Neutral line breakage detection positioning method and system based on third harmonic energy characteristics

Abstract

The invention discloses a neutral line breakage detection and positioning method and system based on third harmonic energy characteristics, and the method comprises the steps: firstly, extracting the current and voltage of a load, calculating the third harmonic component through Fourier decomposition, obtaining the third harmonic energy through calculation, sequentially calculating the third harmonic energy ratio of two adjacent regions, and calculating the third harmonic energy ratio of the two adjacent regions; and comparing the calculated third harmonic energy ratio of each position with a set threshold value, and judging whether a neutral line breaking fault occurs or not and judging a line breaking position according to a result. According to the method, the neutral line breakage fault can be correctly distinguished and positioned, and the neutral line breakage detection capability is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of power systems, relates to the field of neutral line protection, and particularly relates to a neutral line break detection and positioning method based on third harmonic energy characteristics. Background Art

[0002] Low-voltage distribution systems are a crucial component of the power system, primarily utilizing a three-phase, four-wire system. They are widely used in residential, commercial, and light industrial applications. Low-voltage distribution systems typically consist of transformers, distribution lines, distribution boxes, and electrical equipment. Their core function is to reduce the voltage of high-voltage electricity through transformers and transmit it to various users at low voltage. In a three-phase, four-wire system, the neutral conductor is an essential component. Together with the three-phase conductors, it forms the power supply network and is primarily responsible for balancing load voltages. When the system load is unbalanced, the neutral conductor ensures symmetry between the three-phase voltages, ensuring the proper operation of the loads on each phase. Thus, the neutral conductor plays a critical role in maintaining system stability and voltage balance. However, neutral conductor disconnection is a common occurrence in low-voltage distribution systems, particularly in rural and remote areas where load imbalance is common. A broken neutral conductor can cause a shift in the system neutral point potential, leading to overvoltage in lightly loaded phases and undervoltage in heavily loaded phases. These issues pose a threat to electrical equipment and, in severe cases, can even cause fires and personal injury. The hazards of a disconnected neutral line make the detection of this fault of great significance. Existing neutral line disconnection detection methods mainly include two categories: no-signal injection type and small-signal injection type. The no-signal injection type method is usually based on the monitoring of voltage, zero-sequence current and harmonics, and determines whether the neutral line is disconnected by analyzing parameters such as neutral point potential and three-phase harmonic changes. However, when the three-phase load of the system is relatively balanced, the changes in these parameters are small, and the detection accuracy is limited. The small-signal injection type method injects DC or small signals and uses the changes in the circuit under different disconnection conditions to locate the fault point, but this method has challenges in equipment cost and implementation complexity.

[0003] In summary, with the growth of electricity demand and the increase in asymmetric loads, detecting neutral conductor breaks in low-voltage distribution systems has become a critical issue for ensuring safe operation of the power system and protecting user property. Researching and developing more accurate and rapid neutral conductor break detection technologies is crucial for improving the reliability of distribution systems. Summary of the Invention

[0004] The purpose of the present invention is to provide a neutral line break detection and positioning method and system based on the third harmonic energy characteristics to overcome the defects of the existing technology. The present invention can correctly distinguish between normal operation, neutral line break and other working conditions.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for detecting and locating a neutral line break based on third harmonic energy characteristics comprises the following steps: Step 1: Divide the monitoring area into several independent areas; Step 2: Measure the voltage relative to the neutral line of the phase A load in each area and the current flowing through the phase A load, extract the third-order components of the voltage and current through Fourier decomposition, and further calculate the third-order harmonic energy; Step 3: Based on the calculated third harmonic energy of the A-phase load in each area, the third harmonic energy ratio kb of the A-phase load in two adjacent areas is compared in sequence; Step 4: Set the setting value K1. When the third harmonic energy ratio kb of the A-phase load in two adjacent areas satisfies kb ≥ K1, it is determined that a neutral line break fault has occurred and occurred between the two areas.

[0006] Furthermore, the monitoring area is divided into several independent areas, specifically: The area behind each feeder in the monitoring area is treated as an independent area.

[0007] Furthermore, assuming that a line break occurs in region i in step 2, the process of calculating the third harmonic energy of the phase A load in the adjacent region after the line break is as follows: Measure the voltage of the phase A load relative to the neutral line in area i and the current flowing through the phase A load. The voltage and current cubic components obtained by Fourier decomposition are: U i3 and I i3 ; The third harmonic energy of the phase A load in the area before the disconnection location: ; The third harmonic energy of the phase A load in the area after the disconnection location: ; Among them, i means belonging to the i-th region, R i is the resistance portion of the phase A load in the measured region i; n 1 is the ratio of the measured impedance of phase A in region i to the equivalent impedance of the neutral line; k i is the ratio of the measured A-phase load impedance in region i to the load impedance in other regions; I i is the equivalent third harmonic current emitted by the load, θ i3 is the tertiary voltage U i3 and current I i3 Angle.

