Distribution cable fault positioning device and method

Abstract

The invention relates to a distribution cable fault positioning device which comprises a near-end detection device, the near-end detection device comprises a data processing and control module, and an I / O interface of the data processing and control module is connected with a signal generation module, an original signal sampling module and a wire core sampling module; the signal generation module and the original signal sampling module are connected with the input end of the voltage signal follower, and the output end of the voltage signal follower is connected with the wire core sampling module. The invention further relates to a distribution cable fault positioning method, the data processing and control module controls the signal generation module to generate a linear frequency modulation signal, the linear frequency modulation signal is injected into a terminal of a to-be-detected cable after power amplification of the voltage signal follower, and the signal is transmitted along the cable. Refraction and reflection of signals occur at the position where the impedance of a fault is not matched and at the tail end of the cable, and positioning of the fault position is achieved by detecting the time when the reflected signals arrive at a detection point. The detection sensitivity is higher, and the voltage applied to the cable in the detection process is low.

Description

Technical Field

[0001] The present invention belongs to the technical field of power cable fault detection, and in particular relates to a distribution cable fault locating device and method. Background Art

[0002] Distribution cables are the main structure of urban power distribution networks. They may fail during operation and handover tests, leading to unplanned power outages. After a power outage caused by a cable failure, the most urgent thing is to find the fault location, eliminate the fault and resume power supply. However, since most distribution network cables are directly buried, even if there are cable tunnels, they are usually narrow. Therefore, finding the cable fault location after a cable failure usually troubles equipment operation and maintenance personnel.

[0003] According to the size of the fault resistance at the fault point and the connection status of the wire core, the defects can be divided into broken wire faults, low-resistance faults (fault resistance is less than 100Ω) and high-resistance faults (fault resistance is greater than 100Ω). Existing fault detection technologies include time domain signal reflection method (TDR), frequency domain signal reflection method (FDR) and high-frequency impedance spectroscopy (BIS). Among them, the TDR method is the most widely used, but it can usually only be used to detect low-resistance faults and broken wire faults, and the response to high-resistance faults is not obvious. The BIS method improves the detection capability of high-resistance faults to about 1kΩ, and the FDR method improves the detection capability of high-resistance faults to about 10kΩ.

[0004] However, when a cable fails, there is a certain probability that a higher fault resistance fault will occur. Under such conditions, existing means cannot detect it. Therefore, the fault point is usually further destroyed into a low-resistance fault or a disconnection fault by continuously applying a large current, and then the TDR method is used for detection. However, in the process of destroying the fault point, the high-voltage pulse generated by the discharge may cause secondary damage to the cable insulation. After the fault is located and repaired using the above lossy method, there is a probability that a new fault will be caused after a short period of operation. Summary of the invention

[0005] The object of the present invention is to provide a distribution cable fault locating device and method which applies a low voltage to the cable during the detection process and does not cause secondary damage to the cable.

[0006] The technical solution of the present invention:

[0007] A distribution cable fault locating device comprises a proximal detection device, wherein the proximal detection device comprises a data processing and control module, a signal generating module connected to the I / O interface of the data processing and control module, an original signal sampling module and a wire core sampling module; the signal generating module and the original signal sampling module are connected to the input end of a voltage signal follower, and the output end of the voltage signal follower is connected to the wire core sampling module.

[0008] The data processing and control module is the control and computing center of the entire device. It uses FPGA as the core chip and is responsible for the control of the signal generation module, the original signal sampling module and the line core sampling module, as well as the data processing of the collected signals.

[0009] Preferably, it also includes a far-end echo suppression device, the near-end detection device is connected to the detection terminal of the cable to be tested, and the far-end echo suppression device is connected to the other end of the cable to be tested; the far-end echo suppression device includes an adjustable resistor and an adjustable capacitor connected in parallel.

[0010] The remote echo suppression device is composed of an adjustable resistor and an adjustable capacitor in parallel. It suppresses the terminal reflection signal when performing high-resistance fault measurement and reduces the impact of the reflection signal on the fault point.

[0011] Preferably, the signal generating module adopts a DDS chip, and directly outputs a linear frequency modulation signal under the control of the data processing and control module.

[0012] Preferably, the output end of the voltage signal follower is connected to the other end of the cable to be tested, and the input signal and output signal of the voltage signal follower have the same phase and the same voltage amplitude.

