Steady-state temperature prediction method of three-phase multi-loop tunnel cable core and electronic equipment

Abstract

The invention relates to a three-phase multi-loop tunnel cable core steady-state temperature prediction method and electronic equipment, and the method comprises the steps: building a single-phase single-loop tunnel cable steady-state thermal circuit model, and solving the single-phase single-loop cable core steady-state temperature through the built single-phase single-loop tunnel cable steady-state thermal circuit model; solving the steady-state temperature of the cable core under three-phase single-loop laying by using a correction method; for a single-phase four-loop laying situation, the influence of the mutual heating effect between loop cables on the cable core temperature is merged into mutual heating effect thermal resistance, and the mutual heating effect thermal resistance is introduced into a single-phase single-loop tunnel cable steady-state thermal circuit model to form an improved thermal circuit model to predict the cable core steady-state temperature of a single-phase multi-loop cable; the three-phase multi-loop cable is regarded as a single-phase single loop, and the cable core temperature of the three-phase multi-loop cable is predicted through the combination of a three-phase single loop and a single-phase multi-loop. Compared with the prior art, the method has the advantages of quickly and accurately predicting the steady-state temperature of the cable core of the three-phase multi-loop tunnel cable and the like.

Description

Technical Field

[0001] The invention relates to the technical field of cable steady-state temperature rise prediction, and in particular to a steady-state temperature prediction method and electronic equipment for a three-phase multi-circuit tunnel cable core. Background Art

[0002] Tunnel cables are widely used in power transmission and distribution lines in large power plants, urban roads and other areas due to their large transmission capacity, ability to effectively prevent cables from being damaged by external forces, not easily affected by external climate and environment, and ease of inspection and maintenance. However, tunnel cables have a poor heat dissipation environment, and are prone to overheating during operation, which accelerates the aging of insulation. For example, for cross-linked polyethylene (XLPE) insulated cables, when the cable core temperature exceeds 90°C, XLPE will accelerate aging, thus affecting power transmission safety. It can be seen that the cable core temperature needs to be accurately predicted during cable operation to ensure the safe operation of the cable.

[0003] Tunnel cables can accommodate more transmission lines, so cables are usually laid in clusters. During operation, the existence of mutual heat effect between cables in cluster laying will increase the temperature of the cable, which needs to be considered when predicting the cable core temperature. At present, the prediction of cable core temperature under mutual heat effect mainly adopts three general methods for predicting hot spot temperature of power equipment: numerical calculation method, thermal circuit method based on IEC standard and machine learning algorithm. The numerical calculation method directly solves the field variables of the cable numerically based on numerical calculation methods such as finite element, and does not need to consider additional methods to calculate the mutual heat effect when laying in clusters. It has a wide range of applications and high calculation accuracy, but the calculation time is long, which limits its application in engineering. The thermal circuit method establishes a thermal circuit model of the cable heat transfer process based on the thermoelectric analogy theory, and considers the influence of the mutual heat effect between cables by modifying the thermal circuit parameters and introducing new thermal circuit structures. The thermal circuit method has a fast calculation speed and is mostly used for direct buried cables laid in clusters. For tunnel cables with air as the medium between cables, the heat transfer modes between cables include convection heat transfer and radiation heat transfer, which makes it difficult to establish the thermal circuit of the mutual heat effect, and the corresponding thermal circuit research is also less. Machine learning algorithms need to use sample data obtained through experiments or numerical calculations to build the relationship between load current and cable core temperature. The influence of mutual thermal effects is included in the sample data, so the processing of mutual thermal effects is essentially completed by experiments or numerical calculations. In summary, the current prediction method for the cable core temperature of tunnel cables under cluster laying is not mature yet. It is necessary to propose a universal and fast new cable core temperature prediction method for the common cluster laying form in tunnel cables.

[0004] For clustered cables laid in tunnels, the cables in the loop are usually arranged in a herringbone shape and the cables are closely spaced from each other. Therefore, the mutual thermal effect exists both between the loops and within the loops. It is particularly difficult to deal with the mutual thermal effect when predicting the cable core temperature.

[0005] After searching, Chinese invention patent publication number CN112380669A discloses a method for quickly obtaining the maximum temperature of the steady-state core of a four-circuit trench cable, including the following steps: 1) constructing a four-circuit cable core maximum temperature calculation model; 2) performing parameter estimation to obtain the thermal radiation coefficient value and various constant parameters in the four-circuit cable core maximum temperature calculation model under different heat flow and ambient temperature conditions according to the physical model of the trench cable; 3) obtaining the maximum temperature of the trench cable core according to the four-circuit cable core maximum temperature calculation model after fitting and determining the parameters. This existing patent has the problem of not being suitable for predicting the steady-state temperature of cluster-laid cables in tunnels.

[0006] How to achieve steady-state temperature prediction of three-phase multi-circuit tunnel cable core has become a technical problem that needs to be solved. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method and electronic equipment for predicting the steady-state temperature of a three-phase multi-circuit tunnel cable core.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] According to one aspect of the present invention, a method for predicting the steady-state temperature of a three-phase multi-circuit tunnel cable core is provided, the method comprising the following steps:

[0010] Step S1: Establish a steady-state thermal circuit model of a single-phase single-circuit tunnel cable, and use the established steady-state thermal circuit model of a single-phase single-circuit tunnel cable to solve the steady-state temperature T of the cable core of the single-phase single-circuit c0 ;

[0011] Step S2: Based on step S1, the cable core steady-state temperature T is calculated using the correction method under three-phase single-circuit laying. c0 ';

[0012] Step S3: For the single-phase four-circuit laying situation, the influence of the mutual thermal effect between the loop cables on the cable core temperature is merged into the mutual thermal effect thermal resistance, and introduced into the single-phase single-circuit tunnel cable steady-state thermal circuit model to form an improved thermal circuit model to predict the steady-state temperature T of the cable core of the single-phase multi-circuit cable. c1 ;

[0013] Step S4: Treat the three-phase multi-circuit cable as a combination of a single-phase single-circuit, a three-phase single-circuit, and a single-phase multi-circuit, and use the T obtained in steps S1 to S3 c0 、T c0 ' and T c1 Prediction of the core temperature T of three-phase multi-circuit cables c .

