Distribution ring main unit outgoing cable fault monitoring and positioning system and method

Abstract

The invention discloses a power distribution ring main unit outlet cable fault monitoring and positioning system and method, and belongs to the field of automatic monitoring of power systems. The magnetic field sensing unit comprises a power frequency magnetic field sensor for monitoring a power frequency magnetic field signal and a high-frequency magnetic field sensor for monitoring a high-frequency transient magnetic field signal; and the monitoring terminal hardware unit comprises a power supply module for supplying power to the whole system, a signal acquisition module for converting a signal of the magnetic field sensing unit into a digital signal, and a control analysis module for operating a fault monitoring analysis algorithm. According to the method, the power frequency magnetic field signal and the high-frequency transient magnetic field signal are combined to jointly judge whether the fault occurs or not and the occurrence place, possible interference of a single signal source can be effectively eliminated, and the fault misjudgment and missed judgment rate is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic monitoring of power systems, and in particular to a system and method for monitoring and locating faults in outgoing cables of distribution ring network cabinets. Background Art

[0002] With the advancement of smart grid construction, the automation and intelligence level of distribution networks are constantly improving. As a key node equipment in the distribution network, the safe and stable operation of the ring main unit is of vital importance.

[0003] In recent years, "primary-secondary integration" technology has been widely adopted in ring main units (RMUs). This technology aims to deeply integrate, miniaturize, and intelligently design the high-voltage switchgear (primary equipment) within the RMU with protection, measurement and control, metering, and communications units (secondary equipment). Its core goal is to achieve plug-and-play device operation, information interconnection, comprehensive status awareness, and intelligent decision-making. Current RMUs typically integrate voltage / current sensors (such as electronic transformers), intelligent terminals (FTUs / DTUs), and communication modules. These systems enable local and remote telemetry, telesignaling, and remote control, and possess certain fault detection (such as overcurrent and quick-break protection) and isolation capabilities.

[0004] However, existing primary and secondary fusion technologies primarily focus on monitoring and protecting the ring main unit (RMU) itself. Their ability to detect and accurately locate faults in the cables leading out of the RMU, particularly those in the middle of the cable, remains limited. While traditional fault indicators can provide some segment-based identification, their accuracy is limited, and installation and maintenance require power outages. While highly accurate, methods such as traveling wave ranging are typically deployed at higher voltage levels or in substations, making comprehensive deployment across a large number of RMUs prohibitively expensive.

[0005] Therefore, there is an urgent need to develop a distribution network switchgear (ring main unit) outgoing cable fault detection system that can be installed non-invasively, utilizes multiple signal characteristics to improve judgment accuracy, and can achieve fault section judgment and even precise positioning at a low cost. Summary of the Invention

[0006] The purpose of the present invention is to provide a distribution ring network cabinet outgoing cable fault monitoring and positioning system and method, by combining the power frequency magnetic field signal and the high frequency transient magnetic field signal, jointly determine whether the fault occurs and the location of the fault, which can effectively eliminate the possible interference of a single signal source and reduce the fault misjudgment and missed judgment rate.

[0007] The technical solution adopted by the present invention to achieve the above technical objectives is: a distribution ring network cabinet outgoing cable fault monitoring and positioning system, including a magnetic field sensing unit and a monitoring terminal hardware unit, wherein the magnetic field sensing unit includes a power frequency magnetic field sensor for monitoring the power frequency magnetic field signal and a high-frequency magnetic field sensor for monitoring the high-frequency transient magnetic field signal. The power frequency magnetic field signal is a steady-state or slowly varying magnetic field signal generated by the load current when the cable is operating normally, and the high-frequency transient magnetic field signal is a rapidly varying magnetic field signal generated by the transient component of the fault current when a cable fault occurs; The monitoring terminal hardware unit includes a power supply module for supplying power to the entire system, a signal acquisition module for converting the signal of the magnetic field sensing unit into a digital signal, and a control analysis module for running a fault monitoring and analysis algorithm.

[0008] As an optimization solution for the above-mentioned distribution ring network cabinet outgoing cable fault monitoring and positioning system, the magnetic field sensing unit is arranged on the cable surface in the cable trench of the distribution ring network cabinet outgoing cable; the monitoring terminal hardware unit is arranged in the instrument box or secondary equipment compartment of the distribution ring network cabinet, and the power supply module obtains the working power supply from the instrument box of the distribution ring network cabinet, and performs voltage stabilization and isolation processing.

[0009] As another optimization solution for the above-mentioned distribution ring network cabinet outgoing cable fault monitoring and positioning system, a signal conditioning module is provided between the signal acquisition module and the magnetic field sensing unit, and the signal conditioning module amplifies and filters the output signal of the magnetic field sensing unit.

