Transformer excitation inrush current identification method, device, computer storage medium and terminal

Abstract

The present invention relates to a transformer excitation inrush current identification method, device, computer storage medium and terminal. The transformer excitation inrush current identification method includes: processing the three-phase current on the star side of the transformer to obtain the zero-mode current, the approximate circulating current on the triangle side of the transformer and the saturation coefficient of the three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values ​​of the three-phase current on the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase of the iron core; the saturation state of each phase of the iron core is determined based on the magnitude relationship of the three-phase current on the star side of the transformer; using a preset regression model to process the zero-mode current and the approximate circulating current to determine the correlation coefficient between the zero-mode current and the approximate circulating current; according to the correlation coefficient and the saturation coefficient, the excitation inrush current identification result is output. The present application can effectively identify the excitation inrush current, improve the accuracy of identifying the excitation inrush current, and avoid the transformer differential protection from malfunctioning when the excitation inrush current occurs.

Description

Technical Field

[0001] The present invention relates to the technical field of power system relay protection, and in particular to a transformer excitation surge current identification method, device, computer storage medium and terminal. Background Art

[0002] The main protection of transformers usually adopts longitudinal differential protection. The differential protection is based on Kirchhoff's current law, with simple principle and strong applicability. However, transformers have complex electromagnetic transient characteristics. When the transformer is closed under no-load conditions, a large excitation current, i.e., excitation inrush current, may occur. Excitation inrush current may cause false operation of differential protection, endangering the safe operation of the power system.

[0003] With the development of relay protection technology in power systems, due to the importance of transformer protection and the complexity of magnetizing inrush current, identification methods for transformer magnetizing inrush current have been continuously proposed. The traditional second harmonic principle and discontinuity angle principle are difficult to identify the occurrence of magnetizing inrush current when a symmetrical inrush current occurs in the transformer. The identification method that comprehensively utilizes voltage and current to construct judgment criteria, such as the equivalent instantaneous inductance, power differential, and flux characteristic principles, requires the acquisition of voltage or triangle side current data to accurately solve. The traditional scheme for identifying transformer magnetizing inrush current is imperfect, resulting in a relatively high misoperation rate of transformer differential protection.

[0004] During the implementation process, the inventors found that there are at least the following problems in the conventional technology: the conventional solution for identifying transformer excitation inrush current has the problem of low accuracy. Summary of the invention

[0005] Based on this, it is necessary to provide a transformer excitation inrush current identification method, device, computer storage medium and terminal to address the problem of low accuracy in identifying transformer excitation inrush current.

[0006] A transformer excitation inrush current identification method comprises the following steps:

[0007] The three-phase current on the star side of the transformer is processed to obtain the zero-mode current, the approximate circulating current on the triangle side of the transformer and the saturation coefficient of the three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values ​​of the three-phase current on the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase iron core; the saturation state of each phase iron core is determined based on the magnitude relationship of the three-phase current on the star side of the transformer;

[0008] A preset regression model is used to process the zero-mode current and the approximate circulating current, and a correlation coefficient between the zero-mode current and the approximate circulating current is determined;

[0009] According to the correlation coefficient and saturation coefficient, the magnetizing inrush current identification result is output.

[0010] In one embodiment, the step of determining the saturation state of each phase core includes:

[0011] The phase current with the median value of the three-phase current on the star side of the transformer in the middle is confirmed as the phase current to be processed, and the saturation state of the iron core corresponding to the phase current to be processed is determined to be a non-saturated phase;

[0012] Obtaining the absolute value of the difference between the phase current to be processed and any remaining phase current in the three-phase current on the star side of the transformer;

[0013] The saturation state of the iron core corresponding to the phase current whose absolute value is greater than the saturation threshold is determined as a saturation phase;

[0014] The saturation state of the iron core corresponding to the phase current whose absolute value is less than the saturation threshold is determined as the unsaturated phase.

[0015] In one embodiment, before the step of using a preset regression model to process the zero-mode current and the approximate circulating current to determine the correlation coefficient between the zero-mode current and the approximate circulating current, the step further includes:

[0016] According to the transformer zero-mode equivalent circuit, a preset regression model is constructed.

[0017] In one embodiment, the step of determining the saturation coefficient of the three-phase core includes:

[0018] It is determined whether within a preset time interval, the saturation state of the iron core corresponding to at least one phase current is always a saturated phase. If so, the value of the saturation coefficient is determined to be 1; otherwise, the value of the saturation coefficient is determined to be 0.

[0019] In one of the embodiments, the preset time interval includes a sampling data window;

[0020] The steps of outputting the result of magnetizing inrush current identification according to the correlation coefficient and the saturation coefficient include:

[0021] If the correlation coefficient is less than the correlation coefficient threshold, or the value of the saturation coefficient is 1, the excitation inrush current identification result is determined to be a fault, and the protection action is opened.

[0022] In one embodiment, the step of outputting the result of magnetizing inrush current identification according to the correlation coefficient and the saturation coefficient further includes:

[0023] If the correlation coefficient is greater than or equal to the correlation coefficient threshold, and the value of the saturation coefficient is 0, it is determined that the excitation inrush current identification result is normal, and the protection is locked.

[0024] In one of the embodiments, the three-phase current on the star side of the transformer is an instantaneous value.

