A method for predicting the remaining life of an in-service cable driven by current and temperature and a maintenance method

Abstract

The present invention discloses a method for predicting the remaining life of an in-service cable driven by current and temperature and a maintenance method in the technical field of reliability engineering. The method includes: obtaining the inspection data of the in-service cable, including the cable surface temperature, ambient humidity, armor temperature, and load current; inputting the relevant data into a pre-constructed cable equivalent thermal circuit model for iterative calculation to obtain the cable conductor temperature; calculating the heat loss factor based on the difference between the cable conductor temperature and the cable conductor temperature under the preset ideal state, and combining the design life, actual operation years, and heat loss factor of the cable to obtain the corresponding remaining life of the cable; using the inspection data and the remaining life of the cable to establish a dataset of the remaining life of the cable, and combining the rated current-carrying capacity of the in-service cable, inputting the dataset of the remaining life of the cable and the corresponding ambient humidity into a grey prediction model to obtain the predicted value of the remaining life of the cable. The present invention can quantitatively evaluate the degree of cable aging and optimize operation and maintenance management.

Description

Technical Field

[0001] The present invention relates to a method for predicting the remaining life of an in-service cable driven by current and temperature and a maintenance method, belonging to the technical field of reliability engineering. Background Art

[0002] With the continuous increase in the number of in-service cables and the growth of the cable operation years, it is very necessary to evaluate the status and predict the life of cross-linked polyethylene cables. Currently, the mainstream cable status evaluation mainly focuses on real-time monitoring of various operating parameters of power cables, such as voltage, temperature, etc., aiming to identify potential faults and issue early warnings in a timely manner. Through the diagnostic functions of these monitoring systems, necessary reliability and safety measures can be taken after a fault is detected.

[0003] In addition, in addition to the monitoring function, through statistical analysis of on-line monitoring data, a more comprehensive understanding of the cable operation status and its load characteristics can be obtained. However, although the existing monitoring and analysis methods can help identify faults and ensure operation, there is currently no method that can evaluate the remaining life of in-service cables, that is, the existing technologies can only monitor the current status and cannot predict how long the cable can operate safely. Therefore, there is an urgent need for a method to solve these problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for predicting the remaining life of an in-service cable driven by current and temperature and a maintenance method, which can solve the problems of inaccurate evaluation of the aging status of operating cables, lack of quantitative indicators, and inability to predict the remaining life in real time in the existing technologies.

[0005] To solve the above technical problems, the present invention is implemented by adopting the following technical solutions.

[0006] On the one hand, the present invention provides a method for predicting the remaining life of an in-service cable driven by current and temperature, including:

[0007] Obtain the inspection data of the in-service cable, where the inspection data includes the cable surface temperature, ambient humidity, armor temperature, and load current;

[0008] Input the cable surface temperature, armor temperature, and load current into a pre-constructed cable equivalent thermal circuit model for iterative calculation to obtain the cable conductor temperature;

[0009] Calculate the heat loss factor based on the difference between the cable conductor temperature and the cable conductor temperature under the preset ideal state;

[0010] Obtain the remaining life of the cable corresponding to the inspection data through the cable factory design life, actual operation years, and the heat loss factor. The expression of the remaining life of the cable is:

[0011] ;

[0012] Wherein, represents the designed life of the cable when it leaves the factory; represents the actual operation years of the cable; M represents the heat loss factor; represents the actual operation years;

[0013] Based on the cable surface temperature, armor temperature, load current in the inspection data and the corresponding remaining life of the cable, establish a dataset of the remaining life of the cable;

[0014] Combined with the rated current-carrying capacity of the in-service cable, input the dataset of the remaining life of the cable and the corresponding ambient humidity into a pre-constructed grey prediction model to obtain the predicted value of the remaining life of the cable.

[0015] Combined with the first aspect, further, input the cable surface temperature, armor temperature and load current into a pre-constructed cable equivalent thermal circuit model for iterative calculation to obtain the cable conductor temperature, including:

[0016] Based on the cable equivalent thermal circuit model, establish a temperature difference balance equation among the cable conductor, metal shielding layer, armor layer, cable surface temperature and ambient temperature;

[0017] Simultaneously solve the temperature difference balance equation to obtain temperature-related parameters, and the temperature-related parameters include the AC resistance of the cable conductor per unit length, the resistance loss factor of the metal shielding layer, the resistance loss factor of the armor layer and the thermal resistance of the air environment;

[0018] Correct the temperature-related parameters to obtain the corrected temperature-related parameters;

[0019] Substitute the corrected temperature-related parameters into the simultaneously established temperature difference balance equation, and update the cable conductor temperature through iterative calculation until the difference between the cable conductor temperatures of two adjacent iterations is less than a preset convergence judgment threshold, and output the final cable conductor temperature.

[0020] Combined with the first aspect, further, the expression for establishing the temperature difference balance equation among the cable conductor, metal shielding layer, armor layer, cable surface temperature and ambient temperature includes:

[0021] ;

[0022] ;

[0023] ;

[0024] ;

[0025] Wherein, Indicates the cable conductor temperature; Indicates the metal shielding layer temperature; Indicates the armored layer temperature; Indicates the cable surface temperature; Indicates the ambient temperature; Indicates the cable conductor loss; Indicates the dielectric loss of the insulation layer; Indicates the metal shielding layer resistance loss factor; Indicates the armored layer resistance loss factor; Indicates the thermal resistance of the insulation layer; Indicates the thermal resistance of the inner lining layer; Indicates the thermal resistance of the outer sheath; Indicates the thermal resistance of the air environment.

