Locating device for cable fault

Abstract

The application provides a cable fault point positioning detection device. The positioning detection device comprises a power supply, a first switch, a second switch, a current limiter, a connecting line and a voltmeter. Two poles of the power supply are connected with the first switch and the second switch respectively. The first switch, the current limiter, a normal phase line of a fault cable, the connecting line, a faulty and non-break phase line of the fault cable and the second switch are connected in series to form an electrical detection loop. The voltmeter is used for measuring the voltage between the fault phase line of the fault cable and the power supply side and the voltage between the fault phase line and a load side. The device has simple structure, economy and easy operation. The positioning process of the fault point is simple, fast and accurate.

Description

Technical Field

[0001] This application belongs to the field of power detection technology, specifically, it relates to a cable fault location detection device. Background Technology

[0002] Currently, power cables are widely used in various power production units and power-consuming enterprises. Cable faults are a common problem. Most faults occur in visible locations, which can be detected by sight, sound, touch, and smell. However, when faults occur in hidden locations, especially inside the cable or in concealed or buried areas, the fault location cannot be clearly exposed, increasing the difficulty of locating and eliminating the fault. Faults are particularly prominent in high- and low-voltage AC power cables of centralized photovoltaic systems in mountainous areas, which are often directly buried. This is mainly due to the dispersed installation locations of transformer substations and inverters, the complex cable routing caused by terrain, unclear or missing construction drawings, and damage to ground cable routing markings due to agricultural planting and grazing. The varying depths of burial further complicate cable routing identification, making fault location even more difficult.

[0003] Currently, there are many types of cable fault detection devices on the market. The technologies generally used are low-voltage pulse method, high-voltage flashover method, and bridge resistance measurement method for location. 1. Low-voltage pulse method: The cable fault detection device emits a low-voltage pulse signal, and the location of the cable fault is determined by the time and waveform of the voltage or current generated by the signal. 2. High-voltage flashover method: A high-voltage generator emits a high-voltage pulse signal, and the location of the cable fault is detected by the flashover discharge sound generated by the high voltage. 3. Bridge resistance measurement method: A suitable bridge is selected, and the location of the fault is calculated based on the resistance ratio when the bridge is balanced and the known cable length. Existing cable fault detection instruments are technologically mature and widely used. They are highly accurate and quick to locate common faults in exposed power cable lines and directly buried power cable lines with obvious routes. However, the accuracy is lower and the time is longer for locating internal faults and some special faults in power cable lines, requiring auxiliary methods. The main disadvantages are as follows:

[0004] First, while cable fault detection instruments appear simple to operate, their practical application demands a high level of professional skill, making fault identification difficult. Existing cable fault detection instruments are primarily electronic products, integrating various types of cable faults with basic electrical engineering knowledge. Their operation methods and search modes are largely fixed, simple, easy to understand, and quick to learn. However, when general operators cannot handle the diverse and complex types of cable faults encountered in practice, fault finding requires combining knowledge of cable faults with the appropriate instrument operation methods and selection modes to pinpoint the fault. This places high skill demands on operators of cable fault detection instruments. In practical applications, various unique cable faults arise, and operators often have misconceptions about the functions of cable fault detectors and the different types of cable faults. They believe that a cable fault detection instrument that can detect some common faults is universal and can always find the fault. General operators arbitrarily select cable fault detection instruments, operating methods, and search modes, leading to problems with finding faults when encountering unique cable faults. This is time-consuming and labor-intensive, and in severe cases, can cause secondary insulation damage and equipment damage to high- and low-voltage power cables.

[0005] Secondly, the accuracy of distance measurement using waveforms and bridge resistance is poor. Cable fault detection instruments that use existing distance measuring instruments to measure distance using waveforms and bridge resistance are often affected by factors such as different types of cable faults, the laying direction, and the insulation material of the cable core wires, resulting in a large deviation between the measured distance and the actual distance to the fault point.

