A method, device and storage medium for monitoring working state of current transformer

Abstract

The present invention discloses a method, device and storage medium for monitoring the working state of a current transformer, wherein the method comprises: performing equivalent operation on a power transmission system to obtain an equivalent circuit; using a phasor algorithm to solve the first line parameter of the equivalent circuit, performing linear fitting processing on the first line parameter according to a linear regression model to obtain a first fitting line parameter; using a differential equation method to form a differential equation group according to the sampling points of the equivalent circuit, using a least square method to solve the differential equation group to obtain a second fitting line parameter; using the ratio of the first fitting line parameter and the second fitting line parameter to the actual line parameter as a first comparison result and a second comparison result, respectively, and obtaining a working state monitoring result of the current transformer by comparing the first comparison result and the comparison result with a preset threshold range. The embodiment of the present invention can effectively improve the monitoring effect of the working state of the current transformer.

Description

Technical Field

[0001] The present invention relates to the field of monitoring technology, and in particular to a method, a device and a storage medium for monitoring the working state of a current transformer. Background Art

[0002] CT (current transformer) is an important component in the power system. The task of CT is to accurately measure the current flowing through each node in the power grid for use by the secondary side measurement equipment, protection equipment, automatic control equipment, and fault recording equipment. However, the current value of the power grid varies greatly in different states, and CT has to withstand currents with very large amplitude differences; CT is installed outdoors, and the natural environment and electromagnetic environment are relatively harsh, which has a great impact on the reliability and output accuracy of CT. In addition, during the on-site construction process, there will be situations such as CT polarity reverse connection and CT phase sequence connection due to wiring errors. The above factors will cause the measured current value to be inaccurate or even wrong, affecting the reliability of the secondary side equipment operation, resulting in abnormal data uploaded by the monitoring background, and incorrect energy metering; in the event of a fault, the current size and direction are incorrect, resulting in a series of problems such as the protection device refusing to operate and malfunctioning, which seriously affects the safety and reliability of the power grid operation. Therefore, the stability and reliability of the CT working state is of great significance to the safe operation of the power grid.

[0003] According to the various problems that occur in CT, they can be divided into the following two situations: (1) Abnormal performance of CT itself: including reduced accuracy due to CT aging or moisture, abnormal output characteristics due to reduced internal insulation strength of CT, and output interference under strong electromagnetic conditions. (2) CT external wiring errors: including reverse polarity of CT and wrong phase sequence of CT. For the various abnormal conditions that occur in the above-mentioned CT, the existing current transformer working status monitoring method is usually implemented by physical methods, specifically: from the physical properties of CT, its working status is further reflected, such as: dissolved gas chromatography analysis, infrared thermal imaging monitoring, SF6 gas humidity, and silicone rubber jacket hydrophobicity inspection. However, the physical properties of the current transformer cannot accurately reflect its working status. The existing current transformer working status monitoring method is difficult to accurately monitor the working status of the current transformer, resulting in poor monitoring of the working status of the current transformer. Summary of the invention

[0004] The present invention provides a current transformer working state monitoring method, device and storage medium to solve the technical problem that the existing current transformer working state monitoring method is difficult to accurately monitor the working state of the current transformer, resulting in poor current transformer working state monitoring effect.

[0005] An embodiment of the present invention provides a method for monitoring the working state of a current transformer, comprising:

[0006] The power transmission system is equivalently obtained to obtain an equivalent circuit, wherein the power transmission system includes a current transformer, the equivalent circuit includes a power supply voltage, an equivalent capacitor, an equivalent resistor and an equivalent inductor, the input end of the power supply voltage is grounded, the output end of the power supply voltage is connected to the input end of the equivalent inductor through the equivalent resistor, the output end of the equivalent inductor is grounded, and the equivalent capacitor is connected between the power supply voltage and the equivalent resistor;

[0007] A phasor algorithm is used to solve and obtain a first line parameter of the equivalent circuit, and a linear fitting process is performed on the first line parameter according to a linear regression model to obtain a first fitting line parameter;

[0008] A differential equation method is used to form a differential equation group according to the sampling points of the equivalent circuit, and a least square method is used to solve the differential equation group to obtain second fitting line parameters;

[0009] The ratios of the first fitting line parameter and the second fitting line parameter to the actual line parameter are respectively used as the first comparison result and the second comparison result, and the working state monitoring result of the current transformer is obtained by comparing the first comparison result and the comparison result with a preset threshold range.