[0026] Combined with the first aspect, further, the expression for establishing the temperature difference balance equation among the cable conductor, metal shielding layer, armored layer, cable surface temperature and ambient temperature includes:

[0027] ;

[0028] ;

[0029] ;

[0030] ;

[0031] Wherein, Indicates the cable conductor temperature; Indicates the metal shielding layer temperature; Indicates the armored layer temperature; Indicates the cable surface temperature; Indicates the ambient temperature; Indicates the cable conductor loss; Indicates the dielectric loss of the insulation layer; Indicates the metal shielding layer resistance loss factor; Indicates the armored layer resistance loss factor; Indicates the thermal resistance of the insulation layer; Indicates the thermal resistance of the inner lining layer; Indicates the thermal resistance of the outer sheath; Indicates the thermal resistance of the air environment.

[0032] Combined with the first aspect, further, the temperature-related parameters are corrected to obtain the corrected temperature-related parameters, including:

[0033] The AC resistance of the cable conductor per unit length is corrected using the following expression:

[0034] ;

[0035] Among them, represents the AC resistance of the cable conductor per unit length after correction; represents the resistance temperature coefficient of the cable conductor; f represents the power supply frequency; represents the axial distance of the cable conductor; represents the diameter of the metal shielding layer; represents the DC resistance of the cable conductor at 20°C; represents the temperature of the cable conductor;

[0036] The resistance loss factor of the metal shielding layer is corrected using the following expression:

[0037] ;

[0038] Among them, represents the resistance loss factor of the metal shielding layer after correction; represents the resistivity of the metal shielding material; I represents the load current; represents the cross-sectional area of the metal shielding layer; represents the reactance of the metal shielding layer per unit length; represents the dielectric loss of the insulating layer; represents the thermal resistance of the insulating layer; represents the temperature of the metal shielding layer;

[0039] The resistance loss factor of the armor layer is corrected using the following expression:

[0040] ;

[0041] Among them, represents the resistance loss factor of the armor layer after correction; represents the intermediate coefficient; represents the thickness of the armor layer; represents the diameter of the armor layer;

[0042] The thermal resistance of the air environment is corrected using the following expression:

[0043] ;

[0044] Among them, represents the thermal resistance of the air environment after correction; h represents the heat dissipation coefficient; represents the outer diameter of the cable; represents the temperature difference between the cable surface temperature and the ambient temperature; represents the ambient temperature; represents the cable conductor loss; represents the thermal resistance of the inner lining layer; represents the thermal resistance of the outer sheath.

[0045] Combined with the first aspect, further, substituting the corrected temperature-related parameters into the established temperature difference balance equation, and updating the cable conductor temperature through iterative calculation, including:

[0046] Based on the established temperature difference balance equation and the corrected temperature-related parameters, updating the cable conductor temperature by using the following expression:

[0047] ;

[0048] where, represents the heat dissipation coefficient; represents the outer diameter of the cable; represents the cable conductor temperature; represents the ambient temperature; represents the thermal resistance of the insulation layer; represents the cable conductor loss; represents the dielectric loss of the insulation layer; represents the thermal resistance of the inner lining layer; represents the corrected metal shielding layer resistance loss factor; represents the corrected armor layer resistance loss factor; represents the thermal resistance of the outer sheath; represents the corrected air environment thermal resistance; represents the metal shielding layer resistance loss factor; represents the armor layer resistance loss factor.

[0049] Combined with the first aspect, further, the expression of the heat loss factor is as follows:

[0050] ;

[0051] where, represents the heat loss factor; is the cable conductor temperature; is the cable conductor temperature under ideal conditions.

[0052] Combined with the first aspect, further, combining the rated current-carrying capacity of the in-service cable, inputting the cable remaining life dataset and the corresponding ambient humidity into the pre-constructed grey prediction model, and obtaining the predicted value of the cable remaining life, including:

[0053] Taking the cable remaining life in the cable remaining life dataset as the characteristic data sequence, taking the cable surface temperature, ambient humidity, armor temperature, load current and rated current-carrying capacity as the related factor sequences, and accumulating the characteristic data sequence and the related factor sequences to obtain the accumulated generating sequence;

[0054] Select the average value of two adjacent terms in the cumulative generating sequence as the background value;

[0055] Based on the cumulative generating sequence and the related factor sequence, establish a white micro equation between the characteristic data sequence and the related factor sequence, and replace the cumulative generating sequence in the white micro equation with the background value to obtain a grey micro equation;

[0056] Based on the grey micro equation, solve the grey coefficient by the least squares method and establish a grey prediction model;

[0057] Input the related factor sequence into the grey prediction model to obtain the predicted value of the remaining life of the cable.

[0058] Combined with the first aspect, further, the calculation expression of the background value is:

[0059] ;

[0060] where, represents the background value of the characteristic data sequence; represents the th data value at the first time step in the cumulative generating sequence; represents the th data value at the first time step in the cumulative generating sequence.

[0061] Combined with the first aspect, further, the calculation expression of the predicted value of the remaining life of the cable includes:

[0062] ;

[0063] where, represents the th predicted value at the first time step of the original characteristic data sequence; represents the th predicted value at the first time step of the cumulative generating sequence in the characteristic data sequence; represents the th predicted value at the first time step of the cumulative generating sequence in the characteristic data sequence.