[0010] As another optimization solution for the above-mentioned distribution ring network cabinet outgoing cable fault monitoring and positioning system, the signal conditioning module includes a low-frequency signal conditioning module and a high-frequency signal conditioning module, wherein the low-frequency signal conditioning module performs impedance matching, filtering and amplification on the industrial frequency magnetic field signal in the magnetic field sensing unit, and its filtering bandwidth range is 30-100Hz; the high-frequency signal conditioning module performs impedance matching, filtering and amplification on the high-frequency transient magnetic field signal in the magnetic field sensing unit, and its filtering bandwidth range is 100kHz.

[0011] As another optimization solution for the above-mentioned distribution ring network cabinet outgoing cable fault monitoring and positioning system, the signal acquisition module includes a high-speed acquisition module and a low-speed acquisition module, wherein the high-speed acquisition module has a sampling rate of not less than 10MS / s, which is used to capture the waveform details of the high-frequency transient magnetic field signal; the low-speed acquisition module has a sampling rate of 1-100kS / s, which is used to obtain the macro characteristics of the high-frequency transient magnetic field signal.

[0012] As another optimization solution for the above-mentioned distribution ring main unit outgoing cable fault monitoring and positioning system, the monitoring terminal hardware unit has a communication module, which uploads the results output by the control and analysis module to the main station or communicates with other monitoring terminals.

[0013] As another optimization solution for the above-mentioned distribution ring network cabinet outgoing cable fault monitoring and positioning system, the monitoring terminal hardware unit has a GPS timing module, which receives GPS signals and provides high-precision timestamps for the collected signals.

[0014] A method for monitoring and locating a fault in an outgoing cable of a power distribution ring main unit comprises the following steps: 1) A power frequency magnetic field sensor and a high frequency magnetic field sensor are provided. The power frequency magnetic field sensor continuously or periodically collects steady-state or slowly varying magnetic field signals generated by the load current when the cable is operating normally. The high frequency magnetic field sensor continuously or periodically collects rapidly varying magnetic field signals generated by the transient component of the fault current when a cable fault occurs. 2) If, within the set time window, the signal monitored by the power frequency magnetic field sensor experiences a power frequency disturbance, and the signal monitored by the high frequency magnetic field sensor experiences a high frequency mutation, it is determined that the outgoing cable is faulty; The power frequency disturbance refers to a significant change in the monitoring signal of the power frequency magnetic field sensor, including the occurrence of voltage loss characteristics and overcurrent characteristics in its amplitude; The high-frequency mutation refers to the amplitude or energy of the high-frequency magnetic field sensor monitoring signal exceeding the preset high-frequency trigger threshold in a short period of time; 3) Use the low-speed monitoring terminal judgment method or the high-speed monitoring terminal judgment method to determine the location of the fault; The low-speed monitoring terminal judgment method is to set up multiple low-speed monitoring terminals along the outgoing cable. Each low-speed monitoring terminal can perform the operations of steps 1) to 2) to determine whether a fault has occurred, and record the time of the internal clock and the amplitude of the high-frequency mutation signal when the fault occurs. By comparing the amplitudes of the high-frequency mutation signals obtained by two adjacent low-speed monitoring terminals, the cable between the two low-speed monitoring terminals with the highest amplitude is selected as the fault area. The high-speed monitoring terminal judgment method is to set up at least two high-speed monitoring terminals at key positions of the outgoing cable. Each high-speed monitoring terminal is equipped with a GPS timing module and performs the operations of steps 1) to 2), thereby assigning a GPS timestamp to the high-frequency mutation signal collected when the fault occurs. The cable path length between two adjacent high-speed monitoring terminals and the propagation speed of the high-frequency mutation signal in the cable are known. The arrival time difference principle is used to calculate the distance from the fault point to one of the high-speed monitoring terminals, thereby locating the fault location.

[0015] As an optimized solution to the above-mentioned method for monitoring and locating faults in the outgoing cables of the power distribution ring main unit, when it is determined in step 2) that a fault has occurred in the outgoing cable, the signal monitored by the high-frequency magnetic field sensor is first detected to see if a high-frequency mutation has occurred. If a high-frequency mutation has occurred, the signal monitored by the power frequency magnetic field sensor is then checked to see if a power frequency disturbance has occurred. If a power frequency disturbance has occurred, it is finally determined whether the interval between the time of occurrence of the power frequency disturbance and the time of occurrence of the high-frequency mutation exceeds a set time window. If the interval does not exceed the time window, it is determined that a fault has occurred. Alternatively, first detect whether the signal monitored by the power frequency magnetic field sensor has a power frequency disturbance. If a power frequency disturbance occurs, then check whether the signal monitored by the high frequency magnetic field sensor has a high frequency mutation. If a high frequency mutation occurs, finally determine whether the interval between the occurrence time of the power frequency disturbance and the occurrence time of the high frequency mutation exceeds the set time window. If it does not exceed the time window, it is determined that a fault has occurred.

