CN113158504B - Method and system for enhancing insulation of connector of extra-high voltage direct current cable - Google Patents

Abstract

The invention discloses a method and a system for enhancing insulation of a connector of an extra-high voltage direct current cable, and belongs to the technical field of power cable equipment. The method of the invention comprises the following steps: acquiring test data, conducting conductivity fitting on the test data, and determining characterization parameters; determining the length of an insulation interface and an enhanced insulation interface of the extra-high voltage direct current cable connector and the thickness of the connector enhanced insulation; according to the characterization parameters, optimizing data of the insulation and reinforced insulation interface length and the joint reinforced insulation thickness are obtained through simulation calculation; and obtaining the conductivity fitting parameters of the modified reinforced insulating material. The invention solves the problem of optimizing the electric field and thermal field distribution in the extra-high voltage direct current cable joint, effectively controls the joint length, the outer diameter and the thickness, ensures that the extra-high voltage direct current cable joint meets the performance requirements of the electric field and the thermal field, and greatly facilitates the processing, manufacturing and mounting processes of the extra-high voltage direct current cable joint.

Description

A method and system for enhancing insulation of joints of ultra-high voltage direct current cables

Technical Field

The present invention relates to the technical field of power cable equipment, and more specifically, to a method and system for strengthening insulation of a joint of an ultra-high voltage direct current cable.

Background technique

Under a DC electric field, charge conduction in polymer insulating media is limited by the charge injected by the electrode. Due to the existence of phenomena such as electron transitions on local energy bands, electrode electron emission current and space charge limited current, its conductivity shows a nonlinear volt-ampere relationship that depends on temperature and electric field strength. For nonlinear conductive polymer insulating materials under the action of a DC electric field, the electric field distribution in the insulating layer will be reversed under different transmission loads of the cable.

Since the conductivity of the two insulating materials in the DC cable intermediate joint is very different in magnitude, the electric field strength on both sides of the double-layer insulation interface of the joint is quite different, and the electric field strength ratio gradually increases with the increase of the DC cable load current. Space charges will accumulate on the interface between the DC cable main insulation and the joint reinforced insulation, causing the tangential electric field on the interface to be distorted. The enhanced insulation of the DC cable joint has a decisive influence on the electric field distribution in the cable joint. The effective way to reduce the degree of electric field distortion in the joint is to increase the length and thickness of the reinforced insulation material in the joint, which has a direct impact on the heat dissipation, processing, manufacturing and installation of the joint part.

Therefore, the selection of structural parameters for enhanced insulation in the intermediate joint of UHV DC cable becomes a key issue. A design method for enhanced insulation of the joint is needed to achieve electrical and thermal field coordination of the joint, control the geometric dimensions of the UHV DC cable joint, optimize the electric field strength and temperature field distribution in the UHV DC cable joint, reduce the degree of electric field distortion, facilitate heat dissipation of the joint, and facilitate processing, manufacturing and installation.

Summary of the invention

In view of the above problems, the present invention proposes a method for enhancing insulation of a joint of an ultra-high voltage DC cable, comprising:

Conduct conductivity tests at different temperatures and field strengths on the insulation materials and original reinforced insulation materials of characteristic high-voltage DC cable connectors, obtain test data, perform conductivity fitting on the test data, and determine characterization parameters;

For UHV DC cable joints, the UHV DC cable joint model is simulated and calculated under preset conditions by electrothermal coupling physical field to determine the insulation and enhanced insulation interface length of the UHV DC cable joint, as well as the thickness of the joint enhanced insulation;

According to the characterization parameters, the optimization data of the insulation and reinforced insulation interface length and the joint reinforced insulation thickness are obtained by simulation calculation;

Modify the enhanced insulation material of the UHV DC cable joint, test the conductivity data of the modified different enhanced insulation materials, perform conductivity fitting on the test data, and obtain the conductivity fitting parameters of the modified enhanced insulation materials;

The fitting parameters of the conductivity of the modified enhanced insulating material are used to determine the type of enhanced insulating material in the joint of the UHV DC cable;

According to the type of the reinforced insulating material in the joint, the insulating structure is installed according to the size information, and the insulating structure is used to enhance the insulation performance of the joint of the ultra-high voltage DC cable.

Optionally, conductivity fitting of the test data is performed using the following formula:

Where, σ is the conductivity, T is the test temperature, E is the test electric field and E>0, A is the material constant, B is the field strength coefficient, is the activation energy, q is the electron charge, and k _b is the Boltzmann constant;

Characterization parameters include: material constant A, field strength coefficient B, and activation energy parameter

Optionally, the establishment of the UHV DC cable joint model includes:

Determine the shape curves of the stress cone and high-voltage shielding tube in the UHV DC cable joint, obtain the parameters of the outer diameter and thickness of the insulating material and the insulating layer, outer shielding layer, buffer layer, metal sheath and outer sheath of the matching UHV DC cable joint and the reinforced insulating material, establish the axial section two-dimensional graphics of the UHV DC cable joint according to the parameters, and establish the UHV DC cable joint model according to the axial section two-dimensional graphics.

