Transmission Section Search and Section Limit Calculation Method and System Based on Search Cut Set

Abstract

The present invention discloses a method and system for searching transmission sections based on search cut sets and calculating section limits. By simulating the operation of the power system after a fault occurs, it assists power system dispatchers in timely adjusting the operation parameters of the power system. From the perspective of engineering practice, the transmission sections are classified according to whether the faulty equipment and weak-link equipment form a cut set. At the same time, the section power flow when the power flow of the equipment increases or decreases proportionally to the same ratio until the weak-link equipment is just fully loaded after the fault is used as the thermal stability limit of the transmission section. By simulating the operation states of the power system after each fault occurs in the equipment fault concentration, it assists power system operation and dispatch personnel in timely adjusting the system operation parameters, improving the power supply reliability of the power grid; the search and classification of transmission sections based on search cut sets give the types of transmission sections, which conform to the usage habits of the power dispatching department and have strong engineering practicability, and can give guiding opinions when the power dispatching department adjusts the system operation.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and particularly to a transmission section search and section limit calculation method and system based on search cut sets. Background Art

[0002] As the electrification rate of equipment is getting higher and higher, users put forward higher requirements for the reliability of power supply. At the same time, with the proposal of the strategy of building a new power system with new energy as the main body, the proportion of power generation resources represented by wind power generation and photovoltaic power generation in the power system is increasing. The inherent volatility, randomness, intermittency and other characteristics of wind power generation and photovoltaic power generation itself bring new challenges to the power supply reliability of the power system.

[0003] According to the investigation results of power outage events: the vast majority of large-area power outage accidents are caused by the transmission network operating near the limit edge of the transmission section. Due to some small-probability events (such as local faults during maintenance, etc.), the power flow transfers widely to adjacent branches, causing overload of transmission lines or transformers, thereby triggering cascading tripping accidents and resulting in large-area power outages.

[0004] The transmission section and stability limit are one of the basic items in the calculation of the power grid operation mode, and are important bases for arranging the power system operation mode. They are often used as reference standards for measuring the effectiveness of the online transmission limit. The traditional transmission section search method mainly conducts theoretical derivation, and there are great differences in the actual application process. It does not start from the perspective of engineering practicality, and the classified transmission section types are difficult to meet the usage habits of power dispatching departments. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the traditional transmission section search method mainly conducts theoretical derivation, and there are great differences in the actual application process. It does not start from the perspective of engineering practicality, and the classified transmission section types are difficult to meet the usage habits of power dispatching departments. The purpose of the present invention is to provide a transmission section search and section limit calculation method and system based on search cut sets. By simulating the operation of the power system after a fault occurs, it assists power system dispatchers to adjust the operation parameters of the power system in a timely manner. Starting from the perspective of engineering practicality, the transmission section types are classified based on the search cut sets of the transmission section, which meets the usage habits of power dispatching departments and has strong engineering practicality, and can give guiding opinions when the power dispatching department adjusts the system operation.

[0006] The present invention is realized by the following technical solutions:

[0007] The present solution provides a transmission section search and section limit calculation method based on search cut sets, including:

[0008] S1. Collect the basic data of the target power grid to form a network topology structure diagram of the target power grid;

[0009] S2. Set up a set of equipment failures; the set of equipment failures is set according to the standard guidelines;

[0010] S3. Add each failure in the failure set to the target power grid for failure scanning to find the failure channels and weak channels;

[0011] S4. After removing the found failure channels and weak channels, determine whether the target power grid is split into two parts: if so, output the cut-set section A composed of the current failure channel and the current weak channel, and calculate the section limit of the cut-set section A; otherwise, search for the adjacent channels of the current weak channel;

[0012] S5. Determine whether a new radial channel appears in the adjacent channels of the current weak channel: if so, output the cut-set section B composed of the current failure channel, the current weak channel, and the transmission channel with the largest load rate among the radial channels, and calculate the section limit of the cut-set section B; otherwise, output the non-cut-set section composed of the current failure channel and the current weak channel, and calculate the section limit of the non-cut-set section. When a new radial channel appears in the power grid, since each channel of the radial channel is a single-tree cut-set channel, the power grid is split into two parts after removing the single-tree channel. Therefore, according to the concept of the cut-set, select the transmission channel with the largest load rate among them, and form a cut-set section with the current failure channel, the current weak channel, and the transmission channel with the largest load rate among the radial channels, output the cut-set section, and calculate its section limit.

