阅读说明：本技术 变压器励磁涌流识别方法、装置、计算机存储介质和终端 (Transformer excitation inrush current identification method and device, computer storage medium and terminal ) 是由 习伟 尹项根 李肖博 姚浩 刘玢岩 于杨 潘远林 于 2021-08-18 设计创作，主要内容包括：本发明涉及一种变压器励磁涌流识别方法、装置、计算机存储介质和终端。其中,变压器励磁涌流识别方法包括：对变压器星型侧三相电流进行处理,得到零模电流、变压器三角形侧近似环流以及变压器三相铁芯的饱和系数；近似环流为对变压器星型侧三相电流的值进行比较得到；饱和系数为根据每相铁芯的饱和状态确定；每相铁芯的饱和状态为基于变压器星型侧三相电流的大小关系确定；采用预设回归模型处理零模电流与近似环流,确定零模电流与近似环流的相关系数；根据相关系数和饱和系数,输出励磁涌流识别结果。本申请能有效识别励磁涌流,提高了识别励磁涌流的准确率,避免变压器差动保护在发生励磁涌流时误动。(The invention relates to a method and a device for identifying magnetizing inrush current of a transformer, a computer storage medium and a terminal. The method for identifying the magnetizing inrush current of the transformer comprises the following steps: processing three-phase current at the star side of the transformer to obtain zero-mode current, approximate circular current at the triangular side of the transformer and saturation coefficients of a three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values of three-phase current at the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase of iron core; the saturation state of each phase of iron core is determined based on the magnitude relation of three-phase current on the star side of the transformer; processing the zero-mode current and the approximate circulating current by adopting a preset regression model, and determining a correlation coefficient of the zero-mode current and the approximate circulating current; and outputting the magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient. The method and the device can effectively identify the magnetizing inrush current, improve the accuracy of identifying the magnetizing inrush current and avoid the misoperation of the differential protection of the transformer when the magnetizing inrush current occurs.)

1. A transformer magnetizing inrush current identification method is characterized by comprising the following steps:

processing three-phase current at the star side of the transformer to obtain zero-mode current, approximate circular current at the triangular side of the transformer and saturation coefficients of a three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values of three-phase current on the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase of iron core; the saturation state of each phase of iron core is determined based on the magnitude relation of three-phase currents on the star side of the transformer;

processing the zero-mode current and the approximate circulating current by adopting a preset regression model, and determining a correlation coefficient of the zero-mode current and the approximate circulating current;

and outputting a magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient.

2. The transformer magnetizing inrush current identification method of claim 1, wherein the step of determining the saturation state of each phase core comprises:

determining phase current with the median of the three-phase current at the star side of the transformer in the middle as phase current to be processed, and determining the saturated state of an iron core corresponding to the phase current to be processed as an unsaturated phase;

acquiring an absolute value of a difference between the phase current to be processed and any phase current remaining in the star-side three-phase current of the transformer;

determining the saturation state of the iron core corresponding to the phase current of which the absolute value is greater than the saturation threshold value as a saturation phase;

and determining the saturation state of the iron core corresponding to the phase current with the absolute value smaller than the saturation threshold value as a non-saturated phase.

3. The method for identifying the magnetizing inrush current of the transformer according to claim 1 or 2, wherein before the step of processing the zero-mode current and the approximate circulating current by using a preset regression model and determining the correlation coefficient of the zero-mode current and the approximate circulating current, the method further comprises the steps of:

and constructing the preset regression model according to the zero-modulus equivalent circuit of the transformer.

4. The transformer magnetizing inrush current identification method of claim 2, wherein the step of determining the saturation coefficients of the three-phase cores comprises:

and judging whether the saturation state of the iron core corresponding to at least one phase current is always a saturation phase within a preset time interval, if so, determining the value of the saturation coefficient to be 1, and otherwise, determining the value of the saturation coefficient to be 0.

5. The transformer magnetizing inrush current identification method of claim 4, wherein the preset time interval comprises a sampling data window;

the step of outputting the magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient includes:

and if the correlation coefficient is smaller than the correlation coefficient threshold value or the value of the saturation coefficient is 1, determining that the excitation inrush current identification result is a fault, and opening a protection action.

6. The method for identifying inrush current in a transformer according to claim 5, wherein the step of outputting the inrush current identification result according to the correlation coefficient and the saturation coefficient further comprises:

and if the correlation coefficient is greater than or equal to the correlation coefficient threshold value and the saturation coefficient value is 0, determining that the excitation inrush current identification result is normal, and locking protection.

7. The method for identifying the magnetizing inrush current of the transformer according to claim 1, wherein the star-side three-phase current of the transformer is an instantaneous value.

8. A transformer magnetizing inrush current recognition device, comprising:

the data acquisition module is used for acquiring three-phase current of the star side of the transformer;

the data processing module is used for processing the three-phase current at the star side of the transformer to obtain zero-mode current, approximate circular current at the triangular side of the transformer and saturation coefficients of a three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values of three-phase current on the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase of iron core; the saturation state of each phase of iron core is determined based on the magnitude relation of three-phase currents on the star side of the transformer; the system comprises a current source, a current source and a current source, wherein the current source is used for generating a zero-mode current and the current source;

and the result output module is used for outputting the magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient.

