Method and system for evaluating electrical resistance of model cable

Abstract

The invention discloses a method and a system for evaluating the electrical resistance of a model cable. The method comprises the following steps: acquiring the maximum value of an electric field of a real cable under a test voltage; applying a voltage to the model cable, and calculating the electric field distribution in the model cable to obtain the maximum value of the applied voltage when the insulation maximum electric field reaches the maximum value of the electric field; acquiring rated voltage of the model cable based on the maximum value of the applied voltage; and determining a test voltage based on the rated voltage, and performing a withstand voltage test on the model cable based on the test voltage to evaluate the electrical resistance of the model cable. According to the method, the model cable is adopted to replace a real cable to evaluate the insulation processing performance, the insulation performance can be quantitatively analyzed faster, more conveniently and at lower cost, the installation of joints and terminal accessories in the test process of the real cable can be reduced, and the test time is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of cable evaluation, and more specifically, to a method and system for evaluating the electrical resistance performance of a model cable. Background Art

[0002] In the development process of polymer insulation materials and power cables, it is necessary to use cable specimens of different sizes and structures for equivalent testing and analysis to verify the insulation performance of larger cable specimens. This is because the insulation performance of the cable will be affected during processing or post-processing, but there is currently no unified verification method for cables with different sizes and thicknesses of insulation, and the effectiveness has not been verified. In the development of ultra-high voltage cables, it is not enough to test only by traditional methods, that is, the design is based on the average insulation field strength, which is not comprehensive for thick insulation. On the one hand, the size effect during insulation breakdown has not been taken into account. On the other hand, the field strength distribution of cables in thick insulation is different from that of cables with small thickness, and there is a significant difference in the maximum field strength. Therefore, the requirements for insulation during the test of thick insulation cables are higher than those for the electrical resistance of small thickness insulation cables under equal field strength. The traditional equal field strength method is not applicable, and an improved equal field strength test method must be proposed.

[0003] Therefore, in order to evaluate and analyze the comprehensive performance of cable insulation and verify whether it meets the requirements of thick and high voltage grade insulated cables, a method for evaluating the electrical resistance performance of model cables is needed. Summary of the invention

[0004] The present invention provides a method and system for evaluating the electrical resistance performance of a model cable, so as to solve the problem of how to efficiently determine the electrical resistance performance of a cable.

[0005] In order to solve the above problems, according to one aspect of the present invention, a method for evaluating the electrical resistance performance of a model cable is provided, the method comprising:

[0006] Obtain the maximum value of the electric field of the real cable under the test voltage;

[0007] Applying voltage to the model cable and calculating the electric field distribution in the model cable to obtain a maximum value of the applied voltage when the maximum insulation electric field reaches the maximum value of the electric field;

[0008] Obtaining a rated voltage of the model cable based on the maximum applied voltage;

[0009] A test voltage is determined based on the rated voltage, and a withstand voltage test is performed on the model cable based on the test voltage to evaluate the electrical withstand performance of the model cable.

[0010] Preferably, the step of obtaining the maximum electric field value of the real cable under test conditions comprises:

[0011] The maximum value of the electric field of the real cable under the test conditions is obtained by solving the following formula, including:

[0012]

[0013] Among them, E max is the maximum value of the electric field; B is the material temperature coefficient; is the activation energy; q is the electron charge; k b is the Boltzmann constant; T av is the temperature at the middle point of the cable insulation layer; T2 is the core temperature; T1 is the external temperature of the cable insulation layer; r av is the radius of the middle point of the insulation layer; ΔT is the temperature gradient on the insulation layer; R is the insulation outer radius; ΔT = T2-T1; E av is the electric field at the middle point of the cable insulation layer; U is the cable voltage; r c is the insulation inner radius.

[0014] Preferably, the step of applying voltage to the model cable and calculating the electric field distribution in the model cable to obtain the maximum value of the applied voltage when the maximum insulation electric field reaches the maximum value of the electric field comprises:

[0015] S1, initialization iteration number n = 1, determine the initial applied voltage U n =(hs / ht)*U0; where ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; U0 is the test voltage;

[0016] S2, based on the current applied voltage U n Calculate the electric field distribution in the model cable to obtain the current maximum insulation electric field value;

[0017] S3, determining whether the current maximum insulation electric field value is equal to the electric field maximum value, and obtaining a determination result;

[0018] S4, if the judgment result indicates that the current maximum insulation electric field value is equal to the maximum electric field value, then determine that the currently applied voltage is the maximum applied voltage, and end; conversely, if the judgment result indicates that the current maximum insulation electric field value is greater than the maximum electric field value, then update the applied voltage Update n=n+1, and return to step S2 to recalculate; if the judgment result indicates that the current maximum insulation electric field value is less than the maximum electric field value, then update the applied voltage to Update n=n+1, and return to step S2 to recalculate; wherein △U is the voltage adjustment value.

