Fault property diagnostic apparatus and method for cable fault testing

Abstract

The application discloses a fault property diagnosis device and method for cable fault test, and belongs to the technical field of power equipment detection. The fault property diagnosis device comprises a host unit and a multifunctional conversion unit, the multifunctional conversion unit is connected with a central control unit and each test unit; the host unit is integrated with a multimeter unit, a megohmmeter unit, a low-voltage pulse unit and the central control unit, and is used for coordinating the working time sequence of each unit and processing measurement data; the multifunctional conversion unit comprises a test mode selection module and a safety interlocking and discharge detection module, and is used for detecting the residual voltage of a high-voltage output end connected with a cable and allowing switching only when the residual voltage is detected to be lower than a safety threshold. The application realizes the integration, safety and process of the cable fault diagnosis, improves the field detection efficiency and operation safety, and solves the problems of equipment dispersion, complicated operation and high safety risk in the existing cable fault diagnosis.

Description

Technical Field

[0001] This application belongs to the field of power equipment testing technology, specifically relating to a fault nature diagnosis device for cable fault testing, and more particularly to an integrated cable fault nature diagnosis device and diagnostic method that integrates the functions of a multimeter, megohmmeter and low-voltage pulse reflection method testing. Background Technology

[0002] As the arteries of electrical energy transmission, the operating status of power cables directly affects the reliability and security of the power grid. During installation and operation, cables are susceptible to various faults due to mechanical stress, insulation aging, overvoltage, chemical corrosion, and environmental factors. Based on the magnitude of the fault resistance, they can be mainly classified into low-resistance faults (including short-circuit faults, with resistance values ​​typically below several hundred ohms), high-resistance faults (including leakage high-resistance and flashover high-resistance), and open-circuit faults.

[0003] Currently, preliminary diagnosis of cable fault characteristics (i.e., determining the fault type and phase) is a prerequisite for accurate fault location and repair. The conventional diagnostic process typically includes: performing a continuity test using a multimeter in resistance or buzzer mode; measuring the insulation resistance of each phase conductor to ground and between phases using a megohmmeter; if the insulation resistance measurement result is 0MΩ, confirming a low-resistance fault using a multimeter in resistance mode; and for identified low-resistance or open-circuit faults, using a dedicated cable fault tester for low-voltage pulse reflection distance measurement. However, the above traditional diagnostic methods have significant shortcomings: numerous devices, cumbersome operation, requiring the use of multiple instruments such as multimeters, megohmmeters, and cable fault testers on-site, leading to frequent wiring changes; high safety risks, as megohmmeter output voltages can reach several kilovolts, leaving high-voltage residual charge on the cable after testing, which must be fully discharged before proceeding to the next test, otherwise there is a risk of electric shock; fragmented processes, prone to errors, requiring manual recording and comparison of test results from different devices, which can easily lead to misjudgments in complex environments; and high professional requirements and training costs for personnel.

[0004] In the process of developing this application, the inventors discovered that the prior art has at least the following problems: the existing cable fault diagnosis process relies on a variety of scattered instruments, which is cumbersome to operate, has high safety risks, is prone to errors due to fragmented processes, and requires too high professional skills from personnel. There is a lack of an intelligent, integrated diagnostic device that can integrate the main testing functions, guide standardized operating procedures, and has built-in safety mechanisms. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide a highly integrated, safe, and streamlined cable fault nature diagnosis device and method, addressing the aforementioned deficiencies of the prior art.

[0006] The technical solution adopted by this application to solve its technical problem is: On one hand, a fault nature diagnosis device for cable fault testing is provided, comprising: a host unit integrating: a multimeter unit for measuring the DC resistance or continuity of the cable core; a megohmmeter unit for measuring the insulation resistance of the cable; a low-voltage pulse unit for injecting low-voltage pulses into the cable and receiving reflected signals; a central control unit connected to the multimeter unit, the megohmmeter unit, and the low-voltage pulse unit respectively, for coordinating and controlling the working sequence of each unit and processing measurement data; and a multi-function conversion unit connected to the central control unit and each test unit. The multi-function conversion unit includes: a test mode selection module for selecting to enable the multimeter unit, the megohmmeter unit, or the low-voltage pulse unit; and a safety interlock and discharge detection module for detecting the residual voltage at the high-voltage output terminal connected to the cable when the test mode selection module switches from enabling the megohmmeter unit to enabling other test units, and only allowing switching when the detected residual voltage is below a safety threshold. Preferably, the safety interlock and discharge detection module includes a high-voltage divider sampling circuit, a voltage comparator group, an electronic high-voltage relay array, and an active discharge circuit. The central control unit incorporates a discharge state machine to implement residual voltage monitoring, active interlocking, and safe discharge logic. Furthermore, the central control unit is configured for intelligent linkage, automatically matching pulse width / gain based on insulation resistance when switching to low-voltage pulse mode and associating faulty phases. Additionally, the device includes a smart mobile terminal connected to the host via a wireless communication module for waveform display, automatic fault location, and report generation.

