Double-time-scale medium-voltage distribution cable latent fault modeling method and system

Abstract

The invention provides a double-time-scale medium-voltage distribution cable latent fault modeling method and system, and the method comprises the steps: building a carbonization channel resistance model which takes a cable latent fault as a time scale, and comprises a carbonization channel resistance of a carbonization part and a solid dielectric breakdown resistance of a sound part; a step function is used to describe a carbonization channel resistance value with a cable latent fault as a time scale, and a first expression is obtained; describing the solid dielectric breakdown resistance of the sound part by adopting the three-stage model based on the relationship between the current flowing through the solid dielectric and the external voltage to obtain a second expression; and obtaining a medium-voltage distribution cable latent fault model based on the first expression and the second expression.

Description

Technical Field

[0001] The present invention belongs to the technical field of distribution network grounding fault modeling, and in particular relates to a dual-time-scale latent fault modeling method and system for medium-voltage distribution cables. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The distribution network is directly connected to the load and is an important infrastructure that affects people's well-being. However, the primary equipment of the distribution network is weak, the line structure is complex, and the operating environment is harsh, which makes the frequency of failures and abnormalities in the distribution network much higher than that in the transmission network. There are many types of latent fault problems in the distribution network and the mechanisms are complex. Conventional electrical mechanism analysis and probability statistics methods are difficult to play an effective role. Once these latent faults are not effectively handled, they often develop into permanent faults, causing more serious harm to the distribution network.

[0004] The operating experience of medium-voltage cables shows that before a permanent fault occurs, an instantaneous, self-recovering ground fault may occur at the same position of the cable. Since such faults last for a short time (1 / 4 to 4 power frequency cycles) and the fault current is small, traditional protection devices cannot be activated. This stage can be called a latent fault of the medium-voltage distribution cable. A considerable number of cable faults not caused by external forces evolve from latent faults. The key to avoiding serious harm caused by distribution cable faults is to seize the golden detection stage of "latent faults". At present, the industry has reached a consensus that there is a latent fault stage before a permanent fault occurs in the cable, but since there is no clear explanation for the evolution mechanism of latent faults, a widely recognized latent fault model for medium-voltage distribution cables has not yet been formed.

[0005] At present, in the identification and location algorithms of latent faults in medium-voltage distribution cables, the latent fault models used in medium-voltage distribution cables are mostly "black box" models based on thermodynamic theory, such as Mayr model, Cassie model, control theory model and Kizilcay model which has been widely used in recent years. However, these models are mainly derived from the characteristics of long arcs of high-resistance faults in open environments such as air, which are quite different from the environment where latent faults in medium-voltage distribution cables occur. Moreover, in the process of fault modeling, the parameters of the "black box" model are difficult to obtain from the external environment. In many current studies, they tend to set the parameters of the "black box" model to fit the nonlinear arc waveform, and then establish the fault model in the pure mathematical form of differential equations. This is also a manifestation of the "black box" model losing its physical meaning. However, in the transient transition process of the fault, the volt-ampere characteristics of the pure mathematical form of the "black box" model are not stable, and it is difficult to accurately obtain the voltage and current waveforms of the latent fault of the under-cycle cable. Summary of the invention

[0006] In order to overcome the deficiency of the above-mentioned prior art in the current lack of a latent fault model for medium-voltage distribution cables, the present invention provides a dual-time-scale latent fault modeling method for medium-voltage distribution cables, which utilizes dual-time-scale latent fault modeling of medium-voltage distribution cables based on fault mechanism, and realizes fault detection based on the constructed model.

[0007] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0008] In a first aspect, a dual-time-scale latent fault modeling method for medium-voltage distribution cables is disclosed, comprising:

[0009] A carbonization channel resistance model based on the time scale of cable latent fault is established, which includes the carbonization channel resistance of the carbonized part and the solid dielectric breakdown resistance of the sound part.

[0010] The first expression is obtained by using a step function to describe the carbonization channel resistance value with the cable latent fault as the time scale;

[0011] Based on the relationship between the current flowing through the solid dielectric and the applied voltage, the three-stage model is used to describe the solid dielectric breakdown resistance of the healthy part to obtain the second expression;

[0012] Based on the first expression and the second expression, a latent fault model of medium voltage distribution cables is obtained.

