Single-phase earth fault detection method based on adaptive frequency conversion

Abstract

The invention discloses a single-phase earth fault detection method based on adaptive frequency conversion, and relates to the technical field of single-phase earth fault detection, and the method comprises the steps: selecting a first center point of a fault power failure line, and obtaining a signal injection point based on the first center point; connecting a signal source with the signal injection point, switching the signal source to a direct current mode to output current, and collecting a direct current parameter of the signal injection point; switching the signal source to an alternating current mode to output current, and collecting alternating current parameters of the signal injection point; obtaining an optimal frequency based on the direct current parameter and the alternating current parameter; acquiring the output frequency of the signal source, judging whether the output frequency is equal to the optimal frequency or not, and if yes, measuring the signal injection point based on the output frequency and measurement equipment to obtain measurement data; if not, adjusting the output frequency until the output frequency is equal to the optimal frequency, and measuring the signal injection point by the measurement equipment to obtain measurement data; obtaining a fault phase and a fault direction based on the measurement data; and a fault point is obtained based on the fault phase and the fault direction, so that the problem of low single-phase earth fault detection accuracy caused by the fact that a current signal source cannot adapt to different distribution network lines can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of single-phase grounding fault detection, and in particular to a single-phase grounding fault detection method based on adaptive frequency conversion. Background Art

[0002] In the distribution network, single-phase grounding fault is a common fault type, but its search is a rather difficult task. In large-scale distribution networks, traditional search methods mainly rely on detection equipment to detect the current, voltage and other parameters of the distribution line to locate the fault point, but these detection devices often have the problem of single signal and cannot be applied to different types of distribution lines. The causes of single-phase grounding faults are diverse and highly complex, resulting in the inability to effectively search for faults in some cases. For example, arc grounding faults may cause overvoltage, causing the voltage of the non-fault phase to increase abnormally, which is sometimes enough to cause the high-voltage fuse of the voltage transformer to melt or burn the voltage transformer. In this case, the detection equipment may mistakenly detect the non-fault phase as the fault phase, resulting in incorrect detection.

[0003] Moreover, for different types of distribution network lines, different equipment is required to perform fault detection, which increases the cost of the equipment and the difficulty of maintenance. Summary of the invention

[0004] In order to solve the problem that the current signal source cannot adapt to different distribution network lines, resulting in low accuracy of single-phase grounding fault detection, the present invention provides a single-phase grounding fault detection method based on adaptive frequency conversion, the method comprising: selecting a first center point of the faulty power outage line, and obtaining a signal injection point based on the first center point; connecting the signal source to the signal injection point, the signal source switches to a DC mode output current, and collects the DC parameters of the signal injection point; switching the signal source to an AC mode output current, and collecting the AC parameters of the signal injection point; obtaining an optimal frequency based on the DC parameters and the AC parameters; obtaining the output frequency of the signal source, and determining whether the output frequency is equal to the optimal frequency, if so, based on the output frequency, a measuring device measures the signal injection point to obtain measurement data; otherwise, adjusting the output frequency until it is equal to the optimal frequency, and a measuring device measures the signal injection point to obtain measurement data; obtaining a fault phase and a fault direction based on the measurement data; and obtaining a fault point based on the fault phase and the fault direction.

[0005] The principle of the present invention is as follows: by injecting a different frequency signal into the fault line, outputting a direct current and an alternating current to obtain an optimal frequency, adjusting the output frequency of the signal source to be consistent with the signal source, dynamically adjusting the signal frequency to adapt to the characteristics of the electrical line, making it adaptable to different distribution network lines, realizing the variable frequency injection of the signal source, being able to minimize the leakage current of the capacitor and inductor components flowing through the line, being able to enhance the current flow of the fault point, and guiding most of the current to pass through the grounding fault path, making the fault characteristics of the fault point more obvious, thereby reducing the abnormal conditions of the non-fault phase, better distinguishing the fault phase from the non-fault phase, improving the fault detection accuracy, optimizing the injection signal, improving the sensitivity of the detection equipment, improving the detection rate and accuracy of the grounding fault, injecting the signal through the fault point to form a loop, and checking the fault phase and the non-fault phase current in the fault section, each measurement can determine the fault direction, multiple detections ensure the correctness of the fault direction, improve the accuracy of fault detection, and then use the method of finding the center point to gradually narrow the fault section until the fault point is determined, and only the signal source and the current detection device are required to perform fault search, reducing the cost of the equipment and the difficulty of maintenance.