[0013] Preferably, the original signal sampling module collects the output signal of the signal generating module, and the core sampling module directly collects the voltage between the cable core and the ground wire.

[0014] A method for locating a distribution cable fault, in which a data processing and control module controls a signal generation module to generate a linear frequency modulation signal, which is injected into the terminal of a cable to be tested after being amplified by a voltage signal follower. The signal propagates along the cable, and refraction and reflection of the signal occur at the impedance mismatch position where the fault occurs and at the end of the cable. The fault position is located by detecting the time it takes for the reflected signal to arrive at the detection point.

[0015] Preferably, the fault position is located in the case of a low resistance fault, a disconnection fault and a high resistance fault.

[0016] The distribution cable includes a core, an insulation layer and a copper shielding layer. When a fault occurs, there are two situations. One is that the core is burned out at the fault point, which is a broken line fault; the other is that the insulation layer at the fault point is broken down, and the core and the copper shield are bridged. According to the resistance of the bridge position between the core and the copper shield at the fault point, it can be divided into a low-resistance fault and a high-resistance fault. At present, the industry and academia have not reached a consistent standard for distinguishing the resistance values ​​of low-resistance faults and high-resistance faults. In the present invention, a low-resistance fault is defined as a fault with a fault resistance lower than 100Ω, and a high-resistance fault is defined as a fault with a fault resistance not lower than 100Ω.

[0017] Preferably, when a low-resistance fault occurs in the cable, the fault location method of the cable is:

[0018] The detection terminal is connected to the near-end detection device, and the other end of the cable is not connected to the far-end echo suppression device. The time for the linear frequency modulation signal to be injected into the cable is t lr1 , the time it takes for the reflected signal from the fault point to reach the detection point is t lr2 , the time it takes for the end reflected signal to reach the detection point is t lr3 , by matching the signal collected by the core sampling module, a pulse signal will be generated at three time points after matching filtering. Through the three time points, the distance l1 between the fault point and the detection end is obtained by the following formula:

[0019]

[0020] Where L is the total length of the cable.

[0021] Preferably, when a cable short circuit fault occurs, the cable fault location method is:

[0022] First, connect the near-end detection device to the detection terminal. The other end of the cable does not need to be connected to the far-end echo suppression device. The linear frequency modulation signal is injected into the cable for a time t b1 , the time it takes for the reflected signal from the fault point to reach the detection point is t b2 , due to the disconnection, the detection signal does not continue to propagate to the other end of the cable at the disconnection point, so the reflected signal at the other end cannot be detected. The near-end detection device is connected to the other end of the cable, and the linear frequency modulation signal is injected into the cable at the other end of the cable for a time t b3 , the time it takes for the reflected signal from the fault point to reach the detection point is t b4 , through four detection time points, the distance l2 from the fault point to the first connection terminal position is calculated using the following formula:

[0023]

[0024] Where L is the total length of the cable.

[0025] Preferably, when a high-resistance fault occurs in the cable, the fault location method of the cable is:

[0026] The near-end detection device is connected to the detection terminal, and the other end of the cable is connected to the far-end echo suppression device. First, the linear frequency modulation signal is continuously injected from the detection terminal, and the far-end echo suppression device is adjusted to reduce the far-end reflection signal. The original signal sampling module and the core sampling module start working at the same time. The signal collected by the original signal sampling module is u2(t), and the signal collected by the core sampling module is u1(t); the voltage collected by the core sampling module minus the voltage of the original signal sampling module is used as the voltage before the matched filter signal is processed. The time for the linear frequency modulation signal to be injected into the cable is t hr1 , the time it takes for the reflected signal from the fault point to reach the detection point is thr2 , the time it takes for the end reflected signal to reach the detection point is t hr3 , the distance l3 between the fault point and the detection end is calculated as:

[0027]

[0028] Where L is the total length of the cable.

[0029] The voltage collected by the core sampling module minus the voltage of the original signal sampling module is used as the voltage before matched filter signal processing. This process is to reduce the impact of the injected signal on the weak signal reflected by the high-resistance fault point. Although the far-end reflected signal and the detection end transmission signal are suppressed, tiny pulses can still be detected after matched filtering. The location method of high-resistance faults is the same as that of low-resistance faults.

