Medium-voltage distribution network structure evolution method based on three-dimensional quantitative analysis

Abstract

The invention discloses a medium-voltage distribution network structure evolution method based on three-dimensional quantitative analysis, and the three dimensions of the method refer to reliability, economy and construction difficulty, and the method comprises the steps: firstly building a power supply reliability evaluation model of a user through a fault mode consequence analysis method; analyzing main problems in the current medium-voltage power distribution network wiring mode; secondly, the implementation difficulty and engineering quantity of network structure evolution transition are evaluated, a power distribution network gridding planning economical efficiency evaluation index is established, a main technical route for improving the power supply reliability of the power distribution network is selected, and the main technical route can be summarized into three categories including a closed-loop operation mode, a user spare power automatic switching mode and a backbone network self-healing mode; and finally, evaluating the gridding evolution direction of the medium-voltage power distribution network based on the reliability index and the economic index, and determining an optimal evolution scheme in the existing wiring mode according to a result. According to the scheme, the power distribution network structure evolution scheme is established by taking power supply reliability improvement as a main target and taking evolution economy as a constraint condition.

Description

Technical Field

[0001] This invention belongs to the field of power system distribution network planning technology, specifically involving a three-dimensional quantitative analysis method for the evolution of medium-voltage distribution network structure. In particular, it addresses the problems faced by existing medium-voltage distribution network wiring patterns (such as radial, single-ring, and multi-segment moderate interconnection) in improving power supply reliability, including rigid network structure, poor economic efficiency of upgrades, and difficulties in transitional implementation. Through quantitative evaluation and multi-dimensional optimization, it achieves a scientific and gradual upgrade of the distribution network structure. Background Technology

[0002] As users' demands for power supply reliability continue to increase, the traditional medium-voltage distribution network structure has become a key bottleneck restricting the improvement of power quality. Existing distribution networks mostly adopt static connection modes (such as N-1 single-ring networks), whose inherent topology limits the potential for reliability improvement. When user load density increases or sensitive loads increase, traditional modes struggle to meet high reliability requirements, while blindly upgrading to complex structures such as double-ring networks faces the problem of drastically increased investment.

[0003] The industry typically employs discrete technical approaches such as closed-loop operation, user-side automatic transfer switching, and backbone network self-healing. However, these approaches lack scientific basis, such as a quantitative evaluation system for the reliability of wiring modes, a comprehensive comparison method for the economics and implementation difficulty of upgrades, and the ability to plan the path for the gradual evolution of the grid during the transition period. This leads to problems such as over-investment in building highly redundant grids, multiple power outages during the upgrade process causing user complaints, and mismatch between technical approaches and regional load characteristics. For example, blindly deploying backbone network self-healing systems in industrial areas when actual users are more suited to automatic transfer switching modes results in wasted investment. The root cause of the shortcomings of existing technologies lies in the lack of a four-dimensional decision-making model that considers "reliability requirements - technical approach - economics - implementation difficulty," making it impossible to dynamically adapt to the upgrade needs of distribution networks at different stages of development.

[0004] In summary, this invention proposes a systematic method for network structure evolution. By quantifying the reliability gains of different wiring patterns using Failure Mode and Effects Analysis (FMEA), and considering the network construction cost and the complexity of transitional modifications, specific upgrade schemes are determined. This method provides distribution network planners with a scientific and operational tool to support the large-scale construction and upgrading of high-reliability distribution networks. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the fact that the existing technology focuses on the reliability improvement effect of a single technical route and lacks systematic comparison and quantitative analysis of the evolution path of grid structure under different technical routes, resulting in a lack of scientific basis for planning and decision-making.

[0006] To address the aforementioned technical problems, this invention provides a method for the evolution of medium-voltage distribution network structure based on improving user power supply reliability, comprising:

[0007] User power supply reliability improvement assessment: Based on the improvement requirements under the existing wiring modes of the medium-voltage distribution network, the topology, equipment health status, historical fault records and user load data of the medium-voltage distribution network are obtained. Based on the fault mode consequence analysis method, the reliability calculation of various wiring modes is carried out to assess the user power supply reliability.

