A method for measuring residual magnetism of a transformer based on magnetomotive force

Abstract

The present application relates to a kind of transformer remanence measurement methods based on magnetic motive force, belong to electromagnetic measurement field.The method is by the magnetizing voltage to be applied to the transformer to be measured to realize the preset of residual magnetism, again to the transformer to be measured pulse excitation and calculate magnetic motive force integral, to obtain the magnetic motive force integral corresponding to different residual magnetism, using least square method to the relationship between transformer magnetic motive force integral and residual magnetism is fitted.Pulse excitation is applied to the transformer to be measured for residual magnetism unknown, calculate magnetic motive force integral, the calculated magnetic motive force is substituted into the fitting formula of transformer magnetic motive force and residual magnetism, and then the residual magnetism of transformer is calculated.The present application realizes the accurate measurement of the residual magnetism of transformer global residual magnetism interval, provides effective solution for the practical application of residual magnetism measurement method based on pulse response.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electromagnetic measurement, and relates to a transformer residual magnetism measurement method based on magnetic motive force. BACKGROUND

[0002] After the transformer is disconnected from the power supply or the winding DC resistance test is performed, the transformer core will generate a large amount of residual magnetism due to the magnetic hysteresis characteristics of the ferromagnetic material. If the residual magnetism is not eliminated in time, the excitation inrush current several times the rated current will be generated when the transformer is closed again. The excitation inrush current will cause the deformation of the transformer winding and damage the insulation, and the protection device will be burned out. The vibration or oil flow impact generated by the inrush current may cause the protection device such as the gas relay to malfunction, and thus the transformer cannot be successfully closed, which seriously threatens the safe operation of the power grid. At the same time, the existence of residual magnetism will also bring a large error to the transformer winding deformation test and the ratio test, and affect the operation and maintenance of the transformer. Therefore, it is extremely important to accurately obtain the residual magnetism of the transformer core for suppressing the excitation inrush current and evaluating the state of the transformer.

[0003] The measurement of the residual magnetism of the transformer core has always been a difficult problem. Limited by the closed structure of the core, there is currently no sensor that can directly measure the residual magnetism magnetic density in the closed core. The existing residual magnetism measurement methods mostly use indirect measurement methods, but there are problems such as large calculation error and large measurement error at low residual magnetism.

[0004] The different residual magnetism degrees of the transformer core will affect the magnetic permeability, and the excitation inductance of the winding linked with the core will be different, thereby affecting the circuit parameters of the winding. When the same waveform voltage excitation is applied to the transformer, due to the change of the parameters, the time constant of the current change, the injected energy on the excitation side, the area of the hysteresis loop, etc. are different. With the development of the accurate measurement technology of electric quantities such as current and voltage, it is possible to use the electric quantity characteristic parameters to inverse the residual magnetism of the transformer core. Therefore, the present application proposes a transformer residual magnetism measurement method based on magnetic motive force to improve the measurement accuracy of the transformer residual magnetism. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a transformer residual magnetism measurement method based on magnetic motive force, which establishes the relationship between the transformer magnetic motive force and the residual magnetism, thereby realizing the accurate measurement of the transformer residual magnetism and providing a reference for formulating the transformer closing strategy.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0007] A transformer residual magnetism measurement method based on magnetic motive force, specifically comprising the following steps:

[0008] S1: presetting the residual magnetism of the transformer to be measured;

[0009] S2: applying excitation to the transformer to be measured and calculating the integral of the magnetic motive force;

[0010] S3: Calculate the fitting formula of the magnetomotive force integral and residual magnetism of the transformer under test under different residual magnetism;

[0011] S4: Apply excitation to the transformer under test with unknown residual magnetism and calculate the transformer magnetomotive force integral;

[0012] S5: Substitute the magnetomotive force integral into the fitting formula to calculate the residual magnetism of the transformer to be tested.

