Thermal evaluation method and device for pulling and jacking pipe laying double-spliced cable line

Abstract

The invention discloses a thermal evaluation method and device for a double-spliced cable line laid in a pulling and jacking pipe, and the method comprises the steps: obtaining the first AC resistance of a core wire and the second AC resistance of a metal sheath of each cable at the initial temperature of the core wire; actual transmission capacity data and thermal resistance parameters are obtained; obtaining core wire loss and circulating current loss of each cable; obtaining the mutual heating temperature rise of the kth cable to the pth cable; obtaining the self-heating temperature rise of each cable; obtaining a core wire calculation temperature of each cable according to the mutual heating temperature rise, the self-heating temperature rise and the environment boundary temperature of each cable; acquiring a temperature difference value between the core wire initial temperature and the core wire calculation temperature of at least one cable; when the temperature difference value is smaller than or equal to a preset difference value and each core wire calculation temperature is smaller than a first preset temperature, determining the core wire calculation temperature of each cable as a core wire steady-state temperature of each cable; otherwise, determining the core wire calculation temperature of each cable as the core wire initial temperature of each cable; and returning to execute the steps.

Description

Technical Field

[0001] This invention relates to the field of power transmission technology, and in particular to a thermal assessment method and apparatus for laying double-section cable lines using jacking pipes. Background Technology

[0002] With the development of the national economy and the advancement of urbanization, urban electricity load is characterized by high density and rapid growth, which places higher demands on the transmission capacity of power transmission lines. As the mainstay of the power transmission network, the current-carrying capacity of cable lines is determined by the long-term temperature resistance of their insulation. Once this temperature is exceeded, the service life of the cable will be greatly reduced. Therefore, given a fixed actual power transmission capacity, the temperature rise of the cable's core wire is an important indicator for evaluating its transmission capacity.

[0003] The jacking pipe laying method solves the problem of cables crossing rivers and in trenchless areas, and is one of the important cable laying methods. To address the issue that existing cable models cannot meet transmission capacity requirements, two cables of the same phase are used in parallel within the jacking pipe, making double-stranded cables a common practice. When a load current passes through the conductor of a double-stranded cable, an induced voltage is generated on the metal sheath due to electromagnetic induction. When the metal sheath is grounded, forming a loop with the earth, a circulating current is generated. Therefore, the temperature distribution characteristics of the cable are jointly affected by the load current and the circulating current thermal effect.

[0004] However, due to the temperature-dependent changes in the AC resistance of cable conductors and the influence of proximity effects, the AC resistances of two conductors in the same phase are not perfectly matched. Furthermore, the cable arrangement causes significant differences in the inductive reactance of the conductors and the metal sheath. The complex coupling of load current and circulating current in a double-cable group leads to insufficient accuracy in calculating heat source parameters for thermal assessment. In addition, due to the small geometric spacing between double-cable groups, the heat effect of the load current and circulating current of a single cable not only causes its own temperature rise but also raises the temperature of adjacent cables. Moreover, the temperature rise and heat dissipation among the cable group are highly uneven, and the significant differences in temperature distribution among the six cables cause deviations in the core temperature calculation, resulting in inaccurate assessments of its transmission capacity. Summary of the Invention

[0005] This invention provides a method and apparatus for thermal assessment of double-span cable lines laid with jacking pipes, in order to improve the accuracy of thermal assessment of double-span cable lines.

[0006] According to one aspect of the present invention, a thermal assessment method for double-span cable lines laid using jacking pipes is provided, comprising:

[0007] Obtain the first AC resistance of the core wire and the second AC resistance of the metal sheath of each cable at the initial temperature of the core wire;

[0008] Obtain the actual transmission capacity data of the line and the thermal resistance parameters of each cable;

[0009] Based on the first AC resistance, the second AC resistance, and the actual transmission capacity data of each cable, the core wire loss and circulating current loss of each cable are obtained.

[0010] Based on the mirror symmetry method, the mutual thermal temperature rise between the k-th cable and the p-th cable is obtained according to the core wire loss and the circulating current loss of the k-th cable; where k = 1, 2, 3, 4, 5, 6; p = 1, 2, 3, 4, 5, 6; and k ≠ p;

[0011] The self-heating temperature rise of each cable is obtained based on the core wire loss, circulating current loss and thermal resistance parameters of each cable.

[0012] The calculated core temperature of each cable is obtained based on the mutual heat rise, the self-heat rise, and the ambient boundary temperature of each cable.

[0013] Obtain the temperature difference between the initial temperature of at least one of the core wires of the cable and the calculated temperature of the core wire;

[0014] When the temperature difference is less than or equal to a preset difference, and the calculated temperature of each core wire is less than a first preset temperature, the calculated temperature of the core wire of each cable is determined as the steady-state temperature of the core wire of each cable.

[0015] When the temperature difference exceeds a preset difference or at least one of the core wires has a calculated temperature greater than or equal to a first preset temperature, the calculated core wire temperature of each cable is determined as the initial core wire temperature of each cable; then the process returns to the step of obtaining the first AC resistance of the core wire and the second AC resistance of the metal sheath of each cable at the initial core wire temperature.

[0016] Optionally, obtaining the first AC resistance of the core wire at the initial temperature of the core wire in each of the cables includes:

[0017] Obtain the first cross-sectional area, first skin effect factor, first proximity effect factor, and first conductivity and first temperature coefficient of each core wire at a second preset temperature;

[0018] Based on the first formula, the DC resistance of each core wire at the second preset temperature is determined according to the first conductivity and the first cross-sectional area of ​​each core wire.

[0019] The first formula is: R DC1 =ρ1 / S1; where ρ1 is the first conductivity of the core wire, S1 is the first cross-sectional area of ​​the core wire, and R... DC1 The DC resistance of the core wire at a second preset temperature;

[0020] Based on the second formula, the first AC resistance of each core wire is obtained according to the first skin effect factor, the first proximity effect factor, and the initial core wire temperature of each core wire, as well as the DC resistance and the first temperature coefficient of each core wire at the second preset temperature.

[0021] The second formula is: R1 = R DC1 ×g×(1+α1×(θc-θ0))×(1+Y S1 +Y P1 ); where R1 is the first AC resistance of the core wire, g is the gravitational acceleration, θ0 is the second preset temperature, α1 is the first temperature coefficient of the core wire at the second preset temperature θ0, θc is the initial core wire temperature, Y S1 Y is the first skin effect factor of the core wire, and Y is the first proximity effect factor of the core wire. P1 .

[0022] Optionally, obtaining the second AC resistance of the metal sheath of each cable at the initial temperature of the core wire includes:

[0023] Obtain the second cross-sectional area, second skin effect factor, second proximity effect factor, and second conductivity and second temperature coefficient of each metal sheath at a second preset temperature;

[0024] Based on the third formula, the DC resistance of each metal sheath at the second preset temperature is determined according to the second conductivity and the second cross-sectional area of ​​each metal sheath.

[0025] The third formula is: R DC2 = ρ2 / S2; where ρ2 is the second conductivity of the metal sheath, S2 is the second cross-sectional area of ​​the metal sheath, and R... DC2 The DC resistance of the metal sheath at the second preset temperature θ0;

[0026] Based on the fourth formula, the second AC resistance of each metal sheath is obtained according to the second skin effect factor, the second proximity effect factor and the initial core wire temperature of each metal sheath, as well as the DC resistance and the second temperature coefficient of each metal sheath at the second preset temperature.

[0027] The fourth formula is: R2 = R DC2 ×g×(1+α2×(θc-θ0))×(1+Y S2 +Y P2 ); where R2 is the second AC resistance of the metal sheath; α2 is the DC resistance of the metal sheath at the second preset temperature θ0. DC2 Second temperature coefficient, Y S2Y is the second skin effect factor for the metal sheath. P2 This is the second proximity effect factor for the metal sheath.