[0013] Working principle of this solution: The traditional transmission section search method mainly conducts theoretical derivations, which have great differences in the actual application process. It does not start from the perspective of engineering practicality, classify and output the corresponding transmission sections according to whether the failure channels and weak channels form cut-sets, and the types of transmission sections given by the classification are difficult to meet the usage habits of the power dispatching department. The purpose of the present invention is to provide a transmission section search and section limit calculation method and system based on searching for cut-sets. By simulating the operation of the power system after a failure occurs, it assists the power system dispatching personnel to adjust the operation parameters of the power system in a timely manner. Starting from the perspective of engineering practicality, the transmission section types are classified based on searching for cut-sets, which meet the usage habits of the power dispatching department and have strong engineering practicality, and can give guiding opinions for the power dispatching department to adjust the system operation.

[0014] To meet the requirements of the N-1 principle in the national standard GB38755-2019 "Guide for Power System Security and Stability", the equipment failure set is set as the N-1 failure set, including the N-1 failures of lines, transformers, and buses, as well as the N-2 failure of double-circuit lines on the same pole. Then, the target power grid is scanned for N-1 failures one by one to search for the key transmission sections. From the perspective of engineering application, the transmission sections are classified according to whether the failed equipment and weak-link equipment form a cut set. At the same time, the section power flow when the power flow of the equipment increases or decreases proportionally to the weak-link equipment just reaches full load after the failure is used as the thermal stability limit of the transmission section; by simulating the operating state of the power system after each failure in the N-1 failure set, it assists the power system dispatching and operation personnel to adjust the system operating parameters in a timely manner, and further improves the power supply reliability of the power grid.

[0015] In the present invention: A transmission channel refers to a transmission path composed of parallel transmission lines or parallel transformers. The power flow of each device in the transmission channel is distributed according to impedance, and the ratio of the active power flow through each device to the total power flow of the channel is relatively fixed.

[0016] A transmission section refers to a set composed of one or more transmission channels, and operation control limits need to be formulated to ensure the safe operation of the power grid.

[0017] The equipment failure set refers to the failures corresponding to the first-level and second-level safety and stability standards specified in the "Guide for Power System Security and Stability", such as all N-1 failures of transmission lines, N-1 failures of main transformers, N-1 failures of buses, and N-2 failures of double-circuit lines on the same pole in the power grid under study, excluding the failures corresponding to the third-level safety and stability standard.

[0018] The current-carrying capacity of a line refers to the maximum active power transmitted by the transmission line under thermal stability constraints.

[0019] The line load rate refers to the ratio of the active power flow of the line to the current-carrying capacity of the line.

[0020] Weak-link (bottleneck) equipment refers to the equipment whose current-carrying capacity restricts the transmission capacity of the section. There may be two situations:

[0021] (1) Under normal operating conditions, the overloaded equipment, whose long-term current-carrying capacity is the bottleneck restricting the transmission capacity of the section;

[0022] (2) The overloaded equipment after a pre-fault, whose current-carrying capacity is the bottleneck restricting the transmission capacity of the section.

[0023] The power flow transfer ratio refers to the ratio of the active power flow of the weak-link equipment after the failure to the active power flow of the transmission section before the failure.

[0024] The section load rate represents the ratio of the active power flow of the section to the section control limit.

[0025] A cut set is a concept in graph theory, defined as a set of edges in a connected graph. After removing the edges in this set from the connected graph, the graph is no longer connected. In the present invention, a cut set is defined as a set of power transmission channels. After removing the power transmission channels in this set, the power grid will be decomposed into two or more sub-power grids without electrical connection. In particular, in a connected graph, if any one branch is removed and the graph becomes two separate parts (an isolated point is also counted as a part), then this branch is a single-tree cut set.

[0026] The power flow transfer coefficient of the electromagnetic loop network channel refers to the ratio of the active power increment before and after the pre-fault of the "short-board channel" to the power flow before the pre-fault of the fault channel in the electromagnetic loop network.

[0027] A further optimization scheme is that the basic data includes:

[0028] The injected active power P of node i i and the reactive power Q i , the impedance Z between node i and node j ij , the shunt admittance Y of node i i , the rated power of the transformer between node i and node j The maximum transmission power of the line between node i and node j Taking a node of a substation in the target power grid.

[0029] A further optimization scheme is that while outputting the cut set section A, cut set section B and non-cut set section, the sub-types to which they belong are also output.

