Method for monitoring grounding current of iron core and supporting high-frequency alternating-current and direct-current component acquisition

Abstract

The invention discloses a method for supporting high-frequency AC / DC component acquisition in core grounding current monitoring, which belongs to the technical field of transformers and comprises the steps of system initialization and communication establishment, continuous sample acquisition, period preprocessing and frequency spectrum and DC component calculation. The technical problem of accurately collecting and analyzing the high-frequency harmonic component and the direct-current component of the grounding current of the iron core at the same time is solved, the dual-channel sampling and digital signal processing technology is combined, on the basis of calculating the total current and the power frequency component, multi-dimensional monitoring and intelligent analysis of the running state of the transformer are achieved, and the fault diagnosis accuracy of the transformer is improved. According to the invention, various industrial scenes can be covered, missing detection of potential faults is avoided, and the fault early warning capability and the operation state judgment precision are improved.

Description

Technical Field

[0001] This invention belongs to the field of transformer technology, and in particular relates to a method for monitoring core grounding current and supporting high-frequency AC / DC component acquisition. Background Technology

[0002] Power transformers are critical equipment in power systems, and their cores must be grounded at a single point during normal operation. When two or more grounding points occur, circulating currents will form inside the transformer under the influence of the leakage magnetic field, leading to localized overheating and increased core losses. In severe cases, this may cause core burnout or even unplanned shutdowns. During operation, the transformer core grounding current should not exceed 100mA; any value exceeding this must be investigated and addressed.

[0003] Traditional monitoring methods rely on manual inspections, using clamp meters to periodically measure current values. This is not only inefficient but also fails to meet the operational requirements of unattended substations. In recent years, core grounding current monitoring has gradually evolved into online and intelligent systems, employing high-precision sensors and signal conditioning circuits to collect power frequency current in real time and issue alarms, thereby improving the safety of equipment operation.

[0004] Although existing online monitoring technologies have compensated for the shortcomings of manual detection to some extent, they still have significant limitations: Most devices only monitor the total current value and power frequency component, lacking analysis of higher harmonics and DC components, resulting in limited technical specifications.

[0005] During the commutation process, rectifier transformers generate characteristic harmonics (such as the 5th, 7th, 11th, 13th, 23rd, and 25th harmonics). These harmonics increase core losses and insulation stress, and relying solely on fundamental wave monitoring poses a risk of missed detections.

[0006] In high-voltage direct current (HVDC) transmission, geomagnetic storms, and rail transit operations, the excitation current may contain a DC component, leading to core bias, vibration, noise, and overheating. Single-frequency analysis methods cannot capture these operational characteristics, affecting the accuracy of equipment condition assessment. Summary of the Invention

[0007] The purpose of this invention is to provide a method for monitoring iron core grounding current that supports the acquisition of high-frequency AC and DC components, thus solving the technical problem of simultaneously achieving accurate acquisition and analysis of the high-frequency harmonic components and DC components of iron core grounding current.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for monitoring iron core grounding current supporting high-frequency AC / DC component acquisition includes the following steps: Step 1: Establish a high-frequency AC / DC component acquisition system, including a control room computer, an online detection device, an AC current transmitter, and a DC current transmitter. After the control room computer and the online detection device are initialized, the online detection device receives real-time sampling data synchronously acquired by the AC current transmitter and the DC current transmitter at a preset fixed sampling rate. Step 2: The online detection device calculates the sample window length for one sampling period according to the power grid cycle; after acquiring a set of sampling data within one sampling period, the online detection device constructs a processing frame from the sampling data according to the sample window length. Step 3: The online detection device preprocesses the processing frames of each sampling cycle to obtain preprocessed frames; the preprocessing includes DC / bias correction and DC channel preprocessing. Step 4: The online detection device performs spectrum and DC component calculations on each preprocessed frame and generates calculation results. The spectrum and DC component calculations specifically include calculating the AC target harmonic amplitude and DC effective value. Step 5: The online detection device displays the calculation results obtained in Step 4 locally. At the same time, it uploads the calculation results to the computer in the control room via the data bus. The computer in the control room generates a waveform based on the calculation results and displays the waveform and calculation results on the screen.

