A method for predicting the residual life of a cable in the later stage of operation

Abstract

The application discloses a kind of cable operation middle-later period remaining life prediction method, it is related to power equipment state prediction technical field;Including S1, construct sample group A, B, C under the same aging condition;S2, sample group A in S1 with sample group C are carried out short time breakdown experiment;S3, to sample C is carried out constant stress accelerated life test and obtains withstand voltage time under each field intensity, S4, the anti-power model expression in S3 is simultaneously taken logarithm to obtain life curve equation;S5, obtains the voltage resistance index n of sample C;S6, calculate residual insulation damage amount by residual insulation damage model RID;S7, calculate the remaining life of sample group B;S8, verify RID model prediction accuracy;The application adopts the above-mentioned cable operation middle-later period remaining life prediction method, through RID model and its supporting experimental process, solve the problem that only initial time of cable use can be obtained in operation and maintenance work and remaining life in later period cannot be obtained.

Description

Technical Field

[0001] The present 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 later 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 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 cable insulation life is still restricted and poses a long-term threat to 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 of only being able to obtain the initial time of cable use but not the remaining service life in the later stages during 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 rise rate v of 1 kV / s and the breakdown field strength threshold E b Perform analysis and processing 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, get the life curve equation by taking logarithm of the inverse power model expression in S6;

[0010] S5, get the voltage endurance exponent n of sample C by linear fitting according to the life curve equation in S6 and data (E i , t);

[0011] S6, get the value of residual insulation damage ΔD by substituting the above voltage rise rate v, breakdown field strength E b-A and voltage endurance exponent n of sample group A into the residual insulation damage model RID and calculating;

[0012] S7, get the residual life L remainder of sample group B with operating field strength E0 by inverse power model according to the value of ΔD in S6;

[0013] S8, verify the accuracy of RID model in predicting the residual life of sample group B by the life curve equation.

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

[0015] E b = vt (1);

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

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

[0018] t = D c · E -n (2);

[0019] Wherein, t is the voltage endurance time, E is the applied field strength, and D c is the cumulative damage amount required for cable insulation failure.

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

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

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

[0023]

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

[0025]

[0026] Preferably, the residual life Lremainder The expression is as follows:

[0027]

[0028] Wherein, L remainder is the remaining life, E0 is the operating field strength of the sample group B.

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

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

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

[0032] Therefore, the prediction method for the remaining life of a cable in a middle and late running stage has the following beneficial effects compared with the prior art:

[0033] The remaining insulation damage model RID and the inverse power model are used to achieve the goal of predicting the insulation remaining life of the cable in the online running only by using the short-time breakdown experiment result of the offline sample, the method is simple and fast to apply, the difficult problem of online prediction of the cable insulation life is solved, the problem that only the initial time of the cable use can be obtained and the normal use time cannot be obtained in the operation and maintenance work is solved, and it has important significance for ensuring the long-term reliable operation of the cable system.

[0034] The technical solutions of the present application will be further described in detail below with the aid of the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a typical cable running failure curve diagram of the background technology of the prediction method for the remaining life of a cable in a middle and late running stage of the present application;

[0036] Figure 2 It is a flowchart of the embodiment of the prediction method for the remaining life of a cable in a middle and late running stage of the present application;

[0037] Figure 3 It is a sample group construction diagram of the embodiment of the prediction method for the remaining life of a cable in a middle and late running stage of the present application;

[0038] Figure 4 It is a life curve principle diagram of the embodiment of the prediction method for the remaining life of a cable in a middle and late running stage of the present application;

[0039] Figure 5 This is a schematic diagram of the 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 late stage of operation according to the present invention. DETAILED DESCRIPTION

[0041] Example

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only 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 herein 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 as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0044] like Figures 2-5 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 a retired cable sample group A, a service cable sample group B, and a new cable sample group C under the same aging conditions. Sample groups A, B, and C in S1 all use cable insulation slices as samples. The cable insulation is cut into rectangular slices with a thickness of 0.15-0.20 mm along the circumference. The rectangular slices are divided into several circular slices with a diameter of 4-6 mm.