[0025] A transformer excitation inrush current identification device, comprising:

[0026] A data acquisition module, used to obtain the three-phase current on the star side of the transformer;

[0027] A data processing module is used to process the three-phase current on the star side of the transformer to obtain the zero-mode current, the approximate circulating current on the triangle side of the transformer and the saturation coefficient of the three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values ​​of the three-phase current on the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase iron core; the saturation state of each phase iron core is determined based on the magnitude relationship of the three-phase current on the star side of the transformer; and is used to process the zero-mode current and the approximate circulating current using a preset regression model to determine the correlation coefficient between the zero-mode current and the approximate circulating current;

[0028] The result output module is used to output the excitation inrush current identification result according to the correlation coefficient and the saturation coefficient.

[0029] A computer storage medium is used to store a computer program, and when the computer program is executed by a processor, the steps of the transformer excitation inrush current identification method are implemented.

[0030] A transformer excitation inrush current identification terminal comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the transformer excitation inrush current identification method are implemented.

[0031] One of the above technical solutions has the following advantages and beneficial effects:

[0032] This application only uses the three-phase current on the star side of the transformer as the original data, combined with the correlation coefficient and the saturation coefficient, which complement each other in the output excitation inrush current identification result. The excitation inrush current can be identified without knowing any parameters of the transformer in advance. The process of obtaining the correlation coefficient and the saturation coefficient is simple, and the reliability of the output excitation inrush current identification result is high. This application can effectively identify the excitation inrush current, improve the accuracy of identifying the excitation inrush current, avoid the transformer differential protection from malfunctioning when the excitation inrush current occurs, and improve the safety of the transformer during operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of a flow chart of a transformer excitation inrush current identification method in one embodiment;

[0034] Figure 2 is a comparison diagram of approximate circulating current, actual circulating current and zero-mode current under normal inrush current in one embodiment;

[0035] Figure 3 1 is a comparison diagram of approximate circulating current, actual circulating current and zero-mode current under a phase A grounding fault in an embodiment;

[0036] Figure 4 Schematic diagram of correlation coefficient between approximate circulating current and zero-mode current under phase A grounding fault in one embodiment;

[0037] Figure 5 Schematic diagram of correlation coefficient between approximate circulating current and zero mode current under AB phase short circuit fault in one embodiment;

[0038] Figure 6 A schematic diagram of the correlation coefficient between the approximate circulating current and the zero-mode current when the transformer is switched on under fault conditions in one embodiment;

[0039] Figure 7 It is a schematic diagram of the transformer three-phase core saturation condition when the transformer is closed under fault in one embodiment;

[0040] Figure 8 It is a schematic diagram of the correlation coefficient between the approximate circulating current and the zero-mode inrush current when the transformer is switched on with a phase A resistance grounding fault in one embodiment;

[0041] Fig. 9 It is a schematic diagram of the transformer three-phase core saturation condition when the transformer is switched on in the case of a phase A resistance grounding fault in one embodiment;

[0042] Fig.10 is a flow chart of a transformer excitation inrush current identification method in another embodiment;

[0043] Fig.11 Schematic diagram of a transformer excitation inrush current identification device in one embodiment. DETAILED DESCRIPTION

[0044] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0045] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0046] With the development of relay protection technology in power systems, due to the importance of transformer protection and the complexity of magnetizing inrush current, methods for identifying transformer magnetizing inrush current are constantly being proposed. At present, the second harmonic principle is the most widely used. The ratio of the second harmonic to the fundamental content is calculated to identify whether it is an excitation inrush current. However, when a symmetrical inrush current occurs in the transformer, the second harmonic is small, and new core materials may also reduce the second harmonic content, so the inrush current cannot be identified at this time. The discontinuity angle principle identifies the inrush current based on the characteristics of the transformer core magnetic flux periodically entering saturation, but it may not be able to identify the symmetrical inrush current. The waveform symmetry principle divides the waveform within one cycle into two parts, front and back or upper and lower, and compares the symmetry of the two parts to identify the inrush current. Obviously, when the fault waveform has a large distortion, it will refuse to operate. The identification method that comprehensively utilizes the voltage and current construction criteria, such as the equivalent instantaneous inductance, power differential, and flux characteristic principle, requires the acquisition of voltage or triangle side current data to accurately solve.

[0047] This application only uses the three-phase current on the star side of the transformer as the original data, combined with the correlation coefficient and the saturation coefficient, which complement each other in the output excitation inrush current identification result. The excitation inrush current can be identified without knowing any parameters of the transformer in advance. The process of obtaining the correlation coefficient and the saturation coefficient is simple, and the reliability of the output excitation inrush current identification result is high. This application can effectively identify the excitation inrush current, improve the accuracy of identifying the excitation inrush current, avoid the transformer differential protection from malfunctioning when the excitation inrush current occurs, and improve the safety of the transformer during operation.

[0048] The present application is applied to transformer excitation inrush current identification after the transformer is no-load switched on.

