A modeling method and simulation circuit for grounding fault of high voltage cable intermediate joint

Abstract

The present invention relates to the technical field of high-voltage cable intermediate joints, and discloses a modeling method and simulation circuit for a grounding fault of a high-voltage cable intermediate joint. The method includes performing a cable intermediate joint XLPE-SiR insulation interface breakdown experiment based on the physical structure of a real high-voltage cable intermediate joint, and obtaining experimental circuit parameter data; obtaining the dielectric strength of the XLPE-SiR insulation interface gap, the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint, and the XLPE-SiR insulation equivalent interface breakdown resistance; designing a switching function that changes with changes in the interface breakdown voltage; and constructing a circuit equivalent model for the XLPE-SiR insulation interface breakdown of the cable intermediate joint. The present invention can be used to study the electrical characteristics of the XLPE-SiR insulation interface breakdown of a high-voltage cable joint; a person skilled in the art can obtain the current of the fault line through simulation calculation by using the circuit equivalent model.

Description

Technical Field

[0001] The invention relates to the technical field of high-voltage cable intermediate joints, and in particular to a method for modeling a grounding fault of a high-voltage cable intermediate joint. Background Art

[0002] The intermediate joint of high-voltage cables is an important accessory for realizing high-voltage cable connection and ensuring cable insulation. As the use of cables continues to increase, the number of intermediate joints of cables also increases. As the weak point in the power XLPE cable line, the probability of failure of the intermediate joint of the cable is much greater than that of the cable body. The main reason is that the complex XLPE-SiR insulation interface structure of the intermediate joint of the cable is easy to cause interface discharge. When the interface discharge reaches a certain level, it may cause arc breakdown, causing the cable core to short-circuit to the ground, releasing huge energy, and even causing fire and explosion accidents in the intermediate joint of the high-voltage cable in severe cases, causing harm to the surrounding cables and operation and maintenance personnel. Therefore, it is of great practical significance to study the electrical characteristics of the XLPE-SiR insulation interface breakdown of the high-voltage cable joint. Among them, XLPE is cross-linked polyethylene and SiR is silicone rubber.

[0003] At present, most of the research focuses on the characteristics of insulating materials, such as solid insulation breakdown, surface flashover, surface electrothermal ablation and electrical treeing. The research on the interface discharge and breakdown mechanism between two different insulating materials is relatively immature. Summary of the invention

[0004] The present invention aims to at least solve the technical problem that the prior art lacks research on the breakdown electrical characteristics of the XLPE-SiR insulation interface of a high-voltage cable joint.

[0005] To this end, an object of the present invention is to provide a method for modeling a grounding fault of a high-voltage cable intermediate joint, comprising:

[0006] Based on the physical structure of the real high-voltage cable intermediate joint, the cable intermediate joint XLPE-SiR insulation interface breakdown experiment was carried out to obtain the experimental circuit parameter data;

[0007] Using the experimental circuit parameter data, the dielectric strength of the XLPE-SiR insulation interface gap and the XLPE-SiR insulation equivalent interface breakdown resistance are obtained;

[0008] Based on the dielectric strength of the XLPE-SiR insulation interface gap, a switching function that changes with respect to the interface breakdown voltage is designed;

[0009] According to the physical structure of the real high-voltage cable intermediate joint, the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint is calculated;

[0010] The equivalent resistance of the axial semi-conductive layer of the cable intermediate joint is used to simulate the axial equivalent resistance of the insulation shield on the cable body and the axial equivalent resistance of the high-voltage shielding tube on the cable joint of the physical structure of the real high-voltage cable intermediate joint. The XLPE-SiR insulation equivalent interface breakdown resistance is used to simulate the arc resistance of the XLPE-SiR insulation interface of the cable intermediate joint of the physical structure of the real high-voltage cable intermediate joint. Based on the switching function, an equivalent model of the XLPE-SiR insulation interface breakdown circuit of the cable intermediate joint is constructed. When the voltage applied to the XLPE-SiR insulation interface of the cable intermediate joint exceeds the insulation interface breakdown voltage, the series connection of the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint and the XLPE-SiR insulation equivalent interface breakdown resistance is achieved.