[0008] Furthermore, in step 3, assuming that the adjacent areas are a and b, the ratio of the third harmonic energy of the A-phase load in the adjacent areas a and b is specifically: The ratio of the third harmonic energy of the A-phase load in adjacent areas a and b is:

[0009] Among them, Z i is the equivalent load impedance value of phase A in region i, Z L is the equivalent impedance on the neutral line, Z a 、Z b are the equivalent load impedance values of phase A in regions a and b, respectively, R a 、R b are the resistance values of the equivalent load of phase A in regions a and b, respectively, P a 、P b are the third harmonic energy of the equivalent load of phase A in regions a and b respectively, n is the total number of equivalent loads, and k is the value if a line break occurs after the kth region.

[0010] Furthermore, in step 4, the setting value K1 is set to 4.

[0011] Furthermore, the setting method of the set value K1 is as follows: By default, the equivalent load impedance angle of each area is the same, and the generated third harmonic is positively correlated with the equivalent load impedance value of the area. Therefore, the ratio of the third harmonic energy of the A phase load of adjacent areas a and b is:

[0012] Where x means the equivalent load impedance is x times the line impedance, a i,j is the ratio of the equivalent load impedance values of the i-th region and the j-th region; In addition, the equivalent load impedance values of each area are at most 2 times, so the minimum ratio of the third harmonic energy of the A-phase load of adjacent areas a and b is:

[0013] Under normal circumstances and when a line break occurs but the selected area is not the area before or after the line break, the third harmonic energy ratio is:

[0014] Therefore, the setting value K1 is set to 4.

[0015] A neutral line break detection and positioning system based on third harmonic energy characteristics, comprising: Area division module: used to divide the monitoring area into several independent areas; The first calculation module is used to measure the voltage relative to the neutral line of the A-phase load in each area and the current flowing through the A-phase load, and extract the third-order components of the voltage and current through Fourier decomposition, and further calculate the third-order harmonic energy; The second calculation module is used to compare the third harmonic energy ratio kb of the A-phase loads in two adjacent areas according to the calculated third harmonic energy of the A-phase load in each area; Judgment module: used to set the setting value K1. When the third harmonic energy ratio kb of the A-phase load in two adjacent areas meets kb ≥ K1, it is determined that a neutral line break fault occurs and occurs between the two areas.

[0016] Furthermore, the set value K1 is set to 4.

[0017] A computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of a method for detecting and locating a neutral line break based on third harmonic energy characteristics are implemented.

[0018] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a neutral line break detection and positioning method based on third harmonic energy characteristics.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects: The method of the present invention extracts current and voltage information from phase A of the load, obtains the third harmonic component through Fourier decomposition, and further calculates the third harmonic energy. This determination method utilizes the fact that when the neutral line is operating normally, the harmonics generated by each three-phase load flows into the ground through the neutral line. However, when the neutral line is broken, the loads after the break lose the function of the neutral line, and the generated harmonics can only flow between loads. The third harmonic energy in the area before and after the break is different. Therefore, this method can effectively identify neutral line breaks and can identify and locate faults when the load imbalance is very low, effectively improving protection performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings in the specification are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0021] Figure 1 This is the PSCAD simulation system diagram; Figure 2 The figure is a logic block diagram of the neutral line break detection and positioning method based on the third harmonic energy characteristics. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0023] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0024] Example 1 A method for detecting and locating a neutral line break based on third harmonic energy characteristics comprises the following steps: Step 1: Divide the monitoring area into n independent areas; Step 2: Measure the voltage relative to the neutral line of the phase A load in each area and the current flowing through the phase A load, extract the third-order components of the voltage and current through Fourier decomposition, and further calculate the third-order harmonic energy; Step 3: Based on the calculated third harmonic energy of the A-phase load in each area, the third harmonic energy ratio kb of the A-phase load in two adjacent areas is compared in sequence; Step 4: Set the setting value K1. When the third harmonic energy ratio kb of the A-phase load in two adjacent areas satisfies kb ≥ K1, it is determined that a neutral line break fault has occurred and occurred between the two areas.