[0030] Advantages of the present invention:

[0031] The present invention greatly improves the sensitivity of fault detection. The present invention is a non-destructive detection technology. The fault location method used can improve the detection capability of fault resistance to hundreds of kΩ. The voltage applied to the cable during the detection process is relatively low, and no secondary damage to the cable is caused.

[0032] 1. The present invention realizes high-sensitivity cable fault detection and positioning, can test a full range of fault types, and can test a wide range of cable fault resistance.

[0033] 2. The detection voltage adopted by the present invention is relatively low, which will not cause secondary damage to the cable and will not cause harm to personnel during the test process.

[0034] 3. The equipment of the present invention requires less power and is easy to carry for field testing.

[0035] 4. The signal used in the present invention is a linear frequency modulation signal, which can generate a signal gain of up to 50dB after pulse compression, and can effectively detect the reflected signal of a small impedance mismatch point. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of a distribution cable fault locating device according to the present invention;

[0037] Figure 2 It is a schematic diagram of the detection waveform of the low-resistance fault of the present invention;

[0038] Figure 3 This is a schematic diagram of the waveform of the signal received by the detection end after matched filtering of the present invention;

[0039] Figure 4 This is a waveform diagram of the near-end detection result of a disconnection fault according to the present invention;

[0040] Figure 5 This is a waveform diagram of the remote detection result of a disconnection fault according to the present invention;

[0041] Figure 6 This is a flow chart of the fault testing process of the present invention;

[0042] Figure 7-1 This is a test result diagram after low-resistance fault matching filtering of the present invention;

[0043] Figure 7-2 The test result diagram after high-resistance fault matching filtering of the present invention;

[0044] Figure 7-3 The test result diagram of the broken line fault after near-end matching filtering of the present invention;

[0045] Figure 7-4 The test result diagram of the disconnection fault after remote matching filtering of the present invention;

[0046] In the accompanying drawings, 1-proximal detection device,

[0047] 11-data processing and control module, 12-signal generation module, 13-voltage signal follower, 14-original signal sampling module, 15-core sampling module;

[0048] 2- Far-end echo suppression device;

[0049] 3- Cable under test. DETAILED DESCRIPTION

[0050] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0051] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper", "lower", "inner", "back", etc. are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0052] In addition, in the description of the present invention, unless otherwise clearly defined, the terms "installed", "connected", "connected", and "connector" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in combination with specific circumstances.

[0053] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0054] Device Embodiment

[0055] like Figure 1 As shown, the device for detecting and locating distribution cable faults mainly consists of two parts, namely a near-end detection device 1 and a far-end echo suppression device 2. The near-end detection device 1 consists of a data processing and control module 11, a signal generation module 12, a voltage signal follower 13, an original signal sampling module 14 and a core sampling module 15. The far-end echo suppression device 2 consists of an adjustable resistor and an adjustable capacitor in parallel.

[0056] The data processing and control module 11 uses FPGA as the core chip. The I / O interface of the data processing and control module 11 is connected to the signal generation module 12, the original signal sampling module 14 and the line core sampling module 15, and plays the role of control, data acquisition and data processing.

[0057] The signal generating module 12 adopts a DDS chip and directly outputs a linear frequency modulation signal under the control of the data processing and control module 11 .

[0058] The voltage signal follower 13 plays the role of voltage following and signal power amplification. The input signal and output signal of the voltage signal follower 13 have the same phase and voltage amplitude. The output of the voltage signal follower 13 is directly connected to the core of the cable to be tested.

[0059] The original signal sampling module 14 and the core sampling module 15 are two sampling modules, which are respectively controlled by the data processing and control module 11. The core sampling module 15 directly samples the voltage between the cable core and the ground wire, and the original signal sampling module 14 samples the output signal of the signal generating module 12.

[0060] The far-end echo suppression device 2 is composed of an adjustable resistor and an adjustable capacitor in parallel. During the high-resistance fault test, the impedance value of the adjustable resistor and the adjustable capacitor are adjusted to basically match the characteristic impedance of the cable, thereby suppressing the reflected signal at the end.

[0061] The detection signal used is a linear frequency modulation signal, which is expressed as:

[0062]

[0063] Where:

[0064]

[0065] Where T is the time length of the linear frequency modulation signal, f0 is the center frequency, B is the signal bandwidth, t is the time, μ is the intermediate variable, and a(t) is the voltage envelope, which is chosen as a constant 1 here.