[0013] The fault model can be used to fit the actual measured fault waveform, and the fault simulation model that can be used for fault identification and location can be refined and summarized.

[0014] The dual time scale specifically refers to the carbonization channel resistance modeling with the number of fault occurrences as the time scale and the dynamic modeling of the solid breakdown resistance during each latent fault process, so as to fit the actual fault waveform.

[0015] As a further technical solution, the first expression is:

[0016]

[0017] Where A is the original resistance value of the carbonized part when no carbonization occurs, i is the number of occurrences of latent faults of medium-voltage distribution cables, ranging from 1 to n within the effective monitoring data range, A i is the reduction in the resistance of the cable carbonization channel of the ith latent fault of the medium-voltage distribution cable compared to the i-1th latent fault, t i is the time when the i-th latent fault of medium-voltage distribution cable occurs, ε(t) is a step function;

[0018] t iObtained from the experiment, A i is the model parameter, where the original resistance value A of the carbonized part can be given in advance and expressed as A 1 Correction for carbonized channel resistance.

[0019] As a further technical solution, based on the relationship between the current flowing through the solid dielectric and the applied voltage, it is divided into three regions, namely: region a, region b and region c;

[0020] In region a, the voltage and current are linearly related, in accordance with Ohm’s law;

[0021] In region b, the current and voltage have an exponential relationship;

[0022] In region c, the current and voltage have an exponential relationship.

[0023] As a further technical solution, the exponential relationship between the voltage and the current in the region b is approximated by a quadratic function;

[0024] In region c, the solid dielectric resistance R s It is already very small, and at this time it is mainly composed of the carbonized channel resistance R c It works, and it can be considered that the current and voltage of the solid dielectric in the healthy part are in a linear relationship.

[0025] As a further technical solution, in region c, the relationship between current and voltage is expressed by the following formula:

[0026]

[0027] In the formula, u s is the voltage across the solid dielectric of the healthy part, i s is the current flowing through the healthy part of the solid medium, u 1 and u 2 are the voltage dividing points between area a and area b, and area b and area c, respectively. 1 g 2 and k 1 k 2 k 3 k 4 All of them are waveform fitting parameters.

[0028] As a further technical solution, by passing the current i s For voltage u s Taking the derivative, we can get the conductivity g s The expression is as follows:

[0029]

[0030] Among them, u s is the voltage across the solid dielectric of the healthy part, u1 and u 2 are the voltage dividing points between area a and area b, and area b and area c, respectively. 1 g 2 and k 1 k 2 All of them are waveform fitting parameters.

[0031] As a further technical solution, the solid dielectric breakdown resistance of the sound part

[0032] Among them, g s For conductivity.

[0033] As a further technical solution, u s It is the partial pressure of the solid medium in the latent fault model of medium voltage distribution cable, which needs to be expressed by the following formula:

[0034]

[0035] Carbonization channel resistance R of the carbonized part c , g s is the conductivity, u.

[0036] As a further technical solution, the waveform fitting parameter k 1 k 2 k 3 k 4 It can be obtained from the continuity of current and conductance in equations (2) and (3), and the expression is as follows:

[0037]

[0038] Among them, u 1 and u 2 are the voltage dividing points between area a and area b, and area b and area c, respectively. 1 g 2 All of them are waveform fitting parameters.

[0039] As a further technical solution, during a single latent fault of a medium voltage distribution cable, the solid dielectric breakdown resistance R s By the model parameter u 1 u 2 and g 2 The proposed method is used to fit the nonlinear waveform of latent fault in medium voltage distribution cables.

