Power grid bus fault judgment method based on KCL

Abstract

The invention discloses a power grid bus fault judgment method based on KCL. The method comprises the following steps: determining whether a suspicious measuring point corresponding to the maximum value of the peak value of a voltage disturbance quantity curve is located on a bus; responding to the condition that the suspicious measuring point is not located on the bus, determining that the bus has no fault; in response to the fact that the suspicious measuring point is located on the bus, further judging: respectively selecting closed cut set networks on two sides of the suspicious measuring point; for each closed cut-set network, calculating whether the difference value between the line attenuation rate of the line injected into the closed cut-set network and the line attenuation rate of the line injected out of the closed cut-set network is smaller than a second threshold value or not; and responding to the fact that the difference values of the first closed cut-set network and the second closed cut-set network are smaller than the second threshold value, determining that the fault occurs at the bus. The method is not affected by transition resistance and impedance change of an opposite-end system on result precision, can simply, efficiently and accurately judge whether the power grid bus breaks down or not, and has good universality.

Description

Technical Field

[0001] The present invention relates to the field of power transmission, and more specifically to a KCL-based power grid bus fault judgment method. Background Art

[0002] Because the busbar of the power grid plays the role of collecting and distributing electric energy in the power system, busbar protection plays an important role in the entire power system. As the transmission capacity of the power grid increases, the losses caused by the destruction of the stability of the power grid system are also increasing. Therefore, when the busbar fails, the busbar protection requires to act as soon as possible to remove the fault, which is of great significance to maintaining the stability of the power system.

[0003] Traditional busbar protection usually takes power frequency as fault characteristic, and the protection action time is 20-40ms. At the same time, power frequency protection is easily affected by factors such as distributed capacitance and current transformer saturation. With the rapid development of power grid, the time required for relay protection to remove faults is shorter and the reliability requirement is higher. At the same time, most of the transmission lines in the high-voltage power grid are operated in a ring network mode. The original busbar fault location method is only for radial lines, without considering the actual structure of the power grid.

[0004] Therefore, the art still lacks a method that can adapt to various transmission lines in a high-voltage power grid and can accurately and quickly determine whether a power grid busbar fault occurs. Summary of the invention

[0005] The purpose of the present invention is to provide a method for judging a power grid bus fault based on KCL; the method of the present invention is not affected by changes in transition resistance and impedance of the opposite system on the accuracy of the result, can simply, efficiently and accurately judge whether a power grid bus fault occurs, and has good versatility.

[0006] The present invention provides a method for determining a power grid bus fault based on KCL, the method comprising:

[0007] (1) obtaining voltage values ​​at measuring points at different locations in the transmission line;

[0008] (2) obtaining voltage disturbance curves at different measuring points in the transmission line according to the voltage;

[0009] (3) in response to the voltage peak point of the voltage disturbance amount curve being less than a first threshold, determining that no fault has occurred at the location; in response to the voltage peak point of the voltage disturbance amount curve being above the first threshold, determining that a fault disturbance has occurred in the power grid, and determining whether a busbar of the power grid has a fault by the following method:

[0010] (3.1) determining whether the suspicious measuring point corresponding to the maximum value of the peak value of the voltage disturbance curve is located on the bus;

[0011] (3.2) in response to the suspected measuring point not being located on the bus, determining that the bus has not failed; in response to the suspected measuring point being located on the bus, further determining whether the bus has failed:

[0012] (3.2.1) Selecting closed cut set networks on both sides of the suspicious measuring point, respectively, wherein the closed cut set network is composed of a first closed cut set network and a second closed cut set network;

[0013] (3.2.2) for each of the closed cut set networks, calculating whether the difference between the line attenuation rate of the line injected into the closed cut set network and the line attenuation rate of the line injected out of the closed cut set network is less than a second threshold: and

[0014] (3.2.3) In response to the difference between the first closed cut set network and the second closed cut set network being smaller than the second threshold, it is determined that a fault occurs at the bus.

[0015] It should be noted that injection and injection out of the closed cut set network are relative to the current direction in the line. Injection into the closed cut set network means that the current in the line flows into the closed cut set network, and injection out of the closed cut set network means that the current in the line flows out of the closed cut set network.

[0016] In another preferred example, the closed cut set network includes a portion of the suspicious line directly connected to the suspicious measuring point, a proximal normal measuring point connected to the suspicious line, and a portion of the line connecting the proximal normal measuring point and a distal normal measuring point connected to the proximal normal measuring point.