[0030] A further optimization scheme is that the cut set section A takes the section power flow when the equipment power flow increases or decreases proportionally to the power flow of the short-board equipment just reaching full load after the fault as the section limit:

[0031] The calculation formula for the section limit of the transmission line is:

[0032]

[0033] Where: represents the thermal stability limit of the transmission line; P l,max represents the maximum current-carrying capacity of the transmission line; k represents the margin, taking 1 when this section forms a cut set and taking 0.9 or 0.95 when it does not form a cut set; K l represents the power flow transfer ratio;

[0034] The calculation formula for the section limit of the transformer is:

[0035]

[0036] Where: represents the thermal stability limit under the long-term current-carrying capacity of this transformer; P lt,T represents the long-term current-carrying capacity of this transformer; KT represents the power flow transfer ratio;

[0037]

[0038] where: represents the thermal stability limit of the transformer considering short - time current - carrying capacity and short - time overload capacity; P st,T represents the short - time current - carrying capacity of the transformer; l overload represents the overload factor; k represents the margin, taking 1 when the section forms a cut - set, otherwise taking 0.9 or 0.95;

[0039] Thermal stability limit of the transformer is:

[0040] The further optimization plan is that for cut - set section B, the section power flow when the power flow of equipment changes proportionally to the short - time current - carrying capacity of the weakest equipment until it just reaches the short - time current - carrying capacity after the fault is taken as the section limit:

[0041] Section thermal stability limit The calculation formula is:

[0042]

[0043] where, P st represents the short - time current - carrying capacity of all weakest equipment; k represents the margin, taking 0.9; K represents the power flow transfer ratio.

[0044] The further optimization plan is that for non - cut - set sections, the calculation method of the section limit is:

[0045] The section limit based on the electromagnetic loop network section follows the following formula:

[0046]

[0047] where: K HV-LV represents the power flow transfer ratio of the high - voltage channel to the low - voltage channel; P HV represents the high - voltage channel power flow; k represents the margin; P LV represents the low - voltage channel power flow; P st,LV represents the short - time current - carrying capacity of the low - voltage channel.

[0048] The further optimization plan is that the subtypes of cut - set section A include: "one" - shaped section, "V" - shaped section, "two" - shaped section, and "multiple fault channels + weakest channel" section;

[0049] The subtypes of cut - set section B include: "Y" - shaped section, "three" - shaped section, and "multiple fault channels, weakest channels, and adjacent channels" section.

[0050] A further optimization solution is that the "one"-shaped section is a section where two substations are connected by two or more circuits or a section where two busbars of different voltage levels are connected by two or more main transformers; that is, a single-channel section. The relevant constraints are only related to one channel, and its calculation principle is relatively clear. The calculation of this type of section is relatively simple, and it is also the most numerous in the actual power grid.

[0051] The "V"-shaped section has a common sending-end substation or receiving-end substation.

[0052] The "two"-shaped section is a two-channel section without a common sending-end substation or receiving-end substation.

[0053] The "multiple fault channels and short-board channels" type of section is a bus fault or a fault of the same-pole lines located on different transmission channels.

[0054] A further optimization solution is that the "Y"-shaped section is a three-channel section with a common sending-end substation or receiving-end substation on one side.

[0055] The "three"-shaped section is a three-channel section without a common sending-end substation or receiving-end substation.

[0056] The "multiple fault channels, short-board channels and adjacent channels" type of section is a bus fault or a fault of the same-pole lines located on different transmission channels.

[0057] This solution also provides a transmission section search and section limit calculation system based on search cut sets for implementing the above-mentioned transmission section search and section limit calculation method based on search cut sets, including:

[0058] An acquisition module for collecting the basic data of the target power grid to form a network topology structure diagram of the target power grid.

[0059] A setting module for setting a set of equipment faults; the set of equipment faults is set according to standard guidelines.

[0060] A search module for adding each fault in the fault set to the target power grid for fault scanning to find fault channels and short-board channels.

[0061] An output calculation module for determining whether the target power grid is split into two parts after removing the found fault channels and short-board channels: if so, outputting a cut-set section A composed of "the current fault channels and the current short-board channels" and calculating the section limit of the cut-set section A; otherwise, searching for adjacent channels of the current short-board channels.

[0062] The output calculation module is further configured to determine whether a new radial channel appears in the adjacent channels of the current short-board channel: if so, a cut-set section B is output, which is composed of the current fault channel, the current short-board channel, and the transmission channel with the largest load rate among the radial channels, and the section limit of the cut-set section B is calculated; otherwise, a non-cut-set section composed of the current fault channel and the current short-board channel is output, and the section limit of the non-cut-set section is calculated.

