Load monitoring method and line electric leakage detection method for low-voltage transformer area

Abstract

The invention relates to the technical field of load monitoring, and discloses a load monitoring method of a low-voltage transformer area and a line electric leakage detection method based on a low-voltage transformer area load detector device. Comprising the steps of current signal acquisition and processing, current-voltage conversion, signal processing, Fourier transform FFT processing, real-time current value calculation and output, data transmission, remote monitoring and the like. According to the load monitoring method and the line leakage detection method for the low-voltage transformer area, a real-time current signal is acquired through an open current transformer, and is processed by means of a Fourier transform FFT algorithm, so that the load distribution condition of the low-voltage transformer area can be accurately monitored; the problem of randomness of a traditional measurement method is solved, it is ensured that the collected load data accurately reflects the actual power consumption condition of each household, and reliable support is provided for follow-up three-phase load adjustment. The three-phase load condition of each branch line in the multiple branches of the low-voltage line can be accurately monitored by simultaneously monitoring the branch lines in the multiple branches of the low-voltage line.

Description

Technical Field

[0001] The present invention relates to the technical field of load monitoring, and in particular to a load monitoring method for a low-voltage area and a line leakage detection method. Background Art

[0002] At present, there are a series of problems to be solved in the load monitoring and management of low-voltage substations, which seriously affect the stable operation and power quality of the distribution network. First of all, based on the selection of distribution transformers in the early stage and the lack of unified planning for single-phase load access, the phenomenon of three-phase load imbalance often occurs in low-voltage substations. The unbalanced three-phase load will cause problems such as increased zero-line current, neutral point drift, and increased line voltage drop, which will affect the output of the transformer and reduce the reliability of power supply. In addition, due to the uncertainty of each user's power consumption time and load peak, traditional load measurement usually relies on manual on-site surveys in a specific time period, resulting in a large randomness of the data, which cannot fully and accurately reflect the actual load distribution of the low-voltage substation, which brings great difficulties to the load adjustment work. 。

[0003] Especially for the complex environment of low-voltage substations with multiple branch lines, traditional load monitoring equipment can only collect the total load of each phase, and cannot accurately detect specific branches, and cannot reflect the three-phase load distribution of each branch. This makes it difficult to detect and adjust the unbalanced three-phase load, and the adjustment plan lacks strong data support, which cannot effectively improve the output efficiency and voltage quality of the transformer.

[0004] In addition, the leakage problem of low-voltage distribution lines is also a major challenge facing the current distribution network operation and maintenance. Leakage may occur in any part of the line, especially for lines buried in pipelines, where the leakage point is often difficult to observe directly with the naked eye. Traditional detection methods such as "pulling the circuit breaker and checking the current" not only require a lot of work, but can only roughly determine the leakage area, which is easy to cause user complaints and cannot meet the needs of rapid maintenance of modern distribution networks. Summary of the invention

[0005] In order to solve the above problems, a load monitoring method and a line leakage detection method for a low voltage area are provided.

[0006] The technical solution adopted by the present invention is:

[0007] A load monitoring method for a low-voltage area, the load monitoring method for the low-voltage area is based on a low-voltage area load detector device, the low-voltage area load detector device comprises an equipment body, and an open current transformer detachably connected to the equipment body;

[0008] The load monitoring method of the low-voltage area includes the following steps:

[0009] Step 1: Current signal acquisition and processing:

[0010] Use open current transformers to collect three-phase current signals of each branch line in the low-voltage area in real time and transmit them to the main body of the equipment;

[0011] Step 2, current-to-voltage conversion:

[0012] The three-phase current signal is converted into a voltage signal through a current-voltage conversion circuit in the main body of the device;

[0013] Step 3, signal processing:

[0014] After being amplified and adjusted, the voltage signal is transmitted to the analog-to-digital converter ADC of the microcontroller MCU in the device body; the analog-to-digital converter ADC converts the analog voltage signal into a digital signal and obtains the time series of the signal;

[0015] Step 4, Fourier transform FFT processing:

[0016] Based on the sampled signal time series, the microcontroller MCU performs spectrum analysis of the current signal through fast Fourier transform FFT to obtain the frequency components of the signal and accurately reflect the dynamic characteristics of the current load;

