A transformer differential protection anti-malfunction method and system based on kurtosis difference

Abstract

The application relates to the technical field of power system relay protection, and discloses a transformer differential protection anti-maloperation method and system based on kurtosis difference. The method comprises the following steps: obtaining a differential current waveform generated in the operation process of a transformer, and when the transformer is faulty, a first current waveform is obtained by intercepting the differential current waveform based on the linear transformation characteristics of CT transient saturation; a second current waveform is obtained by folding and combining the first current waveform based on the end point of the first current waveform, and a third current waveform is obtained by normalizing the second current waveform; the kurtosis coefficient of the third current waveform is calculated, the fault type of the transformer is judged based on the kurtosis coefficient, and whether the transformer protection device is driven to perform a differential protection action is determined according to the fault type. The application can effectively avoid the maloperation of the transformer differential protection, and significantly improves the discrimination accuracy and operation reliability of the transformer differential protection.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, and in particular to a method and system for preventing maloperation of transformer differential protection based on kurtosis differences. Background Technology

[0002] In engineering, transformer main protection commonly employs ratio-controlled current differential protection schemes to achieve rapid fault clearing within the protected area. However, due to the different voltage levels on each side of the transformer, the corresponding current transformers (CTs) have inherent differences in parameters such as capacity, turns ratio, and rated secondary load, making it impossible to use a uniform model. This makes it easy for CTs on each side to experience varying degrees of transient saturation under external fault conditions, leading to a significant increase in unbalanced current. If a CT on one side is severely saturated while others are not, a large-amplitude false differential current will be generated, making it resemble the characteristics of a fault within the protected area, ultimately causing the transformer differential protection to malfunction. Therefore, developing a reliable CT saturation detection method to avoid the risk of transformer differential protection malfunction has become a key requirement for ensuring the safe operation of transformers.

[0003] To address the aforementioned issues, existing technologies have proposed several solutions. Among them, the time-difference method utilizes the time difference between CT saturation and differential protection output to identify whether CT saturation has occurred in advance, thereby determining the differential protection action behavior. The transformer adaptive protection method based on the equivalent circuit model constructs anti-maloperation criteria by writing multiple types of equivalent circuit equations and identifies winding parameters online to update protection parameters and threshold values ​​in real time. The double-sided unsaturated region equivalent instantaneous inductance method uses the magnitude of the equivalent instantaneous inductance value calculated from the primary and secondary sides of the transformer to identify faults inside and outside the CT saturation zone under CT saturation conditions.

[0004] While existing technologies attempt to address the problem of differential protection maloperation caused by CT saturation to some extent, they all have significant technical shortcomings. Specifically, the time-difference method requires precise location of the fault occurrence and differential current appearance; however, when the CT is severely saturated, the time difference between the two is extremely small, easily leading to location errors and maloperation. The adaptive adjustment method for protection parameters reduces the sensitivity to faults within the protection zone by increasing the braking coefficient and is easily affected by various operating conditions, resulting in insufficient reliability in detecting different degrees of CT saturation and poor universality of the judgment criteria. The method based on equivalent instantaneous inductance not only increases equipment investment costs but also introduces protection risks caused by voltage transformer disconnection, and there is a possibility of misidentifying severe CT saturation as transformer core saturation, easily leading to delayed protection action or even maloperation. Summary of the Invention

[0005] To address the problem of transformer differential protection maloperation caused by transient saturation of CTs during external faults, this invention provides a method and system for preventing maloperation of transformer differential protection based on kurtosis differences.

[0006] In a first aspect, embodiments of the present invention provide a method for preventing maloperation of transformer differential protection based on kurtosis differences, comprising: The differential current waveform generated during transformer operation is obtained, and when the transformer fails, the first current waveform is obtained by intercepting the differential current waveform based on the linear transmission characteristics of CT transient saturation. The first current waveform is folded and combined based on the end point of the first current waveform to obtain the second current waveform, and the second current waveform is normalized to obtain the third current waveform. Calculate the kurtosis coefficient of the third current waveform, determine the fault type of the transformer based on the kurtosis coefficient, and determine whether to drive the transformer protection device to perform differential protection action according to the fault type.