[0008] Technical route selection and optimization: Analyzing the economics of power grid construction and operation, and the difficulty of transitional upgrades, the main technical routes for improving power supply reliability are determined, which can be summarized into three categories: loop operation mode, user backup automatic transfer mode, and backbone network self-healing mode. The difficulty of implementing upgrades under typical wiring modes within different technical routes is quantitatively analyzed.

[0009] Network structure evolution scheme determination: Based on the power supply reliability, network construction and operation economy and transformation implementation difficulty under typical wiring modes, the optimal evolution form under the existing wiring modes is determined.

[0010] Based on the voltage levels of the medium-voltage distribution network, the reliability assessment covers three levels: low-voltage users, medium-voltage distribution transformers, and medium-voltage feeder networks. A specific reliability assessment model is built using the Failure Mode and Effects Analysis (FMEA) method.

[0011] After a power supply failure occurs to a low-voltage user, the power outage will continue until the fault repair is completed. Assuming the line is a single line, the average outage duration T on the low-voltage side is... 0.4kV :

[0012] T 0.4kV =F 0.4kV ×L 0.4kV ×T 0.4kV-repair

[0013] Where F 0.4kV L represents the average failure rate of low-voltage lines. 0.4kV It is the average length of low-voltage lines, T repair It is the mean time to repair low-voltage faults.

[0014] When a medium-voltage distribution transformer fails, the fault can be isolated through protection actions, without affecting other line users and upstream feeders. Therefore, the average outage time T for a distribution transformer fault is [not specified]. b

[0015]

[0016] in Let i be the failure rate of the i-th distribution transformer. Let i be the failure rate of the i-th medium-voltage line. T is the average length of the i-th medium-voltage branch line. repair It is the average repair time for a distribution transformer fault.

[0017] Medium-voltage feeder networks primarily consider outage times caused by trunk cable faults and switchgear faults. In the event of a fault in a section of the trunk line, power can be restored to the non-faulty sections of the line through power transfer operations. The average outage time for a trunk line fault is...

[0018] T 10kV =FL 10kV ×f 10kV ×l 10kV ×(1-D k )

[0019] FL 10kV For the failure rate of medium-voltage cable lines, f 10kV For the time required to troubleshoot medium-voltage faults, l 10kV The failure rate of medium-voltage feeder load transformers. Let D be the failure rate of the i-th medium-voltage line. k It refers to the ratio of dual access to the distribution transformer.

[0020] Based on the current distribution network wiring pattern and given the boundary conditions for reliability index calculation, the reliability result T of the current wiring pattern under different load densities can be calculated:

[0021] T = T 0.4kV +T b +T 10kV

[0022] The differences in distribution network structure mainly stem from different key technical approaches to improving power supply reliability. These main technical approaches can be categorized into three types: closed-loop operation mode, user backup automatic transfer mode, and backbone network self-healing mode. Their characteristics are as follows:

[0023] Closed-loop operation mode: When a single line fails, it can guarantee full power supply without instantaneous power outage, which significantly improves power supply reliability. In particular, it has a clear advantage over the open-loop operation mode in reducing the number of power outages. Typical examples of the connection are Singapore's "single petal", my country's Xiong'an New Area's "double petal" and Hong Kong's closed-loop connection.

[0024] User-based automatic transfer mode: By installing an automatic transfer switch on the 10kV side of the distribution transformer and connecting it to different ring network feeder groups, fault handling adopts a local automatic transfer method. Typical wiring examples include the Tokyo three-radius connection, the Zhejiang "three-double" connection, and the Paris double-ring network.

[0025] Backbone network self-healing mode: Self-healing control of the backbone network is achieved through the construction of intelligent distributed distribution automation. The power outage time for a single faulty line to self-heal and switch over is in the second range. Typical wiring diagrams are the "three supplies and one backup" system in Shenzhen and the "diamond type" wiring diagram in Shanghai.

