Method for selecting phase of short-circuit fault of power grid based on transient quantity

Abstract

This invention discloses a method for selecting phases in a power grid short-circuit fault based on transient quantities. The method includes: S1. Acquiring voltage and current signals at various measuring points in the power grid; S2. Processing the voltage signals at all measuring points using the Hilbert-Huang transform to obtain transient voltage curves for different measuring points; S3. Identifying the measuring point with the largest transient voltage peak based on the transient voltage curves; S4. Obtaining the transient current curve corresponding to the measuring point with the largest transient voltage peak; and S5. Determining whether the power grid is faulty based on whether the polarities of the transient current curves are the same. This invention not only effectively and accurately identifies faulty lines but also requires fewer measuring units due to the system structure, reducing investment in electrical equipment.

Description

Technical Field

[0001] This invention relates to the field of power grid fault detection, and more specifically to a method for selecting phases in a power grid short-circuit fault based on transient quantities. Background Technology

[0002] With the rapid development of the national economy and the continuous increase in social electricity demand, high-voltage transmission lines inevitably experience various faults, which seriously endanger and affect the normal operation and reliable power supply of the entire power system. Therefore, research on fault phase selection for high-voltage transmission lines is particularly important. When a short-circuit fault occurs in an overhead line or cable of the power grid system, the relay protection phase selection device can quickly and effectively identify and disconnect the faulty line, which is of great significance for ensuring the normal and stable operation of non-faulty lines.

[0003] Based on the different principles of collecting electrical quantities such as voltage and current, conventional fault phase selection algorithms include two types: real-time detection quantities and equivalent fault quantities. However, these phase selection algorithms are usually based on 50Hz power frequency steady-state quantities, requiring the acquisition of at least one cycle for fault diagnosis, which cannot meet the requirements for rapid fault clearing. Furthermore, the phase selection results are easily affected by non-periodic components, and the error range is unsatisfactory. Existing wavelet transform-based phase selection algorithms (Zhang Baohui, Ha Hengxu, et al., Research on a new principle of full-line fast-acting protection of ultra-high voltage transmission lines using single-ended transient quantities (III): Fault phase selection and problems that still need to be studied [J], Electric Power Automation Equipment, 2001, 21(8): 1-4) break the time limit, but the zero-mode components on which they rely are greatly distorted between the transmission line and the ground, and the results are often unsatisfactory. Existing technologies also utilize the traveling wave principle to identify faulty phases (Chamia C, Liberman S. Ultra High Speed ​​Relay For EHV / UHV Transmission Lines-Development, Design and Application[J].IEEE Trans on PAS,1978,97(6):2104-2112), but due to the influence of electromagnetic coupling, fault detection components for normal phases may malfunction.

[0004] Therefore, there is currently a lack of a phase selection method in this field that can avoid interference, be simple, fast, and accurate in identifying faulty lines. Summary of the Invention

[0005] The purpose of this invention is to provide a method for selecting the phase of a power grid short-circuit fault based on transient quantities. This invention utilizes the peak value of transient voltage and the polarity of transient current to determine the power grid short-circuit fault. This method provides rapid phase selection, eliminates interference from system operating mode, line parameters, and transition resistance, and not only effectively and accurately identifies the faulty line, but also requires fewer measurement units based on the system structure, reducing investment in electrical equipment.

[0006] This invention provides a method for selecting phases in a power grid short-circuit fault based on transient quantities, the method comprising:

[0007] S1. Collect voltage and current signals at various measuring points in the power grid;

[0008] S2. Use the Hilbert-Huang transform to process the voltage signals at all measuring points to obtain transient voltage curves at different measuring points;

[0009] S3. Based on the transient voltage curve of the measuring point, find the measuring point with the largest transient voltage peak;

[0010] S4. Obtain the transient current curve corresponding to the measurement point with the largest transient voltage peak; and

[0011] S5. Determine whether the power grid is faulty based on whether the polarities of the transient current curves are the same.

[0012] In another preferred embodiment, the transient current curve corresponding to the measurement point with the largest transient voltage peak is obtained by processing the current signal of the measurement point with the largest transient voltage peak using the Hilbert-Huang transform.

[0013] In another preferred embodiment, the voltage and current signals of all measuring points can be processed using the Hilbert-Huang transform in S2 to obtain transient voltage curves and transient current curves for different measuring points; thus, the transient current curve corresponding to the measuring point with the largest transient voltage peak can be directly extracted in S4.

