High-voltage cable optimal arrangement method

Abstract

The invention discloses an optimal arrangement method for a high-voltage cable, and the method comprises the steps: building an optimal arrangement model on the premise of meeting the constraints of sheath induced voltage, sheath ring current, voltage deviation and laying length by comprehensively considering the ultimate power transmission capability, power transmission capability deterioration and economical efficiency of a cable line; and an optimal arrangement scheme is screened out according to the fitting degree of each non-dominant solution and the optimal scheme. Aiming at the optimal arrangement mode of the high-voltage cable of a new line, the invention provides a method capable of optimizing the axial and radial arrangement modes of the high-voltage cable at the same time, and the improved grey wolf algorithm adopted by the method effectively expands the global search range, improves the later convergence speed and improves the accuracy of solving the optimal arrangement mode; the cable arrangement can be effectively planned, the output optimal arrangement mode meets the related specifications of the cable arrangement, and the effects of improving the limit power transmission capacity of the cable, improving the economical efficiency and reducing the loop current of the sheath are obvious.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to an optimal arrangement method for high-voltage cables. Background Art

[0002] With the advancement of my country's urbanization process, high-voltage cables are more popular in power grid construction than overhead lines due to their high reliability, strong resistance to external interference and no impact on the city appearance. The reasonable layout of new cable lines can not only increase the maximum transmission capacity of the lines, but also play a positive role in reducing cable transmission losses and ensuring the quality of transmitted power. At the same time, it also improves the economy and operational stability of the power grid.

[0003] However, in the prior art, in terms of reducing the sheath circulating current, most emphasis is placed on improving the layout method based on numerical calculation methods, without optimizing through algorithms; in terms of improving the current-carrying capacity of the cable, most emphasis is placed on improving the layout method by optimizing a single indicator of the cable current-carrying capacity through optimization algorithms, without associating the sheath circulating current with the current-carrying capacity, and without considering related constraints such as the metal sheath and power quality when the cable is working. It is impossible to simultaneously solve the problem of how to choose the arrangement method, radial arrangement of phase spacing, sheath grounding method, and long axial arrangement of the grounding section when laying the cable line to achieve the optimal cable system. Summary of the invention

[0004] The purpose of the present invention is to provide a method for optimal arrangement of high-voltage cables to solve the problem that the arrangement of high-voltage cables cannot be optimized.

[0005] The present invention provides a method for optimally arranging high-voltage cables, comprising the following steps:

[0006] S1. Determine the evaluation of the advantages and disadvantages of the cable layout mode by the ultimate transmission capacity, transmission capacity degradation and economic indicators, and the objective functions of the multi-objective optimization model corresponding to the optimal layout are cable current carrying capacity, metal sheath circulating current, accessories and operating loss cost;

[0007] S2. According to the high-voltage cable operation standard, the sheath induced voltage, sheath circulating current, voltage deviation and total cable laying length are determined as the constraints of the optimal layout multi-objective optimization model, and then the optimal layout optimization model is established;

[0008] S3. The Grey Wolf multi-objective optimization algorithm is used to solve the optimal layout model. Since the dimensions of the objective functions corresponding to the solution indicators are quite different and the degree of influence of each indicator on the optimal layout is different, when constructing the fitness function of the optimal layout model, it is necessary to normalize and process the objective function through the hierarchical analysis method. By iteratively solving the fitness function, the non-dominated solution set of the optimal layout model is obtained.

[0009] S4. The non-dominated solution set output by the optimal layout model is screened using entropy weight-TOPSIS to obtain the optimal layout of the high-voltage cables.

[0010] Preferably, in step 1, the optimal layout multi-objective optimization model proposes evaluation indicators of the ultimate transmission capacity, transmission capacity degradation and economy of the high-voltage cable layout, and takes maximizing the cable current carrying capacity, minimizing the metal sheath circulation and minimizing the cost as the optimization goals. The proposed indicators comprehensively consider the impact of each layer structure of the high-voltage cable on its operation, and can simultaneously cope with the radial and axial layout optimization of the high-voltage cable, so that the obtained layout has both strong transmission capacity and high economy.