[0040] In a second aspect, a dual-time-scale latent fault modeling system for medium-voltage distribution cables is disclosed, comprising:

[0041] The model building module is configured to: establish a carbonization channel resistance model with the cable latent fault as the time scale, including the carbonization channel resistance of the carbonized part and the solid dielectric breakdown resistance of the sound part;

[0042] The carbonized channel resistance value expression module is configured to: use a step function to describe the carbonized channel resistance value with the cable latent fault as the time scale to obtain a first expression;

[0043] The solid dielectric breakdown resistance expression module is configured to: based on the relationship between the current flowing through the solid dielectric and the applied voltage, describe the solid dielectric breakdown resistance of the healthy part using the three-stage model to obtain a second expression;

[0044] The fault prediction module is configured to obtain a latent fault model of a medium voltage distribution cable based on the first expression and the second expression.

[0045] One or more of the above technical solutions have the following beneficial effects:

[0046] Based on the carbonization process of medium-voltage distribution cable, the fault model is decomposed into two parts: carbonization channel resistance and solid dielectric breakdown resistance. Among them, the development of carbonization channel is a relatively long process. It is determined that the carbonization degree of the cable remains unchanged during a single cable latent fault, and the carbonization channel resistance is constant. As the number of latent faults of medium-voltage distribution cables increases, the carbonization channel resistance gradually decreases. The step function is used to describe the carbonization channel resistance value with the cable latent fault as the time scale; in view of the hysteresis phenomenon of volt-ampere characteristics and the instability of transient characteristics in the "black box" arc model, the dynamic solid dielectric breakdown resistance is obtained by simplifying the three-stage model of solid dielectric breakdown to describe the breakdown process of the healthy part. Finally, a dual-time scale medium-voltage distribution cable latent fault model based on the fault mechanism is established. The dual-time scale medium-voltage distribution cable latent fault model based on the fault mechanism is simulated based on simulation. The application environment of the black box model is long air gap arc breakdown. This model is proposed based on the principle of solid breakdown. There is no significant thermal effect, which is more in line with the cable latent fault environment.

[0047] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0049] Figure 1is a cable radial schematic diagram of the development of latent faults in medium voltage distribution cables proposed in the present disclosure;

[0050] Figure 2 is a radial schematic diagram of a cable with a permanent fault in the final evolution proposed by the present disclosure;

[0051] Figure 3 is a schematic diagram of an equivalent model of cable latent faults proposed in the present disclosure;

[0052] Figure 4 is a schematic diagram of the relationship between the solid dielectric current and the applied voltage used in the present disclosure;

[0053] Figure 5 It is the Simulink fault module designed by the present disclosure;

[0054] Figure 6 It is a 10kV medium voltage distribution network model with a neutral point grounded by a small resistor built by the present disclosure simulation;

[0055] Figure 7 (a)-(c) are respectively the voltage waveform, current waveform and fault equivalent impedance of the latent fault of the medium voltage distribution cable obtained by simulation of the present disclosure;

[0056] Figure 8 It is the volt-ampere characteristic curve of various latent fault models of medium voltage distribution cables provided in the present disclosure. DETAILED DESCRIPTION

[0057] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0058] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0059] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0060] Embodiment 1

[0061] This embodiment discloses a dual-time-scale latent fault modeling method for medium-voltage distribution cables, including:

[0062] Analyze the development mechanism of latent faults in medium voltage distribution cables;

[0063] A carbonization channel resistance model based on the time scale of cable latent fault is established, and the carbonization channel development process is described using a step function.

[0064] A solid dielectric breakdown resistance model describing the dynamic time-varying characteristics is established, and the nonlinear fault characteristics are described by simplifying the three-stage model of solid dielectric breakdown.

[0065] Among them, the development mechanism of latent faults of medium voltage distribution cables is analyzed as follows:

[0066] The latent fault process of distribution cables is a state between partial discharge of cables and permanent ground faults. Defects such as air gaps and burrs on the cable body and its accessories cause local electric field concentration, inducing partial discharge and tree growth, which leads to gradual insulation degradation. As the insulation degradation deepens, the defect position gradually carbonizes and discretely distributed carbonized spots appear in the insulation layer, and the resistance of the carbonized part gradually decreases.