[0013] Furthermore, in step S1, the steps of remanence preset are:

[0014] S11: applying a rectangular wave voltage with an amplitude of a and gradually increasing frequency to the transformer to eliminate residual magnetism;

[0015] S12: Setting the signal generator parameters to preset the magnetizing voltage with a pulse width of b and an amplitude of c;

[0016] S13: applying magnetizing voltage to the primary side of the transformer;

[0017] S14: Calculate the residual magnetism of the preset core cross section using formula (1);

[0018]

[0019] Among them, u g (t) is the induced voltage generated by the magnetizing voltage on the secondary side of the transformer; N2 is the number of turns of the transformer secondary winding, S is the cross-sectional area of ​​the transformer core, is the preset average residual magnetic flux density on the core cross section of the toroidal transformer, t1 and t2 are the starting and ending times of the magnetizing voltage waveform respectively.

[0020] Furthermore, in step S2, the steps of calculating the transformer magnetomotive force integral are:

[0021] S21: Set the signal generator parameters to preset the pulse excitation waveform, where the action time in both the positive and negative directions is d, the pulse amplitude is e, and a resistor is connected to the secondary side of the transformer to operate as a load;

[0022] S22: Apply the pulse excitation in step S21 to the transformer and measure the primary side current i1(t) and the secondary side current i2(t) of the transformer;

[0023] S23: Calculate the transformer magnetomotive force integral S(F ri (t)), as shown in formula (2):

[0024]

[0025] Wherein, N1 is the transformer primary winding turns, t3, t4 are the start time and end time of the remanence pulse, F ri (t) is the magnetic motive force caused by the remanence measurement pulse.

[0026] Further, in step S3, the step of calculating the transformer magnetic motive force integral and the remanence fitting formula is:

[0027] S31: Synchronization step S1 applies a magnetizing voltage with a pulse width of b and an amplitude of c to the transformer to preset the remanence B r1 ; and then applies a magnetizing voltage with a pulse width of b and an amplitude of c+1 to the transformer to preset the remanence B r2 , and so on, to achieve the preset of different remanences of the transformer;

[0028] S32: Repeat step S2 for transformers with different preset remanences to obtain the magnetic motive force integral of the transformer under different remanences;

[0029] S33: The theoretical relationship between remanence and transformer magnetic motive force is shown in formula (3):

[0030]

[0031] Wherein, B r is the remanence, ΔB is the change of magnetic induction intensity caused by the remanence measurement pulse, Δt is the duration of the remanence measurement pulse, μ(t) is the magnetic permeability function of the transformer core, and l is the equivalent magnetic path length of the transformer;

[0032] Analysis shows that they are approximately linear functions, so the least squares method is used for fitting;

[0033] S34: Determine the function f(x) such that the sum of the squared or absolute values of the function value deviations f(x1)-y1, f(x2)-y2, …, f(x n )-y n at each point x1, x2, …, x n is minimized, and set the equation as f(x) = a0+a1x+a2x 2 +a3x 3 ;

[0034] S35: Obtain the function value deviation squared sum M, as shown in formula (4):

[0035]

[0036] S36: Make the partial derivatives of M with respect to a0, a1, a2, and a3 equal to zero, and solve to obtain the equation group:

[0037]

[0038]

[0039]

[0040]

[0041] S37: Solve to obtain a0, a1, a2, and a3, and finally obtain the fitting relationship between the residual magnetism and the integral of the transformer magnetomotive force:

[0042] B ri =W[S(F ri (t))] (9)

[0043] Among them, B ri For the i-th time, a magnetizing voltage with a pulse width of b seconds and an amplitude of c+1 volt is applied to the transformer to obtain a preset residual magnetism, S(F ri (t)) is the magnetomotive force integral calculated by applying the residual magnetization measurement pulse under the current residual magnetization, and W[·] is the fitting function of the residual magnetization and the magnetomotive force integral obtained by the least squares fitting method.

[0044] Furthermore, in step S4, the step of calculating the transformer magnetomotive force integral is:

[0045] S41: Apply pulse excitation to the transformer under test and measure the primary and secondary side currents of the transformer;

[0046] S42: Calculate the transformer magnetomotive force integral using formula (2).