[0011] Further, the experimental circuit parameter data is used to obtain the XLPE-SiR insulation interface gap dielectric strength and the XLPE-SiR insulation equivalent interface breakdown resistance, and also includes:

[0012] Using the experimental circuit parameter data, a plurality of XLPE-SiR insulation equivalent interface breakdown resistance experimental values ​​are obtained;

[0013] Based on the multiple experimental values ​​of the XLPE-SiR insulation equivalent interface breakdown resistance, a breakdown arc conductivity curve of the XLPE-SiR insulation interface of the cable intermediate joint is generated by fitting;

[0014] Based on the XLPE-SiR insulation interface breakdown arc conductivity curve of the cable intermediate joint, a cable intermediate joint XLPE-SiR insulation interface breakdown arc conductivity model is constructed;

[0015] According to the arc conductivity model of the XLPE-SiR insulation interface breakdown of the cable intermediate joint, the XLPE-SiR insulation equivalent interface breakdown resistance is obtained.

[0016] Furthermore, based on the arc conductance curve of the XLPE-SiR insulation interface breakdown of the cable intermediate joint, an arc conductance model of the XLPE-SiR insulation interface breakdown of the cable intermediate joint is constructed. The expression of the arc conductance model of the XLPE-SiR insulation interface breakdown of the cable intermediate joint is as follows:

[0017] ;

[0018] ;

[0019] ;

[0020] In the formula, is the equivalent interface breakdown resistance of XLPE-SiR insulation; A1 is the 1 / r value in the rising area of ​​the XLPE-SiR insulation interface breakdown arc conductivity curve of the cable intermediate joint D-axi The amplitude of the rate of change, in mS / ms; A2 is the 1 / r value in the descending area of ​​the XLPE-SiR insulation interface breakdown arc conductivity curve of the cable intermediate joint D-axi The amplitude of the rate of change, in mS / ms; t0 is the initial time when the XLPE-SiR insulation interface breakdown occurs at the cable intermediate joint, in ms; T a It is the duration of the half-cycle of the arc breakdown at the XLPE-SiR insulation interface of the cable intermediate joint, in ms; t is the time point; T r is the duration of the arc breakdown at the XLPE-SiR insulation interface in the conductivity rise zone, in ms; T f is the duration of the breakdown arc at the XLPE-SiR insulation interface in the conductivity drop zone, in ms; B is an intermediate value and has no real meaning.

[0021] Furthermore, in the rising region of the arc conductivity curve, 1 / r D-axi The calculation formula for the rate of change amplitude A1 is as follows:

[0022] ;

[0023] Where Δt is a sampling time interval; u I (t) is the discrete sampling point of the experimentally obtained XLPE-SiR insulation interface breakdown arc voltage at time t; i b (t) is the discrete sampling point of the arc current breakdown at the XLPE-SiR insulation interface at time t.

[0024] Furthermore, in the falling region of the arc conductivity curve, 1 / r D-axi The calculation formula for the rate of change amplitude A2 is as follows: ;

[0025] Where Δt is a sampling time interval; u I (t) is the discrete sampling point of the experimentally obtained XLPE-SiR insulation interface breakdown arc voltage at time t; i b (t) is the discrete sampling point of the arc current breakdown at the XLPE-SiR insulation interface at time t.

[0026] Furthermore, the experimental circuit parameter data is used to obtain the dielectric strength of the XLPE-SiR insulation interface gap and the XLPE-SiR insulation equivalent interface breakdown resistance. The calculation formula of the dielectric strength of the XLPE-SiR insulation interface gap is as follows:

[0027] ;

[0028] In the formula, is the insulation interface breakdown voltage obtained in the experiment, in V; d I is the axial distance between the two poles of the discharge channel, in mm; K I is the dielectric strength of the XLPE-SiR insulation interface gap.

[0029] Furthermore, based on the dielectric strength of the XLPE-SiR insulation interface gap, a switching function that changes with the interface breakdown voltage is designed. The expression of the switching function is as follows:

[0030] ;

[0031] In the formula, S(u I (t)) is the switching function that changes with the interface breakdown voltage; t0 is the initial time when the XLPE-SiR insulation interface breakdown occurs at the cable intermediate joint, in ms; u I (t0) is the breakdown voltage of the XLPE-SiR insulation interface at the cable intermediate joint, in V; u I (t) is the voltage applied to the XLPE-SiR insulation interface of the cable intermediate joint, unit V; T a is the duration of the half-cycle of the arc breakdown at the XLPE-SiR insulation interface of the cable intermediate joint, in ms; n is the discharge evolution stage; S1 and S2 are different switch contacts; t is the time point; is the dielectric strength of the XLPE-SiR insulation interface gap when the discharge evolution stage is n.