[0067] like Figure 1 As shown in the figure, with the deepening of dendrite and carbonization, the part of the insulation layer of the cross-linked polyethylene (XLPE) cable that maintains sound insulation capacity gradually becomes thinner. At the same time, since the sound part bears the higher power frequency operating voltage, when the insulation capacity of the cable is reduced to a certain extent, the solid dielectric breakdown occurs in the sound part, that is, the cable latent fault occurs.

[0068] As the number of discharges increases, carbonized materials adhere to the surface of the discharge channel and accumulate, such as Figure 2 As shown in the figure, when the carbonized material completely penetrates the cable core and the grounded outer shielding layer, a carbonized channel is formed that runs through the two poles, causing a permanent grounding fault in the cable. Therefore, the latent fault model of the medium-voltage distribution cable can be decomposed into the carbonized channel resistance R c and the solid dielectric breakdown resistance R of the sound part s Two parts, the fault model is as follows Figure 3 shown.

[0069] Among them, the carbonization channel resistance model with cable latent fault as the time scale is established as follows:

[0070] Considering that the carbonization process is a long process, it can be considered that the carbonization degree of the cable remains unchanged during a single cable latent fault, and the carbonization channel resistance is constant. As the number of latent faults of the medium-voltage distribution cable increases, the carbonization channel resistance gradually decreases. Therefore, a step function can be used to describe the carbonization channel resistance value with the cable latent fault as the time scale. Then the carbonization channel resistance R c The expression is as follows:

[0071]

[0072] Where A is the original resistance value of the carbonized part when no carbonization occurs, i is the number of occurrences of latent faults of medium-voltage distribution cables, ranging from 1 to n within the effective monitoring data range, A iis the reduction in the resistance of the cable carbonization channel of the ith latent fault of the medium-voltage distribution cable compared to the i-1th latent fault, t i is the time when the i-th latent fault of the medium voltage distribution cable occurs, and ε(t) is a step function. i Obtained from the experiment, A i is the model parameter, where the original resistance value A of the carbonized part can be given in advance and expressed as A 1 The carbonization channel resistance is corrected, specifically by adjusting it through fitting the actual fault waveform.

[0073] Among them, the solid dielectric breakdown resistance model describing the dynamic time-varying characteristics is established as follows:

[0074] The relationship between the current flowing through a solid dielectric and the applied voltage is as follows Figure 4 As shown, when the voltage is within the range of region a, the electric field in the dielectric is low, the low electric field conductivity zone is dominated by ionic conductivity, and the voltage and current are linearly related, which conforms to Ohm's law; when the voltage is within the range of region b, the electric field in the dielectric increases, the electronic conductivity and ionic conductivity work together, and the current and voltage are exponentially related; when the voltage is within the range of region c, the dielectric presents a high electric field, the conductivity zone is dominated by electronic conductivity, and the current and voltage are exponentially related, which is the general sense of solid medium breakdown.

[0075] During the latent fault of the cable, the solid dielectric breakdown resistance R s The three-stage model can be used for description. For the convenience of calculation, the following simplifications can be made: the exponential relationship between voltage and current in region b can be approximated by a quadratic function, and the solid dielectric resistance R of the healthy part in region c is s Already very small, such as Figure 3 As shown, the carbonized channel resistance R c It can be considered that the current and voltage of the solid medium in the healthy part are in a linear relationship, and the relationship between current and voltage can be expressed by the following formula:

[0076]

[0077] In the formula, u s is the voltage across the solid dielectric of the healthy part, i s is the current flowing through the healthy part of the solid medium, u 1 and u 2 are the voltage dividing points between area a and area b, and area b and area c, respectively. 1 g 2 and k 1 k 2 k 3 k 4 All of them are waveform fitting parameters, passing through the current i s For voltage us Taking the derivative, we can get the conductivity g s The expression is as follows:

[0078]

[0079] The solid dielectric breakdown resistance of the healthy part is Please note s It is the partial pressure of the solid medium in the latent fault model of medium voltage distribution cable. It cannot be measured separately and needs to be expressed by the following formula:

[0080]

[0081] Waveform fitting parameter k 1 k 2 k 3 k 4 It can be obtained from the continuity of current and conductance in equations (2) and (3), and the expression is as follows:

[0082]

[0083] Since region 3 is mainly composed of carbonized channel resistance R c Works, parameter g 2 Can be given in advance and used with R c The complete fault model is modified. During a single latent fault of a medium voltage distribution cable, the solid dielectric breakdown resistance R s By the model parameter u 1 u 2 and g 2 The dielectric breakdown resistance is the reciprocal of gs in formula (5), and the relationship between gs and other parameters is given in formula (5).

