A method for fault diagnosis and location in distribution network

Abstract

The present invention discloses a method for diagnosing and locating faults in a distribution network, and the method comprises the following steps: S01, applying an AC voltage signal to any two-phase circuits in an unloaded circuit, and setting the signal application point as point X; S02, moving to both sides of point X along the length direction of the unloaded circuit and detecting the relevant electromagnetic field related to the applied AC voltage signal; S03, if any side of point X has a relevant electromagnetic field, moving to the side with the relevant electromagnetic field until the relevant electromagnetic field disappears, and recording the vanishing point as point Y, where Y is the fault point, and if neither side of point X has a relevant electromagnetic field, it is determined that the unloaded circuit does not have a fault point. The method solves the problems of the prior art in that the positioning time of the fault point of the distribution network is long, the positioning accuracy is low, it is difficult to find intermittent faults, it is difficult to find the situation where the grounding point is relatively hidden, and it is difficult to find the high-resistance grounding.

Description

Technical Field

[0001] The invention relates to a distribution network fault diagnosis and positioning method, and belongs to the technical field of distribution network fault diagnosis. Background Art

[0002] There are many reasons for the grounding and phase-to-phase short circuit faults in the 10kv distribution network. Some of the phenomena are obvious, such as strong winds causing some light conductors and semiconductors to be blown onto the lines. If it is caused by these reasons, the fault phenomena are obvious and can be checked and eliminated through manual line inspections, drone line inspections, etc.

[0003] However, with the development of the economy, the types and quantities of equipment connected to distribution lines are increasing, such as mutual inductors, transformers, meter boxes, etc. Due to weather reasons such as lightning strikes, a weak insulator is broken, or due to the aging of insulators and equipment caused by workmanship quality, the joint is broken and the drainage line is overlapped on the cross arm, etc., the number of grounding and phase-to-phase short circuit accidents caused by equipment accounts for an increasing proportion, and the cause of the accident is often not visually visible and difficult to find.

[0004] The current solutions to this problem include the following:

[0005] 1) Search based on experience

[0006] Each line has a fixed equipment owner who is responsible for daily inspections and data management. Therefore, he must be clear about the line's historical conditions, channel problems, bird damage, and other first-hand information. Relying on the power supply station's operation and maintenance personnel's familiarity with the line equipment under their jurisdiction, they can quickly determine the possibility of the faulty section and first check the line equipment with problems (causes). Generally speaking, unless affected by extreme weather, there are only a few weak points in the line, and getting straight to the point based on experience can often achieve better results.

[0007] However, this inspection method requires the inspection or understanding of the entire line (including branch lines and user-side equipment), which is obviously very time-consuming. After all, a single trunk line of a line is several kilometers long. If you don’t rely on experience, it is generally impossible to complete the inspection in a short time. In addition, this inspection method is difficult to troubleshoot when the grounding is only intermittent and the fault point that causes the grounding is relatively hidden (such as high-resistance grounding).

[0008] 2) Lalu method + segmented trial delivery

[0009] That is, make full use of the line's section switches, branch switches and other facilities to decompose the entire line into small units, and then repeatedly stop and supply power to these small units until the grounding area is screened out. This method of finding faults consumes a lot of manpower and time. This positioning method can only locate the fault point to the section, and the line at one end is long, and further inspection of the line located to the section is required to find the fault point. In addition, it is difficult to troubleshoot the situation where the grounding is only intermittent and the fault point that causes the grounding is relatively hidden (such as high-resistance grounding).

[0010] 3) Dichotomy + insulation shaking test

[0011] At the halfway point of the 10kV line (a switch position is selected), use an insulation tester to test the insulation of both sides of the line. The side with the lowest insulation to the ground is the side where the ground fault is. Then divide the fault section into two sections and test the insulation. Similarly, the fault point (section) can be found in a relatively short time. This method is complex to calculate for general faults, and is also difficult to troubleshoot for situations where the grounding is only intermittent or the fault point that causes the grounding is relatively hidden (such as high-resistance grounding).