Optionally, perform electrothermal coupling physical field simulation calculations, including:

Each component unit in the UHV DC cable joint model is assigned with conductivity, relative dielectric constant, density, specific heat capacity and thermal conductivity parameters. Under the conditions of rated voltage U, rated current I and preset temperature, coupled simulation calculation is performed according to the electromagnetic field physics equation and solid heat transfer physics equation:

The electromagnetic field physics equation is as follows:

Where J is the total current density, Qj _,V is the total charge, σ is the conductivity, E is the electric field intensity, and _Je is the displacement current density;

The physical equation for solid heat transfer is as follows:

Wherein, t is the preset temperature, k is the thermal conductivity, Q=J·E is the internal heat source of the cable, and Q _out is the external heat source of the cable.

Optionally, obtain insulation and reinforced insulation interface lengths, including:

The initial length L of the insulation and reinforced insulation interface is determined according to the following formula:

Taking the preset distance as an interval, increase the initial length of the joint insulation and enhanced insulation interface, determine the electric field distribution in the UHV DC cable joint model with different interface lengths under no-load and full-load conditions, if the change rate of the tangential electric field of the joint interface under no-load and full-load conditions ΔE% ≥ 1%, continue to increase the interface length until ΔE% < 1%, and take the length before the last calculation as the UHV DC cable joint interface length;

ΔE% is the rate of change of the tangential electric field at the joint interface, and _ET is the critical breakdown field strength of the interface.

Optionally, obtain the joint reinforced insulation thickness, including:

The initial thickness of the joint reinforced insulation layer is determined according to the following formula:

Taking the preset distance as an interval, reduce the initial thickness of the joint reinforced insulation, determine the steady-state temperature of the cable conductor in the UHV DC cable joint model under full load conditions, if the steady-state temperature of the cable conductor under full load conditions is greater than T _max , continue to reduce the thickness of the joint reinforced insulation until the highest steady-state temperature of the conductor is less than and close to T _max , and take the thickness value calculated last time as the thickness of the UHV DC cable joint reinforced insulation;

T _max is the maximum allowable continuous operating temperature of the UHV DC cable insulation material.

The present invention also proposes a system for enhancing insulation of a joint of an ultra-high voltage DC cable, comprising:

The initial module conducts conductivity tests on the insulation materials and original reinforced insulation materials of the characteristic high-voltage DC cable connectors at different temperatures and different field strengths, obtains test data, performs conductivity fitting on the test data, and determines characterization parameters;

The structural optimization calculation module performs electrothermal coupling physical field simulation calculation on the UHV DC cable joint model under preset conditions to determine the insulation and enhanced insulation interface length of the UHV DC cable joint and the thickness of the joint enhanced insulation.

The material optimization module uses simulation calculations to obtain optimized data on the insulation and enhanced insulation interface lengths and the thickness of the joint enhanced insulation based on the characterization parameters;

Modify the enhanced insulation material of the UHV DC cable joint, test the conductivity data of the modified different enhanced insulation materials, perform conductivity fitting on the test data, and obtain the conductivity fitting parameters of the modified enhanced insulation materials;

The fitting parameters of the conductivity of the modified enhanced insulating material are used to determine the type of enhanced insulating material in the joint of the UHV DC cable;

According to the type of the reinforced insulating material in the joint, the insulating structure is installed according to the size information, and the insulating structure is used to enhance the insulation performance of the joint of the ultra-high voltage DC cable.

Optionally, conductivity fitting of the test data is performed using the following formula:

Where, σ is the conductivity, T is the test temperature, E is the test electric field and E>0, A is the material constant, B is the field strength coefficient, is the activation energy, q is the electron charge, and k _b is the Boltzmann constant;

Characterization parameters include: material constant A, field strength coefficient B, and activation energy parameter

Optionally, the establishment of the UHV DC cable joint model includes:

Determine the shape curves of the stress cone and high-voltage shielding tube in the UHV DC cable joint, obtain the parameters of the outer diameter and thickness of the insulating material and the insulating layer, outer shielding layer, buffer layer, metal sheath and outer sheath of the matching UHV DC cable joint and the reinforced insulating material, establish the axial section two-dimensional graphics of the UHV DC cable joint according to the parameters, and establish the UHV DC cable joint model according to the axial section two-dimensional graphics.