[0014] In another preferred embodiment, the measuring point is set on the line used to connect the various busbars.

[0015] In another preferred embodiment, each of the lines used to connect the busbars has two ends.

[0016] In another preferred embodiment, the measuring points are located at both ends of the line, wherein one end is the opposite end of the other.

[0017] In another preferred embodiment, the transient voltage curve is a fluctuating curve, indicating that the fault is a short-circuit fault.

[0018] In another preferred embodiment, for a ring network, S5 includes: if the polarity of the transient current curve at the first measuring point is different from the polarity of the transient current curves at other measuring points, then the short-circuit fault occurs on the line where the first measuring point is located.

[0019] In another preferred embodiment, for a ring network, S5 includes: if the polarity of the transient current curves corresponding to the measurement points with the largest transient voltage peaks is the same, then the circuits at each measurement point are normal.

[0020] In another preferred embodiment, for a ring network, S5 includes: if the polarity of the transient current curves corresponding to the measurement point with the largest transient voltage peak is the same, then a short-circuit fault occurs on the bus.

[0021] In another preferred embodiment, for a linear network, S4 includes: obtaining the transient current curve of the measuring point opposite to the line where the measuring point with the largest transient voltage peak is located.

[0022] In another preferred embodiment, for a linear network, S5 includes: if the polarity of the transient current curves of the measuring point with the largest transient voltage peak and the measuring point at the opposite end of the line where the measuring point with the largest transient voltage peak is located is the same, then a short circuit fault occurs in that section of the line.

[0023] In another preferred embodiment, for a linear network, S5 includes: if the polarity of the transient current curves of the measuring point with the largest transient voltage peak and the measuring point at the opposite end of the line where the measuring point with the largest transient voltage peak is located is opposite, then the line segment is normal.

[0024] In another preferred embodiment, for a linear network, S5 includes: if the polarity of the transient current curves of the measuring point with the largest transient voltage peak and the measuring point at the opposite end of the line where the measuring point with the largest transient voltage peak is located is opposite, then a short-circuit fault occurs on the bus.

[0025] In another preferred embodiment, the measuring point is located between the circuit breaker and the busbar.

[0026] In another preferred embodiment, the measuring point is more than 2m away from the circuit breaker.

[0027] In another preferred embodiment, the polarity of the transient current curve is determined by the value of di(t). If the value of di(t) is greater than 0 during the time period, the polarity is positive; if the value of di(t) is less than 0 during the time period, the polarity is negative.

[0028] In another preferred embodiment, when there are multiple short-circuit faults in the power grid, the first short-circuit fault is first identified according to the above method, and then the first short-circuit fault is repaired and overcome; then the second short-circuit fault is identified according to the above method, and then the second short-circuit fault is repaired and overcome; this process is repeated until the entire power grid is operating normally.

[0029] It should be understood that, within the scope of this invention, the above-described technical features of this invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be described in detail here. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 It is a power network diagram of the power generation, transmission and transformation system;

[0032] Figure 2 It is an equivalent circuit diagram;

[0033] Figure 3 This is a fault diagram of a ring network multi-machine infinite bus system power generation, transmission and transformation system;

[0034] Figure 4 This is a schematic diagram of a fault in a straight line.

[0035] Figure 5 This is a transient voltage curve of a measuring point in an example of the present invention;

[0036] Figure 6 This is another graph of the transient voltage at the measuring point in one embodiment of the present invention;

[0037] Figure 7 This is a transient current curve of a measuring point in an example of the present invention;

[0038] Figure 8 This is another graph of the transient current at the measuring point in one embodiment of the present invention;

[0039] Figure 9 This is another graph of the transient current at the measuring point in one embodiment of the present invention. Detailed Implementation

[0040] Through extensive and in-depth research and screening, the inventors have developed for the first time a method for phase selection in power grid short-circuit faults based on transient quantities. This invention utilizes the transient components generated at the fault point during a short-circuit fault to identify and select the phase in a power system network. This method achieves accurate phase selection using only the transient voltage peak value and current polarity, is simple to operate, and easy to implement. It provides rapid phase selection and eliminates interference from system operating modes, line parameters, and transition resistance. This method not only accurately identifies faulty lines but also requires fewer measurement units based on the actual system structure, reducing investment in electrical equipment. This invention was completed based on these findings.