[0007] On the other hand, a cable fault nature diagnosis method based on the aforementioned equipment is provided, including: connection; continuity test; insulation test; safety switching (activating safety interlock and discharge detection, automatically monitoring discharge until the residual voltage is below the safety threshold); and low-voltage pulse test. This method further includes full-length measurement, fault location, intelligent linkage, and report generation steps.

[0008] One of the above technical solutions has the following advantages or beneficial effects: This application integrates three major functional modules—a multimeter, a megohmmeter, and a low-voltage pulse tester—into a single main unit. This is not a simple combination, but rather a seamless and safe transition between high-voltage and low-voltage testing achieved through the safety interlock and discharge detection module in the multi-functional conversion unit. This solves the problems of numerous devices and cumbersome operation in existing technologies.

[0009] Because the equipment incorporates a safety interlock and discharge detection module that works in concert with hardware circuitry and a central control unit, it can automatically detect and force the discharge of residual high voltage in the cable when switching from the high-voltage megohmmeter test mode to other modes. The discharge continues until the voltage drops below a safe threshold, fundamentally preventing electric shock accidents caused by residual charge. This safety interlock and active discharge mechanism, closely integrated with the test mode switching logic, produces unexpected technical effects: traditional methods require manual discharge and waiting, which carries the risk of forgetting or incomplete discharge; while this application, through the coordinated use of a voltage comparator group, an electronic high-voltage relay array, and a discharge state machine, achieves the integration of physical isolation and intelligent discharge, elevating the safety of cable fault diagnosis to a new level. Simultaneously, the intelligent linkage mechanism automatically configures low-voltage pulse parameters and associates them with the faulty phase based on the insulation test results, guiding operators to perform tests according to the standardized process of "continuity → insulation → pulse ranging," reducing human error and omissions, and lowering the professional requirements for operators.

[0010] The integration of the aforementioned multiple technologies (safety interlocking, active discharge, intelligent linkage based on dual-parameter resistance discrimination, and wireless waveform analysis) is not a simple superposition, but rather a synergistic effect achieved through unified scheduling by the central control unit: safety interlocking ensures that operators can immediately perform low-voltage pulse ranging after high-voltage testing without manual discharge waiting; intelligent linkage enables pulse parameters to adaptively match the fault type, avoiding manual setting errors; and the wireless terminal further provides waveform visualization and automatic ranging capabilities. The synergy of these three technologies improves overall diagnostic efficiency and accuracy, which is impossible to achieve by using a multimeter, megohmmeter, and pulse meter individually, and overcomes the shortcomings of traditional methods such as fragmented processes, safety blind spots, and reliance on experience for parameter settings. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of a fault nature diagnosis device for cable fault testing, according to an exemplary embodiment. Figure 2 This is a flowchart illustrating a fault nature diagnosis method for cable fault testing according to an exemplary embodiment; Figure 1 In the middle: 100, host unit; 101, multimeter unit; 102, megohmmeter unit; 103, low voltage pulse unit; 104, central control unit; 105, multi-function conversion unit; 106, human-machine interface; 107, power management module; 108, wireless communication module; 200, intelligent mobile terminal. Detailed Implementation

[0012] To more clearly illustrate the technical features of this application, the following detailed description is provided through specific embodiments and in conjunction with the accompanying drawings.