[0049] In one embodiment, Figure 1 As shown, a transformer excitation inrush current identification method is provided, and the method is applied to a terminal as an example for explanation, including the following steps:

[0050] Step S100, processing the three-phase current on the star side of the transformer to obtain the zero-mode current, the approximate circulating current on the delta side of the transformer and the saturation coefficient of the three-phase core of the transformer;

[0051] Among them, the approximate circulating current is obtained by comparing the values ​​of the three-phase currents on the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase iron core; the saturation state of each phase iron core is determined based on the magnitude relationship of the three-phase currents on the star side of the transformer;

[0052] Specifically, the terminal obtains the three-phase current on the star side of the transformer, processes the three-phase current on the star side of the transformer, and obtains the zero-mode current, the approximate circulating current on the delta side of the transformer, and the saturation coefficient of the three-phase core of the transformer. Further, the terminal can obtain the zero-mode current by averaging the three-phase current on the star side of the transformer.

[0053] In one embodiment, the three-phase current on the star side of the transformer is an instantaneous value. The approximate circulating current on the delta side of the transformer may be an approximate value of the circulating current on the delta side of the transformer. The saturation state of each phase of the iron core may include a saturated phase and an unsaturated phase. The terminal may determine the saturation coefficient of the three-phase iron core of the transformer according to the saturation state of each phase of the iron core; the saturation coefficient is used to determine whether the transformer has an excitation inrush current.

[0054] In some examples, obtaining the three-phase current on the star side of the transformer includes i A 、i B 、i C , the zero-mode current can be obtained by formula (1):

[0055] i 0 =(i A +i B +i C ) / 3 (1)

[0056] In some examples, when a transformer has an excitation surge current (for example, after the transformer is switched on without load), the excitation surge current flows through one side of the transformer (for example, the star side of the transformer). Without considering the residual magnetism, there is at least one phase of the core being unsaturated, the excitation inductance of the unsaturated phase (i.e., the phase corresponding to the unsaturated core) is large, the excitation current can be ignored, and the phase current of the unsaturated phase (the star side of the transformer) can be approximately substituted for the transformer delta side circulating current. For example, the unsaturated phase current on the star side of the transformer is regarded as the approximate circulating current on the delta side of the transformer, wherein the phase current with a magnitude in the middle of the three-phase current on the star side of the transformer is confirmed as the unsaturated phase current on the star side of the transformer; the approximate circulating current on the delta side of the transformer is obtained by formula (2), wherein median is a value in the middle of the magnitude of the obtained value, and the negative sign indicates that the current direction is opposite.

[0057] i D1 =-median(i A ,i B ,i C ) (2)

[0058] In some examples, the saturation coefficient may be 0 or 1. If the saturation coefficient is 0, it is identified that a magnetizing inrush current occurs, and if the saturation coefficient is 1, it is identified that a fault occurs.

[0059] Step S120, using a preset regression model to process the zero-mode current and the approximate circulating current, and determining a correlation coefficient between the zero-mode current and the approximate circulating current;

[0060] Specifically, the preset regression model may include a regression equation, which processes the zero-mode current and the approximate circulating current to obtain the covariance of the two, the variance of the zero-mode current and the variance of the approximate circulating current; the correlation coefficient is used to reflect the degree of fit of the preset regression model to a certain extent, and further, based on the variance of the zero-mode current and the variance of the approximate circulating current, the standard deviation of the zero-mode current (arithmetic square root of the variance) and the standard deviation of the approximate circulating current are obtained, and the correlation coefficient between the zero-mode current and the approximate circulating current is obtained.

[0061] In some examples, the regression equation may include a slope coefficient and an intercept coefficient, and the slope coefficient and the intercept coefficient in the regression equation may be solved by the least square method; the correlation coefficient between the zero-mode current and the approximate circulating current may be a simple correlation coefficient; the correlation coefficient r between the zero-mode current and the approximate circulating current may be obtained by formula (3), where i 0 is the zero mode current, i D1 is the approximate circulation; where cov(i 0 ,i Dl ) is i 0 with i D1 The covariance of var(i 0 ) is i 0 The variance of var(i D1 ) is i D1 The variance of

[0062]

[0063] Furthermore, the absolute value of the correlation coefficient is between 0 and 1. Generally speaking, the closer the correlation coefficient is to 1, the stronger the correlation between the two quantities is, and conversely, the closer the correlation coefficient is to 0, the weaker the correlation between the two quantities is.

[0064] Step S140: outputting the magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient.

[0065] Specifically, the magnetizing inrush current identification result may include the occurrence of magnetizing inrush current and the occurrence of a fault.

[0066] This application only uses the three-phase current on the star side of the transformer as the original data, combined with the correlation coefficient and the saturation coefficient, which complement each other in the output excitation inrush current identification result. The excitation inrush current can be identified without knowing any parameters of the transformer in advance.

[0067] In one embodiment, the step of determining the saturation state of each phase core includes:

[0068] The phase current with the median value of the three-phase current on the star side of the transformer in the middle is confirmed as the phase current to be processed, and the saturation state of the iron core corresponding to the phase current to be processed is determined to be a non-saturated phase;

[0069] Specifically, when the transformer has an excitation surge current, the excitation current of the saturated phase is much larger than the excitation current of the unsaturated phase. A 、i B 、i C The value is determined by the size of the phase current, and the core corresponding to the phase current with the value in the middle is determined as the unsaturated phase;

[0070] Obtaining the absolute value of the difference between the phase current to be processed and any remaining phase current in the three-phase current on the star side of the transformer;

[0071] The saturation state of the iron core corresponding to the phase current whose absolute value is greater than the saturation threshold is determined as a saturation phase;

[0072] The saturation state of the iron core corresponding to the phase current whose absolute value is less than the saturation threshold is determined as the unsaturated phase.