[0010] Furthermore, the step of using a phasor algorithm to solve and obtain a first line parameter of the equivalent circuit, and performing a linear fitting process on the first line parameter according to a linear regression model to obtain a first fitting line parameter, includes:

[0011] The voltage data and current data of the equivalent circuit are sampled using a preset number of sampling points, and a plurality of sampling points within the first power frequency cycle are selected from the preset number of sampling points, and a voltage phasor and a current phasor of each sampling point are obtained using a Fourier algorithm, and the voltage phasor and the current phasor of each sampling point are used as a group of line parameters to obtain a plurality of groups of line parameters;

[0012] A univariate linear regression process is performed on several groups of the line parameters according to a linear regression model to obtain first fitting line parameters.

[0013] Furthermore, the voltage phasor and current phasor of each sampling point are obtained by using the Fourier algorithm, and the voltage phasor and current phasor of each sampling point are used as a set of line parameters to obtain several sets of line parameters, including:

[0014] The voltage phasor and current phasor of each sampling point are obtained by using the Fourier algorithm, and after obtaining the phasor of each sampling point, the sampling point is moved backward to obtain a new sampling point by using a sliding data window, and the voltage phasor and current phasor of the new sampling point are obtained to obtain several groups of line parameters corresponding to all sampling points.

[0015] Furthermore, the linear regression model includes:

[0016] y=Ax+b

[0017] Among them, y is the line parameter of each group, x is the number of groups, and b is a constant term.

[0018] Furthermore, the step of using the differential equation method to form a differential equation group according to the sampling points of the equivalent circuit, and using the least square method to solve the differential equation group to obtain the second fitting line parameters includes:

[0019] Establishing a differential equation with every three adjacent sampling points of the equivalent circuit, and establishing an overdetermined differential equation group according to the differential equation;

[0020] The overdetermined difference equations are solved by least square method to obtain the second fitting line parameters.

[0021] Furthermore, the method of using the least square method to solve the overdetermined difference equations to obtain the second fitting line parameters includes:

[0022] Establish the minimum error average and expression of the fitting curve at each sampling point:

[0023]

[0024] Among them, (x i ,y i ) is a pair of observations, y i is the second fitting parameter to be fitted, f(x i ,a i ) is the fitting value of the fitting curve;

[0025] Taking partial derivatives of the minimum error average sum expression to obtain a normal equation of the least squares method;

[0026] a=(X T X) -1 X T Y

[0027] Where a is the second fitting line parameter, X is the X matrix, and Y is the Y matrix;

[0028] An X matrix and a Y matrix are calculated based on the current data and the voltage data of the sampling points, and the X matrix and the Y matrix are substituted into the normal equation to calculate the second fitting line parameters.

[0029] Furthermore, the working state monitoring result of the current transformer is obtained by comparing the first comparison result and the comparison result with a preset threshold range:

[0030] If any comparison result of the first comparison result and the second comparison result is less than the lower resistance limit value, greater than the upper resistance limit value, or the variance of the resistance parameter is greater than the maximum fluctuation degree, it is determined that the working state of the current transformer is abnormal;

[0031] Otherwise, it is determined that the working state of the current transformer is normal.

[0032] An embodiment of the present invention provides a current transformer working state monitoring device, comprising:

[0033] A line equivalent module, used for performing equivalent operation on a power transmission system to obtain an equivalent circuit, wherein the power transmission system includes a current transformer, the equivalent circuit includes a power supply voltage, an equivalent capacitor, an equivalent resistor and an equivalent inductor, the input end of the power supply voltage is grounded, the output end of the power supply voltage is connected to the input end of the equivalent inductor through the equivalent resistor, the output end of the equivalent inductor is grounded, and the equivalent capacitor is connected between the power supply voltage and the equivalent resistor;

[0034] A first fitting module, configured to obtain a first line parameter of the equivalent circuit by using a phasor algorithm, and to obtain a first fitting line parameter by performing a linear fitting process on the first line parameter according to a linear regression model;

[0035] A second fitting module is used to form a differential equation group according to the sampling points of the equivalent circuit using a differential equation method, and solve the differential equation group using a least square method to obtain second fitting line parameters;

[0036] The working state judgment module is used to use the ratios of the first fitting line parameter and the second fitting line parameter to the actual line parameter as the first comparison result and the second comparison result respectively, and obtain the working state monitoring result of the current transformer by comparing the first comparison result and the comparison result with the preset threshold range.