[0026] The economic cost C of grid evolution is determined based on investment cost CI, operating cost CL, and power outage loss CR:

[0027] C = CI + CL + CR

[0028] in

[0029]

[0030] C1 represents the total investment cost of the line. k C represents the total investment cost of the switchyard. j Where: _n_ is the total investment cost of the substation bay; _k_ is the return on investment in the power industry; _n_ is the operating life; _U_ is the annual operation and maintenance cost; _p_ is the average electricity price; _I1_ is the current in the unloaded section; _r_ is the resistance per unit length of conductor; _L1_ is the length of the line in the unloaded section; _I2_ is the current in the loaded section; _L2_ is the length of the line in the loaded section; _N_ is the number of line segments; _M_ is the total number of users; _P_ is the total investment cost of the substation bay; _r_ is the return on investment in the power industry; _n_ is the operating life; _U_ is the annual operation and maintenance cost; _p_ is the average electricity price; _I1_ is the current in the unloaded section; _r_ is the resistance per unit length of conductor; _L1_ is the i For the active power at load point i, U i Let R be the annual outage time at load point i, and R be the outage loss per unit of electricity.

[0031] The difficulty of implementing technical upgrades to improve the reliability of medium-voltage distribution networks is quantitatively analyzed from three levels: substation side, line side, and distribution transformer side.

[0032]

[0033] Where ω1, ω2, and ω3 correspond to the construction coefficients on the substation side, line side, and distribution transformer side under the three technical routes of closed-loop operation mode, user backup automatic transfer mode, and backbone network self-healing mode, respectively, and their values ​​are 0 or 1; Y1 is the existing closed-loop device of the substation, Y all The total number of devices required to upgrade to the target network architecture, L n To determine the number of busbar lines that need to be expanded based on the existing switchyard busbar configuration, L all The total number of lines required to upgrade to the target network architecture; The user agreement signing rate under the self-reinforcement mode is ΔR, which represents the reliability improvement effect (SAIDI reduction rate). The more significant the improvement effect, the larger the denominator and the lower the difficulty.

[0034] Employing a comprehensive evaluation approach that considers the applicable scenarios of the three technical routes, differentiated upgrades are achieved. Through quantitative analysis across three dimensions—economic efficiency, difficulty, and reliability—the approach addresses the blind spots of traditional experience-based decision-making. Its comprehensive evaluation is based on the following criteria:

[0035] U = α × (1 - T) + β × C + λ × D

[0036] Where α, β, and λ are the weighting coefficients corresponding to reliability, economy, and construction difficulty, respectively, and their determination rules are as follows:

[0037] Applicable Scenarios Reliability α Economic β Construction difficulty λ Core area 0.7 0.1 0.2 General urban areas 0.6 0.2 0.2 Rural / suburban 0.5 0.4 0.1

[0038] Based on the three-dimensional score, the lower the value, the better. The evolution schemes are divided into priority recommendation, recommendation, cautious selection, and not recommended. The minimum value among the priority recommendation schemes is selected as the evolution scheme. Attached Figure Description

[0039] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0040] Figure 1 The flowchart of the medium-voltage distribution network structure evolution method provided in this application;

[0041] Figure 2 Line graphs of economic costs under different loads are provided for this application;

[0042] Figure 3 Flowchart for selecting the optimal evolution scheme provided in this application;

[0043] Figure 4 The diagram illustrates the evolution of the single-ring network provided in this application into a three-double-connection mode. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0045] Reference Figure 1 As shown, the medium-voltage distribution network structure evolution method provided in this application includes:

[0046] S1. User Power Supply Reliability Improvement Assessment: Based on the improvement requirements under the existing wiring modes of the medium-voltage distribution network, obtain the topology of the medium-voltage distribution network, equipment health status, historical fault records and user load data, and perform reliability calculations for various wiring modes based on the fault mode consequence analysis method to assess the user power supply reliability.