[0032] Furthermore, the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint is calculated, which also includes:

[0033] ;

[0034] ;

[0035] ;

[0036] In the formula, R S-axi The equivalent resistance of the axial semi-conductive layer of the cable intermediate joint, unit: Ω; It is the equivalent resistance of the insulation shielding axial direction of the cable body, in Ω; It is the equivalent resistance of the high-voltage shielding tube in the axial direction of the cable connector, in Ω; is the resistivity of the semi-conductive layer material, in Ω / mm; It is the axial distance from the insulation shield on the cable body to the copper mesh shield, in mm; It is the distance from the end of the high-voltage shielding tube to the crimping tube, in mm; and They are the outer radius and inner radius of the insulation shield on the cable body, in mm; and They are respectively the outer radius and inner radius of the high-voltage shielding tube of the cable intermediate joint, in mm.

[0037] The present invention provides a high-voltage cable intermediate joint grounding fault simulation circuit, which is implemented by using any of the above-mentioned high-voltage cable intermediate joint grounding fault modeling methods, and includes:

[0038] An axial semiconductive layer equivalent resistance of a cable intermediate joint and an XLPE-SiR insulation equivalent interface breakdown resistance are arranged in series, and a switch is arranged between the axial semiconductive layer equivalent resistance of the cable intermediate joint and the XLPE-SiR insulation equivalent interface breakdown resistance.

[0039] The present invention provides a high-voltage cable intermediate joint grounding fault modeling method and simulation circuit, which has the following beneficial effects:

[0040] The present invention conducts a cable intermediate joint XLPE-SiR insulation interface breakdown experiment based on the physical structure of a real high-voltage cable intermediate joint, obtains experimental circuit parameter data, obtains the dielectric strength of the XLPE-SiR insulation interface gap, the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint, and the XLPE-SiR insulation equivalent interface breakdown resistance; based on the dielectric strength of the XLPE-SiR insulation interface gap, designs a switch function that changes with the interface breakdown voltage; uses the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint to simulate the axial equivalent resistance of the insulation shield on the cable body of the real high-voltage cable intermediate joint physical structure and the axial equivalent resistance of the high-voltage shielding tube on the cable joint, uses the XLPE-SiR insulation equivalent interface breakdown resistance to simulate the arc resistance of the XLPE-SiR insulation interface of the cable intermediate joint of the real high-voltage cable intermediate joint physical structure, and based on the switch function, realizes the construction of a cable intermediate joint XLPE-SiR insulation interface breakdown circuit equivalent model. The present invention can realize the study of the electrical characteristics of the XLPE-SiR insulation interface breakdown of the high-voltage cable joint. Those skilled in the art can obtain the current of the fault line through simulation calculation using the equivalent model of the breakdown circuit of the XLPE-SiR insulation interface of the cable intermediate joint.

[0041] At present, most of the research focuses on the characteristics of insulating materials, such as solid insulation breakdown, surface flashover, surface electrothermal ablation and electrical treeing. The research on the interface discharge and breakdown mechanism between two different insulating materials is relatively immature. The modeling method and simulation circuit of the grounding fault of the high-voltage cable intermediate joint proposed in this invention can provide theoretical guidance for the fault analysis of the cable joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0043] Figure 1 is a flow chart of a method for modeling a grounding fault of a high-voltage cable intermediate joint in an embodiment of the present invention;

[0044] Figure 2 It is a schematic diagram of a high-voltage cable intermediate joint grounding fault simulation circuit in an embodiment of the present invention;

[0045] Figure 3 It is a schematic diagram of the arc conductivity curve of the XLPE-SiR insulation interface breakdown of the cable intermediate joint in the embodiment of the present invention. DETAILED DESCRIPTION

[0046] Various aspects and features of the present invention are described herein with reference to the accompanying drawings.

[0047] It should be understood that various modifications may be made to the embodiments of the present application. Therefore, the above description should not be considered as limiting, but only as an example of the embodiments. Other modifications within the scope and spirit of the present invention will occur to those skilled in the art.

[0048] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the general description of the invention given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.

[0049] These and other characteristics of the invention will become apparent from the following description of a preferred form of embodiment given as a non-limiting example, with reference to the accompanying drawings.