[0064] In the second aspect, a method for maintaining an in-service cable driven by current and temperature includes:

[0065] Adopt the method described in the first aspect to obtain the predicted value of the remaining life of the cable;

[0066] In response to the predicted value of the remaining life of the cable being between 30% and 45% of the preset cable life limit value, pay attention to the in-service cable;

[0067] When the predicted value of the remaining life of the cable is between 20% and 30% of the preset cable life limit value, monitor and maintain the in-service cable.

[0068] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0069] By comprehensively considering the cable surface temperature, ambient humidity, armor temperature, and load current in the inspection data, and combining the pre-constructed cable equivalent thermal circuit model and grey prediction model, the present invention realizes the accurate prediction of the remaining life of the in-service cable.

[0070] The present invention uses the equivalent thermal circuit model to iteratively calculate the conductor temperature. By dynamically correcting the AC resistance per unit length of the conductor, the loss factor of the metal shielding layer, the loss factor of the armor layer, and the thermal resistance of the air environment, it effectively overcomes the error problem caused by the traditional method relying on manual experience, and significantly improves the objectivity and accuracy of temperature calculation. At the same time, by introducing a heat loss factor to quantify the degree of cable aging, combined with the factory design life and the actual operation years, it can intuitively reflect the remaining life of the cable, and solves the problem of the lack of quantitative evaluation indicators in the prior art. In addition, the grey prediction model constructed based on historical inspection data not only greatly reduces the time for iterative calculation of the complex thermal circuit model (such as the time-consuming of a conventional computer is reduced from 20 minutes to real-time prediction), but also further optimizes the reliability of the prediction results through the collaborative analysis of ambient humidity and rated current-carrying capacity. Description of the Drawings

[0071] Figure 1 The figure shows a schematic flow chart of a method for predicting the remaining life of an in-service cable driven by current and temperature provided by an embodiment of the present invention;

[0072] Figure 2 The figure shows a schematic diagram of the installation position of the RFID temperature measurement chip provided by an embodiment of the present invention;

[0073] Figure 3 The figure shows a schematic diagram of the equivalent thermal circuit model of a three-core cable provided by an embodiment of the present invention;

[0074] In the figure: 1, cable conductor; 2, insulating layer; 3, metal shielding layer; 4, filling layer; 5, armor layer; 6, outer sheath; 7, RFID temperature measurement chip. Detailed Embodiments

[0075] The technical solution of the present invention will be described in detail below through the drawings and specific embodiments. It should be understood that the specific features in the embodiments of the present invention are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. Without conflict, the technical features in the embodiments of the present invention and the embodiments can be combined with each other.

[0076] The term "and / or" is merely a description of the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, the character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0077] When evaluating the status of power grid cables currently, it mainly relies on human experience to judge online monitoring data such as temperature, current, voltage, etc. The said human experience has the following disadvantages:

[0078] 1. Judging by human experience will cause subjective errors and lack unified and quantitative objective evaluation indicators;

[0079] 2. The internal operation of the cable well is harsh. Factors such as humidity, water accumulation, and high temperature affect the normal operation of online monitoring equipment, resulting in unreliable online monitoring data and making the existing online monitoring data unable to fully reflect the actual operation situation inside the cable well.

[0080] Secondly, there is usually manual daily inspection of cable wells and cable trenches on-site. However, the data obtained during the current cable operation and maintenance inspection process, such as temperature and load current, are not fully utilized and thus cannot be directly used to guide cable operation and maintenance.

[0081] Embodiment 1

[0082] See Figure 1 , which is a schematic flow diagram of a method for predicting the remaining life of in-service cables driven by current and temperature provided by an embodiment of the present invention. This method provides a scientific basis for the operation and maintenance management of cables by comprehensively considering the operation status and aging degree of cables, and includes the following steps:

[0083] Step S1: Obtain the inspection data of in-service cables, where the inspection data includes the surface temperature of the cable, ambient humidity, armor temperature, and load current;

[0084] Step S2: Input the surface temperature of the cable, armor temperature, and load current into a pre-constructed equivalent thermal circuit model of the cable for iterative calculation to obtain the conductor temperature of the cable;

[0085] Here, the embodiment of the present invention uses a three-core cable equivalent thermal circuit model to simulate the heat transfer mechanism inside the cable, including the heat transfer process between the cable conductor 1, insulation layer 2, metal shielding layer 3, filling layer 4, armor layer 5, and outer sheath 6. Through the equivalent thermal circuit model, the complex heat transfer process can be simplified into an equivalent circuit. For details, see Figure 3 , where the circuit contains elements such as thermal resistance and heat capacity, which is convenient for mathematical modeling and calculation, so as to accurately simulate the temperature distribution of the cable under different conditions.

[0086] Step S3: Calculate the heat loss factor based on the difference between the cable conductor temperature and the cable conductor temperature under the preset ideal state;

[0087] Here, the heat loss factor is an important indicator for measuring the degree of cable aging, reflecting the additional heat loss caused by factors such as insulation material aging and increased loss. The introduction of this factor makes the assessment of the cable aging state more quantitative and accurate.

[0088] Step S4: Obtain the remaining life of the cable corresponding to the inspection data through the factory design life of the cable, the actual operation years, and the heat loss factor;

[0089] Step S5: Based on the cable surface temperature, armor temperature, load current in the inspection data, and the corresponding remaining life of the cable, establish a remaining life dataset of the cable;

[0090] Step S6: Combine the rated current-carrying capacity of the in-service cable, input the remaining life dataset of the cable and the corresponding environmental humidity into the pre-constructed grey prediction model, and obtain the predicted value of the remaining life of the cable.

[0091] Here, the environmental humidity and the rated current-carrying capacity are used as auxiliary inputs of the model and are input into the pre-constructed grey prediction model together with the remaining life dataset of the cable, further optimizing the reliability of the prediction result.