[0007] Preferably, the step of acquiring the differential current waveform generated during transformer operation, and obtaining a first current waveform by intercepting the differential current waveform based on the linear transmission characteristics of CT transient saturation when the transformer fails, includes: The differential current waveform is obtained by collecting the current generated by the transformer during operation based on the current transformers installed on each side of the transformer. When the transformer fails, based on the linear transmission characteristics of the CT transient saturation, the waveform segment from the time of the fault occurrence to the time of the first extreme point of the differential current is extracted as the first current waveform.

[0008] Preferably, the step of folding and combining the first current waveform based on the end point of the first current waveform to obtain a second current waveform, and then normalizing the second current waveform to obtain a third current waveform, includes: Draw a perpendicular line to the time axis through the end point of the first current waveform, flip the first current waveform symmetrically along the perpendicular line of the time axis, and combine the first current waveform and the symmetrically flipped first current waveform to obtain the second current waveform. The second current waveform is normalized to obtain the third current waveform.

[0009] Preferably, the step of calculating the kurtosis coefficient of the third current waveform, determining the fault type of the transformer based on the kurtosis coefficient, and determining whether to drive the transformer protection device to perform differential protection action according to the fault type includes: Based on the kurtosis calculation formula, the kurtosis coefficient of the third current waveform is calculated; The fault type of the transformer is determined based on the difference between the kurtosis coefficient of the third current waveform and the kurtosis coefficient of the normal distribution curve, wherein the normal distribution curve is a standard normal distribution curve of the same statistical dimension constructed based on the third current waveform. Based on the fault type, determine whether to drive the transformer protection device to perform differential protection action.

[0010] Preferably, determining the fault type of the transformer based on the difference between the kurtosis coefficient of the third current waveform and the kurtosis coefficient of the normal distribution curve includes: If the kurtosis coefficient of the third current waveform is greater than the kurtosis coefficient of the normal distribution curve, then the fault type of the transformer is determined to be an external fault accompanied by CT saturation. If the kurtosis coefficient of the third current waveform is less than the kurtosis coefficient of the normal distribution curve, then the fault type of the transformer is determined to be an intra-zone fault.

[0011] Preferably, determining whether to drive the transformer protection device to perform differential protection action based on the fault type includes: If the fault type is an external fault accompanied by CT saturation, then it is determined that the transformer protection device will not perform differential protection action; If the fault type is an intra-zone fault, the drive transformer protection device will perform differential protection action.

[0012] Secondly, embodiments of the present invention provide a transformer differential protection anti-maloperation system based on kurtosis difference, comprising: The waveform capture module is used to acquire the differential current waveform generated during transformer operation, and when the transformer fails, it captures the differential current waveform based on the linear transmission characteristics of CT transient saturation to obtain the first current waveform. The waveform processing module is used to fold and combine the first current waveform based on the end point of the first current waveform to obtain a second current waveform, and to normalize the second current waveform to obtain a third current waveform. The anti-maloperation module is used to calculate the kurtosis coefficient of the third current waveform, determine the fault type of the transformer based on the kurtosis coefficient, and determine whether to drive the transformer protection device to perform differential protection action according to the fault type.

[0013] Preferably, the waveform truncation module includes: The waveform acquisition unit is used to collect the current generated by the transformer during operation based on the current transformers installed on each side of the transformer to obtain the differential current waveform. The waveform segment extraction unit is used to extract the waveform segment from the moment of the fault occurrence to the moment when the first extreme point of the differential current appears in the differential current waveform when the transformer fails, based on the linear transmission characteristics of the CT transient saturation.

[0014] Preferably, the waveform processing module includes: The flipping and combining unit is used to draw a time axis perpendicular line through the end point of the first current waveform, flip the first current waveform symmetrically along the time axis perpendicular line, and combine the first current waveform and the symmetrically flipped first current waveform to obtain the second current waveform. The normalization processing unit is used to normalize the second current waveform to obtain the third current waveform.

[0015] Preferably, the anti-malfunction module includes: The kurtosis calculation unit is used to calculate the kurtosis coefficient of the third current waveform based on the kurtosis calculation formula. The fault discrimination unit is used to determine the fault type of the transformer based on the difference between the kurtosis coefficient of the third current waveform and the kurtosis coefficient of the normal distribution curve, wherein the normal distribution curve is a standard normal distribution curve of the same statistical dimension constructed based on the third current waveform. The protection determination unit is used to determine whether to drive the transformer protection device to perform differential protection action based on the fault type.

