Submarine cable group temperature field and current-carrying capacity prediction method based on thermal circuit analysis method

Abstract

The invention discloses a submarine cable group temperature field and current-carrying capacity prediction method based on a thermal circuit analysis method. The method comprises the following steps: calculating related cable parameters according to submarine cable structure parameters; constructing a thermal circuit model of the single submarine cable body according to the submarine cable structure, and performing analysis and calculation; simplifying the thermal circuit model of the single submarine cable to obtain a simplified thermal circuit model; constructing a laying environment model of the single submarine cable; constructing a submarine cable group temperature field calculation model, and calculating a submarine cable group temperature field; calculating the additional thermal resistance of the corresponding submarine cable; and calculating the current-carrying capacity of the cable group. According to the method, the steady-state temperature and the maximum current-carrying capacity of the submarine cable are calculated by constructing a thermal circuit model of a submarine cable body and a laying environment and considering the mutual heat influence between cable groups. Compared with a traditional finite element method, the method is higher in calculation efficiency, good in prediction precision and suitable for temperature field and current-carrying capacity prediction of submarine cable groups with different burial depths, cable distances and cable numbers.

Description

Technical Field

[0001] The present invention belongs to the field of electric power engineering and marine engineering, and more specifically relates to a method for predicting the temperature field and current carrying capacity of a submarine cable group based on a thermal circuit analysis method. Background Art

[0002] The temperature of the submarine cable core conductor is closely related to the current carrying capacity. When the current is conducted on the submarine cable conductor, part of the electrical energy will be converted into heat energy and electromagnetic energy, which will cause the temperature of the submarine cable conductor to rise. When the current carrying capacity of the submarine cable increases, the temperature of the submarine cable conductor increases exponentially. The maximum operating temperature of the submarine cable for normal operation depends on the temperature tolerance of the insulating medium in contact with the submarine cable conductor. For cross-linked polyethylene (XLPE) insulation, the maximum long-term operating temperature allowed is 90°C. Therefore, in order to obtain the maximum current carrying capacity allowed for long-term operation of the submarine cable, the steady-state temperature of the submarine cable core conductor must be calculated. At present, the calculation of the core temperature of the submarine cable is mostly based on the finite element method. However, for the complex cable structure and the external laying environment, the model construction and solution speed using the finite element method are slow, and cannot meet the real-time requirements for calculating the cable conductor temperature.

[0003] Therefore, proposing a simple analytical calculation method for the temperature field and current carrying capacity of submarine cables is of great significance for practical engineering applications. Summary of the invention

[0004] In view of this, the present invention provides a method for predicting the temperature field and current carrying capacity of a submarine cable group based on a thermal circuit analysis method, which can solve the problems of complex calculation and low accuracy of the temperature field and current carrying capacity of a submarine buried cable group.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] The present invention provides a method for predicting the temperature field and current carrying capacity of a submarine cable group based on a thermal circuit analysis method, comprising the following steps:

[0007] Step 1: Calculate relevant cable parameters based on submarine cable structural parameters;

[0008] Step 2: According to the submarine cable structure and related cable parameters, a thermal circuit model of a single submarine cable body is constructed and analyzed and calculated;

[0009] Step 3: Simplify the thermal circuit model of a single submarine cable body to obtain a simplified thermal circuit model and determine the internal temperature rise of the submarine cable;

[0010] Step 4: Construct a single submarine cable laying environment model;

[0011] Step 5: Construct a temperature field calculation model for the submarine cable group and calculate the temperature field of the submarine cable group;

[0012] Step 6: Calculate the additional thermal resistance of the corresponding submarine cable;

[0013] Step 7: Calculate the current carrying capacity of the cable group.

[0014] It can be seen from the above technical scheme that the present invention proposes a method for predicting the temperature field and current carrying capacity of a submarine buried cable group based on the thermal circuit analysis method. The method for predicting the temperature field and current carrying capacity of a submarine buried cable group involves thermal circuit modeling of the submarine cable body, thermal circuit modeling under a buried environment, temperature field calculation of the submarine cable group, and current carrying capacity calculation. Compared with the prior art, the present invention is more comprehensive, clear, and accurate.