9. A computer storage medium for storing a computer program which, when executed by a processor, performs the steps of the transformer magnetizing inrush current identification method according to any of claims 1 to 7.

10. A transformer magnetizing inrush current identification terminal comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the steps of the transformer magnetizing inrush current identification method according to any one of claims 1 to 7 when executing the computer program.

Technical Field

The invention relates to the technical field of power system relay protection, in particular to a transformer magnetizing inrush current identification method and device, a computer storage medium and a terminal.

Background

The main protection of the transformer generally adopts longitudinal differential protection, the differential protection is based on kirchhoff current law, the principle is simple, and the applicability is strong. However, the transformer has a complex electromagnetic transient characteristic, and in the case of no-load closing, a large exciting current, i.e., an exciting inrush current, may occur. The magnetizing inrush current may cause malfunction of differential protection, and endanger the safe operation of the power system.

With the development of relay protection technology of power systems, due to the importance of transformer protection and the complexity of magnetizing inrush current, methods for identifying magnetizing inrush current of transformers are continuously proposed. According to the traditional second harmonic principle and the discontinuous angle principle, when symmetrical inrush current occurs in a transformer, the occurrence of the magnetizing inrush current is difficult to identify. The identification method comprehensively utilizing voltage and current construction criteria, such as utilizing equivalent instantaneous inductance, power differential, magnetic flux characteristic principles and the like, can accurately solve the problem only by acquiring voltage quantity or triangular side current data. The traditional scheme for identifying the magnetizing inrush current of the transformer is imperfect, so that the misoperation rate of the differential protection of the transformer is relatively high.

In the implementation process, the inventor finds that at least the following problems exist in the conventional technology: the traditional scheme for identifying the magnetizing inrush current of the transformer has the problem of low accuracy.

Disclosure of Invention

Therefore, it is necessary to provide a transformer inrush current identification method, a transformer inrush current identification device, a computer storage medium, and a terminal, for solving the problem of low accuracy in identifying transformer inrush currents.

A transformer magnetizing inrush current identification method comprises the following steps:

processing three-phase current at the star side of the transformer to obtain zero-mode current, approximate circular current at the triangular side of the transformer and saturation coefficients of a three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values of three-phase current at the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase of iron core; the saturation state of each phase of iron core is determined based on the magnitude relation of three-phase current on the star side of the transformer;

processing the zero-mode current and the approximate circulating current by adopting a preset regression model, and determining a correlation coefficient of the zero-mode current and the approximate circulating current;

and outputting the magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient.

In one embodiment, the step of determining the saturation state of each phase core comprises:

determining phase current with the median of three-phase current at the star side of the transformer in the middle as phase current to be processed, and determining the saturated state of an iron core corresponding to the phase current to be processed as an unsaturated phase;

acquiring an absolute value of a difference between a phase current to be processed and any residual phase current in a star-side three-phase current of the transformer;

determining the saturation state of the iron core corresponding to the phase current of which the absolute value is greater than the saturation threshold value as a saturation phase;

and determining the saturation state of the iron core corresponding to the phase current with the absolute value smaller than the saturation threshold value as the unsaturated phase.

In one embodiment, before the step of processing the zero-mode current and the approximate circulating current by using a preset regression model and determining the correlation coefficient of the zero-mode current and the approximate circulating current, the method further comprises the steps of:

and constructing a preset regression model according to the zero-modulus equivalent circuit of the transformer.

In one embodiment, the step of determining the saturation factor of the three-phase core comprises:

and judging whether the saturation state of the iron core corresponding to at least one phase current is always a saturation phase within a preset time interval, if so, determining the value of the saturation coefficient to be 1, and otherwise, determining the value of the saturation coefficient to be 0.

In one embodiment, the preset time interval comprises a window of sampled data;

and outputting a magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient, wherein the step comprises the following steps of:

and if the correlation coefficient is smaller than the correlation coefficient threshold value or the value of the saturation coefficient is 1, determining that the excitation inrush current identification result is a fault, and opening a protection action.

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

and if the correlation coefficient is greater than or equal to the correlation coefficient threshold value and the saturation coefficient value is 0, determining that the magnetizing inrush current identification result is normal, and locking protection.

In one embodiment, the star-side three-phase current of the transformer is an instantaneous value.

A transformer magnetizing inrush current identification device, comprising:

the data acquisition module is used for acquiring three-phase current of the star side of the transformer;

the data processing module is used for processing the three-phase current at the star side of the transformer to obtain zero-mode current, approximate circular current at the triangular side of the transformer and saturation coefficients of a three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values of three-phase current at the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase of iron core; the saturation state of each phase of iron core is determined based on the magnitude relation of three-phase current on the star side of the transformer; the device comprises a preset regression model, a zero-mode current and an approximate circulating current, and a correlation coefficient for determining the zero-mode current and the approximate circulating current;

and the result output module is used for outputting the magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient.