Optionally, perform electrothermal coupling physical field simulation calculations, including:

Each component unit in the UHV DC cable joint model is assigned with conductivity, relative dielectric constant, density, specific heat capacity and thermal conductivity parameters. Under the conditions of rated voltage U, rated current I and preset temperature, coupled simulation calculation is performed according to the electromagnetic field physics equation and solid heat transfer physics equation:

The electromagnetic field physics equation is as follows:

Where J is the total current density, Qj _,V is the total charge, σ is the conductivity, E is the electric field intensity, and _Je is the displacement current density;

The physical equation for solid heat transfer is as follows:

Wherein, t is the preset temperature, k is the thermal conductivity, Q=J·E is the internal heat source of the cable, and Q _out is the external heat source of the cable.

Optionally, obtain insulation and reinforced insulation interface lengths, including:

The initial length L of the insulation and reinforced insulation interface is determined according to the following formula:

Taking the preset distance as an interval, increase the initial length of the joint insulation and enhanced insulation interface, determine the electric field distribution in the UHV DC cable joint model with different interface lengths under no-load and full-load conditions, if the change rate of the tangential electric field of the joint interface under no-load and full-load conditions ΔE% ≥ 1%, continue to increase the interface length until ΔE% < 1%, and take the length before the last calculation as the UHV DC cable joint interface length;

ΔE% is the rate of change of the tangential electric field at the joint interface, and _ET is the critical breakdown field strength of the interface.

Optionally, obtain the joint reinforced insulation thickness, including:

The initial thickness of the joint reinforced insulation layer is determined according to the following formula:

Taking the preset distance as an interval, reduce the initial thickness of the joint reinforced insulation, determine the steady-state temperature of the cable conductor in the UHV DC cable joint model under full load conditions, if the steady-state temperature of the cable conductor under full load conditions is greater than T _max , continue to reduce the thickness of the joint reinforced insulation until the highest steady-state temperature of the conductor is less than and close to T _max , and take the thickness value calculated last time as the thickness of the UHV DC cable joint reinforced insulation;

T _max is the maximum allowable continuous operating temperature of the UHV DC cable insulation material.

The present invention gradually optimizes and determines the joint interface length, enhanced insulation thickness and enhanced insulation material parameters that meet the design requirements of the UHV DC cable joint through relatively accurate data fitting of the relationship between the electrical conductivity of the insulating material and the temperature and electric field, solves the optimization problem of the electric field and thermal field distribution in the UHV DC cable joint, and effectively controls the joint length and outer diameter (thickness), so that the UHV DC cable joint meets the electrical and thermal field performance requirements, and greatly facilitates the processing, manufacturing and installation of the UHV DC cable joint.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a flow chart of the method of the present invention;

FIG2 is a diagram showing the simulation calculation result of the interface length of the UHV DC cable joint in an embodiment of the method of the present invention;

FIG3 is a diagram showing simulation calculation results of the thickness of the enhanced insulation of the UHV DC cable in an embodiment of the method of the present invention;

FIG4 is a diagram showing simulation calculation results of the types of UHV DC cable reinforced insulation materials in an embodiment of the method of the present invention;

FIG5 is a structural diagram of the system of the present invention.

Detailed ways

Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units/elements are marked with the same reference numerals.

Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

The present invention proposes a method for enhancing insulation of a joint of an ultra-high voltage DC cable, as shown in FIG1 , comprising:

Conduct conductivity tests at different temperatures and field strengths on the insulation materials and original reinforced insulation materials of characteristic high-voltage DC cable connectors, obtain test data, perform conductivity fitting on the test data, and determine characterization parameters;

For UHV DC cable joints, the UHV DC cable joint model is simulated and calculated under preset conditions by electrothermal coupling physical field to determine the insulation and enhanced insulation interface length of the UHV DC cable joint, as well as the thickness of the joint enhanced insulation;

According to the characterization parameters, the optimization data of the insulation and reinforced insulation interface length and the joint reinforced insulation thickness are obtained by simulation calculation;

Modify the enhanced insulation material of the UHV DC cable joint, test the conductivity data of the modified different enhanced insulation materials, perform conductivity fitting on the test data, and obtain the conductivity fitting parameters of the modified enhanced insulation materials;

The fitting parameters of the conductivity of the modified enhanced insulating material are used to determine the type of enhanced insulating material in the joint of the UHV DC cable;

According to the type of the reinforced insulating material in the joint, the insulating structure is installed according to the size information, and the insulating structure is used to enhance the insulation performance of the joint of the ultra-high voltage DC cable.