[0037] An embodiment of the present invention provides a computer-readable storage medium, which includes a stored computer program; wherein the computer program, when running, controls the device where the computer-readable storage medium is located to execute the current transformer working status monitoring method as described above.

[0038] The embodiment of the present invention can perform online monitoring of the working state of the current transformer, and can effectively improve the convenience of detecting the working state of the current transformer. The embodiment of the present invention adopts the phasor method and the differential equation method to obtain multiple groups of line parameters to perform long-term continuous monitoring of the current transformer, and can accurately and timely obtain the monitoring results when the current transformer has slight performance abnormalities; the embodiment of the present invention can further judge the various abnormal states of the current transformer, and is not affected by the power grid structure and operation mode, thereby effectively improving the reliability of the current transformer working state monitoring; the embodiment of the present invention can rely on the existing protection device or measurement and control device, and realize the working state monitoring of the current transformer by adding a software algorithm, without adding dedicated hardware equipment, which can not only effectively improve the applicability, but also effectively reduce the equipment deployment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flow chart of a method for monitoring the working state of a current transformer provided by an embodiment of the present invention;

[0040] Figure 2 is a schematic diagram of the structure of a power transmission system provided by an embodiment of the present invention;

[0041] Figure 3 is a schematic diagram of the structure of an equivalent circuit provided by an embodiment of the present invention;

[0042] Figure 4 It is a schematic diagram of the structure of a power transmission line simulation model provided by an embodiment of the present invention;

[0043] Figure 5 It is a schematic diagram of obtaining the line resistance of a CT in a normal operating state by using a phasor method provided by an embodiment of the present invention;

[0044] Figure 6 It is a schematic diagram of obtaining the line resistance of CT ab phase sequence wiring error using the phasor method provided by an embodiment of the present invention;

[0045] Figure 7 It is a schematic diagram of obtaining the line resistance of CT output superimposed interference by using the phasor method provided in an embodiment of the present invention;

[0046] Figure 8 It is a schematic diagram of obtaining the line resistance with reduced CT output accuracy using the phasor method provided in an embodiment of the present invention;

[0047] Fig. 9 It is a schematic diagram of obtaining the line resistance of a CT in a normal operating state by using a differential equation method provided by an embodiment of the present invention;

[0048] Fig.10 It is a schematic diagram of obtaining the line resistance of CT ab phase sequence wiring error using the differential equation method provided by an embodiment of the present invention;

[0049] Fig.11 It is a schematic diagram of obtaining the line resistance of the CT output superimposed interference by the differential equation method provided in an embodiment of the present invention;

[0050] Fig.12 It is a schematic diagram of obtaining the line resistance with reduced CT output accuracy by using the differential equation method provided by an embodiment of the present invention;

[0051] Fig.13 It is a schematic diagram of obtaining the line resistance of a CT in a normal operating state by using the phasor method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0053] In the description of this application, 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 one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0054] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0055] See also Figure 1-12 , embodiments of the present invention provide Figure 1 A method for monitoring the working state of a current transformer is shown, comprising:

[0056] S1. Equivalently obtain an equivalent circuit by performing an equivalent operation on the power transmission system, wherein the power transmission system includes a current transformer, the equivalent circuit includes a power supply voltage, an equivalent capacitor, an equivalent resistor and an equivalent inductor, the input end of the power supply voltage is grounded, the output end of the power supply voltage is connected to the input end of the equivalent inductor through an equivalent resistor, the output end of the equivalent inductor is grounded, and the equivalent capacitor is connected between the power supply voltage and the equivalent resistor;

[0057] The embodiments of the present invention are applicable to Figure 2 In the power transmission system shown in FIG. 1 , the power transmission system includes a power supply voltage, a system impedance, a voltage transformer and a current transformer, wherein the output end of the power supply voltage is connected to the system impedance and the current transformer in sequence, and the voltage transformer is connected between the system impedance and the current transformer. In order to simplify the calculation, the embodiment of the present invention uses a "Γ-type" equivalent circuit of a lumped parameter model to perform an equivalent to the system, and obtains Figure 3 The equivalent circuit is shown.

[0058] See also Figure 3 , the power supply is an ideal sinusoidal voltage source, U is the power supply voltage, C is the equivalent capacitance of the line, R is the equivalent resistance of the line, and L is the equivalent inductance of the line. Because the capacitance C parameter is usually small, the calculation error will be large. Therefore, the embodiment of the present invention regards the capacitance as a known quantity and takes the line impedance parameters R and L as the calculation objects.