[0014] Preferably, the single-phase single-loop tunnel cable steady-state thermal circuit model considers the complete flow and heat transfer process in the tunnel cable, wherein in terms of flow, the model includes natural convection between the cable surface and the air in the tunnel; in terms of heat transfer, the model includes heat conduction, convection heat transfer and radiation heat transfer.

[0015] Preferably, the single-phase single-loop tunnel cable steady-state thermal circuit model includes multiple heat sources and thermal resistances, wherein the heat source includes the cable core conductor loss when an alternating current is passed through the cable, and the thermal resistance includes the cable body thermal resistance, the air layer thermal resistance in the tunnel, the tunnel layer thermal resistance and the soil layer thermal resistance;

[0016] The thermal resistance of the air layer in the tunnel is composed of the convection thermal resistance R cov and radiation thermal resistance R rad Parallel composition.

[0017] Preferably, the process of step S2 includes:

[0018] Step S2-1, under a given cable load current I, using finite element simulation software to calculate the single-phase single-circuit cable core temperature T c0 and the core temperature of the three-phase single-circuit cable T c0 ', and then get the cable core temperature correction coefficient C1 at this time:

[0019] C1=T c0 ' / T c0

[0020] Step S2-2, at different currents I i (i=1,2,...,N), repeat the above step S2-1 to obtain C under different currents i , where N is the number of different currents;

[0021] Step S2-3, at different currents I i Lower cable core temperature correction coefficient C i Based on the value, the correction coefficient C is fitted as a function of the load current I:

[0022] C=f(I)

[0023] Step S2-4, when the cable load current I is given, the cable core temperature T of the three-phase single-circuit cable c0 'You can solve:

[0024] T c0 '=CT c0

[0025] Where T c0 It is the steady-state temperature of the cable core of the single-phase single-circuit solved in step S1.

[0026] Preferably, the improved thermal circuit model building process in step S3 includes:

[0027] Step S3-1: The loop cable whose cable core temperature is to be determined is called the target cable, and the cables of the other three loops are called adjacent cables. The effect of the adjacent cables heating on the core temperature of the target cable is constructed as an additional thermal resistance R in the air layer heat path of the target cable. m , and called R m is the thermal resistance of the mutual heat effect. The finite element method is used to calculate the air temperature rise in the tunnel under different working conditions, and then R is determined. m value;

[0028] Step S3-2: Change the current I of each adjacent loop cable separately j , all other loop cables are unloaded, and the finite element method is used to calculate different I j Average temperature rise of air in the lower tunnel ΔT aj , and ΔT aj Fitting to I j Function:

[0029] ΔT aj =f j (I j )

[0030] Where j is the jth adjacent loop. If loop 1 is the target cable, then j = 2, 3, ..., n;

[0031] Step S3-3: When current is applied to all adjacent circuits at the same time, the increase in air temperature ΔT a It is equal to the sum of the increase in air temperature caused by each adjacent circuit when operating individually:

[0032]

[0033] Step S3-4: Apply current I to the target cable and calculate the cable loss Q at this time according to the IEC standard. Then the mutual thermal effect R in the steady-state thermal circuit of the target cable is m The calculation is done using the following formula:

[0034] R m =C2ΔT a / Q

[0035] Where, ΔT a is the temperature rise of the air in the tunnel caused by the heating of the adjacent loops 2 to n; Q is the heat generated by loop 1 under current I; C2 is the correction coefficient;

[0036] Step S3-5: The mutual thermal effect thermal resistance R obtained in step S3-4 is m The expression is substituted into the thermal circuit model constructed in step S1 to form an improved thermal circuit model.

[0037] More preferably, in step S3, the steady-state temperature T of the cable core of the single-phase multi-circuit cable is predicted. c1 Specifically: When n loop currents I1~I n When the cable loss Q is determined according to the target cable current, ΔT is determined according to the adjacent cable current using step S3-3. a value, and then use step S3-4 to obtain the mutual thermal effect thermal resistance R m , and then substitute it into the improved thermal circuit model, and solve the cable core steady-state temperature T under single-phase four-circuit conditions through the improved thermal circuit model. c1 .

[0038] Preferably, in step S4, the cable core temperature T of the three-phase multi-circuit cable is predicted. c The process includes:

[0039] 1) Combine the single-phase single-circuit cable into a single-phase multi-circuit cable, and the cable core temperature is changed from the steady-state temperature T c0 The core steady-state temperature T of the single-phase multi-circuit cable c1 , T c1 Solved by improved thermal circuit model;

[0040] 2) In the case of single-phase multi-circuit laying, each adjacent circuit of circuit 1 adds one phase, and the cable core temperature of circuit 1 is T c1 Change to T c1 +(T c1 -T c0 );

[0041] 3) Each adjacent loop of loop 1 adds one more phase. At this time, all adjacent loops are complete three-phase. The cable core temperature of loop 1 is T c1 +(T c1 -T c0 ) becomes T c1 +2(T c1 -T c0 );

[0042] 4) Loop 1 is changed from single phase to three phase, and the cable core temperature of loop 1 is changed from T c1 +2(T c1 -T c0 ) becomes C1[T c1 +2(T c1 -T c0 )], where C1 is the correction factor between single-phase cable and three-phase cable;

[0043] Therefore, the cable core temperature T of loop 1 in three-phase multi-circuit c The expression is as follows:

[0044] T c=C1[T c1 +2(T c1 -T c0 )], that is: T c =C1[T c0 +3(T c1 -T c0 )].