Among them, the conductivity fitting of the test data uses the following formula:

Where, σ is the conductivity, T is the test temperature, E is the test electric field and E>0, A is the material constant, B is the field strength coefficient, is the activation energy, q is the electron charge, and _kb is the Boltzmann constant;

Characterization parameters include: material constant A, field strength coefficient B, and activation energy parameter

Among them, the establishment of the UHV DC cable joint model includes:

Determine the shape curves of the stress cone and high-voltage shielding tube in the UHV DC cable joint, obtain the parameters of the outer diameter and thickness of the insulating material and the insulating layer, outer shielding layer, buffer layer, metal sheath and outer sheath of the matching UHV DC cable joint and the reinforced insulating material, establish the axial section two-dimensional graphics of the UHV DC cable joint according to the parameters, and establish the UHV DC cable joint model according to the axial section two-dimensional graphics.

Among them, the electrothermal coupling physical field simulation calculation includes:

Each component unit in the UHV DC cable joint model is assigned with conductivity, relative dielectric constant, density, specific heat capacity and thermal conductivity parameters. Under the conditions of rated voltage U, rated current I and preset temperature, coupled simulation calculation is performed according to the electromagnetic field physics equation and solid heat transfer physics equation:

The electromagnetic field physics equation is as follows:

Where J is the total current density, Qj _,V is the total charge, σ is the conductivity, E is the electric field intensity, and _Je is the displacement current density;

The physical equation for solid heat transfer is as follows:

Wherein, t is the preset temperature, k is the thermal conductivity, Q=J·E is the internal heat source of the cable, and Q _out is the external heat source of the cable.

Among them, obtaining the insulation and reinforced insulation interface length includes:

The initial length L of the insulation and reinforced insulation interface is determined according to the following formula:

Taking the preset distance as an interval, increase the initial length of the joint insulation and enhanced insulation interface, determine the electric field distribution in the UHV DC cable joint model with different interface lengths under no-load and full-load conditions, if the change rate of the tangential electric field of the joint interface under no-load and full-load conditions ΔE% ≥ 1%, continue to increase the interface length until ΔE% < 1%, and take the length before the last calculation as the UHV DC cable joint interface length;

ΔE% is the rate of change of the tangential electric field at the joint interface, and _ET is the critical breakdown field strength of the interface.

Among them, obtaining the joint enhanced insulation thickness includes:

The initial thickness of the joint reinforced insulation layer is determined according to the following formula:

Taking the preset distance as an interval, reduce the initial thickness of the joint reinforced insulation, determine the steady-state temperature of the cable conductor in the UHV DC cable joint model under full load conditions, if the steady-state temperature of the cable conductor under full load conditions is greater than T _max , continue to reduce the thickness of the joint reinforced insulation until the highest steady-state temperature of the conductor is less than and close to T _max , and take the thickness value calculated last time as the thickness of the UHV DC cable joint reinforced insulation;

T _max is the maximum allowable continuous operating temperature of the UHV DC cable insulation material.

The present invention will be further described below in conjunction with embodiments:

The present invention adopts finite element simulation to calculate the tangential electric field strength on the joint interface and the electric field strength in the reinforced insulation. By changing the interface length between the cable main insulation and the joint reinforced insulation and the thickness of the reinforced insulation, and adjusting the nonlinear parameters of the conductivity of the reinforced insulation material, the electric field strength and temperature field distribution in the joint are optimized, and the geometric dimensions of the UHV DC cable joint are controlled.

According to the design method of AC cable joints and low voltage (<800kV) DC cable joints, the shape curves of stress cone and high voltage shielding tube in UHV DC cable joints are determined, and the axial section two-dimensional graphics of each component unit of UHV DC cable joints are established. The interface length L of XLPE insulation and reinforced insulation of the joint is calculated according to formula (2):

The thickness Δr of the joint reinforced insulation layer is calculated according to formula (3):

Wherein, σ ₁ and σ ₂ are the conductivity of cable XLPE insulation and joint reinforced insulation respectively when the temperature is 25℃ and the electric field is _Es , S/m; U is the potential difference between the cable conductor and the outer surface of the joint reinforced insulation, V; r ₁ is the radius of the cable conductor, mm; _ri is the outer radius of the cable insulation, mm.

The conductivity, relative dielectric constant, density, specific heat capacity and thermal conductivity of each component unit in the two-dimensional simulation model of the UHV DC cable joint are assigned parameters such as conductivity, relative dielectric constant, density, specific heat capacity and thermal conductivity. Under the conditions of voltage U, rated current I and initial temperature 25℃, according to the electromagnetic field physics equation:

Where, J is the total current density, A/m2; Qj _,V is the total charge, C; σ is the conductivity, S/m; E is the electric field strength, V/m; _Je is the displacement current density, A/m2.

And the solid heat transfer physics equation:

Wherein, T is temperature, K; k is thermal conductivity, W/(m·k2); Q=J·E is the internal heat source of the cable, W; Q _out is the external heat source of the cable, W.

The electric and thermal fields are directly coupled to perform electric and thermal coupling physical field simulation calculation on the UHV DC cable joint model.