[0059] S2, using a phasor algorithm to solve and obtain first line parameters of the equivalent circuit, and performing linear fitting processing on the first line parameters according to a linear regression model to obtain first fitting line parameters;

[0060] S3, using a differential equation method to form a differential equation group according to the sampling points of the equivalent circuit, and using a least square method to solve the differential equation group to obtain the second fitting line parameters;

[0061] S4. Use the ratios of the first fitting line parameter and the second fitting line parameter to the actual line parameter as the first comparison result and the second comparison result respectively, and obtain the working state monitoring result of the current transformer by comparing the first comparison result and the comparison result with the preset threshold range.

[0062] In one embodiment, a phasor algorithm is used to solve and obtain a first line parameter of an equivalent circuit, and a linear fitting process is performed on the first line parameter according to a linear regression model to obtain a first fitting line parameter, including:

[0063] A preset number of sampling points are used to sample the voltage data and current data of the equivalent circuit, and a plurality of sampling points within the first power frequency cycle are selected from the preset number of sampling points, and a voltage phasor and a current phasor of each sampling point are obtained by using a Fourier algorithm, and the voltage phasor and the current phasor of each sampling point are used as a group of line parameters to obtain a plurality of groups of line parameters;

[0064] In a specific implementation, the sampling frequency is 2kHz, and the data of three power frequency cycles are used as an example for explanation, and a total of 120 sampling points are used. The embodiment of the present invention first takes 40 sampling points in the first power frequency cycle, uses the Fourier algorithm to obtain the voltage phasor and the current phasor, and then uses the sliding data window to move back 1 sampling point each time to obtain a new set of phasors, and a total of 80 sets of phasors can be obtained. A set of line parameters can be obtained through each set of phasors, and 80 sets of phasors can obtain 80 sets of line parameters corresponding to them.

[0065] A univariate linear regression process is performed on several groups of line parameters according to the linear regression model to obtain the first fitting line parameters.

[0066] In one embodiment, a voltage phasor and a current phasor of each sampling point are obtained by using a Fourier algorithm, and the voltage phasor and the current phasor of each sampling point are used as a set of line parameters to obtain several sets of line parameters, including:

[0067] The voltage phasor and current phasor of each sampling point are obtained by Fourier algorithm, and the sampling point is moved backward to obtain a new sampling point after the phasor of each sampling point is obtained by sliding data window, and the voltage phasor and current phasor of the new sampling point are obtained to obtain several groups of line parameters corresponding to all sampling points.

[0068] Among them, resistance is the real part of impedance, and inductive reactance is the imaginary part of impedance:

[0069]

[0070] R a =Re(Z a ) (2)

[0071] X a =Im(Z a ) (3)

[0072] The several groups of line parameters calculated by the embodiment of the present invention are multiple offline line parameter calculation values. When the current transformer works in a normal state, the calculated line parameter values ​​will be relatively stable and will be distributed near the actual values. The embodiment of the present invention processes the data through a linear regression model to obtain the fitted line parameters.

[0073] In one embodiment, the linear regression model includes:

[0074] y=Ax+b

[0075] Among them, y is the line parameter of each group, x is the number of groups, and b is a constant term.

[0076] Solve for the constant term b:

[0077]

[0078] in, is the mean value of variable x, is the mean value of the variable y.

[0079] In one embodiment, a differential equation method is used to form a differential equation group according to the sampling points of the equivalent circuit, and a least square method is used to solve the differential equation group to obtain the second fitting line parameters, including:

[0080] A differential equation is established at every three adjacent sampling points of the equivalent circuit, and an overdetermined differential equation group is established based on the differential equation;

[0081] The expression for converting the differential equation to the difference equation is:

[0082]

[0083]

[0084]

[0085] The difference equation is:

[0086]

[0087] The difference equations are:

[0088]

[0089] The least square method is used to solve the overdetermined difference equations to obtain the second fitting line parameters.

[0090] In the embodiment of the present invention, the least square method is used to achieve adequate fitting of data by minimizing the average sum of errors.