[0013] like Figure 1 As shown in the figure, the fault nature diagnosis device for cable fault testing provided in this application embodiment mainly includes a host unit 100, a multi-function conversion unit 105, a human-machine interface 106, a power management module 107, a wireless communication module 108, test leads, and a smart mobile terminal 200. The host unit 100 integrates a multimeter unit 101, a megohmmeter unit 102, a low-voltage pulse unit 103, and a central control unit 104. The multimeter unit 101 uses a precision analog-to-digital converter (ADC, such as a 24-bit Σ-Δ ADC) to measure DC voltage and current and calculate resistance; the megohmmeter unit 102 includes a DC-DC boost circuit to generate a test high voltage (selectable 500V / 1000V / 2500V range) and calculates insulation resistance through a precision resistor network and voltage and current detection circuit; the low-voltage pulse unit 103 includes an adjustable pulse width pulse transmission module (pulse width adjustable from 20ns to 2μs) and a high sampling rate (not less than 100MHz) signal receiving and processing module for time-domain reflectometry analysis; the central control unit 104 is based on an embedded processor (such as an ARM Cortex-M series) to achieve overall control and coordination; the multi-function conversion unit 105 includes a test mode selection knob (multimeter / megohmmeter / low-voltage pulse) and a safety interlock and discharge detection module.

[0014] The safety interlock and discharge detection module specifically includes: a high-voltage voltage divider sampling circuit (a 1000:1 resistor voltage divider network connected in parallel to the high-voltage output terminal of the megohmmeter); a voltage comparator group (setting a safe threshold of 50V and a dangerous threshold of 500V); an electronic high-voltage relay array (connected in series in the output circuit of the megohmmeter and the input circuit of the multimeter / pulse unit); and an active discharge circuit (a power resistor and a MOSFET connected in series between the test port and ground). The typical resistance value of the power resistor in the active discharge circuit is 10kΩ~100kΩ, preferably 47kΩ / 5W, to ensure that the residual high voltage is discharged from several kilovolts to below the safe voltage within a safe time (e.g., within 10 seconds), while limiting the discharge current to avoid damage to equipment or cables.

[0015] The central control unit has a built-in "discharge state machine". When the test mode knob is switched from the "megohmmeter" position, the boost is immediately interrupted. The ADC samples the port voltage at a 100ms cycle. If the voltage is greater than 50V, the switch is locked and an audible and visual alarm is triggered. If it is greater than 500V, the relay is physically cut off. If the voltage does not drop to a safe range after more than 10 seconds, the discharge circuit is automatically opened until the voltage drops below 36V, at which point the circuit is unlocked and the target test unit path is connected.

[0016] The central control unit is also configured to achieve intelligent linkage: when the test mode selection module switches from the megohmmeter range to the low-voltage pulse range, it automatically acquires the DC resistance value R measured by the multimeter unit. dc The insulation resistance value R measured by the megohmmeter unit ins Based on the obtained resistance value, the system automatically selects a low-voltage pulse test algorithm and / or automatically sets the pulse width and signal gain of the low-voltage pulse unit; and automatically associates the fault type determined based on the resistance value with the phase of the low-voltage pulse test, and distinguishes and marks them on the human-machine interface.

[0017] The intelligent linkage mechanism is as follows: (1) If R dc <200Ω (Low Impedance Fault): Automatically selects the low-impedance fault test algorithm, transmits low-voltage pulses to the faulty and non-faulty phases respectively, automatically compares the waveforms of the two, extracts the reflection characteristics of the fault point through waveform differences, and realizes automatic distance measurement of low-impedance faults. At the same time, it automatically sets the pulse width to a narrow pulse width (e.g., 20ns~50ns) and the gain to a low gain.

[0018] (2) If R ins For circuits >200Ω and where the multimeter displays an open circuit (open circuit fault): The open circuit test algorithm is automatically selected, and low-voltage pulses are emitted to both the faulty and non-faulty phases. The reflected waveforms are compared (the open circuit phase shows a positive open circuit reflection), and the distance to the break point is calculated based on the positive pulse delay of the faulty phase. Simultaneously, the pulse width is automatically set to a medium pulse width (e.g., 100ns~500ns), and the gain is set to a medium gain.

[0019] (3) If R ins >200Ω and not broken (high resistance or intact): Automatically select the full-length test algorithm, emit low-voltage pulses to the intact phase, identify open-circuit reflected pulses at the cable terminal, measure the full length and calibrate the wave velocity; for high-resistance fault phases, the interface is marked in gray (not suitable for low-voltage pulse testing).

