Method and device for calibrating transformer ac / dc grounding current on-line monitoring equipment

Abstract

The present application relates to the technical field of current calibration, in particular to a transformer AC / DC grounding current online monitoring device calibration method and device, comprising: collecting the grounding current of the grounding loop in the transformer for frequency spectrum analysis; indexing the preset sensor error calibration table to obtain the corresponding amplitude correction coefficient and phase compensation value; generating a cancellation current opposite to the AC component of the grounding current and injecting the cancellation current into the grounding loop; real-time monitoring the residual current in the grounding loop, iteratively correcting the cancellation current in a closed-loop feedback mode until the AC component in the residual current is less than the preset current threshold and the fluctuation degree of the DC component in the residual current meets the preset fluctuation condition, determining that the comprehensive calibration permission condition is met; injecting a standard calibration current into the grounding loop, recording the detection value of the grounding loop by the online monitoring device for analysis to obtain the calibration result of the AC / DC grounding current, thereby improving the calibration accuracy of the AC / DC grounding current online monitoring device.

Description

Technical Field

[0001] This invention relates to the field of current calibration technology, specifically to a calibration method and apparatus for online monitoring equipment of AC / DC grounding current of transformers. Background Technology

[0002] In power system operation and maintenance, transformers are core equipment, and the state of their grounding circuit current directly determines the safe operation of the equipment and the reliability of power supply. Transformer grounding current includes the power frequency fundamental wave, the DC component generated by DC bias, and various high-order harmonics. Abnormalities in these components can easily lead to faults such as core overheating and insulation aging. Therefore, online monitoring equipment for transformer grounding current is widely used in substations to monitor current parameters in real time to support operation and maintenance decisions.

[0003] Existing solutions primarily target the fundamental and lower harmonic frequencies of transformer core grounding currents, employing an open-loop "injection after quiescence" principle for current verification. However, since the verification primarily considers the transformer core grounding current, this solution has certain limitations, mainly as follows: 1. Lack of DC component verification and high-order harmonic verification: Verification is only performed on the fundamental and low-order harmonics of the core grounding current, lacking high-order harmonic verification and failing to consider the verification of the neutral point grounding current, especially the DC component. However, in modern power grids, influenced by stray currents from subways, DC grounding electrodes, or geomagnetic storms, the transformer neutral point grounding current often contains a significant DC bias component and high-frequency harmonics. If the DC component cannot be verified, the online monitoring equipment will have a large monitoring blind spot. 2. The simple open-loop neutral mode has a high error rate and is only suitable for steady-state current verification: It adopts a unidirectional open-loop cancellation method of "measurement-analysis-output" and ignores the inherent ratio difference (amplitude error) and angle difference (phase error) of the sensor and hardware circuit at different frequencies. Dynamic factors such as stray currents in subways affect the transformer grounding current. If it is directly used for neutral point grounding current verification, without considering the original grounding current at that moment, it may cause forced verification during drastic current fluctuations, which obviously cannot guarantee the accuracy and rationality of the verification. In addition, at high frequencies, the slight phase lag of the sensor will drastically reduce the accuracy of the inverse matching between the neutral current and the original grounding current, resulting in a large residual error. The open-loop system cannot detect and correct this error, so the subsequently injected standard verification current is severely interfered with by the background stray current, and the final verification result loses accuracy. Summary of the Invention

[0004] The purpose of this invention is to provide a verification method and apparatus for transformer AC / DC grounding current online monitoring equipment. By using sensor error lookup table compensation and residual current closed-loop dynamic compensation correction, the AC / DC grounding current of the transformer is offset, and a standard test signal is injected to verify the online monitoring equipment, thereby completing the on-site verification of the transformer AC / DC grounding current monitoring equipment and improving the verification accuracy of the transformer grounding current online monitoring equipment.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a verification method for an online monitoring device for AC / DC grounding current of a transformer, comprising: S1, acquiring the grounding current of the grounding circuit in the transformer and performing spectrum analysis on the grounding current to obtain the amplitude and phase characteristics of the fundamental component, harmonic components, and DC component of the grounding current; S2, obtaining the corresponding amplitude correction coefficient and phase compensation value based on a preset sensor error calibration table with the frequency index of the fundamental component and harmonic components; S3, generating a canceling current opposite to the AC component of the grounding current based on the amplitude correction coefficient and the phase compensation value, and injecting the canceling current into the grounding circuit; S4, monitoring the residual current in the grounding circuit in real time, iteratively correcting the canceling current in a closed-loop feedback manner until the AC component in the residual current is less than a preset current threshold, and the fluctuation degree of the DC component in the residual current meets a preset fluctuation condition, and determining that the comprehensive verification permission condition is met; S5, under the condition that the comprehensive verification permission condition is met, injecting a standard verification current into the grounding circuit, recording the detection value of the online monitoring device on the grounding circuit, and analyzing the change in the detection value to obtain the verification result of the AC / DC grounding current.

[0007] The field verification method provided by this invention collects the grounding current of the transformer grounding circuit and performs spectrum analysis to accurately separate the amplitude and phase characteristics corresponding to different frequency components of the grounding current. Based on a preset sensor error calibration table, the amplitude and phase errors at each frequency are obtained. A compensation current, precisely matched to the original grounding current, is generated based on the amplitude correction coefficient and phase compensation value and injected into the grounding circuit to effectively compensate for the ratio and angle defects of the sensor, achieving preliminary compensation of the grounding background current. Simultaneously, the residual current inside the grounding circuit is continuously monitored in real time. The output parameters of the compensation current are dynamically optimized using a closed-loop feedback iterative control mode, gradually reducing residual errors. This effectively overcomes the shortcomings of insufficient compensation accuracy in traditional open-loop neutralization methods, ensuring that the AC component of the residual current is stably controlled within a preset threshold range, while also ensuring that the fluctuation of the DC component of the residual current meets preset fluctuation conditions. That is, after verifying and determining the permission of both the AC and DC components, the comprehensive verification permission conditions are met, reducing the impact of background stray current, DC bias, and harmonic interference on the verification work. Based on this low residual and clean operating condition, a standard calibration current is injected into the grounding circuit, and comparative analysis is conducted using the actual readings of the online monitoring equipment under test to complete a comprehensive on-site calibration operation. The overall solution relies on a core design that combines spectrum analysis and decomposition, lookup error pre-compensation, and closed-loop dynamic anti-phase cancellation, thereby improving the measurement accuracy, environmental adaptability, and operational stability of transformer grounding current calibration.

[0008] Optionally, the step of real-time monitoring of the residual current in the grounding loop and iteratively correcting the offset current in a closed-loop feedback manner until the AC component in the residual current is less than a preset current threshold includes: S41, real-time monitoring of the residual current in the grounding loop; if the AC component in the monitored residual current is greater than or equal to the preset current threshold, then extracting the waveform characteristics of the residual current; S42, generating an inverse fine-tuning compensation amount based on the waveform characteristics and superimposing it on the offset current, and cyclically executing step S41 with a microsecond period until the residual current is less than the preset current threshold.