A computer storage medium for storing a computer program which, when executed by a processor, implements the steps of the above-described transformer magnetizing inrush current identification method.

A transformer magnetizing inrush current identification terminal comprises a memory, a processor and a computer program which is stored on the memory and can run on the processor, wherein the processor realizes the steps of the transformer magnetizing inrush current identification method when executing the computer program.

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

according to the method, only the three-phase current at the star side of the transformer is used as original data, the correlation coefficient and the saturation coefficient are combined, the magnetizing inrush current identification result is output by complementation, and the magnetizing inrush current can be identified without acquiring any parameter of the transformer in advance. The process of obtaining the correlation coefficient and the saturation coefficient is simple and convenient, and the reliability of the output excitation inrush current identification result is high. The method and the device can effectively identify the magnetizing inrush current, improve the accuracy of identifying the magnetizing inrush current, avoid the false operation of the transformer differential protection when the magnetizing inrush current occurs, and improve the safety of the transformer in the operation process.

Drawings

FIG. 1 is a schematic flow chart of a method for identifying magnetizing inrush current of a transformer according to an embodiment;

FIG. 2 is a graph of approximate circulating current, actual circulating current, and zero mode current for normal inrush current in one embodiment;

FIG. 3 is a graph comparing approximate circulating current, actual circulating current, and zero mode current for an embodiment of phase A ground fault;

FIG. 4 is a graphical representation of correlation coefficients of approximate circulating current and zero mode current for a phase-to-ground fault in one embodiment;

FIG. 5 is a graphical representation of the correlation coefficients of approximate circulating current and zero mode current for an AB interphase short circuit fault in one embodiment;

FIG. 6 is a schematic diagram illustrating correlation coefficients of approximate circulating current and zero-mode current of a transformer switch-on in a fault in one embodiment;

FIG. 7 is a schematic diagram illustrating a saturation condition of a three-phase core of a transformer when the transformer is switched on in a fault according to an embodiment;

FIG. 8 is a diagram illustrating the correlation coefficients of the approximate circulating current and the zero-mode inrush current of the transformer switching on under the A-phase belt resistance ground fault in one embodiment;

FIG. 9 is a schematic diagram illustrating a saturation condition of a three-phase core of a transformer when a phase-A resistive ground fault occurs during a switching-on of the transformer in one embodiment;

FIG. 10 is a flow chart illustrating a transformer magnetizing inrush current identification method according to another embodiment;

fig. 11 is a schematic diagram of a transformer magnetizing inrush current identification device in one embodiment.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

With the development of relay protection technology of power systems, methods for identifying transformer inrush current are continuously proposed due to the importance of transformer protection and the complexity of the inrush current. At present, the second harmonic principle is most widely applied, and whether the second harmonic is magnetizing inrush current or not is identified by calculating the ratio of the second harmonic in the fundamental wave content. However, when the transformer generates symmetrical inrush current, the second harmonic is smaller, the novel iron core material can also reduce the content of the second harmonic, and the inrush current cannot be identified at the moment. The discontinuous angle principle identifies inrush currents based on the characteristic that transformer core flux periodically goes into saturation, but an unrecognizable situation may occur for symmetric inrush currents. The waveform symmetry principle divides the waveform in a cycle into a front part, a rear part or an upper part and a lower part, and the symmetry of the two parts is compared to identify the inrush current, so that the surge current is rejected when the fault waveform has larger distortion obviously. The identification method comprehensively utilizing voltage and current construction criteria, such as utilizing equivalent instantaneous inductance, power differential, magnetic flux characteristic principles and the like, can accurately solve the problem only by acquiring voltage quantity or triangular side current data.

According to the method, only the three-phase current at the star side of the transformer is used as original data, the correlation coefficient and the saturation coefficient are combined, the magnetizing inrush current identification result is output by complementation, and the magnetizing inrush current can be identified without acquiring any parameter of the transformer in advance. The process of obtaining the correlation coefficient and the saturation coefficient is simple and convenient, and the reliability of the output excitation inrush current identification result is high. The method and the device can effectively identify the magnetizing inrush current, improve the accuracy of identifying the magnetizing inrush current, avoid the false operation of the transformer differential protection when the magnetizing inrush current occurs, and improve the safety of the transformer in the operation process.

The method and the device are applied to identification of the magnetizing inrush current of the transformer after no-load closing of the transformer.

In one embodiment, as shown in fig. 1, a method for identifying magnetizing inrush current of a transformer is provided, which is described by taking the method as an example for a terminal, and includes the following steps:

step S100, processing three-phase current at the star side of the transformer to obtain zero-mode current, approximate circular current at the triangular side of the transformer and saturation coefficients of a three-phase iron core of the transformer;

the approximate circulating current is obtained by comparing values of three-phase current on the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase of iron core; the saturation state of each phase of iron core is determined based on the magnitude relation of three-phase current on the star side of the transformer;

specifically, the terminal obtains the three-phase current at the star side of the transformer, and processes the three-phase current at the star side of the transformer to obtain zero-mode current, approximate circular current at the triangular side of the transformer and saturation coefficients of a three-phase iron core of the transformer. Further, the terminal can obtain the zero-mode current by adopting a mode of averaging three-phase currents on the star side of the transformer.