[0047] Furthermore, in step S5, the step of calculating the residual magnetism of the transformer to be tested is:

[0048] S51: Substitute the magnetomotive force integral calculated in step S4 into formula (9);

[0049] S52: Obtain the residual magnetism of the transformer through calculation.

[0050] The beneficial effects of the present invention are as follows: the present invention uses the integral of magnetomotive force over time as a parameter to characterize the remanence, establishes a mathematical relationship between the iron core remanence and the integral of magnetomotive force, realizes accurate measurement of remanence under low iron core remanence, and provides an effective solution for the practical application of the remanence measurement method based on pulse response.

[0051] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to make the objects, technical solutions and advantages of the present application clearer, the preferred embodiments of the present application will be described in detail below with reference to the drawings, in which:

[0053] Figure 1 Flow chart of the transformer residual magnetism measurement method based on the magnetomotive force of the present application;

[0054] Figure 2 Equivalent circuit diagram of the transformer residual magnetism measurement method based on the magnetomotive force of the present application;

[0055] Figure 3 Demagnetization voltage waveform;

[0056] Figure 4 Pulse excitation and magnetization voltage waveform;

[0057] Figure 5 Fitting curve of the residual magnetism and the magnetomotive force of the transformer. DETAILED DESCRIPTION

[0058] The present application will be described in greater detail by way of specific embodiments, from which the skilled person will readily appreciate other advantages and utility of the present application disclosed in the specification. The present application can also be implemented or applied in other different specific embodiments, and the details in the specification can be modified or changed in various ways based on different views and applications without departing from the spirit of the present application. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present application in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0059] The drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical diagram, and should not be understood as a limitation on the present application; in order to better illustrate the embodiments of the present application, some components in the drawings can be omitted, enlarged or reduced, and do not represent the actual size of the product; it is understandable for those skilled in the art that some well-known structures and their descriptions in the drawings can be omitted.

[0060] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that the orientation or position relationship indicated by the terms "upper", "lower", "left", "right", "front", "back" and the like is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the position relationship in the drawings are only used for exemplary illustration, and should not be understood as a limitation on the present application, and for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0061] Please refer to Figures 1 to 5 The embodiment of the present application provides a transformer residual magnetism measuring method based on magnetic motive force, and specifically comprises the following steps:

[0062] S1: preset residual magnetism of a transformer to be measured, and the specific steps are as follows:

[0063] S11: applying a rectangular wave voltage with a gradually reduced amplitude of 10V and a pulse width of 6ms, 4ms, 2ms and 1ms to the transformer to realize elimination of the residual magnetism;

[0064] S12: setting signal generator parameters to preset a pulse width of 8ms and a magnetizing voltage with different amplitudes;

[0065] S13: applying the magnetizing voltage to the primary side of the transformer;

[0066] S14: calculating the preset residual magnetism of the cross section of the iron core by using formula (1);

[0067]

[0068] Wherein, u g (t) is the induced voltage of the magnetizing voltage at the secondary side of the transformer; N2 is the number of turns of the secondary side winding of the transformer, S is the cross-sectional area of the iron core of the transformer, is the preset average residual magnetism of the cross section of the ring-shaped transformer iron core, t1 and t2 are the start time and end time of the magnetizing voltage waveform respectively.

[0069] S2: applying excitation to the transformer to be measured and calculating the integral of the magnetic motive force;

[0070] The specific steps for calculating the integral of the magnetic motive force of the transformer are as follows:

[0071] S21: setting signal generator parameters to preset a pulse excitation waveform, the action time of the positive and negative directions is 3ms, the pulse amplitude is ±4V, and a 1Ω resistor is connected to the secondary side of the transformer to be regarded as a load for operation;

[0072] S22: applying the pulse excitation in step S21 to the transformer, and measuring the primary side current i1(t) and the secondary side current i2(t) of the transformer;

[0073] S23: calculating the integral of the magnetic motive force S(F ri (t)) of the transformer under each preset residual magnetism, as shown in formula (2):

[0074]

[0075] Wherein, N1 is the number of turns of the primary side winding of the transformer, t3 and t4 are the start time and end time of the residual magnetism measurement pulse respectively, and F ri (t) is the magnetic motive force caused by the residual magnetism measurement pulse.