[0016] As another optimization solution for the above-mentioned method for monitoring and locating faults in the outgoing cables of the distribution ring main unit, the distance from the fault point to one of the high-speed monitoring terminals is calculated using the arrival time difference principle in step 3). The specific operation is as follows: Get the timestamps of the high-frequency mutation signal arriving at two adjacent high-speed monitoring terminals, denoted as T1 and T2 respectively. The cable path length between the two high-speed monitoring terminals is L, and the propagation speed of the high-frequency mutation signal is v. Then: Arrival time difference ΔT = |T1-T2|; The distance between the fault point and a high-speed monitoring terminal is D, then: D=(Lv*ΔT) / 2; According to the value of D and the installation position of the high-speed monitoring terminal, the fault point can be located.

[0017] The fault determination method of the present invention is based on the coordinated analysis of low-frequency and high-frequency magnetic field signals, continuously or periodically collecting power-frequency magnetic field sensor signals (PF_Signal) and high-frequency magnetic field sensor signals (HF_Signal). When the system is operating normally, PF_Signal reflects the load current and has a relatively stable amplitude and frequency; the HF_Signal theoretically outputs close to zero or has only a small amount of background noise. The system learns or sets the normal operating range of PF_Signal. It monitors whether the amplitude or energy of HF_Signal suddenly exceeds a preset high-frequency trigger threshold (Th_HF) within a short period of time. This threshold must be set according to the noise level of the on-site environment to avoid false operation caused by interference. It monitors whether PF_Signal undergoes significant changes, such as a rapid drop in amplitude (pressure loss characteristic), a rapid rise (overcurrent characteristic) within a short period of time, or a sharp fluctuation (Th_PF_Dev) greater than a preset percentage relative to the steady-state value before the fault.

[0018] Fault confirmation (cooperative criteria): Time correlation judgment: A line fault is preliminarily determined only when a high-frequency mutation (HF_Signal > Th_HF) and a power frequency disturbance (a significant change in PF_Signal) occur simultaneously or closely together within an extremely short time window (Δt). This time window (Δt) can be set based on the expected fault development speed, for example, 1-10 milliseconds.

[0019] A high-frequency sudden change (possibly due to external electromagnetic interference) or a slow change in the power frequency (normal load fluctuation) alone does not trigger a fault determination. This dual-condition verification effectively improves the anti-interference capability and accuracy of the determination. Once a fault is confirmed, the terminal records the fault and the time of occurrence. The low-speed acquisition module uses the internal clock, while the high-speed acquisition module uses the GPS timestamp.

[0020] The system continuously collects dual-frequency signals. When the high-frequency signal first crosses the threshold, the time of occurrence, T_HF, is recorded. The system then checks whether the power frequency signal also experiences a significant disturbance within the same timeframe (constrained by T_PF and Δt). Only when the two are strongly correlated in time is a fault confirmed, recorded, and reported. The judgment order here can also be to detect the power frequency disturbance first and then check the high-frequency signal. The key is the correlation between the two within Δt.

[0021] Hardware configuration and fault location strategy: To balance cost and positioning accuracy, this paper proposes two hardware configuration solutions and hybrid deployment: High-speed monitoring terminal (with GPS): Equipped with a high-speed data acquisition module and a GPS timing module, it is installed at key locations along a feeder or ring network, such as at feeder terminals or at key nodes in the ring network. In a typical ring network, only two or a few high-speed monitoring terminals are required. In addition to the aforementioned fault detection functions, this terminal is primarily used for precise fault location. When a fault occurs, it accurately records the GPS timestamp of the arrival of high-frequency transient signals.

[0022] Low-speed monitoring terminal (without GPS): Equipped with a low-speed data acquisition module but without a GPS timing module. Installed in other switchgear (ring main unit) cabinets to achieve wide-area coverage. It implements the core fault determination method described above to detect faults and preliminarily determine the faulty section. When a fault is detected, it records the approximate time of occurrence (based on the internal clock) and the amplitude of the high-frequency signal.

[0023] Fault locating method: Fault segment determination based on low-speed monitoring terminals: When a line fault occurs, multiple low-speed monitoring terminals deployed along the line will detect the fault. Because fault signals attenuate as they propagate through the cable, the signal amplitude detected by terminals closer to the fault point is typically greater. By comparing the high-frequency signal amplitudes reported by adjacent low-speed terminals, it is possible to preliminarily determine that the fault occurs in the cable segment between the two terminals with the highest amplitudes.