[0073] Specifically, the saturation state of each phase of the iron core is determined, and more than one phase of the iron core may be an unsaturated phase at the same time. After the transformer is closed under no-load, for the triangle side of the transformer, the three-phase circulating currents in the triangle winding are equal. When the iron core is unsaturated, the phase current on the star side of the transformer is approximately equal to the circulating current on the triangle side of the transformer; further, for the star side of the transformer, the phase currents of the unsaturated phases are also approximately equal. Based on the above principle, after determining that one phase of the iron core on the star side of the transformer is an unsaturated phase, obtain the phase current of the determined unsaturated phase and the phase current of any remaining phase, take the absolute value of the difference between the two and compare it with the saturation threshold, if the absolute value of the difference is less than the saturation threshold, determine the corresponding iron core as an unsaturated phase, otherwise determine the corresponding iron core as a saturated phase. The saturation threshold can be the absolute value of the difference between the phase current of the unsaturated phase and the phase current of the saturated phase.

[0074] In some examples, the saturation threshold may be the minimum value of the absolute value of the difference between the phase current of the unsaturated phase and the phase current of the saturated phase; as shown in equation (4), the saturation state of each phase core may be determined, where S n is the saturated state of the core, including the saturated phase and the unsaturated phase; n can be any phase among the three phases ABC, S n It can be S A , S B , S C ; S n When it is 0, it means that the iron core corresponding to n is unsaturated phase, S n When it is 1, it means that the iron core corresponding to n is in saturation phase; ε is the saturation threshold; i D The actual circulation.

[0075]

[0076] In one embodiment, before the step of using a preset regression model to process the zero-mode current and the approximate circulating current to determine the correlation coefficient between the zero-mode current and the approximate circulating current, the step further includes:

[0077] According to the transformer zero-mode equivalent circuit, a preset regression model is constructed.

[0078] Specifically, the preset regression model may include a regression equation, and the regression equation is constructed according to the zero-mode equivalent circuit of the transformer; the regression equation may include a slope coefficient; according to the zero-mode equivalent circuit of the transformer, the relationship between the system power supply voltage and current when the resistance is ignored, and the relationship between the induced electromotive force of the three-phase excitation branch of the transformer and the actual circulating current on the triangle side of the transformer can be obtained; further, the relationship between the zero-mode current on the star side of the transformer and the circulating current on the triangle side is obtained to construct a regression equation; the correlation coefficient can be used to reflect the degree of fit of the regression equation to a certain extent.

[0079] In some examples, according to the transformer zero-mode equivalent circuit, ignoring the resistance, the system power supply voltage and current should satisfy equation (5), where u A 、u B 、u C are the power supply voltage of the ABC three-phase system, e a 、e b 、e c are the induced electromotive force of the three-phase excitation branch of the transformer; L s , L s0 are the positive-sequence inductance and zero-sequence inductance of the system respectively; L σ is the star-side leakage inductance of the transformer.

[0080]

[0081] The actual circulating current on the delta side of the transformer should satisfy the following formula:

[0082]

[0083] Adding equation (5) and substituting it into equation (6) yields:

[0084]

[0085] The initial closing current is 0. Integrating both sides of equation (7) yields:

[0086]

[0087] Among them, L σD is the leakage inductance of the transformer triangle side. From formula (8), we can see that when the resistance is ignored, the zero-mode current on the star side of the transformer is proportional to the circulating current on the triangle side, and the proportionality coefficient is L σD / (L s0 +Lσ ).

[0088] Furthermore, by using the approximate circulation instead of the actual circulation, the regression equation can be constructed:

[0089]

[0090] in, is the estimator of the slope coefficient, is the estimator of the intercept coefficient, I 0 is the matrix form of zero mode current, I D1 The matrix form of the approximate circulation. The matrix form of the regression equation is:

[0091]

[0092] The least squares method can be used to obtain an unbiased estimate of the slope coefficient β:

[0093]

[0094] In the case of normal excitation inrush current, the zero-mode current is proportional to the actual circulating current, and the approximate circulating current is approximately equal to the actual circulating current. Figure 2 As shown, the zero-mode current can be considered to be proportional to the approximate circulating current. Assume that a data set contains a series of dependent variables y i , the model prediction value is The average is Coefficient of determination R 2 It can be used to measure the proportion of the variation of the dependent variable that can be explained by the independent variable, that is, to measure the goodness of fit of the estimated regression equation. As shown in formula (12), the determination coefficient can be obtained:

[0095]

[0096] The determination coefficient is the square of the correlation coefficient. Furthermore, the correlation coefficient can also reflect the degree of fit of the preset regression model to a certain extent.

[0097] In one embodiment, the step of determining the saturation coefficient of the three-phase core includes:

[0098] It is determined whether within a preset time interval, the saturation state of the iron core corresponding to at least one phase current is always a saturated phase. If so, the value of the saturation coefficient is determined to be 1; otherwise, the value of the saturation coefficient is determined to be 0.

[0099] Specifically, the preset time interval may be a data window; when the excitation surge current occurs normally, it is impossible for a single-phase iron core to always be in the saturated phase within the preset time interval; if a single-phase iron core is always in the saturated phase, it is considered that a fault has occurred, and further, the value of the saturation coefficient is determined to be 1; otherwise, the value of the saturation coefficient is determined to be 0.