[0045] More preferably, the convection thermal resistance R cov The calculation is as follows:

[0046]

[0047] Where A is the cable surface area; h(I) is the cable surface convection heat transfer coefficient, which is a function of the load current I.

[0048] More preferably, the radiation thermal resistance R rad The calculation is as follows:

[0049]

[0050] Where π is the circumference of a circle, T s and T t are the average temperatures of the cable surface and the tunnel wall, respectively; D is the outer diameter of the cable, ε c is the cable surface emissivity, and σ is the blackbody radiation constant.

[0051] Another aspect of the present invention provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor implements the method when executing the program.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] 1) The present invention regards the three-phase multi-circuit cable as a combination of simple laying methods. First, the thermal circuit model is used to solve the steady-state temperature of the single-phase single-circuit tunnel cable core, and then the steady-state temperatures of the cable cores under three-phase single circuit and single-phase multi-circuit are solved respectively. Finally, based on the cable core temperature combination method, the single-phase single circuit is expanded to three-phase multi-circuit, and the thermal circuit model is applied to the prediction of the steady-state temperature of the tunnel cable core, which is fast and accurate.

[0054] 2) The present invention assumes that the heat generation of adjacent circuits is independent of each other. Since the steady-state thermal path of the cable is composed of linear elements, the effect of the heat generation of adjacent circuits on the increase in air temperature satisfies the superposition principle. The finite element method is used to calculate the contribution of each circuit to the air temperature rise when it runs alone, and then polynomial fitting is used to obtain the expression of the contribution of each circuit to the air temperature rise when it runs alone. After that, the total air temperature rise is obtained based on the accumulation and the mutual thermal effect resistance is quickly obtained, which solves the problem of difficulty in establishing the thermal path.

[0055] 3) The present invention adds mutual thermal effect resistance to the thermal circuit model to represent the effect of heating of adjacent cables on the temperature of the target cable core, forming an improved thermal circuit model, and solves the steady-state temperature of the single-phase multi-circuit tunnel cable core based on the improved thermal circuit model, thereby realizing accurate and rapid solution of the steady-state temperature of the cable core under cluster laying.

[0056] 4) The method of the present invention has a certain universality and can be further applied to the steady-state temperature prediction of tunnel cables with more loop numbers, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 Schematic diagram of the calculation process of the method in Example 1 of the present invention;

[0058] Figure 2 Schematic diagram of the process of the method in Example 1 of the present invention;

[0059] Figure 3 A schematic diagram of a physical model of a three-phase four-circuit tunnel cable according to an embodiment of the method of the present invention;

[0060] Figure 4 This is a schematic diagram of the structure of a cable body in one embodiment of the present invention;

[0061] Figure 5 It is a schematic diagram of a thermal circuit model for solving the steady-state temperature of a single-phase single-loop tunnel cable core in the present invention;

[0062] Figure 6 It is a schematic diagram of the improved thermal circuit model for solving the steady-state temperature of the cable core of a single-phase four-circuit tunnel cable in the present invention;

[0063] Figure 7 It is a schematic diagram of the steady-state temperature prediction process of the three-phase four-circuit cable core based on the combination method in the present invention;

[0064] Figure 8 It is the deviation and relative deviation between the solution result of the maximum steady-state temperature of the cable core of loop 1 in the three-phase four-loop cable in the present invention and the finite element calculation result. DETAILED DESCRIPTION

[0065] 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 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 should fall within the scope of protection of the present invention.

[0066] Example 1

[0067] This embodiment relates to a steady-state temperature prediction method for a three-phase four-circuit tunnel cable core. The method proposes a cable core steady-state temperature prediction method based on a combination method for tunnel cables laid in a three-phase four-circuit cluster and in accordance with the spatial arrangement of the cables. The three-phase four-circuit cable is regarded as a combination of simple laying methods. First, the solution of the cable core temperature of the three-phase four-circuit cable is converted into the cable core temperature of single-phase single-circuit, three-phase single-circuit and single-phase four-circuit cables, respectively. During the solution process, the influence of the mutual heat effect between cables is handled by correction and improvement of the thermal circuit model. Then, the solution results are combined to finally obtain the steady-state temperature of the cable core under the three-phase four-circuit laying. .

[0068] The method of the present invention realizes the accurate prediction of the steady-state temperature of the cable core of a three-phase four-circuit tunnel cable, and the method has strong universality and can be further extended to tunnel laying situations with more circuit numbers.