[0006] Furthermore, before collecting the DC parameters and the AC parameters, the signal source outputs current in a stable state. Collecting data after the signal source outputs stably will provide more accurate data.

[0007] Furthermore, the specific steps of obtaining the optimal frequency include: obtaining resistance based on the DC parameters, obtaining impedance based on the AC parameters, obtaining capacitance based on the resistance and the impedance; and obtaining the optimal frequency based on the capacitance. The optimal frequency makes the inductance and capacitance of the transformer reach a resonant state, in which the impedances of the inductance and the capacitance cancel each other out, thereby minimizing the leakage current.

[0008] Furthermore, the measurement data is obtained based on a first measurement method, wherein the first measurement method is: the measuring device measures the large side and the small side of the input point to obtain first measurement data and second measurement data respectively, and the measurement data is obtained based on the first measurement data and the second measurement data.

[0009] Taking the power transmission direction of the line as the standard, the side close to the power transmission end, that is, the starting point of the line or the side facing the starting point is the small side, and the side close to the power receiving end, that is, the end point of the line or the side facing the end point is the large side.

[0010] Further, based on a first judgment method, the fault phase and the fault direction are obtained, and the first judgment method is:

[0011] Based on the first measurement data, a first current value of the three-phase circuit on the large side is obtained; based on the second measurement data, a second current value of the three-phase circuit on the small side is obtained; based on a second judgment method, the first current value and the second current value are judged to obtain a first judgment result and a second judgment result respectively, and the fault phase and the fault direction are obtained based on the first judgment result and the second judgment result; the second judgment method is: judge whether the current values ​​of the three-phase circuits are all equal, if so, the circuit has no fault; if not, an abnormal current value is obtained based on the current value, and a judgment result is obtained based on the abnormal current value.

[0012] Based on the principle of symmetry of current distribution, high-precision measurement of detection equipment can effectively assist the fault diagnosis process.

[0013] Furthermore, the specific steps of obtaining the fault point include:

[0014] S1. Obtain a first fault area based on the fault phase and the fault direction, and select a second center point of the first fault area;

[0015] S2. Based on the first measurement method, the measuring device measures the second center point to obtain third measurement data; based on the third measurement data and the first determination method, obtain a first fault phase and a first fault direction;

[0016] S3. Obtain a second fault region based on the first fault phase and the first fault direction, and determine whether the area of ​​the second fault region is greater than a preset area. If so, return to S1 and update the first fault region to the second fault region; if not, obtain the fault point based on the second fault region.

[0017] Furthermore, a first calculation method for obtaining capacitance is:

[0018]

[0019] Among them, Z represents impedance, R represents resistance, CC represents capacitance, and ω represents angular frequency.

[0020] Furthermore, a second calculation method for obtaining the optimal frequency is:

[0021]

[0022] Among them, f is the optimal frequency, C is the capacitance, and L is the inductance of the transformer.

[0023] A construction site is a location where a construction project is being developed and civil engineering works are being carried out.

[0024] The greening rate refers to the ratio of the land area used for planting trees, lawns and other vegetation in an area to the total land area of ​​the area.

[0025] Furthermore, the first center point is obtained based on a first acquisition method, and the first acquisition method is: obtaining a target area based on a faulty power outage line, dividing the target area into a number of first sub-areas, obtaining the construction age of each of the first sub-areas, obtaining the degree of aging based on the construction age of the community, obtaining a number of first dangerous areas based on the degree of aging, and obtaining the midpoint of all the first dangerous areas to obtain the first center point. Single-phase grounding faults are mostly caused by equipment aging, rupture, and surface dirt. In areas where the community has been built for a longer period of time, the equipment has a higher degree of aging, is more prone to damage, and has more surface stains, making single-phase grounding faults more likely to occur. Starting from the midpoint of the first dangerous area, the fault point can be detected more quickly, improving detection efficiency.