[0092] In addition, the grey prediction model adopted in the embodiment of the present invention is the GM(1, n) model, where 1 indicates that there is one characteristic data sequence in the model, such as the remaining life of the cable; n indicates that there are n related factors, such as the cable surface temperature, load current, etc. This model can effectively handle the uncertainty and incompleteness of data, and is particularly suitable for complex prediction problems such as the remaining life of cables affected by multiple factors.

[0093] To sum up, the embodiment of the present invention not only considers the actual operation state of the cable, but also combines the quantitative index of the aging degree, realizes the dynamic assessment and prediction of the remaining life of the cable, effectively guides the operation and maintenance work of the cable, and improves the reliability and safety of the power system.

[0094] Embodiment 2

[0095] To improve the accuracy of the input parameters of the remaining life assessment model in Embodiment 1, the acquisition method of the armor temperature data is optimized in this embodiment.

[0096] See Figure 2, which is a schematic diagram of the installation position of the RFID temperature measuring chip 7 provided in an embodiment of the present invention, the cable conductor temperature is obtained by inputting the armor temperature obtained by the RFID temperature measuring chip 7 built into the armor layer 5 of the cable, the cable surface temperature, and the load current obtained by retrieving the operation data of the control system into the cable equivalent thermal circuit model for iterative calculation.

[0097] The specific steps of obtaining the cable conductor temperature through iterative calculation are as follows:

[0098] Step S31, based on the cable equivalent thermal circuit model, establishing a temperature difference balance equation among the cable conductor 1, the metal shielding layer 3, the armor layer 5, the cable surface temperature and the ambient temperature;

[0099] The expression of the temperature difference balance equation is:

[0100] ; (1)

[0101] ; (2)

[0102] ; (3)

[0103] ; (4)

[0104] in, Indicates the cable conductor temperature; Indicates the temperature of the metal shielding layer; Indicates the armor layer temperature; Indicates the cable surface temperature; Indicates the ambient temperature; Indicates cable conductor loss; Indicates dielectric loss of insulation layer; Indicates the resistance loss factor of the metal shielding layer; Indicates the armor layer resistance loss factor; Indicates the thermal resistance of the insulation layer; Indicates the thermal resistance of the lining; Indicates the thermal resistance of the outer sheath; Represents the air-to-ambient thermal resistance.

[0105] Due to the bidirectionality of the heat path, the temperature balance equations (1) to (4) are combined to obtain the conductor temperature Armor layer temperature The quantitative relationship between them is the key to evaluating the thermal state and remaining life of the cable, and its expression is:

[0106] (5)

[0107] It should be noted that since the metal shielding layer 3 is located outside the insulating layer 2, the heat will pass through the insulating layer when it is transferred from the conductor to the metal shielding layer 3, so the temperature of the metal shielding layer It can indirectly reflect the temperature condition of the insulation layer.

[0108] Step S32: According to the temperature difference balance equations of formulas (1) to (4), the temperature-related parameters are solved simultaneously, and the temperature-related parameters include the AC resistance R per unit length of the cable conductor, the metal shielding resistance loss factor , Armor layer resistance loss factor And air-to-ambient thermal resistance ;

[0109] Step S33: According to the actual operating conditions of the cable, the AC resistance R of the cable conductor per unit length and the metal shielding resistance loss coefficient , Armor layer loss resistance factor And air-to-ambient thermal resistance Perform correction to obtain corrected temperature-related parameters;

[0110] Among them, the expressions of the corrected temperature-related parameters are:

[0111] a. Use the following expression to correct the AC resistance per unit length of cable conductor:

[0112] When calculating the AC resistance of a cable conductor per unit length, the DC resistance The calculation expression of the conductor temperature can be Obtained, its expression is:

[0113] (6)

[0114] in, Indicates the DC resistance of the cable conductor; It indicates the DC resistance coefficient of the cable conductor at 20℃; A indicates the cross-sectional area of ​​the cable conductor; Indicates the resistance temperature coefficient of the cable conductor; Indicates the twist coefficient, which is 1.024-1.05 for mobile cables and 1.01-1.012 for fixed cables; is the cabling coefficient, which is 1.029~1.17 for mobile cables and 1.002~1.011 for fixed cables; It is the compression effect coefficient, and the fixed cable installation value is 1.004~1.01.

[0115] Then, after combining formula (6) with the temperature difference balance equations (1) to (4), we get an algebraic expression for R, and the integrated expression is:

[0116] ; (7)

[0117] Among them, represents the AC resistance of the cable conductor per unit length after correction; represents the resistance temperature coefficient of the cable conductor; f represents the power supply frequency; represents the axial distance of the cable conductor; represents the diameter of the metal shielding layer; represents the DC resistance of the cable conductor at 20°C.

[0118] b. Correct the metal shielding layer resistance loss factor using the following expression:

[0119] When calculating the metal shielding layer loss factor, according to the temperature node relationship between different parts in the cable (such as cable conductor 1, metal shielding layer 3, etc.), it can be known that when the current is known, represents the temperature of the metal shielding layer and the conductor temperature The quantitative relationship of which is expressed as:

[0120] (8)

[0121] (9)

[0122] Combining formula (7) and formula (9), the corrected metal shielding layer resistance loss factor An algebraic expression of is as follows:

[0123] (10)

[0124] Among them, represents the corrected metal shielding layer resistance loss factor; represents the resistivity of the metal shielding material; I represents the load current; represents the cross-sectional area of the metal shielding layer; represents the reactance of the metal shielding layer per unit length; represents the load current.