[0069] To achieve the above object, the technical solution adopted by the present invention includes the following steps: Figure 2 :

[0070] Step S1: Establish a steady-state thermal circuit model of a single-phase single-circuit (single-core) tunnel cable, determine the thermal circuit parameters according to the IEC standard combined with the finite element calculation results, and use the thermal circuit model to solve the steady-state cable core temperature T of a single-phase single-circuit (i.e., single-core) cable under a given load current. c0 ;

[0071] Step S2: Based on the steady-state temperature of a single cable core, the correction method is used to solve the steady-state temperature T of the cable core under three-phase single-circuit laying. c0 ';

[0072] Step S3: For the single-phase four-circuit laying situation, the influence of the mutual thermal effect between the loop cables on the cable core temperature is merged into the mutual thermal effect thermal resistance, and introduced into the single cable steady-state thermal circuit model to form an improved thermal circuit model for predicting the steady-state temperature T of the cable core of the single-phase four-circuit cable. c1 ;

[0073] Step S4: Treat the three-phase four-circuit cable as a combination of a single-phase single-circuit, a three-phase single-circuit, and a single-phase four-circuit, and use the T obtained in steps S1 to S3 c0 、T c0 ' and T c1 Determine the core temperature T of a three-phase four-circuit cable c ;

[0074] Finally, the core temperature of the three-phase four-circuit cable is calculated using the finite element method and the method of the present invention under different working conditions, and the two results are compared to verify the correctness of the steady-state temperature prediction method for the three-phase four-circuit tunnel cable core proposed by the method of the present invention.

[0075] The steady-state thermal circuit model of the tunnel cable in step S1 includes multiple heat sources and thermal resistances, wherein the heat source includes the cable core conductor loss when the cable is subjected to an alternating current, etc., which is calculated according to the IEC standard; the thermal resistance includes the thermal resistance of the cable body, the thermal resistance of the air layer in the tunnel, the thermal resistance of the tunnel layer, and the thermal resistance of the soil layer, which are determined according to the IEC standard combined with finite element simulation. When the current I is given, the steady-state thermal circuit model of the tunnel cable is used to predict the cable core temperature T of a single-phase single-circuit (single) cable. c0 .

[0076] Step S2 uses the correction method to solve the steady-state temperature T of the three-phase single-circuit cable core c0 The specific steps are as follows:

[0077] Step S2.1: Under a given cable load current I, use finite element simulation software to calculate the single-phase single-circuit cable core temperature T c0 and the core temperature of the three-phase single-circuit cable T c0 ', and then get the cable core temperature correction coefficient C1 at this time:

[0078] C1=T c0 ' / T c0

[0079] Step S2.2: At different currents I i (i=1,2,...,N), repeat the above step S2.1 to obtain the cable core temperature correction coefficient C under different currents i ;

[0080] Step S2.3: At different currents I i Lower C i Based on the value, the correction coefficient C is fitted as a function of the load current I:

[0081] C=f(I)

[0082] Step S2.4: When the load current I is given, use step S1 to solve the steady-state temperature T of the cable core of a single cable under the current I c0 , and use step S2.3 to calculate the cable core temperature correction coefficient C, then the cable core temperature T of the three-phase single-circuit cable c0 'You can solve:

[0083] T c0 '=CT c0

[0084] The specific steps of constructing an improved thermal circuit model for solving the temperature of the single-phase four-circuit cable core in step S3 are as follows:

[0085] Step S3.1: The loop cable with the cable core temperature to be determined is called the target cable, and the cables of the other three loops are called adjacent cables. The effect of the adjacent cable heating on the core temperature of the target cable is constructed as an additional thermal resistance R in the air layer heat path of the target cable. m , and called R m is the thermal resistance of the mutual heat effect. The finite element method is used to calculate the air temperature rise in the tunnel under different working conditions, and then determine R m value;

[0086] Step S3.2: Change the current I of each adjacent loop cable separately j (j is the jth adjacent loop. For four-loop installation, if loop 1 is the target cable, then j = 2, 3, 4). All other loop cables are unloaded (current is zero). The finite element method is used to calculate the different I j Average temperature rise of air in the lower tunnel ΔT aj , and ΔT aj Fitting to I j Function:

[0087] ΔT aj =f j (I j )(j=2,3,4)

[0088] Step S3.3: When current is applied to all adjacent circuits at the same time, the increase in air temperature ΔT a It is equal to the sum of the increase in air temperature caused by each adjacent circuit when operating individually:

[0089]

[0090] Step S3.4: Apply current I to the target cable and calculate the cable loss Q at this time according to the IEC standard. Then the mutual thermal effect R in the steady-state thermal circuit of the target cable is m The calculation is done using the following formula:

[0091] R m =C2ΔT a / Q

[0092] Where, ΔT a is the temperature rise of the air in the tunnel caused by the heating of adjacent circuits 2 to 4; Q is the heat generated by circuit 1 under current I; C2 is the correction factor used to make R m The solution is more accurate and is determined through model calibration.

[0093] Step S3.5: Substitute the mutual thermal resistance R obtained in step S3.4 into m Substitute the expression into the target cable thermal circuit model (i.e., the thermal circuit model constructed in step S1, such as Figure 5 ), an improved thermal circuit model is formed as Figure 6 When four loop currents I1 to I4 are given, the cable loss Q is determined according to the target cable current, and ΔT is determined according to the adjacent cable current using step S3.3. a value, and then use step S3.4 to obtain the mutual thermal effect thermal resistance R m , and then substitute it into the improved thermal circuit model, and solve the cable core steady-state temperature T under single-phase four-circuit conditions through the improved thermal circuit model. c1 .

[0094] In step S4, the three-phase four-circuit installation is regarded as a combination of three simple installation methods: single-phase single-circuit, three-phase single-circuit and single-phase four-circuit. Based on the T obtained in steps S1 to S3, c0 , T c0 ' and T c1 , the cable core temperature T of the three-phase four-circuit cable is solved by combined operation c .