[0019] Preferably, the step of obtaining the rated voltage of the model cable based on the maximum applied voltage comprises:

[0020] U t =U p / (ht / hs)^-m,

[0021] Among them, U t is the rated voltage; U p is the maximum applied voltage; ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; m is the size effect parameter; ^ represents exponential operation.

[0022] Preferably, the test voltage is 1.85 times the rated voltage.

[0023] According to another aspect of the present invention, a system for evaluating the electrical resistance performance of a model cable is provided, the system comprising:

[0024] The electric field maximum value acquisition unit is used to obtain the electric field maximum value of the real cable under the test voltage;

[0025] an applied voltage maximum value acquisition unit, used for applying voltage to the model cable and calculating the electric field distribution in the model cable to obtain the maximum applied voltage value when the insulation maximum electric field reaches the electric field maximum value;

[0026] A rated voltage acquisition unit, used for acquiring the rated voltage of the model cable based on the maximum value of the applied voltage;

[0027] The electrical withstand performance evaluation unit is used to determine a test voltage based on the rated voltage, and to perform a withstand voltage test on the model cable based on the test voltage to evaluate the electrical withstand performance of the model cable.

[0028] Preferably, the electric field maximum value acquisition unit acquires the electric field maximum value of the real cable under the test conditions, including:

[0029] The maximum value of the electric field of the real cable under the test conditions is obtained by solving the following formula, including:

[0030]

[0031] Among them, E max is the maximum value of the electric field; B is the material temperature coefficient; is the activation energy; q is the electron charge; k b is the Boltzmann constant; T av is the temperature at the middle point of the cable insulation layer; T2 is the core temperature; T1 is the external temperature of the cable insulation layer; r avis the radius of the middle point of the insulation layer; ΔT is the temperature gradient on the insulation layer; R is the insulation outer radius; ΔT = T2-T1; E av is the electric field at the middle point of the cable insulation layer; U is the cable voltage; r c is the insulation inner radius.

[0032] Preferably, the applied voltage maximum value acquisition unit applies voltage to the model cable and calculates the electric field distribution in the model cable to obtain the maximum applied voltage value when the insulation maximum electric field reaches the electric field maximum value, including:

[0033] Initialization module, used to initialize the number of iterations n = 1, determine the initial applied voltage U n =(hs / ht)*U0; where ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; U0 is the test voltage;

[0034] The insulation maximum electric field value acquisition module is used to obtain the maximum electric field value based on the current applied voltage U n Calculate the electric field distribution in the model cable to obtain the current maximum insulation electric field value;

[0035] A judgment module, used to judge whether the current maximum insulation electric field value is equal to the electric field maximum value, and obtain a judgment result;

[0036] The maximum applied voltage acquisition module is used to determine that the currently applied voltage is the maximum applied voltage if the judgment result indicates that the current maximum insulation electric field value is equal to the maximum electric field value, and then end; if the judgment result indicates that the current maximum insulation electric field value is greater than the maximum electric field value, then update the applied voltage Update n=n+1, and enter the insulation maximum electric field value acquisition module to recalculate; if the judgment result indicates that the current insulation maximum electric field value is less than the electric field maximum value, then update the applied voltage to Update n=n+1, and enter the insulation maximum electric field value acquisition module to recalculate; where △U is the voltage adjustment value.

[0037] Preferably, the rated voltage acquisition unit acquires the rated voltage of the model cable based on the maximum applied voltage, comprising:

[0038] U t =U p / (ht / hs)^-m,

[0039] Among them, U t is the rated voltage; U p is the maximum applied voltage; ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; m is the size effect parameter; ^ represents exponential operation.

[0040] Preferably, the test voltage is 1.85 times the rated voltage.