In one embodiment, the star-side three-phase current of the transformer is an instantaneous value. The transformer delta-side near circulating current may be an approximation of the transformer delta-side circulating current. The saturation state of each phase of iron core can comprise a saturated phase and an unsaturated phase, and the terminal can determine the saturation coefficient of the three-phase iron core of the transformer according to the saturation state of each phase of iron core; the saturation coefficient is used for judging whether the transformer generates excitation inrush current or not.

In some examples, obtaining the star-side three-phase current of the transformer includes i_A、i_B、i_CThe zero mode current can be obtained by equation (1):

i₀＝(i_A+i_B+i_C)/3 (1)

in some examples, when a magnetizing inrush current occurs in a transformer (e.g., after the transformer is unloaded), the magnetizing inrush current flows through a certain side of the transformer (e.g., the star side of the transformer). Under the condition of not considering the remanence, at least one phase of iron core is unsaturated, the excitation inductance of the unsaturated phase (namely the phase corresponding to the unsaturated iron core) is larger, the excitation current is negligible, and the phase current (star-shaped side of the transformer) of the unsaturated phase can approximately replace the triangular side circulating current of the transformer. For example, the transformer star-side unsaturated phase current is regarded as a transformer triangle-side approximate circulating current, wherein the phase current with the middle transformer star-side three-phase current size is determined as the transformer star-side unsaturated phase current; the approximate circulating current of the triangular side of the transformer is obtained by the formula (2), wherein mean is a value with the value obtained in the middle, and the negative sign indicates that the current direction is opposite.

i_D1＝-median(i_A，i_B，i_C) (2)

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

Step S120, processing the zero-mode current and the approximate circulating current by adopting a preset regression model, and determining a correlation coefficient of the zero-mode current and the approximate circulating current;

specifically, the preset regression model may include a regression equation, and the covariance of the zero-mode current and the approximate circulating current, the variance of the zero-mode current, and the variance of the approximate circulating current are obtained by processing the zero-mode current and the approximate circulating current; the correlation coefficient is used for reflecting the fitting degree of the preset regression model to a certain degree, further, the standard deviation (arithmetic square root of the variance) of the zero-mode current and the standard deviation of the approximate circulating current are obtained according to the variance of the zero-mode current and the variance of the approximate circulating current, and the correlation coefficient of the zero-mode current and the approximate circulating current is obtained.

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 using a least squares method; the correlation coefficient of the zero-mode current with the approximate circulating current may be a simple correlation coefficient; the correlation coefficient r between the zero mode current and the approximate circulating current can be obtained by equation (3), where i₀Is zero mode current, i_D1Is approximately circular; wherein cov (i)₀，i_Dl) Is i₀And i_D1Covariance of (i), var (i)₀) Is i₀Variance of (a), var (i)_D1) Is i_D1The variance of (a);

further, the absolute value of the correlation coefficient is between 0 and 1. In general, a correlation coefficient closer to 1 indicates a stronger correlation between two quantities, whereas a correlation coefficient closer to 0 indicates a weaker correlation between two quantities.

And step S140, outputting a magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient.

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

According to the method, only the three-phase current at the star side of the transformer is used as original data, the correlation coefficient and the saturation coefficient are combined, the magnetizing inrush current identification result is output by complementation, and the magnetizing inrush current can be identified without acquiring any parameter of the transformer in advance.

In one embodiment, the step of determining the saturation state of each phase core comprises:

determining phase current with the median of three-phase current at the star side of the transformer in the middle as phase current to be processed, and determining the saturated state of an iron core corresponding to the phase current to be processed as an unsaturated phase;

specifically, when the transformer generates excitation inrush current, the excitation current of a saturated phase is far larger than that of an unsaturated phase, and star-side three-phase current i of the transformer is compared_A、i_B、i_CDetermining the iron core corresponding to the phase current with the value in the middle as an unsaturated phase;

acquiring an absolute value of a difference between a phase current to be processed and any residual phase current in a star-side three-phase current of the transformer;

determining the saturation state of the iron core corresponding to the phase current of which the absolute value is greater than the saturation threshold value as a saturation phase;

and determining the saturation state of the iron core corresponding to the phase current with the absolute value smaller than the saturation threshold value as the unsaturated phase.

In particular, the saturation state of each phase core is determined, and more than one phase core may be unsaturated at the same time. After the transformer is switched on in an idle load mode, three-phase circulating currents in the triangular winding are equal to one another on the triangular side of the transformer, and the star-shaped side phase current of the transformer is approximately equal to the triangular side circulating current of the transformer under the condition that the iron core is unsaturated; further, the phase currents of the unsaturated phases are also approximately equal for the star side of the transformer. Based on the principle, after the iron core of one phase at the star side of the transformer is determined to be the unsaturated phase, the phase current of the determined unsaturated phase and the phase current of any remaining phase are obtained, the absolute value of the difference value between the two phases is compared with a saturation threshold, if the absolute value of the difference value is smaller than the saturation threshold, the corresponding iron core is determined to be the unsaturated phase, and if not, the corresponding iron core is determined to be the saturated phase. The saturation threshold may be an absolute value of a difference between a preset phase current of the unsaturated phase and a phase current of the saturated phase.