[0025] Example 2 like Figure 2 As shown, the present invention is a neutral line break detection and positioning method based on third harmonic energy characteristics, comprising the following steps: Step 1: Divide the monitoring area into n independent areas. Specifically, the area behind each feeder in the monitoring area is regarded as an independent area. Step 2: Measure the voltage relative to the neutral line of the phase A load in each area and the current flowing through the load. Extract the third-order components of the voltage and current through Fourier decomposition, and further calculate the energy of the third harmonic. Assuming that area i has a line break, the process of calculating the third-order harmonic energy of the phase A load in the adjacent area after the line break is as follows: Measure the voltage of the phase A load relative to the neutral line in area i and the current flowing through the phase A load. The voltage and current cubic components obtained by Fourier decomposition are: U i3 and I i3 ; The third harmonic energy of the phase A load in the area before the disconnection location:

[0026] The third harmonic energy of the phase A load in the area after the disconnection location:

[0027] Among them, i means belonging to the i-th region, R i is the resistance portion of the phase A load in the measured region i; n 1 is the ratio of the measured impedance of phase A in region i to the equivalent impedance of the neutral line; k i is the ratio of the measured A-phase load impedance in region i to the load impedance in other regions; I i is the equivalent third harmonic current emitted by the load, θ i3 is the tertiary voltage U i3 and current I i3 Angle.

[0028] Step 3: Based on the calculated third harmonic energy of the A-phase load in each area, the third harmonic energy ratio kb of the A-phase load in two adjacent areas is compared in turn. The ratio of the third harmonic energy of the A-phase load in adjacent areas a and b is specifically: The ratio of the third harmonic energy of the A-phase load in adjacent areas a and b is:

[0029] Among them, Z i is the equivalent load impedance value of phase A in region i, Z L is the equivalent impedance on the neutral line, Z a 、Z b are the equivalent load impedance values of phase A in regions a and b, respectively, R a 、R b are the resistance values of the equivalent load of phase A in regions a and b, respectively, P a 、P b are the third harmonic energy of the equivalent load of phase A in regions a and b respectively, n is the total number of equivalent loads, and k is the value if a line break occurs after the kth region.

[0030] Step 4: Set the setting value K1 to 4. When the third harmonic energy ratio kb of the A-phase load in two adjacent areas satisfies kb ≥ K1, it is considered that a neutral line break fault has occurred and occurred between the two areas.

[0031] Since users' electricity usage habits are basically the same, it can be assumed that the equivalent load impedance angle of each area is the same. The generated third harmonic and the load impedance value are positively correlated. Therefore, the ratio of the third harmonic energy of the A-phase load in adjacent areas a and b is:

[0032] Where x means the equivalent load impedance is x times the line impedance, a i,j is the ratio of the equivalent load impedance values of the i-th region to the j-th region.

[0033] The equivalent load impedance values of each area are not much different, and the difference is at most 2 times. Therefore, the minimum ratio of the third harmonic energy of the A phase load of adjacent areas a and b is:

[0034] Generally speaking, x can reach dozens or even hundreds. Under normal circumstances and when a line break occurs but the selected area is not the area before or after the line break, the third harmonic energy ratio is:

[0035] Therefore, the setting value K1 is set to 4.

[0036] Example 3 The protection scheme of the present invention is explained in the PSCAD simulation environment. A low-voltage power distribution system is established in PSCAD. The simulation schematic diagram is shown in FIG. Figure 1 F1 to F4 represent different line fault points, G1 is a 10kV equivalent power source, T1 is a 10kV / 380V transformer, Zline i is the line impedance of area i, Zload i is the equivalent load of area i, Z L is the equivalent impedance of the line. The main model parameters are as follows: line positive-sequence resistance: 0.022 Ω / km; line positive-sequence reactance: 0.001889 Ω / km; line positive-sequence capacitive reactance: 0.25477 MΩ / m; line zero-sequence resistance: 0.341 Ω / km; line zero-sequence reactance: 0.002434102 Ω / km; line zero-sequence capacitive reactance: 1.098177 MΩ / m. The distance between loads is 1 km, with the first load 1 km from the transformer. The power factor of all loads is 0.9. Table 1 shows the impedance parameters of the loads in each area.