[0095] Four-circuit load currents I1~I4 are randomly given within the actual scope of the project, and the steady-state temperature of the three-phase four-circuit cable core is solved by the finite element method and the method of the present invention respectively. The calculation results of the two methods are compared, and the deviation and relative deviation between the two are calculated to verify the correctness of the method of the present invention in predicting the steady-state temperature of the three-phase four-circuit tunnel cable core.

[0096] Example 2

[0097] This embodiment relates to a method for predicting the steady-state temperature of a three-phase four-circuit tunnel cable core, which solves the steady-state temperature of the tunnel cable core under three laying modes: single-phase single-circuit, three-phase single-circuit, and single-phase four-circuit, and then solves the steady-state temperature of the three-phase four-circuit cable core.

[0098] The specific steps include:

[0099] Figure 3 This is a schematic diagram of a three-phase four-circuit tunnel cable, where the cable structure is as follows Figure 4 A physical model of tunnel cables is established, which takes into account the complete flow and heat transfer process in the tunnel cables. In terms of flow, the model includes natural convection between the cable surface and the air in the tunnel; in terms of heat transfer, the model includes heat conduction, convection and radiation.

[0100] Construct a steady-state thermal circuit model of a single-phase single-circuit (i.e., single-cable) tunnel cable. Figure 5 The thermal circuit element contains multiple heat sources and thermal resistors, and its parameters are determined according to the IEC standard combined with the finite element calculation results. Table 1 shows the solution results or expressions of each thermal resistor in the thermal circuit model:

[0101] Table 1

[0102] Thermal resistance element <![CDATA[R i ]]> <![CDATA[R p ]]> <![CDATA[R a ]]> <![CDATA[R e ]]> <![CDATA[R air ]]> <![CDATA[R t ]]> <![CDATA[R s ]]> <![CDATA[Value / K·m·W -1 > 0.457 0.106 0.142 0.058 <![CDATA[R cov R rad / (R cov +R rad )]]> 0.0144 0.808

[0103] In Table 1, R i , R p , R a and R e They are the thermal resistance of the cable insulation layer, the thermal resistance of the water barrier layer, the thermal resistance of the air gap and the thermal resistance of the outer sheath, R air is the thermal resistance of the air layer in the tunnel, which is determined by the convection thermal resistance R cov and radiation thermal resistance R rad Parallel connection, R t and R s They are the tunnel layer thermal resistance and the soil layer thermal resistance respectively. Among them, the cable insulation layer thermal resistance, water barrier layer thermal resistance, air gap thermal resistance and outer sheath thermal resistance belong to the cable body thermal resistance.

[0104] The above convection thermal resistance R cov And the radiation thermal resistance R rad The calculation method is as follows:

[0105]

[0106] Where A is the cable surface area / m 2 , π is the circumference of a circle, T s and T t are the average temperatures of the cable surface and the tunnel wall / K, D is the cable outer diameter / m, ε c is the cable surface emissivity, σ=5.67×10 -8 W·m -2 ·K -4 is the blackbody radiation constant, h(I) is the cable surface convection heat transfer coefficient / W·m -2 ·K -1 , is a function of the load current I.

[0107] The finite element calculation results of the surface heat transfer coefficient under different load currents I are used for fitting and determination. The fitting results are as follows:

[0108] h(I)=kI+b=0.001224I+2.785

[0109] Where k and b are the slope and intercept of the fitted line, respectively.

[0110] Compared with single-phase single-circuit laying, there is mutual heating effect between phase cables during three-phase single-circuit laying, which makes the cable core temperature higher. Figure 5 The thermal circuit model shown in the figure is solved to obtain the steady-state temperature T of the single-phase single-circuit tunnel cable core c0 On this basis, the correction method is used to solve the steady-state temperature T of the cable core of the three-phase single-circuit cable c0 ', as shown below:

[0111] T c ′0=C1T c0

[0112] The solution of the correction coefficient C1 is as follows:

[0113] 1) Use finite element simulation software to calculate the single-phase single-circuit cable core temperature T under current I c0 and three-phase single-circuit cable core temperature T c0 ', using C1 = T c0 ' / T c0 Calculate the correction coefficient C1, the finite element calculation conditions and C1 calculation results are shown in Table 2:

[0114] Table 2

[0115] CurrentI / A 400 600 800 1000 1200 1400 <![CDATA[Correction factor C1]]> 1.0046 1.0100 1.0176 1.0272 1.0396 1.0547

[0116] 2) Fit the coefficient C1 at different currents I shown in Table 2 to a function of I: C1 = f(I);

[0117] 3) When the load current I is given, on the one hand, the thermal circuit model is used to solve the single-phase single-circuit cable core temperature T c0 On the other hand, the correction coefficient C1 is solved by using the fitting result C1=f(I). The product of the two is the three-phase single-circuit cable core temperature T c0 '.

[0118] Compared with single-phase single-circuit laying, there is mutual heat effect between the circuits in single-phase multi-circuit laying, which makes the cable core temperature higher. Figure 1 As shown in the figure, when solving the cable core temperature of loop 1, it is necessary to consider the influence of the heat generated by the three adjacent loops 2 to 4 on the cable core temperature of loop 1. For this reason, an improved thermal circuit model based on mutual thermal effect thermal resistance is proposed to solve the steady-state temperature of the single-phase four-loop cable core. The following only gives the solution method of the cable core temperature of loop 1 when the four loops are running at the same time (that is, loop 1 is the target cable, and loops 2 to 4 are adjacent cables). The solution of the cable core temperatures of other loops can be deduced by analogy.