[0012] 4) Tested by DC tester

[0013] The principle is to transmit an equivalent voltage to the line. If the protection device does not work, it is determined that the line has no fault and can transmit power normally. If the protection device works, it is determined that the line is faulty. However, this method cannot detect high-resistance grounding because the mutation amount generated by high-resistance grounding faults is very small. Traditional protection devices may not be able to detect the mutation amount and cannot reliably protect the action. High-resistance grounding faults often occur in mountainous and hilly areas. The fault current of high-resistance grounding faults is weak, random, and hidden, and it is not easy to detect. If it is not discovered and handled in time, it will cause more serious system failures. Summary of the invention

[0014] The technical problem to be solved by the present invention is to provide a distribution network fault diagnosis and positioning method, which determines the distribution network fault location according to the electromagnetic field strength generated by the injected signal on the no-load coil, so as to overcome the shortcomings of the prior art.

[0015] The technical solution of the present invention is:

[0016] A method for diagnosing and locating a distribution network fault, the method comprising the following steps:

[0017] S01, applying an AC voltage signal to any two-phase circuits in the unloaded circuit, and the signal application point is set as point X;

[0018] S02, moving to both sides of point X along the length direction of the unloaded line and detecting the relevant electromagnetic field related to the applied AC voltage signal;

[0019] S03. If any side of point X has a related electromagnetic field, move to the side with the related electromagnetic field until the related electromagnetic field disappears. The vanishing point is recorded as point Y, where Y is the fault point. If neither side of point X has a related electromagnetic field, it is determined that the unloaded line has no fault point.

[0020] The device for detecting the relevant electromagnetic field in step S02 is selected by the following method:

[0021] If the current generated by applying an AC voltage signal is large and the voltage is low, the fault type is determined to be direct grounding, and a detector is used to detect the relevant electromagnetic field and convert it into current;

[0022] If the current and voltage generated by applying the AC voltage signal are large, the fault type is determined to be high-resistance grounding. Use a clamp ammeter to detect the relevant electromagnetic field and convert the detected relevant electromagnetic field into current. When using, mount the clamp ammeter on an unloaded line.

[0023] If the current generated by applying the AC voltage signal is small and the voltage is high, the fault type is determined to be hidden indirect grounding. Use a clamp ammeter to detect the relevant electromagnetic field and convert the detected relevant electromagnetic field into current. When in use, mount the clamp ammeter on an unloaded line.

[0024] Specifically, the AC voltage signal generating device includes:

[0025] A transformer, wherein the output end of the transformer is a signal output end;

[0026] An inverter bridge, wherein an output end of the inverter bridge is electrically connected to an input end of the transformer;

[0027] An isolation driver, the isolation driver being electrically connected to the inverter bridge control terminal;

[0028] A selection module, the selection module comprising two comparators, the output ends of the two comparators being electrically connected to the input end of the isolation driver;

[0029] A sawtooth wave generator, wherein an output terminal of the sawtooth wave generator is electrically connected to two positive and negative input terminals of two comparators;

[0030] A feedback circuit, wherein an input terminal of the feedback circuit is electrically connected to one of the signal output terminals, and an output terminal of the feedback circuit is electrically connected to the other two positive and negative input terminals of the two comparators;

[0031] A control module is electrically connected to the feedback circuit, and the control module is electrically connected to the sawtooth wave generator. The control module is used to input a square wave to the sawtooth wave generator and a sine wave to the feedback circuit.

[0032] Specifically, the sawtooth wave generator comprises:

[0033] an integrator, the integrator being electrically connected to the control module;

[0034] a first amplifier, the first amplifier being electrically connected to an output terminal of the integrator;

[0035] An operational amplifier is electrically connected to the output terminal of the first amplifier, the output terminal of the operational amplifier is electrically connected to the positive input terminal of one of the comparators, and the input terminal of the operational amplifier is electrically connected to the negative input terminal of the other comparator.

[0036] Specifically, the feedback circuit includes:

[0037] The analog-to-digital conversion module, the control module is electrically connected to one of the signal output terminals via the analog-to-digital conversion module;

[0038] A digital-to-analog conversion module, the digital-to-analog conversion module is electrically connected to the control module;

[0039] A second amplifier, the second amplifier is electrically connected to an output end of the digital-to-analog conversion module;

[0040] PID, the PID input end is electrically connected to the second amplifier, and the PID input end is electrically connected to another signal output end.

[0041] Furthermore, the sawtooth wave generator further comprises:

[0042] A first filter capacitor is arranged between the integrator and the control module.