[0037] Table 1

[0038] Table 2

[0039] Table 3

[0040] Table 4

[0041] The simulation results are shown in Tables 2 through 4. F1 through F4 represent the third harmonic energy ratios of the A-phase loads in two adjacent areas when a line break occurs at k1 through k4, respectively. Table 2 shows the simulation results for load parameters in case 1; Table 3 shows the simulation results for load parameters in case 2; and Table 4 shows the simulation results for load parameters in case 3. It can be seen that under these three parameter sets, regardless of the line break location, only the third harmonic energy ratio of the loads in the areas to the left and right of the line break exceeds the set value K1. Under normal circumstances and when no line break occurs, the third harmonic energy ratio of the loads in the areas to the left and right of the line break does not exceed the threshold. Using this neutral line break fault detection scheme, the occurrence of a neutral line break can be reliably identified and its location determined, paving the way for subsequent protection and maintenance.

[0042] Example 4 A neutral line break detection and positioning system based on third harmonic energy characteristics, comprising: Region division module: used to divide the monitoring area into n independent areas. Specifically, the area behind each feeder in the monitoring area is regarded as an independent area. The first calculation module is used to measure the voltage relative to the neutral line of the phase A load in each area and the current flowing through the phase A load, extract the third-order components of the voltage and current through Fourier decomposition, and further calculate the third-order harmonic energy. Assuming that area i has a line break, the process of calculating the third-order harmonic energy of the phase A load in the adjacent area after the line break is as follows: Measure the voltage of the phase A load relative to the neutral line in area i and the current flowing through the phase A load. The voltage and current cubic components obtained by Fourier decomposition are: U i3 and I i3 ; The third harmonic energy of the phase A load in the area before the disconnection location:

[0043] The third harmonic energy of the phase A load in the area after the disconnection location:

[0044] Among them, i means belonging to the i-th region, R iis the resistance portion of the phase A load in the measured region i; n 1 is the ratio of the measured impedance of phase A in region i to the equivalent impedance of the neutral line; k i is the ratio of the measured A-phase load impedance in region i to the load impedance in other regions; I i is the equivalent third harmonic current emitted by the load, θ i3 is the tertiary voltage U i3 and current I i3 Angle.

[0045] The second calculation module is used to compare the third harmonic energy ratio kb of the A-phase loads of two adjacent areas based on the calculated third harmonic energy of the A-phase loads in each area. The ratio of the third harmonic energy of the A-phase loads of adjacent areas a and b is specifically: The ratio of the third harmonic energy of the A-phase load in adjacent areas a and b is:

[0046] Among them, Z i is the equivalent load impedance value of phase A in region i, Z L is the equivalent impedance on the neutral line, Z a , Z b are the equivalent load impedance values of phase A in regions a and b, respectively, R a 、R b are the resistance values of the equivalent load of phase A in regions a and b, respectively, P a 、P b are the third harmonic energy of the equivalent load of phase A in regions a and b respectively, n is the total number of equivalent loads, and k is the value if a line break occurs after the kth region.

[0047] Judgment module: used to set the setting value K1=4. When the third harmonic energy ratio kb of the A-phase load in two adjacent areas meets kb ≥ K1, it is determined that a neutral line break fault has occurred and occurred between the two areas.

[0048] Since users' electricity usage habits are basically the same, it can be assumed that the equivalent load impedance angle of each area is the same. The generated third harmonic and the load impedance value are positively correlated. Therefore, the ratio of the third harmonic energy of the A-phase load in adjacent areas a and b is:

[0049] Where x means the equivalent load impedance is x times the line impedance, a i,j is the ratio of the equivalent load impedance values of the i-th region to the j-th region.

[0050] The equivalent load impedance values of each area are not much different, and the difference is at most 2 times. Therefore, the minimum ratio of the third harmonic energy of the A phase load of adjacent areas a and b is:

[0051] Generally speaking, x can reach dozens or even hundreds. Under normal circumstances and when a line break occurs but the selected area is not the area before or after the line break, the third harmonic energy ratio is:

[0052] Therefore, the setting value K1 is set to 4.

[0053] Example 5 A computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of a method for detecting and locating a neutral line break based on third harmonic energy characteristics are implemented.

[0054] Example 6 A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a neutral line break detection and positioning method based on third harmonic energy characteristics.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit its scope of protection. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that after reading the present invention, those skilled in the art may still make various changes, modifications or equivalent substitutions to the specific implementation methods of the invention, but these changes, modifications or equivalent substitutions are all within the scope of protection of the pending claims of the invention.