[0041] The present invention provides a method and system for evaluating the electrical resistance performance of a model cable, including: obtaining the maximum value of the electric field of a real cable under a test voltage; applying voltage to the model cable, and calculating the electric field distribution in the model cable to obtain the maximum value of the applied voltage when the insulation maximum electric field reaches the maximum value of the electric field; obtaining the rated voltage of the model cable based on the maximum applied voltage; determining the test voltage based on the rated voltage, and performing a withstand voltage test on the model cable based on the test voltage to evaluate the electrical resistance performance of the model cable. The present invention uses a model cable instead of a real cable to evaluate the insulation processing performance. This method can quantitatively analyze the insulation performance faster, more conveniently, and at a lower cost, and can reduce the installation of joints and terminal accessories during the real cable test, saving test time. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0043] Figure 1 is a flow chart of a method 100 for evaluating the electrical resistance performance of a model cable according to an embodiment of the present invention;

[0044] Figure 2 A schematic diagram of a cable calculation model according to an embodiment of the present invention;

[0045] Figure 3 is a schematic diagram of insulation temperature difference according to an embodiment of the present invention;

[0046] Figure 4 A flowchart of determining the maximum value of an applied voltage based on a dichotomy method according to an embodiment of the present invention;

[0047] Figure 5 is a schematic diagram of the size effect according to an embodiment of the present invention;

[0048] Figure 6 A schematic diagram of a device for performing a withstand voltage test according to an embodiment of the present invention;

[0049] Figure 7 is a schematic diagram of different sections of a cable according to an embodiment of the present invention;

[0050] Figure 8 is a cross-sectional view of a model cable according to an embodiment of the present invention;

[0051] Fig. 9 A schematic diagram of the electric field inside and outside the cable insulation layer under different insulation temperature differences according to an embodiment of the present invention;

[0052] Fig.10 Schematic diagram of the structure of a system 1000 for evaluating the electrical resistance performance of a model cable according to an embodiment of the present invention. DETAILED DESCRIPTION

[0053] 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.

[0054] 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.

[0055] Figure 1 FIG. 1 is a flow chart of a method 100 for evaluating the electrical resistance performance of a model cable according to an embodiment of the present invention. Figure 1 As shown, the method for evaluating the electrical resistance performance of a model cable provided by an embodiment of the present invention uses a model cable instead of a real cable to evaluate the insulation processing performance. This method can quantitatively analyze the insulation performance faster, more conveniently, and at a lower cost, and can reduce the installation of connectors and terminal accessories during the real cable test, saving test time. The method 100 for evaluating the electrical resistance performance of a model cable provided by an embodiment of the present invention starts from step 101. In step 101, the maximum value of the electric field of the real cable under the test voltage is obtained.

[0056] Preferably, the step of obtaining the maximum electric field value of the real cable under test conditions comprises:

[0057] The maximum value of the electric field of the real cable under the test conditions is obtained by solving the following formula, including:

[0058]

[0059] Among them, E max is the maximum value of the electric field; B is the material temperature coefficient; is the activation energy; q is the electron charge; k b is the Boltzmann constant; T av is the temperature at the middle point of the cable insulation layer; T2 is the core temperature; T1 is the external temperature of the cable insulation layer; r avis the radius of the middle point of the insulation layer; ΔT is the temperature gradient on the insulation layer; R is the insulation outer radius; ΔT = T2-T1; E av is the electric field at the middle point of the cable insulation layer; U is the cable voltage; r c is the insulation inner radius.

[0060] In the present invention, in order to verify that the small thickness insulation model cable can meet the long-term operation needs of the large thickness real cable under the condition of equal field strength, it is first necessary to know the electric field distribution characteristics of insulation cables of different thicknesses to obtain the maximum electric field Emax of the real cable under test conditions (voltage is U0).

[0061] In the present invention, the electric-thermal field simulation calculation of the target cable is carried out, a simulation model is established, key parameters are input, operating conditions are determined, and the following is constructed: Figure 2 Computational model of the cable shown to solve for the electric field distribution in the polymer insulation.

[0062] Specifically, the method for determining the maximum value of the electric field in the insulation layer includes the following steps: a. fitting the conductivity function of the DC cable insulation material; b. calculating the equivalent conductivity; c. calculating the electric field value and temperature value at the middle of the DC cable insulation layer; d. calculating the leakage current in the insulation layer; e. calculating the electric field distribution based on the current continuity principle; f. determining the maximum value of the electric field in the insulation layer.