[0016] Compared with existing technologies, the present invention discloses a method and system for preventing maloperation of transformer differential protection based on kurtosis differences. The advantages are as follows: It utilizes the linear transmission characteristics of the transient saturation of the transformer current (CT) to extract the differential current waveform after a fault. Waveform processing can be completed simply by locating the fault occurrence time, without the need for precise location of the differential current occurrence time. The algorithm is simple and has a fast response. By calculating the kurtosis coefficient after waveform folding, combination, and normalization, it can accurately distinguish between faults within and outside the transformer zone accompanied by CT saturation. The criterion is constructed based on the linear transmission zone of the differential current within one cycle after the fault. Even in scenarios with severe CT saturation, it still possesses high detection sensitivity, effectively preventing maloperation of the transformer differential protection and significantly improving the discrimination accuracy and operational reliability of the transformer differential protection. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating a method for preventing maloperation of transformer differential protection based on kurtosis difference according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the process of preventing accidental operation by identifying the type of fault in an embodiment of the present invention; Figure 3This is a schematic diagram of the differential current of transformer B phase when an external fault accompanies severe CT saturation in an embodiment of the present invention; Figure 4 This is a schematic diagram comparing the transformed differential current waveform with the normally distributed waveform when an external fault is accompanied by severe CT saturation in an embodiment of the present invention. Figure 5 This is a schematic diagram of the differential current of transformer C phase when an external fault accompanies slight CT saturation in an embodiment of the present invention; Figure 6 This is a schematic diagram comparing the transformed differential current waveform with the normally distributed waveform when an external fault is accompanied by slight CT saturation in an embodiment of the present invention. Figure 7 This is a schematic diagram of the differential current of transformer A phase when the fault CT is not saturated in the area of ​​this embodiment of the invention; Figure 8 This is a schematic diagram comparing the transformed differential current waveform with the normally distributed waveform when the faulty CT in the region is not saturated in an embodiment of the present invention. Figure 9 This is a schematic diagram of a transformer differential protection anti-maloperation system based on kurtosis difference according to an embodiment of the present invention; Figure label: 01. Waveform capture module; 02. Waveform processing module; 03. Anti-malfunction module. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0019] In the description of this invention, it should be understood that the terms "first" and "second," etc., are used to distinguish different objects, rather than to describe a specific order.

[0020] In the description of this invention, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the art. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] During steady-state operation, the transformer current transformer (CT) linearly transmits the primary current of the system. After an external fault occurs, the magnetic flux density of the CT core gradually increases with the aperiodic component of the short-circuit current, resulting in a linear transmission delay region. During this period, the initial value of the differential current is extremely small and the waveform exhibits significant discontinuities when the external fault accompanies CT saturation. However, when the fault occurs within the transformer zone, the differential current increases synchronously with the fault, and the waveform remains uninterrupted. Kurtosis, as a statistical measure quantifying the peak sharpness and tail thickness of a waveform, can accurately characterize the waveform's deviation from a normal distribution. Based on the waveform characteristics of the differential current within one cycle after a fault, after specialized waveform transformation, the differential currents accompanying CT saturation during internal and external faults exhibit diametrically opposite kurtosis coefficient characteristics. This difference can serve as a theoretical basis for identifying fault types and preventing differential protection maloperation. This invention relies on the CT transient saturation mechanism and the waveform statistical characteristics of kurtosis to construct its core theoretical foundation.

[0022] like Figure 1 The diagram shown is a flowchart illustrating a method for preventing maloperation of transformer differential protection based on kurtosis differences, according to an embodiment of the present invention. (Refer to...) Figure 1 This invention provides a method for preventing maloperation of transformer differential protection based on kurtosis differences, comprising the following steps: S1. Obtain the differential current waveform generated during transformer operation, and when the transformer fails, intercept the differential current waveform based on the linear transmission characteristics of CT transient saturation to obtain the first current waveform. Specifically, step S1 includes: 1) The differential current waveform is obtained by collecting the current generated by the transformer during operation based on the current transformers installed on each side of the transformer; CTs are installed at the output terminals of each phase on both the high-voltage and low-voltage sides of the transformer to collect the high current on the primary side of each side of the transformer in real time and convert it into a standard low current signal on the secondary side according to the rated transformation ratio.