[0017] Step 5, calculation and output of real-time current value:

[0018] After the Fourier transform FFT processing is completed, the amplitude and phase information of the signal will be extracted from the frequency domain data. By detecting the amplitude of the fundamental frequency, the effective value of the current, that is, the RMS value, can be obtained, and the current load can be calculated and output in real time;

[0019] Step 6: Data transmission and remote monitoring

[0020] The current load data after Fourier transform FFT analysis, including real-time current value and harmonic analysis results, is transmitted to the remote server or terminal device through the remote communication module in the device body, so that the operation and maintenance personnel can view the current load status of the substation in real time and assist in load adjustment and system optimization.

[0021] Further, in step 2, the current-to-voltage conversion circuit includes a resistive load or an operational amplifier;

[0022] If the current output by the open-type current transformer is I CT , the current passes through the resistor R connected to it, and the voltage signal V can be expressed by the following formula:

[0023] V=I CT ×R

[0024] At this stage, the operational amplifier adjusts the amplitude of the voltage signal Vze to adapt it to the input range of the subsequent analog-to-digital converter ADC.

[0025] Further, in step 3, the analog-to-digital conversion process of the analog-to-digital converter ADC is as follows:

[0026] The analog-to-digital converter ADC discretizes the continuous analog voltage signal into discrete digital values. If the sampling rate is f S , then the time interval between each voltage value is Δt, Finally, a series of discrete voltage data are obtained to form the time series of the signal.

[0027] Further, in step 4, the Fourier transform FFT processing is as follows:

[0028] For a discrete signal x[n], its discrete Fourier transform DFT formula is:

[0029]

[0030] Where X[k] is the Fourier transform result of the kth frequency component; N is the total number of sampling points; x[n] is the sampling value at the nth time point; is the Fourier basis function;

[0031] The direct computational time complexity of the discrete Fourier transform DFT is O(N 2 ), Fourier transform FFT is an efficient implementation of discrete Fourier transform DFT, which uses divide-and-conquer method to reduce the amount of calculation to O(NlogN); therefore, the Fourier transform FFT algorithm can quickly calculate the frequency components of the signal and obtain the spectrum distribution of the current signal.

[0032] Furthermore, in step 4, the spectrum analysis of the current signal is performed by fast Fourier transform FFT, the current data collected from the analog-to-digital converter ADC is analyzed, and its main frequency components are identified; the three-phase current signal usually operates at a basic frequency of 50 Hz or 60 Hz, and the possible high-order harmonics or abnormal frequency components are detected by Fourier transform FFT.

[0033] Further, in step 5, the RMS value calculation process is as follows:

[0034] If the detection base frequency is 50Hz, the amplitude of the 50Hz frequency component obtained by Fourier transform FFT is A 50 ; The effective current value corresponding to this frequency is I rms Calculated by the following formula:

[0035]

[0036] The current load size is determined based on the RMS value of the current, and the data is transmitted to the remote terminal for monitoring and adjustment.

[0037] A line leakage detection method, the line leakage detection method is based on a low-voltage area load detector device, the low-voltage area load detector device comprises an equipment body, and an open current transformer detachably connected to the equipment body;

[0038] The line leakage detection method comprises the following steps:

[0039] Step I, data preprocessing:

[0040] The open current transformer installed on the line collects the three-phase current signal of the line in real time. The digital converter ADC in the main body of the equipment samples the three-phase current signal at a sampling rate of 8kHz, and filters out high-frequency noise and interference signals through the low-pass filter in the main body of the equipment to obtain high-precision current data.