[0125] Correct the armor layer resistance loss factor using the following expression:

[0126] Considering that the RFID temperature measurement chip 7 is mounted on the armor layer 5, the parameters of the armor layer 5 also need to be corrected to ensure the accuracy of the measurement. Through the corrected parameters, Regarding R An algebraic expression of is obtained:

[0127] (11)

[0128] in, Represents the corrected armor layer resistance loss factor; represents the intermediate coefficient; Indicates the thickness of the armor layer; Indicates the diameter of the armor layer.

[0129] Air-to-ambient thermal resistance:

[0130] When calculating the air environment thermal resistance, its definition is There is no way to calculate it directly. By combining formulas (1) to (4), we can get the air-ambient thermal resistance Cable surface temperature rise exceeding the cable surface temperature , which is the difference between the cable surface temperature and the ambient temperature, and its expression is:

[0131] (12)

[0132] in, Indicates the difference between the cable surface temperature and the surrounding environment temperature.

[0133] Then, the corrected air-to-ambient thermal resistance is It can be expressed as:

[0134] (13)

[0135] in, represents the corrected air environment thermal resistance; h represents the heat dissipation coefficient; Indicates the outer diameter of the cable; Indicates the temperature difference between the cable surface temperature and the ambient temperature.

[0136] It should be noted that due to For a given ambient temperature, are other parameters in the thermal circuit model, which can be calculated from known quantities. The expression of The algebraic expression of .

[0137] Step S34: Substitute the corrected temperature-related parameters into the combined temperature difference balance equations (Formulas (1) to (4)), and update the cable conductor temperature through iterative calculation until the difference between the cable conductor temperatures of two adjacent iterations is less than a preset convergence judgment threshold (the threshold can be 0.1°C), and output the final cable conductor temperature.

[0138] Therefore, the corrected cable conductor AC resistance R per unit length and metal shield resistance loss coefficient are , Armor layer loss resistance factor And air-to-ambient thermal resistance All four variables are affected only by The influence of one variable. Based on this, an equation relationship is established from equations (5)-(12), where there is only one variable , and finally the conductor temperature is calculated , the expression of the cable conductor temperature includes:

[0139] (14)

[0140] Furthermore, during the actual long-term operation, due to the continuous action of the thermal field and the electric field, the material properties will gradually deteriorate, which will in turn lead to a significant increase in insulation loss and other related losses, thereby intensifying the cable heating and making the temperature rise more obvious. To ensure the stability and safety of the cable system, it is necessary to fully consider the changes of the material in the actual operating environment, especially the influence of the degradation of its physical and electrical properties on the heat generation and temperature rise

[0141] In order to be able to dynamically and accurately evaluate the influence of the changes of these parameters on the current-carrying capacity, the embodiment of the present invention obtains a heat loss factor based on the normalized difference between the cable conductor temperature and the cable conductor temperature under the preset ideal state, and uses the heat loss factor as a quantitative index of the cable aging degree;

[0142] The heat loss factor M The calculation expression is:

[0143] (15)

[0144] Wherein, represents the heat loss factor; is the cable conductor temperature; is the cable conductor temperature under the ideal state, which can be taken as 60°C

[0145] Through the design life subtracting the actual operation years , and then subtracting the life loss part caused by heat loss (the product of the heat loss factor M and the design life), the remaining life of the cable corresponding to the inspection data can be obtained, and its expression is:

[0146] (16)

[0147] Wherein, is the design life of the cable when it leaves the factory; is the actual operation years of the cable; represents the remaining life of the cable

[0148] Embodiment 3

[0149] This embodiment provides a method for predicting the remaining life of an in-service cable. It is based on the same technical concept as Embodiment 1 and Embodiment 2. This embodiment is based on Embodiment 2 and further provides a detailed implementation step for realizing the rapid prediction of the remaining life of the cable based on historical inspection data and the grey prediction model, which is as follows:

[0150] Since the cable conductor temperature calculated in Embodiment 2 needs to be iterated hundreds of times through the thermal circuit model combined with the Newton-Raphson method, and it takes about 20 minutes to calculate with a conventional computer. In order to achieve a rapid and accurate prediction of the future value of the remaining life of the cable and reduce the calculation time, in this embodiment of the present invention, taking at least 100 sets of inspection data as an example, the steps of outputting the future predicted value of the remaining life of the cable include:

[0151] Step S71: Calculate the remaining life of the cable corresponding to the cable surface temperature, armor temperature, and load current in each set of inspection data to form a remaining life data set containing 100 sets of data;

[0152] The expression of this remaining life data set is:

[0153] (17)

[0154] Wherein, represents the remaining life data set; represents the armor layer temperature in the inspection data; represents the index of the inspection data group, that is, the 1st to 100th groups of inspection data.

[0155] It should be noted that each contains a set of inspection data (cable surface temperature, load current, etc.) and its corresponding remaining life value, which is used to train the grey model and achieve rapid life prediction.

[0156] Step S72: Take the remaining life in the cable remaining life data set as the characteristic data sequence; take the cable surface temperature, ambient humidity, armor temperature, load current, and rated current-carrying capacity as the relevant factor sequences , respectively; then perform accumulation on the characteristic data sequence and the relevant factor sequences to obtain an accumulated generating sequence;

[0157] The expression of this accumulated generating sequence is:

[0158] (18)

[0159] Wherein, represents the accumulated value of the th characteristic data sequence at the th data point; It represents the intermediate index in the accumulation process, that is, the accumulation from the first group of data to the k-th group of data; k represents the end index in the accumulated generated sequence, that is, the k-th accumulated value; It represents the sequence category index, that is is the characteristic data sequence, is the related factor sequence; It represents the total number of groups of inspection data; It represents the original data sequence; m represents the total number of sequences, including 1 characteristic data sequence and 5 related factor sequences.