[0076] S3: Calculate the fitting formula of the magnetomotive force integral and residual magnetism of the transformer under test under different residual magnetism;

[0077] Furthermore, in step S3, the steps of calculating the transformer magnetomotive force integral and residual magnetism fitting formula are as follows:

[0078] S31: Same as step S1, a pulse width of 8ms and an amplitude of 1V is applied to the transformer to preset the residual magnetism B r1 Then apply a magnetizing voltage with a pulse width of 8ms and an amplitude of 2V to the transformer to preset the residual magnetism B r2 , and so on, to achieve the preset of different residual magnetism of the transformer.

[0079] S32: Repeat step S2 for transformers with different preset residual magnetisms, thereby obtaining the magnetomotive force integral of the transformer under different residual magnetisms;

[0080] S33: The theoretical relationship between residual magnetism and transformer magnetomotive force is shown in formula (3):

[0081]

[0082] Among them, B r is the remanence, ΔB is the change in magnetic induction intensity caused by the remanence measurement pulse, Δt is the duration of the remanence measurement pulse, μ(t) is the magnetic permeability function of the transformer core, and l is the equivalent magnetic path length of the transformer;

[0083] Analysis shows that the two are roughly in a linear functional relationship, so the least squares method is used to fit them.

[0084] S34: Determine the function f(x) so that each point x1, x2, ..., x n The function value deviation at f(x1)-y1, f(x2)-y2, ..., f(x n )-y n The sum of squares or absolute values ​​is minimized, and the equation is f(x) = a0 + a1x + a2x 2 +a3x 3 ;

[0085] S35: Obtain the sum of squares of function value deviations M, as shown in formula (4):

[0086]

[0087] S36: Make the partial derivatives of M with respect to a0, a1, a2, and a3 equal to 0, and solve the equations:

[0088]

[0089]

[0090]

[0091]

[0092] S37: Solve a0, a1, a2, a3, and finally get the fitting relationship between residual magnetism and transformer magnetic potential integral:

[0093] B ri = W[S(F ri (t))] (9)

[0094] Where, B ri is the i-th time to apply a pulse width of b seconds, amplitude of c+1 volts of magnetizing voltage to the transformer with a preset residual magnetism, S(F ri (t)) is the magnetic potential integral calculated by applying the residual magnetism measurement pulse under the current residual magnetism, W[·] is the fitting function of residual magnetism and magnetic potential integral obtained by least square fitting.

[0095] S4: Apply excitation to the transformer whose residual magnetism is unknown, and calculate the transformer magnetic potential integral, the specific steps are:

[0096] S41: Apply pulse excitation to the transformer to be measured, and measure the primary and secondary side currents of the transformer;

[0097] S42: Calculate the transformer magnetic potential integral using formula (2).

[0098] S5: Substitute the magnetic potential integral into the fitting formula to calculate the residual magnetism of the transformer to be measured, the specific steps are:

[0099] S51: Substitute the magnetic potential integral calculated in step S4 into formula (9);

[0100] S52: Calculate the residual magnetism of the transformer.

[0101] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should be covered in the scope of the claims of the present application.