The length of the interface between the XLPE insulation and the reinforced insulation of the joint is increased at intervals of 10 cm, and the electric field distribution in the UHV DC cable joint model with different interface lengths under no-load and full-load conditions is calculated. If the rate of change of the tangential electric field at the joint interface under no-load and full-load conditions ΔE% ≥ 1%, the interface length is continued to be increased until ΔE% < 1%. The length before the last calculation is taken as the interface length of the UHV DC cable joint.

The thickness of the joint reinforced insulation is reduced at intervals of 1 cm, and the steady-state temperature of the cable conductor in the UHV DC cable joint model under full load conditions is calculated. If the steady-state temperature of the cable conductor under full load conditions is greater than T _max , the thickness of the joint reinforced insulation is continued to be reduced until the maximum steady-state temperature of the conductor is less than and close to T _max . The thickness value calculated for the last time is taken as the thickness of the UHV DC cable joint reinforced insulation.

The electric field and thermal field coupling simulation calculation is carried out on the UHV DC cable joint model with reinforced insulation materials with different conductivity parameters. The material constant, activation energy and field strength coefficient parameters of the reinforced insulation materials are changed until the tangential electric field at the joint interface is less than the critical breakdown field strength _ET of the interface, the maximum electric field in the reinforced insulation is less than _Es , and the maximum temperature of the conductor under full load conditions is less than and close to 70℃. The modified insulation material closest to the above conditions is selected as the reinforced insulation material for the UHV DC cable joint.

According to the joint interface length, enhanced insulation thickness and type of enhanced insulation determined in the enhanced insulation design process, the design results of enhanced insulation of UHV DC cable joints are formed from the aspects of structure and material requirements.

The change rate of the tangential electric field at the joint interface ΔE% is set to 1%, the critical breakdown field strength of the interface _ET is set to 3kV/mm, the maximum allowable continuous working temperature _Tmax of the UHV DC cable insulation material is set to 70℃, and the normal allowable working DC electric field strength _Es of the reinforced insulation material at 70℃ is set to 9kV/mm;

According to the structural characteristics of 500kV AC cable joints and 320kV and 500kV DC cable joints, the shape curves of stress cone and high-voltage shielding tube in UHV DC cable joints are determined, and the outer diameter and thickness parameters of cross-linked polyethylene insulation layer, outer shielding layer, buffer layer, metal sheath and outer sheath of the matching UHV DC cable are obtained. Combined with the voltage U of the cable conductor, the critical breakdown field strength _ET of the interface, the conductivity of the cable XLPE insulation and the joint reinforced insulation at a temperature of 25℃ and a normal allowable working DC electric field strength of _Es , the interface length and the thickness of the reinforced insulation of the UHV DC cable joint are calculated, and then the axial section two-dimensional graphics of each component unit of the UHV DC cable joint are established;

Using COMSOL finite element simulation software, simulation calculations were carried out to determine the interface length, enhanced insulation thickness and enhanced insulation material types of UHV DC cable joints. Figures 2, 3 and 4 respectively show the simulation calculation results for determining the interface length, enhanced insulation thickness and enhanced insulation material types of UHV DC cable joints.

In the process of determining the interface length of the UHV DC cable joint, when the interface length increases from 0.8m to 0.9m, when the cable is unloaded, the maximum value of the interface tangential electric field decreases from 4.323kV/mm to 4.282kV/mm, and the electric field change rate is 0.95%. When the cable is fully loaded, the maximum value of the interface tangential electric field decreases from 4.023kV/mm to 4.011kV/mm, and the electric field change rate is 0.3%, which meets the judgment conditions of the influence of interface length change on the interface tangential electric field strength. The interface length of the UHV DC cable joint is selected as 0.8m as the basis for the next step of design of the joint insulation structure.

In the process of determining the enhanced insulation thickness of the UHV DC cable joint, under full load conditions, when the enhanced insulation thickness is reduced from 0.19m to 0.18m, the maximum temperature of the cable conductor drops from 70.36℃ to 69.89℃, and the maximum temperature of the cable conductor is less than T _max , which meets the judgment conditions for the influence of the change of enhanced insulation thickness on the maximum temperature of the cable conductor. The enhanced insulation thickness of the UHV DC cable joint is selected as 0.18m as the basis for the next step of design of the joint insulation structure.

In the process of determining the type of enhanced insulation material for UHV DC cable joints, when the XLPE insulation material of the UHV DC cable is matched with the enhanced insulation material D, under no-load conditions, the tangential electric field at the joint interface is 2.954 kV/mm, which is less than the critical breakdown field strength _ET of the interface, and the maximum electric field in the enhanced insulation is 7.947 kV/mm, which is less than the normal allowable working DC electric field strength _Es , and the maximum temperature of the conductor is less than and close to the maximum allowable continuous working temperature _Tmax , which meets the selection conditions of the type of enhanced insulation material. Therefore, the insulation material D is selected as the enhanced insulation material for the UHV DC cable joint.