[0041] Fault phase selection is a crucial step in fault diagnosis of power grid transmission lines. Accurately identifying the faulty phase effectively ensures the correct operation of circuit breaker reclosing and increases the reliability of the power grid system. The transient quantity-based power grid short-circuit fault phase selection method of this invention not only effectively and accurately identifies the faulty line but also requires fewer measurement units due to the system structure, reducing investment in electrical equipment.

[0042] 1. Instantaneous Characteristics Analysis of Transmission Line Short Circuit Fault

[0043] When a short-circuit fault occurs in a large-scale power grid, the transient components at the fault point contain rich information, providing an ideal information source for line fault diagnosis. For example... Figure 1 The power network diagram of the power generation, transmission and transformation system shown indicates that buses M1, M2, and M3 in the high-voltage distribution unit are all connected by transmission lines. At time t = 0s, a three-phase short-circuit fault occurs on the line between buses M2 and M3.

[0044] After a short-circuit fault in a transmission line, it is equivalent to superimposing a fault voltage source at the fault point in the non-faulty state. This superimposed fault voltage source is opposite in direction and equal in magnitude to the original voltage at that point in the non-faulty state. If the effects of the line-to-ground capacitance current and the transition resistance at the fault point are disregarded, the equivalent circuit diagram is as follows: Figure 2 As shown.

[0045] Assume the voltage expression at the short-circuit point under normal operating conditions at t=0s is:

[0046] u(t) = -U m sin(ωt+α) (1)

[0047] Write the total differential equation for the left loop, as shown in equation (2).

[0048]

[0049] The solution to equation (2) is

[0050]

[0051] in

[0052]

[0053]

[0054]

[0055] As can be seen from equation (3), during a short-circuit fault, the current in the inductive devices of the power grid system cannot change abruptly, and the transient component contains abundant attenuated DC components. If the generator is not considered as an ideal voltage source, the fault voltage source network will also generate second harmonic components and harmonic components.

[0056] 2. Characteristics and extraction methods of transient components during faults

[0057] In large-scale power grids, transmission line faults have a significant impact on the entire grid. Line aging, tower equipment failure, and lightning strikes can all cause short-circuit faults. This invention addresses the problem of identifying short-circuit faults from complex and varied power grid disturbances, distinguishing them from other disturbances. Based on the theoretical analysis above, the transient components during a short-circuit fault exhibit the following three characteristics: the voltage of the faulty phase in the line decreases, while the phase current increases; the attenuated DC component accounts for the largest proportion of the extracted transient quantities; and the peak value of the transient voltage extracted from a measuring point connected to the faulty line is the largest. Based on these characteristics, if the transient voltage curve is a fluctuating curve, it indicates a short-circuit fault.

[0058] This invention extracts transient components by interpolating and fitting envelopes based on the Hilbert-Huang transform. The specific method is as follows: 1) Assuming n measuring points are installed in the power grid, when a short-circuit fault occurs in the transmission line, the maximum and minimum values ​​of voltage and current at different measuring points and their corresponding times are extracted and uploaded to the power grid dispatch center; 2) At the dispatch center, the local maxima and minima of the uploaded data are interpolated using the interpolation function of numerical analysis theory to fit upper and lower envelope curves; 3) The two envelope curves are added together and divided by 2 to obtain the transient voltage and current component curves of each measuring point.

[0059] 3. Theories of Fault Phase Selection

[0060] In order to utilize the transient quantities extracted above to achieve fault phase selection in transmission lines, this invention defines the voltage difference k as the line L mn The difference in transient voltage at both measuring points du m -du n The expression is shown in equation (4).

[0061] k = du m -du n (4)

[0062] As can be seen from equation (4), the voltage difference k depends only on the current flowing through the line and the line impedance. When k>0, the current flows from node M to node N; when k<0, the current flows from node N to M. Conversely, the same holds true.

[0063] The above analysis shows that when a short-circuit fault occurs in the power grid, the transient quantity generated at the fault point will cause varying degrees of distortion in the voltage and current at different locations. This is because in the fault component network, only one power source acts at the fault point, resulting in the highest peak value of the transient voltage at that point.