[0063] Wherein, in the step a, the conductivity function of the DC cable insulation material is fitted using the following equation:

[0064]

[0065] Where σ is the conductivity (S / m), A is the coefficient to be determined (S / m), B is the material temperature coefficient (K), and C is the material electric field coefficient ((m / V) 1 / 2 ), T is temperature (K), and E is electric field (V / m).

[0066] Among them, the material temperature coefficient is

[0067] in, is the activation energy (eV); q is the electron charge (C); k b is the Boltzmann constant (J / K).

[0068] Wherein, in step a, fitting can be performed by a two-step algorithm. By σ(T)=A1e -BT The coefficient B of conductivity changing with temperature can be fitted; The coefficient C of conductivity changing with field strength can be fitted, and the coefficients B and C are again introduced into Thus, the coefficient A is obtained.

[0069] Wherein, in step b, the equivalent conductivity represents the value of the insulation conductivity at the middle point of the insulation layer, which is calculated according to the formula obtained in step a as follows:

[0070]

[0071] in, av is the average field strength (V / m); σ av is the equivalent conductivity (V / m); T av is the middle temperature of the insulation layer (K);

[0072] Wherein, in the step c, the electric field at the middle point of the DC cable insulation layer is calculated according to the average field strength formula:

[0073]

[0074] Where, U is the cable voltage (V); R is the outer radius of the insulation (m); r c is the insulation inner radius (m).

[0075] Wherein, in the step c, the electric field at the middle point of the insulation layer of the DC cable does not change with the core temperature and temperature gradient, but is only related to the voltage applied to the cable and the insulation thickness, and is therefore equal to the average field strength.

[0076] Wherein, in the step c, the temperature at the middle point of the DC cable insulation layer is calculated according to the formula:

[0077]

[0078] Where, T2 is the core temperature (K), T1 is the outer temperature of the insulation layer (K), r av is the radius of the middle point of the insulating layer (V / m); ΔT is the temperature gradient on the insulating layer (K).

[0079] The radius of the middle point of the insulating layer is

[0080] Among them, the calculation formula for leakage current in the insulation layer is:

[0081] I0=2πrJ,

[0082] Where I0 is the leakage current (A), r is the radius of the insulation layer (m), and J is the leakage current density (A / m).

[0083] Wherein, in step d, the cable leakage current density J is

[0084] J(r)=E(r)σ(E,T),

[0085] Wherein, in step d, the leakage current value in the cable insulation layer is

[0086] I0=2πr av J(r av )=2πr av E av σ av .

[0087] Wherein, in step e, the electric field distribution in the cable insulation layer satisfies the current continuity principle: I0=2πr av J(r av )=2πr av E av σ av =2πrEσ.

[0088] Among them, in the step f, the maximum field strength E of the insulating layer is designed max As we all know, when the cable is running at maximum load, the field strength is located outside the insulation layer, so the radius is R, which can be calculated as

[0089]

[0090] Among them, in the step f, combined with the leakage current formula, it can be obtained as

[0091]

[0092] Furthermore, by introducing the conductivity fitting function, we can get:

[0093]

[0094] Further, we can get:

[0095]

[0096] Among them, E max is the maximum electric field in the insulation. By solving the above formula, we can get E max .

[0097] In step 102, a voltage is applied to the model cable, and the electric field distribution in the model cable is calculated to obtain the maximum value of the applied voltage when the maximum insulation electric field reaches the maximum value of the electric field.

[0098] Preferably, the step of applying voltage to the model cable and calculating the electric field distribution in the model cable to obtain the maximum value of the applied voltage when the maximum insulation electric field reaches the maximum value of the electric field comprises:

[0099] S1, initialization iteration number n = 1, determine the initial applied voltage U n=(hs / ht)*U0; where ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; U0 is the test voltage;

[0100] S2, based on the current applied voltage U n Calculate the electric field distribution in the model cable to obtain the current maximum insulation electric field value;

[0101] S3, determining whether the current maximum insulation electric field value is equal to the electric field maximum value, and obtaining a determination result;

[0102] S4, if the judgment result indicates that the current maximum insulation electric field value is equal to the maximum electric field value, then determine that the currently applied voltage is the maximum applied voltage, and end; conversely, if the judgment result indicates that the current maximum insulation electric field value is greater than the maximum electric field value, then update the applied voltage Update n=n+1, and return to step S2 to recalculate; if the judgment result indicates that the current maximum insulation electric field value is less than the maximum electric field value, then update the applied voltage to Update n=n+1, and return to step S2 to recalculate; wherein △U is the voltage adjustment value.