According to the interface length, enhanced insulation thickness and type of enhanced insulation determined during the enhanced insulation design process, the design results of enhanced insulation of UHV DC cable joints are formed from the aspects of structure and material requirements.

A system 200 for enhancing insulation of a joint of an ultra-high voltage direct current cable according to the present invention, as shown in FIG5 , comprises:

Initial module 201, conducts conductivity tests on the insulation material and the original reinforced insulation material of the characteristic high-voltage DC cable connector at different temperatures and different field strengths, obtains test data, performs conductivity fitting on the test data, and determines characterization parameters;

The structural optimization calculation module 202 performs an electrothermal coupling physical field simulation calculation on the UHV DC cable joint model under preset conditions to determine the insulation and enhanced insulation interface length of the UHV DC cable joint and the thickness of the joint enhanced insulation;

The material optimization module 203 obtains the optimization data of the insulation and enhanced insulation interface length and the joint enhanced insulation thickness by simulation calculation according to the characterization parameters;

Modify the enhanced insulation material of the UHV DC cable joint, test the conductivity data of the modified different enhanced insulation materials, perform conductivity fitting on the test data, and obtain the conductivity fitting parameters of the modified enhanced insulation materials;

The fitting parameters of the conductivity of the modified enhanced insulating material are used to determine the type of enhanced insulating material in the joint of the UHV DC cable;

According to the type of the reinforced insulating material in the joint, the insulating structure is installed according to the size information, and the insulating structure is used to enhance the insulation performance of the joint of the ultra-high voltage DC cable.

Among them, the conductivity fitting of the test data uses the following formula:

Where, σ is the conductivity, T is the test temperature, E is the test electric field and E>0, A is the material constant, B is the field strength coefficient, is the activation energy, q is the electron charge, and k _b is the Boltzmann constant;

Characterization parameters include: material constant A, field strength coefficient B, and activation energy parameter

Among them, the establishment of the UHV DC cable joint model includes:

Determine the shape curves of the stress cone and high-voltage shielding tube in the UHV DC cable joint, obtain the parameters of the outer diameter and thickness of the insulating material and the insulating layer, outer shielding layer, buffer layer, metal sheath and outer sheath of the matching UHV DC cable joint and the reinforced insulating material, establish the axial section two-dimensional graphics of the UHV DC cable joint according to the parameters, and establish the UHV DC cable joint model according to the axial section two-dimensional graphics.

Among them, the electrothermal coupling physical field simulation calculation includes:

Each component unit in the UHV DC cable joint model is assigned with conductivity, relative dielectric constant, density, specific heat capacity and thermal conductivity parameters. Under the conditions of rated voltage U, rated current I and preset temperature, coupled simulation calculation is performed according to the electromagnetic field physics equation and solid heat transfer physics equation:

The electromagnetic field physics equation is as follows:

Where J is the total current density, Qj _,V is the total charge, σ is the conductivity, E is the electric field intensity, and _Je is the displacement current density;

The physical equation for solid heat transfer is as follows:

Wherein, t is the preset temperature, k is the thermal conductivity, Q=J·E is the internal heat source of the cable, and Q _out is the external heat source of the cable.

Among them, obtaining the insulation and reinforced insulation interface length includes:

The initial length L of the insulation and reinforced insulation interface is determined according to the following formula:

Taking the preset distance as an interval, increase the initial length of the joint insulation and enhanced insulation interface, determine the electric field distribution in the UHV DC cable joint model with different interface lengths under no-load and full-load conditions, if the change rate of the tangential electric field of the joint interface under no-load and full-load conditions ΔE% ≥ 1%, continue to increase the interface length until ΔE% < 1%, and take the length before the last calculation as the UHV DC cable joint interface length;

ΔE% is the rate of change of the tangential electric field at the joint interface, and _ET is the critical breakdown field strength of the interface.

Among them, obtaining the joint enhanced insulation thickness includes:

The initial thickness of the joint reinforced insulation layer is determined according to the following formula:

Taking the preset distance as an interval, reduce the initial thickness of the joint reinforced insulation, determine the steady-state temperature of the cable conductor in the UHV DC cable joint model under full load conditions, if the steady-state temperature of the cable conductor under full load conditions is greater than T _max , continue to reduce the thickness of the joint reinforced insulation until the highest steady-state temperature of the conductor is less than and close to T _max , and take the thickness value calculated last time as the thickness of the UHV DC cable joint reinforced insulation;

T _max is the maximum allowable continuous operating temperature of the UHV DC cable insulation material.