[0024] High-speed terminal-based fault location: Obtain high-precision GPS-synchronized fault signal arrival timestamps (T1, T2) recorded by the two high-speed terminals. Given the cable path length (L) between the two high-speed terminals and the propagation velocity (v) of the fault signal (high-frequency transient) in the cable, calculate the distance (D1) from the fault point to one of the high-speed terminals (e.g., terminal 1) using the Time Difference of Arrival (TDOA) principle: Time difference: ΔT = |T1-T2|; Distance D1 = (Lv*ΔT) / 2; By calculating the distance D1, the fault point can be accurately located on the line map.

[0025] Compared with the prior art, the present invention has the following beneficial effects: 1) This invention combines two signals, power frequency magnetic field (reflecting steady-state and power frequency overcurrent / undervoltage) and high frequency magnetic field (reflecting transient characteristics), for collaborative judgment. This utilizes the characteristics of different physical phenomena and effectively eliminates interference that a single signal source may encounter (such as operational overvoltage, external electromagnetic pulses, normal load fluctuations, etc.), thereby improving the accuracy of fault judgment and reducing the rate of false and missed fault judgments. 2) This invention adopts a hybrid deployment strategy that combines high-speed monitoring terminals (with GPS) and low-speed monitoring terminals (without GPS). Only a small number of high-cost high-speed monitoring terminals are deployed at key nodes for precise positioning, while low-cost low-speed monitoring terminals are deployed at most nodes for fault detection and section judgment. This ensures that faults can be discovered and roughly located in a timely manner, while also enabling high-precision positioning using high-speed monitoring terminals, significantly reducing the overall economic cost of achieving high positioning accuracy in the entire power distribution system. 3) The present invention is non-invasive and easy to modify. The magnetic field sensor is installed in the cable trench without contacting the high-voltage live parts. It can be retrofitted to the switchgear that has been put into operation without power outage, which greatly facilitates the deployment and promotion of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the system structure of the present invention; Figure 2 This is a flowchart of fault determination in Example 2 of the present invention; Figure 3 This is the circuit 1 for converting 220V to 15V in Example 3; Figure 4 This is the circuit 2 for converting 15V into positive and negative 12V in Example 3; Figure 5 This is the circuit 3 for converting 15V to 5V in Example 3; Figure 6 The fourth circuit for converting 5V to 3.3V in Example 3; Figure 7 This is the circuit 5 for converting 5V into negative 5V in Example 3; Figure 8 This is a circuit diagram of the power frequency channel of the signal conditioning module in Example 3; Figure 9 This is a circuit diagram of the high-frequency channel of the signal conditioning module in Example 3; Figure 10 This is a circuit diagram of the signal acquisition module in Example 3; Figure 11 This is a circuit diagram of the control and analysis module in Example 3; Figure 12 This is a circuit diagram of the communication module in Example 3; Figure 13 This is a circuit diagram of the GPS timing module in Example 3; Figure 14 This is a circuit diagram of the ring network line positioning schematic diagram in Example 3. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further elaborated in detail below with reference to specific embodiments. Any parts not explained in the following embodiments of the present invention are deemed to be prior arts known or should be known to those skilled in the art. For example, the model selection and installation of the power frequency magnetic field sensor and the high frequency magnetic field sensor, and the signal acquisition module and the signal conditioning module can adopt existing circuits or module units as long as they can achieve the functions required by the present invention.