[0028] Optionally, based on the first AC resistance, the second AC resistance, and the actual transmission capacity data of each cable, the core wire loss and circulating current loss of each cable are obtained, including:

[0029] Obtain the key parameters of the double-segmented cable line; the key parameters include the length of the double-segmented cable line, the cable spacing, the equivalent unit resistance of the ground, the equivalent depth of the equivalent ground loop, and the geometric mean distance of the core wires of each cable and the geometric radius of the metal sheath.

[0030] The impedance parameters of each cable are obtained based on the key parameters, the first AC resistance, and the second AC resistance. The impedance parameters include the first self-impedance of the core wire, the second self-impedance of the metal sheath, the first mutual impedance when the core wire current and the metal sheath current are in phase, and the second mutual impedance when the core wire current and the metal sheath current are not in phase.

[0031] Based on the actual transmission capacity data, the impedance parameters of each cable, the first AC resistance, and the second AC resistance, the load current value and circulating current value of each cable are obtained;

[0032] The core wire loss of each cable is obtained based on the first AC resistance and the load current value of each cable.

[0033] The circulating current loss of each cable is obtained based on the second AC resistance of each cable and the circulating current value.

[0034] Optionally, the impedance parameters of each cable are obtained based on the key parameters, the first AC resistance, and the second AC resistance, including:

[0035] Based on the fifth formula, the first self-impedance of the core wire in each cable is obtained according to the length of the double-segment cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent loop of the ground, the self-geometric average distance of the core wire in each cable and the first AC resistance.

[0036] The fifth formula is: Z CC =L×[R1+r e +j0.01445×lg(De / Dc)];where, Z CC R is the first self-impedance of the core wire, R1 is the first AC resistance, and r e Let De be the equivalent unit resistance of the earth, De be the equivalent depth of the equivalent loop of the earth, and Dc be the self-geometric mean distance of the core wire.

[0037] Based on the sixth formula, the second self-impedance of the metal sheath in each cable is obtained according to the length of the double-segment cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent loop of the ground, the geometric radius of the metal sheath in each cable, and the second AC resistance.

[0038] The sixth formula is: Z SS =L×[R2+r e +j0.01445×lg(De / Ds)];where, Z SS R2 is the second self-impedance of the metal sheath, Ds is the second AC resistance, and Ds is the geometric radius of the metal sheath.

[0039] Based on the seventh formula, the first mutual impedance when the core current and the metal sheath current in each cable are in phase is obtained according to the length of the double-segment cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent loop of the ground, and the geometric radius of the metal sheath in each cable.

[0040] The seventh formula is: Z SC =L×[r e +j0.01445×lg(De / Ds)];where, Z SC The first mutual impedance when the core current and the metal sheath current are in phase in the cable;

[0041] Based on the eighth formula, according to the length of the double-segment cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent loop of the ground, and the cable spacing, the second mutual impedance when the core current and the metal sheath current of each cable are in different phases is obtained.

[0042] The eighth formula is: Z SC ′=L×[r e +j0.01445×lg(De / D)];where, Z SC ′ is the second mutual impedance when the current in the core wire and the current in the metal sheath of the cable are out of phase; D is the cable spacing.

[0043] Optionally, based on the actual transmission capacity data, the impedance parameters of each cable, the first AC resistance, and the second AC resistance, the load current value and circulating current value of each cable are obtained, including:

[0044] Based on the connection method of double-splitter cables in the circuit, the core wire loops of each double-splitter cable line are constructed according to Kirchhoff's laws.

[0045] Obtain the grounding method and grounding resistance value of the metal sheath, and construct the metal sheath circuit of the double-segment cable line according to Kirchhoff's laws;

[0046] Based on Kirchhoff's laws, a set of nodal voltage equations for the double-section cable line is constructed according to the core wire loop and the metal sheath loop.

[0047] Based on the node voltage equations, the load current and circulating current values ​​of each cable are obtained according to the first self-impedance, the second self-impedance, the first mutual impedance, and the second mutual impedance.

[0048] Optionally, based on the mirror symmetry method, the mutual thermal temperature rise between the k-th cable and the p-th cable is obtained according to the core wire loss and the circulating current loss of the k-th cable, including:

[0049] The heat loss of the k-th cable is obtained based on the core wire loss and the circulating current loss of the k-th cable.

[0050] Based on the geometric position distribution of each cable, the mutual heat coefficient between the k-th cable and the p-th cable is calculated using the mirror symmetry method.

[0051] Based on the mutual heat coefficient and the heat loss of the k-th cable, calculate the mutual heat rise between the k-th cable and the p-th cable.

[0052] Optionally, the thermal resistance parameters include the thermal resistance of the insulation layer in the cable, the thermal resistance of the metal sheath, the thermal resistance of the high thermal conductivity material inside the jacking pipe, the pipe thermal resistance of the jacking pipe, and the thermal resistance of the external soil.

[0053] The self-heating temperature rise of each cable is obtained based on the core wire loss, circulating current loss, and thermal resistance parameters of each cable, including:

[0054] Based on the ninth formula, the self-heating temperature rise of the p-th cable is obtained according to the core wire loss, the circulating current loss and each of the thermal resistance parameters.

[0055] The ninth formula is: △θ pp =Q p1 ×T pi +(Q p1 +Q p2 )×(T ps +T ph +T pd +T e );

[0056] Where, △θ pp Q is the self-heating temperature rise of the p-th cable. p1 Q is the core wire loss of the p-th cable. p2 For the circulating current loss of the p-th cable, T pi T is the thermal resistance of the insulation layer in the p-th cable.ps T is the thermal resistance of the metal sheath in the p-th cable. ph T represents the thermal resistance of the high thermal conductivity material inside the pull tube where the p-th cable is located. pd Let T be the thermal resistance of the jacking pipe where the p-th cable is located. e The external soil thermal resistance is given.

[0057] Optionally, the calculated core temperature of each cable is obtained based on the mutual heat rise, the self-heat rise, and the ambient boundary temperature of each cable, including:

[0058] Based on the tenth formula, the core wire temperature rise of the p-th cable is calculated according to the mutual heat rise between the k-th cable and the p-th cable and the self-heat rise of the p-th cable.

[0059] The tenth formula is: △θ p =△θ pk +△θ pp ; where △θ p Calculate the temperature rise Δθ for the core wire of the p-th cable. pk Let Δθ be the mutual thermal temperature rise between the k-th cable and the p-th cable. pp The self-heating temperature rise of the p-th cable;

[0060] The calculated temperature of the core wire of the p-th cable is obtained based on the calculated temperature rise of the core wire and the ambient boundary temperature.

[0061] According to another aspect of the present invention, a thermal assessment device for double-span cable lines laid with jacking pipes is provided, comprising:

[0062] An AC resistance acquisition module is used to acquire the first AC resistance of the core wire and the second AC resistance of the metal sheath of each cable at the initial temperature of the core wire.

[0063] The information acquisition module is used to acquire the actual transmission capacity data of the line and the thermal resistance parameters of each cable.

[0064] The loss acquisition module is used to acquire the core wire loss and circulating current loss of each cable based on the first AC resistance, the second AC resistance and the actual transmission capacity data of each cable.

[0065] The mutual heat rise acquisition module is used to acquire the mutual heat rise between the k-th cable and the p-th cable based on the mirror symmetry method, according to the core wire loss and the circulating current loss of the k-th cable; where k = 1, 2, 3, 4, 5, 6; p = 1, 2, 3, 4, 5, 6; and k ≠ p;

[0066] The self-heating temperature rise acquisition module is used to acquire the self-heating temperature rise of each cable based on the core wire loss, circulating current loss and thermal resistance parameters of each cable.

[0067] The core wire calculation temperature acquisition module is used to acquire the core wire calculation temperature of each cable based on the mutual heat rise, the self-heat rise and the ambient boundary temperature of each cable.

[0068] A temperature difference acquisition module is used to acquire the temperature difference between the initial temperature of the core wire and the calculated temperature of the core wire of at least one of the cables.