[0041] Step II, load imbalance algorithm:

[0042] The microcontroller MCU in the device body calculates the average value I of the three-phase current based on the collected three-phase current signal avg and each phase current I A ,I B and I C Compare; if the difference between any phase current and the average value exceeds the set threshold, it is determined to be a three-phase unbalanced state, the algorithm generates corresponding alarm information, and transmits the information to the remote terminal through the remote communication module in the device body;

[0043] Step III, overload detection:

[0044] The microcontroller MCU in the device body extracts the amplitude of the fundamental frequency of each phase current based on the Fourier transform FFT algorithm and calculates its effective value I rms ; The calculated I rms With the preset rated current value I 额定 For comparison, if I rms >I 额定 , it is determined that the phase line is in an overload state, an overload alarm message is generated and transmitted to the remote terminal, prompting the operation and maintenance personnel to take load adjustment measures in time;

[0045] Step IV, leakage detection:

[0046] The microcontroller MCU in the main body of the device determines the leakage point by monitoring abnormal fluctuations in line current, aggravation of three-phase imbalance and changes in zero-sequence current; if the current drops suddenly in a short period of time, it is judged as a leakage fault; the fault information is sent to the monitoring system through the remote communication module in the main body of the device, and the possible leakage location is prompted.

[0047] Further, in step II, in the load imbalance algorithm, when there is no single-phase load in the measured line, the mean of the three-phase current and the current I A ,I B and I C Comparison yields:

[0048] ΔI A =|I A -I avg |,ΔI B =|I B -I avg |,ΔI c =|I c -I avg |;

[0049] The imbalance is calculated as:

[0050]

[0051] Based on the unbalance results, adjustment recommendations are generated to reduce or increase the load on a phase and optimize the load distribution of the system.

[0052] Further, in step III, in overload detection, if the amplitude of the fundamental frequency 50 Hz of each phase current is extracted as A 50 , then the effective value I rms for:

[0053] Further, in step IV, the leakage detection includes zero-sequence current detection and current waveform abnormality detection;

[0054] Zero sequence current detection:

[0055] Under normal circumstances, the vector sum of the three-phase current is zero. When leakage occurs, the current leaks in one phase, causing the sum of the three-phase current to be non-zero. By monitoring the vector sum of the three-phase current, that is, I sum Make judgments;

[0056] I sum =I A +I B +I C

[0057] If I sum ≠0, then there is leakage in the current;

[0058] Current sensing in the presence of a single-phase load:

[0059] The theoretical current I of the neutral line is calculated based on the current of each phase of three phases A, B, and C by using the vector calculation method. N

[0060]

[0061] The calculated theoretical current of the neutral line I N Compare it with the neutral current detected by the device, and determine whether there is leakage by observing whether the two are equal;

[0062] Abnormal current waveform detection:

[0063] Monitor the changes in the current waveform. The normal current waveform should be a smooth sine wave. When leakage occurs, the waveform may be distorted. Perform Fourier transform (FFT) on the collected current signal, analyze its spectrum, and detect the increase of high-order harmonics or changes in waveform distortion:

[0064]

[0065] When the harmonic content exceeds the set threshold, a leakage alarm is generated, indicating that there may be a leakage problem.

[0066] The beneficial effects of the present invention are:

[0067] 1. Real-time and accurate load distribution collection: In the above-mentioned load monitoring method for low-voltage substations, real-time current signals are collected through open current transformers and processed with the help of Fourier transform FFT algorithm, so as to accurately monitor the load distribution of low-voltage substations; it solves the randomness problem of traditional measurement methods, ensures that the collected load data accurately reflects the actual power consumption of each household, and provides reliable support for subsequent three-phase load adjustment.

[0068] 2. Accurate monitoring of branch line load: The above-mentioned load monitoring method of the low-voltage substation can be carried out simultaneously on each branch line in the low-voltage line, so as to accurately monitor the three-phase load conditions of each branch line in the low-voltage line. It effectively solves the problem that the existing monitoring system cannot reflect the load distribution of each branch line, facilitates the identification of specific branches with unbalanced loads, and guides more accurate load adjustment operations.

[0069] 3. Improve the efficiency of three-phase load adjustment: In the above-mentioned low-voltage area load monitoring method, the low-voltage area load detector device is portable and can be installed and disassembled at any time, and can be quickly deployed and monitored. It effectively solves the problems of difficult investigation and inaccurate data before load adjustment, greatly improves the efficiency of three-phase load adjustment, ensures that the distribution transformer can work under balanced load, and improves operational reliability and power quality.