[0009] By continuously acquiring the residual current of the grounding loop in real time, and promptly extracting the waveform characteristics of the residual current when it fails to meet accuracy requirements, a matching inverse fine-tuning compensation amount is generated based on the waveform characteristics and superimposed on the original offset current. Simultaneously, with microsecond-level short-cycle cyclic monitoring and iterative control, it can quickly capture weak current fluctuations and phase shifts in the grounding loop. Compared to a fixed-parameter open-loop empty mode, it can dynamically and finely correct the offset current, continuously reducing residual current interference and creating a low-interference, high-purity calibration condition for the subsequent injection of standard calibration current.

[0010] Optionally, the sensor error calibration table can be set up in the following way: S21, performing simulation analysis and experimental testing on the sensor that collects the grounding current and the residual current on a laboratory calibration platform to obtain the amplitude error and phase error of the sensor at each frequency component; S22, constructing the sensor error calibration table based on the amplitude error and the phase error.

[0011] By conducting simulation analysis and experimental testing on sensors that collect grounding current and residual current on a laboratory calibration platform, the inherent amplitude and phase errors of the sensors under different frequency components of DC, fundamental, and various harmonics can be accurately obtained. Based on the obtained error data, a sensor error calibration table is constructed. Completing error calibration and table construction under full-frequency operating conditions in advance in a laboratory environment allows for the pre-quantification of the sensor's inherent ratio and phase error characteristics, avoiding the impact of on-site operating condition interference on error calibration. This provides accurate data support for subsequent rapid table lookup and parameter matching correction based on the amplitude and phase characteristics of each frequency component of the grounding current.

[0012] Optionally, the step of acquiring the grounding current of the grounding circuit in the transformer and performing spectrum analysis on the grounding current to obtain the DC and AC components of the grounding current includes: S11, acquiring the grounding current at the neutral point grounding flat iron position or the core grounding flat iron position using AC / DC sensors; S12, performing fast Fourier transform spectrum analysis on the grounding current to obtain the amplitude and phase characteristics of the DC and AC components, wherein the AC component includes the fundamental component and each harmonic component, and the frequency range of the spectrum analysis covers DC to 1000Hz.

[0013] Employing AC / DC sensors allows for the simultaneous acquisition and detection of DC signals and AC power frequency and harmonic signals. It flexibly selects the transformer neutral point or core location for grounding loop current acquisition, overcoming the limitations of traditional AC verification methods such as insufficient bandwidth and lack of DC verification capability. This expands the verification scenarios from single AC core grounding currents to neutral point grounding currents containing DC components and converter transformer grounding currents with abundant high-order harmonics. Through Fast Fourier Transform (FFT) spectral analysis, complex aliased grounding currents can be accurately decomposed and separated into DC, fundamental, and harmonic components, achieving signal coverage across a wide frequency range of DC to 1000Hz and restoring the amplitude and phase characteristics of the multi-frequency components of the grounding current. This provides comprehensive, detailed, and accurate raw data for subsequent lookup error calibration, accurate generation of offset currents, and closed-loop iterative correction.

[0014] Optionally, the step of injecting a standard verification current into the grounding loop when the comprehensive verification permission conditions are met includes: S51, when the comprehensive verification permission conditions are met, obtaining verification requirements, configuring a DC verification component, a fundamental frequency verification component, or a harmonic verification component based on the verification requirements to obtain a standard verification current, and injecting the standard verification current into the grounding loop; the verification requirements include DC verification requirements and AC verification requirements; the standard verification current includes a standard DC verification current and a standard AC verification current.

[0015] Optionally, the degree of fluctuation of the DC component in the residual current is determined to meet the preset fluctuation condition by the following method: S43, if the DC component in the residual current is maintained within the preset standard deviation range within a preset time period, it is considered to meet the preset fluctuation condition; otherwise, it is considered not to meet the preset fluctuation condition.

[0016] The present invention also provides a verification device for an online monitoring device for AC / DC grounding current of a transformer. The device applies the above-mentioned verification method for an online monitoring device for AC / DC grounding current of a transformer to perform on-site verification of the online monitoring device. The device includes an acquisition module, a preprocessing module, a verification module, and an interaction module. The acquisition module is used to acquire the grounding current of the grounding circuit in the transformer and monitor the residual current in the grounding circuit in real time. The preprocessing module is used to perform spectrum analysis on the grounding current acquired by the acquisition module, generate a canceling current that is opposite to the AC component of the grounding current, perform sensor error lookup table compensation on the canceling current, iteratively correct the canceling current in a closed-loop feedback manner, and inject the iteratively corrected canceling current into the grounding circuit. The interaction module is used to acquire the verification requirements and send the verification requirements to the verification module when the comprehensive verification permission conditions are met, receive and display the data waveforms of the acquisition module, the preprocessing module and the verification module, and analyze and output the field verification results. The verification module is used to determine whether the comprehensive verification permission conditions are met, generate a standard verification current based on the verification requirements acquired by the interaction module, and generate and output a standard DC verification current and a standard AC verification current to the grounding circuit.

[0017] The field verification device provided by this invention, through the coordinated operation of its various modules, precisely adapts to the aforementioned verification method, solving the technical problem of inaccurate verification results caused by large residual errors in existing devices, and improving the accuracy, reliability, and adaptability of field verification. The acquisition module is responsible for accurately acquiring the grounding current and monitoring the residual current in real time, providing accurate and complete raw data for subsequent processing and avoiding the amplification of subsequent errors due to inaccurate acquisition. The preprocessing module performs spectral analysis on the grounding current, generates an anti-phase cancelling current for the AC component, compensates for the static error of the AC component through a lookup table of sensor errors, and iteratively corrects the cancelling current through closed-loop dynamic compensation of the residual current. It captures the cancelling deviation caused by sensor phase lag in the high-frequency band in real time, dynamically fine-tunes the cancelling current parameters, effectively compensates for the dynamic error of the AC component, significantly improves the anti-matching accuracy between the cancelling current and the original grounding current, significantly reduces the residual current, and avoids the residual current interfering with the injection and comparison of the standard AC verification current. The interactive module acquires and sends verification requests to the verification module when the grounding loop meets the verification permission requirements, receives and displays data waveforms, analyzes and outputs on-site verification results, providing excellent human-machine interaction. The verification module determines whether verification is permitted and generates a standard verification current for the grounding loop based on the verification requirements. Each module has a clear division of labor and works in concert, forming a complete closed loop from data acquisition, preprocessing, AC / DC permission judgment and verification to data display and result output. This effectively solves the problems of narrow verification bandwidth and insufficient verification accuracy. It also adapts to the complex operating conditions of transformer cores and neutral point grounding loops, offering convenient operation and rapid response. It can scientifically, stably, and accurately complete on-site verification of online monitoring equipment, providing reliable equipment verification support for power system transformer operation and maintenance.

[0018] Optionally, the preprocessing module includes a Fast Fourier Transform (FFT) analysis unit, a sensor error lookup table compensation unit, and a residual current closed-loop dynamic compensation unit. The FFT analysis unit is used to perform Fast Fourier Transform spectrum analysis on the grounding current acquired by the acquisition module. The sensor error lookup table compensation unit is used to store the sensor error calibration table and index the amplitude correction coefficient and phase compensation value corresponding to the grounding current. The residual current closed-loop dynamic compensation unit is used to generate a canceling current that is in opposite phase to the AC component of the grounding current, and iteratively corrects the canceling current in a closed-loop feedback manner. The iteratively corrected canceling current is then compensated again by the sensor error lookup table compensation unit and injected into the grounding loop.