Claims

1. A transformer residual magnetism measurement method based on magnetomotive force, characterized in that: The method specifically comprises the following steps: S1: Preset the residual magnetism of the transformer to be tested; S2: Apply excitation to the transformer under test and calculate the magnetomotive force integral; S3: Calculate the fitting formula of the magnetomotive force integral and residual magnetism of the transformer under test under different residual magnetism. The specific steps are as follows: S31: Apply a magnetizing voltage with a pulse width of b and an amplitude of c to the transformer in the same manner as step S1 to preset the residual magnetism. ; Then apply a magnetizing voltage with a pulse width of b and an amplitude of c+1 to the transformer to preset the residual magnetism , and so on, to achieve the preset of different residual magnetism of transformer; S32: Repeat step S2 for transformers with different preset residual magnetisms, thereby obtaining the magnetomotive force integral of the transformer under different residual magnetisms; S33: The theoretical relationship between residual magnetism and transformer magnetomotive force is shown in formula (1): （1） in, is the remanence, is the change in magnetic induction intensity caused by the residual magnetization measurement pulse, is the duration of the remanence measurement pulse, is the permeability function of the transformer core, is the equivalent magnetic circuit length of the transformer; The analysis shows that the two are roughly in a linear function relationship, so the least squares method is used to fit them; S34: Determine the function f(x) so that each point x1, x2, ..., x n The function value deviation at f(x1)-y1, f(x2)-y2, ..., f(x n )-y n The sum of squares or absolute values ​​is minimized, and the equation is f(x)=a0+a1x+a2x 2 +a3x 3 ; S35: Obtain the sum of squared deviations of the function value M, as shown in formula (2): （2） S36: Make the partial derivatives of M with respect to a0, a1, a2, and a3 equal to 0, and solve the equations: （3） （4） （5） （6） S37: Solve to obtain a0, a1, a2, and a3, and finally obtain the fitting relationship between the residual magnetism and the integral of the transformer magnetomotive force: （7） in, For the i Apply a magnetizing voltage with a pulse width of b seconds and an amplitude of c+1 volt to the transformer to obtain a preset residual magnetism; is the integral of the magnetomotive force calculated by applying the residual magnetism measurement pulse under the current residual magnetism, The fitting function of the integral of remanence and magnetomotive force is obtained by least square fitting. S4: Apply excitation to the transformer under test with unknown residual magnetism and calculate the transformer magnetomotive force integral; S5: Substitute the magnetomotive force integral into the fitting formula to calculate the residual magnetism of the transformer to be tested.

2. The transformer remanence measurement method based on magnetomotive force according to claim 1, characterized in that: In step S1, the steps of residual magnetism preset are: S11: applying a rectangular wave voltage with an amplitude of a and gradually increasing frequency to the transformer to eliminate residual magnetism; S12: Setting the signal generator parameters to preset the magnetizing voltage with a pulse width of b and an amplitude of c; S13: applying magnetizing voltage to the primary side of the transformer; S14: Calculate the remanence of the preset core cross section using formula (8); （8） in, It is the induced voltage generated by the magnetizing voltage on the secondary side of the transformer; is the number of turns of the transformer secondary winding, is the cross-sectional area of ​​the transformer core, is the average residual magnetic flux density preset on the core section of the toroidal transformer, 、 are the starting and ending times of the magnetizing voltage waveform respectively.

3. The transformer remanence measurement method based on magnetomotive force according to claim 2, characterized in that: In step S2, the steps for calculating the transformer magnetomotive force integral are: S21: Set the signal generator parameters to preset the pulse excitation waveform, where the action time in both the positive and negative directions is d, the pulse amplitude is e, and a resistor is connected to the secondary side of the transformer to operate as a load; S22: Apply the pulse excitation in step S21 to the transformer and measure the primary side current of the transformer and secondary current ; S23: Calculate the transformer magnetomotive force integral under each preset residual magnetism , as shown in formula (9): （9） in, is the number of turns of the transformer primary winding, 、 are the start and end times of measuring the residual magnetic pulse, is the magnetomotive force caused by the remanence measurement pulse.

4. The transformer remanence measurement method based on magnetomotive force according to claim 3, characterized in that: In step S4, the steps for calculating the transformer magnetomotive force integral are: S41: Apply pulse excitation to the transformer under test and measure the primary and secondary side currents of the transformer; S42: Calculate the transformer magnetomotive force integral using formula (9).

5. The transformer remanence measurement method based on magnetomotive force according to claim 4, characterized in that: In step S5, the steps of calculating the residual magnetism of the transformer to be tested are: S51: Substitute the magnetomotive force integral calculated in step S4 into formula (7); S52: Obtain the residual magnetism of the transformer through calculation.

Images