[0043] Furthermore, the feedback circuit further includes:

[0044] A second filter capacitor is provided between the second amplifier and the PID.

[0045] Specifically, the detector includes:

[0046] Induction coil;

[0047] a third amplifier, the third amplifier being electrically connected to the induction coil;

[0048] A second analog-to-digital conversion module, the second analog-to-digital conversion module is electrically connected to the third amplifier;

[0049] A second control module, wherein the second control module is electrically connected to the second analog-to-digital conversion module.

[0050] Specifically, the method for determining the relevant electromagnetic field is:

[0051] Perform Fourier transform on the signal;

[0052] Extract the signal strength f of the signal with the same frequency as the AC voltage signal;

[0053] Get the distance d between the detection point and the unloaded line;

[0054] Correlation between detection distance d and signal strength f;

[0055] If there is a correlation between the distance d and the signal strength f, the detected signal is determined to be a correlated electromagnetic field, otherwise it is not a correlated electromagnetic field.

[0056] Specifically, the method for detecting the correlation between the distance d and the signal strength f is:

[0057] The distance L perpendicular to the length direction of the unloaded line is made to fluctuate during the detection process of the detection point along the length direction of the unloaded line. The correlation between the signal strength f and the distance L is determined. If the signal strength f decreases as the distance L increases, and the signal strength f increases as the distance L decreases, then it is determined that f is correlated with the distance L, otherwise there is no correlation.

[0058] The beneficial effects of the present invention are as follows: the present invention applies a voltage between the short-circuited two-phase lines, and the voltage will form a current loop through the short-circuited fault point, which is equivalent to a current of equal magnitude and opposite direction flowing through the parallel conductors M and N. As long as the corresponding electromagnetic field strength can be detected in a place other than the middle plane of the two parallel conductors, it means that it is between points X and Y. If the corresponding electromagnetic field strength cannot be detected, it means that it is outside points X and Y. The intersection from the detection of the electromagnetic field strength to the detection of the electromagnetic field strength is the fault point. The method locates the distribution network fault point without the need to supply power to the line in sections, and the fault location is faster, and the fault location is accurate to the point, and the fault point location is more accurate. It can quickly locate the fault before the intermittent fault is restored, and it can also accurately locate the fault point in the case where the fault point is relatively hidden. In particular, for high-resistance faults, the method detects the current of the unloaded line through a clamp ammeter, and can accurately detect the line current, thereby judging the line fault point according to the line current, and is more effective in finding high-resistance grounding faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is a schematic diagram of an embodiment of the present invention;

[0060] Figure 2 The circuit schematic diagram of the device for generating an AC voltage signal according to an embodiment of the present invention;

[0061] Figure 3 A circuit schematic diagram of an electromagnetic field detection device according to an embodiment of the present invention;

[0062] Figure 4 is a flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0063] The technical solution in the embodiment of the present invention has the following general idea:

[0064] like Figure 1 As shown in the figure, when two parallel wires M and N are passed with currents of equal magnitude and opposite directions, the electromagnetic field strength at any point in the plane equidistant from the two wires, such as point A, is 0. However, the electromagnetic field strength at any other point, such as point B, is not 0.

[0065] This provides a theoretical basis for solving interphase short circuit faults. That is, at any point of the fault line (assuming point X), a voltage is applied between the short-circuited two-phase lines, and the voltage will form a current loop through the short-circuited fault point (assuming point Y). That is, it is equivalent to a current of equal magnitude and opposite direction flowing through the parallel wires M and N. Then, as long as the corresponding electromagnetic field strength can be detected at a place similar to point B, it means that point B is between points X and Y. Furthermore, if the corresponding electromagnetic field strength cannot be detected, it means that point B is outside points X and Y.

[0066] By designing an electromagnetic field detector, we can gradually find the fault point by changing the detection location, depending on whether the detector can detect the electromagnetic field generated by the specific current injected into the line at point X.

[0067] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution 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 described embodiments are 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 creative work are within the scope of protection of the present invention.