In some examples, the saturation threshold may be a minimum value of an absolute value of a difference between a phase current of the unsaturated phase and a phase current of the saturated phase; as shown in equation (4), the saturation state of each phase of the iron core can be determined, where S_nThe iron core is in a saturated state and comprises a saturated phase and an unsaturated phase; n may be any one of ABC three phases, S_nMay be S_A、S_B、S_C；S_nWhen the value is 0, it means that the iron core corresponding to n is an unsaturated phase, and S_nWhen the value is 1, the iron core corresponding to n is in a saturated phase; epsilon is a saturation threshold; i.e. i_DIs a true circulating current.

In one embodiment, before the step of processing the zero-mode current and the approximate circulating current by using a preset regression model and determining the correlation coefficient of the zero-mode current and the approximate circulating current, the method further comprises the steps of:

and constructing a preset regression model according to the zero-modulus equivalent circuit of the transformer.

Specifically, the preset regression model may include a regression equation, and the regression equation is constructed according to the zero-modulus equivalent circuit of the transformer; the regression equation may include slope coefficients; according to the zero-mode equivalent circuit of the transformer, a relational expression of system power supply voltage and current under neglected resistance and a relational expression of induced electromotive force of a three-phase excitation branch of the transformer and actual circulation on a triangular side of the transformer can be obtained; further, obtaining a relational expression of the zero-mode current at the star side and the circular current at the triangular side of the transformer, and constructing a regression equation; the degree of fitting of the regression equation can be reflected to some extent by the correlation coefficient.

In some examples, the system supply voltage and current should satisfy equation (5) with zero-modulus equivalent circuit of the transformer, ignoring resistance, where u_A、u_B、u_CPower supply voltages of ABC three-phase system, e_a、e_b、e_cRespectively inducing electromotive force for three-phase excitation branches of the transformer; l is_s、L_s0Respectively a positive sequence inductor and a zero sequence inductor of the system; l is_σThe star-shaped side leakage inductor of the transformer is provided.

The actual circulating current on the triangular side of the transformer should satisfy the following formula:

adding formula (5) and substituting formula (6) to obtain:

the initial closing current is 0, and the two sides of the formula (7) are integrated at the same time to obtain:

wherein L is_σDThe transformer is a triangular side leakage inductor. As can be seen from the equation (8), when the resistance is neglected, the star-side zero-mode current of the transformer is proportional to the triangular-side circulating current, and the proportionality coefficient is L_σD/(L_s0+L_σ)。

Further, by replacing the actual circular flow with an approximate circular flow, a regression equation can be constructed:

wherein the content of the first and second substances,is an estimate of the slope coefficient and,as an estimate of the intercept coefficient, I₀In the form of a matrix of zero-mode currents, I_D1Approximating the matrix form of the circulating current. The matrix form of the regression equation is:

an unbiased estimate of the slope coefficient β can be obtained using a least squares method:

in the case of normal occurrence of magnetizing 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. For example, as shown in FIG. 2, 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_iFor the model predicted value isAverage number ofDetermination coefficient R²Can be used to measure the proportion of the variation of the dependent variable that can be accounted for by the independent variable, i.e., to measure how well the estimated regression equation fits. As shown in equation (12), a determination coefficient can be obtained:

the decision coefficient is the square of the correlation coefficient, and further, the correlation coefficient can reflect the fitting degree of the preset regression model to a certain extent.

In one embodiment, the step of determining the saturation factor of the three-phase core comprises:

and judging whether the saturation state of the iron core corresponding to at least one phase current is always a saturation phase within a preset time interval, if so, determining the value of the saturation coefficient to be 1, and otherwise, determining the value of the saturation coefficient to be 0.

Specifically, the preset time interval may be a data window; under the condition that excitation inrush current normally occurs, a phase iron core of which the saturation state is always a saturation phase cannot exist within a preset time interval, if the phase iron core of which the saturation state is always the saturation phase exists, a fault is considered to occur, further, the value of the saturation coefficient is determined to be 1, and otherwise, the value of the saturation coefficient is determined to be 0.

In some examples, without considering flux decay during the initial closing period, the core saturation level for a three-phase transformer can be expressed as:

in the formula, T_A、T_B、T_CRespectively representing the saturation degrees of the phase A, the phase B and the phase C iron cores of the transformer; alpha is an initial phase angle; t is time; omega is angular velocity; k_rA、K_rB、K_rCRespectively representing the remanence occupation ratios of the A phase, the B phase and the C phase of the transformer; when the | T | is less than or equal to 1, the iron core of the corresponding phase is an unsaturated phase, and when the | T | is more than 1, the iron core of the corresponding phase is a saturated phase. In this case, the steady-state value of the remanence can reach 0.7 of the saturation remanence at most, and there is no possibility that | T | > 1 is always satisfied, that is, there is no possibility that a one-phase iron core in which the saturation state is always a saturated phase exists in a case where the magnetizing inrush current normally occurs. And detecting the saturation state of each phase of iron core within a preset time interval, judging whether the saturation state of the iron core corresponding to at least one phase of current is always a saturated phase, if so, determining the value of the saturation coefficient to be 1, and if not, determining the value of the saturation coefficient to be 0.