[0050] It should also be understood that, although the invention has been described with reference to some specific examples, those skilled in the art will be able to realize many other equivalent forms of the invention that have the characteristics recited in the claims and are therefore within the scope of protection defined thereby.

[0051] The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

[0052] Specific embodiments of the present invention are described hereinafter with reference to the accompanying drawings; however, it should be understood that the embodiments claimed are merely examples of the present invention, which may be implemented in a variety of ways. Well-known and / or repeated functions and structures are not described in detail to avoid obscuring the present invention with unnecessary or redundant details. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as a basis and representative basis for the claims to teach those skilled in the art to use the present invention in a variety of ways with substantially any suitable detailed structure.

[0053] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0054] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

[0055] Example

[0056] like Figure 1 As shown, this embodiment provides a method for modeling a grounding fault of a high-voltage cable intermediate joint, comprising the following steps:

[0057] Step S1: performing a cable intermediate joint XLPE-SiR insulation interface breakdown experiment based on the physical structure of a real high-voltage cable intermediate joint to obtain experimental circuit parameter data;

[0058] Step S2: using the experimental circuit parameter data, obtaining the XLPE-SiR insulation interface gap dielectric strength and the XLPE-SiR insulation equivalent interface breakdown resistance;

[0059] Step S3: Based on the dielectric strength of the XLPE-SiR insulation interface gap, designing a switching function that changes with the interface breakdown voltage;

[0060] Step S4: Calculate the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint according to the actual physical structure of the high-voltage cable intermediate joint.

[0061] Step S5: using the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint to simulate the axial equivalent resistance of the insulation shield on the cable body and the axial equivalent resistance of the high-voltage shielding tube on the cable joint of the physical structure of the real high-voltage cable intermediate joint, using the XLPE-SiR insulation equivalent interface breakdown resistance to simulate the arc resistance of the XLPE-SiR insulation interface of the cable intermediate joint of the physical structure of the real high-voltage cable intermediate joint, based on the switching function, constructing an equivalent model of the XLPE-SiR insulation interface breakdown circuit of the cable intermediate joint, when the voltage applied to the XLPE-SiR insulation interface of the cable intermediate joint exceeds the insulation interface breakdown voltage, realizing the series connection of the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint and the XLPE-SiR insulation equivalent interface breakdown resistance.

[0062] According to another specific embodiment of the present invention, on the basis of step S2, the experimental circuit parameter data is used to obtain the dielectric strength of the XLPE-SiR insulation interface gap and the XLPE-SiR insulation equivalent interface breakdown resistance, and the calculation formula of the dielectric strength of the XLPE-SiR insulation interface gap is as follows:

[0063] ;

[0064] In the formula, is the insulation interface breakdown voltage obtained in the experiment, in V; d I is the axial distance between the two poles of the discharge channel, in mm; K I is the dielectric strength of the XLPE-SiR insulation interface gap.

[0065] K I The control function is the zero rest time of the arc breakdown at the XLPE-SiR insulation interface of the cable intermediate joint. The dielectric strength K of the XLPE-SiR insulation interface gap I The value of is related to the evolution state n. The evolution state is the evolution stage. When the applied voltage reaches the insulation interface breakdown voltage, intermittent interface breakdown occurs at the XLPE-SiR insulation interface. This stage is the initial stage of discharge evolution; with the appearance of continuous carbonization channels, the discharge repetition rate gradually increases, resulting in periodic breakdown at the XLPE-SiR insulation interface. This stage is the mid-stage of discharge evolution; then the initial penetrating carbonization channel expands, and the thermal effect of the periodic interface breakdown arc current inside the cable intermediate joint causes RS-axi to increase exponentially. This stage is the transition stage of discharge evolution; finally, under the long-term evolution of periodic XLPE-SiR insulation interface breakdown discharge, the axial semi-conductive layer inside the cable intermediate joint gradually undergoes carbonization and ablation, which is ultimately reflected in a sharp drop in RS-axi. This stage is the late stage of discharge evolution.