[0009] Preferably, in the high-frequency AC / DC component acquisition system, the AC current transmitter and DC current transmitter are connected and communicate with the online detection device via a 485 bus or Modbus bus, and the online detection device is connected and communicates with the control room computer via a 485 bus.

[0010] Preferably, step 1 includes the following steps: Step 1-1: After the high-frequency AC / DC component acquisition system is powered on, the online detection device initializes, and the control room computer initializes at the same time. The online detection device sends a handshake signal to the control room computer through the 485 bus and establishes a data link. The initialization of the online detection device includes configuring sampling parameters, configuring the device ID, initializing the local display screen, and initializing the 485 bus communication configuration. Sampling parameters include the sampling frequency f s The frame length N and the target harmonic set n = {1, 5, 7, 11, 13, 23, 25} represent different harmonic orders. Step 1-2: The online detection device loads sampling parameters, establishes a frame counter, and initializes the frame counter; Steps 1-3: After initialization, the online detection device begins to receive real-time sampling data synchronously collected by the AC current transmitter and the DC current transmitter.

[0011] Preferably, when performing step 2, the online detection device specifically performs the following steps: Step 2-1: According to the sampling frequency f s Real-time reception of sampled data, including AC data f ac [I ac，k ] and DC data f dc [I dc，k ], where k is the kth sampling point, I ac，k I represents the alternating current data for the kth time. dc，k This represents the DC current data for the kth time. Step 2-2: Write the sampled data into the buffer in order of reception time; Steps 2-3: Calculate the sample window length, i.e., the frame length N. The specific formula is as follows: N=f s / f1; Among them, f s f1 represents the sampling frequency, usually 4kHz; f1 represents the fundamental frequency of the power grid, with a value of 50Hz; N is the total number of sampling points in one sampling period, usually 80, representing the length of one frame; Steps 2-4: When N sampled data are received, encapsulate these N sampled data into a processing frame. i， Where i represents the number of the processed frame; Processing Frame i Includes AC current data set f ac [I ac，0 , ..., I ac，N-1 DC current data set f dc [I dc，0 , ..., I dc，N-1 ] and frame timestamp t i .

[0012] Preferably, when performing step 3, the online detection device specifically performs the following steps: Step 3-1: Retrieve a processing frame. i ; Step 3-2: Process the frame i Preprocessing is performed, specifically as follows: Step 3-2-1: DC / Bias Correction: Calculate the ADC bias calibration value offset. ac From f ac Subtract offset from [k] ac : f ac [k]=f ac [k]−offsetac ; Among them, f ac [k]=f ac [k]−offset ac This indicates that f ac [k]−offset ac The result is reassigned to f ac [k]; Step 3-2-2: DC Channel Preprocessing: The DC channel retains the original f dc [k] can be used for small-amplitude low-pass / moving average filtering to suppress high-frequency noise; Step 3-3: Based on the preprocessed data from Step 3-2, construct the preprocessed AC current dataset f. procac [I ac-p，0 , ..., I ac-p，N-1 The preprocessed data set f of ] and DC current procdc [I dc-p，0 , ..., I dc-p，N-1 ]; ac-p and dc-p represent the preprocessed AC and DC data, respectively; I ac-p，k It indicates f ac [I ac，k The I in ] ac，k The result after preprocessing; I dc-p，k It indicates f dc [I dc，k The I in ] dc，k The result after preprocessing; Steps 3-4: f procac [I ac-p，0 , ..., I ac-p，N-1 ] and f procdc [I dc-p，0 , ..., I dc-p，N-1 Perform local caching.

[0013] Preferably, when performing step 4, the online detection device specifically performs the following steps: Step 4-1: Retrieve the preprocessed frame i That is, f procac [I ac-p，0 , ..., I ac-p，N-1 ] and f procdc [I dc-p，0 , ..., I dc-p，N-1 ]; Step 4-2: The AC channel uses the Discrete Fourier Transform algorithm to find each harmonic. Specifically, based on the target harmonic set n = {1, 5, 7, 11, 13, 23, 25}, the Discrete Fourier response coefficient α is calculated for each target harmonic in the target harmonic set n.n With b n Use the following formula: ; ; Where N represents the total number of sampling points in each frame; k represents the k-th sampling, and n j Let j represent the j-th harmonic in the target harmonic set n; Calculate the number of AC channels n j Sub-target harmonic amplitude, i.e., AC target harmonic amplitude : ; Step 4-3: The DC channel obtains the effective value of the DC component by calculating the mean, i.e., the DC effective value. Specifically, this involves integrating the signal over one period. The harmonic components integral over one period are zero. The specific formula is as follows: ; in Indicates the DC component; The average value over one period, where T represents the period. Represents the direct current over continuous time. Take f procdc [I dc-p，0 , ..., I dc-p，N-1 The data in ], ultimately .