[0006] Third, using high-voltage discharge signals to generate high-voltage flashover discharge sounds for fault location in enclosed cables presents problems of misjudgment and difficulty in locating faults. Existing fault location instruments using high-voltage generators to apply pressure and generate flashover discharge sounds at the fault point are susceptible to various issues, including different types of cable faults (especially short circuits and enclosed faults), blind cable laying, extremely small or inconspicuous flashover discharge sounds, multiple discharge points within the cable, difficulty in locating the fault point, and damage to the cable's outer sheath leading to multiple discharge points while the fault point itself does not discharge, resulting in misjudgment of the fault location.

[0007] In summary, using specialized cable fault detection equipment is a reliable, accurate, and quick way to check for common and obvious cable faults. However, when checking for internal cable faults or some special types of faults in concealed cables, problems arise such as inaccurate location and distance measurement, long troubleshooting times, high costs, and low efficiency. Utility Model Content

[0008] The technical problem addressed by this application is: when a cable experiences an internal fault or some special types of faults in a concealed installation, and conventional methods and testing instruments cannot promptly eliminate the fault, how to economically, quickly, and accurately locate the fault point, promptly address the fault point, restore power to the cable line as soon as possible, and reduce fault losses.

[0009] This application provides a cable fault location detection device, which includes a power supply, a first switch, a second switch, a current limiter, a connecting wire, and a voltmeter. The two poles of the power supply are respectively connected to the first switch and the second switch. The first switch, the current limiter, the normal phase line of the faulty cable, the connecting wire, the faulty but unbroken phase line of the faulty cable, and the second switch are connected in series to form an electrical detection circuit. The voltmeter is used to measure the voltage between the faulty phase line of the faulty cable and the power supply side, and the voltage between the faulty phase line and the load side.

[0010] Optionally, the power source is a 220V portable power bank.

[0011] Optionally, the current limiter is a resistance heater or an incandescent lamp.

[0012] Optionally, the faulty but unbroken phase of the faulty cable is the steel-armored grounding wire of the faulty cable.

[0013] The cable fault location detection device provided in this application has the following technical advantages:

[0014] The device is simple in structure, economical and easy to operate, and the fault location process is simple, fast and accurate. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the usage state of a cable fault location detection device according to one or more embodiments. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0017] Before describing the various embodiments of this application in detail, the technical concept of this application is first briefly described: Currently, when locating and detecting fault points, for internal cable faults or some special types of faults in concealed cables, cable fault detection devices often result in inaccurate positioning and distance measurement. Therefore, the cable fault point location and detection device, based on the principle of the applied voltage method, utilizes the location detection device and the relevant lines of the faulty cable to form an electrical circuit. It calculates the distance from the fault point to the cable length by measuring the ratio of the potential difference from the fault point to both ends of the cable to the total potential difference of the cable. This device is simple in structure, economical, and provides simple, fast, accurate, and easy-to-operate positioning. The specific principle of the cable fault point location and detection device of this application will be described below with reference to more embodiments.

[0018] Specifically, such as Figure 1 As shown, the cable fault location detection device in this embodiment includes a power supply 10, a first switch 20, a second switch 30, a current limiter 40, a connecting wire 50, and a voltmeter (not shown). The two poles of the power supply 10 are connected to the first switch 20 and the second switch 30 respectively. The first switch 20, the current limiter 40, the normal phase line of the faulty cable, the connecting wire 50, the faulty but unbroken phase line of the faulty cable, and the second switch 30 are connected in series to form an electrical detection circuit. The voltmeter is used to measure the voltage between the faulty phase line of the faulty cable and the power supply side, and the voltage between the faulty phase line and the load side.

[0019] In one or more embodiments, the power supply 10 is a 220V portable power supply, or it can directly use 220V AC mains power. The current limiter 40 is a resistance heater or an incandescent lamp. The function of the current limiter 40 is to prevent excessive current from causing a short circuit and burning out the equipment when an external voltage is applied to the cable. For example, the power of the current limiter 40 is 1000W to 2000W, and the operating voltage is 220V.