[0103] In the present invention, a voltage is applied to the model cable, and the electric field distribution in the model cable is calculated according to the maximum electric field value Emax, so as to obtain the maximum applied voltage Up when the maximum electric field distribution of the insulation reaches the Emax value. In the above process, the applied voltage needs to be repeatedly adjusted for calculation. Among them, the applied voltage can be adjusted by the dichotomy method. Specifically, the process of determining the maximum applied voltage includes: S1, initializing the number of iterations n=1, determining the initial applied voltage U n =(hs / ht)*U0; where ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; U0 is the test voltage;

[0104] S2, based on the current applied voltage U n Calculate the electric field distribution in the model cable to obtain the current maximum insulation electric field value;

[0105] S3, determining whether the current maximum insulation electric field value is equal to the electric field maximum value, and obtaining a determination result;

[0106] S4, if the judgment result indicates that the current maximum insulation electric field value is equal to the maximum electric field value, then determine that the currently applied voltage is the maximum applied voltage, and end; conversely, if the judgment result indicates that the current maximum insulation electric field value is greater than the maximum electric field value, then update the applied voltage Update n=n+1, and return to step S2 to recalculate; the judgment result indicates

[0107] If the current maximum insulation electric field value is less than the maximum electric field value, the applied voltage is updated to Update n=n+1, and return to step S2 to recalculate; wherein △U is the voltage adjustment value.

[0108] For example, Figure 4 As shown, the initial applied voltage U1=(hs / ht)*U0 is set and substituted into the calculation. If the maximum electric field value is less than Emax, U2=U1±△U is used for calculation, and △U is preferably 50kV. If the maximum electric field value is still not equal to Emax, U3=U2±0.5△U is used for calculation, so as to gradually determine the actual maximum voltage Up.

[0109] The method of the present invention breaks through the limitation of the traditional method of using the average field strength as the calculation, and uses the maximum field strength in the insulating layer as the basis for voltage calculation, which is more in line with the actual field verification.

[0110] In step 103, the rated voltage of the model cable is obtained based on the maximum applied voltage.

[0111] Preferably, the step of obtaining the rated voltage of the model cable based on the maximum applied voltage comprises:

[0112] U t =U p / (ht / hs)^-m,

[0113] Among them, U t is the rated voltage; U p is the maximum applied voltage; ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; m is the size effect parameter; ^ represents exponential operation.

[0114] According to the size effect of insulation, the size effect coefficient of insulation breakdown is considered. In order to ensure the margin of insulation, it is generally a fixed value (about 0.4). The test voltage of the model cable is calculated, that is, the maximum field strength voltage divided by the size effect coefficient:

[0115] Size effect Figure 4 As shown, for polymer insulation, the general size effect parameter m is about 0.4. Preferably, it can be tested by the polarity of the withstand voltage test. For the thickness of the real cable ht and the model cable prototype hs, the maximum voltage is Ut = Up / (ht / hs)^-m. The size effect is as follows Figure 5 shown.

[0116] The method of the present invention corrects the applied voltage of the model cable according to the size effect parameter, obtains the rated voltage for the electrical resistance test, and can better evaluate the application reliability of the thick-insulated real cable.

[0117] In step 104, a test voltage is determined based on the rated voltage, and a withstand voltage test is performed on the model cable based on the test voltage to evaluate the electrical withstand performance of the model cable.

[0118] Preferably, the test voltage is 1.85 times the rated voltage.