[0019] Optionally, the interaction module includes a display unit, a verification requirement setting unit, and a data verification analysis unit; the display unit is used to display the current waveform and spectrum detected by the acquisition module in real time; the verification requirement setting unit is used to set verification requirements based on human-computer interaction, and configure DC verification components or AC verification components based on the verification requirements; the data verification analysis unit is used to analyze the readings of the online monitoring device with the AC verification results and DC verification results to obtain the on-site verification results and output them in the form of a report.

[0020] Optionally, the acquisition module includes a tracking sensor, a feedback sensor, and a verification sensor. The tracking sensor is used to acquire the grounding current of the grounding circuit in the transformer. The feedback sensor is used to monitor the residual current in the grounding circuit in real time. The verification sensor is used to acquire the actual verification current of the grounding circuit after injecting a standard verification current.

[0021] The beneficial effects of this invention are: 1. This invention collects grounding current at the transformer neutral point or core, performs FFT spectrum analysis in the DC to 1000Hz frequency band, and achieves precise amplitude and phase compensation by combining it with a sensor error calibration table. Then, it uses microsecond-level closed-loop iterative correction of the anti-phase canceling current to quickly suppress the residual current in the grounding loop to within a threshold. Subsequently, a multi-component synthesized standard verification current is injected to complete the on-site verification. This significantly improves the real-time performance, accuracy, and automation of on-site verification of grounding current monitoring equipment, adapting to the on-site verification needs under complex harmonic conditions. 2. The addition of DC verification broadens the verification bandwidth and applicable scenarios. This invention overcomes the limitation of only targeting the fundamental and low-order harmonics of core grounding current by employing an incremental method for on-site verification of the DC component. By using high-precision AC / DC sensors and performing wideband FFT spectrum analysis from DC to 1000Hz, this invention expands the verification scenarios from being limited to core grounding current to neutral point grounding current containing DC bias components, as well as converter transformer grounding scenarios containing abundant high-frequency harmonics, achieving comprehensive AC / DC grounding current verification. 3. This invention improves the verification accuracy and dynamic anti-interference capability of the AC component. This invention employs a method of first canceling and then verifying the AC component of the transformer grounding current. By introducing a sensor error lookup table compensation mechanism, and matching the amplitude correction coefficient and phase compensation value based on the spectrum analysis results, it effectively compensates for the inherent static errors of the sensor, such as ratio difference and angle difference. Simultaneously, a residual current closed-loop dynamic compensation mechanism is introduced, which cyclically monitors and iteratively corrects the cancellation current with a microsecond-level period, overcoming the shortcomings of insufficient compensation accuracy in traditional open-loop verification methods and continuously suppressing the residual current within a preset threshold. 4. The present invention adopts an AC-DC integrated calibration permission mechanism to ensure the rationality and stability of the calibration working condition. Only when the residual closed-loop dynamic compensation suppresses the interference of the AC component and stabilizes it within an extremely low threshold, and the DC component remains stable for a certain period of time (within a certain standard deviation range), the injection of the standard calibration current is permitted. This effectively avoids the calibration distortion caused by forced calibration when there is large dynamic interference or severe current fluctuation, and creates a good calibration working condition for the injection of the standard calibration current; 5. The device modules cooperate and link with each other, realizing full-process closed-loop control and automation. The on-site calibration device matched with the present invention accurately adapts to the above calibration logic through the cooperative cooperation of the acquisition module, preprocessing module, interaction module and calibration module. Starting from complete AC-DC broadband acquisition, double error compensation and cancellation, calibration permission judgment, and then synthesizing multi-component standard calibration current for injection according to requirements for calibration and outputting a standard report, the device forms an automatic closed loop, which improves the convenience, real-time performance, accuracy and operational stability of on-site calibration of transformer grounding current monitoring equipment. Description of Drawings

[0022] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments made with reference to the following drawings. The drawings are only for the purpose of illustrating preferred embodiments and are not to be considered as limitations on the present invention. Also, like reference numerals denote like parts throughout the drawings.

[0023] Figure 1 is a flow chart of a calibration method for a transformer AC-DC grounding current on-line monitoring device in the present invention; Figure 2 is a structural diagram of a calibration device for a transformer AC-DC grounding current on-line monitoring device in the present invention. Detailed Description of the Embodiments

[0024] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only the preferred embodiments of the present invention, and are only used to explain the present invention, not to limit the protection scope of the present invention. All other embodiments obtained by those skilled in the art without creative work shall fall within the protection scope of the present invention.

[0025] As an embodiment, as Figure 1 shown, the present invention provides a calibration method for a transformer AC-DC grounding current on-line monitoring device, comprising:

[0026] S1. Collect the grounding current of the grounding circuit in the transformer, and perform spectrum analysis on the grounding current to obtain the amplitude and phase characteristics of the fundamental component, harmonic components and DC component of the grounding current.

[0027] S2. Based on the frequency index of the fundamental component and each harmonic component, a preset sensor error calibration table is used to obtain the corresponding amplitude correction coefficient and phase compensation value.

[0028] S3. Generate a canceling current that is opposite in phase to the AC component of the grounding current based on the amplitude correction coefficient and the phase compensation value, and inject the canceling current into the grounding circuit.

[0029] S4. Monitor the residual current in the grounding loop in real time, and iteratively correct the offset current in a closed-loop feedback manner until the AC component in the residual current is less than the preset current threshold, and the fluctuation of the DC component in the residual current meets the preset fluctuation condition, and determine that the comprehensive verification permission condition is met.

[0030] S5. Under the condition that the comprehensive verification permission conditions are met, inject a standard verification current into the grounding circuit, record the detection value of the grounding circuit by the online monitoring device, and analyze the change in the detection value to obtain the verification result of the AC / DC grounding current.

[0031] It should be noted that a grounding loop is a conductive path formed between the transformer core or neutral point and the earth. Spectrum analysis is the process of decomposing a mixed time-domain current signal into different frequency components, typically implemented using FFT. Frequency components are the various frequency signals that constitute the grounding current, including DC components, fundamental components, and harmonic components. Amplitude characteristics represent the magnitude (RMS value) of the current corresponding to each frequency component. Phase characteristics represent the waveform phase angle corresponding to each frequency component. The sensor error calibration table is pre-calibrated in the laboratory and records the amplitude and phase errors of the sensor at different frequencies. The amplitude correction coefficient is used to correct the current amplitude error. The phase compensation value is used to correct the angle value of the current phase lag. The canceling current is the current that is opposite in phase to and cancels the AC component of the original grounding current, used to equivalently eliminate the background current in the field. The residual current is the remaining current in the grounding loop that is not completely canceled after the original grounding current is injected with the canceling current. The residual current closed-loop dynamic compensation mechanism means that the canceling current is continuously fine-tuned based on the real-time monitored residual, so that the residual current is gradually reduced to below the threshold. The preset current threshold is the upper limit of the current used to determine whether the cancellation operation is complete, typically in the microamp to milliamp range. Meeting the comprehensive verification permitting conditions means simultaneously meeting the following two conditions: first, the AC component of the residual current is less than the preset current threshold; second, the fluctuation of the DC component of the residual current meets the preset fluctuation condition. The amplitude, phase, and frequency information of the standard verification current (including standard AC verification current and standard DC verification current) are known, and it is a standard signal used to verify the accuracy of the online monitoring equipment. The online monitoring equipment reading is the measured current value displayed in real time by the monitoring equipment being verified. The on-site verification result is the pass / fail verification conclusion obtained by comprehensively analyzing the difference between the indicated value and the standard value, according to the respective scheme procedures for AC and DC verification.