[0020] In one or more embodiments, the faulty but unbroken phase of the faulty cable serves as the current loop. Generally, a phase with higher resistance is selected as the current loop, as this results in a larger voltage drop when current flows through it, making the measurement less affected by other factors and thus more accurate. For example, the steel-armored grounding wire of the faulty cable can be used as the faulty but unbroken phase, because the steel-armored grounding wire has a higher resistance and a larger voltage drop, resulting in higher voltage measurement accuracy. If the steel-armored grounding wire is incomplete, the neutral or phase wire can be selected as the current loop conductor.

[0021] In one or more embodiments, a non-faulty phase cable core is typically selected on the faulty cable as the current loop conductor. When all cores are faulty, a single-core cable can be temporarily laid as the current loop conductor.

[0022] Voltage-based cable location utilizes the fact that when the insulation between phases or to ground fails, a short circuit between two or more metal conductors creates molten metal or vaporized metal discharge, forming contact conductors or indirect contact semiconductors that adhere to the damaged insulation points. These conductors are difficult to restore naturally and share the common characteristic of being conductive again during a short circuit. This characteristic is used to select the faulty phase or ground in the cable as the current loop for applying an external voltage, and the other faulty phase or ground as the potential difference measurement loop. The distance from the fault point to the cable is calculated by measuring the ratio of the potential difference from the fault point to the cable's two ends to the total cable potential difference, thus determining the cable length and locating the fault.

[0023] For example, when phase C of the faulty cable is the faulty phase, the power supply 10, the first switch 20, the current limiter 40, the normal phase line B, the connecting wire 50, the steel armor grounding wire, and the second switch 30 are connected in series to form an electrical detection circuit. The fault point of phase C is short-circuited to the steel armor grounding wire. One side of the fault point is terminal C1, and the other side is terminal C2. The first switch 20 and the second switch 30 are closed, and the voltage V1 between terminal C1 and the power supply side and the voltage V2 between terminal C2 and the power supply side are measured using a voltmeter. Assuming the cable length is L, the distance from the fault point to terminal C1 can be calculated as follows:

[0024] The complete positioning and detection process will be described below with reference to specific embodiments.

[0025] 1. Preparations before work. First, disconnect the power supply, remove both ends of the faulty cable, and move the cable ends to a safe area, maintaining a safe distance from operating equipment.

[0026] 2. Faulty cable inspection. Use a multimeter or megohmmeter to check the fault type of the cable core wire (open circuit, short circuit, grounding; resistance greater than 100kΩ is high resistance type, less than 100kΩ is low resistance type, and less than 100Ω is short circuit type).

[0027] 3. Fault location inspection. Based on the confirmed cable fault method and type, use a troubleshooting approach, starting with the easiest faults and progressing to the most difficult ones, to confirm the fault location. Initially rule out obvious faults and identify hidden faults and the difficulty of locating them.

[0028] 4. Selection of Faulty Core Wires. When a cable experiences a hidden fault, it is generally due to insulation damage between two or more metallic conductors, resulting in a short circuit or open circuit, indicating low insulation levels. First, select a non-faulty phase core wire as the current loop conductor. If all core wires are faulty, a temporary single-core cable can be laid as the current loop conductor. Next, select a core wire that is not open-circuited as the current loop conductor (preferably using a steel-armored grounding wire, as its higher resistance and voltage drop result in higher accuracy; if the steel-armored grounding wire is incomplete, then select a neutral or phase wire as the current loop conductor). Then, select a core wire to create a potential difference measurement loop from the fault point to both ends (preferably using a wire with low resistance or an open-circuited wire; no current flows during voltage measurement, and in the case of an open-circuited wire, the potential difference can be measured through the semiconductor formed by the metal vaporization caused by the short circuit).