[0047] S2. Technical Route Selection and Optimization: Analyze the economic efficiency of power grid construction and operation, as well as the difficulty of transitional upgrades, to determine the main technical routes for improving power supply reliability. These can be summarized into three categories: loop-connected operation mode, user backup automatic transfer mode, and backbone network self-healing mode. Quantitatively analyze the difficulty of implementing upgrades under typical wiring modes within different technical routes.

[0048] S3. Determining the Network Structure Evolution Scheme: Based on the power supply reliability, network construction and operation economy, and transformation implementation difficulty under the typical wiring mode, determine the optimal evolution form under the existing wiring mode.

[0049] Taking a single-ring network as the current distribution network wiring mode, the following constraints are set: the fault type is "N-1" fault, the equipment fault outage duration is 2.81h / time, the medium-voltage distribution transformer is 1.4h / time, the ring network unit fault rate is 0.018 times / (unit*year), and the cable fault rate is 0.048 times / (km*year). Double-ring network, "3-1" single-ring network, three-supply-one-backup, and double-ring "three-double" wiring are selected as evolution directions for comparative analysis.

[0050] According to the invention, it includes a reliability assessment model for low-voltage users, medium-voltage distribution transformers, and medium-voltage feeder networks:

[0051] T = T 0.4kV +T b +T 10kV

[0052] The average outage duration T on the low-voltage side 0.4kV :

[0053] T 0.4kV =F 0.4kV ×L 0.4kV ×T 0.4kV-repair

[0054] Where F 0.4kV L represents the average failure rate of low-voltage lines. 0.4kV It is the average length of low-voltage lines, T repair It is the mean time to repair low-voltage faults.

[0055] Average outage time T for medium-voltage distribution transformer faults b

[0056]

[0057] in Let i be the failure rate of the i-th distribution transformer. Let i be the failure rate of the i-th medium-voltage line. T is the average length of the i-th medium-voltage branch line. repair It is the average repair time for a distribution transformer fault.

[0058] Mean Time Between Faults in Medium Voltage Feeder Networks

[0059] T 10kV =FL 10kV ×f 10kV ×l 10kV ×(1-D k )

[0060] FL 10kV For the failure rate of medium-voltage cable lines, f 10kVFor the time required to troubleshoot medium-voltage faults, l 10kV The failure rate of medium-voltage feeder load transformers. Let D be the failure rate of the i-th medium-voltage line. k It refers to the ratio of dual access to the distribution transformer.

[0061] The reliability calculation results for different wiring modes under different loads are shown in the table below:

[0062]

[0063] The table analysis shows that the reliability of single-ring networks is significantly low, and the power supply reliability of various wiring modes gradually improves with increasing load density. The current network structure's reliability does not reach 99.999%, requiring further improvement.

[0064] The economic cost C of grid evolution is determined based on investment cost CI, operating cost CL, and power outage loss CR:

[0065] C = CI + CL + CR

[0066] in

[0067]

[0068] C1 represents the total investment cost of the line. k C represents the total investment cost of the switchyard. j Given the total investment cost of the substation bay, k = 0.1, n = 20; U = 2.5%, p = 0.65, I1 = 60A, r = 0.063, L1 = 100KM, I2 = 90A, L2 = 35KM, N = 5; M = 250, R = 300, the economic costs under different loads are shown in the table below. Figure 2 As shown:

[0069]

[0070] As shown in the table and graph, the annual cost performance of the three-pair connection is the best.

[0071] The difficulty of implementing upgrades for double-ring networks, 3-1 single-ring networks, three-supply-one-standby systems, and three-double-connection modes is quantitatively analyzed from three levels: substation side, line side, and distribution transformer side.