[0119] In the present invention, the test voltage is determined according to the rated voltage, and the test verification is carried out to judge whether the insulation material is reliable by whether the cable is broken down. Specifically, the model cable is subjected to 12 negative polarity withstand voltage tests, 12 positive polarity withstand voltage tests and 3 positive polarity withstand voltage tests at a voltage of 1.85 times Ut to verify the reliability of the insulation, which directly determines whether the cable can meet the application requirements of the cable. The device in the test process is as follows Figure 6 As shown, the structure of different sections of the cable is as follows Figure 7 As shown, the cross-sectional structure of the model cable is as follows Figure 8 As shown. Among them, 1 is a high-voltage generator, 2 is a control system, 3 is a metal clamp, 4 is a cable support, 5 is a through-core transformer, 6 is a model cable, 7 is a temperature measurement system, 8 is a cable unstripped section, 9 is a cable stripped sheath section, 10 is a cable stripped outer shield section, 11 is a cable shield break, 12 is a cable conductor, 13 is a cable insulation layer, 14 is a cable shield layer, and 15 is a cable outer sheath. During the test, the outer sheath 15 and the shielding layer 14 at both ends of the model cable 6 are firstly stripped for a length as required, and then installed on the cable support 4, and the vertical distance from the ground reaches about 2m; the model cable passes through the through-core transformer 5 in the middle to heat up the cable conductor; a temperature measuring thermocouple is installed on the surface of the cable outer sheath and connected to the temperature measurement system 7 to simulate the temperature control of the cable conductor 12; the conductors at both ends of the cable are fixed with metal clamps 3, and connected to the high-voltage generator 1 and the control platform 2, and pressurized according to the test method, and a withstand voltage test is carried out to determine the electrical resistance performance.

[0120] The following specifically illustrates the embodiments of the present invention.

[0121] In the embodiment of the present invention, the ±535kV DC cable currently used in the project is taken as an example to analyze its electric field distribution and current carrying capacity characteristics. The conductor cross-section of the ±535kV DC cable is 3000mm2, the average field strength is 17.83kV / mm, and the insulation design field strength is 23.6kV / mm. The structural dimensions and thermal parameters are shown in Table 1.

[0122] Table 1 Cable structure dimensions and thermal parameters

[0123]

[0124] like Fig. 9As shown, the electric field distribution inside and outside the insulation layer under different temperature differences when the maximum operating temperature of the conductor is 70°C. The model cable model YJV-±160 is produced by three-layer co-extrusion process for dielectric strength test. The conductor cross-sectional area of ​​the model cable is 185mm2, the insulation thickness is 9mm, the inner shield thickness is 1.2mm (including semi-conductive tape), and the outer shield thickness is 0.8mm. According to the same calculation method, when the maximum field strength is 32kV / mm, the voltage applied to the cable is 200kV. According to the size effect, the rated voltage of the model cable should be: 200 / (30 / 10)^-0.4=310kV. According to the test with a voltage of 1.85*310=574KV, the test passed the requirements, that is, it was determined to meet the ±500kV test requirements.

[0125] Fig.10 FIG. 1 is a schematic diagram of a system 1000 for evaluating the electrical resistance performance of a model cable according to an embodiment of the present invention. Fig.10 As shown, the electrical resistance performance evaluation system 1000 of the model cable provided in the embodiment of the present invention includes: an electric field maximum value acquisition unit 1001, an applied voltage maximum value acquisition unit 1002, a rated voltage acquisition unit 1003 and an electrical resistance performance evaluation unit 1004.

[0126] Preferably, the electric field maximum value acquisition unit 1001 is used to obtain the maximum value of the electric field of the real cable under the test voltage.

[0127] Preferably, the electric field maximum value acquisition unit 1001 acquires the electric field maximum value of the real cable under the test conditions, including:

[0128] The maximum value of the electric field of the real cable under the test conditions is obtained by solving the following formula, including:

[0129]

[0130] Among them, E max is the maximum value of the electric field; B is the material temperature coefficient; is the activation energy; q is the electron charge; k b is the Boltzmann constant; T av is the temperature at the middle point of the cable insulation layer; T2 is the core temperature; T1 is the external temperature of the cable insulation layer; r av is the radius of the middle point of the insulation layer; ΔT is the temperature gradient on the insulation layer; R is the insulation outer radius; ΔT = T2-T1; E av is the electric field at the middle point of the cable insulation layer; U is the cable voltage; r c is the insulation inner radius.

[0131] Preferably, the applied voltage maximum value acquisition unit 1002 is used to apply voltage to the model cable and calculate the electric field distribution in the model cable to obtain the maximum applied voltage when the maximum insulation electric field reaches the electric field maximum value.