[0070] 4. Rapid and accurate positioning of leakage points: The above-mentioned line leakage detection method is also based on the low-voltage station area load detector device, which can quickly locate the leakage point in the low-voltage line by detecting the change of line current. The effect is particularly obvious when the buried wire in the PVC pipe leaks, which effectively improves the efficiency of leakage detection, reduces a large amount of manual troubleshooting work in traditional methods, and reduces workload and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0072] Figure 1 It is a schematic diagram of the overall structure of the low-voltage area load detector device of the present invention;

[0073] Figure 2 It is a schematic diagram of the internal structure of the low-voltage area load detector device of the present invention;

[0074] Figure 3 A flow chart of a load monitoring method for a low voltage area of ​​the present invention;

[0075] Figure 4 It is a flow chart of the line leakage detection method of the present invention;

[0076] Markings in the figure: 1. Equipment body; 2. Open current transformer CT; 3. Display screen; 4. Power switch; 5. Power cord interface; 6. Connection cable socket; 7. Circuit board; 8. Lithium iron phosphate battery; 9. Current-voltage conversion circuit; 10. Microcontroller MCU; 11. Remote communication module. DETAILED DESCRIPTION

[0077] The following will be combined with the drawings of the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0078] Example 1

[0079] This embodiment provides a load monitoring method for a low-voltage area, and the load monitoring method for a low-voltage area is based on a low-voltage area load detector device. Figure 1 As shown, the low voltage area load detector device includes a device body 1 and an open current transformer CT2 for data transmission with the device body 1; the device body 1 is provided with a display screen 3, a power switch 4, and a power line interface 5. Figure 2As shown, a circuit board 7 and a lithium iron phosphate battery 8 for power supply are installed in the device body 1; a current-voltage conversion circuit 9, a microcontroller MCU10 with an analog-to-digital converter ADC, and a remote communication module 11 are installed on the circuit board 7; the open current transformer CT2 is connected to the circuit board 7 for data transmission through the remote communication module 11; and the lithium iron phosphate battery 8 can be charged by inserting a power cord through the power cord interface 5.

[0080] Based on the above-mentioned low-voltage area load detector device, the load data of the low-voltage area can be collected, analyzed and remotely transmitted in real time. The specific load monitoring method of the low-voltage area is as follows: Figure 3 As shown, the following steps are included:

[0081] Step 1: Current signal acquisition and processing:

[0082] The open current transformer CT2 is used to collect the three-phase current signals of each branch line in the low-voltage substation in real time and transmit them to the equipment body 1.

[0083] The open-type current transformer CT2 is a non-invasive current detection device that measures the magnitude of the AC current by inducing the magnetic field generated by the current. Since the device works in a low-voltage power distribution environment, the open-type current transformer CT2 can be directly installed on the cable without cutting off the circuit or connecting the cable, which enables quick and convenient installation and removal. The open-type current transformer CT2 senses the magnetic field around the conductor and generates a secondary current signal proportional to the current through Faraday's law of electromagnetic induction. Since the signal output by the open-type current transformer CT2 is a current type, the current signal needs to be converted into a voltage signal for subsequent processing.

[0084] Step 2, current-to-voltage conversion:

[0085] The three-phase current signal is converted into a voltage signal through a current-voltage conversion circuit 9 in the device body 1. The current-voltage conversion circuit 9 includes a resistance load or an operational amplifier.

[0086] If the current output by the open-type current transformer CT2 is I CT , the current passes through the resistor R connected to it, and the voltage signal V can be expressed by the following formula:

[0087] V=I CT ×R

[0088] At this stage, the operational amplifier adjusts the amplitude of the voltage signal Vze to adapt it to the input range of the subsequent analog-to-digital converter ADC.

[0089] Step 3, signal processing:

[0090] After being amplified and adjusted, the voltage signal is transmitted to the analog-to-digital converter ADC of the microcontroller MCU10 in the device body 1; the analog-to-digital converter ADC converts the analog voltage signal into a digital signal and obtains the time series of the signal.

[0091] Specifically, the analog-to-digital conversion process is as follows:

[0092] The analog-to-digital converter ADC inside the microcontroller MCU10 discretizes the continuous analog voltage signal into discrete digital values. If the sampling rate is f S , for example, 8kHz; then the time interval between each voltage value is Δt, Finally, a series of discrete voltage data are obtained to form the time series of the signal.