[0160] Step S73: Select the average value of two adjacent terms in the accumulated generated sequence as the background value;

[0161] The expression of the background value is:

[0162] ; (19)

[0163] Among them, represents the background value of the characteristic data sequence; represents the -th data value at the first time step in the accumulated generated sequence; represents the -th data value at the first time step in the accumulated generated sequence.

[0164] Step S74: According to the accumulated generated sequence and the related factor sequence, establish a white micro-variation equation between the characteristic data sequence and the related factor sequence, and replace the accumulated generated sequence in the white micro-variation equation with the background value to obtain a grey micro-variation equation;

[0165] The expression of the white micro-variation equation is:

[0166] (20)

[0167] Among them, represents the derivative of the main variable accumulated generated sequence with respect to time t; represents the system development coefficient; represents the driving coefficient; represents the driving term.

[0168] Furthermore, the expression of the grey micro-variation equation obtained after replacing the background value is:

[0169] (21)

[0170] Among them, represents the original value of the remaining life of the cable corresponding to the k-th group of inspection data.

[0171] Step S75: Based on the grey weakening equation, solve the grey coefficients by the least square method and establish a grey prediction model. Among them, the grey coefficients include the system development coefficient and the driving coefficient , and this coefficient is used to quantify the influence degree of relevant factors on the characteristic data sequence. That is, if , it indicates that the remaining life shows a decaying trend; if , it indicates that the remaining life may be extended due to maintenance or load reduction; if , it indicates that a certain relevant factor has a positive influence on the remaining life. For example, an increase in the current-carrying capacity may extend the life; if , it indicates that a certain relevant factor has a negative influence on the remaining life. For example, high temperature and high humidity accelerate aging.

[0172] Denote the grey coefficients as A which is a vector, denoted as , and can be calculated by the following formula (24). The specific steps are as follows:

[0173] Step S751: Construct a data matrix B, which is composed of the accumulated generating sequence and the background value, and is used to represent the data relationship between the system characteristic factors and their related influencing factors. Its form is:

[0174] (22)

[0175] Among them, B represents the data matrix; represents the background value corresponding to the second group of inspection data; represents the background value corresponding to the third group of inspection data; represents the background value corresponding to the nth group of inspection data; represents the accumulated generating sequence of the first influencing factor (such as the cable surface temperature) of the second group of inspection data; represents the accumulated generating sequence of the first influencing factor (such as the cable surface temperature) of the third group of inspection data; represents the accumulated generating sequence of the first influencing factor (such as the cable surface temperature) of the nth group of inspection data; represents the accumulated generating sequence of the Nth influencing factor (such as the environmental humidity) of the second group of inspection data; represents the accumulated generating sequence of the Nth influencing factor (such as the environmental humidity) of the third group of inspection data; represents the accumulated generating sequence of the Nth influencing factor (such as the environmental humidity) of the nth group of inspection data.

[0176] Step S752: Construct a constant term vector , and its form is:

[0177] (23)

[0178] Among them, represents the constant term vector; represents the value of the original data sequence of the characteristic data sequence (remaining life of the cable) at the second inspection; represents the value of the original data sequence of the characteristic data sequence (remaining life of the cable) at the third inspection; represents the value of the original data sequence of the characteristic data sequence (remaining life of the cable) at the nth inspection.

[0179] Step S753: Through matrix operations, use the least squares method to solve the grey coefficient A, and the formula is:

[0180] (24)

[0181] Among them, represents the transpose of the data matrix B.

[0182] This step is a key part in the process of establishing the grey prediction model. The model is trained with historical data to obtain the grey coefficient that can be used for prediction.

[0183] Step S76: Substitute the grey coefficient into the grey differential equation to obtain the grey prediction model, and input the relevant factor sequence into the established grey prediction model to obtain the future prediction value of the remaining life of the cable.

[0184] The grey prediction model provided by the embodiment of the present invention, such as the G(1, n) model, can predict the prediction value of the remaining life of the cable through the determined grey coefficient, and its calculation expression is:

[0185] (25)

[0186] Among them, represents the th prediction value of the first time step of the original characteristic data sequence; represents the th prediction value of the first time step of the accumulated generating sequence in the characteristic data sequence; represents the th prediction value of the first time step of the accumulated generating sequence in the characteristic data sequence.

[0187] Embodiment 4

[0188] The embodiment of the present invention provides a method for maintaining an in-service cable driven by current and temperature, including:

[0189] Adopt the method described in any one of Embodiments 1 to 3 to obtain the prediction value of the remaining life of the cable;

[0190] According to different intervals in which the predicted value is located, corresponding maintenance measures are taken for the in-service cable:

[0191] In response to the predicted value of the remaining life of the cable being between 30% and 45% of the preset cable life limit value, it indicates that although the cable has not reached the level that requires immediate maintenance, it has entered a stage that needs to be closely monitored. At this time, attention measures are taken for the in-service cable, the inspection frequency is increased, and the operation status and changes in relevant parameters are closely monitored to promptly detect possible problems and take corresponding measures.

