Power transformer residual magnetism detection verification platform standard parameter generation method

Abstract

The invention belongs to the technical field of power transformer state evaluation and diagnosis, discloses a power transformer standard electromagnetic parameter generation method, and aims at solving the problems that in the prior art, transformer residual magnetism demagnetization is not thorough, the magnetizing precision is low, and errors are large due to the fact that residual magnetism is not considered in inductance generation. In the standard demagnetization stage, sine wave excitation current is introduced into the primary side of a transformer through an adjustable constant current source, in the precise magnetization stage, a maximum positive current and residual magnetism relation table is established through multiple negative saturation excitation, and in the inductance customization stage, the relation between the amplitude of excitation current and inductance is established and subjected to quadratic polynomial fitting. And substituting the instruction inductance value to obtain a corresponding excitation current so as to generate target inductance. According to the method, complex hysteresis modeling is not needed, only conventional equipment is needed, the process is standard, parameter consistency is high, engineering practicability is high, and reliable standard parameters can be provided for transformer optimization design, system simulation and state evaluation.

Description

Technical Field

[0001] This invention relates to the field of calibration technology for residual magnetism detection devices for power transformers, and in particular to a method for generating standard electrical parameters for a calibration platform. Background Technology

[0002] As the core hub for energy transmission and distribution in the power system, the operational reliability of power transformers directly determines the level of power grid security. When a transformer is shut down due to maintenance or a fault, the hysteresis characteristics of the core material result in residual magnetism of a certain strength. This residual magnetism causes an inrush current of 6-8 times the rated current when the transformer is reconnected. This inrush current not only causes the accumulation of mechanical stress in the windings and accelerates insulation aging, but may also trigger malfunctions of relay protection devices and even lead to cascading problems such as harmonic pollution from adjacent equipment. According to a statistical report on power equipment failures published by IEEE, approximately 30% of transformer reconnection failures in the power system are directly related to inrush currents induced by residual magnetism, resulting in grid outage losses and equipment maintenance costs exceeding hundreds of millions of yuan annually. Therefore, the ability of residual magnetism detection devices to accurately detect the residual magnetism state of transformer cores is a key technical aspect for suppressing inrush currents and ensuring the stable operation of the power grid.

[0003] In recent years, residual magnetism detection technologies have encompassed empirical estimation methods, voltage integration methods, pre-magnetization methods, and AC / DC indirect detection methods. Among these, detection technology based on winding inductance measurement is the most widely used in industrial field testing due to its advantages such as non-invasive operation and fast real-time response. Its technical principle is to utilize residual magnetism to change the core permeability, thereby affecting the physical characteristics of the winding inductance parameters. The magnitude of residual magnetism is indirectly inverted through high-precision measurement of the inductance value. However, complex operating conditions in industrial environments, such as fluctuations in ambient temperature, changes in winding mechanical stress, and differences in manufacturing processes, can cause dynamic fluctuations in transformer winding inductance parameters, leading to errors in residual magnetism detection. Therefore, the calibration platform needs to have precise magnetization and dynamic inductance adjustment functions to verify the accuracy of the residual magnetism detection device under inductance disturbances.

[0004] Existing demagnetization methods cannot quickly eliminate historical residual magnetism in the core, leading to the superposition of old residual magnetism with new magnetization during subsequent magnetization. Traditional magnetization methods often employ a single-saturation excitation open-loop approach, which is susceptible to temperature and core material consistency issues, resulting in high residual magnetism deviations after magnetization. Furthermore, these methods lack efficient fine-tuning techniques, requiring remagnetization to the reverse saturation region, which is time-consuming and power-intensive. In addition, existing dynamic inductance adjustments for transformers do not consider the impact of residual magnetism. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the problems of incomplete demagnetization of residual magnetism in transformers, low magnetization accuracy, and large dynamic inductance adjustment error.

[0006] To address the technical problem, the solution of this invention is to provide a progressive process of standardized demagnetization, precise magnetization, and dynamic inductance adjustment to generate standard values ​​for residual magnetism and inductance. First, demagnetization eliminates historical interference; then, magnetization fixes the residual magnetism reference; and finally, dynamic inductance adjustment is performed based on the fixed residual magnetism. This avoids residual magnetism superposition caused by skipping demagnetization, or inductance value deviation caused by reversing the order of magnetization and inductance adjustment, ensuring parameter consistency.

[0007] The specific steps for the standardized demagnetization process are as follows: (2.1) Connect an adjustable constant current source capable of generating sinusoidal excitation current to the primary winding of the power transformer; (2.2) The initial excitation current amplitude is 1.414 times the rated current of the transformer, and the amplitude decays at twice the rated frequency of the transformer; (2.3) The current amplitude decreases by one-W times in each decay, and a total of W rapid decays are performed. The duration of this demagnetization cycle is W / 2 / rated frequency. (2.4) The residual magnetism of the iron core is monitored in real time by a high-precision magnetic flux sensor. If the residual magnetism value is less than the allowable value, it is determined to be in a magnetically neutral state, that is, the demagnetization is completed. If the residual magnetism value is greater than or equal to the allowable value, the amplitude of the new initial excitation current is adjusted to half of the original initial excitation current amplitude. (2.5) If demagnetization has been completed, then the process ends; otherwise, repeat steps 2.3 and 2.4.