[0093] Step 4, Fourier transform FFT processing:

[0094] The microcontroller MCU10 performs spectrum analysis of the current signal through fast Fourier transform (FFT) based on the sampled signal time series to obtain the frequency components of the signal and accurately reflect the dynamic characteristics of the current load.

[0095] The Fourier transform FFT process is as follows:

[0096] Fourier transform is a mathematical tool that converts time domain signals into frequency domain; for a discrete signal x[n], its discrete Fourier transform DFT formula is:

[0097]

[0098] Where X[k] is the Fourier transform result of the kth frequency component;

[0099] N is the total number of sampling points;

[0100] x[n] is the sampling value at the nth time point;

[0101] are the Fourier basis functions.

[0102] The direct computational time complexity of the discrete Fourier transform DFT is O(N 2 ), Fourier transform FFT is an efficient implementation of discrete Fourier transform DFT, which uses divide-and-conquer method to reduce the amount of calculation to O(NlogN); therefore, the Fourier transform FFT algorithm can quickly calculate the frequency components of the signal and obtain the spectrum distribution of the current signal.

[0103] The spectrum analysis of the current signal is performed through the fast Fourier transform FFT, and the current data collected from the analog-to-digital converter ADC is analyzed to identify its main frequency components; the three-phase current signal usually operates at a basic frequency of 50Hz or 60Hz, and the possible high-order harmonics or abnormal frequency components are detected through the Fourier transform FFT.

[0104] In the device, the microcontroller MCU10 executes a Fourier transform FFT algorithm to analyze the current data collected from the analog-to-digital converter ADC and identify its main frequency components. The three-phase current signal usually operates at a basic frequency of 50Hz or 60Hz, and the Fourier transform FFT can help detect possible high-order harmonics or abnormal frequency components.

[0105] Step 5, calculation and output of real-time current value:

[0106] After the Fourier transform FFT processing is completed, the amplitude and phase information of the signal will be extracted from the frequency domain data. By detecting the amplitude of the fundamental frequency, the effective value of the current, that is, the RMS value, can be obtained, and the current load can be calculated and output in real time.

[0107] The RMS value calculation process is as follows:

[0108] If the detection base frequency is 50Hz, the amplitude of the 50Hz frequency component obtained by Fourier transform FFT is A 50 ; The effective current value corresponding to this frequency is I rms Calculated by the following formula:

[0109]

[0110] In this way, the size of the current load can be determined based on the RMS value of the current, and the data can be transmitted to the remote terminal for monitoring and adjustment by the remote terminal.

[0111] Step 6: Data transmission and remote monitoring

[0112] The current load data after Fourier transform FFT analysis, including the real-time current value and harmonic analysis results, is transmitted to the remote server or terminal device and the display screen 3 through the remote communication module 11 in the device body 1, so that the operation and maintenance personnel can view the current load status of the substation in real time and assist in load adjustment and system optimization.

[0113] In summary, the load monitoring method of the low-voltage substation uses an open current transformer CT2 to collect the three-phase current signals of each branch line, converts the current signals into voltage signals through current-voltage conversion, and then processes them through a low-power microcontroller MCU10 to perform analog-to-digital conversion ADC and Fourier transform FFT calculation on the signals to obtain real-time current values, providing key data support for load analysis and three-phase imbalance adjustment.

[0114] Since the load monitoring method of the low-voltage area is based on the low-voltage area load detector device, the device has portability and modular design, can be flexibly installed on different lines, and quickly detect three-phase load imbalance. In addition, the device is equipped with a high-efficiency lithium iron phosphate battery 8 to ensure that it can work continuously for a long time, in high or low temperature environments. The battery is charged through a conventional mobile phone charger, which is convenient for on-site operation. Another highlight of the device is its built-in remote communication module 11, which supports wireless communication and can transmit the collected load data to the remote monitoring terminal in real time. The operation and maintenance personnel can view the load distribution data in real time through the remote terminal without going to the site, and quickly discover problems such as three-phase imbalance and load overload.