[0020] Automatic fault type association: For phases that are determined to have "high resistance" in the insulation test, the system will automatically mark them in gray on the low-voltage pulse interface (low-voltage pulse testing is not recommended) to prevent operators from mistesting high resistance faults and causing waveforms to be unrecognizable; For phases that are determined to have "low resistance" or "open circuit" in the insulation test, the system will automatically mark them in red (to be tested) on the low-voltage pulse interface and display them at the top.

[0021] The low-resistance fault database and full-length test database are constructed as follows: Low-voltage pulse reflection waveforms of various typical cables (e.g., YJV, VV, cross-linked polyethylene, etc., with different cross-sections and lengths) under normal, low-resistance, and open-circuit fault conditions are collected in advance through experiments or simulations. Characteristic parameters of the reflected waveforms (including reflection coefficient, rise time, pulse width attenuation, and terminal reflection polarity) are extracted and associated with the corresponding cable type, fault type, and fault distance, and stored in the memory of the central control unit. During actual testing, the equipment matches the measured waveforms with templates in the database (e.g., using cross-correlation algorithms or neural network classifiers) to assist in determining the fault type and distance. The full-length test database stores typical characteristics of the terminal reflection waveforms of intact cables (e.g., open-circuit reflected positive pulses). The database can be pre-configured at the factory and supports upgrades and updates via external interfaces.

[0022] The intelligent mobile terminal 200 (e.g., a tablet or smartphone) connects to the central control unit 104 via a wireless communication module 108 (e.g., a Wi-Fi module). The communication protocol uses TCP / IP+JSON. After the host is powered on, a wireless local area network hotspot (e.g., Wi-Fi) named "CableTester_XXXX" is established. After the terminal connects, a long connection is established via a UDP handshake. The central control unit 104 pushes waveform binary streams and status JSON (e.g., {"Mode":"Megger","Phase":"A","Res":0.25,"Unit":"MΩ"}) in real time. The terminal sends control commands (e.g., {"Cmd":"StartPulse","Width":100,"Gain":3}). Low-voltage pulse ranging automatically calculates the fault distance based on the formula L=V×Δt / 2. The intelligent mobile terminal is configured to function as an advanced human-machine interface when the low-voltage pulse unit is working, for purposes including but not limited to pulse parameter setting, real-time display of reflected waveforms, waveform analysis, automatic calculation and calibration of fault distance, and generation of test reports.

[0023] After wiring on-site, the operator switched the "Test Mode" to the "Multimeter" setting to measure the resistance of each phase to determine if there was a break in the wire. Then, they switched it to the "Megohmmeter" setting and selected 2500V to measure the resistance between A and ground, B and ground, etc. If the resistance between A and ground was 0.2MΩ, it indicated low insulation. When attempting to switch to the "Low Voltage Pulse" setting, the central control unit detected residual high voltage, the red LED flashed, and the screen displayed "High Voltage Danger, Please Discharge!" The internal active discharge circuit automatically activated, and the alarm was deactivated after the voltage dropped below 36V. The system then automatically switched to the low voltage pulse setting. The operator selected phase B (intact phase) on the tablet to measure the full length and calibrate the wave velocity. Then, they selected phase A (faulty phase) to transmit a pulse. The tablet displayed a negative reflected wave and automatically calculated the fault distance as 500 meters. Finally, a PDF report was generated with one click and uploaded to the cloud.

[0024] like Figure 2 As shown in the figure, an embodiment of this application provides a method for diagnosing the nature of cable faults based on the device, comprising the following steps: Step 1: Connect the test leads of the device to the cable under test; Step 2: Switch the test mode selection module to the multimeter setting, measure and record the resistance of each phase core of the cable in sequence to determine the wire breakage fault. Step 3: Switch the test mode selection module to the megohmmeter setting, and measure and record the insulation resistance of each phase to ground and between each phase of the cable in sequence to determine the fault type and the faulty phase. Step 4: When the test mode selection module is switched from the megohmmeter range to other ranges, the safety interlock and discharge detection are activated, and the cable is automatically monitored and discharged until the residual voltage is lower than the safety threshold. Step 5: Switch the test mode selection module to the low-voltage pulse position, emit low-voltage pulses to the intact or faulty phase determined in the insulation test, receive the reflected signal and calculate the total length of the cable or the distance to the fault point.