In some examples, the preset time interval may be one window of periodic data (e.g., 20 ms). The saturation coefficient of the three-phase iron core can be determined according to the formula (12), whether the saturation state of the iron core corresponding to at least one phase current is always a saturated phase is judged within one cycle, if yes, the saturation coefficient of the three-phase iron core is determined to be 1, a fault is judged to occur, and a protection action is opened; if not, determining that the saturation coefficient of the three-phase iron core is 0, judging that excitation inrush current occurs, and locking the protection action; wherein sat represents the saturation coefficient of the three-phase iron core, and t represents the starting time of a periodic data window.

And outputting a magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient, wherein the step comprises the following steps of:

and if the correlation coefficient is smaller than the correlation coefficient threshold value or the value of the saturation coefficient is 1, determining that the excitation inrush current identification result is a fault, and opening a protection action.

Specifically, the preset time interval includes a sampling data window; when the correlation coefficient is smaller than the correlation coefficient threshold value, part of the approximate circulating current is different from the actual circulating current, the relation 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, in a preset time interval, the saturation state of the iron core corresponding to at least one phase current is always in a saturated phase; and if the situation does not belong to normal magnetizing inrush current, determining that the magnetizing inrush current identification result is a fault, and opening a protection action. It should be noted that, in the case where the switching-on failure is supplemented by determining whether or not the value of the saturation coefficient is 1, and in the case where the correlation coefficient is smaller than the correlation coefficient threshold value, the correlation is "or", and if one of the determination results is yes, the magnetizing inrush current recognition result is determined to be a failure, and the protection operation is released.

In some examples, the preset time interval may be one window of periodic data (e.g., 20 ms); for the case of ground fault, the approximate circulating current and transformer zero-modulus equivalent circuit changes. Specifically, when a ground fault occurs, the current of the fault phase is affected by the combined action of the fault current and the exciting current, and is not always biased to one side of the time axis, the fault phase current and the unsaturated phase current have a crossed part, and at this time, the approximate circulating current obtained according to the formula (2) is partially different from the actual circulating current; as shown in fig. 3, in the case of a phase a ground fault, the correlation coefficient is significantly reduced at the time of the fault occurrence; in addition, the zero-mode equivalent circuit of the transformer is changed, and the relation (8) between the zero-mode current and the actual circulating current is changed, so that the preset regression model is not applicable after the fault occurs, and the slope coefficient obtained by using the current after the fault is different from the slope coefficient obtained before the fault.

In some examples, when the predetermined time interval is a periodic data window, and the data window includes data before and after the fault, as shown in fig. 4, the predetermined regression model cannot be accurately fitted, and the correlation coefficient is significantly smaller than 1.

In some examples, for the case of phase-to-phase fault, the zero-modulus equivalent circuit of the transformer is not changed, and the slope coefficients before and after the fault are theoretically the same, but as can be seen from the above analysis, the approximate circulating current obtained according to equation (2) at this time is partially different from the actual circulating current; as shown in fig. 5, the correlation coefficient will still be less than 1.

In some examples, through a large number of simulations, the relationship number threshold is set to 0.8, and various types of faults can be effectively identified; the action criterion is shown as the following formula, if the correlation coefficient is less than 0.8, the magnetizing inrush current identification result is determined to be a fault, and a protection action is opened; otherwise, determining that the magnetizing inrush current identification result is normal, and locking protection.

r(I₀,I_D1)＜0.8 (15)

In some examples, when no-load switching-on is performed under a fault condition, the current of a fault phase is subjected to the combined action of the fault current and the exciting current, the fault current may still be biased to one side of a time axis, the fault phase current and the unsaturated phase current are not intersected, the approximate circulating current obtained according to the 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 whether the correlation coefficient is smaller than the correlation coefficient threshold value or not is judged so as to determine that the step of the exciting inrush current identification result is invalid. Since the above-mentioned proved that there is no always saturated phase, when no-load switching is in a fault condition, it can be determined whether the value of the saturation coefficient is 1, so as to determine the magnetizing inrush current identification result.

In some examples, as shown in fig. 6, when a transformer is switched on in a no-load state in a case of a ground fault occurring in phase a, a zero-modulus equivalent circuit of the transformer changes, a proportional coefficient corresponding to a zero-modulus current on a star side of the transformer and a triangular side loop current of the transformer also changes, but the approximate loop current accurately restores an actual loop current and is proportional to the zero-modulus current, and at this time, it is determined whether a correlation coefficient is smaller than a correlation coefficient threshold value, so that a step of determining a magnetizing inrush current identification result fails.