[0017] In another preferred example, the closed cut set network includes a portion of the suspicious line directly connected to the suspicious measuring point, a proximal normal measuring point connected to the suspicious line, and a portion of the line connecting the proximal normal measuring point and a distal normal measuring point directly connected to the proximal normal measuring point.

[0018] In another preferred example, the transmission line is divided into a radial line and a ring line.

[0019] In another preferred example, the voltage quantity at the measuring point is collected by a voltage transformer installed at the measuring point.

[0020] In another preferred example, in step (2), the voltage disturbance curve at different positions in the transmission line is obtained by extracting the maximum and minimum values ​​of the voltage in step (1), fitting them into an envelope curve, and adding and averaging them.

[0021] In another preferred example, in response to the difference of the first closed cut set network being greater than or equal to the second threshold and / or the difference of the second closed cut set network being greater than or equal to the second threshold, it is determined that a line in the first closed cut set network and / or a line in the second closed cut set network has a fault.

[0022] In another preferred example, in response to the difference value of the first closed cut set network being greater than or equal to the second threshold, it is determined that one or more lines in the first closed cut set network fail.

[0023] In another preferred example, in response to the difference value of the second closed cut set network being greater than or equal to the second threshold, it is determined that one or more lines in the second closed cut set network fail.

[0024] In another preferred example, in response to the difference of the first closed cut set network being greater than or equal to the second threshold and the difference of the second closed cut set network being greater than or equal to the second threshold, it is determined that one or more lines in the first closed cut set network and one or more lines in the second closed cut set network are both faulty.

[0025] In another preferred embodiment, the line attenuation rate ρ mn for:

[0026]

[0027] Among them, m is the peak value of the voltage disturbance at the measuring point m on the transmission line, unit: V;

[0028] du n is the peak value of the voltage disturbance at the measuring point n on the transmission line, unit: V;

[0029] l mn It is the line length between the measuring point m and the measuring point n, in meters.

[0030] The main advantages of the present invention include:

[0031] (a) The accuracy of the results is not affected by changes in transition resistance and impedance of the opposite end system;

[0032] (b) It can simply, efficiently and accurately determine whether a power grid busbar fault occurs;

[0033] (c) It has good versatility.

[0034] It should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described below (such as embodiments) can be combined with each other to form a new or preferred technical solution. Due to space limitations, they will not be described one by one here. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 It is a flow chart of a method for determining a power grid bus fault based on KCL in an example of the present invention;

[0037] Figure 2 It is a schematic diagram of a radial line based on which the fault judgment of a power grid busbar in an example of the present invention is based;

[0038] Figure 3 It is a schematic diagram of a ring circuit based on which the grid bus fault judgment in an example of the present invention is based. DETAILED DESCRIPTION

[0039] After extensive and in-depth research and a large number of screenings, the inventors have developed for the first time a KCL-based power grid bus fault judgment method; the method proposed in the present invention uses the measured transient voltage to achieve fault phase selection without considering the line-to-ground capacitance and conductivity; the method is not affected by the change in transition resistance and the impedance of the opposite system, and can simply, efficiently and accurately determine whether a power grid bus fault occurs, and has good versatility; the present invention was completed on this basis.

[0040] the term

[0041] As used herein, the term "closed cut set network" refers to a virtual closed curve containing at least one node in the power system topology network. If the closed curve contains one or more branches (including the entire branch or part of the branch), these branches are said to be associated with the cut set network. It should be noted that in the present invention, the direction of the current flowing into the closed curve in the branch is positive, and the direction of the current flowing out of the closed curve is negative).

[0042] As used in this article, the term "transient component" refers to the electrical quantity generated by energy storage elements such as inductors and capacitors in the network when the system network structure changes; it decays exponentially and no longer exists after the transition process ends.

[0043] As used herein, the term "busbar" refers to an electrical device made of high-conductivity copper (copper busbar) or aluminum material for transmitting electrical energy and having the function of collecting and distributing electrical power.

[0044] As used herein, the term "ring network" refers to a system in which nodes are connected together through branches to form a ring, and the ring formed by the nodes and branches as a whole constitutes a "ring network".

[0045] As used herein, the terms “voltage change rate”, “line decay rate”, etc. may be used interchangeably.

[0046] As used herein, the terms "point", "node", etc. may be used interchangeably.