[0069] The core wire steady-state temperature acquisition module is used to determine the calculated core wire temperature of each cable as the core wire steady-state temperature of each cable when the temperature difference is less than or equal to a preset difference and the calculated temperature of each core wire is less than a first preset temperature.

[0070] The core wire initial temperature update module is used to determine the core wire calculated temperature of each cable as the core wire initial temperature of each cable when the temperature difference exceeds a preset difference or at least one core wire calculated temperature is greater than or equal to a first preset temperature.

[0071] The loop module is used to return to the AC resistance acquisition module after the core wire initial temperature update module determines the calculated core wire temperature of each cable as the core wire initial temperature of each cable, and then perform the step of acquiring the first AC resistance of the core wire and the second AC resistance of the metal sheath of each cable at the core wire initial temperature.

[0072] The thermal assessment method for double-core cable lines laid with jacking pipes provided by this invention, through an iterative approach, comprehensively considers the installation location of each cable, the mutual thermal influence between the metal sheath and the core wire, and the mutual thermal influence between the cables, under the condition of known transmission capacity, to obtain the steady-state temperature of each core wire in the double-core cable line during transmission. This method can effectively improve the accuracy of thermal assessment of double-core cable lines, and can accurately adjust the dispatch margin of the line load based on the thermal assessment results, while also helping to reduce power grid investment costs.

[0073] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0074] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0075] Figure 1 This is a flowchart of a thermal assessment method for laying double-section cable lines using jacking pipes, provided by an embodiment of the present invention.

[0076] Figure 2 This is a schematic diagram of the cross-sectional structure of a cable laid using a jacking pipe, provided in an embodiment of the present invention.

[0077] Figure 3 This is a schematic diagram illustrating the relative positional relationship between a cable and a jacking pipe, provided in an embodiment of the present invention.

[0078] Figure 4 This is a schematic diagram of the core wire circuit of a double-stranded cable line;

[0079] Figure 5 This is a schematic diagram of the metal sheath circuit of a double-segment cable line;

[0080] Figure 6 This is a schematic diagram of a mirrored distribution of a cable provided in an embodiment of the present invention;

[0081] Figure 7 This is a schematic diagram of the structure of a thermal assessment device for laying double-section cable lines with jacking pipes, provided in an embodiment of the present invention. Detailed Implementation

[0082] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0083] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0084] This invention provides a thermal assessment method for double-span cable lines laid with jacking pipes, which can accurately assess the steady-state temperature of the cable during power transmission. Figure 1 This is a flowchart of a thermal assessment method for laying double-section cable lines using jacking pipes, as provided in an embodiment of the present invention. Figure 1 As shown, the method includes:

[0085] S110. Obtain the first AC resistance of the core wire and the second AC resistance of the metal sheath of each cable at the initial temperature of the core wire.

[0086] Specifically, Figure 2 This is a schematic diagram of the cross-sectional structure of a cable laid in a jacking pipe according to an embodiment of the present invention, as shown below. Figure 2 As shown, cable 10 includes a core conductor 11 (referred to as core wire) for transmitting power, an insulation layer 12 surrounding the core conductor, and a metal sheath 13 surrounding the insulation layer. Cable 10 is disposed in a pull-top pipe 20, and a high thermal conductivity material 30 is disposed between the pull-top pipe 20 and cable 10 for heat dissipation. The metal sheath is grounded at both ends for protection. The initial core wire temperature in the first iteration can be set according to design requirements. In one feasible embodiment, the initial core wire temperature in the first iteration can be a temperature value lower than the core wire's withstand temperature, or it can be the core wire's maximum withstand temperature. For example, if the current carrying capacity of the core wire decreases significantly when the core wire temperature exceeds 90°C, then the maximum withstand temperature of the core wire is 90°C, and 90°C can be used as the initial core wire temperature of each cable in the first iteration.

[0087] The AC resistance of the core wire (i.e., the first AC resistance) is related to its cross-sectional area, skin effect, and proximity effect. Similarly, the AC resistance of the metal sheath (i.e., the second AC resistance) is related to its cross-sectional area, skin effect, and proximity effect. Obtaining the first AC resistance of the core wire allows us to determine its current-carrying capacity. When current flows through the core wire, it generates a magnetic field around it, inducing a voltage on the metal sheath. Grounding the two ends of the metal sheath induces a current in it; therefore, we can obtain the second AC current in the metal sheath to determine its current-carrying capacity.

[0088] For example, obtaining the first AC resistance of the core wire of each cable at the initial temperature of the core wire includes:

[0089] S111. Obtain the first cross-sectional area, first skin effect factor, first proximity effect factor, and first conductivity and first temperature coefficient of each core wire at a second preset temperature.

[0090] S112. Based on the first formula, determine the DC resistance of each core wire at the second preset temperature according to the first conductivity and the first cross-sectional area of ​​each core wire.

[0091] The first formula is: R DC1 =ρ1 / S1; where ρ1 is the first conductivity of the core wire, S1 is the first cross-sectional area of ​​the core wire, and R... DC1 The DC resistance of the core wire at the second preset temperature.

[0092] S113. Based on the second formula, according to the first skin effect factor Y of each core wire S1 First Proximity Factor Y P1 and the initial core wire temperature θc, and the DC resistance R of each core wire at the second preset temperature θ0. DC1 Using the first temperature coefficient α1, obtain the first AC resistance R1 of each core wire.

[0093] The second formula is R1 = R DC1 ×g×(1+α1×(θc-θ0))×(1+Y S1 +Y P1 ); where R1 is the first AC resistance of the core wire, g is the gravitational acceleration, θ0 is the second preset temperature, α1 is the first temperature coefficient of the core wire at the second preset temperature θ0, θc is the initial core wire temperature, Y S1 Y is the first skin effect factor of the core wire, and Y is the first proximity effect factor of the core wire. P1 ;

[0094] Specifically, the first cross-sectional area S1 of the core wire and the first skin effect factor Y S1 First Proximity Factor Y P1The first conductivity ρ1 and first temperature coefficient α1 of each core wire at a second preset temperature θ0 can be pre-calibrated and stored. The second preset temperature θ0 can be the ambient temperature of the cable's environment, for example, 20°C. When calculating the first AC resistance of each core wire in the cable, the first cross-sectional area S1 and the first conductivity ρ1 of that core wire can be substituted into the first formula to calculate the DC resistance R of the core wire at the second preset temperature. DC1 The DC resistance R of the core wire at the second preset temperature is determined. DC1 Then, based on the first skin effect factor Y of the core wire S1 First Proximity Factor Y P1 and the initial core wire temperature θc, and the DC resistance R of each core wire at the second preset temperature. DC1 Substitute the first temperature coefficient α1 into the second formula to calculate the first AC resistance R1 of the core wire.

[0095] For example, obtaining the second AC resistance of the metal sheath of each cable at the initial temperature of the core wire includes:

[0096] S114. Obtain the second cross-sectional area, second skin effect factor, second proximity effect factor, and second conductivity and second temperature coefficient of each metal sheath at a second preset temperature.

[0097] S115. Based on the third formula, determine the DC resistance of each metal sheath at the second preset temperature according to the second conductivity and the second cross-sectional area of ​​each metal sheath.

[0098] The third formula is: R DC2 =ρ2 / S2; where ρ2 is the second conductivity of the metal sheath, S2 is the second cross-sectional area of ​​the metal sheath, and R... DC2 The DC resistance of the metal sheath at the second preset temperature θ0.

[0099] S116. Based on the fourth formula, the second AC resistance of each metal sheath is obtained according to the second skin effect factor, the second proximity effect factor and the initial core wire temperature of each metal sheath, as well as the DC resistance and the second temperature coefficient of each metal sheath at the second preset temperature.