[0063] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0064] The method and system for searching transmission sections and calculating section limits based on searching cut-sets provided by the present invention simulate the operation of the power system after a fault occurs, assist power system dispatchers in adjusting the operation parameters of the power system in a timely manner, and from the perspective of engineering practicality, classify the transmission section types based on the search of cut-sets for transmission sections, which conforms to the usage habits of power dispatch departments, has strong engineering practicality, and can give guiding opinions when the power dispatch department adjusts the system operation. Brief Description of the Drawings

[0065] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts. In the drawings:

[0066] Figure 1 is a schematic flow chart of a method for searching transmission sections and calculating section limits based on searching cut-sets;

[0067] Figure 2 is a topological diagram of a "V"-shaped section for a line fault;

[0068] Figure 3 is a topological diagram of a "two"-shaped section for a line fault;

[0069] Figure 4 is a topological diagram of a "V"-shaped section for a bus fault;

[0070] Figure 5 is a topological diagram of a "Y"-shaped section for a bus fault;

[0071] Figure 6 is a topological diagram of a star-shaped section for a bus fault;

[0072] Figure 7 is a topological diagram of a "Y"-shaped section for a bus fault;

[0073] Figure 8 is a topological diagram of a "two"-shaped section for a fault of double-circuit lines on the same tower;

[0074] Figure 9 It is a "three"-shaped cross-section topology diagram for the faults of the same-pole lines;

[0075] Figure 10 It is a cross-section topology diagram for the inconsistent power flow directions of the fault channels;

[0076] Figure 11 It is a "Y"-shaped cross-section topology diagram;

[0077] Figure 12 It is a "three"-shaped cross-section topology diagram;

[0078] Figure 13 It is a cross-section topology diagram of the electromagnetic loop network;

[0079] Figure 14 It is a schematic diagram of a single-channel cross-section;

[0080] Figure 15 It is a schematic diagram where the fault channel and the short-board channel are not in the same channel;

[0081] Figure 16 It is a schematic diagram of a cut set cross-section composed of "fault channel + short-board channel + adjacent channel";

[0082] Figure 17 It is a schematic diagram of a non-cut set cross-section composed of "fault channel + short-board channel". Detailed implementation manners

[0083] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in combination with embodiments and drawings. The illustrative implementation manners and descriptions of the present invention are only used to explain the present invention and do not limit the present invention.

[0084] Embodiment 1

[0085] This embodiment provides a transmission section search and section limit calculation method based on searching for cut sets, including:

[0086] S1. Collect the basic data of the target power grid to form a network topology structure diagram of the target power grid; the basic data includes:

[0087] The injected active power P of node i i and the reactive power Q i , the impedance Z between node i and node j ij , the shunt admittance Y of node i i , the rated power of the transformer between node i and node j The maximum transmission power of the line between node i and node j Taking a node of a substation in the target power grid.

[0088] S2, set the equipment failure set; the equipment failure set is set according to the standard guidelines; in this embodiment, a failure set that meets the requirements of the N-1 principle in the "Power System Safety and Stability Guidelines" is set, including: line N-1 failure, main transformer N-1 failure, bus N-1 failure, and double-circuit line on the same pole N-2 failure.

[0089] S3, add each failure in the failure set to the target power grid for failure scanning to find the failure channels and short-board channels;

[0090] S4, after removing the found failure channels and short-board channels, determine whether the target power grid is split into two parts. According to the concept of cut set in graph theory: if so, output the cut set section A composed of the current failure channel and the current short-board channel, and calculate the section limit of the cut set section A; otherwise, search for the adjacent channels of the current short-board channel;

[0091] In the calculation process of the section limit of the cut set section A, the section power flow when the equipment power flow increases or decreases proportionally to the power flow of the short-board equipment after the failure just reaches full load is used as the section limit:

[0092] The calculation formula for the section limit of the transmission line is:

[0093]

[0094] Where: represents the thermal stability limit of the transmission line; P l,max represents the maximum current-carrying capacity of the transmission line; k represents the margin, which is taken as 1 when the section forms a cut set and 0.9 or 0.95 when it does not form a cut set; K l represents the power flow transfer ratio;

[0095] The calculation formula for the section limit of the transformer is:

[0096]