[0025] Step 5 further includes: Select the phase wire that has been determined to be intact by insulation testing, and emit a low-voltage pulse to measure the total length of the cable and calibrate the pulse wave velocity; Select the phase line that has been determined to have a low resistance fault or open circuit fault by insulation testing, transmit a low voltage pulse, and calculate the distance to the fault point based on the time difference between the received fault point reflected pulse and the transmitted pulse, as well as the calibrated wave velocity.

[0026] After step 3 and before step 5, it also includes: The system automatically acquires the insulation resistance value measured during the insulation test; automatically presets the pulse width and gain parameters of the low-voltage pulse test based on the insulation resistance value; and automatically distinguishes between measurable and unmeasurable phases on the low-voltage pulse test interface based on the fault type determined by the insulation resistance value.

[0027] The cable fault nature diagnosis method further includes the following steps: Summarize the test results from steps 2, 3, and 5; generate a diagnostic report containing test data, fault type judgment conclusions, and fault point distance information; transmit the diagnostic report to a server or external device via a wireless network, preferably a cloud server, but also a laptop, USB flash drive, or printer.

[0028] The fault nature diagnosis device described in this application is an integrated fault nature diagnosis device, whose system mainly consists of a host unit, test leads and a smart mobile terminal (tablet computer).

[0029] The main unit integrates a core circuit board, on which: Central control unit: Employs a high-performance embedded processor and is responsible for overall control.

[0030] Low-voltage pulse unit: A programmable pulse generator produces nanosecond-level pulses, which are output through a high-speed drive circuit; the receiving section consists of a broadband amplifier, a high-speed ADC, and a digital signal processor (DSP) to achieve high-speed acquisition and digital filtering of reflected waves.

[0031] Multimeter Unit: Uses a precision analog-to-digital converter to measure DC voltage and current, and calculate resistance.

[0032] Megohmmeter unit: Includes a DC-DC boost circuit to generate a high test voltage, and calculates the insulation resistance through a precision resistor network and voltage and current detection circuit.

[0033] Power management module: Provides power to each unit.

[0034] Multifunctional conversion unit: Located on the front panel, its "Test Mode" knob and "Phase Selection" knob are both high-voltage, long-life industrial-grade components. The hardware of the safety interlock and discharge detection module consists of a high-voltage sampling resistor, a comparator circuit, and a relay group, and its status signal is sent to the central control unit in real time.

[0035] The workflow of the aforementioned integrated fault diagnosis equipment is as follows.

[0036] 1) On-site wiring: Ground the equipment, and connect the test leads to the three phases (A, B, C) of the cable and the grounding wire of the cable armor respectively.

[0037] 2) Continuity Test: Rotate the "Test Mode" to "Multimeter" and select phases A, B, and C in sequence. The panel screen displays the resistance value of each phase. If a phase displays "OL" (over-range), record it as "suspected open circuit".

[0038] 3) Insulation Test: Rotate the "Test Mode" to "Megohmmeter" and select the 2500V voltage range. Test the insulation resistance of A to ground, B to ground, C to ground, between AB, between BC, and between CA in sequence. Assume that the measured insulation resistance of A to ground is 0.2MΩ, and the resistances of B and C phases and the same phase are all greater than 1000MΩ. The equipment screen will display "Low insulation of phase A".

[0039] 4) Safety Switching: The operator turns the knob from "Megohmmeter" to "Low Voltage Pulse". At this time, the MCU detects the mode switching command and first starts the discharge detection. If the detection circuit detects that there is still high voltage to ground on phase A test line, the panel will be locked immediately, the red alarm light will flash, and the screen will display "High Voltage Danger, Please Discharge!". The operator uses the discharge rod provided with the equipment or discharges the cable through the internal discharge circuit of the equipment (a discharge button can be set) until the alarm is cleared.