[0100] The fourth formula is: R² = R DC2 ×g×(1+α2×(θc-θ0))×(1+Y S2 +Y P2 ); where R2 is the second AC resistance of the metal sheath; α2 is the DC resistance of the metal sheath at the second preset temperature θ0. DC2 Second temperature coefficient, Y S2 Y is the second skin effect factor for the metal sheath. P2This is the second proximity effect factor for the metal sheath.

[0101] Based on similar principles, the second cross-sectional area S2 and the second skin effect factor Y of each metal sheath... S2 Second Proximity Factor Y P2 The second conductivity ρ2 and second temperature coefficient α2 of each metal sheath at the second preset temperature θ0 can be pre-calibrated and stored. When calculating the second AC resistance of the metal sheath in each cable, the second cross-sectional area S2 and the second conductivity ρ2 of the metal sheath can be substituted into the third formula to calculate the DC resistance R of the metal sheath at the second preset temperature. DC2 The DC resistance R of the metal sheath at the second preset temperature is determined. DC2 Then, the second skin effect factor Y of the metal sheath can be... S2 Second Proximity Factor Y P2 and the initial core wire temperature θc, and the DC resistance R of each metal sheath at the second preset temperature. DC2 The first temperature coefficient α2 is substituted into the fourth formula to calculate the second AC resistance R2 of the metal sheath. Since the metal sheath and core wire are separated by only one insulation layer in the same cable, the temperature difference is small. Therefore, when calculating the second AC resistance R2 of the metal sheath, the initial temperature θc of the core wire can be used as its initial temperature.

[0102] S120: Obtain the actual transmission capacity data of the line and the thermal resistance parameters of each cable.

[0103] Specifically, the actual transmission capacity data of the line can be the three-phase AC voltage U A U B U C and three-phase alternating current I A I B I C .

[0104] Thermal resistance parameters can include the thermal resistance parameters of each layer in the cable and the ambient thermal resistance parameter. For example, thermal resistance parameters can include the thermal resistance T of the insulation layer in the cable. i The thermal resistance T of the metal sheath s The thermal resistance T of the high thermal conductivity material inside the top tube h The thermal resistance T of the jacking pipe d Thermal resistance of the soil to the outside environment T e .

[0105] The thermal resistance T of the insulating layer can be calculated based on the thermal resistance calculation formula T=ln(d1 / d2) / (2×π×λ). i Metal sheath thermal resistance T s The thermal resistance T of the jacking pipe d Thermal resistance of the soil to the outside environment (T)e Where λ is the thermal conductivity of the material, and d1 and d2 are the outer and inner diameters of each layer of the cable structure, respectively. For example, in calculating the thermal resistance T of the insulation layer... i When d1 and d2 are the outer and inner diameters of the insulation layer, respectively, and λ is the thermal conductivity of the insulation layer material; in calculating the thermal resistance T of the metal sheath... s When d1 and d2 are the outer and inner diameters of the metal sheath, respectively, and λ is the thermal conductivity of the metal sheath material; in calculating the pipe thermal resistance T of the jacking pipe... d When d1 and d2 are the outer and inner diameters of the jacking pipe, respectively, and λ is the thermal conductivity of the jacking pipe material; in calculating the external soil thermal resistance T... e In this context, d1 and d2 represent the outer and inner diameters of the external soil, respectively, and λ represents the thermal conductivity of the external soil material. The external soil can be understood as the soil including the predetermined thickness of the jacking pipe.

[0106] in addition, Figure 3 This is a schematic diagram illustrating the relative positional relationship between a cable and a jacking pipe, provided in an embodiment of the present invention. Figure 3 As shown, the radius of cable 10 is r1, the radius of the jacking pipe 20 is r2, and the eccentricity between cable 10 and jacking pipe 20 under gravity is e. A high thermal conductivity material layer 30 is formed between cable 10 and jacking pipe 20. Due to the eccentricity e between cable 10 and jacking pipe 20 under gravity, the high thermal conductivity material layer 30 does not conform to the cylindrical wall structure. Therefore, the thermal resistance T of the high thermal conductivity material cannot be calculated using the above thermal resistance calculation formula. h The thermal resistance Th of the high thermal conductivity material can be calculated using the shape factor method based on the relative positional relationship between cable 10 and jacking pipe 20. The formula for calculating the thermal resistance Th of the high thermal conductivity material is: T h =arcosh[(r1 2 +r2 2 -e 2 ) / 2×r1×r2. Where arcosh is the inverse hyperbolic cosine function.

[0107] S130. Based on the first AC resistance, second AC resistance and actual transmission capacity data of each cable, obtain the core wire loss and circulating current loss of each cable.

[0108] Specifically, core wire loss reflects the temperature rise of the core conductor in the cable, while circulating current loss reflects the temperature rise of the metal sheath in the cable. Therefore, core wire loss and circulating current loss can be calculated to obtain the steady-state temperature of the core wire in the cable.

[0109] For example, based on the first AC resistance, second AC resistance, and actual transmission capacity data of each cable, the core wire loss and circulating current loss of each cable are obtained, including:

[0110] S131. Obtain the key parameters of the double-section cable line.

[0111] Key parameters include the length L of the double-span cable line, the cable spacing D, and the equivalent unit resistance r of the ground. e The equivalent depth De of the earth equivalent loop, the geometric mean distance Dc of the core wires in each cable, and the geometric radius Ds of the metal sheath.

[0112] The equivalent unit resistance of the earth, re, can be taken as 0.0493 Ω / km. The spacing between the six cables can be considered the same, i.e., the cable spacing D. All key parameters can be pre-calibrated and stored for direct retrieval during calculations.

[0113] S132. Obtain the impedance parameters of each cable based on the key parameters, the first AC resistance, and the second AC resistance.

[0114] Impedance parameters include the first self-impedance Zcc of the core wire in each cable, the second self-impedance Zss of the metal sheath, the first mutual impedance Zsc when the core wire current and the metal sheath current are in phase, and the second mutual impedance Zsc′ when the core wire current and the metal sheath current are not in phase.

[0115] For example, the impedance parameters of each cable are obtained based on key parameters, a first AC resistance, and a second AC resistance, including:

[0116] Based on the fifth formula, the first self-impedance of each cable core is obtained according to the length of the double-section cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent ground loop, the self-geometric average distance of each cable core, and the first AC resistance; the fifth formula is: Z CC =L×[R1+r e +j0.01445×lg(De / Dc)];where, Z CC R is the first self-impedance of the core wire, R1 is the first AC resistance of the core wire, and r e Let De be the equivalent unit resistance of the earth, De be the equivalent depth of the equivalent earth loop, and Dc be the self-geometric mean distance of the core wire.

[0117] Based on the sixth formula, the second self-impedance of the metal sheath in each cable is obtained according to the length of the double-section cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent ground loop, the geometric radius of the metal sheath in each cable, and the second AC resistance; the sixth formula is: Z SS =L×[R2+r e +j0.01445×lg(De / Ds)];where, Z SS R1 is the second self-impedance of the metal sheath, R2 is the second AC resistance, and Ds is the geometric radius of the metal sheath.

[0118] Based on the seventh formula, considering the length of the double-stranded cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent ground loop, and the geometric radius of the metal sheath in each cable, the first mutual impedance when the core current and the metal sheath current in each cable are in phase is obtained; the seventh formula is: Z SC =L×[r e +j0.01445×lg(De / Ds)];where, Z SC It is the first mutual impedance when the current in the core wire and the current in the metal sheath of the cable are in phase.

[0119] Based on the eighth formula, and taking into account the length of the double-span cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent ground loop, and the cable spacing, the second mutual impedance when the core current and the metal sheath current of each cable are in different phases is obtained; the eighth formula is: Z SC ′=L×[r e +j0.01445×lg(De / D)];where, Z SC ′ is the second mutual impedance when the current in the cable core and the current in the metal sheath are out of phase; D is the cable spacing.

[0120] S133. Based on the actual transmission capacity data, the impedance parameters of each cable, the first AC resistance and the second AC resistance, obtain the load current value and circulating current value of each cable.