[0028] Example 1 A distribution ring network cabinet outgoing cable fault monitoring and positioning system, such as Figure 1As shown, it includes a magnetic field sensing unit and a monitoring terminal hardware unit. The magnetic field sensing unit is arranged on the surface of the cable in the cable trench of the distribution ring network cabinet, and the monitoring terminal hardware unit is arranged in the instrument box or secondary equipment compartment of the distribution ring network cabinet, and is used to process the signal from the magnetic field sensing unit and perform fault judgment and communication; the magnetic field sensing unit includes a power frequency magnetic field sensor for monitoring the power frequency magnetic field signal and a high-frequency magnetic field sensor for monitoring the high-frequency transient magnetic field signal. The power frequency magnetic field signal is a steady-state or slowly varying magnetic field signal generated by the load current when the cable is operating normally, and the high-frequency transient magnetic field signal is a rapidly varying magnetic field signal generated by the transient component of the fault current when a cable fault occurs; The monitoring terminal hardware unit includes a power supply module that supplies power to the entire system, a signal acquisition module that converts the signal of the magnetic field sensing unit into a digital signal, and a control analysis module that runs a fault monitoring and analysis algorithm; The power supply module obtains the working power from the instrument box of the power distribution ring network cabinet and performs voltage stabilization and isolation processing; A signal conditioning module is provided between the signal acquisition module and the magnetic field sensing unit. The signal conditioning module amplifies and filters the output signal of the magnetic field sensing unit to make it suitable for subsequent acquisition. The signal conditioning module has two types of conditioning modules, which are divided into low-frequency signal conditioning modules and high-frequency signal conditioning modules according to different configurations. The low-frequency signal conditioning module performs impedance matching, filtering and amplification on the power frequency magnetic field signal in the magnetic field sensing unit, and its filtering bandwidth range is 30-100Hz; the high-frequency signal conditioning module performs impedance matching, filtering and amplification on the high-frequency transient magnetic field signal in the magnetic field sensing unit, and its filtering bandwidth range is 100kHz; The signal acquisition module is responsible for converting the conditioned analog signal into a digital signal. Depending on the configuration, it is divided into a high-speed acquisition module and a low-speed acquisition module. The high-speed acquisition module has a sampling rate of no less than 10MS / s and is used to capture the waveform details of the high-frequency transient magnetic field signal; the low-speed acquisition module has a sampling rate of 1-100kS / s and is used to obtain the macroscopic characteristics of the high-frequency transient magnetic field signal, such as amplitude and effective value. The control and analysis module is usually a microprocessor (MCU) or a digital signal processor (DSP), which runs the core fault detection and analysis algorithm; The monitoring terminal hardware unit has a communication module, which uses methods such as RS485, Ethernet, wireless (such as 4G / 5G, LoRa, NB-IoT), etc. to upload detection results, status information, alarm information, and (for high-speed modules) possible waveform data to the main station or communicate with other monitoring terminals.

[0029] The monitoring terminal hardware unit may also include a GPS timing module configured in the high-speed acquisition module. The GPS timing module receives GPS signals and provides high-precision timestamps (such as microsecond or nanosecond synchronization accuracy) for the collected signals (especially high-frequency fault signals).

[0030] Example 2 A method for monitoring and locating faults in outgoing cables of a power distribution ring main unit, such as Figure 2 As shown, the following steps are included: 1) A power frequency magnetic field sensor and a high frequency magnetic field sensor are provided. The power frequency magnetic field sensor continuously or periodically collects steady-state or slowly varying magnetic field signals generated by the load current when the cable is operating normally. The high frequency magnetic field sensor continuously or periodically collects rapidly varying magnetic field signals generated by the transient component of the fault current when a cable fault occurs. 2) If, within the set time window, the signal monitored by the power frequency magnetic field sensor experiences a power frequency disturbance, and the signal monitored by the high frequency magnetic field sensor experiences a high frequency mutation, it is determined that the outgoing cable is faulty; The power frequency disturbance refers to a significant change in the monitoring signal of the power frequency magnetic field sensor, including the occurrence of voltage loss characteristics and overcurrent characteristics in its amplitude; The high-frequency mutation refers to the amplitude or energy of the high-frequency magnetic field sensor monitoring signal exceeding the preset high-frequency trigger threshold in a short period of time; In this step, when determining that the outgoing cable has a fault, it is possible to first detect whether the signal monitored by the high-frequency magnetic field sensor has a high-frequency mutation. If a high-frequency mutation occurs, then check whether the signal monitored by the power frequency magnetic field sensor has a power frequency disturbance. If a power frequency disturbance occurs, finally determine whether the interval between the occurrence time of the power frequency disturbance and the occurrence time of the high-frequency mutation exceeds the set time window. If it does not exceed the time window, it is determined that a fault has occurred. Alternatively, first detect whether the signal monitored by the power frequency magnetic field sensor has a power frequency disturbance. If a power frequency disturbance has occurred, then check whether the signal monitored by the high frequency magnetic field sensor has a high frequency mutation. If a high frequency mutation has occurred, finally determine whether the interval between the time of occurrence of the power frequency disturbance and the time of occurrence of the high frequency mutation exceeds a set time window. If it does not exceed the time window, it is determined that a fault has occurred. 3) Use the low-speed monitoring terminal judgment method or the high-speed monitoring terminal judgment method to determine the location of the fault; The low-speed monitoring terminal judgment method is as follows: multiple low-speed monitoring terminals are set up along the outgoing cable. The structure of the low-speed monitoring terminals is the same as that of the distribution ring network cabinet outgoing cable fault monitoring and positioning system. Each low-speed monitoring terminal can perform the operations of steps 1) to 2) to determine whether a fault has occurred, and record the time of the internal clock and the amplitude of the high-frequency mutation signal when the fault occurs. By comparing the amplitudes of the high-frequency mutation signals obtained by two adjacent low-speed monitoring terminals, the cable between the two low-speed monitoring terminals with the highest amplitude is selected as the fault occurrence area. The high-speed monitoring terminal judgment method is as follows: at least two high-speed monitoring terminals are set at key locations of the outgoing cable. The structure of the high-speed monitoring terminals is the same as that of the above-mentioned distribution ring network cabinet outgoing cable fault monitoring and positioning system; each high-speed monitoring terminal is equipped with a GPS timing module and performs the operations of steps 1) to 2), thereby assigning a GPS timestamp to the high-frequency mutation signal collected when the fault occurs. The cable path length between two adjacent high-speed monitoring terminals and the propagation speed of the high-frequency mutation signal in the cable are known. The time difference of arrival principle is used to calculate the distance from the fault point to one of the high-speed monitoring terminals, thereby locating the fault location; In this step, the time difference of arrival principle is used to calculate the distance from the fault point to one of the high-speed monitoring terminals. The specific operations are as follows: Get the timestamps of the high-frequency mutation signal arriving at two adjacent high-speed monitoring terminals, denoted as T1 and T2 respectively. The cable path length between the two high-speed monitoring terminals is L, and the propagation speed of the high-frequency mutation signal is v. Then: Arrival time difference ΔT = |T1-T2|; The distance between the fault point and a high-speed monitoring terminal is D, then: D=(Lv*ΔT) / 2; According to the value of D and the installation position of the high-speed monitoring terminal, the fault point can be located.