[0072]

[0073] Where ω1, ω2, and ω3 correspond to the construction coefficients on the substation side, line side, and distribution transformer side under the three technical routes of closed-loop operation mode, user backup automatic transfer mode, and backbone network self-healing mode, respectively, and their values ​​are 0 or 1; Y1 = 100, Y all =150, L n =6,Lall =20; ΔR = 0.7. The implementation difficulty of upgrading and evolving different network architectures is shown in the table below:

[0074]

[0075] Employing a comprehensive evaluation approach that considers the applicable scenarios of the three technical routes, differentiated upgrades are achieved. Through quantitative analysis across three dimensions—economic efficiency, difficulty, and reliability—the approach addresses the blind spots of traditional experience-based decision-making. The judgment flowchart is as follows: Figure 2 As shown, the comprehensive evaluation is based on U:

[0076] U = α × (1 - T) + β × C + λ × D

[0077] Given α = 0.7, β = 0.1, and λ = 0.2, and considering the above three aspects, the double-ring triple-double distribution network connection based on the switching station is the preferred recommendation. A schematic diagram of a single-ring network evolving into a triple-double connection is shown below. Figure 4 As shown, two branch switches are configured at the substation outlet to integrate two independent single-ring networks with roughly the same path into a double-ring "triple double" connection.

[0078] The above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for the evolution of medium-voltage distribution network structure based on three-dimensional quantitative analysis, characterized in that, include: S1. User Power Supply Reliability Improvement Assessment: Based on the improvement requirements under the existing wiring modes of the medium-voltage distribution network, obtain the topology of the medium-voltage distribution network, equipment health status, historical fault records and user load data, and perform reliability calculations for various wiring modes based on the fault mode consequence analysis method to assess the user power supply reliability. S2. Technical Route Selection and Optimization: Analyze the economic efficiency of power grid construction and operation, as well as the difficulty of transitional upgrades, to determine the main technical routes for improving power supply reliability. These can be summarized into three categories: loop-connected operation mode, user backup automatic transfer mode, and backbone network self-healing mode. Quantitatively analyze the difficulty of implementing upgrades under typical wiring modes within different technical routes. S3. Determining the Network Structure Evolution Scheme: Based on the power supply reliability, network construction and operation economy, and transformation implementation difficulty under typical wiring modes, determine the optimal evolution form under the existing wiring modes.

2. The user power supply reliability improvement assessment according to claim 1, characterized in that, Based on the voltage levels of the medium-voltage distribution network, the reliability assessment covers three levels: low-voltage users, medium-voltage distribution transformers, and medium-voltage feeder networks. A specific reliability assessment model is built using the Failure Mode and Effects Analysis (FMEA) method. After a power supply failure occurs to a low-voltage user, the power outage will continue until the fault repair is completed. Assuming the line is a single line, the average outage duration T on the low-voltage side is... 0.4kV : T 0.4kV =F 0.4kV ×L 0.4kV ×T 0.4kV-repair Where F 0.4kV L represents the average failure rate of low-voltage lines. 0.4kV It is the average length of low-voltage lines, T repair It is the mean time to repair low-voltage faults. When a medium-voltage distribution transformer fails, the fault can be isolated through protection actions, without affecting other line users and upstream feeders. Therefore, the average outage time T for a distribution transformer fault is [not specified]. b in Let i be the failure rate of the i-th distribution transformer. Let i be the failure rate of the i-th medium-voltage line. T is the average length of the i-th medium-voltage branch line. repair It is the average repair time for a distribution transformer fault. Medium-voltage feeder networks primarily consider outage times caused by trunk cable faults and switchgear faults. In the event of a fault in a section of the trunk line, power can be restored to the non-faulty sections of the line through power transfer operations. The average outage time for a trunk line fault is... T 10kV =FL 10kV ×f 10kV ×l 10kV ×(1-D k ) FL 10kV For the failure rate of medium-voltage cable lines, f 10kV For the time required to troubleshoot medium-voltage faults, l 10kV The failure rate of medium-voltage feeder load transformers. Let D be the failure rate of the i-th medium-voltage line. k It refers to the ratio of dual access to the distribution transformer.