[0066] According to another specific embodiment of the present invention, on the basis of step S3, based on the dielectric strength of the XLPE-SiR insulation interface gap, a switching function that changes with the interface breakdown voltage is designed, and the expression of the switching function is as follows:

[0067] ;

[0068] In the formula, S(u I (t)) is the switching function that changes with the interface breakdown voltage; t0 is the initial time when the XLPE-SiR insulation interface breakdown occurs at the cable intermediate joint, in ms; u I (t0) is the breakdown voltage of the XLPE-SiR insulation interface at the cable intermediate joint, in V; u I (t) is the voltage applied to the XLPE-SiR insulation interface of the cable intermediate joint, unit V; T a is the duration of the half-cycle of the arc breakdown at the XLPE-SiR insulation interface of the cable intermediate joint, in ms; n is the discharge evolution stage; S1 and S2 are different switch contacts; t is the time point; is the dielectric strength of the XLPE-SiR insulation interface gap when the discharge evolution stage is n.

[0069] The control function of t0 is the arc starting time of the breakdown arc at the XLPE-SiR insulation interface of the cable intermediate joint.

[0070] like Figure 2 As shown, S(u I (t)) is a switching function that changes with the interface breakdown voltage, which characterizes the zero rest time of the interface breakdown current. When the voltage applied to the XLPE-SiR insulation interface of the cable intermediate joint exceeds the interface breakdown voltage, an XLPE-SiR insulation interface breakdown arc will be formed, and the switching function S(u I (t)) switches from S1 to S2. Due to the voltage u applied to the XLPE-SiR insulation interface of the cable intermediate joint I (t) decreases when it approaches the zero crossing point and R S-axi The arc is often extinguished due to the current limiting effect. I (t)) Switch back from S2 to S 1。

[0071] According to another specific embodiment of the present invention, on the basis of step S4, according to the physical structure of the real high-voltage cable intermediate joint, the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint is calculated, and the calculation formula is as follows:

[0072] ;

[0073] ;

[0074] ;

[0075] In the formula, R S-axi is the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint, Ω; It is the equivalent resistance of the insulation shielding axial direction of the cable body, in Ω; It is the equivalent resistance of the high-voltage shielding tube in the axial direction of the cable connector, in Ω; is the resistivity of the semi-conductive layer material, in Ω / mm; It is the axial distance from the insulation shield on the cable body to the copper mesh shield, in mm; It is the distance from the end of the high-voltage shielding tube to the crimping tube, in mm; and They are the outer radius and inner radius of the insulation shield on the cable body, in mm; and They are respectively the outer radius and inner radius of the high-voltage shielding tube of the cable intermediate joint, in mm.

[0076] According to another specific embodiment of the present invention, based on the step S2, the XLPE-SiR insulation interface gap dielectric strength and the XLPE-SiR insulation equivalent interface breakdown resistance are obtained by using the experimental circuit parameter data, further comprising:

[0077] Step H21: using the experimental circuit parameter data, obtaining a plurality of XLPE-SiR insulation equivalent interface breakdown resistance experimental values;

[0078] Step H22: Based on the multiple XLPE-SiR insulation equivalent interface breakdown resistance experimental values, a cable intermediate joint XLPE-SiR insulation interface breakdown arc conductivity curve is generated by fitting, such as Figure 3 As shown;

[0079] Step H23: constructing a cable intermediate joint XLPE-SiR insulation interface breakdown arc conductivity model based on the cable intermediate joint XLPE-SiR insulation interface breakdown arc conductivity curve;

[0080] Step H24: According to the arc conductivity model of the XLPE-SiR insulation interface breakdown of the cable intermediate joint, the XLPE-SiR insulation equivalent interface breakdown resistance is obtained.

[0081] According to another specific embodiment of the present invention, on the basis of step H23, based on the arc conductivity curve of the XLPE-SiR insulation interface breakdown of the cable intermediate joint, a XLPE-SiR insulation interface breakdown arc conductivity model of the cable intermediate joint is constructed, as follows:

[0082] By observation Figure 3 From the arc conductivity curve of the XLPE-SiR insulation interface breakdown of the cable intermediate joint, it can be seen that the curve is difficult to fit using a quadratic function. If the conventional fitting method is used, a function of order 6 or above is required to achieve accurate fitting.