[0032] Understandably, this invention addresses the need for on-site verification of the AC component of transformer grounding current by proposing an on-site verification method based on a first-cancellation-then-verification scheme, incorporating a sensor error lookup table compensation mechanism and a residual current closed-loop dynamic compensation mechanism. First, a high-precision AC / DC sensor (which can be a tracking sensor) is used to collect the measured value of the on-site grounding current on the transformer core / neutral grounding flat iron (wire), i.e., the original grounding current. Second, hardware and architecture with low latency, such as a field-programmable gate array (FPGA), are selected to fundamentally reduce the phase error between the original grounding current and the output cancellation current. Based on this, FFT spectrum analysis is performed, and a sensor error calibration table is introduced to compensate for the ratio and angle differences of each harmonic, generating a high-precision cancellation current to cancel the original grounding current. Third, another high-precision AC / DC sensor (which can be a feedback sensor) monitors the residual current after cancellation, and a residual current closed-loop dynamic compensation mechanism is introduced to correct the output cancellation current. Finally, after obtaining comprehensive verification permission, a standard AC verification current is injected as required to accurately verify the AC component of the online monitoring equipment and output a report.

[0033] Understandably, this invention addresses the need for on-site verification of the DC component of transformer grounding current by proposing an incremental method for on-site verification. First, a high-precision AC / DC sensor (which can be a verification sensor) is used to obtain the DC component of the grounding current. Second, a comprehensive verification permission mechanism determines whether DC verification is permitted based on whether the DC component of the on-site grounding current has remained stable for a certain period. Finally, after obtaining permission from the verification mechanism, a standard DC verification current is injected into the grounding circuit as needed. The change in the reading of the online monitoring equipment is compared with the injected standard DC verification current to obtain the verification result of the DC component of the grounding current, and a report is output.

[0034] The principles and mechanisms for performing the above operations and achieving the above effects include: the principle of first canceling and then verifying to realize the basic verification, and the principle of sensor error lookup table compensation and residual current closed-loop dynamic compensation to improve verification accuracy, as follows:

[0035] The principle of cancellation before verification can be as follows: when the current sensor is measuring the original current signal, if a current signal that is opposite in phase to the original current signal is passed through another wire, the magnetic field generated by it will be opposite to the original current signal, and the value sensed by the sensor will be zero. Therefore, the value measured by the sensor can be set to zero in this way, providing a good background environment for subsequent standard current injection for verification.

[0036] The principle of sensor error lookup table compensation is that when sensors and power amplifier circuits operate, especially at high frequencies, there may be inherent phase lag, which cannot be completely canceled if directly output. To address this, this invention proposes a sensor error lookup table compensation method. First, the measurement performance of the sensor at various frequencies is simulated and experimentally tested to obtain the amplitude and phase errors at each frequency, forming a sensor error calibration table, which is then stored. When generating the cancellation current, corresponding phase compensation values ​​and amplitude correction coefficients are pre-applied to each frequency component by looking up the table, thus compensating for the sensor's ratio and angle differences, improving cancellation accuracy, and achieving high-precision calibration. As the sensor's usage time changes, the sensor can be recalibrated, and the sensor error calibration table can be updated.

[0037] The principle of residual current closed-loop dynamic compensation is that, due to uncontrollable factors such as hardware delay, changes in the field environment, and hysteresis effects, there may still be small or even considerable residuals after initial compensation. Therefore, a closed-loop dynamic compensation method for residuals is introduced. A high-precision sensor monitors the residual after compensation, and a threshold is set. If the effective value of the residual is greater than this threshold, the original compensation current is dynamically adjusted through negative feedback until the effective value of the residual is less than the threshold, effectively improving the compensation accuracy and achieving high-precision verification.

[0038] The comprehensive verification permission mechanism assesses the residual current situation before injecting the standard verification current to determine if verification is feasible. Since field AC interference is dynamically changing, even after cancellation and correction through residual current closed-loop dynamic compensation, the cancellation state may not be stable or the residual current may still be large. Injecting the standard AC verification current at this time will lead to distorted verification results due to the instability of the verification benchmark. Therefore, this mechanism continuously assesses whether the residual current closed-loop dynamic compensation mechanism effectively suppresses the residual current, requiring it to remain stable within a very low preset threshold for a certain time window. Only when this condition is met does the system determine that the field AC interference has been completely canceled and is in a steady state, allowing the injection of the standard AC verification current; otherwise, the field AC interference is deemed still significant, and forced verification is not permitted. This ensures the scientific rigor and accuracy of AC verification.

[0039] Meanwhile, the comprehensive verification and approval mechanism also includes the following: Since the incremental method relies on the stability of the DC component of the grounding current before and after injection, if the on-site DC current (such as that affected by stray currents from the subway) is in a period of sharp fluctuation, the calculated change in the indicated value will be mixed with the fluctuation error of the background itself, leading to verification failure. Therefore, this mechanism calculates the fluctuation of the DC component of the on-site grounding current in real time within a certain sliding time window. Only when the DC component remains stable for a certain period of time (i.e., its fluctuation amplitude remains within a certain standard deviation range) is the on-site grounding current DC component deemed to meet the verification conditions, and the injection of the standard DC verification current is permitted. If the fluctuation is too large, the verification conditions are deemed not met.

[0040] The principle of the incremental DC verification method is based on the physical characteristic that DC components cannot be precisely canceled out in real time using inverted waveforms like AC components. Verification is performed based on the change in the DC component of the grounding current before and after the injection of a standard DC verification current. Specifically, the reading of the grounding current DC component before the injection of the standard DC verification current from the online monitoring equipment is first read and recorded as the initial DC value. Then, a standard DC verification current with precise amplitude is injected into the grounding loop. The reading of the grounding current DC component from the online monitoring equipment is read again as the current DC value. Finally, the difference between the current DC value and the initial DC value is calculated to obtain the change in reading. This change in reading is then compared with the actual injected standard DC verification current to determine the on-site verification error of the DC component by the monitoring equipment.

[0041] This invention collects the grounding current in the grounding loop of a transformer and performs spectral analysis. Based on the analysis results, a sensor error calibration table is indexed to obtain the amplitude correction coefficient and phase compensation value, generating an inverse canceling current to achieve static compensation of the grounding current. By real-time monitoring of the residual current in the grounding loop, the canceling current is corrected in a closed-loop feedback manner to achieve dynamic compensation of the grounding current. When the AC component in the residual current is less than a preset current threshold, and the fluctuation of the DC component in the residual current meets the preset fluctuation conditions, the comprehensive verification permission conditions are met. A standard verification current is injected to perform verification of the wide-bandwidth, high-precision transformer AC / DC grounding current online monitoring equipment, improving the verification accuracy of the AC / DC grounding current online monitoring equipment.

[0042] As one implementation method, S1 includes:

[0043] S11. Use AC / DC sensors to collect data at the location of the neutral point grounding flat iron or the location of the core grounding flat iron of the transformer to obtain the grounding current. The connection point where the three tails of the transformer A, B, and C phases are connected together is the neutral point. The neutral point is usually grounded, and the current flowing through the neutral point is the neutral point grounding current. The neutral point grounding current will have a DC component (DC bias magnetism, stray current from the subway, and the influence of the DC grounding electrode).

