Difference flow anomaly early warning method and device, computer equipment and computer readable storage medium

Abstract

The application relates to a differential current anomaly early warning method and device, computer equipment and a computer readable storage medium. Through harmonic decomposition of each three-phase current signal, component signals corresponding to the three-phase current signals are obtained, and the component signals in the same phase are fused to obtain differential current signals including at least a fundamental wave differential current signal and a second harmonic differential current signal; based on the relative relationship between the fundamental wave differential current signal and the second harmonic differential current signal, an inhibition factor is determined, and the differential current signal is corrected based on the inhibition factor to obtain a target differential current signal; the change characteristics of the load current representation quantity are determined according to the component signals, and the basic differential current threshold value is corrected according to the change characteristics to obtain a target differential current threshold value; the target differential current signal is compared with the target differential current threshold value to obtain target anomaly information, and corresponding prompt information is output according to the target anomaly information, so that the damage expansion of equipment is effectively reduced, and the safety and reliability of the operation of the protected object are improved.

Description

Technical Field

[0001] This application relates to the field of equipment safety technology, and in particular to a differential current anomaly early warning method, device, computer equipment, and computer-readable storage medium. Background Technology

[0002] Pumped storage power stations are important peak-shaving, frequency regulation, and emergency backup power sources for the power grid. The protection and monitoring of their main transformers, generators, and other electrical equipment generally adopt the differential principle. That is, three-phase currents are collected from multiple current acquisition sides of the protected object, and after being converted by the current transformer (CT) ratio, the differential current is obtained by summing them by phase. The differential current is then compared with a pre-set fixed threshold. When the differential current exceeds the threshold, it is determined that there is an abnormality in the protected object.

[0003] However, differential current is not solely generated by anomalies within the protected object. Inrush current generated when a transformer is switched on, and severe load fluctuations during unit start-up, shutdown, and switching of operating conditions can all create considerable differential current even when the protected object is intact. Therefore, when using a fixed threshold for judgment, setting the threshold too high makes it difficult to detect early defects, while setting it too low leads to frequent interference triggering of early warnings.

[0004] Therefore, early defects in the protected objects often remain hidden for a long time, and are often not detected until they develop into through-faults and are cut off by the protection device. This leads to passive maintenance arrangements, extended unplanned downtime, and poses a threat to the operational safety of the unit and the power grid. Summary of the Invention

[0005] Therefore, it is necessary to provide a differential current anomaly early warning method, device, computer equipment, and computer-readable storage medium that can improve the accuracy of differential current anomaly identification, in order to address the above-mentioned technical problems.

[0006] Firstly, this application provides a differential current anomaly early warning method, including:

[0007] Acquire multiple three-phase current signals from at least two acquisition sides;

[0008] Harmonic decomposition is performed on each of the three-phase current signals to obtain the component signals corresponding to the three-phase current signals, and the component signals in the same phase are fused to obtain the corresponding differential current signals; wherein, the differential current signals include at least the fundamental differential current signal and the second harmonic differential current signal;

[0009] Based on the relative relationship between the fundamental differential current signal and the second harmonic differential current signal, the suppression factor is determined, and the differential current signal is corrected based on the suppression factor to obtain the target differential current signal;

[0010] The variation characteristics of the load current characterization quantity are determined based on the component signals, and the basic differential current threshold is corrected based on the variation characteristics to obtain the target differential current threshold.

[0011] The differential current change rate of the target differential current signal is compared with the target differential current threshold to obtain the target anomaly information, and the corresponding prompt information is output according to the target anomaly information.

[0012] In one embodiment, after acquiring multiple three-phase current signals from at least two acquisition sides, the method further includes:

[0013] Determine the initial conversion factors for at least two acquisition sides, calculate the positive direction based on the current reference direction and differential current of the acquisition sides, and determine the target conversion factor based on the initial conversion factors;

[0014] Based on the phase difference at the acquisition side, phase correction is performed on multiple three-phase current signals to obtain the corrected three-phase current signals;

[0015] Based on the target conversion factor and the corrected three-phase current signal, the three-phase current signal is corrected and calculated to obtain the corrected three-phase current signal.

[0016] In one embodiment, the steps of determining a suppression factor based on the relative relationship between the fundamental differential current signal and the second harmonic differential current signal, and correcting the differential current signal based on the suppression factor to obtain the target differential current signal include:

[0017] Calculate the ratio of the second harmonic differential current signal to the fundamental differential current signal in the same phase to obtain the proportion of the second harmonic content in the current phase;

[0018] The suppression factor for the current phase is determined based on the proportion of the second harmonic content; the suppression factor is inversely proportional to the proportion of the second harmonic content.

[0019] Based on the fundamental differential current signal and the suppression factor, the target differential current signal in the current phase is calculated.

[0020] In one embodiment, the step of determining the suppression factor of the current phase based on the proportion of second harmonic content includes:

[0021] When the proportion of second harmonic content is less than or equal to the first preset proportion threshold, the suppression factor is set to zero;

[0022] When the proportion of second harmonic content is greater than the first preset proportion threshold and less than the second preset proportion threshold, the suppression factor is set to the target suppression value; wherein, the target suppression value is a continuous value that increases monotonically according to the proportion of second harmonic content.

[0023] When the proportion of second harmonic content is greater than or equal to the second preset proportion threshold, the suppression factor is set to the corresponding upper limit value; wherein, the second preset proportion threshold is greater than the first preset proportion threshold.

[0024] In one embodiment, the component signal includes a fundamental component, and the variation characteristics include load fluctuation and load change rate. The steps of determining the variation characteristics of the load current characteristic based on the component signal, and correcting the basic differential current threshold based on the variation characteristics to obtain the target differential current threshold include:

[0025] The amplitude of the fundamental component of the same phase at each acquisition side is averaged to obtain the load current characterization of the current phase.

[0026] Within a preset time window, the dispersion of the load current characterization is calculated to obtain the load fluctuation, and the ratio of the change in the load current characterization at adjacent times to the time interval is calculated to obtain the load change rate.

[0027] The target differential current threshold is obtained by calculating the basic differential current threshold, the first correction term which is positively correlated with the load current characterization, the second correction term which is positively correlated with the load fluctuation, and the third correction term which is positively correlated with the load change rate.

[0028] In one embodiment, the step of comparing the target differential current signal with the target differential current threshold to obtain target anomaly information, and outputting corresponding prompt information based on the target anomaly information includes:

[0029] Calculate the differential current change rate of the target differential current signal;

[0030] If the target differential current signal is greater than the target differential current threshold, an anomaly is determined to exist in the target, and a corresponding prompt message is output.

[0031] If the target differential current signal is less than or equal to the target differential current threshold, it is determined that there is no target anomaly.

[0032] In one embodiment, the step of determining the existence of a target anomaly and outputting a corresponding prompt message when the target differential current signal is greater than the target differential current threshold includes:

[0033] The maximum load change rate of the target differential current signal at adjacent time points is obtained to obtain the differential current change rate. The base change rate threshold and the load change rate are also obtained. The target change rate threshold is calculated based on the base change rate threshold and the load change rate.

[0034] If the target differential current signal is greater than the target differential current threshold and the differential current change rate is greater than the target change rate threshold, the target anomaly will be determined as the first level, and a prompt message corresponding to the first level will be output.

[0035] If the target differential current signal is greater than the target differential current threshold and the differential current change rate is less than or equal to the target change rate threshold, the target anomaly is determined to be of the second level, and a prompt message corresponding to the second level is output; wherein, the second level is lower than the first level.

[0036] Secondly, this application also provides a differential current anomaly early warning device, the device comprising:

[0037] The acquisition module is used to acquire multiple three-phase current signals from at least two acquisition sides;

[0038] The differential current calculation module is used to perform harmonic decomposition on each three-phase current signal to obtain the component signals corresponding to the multiple three-phase current signals, and to fuse the component signals in the same phase to obtain the corresponding differential current signal; wherein, the differential current signal includes at least the fundamental differential current signal and the second harmonic differential current signal;

[0039] The differential current correction module is used to determine the suppression factor based on the relative relationship between the fundamental differential current signal and the second harmonic differential current signal, and to correct the differential current signal based on the suppression factor to obtain the target differential current signal.

[0040] The threshold correction module is used to determine the variation characteristics of the load current characterization quantity based on the component signal, and to correct the basic differential current threshold according to the variation characteristics to obtain the target differential current threshold.

[0041] The anomaly determination module is used to compare the differential current change rate of the target differential current signal with the target differential current threshold to obtain target anomaly information, and output corresponding prompt information based on the target anomaly information.

[0042] Thirdly, this application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps performed by the above-mentioned differential current anomaly early warning method.

[0043] Fourthly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps performed by the aforementioned differential current anomaly early warning method.

[0044] Fifthly, this application also provides a computer program product, including a computer program that, when executed by a processor, implements the steps performed by the aforementioned differential current anomaly early warning method.

[0045] The aforementioned differential current anomaly early warning method, device, computer equipment, and computer-readable storage medium acquire multiple three-phase current signals from at least two acquisition sides; perform harmonic decomposition on each three-phase current signal to obtain the corresponding component signals of the three-phase current signals, and fuse the component signals in the same phase to obtain a differential current signal that includes at least a fundamental differential current signal and a second harmonic differential current signal; determine a suppression factor based on the relative relationship between the fundamental differential current signal and the second harmonic differential current signal, and correct the differential current signal based on the suppression factor to obtain a target differential current signal; determine the change characteristics of the load current characterization quantity according to the component signals, and correct the basic differential current threshold according to the change characteristics to obtain a target differential current threshold; compare the target differential current signal with the target differential current threshold to obtain target anomaly information, and output corresponding prompt information according to the target anomaly information.

[0046] Therefore, the fundamental differential current signal obtained by fusing the fundamental components of the same phase on each acquisition side characterizes whether the internal current of the protected object is balanced. The relative relationship between the second harmonic differential current signal and the fundamental differential current signal of the same phase characterizes the significance of the inrush current characteristics in the differential current. The two together constitute the basis for judging the reliability of the differential current signal itself, so that the differential current caused by the transformer closing inrush current can be weakened according to the significance of its inrush current characteristics, while the differential current without inrush current characteristics can be retained in its original quantity. This overcomes the problem that under the fixed threshold method, the inrush current interference and internal anomalies are exactly the same in amplitude, which can only be avoided by raising the overall setting value, thus sacrificing sensitivity. At the same time, the load current characterization quantity determined by the fundamental component and its change characteristics characterize the reliability of the current measurement results under the current operating condition, and the basic differential current threshold is corrected accordingly, so that the reliability of the current measurement results under the current operating condition is improved during unit start-up and shutdown, operating condition switching and load change. False differential currents caused by inconsistent transient responses at the acquisition side are accommodated by a correspondingly raised judgment threshold. During steady-state low-load periods, the judgment threshold automatically falls back, and sensitivity is maintained. This overcomes the problem that false differential currents caused by load fluctuations are completely identical in waveform composition to real abnormal differential currents, making them indistinguishable from the differential currents themselves. Two corrections are applied to the differential current signal being judged and the threshold on which the judgment is based, respectively. The two are combined in the same comparison. Only when the target differential current signal after surge suppression still exceeds the target differential current threshold corrected according to the operating conditions is a target anomaly determined and a prompt message is output. The two types of interference are processed separately in the same judgment process and do not mask each other. Thus, at the small differential current level corresponding to early defects, the real anomalies inside the protected object are distinguished from the two types of interferences. This effectively improves the accuracy of differential current anomaly identification and reduces the risk that early defects will remain dormant for a long time until they develop into penetrating faults before being discovered. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a diagram illustrating the application environment of the differential current anomaly early warning method in one embodiment.