[0066] The process of matching filter on the signal u1(t) collected by the core sampling module is described as:

[0067]

[0068] Here, τ is the integral element in the integral formula and no additional definition is required.

[0069] After matched filtering, the gain that the signal can generate is calculated as T·B.

[0070] When testing low-resistance faults and line break faults, the time length of the FM signal is selected to be 1ms, the center frequency is selected to be 25MHz, the frequency width is selected to be 40MHz, and the signal gain is 40,000 times.

[0071] When testing a high-resistance fault, since the high-resistance fault signal echo is small, a higher signal gain is required, and the time length of the FM signal is extended to 100ms. At this time, the signal gain is 4 million times.

[0072] Method Embodiment

[0073] Perform fault setting and detection tests on a cable in the laboratory.

[0074] The steps for setting the fault resistance for low resistance fault and high resistance fault are:

[0075] Break the cable sheath and destroy the copper shielding layer to form a round hole.

[0076] Insert a steel nail into the gap in the shielding layer. The insertion depth of the steel nail reaches the wire core, and there is no connection between the steel nail and the shielding layer.

[0077] A resistor is connected between the steel nail head and the shielding layer, and the size of the connection resistance determines whether it is a low-resistance fault or a high-resistance fault.

[0078] Wire break fault Two cables of the same length with their copper shields connected together simulate a wire break fault.

[0079] Method Example 1

[0080] When testing low resistance faults, the device is configured as follows:

[0081] 1) The detection end is connected to the near-end detection device 1, and the original signal adopts the module 14 to exit the operation.

[0082] 2) The far end is not connected to the far end echo suppression device 2.

[0083] The testing process is:

[0084] 1) At the detection end, a linear frequency modulation signal is injected into the cable by the near-end detection device 1.

[0085] 2) After the signal propagates to the fault point, it will be refracted and reflected. The reflected signal is transmitted back to the detection end, and the refracted signal continues to propagate forward and emits total reflection at the terminal position at the far end. The signal received at the detection end after the transmission signal, the reflected signal at the fault point, the reflected signal at the end and the three signals are aliased is as follows: Figure 2 The time of transmitting signal is t lr1 , the time it takes for the reflected signal from the fault point to reach the detection point is t lr2 , the time it takes for the end reflected signal to reach the detection point is t lr3 When the three signals reach the detection end, some signal aliasing will occur, making it impossible to determine t lr2 and the arrival time of t3.

[0086] 3) The signal detected by the receiving end is matched filtered according to the matched filtering process formula. The signal waveform after matched filtering is as follows: Figure 3 As shown in the figure, the signal is compressed into three pulses. The position of the pulse peak is the time of signal arrival, which can be identified by the peak extraction method. lr1 ,t lr2 and t lr3 Three time points.

[0087] 4) After the identification and collection of the three time points are completed, the fault location can be calculated by the following formula:

[0088]

[0089] Where: L is the total length of the cable, l1 is the distance between the fault point and the detection point.

[0090] The calculation results are shown in Figure 7-1 .

[0091] Method Example 2

[0092] When testing for a line break fault, the device is configured as follows:

[0093] 1) The detection end is connected to the near-end detection device 1, and the original signal adopts the module 14 to exit the operation.

[0094] 2) The far end is not connected to the far end echo suppression device.

[0095] The testing process can be described as:

[0096] 1) At the detection end, a linear frequency modulation signal is injected into the cable by the near-end detection device 1.

[0097] 2) After the signal propagates to the disconnection point, it will be reflected. The transmitted signal, the reflected signal at the fault point, the signal received at the detection end after the two signals are aliased, and the signal after matched filtering is as follows: Figure 4 The time of transmitting signal is t b1 , the time it takes for the reflected signal from the fault point to reach the detection point is t b2 .

[0098] 3) Replace the detection end, connect the near-end detection device to the other end of the faulty cable, and inject a linear frequency modulation signal into the cable.

[0099] 4) After the signal propagates to the disconnection point, it will be reflected. The transmitted signal, the reflected signal at the fault point, the signal received at the detection end after the two signals are aliased, and the signal after matched filtering is as follows: Figure 5 The time for transmitting the signal at the other end is t b3 , the time it takes for the reflected signal from the fault point to reach the detection point is t b4 .