[0084] In this implementation example, the fault model is decomposed into two parts, the carbonization channel resistance and the solid dielectric breakdown resistance, based on the carbonization process of the medium-voltage distribution cable. It is assumed that the carbonization channel resistance is constant during a single cable latent fault, and a step function is used to describe the carbonization channel resistance value with the cable latent fault as the time scale. The three-stage model of solid dielectric breakdown is simplified to establish a dynamic solid dielectric breakdown resistance for describing the breakdown process of the sound part. Finally, a dual-time-scale latent fault model of medium-voltage distribution cable based on the fault mechanism is established, and the fault model is simulated based on the matlab / Simulink system.

[0085] A dual-time-scale latent fault model of medium-voltage distribution cables based on fault mechanism was established through the Matlab / Simulink system.

[0086] A 10kV medium-voltage low-resistance grounded distribution network model was built in the matlab / Simulink environment, and the voltage waveform, fault current waveform and fault equivalent impedance of the fault model were obtained by simulation.

[0087] The volt-ampere characteristics of the proposed dual-time-scale latent fault model for medium-voltage distribution cables based on fault mechanism are compared with other "black box" models.

[0088] A dual-time-scale latent fault model for medium-voltage distribution cables based on fault mechanism was proposed and compared with other models under the same working conditions.

[0089] The following steps are involved:

[0090] Step S01: Construct a dual-time-scale latent fault model of medium-voltage distribution cables based on fault mechanism in the matlab / Simulink environment. Simulate a single latent fault of medium-voltage distribution cables. Given the carbonized channel resistance R c =500Ω, using the resistance module to represent the carbonization channel resistance, fault parameter g 1 =0.0002S, g 2 =0.01S,u 1 =500V,u 2 =8000V, use formula (2), formula (3) and formula (5) to calculate the model parameters, use the controlled current source to represent the nonlinear sound part of the solid dielectric breakdown resistance, the designed Simulink fault module is as follows Figure 5 shown.

[0091] Figure 5 In the simulink module of the fault model, ports 1 and 2 on the left are connected to the cable core and ground respectively. The resistance module is used to represent the carbonization channel resistance. The voltage and starting criteria are used as inputs to represent the dielectric breakdown dynamic resistance through a controlled current source controlled by a function. Considering the uncertainty and randomness of arc occurrence, the starting criteria is set by the impulse function generator, and the fault module is connected to the circuit through logical relationships and circuit breakers.

[0092] Step S02: Build the following in Matlab / Simulink environment: Figure 6The 10kV medium voltage low resistance grounding distribution network model shown in the figure has a system grounding resistance of 10Ω, and feeders L1 and L2 are cable lines of 10km and 8km respectively. The line parameters are as follows: positive sequence impedance Z1 = 0.27 + j0.08Ω / km; positive sequence admittance b1 = j118.12μS / km; zero sequence impedance Z0 = 2.7 + j0.35Ω / km; zero sequence admittance b0 = j86.71μS / km. The fault parameters of the latent fault of the distribution cable are set as in step S01. It is assumed that the latent fault of the cable occurs at a distance of 4km from the busbar on feeder L1, and the fault occurs at the peak of the operating voltage. The fault lasts for 4 cycles. The measured fault voltage waveform, fault current waveform and fault equivalent impedance are as follows: Figure 7 As shown in (a)-(c) in the figure, it can be found that the fault phase voltage changes slightly, the fault current has a good zero-break characteristic, and the voltage and current amplitudes are consistent with the latent fault characteristics of the medium-voltage distribution cable.