[0014] This invention discloses a method for monitoring core grounding current that supports high-frequency AC and DC component acquisition. It solves the technical problem of simultaneously and accurately acquiring and analyzing the high-frequency harmonic components and DC components of the core grounding current. Combining dual-channel sampling and digital signal processing technology, this invention, in addition to calculating the total current and power frequency components, can also extract the 5th, 7th, 11th, 13th, 23rd, and 25th order characteristic harmonics and DC components, enabling multi-dimensional monitoring and intelligent analysis of transformer operating status. Compared to traditional clamp meter methods, which are limited by the 1kHz frequency band and cannot measure higher harmonics, and existing online devices that only consider power frequency components, this invention can cover various industrial scenarios, avoid missing potential faults, and improve early fault warning capabilities and the accuracy of operating status judgment. Attached Figure Description

[0015] Figure 1 This is the main process algorithm flowchart of the present invention; Figure 2 This is a schematic diagram of the system architecture of the high-frequency AC / DC component acquisition system of the present invention; Figure 3This is a diagram of the DC and {5th, 7th, 11th} harmonic display interface locally displayed by the online detection device of the present invention; Figure 4 This is a diagram of the DC and {13th, 23rd, 25th} harmonic display interface of the online detection device of the present invention. Detailed Implementation

[0016] Depend on Figures 1-4 The method for monitoring iron core grounding current and supporting high-frequency AC / DC component acquisition, as shown, includes the following steps: Step 1: Establish a high-frequency AC / DC component acquisition system, including a control room computer, an online detection device, an AC current transmitter, and a DC current transmitter. After the control room computer and the online detection device are initialized, the online detection device receives real-time sampling data synchronously acquired by the AC current transmitter and the DC current transmitter at a preset fixed sampling rate. In a high-frequency AC / DC component acquisition system, AC current transmitters and DC current transmitters are connected and communicate with the online detection device via a 485 bus or Modbus bus, and the online detection device is connected and communicates with the control room computer via a 485 bus.

[0017] In this embodiment, the AC current transmitter and the DC current transmitter are used to convert the primary current signal into a low-level signal suitable for sampling.

[0018] The online detection device is used in the core acquisition and preprocessing equipment, and is responsible for receiving and transmitting sampling data. In this embodiment, the online detection device is specifically a micro industrial control computer.

[0019] Step 1 includes the following steps: Step 1-1: After the high-frequency AC / DC component acquisition system is powered on, the online detection device initializes, and the control room computer initializes at the same time. The online detection device sends a handshake signal to the control room computer through the 485 bus and establishes a data link. The initialization of the online detection device includes configuring sampling parameters, configuring the device ID, initializing the local display screen, and initializing the 485 bus communication configuration. The sampling parameters include the sampling frequency fs, the frame length N, and the target harmonic set n={1,5,7,11,13,23,25}, where {1,5,7,11,13,23,25} represent different harmonic orders. These parameters determine the accuracy of subsequent spectrum calculations.

[0020] Step 1-2: The online detection device loads sampling parameters, establishes a frame counter, and initializes the frame counter; The frame counter ensures that each sampling period has a unique number to distinguish different sampling frames. Steps 1-3: After initialization, the online detection device begins to receive real-time sampling data synchronously acquired by the AC current transmitter and the DC current transmitter.

[0021] During data acquisition, the online detection device samples simultaneously through both AC and DC channels to ensure timing consistency. The AC channel is used for harmonic analysis, while the DC channel is used for DC component and noise detection.