[0015] In the calculation process, the present invention proposes a cable thermal circuit model construction method based on the thermal circuit analysis method, which can calculate the structural parameters of each layer of the submarine cable, and can also construct a submarine cable thermal circuit model in this environment according to the buried environment, and proposes a calculation method for the external environment thermal resistance. At the same time, a calculation model for the temperature field and current carrying capacity of the submarine buried cable group is constructed, which can calculate the temperature field and current carrying capacity of the submarine buried cable group according to different burial depths, different numbers of cables, and different cable spacings. The calculation logic is clear and has strong versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0017] Figure 1 This is a flow chart of the method for predicting the temperature field and current carrying capacity of a submarine cable group based on the thermal path analysis method provided by the present invention.

[0018] Figure 2 This is the equivalent thermal circuit diagram of the submarine cable provided by the present invention.

[0019] Figure 3 This is a simplified equivalent thermal circuit diagram provided by the present invention.

[0020] Figure 4 The present invention provides Figure 3 The equivalent thermal diagram obtained after further simplification.

[0021] Figure 5 A scene diagram of the soil thermal field provided by the present invention.

[0022] Figure 6This is a schematic diagram of the thermal impact of surrounding cables on cable x provided by the present invention.

[0023] Figure 7 This is the finite element simulation temperature field calculation result diagram when the cable spacing is 0.2m.

[0024] Figure 8 This is the finite element simulation temperature field calculation result diagram when the cable spacing is 0.3m.

[0025] Fig. 9 This is the finite element simulation temperature field calculation result diagram when the cable spacing is 0.4m.

[0026] Fig.10 This is the finite element simulation temperature field calculation result diagram when the cable spacing is 0.5m. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The embodiment of the present invention discloses a method for predicting the temperature field and current carrying capacity of a submarine cable group based on a thermal circuit analysis method. Figure 1 As shown, the following steps are included:

[0029] Step 1: Calculate relevant cable parameters based on submarine cable structural parameters;

[0030] Step 2: According to the submarine cable structure and related cable parameters, a thermal circuit model of a single submarine cable body is constructed and analyzed and calculated;

[0031] Step 3: Simplify the thermal circuit model of a single submarine cable body to obtain a simplified thermal circuit model and determine the internal temperature rise of the submarine cable;

[0032] Step 4: Construct a single submarine cable laying environment model;

[0033] Step 5: Construct a temperature field calculation model for the submarine cable group and calculate the temperature field of the submarine cable group;

[0034] Step 6: Calculate the additional thermal resistance of the corresponding submarine cable;

[0035] Step 7: Calculate the current carrying capacity of the cable group.

[0036] The following is a detailed description of each of the above steps:

[0037] For step 1: calculate the parameters of each layer of the submarine cable according to the submarine cable structure;

[0038] Includes: Calculation of submarine cable conductor loss W c , calculate the insulation dielectric loss W d , Calculate the lead alloy sheath loss W l And calculate the submarine cable armor loss W a The units of thermal resistance are K·m / W, heat capacity is J / K, and loss is W / m.

[0039] 1) Submarine cable conductor loss W c calculate:

[0040] W c =I 2 R (1)

[0041] I is the current passing through the cable conductor; calculate the AC resistance R of the conductor. The specific calculation method is:

[0042] R=R′(1+Y s +Y p ) (2)

[0043] Y s — is the skin effect coefficient;

[0044] Y p — proximity effect coefficient;

[0045] R' is the DC resistance per unit length of conductor at operating temperature.

[0046] Among them, the specific calculation method of R′ is:

[0047]

[0048] ρ θ =ρ 20 +0.68×10 -4 (θ-20) (4)

[0049] A=πr 2 (5)

[0050] l—is the length of the submarine cable conductor, in meters (m).

[0051] A—is the cross-sectional area of ​​the submarine cable conductor, in square meters (m 2 ).