[0100] 5) Complete t b1 ,t b2 ,t b3 and t b4 After the time points are collected, the distance from the fault point to the first connection terminal position can be calculated using the following formula:

[0101]

[0102] Where: L is the total length of the cable, l2 is the distance between the fault point and the detection point.

[0103] The calculation results are shown in Figure 7-3 and Figure 7-4 .

[0104] Method Example 3

[0105] When testing a high resistance fault, the device is configured as follows:

[0106] 1) The detection end is connected to the near-end detection device 1, and the original signal adopting module 14 is put into operation.

[0107] 2) The far end is connected to the far end echo suppression device 2.

[0108] The testing process can be described as:

[0109] 1) At the detection end, a linear frequency modulation signal is injected into the cable by the near-end detection device 1.

[0110] 2) Adjust the far-end echo suppression device 2 so that the impedance value of the far-end echo suppression device 2 is close to the characteristic impedance of the cable. The adjustment process can be described as:

[0111] Step 1: Preliminarily adjust the remote echo suppression device 2 to an impedance value that is close to the characteristic impedance value of the cable body, which is 20Ω to 40Ω. The impedance value of the distribution cable body is about 20Ω to 40Ω.

[0112] Step 2: The near-end detection device injects a linear frequency modulation signal into the cable. The time length of the frequency modulation signal is 1ms. The signal collected by the original signal sampling module 14 is u2(t) and the signal collected by the core sampling module 15 is u1(t);

[0113] Step 3: Perform matched filtering on the difference between u1(t) and u2(t). In this process, the pulse peak of the incident signal after matched filtering can be significantly suppressed, and then the pulse peak size of the far-end reflected signal after matched filtering is observed;

[0114] Step 4: fine-tune the adjustable resistance and the adjustable capacitance of the far-end echo suppression device 2, and then repeat steps 2 to 4 until the pulse peak value of the far-end reflected signal after matched filtering is reduced to a minimum.

[0115] The second and third steps of the process are automatically processed in the data processing and control module 11, while the fine-tuning of the far-end echo device requires human intervention.

[0116] 3) At the detection end, a linear frequency modulation signal is injected into the cable by a near-end detection device, and the time length of the linear frequency modulation signal is 100ms.

[0117] 4) The injection signal, the reflected signal at the fault point and the end reflected signal are collected through the detection end signal, and the positioning is performed using the same method as the low-resistance positioning.

[0118] During the high-resistance fault test, the original signal sampling module 14 and the far-end echo suppression device 2 are introduced. This is because the reflected signal of the high-resistance fault is small. Even after matched filtering, the pulse compressed by the reflected signal after matched filtering may be submerged in the pulse sidelobes compressed by the transmitted signal and the end reflected signal, making it impossible to determine the time when the echo signal arrives at the detection point.

[0119] The pulse peak value compressed by the incident signal matching filter is suppressed by making a difference between the collected signals of the core sampling module 15 and the original signal sampling module 14, and the value of the end reflection signal is reduced by connecting a suppression resistor at the end to suppress the pulse peak value compressed by the far-end reflection signal matching filter.

[0120]

[0121] Where: L is the total length of the cable, l3 is the distance between the fault point and the detection point.

[0122] The calculation results are shown in Figure 7-2 .

[0123] The complete fault testing process of the first embodiment, the second embodiment and the third embodiment is as follows: Figure 6 shown.

[0124] The laboratory test results of Example 1, Example 2 and Example 3 are shown in Table 1;

[0125] Table 1

[0126] Cable length Fault location Fault resistance Test Results error Low resistance 400m 200m 5Ω 199.5m 0.125％ High resistance 400m 200m 10kΩ 198.9m 0.275％ Disconnection 400m 200m --- 199.8m 0.05％

[0127] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A distribution cable fault location device, characterized in that: The invention comprises a near-end detection device (1), wherein the near-end detection device (1) comprises a data processing and control module (11), a signal generation module (12), an original signal sampling module (14) and a wire core sampling module (15) connected to the I / O interface of the data processing and control module (11); the signal generation module (12) and the original signal sampling module (14) are connected to the input end of a voltage signal follower (13), and the output end of the voltage signal follower (13) is connected to the wire core sampling module (15).