[0132] Preferably, the applied voltage maximum value acquisition unit 1002 applies voltage to the model cable and calculates the electric field distribution in the model cable to obtain the maximum applied voltage value when the insulation maximum electric field reaches the electric field maximum value, including:

[0133] Initialization module, used to initialize the number of iterations n = 1, determine the initial applied voltage U n =(hs / ht)*U0; where ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; U0 is the test voltage;

[0134] The insulation maximum electric field value acquisition module is used to obtain the maximum electric field value based on the current applied voltage U n Calculate the electric field distribution in the model cable to obtain the current maximum insulation electric field value;

[0135] A judgment module, used to judge whether the current maximum insulation electric field value is equal to the electric field maximum value, and obtain a judgment result;

[0136] The maximum applied voltage acquisition module is used to determine that the currently applied voltage is the maximum applied voltage if the judgment result indicates that the current maximum insulation electric field value is equal to the maximum electric field value, and then end; if the judgment result indicates that the current maximum insulation electric field value is greater than the maximum electric field value, then update the applied voltage Update n=n+1, and enter the insulation maximum electric field value acquisition module to recalculate; if the judgment result indicates that the current insulation maximum electric field value is less than the electric field maximum value, then update the applied voltage to Update n=n+1, and enter the insulation maximum electric field value acquisition module to recalculate; where △U is the voltage adjustment value.

[0137] Preferably, the rated voltage acquisition unit 1003 is used to acquire the rated voltage of the model cable based on the maximum applied voltage.

[0138] Preferably, the rated voltage acquisition unit 1003 acquires the rated voltage of the model cable based on the maximum applied voltage, including:

[0139] U t =U p / (ht / hs)^-m,

[0140] Among them, U t is the rated voltage; U pis the maximum applied voltage; ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; m is the size effect parameter; ^ represents exponential operation.

[0141] Preferably, the electrical withstand performance evaluation unit 1004 is used to determine a test voltage based on the rated voltage, and perform a withstand voltage test on the model cable based on the test voltage to evaluate the electrical withstand performance of the model cable.

[0142] Preferably, the test voltage is 1.85 times the rated voltage.

[0143] The electrical resistance performance evaluation system 1000 of the model cable in the embodiment of the present invention corresponds to the electrical resistance performance evaluation method 100 of the model cable in another embodiment of the present invention, which will not be described in detail here.

[0144] The invention has been described above with reference to a few embodiments. However, it is readily apparent to a person skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

[0145] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise therein. All references to "a / said / the [means, components, etc.]" are to be openly interpreted as at least one instance of said means, components, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily have to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0146] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take 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 code.

[0147] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks 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 produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0148] These computer program instructions may also be stored in a computer-readable memory capable of directing 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 an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0149] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for evaluating the electrical resistance performance of a model cable, characterized in that: The method comprises: Obtain the maximum value of the electric field of the real cable under the test voltage; Applying voltage to the model cable and calculating the electric field distribution in the model cable to obtain a maximum value of the applied voltage when the maximum insulation electric field reaches the maximum value of the electric field; Obtaining a rated voltage of the model cable based on the maximum applied voltage; A test voltage is determined based on the rated voltage, and a withstand voltage test is performed on the model cable based on the test voltage to evaluate the electrical withstand performance of the model cable.

2. The method according to claim 1, characterized in that The step of obtaining the maximum value of the electric field of the real cable under the test conditions comprises: The maximum value of the electric field of the real cable under the test conditions is obtained by solving the following formula, including: Among them, E max is the maximum value of the electric field; B is the material temperature coefficient; is the activation energy; q is the electron charge; k b is the Boltzmann constant; T av is the temperature at the middle point of the cable insulation layer; T2 is the core temperature; T1 is the external temperature of the cable insulation layer; r av is the radius of the middle point of the insulation layer; ΔT is the temperature gradient on the insulation layer; R is the insulation outer radius; ΔT = T2-T1; E av is the electric field at the middle point of the cable insulation layer; U is the cable voltage; r c is the insulation inner radius.