[0022] Step 2: The online detection device calculates the sample window length for one sampling period according to the power grid cycle; after acquiring a set of sampling data within one sampling period, the online detection device constructs a processing frame from the sampling data according to the sample window length. When performing step 2, the online detection device specifically performs the following steps: Step 2-1: According to the sampling frequency f s Real-time reception of sampled data, including AC data f ac [I ac，k ] and DC data f dc [I dc，k ], where k is the kth sampling point, I ac，k I represents the alternating current data for the kth time. dc，k This represents the DC current data for the kth time. Step 2-2: Write the sampled data into the buffer in order of reception time; write the data into the buffer in chronological order to ensure the continuity of the data stream and prevent it from being out of order during subsequent packaging.

[0023] Steps 2-3: Calculate the sample window length, i.e., the frame length N. The specific formula is as follows: N=f s / f1; Among them, f s f1 represents the fundamental frequency of the power grid, with a value of 50Hz; N is the total number of sampling points in one sampling period, representing the length of one frame. 50Hz is the common fundamental frequency of power grids. The number of sampling points in one cycle = sampling frequency ÷ fundamental frequency. Such a frame length can avoid spectrum leakage.

[0024] Steps 2-4: When N sampled data are received, encapsulate these N sampled data into a processing frame. i， Where i represents the number of the processed frame; Processing Frame i Includes AC current data set f ac [I ac，0 , ..., I ac，N-1 DC current data set f dc [Idc，0 , ..., I dc，N-1 ] and frame timestamp t i .

[0025] In this embodiment, when N points have been collected, they are packaged into a processing frame. i Frame i The content includes [AC data sequence, DC data sequence, timestamp t] i ].

[0026] Step 3: The online detection device preprocesses the processing frames of each sampling cycle to obtain preprocessed frames; the preprocessing includes DC / bias correction and DC channel preprocessing. When performing step 3, the online detection device specifically performs the following steps: Step 3-1: Retrieve a processing frame. i ; Step 3-2: Process the frame i Preprocessing is performed, specifically as follows: Step 3-2-1: DC / Bias Correction: Calculate the ADC bias calibration value offset. ac From f ac Subtract offset from [k] ac : f ac [k]=f ac [k]−offset ac ; Among them, f ac [k]=f ac [k]−offset ac This indicates that f ac [k]−offset ac The result is reassigned to f ac [k].

[0027] offset ac The data is obtained using the no-load calibration method, specifically by sampling data for a period of time when there is no input signal on the AC channel. Ideally, the average value of these data should be 0, but due to bias, the average value is not equal to 0. Recording this average value is the offset. ac .

[0028] ; Where f(k) represents the data collected within a preset time period, and k represents the sampling point, which is generally the offset. ac The default value is the factory setting.

[0029] Step 3-2-2: DC Channel Preprocessing: The DC channel retains the original f dc [k] can be used for small-amplitude low-pass / moving average filtering to suppress high-frequency noise; Step 3-3: Based on the preprocessed data from Step 3-2, construct the preprocessed AC current dataset f. procac [I ac-p，0 , ..., I ac-p，N-1 The preprocessed data set f of ] and DC current procdc [I dc-p，0 , ..., I dc-p，N-1 ]; ac-p and dc-p represent the preprocessed AC and DC data, respectively; I ac-p，k It indicates f ac [I ac，k The I in ] ac，k The result after preprocessing; I dc-p，k It indicates f dc [I dc，k The I in ] dc，k The result after preprocessing; Steps 3-4: f procac [I ac-p，0 , ..., I ac-p，N-1 ] and f procdc [I dc-p，0 , ..., I dc-p，N-1 Perform local caching.

[0030] Step 4: The online detection device performs spectrum and DC component calculations on each preprocessed frame and generates calculation results. The spectrum and DC component calculations specifically include calculating the AC target harmonic amplitude and DC effective value. When performing step 4, the online detection device specifically performs the following steps: Step 4-1: Retrieve the preprocessed frame i That is, f procac [I ac-p，0 , ..., I ac-p，N-1 ] and f procdc [I dc-p，0 , ..., I dc-p，N-1 ]; Step 4-2: The AC channel uses the Discrete Fourier Transform algorithm to find each harmonic. Specifically, based on the target harmonic set n = {1, 5, 7, 11, 13, 23, 25}, the Discrete Fourier response coefficient α is calculated for each target harmonic in the target harmonic set n. n With b n Use the following formula: ; ; Where N represents the total number of sampling points in each frame; k represents the k-th sampling, and n j Let j represent the j-th harmonic in the target harmonic set n; Calculate the number of AC channels n j Sub-target harmonic amplitude, i.e., AC target harmonic amplitude : ; Step 4-3: The DC channel obtains the effective value of the DC component by calculating the mean, i.e., the DC effective value. Specifically, this involves integrating the signal over one period. The harmonic components integral over one period are zero. The specific formula is as follows: ; in Indicates the DC component; The average value over one period, where T represents the period. Represents the direct current over continuous time. Take f procdc [I dc-p，0 , ..., I dc-p，N-1 The data in ], ultimately .