[0068] Embodiment 1

[0069] In order to solve the problems of long time for locating the fault point of the distribution network, low positioning accuracy, difficulty in finding intermittent faults, difficulty in finding the hidden grounding point and difficulty in finding high-resistance grounding in the existing technology, reference is made to Figure 4 , an embodiment of the present invention provides a distribution network fault diagnosis and positioning method, the method comprising the following steps:

[0070] S01, applying an AC voltage signal to any two-phase line in the unloaded line, where the frequency of the AC voltage signal is preferably 60 Hz to distinguish it from the 50 Hz frequency of the power system, and the signal application point is set as point X;

[0071] S02, moving to both sides of point X along the length direction of the unloaded line and detecting the relevant electromagnetic field related to the applied AC voltage signal;

[0072] S03. If any side of point X has a related electromagnetic field, move to the side with the related electromagnetic field until the related electromagnetic field disappears. The vanishing point is recorded as point Y, where Y is the fault point. If neither side of point X has a related electromagnetic field, it is determined that the unloaded line has no fault point.

[0073] The device for detecting the relevant electromagnetic field in step S02 is selected by the following method: if the current generated by applying the AC voltage signal is large and the voltage is low, the fault type is determined to be direct grounding, and a detector is used to detect the relevant electromagnetic field and convert it into current; if the current generated by applying the AC voltage signal is large and the voltage is high, the fault type is determined to be high-resistance grounding, a clamp ammeter is used to detect the relevant electromagnetic field, and the detected relevant electromagnetic field is converted into current, and the clamp ammeter is mounted on an unloaded line when in use; if the current generated by applying the AC voltage signal is small and the voltage is high, the fault type is determined to be implicit non-direct grounding, a clamp ammeter is used to detect the relevant electromagnetic field, and the detected relevant electromagnetic field is converted into current, and the clamp ammeter is mounted on an unloaded line when in use.

[0074] If a voltage is applied between the short-circuited two-phase lines, the voltage will form a current loop through the short-circuited fault point, which is equivalent to a current of equal magnitude and opposite direction flowing through the parallel conductors M and N. As long as the corresponding electromagnetic field strength can be detected in places other than the middle plane of the two parallel conductors, it means that it is between X and Y. If the corresponding electromagnetic field strength cannot be detected, it means that it is outside the X and Y points. The intersection from the detection of the electromagnetic field strength to the detection of the electromagnetic field strength is the fault point. The method can locate the distribution network fault point without the need to supply power to the line in sections. The fault location is faster, and the fault location is accurate to the point. The fault point location is more accurate. It can be quickly located before the intermittent fault is restored, and it can also be accurately located for the situation where the fault point is relatively hidden. In particular, for high-resistance faults, the method detects the current of the unloaded line through a clamp ammeter, and can accurately detect the line current, thereby judging the line fault point based on the line current, which is more effective for finding high-resistance grounding faults.

[0075] Specifically, refer to Figure 2 , the AC voltage signal generating device comprises:

[0076] A transformer, wherein the output end of the transformer is a signal output end;

[0077] An inverter bridge, wherein an output end of the inverter bridge is electrically connected to an input end of the transformer;

[0078] An isolation driver, the isolation driver being electrically connected to the inverter bridge control terminal;

[0079] A selection module, the selection module comprising two comparators, the output ends of the two comparators being electrically connected to the input end of the isolation driver;

[0080] A sawtooth wave generator, wherein an output terminal of the sawtooth wave generator is electrically connected to two positive and negative input terminals of two comparators;

[0081] A feedback circuit, wherein an input terminal of the feedback circuit is electrically connected to one of the signal output terminals, and an output terminal of the feedback circuit is electrically connected to the other two positive and negative input terminals of the two comparators;

[0082] A control module is electrically connected to the feedback circuit, and the control module is electrically connected to the sawtooth wave generator. The control module is used to input a square wave to the sawtooth wave generator and a sine wave to the feedback circuit.

[0083] In order to generate an AC voltage signal of a specified frequency, a control module is used here to generate a 60Hz control signal, and then an inverter is used to generate a high-voltage AC signal, which is then boosted by a transformer, so that the output voltage of the device can reach 3000V. Compared with simply using a transformer to boost the voltage, the number of transformer coil turns required is less, making the device more portable.