[0097] Where: represents the thermal stability limit under the long-term current-carrying capacity of the transformer; P lt,T represents the long-term current-carrying capacity of the transformer; K T represents the power flow transfer ratio;

[0098]

[0099] Where: represents the thermal stability limit of the transformer considering the short-term current-carrying capacity and short-term overload capacity; P st,T represents the short-term current-carrying capacity of the transformer; l overload represents the overload coefficient; k represents the margin, which is taken as 1 when the section forms a cut set and otherwise 0.9 or 0.95;

[0100] Thermal stability limit of transformer is as follows:

[0101] The subtypes of the cut-set section A include: "one"-shaped section, "V"-shaped section, "two"-shaped section, and "multiple fault channels + short-board channel" section;

[0102] The so-called "one"-shaped section, that is, a single-channel section, is a section where two substations are connected by two or more circuits or a section where two busbars of different voltage levels are connected by two or more main transformers; the relevant constraints are only related to one channel, and its calculation principle is relatively clear. The calculation of this type of section is relatively simple, and it also has the largest quantity in the actual power grid.

[0103] The "V"-shaped section has a common sending-end substation or receiving-end substation; its topological structure is as Figure 2 shown. In the figure, the solid straight line represents the channel, the dotted line represents the direct or indirect electrical connection; the arrow represents the power flow direction; the curve represents the section, and the section has a common sending-end substation or receiving-end substation (substation A).

[0104] The "two"-shaped section is a two-channel section without a common sending-end substation or receiving-end substation; its topological structure is as Figure 3 shown, and the section has no common sending-end substation or receiving-end substation.

[0105] For the "multiple fault channels and short-board channel" type section: For busbar faults or faults of the same-pole lines located on different transmission channels, the fault-breaking equipment may be located in multiple channels, so a section composed of "multiple fault channels and short-board channels" may appear, mainly including two situations: (1) The short-board channel is located in a certain fault channel; (2) The short-board channel is not a fault channel and is located outside the fault channel.

[0106] For the situation where the short-board channel is located in a certain fault channel, generally, the fault channel with the same power flow direction as the short-board channel is classified as one section.

[0107] An important feature of the busbar fault is that the fault channels have a common substation (or a common busbar), and the typical topological structures are "V"-shaped, "Y"-shaped, star-shaped, and dispersed, etc.; The "V"-shaped section of the busbar fault is as Figure 4 shown, the "Y"-shaped section of the busbar fault is as Figure 5 shown, the star-shaped section of the busbar fault is as Figure 6 shown, and the "Y"-shaped section of the busbar fault is as Figure 7 shown.

[0108] Figure 8The shown fault sets may include various situations such as AC double-line fault, BD double-line fault, AC single-line fault + BC single-line fault, etc. The "Z"-shaped section of the faults on the same-pole lines refers to a three-channel section without common sending and receiving substations, and its topological structure is as Figure 9 shown. In fact, both the "Z"-shaped and "Z"-shaped sections of the faults on the same-pole lines can be regarded as special cases of the dispersed section. For the case where the "Z"-shaped section of the faults on the same-pole lines forms a cut set, no margin is left for the short-time current-carrying capacity of the short board during calculation, otherwise a 10% margin needs to be left.

[0109] The above structural forms all refer to the situation where the power flows in the fault channels are in the same direction. In some cases, the power flow directions between the fault channels are inconsistent. Such as Figure 10 shown. Assume that both AB and BC are double-circuit lines. If a same-pole fault occurs on one circuit of AB and one circuit of BC (or a bus fault at substation B opens one circuit of AB and one circuit of BC each), resulting in overload of equipment DE; in this case, it needs to be processed according to 2 sections.

[0110] S5. Judge whether a new radial channel appears in the adjacent channels of the current short-board channel: If so, a cut set section B is output composed of "the current fault channel + the current short-board channel + the transmission channel with the largest load rate in the radial channels", and the section limit of the cut set section B is calculated; otherwise, a non-cut set section composed of "the current fault channel and the current short-board channel" is output, and the section limit of the non-cut set section is calculated.

[0111] When outputting the cut set section A, the cut set section B and the non-cut set section, the sub-types to which they belong are output at the same time;

[0112] The cut set section B takes the section power flow when the equipment power flows increase or decrease proportionally to the short-time current-carrying capacity of the short-board equipment just after the fault as the section limit:

[0113] Section thermal stability limit The calculation formula is:

[0114] Among them, P st represents the short-time current-carrying capacity of all short-board equipment; k represents the margin, taking 0.9; K represents the power flow transfer ratio.