[0119] The thermal influence of adjacent loops 2 to 4 on loop 1 is represented by a thermal resistance R placed in the air layer. air The thermal resistance of the tunnel layer R t Additional thermal resistance R m , and called R m is the mutual heating effect thermal resistance, such as Figure 6 As shown. Thermal resistance R m This shows that the heating of the adjacent loop increases the air temperature. It is because the heating of the adjacent loop cable increases the air temperature between the cables that the cable core temperature of loop 1 is higher than when it is laid alone. m Use the following formula to calculate:

[0120]

[0121] Where, ΔT a is the temperature rise of the air in the tunnel caused by the heating of the adjacent circuits 2 to 4 / K; Q1 is the heat generated by circuit 1 under current I1 / W; C2 is the correction factor used to make R m The solution is more accurate and is determined through model calibration.

[0122] The specific values ​​need to be determined by comparing the predicted results with the finite element calculation results. The purpose is to make small corrections to the predicted results to make them closer to the finite element calculation results.

[0123] The following is the air temperature rise ΔT a To solve:

[0124] Air temperature rise ΔT a It is generated by the combined effect of the heat generated by the adjacent circuits 2 to 4, so ΔT a is a ternary function of the currents I2 to I4 of loops 2 to 4. Assuming that the heating of adjacent loops 2 to 4 is independent of each other, and because the steady-state thermal path of the cable is composed of linear elements, the effect of the heating of adjacent loops on the increase of air temperature satisfies the superposition principle, that is:

[0125] ΔT a =ΔT a2 (I2)+ΔT a3 (I3)+ΔT a4 (I4)

[0126] Where, ΔT a2 (I2), ΔT a3 (I3), ΔT a4 (I4) is the amount of increase in air temperature (or air temperature rise ΔT) when circuits 2, 3, and 4 are operated separately. a To obtain ΔT a2 (I2), ΔT a3 (I3), ΔT a4 The specific expression of (I4) is calculated using finite element simulation software when loops 2 to 4 are operated separately. a The contribution of is shown in Table 3:

[0127] Table 3

[0128] <![CDATA[I2 / A]]> <![CDATA[ΔT a2 / K]]> <![CDATA[I3 / A]]> <![CDATA[ΔT a3 / K]]> <![CDATA[I4 / A]]> <![CDATA[ΔT a4 / K]]> 0 0 0 0 0 0 200 0.33 200 0.33 200 0.35 400 1.47 400 1.44 400 1.41 600 3.24 600 3.26 600 3.42 800 5.76 800 5.73 800 5.86 1000 8.89 1000 9.14 1000 9.09

[0129] Perform polynomial fitting on the data in Table 3 to obtain ΔT a2 (I2), ΔT a3 (I3), ΔT a4Substituting ΔT into the expression (I4) a =ΔT a2 (I2)+ΔT a3 (I3)+ΔT a4 (I4) The air temperature rise ΔT is obtained a , and then the mutual thermal effect thermal resistance R m When four loop currents I1 to I4 are given, on the one hand, the heat generation Q1 of loop 1 is solved according to the current I1 of loop 1 (target cable), and on the other hand, the air temperature rise ΔT is solved according to the current I2 to I4 of loops 2 to 4 (adjacent cables). a , then R m =ΔT a / Q1.

[0130] The R obtained by the above solution m Value Substitution Figure 6 In the improved thermal circuit model shown in the figure, the cable core temperature T of loop 1 under given working conditions can be determined by solving the thermal circuit. c1 .

[0131] At a single cable core temperature T c0 , three-phase single-circuit cable core temperature T c0 ' and the core temperature of the single-phase four-circuit cable T c1 Based on the solution results, the three-phase four-circuit cable core temperature T is solved by combining c The combination process is divided into the following four steps: Figure 7 :

[0132] 1) A single cable is combined into a single-phase four-circuit cable, and the cable core temperature is determined by T c0 Change to T c1 , T c1 Solved by the improved thermal circuit model based on mutual heat effect thermal resistance mentioned above;

[0133] 2) In the case of single-phase four-circuit laying, each adjacent circuit of circuit 1 adds one phase, and the cable core temperature of circuit 1 changes from T c1 Change to T c1 +(T c1 -T c0 );

[0134] 3) Each adjacent loop of loop 1 adds one more phase. At this time, all adjacent loops are complete three-phase. The cable core temperature of loop 1 is T c1 +(T c1 -T c0 ) becomes T c1 +2(T c1 -T c0 );

[0135] 4) Loop 1 is changed from single phase to three phase, and the cable core temperature of loop 1 is changed from T c1 +2(T c1 -T c0 ) becomes C1[T c1 +2(T c1 -T c0 )], C1 is the correction factor between single-phase cable and three-phase cable.

[0136] In summary, the cable core temperature T of loop 1 in three-phase four-circuit c The expression is as follows:

[0137] T c =C1[T c1 +2(T c1 -T c0 )], that is: T c =C1[T c0 +3(T c1 -T c0 )]

[0138] The accuracy of the above three-phase four-circuit tunnel cable steady-state temperature prediction method is tested. Independent and random currents I1~I4 are applied to the four circuits to obtain the working conditions required for the test. Some working condition data are shown in Table 4:

[0139] Table 4

[0140] Working conditions 1 2 3 4 ... 19 20 <![CDATA[I1 / A]]> 596 752 1206 696 ... 682 421 <![CDATA[I2 / A]]> 651 1231 977 869 ... 291 488 <![CDATA[I3 / A]]> 1016 985 583 411 ... 488 701 <![CDATA[I4 / A]]> 873 950 640 737 ... 348 259

[0141] Under the 20 working conditions in Table 4, the steady-state temperature rise of the cable core of loop 1 in the three-phase four-loop cable is calculated using the method of the present invention and the finite element simulation software, and the deviation and relative deviation between the two under different working conditions are obtained as follows: Figure 8 As shown. Figure 8 It can be seen that within the range of working conditions considered, the maximum deviation between the steady-state temperature rise of the cable core predicted by the method of the present invention and the finite element calculation result is within 2K, and the maximum relative deviation is within 2.5%, which verifies the accuracy of the steady-state temperature prediction method for the three-phase four-circuit tunnel cable proposed by the method of the present invention.