[0091] In one embodiment, the least square method is used to solve the overdetermined difference equations to obtain the second fitting line parameters, including:

[0092] Let the multivariate function be:

[0093]

[0094] in, is a set of selected linearly independent functions, a k is the unknown coefficient (k=1,2,…,m <j)。

[0095] Establish the minimum error average and expression between each sampling point and the fitting curve at the sampling point:

[0096]

[0097] Among them, (x i ,y i ) is a pair of observations, y i is the second fitting parameter to be fitted, f(x i ,a i ) is the fitting value of the fitting curve;

[0098] Taking partial derivatives of the minimum error average and expression, we obtain the normal equation of the least squares method;

[0099] a=(X T X) -1 X T Y (13)

[0100] Where a is the second fitting line parameter, X is the X matrix, and Y is the Y matrix;

[0101] In the embodiment of the present invention, if f(x) is to be minimized, f(x) should be at an extreme point, that is, f(x) is i The partial derivative of should be zero.

[0102] In the above formula (13):

[0103]

[0104] Calculate the coefficients a in the above formula j , achieving least squares fitting.

[0105] The X matrix and the Y matrix are calculated based on the current data and the voltage data of the sampling points, and the X matrix and the Y matrix are substituted into the normal equation to calculate the second fitting line parameters.

[0106] In the embodiment of the present invention, the derivatives of the current data and the voltage data are set as two variables, and the resistance R' and the inductance L' are used as two unknown coefficients, and the solution format of the least square method can be obtained. That is:

[0107]

[0108] In the embodiment of the present invention, the current data and voltage data of each sampling point are substituted into the X matrix and the Y matrix, and the resistance and inductance of the line are obtained by fitting according to formula (13).

[0109] The embodiment of the present invention can obtain multiple groups of line parameters through the phasor method and the differential equation method, so as to accurately reflect the changing trend of the line parameters, and fit the fitted line parameters based on the multiple groups of line parameters, and compare the fitted line parameters with the actual parameters, which can effectively improve the accuracy of current transformer working status monitoring.

[0110] In one embodiment, the working state monitoring result of the current transformer is obtained by comparing the first comparison result and the comparison result with a preset threshold range:

[0111] If any comparison result of the first comparison result and the second comparison result is smaller than the lower resistance limit value, larger than the upper resistance limit value, or the variance of the resistance parameter is larger than the maximum fluctuation degree, it is determined that the working state of the current transformer is abnormal.

[0112] In the embodiment of the present invention, the following formula is used as a basis for judging whether the working state of the current transformer is abnormal:

[0113] a=R′ / R (14)

[0114]

[0115] Where, a is the ratio of the line parameter fitting value (R′) to the actual value (R), which is used to describe the degree of conformity between the resistance fitting value and the actual value. max is the upper limit criterion of the resistance of the current transformer under normal operation, and a min It is the lower limit criterion of resistance under normal operation of current transformer. R To calculate the variance of the resistance parameter, σ is used to describe the fluctuation of the resistance. max It is the maximum fluctuation degree under normal operation of CT.

[0116] In the embodiment of the present invention, when one of the first comparison result and the second comparison result satisfies formula (14), it is judged that the working state of the current transformer is abnormal; when both the first comparison result and the second comparison result do not satisfy formula (14), it is judged that the working state of the current transformer is normal.

[0117] The implementation of the embodiments of the present invention has the following beneficial effects:

[0118] The embodiments of the present invention respectively adopt the phasor method and the differential equation method to obtain multiple groups of line parameters, so as to accurately reflect the changing trend of the line parameters, and fit the fitted line parameters based on the multiple groups of line parameters, and compare the fitted line parameters with the actual parameters, which can effectively improve the accuracy of current transformer working status monitoring.

[0119] Furthermore, the embodiment of the present invention adopts the phasor method and the differential equation method to respectively obtain multiple groups of line parameters to fit the line parameters, and judges the working state of the current transformer by combining the fitted line parameters obtained by the two methods. When the current transformer has different abnormal working states, it can accurately judge that the working state of the current transformer is abnormal, thereby further improving the accuracy of current transformer working state monitoring.

[0120] One embodiment of the present invention is:

[0121] Step 1: Establish a calculation model. The embodiment of the present invention adopts Figure 4 The transmission line simulation model shown in the figure takes the LGJ-150 line as an example. The total length of the line is 100km and the line voltage level is 110kV. The line resistance is 0.21Ω / km, the line reactance is 0.40Ω / km, and the line susceptance is 2.85×10 -6 S / km

[0122] The following four conditions are set for the operation status of the current transformer: (1) normal operation of CT; (2) wrong CT ab phase sequence wiring; (3) CT output is interfered by noise; (4) CT output accuracy decreases.

[0123] Step 2: Use the phasor method to calculate the line parameter resistance value R, perform linear regression on the calculation results, and obtain the final calculated value of the line parameter. Figure 5-8 , which is a schematic diagram of solving line parameters under different CT operating states using the phasor method according to an embodiment of the present invention.