[0023] The transformer protection device performs synchronous high-speed sampling and analog-to-digital conversion of the secondary current output by each CT, then completes current phase compensation according to the transformer connection group, and realizes normalized conversion of the current on each side by combining the CT ratio parameters. Finally, the differential current waveform of the transformer throughout its operation is calculated according to the vector summation rule.

[0024] 2) When a transformer fails, based on the linear transmission characteristics of CT transient saturation, the waveform segment from the time of the fault occurrence to the time of the first extreme point of the differential current is extracted as the first current waveform.

[0025] Transformer protection devices identify transformer fault states by jointly using a current surge trigger criterion and a differential current over-limit criterion, accurately pinpointing the fault occurrence time and using it as the zero point of the time axis. The current surge trigger criterion calculates the second-order differential surge from continuously sampled current signals on each side of the transformer. When the current surge in any phase exceeds a preset setting threshold (set according to the transformer's rated current, typically 0.1 to 0.3 times the transformer's rated secondary current), a fault-level current surge is determined. The differential current over-limit criterion involves real-time calculation of the transformer's differential current amplitude. When the differential current amplitude exceeds a preset differential protection trigger threshold (set to avoid the maximum unbalanced current during normal transformer operation and external faults without CT saturation, typically 0.2 to 0.5 times the transformer's rated secondary current), the transformer is determined to have entered a fault condition. Meeting either criterion is sufficient to identify a transformer fault state.

[0026] Based on the inherent characteristic of the linear transmission delay region in the transient saturation process of CT, the amplitude change of differential current is continuously tracked, and the occurrence time of the first extreme point of differential current is captured in real time. Taking the fault occurrence time as the starting point and the occurrence time of the first extreme point as the ending point, the differential current waveform segment within this period is extracted to obtain the first current waveform for subsequent waveform transformation processing.

[0027] It should be noted that the time of the first extreme point of the differential current is taken because the period from the occurrence of the fault to the first extreme value of the differential current completely covers the critical linear transmission interval before the transient saturation of the CT. The difference in the discontinuity characteristics of the differential current waveform of the fault outside the interval accompanied by CT saturation and the fault inside the interval is the most prominent in this section. This can provide the most distinguishable raw data for subsequent processing and ensure the accuracy and sensitivity of the fault type identification results.

[0028] S2. Based on the end point of the first current waveform, the first current waveform is folded and combined to obtain the second current waveform, and the second current waveform is normalized to obtain the third current waveform. Specifically, step S2 includes: 1) Draw a perpendicular line to the time axis through the end point of the first current waveform, perform an axisymmetric flip of the first current waveform along the perpendicular line of the time axis, and combine the first current waveform and the axisymmetric flipped first current waveform to obtain the second current waveform; Draw a perpendicular line from the end point of the first current waveform, which corresponds to the first extreme point of the differential current, to the time axis and use it as the axis of symmetry. Perform axisymmetric flipping on the first current waveform to obtain the flipped waveform. Then, sequentially splice and combine the first current waveform and the flipped waveform in time sequence to form a complete and continuous second current waveform.

[0029] 2) Normalize the second current waveform to obtain the third current waveform.

[0030] Using the maximum current amplitude of the second current waveform as the normalization benchmark, the instantaneous current value of each sampling point in the second current waveform is divided by the maximum amplitude to complete the dimensionless normalization of the amplitude, thus obtaining the third current waveform that retains only the waveform morphology characteristics.

[0031] S3. Calculate the kurtosis coefficient of the third current waveform, determine the fault type of the transformer based on the kurtosis coefficient, and determine whether to drive the transformer protection device to perform differential protection action according to the fault type.