[0115] The sub-types of the cut set section B include: "Y"-shaped section, "Z"-shaped section, and "multiple fault channels + short-board channel + adjacent channel" section.

[0116] The so-called "Y"-shaped section is a three-channel section with a common sending substation or receiving substation on one side; its topological structure is as Figure 11 shown.

[0117] The so-called "Z"-shaped section is a three-channel section without a common sending substation or receiving substation; its topological structure is asFigure 12 as shown

[0118] The cross-section of "multiple fault channels + short-board channel + adjacent channel": For bus faults or faults of double-circuit lines on different transmission channels, the fault interruption equipment may be located in multiple channels. If the "multiple fault channels + short-board channel" does not form a cut-set cross-section, at this time, the "multiple fault channels + short-board channel + adjacent channel" can be used to form a cut-set cross-section, and its topological structure is similar to the case of the above-mentioned "multiple fault channels + short-board channel" cross-section.

[0119] The calculation method of the cross-section limit for non-cut-set cross-sections is as follows: Taking the electromagnetic loop network cross-section as an example, it illustrates the composition of the non-cut-set cross-section of "fault channel + short-board channel" and its limit calculation.

[0120] The 500kV / 220kV electromagnetic loop network cross-section can be regarded as a special type of cross-section of "fault channel and short-board channel", corresponding to the case where the "fault channel" is a 500kV line or main transformer, and the "short-board channel" is a 220kV line. Considering that under the non-cut-set cross-section, the cross-section limit based on the electromagnetic loop network cross-section follows the following formula:

[0121]

[0122] Where: K HV-LV represents the power flow transfer ratio of the high-voltage channel to the low-voltage channel; P HV represents the power flow of the high-voltage channel; k represents the margin; P LV represents the power flow of the low-voltage channel; P st,LV represents the short-time current-carrying capacity of the low-voltage channel.

[0123] The topological structure of the electromagnetic loop network cross-section is as follows Figure 13 as shown. In the figure, the thick line represents the 500kV line, and the thin line represents the 220kV line. In the actual system, Substation A and Substation B may be the same 500kV substation, and similarly, Substation C and Substation D may also be the same 500kV substation.

[0124] Embodiment 2

[0125] This embodiment provides a transmission cross-section search and cross-section limit calculation system based on search cut-sets, which is used to implement the transmission cross-section search and cross-section limit calculation method described in the previous embodiment, including:

[0126] An acquisition module, configured to collect the basic data of the target power grid to form a network topology structure diagram of the target power grid;

[0127] A setting module, configured to set a device fault set; the device fault set is set according to the standard guidelines;

[0128] A search module, configured to add each fault in the fault set to the target power grid for fault scanning to find fault channels and weak channels;

[0129] An output calculation module, configured to determine whether the target power grid is split into two parts after removing the found fault channels and weak channels: if so, output a cut-set section A composed of "the current fault channel and the current weak channel", and calculate the section limit of the cut-set section A; otherwise, search for adjacent channels of the current weak channel;

[0130] The output calculation module is further configured to determine whether a new radial channel appears among the adjacent channels of the current weak channel: if so, output a cut-set section B composed of the current fault channel, the current weak channel, and the transmission channel with the largest load rate among the radial channels, and calculate the section limit of the cut-set section B; otherwise, output a non-cut-set section composed of the current fault channel and the current weak channel, and calculate the section limit of the non-cut-set section.

[0131] Embodiment 3

[0132] This embodiment takes a provincial power grid as an example to give the transmission section search results, specifically including the following three embodiments. The relevant information of this provincial power grid is as follows:

[0133] Table 1 Relevant information of a provincial power grid

[0134] Item Quantity The power system contains 3542 The power system contains 4667 The number of power sources in the power system 518

[0135] (1) Cut-set section A composed of "fault channel + weak channel"

[0136] ①Typically, in a single-channel section, two substations are connected by a double-circuit line, and one of the double-circuit lines trips: as Figure 14 shown, where Pingfu Line 1 and Line 2 are of 220 kV voltage level, the arc represents the cut-set, "×" represents the line trip, "168-j74" and the arrow represent the initial power flow, and "(2)" represents the power flow of the double circuit.