3. The method according to claim 1, characterized in that The step of applying voltage to the model cable and calculating the electric field distribution in the model cable to obtain the maximum value of the applied voltage when the maximum insulation electric field reaches the maximum value of the electric field comprises: S1, initialization iteration number n = 1, determine the initial applied voltage U n =(hs / ht)*U0; where ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; U0 is the test voltage; S2, based on the current applied voltage U n Calculate the electric field distribution in the model cable to obtain the current maximum insulation electric field value; S3, determining whether the current maximum insulation electric field value is equal to the electric field maximum value, and obtaining a determination result; S4, if the judgment result indicates that the current maximum insulation electric field value is equal to the maximum electric field value, then determine that the currently applied voltage is the maximum applied voltage, and end; conversely, if the judgment result indicates that the current maximum insulation electric field value is greater than the maximum electric field value, then update the applied voltage Update n=n+1, and return to step S2 to recalculate; if the judgment result indicates that the current maximum insulation electric field value is less than the maximum electric field value, then update the applied voltage to Update n=n+1, and return to step S2 to recalculate; wherein △U is the voltage adjustment value.

4. The method according to claim 1, characterized in that: The step of obtaining the rated voltage of the model cable based on the maximum applied voltage comprises: U t =U p / (ht / hs)^-m, Among them, U t is the rated voltage; U p is the maximum applied voltage; ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; m is the size effect parameter; ^ represents exponential operation.

5. The method according to claim 1, characterized in that: The test voltage is 1.85 times the rated voltage.

6. A system for evaluating the electrical resistance performance of a model cable, characterized in that: The system comprises: The electric field maximum value acquisition unit is used to obtain the electric field maximum value of the real cable under the test voltage; an applied voltage maximum value acquisition unit, used for applying voltage to the model cable and calculating the electric field distribution in the model cable to obtain the maximum applied voltage value when the insulation maximum electric field reaches the electric field maximum value; A rated voltage acquisition unit, used for acquiring the rated voltage of the model cable based on the maximum value of the applied voltage; The electrical withstand performance evaluation unit is used to determine a test voltage based on the rated voltage, and to perform a withstand voltage test on the model cable based on the test voltage to evaluate the electrical withstand performance of the model cable.

7. The system according to claim 6, characterized in that The electric field maximum value acquisition unit acquires the electric field maximum value of the real cable under the test conditions, including: The maximum value of the electric field of the real cable under the test conditions is obtained by solving the following formula, including: Among them, E max is the maximum value of the electric field; B is the material temperature coefficient; is the activation energy; q is the electron charge; k b is the Boltzmann constant; T av is the temperature at the middle point of the cable insulation layer; T2 is the core temperature; T1 is the external temperature of the cable insulation layer; r av is the radius of the middle point of the insulation layer; ΔT is the temperature gradient on the insulation layer; R is the insulation outer radius; ΔT = T2-T1; E av is the electric field at the middle point of the cable insulation layer; U is the cable voltage; r c is the insulation inner radius.

8. The system according to claim 6, characterized in that The applied voltage maximum value acquisition unit applies voltage to the model cable and calculates the electric field distribution in the model cable to obtain the applied voltage maximum value when the insulation maximum electric field reaches the electric field maximum value, including: Initialization module, used to initialize the number of iterations n = 1, determine the initial applied voltage U n =(hs / ht)*U0; where ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; U0 is the test voltage; The insulation maximum electric field value acquisition module is used to obtain the maximum electric field value based on the current applied voltage U n Calculate the electric field distribution in the model cable to obtain the current maximum insulation electric field value; A judgment module, used to judge whether the current maximum insulation electric field value is equal to the electric field maximum value, and obtain a judgment result; The maximum applied voltage acquisition module is used to determine that the currently applied voltage is the maximum applied voltage if the judgment result indicates that the current maximum insulation electric field value is equal to the maximum electric field value, and then end; if the judgment result indicates that the current maximum insulation electric field value is greater than the maximum electric field value, then update the applied voltage Update n=n+1, and enter the insulation maximum electric field value acquisition module to recalculate; if the judgment result indicates that the current insulation maximum electric field value is less than the electric field maximum value, then update the applied voltage to Update n=n+1, and enter the insulation maximum electric field value acquisition module to recalculate; where △U is the voltage adjustment value.

9. The system according to claim 6, characterized in that The rated voltage acquisition unit acquires the rated voltage of the model cable based on the maximum applied voltage, including: U t =U p / (ht / hs)^-m, Among them, U t is the rated voltage; U p is the maximum applied voltage; ht is the insulation thickness of the real cable; hs is the insulation thickness of the model cable; m is the size effect parameter; ^ represents exponential operation.

10. The system according to claim 6, characterized in that The test voltage is 1.85 times the rated voltage.

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