[0052] θ—is the core operating temperature, in °C;

[0053] ρ 20 — is the material temperature coefficient at 20°C, take

[0054] r—is the core radius of the wire, in meters (m).

[0055] Y s and Y p Calculated by the following formula:

[0056]

[0057] in:

[0058] k s , k p — are structural constants, generally taking values ​​of 1 and 0.8;

[0059] f—operating frequency, 50HZ;

[0060] d c —Outer diameter of the wire core, in meters (m);

[0061] s—spacing between the center axes of the wire cores, in meters (m).

[0062] 2) Insulation dielectric loss W d calculate:

[0063]

[0064] W d =ω·C(U0) 2 ·tgδ (8)

[0065] in:

[0066] C represents the insulation layer capacitance;

[0067] D i , D ic , respectively the parameters of the outer diameter and inner diameter of the insulation layer;

[0068] ω is the angular frequency, corresponding to the frequency f, that is: ω = 2πf;

[0069] U0—voltage to ground;

[0070] ε—insulation dielectric constant;

[0071] tgδ—Dielectric loss tangent of insulation, 0.001.

[0072] 3) Lead alloy sheath loss W l calculate:

[0073] The calculation formula is as follows.

[0074] W l =λ1W c (9)

[0075] λ1=λ1′+λ1″ (10)

[0076] in:

[0077] λ1′——circulating current loss, the calculation method is shown in the following formula (11);

[0078] λ1″——Eddy current loss does not need to be considered, so the eddy current loss is 0.

[0079]

[0080] in:

[0081] R c ——The resistance of the wire core at the operating temperature;

[0082] R s ——Resistance of alloy lead sheath at 90℃, calculated as shown in formula (12);

[0083] X is the impedance value of the alloy lead sheath material. The calculation method is shown in formula (13).

[0084]

[0085] in:

[0086] ρ s ——Indicates the resistivity of the alloy lead sheath at 20℃;

[0087] A s ——Cross-sectional area of ​​alloy lead sheath;

[0088] α s ——Resistance temperature coefficient of alloy lead sheath material;

[0089] θ s - operating temperature;

[0090] η——The temperature ratio of alloy lead sheath and conductor, generally taken as 0.7~0.8.

[0091]

[0092] Where d l ——Outer diameter of metal sheath.

[0093] 4) Submarine cable armor layer loss W a Calculation:

[0094] W a =λ2W c (14)

[0095]

[0096] Where Rsa ——resistance of the armor layer at working temperature;

[0097] Lowercase c – the distance from the conductor to the axis of the submarine cable;

[0098] d a ——Average outer diameter of armor layer.

[0099] Step 2: Construct a thermal circuit model of the submarine cable body according to the submarine cable structure, and perform analysis and calculation;

[0100] Specifically:

[0101] For submarine cables, their main structure is layered according to water-blocking copper conductor, water-blocking copper conductor shield, XLPE insulation layer, insulation shield, semiconductor water-blocking tape, lead alloy sheath, PE sheath, filling layer, inner cushion layer, galvanized steel wire armor layer and PP outer sheath layer, and the heat transfer characteristics of different materials are not the same.

[0102] In the heat circuit, the main considerations are the thermal resistance of the XLPE insulation layer T1, the thermal resistance of the filling layer and the inner cushion layer T2, the thermal resistance of the PP outer sheath T3, the thermal capacity of the water-blocking copper conductor Q1, the thermal capacity of the XLPE insulation layer Q2, the thermal capacity between the alloy lead sheath and the PE sheath Q3, the thermal capacity of the filling layer and the inner cushion layer Q4, the thermal capacity of the galvanized steel wire armor layer Q5, and the thermal capacity of the PP outer sheath Q6. In addition, the conductor loss W must also be considered. C , dielectric loss of insulation layer W d , metal sheath and metal shield loss W l , Armor layer loss W a .