[0121] Specifically, by combining the connection methods of each cable in each double-span cable line, the load current value of the cable and the circulating current value generated on the metal sheath can be calculated.

[0122] For example, based on actual transmission capacity data, impedance parameters of each cable, first AC resistance, and second AC resistance, the load current value and circulating current value of each cable are obtained, including:

[0123] S1331. Based on the connection method of double-paired cables in the circuit, construct the core wire loop of each double-paired cable line according to Kirchhoff's laws.

[0124] Specifically, a double-ended cable refers to a cable in which each phase voltage is transmitted by two cables connected in parallel. Based on this, and according to Kirchhoff's laws, the core circuit of a double-ended cable line is constructed as follows: Figure 4 As shown in the figure. Z A Z B Z C For a three-phase load in a double-cable system, Z N For neutral line load, R 1ai +jX 1ai Let Zcc be the impedance value of the i-th core wire in phase A, and ΔU be the impedance value of the core wire. ai I refers to the voltage drop of the i-th core wire in phase A of the cable. ai Let R be the load current of the i core conductors in phase A of the cable, where i = {1, 2};1bi +jX 1bi Let Zcc be the impedance value of the i-th cable in phase B, and ΔU be the impedance value of the cable in phase B. bi I refers to the voltage drop of the i-th core wire in phase B of the cable. bi Let R be the load current of the i core conductors in phase B of the cable, where i = {1, 2}; 1ci +jX 1ci Let Zcc be the impedance value of the i-th cable in phase C, and ΔU be the impedance value of the cable in phase C. ci I refers to the voltage drop of the i-th core wire in phase C of the cable. ci Let I be the load current of the i core conductors in phase C of the cable, where i = {1, 2}. Based on the connection method of the double-stranded cable, I... A =I a1 +I a2 I B =I b1 +I b2 I C =I c1 +I c2 and ΔU a1 =ΔU a2 =U A ΔU b1 =ΔU b2 =U B ΔU c1 =ΔU c2 =U C .

[0125] S1332. Obtain the grounding method and grounding resistance value of the metal sheath, and construct the metal sheath circuit of the double-section cable line according to Kirchhoff's laws.

[0126] Specifically, in this embodiment, the metal sheath is grounded at both ends, and the metal sheath circuit of the double-ended cable line is constructed according to Kirchhoff's laws as follows: Figure 5 As shown in the figure. ΔU awi I represents the voltage drop across the metal sheath of the i-th cable in phase A; awi R represents the circulating current (Ri) in the metal sheath of the i-th cable in phase A. 2ai +jX 2ai Let Z be the impedance of the metal sheath in the i-th cable of phase A. SS ;ΔU bwi I is the voltage drop across the metal sheath of the i-th cable in phase B; bwi R represents the circulating current (Ri) in the metal sheath of the i-th cable in phase B. 2bi +jX 2bi Let Z be the impedance of the metal sheath in the i-th cable of phase B. SS ;ΔU cwi I is the voltage drop across the metal sheath of the i-th cable in phase C; cwiR represents the circulating current (Ri) in the metal sheath of the i-th cable in phase C. 2ci +jX 2ci Let Z be the impedance of the metal sheath in the i-th cable of phase C. SS R e1 R is the earth resistance of the ground wire when the metal sheath of the first cable in phases A, B, and C is grounded. 11 and R 21 These are the grounding resistances on both sides of the earth wire resistance when the metal sheath of the first cable in phases A, B, and C is grounded; R e2 R is the earth resistance of the metal sheath of the second cable in phases A, B, and C when it is grounded. 12 and R 22 These are the grounding resistances on both sides of the earth wire resistance when the metal sheath of the second cable in phases A, B, and C is grounded.

[0127] Since circulating current is generated when the two ends of the metal sheath are directly grounded, it can be concluded that:

[0128] ΔU aw1 =ΔU bw1 =ΔU cw1 =(I aw1 +I bw1 +I cw1 )×(R 11 +R e1 +R 21 );

[0129] ΔU aw2 =ΔU bw2 =ΔU cw2 =(I aw2 +I bw2 +I cw2 )×(R 12 +R e2 +R 22 );

[0130] Since the two ends of the six metal sheaths are grounded respectively, it is equivalent to the six metal sheaths being connected in parallel. Therefore, ΔU can be considered as... aw1 =ΔU aw2 .

[0131] S1333. Based on Kirchhoff's laws, a set of nodal voltage equations for double-section cable lines is constructed according to the core wire loop and the metal sheath loop.

[0132] Specifically, after constructing the core wire loop and the metal sheath loop, the nodal voltage equations for the double-section cable line can be constructed based on Ernst-Hoff's laws, combining the core wire loop and the metal sheath loop. Due to the large number of loops, the nodal voltage equations can be represented in matrix form, thus the nodal voltage equations are:

[0133]

[0134] The simplified loop equations after applying the nodal voltage equations are as follows:

[0135]

[0136] S1334. Based on the node voltage equation set, obtain the load current value and circulating current value of each cable according to the first self-impedance, the second self-impedance, the first mutual impedance and the second mutual impedance.

[0137] Specifically, ΔU a1 ΔU b1 ΔU c1 (that is, U) A U B U C Substituting the impedance parameters into the above loop equation, the load current value I of the core wire can be calculated. a1 I b1 I c1 I a2 I b2 I c2 and the circulating current value I of the metal sheath. aw1 I bw1 I cw1 I aw2 I bw2 I cw2 .

[0138] S134. Obtain the core wire loss of each cable based on the first AC resistance and load current value of each cable.

[0139] Specifically, the loss can be calculated using the formula Q = I. 2 ×R, the core wire loss of each cable is obtained based on the first AC resistance and load current value of the cable. During calculation, the core wire loss of the cable is determined by substituting the load current and the first AC resistance into the loss calculation formula.

[0140] S135. Obtain the circulating current loss of each cable based on the second AC resistance and circulating current value of each cable.

[0141] Specifically, based on the same principle, the loss can be calculated using the formula Q = I. 2 ×R, the circulating current loss of each cable is obtained based on the second AC resistance and circulating current value of the cable. In the calculation, the circulating current value of the metal sheath and the second AC resistance of the cable are substituted into the loss calculation formula to determine the circulating current loss of the cable.

[0142] S140. Based on the mirror symmetry method, obtain the mutual heat rise between the k-th cable and the p-th cable according to the core wire loss and circulating current loss of the k-th cable.

[0143] Where k = 1, 2, 3, 4, 5, 6; p = 1, 2, 3, 4, 5, 6; and k ≠ p.

[0144] Specifically, by combining the geometrical distribution of each cable in a double-cable line, and using the mirror symmetry method, the mutual heat rise between the k-th cable and the p-th cable can be obtained based on the core loss and circulating current loss of the k-th cable. Figure 6 This is a schematic diagram of a mirrored cable distribution provided in an embodiment of the present invention, as shown below. Figure 6 As shown, the distance between the geometric center of the p-th cable 10p and the geometric center of the k-th cable 10k is d. pk Point k′ is mirror-symmetric to the geometric center of the k-th cable 10k about the ground plane, and point p′ is mirror-symmetric to the geometric center of the p-th cable 10p about the horizon L0. The distance between the geometric center of the p-th cable 10p and point k′ is d. pk ′.

[0145] For example, based on the mirror symmetry method, the mutual heat rise between the k-th cable and the p-th cable is obtained according to the core wire loss and circulating current loss of the k-th cable, including:

[0146] S141. Obtain the heat loss of the k-th cable based on the core wire loss and circulating current loss of the k-th cable.

[0147] Specifically, the heat loss W of the cable c It can be expressed as the sum of its core wire loss Q1 and circulating current loss Q2, i.e., W. c =Q1 + Q2, assuming the core loss of the k-th cable is Q. k1 The circulating current loss of the k-th cable is Q. k2 The heat loss W of the k-th cable kc Then W kc =Q k1 +Q k2 .