[0026] Furthermore, the second center point is obtained based on a second acquisition method, and the second acquisition method is: determine whether there is a construction site in the first fault area, if so, obtain a number of second dangerous areas based on the construction site, obtain the first greening rate of each second dangerous area, and obtain the second center point based on the maximum first greening rate; otherwise, divide the first fault area into a number of second sub-areas, obtain the second greening rate of each second sub-area, obtain a number of third dangerous areas based on a preset range and the second greening rate, obtain the age of power equipment and the number of power equipment in each third dangerous area, and obtain the second center point based on the age of power equipment and the number of power equipment. The causes of single-phase grounding faults are also mostly caused by external forces such as barbaric construction, large moving machinery hitting overhead lines or digging cables, and severe weather conditions causing wire breakage or tree breakage, which in turn causes wire breakage, etc. Therefore, this method starts with checking construction sites and areas with a lot of vegetation, and then considers power equipment factors, which can detect fault points faster and improve detection efficiency.

[0027] One or more technical solutions provided by the present invention have at least the following technical effects or advantages:

[0028] 1. By injecting a different frequency signal into the fault line, the DC current and AC current are output to obtain the optimal frequency, the output frequency of the signal source is adjusted to be consistent with it, and the signal frequency is dynamically adjusted to adapt to the characteristics of the electrical line, so that it can adapt to different distribution network lines, and the variable frequency injection of the signal source is realized. It can minimize the leakage current of the capacitor and inductor components flowing through the line, and at the same time guide most of the current through the ground fault path, optimize the injection signal, improve the sensitivity of the detection equipment, and improve the detection rate and accuracy of the ground fault. The injected signal flows through the fault point to form a loop, and the fault phase and non-fault phase currents are checked in the fault section. Each measurement can determine the fault direction, and then use the method of finding the center point to gradually narrow the fault section until the fault point is determined.

[0029] 2. Compared with the traditional fixed frequency signal injection, it can accurately inject the optimal frequency signal into the line. Through the injection of the optimal frequency signal, the current flow at the fault point is effectively enhanced, and the leakage current in the line is reduced, thereby optimizing the signal transmission efficiency and accuracy, making the fault characteristics of the fault point more obvious, facilitating fault detection and positioning, and improving the accuracy and efficiency of fault diagnosis.

[0030] 3. Obtain the first center based on the first acquisition method. Single-phase grounding faults are mostly caused by equipment aging, breakage, and surface dirt. In areas where the community has been built for a longer time, the equipment is more aged, more easily damaged, and has more surface stains, which makes single-phase grounding faults more likely to occur. Starting from the midpoint of the first dangerous area, the fault point can be detected faster and the detection efficiency can be improved.

[0031] 4. Obtain the second center based on the second acquisition method. Single-phase grounding faults are mostly caused by external forces such as rough construction, large moving machinery hitting overhead lines or digging cables, and severe weather conditions that cause wire breakage or tree breakage, which in turn causes wire breakage. Therefore, this method starts with construction sites and areas with a lot of vegetation, and then considers power equipment factors, which can detect fault points faster and improve detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of the present invention, and do not constitute a limitation on the embodiments of the present invention;

[0033] Figure 1 It is a flow chart of a single-phase grounding fault detection method based on adaptive frequency conversion in the present invention. DETAILED DESCRIPTION

[0034] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0035] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those within the scope of this description. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0036] Embodiment 1

[0037] refer to Figure 1 This embodiment provides a single-phase ground fault detection method based on adaptive frequency conversion, the method comprising:

[0038] Select the first center point of the faulty power outage line, and obtain the signal injection point based on the first center point; wherein the first center point is obtained based on a first acquisition method, and the first acquisition method is: obtain a target area based on the faulty power outage line, divide the target area into a number of first sub-areas, obtain the construction age of a cell in each of the first sub-areas, obtain the degree of aging based on the construction age of the cell, obtain a number of first dangerous areas based on the aging degree, and obtain the midpoint of all the first dangerous areas to obtain the first center point.

[0039] Connect a signal source to the signal injection point, switch the signal source to a DC mode to output current, and collect DC parameters of the signal injection point; switch the signal source to an AC mode to output current, and collect AC parameters of the signal injection point; wherein, before collecting the DC parameters and the AC parameters, the signal source outputs current in a stable state.

[0040] Based on the DC parameters and the AC parameters, an optimal frequency is obtained; the specific steps of obtaining the optimal frequency include: obtaining resistance based on the DC parameters, obtaining impedance based on the AC parameters, and obtaining capacitance based on the resistance and the impedance; and obtaining the optimal frequency based on the capacitance.