2. A distribution cable fault location device according to claim 1, characterized in that: It also includes a far-end echo suppression device (2), wherein the near-end detection device (1) is connected to the detection terminal of the cable to be tested, and the far-end echo suppression device (2) is connected to the other end of the cable to be tested; the far-end echo suppression device (2) includes an adjustable resistor and an adjustable capacitor connected in parallel.

3. A distribution cable fault location device according to claim 2, characterized in that: The signal generation module (12) adopts a DDS chip and directly outputs a linear frequency modulation signal under the control of the data processing and control module (11).

4. A distribution cable fault location device according to claim 2, characterized in that: The output end of the voltage signal follower (13) is connected to the other end of the cable to be tested, and the input signal and output signal of the voltage signal follower (13) have the same phase and the same voltage amplitude.

5. A distribution cable fault location device according to claim 2, characterized in that: The original signal sampling module (14) collects the output signal of the signal generating module (12), and the core sampling module (15) directly collects the voltage between the cable core and the grounding wire.

6. A method for locating a distribution cable fault, using a distribution cable fault locating device according to any one of claims 1 to 5, characterized in that: The data processing and control module (11) controls the signal generation module (12) to generate a linear frequency modulation signal, which is injected into the terminal of the cable to be tested after being power-amplified by the voltage signal follower (13). The signal propagates along the cable, and refraction and reflection of the signal occur at the impedance mismatch position where the fault occurs and at the end of the cable. The fault position is located by detecting the time when the reflected signal arrives at the detection point.

7. A distribution cable fault location method according to claim 6, characterized in that: It includes the positioning of fault positions in the cases of low-resistance fault, line break fault and high-resistance fault; a low-resistance fault is a fault with a fault resistance lower than 100Ω, and a high-resistance fault is a fault with a fault resistance not lower than 100Ω.

8. A distribution cable fault location method according to claim 7, characterized in that: When a low-resistance fault occurs in the cable, the fault location method is as follows: The detection terminal is connected to a near-end detection device (1), the other end of the cable is not connected to a far-end echo suppression device (2), and the linear frequency modulation signal is injected into the cable for a time t lr1 , the time it takes for the reflected signal from the fault point to reach the detection point is t lr2 , the time it takes for the end reflected signal to reach the detection point is t lr3 , by performing matched filtering on the signal collected by the core sampling module (15), pulse signals will be generated at three time points after matched filtering. At the three time points, the distance l1 between the fault point and the detection end is calculated using the following formula: Where L is the total length of the cable.

9. A distribution cable fault location method according to claim 7, characterized in that: When a cable breaks, the cable fault location method is as follows: First, the near-end detection device (1) is connected to the detection terminal. The other end of the cable does not need to be connected to the far-end echo suppression device (2). The linear frequency modulation signal is injected into the cable for a time t b1 , the time it takes for the reflected signal from the fault point to reach the detection point is t b2 Since the cable is disconnected, the detection signal does not continue to propagate toward the other end of the cable at the disconnection point, so the reflected signal at the other end cannot be detected. The near-end detection device (1) is connected to the other end of the cable. The linear frequency modulation signal at the other end of the cable is injected into the cable for a time t b3 , the time it takes for the reflected signal from the fault point to reach the detection point is t b4 , through four detection time points, the distance l2 from the fault point to the first connection terminal position is calculated using the following formula: Where L is the total length of the cable.

10. A method for locating a distribution cable fault according to claim 9, characterized in that: When a high-resistance fault occurs in the cable, the cable fault location method is as follows: A near-end detection device (1) is connected to the detection terminal, and the other end of the cable is connected to a far-end echo suppression device (2). First, a linear frequency modulation signal is continuously injected from the detection terminal, and the far-end echo suppression device (2) is adjusted to reduce the far-end reflection signal. The original signal sampling module (14) and the wire core sampling module (15) start working at the same time. The signal collected by the original signal sampling module (14) is u2(t), and the signal collected by the wire core sampling module (15) is u1(t). The voltage collected by the wire core sampling module (15) minus the voltage of the original signal sampling module (14) is used as the voltage before the matched filter signal is processed. The time for the linear frequency modulation signal to be injected into the cable is t hr1 , the time it takes for the reflected signal from the fault point to reach the detection point is t hr2 , the time it takes for the end reflected signal to reach the detection point is t hr3 , the distance l3 between the fault point and the detection end is calculated as: Where L is the total length of the cable.

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