[0083] Therefore, in order to avoid the problem of too many fitting coefficients and unclear physical parameter representation when using high-order functions for fitting, the 1 / 2 cosine-1 / 4 sine curve approximation method is used to approximate the main characteristics of the dynamic arc conductivity. The 1 / 2 cosine-1 / 4 sine curve approximation method is as follows: in the conductivity rising area, the arc conductivity curve of the XLPE-SiR insulation interface of the cable intermediate joint is approximately fitted to an angular frequency of π / (BT a ) and the cosine function of the phase in the interval [π, 2π], then 1 / r D-axi The first-order derivative of the curve is a sinusoidal function with a phase in the interval [π, 2π]. In the conductivity drop region, the arc conductivity curve of the XLPE-SiR insulation interface breakdown of the cable intermediate joint is approximately fitted to an angular frequency of π / (2(1-B)T a ) and the sine function of the phase in the interval [π / 2, π], then 1 / r D-axi The first-order derivative of the curve is the cosine function at the phase [π / 2, π]. The specific arc resistance model of the XLPE-SiR insulation interface of the cable intermediate joint is as follows:

[0084] ;

[0085] ;

[0086] ;

[0087] In the formula, is the equivalent interface breakdown resistance of XLPE-SiR insulation; A1 is the 1 / r value in the rising area of ​​the XLPE-SiR insulation interface breakdown arc conductivity curve of the cable intermediate joint D-axi The amplitude of the rate of change, in mS / ms; A2 is the 1 / r value in the descending area of ​​the XLPE-SiR insulation interface breakdown arc conductivity curve of the cable intermediate joint D-axi The amplitude of the rate of change, in mS / ms; t0 is the initial time when the XLPE-SiR insulation interface breakdown occurs at the cable intermediate joint, in ms; T a It is the duration of the half-cycle of the arc breakdown at the XLPE-SiR insulation interface of the cable intermediate joint, in ms; t is the time point; T r is the duration of the arc breakdown at the XLPE-SiR insulation interface in the conductivity rise zone, in ms; T fIt is the duration of the XLPE-SiR insulation interface breakdown arc in the conductivity drop zone, in ms; B is an intermediate value and has no real meaning. The control function of B is the width of the conductivity rise zone of the XLPE-SiR insulation interface breakdown arc at the cable intermediate joint; the control function of A1 is the curvature of the conductivity rise zone of the XLPE-SiR insulation interface breakdown arc at the cable intermediate joint; the control function of A2 is the smoothness of the conductivity drop zone of the XLPE-SiR insulation interface breakdown arc at the cable intermediate joint.

[0088] In actual application, A1 and A2 can be obtained respectively according to the experimental arc voltage and current discrete sampling points using the derivative operation rule, where A1 is equal to the maximum value of the time derivative of the arc conductivity in the conductivity rising area, and A2 is equal to the absolute value of the minimum value of the time derivative of the arc conductivity in the falling area, as follows:

[0089] In the rising region of the arc conductivity curve, 1 / r D-axi The calculation formula for the rate of change amplitude A1 is as follows:

[0090] ;

[0091] Where Δt is a sampling time interval; u I (t) is the discrete sampling point of the experimentally obtained XLPE-SiR insulation interface breakdown arc voltage at time t; i b (t) is the discrete sampling point of the arc current breakdown at the XLPE-SiR insulation interface at time t.

[0092] The arc conductivity curve falls in the 1 / r D-axi The calculation formula for the rate of change amplitude A2 is as follows: ;

[0093] Where Δt is a sampling time interval; u I (t) is the discrete sampling point of the experimentally obtained XLPE-SiR insulation interface breakdown arc voltage at time t; i b (t) is the discrete sampling point of the arc current breakdown at the XLPE-SiR insulation interface at time t.

[0094] like Figure 2 As shown, according to another specific embodiment of the present invention, a high-voltage cable intermediate joint grounding fault simulation circuit is provided, which is implemented by using the above-mentioned high-voltage cable intermediate joint grounding fault modeling method, including:

[0095] An axial semiconductive layer equivalent resistance of a cable intermediate joint and an XLPE-SiR insulation equivalent interface breakdown resistance are arranged in series, and a switch is arranged between the axial semiconductive layer equivalent resistance of the cable intermediate joint and the XLPE-SiR insulation equivalent interface breakdown resistance.

[0096] Those skilled in the art can use the circuit equivalent model to obtain the current of the fault line through simulation calculation.

[0097] The present invention can be used to study the electrical characteristics of the XLPE-SiR insulation interface breakdown of high-voltage cable joints. Those skilled in the art can obtain the current of the fault line through simulation calculation using the equivalent model of the XLPE-SiR insulation interface breakdown circuit of the cable intermediate joint.