[0031] Example 3 In a typical 10kV distribution ring network, some ring network cabinets (such as the beginning and end of the line, important branch points) are selected to install high-speed monitoring terminals, and the remaining ring network cabinets are installed with low-speed monitoring terminals. Each monitoring terminal includes the magnetic field sensing unit and the monitoring terminal hardware unit of Example 1. The monitoring terminal hardware unit is installed in the instrument box of the ring network cabinet, and draws power from the secondary side of the PT in the cabinet through the power supply module. The magnetic field sensing unit is connected to the monitoring terminal hardware unit through a shielded cable and is fixedly installed in the cable trench below the ring network cabinet, close to the surface of the target outgoing cable. The magnetic field sensing unit includes an industrial frequency magnetic field sensor and a high-frequency magnetic field sensor. All monitoring terminals are connected to the distribution master station or regional monitoring unit through a communication module (such as a wired optical fiber ring network or wireless 4G / 5G).

[0032] Among them, the circuit of the power supply module includes a circuit that converts 220V into 15V, such as Figure 3 As shown; the circuit 2 that converts 15V into positive and negative 12V is as follows Figure 4 As shown; the circuit 3 that converts 15V into 5V is as follows Figure 5 As shown; the circuit 4 that converts 5V to 3.3V is as follows Figure 6 As shown; the circuit 5 that converts 5V into negative 5V is as follows Figure 7 As shown; The signal conditioning module has a power frequency channel and a high frequency channel: Power frequency channel: pre-amplify the output signal of the power frequency magnetic field sensor, perform 50Hz bandpass filtering (filter out high-frequency noise and DC components), and adjust the amplitude. The circuit diagram is as follows Figure 8 As shown; High-frequency channel: pre-amplify, high-pass filter (filter out power frequency and low-frequency interference, retain kHz-MHz transient components), and adjust the amplitude of the high-frequency magnetic field sensor output signal. The circuit diagram is as follows: Figure 9 As shown; The signal acquisition module includes a high-speed acquisition terminal and a low-speed acquisition terminal. The high-speed acquisition terminal uses a high-speed ADC with a sampling rate of 10MHz and 14-bit or 16-bit accuracy; the low-speed acquisition terminal uses a built-in ADC of a single-chip microcomputer with a sampling rate of, for example, 10kHz and 12-bit vertical resolution. Figure 10 As shown; The control and analysis module uses an ARM Cortex-M series MCU. It runs embedded software to implement data processing, threshold comparison, collaborative judgment logic, event recording, synchronization with the GPS module (if any), communication protocol stack, etc. Figure 11 As shown; The communication module can be equipped with an Ethernet interface or a built-in 4G / 5G module. Figure 12 As shown; The GPS timing module configured in the high-speed acquisition terminal receives GPS or other satellite navigation system signals, synchronizes with the internal clock through PPS (Pulse Per Second), and provides microsecond-level precision timestamps, such as Figure 13 shown.

[0033] The fault determination and location process is as follows: like Figure 14 As shown, there are five ring network cabinets A, B, C, D, and E on the ring network line, among which A and E are installed with high-speed monitoring terminals, and B, C, and D are installed with low-speed monitoring terminals.

[0034] Fault occurs: A short circuit fault occurs at point F on the cable (L_CD) between C and D.

[0035] Fault Detection: All monitoring terminals (A to E) have detected a fault.