[0049] Figure 2 This is a flowchart illustrating a differential current anomaly early warning method in one embodiment;

[0050] Figure 3 This is a schematic diagram of the differential current anomaly early warning device in one embodiment;

[0051] Figure 4 This is a schematic diagram of the internal structure of a computer device in one embodiment. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0053] It should be noted that the terms "first," "second," etc., used in this application can be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from the second element. The terms "comprising" and "having," and any variations thereof, used in this application, are intended to cover non-exclusive inclusion. The term "multiple" used in this application refers to two or more. The term "and / or" used in this application refers to one of the embodiments, or any combination of multiple embodiments.

[0054] In traditional differential current monitoring technology, the anomaly identification process is based solely on whether the differential current amplitude exceeds a pre-set fixed threshold, lacking analysis of the causes of the differential current, resulting in insufficient accuracy in anomaly identification. Specifically, the harmonic characteristics carried by the differential current signal itself, as well as the load conditions of the protected object at the time of differential current generation, are not included in the anomaly judgment criteria. This makes it impossible to distinguish the amplitudes of differential current caused by transformer closing excitation inrush current, false differential current caused by severe load fluctuations, and real differential current caused by early defects within the protected object, leading to frequent false alarms and missed alarms. Furthermore, the judgment threshold remains constant throughout the entire operating cycle, without a threshold adjustment mechanism adapted to real-time operating conditions. This results in insufficient sensitivity during steady-state low load periods and insufficient anti-interference capability during operating condition transitions, forcing operators to set the threshold at a high level to suppress false alarms. Consequently, the investigation of early defects loses its basis, directly affecting the timeliness and targeted nature of equipment maintenance.

[0055] For example, during the no-load closing of the main transformer of a pumped storage power station, the protected object itself is intact, but at the moment of closing, the iron core enters a deep saturation state, and the excitation current only flows in from the power supply side and does not flow out from the other side. The differential current formed by summing the currents of each acquisition side according to phase can be several times the rated current. The existing method only judges that the protected object is abnormal and outputs an early warning based on the fact that the differential current has exceeded a fixed threshold, which causes false alarms. After experiencing such false alarms many times, the operators are often forced to continue to raise the threshold. For example, during the switching of the power plant unit from power generation to pumping operation, the load current changes significantly within several power frequency cycles. The transient responses of the current transformers on each acquisition side are not completely synchronized, and the measurement errors cannot cancel each other out during the summation process, forming a false differential current that is small in magnitude but persistent. Specifically, the waveform of this false differential current is the same as the differential current generated by the real anomaly inside the protected object, which is a power frequency sine wave. It exhibits the same numerical and waveform characteristics on the protection device side, and existing methods cannot identify its cause. If the threshold is set to a higher level to cover such operating conditions, the real differential currents with similar magnitudes caused by early defects such as loose wiring of the secondary circuit terminal block of the CT of the same protected object and slow deterioration of the inter-turn insulation of the winding will also be masked by the judgment threshold, resulting in the anomaly not being detected for a long time, and it is impossible to determine which phase or which acquisition side current loop the anomaly originates from.

[0056] If the above problems are not resolved, the early defects of the protected objects will remain hidden in the primary equipment and secondary circuits for a long time. Because the judgment criteria are singular, they cannot be identified in the early stages of development or targeted investigation. As a result, the protection device may only be activated to cut off the fault when the defect continues to develop and forms a through-fault. This will result in irreversible equipment damage, an expanded fault range, extended unplanned downtime, and passive maintenance arrangements when the fault is cleared, which seriously threatens the safe operation of the unit and the reliability of the power grid system.

[0057] To address the aforementioned problems, embodiments of this application provide a differential current anomaly early warning method, which can be applied to, for example... Figure 1 In the application environment shown, terminal 102 communicates with server 104 via a network. A data storage system can store the data that server 104 needs to process. The data storage system can be integrated onto server 104, or it can be located in the cloud or on another network server.

[0058] Terminal 102 can be, but is not limited to, various personal computers, laptops, smartphones, tablets, drones, aircraft, low-altitude aircraft, IoT devices, and portable wearable devices. IoT devices can include smart speakers, smart TVs, smart air conditioners, smart in-vehicle devices, projection devices, etc. Portable wearable devices can include smartwatches, smart bracelets, head-mounted devices, etc. Head-mounted devices can include virtual reality (VR) devices, augmented reality (AR) devices, smart glasses, etc.

[0059] Server 104 can be a standalone physical server, a server cluster or distributed system consisting of multiple physical servers, or a cloud server that provides cloud computing services.

[0060] This application provides a differential current anomaly early warning method, such as Figure 2 As shown, this method is applied to Figure 1 Taking server 104 as an example, by analyzing the three-phase current signals of each current acquisition side of the protected object, potential differential current anomalies can be detected in a timely manner under the condition of both interference and actual anomalies, and corresponding early warning information can be output to ensure the safe and stable operation of the equipment. This differential current anomaly early warning method may include steps 21 to 25, wherein:

[0061] Step 21: Acquire multiple three-phase current signals from at least two acquisition sides.

[0062] The acquisition side can be a current measurement location set on the current inflow or outflow path of the protected object. Each acquisition side is equipped with a set of current transformers to proportionally transform the large primary current into a small secondary current and output it. For protected objects such as generators, main transformers, etc., the acquisition side can be set at each boundary of its current inflow and outflow.

[0063] Three-phase current signals can be current sampling sequences of three phases (A, B, and C) on the same acquisition side, which can be used to reflect the magnitude and direction of the current flowing through the boundary of the protected object at each sampling moment on the acquisition side.

[0064] Multiple three-phase current signals can be used to indicate that the acquired three-phase current signals come from different acquisition sides, with each acquisition side corresponding to one channel.

[0065] It should be noted that there must be at least two acquisition sides, which is a prerequisite for differential current. The principle of differential current is based on the balance relationship of current at the boundaries of the protected object. That is, when there is no abnormality inside the protected object, the current flowing into each boundary and the current flowing out of each boundary should cancel each other out. If there is only one acquisition side, there is no other current available for comparison, it is impossible to determine whether the current is balanced, and therefore differential current cannot be formed.

[0066] One implementation method is for the server to periodically send data request commands to the corresponding measurement and control devices or protection devices on each acquisition side, and read the three-phase current signals of each channel according to a unified sampling time standard. Another implementation method is for the corresponding devices on each acquisition side to actively send sampling data at fixed intervals, and the server to obtain multiple three-phase current signals after aligning them according to the sampling time standard.

[0067] Step 22: Perform harmonic decomposition on each three-phase current signal to obtain the component signals corresponding to the three-phase current signals, and fuse the component signals in the same phase to obtain the corresponding differential current signal.

[0068] The differential current signal includes at least the fundamental differential current signal and the second harmonic differential current signal.

[0069] After acquiring the three-phase current signal, the current sampling sequence in the time domain can be expanded according to frequency components, and the components corresponding to each frequency of the three-phase current signal can be output. Understandably, periodic current waveforms can be decomposed into a superposition of power frequency components and several higher harmonic components, and the difference in waveform shape after decomposition is manifested as the difference in the proportion of each harmonic.

[0070] The component signal can be a current component corresponding to a specific frequency output by harmonic decomposition, including at least the fundamental component and the second harmonic component. The fundamental component can be a component corresponding to the power frequency and can be used to reflect the main component of the current; the second harmonic component can be a component corresponding to twice the power frequency and can be used to reflect the degree to which the current waveform deviates from a symmetrical sinusoidal shape.

[0071] After determining the fundamental component and second harmonic component of the three-phase current signal, the fundamental component and the second harmonic component can be fused separately. The same type of component signal of the same phase on each acquisition side is vector summed in the positive direction of differential current calculation. The vector summation takes into account both the amplitude and phase of the component, and the corresponding differential current signal is obtained, which is used to indicate whether the same component on each acquisition side cancels each other out on that phase.

[0072] The fundamental differential current signal can be obtained by fusing the fundamental components of the same phase at each acquisition side, and is used to represent the degree of imbalance of the current in that phase at the boundary of the protected object. The second harmonic differential current signal can be obtained by fusing the second harmonic components of the same phase at each acquisition side, and is used to represent the magnitude of the component in the phase imbalance that deviates from the symmetrical sinusoidal shape.

[0073] It should be noted that both the fundamental component and the second harmonic component must undergo the same fusion process; that is, both are the result of summing the corresponding component vectors from each acquisition side, rather than being components taken from a single acquisition side. When both quantities are fused differential current signals, they are under the same scope, and their relative relationship can characterize the proportion of components deviating from the symmetrical sinusoidal shape in the differential current signal. In particular, if the second harmonic component from a certain acquisition side is compared with the fused fundamental differential current signal, they belong to different levels of physical quantities, and the results obtained have no interpretable physical meaning.

[0074] It should also be noted that fusion along the acquisition side direction can maintain the same phase across different acquisition sides to form a differential current signal. In addition, after obtaining the differential current signals of each phase, further fusion can be performed along the phase direction, that is, across different phases but targeting the same protected object, to distinguish between the overall and single-phase differential currents that have been formed.

[0075] Step 23: Based on the relative relationship between the fundamental differential current signal and the second harmonic differential current signal, determine the suppression factor, and correct the differential current signal based on the suppression factor to obtain the target differential current signal.

[0076] The relative relationship can be the degree of enrichment of the second harmonic differential current signal relative to the fundamental differential current signal in the same phase. It can be characterized by the ratio of the two, or by their normalized difference, logarithmic ratio, or other quantities that can reflect the relative amount of the second harmonic component. The larger the value of the relative relationship, the greater the proportion of components deviating from the symmetrical sinusoidal shape in the differential current signal of that phase.

[0077] Here, the suppression factor can be a continuous coefficient generated based on the above relative relationship, used to weaken the influence of excitation inrush current on differential current anomaly determination. The suppression factor does not decrease as the value of the relative relationship increases; that is, the more significant the inrush current characteristics in the differential current signal, the larger the value of the suppression factor, and the stronger the weakening effect on the differential current signal.

[0078] In some implementations, the target differential current signal can be the amount obtained by correcting the fundamental differential current signal with a suppression factor.

[0079] It should be noted that the suppression factor can be determined based on the above relative relationship because the inrush current and the abnormal current inside the protected object have fundamentally different waveforms. When the transformer is closed, the iron core enters a deep saturation state due to the combined effect of residual magnetism and the closing phase angle. The excitation current exhibits obvious unipolar bias and discontinuity characteristics, and its waveform deviates significantly from a symmetrical sinusoidal shape. After harmonic decomposition, its second harmonic component accounts for a considerable proportion. On the other hand, the current generated by abnormalities such as insulation degradation and inter-turn short circuits inside the protected object is a nearly symmetrical power frequency sinusoidal current, and after harmonic decomposition, the second harmonic component is very small. Therefore, the enrichment of the second harmonic differential current signal relative to the fundamental differential current signal essentially quantifies the similarity of the current differential current signal's waveform to the inrush current. Based on this, it can be determined to what extent the differential current signal can be identified as an abnormal current inside the protected object.

[0080] As an example, modifying the differential current signal based on a suppression factor allows for proportional attenuation based on the degree of suspicion of the differential current signal, rather than separating and subtracting the inrush current component from the differential current signal. The value of the suppression factor reflects the degree to which the differential current signal is not accepted, and there is no quantitative correspondence between it and the absolute magnitude of the inrush current component in the differential current signal. The reason for using proportional attenuation instead of separation and subtraction is that the inrush current and the internal abnormal current are superimposed on the same differential current signal at the same time and cannot be separated in the time domain. However, the difference in their waveform morphology can be quantified into a continuous degree of confidence, making proportional attenuation feasible in engineering.