[0041] The output frequency of the signal source is obtained, and it is determined whether the output frequency is equal to the optimal frequency. If so, based on the output frequency, a measuring device measures the signal injection point to obtain measurement data; otherwise, the output frequency is adjusted until it is equal to the optimal frequency, and the measuring device measures the signal injection point to obtain measurement data. In this embodiment, the measuring device may be an intelligent clamp ammeter.

[0042] The measurement data is obtained based on a first measurement method, wherein the first measurement method is: a measuring device measures the large side and the small side of an input point to obtain first measurement data and second measurement data respectively, and the measurement data is obtained based on the first measurement data and the second measurement data.

[0043] Wherein, based on a first judgment method, the fault phase and the fault direction are obtained, and the first judgment method is: based on the first measurement data, a first current value of the three-phase circuit on the large side is obtained; based on the second measurement data, a second current value of the three-phase circuit on the small side is obtained; based on a second judgment method, the first current value and the second current value are judged to obtain a first judgment result and a second judgment result respectively, and the fault phase and the fault direction are obtained based on the first judgment result and the second judgment result;

[0044] The second judgment method is: judging whether the current values ​​of the three-phase circuits are all equal, if so, the circuit is fault-free; if not, obtaining an abnormal current value based on the current value, and obtaining a judgment result based on the abnormal current value.

[0045] For example, if the three-phase circuit on the large side is A, B and C, use an intelligent clamp ammeter to measure the current of phases A, B and C. If the three-phase current values ​​are equal, it can be determined that the fault direction is the small side; if it is found that the current of one phase is different from the other two phases, it can be determined that this phase is the fault phase, and the large measurement direction is the direction in which the ground fault occurs.

[0046] A fault phase and a fault direction are obtained based on the measurement data; and a fault point is obtained based on the fault phase and the fault direction.

[0047] The specific steps of obtaining the fault point include:

[0048] S1. Obtain a first fault area based on the fault phase and the fault direction, and select a second center point of the first fault area; wherein the second center point is obtained based on a second acquisition method, and the second acquisition method is: determine whether there is a construction site in the first fault area, and if so, obtain a number of second dangerous areas based on the construction site, obtain the first greening rate of each second dangerous area, and obtain the second center point based on the maximum first greening rate; otherwise, divide the first fault area into a number of second sub-areas, obtain the second greening rate of each second sub-area, obtain a number of third dangerous areas based on a preset range and the second greening rate, obtain the service life of the power equipment and the number of power equipment in each of the third dangerous areas, and obtain the second center point based on the service life of the power equipment and the number of power equipment.

[0049] S2. Based on the first measurement method, the measuring device measures the second center point to obtain third measurement data; based on the third measurement data and the first determination method, obtain a first fault phase and a first fault direction;

[0050] S3. Obtain a second fault region based on the first fault phase and the first fault direction, and determine whether the area of ​​the second fault region is greater than a preset area. If so, return to S1 and update the first fault region to the second fault region; if not, obtain the fault point based on the second fault region.

[0051] In this embodiment, the method for obtaining the first center point and the second center point can also recursively apply the binary search method, and the fault area can be gradually narrowed by repeatedly obtaining the center point of the area for investigation until the fault point is accurately located.

[0052] Embodiment 2

[0053] Based on the above embodiment, in this embodiment, the calculation method for obtaining the resistance can be:

[0054]

[0055] Among them, R represents resistance, Ud represents DC voltage, and Id represents DC current.

[0056] The impedance can be calculated as:

[0057]

[0058] Among them, Z represents impedance, Ua represents AC voltage, and Ia represents AC current.

[0059] The first calculation method to obtain the capacitance is:

[0060]

[0061] Among them, Z represents impedance, R represents resistance, C represents capacitance, and ω represents angular frequency.

[0062] Among them, simplify the formula and calculate the capacitance:

[0063]

[0064] The second calculation method to obtain the optimal frequency is:

[0065]

[0066] Among them, f is the optimal frequency, C is the capacitance, and L is the inductance of the transformer.

[0067] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0068] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A single-phase ground fault detection method based on adaptive frequency conversion, characterized in that: The method comprises: Selecting a first center point of the faulty power outage line, and obtaining a signal injection point based on the first center point; Connecting a signal source to the signal injection point, switching the signal source to a DC mode to output current, and collecting DC parameters of the signal injection point; switching the signal source to an AC mode to output current, and collecting AC parameters of the signal injection point; obtaining an optimal frequency based on the DC parameters and the AC parameters; Obtaining the output frequency of the signal source, determining whether the output frequency is equal to the optimal frequency, and if so, measuring the signal injection point based on the output frequency by a measuring device to obtain measurement data; otherwise, adjusting the output frequency until it is equal to the optimal frequency, and measuring the signal injection point by a measuring device to obtain measurement data; A fault phase and a fault direction are obtained based on the measurement data; and a fault point is obtained based on the fault phase and the fault direction.