[0103] Construct the equivalent thermal circuit diagram of submarine cables Figure 2 As shown, there are three cable core conductors, so ×3:

[0104] The thermal resistance and heat capacity of each layer inside the cable are calculated using the following formula:

[0105]

[0106] Where:

[0107] ρ—thermal resistance coefficient of corresponding material;

[0108] D i —Outer diameter of the corresponding layer;

[0109] D i-1 —Outer diameter of the inner layer of the corresponding layer;

[0110] c—Thermal characteristic coefficient of the corresponding material.

[0111] For step 3: simplify the submarine cable thermal circuit model to obtain a simplified thermal circuit model; for the simplified equivalent thermal circuit, Figure 3 shown.

[0112] The calculation formulas for thermal resistance and heat capacity in the equivalent transient thermal circuit are as follows:

[0113] T A =T1 / 3 (18)

[0114] T B =T2 (19)

[0115] T C =q s T3 (20)

[0116] Q A =Q1+pQ2 (21)

[0117] Q B =(1-p)Q1+Q3+p′Q4 (22)

[0118] Q C =(1-p′)Q4+(Q5+p″Q6) / q s (twenty three)

[0119] Q D =(1-p″)Q6 / q s (twenty four)

[0120] Q a =Q A (25)

[0121] Q b =Q B / q s (26)

[0122] Q c =Q C / q s (27)

[0123] Q d =Q d / q s (28)

[0124] in:

[0125]

[0126]

[0127] for Figure 3 The transient thermal circuit model is simplified again to obtain the final simplified thermal circuit diagram, such as Figure 4 shown.

[0128] Figure 4The calculation formulas for each parameter are as follows:

[0129] Q A1 =Q a (35)

[0130]

[0131] T A1 =T A (37)

[0132] T B1 =T B +q s T C (38)

[0133] The calculation formula for the internal temperature rise of the submarine cable is as follows:

[0134] θ c (t) = W c [T a (1-e -at )+T b (1-e -bt )] (39)

[0135] in:

[0136]

[0137] T b =(T A1 +T B1 )-T a (41)

[0138]

[0139] N0=Q A1 T A1 Q B1 T B1 (43)

[0140] M0=0.5[Q A1 (T A1 +T B1 )+Q B1 T B1 ] (44)

[0141] Step 4: Construct a single submarine cable model;

[0142] Environmental modeling for a single submarine cable buried beneath the seabed.

[0143] The temperature rise of the submarine cable under soil burial conditions is calculated by dividing it into two parts. One part is the temperature rise formula inside the submarine cable itself, and the other part is the temperature rise caused by the external soil, that is, the temperature rise formula of the soil is used to calculate the temperature rise value. The sum of the two formulas is the temperature rise formula of the submarine cable under soil burial conditions.

[0144] For the calculation of the external soil thermal resistance of the submarine cable, the following formula is used;

[0145]

[0146] in

[0147] L—burial depth, m;

[0148] ρ s —Soil thermal resistivity, K·m / W;

[0149] D e —Outer diameter of cable surface, m;

[0150] For the calculation of soil thermal field, the following assumptions are made:

[0151] The submarine cable is used as a linear heat source and laid in a uniform and homogeneous medium soil, and the soil surface is set as an isothermal surface. The temperature of any point T in the soil is caused by the heat source W and the surface as the axial mirror heat source. The mirror heat source emits -W heat energy, such as Figure 5 shown.

[0152] The calculation formula for the external soil temperature rise of the submarine cable is as follows:

[0153]

[0154] δ is the heat dissipation factor of the soil, m 2 / S; t is time (in seconds); Ei is a function expression;

[0155]

[0156] W t =W c +W d +W l +W a (48)

[0157] W t Indicates the total loss of the cable;

[0158] The temperature rise formula of the cable buried in the soil is:

[0159] θ(t)=θ c (t)+α(t)θ e (t) (49)

[0160] in:

[0161]

[0162] For step 5: construct a calculation model for the temperature field of the submarine cable group and calculate the temperature field of the submarine cable group;

[0163] In a group of cables laid underground, when calculating the temperature rise of cable x, it is necessary to superimpose the mutual thermal effects of other cable heat sources and image heat sources on cable x. Figure 6 shown.