[0011] Preferably, the limit power transmission capacity index adopts the inverse of the current carrying capacity of the high-voltage cable as the objective function f1 of the limit power transmission capacity index. According to IEC-60287, the objective function of the index is shown in the following formula:

[0012]

[0013] Where: I is the current carrying capacity of the cable; Δθ is the difference between the conductor temperature and the ambient temperature; W d is the dielectric loss of the insulation layer; T1, T2, T3, T4 are the thermal resistance per unit length of the insulation layer, metal sheath and armor layer, outer sheath, and exterior respectively; n is the number of current-carrying conductors; R is the AC resistance; λ1 and λ2 are the loss factors of each layer respectively. The size of I is related to the cable arrangement and grounding method. A line may adopt multiple grounding methods, but a line can only have one current carrying capacity. For this reason, I is taken as the minimum current carrying capacity in the line.

[0014] Preferably, the transmission capacity degradation index uses the high-voltage cable metal sheath circulating current as the target function f2 of the transmission capacity degradation, as shown in the following formula:

[0015]

[0016] Where: l, l i 、n i ,I Simax and I Ci They are the total cable laying length, the single-section cable laying length under a certain grounding method, the number of selections, the maximum phase sheath induced current and leakage current in the same circuit. The subscripts i=2 and 3 represent the double-end grounding and cross-interconnection grounding methods of the sheath, respectively.

[0017] Preferably, the economic index adopts the objective function f3 of the economic index of the high-voltage cable layout mode, which is to equate the active power loss of the line to the electric energy cost generated by consuming the same amount of electricity, and to take the sum of the cable accessories cost and the electric energy cost corresponding to the active power loss of the transmission line as the following formula:

[0018] minf3=P1+P2

[0019] Where: P1 and P2 represent the electric energy cost corresponding to the line active loss and the cable accessories cost respectively.

[0020] Preferably, in step 2, the sheath induced voltage constraint adopts single-end grounding, double-end grounding, and cross-connected grounding modes, respectively taking the induced voltage at the ungrounded end of the same sheath induced voltage maximum phase, the midpoint induced voltage, and the induced voltage at the first small section as constraint targets. The sheath induced voltage constraint is expressed as

[0021] max(E si +E ti )≤300(i=a,b,c).

[0022] Preferably, in step 2, the sheath circulation constraint is that the metal sheath circulation shall not exceed 100A according to QGDW11316-2018, and the sheath circulation constraint is expressed as

[0023] max(I Si +I Ci )≤100(i=a,b,c).

[0024] Preferably, in step 2, the voltage deviation constraint is less than 10% according to GB / T12325-2008. The voltage deviation constraint is expressed as

[0025]

[0026] Preferably, in step 2, the cable laying length constraint is: the sum of the cable segments using different sheath grounding methods should be equal to the total cable laying length, and the constraint is expressed as

[0027]

[0028] Where: n i , l i They are the number of selections of different grounding methods and the length of a single segment, and i=1, 2, and 3 represent the single-end grounding, double-end grounding, and cross-connected grounding methods of the metal sheath, respectively.

[0029] The beneficial effects of the present invention are as follows: aiming at the optimal layout of high-voltage cables in newly built lines, a method is proposed that can simultaneously optimize the axial and radial layouts of high-voltage cables. The improved grey wolf algorithm adopted in this method effectively expands the global search range, improves the late convergence speed, and improves the accuracy of solving the optimal layout. The cable layout can be effectively planned, and the output optimal layout meets the relevant specifications for cable layout, and is effective in improving the ultimate power transmission capacity of the cable, improving economy, and reducing sheath circulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the overall block diagram of the optimal cable arrangement method proposed by the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further explained below in conjunction with specific embodiments.