In some examples, when the transformer is switched on in a fault, the three-phase core of the transformer is saturated as shown in fig. 7, the phase a current is large, and the calculation of the approximate circulating current is not affected, so that the phase a is considered to be always saturated, the saturation coefficient sat is 1, and the protection is opened.

In order to verify the applicability of the application, in some examples, after the transformer is switched on in an idle state, optionally setting the time at 0.1s, the system has an a-phase grounding fault, the resistance value of the transition resistor is 500 Ω, the three-phase remanence of the transformer is 0.7pu, -0.35pu respectively, the correlation coefficient of the approximate circulating current and the zero-mode inrush current is as shown in fig. 8, after the fault occurs at 0.1s, the correlation coefficient immediately drops to a negative value and is smaller than the correlation coefficient threshold, and then it is determined that the excitation inrush current identification result is a fault, and a protection action is opened.

In some examples, after the transformer is switched on in an idle state, optionally, the system has an a-phase ground fault at a time of 0.1s, the resistance value of the transition resistor is 500 Ω, the three-phase remanence of the transformer is 0.7pu, -0.35pu, respectively, the saturation condition of the three-phase iron core of the transformer is as shown in fig. 9, the a-phase current is affected by the joint action of fault current and exciting current, so that the calculation of approximate circulating current is influenced, the time that the a-phase iron core is in a saturated phase after the fault occurs for 0.1s is continuously close to 0.02s, and at this time, whether the value of the saturation coefficient is 1 or not is judged, so that the step of determining the magnetizing inrush current identification result is failed.

In summary, if the correlation coefficient is smaller than the correlation coefficient threshold, it is determined that the magnetizing inrush current identification result is a fault, and a protection action is opened. Therefore, the magnetizing inrush current identification method is not influenced by the transition resistance and the residual magnetism of the iron core.

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

and if the correlation coefficient is greater than or equal to the correlation coefficient threshold value and the saturation coefficient value is 0, determining that the magnetizing inrush current identification result is normal, and locking protection.

Specifically, for the case of normal occurrence of magnetizing inrush current, the zero-mode current is proportional to the actual circulating current, the approximate circulating current is approximately equal to the actual circulating current, and the actual circulating current is replaced by the approximate circulating current, which can be considered that the zero-mode current is proportional to the approximate circulating current; the correlation coefficient can reflect the fitting degree of a preset regression model to a certain degree, and is greater than or equal to a correlation coefficient threshold value under the condition that excitation inrush current normally occurs; in the case of normal occurrence of magnetizing inrush current, it is impossible to have a one-phase iron core whose saturation state is always the saturated phase, and it is confirmed that the saturation factor of the three-phase iron core is 0 from the saturation state of each phase iron core. Further, when the inrush current occurs normally, if the correlation coefficient is greater than or equal to the correlation coefficient threshold value and the saturation coefficient is 0, it is determined that the inrush current identification result is normal, and protection is locked.

In some examples, the zero-mode current is strongly linearly related to the approximate circulating current, the correlation coefficient is greater than or equal to a correlation coefficient threshold, and there is no one-phase iron core whose saturation state is always a saturated phase, and the saturation coefficient has a value of 0; determining that the magnetizing inrush current identification result is normal according to the correlation coefficient and the saturation coefficient, and locking for protection; the correlation coefficient threshold may be 0.8, which may effectively identify various fault conditions.

In order to further explain the scheme of the application, a specific example is described below, and as shown in fig. 10, after the transformer is switched on in an idle load, the three-phase current at the star side of the transformer is processed to obtain a zero-mode current, so as to obtain an approximate circular current at the triangle side of the transformer;

constructing a preset regression model according to the zero-modulus equivalent circuit of the transformer; determining a correlation coefficient r of the zero-mode current and the approximate circulating current, for example, processing the zero-mode current and the approximate circulating current by using a preset regression model; if the correlation coefficient r is less than 0.8, determining the flag bit d₁Has a value of 1; otherwise, determining the flag bit d₁The value of (d) is 0.

Determining the saturation state of each phase of iron core of the transformer, for example, determining the saturation state of each phase of iron core of the transformer based on the magnitude relation of three-phase currents on the star side of the transformer; determining a cycle internal saturation coefficient sat, for example, determining the saturation coefficients of three-phase iron cores of the transformer according to the saturation state of each phase of iron core; if the value of the saturation coefficient sat is 1, determining a flag bit d₂Has a value of 1; otherwise, determining the flag bit d₂Is 0;

will mark bitd₁And a flag bit d₂The sum of the two values is obtained by adding, if the sum value is 1, the magnetizing inrush current identification result is determined to be a fault, and a protection action is opened; otherwise, determining that the magnetizing inrush current identification result is the magnetizing inrush current, and locking the protection.

Specifically, determining that the magnetizing inrush current identification result is a fault includes: the correlation coefficient is smaller than the correlation coefficient threshold value and the saturation coefficient is 0, or the correlation coefficient is larger than the correlation coefficient threshold value and the saturation coefficient is 1, or the correlation coefficient is smaller than the correlation coefficient threshold value and the saturation coefficient is 1; the determining that the magnetizing inrush current identification result is the condition of the occurrence of the magnetizing inrush current comprises the following steps: the correlation coefficient is greater than the correlation coefficient threshold and the saturation coefficient has a value of 0.