[0081] Step 24: Determine the variation characteristics of the load current characterization quantity based on the component signal, and correct the basic differential current threshold according to the variation characteristics to obtain the target differential current threshold.

[0082] The load current characterization quantity can be determined based on the fundamental component of each acquisition side, reflecting the current load level borne by the protected object. Unlike differential current signals, the load current characterization quantity is not the imbalance of currents at each acquisition side, but rather the overall level of current amplitude at each acquisition side. It reflects the current operating status of the protected object rather than the degree of abnormality.

[0083] The variation characteristics can be the changes in load current over a period of time, including at least the degree of fluctuation within the time window and the rate of change between adjacent moments.

[0084] The baseline differential current threshold can be a benchmark threshold used to determine whether the differential current is abnormal under steady-state low load conditions. The target differential current threshold can be a judgment threshold that is adapted to the current operating conditions, obtained by correcting the baseline differential current threshold for changes in characteristics.

[0085] It should be noted that the reason why spurious differential current caused by load fluctuations is handled using a threshold correction method, rather than the same method used for inrush current, is because the traces they leave in the differential current signal are different. Inrush current leaves identifiable characteristics in the frequency composition of the differential current signal, thus it can be identified and weakened from within the differential current signal itself. However, when the load changes drastically, the measurement error caused by the asynchronous transient response of the current transformers on each acquisition side is itself a power frequency sine wave. The spurious component it forms in the differential current signal is completely consistent in frequency composition with the real component formed by the internal anomaly of the protected object, and cannot be distinguished from the differential current signal itself. Therefore, for this type of interference, we can only rely on circumstantial evidence other than the differential current signal, namely whether the current load current itself is undergoing drastic fluctuations, to determine the reliability of the current measurement result at the current moment, and this judgment is reflected in the corresponding adjustment of the decision threshold.

[0086] It should be noted that the effect of using a judgment threshold that adjusts according to operating conditions is that the threshold automatically drops to a lower level during periods of stable load, thus maintaining sensitivity to small differential currents corresponding to early defects; while it automatically rises during periods of drastic load changes, thus accommodating unavoidable measurement errors during those periods. This is fundamentally different from setting the threshold at a consistently high level, which permanently sacrifices sensitivity while gaining disturbance rejection capability.

[0087] Step 25: Compare the differential current change rate of the target differential current signal with the target differential current threshold to obtain target anomaly information, and output corresponding prompt information based on the target anomaly information.

[0088] The target anomaly information can be a conclusion regarding whether a differential current anomaly exists in the protected object, determined based on comparison results. The alert information can be a warning message output to operation and maintenance personnel or higher-level systems when a target anomaly is confirmed; it may include information such as the phase of the anomaly, the time of its occurrence, and the severity of the anomaly.

[0089] As one implementation method, if the target differential current signal is greater than the target differential current threshold, it can be determined that there is a target anomaly and the corresponding prompt message can be output; if the target differential current signal is less than or equal to the target differential current threshold, it can be determined that there is no target anomaly and no prompt message can be output.

[0090] It should be noted that the aforementioned two corrections apply to both ends of the comparison relationship: the correction for the differential current signal applies to the quantity being judged, addressing inrush current interference; the correction for the basic differential current threshold applies to the threshold on which the judgment is based, addressing load fluctuation interference. The two corrections are independent and parallel, each targeting a specific type of interference, and converge in the same comparison within this step. Because each type of interference is handled by its corresponding end, they do not mask each other, nor does handling one type sacrifice the ability to handle the other. This ensures that even when both types of interference coexist or alternate, the true anomalies within the protected object can still be identified.

[0091] Traditional differential current monitoring schemes typically rely solely on whether the differential current amplitude exceeds a fixed threshold for judgment and alarm. However, this single-criterion judgment method suffers from low accuracy and is prone to false alarms and missed alarms: since the differential current caused by inrush current and load fluctuations is indistinguishable in amplitude from that caused by real anomalies, raising the threshold to suppress false alarms will simultaneously mask real early defects, while lowering the threshold to improve sensitivity will cause interference to frequently trigger warnings.

[0092] In the above implementation, the limitations mentioned above are overcome by analyzing the harmonic composition of the differential current signal itself and the current load conditions. Although the differential current amplitude itself cannot explain its cause, the enrichment of the second harmonic differential current signal relative to the fundamental differential current signal indicates the similarity of the differential current waveform to the inrush current. The changing characteristics of the load current characterization quantity indicate the reliability of the current measurement result at the current moment. Both of these separate the interference from the judgment quantity and the judgment threshold, respectively, allowing the differential current that should not exist to be accurately identified. In addition, since the processing at both ends is independent, the two types of interference can still be processed separately when inrush current and load fluctuations coexist, avoiding the problem that the processing effect of one type of interference in a single criterion scheme is canceled out by the other type of interference.

[0093] Compared to existing technologies where criteria are singular and early defects are difficult to detect, this embodiment can detect differential current anomalies and provide early warnings before defects develop into through-faults. This effectively reduces the probability of equipment damage expansion and unplanned downtime extension due to long-term latency of early defects, and improves the safety and reliability of protected objects in important situations such as pumped storage power stations.

[0094] In one exemplary embodiment, the differential current that occurs during the operation of the protected object can be classified into three categories. This embodiment adopts different methods to deal with the three categories of causes at different stages, depending on the degree of identifiability of the causes.

[0095] The first type is false differential current caused by inconsistencies in the parameters of the current transformers on each acquisition side. This type of cause is constant and systematic. The transformation ratio, polarity direction, and wiring method of each acquisition side are determined and can be known in advance after the equipment is put into operation. Therefore, it can be eliminated before the differential current is formed.

[0096] The second type is the differential current caused by the inrush current of the transformer during closing. This type of interference is a transient disturbance that occurs with the operating conditions and cannot be eliminated in advance. However, it retains identifiable characteristics in the frequency composition of the differential current signal, so it can be identified from the differential current signal and weakened according to its degree.

[0097] The third type is spurious differential current caused by asynchronous transient responses at different acquisition sides during periods of severe load fluctuation. This type of interference is also transient, and its frequency composition is completely consistent with the real differential current caused by internal anomalies of the protected object. It cannot be distinguished from the differential current signal, so it can only be accommodated by using circumstantial evidence other than the differential current signal and by modifying the judgment threshold.

[0098] Therefore, the three types of causes are treated in descending order of their identifiability, using elimination, weakening, and containment methods respectively. Differential currents that still exceed the threshold and persist after treatment are considered genuine anomalies within the protected object. The following is a step-by-step explanation; specifically, the differential current anomaly early warning method may include steps 301 to 314, wherein:

[0099] Step 301: Acquire multiple three-phase current signals from at least two acquisition sides.

[0100] The acquisition side can be a current measurement location set on the current inflow or outflow path of the protected object. Each acquisition side is equipped with a set of current transformers to proportionally transform the large primary current into a small secondary current and output it. Multiple channels can be used to indicate that the acquired three-phase current signals come from different acquisition sides, with each acquisition side corresponding to one channel, and each channel containing three channels: phase A, phase B, and phase C.

[0101] For example, when the protected object is a generator motor, the data acquisition side can be set at both the generator terminal side and the neutral point side, in which case there are two data acquisition sides. When the protected object is a combined unit consisting of a generator motor and a main transformer, the data acquisition side can further include the high-voltage side of the main transformer, in which case there are three data acquisition sides. The number of data acquisition sides depends on the number of current boundaries of the protected object. This embodiment does not limit the specific location and number of data acquisition sides. Current measurement locations that are on the same current boundary of the protected object and can jointly form a current balance relationship can all be used as data acquisition sides in this embodiment.

[0102] As one approach, sampling on each acquisition side can be completed by the same set of sampling units, with natural synchronization between channels. As another approach, sampling on each acquisition side can be completed by multiple sets of devices distributed in different locations. In this case, a unified time synchronization signal can be used to provide a common time reference for each set of devices, and each signal can be aligned according to the sampling time scale.

[0103] It should be noted that the time alignment accuracy of each signal directly affects the accuracy of the subsequent summation result. If there is a time scale deviation between the signals, even if the protected object is intact, there will be spurious components caused by asynchrony after summation.

[0104] It is understandable that the multiple three-phase current signals acquired in step 301 come from different acquisition sides. The current transformer ratios, polarity directions, and wiring methods of each acquisition side are usually different. If they are directly sent to the differential current forming stage for summation, the summation result will not be zero even if the protected object is intact. Therefore, before entering the differential current forming stage, each signal needs to be standardized through steps 302 to 304 to ensure that it is under the same comparison reference.

[0105] Step 302: Determine the initial conversion factors for at least two acquisition sides, and calculate the positive direction based on the current reference direction and differential current of the acquisition sides, and determine the target conversion factor based on the initial conversion factors.

[0106] The initial conversion factor can be a proportional coefficient determined based on the turns ratio of the current transformers on each acquisition side, used to convert the secondary current of the acquisition side to a unified comparison benchmark. Since the rated current of the primary side of each acquisition side is different, the turns ratio of their current transformers is usually also different. If the secondary current is directly used for summation, even if the primary current is actually balanced, the secondary current will not be equal in value.

[0107] The current reference direction can be the positive current direction agreed upon by each acquisition side during measurement; the positive direction for differential current calculation can be the positive direction uniformly agreed upon when forming the differential current, usually taken as the direction from the outside of the protected object into the inside. The target conversion factor can be the coefficient obtained by adding direction correction to the initial conversion factor.

[0108] As one implementation method, when the current reference direction of a certain acquisition side is consistent with the positive direction of differential current calculation, the initial conversion factor of that acquisition side can be directly used as the target conversion factor; when the current reference direction of a certain acquisition side is opposite to the positive direction of differential current calculation, the initial conversion factor of that acquisition side can be negativeized and used as the target conversion factor.

[0109] Step 303: Based on the phase difference at the acquisition side, perform phase correction on the multiple three-phase current signals to obtain the corrected three-phase current signals.

[0110] The phase difference can be a fixed offset in the current phase introduced by the different wiring methods of the locations of the acquisition sides. For two acquisition sides separated by transformer windings, the wiring group of the transformer windings will cause a fixed phase offset between the currents of the same phase on both sides; if the sum is directly calculated without correction, even if the primary power is balanced, the sum will not be zero.

[0111] As one implementation method, the phase rotation angle to be applied to the protected object can be determined according to the wiring group of the windings on each side, and the corresponding phase rotation can be applied to the three-phase current signal on that side. For the winding side with neutral point grounding, the zero-sequence component in the three-phase current can also be filtered out while rotating the phase, so that the currents participating in the summation on each acquisition side remain consistent in the zero-sequence path.

[0112] It should be noted that phase correction and zero-sequence component processing, like turns ratio conversion and direction correction, are all necessary steps to ensure that the currents on each acquisition side are at the same comparison benchmark. If only turns ratio conversion is performed without phase correction, the unification process is incomplete, and the summation result will still contain fixed spurious components caused by differences in wiring methods.

[0113] Step 304: Based on the target conversion factor and the corrected three-phase current signal, perform correction calculation on the three-phase current signal to obtain the corrected three-phase current signal.

[0114] One implementation method is to multiply the corrected three-phase current signal obtained in step 303 with the target conversion factor obtained in step 302 on the acquisition side to obtain the corrected three-phase current signal.