[0124] Step 3: Use differential equations and least squares algorithm to obtain the calculation result of line resistance parameter R, please refer to Figure 9-12 , which is a schematic diagram of solving line parameters under different CT operating states using a differential equation method according to an embodiment of the present invention.

[0125] Step 4: Substitute the calculation results of steps 2 and 3 into the following formula to determine the CT operating status:

[0126] a=R′ / R

[0127]

[0128] Let a min =0.8, a max =1.3, select the maximum variance σ max = 10. If the obtained simulation result is within the threshold, it is determined that the current transformer is working in a normal state, otherwise it is considered that the current transformer is working in an abnormal state.

[0129] The results are shown in Table 1 below:

[0130] Table 1: Judgment results

[0131]

[0132] The specific analysis based on Table 1 is as follows:

[0133] When the current transformer works normally, the line parameters calculated by the two algorithms are consistent with the actual parameters and have small fluctuations.

[0134] When the two phases ab are connected in reverse, the current phase measured by the current transformer will change by 120°. At this time, the resistance obtained will be too large and the phase will be opposite. The a value of the resistance criterion is -2.149, which is less than the lower limit a. min =0.8, it can be judged that the working state of the current transformer is abnormal.

[0135] When the output of the current transformer is interfered by noise, the Fourier algorithm in the phasor method has good high-frequency noise filtering capabilities, so its calculation results are less affected by noise interference. However, in the differential equation algorithm, the calculated resistance parameters will fluctuate greatly, with a variance of 33.618, exceeding the upper limit of the variance σ max =10, it can be judged that the working state of the current transformer is abnormal.

[0136] When the output accuracy of the current transformer decreases due to various reasons, there will be a deviation between the actual output value of the CT and the true value, resulting in the resistance parameter being smaller or larger than the actual value. The simulation results show that the resistance values ​​calculated by the two methods are smaller than the actual value, and the a value of the resistance criterion is 0.667, which is smaller than the lower limit a. min =0.8, it can be judged that the working status is abnormal.

[0137] The embodiment of the present invention can perform online monitoring of the working state of the current transformer, and can effectively improve the convenience of detecting the working state of the current transformer. The embodiment of the present invention adopts the phasor method and the differential equation method to obtain multiple groups of line parameters to perform long-term continuous monitoring of the current transformer, and can accurately and timely obtain the monitoring results when the current transformer has slight performance abnormalities; the embodiment of the present invention can further judge the various abnormal states of the current transformer, and is not affected by the power grid structure and operation mode, thereby effectively improving the reliability of the current transformer working state monitoring; the embodiment of the present invention can rely on the existing protection device or measurement and control device, and realize the working state monitoring of the current transformer by adding a software algorithm, without adding dedicated hardware equipment, which can not only effectively improve the applicability, but also effectively reduce the equipment deployment cost.

[0138] See also Fig.13 Based on the same inventive concept as the above-mentioned embodiment of the invention, an embodiment of the present invention provides a current transformer working state monitoring device, comprising:

[0139] The line equivalent module 10 is used to obtain an equivalent circuit by equivalentizing the power transmission system, wherein the power transmission system includes a current transformer, the equivalent circuit includes a power supply voltage, an equivalent capacitor, an equivalent resistor and an equivalent inductor, the input end of the power supply voltage is grounded, the output end of the power supply voltage is connected to the input end of the equivalent inductor through the equivalent resistor, the output end of the equivalent inductor is grounded, and the equivalent capacitor is connected between the power supply voltage and the equivalent resistor;

[0140] A first fitting module 20 is used to obtain first line parameters of the equivalent circuit by using a phasor algorithm, and to obtain first fitting line parameters by performing linear fitting processing on the first line parameters according to a linear regression model;

[0141] A second fitting module 30 is used to form a differential equation group according to the sampling points of the equivalent circuit using a differential equation method, and solve the differential equation group using a least square method to obtain second fitting line parameters;

[0142] The working state judgment module 40 is used to take the ratios of the first fitting line parameter and the second fitting line parameter to the actual line parameter as the first comparison result and the second comparison result respectively, and obtain the working state monitoring result of the current transformer by comparing the first comparison result and the comparison result with the preset threshold range.