[0040] 5) Pulse ranging: First, select the well-insulated phase B, set an appropriate wave velocity on the tablet software (or use a known full-length back calibration), and transmit a pulse. The total cable length is measured to be 1250 meters, and the wave velocity V is accurately calibrated. Then, select the faulty phase A and transmit a pulse. The tablet software interface clearly displays the transmitted pulse and a distinct negative pulse reflection (a characteristic of low-resistance faults). The software automatically calibrates the time difference Δt to 4.0 μs. Based on the formula L=(V×Δt) / 2 and the calibrated V value, the fault distance L=500 meters is automatically calculated and displayed on the screen.

[0041] 6) Report generation: The tablet software summarizes all test data and automatically generates a test report that includes test time, location, cable information, test results, and fault diagnosis conclusion ("A phase low resistance fault, about 500 meters from the test end"). The report can be saved or printed.

[0042] Through the above process, the embodiments of this application realize a safe, fast, and integrated operation from fault nature judgment to preliminary distance measurement, which is significantly better than the traditional device-specific testing mode.

[0043] Compared with the prior art, this application has the following significant advantages: Highly integrated and multifunctional: It integrates three major functional modules—multimeter, megohmmeter, and low-voltage pulse tester—into one unit, avoiding the hassle of carrying and replacing multiple devices and greatly simplifying field equipment.

[0044] Process guidance and standardized operation: Through clear mode knobs and phase selection, operators are guided to conduct tests according to the standard process of "continuity → insulation → pulse ranging", which reduces the risk of misjudgment due to omissions or incorrect sequences of operation steps.

[0045] Intrinsically safe and with controllable risks: The embedded safety interlock and discharge detection module is a core safety innovation that fundamentally eliminates electric shock accidents caused by performing other operations after the high-voltage insulation test without discharge, thus ensuring the safety of personnel and equipment.

[0046] Intelligent diagnostics, improved efficiency: The equipment can automatically record test data and provide preliminary fault classification prompts based on insulation resistance values. Combined with low-voltage pulse waveform analysis, it can quickly complete the entire diagnostic process from fault nature determination to preliminary location, significantly improving on-site testing efficiency.

[0047] User-friendly interface and highly adaptable: The main panel meets basic operation requirements and also supports wireless connection to smart terminals, providing more powerful waveform analysis, data management and report generation functions to meet the needs of different scenarios.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation methods of this application. Any modifications or equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of the claims of this application.

Claims

1. A fault property diagnosis device for cable fault testing, characterized by, Includes a main unit and a multi-functional conversion unit; The main unit integrates: a multimeter unit for measuring the DC resistance or continuity of the cable core; and a megohmmeter unit for measuring the insulation resistance of the cable. The low-voltage pulse unit is used to inject low-voltage pulses into the cable and receive reflected signals; the central control unit is connected to the multimeter unit, the megohmmeter unit and the low-voltage pulse unit respectively, and is used to coordinate and control the working sequence of each unit and process measurement data. The multi-functional conversion unit is connected to the central control unit and each test unit. The multi-functional conversion unit includes a test mode selection module, which is used to select and enable the multimeter unit, the megohmmeter unit or the low-voltage pulse unit. The safety interlock and discharge detection module is used to detect the residual voltage at the high-voltage output terminal connected to the cable when the test mode selection module switches from enabling the megohmmeter unit to enabling other test units, and only allows switching when the residual voltage is detected to be lower than a safety threshold.

2. The fault property diagnosing device for a cable fault test according to claim 1, characterized by, The safety interlock and discharge detection module includes: a high-voltage divider sampling circuit connected in parallel to the high-voltage output terminal of the megohmmeter unit, used to collect the residual voltage proportionally; a voltage comparator group, used to compare the residual voltage with preset safety thresholds and danger thresholds and output the comparison results; an electronic high-voltage relay array, connected in series in the output circuit of the megohmmeter unit and the input circuits of the multimeter unit and the low-voltage pulse unit, used to physically disconnect or connect the corresponding circuit according to the comparison results; and an active discharge circuit connected between the test port and ground, used to form a controllable discharge channel according to the instructions of the central control unit.