[0148] S142. Based on the geometric distribution of each cable, calculate the mutual heat coefficient between the k-th cable and the p-th cable using the mirror symmetry method.

[0149] Specifically, refer to the following: Figure 6 According to the mirror symmetry method, the formula for calculating the mutual heat coefficient can be used: a pk =ρ T ×ln(d pk ′ / d pk ) / (2×π), calculate the mutual heat coefficient between the k-th cable and the p-th cable, where a pk Let ρ be the mutual heat coefficient between the k-th cable and the p-th cable. T This is the soil thermal resistivity.

[0150] S143. Calculate the mutual temperature rise between the k-th cable and the p-th cable based on the mutual heat coefficient and the heat loss of the k-th cable.

[0151] Specifically, the mutual temperature rise Δθ between the k-th cable and the p-th cable pk The mutual heat coefficient α between the k-th cable and the p-th cable can be denoted as α. pk The product of W and the heat loss of the k-th cable kc That is, △θ pk =a pk ×W kc .

[0152] S150. Obtain the self-heating temperature rise of each cable based on the core wire loss, circulating current loss and thermal resistance parameters of each cable.

[0153] For example, the self-heating temperature rise of the p-th cable can be obtained based on the ninth formula, according to the core wire loss, circulating current loss and various thermal resistance parameters of the p-th cable.

[0154] The ninth formula is: △θ pp =Q p1 ×T pi +(Q p1 +Q p2 )×(T ps +T ph +T pd +T e ).

[0155] Where, △θ pp Q is the self-heating temperature rise of the p-th cable. p1 Let Q be the core loss of the p-th cable. p2 Let T be the circulating current loss of the p-th cable. pi Let T be the thermal resistance of the insulation layer in the p-th cable. ps Let T be the thermal resistance of the metal sheath in the p-th cable. ph T represents the thermal resistance of the high thermal conductivity material inside the jacking pipe where the p-th cable is located. pd Let T be the thermal resistance of the jacking pipe containing the p-th cable. e For external soil thermal resistance.

[0156] S160. Based on the mutual heat rise, self-heat rise and ambient boundary temperature of each cable, obtain the core wire calculation temperature of each cable.

[0157] For example, the core temperature rise of the p-th cable can be calculated based on the tenth formula, taking into account the mutual heat rise between the k-th and p-th cables and the self-heat rise of the p-th cable; the tenth formula is: △θ p =△θ pk +△θ pp ; where △θp Calculate the temperature rise of the core wire of the p-th cable; then, based on the calculated temperature rise of the core wire of the p-th cable and the ambient boundary temperature, obtain the calculated temperature of the core wire of the p-th cable.

[0158] Among them, based on the tenth formula, △θ p =△θ pk +△θ pp＝ a pk ×W kc +△θ pp, The formulas for calculating the core temperature of each cable can be represented by a matrix as follows:

[0159]

[0160] Among them, a 11 a 22 a 33 a 44 a 55 a 66 This can be understood as the self-heating coefficient of the six cables, all of which can be taken as 1. Substituting the parameters into the above matrix, the calculated temperature rise of the core wire of each cable can be calculated as Δθ1, Δθ2, Δθ3, Δθ4, Δθ5, and Δθ6. This temperature rise takes into account the mutual heating effect of the metal sheath on the core wire, as well as the mutual heating effect between any two cables among the six cables.

[0161] The ambient boundary temperature can be the soil temperature at a preset depth, which can be set according to the cable laying depth. The core wire temperature rise Δθ is calculated. p Calculation temperature θ of the core wire p and ambient boundary temperature θ e θ p＝ θ e +△θ p After obtaining the temperature rise of the core wire of the p-th cable, the temperature rise Δθ can be calculated from the core wire of that cable. p and ambient boundary temperature θ e Calculate the core temperature θ of the p-th cable. p Therefore, the core temperature θ of the six cables can be calculated. p .

[0162] S170. Obtain the temperature difference between the initial temperature of the core wire and the calculated temperature of the core wire of at least one cable.

[0163] S180. Determine whether the temperature difference is less than or equal to the preset difference, and whether the calculated temperature of each core wire is less than the first preset temperature; if yes, proceed to step S190; if no, proceed to step S200.

[0164] S190. The calculated core temperature of each cable is determined as the steady-state core temperature of each cable.

[0165] Specifically, the initial core temperature of each cable can be subtracted from its calculated core temperature to obtain the temperature difference. This temperature difference is then compared to a preset difference. If the temperature difference for each cable is less than the preset error, and the calculated core temperature for each cable is less than a first preset temperature, then the current calculated core temperature for each cable can be determined as its steady-state core temperature. The first preset temperature can be the maximum withstand temperature of the core, for example, 90℃.

[0166] Alternatively, the maximum calculated temperature of the core wire in each cable can be selected first, and the difference between the maximum calculated core wire temperature and the initial core wire temperature can be used to determine the temperature difference. If the temperature difference is less than the preset error and the calculated temperature of each core wire is less than the first preset temperature, the current calculated core wire temperature of each cable can be determined as the steady-state core wire temperature of each cable.

[0167] Specifically, the preset difference can be the iterative convergence error, which can be set according to the calculation requirements.

[0168] S200: Determine the calculated core temperature of each cable as the initial core temperature of each cable; return to step S110.

[0169] Specifically, if at least one cable has a temperature difference exceeding a preset value, it indicates a large error between the calculated core wire temperature and the steady-state core wire temperature, resulting in low accuracy. In this case, the calculated core wire temperature of each cable can be assigned to the initial core wire temperature, updating the current initial core wire temperature as the calculated core wire temperature. The calculated core wire temperature of each cable can then be recalculated using the above method. Alternatively, if at least one core wire has a calculated core wire temperature greater than or equal to the first preset temperature, it indicates that the obtained calculated core wire temperature has exceeded its maximum withstand temperature and cannot handle the current actual transmission capacity. In this case, the initial core wire temperature of each cable can also be updated to the current calculated core wire temperature, and the calculated core wire temperature of each cable can be recalculated using the above method.

[0170] The thermal assessment method for double-core cable lines laid with jacking pipes provided in this invention uses an iterative approach. Under known transmission capacity, it comprehensively considers the installation location of each cable, the mutual thermal influence between the metal sheath and the core wire, and the mutual thermal influence between the cables to obtain the steady-state temperature of each core wire in the double-core cable line during transmission. This method can effectively improve the accuracy of thermal assessment of double-core cable lines, and can accurately adjust the dispatch margin of the line load based on the thermal assessment results. At the same time, it can help reduce the power grid investment cost.

[0171] Based on the same inventive concept, embodiments of the present invention also provide a thermal assessment device for double-section cable lines laid with jacking pipes. This thermal assessment device is used to execute the thermal assessment method for double-section cable lines laid with jacking pipes provided in any embodiment of the present invention. The thermal assessment device for double-section cable lines laid with jacking pipes can be implemented by software and / or hardware. Therefore, the thermal assessment device for double-section cable lines laid with jacking pipes provided in embodiments of the present invention includes the technical features of the thermal assessment method for double-section cable lines laid with jacking pipes provided in any embodiment of the present invention, and can achieve the beneficial effects of the thermal assessment method for double-section cable lines laid with jacking pipes provided in any embodiment of the present invention. Similarities can be referred to the above description of the thermal assessment method for double-section cable lines laid with jacking pipes provided in embodiments of the present invention, and will not be repeated here.