[0115] Example 2

[0116] This embodiment provides a line leakage detection method, which is based on the low-voltage area load detector device in Embodiment 1. The specific structure of the low-voltage area load detector device is not described in detail here.

[0117] like Figure 4 As shown, the line leakage detection method specifically includes the following steps:

[0118] The line leakage detection method comprises the following steps:

[0119] Step I, data preprocessing:

[0120] Sampling: The open current transformer CT2 installed on the line collects the three-phase current signal of the line in real time, and the digital converter ADC in the equipment body 1 samples the three-phase current signal at a sampling rate of 8kHz.

[0121] Noise filtering: High-frequency noise and interference signals are filtered out through the low-pass filter in the device body 1 to obtain high-precision current data, ensuring that the data used for analysis is a pure current signal.

[0122] Step II, load imbalance algorithm:

[0123] Three-phase current comparison: The microcontroller MCU10 in the device body 1 calculates the average value I of the three-phase current based on the collected three-phase current signal avg and each phase current I A ,I B and I C Make comparisons;

[0124] If the difference between any phase current and the average value exceeds the set threshold, it is determined to be a three-phase unbalanced state, the algorithm generates corresponding alarm information, and transmits the information to the remote terminal and the display screen 3 through the remote communication module 11 in the device body 1.

[0125] In the load imbalance algorithm, when there is no single-phase load in the measured line, the mean of the three-phase current and the current of each phase I A ,I B and I C Comparison yields:

[0126] ΔI A =|I A -I avg |,ΔI B =|I B -I avg |,ΔI c =|I c -I avg |;

[0127] The imbalance is calculated as:

[0128]

[0129] Adjustment suggestions: Based on the results of the imbalance, generate adjustment suggestions to reduce or increase the load on a certain phase and optimize the load distribution of the system.

[0130] Step III, overload detection:

[0131] Real-time current calculation: The microcontroller MCU10 in the device body 1 extracts the amplitude of the fundamental frequency of each phase current based on the Fourier transform FFT algorithm and calculates its effective value I rms ;

[0132] In overload detection, if the amplitude of the fundamental frequency 50Hz of each phase current is extracted as A 50 , then the effective value I rms for:

[0133]

[0134] Load status judgment: The calculated I rms With the preset rated current value I 额定 Make a comparison;

[0135] If I rms >I 额定 , it is determined that the phase line is in an overload state, an overload alarm message is generated and transmitted to the remote terminal, prompting the operation and maintenance personnel to take load adjustment measures in time.

[0136] Step IV, leakage detection:

[0137] Leakage detection: The microcontroller MCU10 in the device body 1 determines the leakage point by monitoring abnormal fluctuations in line current, aggravation of three-phase imbalance and changes in zero-sequence current;

[0138] The device's algorithm implements auxiliary identification of leakage through the following steps:

[0139] Zero sequence current detection:

[0140] Under normal circumstances, the vector sum of the three-phase current is zero. When leakage occurs, the current leaks in one phase, causing the sum of the three-phase current to be non-zero. By monitoring the vector sum of the three-phase current, that is, I sum Make judgments;

[0141] I sum =I A +I B +I C

[0142] If I sum ≠0, it means there is current leakage.

[0143] Current sensing in the presence of a single-phase load:

[0144] The theoretical current I of the neutral line is calculated based on the current of each phase of three phases A, B, and C by using the vector calculation method. N

[0145]

[0146] The calculated theoretical current of the neutral line I N Compare it with the neutral current detected by the device and determine whether there is leakage by observing whether the two are equal.

[0147] Abnormal current waveform detection:

[0148] Monitor the changes in the current waveform. The normal current waveform should be a smooth sine wave. When leakage occurs, the waveform may be distorted. Perform Fourier transform (FFT) on the collected current signal, analyze its spectrum, and detect the increase of high-order harmonics or changes in waveform distortion:

[0149]

[0150] When the harmonic content exceeds the set threshold, a leakage alarm is generated, indicating that there may be a leakage problem.