[0064] The following example illustrates a multi-machine infinite bus system containing a polygonal ring network, demonstrating a specific method for implementing fault phase selection. Figure 3 As shown in the system diagram. Figure 3 In this system, G1 and G2 are two generator systems, and M1-M6 are busbars. The busbars are connected by lines. Twelve current transformers (C1-C12) are connected in series on the incoming and outgoing lines on both sides of the busbars. The direction of the current, from the busbar to the line, is defined as the positive direction. Assume a short-circuit fault occurs on transmission line L. 23 At a certain location.

[0065] Extract the transient voltage and current curves of each measuring point, and calculate the voltage difference k between the measuring points using formula (4). The peak value of the transient voltage curve extracted from measuring point C3 (or C2, C7) is the largest. We can analyze that the line L 31 L 23 and L 3n This is a possible faulty circuit. The calculated voltage difference satisfies k. 31 >0, k 3n >0 indicates that line L 31 Current di 31 The line flows from M3 through M1, line L 3n Shangdi 3n Current flows from M3 through M n Due to line L 23 A short circuit fault occurred, therefore the faulty line L 23 Left side upper current di f3 The current flows through M3 from the fault point. Equation (5) can be obtained from Kirchhoff's Current Law (KCL) in circuit theory.

[0066] di f3 =-(di 31 +di 3n (5)

[0067] Analysis of equation (5) shows that the polarity of the transient current curve extracted at measuring point C3 is opposite to that of the curves at measuring points C2 and C7. Therefore, it can be determined that the high-voltage transmission line L 23It is a faulty line. Therefore, we can derive a method for identifying faulty phases in transmission lines using transient quantities: In the case of a loop fault, the line containing the measurement point with the maximum peak transient voltage is a possible faulty line. Among all the detected measurement points with the maximum peak transient voltage, the line containing the measurement point where the polarity of the transient current changes is the faulty line. Similarly, if the curves of measurement points C2, C3, and C7 have the same polarity, then a short-circuit fault has occurred on bus M2.

[0068] Taking a straight line as an example, the specific method for fault phase selection is as follows: When a straight line is faulty, the line where the peak value of the transient voltage is located is the possible faulty line. Among all the detected peak values ​​of the transient voltage, the polarity of the transient current and the current on the opposite side of the line is extracted. The current polarity on the two opposite sides of the faulty line is the same, while the current polarity on the opposite side of the non-faulty line is opposite.

[0069] like Figure 4 As shown, assume the short-circuit fault occurs on transmission line L. cd At a certain location, extract the transient voltage and current curves of each measuring point, and use formula (4) to calculate the voltage difference k between the measuring points. Assuming that the peak value of the transient voltage curve extracted from measuring point C2 (or C3) is the largest, we can analyze that the line L bc and L cd This is a potentially faulty line. The current polarity at measuring point C2 (or C3) and the measuring point C1 (or C4) on the opposite side of the comparison line is the same for C3 and C4, while the current polarity for C2 and C1 is opposite. Therefore, it can be determined that the high-voltage transmission line L... cd It's a faulty circuit.

[0070] The main advantages of this invention include:

[0071] This invention uses the peak value of transient voltage and the polarity of transient current to determine short-circuit faults in the power grid. This method selects the phase quickly and eliminates the interference of system operating mode, line parameters and transition resistance on the results. It not only effectively and accurately identifies the faulty line, but also requires fewer measuring units to be installed according to the system structure, thus reducing investment in electrical equipment.

[0072] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, the accompanying drawings are schematic diagrams, and therefore the apparatus and device of the present invention are not limited to the size or scale of the schematic diagrams.

[0073] It should be noted that in the claims and specification of this patent, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0074] Example

[0075] After a transmission line fault, its transient quantities contain a large amount of fault information, and the fault phase selection element extracts this information and performs effective identification. This embodiment provides a method for selecting phases for power grid short-circuit faults based on transient quantities.

[0076] Since most high-voltage power transmission lines are arranged in a ring network, this embodiment analyzes transmission line fault selection based on a polygonal ring network. This method draws on the basic idea of ​​equivalent fault quantities, requiring only the detection of the peak value of transient voltage and the polarity of current to determine the faulty line. Similink simulation software results demonstrate the high feasibility of this method.

[0077] Referring to the power supply diagram shown in Figure 3, a simulation model was built using Simulink. Transmission lines were selected with identical parameter models, and the lengths of each transmission line are shown in Table 1. At t = 0s, the high-voltage transmission line L... 23 A three-phase short-circuit fault occurred 80km from the M2 end of the ring network node bus.