[0172] Figure 7 This is a schematic diagram of the structure of a thermal assessment device for laying double-section cable lines with jacking pipes, provided in an embodiment of the present invention. Figure 7As shown, a thermal assessment device for a double-span cable line laid with jacking pipes includes: an AC resistance acquisition module 100, used to acquire the first AC resistance of the core wire and the second AC resistance of the metal sheath of each cable at the initial temperature of the core wire; an information acquisition module 200, used to acquire the actual transmission capacity data of the line and the thermal resistance parameters of each cable; a loss acquisition module 300, used to acquire the core wire loss and circulating current loss of each cable based on the first AC resistance, second AC resistance and actual transmission capacity data of each cable; a mutual heat rise acquisition module 400, used to acquire the mutual heat rise of the k-th cable to the p-th cable based on the core wire loss and circulating current loss of the k-th cable using the mirror symmetry method; where k = 1, 2, 3, 4, 5, 6; p = 1, 2, 3, 4, 5, 6; and k ≠ p; a self-heating temperature rise acquisition module 500, used to acquire the self-heating temperature rise of each cable based on the core wire loss, circulating current loss and thermal resistance parameters of each cable; and a core wire calculation temperature acquisition module 600, used to acquire the self-heating temperature rise of each cable based on the core wire loss, circulating current loss and thermal resistance parameters of each cable; and a core wire calculation temperature acquisition module 600, used to acquire the self-heating temperature rise of each cable based on the core wire loss, circulating current loss and thermal resistance parameters of each cable. The system uses the mutual heat rise, self-heat rise, and ambient boundary temperature of each cable to obtain the calculated core temperature of each cable; a temperature difference acquisition module 700 is used to obtain the temperature difference between the initial core temperature and the calculated core temperature of at least one cable; a core steady-state temperature acquisition module 800 is used to determine the calculated core temperature of each cable as the steady-state core temperature when the temperature difference is less than or equal to a preset difference and the calculated core temperature of each cable is less than a first preset temperature; a core initial temperature update module 900 is used to determine the calculated core temperature of each cable as the initial core temperature when the temperature difference exceeds a preset difference or the calculated core temperature of at least one cable is greater than or equal to the first preset temperature; and a loop module 1000 is used to return to the AC resistance acquisition module to perform the steps of obtaining the first AC resistance of the core and the second AC resistance of the metal sheath of each cable at the initial core temperature after the core initial temperature update module has determined the calculated core temperature of each cable as the initial core temperature of each cable.

[0173] The thermal assessment device for double-core cable lines laid with jacking pipes provided in this invention uses an iterative method to obtain the steady-state temperature of each core wire in the double-core cable line during transmission, taking into account the installation location of each cable, the mutual thermal influence between the metal sheath and the core wire, and the mutual thermal influence between each cable, given the known transmission capacity. This effectively improves the accuracy of the thermal assessment of double-core cable lines, and allows for accurate adjustment of the line load scheduling margin based on the thermal assessment results, while also helping to reduce power grid investment costs.

[0174] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0175] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A thermal assessment method for double-section cable lines laid with jacking pipes, characterized in that, include: Obtain the first AC resistance of the core wire and the second AC resistance of the metal sheath of each cable at the initial temperature of the core wire; Obtain the actual transmission capacity data of the line and the thermal resistance parameters of each cable; Based on the first AC resistance, the second AC resistance, and the actual transmission capacity data of each cable, the core wire loss and circulating current loss of each cable are obtained. Based on the mirror symmetry method, the mutual thermal temperature rise between the k-th cable and the p-th cable is obtained according to the core wire loss and the circulating current loss of the k-th cable; where k = 1, 2, 3, 4, 5, 6; p = 1, 2, 3, 4, 5, 6; and k ≠ p; The self-heating temperature rise of each cable is obtained based on the core wire loss, circulating current loss and thermal resistance parameters of each cable. The calculated core temperature of each cable is obtained based on the mutual heat rise, the self-heat rise, and the ambient boundary temperature of each cable. Obtain the temperature difference between the initial temperature of at least one of the core wires of the cable and the calculated temperature of the core wire; When the temperature difference is less than or equal to a preset difference, and the calculated temperature of each core wire is less than a first preset temperature, the calculated temperature of the core wire of each cable is determined as the steady-state temperature of the core wire of each cable. When the temperature difference exceeds a preset difference or at least one of the core wires has a calculated temperature greater than or equal to a first preset temperature, the calculated core wire temperature of each cable is determined as the initial core wire temperature of each cable; then the process returns to the step of obtaining the first AC resistance of the core wire and the second AC resistance of the metal sheath of each cable at the initial core wire temperature.

2. The thermal assessment method for double-section cable lines laid with jacking pipes according to claim 1, characterized in that, Obtaining the first AC resistance of the core wire of each cable at its initial core temperature includes: Obtain the first cross-sectional area, first skin effect factor, first proximity effect factor, and first conductivity and first temperature coefficient of each core wire at a second preset temperature; Based on the first formula, the DC resistance of each core wire at the second preset temperature is determined according to the first conductivity and the first cross-sectional area of ​​each core wire. The first formula is: R DC1 =ρ1 / S1; where ρ1 is the first conductivity of the core wire, S1 is the first cross-sectional area of ​​the core wire, and R... DC1 The DC resistance of the core wire at a second preset temperature; Based on the second formula, the first AC resistance of each core wire is obtained according to the first skin effect factor, the first proximity effect factor, and the initial core wire temperature of each core wire, as well as the DC resistance and the first temperature coefficient of each core wire at the second preset temperature. The second formula is: R1 = R DC1 ×g×(1+α1×(θc-θ0))×(1+Y S1 +Y P1 ); where R1 is the first AC resistance of the core wire, g is the gravitational acceleration, θ0 is the second preset temperature, α1 is the first temperature coefficient of the core wire at the second preset temperature θ0, θc is the initial core wire temperature, Y S1 Y is the first skin effect factor of the core wire, and Y is the first proximity effect factor of the core wire. P1 .

3. The thermal assessment method for double-section cable lines laid with jacking pipes according to claim 1, characterized in that, Obtaining the second AC resistance of the metal sheath of each cable at the initial temperature of the core wire includes: Obtain the second cross-sectional area, second skin effect factor, second proximity effect factor, and second conductivity and second temperature coefficient of each metal sheath at a second preset temperature; Based on the third formula, the DC resistance of each metal sheath at the second preset temperature is determined according to the second conductivity and the second cross-sectional area of ​​each metal sheath. The third formula is: R DC2 =ρ2 / S2; where ρ2 is the second conductivity of the metal sheath, S2 is the second cross-sectional area of ​​the metal sheath, and R... DC2 The DC resistance of the metal sheath at the second preset temperature θ0; Based on the fourth formula, the second AC resistance of each metal sheath is obtained according to the second skin effect factor, the second proximity effect factor and the initial core wire temperature of each metal sheath, as well as the DC resistance and the second temperature coefficient of each metal sheath at the second preset temperature. The fourth formula is: R2 = R DC2 ×g×(1+α2×(θc-θ0))×(1+Y S2 +Y P2 ); where R2 is the second AC resistance of the metal sheath; α2 is the DC resistance of the metal sheath at the second preset temperature θ0. DC2 Second temperature coefficient, Y S2 Y is the second skin effect factor for the metal sheath. P2 This is the second proximity effect factor for the metal sheath.

4. The thermal assessment method for double-section cable lines laid with jacking pipes according to claim 1, characterized in that, Based on the first AC resistance, the second AC resistance, and the actual transmission capacity data of each cable, the core wire loss and circulating current loss of each cable are obtained, including: Obtain the key parameters of the double-segmented cable line; the key parameters include the length of the double-segmented cable line, the cable spacing, the equivalent unit resistance of the ground, the equivalent depth of the equivalent ground loop, and the geometric mean distance of the core wires of each cable and the geometric radius of the metal sheath. The impedance parameters of each cable are obtained based on the key parameters, the first AC resistance, and the second AC resistance. The impedance parameters include the first self-impedance of the core wire, the second self-impedance of the metal sheath, the first mutual impedance when the core wire current and the metal sheath current are in phase, and the second mutual impedance when the core wire current and the metal sheath current are not in phase. Based on the actual transmission capacity data, the impedance parameters of each cable, the first AC resistance, and the second AC resistance, the load current value and circulating current value of each cable are obtained; The core wire loss of each cable is obtained based on the first AC resistance and the load current value of each cable. The circulating current loss of each cable is obtained based on the second AC resistance of each cable and the circulating current value.