[0098] At present, most of the research focuses on the characteristics of insulating materials, such as solid insulation breakdown, surface flashover, surface electrothermal ablation and electrical treeing. The research on the interface discharge and breakdown mechanism between two different insulating materials is relatively immature. The modeling method and simulation circuit of the grounding fault of the high-voltage cable intermediate joint proposed in this invention can provide theoretical guidance for the fault analysis of the cable joint.

[0099] The above description is only a preferred embodiment of the present disclosure and an explanation of the technical principles used. Those skilled in the art should understand that the scope of disclosure involved in the present disclosure is not limited to the technical solutions formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above disclosed concept. For example, the above features are replaced with the technical features with similar functions disclosed in the present disclosure (but not limited to) by each other to form a technical solution.

Claims

1. A method for modeling a grounding fault of a high-voltage cable intermediate joint, characterized in that: include: Based on the physical structure of the real high-voltage cable intermediate joint, the cable intermediate joint XLPE-SiR insulation interface breakdown experiment was carried out to obtain the experimental circuit parameter data; Using the experimental circuit parameter data, the dielectric strength of the XLPE-SiR insulation interface gap and the XLPE-SiR insulation equivalent interface breakdown resistance are obtained; Based on the dielectric strength of the XLPE-SiR insulation interface gap, a switching function that changes with respect to the interface breakdown voltage is designed; According to the physical structure of the real high-voltage cable intermediate joint, the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint is calculated; The equivalent resistance of the axial semi-conductive layer of the cable intermediate joint is used to simulate the axial equivalent resistance of the insulation shield on the cable body and the axial equivalent resistance of the high-voltage shielding tube on the cable joint of the physical structure of the real high-voltage cable intermediate joint. The XLPE-SiR insulation equivalent interface breakdown resistance is used to simulate the arc resistance of the XLPE-SiR insulation interface of the cable intermediate joint of the physical structure of the real high-voltage cable intermediate joint. Based on the switching function, an equivalent model of the XLPE-SiR insulation interface breakdown circuit of the cable intermediate joint is constructed. When the voltage applied to the XLPE-SiR insulation interface of the cable intermediate joint exceeds the insulation interface breakdown voltage, the series connection of the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint and the XLPE-SiR insulation equivalent interface breakdown resistance is achieved.

2. The high-voltage cable intermediate joint grounding fault modeling method according to claim 1 is characterized in that: Using the experimental circuit parameter data, the XLPE-SiR insulation interface gap dielectric strength and the XLPE-SiR insulation equivalent interface breakdown resistance are obtained, and also include: Using the experimental circuit parameter data, a plurality of XLPE-SiR insulation equivalent interface breakdown resistance experimental values ​​are obtained; Based on the multiple experimental values ​​of the XLPE-SiR insulation equivalent interface breakdown resistance, a breakdown arc conductivity curve of the XLPE-SiR insulation interface of the cable intermediate joint is generated by fitting; Based on the XLPE-SiR insulation interface breakdown arc conductivity curve of the cable intermediate joint, a cable intermediate joint XLPE-SiR insulation interface breakdown arc conductivity model is constructed; According to the arc conductivity model of the XLPE-SiR insulation interface breakdown of the cable intermediate joint, the XLPE-SiR insulation equivalent interface breakdown resistance is obtained.

3. The high-voltage cable intermediate joint grounding fault modeling method according to claim 1 is characterized in that: Based on the XLPE-SiR insulation interface breakdown arc conductivity curve of the cable intermediate joint, a cable intermediate joint XLPE-SiR insulation interface breakdown arc conductivity model is constructed. The expression of the cable intermediate joint XLPE-SiR insulation interface breakdown arc conductivity model is as follows: ； ; ; In the formula, is the equivalent interface breakdown resistance of XLPE-SiR insulation; A 1 is in the rising area of ​​the arc conductivity curve of the XLPE-SiR insulation interface breakdown of the cable intermediate joint 1 / r D-axi The amplitude of the rate of change, in mS / ms; A 2 is the falling area of ​​the XLPE-SiR insulation interface breakdown arc conductivity curve of the cable intermediate joint 1 / r D-axi The amplitude of the rate of change, in mS / ms; t 0 is the initial time of breakdown of the XLPE-SiR insulation interface at the cable intermediate joint, in ms; T a It is the duration of half-cycle of arc breakdown at the XLPE-SiR insulation interface of the cable intermediate joint, in ms; t is the time point; T r is the duration of the arc breakdown at the XLPE-SiR insulation interface in the conductivity rise zone, in ms; T f is the arc breakdown duration of the XLPE-SiR insulation interface in the conductivity drop region, in ms; B It is an intermediate value and has no real meaning.