[0047] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, the accompanying drawings are schematic diagrams, so the device and apparatus of the present invention are not limited by the size or ratio of the schematic diagrams.

[0048] It should be noted that in the claims and description of this patent, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "including one" do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0049] Example

[0050] When a power grid bus fails, a transient DC quantity will be generated. Although it lasts for a short time, it contains rich fault information, which makes it possible to quickly and accurately locate short-circuit faults in the power grid. A large amount of fault information in the transient component generated when the power grid bus fails includes line length, line parameters, fault distance and fault time. According to the superposition principle, the network after the short circuit can be equivalent to two parts: the normal state and the disturbance component network. The disturbance component network is a network under the action of a disturbance voltage source (the voltage source is equal to the voltage at the short-circuit point under normal circumstances and opposite in direction). In the event of a short circuit fault, the disturbance component generated under the action of a single disturbance voltage source contains two components: the baseband component and the attenuation disturbance quantity. This embodiment uses the extracted transient quantity to realize the bus fault judgment of radial lines and ring lines.

[0051] The flowchart of the method for locating bus fault based on the characteristics of transient DC quantity in this embodiment is as follows: Figure 1 As shown, the method includes:

[0052] (1) Use voltage transformers installed at different locations in the transmission line to collect the voltage at that location and transmit it to the measuring device unit in the electronic room through the OPGW communication wire. Voltage transformers are arranged at the power grid busbars;

[0053] (2) The measuring device unit uses a programmed program to extract the maximum and minimum values ​​of each voltage quantity and fits them into an envelope curve. The curve obtained by adding and averaging the values ​​is the voltage disturbance quantity curve at different locations in the transmission line;

[0054] (3) Based on the extracted voltage disturbance curve, first determine whether a short-circuit fault disturbance occurs in the power grid; if the voltage peak point of the voltage disturbance curve is less than the preset threshold, du max <ε 1 , then there is no fault in the power grid, that is, there is no bus fault; otherwise, a short circuit fault disturbance occurs in the power grid, that is, the bus may have a fault, and step (4) is executed;

[0055] (4) Determine whether the busbar is faulty;

[0056] First, determine whether the suspected measuring point corresponding to the peak value / maximum value of the voltage disturbance among all measuring points is located at the busbar. If it is located at the busbar, there is a possibility of busbar fault; if it is not located at the busbar, then there is no busbar fault.

[0057] Further judgment is made based on the possible failure of the above busbar:

[0058] Select closed cut set networks on both sides of the suspicious measuring point. For each closed cut set network, calculate whether the difference between the line attenuation rate of the line injected into the closed cut set network and the line attenuation rate of the line injected out of the closed cut set network is less than ε 2 , that is, calculate whether the line attenuation rate of the line injected into the closed network satisfies the KCL equation:

[0059] ∑ρ in -∑ρ out <ε 2

[0060] When the difference in the line attenuation rate of the closed cut set networks on both sides is less than ε 2 When , the fault occurs at the busbar; otherwise, the busbar does not fail, and the fault occurs in the lines contained in the closed cut set networks on both sides.

[0061] When it is determined that the fault occurs in the lines included in the closed cut set networks on both sides, and a single closed cut set network includes multiple lines, the range of the closed cut set network can be further narrowed, and the difference between the line attenuation rate of the line injected into the closed cut set network and the line attenuation rate of the line injected out of the closed cut set network can be calculated again to see whether it is less than ε 2 , if the difference of the closed cut set network in the reduced range is less than ε 2 , then the network has no fault, otherwise the network has a fault until the faulty line is screened out.

[0062] If there is only one transmission line connected to the upstream and / or downstream of the busbar, then the adjacent node can be selected to directly calculate whether the difference in line attenuation rate of the line connected to the adjacent node is less than ε 2 ; If the busbar is connected to at least two transmission lines upstream and / or downstream, then the closed cut set network is preferably selected for judgment. If the difference in line attenuation rate of the busbar upstream and / or downstream is less than ε 2 , it is determined that the busbar is faulty; otherwise, the fault is not on the busbar.

[0063] The busbar fault is divided into two types: a busbar fault in a radial network and a busbar fault in a ring network.