[0142] The method of the present invention is based on the combination of cable core temperatures, and realizes the expansion of the thermal circuit model from single-phase single circuit to three-phase four circuits when applied to the steady-state temperature prediction of the tunnel cable core, with high prediction accuracy. In addition, the method of the present invention has a certain universality and can be further applied to the steady-state temperature prediction of tunnel cables with more circuit numbers, with a wide range of applications.

[0143] Example 3

[0144] This embodiment also relates to a method for predicting the steady-state temperature of a three-phase multi-circuit tunnel cable core. This method is different from Embodiment 1 and Embodiment 2 in that it can be extended to three-phase multi-circuit tunnel cables, where the number of circuits is more than 4, and can be 5, 6 or even more.

[0145] The difference lies in the calculation of air temperature rise, air temperature rise ΔT a It is equal to the sum of the increase in air temperature when each adjacent circuit operates independently, calculated as follows:

[0146]

[0147] ΔT aj =f j (I j )(j=2,3,…,n)

[0148] Where n is the number of loops.

[0149] Example 4

[0150] The electronic device of the present invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in a read-only memory (ROM) or loaded from a storage unit into a random access memory (RAM). In the RAM, various programs and data required for device operation can also be stored. The CPU, ROM and RAM are connected to each other via a bus. An input / output (I / O) interface is also connected to the bus.

[0151] Multiple components in the device are connected to the I / O interface, including: input units, such as keyboards, mice, etc.; output units, such as various types of displays, speakers, etc.; storage units, such as disks, optical disks, etc.; and communication units, such as network cards, modems, wireless communication transceivers, etc. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunication networks.

[0152] The processing unit performs the various methods and processes described above, such as methods S1 to S4. For example, in some embodiments, methods S1 to S4 may be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program may be loaded and / or installed on the device via a ROM and / or a communication unit. When the computer program is loaded into the RAM and executed by the CPU, one or more steps of methods S1 to S4 described above may be performed. Alternatively, in other embodiments, the CPU may be configured to execute methods S1 to S4 in any other appropriate manner (e.g., by means of firmware).

[0153] The functions described above herein may be performed at least in part by one or more hardware logic components. For example, without limitation, exemplary types of hardware logic components that may be used include: field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), complex programmable logic devices (CPLDs), and the like.

[0154] The program code for implementing the method of the present invention can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer or other programmable data processing device, so that the program code, when executed by the processor or controller, enables the functions / operations specified in the flow chart and / or block diagram to be implemented. The program code can be executed entirely on the machine, partially on the machine, partially on the machine as a stand-alone software package and partially on a remote machine, or entirely on a remote machine or server.

[0155] In the context of the present invention, a machine-readable medium may be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, device, or equipment. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0156] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for predicting steady-state temperature of a three-phase multi-circuit tunnel cable core, characterized in that: The method comprises the following steps: Step S1: Establish a steady-state thermal circuit model of a single-phase single-circuit tunnel cable, and use the established steady-state thermal circuit model of a single-phase single-circuit tunnel cable to solve the steady-state temperature T of the cable core of the single-phase single-circuit c0 ; Step S2: Based on step S1, the cable core steady-state temperature T is calculated using the correction method under three-phase single-circuit laying. c0 '; Step S3: For the single-phase four-circuit laying situation, the influence of the mutual thermal effect between the loop cables on the cable core temperature is merged into the mutual thermal effect thermal resistance, and introduced into the single-phase single-circuit tunnel cable steady-state thermal circuit model to form an improved thermal circuit model to predict the steady-state temperature T of the cable core of the single-phase multi-circuit cable. c1 ; Step S4: Treat the three-phase multi-circuit cable as a combination of a single-phase single-circuit, a three-phase single-circuit, and a single-phase multi-circuit, and use the T obtained in steps S1 to S3 c0 、T c0 ' and T c1 Prediction of the core temperature T of three-phase multi-circuit cables c .

2. A method for predicting steady-state temperature of a three-phase multi-circuit tunnel cable core according to claim 1, characterized in that: The single-phase single-circuit tunnel cable steady-state thermal circuit model considers the complete flow and heat transfer process in the tunnel cable, wherein in terms of flow, the model includes natural convection between the cable surface and the air in the tunnel; In terms of heat transfer, the model includes conduction, convection and radiation.

3. The method for predicting steady-state temperature of a three-phase multi-circuit tunnel cable core according to claim 1, characterized in that: The single-phase single-loop tunnel cable steady-state thermal circuit model includes multiple heat sources and thermal resistances, wherein the heat source includes the cable core conductor loss when an alternating current is passed through the cable, and the thermal resistance includes the cable body thermal resistance, the air layer thermal resistance in the tunnel, the tunnel layer thermal resistance and the soil layer thermal resistance; The thermal resistance of the air layer in the tunnel is composed of the convection thermal resistance R cov and radiation thermal resistance R rad Parallel composition.