[0115] For example, a generator motor has two data acquisition sides: the generator terminal side and the neutral point side. The current transformer ratios on both sides are different, and the current reference direction on the neutral point side is opposite to the positive direction of the differential current calculation. Step 302 determines the target conversion coefficients on both sides, with the target conversion coefficient on the neutral point side being negative. Step 303 applies phase corrections to both sides. After multiplication in step 304, under the condition that the protected object is intact and the load is stable, the corrected three-phase currents of the same phase on both sides are nearly equal in amplitude and nearly opposite in phase, and their vector sum is close to zero.

[0116] Therefore, steps 302 to 304 together complete the processing of the first type of cause. After the above-mentioned unification process, the differential current faced by subsequent links no longer contains the fixed component caused by the difference in current transformer parameters, so that the change in differential current can truly reflect the change in the state and operating conditions of the protected object itself.

[0117] Step 305: Perform harmonic decomposition on each three-phase current signal to obtain the component signals corresponding to the three-phase current signals, and fuse the component signals in the same phase to obtain the corresponding differential current signal.

[0118] The differential current signal includes at least the fundamental differential current signal and the second harmonic differential current signal.

[0119] Here, the current sampling sequence in the time domain can be expanded according to frequency components to perform harmonic decomposition. Periodic current waveforms can all be decomposed into a superposition of the power frequency component and several higher harmonic components. The difference in waveform shape after decomposition manifests as a difference in the proportion of each harmonic. The component signal can be the current component corresponding to a specific frequency output by harmonic decomposition, including at least the fundamental component corresponding to the power frequency and the second harmonic component corresponding to twice the power frequency.

[0120] After determining each component signal, the same type of component signals of the same phase on each acquisition side can be vector-summed in the positive direction of differential current calculation to fuse the component signals. Here, the vector summation can simultaneously consider the amplitude and phase of the component signals so that the fused differential current signal reflects the mutual cancellation of the same components on each acquisition side in that phase. After fusion, the fundamental component corresponds to the fundamental differential current signal of that phase, and the second harmonic component corresponds to the second harmonic differential current signal of that phase.

[0121] In one embodiment, harmonic decomposition is performed on multiple three-phase current signals to obtain the component signals of each phase on each acquisition side, including: performing a sliding window discrete Fourier transform on the three-phase current signals of each phase on each acquisition side according to the power frequency cycle, and synchronously outputting the fundamental component and the second harmonic component from the same data window; wherein, the length of the sliding window is one power frequency cycle or half a power frequency cycle.

[0122] Here, the sliding window discrete Fourier transform can be a processing method that performs a discrete Fourier transform on the sampled sequence within a data window of fixed length, and pushes the window forward point by point as new sampling points arrive.

[0123] Using a sliding window approach, a decomposition result can be output at each sampling time, thus ensuring continuity in subsequent judgments. A window length of one power frequency cycle provides strong frequency resolution and good suppression of non-integer harmonics and DC components, but the response speed is relatively slow. A window length of half a power frequency cycle increases the response speed by approximately double, but reduces the resolution of even harmonics. The choice can be made based on different priorities regarding response speed and decomposition accuracy.

[0124] It should be noted that the fundamental component and the second harmonic component are output synchronously from the same data window. If they are taken from different data windows, their corresponding time intervals will be different. During rapid load changes or transient processes, the two quantities do not reflect the current state at the same moment, and the relative relationship calculated accordingly will lose its physical meaning. Synchronous output from the same data window can ensure that the two are strictly corresponding in time and provide data from the same source.

[0125] It should be noted that harmonic decomposition can also be achieved using recursive discrete Fourier transform (DFT) and windowed DFT. The recursive method only performs incremental correction on the result of the previous time step at each sampling time step, which can significantly reduce the amount of computation; the windowed method applies a window function to the data window before the transform, which can suppress spectral leakage caused by window asynchrony.

[0126] Understandably, both the second harmonic component and the fundamental component need to undergo the same fusion process. That is, both are the result of summing the corresponding component vectors from each acquisition side, rather than being derived from a single acquisition side. This is because the subsequent steps determine the waveform composition of the differential current signal itself, not the waveform composition of the current from a single acquisition side. Only when both quantities are fused differential currents are they considered to be on the same scale, and their relative relationship can characterize the proportion of components deviating from a symmetrical sinusoidal shape in the differential current signal. If the second harmonic component from a single acquisition side is compared with the fused fundamental differential current signal, they belong to different physical levels, and the resulting result lacks interpretable physical meaning.

[0127] It should be noted that fusion is performed along the acquisition side direction, that is, across different acquisition sides while maintaining the same phase, with the aim of forming the differential current itself. In addition, after obtaining the differential current signals of each phase, further fusion can be performed along the phase direction, that is, across different phases but targeting the same protected object, with the aim of distinguishing between the overall and single-phase differential currents that have been formed.

[0128] In one implementation, after determining the fundamental differential current signal and the second harmonic differential current signal, the following can be further performed: the target differential current signals of each phase are combined into a three-phase comprehensive differential current, and the maximum value among the target differential current signals of each phase is taken as the maximum phase differential current; if the target differential current signal of any phase is greater than the target differential current threshold, the target anomaly is determined; if the relationship between the three-phase comprehensive differential current and the maximum phase differential current satisfies a preset imbalance criterion, the target anomaly is determined as a single-phase anomaly; if the preset imbalance criterion is not satisfied, the target anomaly is determined as an overall anomaly; and the type of target anomaly is carried in the warning message.

[0129] Among them, the three-phase integrated differential current can be a quantity reflecting the overall differential current level of the protected object, synthesized from the target differential current signals of the three phases; the maximum phase differential current can be the largest value among the target differential current signals of the three phases. The imbalance criterion can be a condition used to determine whether the three-phase differential current distribution is balanced.

[0130] It is understandable that when the three-phase differential current levels are similar, the total three-phase differential current is close to the maximum phase differential current. When only one phase exhibits a significant differential current while the other two phases are essentially normal, the total three-phase differential current will be significantly lower than the maximum phase differential current. Based on this, it can be determined whether the anomaly is concentrated in a single phase or pervades all three phases: the former is commonly seen in scenarios such as single-phase grounding, single-phase current transformer anomalies, and local winding anomalies, while the latter is commonly seen in scenarios such as common three-phase sampling channel drift or overall insulation degradation.

[0131] It should be noted that this implementation adopts a processing sequence of first triggering a single phase and then verifying the three phases. That is, if the target differential current signal of any phase exceeds the judgment threshold, the anomaly judgment process can be initiated, and then the anomaly type is determined based on the three-phase distribution characteristics. The reason for not requiring all three phases to exceed the limit simultaneously before triggering is that the aforementioned single-phase defects often only manifest in a single phase in the early stages of development. If all three phases were required to exceed the limit simultaneously, such defects would be missed.

[0132] As one implementation method, if the anomaly is determined to be a single-phase anomaly, the prompt message can also include the identifier of the phase with the largest differential current, so that operation and maintenance personnel can directly check the current loop corresponding to that phase. If the anomaly is determined to be a systemic anomaly, the message will prompt an inspection of the entire protected object. When multiple phases experience anomalies simultaneously, the order of handling can be determined according to the degree to which the target differential current signal of each phase exceeds the judgment threshold, with the phase with the largest degree of exceedance listed as the priority for investigation.

[0133] Therefore, after step 305, this embodiment has obtained two sets of quantities: one set is the fundamental differential current signal and the second harmonic differential current signal of each phase, which will be used as the input of the inrush suppression path; the other set is the fundamental component of each phase on each acquisition side, which will be used as the input of the dynamic threshold path. The two paths will be described below.

[0134] Step 306: Calculate the ratio of the second harmonic differential current signal to the fundamental differential current signal in the same phase to obtain the proportion of the second harmonic content in the current phase.

[0135] Steps 306 to 308 constitute the first of the two aforementioned pathways, namely the modified pathway for the quantified result, used to address the second type of cause.

[0136] The proportion of second harmonic content can be a dimensionless quantity used to quantify the relative amount of second harmonic components in the differential current signal of that phase. As one implementation method, the proportion can be obtained by dividing the amplitude of the second harmonic differential current signal by the amplitude of the fundamental differential current signal; when the amplitude of the fundamental differential current signal is close to zero, in order to avoid division by zero, a small positive quantity much smaller than the rated current can be added to the denominator.

[0137] It should be noted that this percentage can serve as a criterion for identifying inrush current because the waveforms of inrush current and abnormal currents within the protected object are fundamentally different. When a transformer is switched on, the core enters a deep saturation state due to the combined effect of residual magnetism and the switching phase angle. The excitation current exhibits obvious unipolar bias and discontinuity characteristics, with its waveform significantly deviating from a symmetrical sinusoidal shape. After harmonic decomposition, its second harmonic component accounts for a considerable proportion. In contrast, the current generated by abnormalities such as insulation degradation and inter-turn short circuits within the protected object is a nearly symmetrical power frequency sinusoidal current, with very little second harmonic content after harmonic decomposition. Therefore, the percentage of second harmonic content essentially quantifies the degree of similarity between the current differential current signal and the inrush current in terms of waveform.

[0138] It should be noted that the proportion of second harmonic content is a relative quantity, not an absolute quantity. It can be used to reflect the degree to which the differential current signal deviates from a symmetrical sinusoidal shape, but it does not reflect the absolute magnitude of the differential current signal. The same proportion can correspond to differential currents of different amplitudes. Therefore, this proportion is only used to judge the reliability of the differential current, and cannot be used alone to judge the severity of the anomaly.

[0139] Step 307: Determine the suppression factor of the current phase based on the proportion of the second harmonic content; wherein the suppression factor is inversely proportional to the proportion of the second harmonic content.

[0140] The suppression factor can be a continuous suppression coefficient generated based on the proportion of second harmonic content, and its value can range from zero to one. A value of zero indicates that the differential current signal is not weakened and the original differential current signal participates in the subsequent judgment; a value close to one indicates that the differential current signal is strongly weakened, and the contribution of the differential current signal to the subsequent judgment is greatly reduced.

[0141] In one embodiment, the step of determining the suppression factor of the current phase based on the proportion of second harmonic content includes: setting the suppression factor to zero when the proportion of second harmonic content is less than or equal to a first preset proportion threshold; setting the suppression factor to a target suppression value when the proportion of second harmonic content is greater than the first preset proportion threshold and less than a second preset proportion threshold; wherein the target suppression value is a continuous value that monotonically increases according to the proportion of second harmonic content; and setting the suppression factor to a corresponding upper limit value when the proportion of second harmonic content is greater than or equal to the second preset proportion threshold; wherein the second preset proportion threshold is greater than the first preset proportion threshold.

[0142] Here, the first preset percentage threshold can be the starting threshold for the influence of inrush current. Its value should be higher than the inherent second harmonic background level in the differential current when the equipment is running normally, so as to avoid the differential current under normal operating conditions being weakened by mistake. The second preset percentage threshold can be the threshold when the characteristics of inrush current are sufficiently clear. When the percentage reaches this level, it can be considered that the differential current signal is mainly caused by inrush current.

[0143] It should be noted that this implementation uses a continuous value that monotonically increases with the proportion between the two proportion thresholds, rather than jumping directly from no weakening to complete weakening at a single threshold. The reason for using continuous values ​​is that if a single threshold is used, when the proportion of the second harmonic content fluctuates around that threshold, the judgment result will repeatedly switch between complete acceptance and complete disacceptance, causing frequent fluctuations in the warning state. With a continuous transition, small changes in the proportion only cause small changes in the degree of weakening, and the judgment result evolves smoothly with the operating conditions. In addition, continuous values ​​also ensure that intermediate states with less obvious inrush characteristics are treated commensurate with their level of confidence, rather than being simply categorized into one of the two extremes.