[0164] In a cable group, the temperature rise of a single cable x caused by a single cable y can be calculated using the following formula.

[0165]

[0166] W y is the loss of cable y;

[0167] d xy is the straight-line distance between cables x and y (x is not equal to y);

[0168] d x ' y is the straight-line distance between the cable x and its mirror image y.

[0169] In a cable group, the total temperature rise of a single cable x caused by the surrounding cables.

[0170]

[0171] n represents the number of load conductors in the cable; in the cable group, the total temperature rise of cable x is

[0172] θ x (t) = θ(t) + α(t)θ x (53)

[0173] α(t), defined as the ratio of the transient temperature rise to the steady-state temperature rise of the thermal circuit inside the cable, is usually called the arrival coefficient and is 1 in the steady state.

[0174] Step 6: Calculate the additional thermal resistance of the corresponding submarine cable;

[0175]

[0176] Step 7: Calculate the current carrying capacity of the cable group;

[0177] The calculation formula for the current carrying capacity of submarine cable groups is:

[0178]

[0179] Among them, Δθ is the conductor temperature rise relative to the ambient temperature; n represents the number of loaded conductors in the cable; T4 is the external environmental thermal resistance, that is, the external soil thermal resistance of the submarine cable; λ1 is the ratio of the insulation medium loss to the conductor loss; λ2 is the ratio of the metal shielding loss to the conductor loss; R is taken from the AC resistance of the cable at the operating temperature. This resistance value changes with the conductor core temperature. In engineering, it can be roughly selected as the AC resistance at the highest core temperature.

[0180] This method calculates the steady-state temperature and maximum current carrying capacity of submarine cables by constructing a thermal circuit model of the submarine cable body and the laying environment, and considering the mutual heat influence between cable groups. Compared with the traditional finite element method, this method has higher calculation efficiency and good prediction accuracy, and is suitable for the prediction of temperature field and current carrying capacity of submarine cable groups with different burial depths, cable spacing and cable numbers.

[0181] The technical solution of the present invention is described in detail below by way of specific examples:

[0182] A method for predicting the temperature rise and current carrying capacity of a submarine cable group based on a thermal path analysis method comprises the following steps:

[0183] Step 1: Determine the structure and parameters of each layer of the submarine cable.

[0184] Taking 35kV three-core DC submarine XLPE cable as an example, the structural parameters of each layer are shown in Table 1.

[0185] Table 1

[0186] layer Structure Name Thickness / mm Inner diameter / mm Outer diameter / mm 1 Water blocking conductor —— —— 20.5 2 XLPE insulation layer 12.1 14.55 44.7 3 Semiconductor water blocking tape 0.8 30.55 46.3 4 Alloy lead sleeve 3.2 31.55 52.7 5 PE sheath 2.1 32.55 56.9 6 Filling layer - 35.45 122.8 7 Lining 1.95 45.7 126.7 8 Armor layer 5.0 57.7 136.7 9 PP outer layer 4.0 61.7 144.7

[0187] Calculate the conductor loss according to formula (1-6), where k s Take 1,k p Take 0.8.

[0188] Calculate the insulation dielectric loss W according to formula (7-8) d The dielectric loss W is obtained when the dielectric constant ε is taken as 2.35 and the ground voltage U0 is taken as 35 kV. d =0.0643W / m.

[0189] For step 2: construct a thermal path model of the submarine cable body according to the submarine cable structure.

[0190] Firstly, the thermal resistance and capacity of each layer of the submarine cable structure are calculated according to formula (16-17): thermal resistance of XLPE insulation layer T1 = 0.455K·m / W, thermal resistance of filling layer and inner cushion layer T2 = 0.007K·m / W, thermal resistance of PP outer sheath T3 = 0.020K·m / W, thermal capacity of water-blocking copper conductor Q1 = 1138.719J / K, thermal capacity of XLPE insulation layer Q2 = 4870.184J / K, thermal capacity between alloy lead sheath and PE sheath Q3 = 2178.049J / K, thermal capacity of filling layer and inner cushion layer Q4 = 11035.740J / K, thermal capacity of galvanized steel wire armor layer Q5 = 5171.846J / K, thermal capacity of PP outer sheath Q6 = 3279.803J / K.