[0044] S12. Perform fast Fourier transform spectrum analysis on the grounding current to obtain the amplitude and phase characteristics of the DC component, fundamental component, and each harmonic component, with a frequency coverage range of DC to 1000Hz.

[0045] As one implementation method, the sensor error calibration table is set up in the following manner, S2 including:

[0046] S21. On a laboratory calibration platform, the sensor that collects the grounding current and the residual current is simulated and tested to obtain the amplitude error and phase error of the sensor at each frequency component.

[0047] S22. Based on the amplitude error and the phase error, a sensor error calibration table is constructed, as shown in Table 1: Table 1. Schematic diagram of sensor error calibration table (data is for illustrative purposes only and is not fixed; it can be changed based on different sensors).

[0048] As one implementation, S4 includes:

[0049] S41. Monitor the residual current in the grounding loop in real time. If the AC component of the monitored residual current is greater than or equal to a preset current threshold, extract the waveform characteristics of the residual current.

[0050] S42. Based on the waveform characteristics, generate an inverse fine-tuning compensation amount and add it to the offset current. Execute step S41 repeatedly with a microsecond period until the residual current is less than a preset current threshold.

[0051] As one implementation, S5 includes: S51, under the condition of satisfying the comprehensive verification permission conditions, obtaining verification requirements, configuring DC verification components, fundamental frequency verification components, or harmonic verification components based on the verification requirements to obtain a standard verification current, and injecting the standard verification current into the grounding loop; the verification requirements include DC verification requirements and AC verification requirements; the standard verification current includes a standard DC verification current and a standard AC verification current. Satisfying the comprehensive verification permission conditions means simultaneously satisfying the following two conditions: condition one is that the AC component in the residual current is less than a preset current threshold, and condition two is that the fluctuation degree of the DC component in the residual current satisfies a preset fluctuation condition.

[0052] As one implementation method, the workflow for on-site verification using the method of the present invention is as follows: S01, system initialization and self-test, start the verification device, automatically demagnetize and zero each current sensor to ensure that static zero drift meets the requirements.

[0053] S02. Measure and analyze the original grounding current, and use the tracking sensor to measure the on-site grounding current. The original grounding current is obtained. Perform FFT analysis to extract characteristic parameters such as amplitude and phase of DC component and each harmonic (up to 20th order).

[0054] S03. For AC component calibration, perform sensor error lookup table compensation and preliminary cancellation. Based on the analyzed frequency points, index the sensor error calibration table to obtain the corresponding phase compensation value and amplitude correction coefficient, and then synthesize and output the cancellation current. Specifically, the original grounding current was detected to contain a 50Hz component with an effective value of 50mA and a 600Hz component with an effective value of 20mA. The sensor amplitude correction coefficient at 50Hz was obtained from Table 1. Phase compensation value Sensor amplitude correction factor at 600Hz Phase compensation value The automatically generated corrected inverted waveform is as follows: the 50Hz component is inverted and outputs 50mA × 0.9995 = 49.975mA to compensate for the ratio difference, and the phase is led. To compensate for the angular difference; the 600Hz component will output 20mA × 1.0027 = 20.054mA in reverse phase, and the phase will be ahead. .

[0055] S04. For AC component verification, residual current closed-loop dynamic compensation is performed. The feedback sensor monitors the residual current after cancellation in real time. If the residual current exceeds the set threshold (which can be 0.2mA), the waveform characteristics of the residual current are extracted, and an inverse fine-tuning compensation amount is generated and superimposed on the original cancellation current. This process is repeated in microseconds until the loop residual current is less than the set threshold.

[0056] S05. For AC component verification, an AC verification permission mechanism is established. Specifically, the allowable threshold for AC residual current is set to 0.2mA, and the settling time window is set to 5 seconds. After the residual current closed-loop dynamic compensation mechanism starts working, if the residual current is not kept below 0.2mA for a certain period of time, such as fluctuating between 0.15mA and 0.25mA, the AC verification permission mechanism determines that steady state has not been reached. At this time, the system is in a waiting state and standard AC verification current is not allowed to be injected. If the residual current is kept within 0.2mA for a certain period of time, such as between 0.05mA and 0.15mA, and this state is maintained for 5 seconds, the AC verification permission mechanism determines that steady state has been reached.

[0057] S06. For DC component verification, a DC verification permission mechanism is used for judgment. Specifically, the judgment condition for DC stability is set as follows: within 5 consecutive minutes, the fluctuation range of the DC component of the field grounding current does not exceed 0.2A (i.e., it remains within a small standard deviation range). If, during a certain verification, due to the influence of stray current, the DC current at the transformer neutral point is monitored to fluctuate drastically between 5A and 12A, the DC verification permission mechanism determines that the fluctuation of the field DC current is too large and DC verification is not allowed; however, in another test, the stray current tends to stabilize, and the system monitors that the fluctuation range of the DC current within 5 consecutive minutes is only 2.45A to 2.52A (fluctuation range 0.07A, less than the set threshold of 0.2A). In this case, the DC verification permission mechanism determines that the environment has met the stability condition and allows the injection of standard DC verification current for incremental DC component verification. When both the AC verification permission mechanism and the AC verification permission mechanism are met simultaneously, the comprehensive verification permission condition is met, and the injection of standard verification current can be performed.

[0058] S07. For AC component verification, inject and verify the grounding circuit with standard AC verification current. Inject the preset standard AC verification current or the user-defined standard AC verification current into the grounding circuit, read the AC component reading of the online monitoring equipment being calibrated, compare it with the set value of the selected standard source, calculate the error, complete the AC verification and generate a report.

[0059] S08. For DC verification, standard DC verification current injection and incremental verification are performed on the grounding circuit as needed. Specifically, if permitted by the DC verification authorization mechanism, at the start of verification, the system records the DC component reading of the grounding current of the online monitoring equipment before the injection of the standard DC verification current, i.e., the initial DC value is 1.2A. Subsequently, a preset or user-defined standard DC verification current, such as 5.0A, is precisely injected into the grounding circuit as needed. After the injection stabilizes, the system records the DC component reading of the grounding current of the online monitoring equipment at this time, i.e., the current DC reading is 6.1A. The system automatically calculates the change in reading as 6.1A - 1.2A = 4.9A. Comparing this change in reading of 4.9A with the actual injected standard value of 5.0A, the DC measurement error of the monitoring equipment is found to be -0.1A, thus completing the DC verification.

[0060] S09. Combining the AC and DC verification results obtained from S07 and S08, complete the AC and DC integrated verification of the transformer grounding current monitoring equipment.

[0061] The present invention also provides a verification device for an online monitoring device for AC / DC grounding current of a transformer. The device applies the above-mentioned on-site verification method for an online monitoring device for grounding current of a transformer to perform on-site verification of the online monitoring device. The device includes an acquisition module, a preprocessing module, a verification module, and an interaction module.