The present invention gradually optimizes and determines the joint interface length, enhanced insulation thickness and enhanced insulation material parameters that meet the design requirements of the UHV DC cable joint through relatively accurate data fitting of the relationship between the electrical conductivity of the insulating material and the temperature and electric field, solves the optimization problem of the electric field and thermal field distribution in the UHV DC cable joint, and effectively controls the joint length and outer diameter (thickness), so that the UHV DC cable joint meets the electrical and thermal field performance requirements, and greatly facilitates the processing, manufacturing and installation of the UHV DC cable joint.

Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The schemes in the embodiments of the present application may be implemented in various computer languages, such as object-oriented programming language Java and literal scripting language JavaScript, etc.

The present application is described with reference to the flowchart and/or block diagram of the method, device (system), and computer program product according to the embodiment of the present application. It should be understood that each process and/or box in the flowchart and/or block diagram, as well as the combination of the process and/or box in the flowchart and/or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate a device for implementing the functions specified in one process or multiple processes in the flowchart and/or one box or multiple boxes in the block diagram.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device that implements the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

These computer program instructions may also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce computer-implemented processing, whereby the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

Although the preferred embodiments of the present application have been described, other changes and modifications may be made to these embodiments once those skilled in the art have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims (8)

1. A method for enhancing insulation of a joint of an ultra-high voltage direct current cable, the method comprising: Conduct conductivity tests at different temperatures and field strengths on the insulation materials and original reinforced insulation materials of characteristic high-voltage DC cable connectors, obtain test data, perform conductivity fitting on the test data, and determine characterization parameters; For UHV DC cable joints, the electrothermal coupling physical field simulation calculation is performed on the UHV DC cable joint model under preset conditions to determine the insulation and enhanced insulation interface length of the UHV DC cable joint, as well as the enhanced insulation thickness of the joint; According to the characterization parameters, the optimization data of the insulation and reinforced insulation interface length and the joint reinforced insulation thickness are obtained by simulation calculation; Modify the enhanced insulation material of the UHV DC cable joint, test the conductivity data of the modified different enhanced insulation materials, perform conductivity fitting on the test data, and obtain the conductivity fitting parameters of the modified enhanced insulation material; The fitting parameters of the conductivity of the modified enhanced insulating material are used to determine the type of enhanced insulating material in the joint of the UHV DC cable; According to the type of the reinforced insulation material in the joint, the insulation structure is installed according to the size information, and the insulation structure is used to enhance the insulation performance of the joint of the UHV DC cable; The electrothermal coupling physical field simulation calculation comprises: Each component unit in the UHV DC cable joint model is assigned with conductivity, relative dielectric constant, density, specific heat capacity and thermal conductivity parameters. Under the conditions of rated voltage U, rated current I and preset temperature, coupled simulation calculation is performed according to the electromagnetic field physics equation and solid heat transfer physics equation: The electromagnetic field physics equation is as follows: Where J is the total current density, Q _j,v is the total charge, σ is the conductivity, E is the electric field intensity, and J _e is the displacement current density; The physical equation for solid heat transfer is as follows: Where t is the preset temperature, k is the thermal conductivity, Q = J·E is the internal heat source of the cable, and Q _out is the external heat source of the cable; The step of obtaining the insulation and enhanced insulation interface length comprises: The initial length L of the insulation and reinforced insulation interface is determined according to the following formula: Taking the preset distance as an interval, increase the initial length of the joint insulation and enhanced insulation interface, determine the electric field distribution in the UHV DC cable joint model with different interface lengths under no-load and full-load conditions, if the change rate of the tangential electric field of the joint interface under no-load and full-load conditions ΔE% ≥ 1%, continue to increase the interface length until ΔE% < 1%, and take the length before the last calculation as the UHV DC cable joint interface length; ΔE% is the rate of change of the tangential electric field at the joint interface, and _ET is the critical breakdown field strength of the interface. 2. The method according to claim 1, wherein the conductivity fitting of the test data uses the following formula: Where, σ is the conductivity, T is the test temperature, E is the test electric field and E>0, A is the material constant, B is the field strength coefficient, is the activation energy, q is the electron charge, and k _b is the Boltzmann constant; Characterization parameters include: material constant A, field strength coefficient B, and activation energy parameter 3. According to the method of claim 1, the establishment of the UHV DC cable joint model comprises: Determine the shape curves of the stress cone and high-voltage shielding tube in the UHV DC cable joint, obtain the parameters of the outer diameter and thickness of the insulating layer, outer shielding layer, buffer layer, metal sheath and outer sheath of the insulating material and reinforced insulating material of the matching UHV DC cable joint, establish the axial section two-dimensional graphics of the UHV DC cable joint according to the parameters, and establish the UHV DC cable joint model according to the axial section two-dimensional graphics. 