[0191] Secondly, according to formula (18-38), the simplified parameter T of the submarine cable thermal circuit model is A1 , T B1 , Q A1 , Q B1 Solve and get T A1 =0.152K·m / W, T B1 =0.096K·m / W, Q A1 =2965.290K·m / W, Q B1 =8857.88K·m / W.

[0192] According to formula (39-44), the temperature rise calculation formula of the submarine cable body (39) is obtained.

[0193] Step 4: Construct a single submarine cable laying environment model;

[0194] According to the laying soil environment parameters, a thermal path model of a single submarine cable under the laying environment is constructed. Here are some corresponding parameters, as shown in Table 2:

[0195] Table 2

[0196] parameter Login segment Shallow water section Deepwater section Buried depth / m 2 1 2 <![CDATA[Soil thermal resistance coefficient ρ s / (K·m / W)]]> 1 0.8 0.8 Soil heat dissipation coefficient δ <![CDATA[0.5×10 -6 ]]> <![CDATA[0.6×10 -6 ]]> <![CDATA[0.6×10 -6 ]]>

[0197] Substituting the relevant parameters of the shallow water section into formula (45), the external soil thermal resistance T4 = 0.422 K·m / W is calculated.

[0198] For the submarine cable model, the external thermal resistance T4 is related to the specific laying factor of the submarine cable. The specific parameters are shown in Table 3 below.

[0199] Table 3

[0200]

[0201] When calculating the soil ambient temperature rise, the soil heat dissipation coefficient δ is taken according to Table 2.

[0202] Step 5: Construct a temperature field calculation model for submarine cable groups;

[0203] Take the burial depth of 1m, the distance between submarine cables is 0.5m, the number of cables is 5, and they are laid horizontally with equal spacing as an example.

[0204] Observe the geometric relationship and calculate the geometric center cable x of the cable group and its distance d relative to other cables xy and the distance d between the mirror cables x ' y .

[0205] The calculation results are:

[0206]

[0207] The temperature rise of the five cables from left to right is calculated as follows:

[0208] θ1=θ 12 +θ 13 +θ 14 +θ 15

[0209] θ2=θ 21 +θ 23 +θ 24 +θ 25

[0210] θ3=θ 31 +θ 32 +θ 34 +θ 35

[0211] θ4=θ 41 +θ 42 +θ 43 +θ 45

[0212] θ5=θ 51 +θ 52 +θ 53 +θ 54

[0213] Step 6: Calculate the additional thermal resistance of the corresponding submarine cable:

[0214] Take the burial depth of 1m, the distance between submarine cables is 0.5m, the number of cables is 5, and they are laid horizontally with equal spacing as an example.

[0215] Obviously, the third cable from left to right is at the geometric center of the cable group. The additional thermal resistance corresponding to the third cable is calculated as follows:

[0216]

[0217] Step 7: Calculate the current carrying capacity of the submarine buried cable group.

[0218] The calculation results of the example are as follows:

[0219] Take the current of 400A, the power-on time of 24h, the burial depth of 1m, the submarine cable spacing of 0.5m, the number of cables of 5, and the horizontal equal spacing as an example.

[0220] The temperature prediction value of the 35kV three-core DC submarine XLPE cable group laid in the shallow water section (assuming the initial ambient temperature is 25°C) is used. The above-mentioned submarine cable is modeled and simulated according to the same current size using the COMSOL finite element simulation software. The comparison between the temperature of each cable in the cable group temperature field and the simulation calculation temperature is shown in Table 4 below.