[0036] The high-frequency magnetic field sensor captures the strong transient magnetic field pulse generated by the fault current, and its output signal HF_Signal quickly exceeds the threshold Th_HF.

[0037] The power frequency magnetic field sensor detects a sharp increase in current (or a change in magnetic field caused by a sudden voltage drop), and its output signal PF_Signal changes significantly.

[0038] The control analysis module of each terminal confirms that the high-frequency mutation and the power frequency disturbance occur in association within Δt and determines it as a fault.

[0039] Information reporting: Low-speed monitoring terminals B, C, and D report: fault alarm, fault time recorded by the internal clock, and detected HF_Signal peak value (for example: B reports 1V, C reports 5V, and D reports 4V).

[0040] High-speed monitoring terminals A and E report: fault alarm, fault signal arrival time (T_A, T_E) recorded by high-precision GPS timestamp, HF_Signal peak value, and optional transient waveform data.

[0041] Fault segment determination: The master station receives the information and compares the HF peaks of B, C, and D. It finds that C (5V) and D (4V) have the highest amplitudes, with C > D > B. The preliminary judgment is that the fault occurs in segments CD, closer to C.

[0042] Accurate fault location: The master station uses the GPS timestamps T_A and T_E reported by A and E. The total cable length L_AE from A to E (or the path calculated by segmenting C and D) and the signal propagation speed v are known.

[0043] Calculate the time difference: ΔT=|T_E-T_A|; Assume that the distance between fault point F and A is D_A and the distance between F and E is D_E, then: D_A+D_E=L_AE (along the cable path).

[0044] And T_A=T_fault+D_A / v, T_E=T_fault+D_E / v.

[0045] It can be solved that D_A=(L_AE+v*(T_A-T_E)) / 2.

[0046] After calculating D_A, the position of the fault point F can be accurately located on the map.

[0047] The signal propagation velocity v can be estimated from the cable model parameters or calibrated by performing an artificial short-circuit test at the end of the line.

[0048] In practical applications, more than two high-speed terminals can be deployed according to the ring network structure and branch conditions, and multi-point time information can be used for more robust positioning.

[0049] The fault analysis algorithm can be further optimized, for example, by combining waveform feature analysis (such as polarity and steepness) to distinguish fault types (short circuit, grounding) or exclude certain specific interferences.

Claims

1. A distribution ring main unit outgoing cable fault monitoring and positioning system, characterized by: It includes a magnetic field sensing unit and a monitoring terminal hardware unit, wherein the magnetic field sensing unit includes a power frequency magnetic field sensor for monitoring the power frequency magnetic field signal and a high frequency magnetic field sensor for monitoring the high frequency transient magnetic field signal. The power frequency magnetic field signal is a steady-state or slowly varying magnetic field signal generated by the load current when the cable is operating normally, and the high frequency transient magnetic field signal is a rapidly varying magnetic field signal generated by the transient component of the fault current when a cable fault occurs; The monitoring terminal hardware unit includes a power supply module for supplying power to the entire system, a signal acquisition module for converting the signal of the magnetic field sensing unit into a digital signal, and a control analysis module for running a fault monitoring and analysis algorithm.

2. The distribution ring main unit outgoing cable fault monitoring and positioning system according to claim 1 is characterized in that: The magnetic field sensing unit is arranged on the surface of the cable in the cable trench of the distribution ring network cabinet; the monitoring terminal hardware unit is arranged in the instrument box or secondary equipment compartment of the distribution ring network cabinet, and the power supply module obtains the working power from the instrument box of the distribution ring network cabinet, and performs voltage stabilization and isolation processing.

3. The distribution ring main unit outgoing cable fault monitoring and positioning system according to claim 1 is characterized in that: A signal conditioning module is provided between the signal acquisition module and the magnetic field sensing unit, and the signal conditioning module amplifies and filters the output signal of the magnetic field sensing unit.

4. The distribution ring main unit outgoing cable fault monitoring and positioning system according to claim 3 is characterized in that: The signal conditioning module includes a low-frequency signal conditioning module and a high-frequency signal conditioning module. The low-frequency signal conditioning module performs impedance matching, filtering and amplification on the industrial frequency magnetic field signal in the magnetic field sensing unit, and its filtering bandwidth range is 30-100Hz; the high-frequency signal conditioning module performs impedance matching, filtering and amplification on the high-frequency transient magnetic field signal in the magnetic field sensing unit, and its filtering bandwidth range is 100kHz.

5. The distribution ring main unit outgoing cable fault monitoring and positioning system according to claim 1 is characterized in that: The signal acquisition module includes a high-speed acquisition module and a low-speed acquisition module, wherein the high-speed acquisition module has a sampling rate of not less than 10MS / s and is used to capture the waveform details of the high-frequency transient magnetic field signal; the low-speed acquisition module has a sampling rate of 1-100kS / s and is used to obtain the macroscopic characteristics of the high-frequency transient magnetic field signal.