[0064] The specific method for judging bus fault in radial network is:

[0065] Figure 2 A radial network is shown, in which the generator and bus m 1 Connected by transmission line, busbar m 1 Through the line 3 With busbar m 2 Connect, while busbar m 1 Through the line 4 With busbar m 3 Connection, busbar m 3 Through the line 7 With busbar m 2 Connection, busbar m 2 Through line l 5 and l 6 With busbar m 4 Connection, busbar m 3 Through the line 8 With busbar m 4 Connection, optionally busbar m 4 It can be connected to an infinite system. Six voltage transformers are used to collect voltage values ​​at different measuring points, where measuring points ① and ② are arranged at the connection between the generator and the busbar m 1 On the line, the measuring point ① is close to the generator, and the measuring point ② is close to the busbar m 1 , the line between measuring point ① and measuring point ② is l 1, measuring point ② and busbar m 1 The line between 2 ; Measurement point ③ is arranged on busbar m 1 On the busbar, measuring point ④ is arranged on the busbar m 2 On the busbar, measuring point ⑤ is arranged on the busbar m 3 On the busbar, the measuring point ⑥ is arranged on the busbar m 4 superior.

[0066] Assume that through the above steps (1)-(4), it is determined that the peak value extracted from the measuring point ③ is the largest and exceeds ε 1 , which is a suspicious measuring point, measuring point ③ is on busbar m 1 Then the busbar m 1 If there is a possibility of failure, further judgment is made:

[0067] Busbar m 1 Only one transmission line is connected upstream, and a closed cut set network surrounding the neighboring node ② is selected (see Figure 2 The elliptical closed curve network enclosing the measuring point ② in the figure calculates the line l connected to the node ②. 1 , l 2 Line attenuation rate ρ 21 , 32 Whether it satisfies ρ 21 -ρ 32 <ε 2 ; Busbar m 1 The downstream is connected to five transmission lines, so we select the closed cut set network surrounding the neighboring nodes ④ and ⑤ (see Figure 2 The elliptical closed curve network enclosing the measuring points ④ and ⑤ in the figure is used to calculate whether the line attenuation rate satisfies ρ 34 +ρ 35 -(2ρ 46 +ρ 56 )<ε 2 Combined with the above analysis, when the obtained line attenuation rate satisfies ρ 21 -ρ 32 <ε 2 and ρ 34 +ρ 35 -(2ρ 46 +ρ 56 )<ε 2 When the busbar m 1 There is a fault at the busbar, otherwise there is no fault at the busbar.

[0068] The specific method for determining bus faults in a ring network is:

[0069] Figure 3 A ring network is shown, in which the generator and bus m 1 Connected by transmission line, busbar m 1 Through the line3 With busbar m 2 Connect, while busbar m 1 Through the line 2 With busbar m 3 Connection, busbar m 2 Through the line 5 With busbar m 5 Connection, busbar m 3 Through the line 6 With busbar m 4 Connection, busbar m 2 Through the line 4 With busbar m 3 Connection, optionally busbar m 4 and busbar m 5 Seven voltage transformers are used to collect voltages at different measuring points, of which measuring points ① and ⑦ are arranged at the connection between the generator and the busbar m 1 On the line, the measuring point ① is close to the bus m 1 , measuring point ⑦ is close to the generator, and the line between measuring point ① and measuring point ⑦ is l 7 , measuring point ① and busbar m 1 The line between 1 ; Measurement point ② is arranged on busbar m 1 On the busbar, measuring point ③ is arranged on the busbar m 3 On the busbar, measuring point ④ is arranged on the busbar m 2 On the busbar, measuring point ⑤ is arranged on the busbar m 5 On the busbar, the measuring point ⑥ is arranged on the busbar m 4 superior.

[0070] Assume that through the above steps (1)-(4), it is determined that the peak value extracted from the measuring point ② is the largest and exceeds ε 1 , which is a suspicious measuring point, measuring point ② is on busbar m 1 Then the busbar m 1 If there is a possibility of failure, further judgment is made:

[0071] Busbar m 1 Only one transmission line is connected upstream, and a closed cut set network surrounding the neighboring node ① is selected (see Figure 3 The elliptical closed curve network surrounding the measuring point ① in the figure calculates the line l connected to the node ①. 1 , l 7 Line attenuation rate ρ 21 , 17 Whether it satisfies |ρ 21 -ρ 17 |<ε 2 ; Busbar m 1The downstream connected ring line is similar to the above radial network, and a closed cut set network including the line connected to the measuring point ② is made, that is, a closed cut set network surrounding the adjacent measuring points ③ and ④ (see Figure 3 The elliptical closed curve network enclosing the measuring points ③ and ④ in the figure is used to calculate whether the line attenuation rate of the injection and injection closed cut set network satisfies the KCL equation, that is, whether the line attenuation rate satisfies ρ 21 +ρ 24 -(ρ 36 +ρ 45 )<ε 2 Combined with the above analysis, when the obtained line attenuation rate satisfies both

[0072] |ρ 21 -ρ 17 |<ε 2 and ρ 21 +ρ 24 -(ρ 36 +ρ 45 )<ε 2 When the busbar m 1 There is a fault at the busbar, otherwise there is no fault at the busbar.

