RID model

[0078]

[0079]

[0080] Therefore, the RID model was used to calculate that the residual insulation damage of sample group B, which was continuously pressurized under the condition of an external electric field strength of 3.5 kV / mm, was ΔD. B =1.84×10 13 Substituting this value and the operating field strength E0 = 3.5 kV / mm into formula (6), the remaining service life of sample group B can be calculated as L remainder =1710256581s≈54 years.

[0081] Obviously, it is impossible to verify the accuracy of the above predictions through the results of 54-year aging tests, so it is necessary to design an accelerated life test method to evaluate the life curve of the aged samples, and thus calculate the insulation life time when the external applied field strength is 3.5kV / mm. Therefore, after 20 days of electrical aging, some sample group B was selected to stop pressurization and subjected to a constant stress accelerated life test.

[0082] (8) Test results verification and analysis:

[0083] Selection of applied voltage for accelerated life test and E b-AConsidering the requirement of insulation life under the estimated operating field strength of 3.5kV / mm, the applied field strength should not be too high, and is set to E1 = 12% E b-A =13.28kV / mm, E2 = 14%E b-A =15.49kV / mm,

[0084] E3=16%E b-A =17.70kV / mm, the failure time data obtained under different applied field strengths are shown in Table 2:

[0085] Table 2 Verification experiment failure time data

[0086]

[0087] From the data in Table 2, the sample life curve can be drawn in the lnE-lnt double logarithmic coordinate system, such as Figure 6 shown.

[0088] Figure 6 The sample life curve is obtained, and its equation is:

[0089] lnt=-7.88lnE+31.18 (7);

[0090] From formula 7, we can know that the voltage tolerance index n of test sample group B is B =7.88, the cumulative damage required for insulation failure D c-B =e 31.18 =3.48×10 13 Therefore, substituting E0=3.5kV / mm into formula 7, we can get the insulation life of t=1794922726s≈56 years.

[0091] In summary, the predicted insulation life of sample group B obtained by the RID model under the external applied field strength of operating field strength E0=3.5kV / mm is 1710256581s, and the insulation life of group B samples obtained by the verification test is 1794922726s. The relative difference between the two results is 4.9%, which shows the accuracy of using the RID model to predict the insulation life of cables or their insulation layer slice samples under operating conditions.

[0092] Therefore, the present invention adopts a method for predicting the remaining life of a cable in the later stages of operation using the above-mentioned structure. Through the RID model and its supporting experimental process, it solves the problem that only the initial time of cable use can be obtained during operation and maintenance work, but the remaining life in the later stages cannot be obtained.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for predicting the remaining service life of a cable in the later period of operation, characterized in that: The following steps are involved: S1. Construct retired sample group A, service sample group B and new cable sample group C of the same factory batch model under the same aging conditions; S2, the sample group A and sample group C in S1 were subjected to a short-time breakdown test with a voltage increase rate v of 1 kV / s and the breakdown field strength threshold E b Analyze and process to obtain the breakdown field strength E of sample group A b-A The breakdown field strength E of sample group C b-C ; S3, according to E in S3 b-C Set the external field strength E i , where i = 1, 2, 3…, a constant stress accelerated life test is performed on sample C, and the withstand time t under each field strength is obtained based on the inverse power model. S4, taking the logarithm of the inverse power model expression in S3 to obtain the life curve equation; S5, according to the life curve equation and data in S4 (E i， t) performing linear fitting to obtain the voltage tolerance index n of sample C; S6, the above voltage increase rate v, the breakdown field strength E of sample group A are converted into b-A Substitute the values ​​of the voltage withstand index n into the calculation to calculate the value of the remaining insulation damage ΔD; S7. Use the value of ΔD in S6 to calculate the remaining life L of sample group B with an operating field strength of E0 through the inverse power model. remainder ; S8. Verify the accuracy of the RID model in predicting the remaining life of sample group B through the life curve equation.

2. The method for predicting the remaining service life of a cable in the middle and late stages of operation according to claim 1 is characterized by: S2 E b The calculation formula is as follows: From b =vt (1); Among them, E b is the breakdown field strength threshold, v is the voltage rise rate, and t is the withstand time.

3. The method for predicting the remaining service life of a cable in the middle and late stages of operation according to claim 2 is characterized by: The calculation formula of the inverse power model in S3 is as follows: t=D c ·E -n (2); Where E is the external field strength, D c It is the cumulative amount of damage required for the cable insulation to fail.

4. The method for predicting the remaining service life of a cable in the middle and late stages of operation according to claim 3 is characterized by: The life curve equation in S4 is as follows: lnt=-nlnE+lnD c (3)。 5. The method for predicting the remaining service life of a cable in the middle and late stages of operation according to claim 4 is characterized by: The calculation process of voltage tolerance index n in S5 is as follows:

6. A method for predicting the remaining service life of a cable in the later period of operation according to claim 5, characterized in that: The RID model expression in S6 is as follows:

7. A method for predicting the remaining service life of a cable in the later period of operation according to claim 6, characterized in that: Remaining life L in S7 remainder The expression is as follows: Among them, L remainder is the remaining lifetime, and E0 is the operating field strength of sample group B.

8. A method for predicting the remaining service life of a cable in the middle and late stages of operation according to claim 7, characterized in that: Sample groups A, B and C in S1 all use cable insulation layer slices as samples. The cable insulation layer is cut along the circumference into rectangular long slices with a thickness of 0.15-0.20 mm. The rectangular long slices are divided into several circular slices with a diameter of 4-6 mm.

9. A method for predicting the remaining service life of a cable in the middle and late stages of operation according to claim 8, characterized in that: The temperature control device for the short-time breakdown experiment in S2 is a constant temperature box. The temperature of the constant temperature box is set at 30°C during the experiment, and dimethyl silicone oil is used as the medium around the electrode.

10. A method for predicting the remaining service life of a cable in the later period of operation according to claim 9, characterized in that: In S8, the calculation results of the RID model are verified by the prediction results of the life curve equation, and the relative difference between the two ranges from 4.9 to 5%.

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