[0192] In response to the predicted value of the remaining life of the cable being between 20% and 30% of the preset cable life limit value, it shows that the remaining life of the cable is already relatively low and the potential failure risk increases. At this time, more stringent monitoring and maintenance are carried out on the in-service cable, including detailed inspection of the cable, assessment of its health status, and necessary repair or replacement according to the inspection results to prevent serious impacts on the power system caused by cable failures.

[0193] Embodiment 5

[0194] In this embodiment, according to the methods described in Embodiments 1 to 4, taking the cable wells on a certain road as an example, the life assessments of three cables A, B, and C in the cable wells are carried out, and the calculation process and results are as shown in Tables 1 and 2 below:

[0195] Table 1 Inspection data

[0196]

[0197] Table 2 Evaluation results

[0198]

[0199] According to the evaluation results, it can be seen that the operating life of Cable B is significantly lower than that of Cables A and C. On-site operation and maintenance found that it is because Cable B has been in a state of being soaked in accumulated water for a long time, resulting in the moisture absorption of the insulating layer 2 and the corrosion of metal components, accelerating the cable aging. At this time, the further adverse effects on the cable include:

[0200] Decrease in insulation performance: Moisture intrusion into the cross-linked polyethylene (XLPE) insulating layer causes partial discharge and electrical tree aging;

[0201] Increase in thermal resistance: The accumulated water hinders heat dissipation, resulting in abnormal cable core temperature (for example, the surface temperature of Cable B is 31.06°C, lower than 32.53°C of Cables A / C, which may be due to the accumulated water preventing effective heat dissipation);

[0202] Current-carrying capacity decline: The rated current-carrying capacity of Cable B (633.13 A) is significantly lower than that of Cable A (674.46 A), reflecting that its actual load-bearing capacity has decreased due to aging. Although the humidity of Cable B (76.63%) in a single inspection is not much different from that of Cables A / C (77.32%), the GM(1,n) grey prediction model captures the cumulative impact of long-term humidity fluctuations on the lifespan through the cumulative analysis of historical data.

[0203] For example, the periodic humidity peaks caused by water accumulation may be identified by the model in the historical data. In the calculation formula of the heat loss factor M, the conductor temperature of the cable is affected by the poor heat dissipation caused by water accumulation, and the actual value deviates from the ideal state ( =60 °C), thus increasing M and shortening the remaining lifespan. The armored temperature of Cable B (31.25 °C) is lower than that of Cables A / C (33.24 °C, 33.34 °C), which may be due to the blocked heat conduction caused by water accumulation and the distortion of the surface temperature. At the same time, its load current (28.18 A) is within the normal range, but combined with the decline in current-carrying capacity (633.13 A), it indicates that the cable can no longer safely carry the designed current. The model dynamically adjusts the driving coefficient by inputting multiple parameters such as humidity, temperature, and current , and quantifies the negative impact of water accumulation on the lifespan.

[0204] The remaining lifespan of Cable B (26.786 years) is significantly lower than that of Cables A / C (27.743 years, 27.673 years), which directly reflects its aging degree. The output result of the model provides a clear basis for operation and maintenance, such as preferentially inspecting Cable B or improving its operating environment (such as drainage measures).

[0205] In summary, the method of the present invention can quickly identify Cable B as a high-risk object, formulate replacement or repair plans in combination with the remaining lifespan prediction, and dynamically update the prediction results by regularly inputting new inspection data to achieve preventive maintenance.

[0206] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit and scope protected by the claims of the present invention. These all fall within the protection scope of the present invention.

Claims

1. A current and temperature driven method for predicting the remaining life of an in-service cable, characterized in that: include: Obtaining inspection data of the in-service cables, the inspection data including cable surface temperature, ambient humidity, armor temperature and load current; The cable surface temperature, armor temperature and load current are input into a pre-constructed cable equivalent thermal circuit model for iterative calculation to obtain the cable conductor temperature; wherein, based on the cable equivalent thermal circuit model, a temperature difference balance equation is established between the cable conductor (1), the metal shielding layer (3), the armor layer (5), the cable surface temperature and the ambient temperature; the temperature difference balance equation is solved jointly to obtain temperature-related parameters, wherein the temperature-related parameters include the AC resistance of the cable conductor per unit length, the metal shielding resistance loss factor, the armor layer resistance loss factor and the air environment thermal resistance; the temperature-related parameters are corrected to obtain corrected temperature-related parameters; the corrected temperature-related parameters are substituted into the combined temperature difference balance equation, the cable conductor temperature is updated through iterative calculation, until the difference between the cable conductor temperatures of two adjacent iterations is less than a preset convergence judgment threshold, and the final cable conductor temperature is output; Calculating a heat loss factor based on a difference between the cable conductor temperature and the cable conductor temperature under a preset ideal state; The remaining life of the cable corresponding to the inspection data is obtained by the factory design life of the cable, the actual operating life and the heat loss factor. The expression of the remaining life of the cable is: ； in, Indicates the design life of the cable when it leaves the factory; Indicates the actual service life of the cable; M indicates the heat loss factor; Indicates the actual operating years; Establishing a cable remaining life data set based on the cable surface temperature, armor temperature, load current and corresponding cable remaining life in the inspection data; Combined with the rated current carrying capacity of the cables in service, the cable remaining life data set and the corresponding ambient humidity are input into a pre-built grey prediction model to obtain the predicted value of the cable remaining life.