[0032] like Figure 2 As shown, this is a flowchart illustrating step S3. (Refer to...) Figure 2 Step S3 includes: S301. Calculate the kurtosis coefficient of the third current waveform based on the kurtosis calculation formula; Kurtosis is a statistical measure that quantifies the thickness of the tail and the sharpness of the peak of a waveform. It is defined as the ratio of the fourth central moment to the square of the variance, and its calculation formula is as follows: in, Indicates kurtosis, Indicates the total number of sampling points. Indicates the first One sampled data, This represents the population mean. Represents the fourth-order central moment. Indicates variance.

[0033] By substituting the data from each sampling point of the third current waveform and the statistically obtained mean value into the above kurtosis calculation formula, the kurtosis coefficient of the third current waveform can be calculated.

[0034] S302. Based on the difference between the kurtosis coefficient of the third current waveform and the kurtosis coefficient of the normal distribution curve, determine the fault type of the transformer; The normal distribution curve is a standard normal distribution curve with the same statistical dimension constructed based on the third current waveform. That is, using the number of sampling points, mean, and variance of the third current waveform as statistical benchmarks, a standard normal distribution curve with a mean of 0 and a variance of 1 is constructed. The theoretical kurtosis coefficient of this standard normal distribution curve is always 0, and it serves as a benchmark reference value for subsequent fault type identification, used to quantify the degree to which the third current waveform deviates from a normal distribution.

[0035] Specifically, step S302 includes: 1) If the kurtosis coefficient of the third current waveform is greater than that of the normal distribution curve, then the fault type of the transformer is determined to be an external fault accompanied by CT saturation. Under this operating condition, the third current waveform exhibits a peak shape after being folded and combined. The kurtosis coefficient is significantly greater than the 0 value of the standard normal distribution, which can clearly identify faults outside the zone and CT transient saturation leading to false differential current.

[0036] 2) If the kurtosis coefficient of the third current waveform is less than the kurtosis coefficient of the normal distribution curve, then the fault type of the transformer is determined to be an intra-zone fault.

[0037] Under this operating condition, the third current waveform approaches a smooth sinusoidal shape, and the kurtosis coefficient is less than the 0 value of the standard normal distribution, which confirms that there is a real fault in the transformer body.

[0038] S303. Based on the fault type, determine whether to drive the transformer protection device to perform differential protection action.

[0039] Specifically, if the fault type is an external fault accompanied by CT saturation, the transformer protection device will not perform differential protection; if the fault type is an internal fault, the transformer protection device will be driven to perform differential protection.

[0040] To verify that the transformer differential protection anti-maloperation method based on kurtosis difference in this embodiment of the invention has stable and reliable detection capabilities for different saturation levels of CT under external faults and for CTs not being saturated under internal faults, the following is a detailed description with reference to three embodiments.

[0041] 1) External malfunction accompanied by severe CT saturation: like Figure 3 The diagram shown illustrates the differential current of transformer B phase when an external fault occurs accompanied by severe CT saturation, according to an embodiment of the present invention. (Refer to...) Figure 3 In the extreme case of a three-phase short-circuit fault occurring outside the transformer angle side at t=0.400s, the low-voltage side B-phase CT rapidly enters a severely saturated state within 5ms after the fault occurs, while all CTs on the high-voltage side remain unsaturated. The differential current of phase B is selected for analysis. This differential current increases significantly only about 3.2ms after the fault occurs and reaches the first extreme point at t=0.414s.

[0042] like Figure 4 As shown, this is a schematic diagram comparing the transformed differential current waveform with the normally distributed waveform when an external fault accompanies severe CT saturation in an embodiment of the present invention. Using the present invention, the differential current waveform is sequentially truncated, folded, combined, and normalized to obtain a transformed waveform exhibiting sharp peaks and thin tails. Figure 4 The red curve in the middle represents the transformed waveform. Figure 4The black curve in the middle is a normally distributed waveform. The kurtosis coefficient of this waveform is calculated to be K=1.1054 by the kurtosis calculation formula. This value is greater than 0. Based on the criterion of this invention, it can be accurately identified as an external fault accompanied by CT saturation. This fully verifies that in the extreme scenario of CT extremely rapid and severe saturation, this invention can complete the accurate identification by only locating the time of fault occurrence, without locking the time of differential current occurrence. The algorithm process is simple, the identification response is fast, and the detection results are accurate and reliable.