[0100] In some examples, without considering the flux decay at the initial stage of closing, the core saturation degree of the three-phase transformer can be expressed as:

[0101]

[0102] Where, T A 、T B 、T C Respectively represent the saturation degree of transformer A phase, B phase, and C phase iron core; α is the initial phase angle; t is the time; ω is the angular velocity; K rA , K rB , K rC Respectively represent the residual magnetism ratio of phase A, phase B, and phase C of the transformer; when |T|≤1, it means that the iron core of the corresponding phase is an unsaturated phase, and when |T|>1, it means that the iron core of the corresponding phase is a saturated phase. In this case, the maximum value of the residual magnetism steady-state value can reach 0.7 of the saturated residual magnetism, and it is impossible to always satisfy |T|>1. In other words, when the excitation surge current occurs normally, it is impossible for a phase of the iron core to always be in a saturated state. Then, the saturation state of each phase of the iron core is detected within a preset time interval to determine whether the saturation state of the iron core corresponding to at least one phase current is always in a saturated phase. If so, the value of the saturation coefficient is determined to be 1, otherwise the value of the saturation coefficient is determined to be 0.

[0103] In some examples, the preset time interval can be a cycle data window (for example, 20ms). The saturation coefficient of the three-phase iron core can be determined according to formula (12). In one cycle, it is determined whether the saturation state of the iron core corresponding to at least one phase current is always a saturated phase. If so, the saturation coefficient of the three-phase iron core is determined to be 1, and it is determined that a fault has occurred, and the protection action is opened; otherwise, the saturation coefficient of the three-phase iron core is determined to be 0, and it is determined that an excitation inrush current has occurred, and the protection action is locked; wherein sat represents the saturation coefficient of the three-phase iron core, and t represents the starting time of a cycle data window.

[0104]

[0105] The steps of outputting the result of magnetizing inrush current identification according to the correlation coefficient and the saturation coefficient include:

[0106] If the correlation coefficient is less than the correlation coefficient threshold, or the value of the saturation coefficient is 1, the excitation inrush current identification result is determined to be a fault, and the protection action is opened.

[0107] Specifically, the preset time interval includes a sampling data window; when the correlation coefficient is less than the correlation coefficient threshold, the approximate circulating current is partially different from the actual circulating current, the relationship between the zero-mode current and the actual circulating current changes, and the preset regression model cannot be accurately fitted; when the value of the saturation coefficient is 1, within the preset time interval, there is at least one phase current corresponding to the saturation state of the core that is always a saturated phase; the above situation does not belong to a normal excitation inrush current, then the excitation inrush current identification result is determined to be a fault, and the protection action is opened. It should be noted that judging whether the value of the saturation coefficient is 1 as a supplement to closing the circuit breaker in a fault situation is in an "or" relationship with the aforementioned judgment of whether the correlation coefficient is less than the correlation coefficient threshold. As long as one of the judgment results is yes, the excitation inrush current identification result is determined to be a fault, and the protection action is opened.

[0108] In some examples, the preset time interval can be a cycle data window (for example, 20ms); in the case of a ground fault, the approximate circulating current and the transformer zero-mode equivalent circuit change. Specifically, in the case of a ground fault, the current of the fault phase is affected by the fault current and the excitation current, and often will not deviate to one side of the time axis. The fault phase current and the unsaturated phase current have an intersection. At this time, the approximate circulating current obtained by formula (2) will be partially different from the actual circulating current; Figure 3 The figure shows the situation when a phase A ground fault occurs. At the moment of the fault, the correlation coefficient will be significantly reduced. In addition, the transformer zero-mode equivalent circuit changes, and the relationship between the zero-mode current and the actual circulating current (8) changes. Therefore, the preset regression model is no longer applicable after the fault occurs. Therefore, the slope coefficient obtained by the current after the fault will be different from the slope coefficient obtained before the fault.

[0109] In some examples, when the preset time interval is a cycle data window, the data window includes data before and after the fault, such as Figure 4 As shown in the figure, the preset regression model cannot be accurately fitted, and the correlation coefficient will be significantly less than 1.

[0110] In some examples, when a phase-to-phase fault occurs, the transformer zero-mode equivalent circuit does not change, and the slope coefficient before and after the fault is theoretically the same. However, from the above analysis, it can be seen that the approximate circulating current obtained by formula (2) will be partially different from the actual circulating current; Figure 5 As shown, the correlation coefficient will still be less than 1.

[0111] In some examples, after a large number of simulations, the correlation coefficient threshold is set to 0.8, which can effectively identify various types of faults; the action criterion is shown in the following formula: if the correlation coefficient is less than 0.8, the excitation inrush current identification result is determined to be a fault, and the protection action is opened; otherwise, the excitation inrush current identification result is determined to be normal, and the protection is locked.

[0112] r(I 0 ,ID1 )<0.8 (15)

[0113] In some examples, when the no-load switch is closed under fault conditions, the current of the fault phase is affected by the fault current and the excitation current. The fault current may still be biased to one side of the time axis, and the fault phase current does not intersect with the unsaturated phase current. The approximate circulating current obtained by formula (2) is still the actual circulating current. At this time, the correlation coefficient between the zero-mode current and the approximate circulating current is close to 1, and the step of determining whether the correlation coefficient is less than the correlation coefficient threshold to determine the result of the excitation inrush current identification is invalid. Since it has been proved above that there is no phase that is always saturated, when the no-load switch is closed under fault conditions, it can be determined whether the value of the saturation coefficient is 1 to determine the result of the excitation inrush current identification.