[0046] S2, the sample group A and sample group C in S1 were subjected to a short-time breakdown test with a voltage rise rate v of 1 kV / s and the breakdown field strength threshold E b Perform analysis and processing 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 bFor breakdown field strength threshold, v is the boost rate, t is the withstand voltage time; S2 short time breakdown experiment temperature control device selects constant temperature box, the temperature of the constant temperature box is set to 30 DEG C in the test, the medium around the electrode is selected as dimethyl silicone oil;

[0049] S3, according to S3 in E b-C Set the applied field strength E i (i = 1, 2, 3...) to sample C for constant stress accelerated life test, and the withstand voltage 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] Wherein, t is the withstand voltage time, E is the applied field strength, D c is the cumulative damage required when the cable insulation fails;

[0052] S4, the inverse power model expression in S6 is taken logarithm at the same time 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 in S6 and the data (E i , t), the voltage endurance index n of sample C is obtained by linear fitting; The voltage endurance index n calculation process is as follows:

[0055]

[0056] S6, the above boost rate v, the breakdown field strength E b-A and the voltage endurance index n of sample group A are substituted into the residual insulation damage model RID and the value of residual insulation damage amount ΔD is calculated; The RID model expression is as follows:

[0057]

[0058] S7, the residual life L remainder of sample group B with E0 operating field strength is calculated by the inverse power model using the value of ΔD in S6; The expression of residual life L remainder is as follows:

[0059]

[0060] Wherein, L remainder is the residual life, E0 is the operating field strength of sample group B

[0061] S8, verify the accuracy of the RID model in predicting the remaining life of sample group B through the life curve equation; verify the calculation results of the RID model through the prediction results of the life curve equation, and the relative difference between the two is in the range of 4.5-4.9%.

[0062] The specific experimental process is as follows:

[0063] (1) Sample preparation

[0064] The cable insulation layer section is selected as the sample scheme. An XLPE power cable with a voltage level of 35 kV is used, and the insulation layer is cut along the circumference to form a rectangular long thin slice with a thickness of 0.17 mm. Then the rectangular long thin slice is divided into several circular thin slice samples with a diameter of 5 mm. The obtained multiple samples are divided into groups A, B and C, and the sample preparation is completed to perform the test.

[0065] (2) Test equipment

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

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

[0068] Select 7 XLPE thin slices from sample group C, and perform a short-time breakdown test at a voltage rise rate of v=1000 V / s in the breakdown and aging test temperature control device, and record the test data.

[0069] Get the breakdown field strength of the unaged sample C E b-C , select 9 samples from sample group C, divide every 3 samples into a group, a total of 3 groups; each group of samples is subjected to constant stress accelerated life test at electric field E i (i=1, 2, 3), and the sample failure time is recorded. After statistical analysis, the withstand time t of sample C at E i (i=1, 2, 3) is obtained. The selection of E i is related to the breakdown field strength of sample C. According to relevant experience, three values lower than the breakdown field strength can be selected in proportion, such as E1=46% E b-C , E2=42% E b-C , and 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. Since the thickness of the selected cable insulation layer is 10 mm, the external aging field strength is selected.

[0072] (6) Short time breakdown test of sample group A after exiting the aging test

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

[0074] (7) Calculation of the remaining life of sample group B using the test results above

[0075] The values of the voltage increasing rate v, the breakdown field strength E b-A of sample group A, and the voltage resistance index n were substituted into the RID model and the value of the remaining insulation damage amount ΔD was calculated, and then the remaining life of sample group B was calculated using the inverse power model.

[0076] Calculation and verification of the remaining life of sample group B, based on the obtained parameter values, including n, v, Eb-A, the remaining insulation damage amount ΔD of sample group B which has not yet terminated the aging test was calculated using the RID model formula (5), and the results are shown in Table 1.