[0029] 5. Electrical connection of the positioning detection device. Select either the power supply side or the load side of the faulty cable as the detection side, based on the actual site conditions. Then proceed as follows... Figure 1 As shown, a 5-10A current limiter of the same type as the power supply is connected to the core wire of the current loop on the detection side. (When using a 220V power supply, a 1000-2000W / 220V resistance heater or incandescent lamp can be used as a substitute for the current limiter; avoid high-temperature burns during use.) One end of the current limiter is connected to the core wire of the current loop, and the other end is connected to the first switch 20 with a connecting wire. At the same time, the other wire of the current loop is also connected to the second switch 30. Then, the two ends of the current loop are connected. The incoming lines of the first switch 20 and the second switch 30 are connected to the mains power or a 220V mobile power supply to form a complete closed electrical circuit.

[0030] 6. Voltage test. After verifying that the wiring is correct, turn on the power and use a multimeter to measure the voltage value from the fault point to both ends of the faulty cable through the potential difference measurement circuit wire, and record the result.

[0031] 7. Voltage-based fault location calculation. As shown in the diagram, if the potential difference V1 from the probe side to the fault point is 3.5V, and the potential difference V2 from the other end to the fault point is 4.8V, the sum of the potential differences at both ends is a total voltage of 8.2V. The percentage of the probe side voltage divided by the total voltage is 3.5 ÷ 8.2 × 100% = 42.7%. Using this voltage ratio to calculate the cable fault point length, if the cable length is 180 meters, then 42.7% × 180 = 76 meters, meaning the distance from the probe side to the fault point is 76 meters. Retesting after changing the direction confirms the same principle. The percentage of the probe side voltage divided by the total voltage is 4.8 ÷ 8.2 × 100% = 58.5%. Using this voltage ratio, the remaining cable length is 58.5% × 180 = 104 meters, meaning the distance from the probe side to the fault point is 104 meters. The sum of the two distances after the two measurements is 180 meters, which equals the total cable length.

[0032] 8. Location Re-verification. To prevent location errors caused by multiple fault points in the cable, re-verification is necessary. The re-verification reference method is that if the sum of the potential differences V1+V2 from the fault point to both ends is the same as the actual potential difference V3 in the current loop, or if the error between the two is less than 3%, the fault point location is considered reliable. If the error between the two potential differences is large, two fault points may appear, requiring judgment based on the actual situation.

[0033] The advantages of this cable fault location and detection device are mainly as follows:

[0034] 1. The device is simple and economical. During testing, a common electrician's multimeter can be used to measure voltage, mains power or mobile power supply, and a common resistor (used for current limiting) can be inserted into the faulty cable. The fault point of the cable can be located by connecting the connection wires. No external instruments are required.

[0035] 2. Easy to understand and operate; only basic electrical knowledge is required. Operators only need to be able to connect basic circuits, measure voltage, calculate fault point ratios, and convert cable lengths and locations to meet the requirements.

[0036] 3. Simple, fast, and accurate fault location. High accuracy in detecting single fault points. When a cable fault occurs, it is usually due to multiple fault points, resulting in short circuits or open circuits caused by insulation damage between two or more conductors. The faulty phase or ground is selected as the current loop for the applied voltage, and the faulty phase or ground is selected as the potential difference measurement loop. When the potential difference from the fault point to the cable ends and the difference from the total cable potential are small, there are no other influencing factors. The measurement accuracy is very high, and the calculated fault point location is accurate. When the potential difference from the fault point to the cable ends and the difference from the total cable potential are large, multiple fault points may appear, provided there are no other influencing factors. The fault point location calculated using the multi-segment difference method is also highly accurate.

[0037] 4. Safe and reliable. The applied voltage to the faulty cable is only a few volts or tens of volts, which is a safe voltage and will generally not cause personal injury or damage to instruments. It also avoids secondary damage to the insulation of the low-voltage power cable core wires caused by improper positioning operations.