3. The reliability assessment model according to claim 2, characterized in that, Based on the current distribution network wiring pattern and given the boundary conditions for reliability index calculation, the reliability result T of the current wiring pattern under different load densities can be calculated: T=T 0.4kV +T b +T 10kV。 4. The main technical route for improving power supply reliability according to claim 1, characterized in that, The differences in distribution network structure mainly stem from different key technical approaches to improving power supply reliability. These main technical approaches can be categorized into three types: closed-loop operation mode, user backup automatic transfer mode, and backbone network self-healing mode. Their characteristics are as follows: Closed-loop operation mode: When a single line fails, it can guarantee full power supply without instantaneous power outage, which significantly improves power supply reliability. In particular, it has a clear advantage over open-loop operation mode in reducing the number of power outages. Typical examples of connection are Singapore's "single petal", my country's Xiong'an New Area's "double petal" and Hong Kong's closed-loop connection. User-based automatic transfer mode: By installing an automatic transfer switch on the 10kV side of the distribution transformer and connecting it to different ring network feeder groups, fault handling adopts a local automatic transfer method. Typical wiring examples include the Tokyo three-radius connection, the Zhejiang "three-double" connection, and the Paris double-ring network. Backbone network self-healing mode: Self-healing control of the backbone network is achieved through the construction of intelligent distributed distribution automation. The power outage time for a single faulty line to self-heal and switch over is in the second range. Typical wiring diagrams are the "three supplies and one backup" system in Shenzhen and the "diamond type" wiring diagram in Shanghai.

5. The economic efficiency of space frame construction and operation according to claim 1, characterized in that, The economic cost C of grid evolution is determined based on investment cost CI, operating cost CL, and power outage loss CR: C = CI + CL + CR in C1 represents the total investment cost of the line. k C represents the total investment cost of the switchyard. j Where: _n_ is the total investment cost of the substation bay; _k_ is the return on investment in the power industry; _n_ is the operating life; _U_ is the annual operation and maintenance cost; _p_ is the average electricity price; _I1_ is the current in the unloaded section; _r_ is the resistance per unit length of conductor; _L1_ is the length of the line in the unloaded section; _I2_ is the current in the loaded section; _L2_ is the length of the line in the loaded section; _N_ is the number of line segments; _M_ is the total number of users; _P_ is the total investment cost of the substation bay; _r_ is the return on investment in the power industry; _n_ is the operating life; _U_ is the annual operation and maintenance cost; _p_ is the average electricity price; _I1_ is the current in the unloaded section; _r_ is the resistance per unit length of conductor; _L1_ is the i For the active power at load point i, U i Let R be the annual outage time at load point i, and R be the outage loss per unit of electricity.

6. The difficulty of implementing the modification as described in claim 1, characterized in that, The difficulty of implementing technical upgrades to improve the reliability of medium-voltage distribution networks is quantitatively analyzed from three levels: substation side, line side, and distribution transformer side. Where ω1, ω2, and ω3 correspond to the construction coefficients on the substation side, line side, and distribution transformer side under the three technical routes of closed-loop operation mode, user backup automatic transfer mode, and backbone network self-healing mode, respectively, and their values ​​are 0 or 1; Y1 is the existing closed-loop device of the substation, Y all The total number of devices required to upgrade to the target network architecture, L n To determine the number of busbar lines that need to be expanded based on the existing switchyard busbar configuration, L all The total number of lines required to upgrade to the target network architecture; The user agreement signing rate under the self-reinforcement mode is ΔR, which represents the reliability improvement effect (SAIDI reduction rate). The more significant the improvement effect, the larger the denominator and the lower the difficulty.

7. The network structure evolution scheme according to claim 1, characterized in that, Employing a comprehensive evaluation approach that considers the applicable scenarios of the three technical routes, differentiated upgrades are achieved. Through quantitative analysis across three dimensions—economic efficiency, difficulty, and reliability—the approach addresses the blind spots of traditional experience-based decision-making. Its comprehensive evaluation is based on the following criteria: U = α × (1 - T) + β × C + λ × D Where α, β, and λ are the weighting coefficients corresponding to reliability, economy, and construction difficulty, respectively, and their determination rules are as follows:

8. The differentiated upgrade strategy according to claim 7, characterized in that, Based on the three-dimensional scoring, the evolution schemes are divided into priority recommendation, recommendation, cautious selection, and not recommended. The minimum value among the priority recommendation schemes is selected as the evolution scheme.

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