[0062] The acquisition module is used to acquire the grounding current of the grounding circuit in the transformer and monitor the residual current in the grounding circuit in real time. The preprocessing module is used to perform spectrum analysis on the grounding current acquired by the acquisition module, generate a canceling current that is opposite to the AC component of the grounding current, perform sensor error lookup table compensation on the canceling current, iteratively correct the canceling current in a closed-loop feedback manner, and inject the iteratively corrected canceling current into the grounding circuit. The interaction module is used to acquire the verification requirements and send the verification requirements to the verification module when the comprehensive verification permission conditions are met, receive and display the data waveforms of the acquisition module, the preprocessing module and the verification module, and analyze and output the field verification results. The verification module is used to determine whether the comprehensive verification permission conditions are met, generate a standard verification current based on the verification requirements acquired by the interaction module, and generate and output a standard DC verification current and a standard AC verification current to the grounding circuit.

[0063] The preprocessing module includes an FFT analysis unit, a sensor error lookup table compensation unit, and a residual current closed-loop dynamic compensation unit. The FFT analysis unit is used to perform fast Fourier transform spectrum analysis on the grounding current acquired by the acquisition module. The sensor error lookup table compensation unit is used to store the sensor error calibration table and index the amplitude correction coefficient and phase compensation value corresponding to the grounding current. The residual current closed-loop dynamic compensation unit is used to generate a canceling current that is opposite in phase to the AC component of the grounding current, and iteratively corrects the canceling current in a closed-loop feedback manner. The iteratively corrected canceling current is then compensated again by the sensor error lookup table compensation unit and injected into the grounding loop.

[0064] The interactive module includes a display unit, a verification requirement setting unit, and a data verification analysis unit. The display unit is used to display the current waveform and spectrum detected by the acquisition module in real time. The verification requirement setting unit is used to set verification requirements based on human-computer interaction and configure DC verification components or AC verification components based on the verification requirements. The data verification analysis unit is used to analyze the readings of the online monitoring equipment with the AC verification results and DC verification results to obtain the on-site verification results and output them in the form of a report.

[0065] The acquisition module includes at least one of a tracking sensor, a feedback sensor, and a verification sensor. The tracking sensor is used to acquire the grounding current of the grounding circuit in the transformer. The feedback sensor is used to monitor the residual current in the grounding circuit in real time. The verification sensor is used to acquire the actual verification current of the grounding circuit after injecting a standard verification current.

[0066] Reference Figure 2As one implementation method, the architecture of the field verification device adapted to the method proposed in this invention includes the following four main modules, each of which is implemented using low-latency devices and circuit configurations:

[0067] Acquisition Module (also known as High-Precision Acquisition Module): All sensors in this module are high-precision AC / DC current sensors, and it is important to ensure that the sensor design meets the dimensional requirements of the transformer core / neutral grounding flat iron (wire). The tracking sensor (red) is used to acquire the transformer's on-site grounding current in real time. To obtain its measured value of the original ground current. The feedback sensor (yellow) is used to measure the injected offset current. Residual current after , Verify the sensor (purple) by injecting a standard calibration current. The current is used to provide a basis for verifying the authorization unit and inject a standard verification current. It is then used to measure the permissible response current. , .

[0068] The preprocessing module includes an FFT analysis unit, a sensor error lookup table compensation unit, and a residual current closed-loop dynamic compensation unit. The FFT analysis unit processes the acquired raw grounding current... The error is decomposed into DC components and harmonic components, including amplitude and phase information. The sensor error lookup table compensation unit stores a "sensor error calibration table," providing the ratio and angle difference data of the sensor at different frequency points, as illustrated in Table 1. The residual current closed-loop dynamic compensation unit compensates based on the lookup table results and then synthesizes the offset current. And based on the residual current Perform closed-loop adjustment to control the residual within a preset threshold, ideally approaching zero. Adjust the output offset current. Directly inject into the grounding loop to offset the background current at the site, creating a low-interference working condition for AC calibration.

[0069] The verification module includes a verification authorization unit and a standard verification current modulation unit. The verification authorization unit implements comprehensive verification authorization conditions to determine whether AC or DC verification is permissible. The standard verification current modulation unit synthesizes and outputs a standard verification current according to the verification requirements set in the interactive module. Including standard AC calibration current Standard DC calibration current For standard AC verification current, the fundamental frequency component and harmonic components are modulated and synthesized into an output according to the requirements of the verification requirement setting unit in the interactive module; for standard DC verification current, the DC component is modulated and output according to the requirements of the verification requirement setting unit in the interactive module.

[0070] The interactive module includes a display unit, a verification requirement setting unit, and a data verification and analysis unit. The display unit shows important time-domain waveforms, spectra, etc., in real time, and displays the acquired raw current. , offset current residual current Waveform and spectrum (corresponding to channels CH1~CH3), and permissible response current. Standard calibration current (Corresponding to CH4 and CH5 channels). The verification requirement setting unit is used to set verification requirements based on human-computer interaction, and to configure DC verification components and AC verification components (fundamental wave verification component and harmonic verification component) based on these requirements; the data verification analysis unit is used to analyze the readings of the online monitoring equipment and the AC and DC verification results to obtain the on-site verification results and output them in the form of a standardized report.

[0071] To cover the verification scenarios of core / neutral point grounding current of various types of transformers, the AC and DC verification ranges are divided as shown in Tables 2 and 3.

[0072] Table 2. Scope of AC Verification

[0073] Table 3 DC Verification Range Division Table

[0074] The following are some preset verification scenarios:

[0075] 1. Verification via communication: ① For conventional transformers, inject power frequency current, selecting current points of 10mA, 30mA, 50mA, 90mA, 95mA, 100mA, 105mA, 110mA, 150mA, 500mA, 1A, 2A, 5A, and 10A, focusing on the area around the alarm threshold of 100mA, and record the readings of the monitoring equipment. ② For converter transformers and UHV transformers, inject power frequency current, selecting current points of 10mA, 50mA, 100mA, 150mA, 290mA, 295mA, 300mA, 305mA, 310mA, 500mA, 1A, 2A, 5A, 10A, and 20A, focusing on the area around the alarm threshold of 300mA, and record the readings of the monitoring equipment.

[0076] 2. DC verification: ① For core grounding current monitoring equipment, ±0.1A, ±0.3A, ±0.5A, or ±1A DC current can be injected, and the monitoring equipment readings can be recorded. ② For neutral point grounding current monitoring equipment, ±1A, ±3A, ±5A, ±10A, ±20A, or ±40A DC current can be injected, and the monitoring equipment readings can be recorded.

[0077] 3. Harmonic verification: ① Inject harmonics of the 3rd, 5th, 6th, 7th, 9th, 11th, and 12th orders with an amplitude of 50mA individually, and record the readings on the monitoring equipment. ② Perform a preset mixing calibration of the fundamental frequency, 3rd, 5th, and 7th harmonics: fundamental frequency 40mA + 3rd harmonic 20mA + 5th harmonic 10mA + 7th harmonic 10mA, and record the readings on the monitoring equipment. ③ Based on the measured changes in the harmonic order and proportion, manually select the components to be mixed for mixing calibration, and record the readings on the monitoring equipment.

[0078] 4. Select the 13th to 20th harmonic for verification as needed.

[0079] This invention covers the frequency range of the original grounding current and standard verification current from DC to 1000Hz (20th harmonic), the effective value of AC amplitude from 0.1mA to 20A, and the DC amplitude from ±0.1A to ±50A. It is suitable for verifying the core grounding current and neutral point grounding current (including DC bias) of ordinary transformers and converter transformers. It also has a variety of preset verification configurations to help users improve verification efficiency.