4. The method for predicting steady-state temperature of a three-phase multi-circuit tunnel cable core according to claim 1, characterized in that: The process of step S2 includes: Step S2-1, under a given cable load current I, using finite element simulation software to calculate the single-phase single-circuit cable core temperature T c0 and the core temperature of the three-phase single-circuit cable T c0 ', and then get the cable core temperature correction coefficient C1 at this time: C1=T c0 ' / T c0 Step S2-2, at different currents I i (i=1,2,...,N), repeat the above step S2-1 to obtain C under different currents i , where N is the number of different currents; Step S2-3, at different currents I i Lower cable core temperature correction coefficient C i Based on the value, the correction coefficient C is fitted as a function of the load current I: C=f(I) Step S2-4, when the cable load current I is given, the cable core temperature T of the three-phase single-circuit cable c0 'You can solve: T c0 '=CT c0 Where T c0 It is the steady-state temperature of the cable core of the single-phase single-circuit solved in step S1.

5. The method for predicting steady-state temperature of a three-phase multi-circuit tunnel cable core according to claim 1, characterized in that: The improved thermal circuit model building process in step S3 includes: Step S3-1: The loop cable whose cable core temperature is to be determined is called the target cable, and the cables of the other three loops are called adjacent cables. The effect of the adjacent cables heating on the core temperature of the target cable is constructed as an additional thermal resistance R in the air layer heat path of the target cable. m , and called R m is the thermal resistance of the mutual heat effect. The finite element method is used to calculate the air temperature rise in the tunnel under different working conditions, and then R is determined. m value; Step S3-2: Change the current I of each adjacent loop cable separately j , all other loop cables are unloaded, and the finite element method is used to calculate different I j Average temperature rise of air in the lower tunnel ΔT aj , and ΔT aj Fitting to I j Function: ΔT aj =f j (I j ) Where j is the jth adjacent loop. If loop 1 is the target cable, then j = 2, 3, ..., n; Step S3-3: When current is applied to all adjacent circuits at the same time, the increase in air temperature ΔT a It is equal to the sum of the increase in air temperature caused by each adjacent circuit when operating individually: Step S3-4: Apply current I to the target cable and calculate the cable loss Q at this time according to the IEC standard. Then the mutual thermal effect R in the steady-state thermal circuit of the target cable is m The calculation is done using the following formula: R m =C2ΔT a / Q Where, ΔT a is the temperature rise of the air in the tunnel caused by the heating of the adjacent loops 2 to n; Q is the heat generated by loop 1 under current I; C2 is the correction coefficient; Step S3-5: The mutual thermal effect thermal resistance R obtained in step S3-4 is m The expression is substituted into the thermal circuit model constructed in step S1 to form an improved thermal circuit model.

6. A method for predicting steady-state temperature of a three-phase multi-circuit tunnel cable core according to claim 5, characterized in that: The steady-state temperature T of the cable core of the single-phase multi-circuit cable is predicted in step S3. c1 Specifically: When n loop currents I1~I n When the cable loss Q is determined according to the target cable current, ΔT is determined according to the adjacent cable current using step S3-3. a value, and then use step S3-4 to obtain the mutual thermal effect thermal resistance R m , and then substitute it into the improved thermal circuit model, and solve the cable core steady-state temperature T under single-phase four-circuit conditions through the improved thermal circuit model. c1 .

7. A method for predicting steady-state temperature of a three-phase multi-circuit tunnel cable core according to claim 1, characterized in that: The cable core temperature T of the three-phase multi-circuit cable is predicted in step S4. c The process includes: 1) Combine the single-phase single-circuit cable into a single-phase multi-circuit cable, and the cable core temperature is changed from the steady-state temperature T c0 The core steady-state temperature T of the single-phase multi-circuit cable c1 , T c1 Solved by improved thermal circuit model; 2) In the case of single-phase multi-circuit laying, each adjacent circuit of circuit 1 adds one phase, and the cable core temperature of circuit 1 is T c1 Change to T c1 +(T c1 -T c0 ); 3) Each adjacent loop of loop 1 adds one more phase. At this time, all adjacent loops are complete three-phase. The cable core temperature of loop 1 is T c1 +(T c1 -T c0 ) becomes T c1 +2(T c1 -T c0 ); 4) Loop 1 is changed from single phase to three phase, and the cable core temperature of loop 1 is changed from T c1 +2(T c1 -T c0 ) becomes C1[T c1 +2(T c1 -T c0 )], where C1 is the correction factor between single-phase cable and three-phase cable; Therefore, the cable core temperature T of loop 1 in three-phase multi-circuit c The expression is as follows: T c = C1[T c1 + 2(T c1 - T c0 )], that is: T c = C1[T c0 + 3(T c1 - T c0 )].

8. The method for predicting steady-state temperature of a three-phase multi-circuit tunnel cable core according to claim 3, characterized in that: The convection thermal resistance R cov The calculation is as follows: Where A is the cable surface area; h(I) is the cable surface convection heat transfer coefficient, which is a function of the load current I.

9. The method for predicting steady-state temperature of a three-phase multi-circuit tunnel cable core according to claim 3, characterized in that: The radiation thermal resistance R rad The calculation is as follows: Where π is the circumference of a circle, T s and T t are the average temperatures of the cable surface and the tunnel wall, respectively; D is the outer diameter of the cable, ε c is the cable surface emissivity, and σ is the blackbody radiation constant.

10. An electronic device comprising a memory and a processor, wherein a computer program is stored in the memory, wherein: When the processor executes the program, the method according to any one of claims 1 to 9 is implemented.

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