[0144] One implementation method is to use a linearly increasing form for the continuous value between the two percentage thresholds, where the suppression factor increases proportionally from zero to the upper limit between the two thresholds as the percentage increases. Another implementation method is to use a cosine transition, an S-curve, or other forms with gentle ends and a steep middle, to make the weakening degree change more gradually near the two thresholds. All of these forms satisfy the requirement of monotonically increasing and continuous with the percentage, and can be selected according to different requirements for the smoothness of the transition on-site. The specific values ​​of the two percentage thresholds can be determined based on field tests, historical waveform data, and experience in protection setting: if the first preset percentage threshold is too low, normal differential flow will be unnecessarily weakened; if it is too high, the inrush effect cannot be suppressed in time. If the second preset percentage threshold is too low, differential flow containing real abnormal components will be excessively weakened; if it is too high, the weakening under strong inrush conditions will be insufficient.

[0145] Step 308: Calculate the target differential current signal in the current phase based on the fundamental differential current signal and the suppression factor.

[0146] One implementation method is to multiply the fundamental differential current signal by the complement of the suppression factor to obtain the target differential current signal, where the complement is the difference between one and the suppression factor. When the suppression factor is zero, the target differential current signal is equal to the fundamental differential current signal; as the value of the suppression factor increases, the target differential current signal decreases accordingly.

[0147] It should be noted that the correction in this step is a proportional reduction based on the degree of suspicion of the differential current signal, rather than separating and subtracting the inrush current component from the differential current signal. The value of the suppression factor reflects the degree to which the differential current signal is not accepted, and there is no quantitative correspondence between it and the absolute magnitude of the inrush current component in the differential current signal. By using proportional reduction rather than separation and subtraction, the inrush current and the internal abnormal current are superimposed on the same differential current signal at the same time, and cannot be separated in the time domain. However, the difference in their waveform morphology can be quantified as a continuous degree of confidence.

[0148] Regarding the method for determining the upper limit of the inhibition factor after the second harmonic content reaches the second preset threshold, there are two implementation methods. The two methods focus on different objectives, and one method should be chosen during implementation.

[0149] The first implementation method is to set the upper limit value to less than one, so that when the proportion of the second harmonic content is greater than or equal to the second preset proportion threshold, the target differential current signal still increases with the increase of the fundamental differential current signal, so as to retain the ability to identify real anomalies under strong inrush conditions.

[0150] As mentioned above, the suppression factor weakens the differential current signal proportionally. Therefore, when a real anomaly and inrush current occur simultaneously within the protected object, the differential current component contributed by the real anomaly will also be weakened proportionally. If the upper limit is set to one, the target differential current signal will be completely reduced to zero under this condition. No matter how large the differential current caused by the real anomaly is, it will not be able to enter the subsequent judgment, resulting in a missed detection. After setting the upper limit to a value less than one, although the target differential current signal is significantly weakened during strong inrush current, it still maintains a positive correlation with the fundamental differential current signal. Therefore, the differential current caused by the real anomaly, which is significantly higher than the inrush current level, can still cause the target differential current signal to exceed the judgment threshold and be identified.

[0151] The second implementation method is as follows: the upper limit is equal to one; when the proportion of the second harmonic content is greater than or equal to the second preset proportion threshold, the differential current of the phase is determined to be caused by the excitation inrush current, and the output of the prompt information of the phase is blocked, so as to completely avoid false alarms during the period when the inrush current characteristics are clear.

[0152] The inrush current amplitude during transformer closing can be several times the rated current. If some judgment capability is still retained during this period, the risk of false alarm is high. Using a blocking method can ensure that no warning output is generated during this period, and the judgment stability is better.

[0153] Furthermore, in the second implementation method, to reduce the risk of missed detection during the blocking period, after the output of the prompt information for the blocked phase, the second harmonic content ratio and the target differential current signal of the phase can be reacquired after a preset re-judgment period; if the reacquired second harmonic content ratio is less than the second preset ratio threshold and the reacquired target differential current signal is greater than the target differential current threshold, the blocking is released and the prompt information is output; if the above two conditions are not met at the same time, the blocking is maintained.

[0154] The preset re-judgment duration can be the waiting time from the moment the interlock takes effect until the moment of re-judgment. As one implementation method, this duration can be slightly longer than the typical decay time of the inrush current to ensure that the inrush current has basically subsided by the time of re-judgment.

[0155] The purpose of the reassessment mechanism is to distinguish between two scenarios: if the large differential current during the blocking period is indeed caused by inrush current, then as the inrush current decays, the proportion of second harmonic content will fall below the second preset threshold, and the differential current itself will also disappear. In this case, neither condition is met, and the blocking is naturally released without generating an early warning. If there is a real anomaly inside the protected object, then although the proportion of second harmonic content will decrease after the inrush current decays, the differential current will not disappear and will continue to exceed the judgment threshold. In this case, both conditions are met, the blocking is released, and an early warning is output. Thus, the second implementation method, while maintaining the stability of the judgment during strong inrush current, limits the window of missed reports to within the reassessment time, rather than extending it indefinitely.

[0156] It should be noted that the two implementation methods described above are mutually exclusive at the same determination time for the same phase and cannot be used simultaneously: the former aims to retain the identification capability during periods of strong inrush, at the cost of a certain possibility of false alarms during this period; the latter aims to completely eliminate false alarms during periods of strong inrush, at the cost of losing the ability to identify real anomalies within the reassessment time during this period. In implementation, one method can be chosen based on the importance of the protected object, the frequency of closing operations, and the different tolerance levels for false alarms and missed alarms at the site.

[0157] At this point, the inrush suppression pathway is complete, and its output is the target differential current signal for each phase, which is the judgment quantity directly based on subsequent determinations. The second pathway is explained below.

[0158] Step 309: Average the amplitude of the fundamental component of the same phase on each acquisition side to obtain the load current characterization of the current phase.

[0159] Steps 309 to 311 constitute the second of the aforementioned two pathways, namely the modified pathway for determining the threshold, which is used to handle the third type of cause.

[0160] Among them, the load current characterization quantity can be the arithmetic mean of the fundamental component amplitude of the same phase on each acquisition side, which is used to reflect the current load level borne by the protected object.

[0161] It should be noted that this step uses amplitude averaging, while step 305 uses vector summation. Although both use the fundamental component as input, their physical meanings are completely different. Vector summation yields the residual current after the currents on each acquisition side cancel each other out, i.e., differential current, which characterizes the degree of anomaly. Amplitude averaging yields the overall current level on each acquisition side, i.e., load, which characterizes the operating condition. The former is used to answer whether there is an anomaly in the protected object, while the latter is used to answer the extent to which the current measurement results at the current moment can be accepted.

[0162] It should be noted that the load current characterization is based on the average amplitude of all acquisition sides, rather than the amplitude of a single acquisition side, to avoid distortion of the operating condition judgment due to measurement anomalies on a single acquisition side. By averaging, the impact of anomalies on a single acquisition side on the load current characterization is diluted, thus improving the robustness of the operating condition judgment.

[0163] One approach is to calculate the load current characteristics for each phase separately, with each phase's determination using a threshold modified by its own load current characteristics. Another approach is to synthesize a three-phase composite load current characteristic after obtaining the load current characteristics for each phase, with the determination of all three phases using the same threshold modified by this composite value. The former approach is more adaptable to situations where the loads are unbalanced in each phase, while the latter approach reduces computational complexity and maintains consistent determination thresholds for three-phase loads when they are basically balanced. Both approaches are viable.

[0164] Step 310: Within a preset time window, calculate the dispersion of the load current characterization quantity to obtain the load fluctuation quantity, and calculate the ratio of the change in the load current characterization quantity at adjacent times to the time interval to obtain the load change rate.

[0165] The time window can be an observation interval of a fixed length that traces back from the current moment, and its length should be able to cover the duration of the typical operating condition switching process.

[0166] The dispersion measure can be used to assess the degree of dispersion of load current values ​​within a given time window. One implementation method is to use the standard deviation of the load current within the window; another method is to use the variance, mean absolute deviation, or the range (the difference between the maximum and minimum values ​​within the window). Although these quantities are calculated differently, they all reflect the degree of load fluctuation within the window and can all be used as implementation methods for this step. Among them, the standard deviation responds to fluctuations throughout the entire window, providing a more comprehensive reflection; the range requires the least computation and is most sensitive to single drastic jumps within the window, making it suitable for situations with limited computational resources.

[0167] It should be noted that load fluctuation and load change rate reflect two different aspects of load variation: load fluctuation reflects the overall instability of the load over a period of time, and is sensitive to continuous and repeated fluctuations, corresponding to the operating conditions where the unit repeatedly adjusts its output; load change rate reflects the instantaneous speed of load change at the current moment, and is sensitive to single, sudden jumps, corresponding to the instant of operating condition switching or sudden load changes. Together, they constitute a complete description of the current operating conditions; the absence of either one will result in a type of operating condition not being covered.

[0168] Step 311: Calculate the basic differential current threshold, the first correction term which is positively correlated with the load current characterization, the second correction term which is positively correlated with the load fluctuation, and the third correction term which is positively correlated with the load change rate to obtain the target differential current threshold.

[0169] As one implementation method, the basic differential current threshold can be summed with the three correction terms mentioned above to obtain the target differential current threshold.

[0170] The basic differential current threshold can be the minimum judgment threshold allowed under stable and low load conditions, and its value should be higher than the inherent differential current background level during normal operation of the equipment. The first correction term is positively correlated with the load current characterization quantity, and its function is to compensate for the inherent characteristic that the measurement error of the current transformer increases with the increase of the primary current; the second correction term is positively correlated with the load fluctuation quantity, and its function is to raise the threshold during periods of repeated load fluctuations; the third correction term is positively correlated with the load change rate, and its function is to raise the threshold at the moment when the load changes rapidly.

[0171] It should be noted that the load change rate corresponding to the third correction term is a ratio of current to time, which is different from the current dimension of the basic differential current threshold and the first two correction terms. Therefore, the coefficient multiplied by the load change rate to form the third correction term should itself have a time dimension, so that the third correction term maintains dimensional consistency with the other terms after summation. Similarly, the coefficients multiplied by the load current and the load fluctuation are dimensionless coefficients. The specific values ​​of the above coefficients can be adjusted based on historical operating data and operating condition statistics.

[0172] It should be noted that all three correction terms are positively correlated with the corresponding operating conditions. Their common effect is to automatically raise or lower the judgment threshold according to the severity of the operating conditions: during steady-state periods with stable loads, all three correction terms are relatively small, and the judgment threshold falls back to a level close to the basic differential current threshold, thereby maintaining sensitivity to small differential currents corresponding to early defects; during periods of unit start-up and shutdown, operating condition switching, or sudden load changes, the corresponding correction terms increase, and the judgment threshold automatically rises, thereby accommodating unavoidable measurement errors during these periods.

[0173] At this point, the dynamic thresholding process is complete, and its output is the target differential threshold, which is the threshold used for the determination. The outputs of the two paths are combined in the following steps.

[0174] Step 312: Calculate the differential current change rate of the target differential current signal.

[0175] The differential current change rate can be the speed at which the target differential current signal changes over time, reflecting the rate of anomaly development. One implementation method is to take the maximum value of the target differential current signal's change rate between adjacent sampling times within a set decision window as the differential current change rate.

[0176] It should be noted that the maximum value within the judgment window is used here, rather than directly taking the rate of change between two adjacent sampling times. The reason is that anomalies within the protected object often experience a rapid increase in differential current during their development, followed by a stabilization at a higher level. If the rate of change between two adjacent sampling times is directly taken, the change between the two points approaches zero once the differential current has stabilized at a high level, resulting in a rate of change that also approaches zero and fails to reflect the rapid development process the anomaly previously underwent. By taking the maximum value within the judgment window, as long as a rapid increase has occurred within that window, the rate of change in differential current remains at a high level, thus ensuring that rapidly developing anomalies can still be correctly classified after their differential current stabilizes.