[0043] 2) External fault accompanied by slight CT saturation: like Figure 5 The diagram shown illustrates the differential current of transformer C-phase when an external fault occurs accompanied by slight CT saturation, according to an embodiment of the present invention. (Refer to...) Figure 5 A three-phase short-circuit fault occurred on the transformer angle side at t=0.4s. Under this condition, the low-voltage side C-phase CT entered a slightly saturated state about 18ms after the fault occurred, while all CTs on the high-voltage side remained unsaturated. The differential current of the C-phase was selected for analysis, and the differential current reached its first extreme point at t=0.4268s.

[0044] like Figure 6 As shown, this is a schematic diagram comparing the transformed differential current waveform with the normally distributed waveform when an external fault accompanies slight CT saturation in an embodiment of the present invention. Using the present invention, the differential current waveform is sequentially truncated, folded, combined, and normalized to obtain a transformed waveform exhibiting sharp peaks and thin tails. Figure 6 The red curve in the middle represents the transformed waveform. Figure 6 The black curve in the middle is a normally distributed waveform. The kurtosis coefficient of this waveform is calculated to be K=3.4965 by the kurtosis calculation formula. This value is greater than 0. Based on the criterion of this invention, it can be accurately identified as an external fault accompanied by CT saturation. This fully verifies that the present invention can still accurately detect external faults in the normal scenario of slight CT saturation, and the discrimination result is stable and reliable.

[0045] 3) The faulty CT within the area did not saturate: like Figure 7 The diagram shown illustrates the differential current of transformer A phase when the fault CT is not saturated within the fault zone according to an embodiment of the present invention. (Refer to...) Figure 7 A three-phase short-circuit fault occurred on the transformer corner side at t=0.4s. Under this condition, all CTs on the high and low voltage sides of the transformer remained unsaturated. The differential current of phase A was selected for analysis. After the fault occurred, the differential current immediately increased and reached the first extreme point at t=0.406s.

[0046] like Figure 8As shown, this is a schematic diagram comparing the transformed differential current waveform with the normally distributed waveform when the faulty CT is not saturated in the region according to an embodiment of the present invention. Using the present invention, the differential current waveform is sequentially truncated, folded, combined, and normalized to obtain a transformed waveform exhibiting flat peaks and thick tails. Figure 8 The blue curve in the middle represents the transformed waveform. Figure 8 The black curve in the middle is a normally distributed waveform. The kurtosis coefficient of the waveform is calculated to be K=-1.2683 by the kurtosis calculation formula. This value is less than 0. Based on the criterion of this invention, it can be accurately determined to be a fault in the transformer area. The protection device can immediately drive the differential protection to trip the output circuit breaker. This fully verifies that the present invention has high accuracy and sensitivity in identifying faults in the area, and the algorithm is simple and the fault response is rapid.

[0047] This invention discloses a method for preventing maloperation of transformer differential protection based on kurtosis differences. It utilizes the linear transmission characteristics of the transient saturation of the transformer current (CT) to extract the differential current waveform after a fault. Waveform processing can be completed simply by locating the fault occurrence time, without requiring precise location of the differential current occurrence time. The algorithm is simple and has a fast response. By calculating the kurtosis coefficient after waveform folding, combination, and normalization, it can accurately distinguish between faults within and outside the transformer zone accompanied by CT saturation. A criterion is constructed based on the linear transmission zone of the differential current within one cycle after the fault. Even in scenarios with severe CT saturation, it maintains high detection sensitivity, effectively preventing maloperation of transformer differential protection and significantly improving the discrimination accuracy and operational reliability of transformer differential protection.

[0048] like Figure 9 The diagram shown is a structural schematic of a transformer differential protection anti-maloperation system based on kurtosis difference according to an embodiment of the present invention. (Refer to...) Figure 9 An embodiment of the present invention provides a transformer differential protection anti-maloperation system based on kurtosis difference, comprising: The waveform capture module 01 is used to acquire the differential current waveform generated during transformer operation, and when the transformer fails, it captures the differential current waveform based on the linear transmission characteristics of CT transient saturation to obtain the first current waveform. Specifically, the waveform truncation module includes: The waveform acquisition unit is used to collect the current generated by the transformer during operation based on the current transformers installed on each side of the transformer to obtain the differential current waveform. The waveform segment extraction unit is used to extract the waveform segment from the moment of fault occurrence to the moment of occurrence of the first extreme point of the differential current as the first current waveform when a transformer fault occurs, based on the linear transmission characteristics of CT transient saturation.