4. The high-voltage cable intermediate joint grounding fault modeling method according to claim 3 is characterized in that: In the rising area of ​​the arc conductivity curve 1 / r D-axi The rate of change of A The calculation formula of 1 is as follows: ; In the formula, Δ t is a sampling time interval; u I ( t ) is the experimentally obtained XLPE-SiR insulation interface breakdown arc voltage t Discrete sampling points at time; i b ( t ) is the XLPE-SiR insulation interface breakdown arc current t Discrete sampling points at time.

5. The high-voltage cable intermediate joint grounding fault modeling method according to claim 3 is characterized in that: The arc conductivity curve falls in the 1 / r D-axi The rate of change of A The calculation formula of 2 is as follows: ; In the formula, Δ t is a sampling time interval; u I ( t ) is the experimentally obtained XLPE-SiR insulation interface breakdown arc voltage t Discrete sampling points at time; i b ( t ) is the arc breakdown current of XLPE-SiR insulation interface t Discrete sampling points at time.

6. The high-voltage cable intermediate joint grounding fault modeling method according to claim 1 is characterized in that: Using the experimental circuit parameter data, the dielectric strength of the XLPE-SiR insulation interface gap and the XLPE-SiR insulation equivalent interface breakdown resistance are obtained. The calculation formula of the dielectric strength of the XLPE-SiR insulation interface gap is as follows: ; In the formula, is the insulation interface breakdown voltage obtained in the experiment, in V; d I is the axial distance between the two poles of the discharge channel, in mm; K I is the dielectric strength of the XLPE-SiR insulation interface gap.

7. The high-voltage cable intermediate joint grounding fault modeling method according to claim 6 is characterized in that: Based on the dielectric strength of the XLPE-SiR insulation interface gap, a switching function that changes with the interface breakdown voltage is designed. The expression of the switching function is as follows: ; In the formula, S ( u I ( t )) is a switching function that changes with the interface breakdown voltage; t 0 is the initial time of the breakdown of the XLPE-SiR insulation interface at the cable intermediate joint, in ms; u I ( t 0) is the breakdown voltage of the XLPE-SiR insulation interface of the cable intermediate joint, in V; u I ( t ) is the voltage applied to the XLPE-SiR insulation interface of the cable intermediate joint, unit V; T a is the duration of the half-cycle of the arc breakdown at the XLPE-SiR insulation interface of the cable intermediate joint, in ms; n is the discharge evolution stage; S1 and S2 are different switch contacts; t is the time point; is the dielectric strength of the XLPE-SiR insulation interface gap when the discharge evolution stage is n.

8. The high-voltage cable intermediate joint grounding fault modeling method according to claim 1 is characterized in that: According to the physical structure of the real high-voltage cable intermediate joint, the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint is calculated. The calculation formula of the equivalent resistance of the axial semi-conductive layer of the cable intermediate joint is as follows: ; ; ; In the formula, R S-axi The equivalent resistance of the axial semi-conductive layer of the cable intermediate joint, unit: Ω; It is the equivalent resistance of the insulation shielding axial direction of the cable body, in Ω; It is the equivalent resistance of the high-voltage shielding tube in the axial direction of the cable connector, in Ω; is the resistivity of the semi-conductive layer material, in Ω / mm; It is the axial distance from the insulation shield on the cable body to the copper mesh shield, in mm; It is the distance from the end of the high-voltage shielding tube to the crimping tube, in mm; and They are the outer radius and inner radius of the insulation shield on the cable body, in mm; and They are respectively the outer radius and inner radius of the high-voltage shielding tube of the cable intermediate joint, in mm.

9. A high voltage cable intermediate joint grounding fault simulation circuit, characterized in that: The method for modeling a grounding fault of a high-voltage cable intermediate joint according to any one of claims 1 to 8 is used to implement the method, comprising: An axial semiconductive layer equivalent resistance of a cable intermediate joint and an XLPE-SiR insulation equivalent interface breakdown resistance are arranged in series, and a switch is arranged between the axial semiconductive layer equivalent resistance of the cable intermediate joint and the XLPE-SiR insulation equivalent interface breakdown resistance.

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