3. The fault property diagnosis device for cable fault test according to claim 2, characterized by, The central control unit has a built-in discharge state machine configured to perform the following operations: when the test mode selection module switches from the megohmmeter range, the high voltage output of the megohmmeter unit is interrupted; the residual voltage value monitored by the high voltage divider sampling circuit is acquired in real time. If the residual voltage value exceeds the safety threshold, the interlocking mechanism is activated to prevent switching to the multimeter unit or the low-voltage pulse unit. If the lockout time exceeds the preset duration and the residual voltage value still does not drop below the safety threshold, the active discharge circuit will be automatically opened to discharge; and when the residual voltage value drops below the safety threshold, the lockout will be released and switching will be allowed.

4. The fault property diagnosing device for a cable fault test according to claim 3, characterized by, The central control unit is also configured to achieve intelligent linkage: when the test mode selection module switches from the megohmmeter range to the low-voltage pulse range, it automatically acquires the DC resistance value measured by the multimeter unit and the insulation resistance value measured by the megohmmeter unit; based on the acquired resistance value, it automatically selects the low-voltage pulse test algorithm and / or automatically sets the pulse width and signal gain of the low-voltage pulse unit; and it automatically associates the fault type determined based on the resistance value with the phase of the low-voltage pulse test, and distinguishes and marks them on the human-machine interface.

5. The fault property diagnosing apparatus for cable fault test according to any one of claims 1 to 4, characterized by, It also includes a smart mobile terminal, which is connected to the central control unit via a wireless communication module; the smart mobile terminal is configured to serve as an advanced human-machine interface when the low-voltage pulse unit is working, for setting pulse parameters, real-time display of reflected waveforms, waveform analysis, automatic calculation and calibration of fault distance, and generation of test reports.

6. The fault property diagnosis device for cable fault test according to claim 5, characterized in that, The communication process between the host unit and the smart mobile terminal includes: the host unit automatically establishing a wireless network hotspot after power-on; the smart mobile terminal connecting to the wireless network hotspot and establishing a communication connection through a handshake protocol; the host unit pushing the waveform data collected by the low-voltage pulse unit and the measurement status data of each test unit to the smart mobile terminal in real time in the form of a data stream; and the smart mobile terminal encapsulating the user's operation instructions into control commands and sending them to the central control unit of the host unit to control it to perform corresponding operations.

7. A method of diagnosing a cable fault nature based on the apparatus of any one of claims 1 to 6, characterized by, Includes the following steps: Step 1: Connect the test lead of the device according to any one of claims 1 to 6 to the cable under test; Step 2: Switch the test mode selection module to the multimeter setting, measure and record the resistance of each phase core of the cable in sequence to determine the wire breakage fault. Step 3: Switch the test mode selection module to the megohmmeter setting, and measure and record the insulation resistance of each phase to ground and between each phase of the cable in sequence to determine the fault type and the faulty phase. Step 4: When the test mode selection module is switched from the megohmmeter range to other ranges, the safety interlock and discharge detection are activated, and the cable is automatically monitored and discharged until the residual voltage is lower than the safety threshold. Step 5: Switch the test mode selection module to the low-voltage pulse position, emit low-voltage pulses to the intact or faulty phase determined in the insulation test, receive the reflected signal and calculate the total length of the cable or the distance to the fault point.

8. The method of claim 7, wherein, Step 5 further includes: Select the phase wire that has been determined to be intact by insulation testing, and emit a low-voltage pulse to measure the total length of the cable and calibrate the pulse wave velocity; Select the phase line that has been determined to have a low resistance fault or open circuit fault by insulation testing, transmit a low voltage pulse, and calculate the distance to the fault point based on the time difference between the received fault point reflected pulse and the transmitted pulse, as well as the calibrated wave velocity.

9. The method of claim 7, wherein, After step 3 and before step 5, it also includes: The system automatically acquires the insulation resistance value measured during the insulation test and the DC resistance value measured by the multimeter; it automatically determines the low-voltage pulse test mode based on the acquired resistance value, and automatically presets the pulse width and gain parameters of the low-voltage pulse test based on the resistance value; based on the fault type determined by the resistance value, it automatically distinguishes and identifies the measurable phase and the non-measurable phase on the low-voltage pulse test interface.

10. The cable fault property diagnosing method according to any one of claims 7 to 9, characterized by, It also includes the following steps: Summarize the test results from steps 2, 3, and 5; generate a diagnostic report containing test data, fault type judgment conclusions, and fault point distance information; and transmit the diagnostic report to a server or external device via a wireless network.

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