[0151] Detection of rapid current changes:

[0152] Leakage may cause a phase current to decrease or increase sharply. The possible leakage point is determined by detecting the sudden change of the current value. If the current drops suddenly in a short period of time, it is determined to be a leakage fault; the fault information is sent to the monitoring system and the display screen 3 through the remote communication module 11 in the device body 1, and the possible leakage location is prompted.

[0153] In summary, the line leakage detection method can quickly locate the leakage point in the low-voltage line by detecting the change of line current, especially when the buried wire in the PVC pipe leaks. It improves the efficiency of leakage detection, reduces a lot of manual troubleshooting work in traditional methods, and reduces workload and maintenance costs.

[0154] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A load monitoring method for a low voltage area, characterized in that: The load monitoring method of the low-voltage area is based on a low-voltage area load detector device, which includes an equipment body and an open current transformer for data transmission with the equipment body; The load monitoring method of the low-voltage area includes the following steps: Step 1: Current signal acquisition and processing: Use open current transformers to collect three-phase current signals of each branch line in the low-voltage area in real time and transmit them to the main body of the equipment; Step 2, current-to-voltage conversion: The three-phase current signal is converted into a voltage signal through a current-voltage conversion circuit in the main body of the device; Step 3, signal processing: After being amplified and adjusted, the voltage signal is transmitted to the analog-to-digital converter ADC of the microcontroller MCU in the device body; the analog-to-digital converter ADC converts the analog voltage signal into a digital signal and obtains the time series of the signal; Step 4, Fourier transform FFT processing: Based on the sampled signal time series, the microcontroller MCU performs spectrum analysis of the current signal through fast Fourier transform FFT to obtain the frequency components of the signal and accurately reflect the dynamic characteristics of the current load; Step 5, calculation and output of real-time current value: After the Fourier transform FFT processing is completed, the amplitude and phase information of the signal will be extracted from the frequency domain data. By detecting the amplitude of the fundamental frequency, the effective value of the current, that is, the RMS value, can be obtained, and the current load can be calculated and output in real time; Step 6: Data transmission and remote monitoring The current load data after Fourier transform FFT analysis, including real-time current value and harmonic analysis results, is transmitted to the remote server or terminal device through the remote communication module in the device body, so that the operation and maintenance personnel can view the current load status of the substation in real time and assist in load adjustment and system optimization.

2. The load monitoring method for low voltage area according to claim 1 is characterized in that: In step 2, the current-to-voltage conversion circuit includes a resistive load or an operational amplifier; If the current output by the open-type current transformer is I CT , the current passes through the resistor R connected to it, and the voltage signal V can be expressed by the following formula: V=I CT ×R At this stage, the operational amplifier adjusts the amplitude of the voltage signal Vze to adapt it to the input range of the subsequent analog-to-digital converter ADC.

3. The load monitoring method for low voltage area according to claim 1 is characterized in that: In step 3, the analog-to-digital conversion process of the analog-to-digital converter ADC is as follows: The analog-to-digital converter ADC discretizes the continuous analog voltage signal into discrete digital values. If the sampling rate is f S , then the time interval between each voltage value is Δt, Finally, a series of discrete voltage data are obtained, forming a time series of the signal.

4. The load monitoring method for low voltage area according to claim 1 is characterized in that: In step 4, the Fourier transform FFT process is as follows: For a discrete signal x[n], its discrete Fourier transform DFT formula is: Where X[k] is the Fourier transform result of the kth frequency component; N is the total number of sampling points; x[n] is the sampling value at the nth time point; is the Fourier basis function; The direct computational time complexity of the discrete Fourier transform DFT is O(N 2 ), Fourier transform FFT is an efficient implementation of discrete Fourier transform DFT, which uses divide-and-conquer method to reduce the amount of calculation to O(N log N); therefore, the Fourier transform FFT algorithm can quickly calculate the frequency components of the signal and obtain the spectrum distribution of the current signal.

5. The load monitoring method for low voltage area according to claim 1 is characterized in that: In step 4, the spectrum analysis of the current signal is performed by fast Fourier transform FFT, the current data collected from the analog-to-digital converter ADC is analyzed, and its main frequency components are identified; the three-phase current signal usually operates at a basic frequency of 50Hz or 60Hz, and the possible high-order harmonics or abnormal frequency components are detected by Fourier transform FFT.