[0137] Table 2 Single-channel section

[0138] Operation mode Normal mode Section name Pingfu Line 1 + Pingfu Line 2 Contingency Tripping of any one AC line (Pingfu Line 1) Bottleneck equipment Pingfu Line 2 Branch power flow before fault (MW) Pingfu Line 2: 92.61; Pingfu Line 1: 75.01 Branch power flow after fault (MW) Pingfu Line 2: 132.54; Pingfu Line 1: 0 Section thermal stability limit (MW) 265.58654

[0139] ②The case where the fault channel and the weak channel are not in the same channel: The circuit topology diagram is as Figure 15 shown, and all in the figure are of 500 kV voltage level; the arc represents the cut-set, "×" represents the line trip, the numbers and the arrow represent the initial power flow, and "(2)" represents the power flow of the double circuit.

[0140] Table 3 The fault channel and the weak channel are not in the same channel

[0141] Operation mode Normal mode Section name Erbai Line + Lanpu Line 2 Contingency Tripping of any one AC line (Erbai Line) Bottleneck equipment Lanpu Line 2 Branch power flow before fault (MW) Erbai Line: 767.78; Lanpu Line 2: 1102.73 Branch power flow after fault (MW) Erbai Line: 0; Lanpu Line 2: 1435.24 Section thermal stability limit (MW) 1980

[0142] (2). Cut set section B composed of "fault channel + short board channel + adjacent channel", and the section topology diagram is as Figure 16 shown; among them, the Zhaohua station is at the 500 kV voltage level, and the rest are at the 220 kV voltage level. The numbers and arrows represent the initial power flow, and "(2)" represents the power flow of the double circuit.

[0143] Table 4 Section of "fault channel + short board channel + adjacent channel"

[0144] Operation mode Normal mode Section name Cangjiang Line + Yuanxue Line + Zhaoxue Line 1 + Zhaoxue Line 2 Contingency Tripping of parallel double - circuit lines (Zhaoxue Line 1 + Zhaoxue Line 2) Bottleneck equipment Yuanxue Line Branch power flow before fault (MW) Cangjiang Line: 63.63; Yuanxue Line: 98.83; Zhaoxue Line 2: 103.69; Zhaoxue Line 1: 103.72 Branch power flow after fault (MW) Cangjiang Line: 106.09; Yuanxue Line: 267.35; Zhaoxue Line 2: 0; Zhaoxue Line 1: 0 Section thermal stability limit (MW) 498.0365

[0145] (3). Non-cut set section composed of "fault channel + short board channel", and the section topology diagram is as Figure 17 shown; among them, the Chuanchangpingshan substation, Nanchong station and the line between them are at the 500 kV voltage level, and the rest are at the 220 kV voltage level. The numbers and arrows represent the initial power flow, and "(3)" represents the power flow of the triple circuit.

[0146] Table 5 Non-cut set section composed of "fault channel + short board channel"

[0147]

[0148] The specific embodiments described above further elaborate on the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Transmission section search and section limit calculation method based on search cut sets, characterized in that, it includes: S1. Collect the basic data of the target power grid to form the network topology structure diagram of the target power grid; S2. Set the fault set; The fault set is set according to the standard guidelines; S3. Add each fault in the fault set to the target power grid for fault scanning to find the fault channels and short-board channels; S4. After removing the found fault channels and short-board channels, determine whether the target power grid is split into two parts: if so, output the cut set section A composed of the current fault channel and the current short-board channel, and calculate the section limit of the cut set section A; otherwise, search for the adjacent channels of the current short-board channel; S5. Determine whether a new radial channel appears in the adjacent channels of the current short-board channel: if so, output the cut set section B composed of the current fault channel, the current short-board channel, and the transmission channel with the largest load rate among the radial channels, and calculate the section limit of the cut set section B; otherwise, output the non-cut set section composed of the current fault channel and the current short-board channel, and calculate the section limit of the non-cut set section.

2. The transmission section search and section limit calculation method based on search cut sets according to claim 1, characterized in that, the basic data includes: The active power injection $P$ at node $i$ i and the reactive power $Q$ i , the impedance $Z$ between node $i$ and node $j$ ij , the shunt admittance $Y$ of node $i$ i , the rated power of the transformer between node $i$ and node $j$ The maximum transmission power of the line between node $i$ and node $j$ 3. The transmission section search and section limit calculation method based on search cut sets according to claim 2, characterized in that, while outputting the cut set section A, the cut set section B and the non-cut set section, output the sub-type to which they belong.