[0221] Table 4 Comparison of predicted values ​​and simulated values ​​at 0.5m spacing

[0222] Cable 1 Cable 2 Cable 3 Cable 4 Cable 5 Temperature prediction value (℃) 65.2 70.5 71.9 70.5 65.2 Simulation temperature value (℃) 67.8 73.2 74.8 73.2 67.8 error 2.6 2.7 2.9 2.7 2.6

[0223] Observe Table 4 above, when the submarine cable is laid in shallow water, the error between the temperature prediction value and the simulation calculation value of the temperature field of the cable group is about 2.7°C, indicating that the temperature prediction of the present invention has a certain accuracy.

[0224] In order to verify the universality of the present invention, the predicted values ​​and simulation calculated values ​​of the temperature field of cable groups with spacings of 0.2m, 0.3m, and 0.4m are listed in the following Tables 5, 6, and 7.

[0225] Table 5 Comparison of predicted values ​​and simulated values ​​at 0.2m spacing

[0226] Cable 1 Cable 2 Cable 3 Cable 4 Cable 5 Temperature prediction value (℃) 80.5 86.9 88.8 86.9 80.5 Simulation temperature value (℃) 83.3 89.3 91.3 89.3 83.3 error 2.8 2.4 2.5 2.4 2.8

[0227] Table 6 Comparison of predicted values ​​and simulated values ​​at 0.3m spacing

[0228]

[0229]

[0230] Table 7 Comparison of predicted values ​​and simulated values ​​at 0.4m spacing

[0231] Cable 1 Cable 2 Cable 3 Cable 4 Cable 5 Temperature prediction value (℃) 68.5 74.2 75.8 74.2 68.5 Simulation temperature value (℃) 71.3 77 78.7 77 71.3 error 2.8 2.8 2.9 2.8 2.8

[0232] The predicted current carrying capacity of the cable group at cable spacings of 0.2m, 0.3m, 0.4m, and 0.5m (simulation comparison and verification) is shown in Table 8 below:

[0233] Table 8 Predicted current carrying capacity of cable groups at cable spacings of 0.2m, 0.3m, 0.4m and 0.5m

[0234] 0.2m 0.3m 0.4m 0.5m Prediction value (A) 399.4 399.3 399.1 399.1 Simulation value (A) 400 400 400 400 error 0.6 0.7 0.9 0.9

[0235] By observing the above table, it is not difficult to find that the errors in the temperature field and current carrying capacity prediction results of the submarine buried cable group at different cable spacings are relatively small and within an acceptable range. Therefore, the method for predicting the temperature field and current carrying capacity of the submarine buried cable group based on the thermal path analysis method proposed in the present invention has high accuracy and a wide range of applications.

[0236] For a 35kV three-core DC submarine XLPE cable group, the finite element simulation temperature field calculation results (25℃ is the initial temperature) are as follows when the rated current carrying capacity is 400A and the cable spacing is 0.2m, 0.3m, 0.4m, and 0.5m respectively: Figure 7 , Figure 8 , Fig. 9 and Fig.10 shown.

[0237] These four figures show the finite element simulation temperature field calculation results of a 35kV three-core DC submarine XLPE cable group at different cable spacings, and are compared with the prediction method based on the thermal path analysis method proposed in this invention. By observing these figures, the following conclusions can be drawn:

[0238] 1. The prediction method is highly consistent with the simulation results:

[0239] from Figures 7 to 10 It can be seen that no matter the cable spacing is 0.2m, 0.3m, 0.4m or 0.5m, the predicted results of the temperature field of the cable group are close to the simulation results.

[0240] The distribution trend and maximum temperature value of the cable temperature are relatively consistent, which proves the accuracy and reliability of the prediction method proposed in the present invention.

[0241] 2. Cable spacing has a significant impact on temperature field distribution:

[0242] As the cable spacing decreases, the mutual thermal influence between cables intensifies, resulting in an overall increase in cable temperature.

[0243] from Figures 7 to 10 It can be clearly seen that the smaller the cable spacing, the higher the cable temperature and the more uneven the temperature distribution. This shows that in actual engineering, reasonable design of cable spacing is crucial to ensure the safe operation of cables.