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

[0078]

[0079]

[0080] Therefore, using the RID model, it was calculated that the remaining insulation damage amount of sample group B which was continuously subjected to voltage stress at an applied field strength of 3.5 kV / mm, which is the operating field strength, is ΔD B = 1.84 x 10 13 . Substituting this value and the operating field strength E0 = 3.5 kV / mm into formula (6) can calculate the remaining life of sample group B as L remainder = 1710256581 s ≈ 54 years.

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

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

[0083] Selection of the applied voltage for the accelerated life test and E b-ACorrelation, considering the need to estimate the insulation life under the operating field strength of 3.5kV / mm, the applied field strength should not be too high, and E1=12%E is taken 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 Failure time data of verification experiment

[0086]

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

[0088] Figure 6 The sample life curve is obtained in the equation:

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

[0090] From equation 7, the voltage resistance index n B =7.88 of the test sample group B c-B =3.48x10 31.18 =3.48x10 13 . Therefore, E0=3.5kV / mm is substituted into equation 7 to obtain the insulation life t=1794922726s≈56 years.

[0091] From the above, the predicted insulation life of sample group B obtained by the RID model under the applied field strength of the operating field strength E0=3.5kV / mm is 1710256581s, and the insulation life of the B group sample obtained by the verification experiment is 1794922726s, and the relative difference between the two results is 4.9%, which indicates that the accuracy of using the RID model to predict the insulation life of the cable or the insulation layer of the cable sample under the operating state.

[0092] Therefore, the application adopts the above structure, and the method for predicting the residual life of the cable in the later period of operation, through the RID model and the supporting experimental process, solves the problem that only the initial time of the cable can be obtained in the operation and maintenance work, and the residual life in the later period cannot be obtained.

[0093] It should be pointed out finally that the above examples are only used to illustrate the technical solutions of the present application but not to limit it, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can still be modified or replaced equivalently, and these modifications or equivalent replacements should not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

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. Increase the pressure of sample group A and sample group C in S1. The short-time breakdown test of 1 kV / s and the breakdown field strength threshold Perform analysis and processing to obtain the breakdown field strength of sample group A The breakdown field strength of sample group C ; S3, according to S3 Set the external field strength ,in , a constant stress accelerated life test was conducted on sample C, and the withstand time under various field strengths was 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 Perform linear fitting to obtain the voltage tolerance index of sample C ; S6, the above-mentioned boost rate is converted to the residual insulation damage model RID , breakdown field strength of sample group A and voltage tolerance index Substitute the value of and calculate the remaining insulation damage The value of S7, using S6 The numerical value of the operating field strength is calculated by the inverse power model: The remaining life of sample group B ; S8. Verify the accuracy of the RID model in predicting the remaining life of sample group B using the life curve equation; The RID model expression in S6 is as follows: （5）。 2. The method for predicting the remaining service life of a cable in the later period of operation according to claim 1, characterized in that: S2 The calculation formula is as follows: （1）； in, is the breakdown field strength threshold, for Boost rate, For the withstand voltage time.

3. The method for predicting the remaining service life of a cable in the later period of operation according to claim 2, characterized in that: The calculation formula of the inverse power model in S3 is as follows: （2）； in, To apply external field strength, It is the cumulative damage required for the cable insulation to fail.

4. The method for predicting the remaining service life of a cable in the later period of operation according to claim 3, characterized in that: The life curve equation in S4 is as follows: （3）。 5. The method for predicting the remaining service life of a cable in the later period of operation according to claim 4, characterized in that: Voltage Withstand Index in S5 The calculation process is as follows: （4）。 6. The method for predicting the remaining service life of a cable in the later period of operation according to claim 5, characterized in that: Remaining life in S7 The expression is as follows: （6）； in, is the remaining life, is the operating field strength of sample group B.

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

8. The method for predicting the remaining service life of a cable in the later period of operation according to claim 7, 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.

9. The method for predicting the remaining service life of a cable in the later period of operation according to claim 8, characterized in that: In S8, the calculation results of the RID model were verified by the prediction results of the life curve equation, and the relative difference between the two ranged from 4.9% to 5%.

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