Claims

1. A neutral line break detection and positioning method based on third harmonic energy characteristics, characterized in that: The steps include: Step 1: Divide the monitoring area into several independent areas; Step 2: Measure the voltage relative to the neutral line of the phase A load in each area and the current flowing through the phase A load, extract the third-order components of the voltage and current through Fourier decomposition, and further calculate the third-order harmonic energy; Step 3: Based on the calculated third harmonic energy of the A-phase load in each area, the third harmonic energy ratio kb of the A-phase load in two adjacent areas is compared in sequence; Step 4: Set the setting value K1. When the third harmonic energy ratio kb of the A-phase load in two adjacent areas satisfies kb ≥ K1, it is determined that a neutral line break fault has occurred and occurred between the two areas.

2. A neutral line break detection and positioning method based on third harmonic energy characteristics according to claim 1, characterized in that: The monitoring area is divided into several independent areas, specifically: The area behind each feeder in the monitoring area is treated as an independent area.

3. The method for detecting and locating a neutral line break based on third harmonic energy characteristics according to claim 1, characterized in that: In step 2, it is assumed that a line break occurs in area i. The process of calculating the third harmonic energy of the load on phase A in the adjacent area after the line break is as follows: Measure the voltage of the phase A load relative to the neutral line in area i and the current flowing through the phase A load. The voltage and current cubic components obtained by Fourier decomposition are: U i3 and I i3 ; The third harmonic energy of the phase A load in the area before the disconnection location: ; The third harmonic energy of the phase A load in the area after the disconnection location: ; Among them, i means belonging to the i-th region, R i is the resistance portion of the phase A load in the measured region i; n 1 is the ratio of the measured impedance of phase A in region i to the equivalent impedance of the neutral line; k i is the ratio of the measured A-phase load impedance in region i to the load impedance in other regions; I i is the equivalent third harmonic current emitted by the load, θ i3 is the tertiary voltage U i3 and current I i3 Angle.

4. The method for detecting and locating a neutral line break based on third harmonic energy characteristics according to claim 3, characterized in that: In step 3, let the adjacent areas be a and b. Then the ratio of the third harmonic energy of the A-phase load in the adjacent areas a and b is specifically: The ratio of the third harmonic energy of the A-phase load in adjacent areas a and b is: Among them, Z i is the equivalent load impedance value of phase A in region i, Z L is the equivalent impedance on the neutral line, Z a , Z b are the equivalent load impedance values of phase A in regions a and b, respectively, R a 、R b are the resistance values of the equivalent load of phase A in regions a and b, respectively, P a 、P b are the third harmonic energy of the equivalent load of phase A in regions a and b respectively, n is the total number of equivalent loads, and k is the value if a line break occurs after the kth region.

5. The method for detecting and locating a neutral line break based on third harmonic energy characteristics according to claim 4, characterized in that: In step 4, the setting value K1 is set to 4.

6. A neutral line break detection and positioning method based on third harmonic energy characteristics according to claim 5, characterized in that: The setting method of the set value K1 is as follows: By default, the equivalent load impedance angle of each area is the same, and the generated third harmonic is positively correlated with the equivalent load impedance value of the area. Therefore, the ratio of the third harmonic energy of the A phase load of adjacent areas a and b is: Where x means the equivalent load impedance is x times the line impedance, a i,j is the ratio of the equivalent load impedance values of the i-th region and the j-th region; In addition, the equivalent load impedance values of each area are at most 2 times, so the minimum ratio of the third harmonic energy of the A-phase load of adjacent areas a and b is: Under normal circumstances and when a line break occurs but the selected area is not the area before or after the line break, the third harmonic energy ratio is: Therefore, the setting value K1 is set to 4.

7. A neutral line break detection and positioning system based on third harmonic energy characteristics, characterized in that: include: Area division module: used to divide the monitoring area into several independent areas; The first calculation module is used to measure the voltage relative to the neutral line of the A-phase load in each area and the current flowing through the A-phase load, and extract the third-order components of the voltage and current through Fourier decomposition, and further calculate the third-order harmonic energy; The second calculation module is used to compare the third harmonic energy ratio kb of the A-phase loads in two adjacent areas according to the calculated third harmonic energy of the A-phase load in each area; Judgment module: used to set the setting value K1. When the third harmonic energy ratio kb of the A-phase load in two adjacent areas meets kb≥K1, it is judged that a neutral line break fault occurs and occurs between the two areas.

8. The neutral line break detection and positioning system based on third harmonic energy characteristics according to claim 7 is characterized in that: The set value K1 is set to 4.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the neutral line break detection and positioning method based on third harmonic energy characteristics as described in any one of claims 1 to 6 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the neutral line break detection and positioning method based on third harmonic energy characteristics as claimed in any one of claims 1 to 6 are implemented.

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