4. The method according to claim 1, wherein obtaining the joint enhanced insulation thickness comprises: The initial thickness of the joint reinforced insulation layer is determined according to the following formula: Taking the preset distance as an interval, reduce the initial thickness of the joint reinforced insulation, determine the steady-state temperature of the cable conductor in the UHV DC cable joint model under full load conditions, if the steady-state temperature of the cable conductor under full load conditions is greater than T _max , continue to reduce the thickness of the joint reinforced insulation until the highest steady-state temperature of the conductor is less than and close to T _max , and take the thickness value calculated last time as the thickness of the UHV DC cable joint reinforced insulation; T _max is the maximum allowable continuous operating temperature of the UHV DC cable insulation material. 5. A system for enhancing insulation of a joint of an ultra-high voltage direct current cable, the system comprising: The initial module conducts conductivity tests on the insulation materials and original reinforced insulation materials of the characteristic high-voltage DC cable connectors at different temperatures and different field strengths, obtains test data, performs conductivity fitting on the test data, and determines characterization parameters; The structural optimization calculation module performs electrothermal coupling physical field simulation calculation on the UHV DC cable joint model under preset conditions to determine the insulation and enhanced insulation interface length of the UHV DC cable joint and the thickness of the joint enhanced insulation. The material optimization module uses simulation calculation to obtain the optimization data of the insulation and reinforced insulation interface length and the joint reinforced insulation thickness according to the characterization parameters; Modify the enhanced insulation material of the UHV DC cable joint, test the conductivity data of the modified different enhanced insulation materials, perform conductivity fitting on the test data, and obtain the conductivity fitting parameters of the modified enhanced insulation material; The fitting parameters of the conductivity of the modified enhanced insulating material are used to determine the type of enhanced insulating material in the joint of the UHV DC cable; According to the type of the reinforced insulation material in the joint, the insulation structure is installed according to the size information, and the insulation structure is used to enhance the insulation performance of the joint of the UHV DC cable; The electrothermal coupling physical field simulation calculation comprises: Each component unit in the UHV DC cable joint model is assigned with conductivity, relative dielectric constant, density, specific heat capacity and thermal conductivity parameters. Under the conditions of rated voltage U, rated current I and preset temperature, coupled simulation calculation is performed according to the electromagnetic field physics equation and solid heat transfer physics equation: The electromagnetic field physics equation is as follows: Where J is the total current density, Qj _,V is the total charge, σ is the conductivity, E is the electric field intensity, and _Je is the displacement current density; The physical equation for solid heat transfer is as follows: Where t is the preset temperature, k is the thermal conductivity, Q = J·E is the internal heat source of the cable, and Q _out is the external heat source of the cable; The step of obtaining the insulation and enhanced insulation interface length comprises: The initial length L of the insulation and reinforced insulation interface is determined according to the following formula; Taking the preset distance as an interval, increase the initial length of the joint insulation and enhanced insulation interface, determine the electric field distribution in the UHV DC cable joint model with different interface lengths under no-load and full-load conditions, if the change rate of the tangential electric field of the joint interface under no-load and full-load conditions ΔE% ≥ 1%, continue to increase the interface length until ΔE% < 1%, and take the length before the last calculation as the UHV DC cable joint interface length; ΔE% is the rate of change of the tangential electric field at the joint interface, and _ET is the critical breakdown field strength of the interface. 6. The system according to claim 5, wherein the conductivity fitting of the test data uses the following formula: Where, σ is the conductivity, T is the test temperature, E is the test electric field and E>0, A is the material constant, B is the field strength coefficient, is the activation energy, q is the electron charge, and k _b is the Boltzmann constant; Characterization parameters include: material constant A, field strength coefficient B, and activation energy parameter 7. According to the system of claim 5, the establishment of the UHV DC cable joint model comprises: Determine the shape curves of the stress cone and high-voltage shielding tube in the UHV DC cable joint, obtain the parameters of the outer diameter and thickness of the insulating layer, outer shielding layer, buffer layer, metal sheath and outer sheath of the insulating material and reinforced insulating material of the matching UHV DC cable joint, establish the axial section two-dimensional graphics of the UHV DC cable joint according to the parameters, and establish the UHV DC cable joint model according to the axial section two-dimensional graphics. 8. The system according to claim 5, wherein obtaining the joint enhanced insulation thickness comprises: The initial thickness of the joint reinforced insulation layer is determined according to the following formula: Taking the preset distance as an interval, reduce the initial thickness of the joint reinforced insulation, determine the steady-state temperature of the cable conductor in the UHV DC cable joint model under full load conditions, if the steady-state temperature of the cable conductor under full load conditions is greater than T _max , continue to reduce the thickness of the joint reinforced insulation until the highest steady-state temperature of the conductor is less than and close to T _max , and take the thickness value calculated last time as the thickness of the UHV DC cable joint reinforced insulation; T _max is the maximum allowable continuous operating temperature of the UHV DC cable insulation material.