[0093] Step S03: Compare the volt-ampere characteristics of the proposed dual-time-scale medium-voltage distribution cable latent fault model based on fault mechanism with other “black box” models. Most of the “black box” models are derived based on the arc energy balance theory in gas medium. The principle is shown in formula (6):

[0094]

[0095] Among them, τ is the arc time constant, p is the arc power dissipation, u, i, g are the voltage at both ends of the arc, the arc current and the arc conductivity respectively. By introducing various restrictions on the parameters τ and p, the Cassie model, Mayr model, cybernetics model, etc. are deduced in turn. The Cassie model and the Mayr model are the two most important arc models. The Kizilcay arc model is developed from the cybernetics model and has been widely used in the field of latent fault modeling in recent years. The volt-ampere characteristic curves of the Cassie model, the Mayr model, the Kizilcay model and the dual-time-scale medium-voltage distribution cable latent fault model based on the fault mechanism disclosed in this disclosure are shown in Figure 2. Figure 8 As shown, since the "black box" model is mostly derived from the energy balance theory of arc breakdown in gas dielectrics, its arcing and arc extinction are obviously affected by the heat dissipation factor of the gas environment, which is manifested as the current change lags behind the voltage change during arcing and arc extinction, and the volt-ampere characteristic curves of the arcing and arc extinction processes do not overlap. Since the heat dissipation conditions of solid dielectrics are much better than those of gas dielectrics, the volt-ampere characteristic curves of the arcing and arc extinction processes should be similar. The dual-time scale latent fault model replacement of medium-voltage distribution cables based on fault mechanism proposed in the present disclosure is in line with the actual situation; at the same time, Figure 8It can be seen that the "black box" model has large distortion in the transient state of the fault, and the transient volt-ampere characteristics have large errors. The purely mathematical "black box" model is difficult to accurately simulate the latent fault of the under-cycle cable. The dual-time scale medium-voltage distribution cable latent fault model based on the fault mechanism proposed in the present invention has no transient distortion in the volt-ampere characteristics, and can effectively model the latent fault of the under-cycle cable from the perspective of the fault mechanism.

[0096] Embodiment 2

[0097] The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0098] Embodiment 3

[0099] The purpose of this embodiment is to provide a computer-readable storage medium.

[0100] A computer-readable storage medium stores a computer program, which executes the steps of the above method when executed by a processor.

[0101] Embodiment 4

[0102] The purpose of this embodiment is to provide a dual-time scale medium voltage distribution cable latent fault modeling system, including:

[0103] The model building module is configured to: establish a carbonization channel resistance model with the cable latent fault as the time scale, including the carbonization channel resistance of the carbonized part and the solid dielectric breakdown resistance of the sound part;

[0104] The carbonized channel resistance value expression module is configured to: use a step function to describe the carbonized channel resistance value with the cable latent fault as the time scale to obtain a first expression;

[0105] The solid dielectric breakdown resistance expression module is configured to: based on the relationship between the current flowing through the solid dielectric and the applied voltage, describe the solid dielectric breakdown resistance of the healthy part using the three-stage model to obtain a second expression;

[0106] The fault prediction module is configured to obtain a latent fault model of a medium voltage distribution cable based on the first expression and the second expression.

[0107] Embodiment 5

[0108] The purpose of this embodiment is to provide a computer program product containing instructions, which, when running on a computer, enables the computer to execute the methods and functions involved in any of the above embodiments.

[0109] The steps involved in the apparatus of the above embodiment correspond to the method embodiment 1, and the specific implementation method can refer to the relevant description part of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0110] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0111] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A dual-time-scale latent fault modeling method for medium-voltage distribution cables, characterized in that: include: A carbonization channel resistance model based on the time scale of cable latent fault is established, which includes the carbonization channel resistance of the carbonized part and the solid dielectric breakdown resistance of the sound part. The first expression is obtained by using a step function to describe the carbonization channel resistance value with the cable latent fault as the time scale; Based on the relationship between the current flowing through the solid dielectric and the applied voltage, the three-stage model is used to describe the solid dielectric breakdown resistance of the healthy part to obtain the second expression; Based on the first expression and the second expression, a latent fault model of medium voltage distribution cables is obtained.