[0008] The precise magnetization stage involves the following steps: (3.1) The primary excitation current of the transformer changes from zero to negative saturation current. After the negative saturation excitation is completed, the current increases to a certain positive current, and then the excitation current gradually decreases to zero. Record the maximum positive current after negative saturation excitation and the final residual magnetism of the iron core during this process. (3.2) Repeat the previous step M times. After completing the negative saturation excitation, the maximum positive current increases from zero, and each increment is one-M times the positive saturation current. (3.3) Based on the test results of the above two steps, formulate a table showing the relationship between the maximum positive current and the residual magnetism after completing negative saturation excitation; (3.4) According to the residual magnetism value of the magnetization command, look up the table to obtain the maximum positive current after negative saturation excitation corresponding to the residual magnetism value that is closest to the command residual magnetism value in the table; (3.5) The primary excitation current of the transformer changes from zero to negative saturation current. After completing negative saturation excitation, the current increases to the maximum positive current obtained in the previous step. Then the excitation current gradually decreases to zero, and the residual magnetism of the iron core is recorded. (3.6) Determine whether the residual magnetism of the iron core meets the accuracy requirements. If it does, the magnetization ends. Otherwise, use a small pulse current opposite to the last excitation current to fine-tune the residual magnetism of the iron core until the residual magnetism of the iron core meets the accuracy requirements. The specific steps for the dynamic inductance adjustment stage are as follows: (4.1) After the transformer core is precisely magnetized and a certain residual magnetism is fixed, a sinusoidal AC excitation current with an initial phase angle of zero and a frequency of power frequency is passed through the primary winding. After one cycle of the rated frequency, the inductance of the transformer primary winding is calculated based on the measured BH curve. (4.2) Repeat the previous step X times, and the amplitude of the AC excitation current increases from zero, with each increment being one-Xth of the positive saturation current; (4.3) Based on the test results of the above two steps, formulate a table showing the relationship between the AC excitation current amplitude and the inductance; (4.4) Based on the table data prepared in the previous step, the relationship expression between the AC excitation current amplitude and the inductance is obtained by fitting a quadratic polynomial; (4.5) Substitute the command inductance value into the relational expression to obtain the corresponding AC excitation current amplitude; (4.6) A sinusoidal AC excitation current is passed through the primary winding. The initial phase angle of this current is zero, the frequency is the rated frequency, and the amplitude is the amplitude calculated in the previous step. After one cycle of the rated frequency, the required primary winding inductance value is obtained.

[0009] The beneficial effects of this invention are: it clarifies the progressive sequence of "demagnetization-magnetization-dynamic inductance adjustment", eliminates the need for complex hysteresis modeling, and can be implemented with only conventional adjustable constant current sources and sensors, making it highly practical for engineering applications. Attached Figure Description Figure 1 Structural diagram of a device for generating standard electromagnetic parameters of a power transformer. Detailed Implementation

[0010] The present invention is based on a standard electromagnetic parameter generation device for power transformers, comprising a control unit, an adjustable constant current source, a current sensor, a magnetic flux sensor, and a transformer. The adjustable constant current source generates an excitation current flowing into the primary winding of the transformer. The control unit calculates the magnetic field strength based on the excitation current signal acquired by the current sensor, and calculates the magnetic field density inside the core based on the signal acquired by the magnetic flux sensor attached to the side of the transformer. The control unit also controls the output excitation current of the adjustable constant current source, plots the BH curve, and calculates the inductance value. Z times the rated current of the transformer primary winding is defined as the positive saturation excitation current Imax, and -Z times the rated current of the transformer primary winding is defined as the positive saturation excitation current Imin. The standard values ​​of residual magnetism and inductance are generated according to a progressive process of demagnetization, precise magnetization, and dynamic inductance adjustment.

[0011] The specific steps for the standardized demagnetization process are as follows: (2.1) Connect an adjustable constant current source capable of generating sinusoidal excitation current to the primary winding of the power transformer; (2.2) The initial excitation current amplitude is 1.414 times the rated current of the transformer, and the amplitude decays at twice the rated frequency of the transformer; (2.3) The current amplitude decreases by one-W times in each decay, and a total of W rapid decays are performed. The duration of this demagnetization cycle is W / 2 / rated frequency. (2.4) The residual magnetism of the iron core is monitored in real time by a high-precision magnetic flux sensor. If the residual magnetism value is less than the allowable value, it is determined to be in a magnetically neutral state, that is, the demagnetization is completed. If the residual magnetism value is greater than or equal to the allowable value, the amplitude of the new initial excitation current is adjusted to half of the original initial excitation current amplitude. (2.5) If demagnetization has been completed, then the process ends; otherwise, repeat steps 2.3 and 2.4.