[0032] The optimal arrangement method of high-voltage cables proposed in this embodiment includes the selection of cable arrangement, phase spacing, sheath grounding method and sheath grounding section length. Figure 1 The present invention provides an optimal arrangement method for high-voltage cables, which includes the following steps:

[0033] S1. Determine the evaluation of the advantages and disadvantages of the cable layout mode by the ultimate transmission capacity, transmission capacity degradation and economic indicators, and the objective functions of the multi-objective optimization model corresponding to the optimal layout are cable current carrying capacity, metal sheath circulating current, accessories and operating loss cost;

[0034] S2. According to the high-voltage cable operation standard, the sheath induced voltage, sheath circulating current, voltage deviation and total cable laying length are determined as the constraints of the optimal layout multi-objective optimization model, and then the optimal layout optimization model is established;

[0035] S3. The Grey Wolf multi-objective optimization algorithm is used to solve the optimal layout model. Since the dimensions of the objective functions corresponding to the solution indicators are quite different and the degree of influence of each indicator on the optimal layout is different, when constructing the fitness function of the optimal layout model, it is necessary to normalize and process the objective function through the hierarchical analysis method. By iteratively solving the fitness function, the non-dominated solution set of the optimal layout model is obtained.

[0036] S4. The non-dominated solution set output by the optimal layout model is screened using entropy weight-TOPSIS to obtain the optimal layout of the high-voltage cables.

[0037] Among them, the optimal layout of high-voltage cables needs to meet the conditions of strong power transmission capacity, high safety and reliability, and minimum investment cost and operating cost. This embodiment proposes evaluation indicators of the maximum power transmission capacity, power transmission capacity degradation and economy of the high-voltage cable layout, and takes maximizing the cable current carrying capacity, minimizing the metal sheath circulation and minimizing the cost as the optimization goals. The proposed indicators comprehensively consider the impact of each layer structure of the high-voltage cable on its operation, and can simultaneously cope with the radial and axial layout optimization of the high-voltage cable, so that the obtained layout has both strong power transmission capacity and high economy.

[0038] 1) Limit transmission capacity index: The current carrying capacity is the current passing through the conductor when the conductor temperature reaches the maximum temperature that the main insulation can withstand for a long time, which reflects the power transmission capacity of the line. Reasonable planning of cable layout can effectively improve the heat dissipation capacity of the conductor and increase the limit transmission capacity of the line. Therefore, this paper takes the opposite number of the current carrying capacity of the high-voltage cable as the objective function f1 of the limit transmission capacity index. According to IEC-60287, the objective function of this index is shown in formula (1).

[0039]

[0040] Where: I is the current carrying capacity of the cable; Δθ is the difference between the conductor temperature and the ambient temperature; W d is the dielectric loss of the insulation layer; T1, T2, T3, T4 are the thermal resistance per unit length of the insulation layer, metal sheath and armor layer, outer sheath, and exterior respectively; n is the number of current-carrying conductors; R is the AC resistance; λ1 and λ2 are the loss factors of each layer respectively. The size of I is related to the cable arrangement and grounding method. A line may adopt multiple grounding methods, but a line can only have one current carrying capacity. For this reason, I is taken as the minimum current carrying capacity in the line.

[0041] 2) Transmission capacity degradation index: The high-voltage cable metal sheath circulation is used as an index to measure the degree of transmission capacity degradation. A larger index will cause serious heat generation, affecting the heat dissipation of the core conductor, making it easier for the conductor temperature to reach the critical temperature that the main insulation material can withstand for a long time. The smaller the sheath circulation, the lower the impact on the transmission capacity. Therefore, this embodiment uses the high-voltage cable metal sheath circulation as the target function f2 of transmission capacity degradation, as shown in formula (2).

[0042]

[0043] Where: l, l i 、n i ,I Simax and I Ci They are the total cable laying length, the single-section cable laying length under a certain grounding method, the number of selections, the maximum phase sheath induced current and leakage current in the same circuit. The subscripts i=2 and 3 represent the double-end grounding and cross-interconnection grounding methods of the sheath, respectively.