[0084] Specifically, the sawtooth wave generator comprises:

[0085] an integrator, the integrator being electrically connected to the control module;

[0086] a first amplifier, the first amplifier being electrically connected to an output terminal of the integrator;

[0087] An operational amplifier is electrically connected to the output terminal of the first amplifier, the output terminal of the operational amplifier is electrically connected to the positive input terminal of one of the comparators, and the input terminal of the operational amplifier is electrically connected to the negative input terminal of the other comparator.

[0088] Specifically, the feedback circuit includes:

[0089] The analog-to-digital conversion module, the control module is electrically connected to one of the signal output terminals via the analog-to-digital conversion module;

[0090] A digital-to-analog conversion module, the digital-to-analog conversion module is electrically connected to the control module;

[0091] A second amplifier, the second amplifier is electrically connected to an output end of the digital-to-analog conversion module;

[0092] PID, the PID input end is electrically connected to the second amplifier, and the PID input end is electrically connected to another signal output end.

[0093] Here, the output voltage is collected and fed back to the control module through the feedback circuit, and PID is used to adjust it to make the output voltage more accurate.

[0094] Furthermore, the sawtooth wave generator further includes: a first filter capacitor, which is arranged between the integrator and the control module.

[0095] The low-frequency signal is filtered through the first filter capacitor to prevent the low-frequency signal from affecting the comparator output signal and causing the frequency of the output signal to change.

[0096] Furthermore, the feedback circuit further includes: a second filter capacitor, and the second filter capacitor is arranged between the second amplifier and the PID.

[0097] The low-frequency signal is filtered through the second filter capacitor to prevent the low-frequency signal from affecting the comparator output signal and causing the frequency of the output signal to change.

[0098] Specifically, refer to Figure 3 , the detector comprises:

[0099] Induction coil;

[0100] a third amplifier, the third amplifier being electrically connected to the induction coil;

[0101] A second analog-to-digital conversion module, the second analog-to-digital conversion module is electrically connected to the third amplifier;

[0102] A second control module, wherein the second control module is electrically connected to the second analog-to-digital conversion module.

[0103] The electromagnetic field strength is received through the induction coil, the signal is amplified by the third amplifier, and then the analog signal is converted into a digital signal through the second analog-to-digital conversion module.

[0104] Specifically, the method for determining the relevant electromagnetic field is:

[0105] Perform Fourier transform on the signal;

[0106] Extract the signal strength f of the signal with the same frequency as the AC voltage signal;

[0107] Get the distance d between the detection point and the unloaded line;

[0108] Correlation between detection distance d and signal strength f;

[0109] If there is a correlation between the distance d and the signal strength f, the detected signal is determined to be a correlated electromagnetic field, otherwise it is not a correlated electromagnetic field.

[0110] The spectral components of the received electromagnetic waves can be decomposed through Fourier transform. Since the electromagnetic field intensity generated by the line is related to the distance from the detector to the line, while other noise electromagnetic waves are not related to the distance from the detector to the line, a correlation analysis is performed on the signal intensity and detection distance with the same frequency as the AC voltage signal to distinguish between noise and electromagnetic waves generated by the line.

[0111] Specifically, the method for detecting the correlation between distance d and signal strength f is: making the distance L perpendicular to the length direction of the unloaded line fluctuate during the detection process of the detection point along the length direction of the unloaded line, and detecting the correlation between signal strength f and distance L. If the signal strength f decreases as the distance L increases, and the signal strength f increases as the distance L decreases, then it is determined that f is correlated with distance L, otherwise there is no correlation.

[0112] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A distribution network fault diagnosis and positioning method, characterized in that: The method comprises the following steps: S01, applying an AC voltage signal to any short-circuited two-phase line in the unloaded line, and the signal application point is set as point X; S02, moving toward both sides of point X along the length direction of the unloaded line and detecting the relevant electromagnetic field related to the applied AC voltage signal; S03. If any side of point X has a related electromagnetic field, move to the side with the related electromagnetic field until the related electromagnetic field disappears. The vanishing point is recorded as point Y, where Y is the fault point. If neither side of point X has a related electromagnetic field, it is determined that the unloaded line has no fault point. The device for detecting the relevant electromagnetic field in step S02 is selected by the following method: If the current generated by applying an AC voltage signal is large and the voltage is low, the fault type is determined to be direct grounding, and a detector is used to detect the relevant electromagnetic field and convert it into current; If the current and voltage generated by applying the AC voltage signal are large, the fault type is determined to be high-resistance grounding. Use a clamp ammeter to detect the relevant electromagnetic field and convert the detected relevant electromagnetic field into current. When using, mount the clamp ammeter on an unloaded line. If the current generated by applying the AC voltage signal is small and the voltage is high, the fault type is determined to be hidden indirect grounding. Use a clamp ammeter to detect the relevant electromagnetic field and convert the detected relevant electromagnetic field into current. When in use, mount the clamp ammeter on an unloaded line.