2. A dual-time-scale latent fault modeling method for medium-voltage distribution cables according to claim 1, characterized in that: The first expression is: Where A is the original resistance value of the carbonized part when no carbonization occurs, i is the number of occurrences of latent faults of medium-voltage distribution cables, ranging from 1 to n within the effective monitoring data range, A i is the reduction in the resistance of the cable carbonization channel of the ith latent fault of the medium-voltage distribution cable compared to the i-1th latent fault, t i is the time when the i-th latent fault of medium-voltage distribution cable occurs, ε(t) is a step function; t i Obtained from the experiment, A i is the model parameter, where the original resistance value A of the carbonized part can be given in advance, and A1 is used to correct the carbonized channel resistance.

3. A dual-time-scale latent fault modeling method for medium-voltage distribution cables according to claim 1, characterized in that: Based on the relationship between the current flowing through the solid dielectric and the applied voltage, it is divided into three regions: region a, region b and region c; In region a, the voltage and current are linearly related, in accordance with Ohm’s law; In region b, the current and voltage have an exponential relationship; In region c, the current and voltage have an exponential relationship.

4. A dual-time-scale latent fault modeling method for medium-voltage distribution cables as claimed in claim 3, characterized in that: The exponential relationship between voltage and current in the region b is approximated by a quadratic function; In region c, the solid dielectric resistance R s It is already very small, and at this time it is mainly composed of the carbonized channel resistance R c It works, and it can be considered that the current and voltage of the solid dielectric in the healthy part are in a linear relationship.

5. A dual-time-scale latent fault modeling method for medium-voltage distribution cables as claimed in claim 4, characterized in that: In region c, the relationship between current and voltage is expressed by the following equation: In the formula, u s is the voltage across the solid dielectric of the healthy part, i s is the current flowing through the healthy part of the solid medium, u1 and u2 are the voltage dividing points between area a and area b, and area b and area c respectively, g1 g2 and k1 k2 k3 k4 are all waveform fitting parameters.

6. A dual-time-scale latent fault modeling method for medium-voltage distribution cables as claimed in claim 5, characterized in that: The current i s For voltage u s Taking the derivative, we can get the conductivity g s The expression is as follows: Among them, u s To improve the voltage across some solid dielectrics, u1 and u2 are the voltage dividing points between area a and area b, and area b and area c, respectively. g1 g2 and k1 k2 are waveform fitting parameters. Solid dielectric breakdown resistance of the healthy part The complete expression is as follows: Preferably, u s It is the partial pressure of the solid medium in the latent fault model of medium voltage distribution cable, which needs to be expressed by the following formula: Carbonization channel resistance R of the carbonized part c , g s is the conductance, u is the voltage across the fault model; Preferably, the waveform fitting parameters k1 k2 k3 k4 can be obtained from the continuity of current and conductance in equations (2) and (3), and the expressions are as follows: Among them, u1 and u2 are the voltage dividing points between area a and area b, and area b and area c respectively, and g1g2 are waveform fitting parameters; Preferably, during a single latent fault of a medium voltage distribution cable, the solid dielectric breakdown resistance R s It is determined by the model parameters u1u2 and g2 and is used to fit the nonlinear waveform of latent faults in medium voltage distribution cables.

7. A dual-time-scale latent fault modeling system for medium-voltage distribution cables, characterized in that: include: The model building module is configured to: establish a carbonization channel resistance model with the cable latent fault as the time scale, including the carbonization channel resistance of the carbonized part and the solid dielectric breakdown resistance of the sound part; The carbonized channel resistance value expression module is configured to: use a step function to describe the carbonized channel resistance value with the cable latent fault as the time scale to obtain a first expression; The solid dielectric breakdown resistance expression module is configured to: based on the relationship between the current flowing through the solid dielectric and the applied voltage, describe the solid dielectric breakdown resistance of the healthy part using the three-stage model to obtain a second expression; The fault prediction module is configured to obtain a latent fault model of a medium voltage distribution cable based on the first expression and the second expression.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps of the method described in any one of claims 1 to 6 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method described in any one of claims 1 to 6 are performed.

Images