[0177] The target rate of change threshold can be used to determine whether the differential current development speed is significant. It should be noted that the reason for dynamically adjusting the rate of change threshold is the same as that for dynamically adjusting the differential current threshold: when the load changes rapidly, the spurious differential current caused by the asynchronous transient response of each acquisition side also has a relatively fast rate of change. If the rate of change threshold remains fixed, the spurious differential current under such conditions will be misjudged as a rapidly developing anomaly.

[0178] Step 313: If the target differential current signal is greater than the target differential current threshold, determine that there is a target anomaly and output the corresponding prompt information.

[0179] It is understood that the inrush current suppression path has weakened the differential current caused by the second type of cause according to the significance of its inrush characteristics, the dynamic threshold path has accommodated the spurious differential current caused by the third type of cause by correspondingly raising the threshold, and the spurious differential current caused by the first type of cause has been eliminated in steps 302 to 304. Therefore, the differential current that can still cause the target differential current signal to exceed the target differential current threshold in this step points to a real anomaly inside the protected object. Since the two paths each handle one type of cause independently, under the condition that excitation inrush current and severe load fluctuations occur simultaneously or alternately, the two types of interference can still be handled separately, and there will be no situation where the processing effect of one type of interference is canceled out by the other type of interference.

[0180] In one embodiment, when the target differential current signal is greater than the target differential current threshold, a target anomaly is determined and a corresponding prompt message is output, including: counting the duration for which the target differential current signal is continuously greater than the target differential current threshold; when the duration reaches a preset duration threshold, a target anomaly is determined and a prompt message is output; when the duration does not reach the preset duration threshold, no prompt message is output.

[0181] The preset duration threshold can be used as a time threshold to filter transient disturbances. It should be noted that setting the duration condition serves to filter out short-term disturbances such as sampling spikes, communication interference, and transient impacts caused by switching operations. While such disturbances may cause the target differential current signal to exceed the judgment threshold at individual sampling moments, they are not persistent; however, once a real defect forms within the protected object, the resulting differential current will persist. Therefore, requiring the over-limit state to persist for a certain duration before issuing a warning can significantly reduce false alarms caused by transient disturbances without raising the judgment threshold.

[0182] In another implementation, the cumulative duration for which the target differential current signal exceeds the target differential current threshold within a set statistical period can be used instead of the duration of continuous exceedance of the target differential current threshold, and compared with the preset duration threshold. It should be noted that the two statistical methods are applicable to different situations: the continuous duration method has stronger anti-interference capabilities, but for intermittent anomalies where the differential current repeatedly crosses the threshold, it may be missed because each exceedance does not meet the duration requirement; the cumulative duration method can capture such intermittent anomalies, but its ability to suppress recurring short-term disturbances is relatively weak. One method can be selected based on the operating environment and interference level of the protected object, or both conditions can be set simultaneously, with an output prompt message when either condition is met.

[0183] After confirming the existence of a target anomaly, the level of the alert message can be further determined based on the anomaly's development speed and the degree of exceeding the limits.

[0184] In one embodiment, the step of determining the existence of a target anomaly and outputting a corresponding prompt message when the target differential current signal is greater than the target differential current threshold includes: when the target differential current signal is greater than the target differential current threshold and the differential current change rate is greater than the target change rate threshold, determining the target anomaly as a first level and outputting a prompt message corresponding to the first level; when the target differential current signal is greater than the target differential current threshold and the differential current change rate is less than or equal to the target change rate threshold, determining the target anomaly as a second level and outputting a prompt message corresponding to the second level; wherein the second level is lower than the first level.

[0185] It should be noted that the differential current change rate is used as a basis for grade classification in this embodiment, rather than as a necessary condition for triggering an early warning. The reason for not setting an excessive differential current change rate as a necessary condition for triggering an early warning is that a significant portion of the early defects to be detected in this embodiment are of the slowly developing type, such as a slow increase in the contact resistance of the current transformer secondary circuit, slow deterioration of the winding insulation, and slow zero-point drift of the sampling channel. The differential current rise caused by these defects is extremely gradual, and their differential current change rate remains at a low level. If setting an excessive differential current change rate as a necessary condition, such defects will not trigger an early warning, which is precisely what this embodiment needs to detect. After reducing the differential current change rate to a grade classification basis, slowly developing anomalies can still be reported at a lower level for operation and maintenance personnel to arrange observation and review; rapidly developing anomalies are reported at a higher level, prompting priority handling.

[0186] In one embodiment, outputting corresponding prompt information includes: calculating the ratio of the target differential current signal to the target differential current threshold to obtain the differential current over-limit multiple; comparing the differential current over-limit multiple with at least one preset grading threshold; determining the level of the prompt information based on the comparison result; and pushing the prompt information according to the level.

[0187] It should be noted that the over-limit multiple, rather than the absolute value of the differential current, is used as the grading basis because the judgment threshold itself changes dynamically with the operating conditions. The severity of the anomaly corresponding to the same absolute value of differential current varies under different operating conditions. Measuring by a multiple relative to the current threshold ensures that the grading results remain comparable across various operating conditions. As one implementation method, two preset grading thresholds can be set to divide the over-limit multiple into three intervals: when the over-limit multiple is in the lowest interval and the duration meets the requirements, it can be identified as a slight differential current anomaly trend, prompting inclusion in observation; when the over-limit multiple is in the middle interval, it can be identified as a significant anomaly trend, prompting inspection or re-verification of waveform recordings; when the over-limit multiple is in the highest interval, it can be identified as a rapidly developing anomaly, prompting priority handling.

[0188] In one embodiment, the method further includes: weighting and summing the ratio of the target differential current signal to the target differential current threshold and the ratio of the differential current change rate to the target change rate threshold according to preset weights to obtain an anomaly severity score; comparing the anomaly severity score with at least one preset score threshold, determining the level of the prompting information based on the comparison result, and pushing the prompting information according to the level.

[0189] It should be noted that the weighted summation score used for grading differs from grading solely based on the exceedance multiple in that it also considers the anomaly's development rate. For anomalies with relatively low exceedance multiples but rapid development, grading based solely on the exceedance multiple would place them in a lower category, while incorporating the rate of change could elevate them to a higher category, thus attracting attention earlier. The values ​​of these two weights can be determined based on the relative importance placed on amplitude and development rate on-site.

[0190] As one implementation method, pushing notifications according to different levels can include: for the lowest level, the notification is recorded in the operation log and displayed as an alert on the monitoring screen without triggering an alarm; for the intermediate level, the notification is pushed to the work terminals of operation and maintenance personnel, along with the phase of the anomaly and suggested troubleshooting directions; for the highest level, in addition to pushing to work terminals, it can also be pushed simultaneously to the mobile terminals of on-duty personnel, triggering audible and visual alarms, and automatically retrieving waveform data for that period for analysis. It should be noted that using different push methods according to different levels can prevent low-level observational information from overshadowing high-level urgent information, ensuring that the attention of operation and maintenance personnel matches the urgency of the anomaly.

[0191] Step 314: If the target differential current signal is less than or equal to the target differential current threshold, it is determined that there is no target anomaly.

[0192] As one implementation method, if it is determined that there is no target anomaly, no prompt information can be output, and the above steps can be repeated for the current signal at the next sampling time, thereby forming continuous online monitoring.

[0193] To better illustrate the technical solution of this embodiment, an exemplary description is provided below. In an exemplary embodiment, a differential current anomaly early warning method is provided, which can be applied to the diagnosis of potential neutral line breakage in the secondary circuit of the CT of the protected objects such as the main transformer and generator motor in a pumped storage power station.

[0194] In one exemplary embodiment, a differential current anomaly early warning method is provided, which can be applied to differential current anomaly early warning scenarios for protected objects such as generator motors and main transformers in pumped storage power stations.

[0195] First, multiple current acquisition sides are set up within the protection range of the protected object, such as the generator terminal side, neutral point side, main transformer high-voltage side, or other current acquisition locations related to the protection range. The three-phase currents of the m-th acquisition side are acquired separately to obtain i_mA(t), i_mB(t), and i_mC(t), where the subscripts A, B, and C represent the three phases, and ph is used to uniformly represent any one of the phases.

[0196] To ensure that the currents of each acquisition side are at the same comparison benchmark, the currents of each acquisition side are first uniformly converted based on the current transformer ratio, wiring method, polarity direction, and phase relationship. The converted current of the m-th acquisition side at the ph-th sampling time is:

[0197] I'_m,ph(k)=σ_m×K_CT,m×i_m,ph(k);

[0198] Where K_CT,m is the current transformer ratio conversion factor for the m-th acquisition side, and σ_m is the current direction correction factor for that acquisition side. When the current reference direction of a certain acquisition side is opposite to the positive direction of the differential current calculation, σ_m takes a negative value; when the directions are the same, it takes a positive value. For acquisition sides separated by transformer windings, before applying the above formula, the phase of the three-phase current should be rotated according to the phase offset corresponding to the winding connection group of that side, and the zero-sequence component should be filtered out on the neutral grounding side to ensure that the currents of each acquisition side are consistent in phase relationship and zero-sequence path.

[0199] After unified conversion, harmonic filtering is performed on the converted three-phase current to extract the fundamental and second harmonic components. This example preferably uses the sliding full-cycle discrete Fourier transform algorithm, which can stably extract the fundamental component within one power frequency cycle and simultaneously obtain the second harmonic component, providing consistent data for subsequent inrush current identification. The fundamental and second harmonic phasors of the m-th acquisition side at the k-th sampling time are as follows:

[0200] I_1,m,ph(k)=(√2 / N)×Σ_{r=0}^{N-1}I'_m,ph(kr)×exp(-j2πr / N);

[0201] I_2,m,ph(k)=(√2 / N)×Σ_{r=0}^{N-1}I'_m,ph(kr)×exp(-j4πr / N);

[0202] Where N is the number of sampling points within one power frequency cycle. If it is necessary to improve the response speed, a half-cycle sliding window, recursive discrete Fourier transform, or windowed discrete Fourier transform can be used as equivalent alternatives, but the core is still to extract the fundamental phasor and the second harmonic phasor.

[0203] After obtaining the fundamental phasor of each acquisition side, this example does not judge the current of each acquisition side in isolation, but instead performs vector summation on the fundamental current of the same phase on different acquisition sides to obtain the differential current of each phase:

[0204] I_d,A(k)=|Σ_mI_1,m,A(k)|;

[0205] I_d,B(k)=|Σ_mI_1,m,B(k)|;

[0206] I_d,C(k)=|Σ_mI_1,m,C(k)|;

[0207] The above processing reflects the organic combination of the three-phase current signals from each acquisition side: the currents from multiple acquisition sides of the same phase are used to form a differential relationship, which can reflect whether the currents inside and outside the protection range are balanced; different acquisition sides only participate in the summation after the transformation ratio, direction and phase are unified, thereby avoiding false differential current caused by the difference in current transformer parameters.

[0208] For the same protected object, the differential currents of the three phases are not only retained separately for single-phase anomaly identification, but can also be further used to form the effective value of the three-phase comprehensive differential current and the maximum phase difference current, which is used to take into account both overall anomalies and single-phase anomalies:

[0209] I_D(k)=√[(I_d,A(k)²+I_d,B(k)²+I_d,C(k)²) / 3];

[0210] I_D,max(k)=max(I_d,A(k),I_d,B(k),I_d,C(k));

[0211] Wherein, I_D(k) is used to characterize the overall differential current anomaly degree of the protected object, and I_D,max(k) is used to capture unbalanced scenarios such as single-phase grounding, single-phase current transformer anomaly, and local winding anomaly. In actual judgment, a combination of single-phase triggering and three-phase comprehensive verification can be adopted. That is, if the differential current of any phase meets the condition, the early warning judgment can be initiated. At the same time, the type of anomaly and the overall severity are evaluated by the relationship between I_D(k) and I_D,max(k). It should be noted that, in order to keep this combined quantity from the same source as the quantity on which the subsequent judgment is based, in actual implementation, the above two combined quantities can also be constructed using the differential current of each phase after inrush current suppression.