[0038] 5. It can be manufactured into a commercially viable measuring instrument. Cables are widely used in power generation, and faults are a common occurrence. The principle of voltage measurement is simple, the method is easy to use, and the cost of manufacturing the instrument is low. It can be integrated into existing testing instruments to improve cable fault detection capabilities. Alternatively, a lightweight, single-function design can be launched on the market to meet the needs of general cable fault repairers.

[0039] The cable fault location detection device has been applied to actual testing.

[0040] Case 1: On March 13, 2024, the applicant discovered a grounding fault in the AC cable of inverter NB0212 in the Xiaomi area of ​​the Haidong Liangzi Photovoltaic Power Station. On-site inspection revealed the cable to be a 3×120 aluminum core 1kV low-voltage cable with a grounding fault on phase B. A megohmmeter measured the grounding resistance at 0.2kΩ. The cable length was visually estimated at 250 meters. After applying voltage to 15kV using a high-voltage generator, both a cable fault distance meter and a cable fault location instrument were used, but the actual fault point could not be found. The cable fault location detection device of this embodiment was then used. The A phase and sheath steel armor of the cable were used as the current loop, and the B phase was used as the potential difference measuring wire from the fault point to the steel armor on both sides of the cable. The voltage of the measuring loop was selected from a 220V mobile power supply and a 220V 1000W iodine tungsten lamp with a series resistance. The actual current of the loop was 4.3A. The voltage from the fault point to the transformer side was 5.13V, and the voltage from the fault point to the inverter side was 8.37V. The total voltage drop was 13.5V. After calculation, the fault point was located in the 38% area on the transformer side. The fault point was located about 95 meters away from the transformer. Then, the voltage flashover method was used to hear a faint discharge sound at the cable fault point at about 95 meters of the cable. After digging out about 1 meter of soil above the cable, it was found that the cable was damaged during construction, the insulation of the B phase core wire was damaged and broken down, and the cable sheath steel armor was discharged, causing a closed fault.

[0041] Case 2: On April 26, 2024, the applicant discovered a grounding fault in the AC cable of the NB2701 inverter at the Douguwa Factory photovoltaic power station. On-site inspection revealed the cable to be a 3×70 aluminum core 1kV low-voltage cable with a grounding fault in phase A. A megohmmeter measured the grounding resistance at 0.Ω. The cable length was visually estimated at 40 meters. After applying voltage to 10kV using a high-voltage generator, both a cable fault distance meter and a cable fault location instrument were used, but the actual fault point could not be found. The cable fault location detection device of this embodiment was then used. The B phase and the sheath steel armor of the cable were used as the current loop, and the A phase was used as the potential difference measuring wire from the fault point to the steel armor on both sides of the cable. The voltage of the measuring loop was selected from a 220V mobile power supply and a 220V 1000W iodine tungsten lamp with a series resistor. The actual current of the loop was 4.5A. The voltage from the fault point to the transformer side was 1.13V, and the voltage from the fault point to the inverter side was 0.38V. The total voltage drop was 1.51V. After calculation, the fault point was located in the 25% area on the inverter side. The fault point was located about 10 meters away from the inverter. Due to the large influence of environmental noise, a high-voltage generator was not used to check the fault point. Instead, the soil layer above the cable was dug up to about 1.3 meters. The inspection revealed that the cable was damaged by stones during construction, resulting in insulation damage to the A phase core wire and a short circuit in contact with the cable sheath steel armor.