2. The current and temperature driven remaining life prediction method for in-service cables according to claim 1 is characterized in that: The expression for establishing the temperature difference balance equation between the cable conductor (1), the metal shielding layer (3), the armor layer (5), the cable surface temperature and the ambient temperature comprises: ； ； ； ； in, Indicates the cable conductor temperature; Indicates the temperature of the metal shielding layer; Indicates the armor layer temperature; Indicates the cable surface temperature; Indicates the ambient temperature; Indicates cable conductor loss; Indicates dielectric loss of insulation layer; Indicates the resistance loss factor of the metal shielding layer; Indicates the armor layer resistance loss factor; Indicates the thermal resistance of the insulation layer; Indicates the thermal resistance of the lining; Indicates the thermal resistance of the outer sheath; Represents the air-to-ambient thermal resistance.

3. The current and temperature driven remaining life prediction method for in-service cables according to claim 1 is characterized in that: Correcting the temperature-related parameters to obtain corrected temperature-related parameters includes: Use the following expression to correct the AC resistance per unit length of cable conductor: ； in, It represents the corrected AC resistance per unit length of cable conductor; Indicates the resistance temperature coefficient of the cable conductor; f Indicates the power supply frequency; Indicates the axial distance of the cable conductor; Indicates the diameter of the metal shield; Indicates the DC resistance of the cable conductor at 20°C; Indicates the cable conductor temperature; The metal shielding layer resistance loss factor is corrected using the following expression: ； in, It represents the corrected metal shielding layer resistance loss factor; represents the resistivity of metal shielding material; I represents the load current; Indicates the cross-sectional area of ​​the metal shielding layer; It represents the reactance of the metal shield per unit length; Indicates dielectric loss of insulation layer; Indicates the thermal resistance of the insulation layer; Indicates the temperature of the metal shielding layer The armor layer resistance loss factor is corrected using the following expression: ； in, Represents the corrected armor layer resistance loss factor; represents the intermediate coefficient; Indicates the thickness of the armor layer; Indicates the diameter of the armor layer; Correct the air-to-ambient thermal resistance using the following expression: ； in, represents the corrected air environment thermal resistance; h represents the heat dissipation coefficient; Indicates the outer diameter of the cable; Indicates the temperature difference between the cable surface temperature and the ambient temperature; Indicates the ambient temperature; Indicates cable conductor loss; Indicates the thermal resistance of the lining; Indicates the thermal resistance of the outer sheath; Indicates the resistance loss factor of the metal shielding layer; Represents the armor layer resistance loss factor.

4. The current and temperature driven remaining life prediction method for in-service cables according to claim 1 is characterized in that: Substituting the corrected temperature-related parameters into the combined temperature difference balance equation, and updating the cable conductor temperature through iterative calculation, including: Based on the combined temperature balance equation and the corrected temperature-related parameters, the cable conductor temperature is updated using the following expression: ； Where, h represents the heat dissipation coefficient; Indicates the outer diameter of the cable; Indicates the cable conductor temperature; Indicates the ambient temperature; Indicates the thermal resistance of the insulation layer; Indicates cable conductor loss; Indicates dielectric loss of insulation layer; Indicates the thermal resistance of the lining; It represents the corrected metal shielding layer resistance loss factor; Represents the corrected armor layer resistance loss factor; Indicates the thermal resistance of the outer sheath; represents the corrected air-to-ambient thermal resistance.

5. The current and temperature driven remaining life prediction method for in-service cables according to claim 1 is characterized in that: The expression of the heat loss factor is as follows: ； Where M represents the heat loss factor; is the cable conductor temperature; is the cable conductor temperature under ideal conditions.

6. The current and temperature driven remaining life prediction method for in-service cables according to claim 1, characterized in that: The method combines the rated current carrying capacity of the in-service cable, inputs the cable remaining life data set and the corresponding ambient humidity into a pre-built grey prediction model, and obtains the predicted value of the cable remaining life, including: The remaining life of the cable in the remaining life data set of the cable is used as a characteristic data sequence, the surface temperature of the cable, the ambient humidity, the armor temperature, the load current and the rated current carrying capacity are used as a correlation factor sequence, and the characteristic data sequence and the correlation factor sequence are accumulated to obtain an accumulated generated sequence; Selecting the average value of two adjacent terms in the cumulative generated sequence as the background value; According to the cumulative generation sequence and the correlation factor sequence, a white micronization equation between the feature data sequence and the correlation factor sequence is established, and the cumulative generation sequence in the white micronization equation is replaced by the background value to obtain a gray micronization equation; Based on the gray micronization equation, the gray coefficient is solved by the least square method, and a gray prediction model is established; The related factor sequence is input into the grey prediction model to obtain the predicted value of the remaining life of the cable.

7. The current and temperature driven remaining service life prediction method for an in-service cable according to claim 6, characterized in that: The calculation expression of the background value is: ； in, Represents the background value of the feature data sequence; Indicates the first time step in the cumulative generated sequence. data values; Indicates the first time step in the cumulative generated sequence. data value.

8. The current and temperature driven remaining service life prediction method for in-service cables according to claim 6, characterized in that: The calculation expression of the predicted value of the remaining life of the cable includes: ； in, Represents the first time step of the original feature data sequence predicted values; Represents the first time step of the cumulative generated sequence in the feature data sequence predicted values; Represents the first time step of the cumulative generated sequence in the feature data sequence predicted value.

9. A current and temperature driven cable maintenance method in operation, characterized in that: include: The method according to any one of claims 1 to 8 is used to obtain a predicted value of the remaining life of the cable; In response to the predicted value of the remaining life of the cable being between 30% and 45% of the preset cable life limit, attention is paid to the cable in operation; In response to the predicted value of the remaining life of the cable being between 20% and 30% of the preset cable life limit, the in-service cable is monitored and repaired.

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