[0212] In terms of inrush current identification, this example introduces an inrush current suppression factor, which is a continuous suppression coefficient generated based on the proportion of second harmonic content in the differential current signal. This factor is used to weaken the impact of inrush current on the differential current anomaly warning criteria. This factor is denoted as η_ph(k), and its value ranges from zero to one. When η_ph(k) is close to zero, it indicates that the inrush current characteristics in the differential current are not obvious, and the algorithm basically preserves the differential current. When η_ph(k) is close to one, it indicates that there are obvious inrush current characteristics in the differential current, and the algorithm strongly suppresses or blocks the differential current.

[0213] Based on the fundamental and second harmonic phasors obtained by the aforementioned sliding discrete Fourier transform, the fundamental and second harmonic differential currents for each phase are calculated separately:

[0214] I_d1,ph(k)=|Σ_mI_1,m,ph(k)|;

[0215] I_d2,ph(k)=|Σ_mI_2,m,ph(k)|;

[0216] Then calculate the proportion of the second harmonic content:

[0217] H_2,ph(k)=I_d2,ph(k) / (I_d1,ph(k)+ε);

[0218] Where ε is a small quantity to prevent the denominator from being zero. A larger H_2,ph(k) indicates a more significant second harmonic component in the phase differential current, and a higher possibility of inrush current. It should be particularly noted that the numerator and denominator in the above formula are both differential currents obtained after summing the vectors of the same-name components at each collection side, and the two are of the same source and same caliber, so that their ratio can characterize the degree to which the waveform of the differential current itself deviates from a symmetrical sine wave.

[0219] This example does not adopt simple second harmonic fixed-value blocking, but generates an inrush current suppression factor through a piecewise continuous function:

[0220] When H_2,ph(k)≤H_low, η_ph(k)=0;

[0221] When H_low<H_2,ph(k)<H_high, η_ph(k)=(H_2,ph(k)-H_low) / (H_high-H_low);

[0222] When H_2,ph(k)≥H_high, η_ph(k)=η_max;

[0223] Where H_low is the starting threshold of inrush current influence, H_high is the strong inrush current suppression or blocking threshold, and η_max is the upper limit of the suppression factor. H_low and H_high can be determined according to field tests, historical recorded waveforms and protection setting experience. In addition to the above-mentioned linear increasing form, the intermediate section can also adopt forms such as cosine transition or S-shaped curve, as long as it satisfies monotonic increase and continuity with H_2,ph(k) in this section.

[0224] The inrush current suppression factor acts on the fundamental differential current to obtain the target differential current after weakening the inrush current influence:

[0225] I_pure,ph(k)=I_d1,ph(k)×(1-η_ph(k));

[0226] When H_2,ph(k) is lower than H_low, η_ph(k) is zero and I_pure,ph(k) is equal to the fundamental differential current; when H_2,ph(k) is between H_low and H_high, the algorithm weakens the differential current proportionally; when H_2,ph(k) is higher than H_high, the suppression factor takes the upper limit value η_max.

[0227] Regarding the selection of the upper limit value η_max, there are two possible implementation methods. In the first implementation, η_max is a value less than one, such as 0.9 or 0.95. In this case, even during periods of strong inrush, I_pure,ph(k) remains positively correlated with I_d1,ph(k). The differential current caused by the actual anomaly within the protected object, which is significantly higher than the inrush level, can still cause I_pure,ph(k) to exceed the judgment threshold, thereby avoiding complete false negatives when anomalies and inrushes coexist. In the second implementation, η_max is set to one. In this case, I_pure,ph(k) is always zero, and the contribution of the differential current of this phase to the early warning judgment is suppressed to zero, entering the inrush blocking state. To reduce the risk of false negatives under this method, after the blocking takes effect, after a review period T_recheck, H_2,ph and I_pure,ph are recalculated. If H_2,ph has fallen below H_high and I_pure,ph is still greater than the judgment threshold, the blocking is released and an early warning is output; otherwise, the blocking is maintained. The two implementation methods described above are mutually exclusive at the same determination time of the same phase, and one of them should be chosen for implementation.

[0228] Regarding dynamic thresholds, pumped storage power stations operate under various scenarios, including power generation, pumping, phase adjustment, start-up and shutdown, and mode switching, resulting in rapid changes in load current. To avoid insensitivity to low load conditions or false alarms under high load conditions caused by fixed thresholds, this example correlates the threshold with the load current and its fluctuation characteristics. The load current characteristics for each phase and the three-phase combined load current characteristics are as follows:

[0229] I_L,ph(k)=(1 / M)×Σ_m|I_1,m,ph(k)|;

[0230] I_L(k)=√[(I_L,A(k)²+I_L,B(k)²+I_L,C(k)²) / 3];

[0231] Where M represents the number of current acquisition sides. It should be noted that the arithmetic mean of the fundamental component amplitude is used for each acquisition side, which differs from the vector summation used when forming the differential current. The former reflects the overall load level, while the latter reflects the current imbalance. In cases where the three-phase load is basically balanced, I_L(k) can be used to uniformly correct the three-phase judgment threshold; in cases where there is a significant imbalance in the load of each phase, I_L,ph(k) can be used to directly correct the judgment threshold of each phase.

[0232] The standard deviation of the load current is calculated within the sliding time window W to characterize the degree of load fluctuation, and the rate of change of the load current is also calculated.

[0233] σ_L(k)=√[(1 / W)×Σ_{r=0}^{W-1}(I_L(kr)-mean(I_L))²];

[0234] G_L(k)=|I_L(k)-I_L(k-1)| / Δt;

[0235] σ_L(k) can also be replaced by other discrete quantities such as variance, mean absolute deviation, or range within the window.

[0236] Differential current warning thresholds are dynamically adjusted as follows:

[0237] I_set(k)=I_0+α×I_L(k)+β×σ_L(k)+γ×G_L(k);

[0238] Where I_0 is the basic start-up threshold, α is the load ratio correction coefficient, β is the load fluctuation correction coefficient, and γ is the load rapid change correction coefficient. It should be noted that I_0, I_L(k), and σ_L(k) are all in the dimension of current, while G_L(k) is in the dimension of the ratio of current to time. Therefore, α and β are dimensionless coefficients, while γ should have the dimension of time to ensure that the dimensions of all terms in the above formula are consistent after summation. This formula ensures that the threshold maintains high sensitivity under steady-state low load conditions and automatically improves its disturbance rejection capability during load fluctuations or operating condition changes.

[0239] The differential flow rate threshold can be dynamically adjusted synchronously.

[0240] R_set(k) = R_0 + μ × G_L(k);

[0241] Here, R_0 is the basic rate of change threshold, and μ is the load change rate correction coefficient, which also has corresponding dimensions. This threshold is used to distinguish between rapid growth in differential flow caused by real anomalies and short-term disturbances caused by load switching.

[0242] In the judgment phase, the differential flow change rate is calculated based on the target differential flow. To ensure that this quantity reflects the previous development process of the anomaly, the maximum value of the change rate at adjacent sampling times is taken within the set judgment window:

[0243] R_D,ph(k)=max_{kL <i≤k}{|I_pure,ph(i)-I_pure,ph(i-1)| / Δt};

[0244] Where L is the number of sampling points included in the judgment window. It should be noted that if the rate of change between two adjacent sampling times is taken directly, when the differential current has risen to a high level and tends to stabilize, this amount will fall back to near zero, and cannot reflect the previous rapid rise process; taking the maximum value within the window can avoid this problem, so that anomalies of the rapid development type can still be correctly classified after their differential current stabilizes.

[0245] The basic triggering condition is as follows: For any phase ph, when I_pure,ph(k) is greater than I_set(k), and the duration T_continue of the out-of-limit state reaches the duration threshold T_set, the phase is considered to enter an abnormal warning state. T_continue can be taken as the duration for which the amplitude condition is continuously met, or as the duration for which the amplitude condition is met cumulatively within a set statistical period. The former has a stronger ability to resist instantaneous disturbances, while the latter has a stronger ability to capture intermittent anomalies. Setting the duration condition can filter sampling spikes, short-term disturbances, and transient errors.

[0246] It should be noted that this example does not set R_D,ph(k) being greater than R_set(k) as a necessary condition for triggering an early warning, but rather uses it as a basis for classifying the anomaly type and level. The reason is that the differential current rise caused by early defects such as deterioration of the secondary circuit contact of the current transformer, slow aging of the winding insulation, and zero-point drift of the sampling channel is extremely gradual, and its differential current change rate is consistently low. If exceeding the change rate limit is set as a necessary condition, such defects will not be detected by early warning, and these defects are precisely the objects that this scheme most needs to detect. Accordingly, when I_pure,ph(k) is greater than I_set(k) and R_D,ph(k) is greater than R_set(k), it is judged as a rapidly developing anomaly and a higher-level early warning is given; when I_pure,ph(k) is greater than I_set(k) but R_D,ph(k) is not greater than R_set(k), it is judged as a slowly developing anomaly and a lower-level observation-type early warning is given.

[0247] It should be noted that this example does not separately set the condition that H_2,ph(k) is less than H_high in the basic triggering conditions. The reason is that the influence of the inrush current on the judgment is already reflected in I_pure,ph(k) through the suppression factor. If a separate second harmonic setpoint threshold were set, this threshold would override the aforementioned piecewise continuous suppression effect, causing the continuous suppression to degenerate into a setpoint lockout, which contradicts the original intention of using continuous suppression in this example. In cases where a lockout method is required, it can be achieved by setting η_max to one, without the need for a separate independent condition.

[0248] Regarding severity grading, in order to generate graded early warning information that can be used for operation and maintenance, the differential current over-limit multiple is calculated:

[0249] S_ph(k)=I_pure,ph(k) / I_set(k);

[0250] A comprehensive score can also be constructed by combining the rate of change:

[0251] Score_ph(k)=w_1×I_pure,ph(k) / I_set(k)+w_2×R_D,ph(k) / R_set(k);

[0252] Where w_1 and w_2 are preset weights. The warning level can be determined as follows: when S_ph(k) is between S_1 and S_2 and the duration reaches T_set, it is judged as a level 1 warning, indicating that there is a slight differential current abnormality trend, which can be included in the observation; when S_ph(k) is between S_1 and S_2, or when Score_ph(k) reaches the level 2 threshold, it is judged as a level 2 warning, indicating that the abnormal trend is obvious, and inspection or review of waveform recording should be arranged; when S_ph(k) is not less than S_2, or when the differential current amplitude, rate of change and duration all significantly exceed the limits, it is judged as a level 3 warning, indicating that the abnormality is developing rapidly and should be dealt with first.

[0253] Regarding the push notification of early warning information, different push methods can be adopted according to the above levels: Level 1 early warnings are only recorded in the operation log and displayed as a prompt on the monitoring screen; Level 2 early warnings are pushed to the work terminals of operation and maintenance personnel, along with the phase identifier of the anomaly and suggested troubleshooting directions; Level 3 early warnings are pushed to the work terminals and simultaneously to the mobile terminals of on-duty personnel, triggering audible and visual alarms, and automatically retrieving waveform data for that period for analysis. In the event of multiple phases experiencing anomalies simultaneously, the order of handling can be determined according to the magnitude of S_ph(k) for each phase.