5. The thermal assessment method for double-section cable lines laid with jacking pipes according to claim 4, characterized in that, The impedance parameters of each cable are obtained based on the key parameters, the first AC resistance, and the second AC resistance, including: Based on the fifth formula, the first self-impedance of the core wire in each cable is obtained according to the length of the double-segment cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent loop of the ground, the self-geometric average distance of the core wire in each cable and the first AC resistance. The fifth formula is: Z CC =L×[R1+r e +j0.01445×lg(De / Dc)];where, Z CC R is the first self-impedance of the core wire, R1 is the first AC resistance, and r e Let De be the equivalent unit resistance of the earth, De be the equivalent depth of the equivalent loop of the earth, and Dc be the self-geometric mean distance of the core wire. Based on the sixth formula, the second self-impedance of the metal sheath in each cable is obtained according to the length of the double-segment cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent loop of the ground, the geometric radius of the metal sheath in each cable, and the second AC resistance. The sixth formula is: Z SS =L×[R2+r e +j0.01445×lg(De / Ds)];where, Z SS R2 is the second self-impedance of the metal sheath, Ds is the second AC resistance, and Ds is the geometric radius of the metal sheath. Based on the seventh formula, the first mutual impedance when the core current and the metal sheath current in each cable are in phase is obtained according to the length of the double-segment cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent loop of the ground, and the geometric radius of the metal sheath in each cable. The seventh formula is: Z SC =L×[r e +j0.01445×lg(De / Ds)];where, Z SC The first mutual impedance when the core current and the metal sheath current are in phase in the cable; Based on the eighth formula, according to the length of the double-segment cable line, the equivalent unit resistance of the ground, the equivalent depth of the equivalent loop of the ground, and the cable spacing, the second mutual impedance when the core current and the metal sheath current of each cable are in different phases is obtained. The eighth formula is: Z SC ′=L×[r e +j0.01445×lg(De / D)];where, Z SC ′ is the second mutual impedance when the current in the core wire and the current in the metal sheath of the cable are out of phase; D is the cable spacing.

6. The thermal assessment method for double-section cable lines laid with jacking pipes according to claim 4, characterized in that, Based on the actual transmission capacity data, the impedance parameters of each cable, the first AC resistance, and the second AC resistance, the load current value and circulating current value of each cable are obtained, including: Based on the connection method of double-splitter cables in the circuit, the core wire loops of each double-splitter cable line are constructed according to Kirchhoff's laws. Obtain the grounding method and grounding resistance value of the metal sheath, and construct the metal sheath circuit of the double-segment cable line according to Kirchhoff's laws; Based on Kirchhoff's laws, a set of nodal voltage equations for the double-section cable line is constructed according to the core wire loop and the metal sheath loop. Based on the node voltage equations, the load current and circulating current values ​​of each cable are obtained according to the first self-impedance, the second self-impedance, the first mutual impedance, and the second mutual impedance.

7. The thermal assessment method for double-section cable lines laid with jacking pipes according to claim 1, characterized in that, Based on the mirror symmetry method, the mutual thermal temperature rise between the k-th cable and the p-th cable is obtained according to the core wire loss and circulating current loss of the k-th cable, including: The heat loss of the k-th cable is obtained based on the core wire loss and the circulating current loss of the k-th cable. Based on the geometric position distribution of each cable, the mutual heat coefficient between the k-th cable and the p-th cable is calculated using the mirror symmetry method. Based on the mutual heat coefficient and the heat loss of the k-th cable, calculate the mutual heat rise between the k-th cable and the p-th cable.

8. The thermal assessment method for double-section cable lines laid with jacking pipes according to claim 1, characterized in that, The thermal resistance parameters include the thermal resistance of the insulation layer in the cable, the thermal resistance of the metal sheath, the thermal resistance of the high thermal conductivity material inside the jacking pipe, the thermal resistance of the jacking pipe, and the thermal resistance of the external soil. The self-heating temperature rise of each cable is obtained based on the core wire loss, circulating current loss, and thermal resistance parameters of each cable, including: Based on the ninth formula, the self-heating temperature rise of the p-th cable is obtained according to the core wire loss, the circulating current loss and each of the thermal resistance parameters. The ninth formula is: △θ pp =Q p1 ×T pi +(Q p1 +Q p2 )×(T ps +T ph +T pd +T e ); Where, △θ pp Q is the self-heating temperature rise of the p-th cable. p1 Q is the core wire loss of the p-th cable. p2 For the circulating current loss of the p-th cable, T pi T is the thermal resistance of the insulation layer in the p-th cable. ps T is the thermal resistance of the metal sheath in the p-th cable. ph T represents the thermal resistance of the high thermal conductivity material inside the pull tube where the p-th cable is located. pd Let T be the thermal resistance of the jacking pipe where the p-th cable is located. e The external soil thermal resistance is given.

9. The thermal assessment method for double-section cable lines laid with jacking pipes according to claim 1, characterized in that, The calculated core temperature of each cable is obtained based on the mutual thermal temperature rise, the self-thermal temperature rise, and the ambient boundary temperature, including: Based on the tenth formula, the core wire temperature rise of the p-th cable is calculated according to the mutual heat rise between the k-th cable and the p-th cable and the self-heat rise of the p-th cable. The tenth formula is: △θ p =△θ pk +△θ pp ; where △θ p Calculate the temperature rise Δθ for the core wire of the p-th cable. pk Let Δθ be the mutual thermal temperature rise between the k-th cable and the p-th cable. pp The self-heating temperature rise of the p-th cable; The calculated temperature of the core wire of the p-th cable is obtained based on the calculated temperature rise of the core wire and the ambient boundary temperature.

10. A thermal assessment device for double-span cable lines laid with jacking pipes, characterized in that, include: An AC resistance acquisition module is used to acquire the first AC resistance of the core wire and the second AC resistance of the metal sheath of each cable at the initial temperature of the core wire. The information acquisition module is used to acquire the actual transmission capacity data of the line and the thermal resistance parameters of each cable. The loss acquisition module is used to acquire the core wire loss and circulating current loss of each cable based on the first AC resistance, the second AC resistance and the actual transmission capacity data of each cable. The mutual heat rise acquisition module is used to acquire the mutual heat rise between the k-th cable and the p-th cable based on the mirror symmetry method, according to the core wire loss and the circulating current loss of the k-th cable; where k = 1, 2, 3, 4, 5, 6; p = 1, 2, 3, 4, 5, 6; and k ≠ p; The self-heating temperature rise acquisition module is used to acquire the self-heating temperature rise of each cable based on the core wire loss, circulating current loss and thermal resistance parameters of each cable. The core wire calculation temperature acquisition module is used to acquire the core wire calculation temperature of each cable based on the mutual heat rise, the self-heat rise and the ambient boundary temperature of each cable. A temperature difference acquisition module is used to acquire the temperature difference between the initial temperature of the core wire and the calculated temperature of the core wire of at least one of the cables. The core wire steady-state temperature acquisition module is used to determine the calculated core wire temperature of each cable as the core wire steady-state temperature of each cable when the temperature difference is less than or equal to a preset difference and the calculated temperature of each core wire is less than a first preset temperature. The core wire initial temperature update module is used to determine the core wire calculated temperature of each cable as the core wire initial temperature of each cable when the temperature difference exceeds a preset difference or at least one core wire calculated temperature is greater than or equal to a first preset temperature. The loop module is used to return to the AC resistance acquisition module after the core wire initial temperature update module determines the calculated core wire temperature of each cable as the core wire initial temperature of each cable, and then perform the step of acquiring the first AC resistance of the core wire and the second AC resistance of the metal sheath of each cable at the core wire initial temperature.

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