[0143] In one embodiment, the first fitting module 20 is specifically configured to:

[0144] A preset number of sampling points are used to sample the voltage data and current data of the equivalent circuit, and a plurality of sampling points within the first power frequency cycle are selected from the preset number of sampling points, and a voltage phasor and a current phasor of each sampling point are obtained by using a Fourier algorithm, and the voltage phasor and the current phasor of each sampling point are used as a group of line parameters to obtain a plurality of groups of line parameters;

[0145] A univariate linear regression process is performed on several groups of line parameters according to the linear regression model to obtain the first fitting line parameters.

[0146] In one embodiment, a voltage phasor and a current phasor of each sampling point are obtained by using a Fourier algorithm, and the voltage phasor and the current phasor of each sampling point are used as a set of line parameters to obtain several sets of line parameters, including:

[0147] The voltage phasor and current phasor of each sampling point are obtained by Fourier algorithm, and the sampling point is moved backward to obtain a new sampling point after the phasor of each sampling point is obtained by sliding data window, and the voltage phasor and current phasor of the new sampling point are obtained to obtain several groups of line parameters corresponding to all sampling points.

[0148] In one embodiment, the linear regression model includes:

[0149] y=Ax+b

[0150] Among them, y is the line parameter of each group, x is the number of groups, and b is a constant term.

[0151] In one embodiment, the second fitting module 30 is specifically configured to:

[0152] A differential equation is established at every three adjacent sampling points of the equivalent circuit, and an overdetermined differential equation group is established based on the differential equation;

[0153] The least square method is used to solve the overdetermined difference equations to obtain the second fitting line parameters.

[0154] In one embodiment, the least square method is used to solve the overdetermined difference equations to obtain the second fitting line parameters, including:

[0155] Establish the minimum error average and expression between each sampling point and the fitting curve at the sampling point:

[0156]

[0157] Among them, (x i ,y i ) is a pair of observations, y i is the second fitting parameter to be fitted, f(x i ,a i ) is the fitting value of the fitting curve;

[0158] Taking partial derivatives of the minimum error average and expression, we obtain the normal equation of the least squares method;

[0159] a=(X T X) -1 X T Y

[0160] Where a is the second fitting line parameter, X is the X matrix, and Y is the Y matrix;

[0161] The X matrix and the Y matrix are calculated based on the current data and the voltage data of the sampling points, and the X matrix and the Y matrix are substituted into the normal equation to calculate the second fitting line parameters.

[0162] In one embodiment, the working state determination module 40 is specifically used for:

[0163] If any comparison result of the first comparison result and the second comparison result is smaller than the lower resistance limit value, larger than the upper resistance limit value, or the variance of the resistance parameter is larger than the maximum fluctuation degree, it is determined that the working state of the current transformer is abnormal.

[0164] An embodiment of the present invention provides a computer-readable storage medium, which includes a stored computer program; wherein the computer program, when running, controls a device where the computer-readable storage medium is located to execute the current transformer working state monitoring method as described above.

[0165] The above are preferred embodiments of the present invention. It should be noted that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for monitoring the working state of a current transformer, characterized in that: include: The power transmission system is equivalently obtained to obtain an equivalent circuit, wherein the power transmission system includes a current transformer, the equivalent circuit includes a power supply voltage, an equivalent capacitor, an equivalent resistor and an equivalent inductor, the input end of the power supply voltage is grounded, the output end of the power supply voltage is connected to the input end of the equivalent inductor through the equivalent resistor, the output end of the equivalent inductor is grounded, and the equivalent capacitor is connected between the power supply voltage and the equivalent resistor; A phasor algorithm is used to solve and obtain a first line parameter of the equivalent circuit, and a linear fitting process is performed on the first line parameter according to a linear regression model to obtain a first fitting line parameter, including: sampling voltage data and current data of the equivalent circuit using a preset number of sampling points, selecting a plurality of sampling points within a first power frequency cycle from the preset number of sampling points, using a Fourier algorithm to obtain a voltage phasor and a current phasor of each sampling point, and taking the voltage phasor and the current phasor of each sampling point as a group of line parameters to obtain a plurality of groups of line parameters; and performing a univariate linear regression process on the plurality of groups of line parameters according to a linear regression model to obtain a first fitting line parameter; A differential equation method is used to form a differential equation group according to the sampling points of the equivalent circuit, and a least square method is used to solve the differential equation group to obtain second fitting line parameters; The ratios of the first fitting line parameter and the second fitting line parameter to the actual line parameter are respectively used as the first comparison result and the second comparison result, and the working state monitoring result of the current transformer is obtained by comparing the first comparison result and the second comparison result with a preset threshold range.