According to the flag bit d₁And a flag bit d₂The method for determining the magnetizing inrush current identification result combines the correlation coefficient and the saturation coefficient, the correlation coefficient and the saturation coefficient are complementary to each other, the operation process is simple and convenient, the reliability of the output magnetizing inrush current identification result is high, the magnetizing inrush current can be effectively identified, the accuracy of identifying the magnetizing inrush current is improved, the misoperation of the transformer differential protection when the magnetizing inrush current occurs is avoided, and the safety of the transformer in the operation process is improved.

It should be understood that, although the steps in the flowcharts of fig. 1 and 10 are shown in sequence as indicated by the arrows, the steps are not necessarily performed in sequence as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least some of the steps in fig. 1 and 10 may include multiple sub-steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of performing the sub-steps or stages is not necessarily sequential, but may be performed alternately or alternately with other steps or at least some of the sub-steps or stages of other steps.

In one embodiment, as shown in fig. 11, there is provided a transformer magnetizing inrush current identification device, including:

the data acquisition module 200 is used for acquiring three-phase current of the star side of the transformer;

the data processing module 220 is used for processing the three-phase current at the star side of the transformer to obtain zero-mode current, approximate circular current at the triangular side of the transformer and saturation coefficients of a three-phase iron core of the transformer; the approximate circulating current is obtained by comparing the values of three-phase current at the star side of the transformer; the saturation coefficient is determined according to the saturation state of each phase of iron core; the saturation state of each phase of iron core is determined based on the magnitude relation of three-phase current on the star side of the transformer; the device comprises a preset regression model, a zero-mode current and an approximate circulating current, and a correlation coefficient for determining the zero-mode current and the approximate circulating current;

and a result output module 240, configured to output the magnetizing inrush current identification result according to the correlation coefficient and the saturation coefficient.

In one embodiment, the data processing module 220 is configured to determine a phase current with a median value of three-phase currents on a star side of the transformer as a to-be-processed phase current, and determine that a saturated state of an iron core corresponding to the to-be-processed phase current is an unsaturated phase; acquiring an absolute value of a difference between a phase current to be processed and any residual phase current in a star-side three-phase current of the transformer; determining the saturation state of the iron core corresponding to the phase current of which the absolute value is greater than the saturation threshold value as a saturation phase; and determining the saturation state of the iron core corresponding to the phase current with the absolute value smaller than the saturation threshold value as the unsaturated phase.

In one embodiment, the method further comprises the following steps:

and the preset regression model building module is used for building a preset regression model according to the transformer zero-modulus equivalent circuit.

In one embodiment, the method further comprises the following steps:

and the saturation coefficient determining module is used for judging whether the saturation state of the iron core corresponding to at least one phase current is always a saturation phase within a preset time interval, if so, determining the value of the saturation coefficient to be 1, and if not, determining the value of the saturation coefficient to be 0.

In one embodiment, the preset time interval comprises a window of sampled data;

and the result output module 240 is configured to determine that the magnetizing inrush current identification result is a fault and open a protection operation if the correlation coefficient is smaller than the correlation coefficient threshold or the value of the saturation coefficient is 1.

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

In one embodiment, the star-side three-phase current of the transformer is an instantaneous value.

For specific limitations of the transformer inrush current identification device, reference may be made to the above limitations of the transformer inrush current identification method, and details thereof are not repeated here. All or part of each module in the transformer magnetizing inrush current identification device can be realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent of a processor in the terminal, and can also be stored in a memory in the terminal in a software form, so that the processor can call and execute operations corresponding to the modules. It should be noted that, in the embodiment of the present application, the division of the module is schematic, and is only one logic function division, and there may be another division manner in actual implementation.

In one embodiment, a transformer magnetizing inrush current identification terminal is provided, which includes a memory, a processor, and a computer program stored on the memory and executable on the processor, and the processor implements the steps of the transformer magnetizing inrush current identification method when executing the computer program.

In some examples, the terminal may include a processor, a memory, a network interface, a display screen, and an input device connected by a system bus. Wherein the processor of the terminal is configured to provide computing and control capabilities. The memory of the terminal comprises a nonvolatile 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 an operating system and computer programs in the non-volatile storage medium. The network interface of the terminal is used for connecting and communicating with an external terminal through a network. The computer program is executed by a processor to implement a transformer magnetizing inrush current identification method. The display screen of the terminal can be a liquid crystal display screen or an electronic ink display screen, and the input device of the terminal can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on a shell of the terminal, an external keyboard, a touch pad or a mouse and the like.

A computer storage medium for storing a computer program which, when executed by a processor, implements the steps of the above-described transformer magnetizing inrush current identification method.

It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database or other medium used in the embodiments provided herein can include at least one of non-volatile and volatile memory. Non-volatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical storage, or the like. Volatile Memory can include Random Access Memory (RAM) or external cache Memory. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), among others.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.