[0049] The waveform processing module 02 is used to fold and combine the first current waveform based on the end point of the first current waveform to obtain the second current waveform, and to normalize the second current waveform to obtain the third current waveform. Specifically, the waveform processing module includes: The flipping combination unit is used to draw a time axis perpendicular line through the end point of the first current waveform, flip the first current waveform symmetrically along the time axis perpendicular line, and combine the first current waveform and the symmetrically flipped first current waveform to obtain the second current waveform. The normalization processing unit is used to normalize the second current waveform to obtain the third current waveform.

[0050] The anti-maloperation module 03 is used to calculate the kurtosis coefficient of the third current waveform, determine the fault type of the transformer based on the kurtosis coefficient, and determine whether to drive the transformer protection device to perform differential protection action according to the fault type.

[0051] Specifically, the anti-misoperation module includes: The kurtosis calculation unit is used to calculate the kurtosis coefficient of the third current waveform based on the kurtosis calculation formula. The fault discrimination unit is used to determine the fault type of the transformer based on the difference between the kurtosis coefficient of the third current waveform and the kurtosis coefficient of the normal distribution curve, wherein the normal distribution curve is a standard normal distribution curve of the same statistical dimension constructed based on the third current waveform. The protection determination unit is used to determine whether to drive the transformer protection device to perform differential protection action based on the fault type.

[0052] It should be noted that the modules in the aforementioned transformer differential protection anti-maloperation system based on kurtosis differences can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each module. For specific limitations regarding the transformer differential protection anti-maloperation system based on kurtosis differences, please refer to the limitations of the transformer differential protection anti-maloperation method based on kurtosis differences mentioned above; both have the same function and role, and will not be repeated here.

[0053] In summary, the present invention provides a method and system for preventing maloperation of transformer differential protection based on kurtosis differences. This method utilizes the linear transmission characteristics of the transient saturation of the transformer current (CT) to extract the differential current waveform after a fault. Waveform processing can be completed simply by locating the fault occurrence time, without requiring precise location of the differential current occurrence time. The algorithm is simple and has a fast response. By calculating the kurtosis coefficient after waveform folding, combination, and normalization, it can accurately distinguish between faults within and outside the transformer zone accompanied by CT saturation. The criterion is constructed based on the linear transmission zone of the differential current within one cycle after the fault. Even in scenarios with severe CT saturation, it maintains high detection sensitivity, effectively preventing maloperation of transformer differential protection and significantly improving the discrimination accuracy and operational reliability of transformer differential protection.

[0054] The various embodiments in this specification are described in a progressive manner. For directly identical or similar parts of the embodiments, refer to each other. Each embodiment focuses on its differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. It should be noted that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preventing maloperation of transformer differential protection based on kurtosis difference, characterized in that, include: The differential current waveform generated during transformer operation is obtained, and when the transformer fails, the first current waveform is obtained by intercepting the differential current waveform based on the linear transmission characteristics of CT transient saturation. The first current waveform is folded and combined based on the end point of the first current waveform to obtain the second current waveform, and the second current waveform is normalized to obtain the third current waveform. Calculate the kurtosis coefficient of the third current waveform, determine the fault type of the transformer based on the kurtosis coefficient, and determine whether to drive the transformer protection device to perform differential protection action according to the fault type; The step of folding and combining the first current waveform based on the end point of the first current waveform to obtain the second current waveform, and then normalizing the second current waveform to obtain the third current waveform, includes: Draw a perpendicular line to the time axis through the end point of the first current waveform, flip the first current waveform symmetrically along the perpendicular line of the time axis, and combine the first current waveform and the symmetrically flipped first current waveform to obtain the second current waveform. The second current waveform is normalized to obtain the third current waveform.