4. The transmission section search and section limit calculation method based on search cut sets according to claim 2, characterized in that, The section limit of the cut set section A is the section power flow when the equipment power flow increases or decreases proportionally to the power flow of the short-board equipment after the fault just reaches full load: The calculation formula for the section limit of the transmission line section is: Wherein: represents the thermal stability limit of the transmission line; P l,max represents the maximum current-carrying capacity of the transmission line; k represents the margin, taking 1 when the section forms a cut set and taking 0.9 or 0.95 when it does not form a cut set; K l represents the power flow transfer ratio; The calculation formula for the section limit of the transformer section is: Wherein: represents the thermal stability limit under the long-term current-carrying capacity of the transformer; P lt,T represents the long-term current-carrying capacity of the transformer; K T represents the power flow transfer ratio; Wherein: represents the thermal stability limit of the transformer considering short-time current-carrying capacity and short-time overload capacity; P st,T represents the short-time current-carrying capacity of the transformer; l overload represents the overload factor; k represents the margin, taking 1 when this section forms a cut set, otherwise taking 0.9 or 0.95; Thermal stability limit of the transformer is as follows:

5. The transmission section search and section limit calculation method based on search cut sets according to claim 2, characterized in that, The section limit of the cut set section B is the section power flow when the equipment power flow increases or decreases proportionally to the short-time current-carrying capacity of the short-board equipment after the fault: Thermal stability limit of cross-section The calculation formula is as follows: Among them, P st represents the short-time current-carrying capacity of all short-board devices; k represents the margin, taking 0.9; K represents the power flow transfer ratio.

6. The transmission section search and section limit calculation method based on search cut sets according to claim 2, characterized in that, The calculation method for the section limit of the non-cut set section is: The section limit based on the electromagnetic loop network section follows the following formula: Where: K HV-LV represents the power flow transfer ratio of the high-voltage channel to the low-voltage channel; P HV represents the high-voltage channel power flow; k represents the margin; P LV represents the low-voltage channel power flow; P st,LV represents the short-time current-carrying capacity of the low-voltage channel.

7. The transmission section search and section limit calculation method based on search cut sets according to claim 3, characterized in that, The sub-types of the cut set section A include: "one"-shaped section, "V"-shaped section, "two"-shaped section, and "multiple fault channels and short-board channels" section; The sub-types of the cut set section B include: "Y"-shaped section, "three"-shaped section, and "multiple fault channels, short-board channels and adjacent channels" section.

8. The transmission section search and section limit calculation method based on search cut sets according to claim 7, characterized in that, The "one"-shaped section is a section where two substations are connected by two or more circuits or a section where two busbars of different voltage levels are connected by two or more main transformers; The "V"-shaped section has a common sending-end substation or receiving-end substation in the section; The "two"-shaped section is a two-channel section without a common sending-end substation or receiving-end substation; The "multiple fault channels and short-board channels" type section is a bus fault or a fault of a double-circuit line on different transmission channels; 9. The method for searching transmission sections based on search cut sets and calculating section limits according to claim 7, characterized in that, The "Y"-shaped section is a three-channel section with a common sending-end substation or receiving-end substation on one side; The "three"-shaped section is a three-channel section without a common sending-end substation or receiving-end substation; The "multiple fault channels, short-board channels and adjacent channels" type section is a bus fault or a fault of a double-circuit line on different transmission channels; 10. A system for searching transmission sections based on search cut sets and calculating section limits, characterized in that, It is used to implement the method for searching transmission sections based on search cut sets and calculating section limits according to any one of claims 1-9, including: An acquisition module, which is used to collect the basic data of the target power grid and form a network topology structure diagram of the target power grid; A setting module, which is used to set a fault set; the fault set is set according to standard guidelines; A search module, which is used to add each fault in the fault set to the target power grid for fault scanning to find fault channels and short-board channels; An output calculation module, which is used to determine whether the target power grid is split into two parts after removing the found fault channels and short-board channels: if so, output a cut set section A composed of "the current fault channel and the current short-board channel", and calculate the section limit of the cut set section A; otherwise, search for adjacent channels of the current short-board channel; The output calculation module is also used to determine whether a new radial channel appears in the adjacent channels of the current short-board channel: if so, output a cut set section B composed of the current fault channel, the current short-board channel and the transmission channel with the largest load rate among the radial channels, and calculate the section limit of the cut set section B; otherwise, output a non-cut set section composed of the current fault channel and the current short-board channel, and calculate the section limit of the non-cut set section.

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