2. The method for monitoring the working state of a current transformer according to claim 1, characterized in that: The voltage phasor and current phasor of each sampling point are obtained by using the Fourier algorithm, and the voltage phasor and current phasor of each sampling point are used as a set of line parameters to obtain several sets of line parameters, including: The voltage phasor and current phasor of each sampling point are obtained by using the Fourier algorithm, and after obtaining the phasor of each sampling point, the sampling point is moved backward to obtain a new sampling point by using a sliding data window, and the voltage phasor and current phasor of the new sampling point are obtained to obtain several groups of line parameters corresponding to all sampling points.

3. The method for monitoring the working state of a current transformer according to claim 1, characterized in that: The linear regression model comprises: y=Ax+b Among them, y is the line parameter of each group, x is the number of groups, and b is a constant term.

4. The current transformer working state monitoring method according to claim 1, characterized in that: The method of using a differential equation to form a differential equation group according to the sampling points of the equivalent circuit, and using a least square method to solve the differential equation group to obtain the second fitting line parameters includes: Establishing a differential equation with every three adjacent sampling points of the equivalent circuit, and establishing an overdetermined differential equation group according to the differential equation; The overdetermined difference equations are solved by least square method to obtain the second fitting line parameters.

5. The method for monitoring the working state of a current transformer according to claim 4, characterized in that: The method of using the least square method to solve the overdetermined difference equation group to obtain the second fitting line parameters includes: Establish the minimum error average and expression of the fitting curve at each sampling point: Among them, (x i ,y i ) is a pair of observations, y i is the second fitting parameter to be fitted, f(x i ,a i ) is the fitting value of the fitting curve; Taking partial derivatives of the minimum error average sum expression to obtain a normal equation of the least squares method; a=(X T X) -1 X T Y Where a is the second fitting line parameter, X is the X matrix, and Y is the Y matrix; An X matrix and a Y matrix are calculated based on the current data and the voltage data of the sampling points, and the X matrix and the Y matrix are substituted into the normal equation to calculate the second fitting line parameters.

6. The method for monitoring the working state of a current transformer according to claim 1, characterized in that: The working state monitoring result of the current transformer is obtained by comparing the first comparison result and the second comparison result with a preset threshold range: If any comparison result of the first comparison result and the second comparison result is less than the lower resistance limit value, greater than the upper resistance limit value, or the variance of the resistance parameter is greater than the maximum fluctuation degree, it is determined that the working state of the current transformer is abnormal; Otherwise, it is determined that the working state of the current transformer is normal.

7. A current transformer working status monitoring device, characterized in that: include: A line equivalent module, used for performing equivalent operation on a power transmission system to obtain an equivalent circuit, wherein the power transmission system includes a current transformer, the equivalent circuit includes a power supply voltage, an equivalent capacitor, an equivalent resistor and an equivalent inductor, the input end of the power supply voltage is grounded, the output end of the power supply voltage is connected to the input end of the equivalent inductor through the equivalent resistor, the output end of the equivalent inductor is grounded, and the equivalent capacitor is connected between the power supply voltage and the equivalent resistor; The first fitting module is used to use a phasor algorithm to solve and obtain a first line parameter of the equivalent circuit, and to perform a linear fitting process on the first line parameter according to a linear regression model to obtain a first fitting line parameter; specifically used to: use a preset number of sampling points to sample the voltage data and current data of the equivalent circuit, and select a plurality of sampling points within the first power frequency cycle from the preset number of sampling points, use a Fourier algorithm to obtain a voltage phasor and a current phasor of each sampling point, and use the voltage phasor and the current phasor of each sampling point as a group of line parameters to obtain a plurality of groups of line parameters; perform a univariate linear regression process on the plurality of groups of line parameters according to a linear regression model to obtain a first fitting line parameter; A second fitting module is used to form a differential equation group according to the sampling points of the equivalent circuit using a differential equation method, and solve the differential equation group using a least square method to obtain second fitting line parameters; The working state judgment module is used to use the ratios of the first fitting line parameter and the second fitting line parameter to the actual line parameter as the first comparison result and the second comparison result respectively, and obtain the working state monitoring result of the current transformer by comparing the first comparison result and the second comparison result with a preset threshold range.

8. A computer-readable storage medium, characterized in that: The computer-readable storage medium includes a stored computer program; wherein, when the computer program is run, it controls the device where the computer-readable storage medium is located to execute the current transformer working state monitoring method according to any one of claims 1-6.

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