2. A single-phase grounding fault detection method based on adaptive frequency conversion according to claim 1, characterized in that: Before collecting the DC parameters and the AC parameters, the signal source outputs current in a stable state.

3. A single-phase grounding fault detection method based on adaptive frequency conversion according to claim 1, characterized in that: The specific steps to obtain the optimal frequency include: The resistance is obtained based on the DC parameters, the impedance is obtained based on the AC parameters, the capacitance is obtained based on the resistance and the impedance; and the optimal frequency is obtained based on the capacitance.

4. A single-phase grounding fault detection method based on adaptive frequency conversion according to claim 1, characterized in that: The measurement data is obtained based on a first measurement method, where the first measurement method is: The measuring device measures the large side and the small side of the input point to obtain first measurement data and second measurement data respectively, and obtains the measurement data based on the first measurement data and the second measurement data.

5. A single-phase grounding fault detection method based on adaptive frequency conversion according to claim 4, characterized in that: The fault phase and the fault direction are obtained based on a first judgment method, wherein the first judgment method is: Obtaining a first current value of a three-phase circuit on the large side based on the first measurement data; Obtaining a second current value of the three-phase circuit on the trumpet side based on the second measurement data; Based on a second judgment method, the first current value and the second current value are judged to obtain a first judgment result and a second judgment result respectively, and the fault phase and the fault direction are obtained based on the first judgment result and the second judgment result; The second judgment method is: It is determined whether the current values ​​of the three-phase circuits are all equal. If so, the circuit is fault-free; if not, an abnormal current value is obtained based on the current value, and a determination result is obtained based on the abnormal current value.

6. A single-phase grounding fault detection method based on adaptive frequency conversion according to claim 5, characterized in that: The specific steps to obtain the fault point include: S1. Obtain a first fault area based on the fault phase and the fault direction, and select a second center point of the first fault area; S2. Based on the first measurement method, the measuring device measures the second center point to obtain third measurement data; based on the third measurement data and the first determination method, obtain a first fault phase and a first fault direction; S3. Obtain a second fault region based on the first fault phase and the first fault direction, and determine whether the area of ​​the second fault region is greater than a preset area. If so, return to S1 and update the first fault region to the second fault region; if not, obtain the fault point based on the second fault region.

7. A single-phase grounding fault detection method based on adaptive frequency conversion according to claim 3, characterized in that: The first calculation method to obtain the capacitance is: Among them, Z represents impedance, R represents resistance, CC represents capacitance, and ω represents angular frequency.

8. The single-phase grounding fault detection method based on adaptive frequency conversion according to claim 3 is characterized in that: The second calculation method to obtain the optimal frequency is: Among them, f is the optimal frequency, C is the capacitance, and L is the inductance of the transformer.

9. The single-phase grounding fault detection method based on adaptive frequency conversion according to claim 1 is characterized in that: The first center point is obtained based on a first acquisition method, where the first acquisition method is: A target area is obtained based on the faulty power outage line, and the target area is divided into several first sub-areas. The construction age of the community in each of the first sub-areas is obtained, and the aging degree is obtained based on the construction age of the community. Based on the aging degree, several first danger areas are obtained, and the midpoints of all the first danger areas are obtained to obtain a first center point.

10. A single-phase grounding fault detection method based on adaptive frequency conversion according to claim 6, characterized in that: The second center point is obtained based on a second acquisition method, where the second acquisition method is: Determine whether there is a construction site in the first fault area, and if so, obtain a plurality of second dangerous areas based on the construction site, obtain a first greening rate of each second dangerous area, and obtain a second center point based on the maximum first greening rate; Otherwise, the first fault area is divided into several second sub-areas, the second greening rate of each second sub-area is obtained, several third danger areas are obtained based on the preset range and the second greening rate, the service life of the power equipment and the number of power equipment in each third danger area are obtained, and the second center point is obtained by the service life of the power equipment and the number of the power equipment.

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