[0044] 3) Economic index: The cost of high-voltage cable accessories of newly built lines and the active power loss of cables during operation are the main factors to measure the economic efficiency of cable layout. Since there are unit dimensions and unit differences between the two, this paper equates the active power loss of the line to the electric energy cost generated by consuming an equal amount of electricity. The sum of the cable accessory cost and the electric energy cost corresponding to the active power loss of the transmission line is used as the objective function f3 of the economic index of high-voltage cable layout, see formula (3).

[0045] minf3=P1+P2(3)

[0046] Where: P1 and P2 represent the electric energy cost corresponding to the line active loss and the cable accessories cost respectively.

[0047] The constraints of the multi-objective optimization model for optimal layout include the following four points:

[0048] 1) Sheath induced voltage constraint: Excessive induced voltage on the metal sheath of high-voltage cables can endanger personal safety. If the sheath has a grounding fault, excessive circulating current will be generated, endangering the normal operation of the cable. GB50217-2018 stipulates that when safety measures are taken for high-voltage single-core cables, the sheath induced voltage shall not exceed 300V. The single-end grounding, double-end grounding, and cross-connected grounding methods use the maximum phase ungrounded end induced voltage, midpoint induced voltage, and induced voltage at the first section as constraint targets. The sheath induced voltage constraint is expressed as:

[0049] max(E si +E ti )≤300(i=a,b,c) (4)

[0050] 2) Sheath circulation constraint: When the metal sheath circulation of high-voltage cables is abnormal, it will accelerate insulation aging, weaken the power transmission capacity of the cable, and even cause cable failure in severe cases. QGDW11316-2018 stipulates that the metal sheath circulation shall not exceed 100A. The sheath circulation constraint is expressed as

[0051] max(I Si +I Ci )≤100(i=a,b,c) (5)

[0052] 3) Voltage deviation constraint: Voltage deviation is closely related to the operating stability and life of high-voltage cables and is an important indicator of power quality. GB / T12325-2008 stipulates that the voltage deviation should be less than 10%. The voltage deviation constraint is expressed as

[0053]

[0054] 4) Cable laying length constraint: The sum of the cable segments using different sheath grounding methods should be equal to the total cable laying length. This constraint is expressed as

[0055]

[0056] Where: n i , l i They are the number of selections of different grounding methods and the length of a single segment, and i=1, 2, and 3 represent the single-end grounding, double-end grounding, and cross-connected grounding methods of the metal sheath, respectively.

[0057] This embodiment proposes a method for optimizing the axial and radial layout of high-voltage cables for the optimal layout of newly built lines. The improved grey wolf algorithm adopted by the method effectively expands the global search range, improves the late convergence speed, and improves the accuracy of solving the optimal layout.

[0058] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An optimal arrangement method for high voltage cables, It is characterized in that The following steps are involved: S1. Determine the evaluation of the advantages and disadvantages of the cable layout mode by the ultimate transmission capacity, transmission capacity degradation and economic indicators, and the objective functions of the multi-objective optimization model corresponding to the optimal layout are cable current carrying capacity, metal sheath circulating current, accessories and operating loss cost; S2. According to the high-voltage cable operation standard, the sheath induced voltage, sheath circulating current, voltage deviation and total cable laying length are determined as the constraints of the optimal layout multi-objective optimization model, and then the optimal layout optimization model is established; S3. The Grey Wolf multi-objective optimization algorithm is used to solve the optimal layout model. Since the dimensions of the objective functions corresponding to the solution indicators are quite different and the degree of influence of each indicator on the optimal layout is different, when constructing the fitness function of the optimal layout model, it is necessary to normalize and process the objective function through the hierarchical analysis method. By iteratively solving the fitness function, the non-dominated solution set of the optimal layout model is obtained. S4. The non-dominated solution set output by the optimal layout model is screened using entropy weight-TOPSIS to obtain the optimal layout of the high-voltage cables.