[0080] This invention proposes a wide-bandwidth, high-precision method for comprehensive on-site verification of transformer AC / DC grounding current. This method adds DC verification, broadening the verification bandwidth and applicable scenarios. It overcomes the limitation of only addressing the fundamental and low-order harmonics of core grounding current by employing an incremental method for on-site verification of the DC component. By using high-precision AC / DC sensors and performing wide-bandwidth FFT spectrum analysis from DC to 1000Hz, this invention expands the verification scenarios from being limited to core grounding current to neutral point grounding current containing DC bias components, and converter transformer grounding scenarios containing abundant high-frequency harmonics, achieving comprehensive AC / DC grounding current verification. This invention improves the verification accuracy and dynamic anti-interference capability of the AC component. This invention employs a method of first canceling and then verifying the AC component of transformer grounding current. By introducing a sensor error lookup table compensation mechanism, and matching amplitude correction coefficients and phase compensation values ​​based on spectrum analysis results, it effectively compensates for inherent static errors such as ratio and angle errors of the sensor. Simultaneously, a residual current closed-loop dynamic compensation mechanism is introduced, which cyclically monitors and iteratively corrects the canceling current with a microsecond cycle, overcoming the shortcomings of insufficient compensation accuracy in traditional open-loop verification methods and continuously suppressing the residual current within a preset threshold. This invention innovatively adopts a differentiated verification permission mechanism to ensure the rationality and stability of the verification conditions. This invention sets a comprehensive verification permission mechanism for the different characteristics and processing logics of AC and DC. The comprehensive verification conditions are only met when the residual closed-loop dynamic compensation suppresses the interference and stabilizes it within an extremely low threshold, and the DC component on site remains stable for a certain period (within a certain standard deviation range). This effectively avoids distortion caused by forced verification under conditions of large dynamic interference or drastic current fluctuations, creating favorable verification conditions for the injection of standard verification current. This method broadens the applicable range of AC and DC grounding currents, covering the frequency range of DC to 1000Hz, and effectively improves the measurement accuracy, environmental adaptability and operational stability of transformer grounding current verification.

[0081] The field verification device provided by this invention, through the coordinated operation of the acquisition module, preprocessing module, verification module, and interaction module, accurately adapts to the field verification method logic of the aforementioned wideband, high-precision AC / DC grounding current monitoring equipment. It solves, from the hardware and system architecture perspective, the problems of existing verification devices, such as limited bandwidth, large residual compensation errors, and failure to consider whether verification is possible under the conditions of the field grounding current, leading to distorted verification results. This improves the accuracy, environmental reliability, and scenario adaptability of field verification of transformer AC / DC grounding current. The acquisition module of this invention ensures wideband, high-fidelity data input, employing a high-precision wideband AC / DC sensor to accurately acquire the original field grounding current, including DC to 1000Hz high-order harmonics, in real time. It also monitors the minute residual current after the injection of compensation current, providing reliable original wideband data support for subsequent spectrum analysis, residual current closed-loop dynamic compensation, and verification permission judgment. The preprocessing module of the device of this invention takes into account the static and dynamic errors of the AC component. When generating the AC anti-phase cancellation current, it first calls the sensor error calibration table stored in the memory to intervene in advance and compensate for the inherent ratio and angle defects of the sensor, thereby reducing static errors. Then, through the residual current closed-loop dynamic compensation unit, the cancellation current is continuously iteratively corrected at a microsecond-level feedback frequency. It keenly captures and dynamically compensates for the cancellation deviation caused by hardware phase lag in the high-frequency band, reduces dynamic errors, and suppresses residual interference within an extremely low threshold, thereby effectively improving the AC component cancellation accuracy.

[0082] The verification module of this invention determines whether verification is permitted and incorporates a comprehensive verification permission mechanism. This module analyzes the real-time operating conditions of the original AC / DC grounding currents, strictly determining whether verification permission is granted based on the steady-state performance of the AC residual current and the stability of the DC component. Only after environmental conditions meet the requirements and permission is triggered will the device precisely modulate and output standard AC / DC verification currents according to the interactive requirements, effectively preventing blind injection under dynamic strong interference or drastic current jumps, ensuring the scientific nature and accuracy of the verification. The interactive module of this invention provides user-friendly human-computer interaction, allowing interactive selection of built-in schemes or custom configuration requirements. It can also present the waveform trajectory and spectrum distribution of the current in each channel in real-time and in multiple dimensions, automatically compare the readings of online monitoring equipment, automatically analyze field errors by combining the DC component incremental method and the AC component cancellation-before-injection method, and generate a standardized field verification report. By leveraging the collaborative operation of four low-latency modules—acquisition, preprocessing, verification, and interaction—a fully automated closed-loop system has been created, encompassing wideband signal acquisition, dual error correction and cancellation, adaptive determination of AC / DC differential permission, synthesis of multi-component standard verification current loops, and automatic output of standard reports. This enhances the environmental adaptability, operational stability, measurement accuracy, and convenience of the verification device under complex substation conditions.

[0083] Compared with the prior art, the present invention based on the above embodiments has the following beneficial effects: 1. In the present invention, the grounding current is collected at the neutral point or iron core of the transformer, FFT spectrum analysis in the frequency band from direct current to 1000 Hz is carried out, and accurate amplitude and phase compensation is realized by combining with a sensor error calibration table, then the inverse-phase cancellation current is corrected by microsecond closed-loop iteration, the residual current of the grounding loop is quickly suppressed to be within the threshold, and then a multi-component synthesized standard calibration current is injected to complete on-site calibration. The real-time performance, accuracy and automation degree of on-site calibration of the grounding current monitoring device are greatly improved, and the invention is suitable for on-site calibration requirements under complex harmonic working conditions; 2. Adding direct current calibration broadens the calibration frequency band and applicable scenarios. The present invention breaks through the limitation that the prior art only targets the fundamental wave and low-order harmonics of the iron core grounding current, and adopts an incremental method to perform on-site calibration on the direct current component. By adopting a high-precision AC-DC sensor and carrying out broadband FFT spectrum analysis of DC~1000 Hz, the present invention expands the calibration scenario from being limited to the iron core grounding current to the neutral point grounding current containing DC bias components and the grounding scenario of converter transformers rich in high-order harmonics, and realizes comprehensive AC-DC grounding current comprehensive calibration; 3. The present invention improves the calibration accuracy and dynamic anti-interference capability of alternating current components. In the present invention, a method of canceling first and calibrating second is adopted for the alternating current component of transformer grounding current. By introducing a sensor error look-up table compensation mechanism, the amplitude correction coefficient and phase compensation value are matched based on the spectrum analysis result, which effectively compensates for the inherent static errors such as ratio error and angle error of the sensor. Meanwhile, a residual current closed-loop dynamic compensation mechanism is introduced, which circularly monitors and iteratively corrects the cancellation current with a microsecond-level period, overcomes the disadvantage of insufficient compensation accuracy of the traditional open-loop calibration method, and continuously suppresses the residual current within a preset threshold; 4. The present invention adopts an AC-DC comprehensive calibration permission mechanism to ensure the rationality and stability of the calibration working condition. When the closed-loop dynamic compensation for residual current suppresses the interference of alternating current components and stabilizes it within a very low threshold, and the direct current component remains stable for a certain period of time (within a certain standard deviation range), the permission is granted to inject the standard calibration current. This effectively avoids calibration distortion caused by forced calibration when dynamic interference is large or current fluctuates violently, and creates a good calibration working condition for the injection of the standard calibration current; 5. The device modules cooperate and link with each other, realizing the full-process closed loop and automation. The on-site calibration device matched with the present invention accurately adapts to the above calibration logic through the cooperation of the acquisition module, preprocessing module, interaction module and calibration module. From complete AC-DC broadband acquisition, double error compensation cancellation, calibration permission judgment, to synthesizing and injecting multi-component standard calibration current according to requirements for calibration and outputting a standard report, the device forms an automatic closed loop, which improves the convenience, real-time performance, accuracy and operation stability of on-site calibration of transformer grounding current monitoring equipment.