2. The method for preventing maloperation of transformer differential protection based on kurtosis difference according to claim 1, characterized in that, The process of acquiring the differential current waveform generated during transformer operation, and obtaining a first current waveform by intercepting the differential current waveform based on the linear transmission characteristics of CT transient saturation when the transformer fails, includes: The differential current waveform is obtained by collecting the current generated by the transformer during operation based on the current transformers installed on each side of the transformer. When the transformer fails, based on the linear transmission characteristics of the CT transient saturation, the waveform segment from the time of the fault occurrence to the time of the first extreme point of the differential current is extracted as the first current waveform.

3. The method for preventing maloperation of transformer differential protection based on kurtosis difference according to claim 1, characterized in that, The calculation of the kurtosis coefficient of the third current waveform, the determination of the transformer fault type based on the kurtosis coefficient, and the determination of whether to drive the transformer protection device to perform differential protection action based on the fault type include: Based on the kurtosis calculation formula, the kurtosis coefficient of the third current waveform is calculated; The fault type of the transformer is determined based on the difference between the kurtosis coefficient of the third current waveform and the kurtosis coefficient of the normal distribution curve, wherein the normal distribution curve is a standard normal distribution curve of the same statistical dimension constructed based on the third current waveform. Based on the fault type, determine whether to drive the transformer protection device to perform differential protection action.

4. The method for preventing maloperation of transformer differential protection based on kurtosis difference according to claim 3, characterized in that, The method of determining the fault type of the transformer based on the difference between the kurtosis coefficient of the third current waveform and the kurtosis coefficient of the normal distribution curve includes: If the kurtosis coefficient of the third current waveform is greater than the kurtosis coefficient of the normal distribution curve, then the fault type of the transformer is determined to be an external fault accompanied by CT saturation. If the kurtosis coefficient of the third current waveform is less than the kurtosis coefficient of the normal distribution curve, then the fault type of the transformer is determined to be an intra-zone fault.

5. The method for preventing maloperation of transformer differential protection based on kurtosis difference according to claim 4, characterized in that, The step of determining whether to drive the transformer protection device to perform differential protection action based on the fault type includes: If the fault type is an external fault accompanied by CT saturation, then it is determined that the transformer protection device will not perform differential protection action; If the fault type is an intra-zone fault, the drive transformer protection device will perform differential protection action.

6. A transformer differential protection anti-maloperation system based on kurtosis difference, characterized in that, include: The waveform capture module is used to acquire the differential current waveform generated during transformer operation, and when the transformer fails, it captures the differential current waveform based on the linear transmission characteristics of CT transient saturation to obtain the first current waveform. The waveform processing module is used to fold and combine the first current waveform based on the end point of the first current waveform to obtain a second current waveform, and to normalize the second current waveform to obtain a third current waveform. The anti-maloperation module is used to calculate the kurtosis coefficient of the third current waveform, determine the fault type of the transformer based on the kurtosis coefficient, and determine whether to drive the transformer protection device to perform differential protection action according to the fault type. The waveform processing module includes: The flipping and combining unit is used to draw a time axis perpendicular line through the end point of the first current waveform, flip the first current waveform symmetrically along the time axis perpendicular line, and combine the first current waveform and the symmetrically flipped first current waveform to obtain the second current waveform. The normalization processing unit is used to normalize the second current waveform to obtain the third current waveform.

7. The transformer differential protection anti-maloperation system based on kurtosis difference according to claim 6, characterized in that, The waveform truncation module includes: The waveform acquisition unit is used to collect the current generated by the transformer during operation based on the current transformers installed on each side of the transformer to obtain the differential current waveform. The waveform segment extraction unit is used to extract the waveform segment from the moment of the fault occurrence to the moment when the first extreme point of the differential current appears in the differential current waveform when the transformer fails, based on the linear transmission characteristics of the CT transient saturation.

8. The transformer differential protection anti-maloperation system based on kurtosis difference according to claim 6, characterized in that, The anti-misoperation module includes: The kurtosis calculation unit is used to calculate the kurtosis coefficient of the third current waveform based on the kurtosis calculation formula. The fault discrimination unit is used to determine the fault type of the transformer based on the difference between the kurtosis coefficient of the third current waveform and the kurtosis coefficient of the normal distribution curve, wherein the normal distribution curve is a standard normal distribution curve of the same statistical dimension constructed based on the third current waveform. The protection determination unit is used to determine whether to drive the transformer protection device to perform differential protection action based on the fault type.

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