2. A high voltage cable optimal arrangement method according to claim 1, It is characterized in that In step 1, the optimal layout multi-objective optimization model proposes evaluation indicators of the ultimate transmission capacity, transmission capacity degradation and economy of the high-voltage cable layout, and takes maximizing the cable current carrying capacity, minimizing the metal sheath circulation and minimizing the cost as the optimization goals. The proposed indicators comprehensively consider the impact of each layer structure of the high-voltage cable on its operation, and can simultaneously cope with the radial and axial layout optimization of the high-voltage cable, so that the obtained layout has both strong transmission capacity and high economy.

3. A high voltage cable optimal arrangement method according to claim 2, It is characterized in that The limit power transmission capacity index adopts the inverse of the current carrying capacity of the high-voltage cable as the objective function f of the limit power transmission capacity index. 1 According to IEC-60287, the objective function of this indicator is as follows: Where: I is the current carrying capacity of the cable; Δθ is the difference between the conductor temperature and the ambient temperature; W d is the dielectric loss of the insulation layer; T 1 , T 2 , T 3 , T 4 are the thermal resistance per unit length of the insulation layer, the metal sheath and the armor layer, the outer sheath, and the exterior; n is the number of current-carrying conductors; R is the AC resistance; λ 1 , 2 are the loss factors of each layer respectively. The size of I is related to the cable arrangement and grounding method. A line may adopt multiple grounding methods, but a line can only have one current carrying capacity. Therefore, I is taken as the minimum current carrying capacity in the line.

4. A high voltage cable optimal arrangement method according to claim 2, It is characterized in that The transmission capacity degradation index adopts the high-voltage cable metal sheath circulating current as the target function of transmission capacity degradation. 2 , see the following formula: Where: l, l i 、n i ,I Simax and I Ci They are the total cable laying length, the single-section cable laying length under a certain grounding method, the number of selections, the maximum phase sheath induced current and leakage current in the same circuit. The subscripts i=2 and 3 represent the double-end grounding and cross-interconnection grounding methods of the sheath, respectively.

5. A high voltage cable optimal arrangement method according to claim 2, It is characterized in that The economic index adopts the method of equating the active power loss of the line to the electric energy cost generated by consuming the same amount of electricity, and taking the sum of the cable accessories cost and the electric energy cost corresponding to the active power loss of the transmission line as the objective function f of the economic index of the high-voltage cable layout mode 3 , see the following formula: minf 3 =P 1 +P 2 Where: P 1 , P 2 They respectively represent the electric energy cost corresponding to the active power loss of the line and the cost of cable accessories.

6. A high voltage cable optimal arrangement method according to claim 1, It is characterized in that In step 2, the sheath induced voltage constraint adopts single-end grounding, double-end grounding, and cross-connected grounding modes, respectively taking the induced voltage at the ungrounded end of the same sheath induced voltage maximum phase, the midpoint induced voltage, and the induced voltage at the first small section as constraint targets. The sheath induced voltage constraint is expressed as max(E si +E ti )≤300 (i=a,b,c)。 7. A high voltage cable optimal arrangement method according to claim 1, It is characterized in that In step 2, the sheath circulation constraint is that the metal sheath circulation shall not exceed 100A according to QGDW11316-2018. The sheath circulation constraint is expressed as max(I Si +I Ci )≤100 (i=a,b,c)。 8. A high voltage cable optimal arrangement method according to claim 1, It is characterized in that In step 2, the voltage deviation constraint is specified in GB / T12325-2008 as being less than 10%. The voltage deviation constraint is expressed as 9. A high voltage cable optimal arrangement method according to claim 1, It is characterized in that In step 2, the cable laying length constraint is: the sum of the cable segments using different sheath grounding methods should be equal to the total cable laying length. This constraint is expressed as Where: n i , l i They are the number of selections of different grounding methods and the length of a single segment, and i=1, 2, and 3 represent the single-end grounding, double-end grounding, and cross-connected grounding methods of the metal sheath, respectively.

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