6. The distribution ring main unit outgoing cable fault monitoring and positioning system according to claim 1, characterized in that: The monitoring terminal hardware unit includes a communication module, which uploads the results output by the control and analysis module to the main station or communicates with other monitoring terminals.

7. The distribution ring main unit outgoing cable fault monitoring and positioning system according to claim 1 is characterized in that: The monitoring terminal hardware unit has a GPS timing module, which receives GPS signals and provides high-precision timestamps for the collected signals.

8. A method for monitoring and locating faults in outgoing cables of a power distribution ring main unit, characterized in that: The steps include: 1) A power frequency magnetic field sensor and a high frequency magnetic field sensor are provided. The power frequency magnetic field sensor continuously or periodically collects steady-state or slowly varying magnetic field signals generated by the load current when the cable is operating normally. The high frequency magnetic field sensor continuously or periodically collects rapidly varying magnetic field signals generated by the transient component of the fault current when a cable fault occurs. 2) If, within the set time window, the signal monitored by the power frequency magnetic field sensor experiences a power frequency disturbance, and the signal monitored by the high frequency magnetic field sensor experiences a high frequency mutation, it is determined that the outgoing cable is faulty; The power frequency disturbance refers to a significant change in the monitoring signal of the power frequency magnetic field sensor, including the occurrence of voltage loss characteristics and overcurrent characteristics in its amplitude; The high-frequency mutation refers to the amplitude or energy of the high-frequency magnetic field sensor monitoring signal exceeding the preset high-frequency trigger threshold in a short period of time; 3) Use the low-speed monitoring terminal judgment method or the high-speed monitoring terminal judgment method to determine the location of the fault; The low-speed monitoring terminal judgment method is to set up multiple low-speed monitoring terminals along the outgoing cable. Each low-speed monitoring terminal can perform the operations of steps 1) to 2) to determine whether a fault has occurred, and record the time of the internal clock and the amplitude of the high-frequency mutation signal when the fault occurs. By comparing the amplitudes of the high-frequency mutation signals obtained by two adjacent low-speed monitoring terminals, the cable between the two low-speed monitoring terminals with the highest amplitude is selected as the fault area. The high-speed monitoring terminal judgment method is to set up at least two high-speed monitoring terminals at key positions of the outgoing cable. Each high-speed monitoring terminal is equipped with a GPS timing module and performs the operations of steps 1) to 2), thereby assigning a GPS timestamp to the high-frequency mutation signal collected when the fault occurs. The cable path length between two adjacent high-speed monitoring terminals and the propagation speed of the high-frequency mutation signal in the cable are known. The arrival time difference principle is used to calculate the distance from the fault point to one of the high-speed monitoring terminals, thereby locating the fault location.

9. The method for monitoring and locating a fault in an outgoing cable of a power distribution ring main unit according to claim 8, characterized in that: When determining that the outgoing cable has a fault in step 2), first detect whether the signal monitored by the high-frequency magnetic field sensor has a high-frequency mutation. If a high-frequency mutation has occurred, then check whether the signal monitored by the power frequency magnetic field sensor has a power frequency disturbance. If a power frequency disturbance has occurred, finally determine whether the interval between the time of occurrence of the power frequency disturbance and the time of occurrence of the high-frequency mutation exceeds a set time window. If it does not exceed the time window, it is determined that a fault has occurred. Alternatively, first detect whether the signal monitored by the power frequency magnetic field sensor has a power frequency disturbance. If a power frequency disturbance occurs, then check whether the signal monitored by the high frequency magnetic field sensor has a high frequency mutation. If a high frequency mutation occurs, finally determine whether the interval between the occurrence time of the power frequency disturbance and the occurrence time of the high frequency mutation exceeds the set time window. If it does not exceed the time window, it is determined that a fault has occurred.

10. The method for monitoring and locating a fault in an outgoing cable of a power distribution ring main unit according to claim 8, wherein: In step 3), the distance from the fault point to one of the high-speed monitoring terminals is calculated using the arrival time difference principle. The specific operation is as follows: Get the timestamps of the high-frequency mutation signal arriving at two adjacent high-speed monitoring terminals, denoted as T1 and T2 respectively. The cable path length between the two high-speed monitoring terminals is L, and the propagation speed of the high-frequency mutation signal is v. Then: Arrival time difference ΔT = |T1-T2|; The distance between the fault point and a high-speed monitoring terminal is D, then: D=(Lv*ΔT) / 2; According to the value of D and the installation position of the high-speed monitoring terminal, the fault point can be located.

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