[0244] 3. The prediction method has good versatility:

[0245] The prediction method proposed in the present invention can be applied to the temperature field calculation of submarine buried cable groups under different cable spacings, which shows that the method has a wide range of applications and can meet actual engineering needs.

[0246] 4. Advantages of the prediction method:

[0247] Compared with the finite element simulation method, the prediction method proposed in the present invention has higher calculation efficiency and can quickly obtain the temperature field and current carrying capacity of the cable group. The method is easy to understand and apply and can be conveniently used in engineering design and operation and maintenance.

[0248] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0249] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for predicting the temperature field and current carrying capacity of a submarine cable group based on a thermal circuit analysis method, characterized in that: The following steps are involved: Step 1: Calculate relevant cable parameters based on submarine cable structural parameters; Step 2: According to the submarine cable structure and related cable parameters, a thermal circuit model of a single submarine cable body is constructed and analyzed and calculated; Step 3: Simplify the thermal circuit model of a single submarine cable body to obtain a simplified thermal circuit model and determine the internal temperature rise of the submarine cable; Step 4: Construct a single submarine cable laying environment model; Step 5: Construct a temperature field calculation model for the submarine cable group and calculate the temperature field of the submarine cable group; Step 6: Calculate the additional thermal resistance of the corresponding submarine cable; Step 7: Calculate the current carrying capacity of the cable group.

2. The method for predicting the temperature field and current carrying capacity of a submarine cable group based on the thermal circuit analysis method according to claim 1 is characterized in that: The relevant cable parameters are calculated in step 1, including: Calculate the conductor loss of submarine cables, calculate the insulation medium loss, calculate the lead alloy sheath loss and calculate the armor layer loss of submarine cables.

3. The method for predicting the temperature field and current carrying capacity of a submarine cable group based on the thermal circuit analysis method according to claim 2 is characterized in that: The step 2 comprises: According to the submarine cable structure and related cable parameters, an equivalent thermal circuit model of the submarine cable is constructed, and the thermal resistance and heat capacity of each layer inside the cable are calculated.

4. The method for predicting the temperature field and current carrying capacity of a submarine cable group based on the thermal circuit analysis method according to claim 3 is characterized in that: The step 3 comprises: The thermal circuit model of a single submarine cable is simplified to obtain a simplified thermal circuit model, and the thermal resistance and thermal capacity in the equivalent transient thermal circuit are calculated, and the temperature rise inside the submarine cable itself is calculated.

5. The method for predicting the temperature field and current carrying capacity of a submarine cable group based on the thermal circuit analysis method according to claim 4 is characterized in that: The step 4 comprises: A single submarine cable laying environment model is constructed, and the external soil thermal resistance and soil temperature rise of the submarine cable are calculated. Based on the temperature rise inside the submarine cable itself and the temperature rise of the external soil, the temperature rise of the submarine cable under soil burial conditions is comprehensively obtained.

6. A method for predicting the temperature field and current carrying capacity of a submarine cable group based on thermal circuit analysis according to claim 5, characterized in that: The step 5 comprises: A temperature field calculation model for a submarine cable group is constructed, and the temperature rise and total temperature rise of a single cable in the cable group caused by surrounding cables are calculated.

7. A method for predicting the temperature field and current carrying capacity of a submarine cable group based on thermal circuit analysis according to claim 6, characterized in that: The step 6 comprises: Calculate the additional thermal resistance of a single cable in a cable group based on the cable spacing and soil thermal resistivity.

8. The method for predicting the temperature field and current carrying capacity of a submarine cable group based on the thermal circuit analysis method according to claim 7 is characterized in that: The step 7 comprises: The current carrying capacity of the cable group is calculated based on the cable temperature rise, external environment thermal resistance, the ratio of insulation medium loss to conductor loss, the ratio of metal shielding loss to conductor loss, the cable AC resistance and the cable insulation medium loss.

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