[0084] The specific embodiments described above are preferred embodiments of the verification method and device for the transformer AC / DC grounding current online monitoring equipment of this application, and are not intended to limit the specific implementation scope of this application. The scope of this application includes but is not limited to the specific embodiments described above. All equivalent changes made in accordance with the shape and structure of this application are within the protection scope of this application.

Claims

1. A verification method for an online monitoring device for AC / DC grounding current of a transformer, characterized in that, include: S1. Collect the grounding current of the grounding circuit in the transformer, and perform spectrum analysis on the grounding current to obtain the amplitude and phase characteristics of the fundamental component, harmonic components and DC component of the grounding current. S2. Based on the frequency index of the fundamental component and each harmonic component, a preset sensor error calibration table is used to obtain the corresponding amplitude correction coefficient and phase compensation value. S3. Generate a canceling current that is opposite to the AC component of the grounding current based on the amplitude correction coefficient and the phase compensation value, and inject the canceling current into the grounding loop; S4. Monitor the residual current in the grounding loop in real time, and iteratively correct the offset current in a closed-loop feedback manner until the AC component in the residual current is less than the preset current threshold and the fluctuation of the DC component in the residual current meets the preset fluctuation condition, and determine that the comprehensive verification permission condition is met. The degree of fluctuation in the DC component of the residual current is determined to meet the preset fluctuation condition by means of the following methods: If the DC component of the residual current remains within the preset standard deviation range within a preset time period, it is considered that the preset fluctuation condition is met; otherwise, it is considered that the preset fluctuation condition is not met. S5. Under the condition of meeting the comprehensive verification permission conditions, obtain the verification requirements, configure the DC verification component, fundamental frequency verification component or harmonic verification component based on the verification requirements to obtain the standard verification current, and inject the standard verification current into the grounding loop, record the detection value of the grounding loop by the online monitoring device, analyze the change of the detection value to obtain the verification result of the AC / DC grounding current; the standard verification current includes the standard DC verification current and the standard AC verification current.

2. The verification method for an online monitoring device for AC / DC grounding current of a transformer according to claim 1, characterized in that, The step of real-time monitoring of the residual current in the grounding loop and iteratively correcting the offset current using a closed-loop feedback method until the AC component of the residual current is less than a preset current threshold includes: S41. Monitor the residual current in the grounding loop in real time. If the AC component of the monitored residual current is greater than or equal to a preset current threshold, extract the waveform characteristics of the residual current. S42. Based on the waveform characteristics, generate an inverse fine-tuning compensation amount and add it to the offset current. Execute step S41 repeatedly with a microsecond period until the residual current is less than a preset current threshold.

3. The verification method for an online monitoring device for AC / DC grounding current of a transformer according to claim 1, characterized in that, The sensor error calibration table is set up in the following ways: S21. On the laboratory calibration platform, the sensor that collects the grounding current and the residual current is simulated and tested to obtain the amplitude error and phase error of the sensor at each frequency component. S22. Based on the amplitude error and the phase error, construct the sensor error calibration table.

4. The verification method for an online monitoring device for AC / DC grounding current of a transformer according to claim 1, characterized in that, The steps of collecting the grounding current in the grounding circuit of the transformer and performing spectrum analysis on the grounding current to obtain the DC and AC components of the grounding current include: S11. Use AC / DC sensors to collect data at the location of the neutral point grounding flat iron or the location of the core grounding flat iron of the transformer to obtain the grounding current. S12. Perform fast Fourier transform spectrum analysis on the grounding current to obtain the amplitude and phase characteristics of the DC and AC components. The AC components include the fundamental component and each harmonic component. The frequency range of the spectrum analysis covers DC to 1000Hz.

5. A calibration device for an online monitoring device for AC / DC grounding current of a transformer, comprising applying the calibration method for an online monitoring device for AC / DC grounding current of a transformer as described in any one of claims 1 to 4 to perform on-site calibration of the online monitoring device, characterized in that, The device includes a data acquisition module, a preprocessing module, a verification module, and an interaction module; The acquisition module is used to acquire the grounding current of the grounding circuit in the transformer and monitor the residual current in the grounding circuit in real time. The preprocessing module is used to perform spectrum analysis on the grounding current acquired by the acquisition module, generate a canceling current that is opposite to the AC component of the grounding current, perform sensor error lookup table compensation on the canceling current, iteratively correct the canceling current in a closed-loop feedback manner, and inject the iteratively corrected canceling current into the grounding circuit. The interaction module is used to obtain the verification requirements and send the verification requirements to the verification module when the comprehensive verification permission conditions are met, receive and display the data waveforms of the acquisition module, the preprocessing module and the verification module, and analyze and output the on-site verification results. The verification module is used to determine whether the comprehensive verification permission conditions are met, and to generate a standard verification current based on the verification requirements obtained by the interaction module, and to generate and output the standard DC verification current and the standard AC verification current to the grounding circuit.

6. The calibration device for an online monitoring equipment for AC / DC grounding current of a transformer according to claim 5, characterized in that, The preprocessing module includes an FFT analysis unit, a sensor error lookup table compensation unit, and a residual current closed-loop dynamic compensation unit. The FFT analysis unit is used to perform fast Fourier transform spectrum analysis on the grounding current acquired by the acquisition module. The sensor error lookup table compensation unit is used to store the sensor error calibration table and index the amplitude correction coefficient and phase compensation value corresponding to the grounding current. The residual current closed-loop dynamic compensation unit is used to generate a canceling current that is opposite in phase to the AC component of the grounding current, and iteratively corrects the canceling current in a closed-loop feedback manner. The iteratively corrected canceling current is then compensated again by the sensor error lookup table compensation unit and injected into the grounding loop.

7. The calibration device for an online monitoring equipment for AC / DC grounding current of a transformer according to claim 5, characterized in that, The interactive module includes a display unit, a verification requirement setting unit, and a data verification analysis unit; the display unit is used to display the current waveform and spectrum detected by the acquisition module in real time; the verification requirement setting unit is used to set verification requirements based on human-computer interaction, and configure DC verification components or AC verification components based on the verification requirements. The data verification and analysis unit is used to analyze the readings of the online monitoring equipment with the AC and DC verification results to obtain the on-site verification results and output them in the form of a report.

8. The calibration device for an online monitoring device for AC / DC grounding current of a transformer according to claim 5, characterized in that, The acquisition module includes an AC / DC sensor, a feedback sensor, and a calibration sensor. The AC / DC sensor is used to acquire the grounding current of the grounding circuit in the transformer. The feedback sensor is used to monitor the residual current in the grounding circuit in real time. The calibration sensor is used to acquire the actual calibration current of the grounding circuit after injecting a standard calibration current.

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