[0114] In some examples, such as Figure 6 As shown in the figure, when the transformer is closed with no-load and a ground fault occurs on phase A, the transformer zero-mode equivalent circuit changes, and the corresponding proportional coefficient between the zero-mode current on the star side of the transformer and the circulating current on the triangle side also changes. However, the approximate circulating current accurately restores the actual circulating current and is proportional to the zero-mode current. At this time, the step of determining whether the correlation coefficient is less than the correlation coefficient threshold to determine the excitation inrush current identification result fails.

[0115] In some examples, the transformer is closed under fault conditions, and the transformer three-phase core saturation condition is as follows: Figure 7 As shown, the current of phase A is relatively large and does not affect the calculation of the approximate circulating current. Therefore, it is considered that phase A is always saturated, resulting in a saturation coefficient sat of 1 and open protection.

[0116] In order to verify the applicability of the present application, in some examples, after the transformer is closed without load, it is optionally set at 0.1s that a phase A grounding fault occurs in the system, the transition resistance is 500Ω, the three-phase residual magnetism of the transformer is 0.7pu, -0.35pu, and -0.35pu respectively, and the correlation coefficient between the approximate circulating current and the zero-mode inrush current is as follows: Figure 8 As shown in the figure, 0.1s after the fault occurs, the correlation coefficient immediately drops to a negative value, which is less than the correlation coefficient threshold, and then the excitation inrush current identification result is determined to be a fault, and the protection action is opened.

[0117] In some examples, after the transformer is closed without load, it is optionally set at 0.1s that a phase A ground fault occurs in the system, the transition resistance is 500Ω, the three-phase residual magnetism of the transformer is 0.7pu, -0.35pu, and -0.35pu respectively, and the saturation of the three-phase core of the transformer is as follows: Fig. 9 As shown, the A-phase current is affected by the fault current and the excitation current, which affects the calculation of the approximate circulating current. After the fault occurs 0.1s, the time when the A-phase core is in the saturated phase continues to be close to 0.02s. At this time, the step of judging whether the value of the saturation coefficient is 1 to determine the excitation surge current identification result fails.

[0118] In summary, if the correlation coefficient is less than the correlation coefficient threshold, the excitation inrush current identification result is determined to be a fault, and the protection action is opened. It can be seen that the excitation inrush current identification method proposed in this application is not affected by the transition resistance and the residual magnetism of the iron core.

[0119] In one embodiment, the step of outputting the result of magnetizing inrush current identification according to the correlation coefficient and the saturation coefficient further includes:

[0120] If the correlation coefficient is greater than or equal to the correlation coefficient threshold, and the value of the saturation coefficient is 0, it is determined that the excitation inrush current identification result is normal, and the protection is locked.

[0121] Specifically, for the case of normal occurrence of excitation inrush current, the zero-mode current is proportional to the actual circulating current, and the approximate circulating current is approximately equal to the actual circulating current. Then, the approximate circulating current is used to replace the actual circulating current, and it can be considered that the zero-mode current is proportional to the approximate circulating current; the correlation coefficient can reflect the fitting degree of the preset regression model to a certain extent. For the case of normal occurrence of excitation inrush current, the correlation coefficient is greater than or equal to the correlation coefficient threshold; for the case of normal occurrence of excitation inrush current, it is impossible for a single-phase iron core to always be in the saturated state, and then the saturation coefficient of the three-phase iron core is confirmed to be 0 according to the saturation state of each phase of the iron core. Furthermore, for the case of normal occurrence of excitation inrush current, the correlation coefficient is greater than or equal to the correlation coefficient threshold, and the saturation coefficient is 0, then the excitation inrush current identification result is determined to be normal, and the protection is locked.

[0122] In some examples, the zero-mode current is linearly strongly correlated with the approximate circulating current, the correlation coefficient is greater than or equal to the correlation coefficient threshold, and there is no single-phase core whose saturation state is always in the saturated phase, and the saturation coefficient value is 0; based on the correlation coefficient and the saturation coefficient, the excitation surge current identification result is determined to be normal, and the protection is locked; the correlation coefficient threshold can be 0.8, which can effectively identify various fault conditions.

[0123] In order to further illustrate the present application scheme, a specific example is given below. Fig.10 As shown, after the transformer is switched on without load, the three-phase current on the star side of the transformer is processed to obtain the zero-mode current, and then the approximate circulating current on the delta side of the transformer is obtained;

[0124] According to the transformer zero-mode equivalent circuit, a preset regression model is constructed; the correlation coefficient r between the zero-mode current and the approximate circulating current is determined, for example, the preset regression model is used to process the zero-mode current and the approximate circulating current; if the correlation coefficient r is less than 0.8, the flag bit d is determined. 1 The value of is 1; otherwise, determine the flag bit d 1 The value of is 0.