6. The load monitoring method for low voltage area according to claim 1 is characterized in that: In step 5, the RMS value calculation process is as follows: If the detection base frequency is 50Hz, the amplitude of the 50Hz frequency component obtained by Fourier transform FFT is A 50 ; The effective current value corresponding to this frequency is I rms Calculated by the following formula: The current load size is determined based on the RMS value of the current, and the data is transmitted to the remote terminal for monitoring and adjustment.

7. A line leakage detection method, characterized in that: The line leakage detection method is based on a low-voltage area load detector device, which includes an equipment body and an open current transformer for data transmission with the equipment body; The line leakage detection method comprises the following steps: Step I, data preprocessing: The open current transformer installed on the line collects the three-phase current signal of the line in real time. The digital converter ADC in the main body of the equipment samples the three-phase current signal at a sampling rate of 8kHz, and filters out high-frequency noise and interference signals through the low-pass filter in the main body of the equipment to obtain high-precision current data. Step II, load imbalance algorithm: The microcontroller MCU in the device body calculates the average value I of the three-phase current based on the collected three-phase current signal avg and each phase current I A ,I B and I C Compare; if the difference between any phase current and the average value exceeds the set threshold, it is determined to be a three-phase unbalanced state, the algorithm generates corresponding alarm information, and transmits the information to the remote terminal through the remote communication module in the device body; Step III, overload detection: The microcontroller MCU in the device body extracts the amplitude of the fundamental frequency of each phase current based on the Fourier transform FFT algorithm and calculates its effective value I rms ; The calculated I rms With the preset rated current value I 额定 For comparison, if I rms >I 额定 , it is determined that the phase line is in an overload state, an overload alarm message is generated and transmitted to the remote terminal, prompting the operation and maintenance personnel to take load adjustment measures in time; Step IV, leakage detection: The microcontroller MCU in the main body of the device determines the leakage point by monitoring abnormal fluctuations in line current, aggravation of three-phase imbalance and changes in zero-sequence current; if the current drops suddenly in a short period of time, it is judged as a leakage fault; the fault information is sent to the monitoring system through the remote communication module in the main body of the device, and the possible leakage location is prompted.

8. The line leakage detection method according to claim 7, characterized in that: Step II: In the load imbalance algorithm, when there is no single-phase load in the measured line, the mean of the three-phase current and the current I A ,I B and I C Comparison yields: ΔI A =|I A -I avg |,ΔI B =|I B -I avg |,ΔI c =|I c -I avg |; The imbalance is calculated as: Based on the unbalance results, adjustment recommendations are generated to reduce or increase the load on a phase and optimize the load distribution of the system.

9. The line leakage detection method according to claim 7, characterized in that: Step III, in overload detection, if the amplitude of the fundamental frequency 50Hz of each phase current is extracted as A 50 , then the effective value I rms for:

10. The line leakage detection method according to claim 8, characterized in that: Step IV, leakage detection includes zero-sequence current detection and current waveform abnormality detection; Zero sequence current detection: Under normal circumstances, the vector sum of the three-phase current is zero. When leakage occurs, the current leaks in one phase, causing the sum of the three-phase current to be non-zero. By monitoring the vector sum of the three-phase current, that is, I sum Make judgments; I sum =I A +I B +I C If I sum ≠0, then there is leakage in the current; Current sensing in the presence of a single-phase load: The theoretical current I of the neutral line is calculated based on the current of each phase of three phases A, B, and C by using the vector calculation method. N The calculated theoretical current of the neutral line I N Compare it with the neutral current detected by the device, and determine whether there is leakage by observing whether the two are equal; Abnormal current waveform detection: Monitor the changes in the current waveform. The normal current waveform should be a smooth sine wave. When leakage occurs, the waveform may be distorted. Perform Fourier transform (FFT) on the collected current signal, analyze its spectrum, and detect the increase of high-order harmonics or changes in waveform distortion: When the harmonic content exceeds the set threshold, a leakage alarm is generated, indicating that there may be a leakage problem.

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