2. The method for diagnosing and locating a distribution network fault according to claim 1, characterized in that: The AC voltage signal generating device comprises: A transformer, wherein the output end of the transformer is a signal output end; An inverter bridge, wherein an output end of the inverter bridge is electrically connected to an input end of the transformer; An isolation driver, the isolation driver being electrically connected to the inverter bridge control terminal; A selection module, the selection module comprising two comparators, the output ends of the two comparators being electrically connected to the input end of the isolation driver; A sawtooth wave generator, wherein an output terminal of the sawtooth wave generator is electrically connected to two positive and negative input terminals of two comparators; A feedback circuit, wherein an input terminal of the feedback circuit is electrically connected to one of the signal output terminals, and an output terminal of the feedback circuit is electrically connected to the other two positive and negative input terminals of the two comparators; A control module is electrically connected to the feedback circuit, and the control module is electrically connected to the sawtooth wave generator. The control module is used to input a square wave to the sawtooth wave generator and a sine wave to the feedback circuit.

3. The method for diagnosing and locating a distribution network fault according to claim 2, characterized in that: The sawtooth wave generator comprises: an integrator, the integrator being electrically connected to the control module; a first amplifier, the first amplifier being electrically connected to an output terminal of the integrator; An operational amplifier is electrically connected to the output terminal of the first amplifier, the output terminal of the operational amplifier is electrically connected to the positive input terminal of one of the comparators, and the input terminal of the operational amplifier is electrically connected to the negative input terminal of the other comparator.

4. The method for diagnosing and locating a distribution network fault according to claim 2, characterized in that: The feedback circuit comprises: The analog-to-digital conversion module, the control module is electrically connected to one of the signal output terminals via the analog-to-digital conversion module; A digital-to-analog conversion module, the digital-to-analog conversion module is electrically connected to the control module; A second amplifier, the second amplifier is electrically connected to an output end of the digital-to-analog conversion module; PID, the PID input end is electrically connected to the second amplifier, and the PID input end is electrically connected to another signal output end.

5. The method for diagnosing and locating faults in a distribution network according to claim 3, characterized in that: The sawtooth wave generator also includes: A first filter capacitor is arranged between the integrator and the control module.

6. The method for diagnosing and locating faults in a distribution network according to claim 4, characterized in that: The feedback circuit further includes: A second filter capacitor is provided between the second amplifier and the PID.

7. The method for diagnosing and locating faults in a distribution network according to claim 1, characterized in that: The detector comprises: Induction coil; a third amplifier, the third amplifier being electrically connected to the induction coil; A second analog-to-digital conversion module, the second analog-to-digital conversion module is electrically connected to the third amplifier; A second control module, wherein the second control module is electrically connected to the second analog-to-digital conversion module.

8. The method for diagnosing and locating faults in a distribution network according to claim 1, characterized in that: The determination method of the relevant electromagnetic field is: Perform Fourier transform on the signal; Extract the signal strength f of the signal with the same frequency as the AC voltage signal; Get the distance d between the detection point and the unloaded line; Correlation between detection distance d and signal strength f; If there is a correlation between the distance d and the signal strength f, the detected signal is determined to be a correlated electromagnetic field, otherwise it is not a correlated electromagnetic field.

9. The method for diagnosing and locating faults in a distribution network according to claim 1, characterized in that: The method for detecting the correlation between the distance d and the signal strength f is: The distance L perpendicular to the length direction of the unloaded line is made to fluctuate during the detection process of the detection point along the length direction of the unloaded line. The correlation between the signal strength f and the distance L is determined. If the signal strength f decreases as the distance L increases, and the signal strength f increases as the distance L decreases, then it is determined that f is correlated with the distance L, otherwise there is no correlation.

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