[0078] Table 1. Length of each transmission line (km)

[0079]

[0080] The voltage and current signals at all measuring points were processed using the Hilbert-Huang transform to obtain transient voltage and current curves at different measuring points, such as... Figures 5-9 As shown. Since the transient voltage curves at some measuring points are the same, this paper only lists some of the curves.

[0081] pass Figure 5 and Figure 6 As can be seen from the transient voltage curve, the peak value of the transient voltage line at measuring point C3 (or C2, C7) is the largest. Theoretical analysis shows that line L...31 L 23 and L 3n This is a possible faulty circuit. And because it passes through... Figure 7 , Figure 8 and Figure 9 From the transient current curves at measuring points C2 and C7, we can see that the polarity of the transient current curves at measuring point C3 is the same, while the polarity of the transient current curve at measuring point C3 is different from that at measuring points C2 and C7. Therefore, we can determine that the transmission line L... 23 It is a faulty line. Furthermore, the polarity of the transient current curve extracted from measuring point C4 differs from that of the curves from measuring points C5 and C9. The current polarity relationship at bus node M4 can also be used to determine the transmission line L. 23 It is a faulty line. Therefore, this method can identify short-circuit faults in loop lines with relatively high accuracy.

[0082] This embodiment presents a novel method for short-circuit fault identification and phase selection in power system ring networks, utilizing the transient components generated at the fault point during a short-circuit fault. This method achieves accurate phase selection using only the transient voltage peak value and current polarity, is simple to operate and easy to implement, and provides rapid phase selection, eliminating interference from system operating conditions, line parameters, and transition resistance. Simulation results show that this method not only accurately identifies the faulty line but also requires fewer measurement units based on the actual system structure, reducing investment in electrical equipment.

[0083] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing teachings of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for selecting phases in a power grid short-circuit fault based on transient quantities, characterized in that, The method includes: S1. Collect voltage and current signals at various measuring points in the power grid; S2. Use the Hilbert-Huang transform to process the voltage signals at all measuring points to obtain transient voltage curves at different measuring points; S3. Based on the transient voltage curve of the measuring point, find the measuring point with the largest transient voltage peak; S4. Obtain the transient current curve corresponding to the measurement point with the largest transient voltage peak; and S5. Determine whether the power grid is faulty based on whether the polarities of the transient current curves are the same.

2. The method as described in claim 1, characterized in that, For a ring network, S5 includes: if the polarity of the transient current curve at the first measuring point is different from the polarity of the transient current curves at other measuring points, then the short-circuit fault occurs on the line where the first measuring point is located.

3. The method as described in claim 1, characterized in that, For a ring network, S5 includes: if the polarity of the transient current curves corresponding to the measurement points with the largest transient voltage peaks is the same, then the circuits at each measurement point are normal.

4. The method as described in claim 1, characterized in that, For a ring network, S5 includes: if the polarity of the transient current curves corresponding to the measurement point with the largest transient voltage peak is the same, then a short-circuit fault occurs on the bus.

5. The method as described in claim 1, characterized in that, For a linear network, S4 includes: obtaining the transient current curve of the measuring point at the end of the line opposite to the measuring point where the transient voltage peak is largest.

6. The method as described in claim 4, characterized in that, For a linear network, S5 includes: if the polarity of the transient current curves of the measuring point with the largest transient voltage peak and the measuring point at the opposite end of the line where the measuring point with the largest transient voltage peak is located is the same, then a short circuit fault occurs in that section of the line.

7. The method as described in claim 4, characterized in that, For a linear network, S5 includes: if the polarity of the transient current curves of the measuring point with the largest transient voltage peak and the measuring point at the opposite end of the line where the measuring point with the largest transient voltage peak is located is opposite, then the line segment is normal.

8. The method as described in claim 4, characterized in that, For a linear network, S5 includes: if the polarity of the transient current curves of the measuring point with the largest transient voltage peak and the measuring point at the opposite end of the line where the measuring point with the largest transient voltage peak is located is opposite, then a short-circuit fault occurs on the bus.

9. The method according to any one of claims 1-8, characterized in that, The measuring points are set at both ends of a section of the line.

10. The method according to any one of claims 1-8, characterized in that, The polarity of the transient current curve is determined by the value of di(t). If the value of di(t) is greater than 0 during the time period, the polarity is positive; if the value of di(t) is less than 0 during the time period, the polarity is negative.

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