[0031] Step 5: The online detection device displays the calculation results obtained in Step 4 locally. At the same time, it uploads the calculation results to the computer in the control room via the data bus. The computer in the control room generates a waveform based on the calculation results and displays the waveform and calculation results on the screen.

[0032] In this embodiment, the online detection device displays the data locally in real time to ensure on-site visibility. At the same time, the online detection device uploads the data obtained in step 4 to the computer in the control room, and the computer in the control room uses the calculation results to generate trend waveforms and harmonic spectrum diagrams.

[0033] This invention discloses a method for monitoring core grounding current that supports high-frequency AC and DC component acquisition. It solves the technical problem of simultaneously and accurately acquiring and analyzing the high-frequency harmonic components and DC components of the core grounding current. Combining dual-channel sampling and digital signal processing technology, this invention, in addition to calculating the total current and power frequency components, can also extract the 5th, 7th, 11th, 13th, 23rd, and 25th order characteristic harmonics and DC components, enabling multi-dimensional monitoring and intelligent analysis of transformer operating status. Compared to traditional clamp meter methods, which are limited by the 1kHz frequency band and cannot measure higher harmonics, and existing online devices that only consider power frequency components, this invention can cover various industrial scenarios, avoid missing potential faults, and improve early fault warning capabilities and the accuracy of operating status judgment.

Claims

1. A method for monitoring core grounding current supporting high-frequency AC / DC component acquisition, characterized in that: Includes the following steps: Step 1: Establish a high-frequency AC / DC component acquisition system, including a control room computer, an online detection device, an AC current transmitter, and a DC current transmitter. After the control room computer and the online detection device are initialized, the online detection device receives real-time sampling data synchronously acquired by the AC current transmitter and the DC current transmitter at a preset fixed sampling rate. Step 2: The online detection device calculates the sample window length for one sampling period according to the power grid cycle; after acquiring a set of sampling data within one sampling period, the online detection device constructs a processing frame from the sampling data according to the sample window length. Step 3: The online detection device preprocesses the processing frames of each sampling cycle to obtain preprocessed frames; the preprocessing includes DC / bias correction and DC channel preprocessing. Step 4: The online detection device performs spectrum and DC component calculations on each preprocessed frame and generates calculation results. The spectrum and DC component calculations specifically include calculating the AC target harmonic amplitude and DC effective value. Step 5: The online detection device displays the calculation results obtained in Step 4 locally. At the same time, it uploads the calculation results to the computer in the control room via the data bus. The computer in the control room generates a waveform based on the calculation results and displays the waveform on the screen.

2. The method for monitoring iron core grounding current and supporting high-frequency AC / DC component acquisition as described in claim 1, characterized in that: In a high-frequency AC / DC component acquisition system, AC current transmitters and DC current transmitters are connected and communicate with the online detection device via a 485 bus or Modbus bus, and the online detection device is connected and communicates with the control room computer via a 485 bus.

3. The method for monitoring iron core grounding current and supporting high-frequency AC / DC component acquisition as described in claim 1, characterized in that: Step 1 includes the following steps: Step 1-1: After the high-frequency AC / DC component acquisition system is powered on, the online detection device initializes, and the control room computer initializes at the same time. The online detection device sends a handshake signal to the control room computer through the 485 bus and establishes a data link. The initialization of the online detection device includes configuring sampling parameters, configuring the device ID, initializing the local display screen, and initializing the 485 bus communication configuration. Sampling parameters include the sampling frequency f s The frame length N and the target harmonic set n = {1, 5, 7, 11, 13, 23, 25} represent different harmonic orders. Step 1-2: The online detection device loads sampling parameters, establishes a frame counter, and initializes the frame counter; Steps 1-3: After initialization, the online detection device begins to receive real-time sampling data synchronously collected by the AC current transmitter and the DC current transmitter.