[0073] Where, line decay rate / voltage change rate ρ mn The expression is

[0074]

[0075] In the formula m 、 n --------The peak value of voltage disturbance at the measuring points at both ends of the transmission line;

[0076] l mn ----------Line length.

[0077] All documents mentioned in the present invention are cited as references in this application, just as each document is cited as reference individually. In addition, it should be understood that after reading the above teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for judging power grid bus fault based on KCL, characterized in that: The method comprises: (1) obtaining voltage values ​​at measuring points at different locations in the transmission line; (2) obtaining voltage disturbance curves at different measuring points in the transmission line according to the voltage; (3) in response to the voltage peak point of the voltage disturbance amount curve being less than a first threshold, determining that no fault has occurred at the location; in response to the voltage peak point of the voltage disturbance amount curve being above the first threshold, determining that a fault disturbance has occurred in the power grid, and determining whether a busbar of the power grid has a fault by the following method: (3.1) determining whether the suspicious measuring point corresponding to the maximum value of the peak value of the voltage disturbance curve is located on the bus; (3.2) in response to the suspected measuring point not being located on the bus, determining that the bus has not failed; in response to the suspected measuring point being located on the bus, further determining whether the bus has failed: (3.2.1) Selecting closed cut set networks on both sides of the suspicious measuring point, respectively, wherein the closed cut set network is composed of a first closed cut set network and a second closed cut set network; (3.2.2) for each of the closed cut set networks, calculating whether the difference between the line attenuation rate of the line injected into the closed cut set network and the line attenuation rate of the line injected out of the closed cut set network is less than a second threshold: and (3.2.3) In response to the difference between the first closed cut set network and the second closed cut set network being smaller than the second threshold, it is determined that a fault occurs at the bus.

2. The method according to claim 1, characterized in that The closed cut set network includes a portion of a suspicious line directly connected to the suspicious measuring point, a proximal normal measuring point connected to the suspicious line, and a portion of a line connecting the proximal normal measuring point and a distal normal measuring point connected to the proximal normal measuring point.

3. The method according to claim 2, characterized in that The closed cut set network includes a portion of a suspicious line directly connected to the suspicious measuring point, a proximal normal measuring point connected to the suspicious line, and a portion of a line connecting the proximal normal measuring point and a distal normal measuring point directly connected to the proximal normal measuring point.

4. The method according to claim 2, characterized in that The transmission lines are divided into radial lines and ring lines.

5. The method according to any one of claims 1 to 4, characterized in that The voltage quantity at the measuring point is collected by a voltage transformer installed at the measuring point.

6. The method according to any one of claims 1 to 4, characterized in that In step (2), the voltage disturbance curve at different positions in the transmission line is obtained by extracting the maximum and minimum values ​​of the voltage in step (1), fitting them into an envelope curve, and adding and averaging them.

7. The method according to any one of claims 1 to 4, characterized in that In response to the difference of the first closed cut set network being greater than or equal to the second threshold and / or the difference of the second closed cut set network being greater than or equal to the second threshold, it is determined that a line in the first closed cut set network and / or a line in the second closed cut set network fails.

8. The method according to any one of claims 1 to 4, characterized in that In response to the difference value of the first closed cut set network being greater than or equal to the second threshold, it is determined that one or more lines in the first closed cut set network fail.

9. The method according to any one of claims 1 to 4, characterized in that In response to the difference value of the second closed cut set network being greater than or equal to the second threshold, it is determined that one or more lines in the second closed cut set network fail.

10. The method according to claim 1, characterized in that The line attenuation rate ρ mn for: Among them, m is the peak value of the voltage disturbance at the measuring point m on the transmission line, unit: V; du n is the peak value of the voltage disturbance at the measuring point n on the transmission line, unit: V; l mn It is the line length between the measuring point m and the measuring point n, in meters.

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