[0042] Case 3: On February 14, 2025, the applicant discovered a grounding fault in the AC cable of inverter NB0515 in the Xiajiapingzi area of ​​the Liangzi Photovoltaic Power Station in Haidong. On-site inspection revealed the cable to be a 3×120 aluminum core 1kV low-voltage cable with a C-phase grounding fault. A megohmmeter measured a grounding resistance of 0kΩ. The cable length was visually estimated at 170 meters. After applying voltage to 15kV using a high-voltage generator, both a cable fault distance meter and a cable fault location instrument were used, but the actual fault point could not be found. The cable fault location detection device of this embodiment was then used. The A phase and the sheath steel armor of the cable were used as the current loop, and the C phase was used as the potential difference measuring wire from the fault point to the steel armor on both sides of the cable. The voltage of the measuring loop was selected from a 220V mobile power supply and a 220V 1000W iodine tungsten lamp with series resistance. The actual current of the loop was 4.4A. The voltage from the fault point to the transformer side was 3.88V, and the voltage from the fault point to the inverter side was 0.48V. The total voltage drop was 4.36V. After calculation, the fault point was located in the 11% area on the inverter side. The fault point was located about 19 meters away from the inverter side. The cable fault point was located directly above the farm machinery road. The soil layer was compacted. Then, the voltage flashover method was used. No discharge sound was heard at about 19 meters of the cable. The soil layer above the cable was dug up to a depth of about 1.5 meters. It was covered with protective bricks. The inspection revealed that the cable was damaged during construction. The insulation of the C phase core wire was damaged and broke down, which caused a short circuit in the cable sheath steel armor.

[0043] Case 4: On February 25, 2025, the applicant discovered a grounding fault in the AC cable of the NB2906 inverter in the No. 1 station area of ​​the forest farm photovoltaic power station. On-site inspection revealed the cable to be a 3×95 aluminum core 1kV low-voltage cable with a grounding fault in phase A. A megohmmeter measured the grounding resistance at 0.4kΩ. The cable length was visually estimated at 120 meters. After applying voltage to 15kV using a high-voltage generator, both a cable fault distance meter and a cable fault location instrument were used, but the actual fault point could not be found. The cable fault location detection device of this embodiment was then used. The B phase and the sheath steel armor of the cable were used as the current loop, and the A phase was used as the potential difference measuring wire from the fault point to the steel armor on both sides of the cable. The voltage of the measuring loop was selected from a 220V mobile power supply and a 220V 1000W iodine tungsten lamp with a series resistance. The actual current of the loop was 4.4A. The voltage from the fault point to the inverter side was 1.88V, and the voltage from the fault point to the transformer side was 0.6V. The total voltage drop was 2.48V. After calculation, the fault point was located in the 24% area on the transformer side, and the fault point was located about 28 meters away from the transformer. Then, the voltage flashover method was used to hear a faint discharge sound at the cable fault point at about 28 meters of the cable. After digging about 0.2 meters of soil above the cable, it was found that the cable was damaged during construction, the insulation of the A phase core wire was damaged and broken down, and the cable sheath steel armor was discharged, resulting in a closed fault.

[0044] The specific embodiments of this application have been described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that modifications and improvements can be made to these embodiments without departing from the principles and spirit of this application as defined by the claims and their equivalents, and such modifications and improvements should also be within the protection scope of this application.

Claims

1. A cable fault location detection device, characterized in that, The positioning detection device includes a power supply, a first switch, a second switch, a current limiter, a connecting wire, and a voltmeter. The two poles of the power supply are respectively connected to the first switch and the second switch. The first switch, the current limiter, the normal phase line of the faulty cable, the connecting wire, the faulty but unbroken phase line of the faulty cable, and the second switch are connected in series to form an electrical detection circuit. The voltmeter is used to measure the voltage between the faulty phase line of the faulty cable and the power supply side, and the voltage between the faulty phase line and the load side.

2. The cable fault location detection device according to claim 1, characterized in that, The power source is a 220V portable power bank.

3. The cable fault location detection device according to claim 1, characterized in that, The current limiter is a resistance heater or an incandescent lamp.

4. The cable fault location detection device according to claim 1, characterized in that, The faulty but unbroken phase of the faulty cable is the steel armor grounding wire of the faulty cable.

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