4. The method for monitoring iron core grounding current and supporting high-frequency AC / DC component acquisition as described in claim 3, characterized in that: When performing step 2, the online detection device specifically performs the following steps: Step 2-1: According to the sampling frequency f s Real-time reception of sampled data, including AC data f ac [I ac，k ] and DC data f dc [I dc，k ], where k is the kth sampling point, I ac，k I represents the alternating current data for the kth time. dc，k This represents the DC current data for the kth time. Step 2-2: Write the sampled data into the buffer in order of reception time; Steps 2-3: Calculate the sample window length, i.e., the frame length N. The specific formula is as follows: N=f s / f1; Among them, f s f1 represents the fundamental frequency of the power grid, with a value of 50Hz; N is the total number of sampling points in one sampling period, representing the length of one frame. Steps 2-4: When N sampled data are received, encapsulate these N sampled data into a processing frame. i， Where i represents the number of the processed frame; Processing Frame i Includes AC current data set f ac [I ac，0 , ..., I ac，N-1 DC current data set f dc [I dc，0 , ..., I dc，N-1 ] and frame timestamp t i .

5. The method for monitoring iron core grounding current and supporting high-frequency AC / DC component acquisition as described in claim 4, characterized in that: When performing step 3, the online detection device specifically performs the following steps: Step 3-1: Retrieve a processing frame. i ; Step 3-2: Process the frame i Preprocessing is performed, specifically as follows: Step 3-2-1: DC / Bias Correction: Calculate the ADC bias calibration value offset. ac From f ac Subtract offset from [k] ac : f ac [k]=f ac [k]−offset ac ; Among them, f ac [k]=f ac [k]−offset ac This indicates that f ac [k]−offset ac The result is reassigned to f ac [k]; Step 3-2-2: DC Channel Preprocessing: The DC channel retains the original f dc [k] can be used for small-amplitude low-pass / moving average filtering to suppress high-frequency noise; Step 3-3: Based on the preprocessed data from Step 3-2, construct the preprocessed AC current dataset f. procac [I ac-p，0 , ..., I ac-p，N-1 The preprocessed data set f of ] and DC current procdc [I dc-p，0 , ..., I dc-p，N-1 ]; ac-p and dc-p represent the preprocessed AC and DC data, respectively; I ac-p，k It indicates f ac [I ac，k The I in ] ac，k The result after preprocessing; I dc-p，k It indicates f dc [I dc，k The I in ] dc，k The result after preprocessing; Steps 3-4: f procac [I ac-p，0 , ..., I ac-p，N-1 ] and f procdc [I dc-p，0 , ..., I dc-p，N-1 Perform local caching.

6. The method for monitoring iron core grounding current and supporting high-frequency AC / DC component acquisition as described in claim 5, characterized in that: When performing step 4, the online detection device specifically performs the following steps: Step 4-1: Retrieve the preprocessed frame i That is, f procac [I ac-p，0 , ..., I ac-p，N-1 ] and f procdc [I dc-p，0 , ..., I dc-p，N-1 ]; Step 4-2: The AC channel uses the Discrete Fourier Transform algorithm to find each harmonic. Specifically, based on the target harmonic set n = {1, 5, 7, 11, 13, 23, 25}, the Discrete Fourier response coefficient α is calculated for each target harmonic in the target harmonic set n. n With b n Use the following formula: ； ； Where N represents the total number of sampling points in each frame; k represents the k-th sampling, and n j Let j represent the j-th harmonic in the target harmonic set n; Calculate the number of AC channels n j Sub-target harmonic amplitude, i.e., AC target harmonic amplitude : ； Step 4-3: The DC channel obtains the effective value of the DC component by calculating the mean, i.e., the DC effective value. Specifically, this involves integrating the signal over one period. The harmonic components integral over one period are zero. The specific formula is as follows: ； in Indicates the DC component; The average value over one period, where T represents the period. Represents the direct current over continuous time. Take f procdc [I dc-p，0 , ..., I dc-p，N-1 The data in ], ultimately .

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