[0125] Determine the saturation state of each phase of the transformer core, for example, determine the saturation state of each phase of the transformer core based on the magnitude relationship of the three-phase current on the star side of the transformer; determine the saturation coefficient sat within a cycle, for example, determine the saturation coefficient of the three-phase core of the transformer according to the saturation state of each phase of the core; if the value of the saturation coefficient sat is 1, determine the flag bit d 2 The value of is 1; otherwise, determine the flag bit d 2 The value of is 0;

[0126] Set the flag bit d 1 and flag bit d 2 The values ​​of are added to obtain the sum of the two. If the sum is 1, the result of the excitation inrush current identification is determined to be a fault, and the protection action is opened; otherwise, the result of the excitation inrush current identification is determined to be an excitation inrush current, and the protection is locked.

[0127] Specifically, the situations in which the excitation surge current identification result is determined to be a fault include: the correlation coefficient is less than the correlation coefficient threshold and the saturation coefficient value is 0, or the correlation coefficient is greater than the correlation coefficient threshold and the saturation coefficient value is 1, or the correlation coefficient is less than the correlation coefficient threshold and the saturation coefficient value is 1; the situations in which the excitation surge current identification result is determined to be the occurrence of an excitation surge current include: the correlation coefficient is greater than the correlation coefficient threshold and the saturation coefficient value is 0.

[0128] According to the flag bit d 1 and flag bit d 2 The method for determining the excitation surge current identification result combines the correlation coefficient and the saturation coefficient, and the two complement each other. The calculation process is simple, the reliability of the output excitation surge current identification result is high, the excitation surge current can be effectively identified, the accuracy of identifying the excitation surge current is improved, the transformer differential protection is avoided from malfunctioning when the excitation surge current occurs, and the safety of the transformer operation is improved.

[0129] It should be understood that although Figure 1 , Fig.10 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 , Fig.10 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0130] In one embodiment, Fig.11As shown, a transformer excitation inrush current identification device is provided, comprising:

[0131] The data acquisition module 200 is used to acquire the three-phase current of the star side of the transformer;

[0132] The data processing module 220 is used to process the three-phase current on the star side of the transformer to obtain the zero-mode current, the approximate circulating current on the delta side of the transformer and the saturation coefficient of the three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values ​​of the three-phase current on the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase iron core; the saturation state of each phase iron core is determined based on the magnitude relationship of the three-phase current on the star side of the transformer; and is used to process the zero-mode current and the approximate circulating current using a preset regression model to determine the correlation coefficient between the zero-mode current and the approximate circulating current;

[0133] The result output module 240 is used to output the excitation inrush current identification result according to the correlation coefficient and the saturation coefficient.

[0134] In one of the embodiments, the data processing module 220 is used to identify the phase current with the middle value of the median of the three-phase current on the star side of the transformer as the phase current to be processed, and determine that the saturation state of the iron core corresponding to the phase current to be processed is an unsaturated phase; obtain the absolute value of the difference between the phase current to be processed and any remaining phase current in the three-phase current on the star side of the transformer; determine the saturation state of the iron core corresponding to the phase current whose absolute value is greater than the saturation threshold as a saturated phase; determine the saturation state of the iron core corresponding to the phase current whose absolute value is less than the saturation threshold as an unsaturated phase.

[0135] In one embodiment, it also includes:

[0136] The preset regression model building module is used to build a preset regression model according to the transformer zero-mode equivalent circuit.

[0137] In one embodiment, it also includes:

[0138] The saturation coefficient determination module is used to determine whether the saturation state of the iron core corresponding to at least one phase current is always a saturated phase within a preset time interval. If so, the value of the saturation coefficient is determined to be 1; otherwise, the value of the saturation coefficient is determined to be 0.

[0139] In one of the embodiments, the preset time interval includes a sampling data window;

[0140] The result output module 240 is used to determine that the excitation inrush current identification result is a fault and open a protection action if the correlation coefficient is less than the correlation coefficient threshold or the value of the saturation coefficient is 1.

[0141] In one embodiment, the result output module 240 is used to determine that the result of the magnetizing inrush current identification is normal and lock the protection if the correlation coefficient is greater than or equal to the correlation coefficient threshold and the value of the saturation coefficient is 0.

[0142] In one of the embodiments, the three-phase current on the star side of the transformer is an instantaneous value.

[0143] For the specific limitations of the transformer excitation surge current identification device, please refer to the limitations of the transformer excitation surge current identification method mentioned above, which will not be repeated here. Each module in the above-mentioned transformer excitation surge current identification device can be implemented in whole or in part by software, hardware and a combination thereof. The above-mentioned modules can be embedded in or independent of the processor in the terminal in the form of hardware, or can be stored in the memory in the terminal in the form of software, so that the processor can call and execute the operations corresponding to the above modules. It should be noted that the division of modules in the embodiment of the present application is schematic and is only a logical function division. There may be other division methods in actual implementation.

[0144] In one embodiment, a transformer excitation inrush current identification terminal is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the transformer excitation inrush current identification method when executing the computer program.

[0145] In some examples, the terminal may include a processor, a memory, a network interface, a display screen, and an input device connected via a system bus. The processor of the terminal is used to provide computing and control capabilities. The memory of the terminal includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The network interface of the terminal is used to communicate with an external terminal via a network connection. When the computer program is executed by the processor, a method for identifying a transformer excitation inrush current is implemented. The display screen of the terminal may be a liquid crystal display screen or an electronic ink display screen, and the input device of the terminal may be a touch layer covering the display screen, or a key, trackball, or touchpad provided on the terminal housing, or an external keyboard, touchpad, or mouse, etc.