[0254] In the above exemplary description, spurious differential currents caused by differences in the parameters of current transformers on each acquisition side are eliminated before they form due to unified conversion of the ratio, direction, and phase. Differential currents caused by inrush currents are identified by their second harmonic enrichment characteristics in frequency composition and are continuously weakened according to their significance. False differential currents caused by severe load fluctuations, which are indistinguishable from true differential currents in frequency composition, are accommodated through dynamic correction of the judgment threshold based on load level, load fluctuation amount, and load change rate. These three types of interference are treated using elimination, weakening, and accommodation methods according to their identifiability. Differential currents that still exceed the threshold and persist after processing are judged as true anomalies within the protected object and are graded and warned according to severity.

[0255] It should be understood that although the steps in the flowcharts of the above embodiments are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the above embodiments may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages in other steps. It is understood that the steps in different embodiments can be freely combined as needed, and all non-contradictory solutions formed by such combinations are within the scope of protection of this application.

[0256] In other embodiments, this application proposes a differential current anomaly early warning device, please refer to... Figure 3 The differential current anomaly early warning device includes: an acquisition module, a differential current calculation module, a differential current correction module, a threshold correction module, and an anomaly determination module, wherein:

[0257] The acquisition module is used to acquire multiple three-phase current signals from at least two acquisition sides;

[0258] The differential current calculation module is used to perform harmonic decomposition on each three-phase current signal to obtain the component signals corresponding to the multiple three-phase current signals, and to fuse the component signals in the same phase to obtain the corresponding differential current signal; wherein, the differential current signal includes at least the fundamental differential current signal and the second harmonic differential current signal;

[0259] The differential current correction module is used to determine the suppression factor based on the relative relationship between the fundamental differential current signal and the second harmonic differential current signal, and to correct the differential current signal based on the suppression factor to obtain the target differential current signal.

[0260] The threshold correction module is used to determine the variation characteristics of the load current characterization quantity based on the component signal, and to correct the basic differential current threshold according to the variation characteristics to obtain the target differential current threshold.

[0261] The anomaly determination module is used to compare the target differential current signal with the target differential current threshold to obtain target anomaly information, and output corresponding prompt information based on the target anomaly information.

[0262] In one exemplary embodiment, the acquisition module further includes a conversion unit, which is used to determine initial conversion coefficients for at least two acquisition sides, and determine target conversion coefficients based on the current reference direction of the acquisition side and the positive direction of differential current calculation according to the initial conversion coefficients; perform phase correction on multiple three-phase current signals based on the phase difference of the acquisition sides to obtain corrected three-phase current signals; and perform correction calculation on the three-phase current signals based on the target conversion coefficients and the corrected three-phase current signals to obtain corrected three-phase current signals.

[0263] In one exemplary embodiment, the differential flow correction module includes a percentage calculation unit, a factor generation unit, and a differential flow correction unit, wherein:

[0264] The proportion calculation unit is used to calculate the ratio of the second harmonic differential current signal to the fundamental differential current signal in the same phase, so as to obtain the proportion of the second harmonic content in the current phase.

[0265] The factor generation unit is used to determine the suppression factor of the current phase based on the proportion of the second harmonic content, wherein the suppression factor does not decrease as the proportion of the second harmonic content increases;

[0266] The differential current correction unit is used to calculate the target differential current signal in the current phase based on the fundamental differential current signal and the suppression factor.

[0267] In one exemplary embodiment, the threshold correction module includes a characterization calculation unit, a change feature calculation unit, and a threshold generation unit, wherein:

[0268] The characterization calculation unit is used to average the amplitude of the fundamental component of the same phase on each acquisition side to obtain the load current characterization of the current phase.

[0269] The variation characteristic calculation unit is used to calculate the dispersion of the load current characterization quantity within a preset time window to obtain the load fluctuation quantity, and to calculate the ratio of the change of the load current characterization quantity at adjacent times to the time interval to obtain the load change rate.

[0270] The threshold generation unit is used to calculate the target differential current threshold by combining the basic differential current threshold with a first correction term that is positively correlated with the load current characterization, a second correction term that is positively correlated with the load fluctuation, and a third correction term that is positively correlated with the load change rate.

[0271] In one exemplary embodiment, the anomaly determination module includes a rate of change calculation unit, a level determination unit, and an information push unit, wherein:

[0272] The rate of change calculation unit is used to calculate the differential rate of change of the target differential current signal, and to calculate the target rate of change threshold based on the basic rate of change threshold and the load rate of change.

[0273] The level determination unit is used to determine the target anomaly as the first level when the target differential current signal is greater than the target differential current threshold and the differential current change rate is greater than the target change rate threshold; and to determine the target anomaly as the second level when the target differential current signal is greater than the target differential current threshold and the differential current change rate is less than or equal to the target change rate threshold.

[0274] The information push unit is used to output corresponding prompts according to the level of the target anomaly.

[0275] In one exemplary embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 4 As shown, the computer device includes a processor, memory, input / output interfaces, a communication interface, a display unit, and an input device. The processor, memory, and input / output interfaces are connected via a system bus, and the communication interface, display unit, and input device are also connected to the system bus via the input / output interfaces. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The input / output interfaces are used for exchanging information between the processor and external devices. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, mobile cellular networks, Near Field Communication (NFC), or other technologies. When executed by the processor, the computer program implements a differential current anomaly early warning method. The display unit is used to form a visually visible image and can be a display screen, a projection device, or a virtual reality imaging device. The display screen can be an LCD screen or an e-ink screen. The input device of the computer device can be a touch layer covering the display screen, or buttons, trackballs, or touchpads set on the casing of the computer device, or external keyboards, touchpads, or mice, etc.

[0276] Those skilled in the art will understand that Figure 4The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0277] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, artificial intelligence (AI) processors, etc., and are not limited to these.

[0278] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0279] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A differential current anomaly early warning method, characterized in that, The method includes: Acquire multiple three-phase current signals from at least two acquisition sides; Harmonic decomposition is performed on each of the three-phase current signals to obtain the component signals corresponding to the three-phase current signals, and the component signals in the same phase are fused to obtain the corresponding differential current signal; wherein, the differential current signal includes at least the fundamental differential current signal and the second harmonic differential current signal; Based on the relative relationship between the fundamental differential current signal and the second harmonic differential current signal, a suppression factor is determined, and the differential current signal is corrected based on the suppression factor to obtain the target differential current signal. The load current characterization parameters are determined based on the component signals, and the basic differential current threshold is corrected based on the change characteristics to obtain the target differential current threshold. The differential current change rate of the target differential current signal is compared with the target differential current threshold to obtain target anomaly information, and corresponding prompt information is output based on the target anomaly information.

2. The method according to claim 1, characterized in that, After the step of acquiring multiple three-phase current signals from at least two acquisition sides, the method further includes: Determine initial conversion factors for at least two of the acquisition sides, and determine target conversion factors based on the current reference direction and differential current calculation positive direction of the acquisition sides, according to the initial conversion factors; Based on the phase difference at the acquisition side, the phase of the multiple three-phase current signals is corrected to obtain the corrected three-phase current signals; Based on the target conversion factor and the corrected three-phase current signal, the three-phase current signal is corrected and calculated to obtain the corrected three-phase current signal.

3. The method according to claim 1, characterized in that, The steps of determining a suppression factor based on the relative relationship between the fundamental differential current signal and the second harmonic differential current signal, and correcting the differential current signal based on the suppression factor to obtain the target differential current signal include: Calculate the ratio of the second harmonic differential current signal to the fundamental differential current signal in the same phase to obtain the proportion of the second harmonic content in the current phase; Based on the proportion of the second harmonic content, the suppression factor of the current phase is determined; wherein, the suppression factor is inversely proportional to the proportion of the second harmonic content; The target differential current signal in the current phase is calculated based on the fundamental differential current signal and the suppression factor.

4. The method according to claim 3, characterized in that, The step of determining the suppression factor of the current phase based on the proportion of the second harmonic content includes: When the proportion of the second harmonic content is less than or equal to the first preset proportion threshold, the suppression factor is set to zero; When the proportion of the second harmonic content is greater than the first preset proportion threshold and less than the second preset proportion threshold, the suppression factor is set as a target suppression value; wherein, the target suppression value is a continuous value that increases monotonically according to the proportion of the second harmonic content. When the proportion of the second harmonic content is greater than or equal to the second preset proportion threshold, the suppression factor is set to the corresponding upper limit value; wherein, the second preset proportion threshold is greater than the first preset proportion threshold.

5. The method according to claim 1, characterized in that, The component signal includes a fundamental component, and the variation characteristics include load fluctuation and load change rate. The step of determining the variation characteristics of the load current characterization quantity based on the component signal, and correcting the basic differential current threshold based on the variation characteristics to obtain the target differential current threshold includes: The amplitude of the fundamental component of the same phase at each of the acquisition sides is averaged to obtain the load current characterization of the current phase. Within a preset time window, the dispersion of the load current characterization quantity is calculated to obtain the load fluctuation quantity, and the ratio of the change in the load current characterization quantity at adjacent times to the time interval is calculated to obtain the load change rate. The target differential current threshold is obtained by calculating the basic differential current threshold, a first correction term positively correlated with the load current characterization, a second correction term positively correlated with the load fluctuation, and a third correction term positively correlated with the load change rate.

6. The method according to claim 1, characterized in that, The step of comparing the target differential current signal with the target differential current threshold to obtain target anomaly information, and outputting corresponding prompt information based on the target anomaly information includes: Calculate the differential current change rate of the target differential current signal; If the target differential current signal is greater than the target differential current threshold, it is determined that there is a target anomaly, and a corresponding prompt message is output; If the target differential current signal is less than or equal to the target differential current threshold, it is determined that there is no target anomaly.

7. The method according to claim 6, characterized in that, The step of determining that there is a target anomaly and outputting a corresponding prompt message when the target differential current signal is greater than the target differential current threshold includes: The maximum load change rate of the target differential current signal at adjacent time points is obtained to obtain the differential current change rate, and the basic change rate threshold and the load change rate are obtained. The target change rate threshold is calculated based on the basic change rate threshold and the load change rate. If the target differential current signal is greater than the target differential current threshold and the differential current change rate is greater than the target change rate threshold, the target anomaly is determined to be of the first level, and a prompt message corresponding to the first level is output. If the target differential current signal is greater than the target differential current threshold and the differential current change rate is less than or equal to the target change rate threshold, the target anomaly is determined to be of the second level, and a prompt message corresponding to the second level is output; wherein, the second level is lower than the first level.

8. A differential current anomaly early warning device, characterized in that, The device includes: The acquisition module is used to acquire multiple three-phase current signals from at least two acquisition sides; The differential current calculation module is used to perform harmonic decomposition on each of the three-phase current signals to obtain component signals corresponding to multiple three-phase current signals, and to fuse the component signals in the same phase to obtain the corresponding differential current signal; wherein, the differential current signal includes at least the fundamental differential current signal and the second harmonic differential current signal; The differential current correction module is used to determine a suppression factor based on the relative relationship between the fundamental differential current signal and the second harmonic differential current signal, and to correct the differential current signal based on the suppression factor to obtain the target differential current signal. The threshold correction module is used to determine the change characteristics of the load current characterization quantity based on the component signal, and to correct the basic differential current threshold based on the change characteristics to obtain the target differential current threshold. The anomaly determination module is used to compare the differential current change rate of the target differential current signal with the target differential current threshold to obtain target anomaly information, and output corresponding prompt information based on the target anomaly information.

9. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the differential flow anomaly early warning method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

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