[0146] A computer storage medium is used to store a computer program, and when the computer program is executed by a processor, the steps of the transformer excitation inrush current identification method are implemented.

[0147] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory or optical memory, etc. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0148] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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 specification.

[0149] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for identifying transformer excitation inrush current, characterized in that: The following steps are involved: The three-phase current on the star side of the transformer is processed to obtain the zero-mode current, the approximate circulating current on the delta side of the transformer and the saturation coefficient of the three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values ​​of the three-phase current on the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase iron core; the saturation state of each phase iron core is determined based on the magnitude relationship of the three-phase current on the star side of the transformer; Processing the zero-mode current and the approximate circulating current using a preset regression model to determine a correlation coefficient between the zero-mode current and the approximate circulating current; Outputting a magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient; The step of determining the approximate circulation comprises: The phase current with a middle magnitude among the three-phase currents on the star side of the transformer is identified as the approximate circulating current; The step of determining the saturation state of each phase core comprises: The phase current with the median value of the three-phase current on the star side of the transformer being in the middle is confirmed as the phase current to be processed, and the saturation state of the iron core corresponding to the phase current to be processed is determined to be a non-saturated phase; Obtaining the absolute value of the difference between the phase current to be processed and any remaining phase current in the three-phase current on the star side of the transformer; Determine the saturation state of the iron core corresponding to the phase current whose absolute value is greater than the saturation threshold as a saturated phase; Determine the saturation state of the iron core corresponding to the phase current whose absolute value is less than the saturation threshold as an unsaturated phase; The step of determining the saturation coefficient of the three-phase iron core comprises: Determine whether within a preset time interval, whether the saturation state of the iron core corresponding to at least one phase current is always a saturated phase, if so, determine the value of the saturation coefficient to be 1, otherwise, determine the value of the saturation coefficient to be 0; The step of outputting the result of magnetizing inrush current identification according to the correlation coefficient and the saturation coefficient comprises: If the correlation coefficient is less than the correlation coefficient threshold or the value of the saturation coefficient is 1, it is determined that the excitation inrush current identification result is a fault, and a protection action is opened.

2. The transformer excitation inrush current identification method according to claim 1, characterized in that: Before the step of using a preset regression model to process the zero-mode current and the approximate circulating current to determine the correlation coefficient between the zero-mode current and the approximate circulating current, the step further includes: The preset regression model is constructed according to the transformer zero-mode equivalent circuit.

3. The transformer excitation inrush current identification method according to claim 1, characterized in that: The preset time interval includes a sampling data window.

4. The transformer excitation inrush current identification method according to claim 1, characterized in that: The step of outputting the result of magnetizing inrush current identification according to the correlation coefficient and the saturation coefficient further includes: If the correlation coefficient is greater than or equal to the correlation coefficient threshold and the value of the saturation coefficient is 0, it is determined that the excitation inrush current identification result is normal, and protection is locked.

5. The transformer excitation inrush current identification method according to claim 1, characterized in that: The three-phase current on the star side of the transformer is an instantaneous value.

6. A transformer excitation inrush current identification device, characterized in that: include: A data acquisition module, used to obtain the three-phase current on the star side of the transformer; A data processing module, for processing the three-phase current on the star side of the transformer, obtaining the zero-mode current, the approximate circulating current on the delta side of the transformer, and the saturation coefficient of the three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values ​​of the three-phase current on the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase of the iron core; the saturation state of each phase of the iron core is determined based on the magnitude relationship of the three-phase current on the star side of the transformer; and for using a preset regression model to process the zero-mode current and the approximate circulating current to determine the correlation coefficient between the zero-mode current and the approximate circulating current; The data processing module is further used to identify the phase current with a middle magnitude among the three-phase currents on the star side of the transformer as the approximate circulating current; The data processing module is further used to identify the phase current whose median value is in the middle of the three-phase current on the star side of the transformer as the phase current to be processed, and determine that the saturation state of the iron core corresponding to the phase current to be processed is an unsaturated phase; obtain the absolute value of the difference between the phase current to be processed and any remaining phase current in the three-phase current on the star side of the transformer; determine the saturation state of the iron core corresponding to the phase current whose absolute value is greater than the saturation threshold as a saturated phase; determine the saturation state of the iron core corresponding to the phase current whose absolute value is less than the saturation threshold as an unsaturated phase; the data processing module is further used to determine whether there is at least one phase current within a preset time interval whose saturation state of the iron core is always a saturated phase, and if so, determine the value of the saturation coefficient to be 1, otherwise determine the value of the saturation coefficient to be 0; A result output module, used for outputting the excitation inrush current identification result according to the correlation coefficient and the saturation coefficient; The result output module is further used to determine that the excitation inrush current identification result is a fault and open a protection action if the correlation coefficient is less than a correlation coefficient threshold or the value of the saturation coefficient is 1.

7. A computer storage medium, characterized in that: Used to store a computer program, which, when executed by a processor, implements the steps of the transformer excitation inrush current identification method according to any one of claims 1 to 5.

8. A transformer excitation inrush current identification terminal, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the transformer excitation inrush current identification method according to any one of claims 1 to 5 are implemented.

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