[0012] The precise magnetization stage involves the following steps: (3.1) The excitation current of the transformer primary side generated by the constant current power supply changes from zero to the negative saturation current Imin. After the negative saturation excitation is completed, the current increases to a certain positive current, and then the excitation current gradually decreases to zero. Record the maximum positive current after the negative saturation excitation and the final iron core remanence during this process. (3.2) Repeat the previous step M times. After completing the negative saturation excitation, the maximum positive current increases from zero. Each increment is one-M times the positive saturation current Imax. (3.3) Based on the test results of the above two steps, formulate a table showing the relationship between the maximum positive current and the residual magnetism after completing negative saturation excitation; (3.4) According to the residual magnetism value of the magnetization command, look up the table to obtain the maximum positive current after negative saturation excitation corresponding to the residual magnetism value that is closest to the command residual magnetism value in the table; (3.5) The primary excitation current of the transformer generated by the constant current power supply changes from zero to negative saturation current. After completing negative saturation excitation, the current increases to the maximum positive current obtained in the previous step, and then the excitation current gradually decreases to zero. Record the residual magnetism of the iron core. (3.6) Determine whether the residual magnetism of the iron core meets the accuracy requirements. If it does, the magnetization ends. Otherwise, use a sinusoidal small pulse excitation current that is opposite to the last excitation current to fine-tune the residual magnetism of the iron core until the residual magnetism of the iron core meets the accuracy requirements. The specific parameters of the sinusoidal small pulse excitation current are: the amplitude is one-Y of the rated current of the transformer, the frequency is the rated frequency of the transformer, and the initial phase is 180°.

[0013] The specific steps for the dynamic inductance adjustment stage are as follows: (4.1) After the transformer core is precisely magnetized and a certain residual magnetism is fixed, a sinusoidal AC excitation current with an initial phase angle of zero and a frequency of power frequency is passed through the primary winding. After one cycle of the rated frequency, the inductance of the transformer primary winding is calculated according to the formula L=N2S / l*dB / dH based on the measured BH curve. In the formula, L is the inductance, N is the number of turns, S is the core area, l is the magnetic path length, B is the magnetic flux density, and H is the magnetic field strength. (4.2) Repeat the previous step X times, and the amplitude of the AC excitation current increases from zero, with each increment being one-Xth of the positive saturation current Imax; (4.3) Based on the test results of the above two steps, formulate a table showing the relationship between the AC excitation current amplitude and the inductance; (4.4) Based on the table data prepared in the previous step, the relationship expression between the AC excitation current amplitude and the inductance is obtained by fitting a quadratic polynomial; (4.5) Substitute the command inductance value into the relational expression to obtain the corresponding AC excitation current amplitude; (4.6) A sinusoidal AC excitation current is passed through the primary winding. The initial phase angle of this current is zero, the frequency is the rated frequency, and the amplitude is the amplitude calculated in the previous step. After one cycle of the rated frequency, the required primary winding inductance value is obtained.

[0014] The invention will be further described below with reference to the accompanying drawings.

[0015] Figure 1 The diagram shows the structure of a standard electromagnetic parameter generation device for a power transformer. The device consists of a control unit, an adjustable constant current source, a current sensor, a magnetic flux sensor, and a transformer. The adjustable constant current source generates an excitation current flowing into the primary winding of the transformer. Based on the excitation current signal acquired by the current sensor, the control unit calculates the magnetic field strength. Based on the signal acquired by the magnetic flux sensor attached to the side of the transformer, the control unit calculates the magnetic field density inside the core. The control unit's tasks also include controlling the output excitation current of the adjustable constant current source, plotting the BH curve, and calculating the inductance value.

Claims

1. A method for generating standard parameters for a power transformer residual magnetism detection and verification platform, characterized in that, The device consists of a control unit, an adjustable constant current source, a current sensor, a magnetic flux sensor, and a transformer. The adjustable constant current source generates an excitation current flowing into the primary winding of the transformer. The control unit calculates the magnetic field strength based on the excitation current signal collected by the current sensor, and calculates the magnetic field density inside the core based on the signal collected by the magnetic flux sensor attached to the side of the transformer. The control unit's tasks also include controlling the output excitation current of the adjustable constant current source, plotting the BH curve, and calculating the inductance value. The positive saturation excitation current Imax is defined as Z times the rated current of the transformer's primary winding, and the positive saturation excitation current Imin is defined as -Z times the rated current of the transformer's primary winding. The standard values ​​of residual magnetism and inductance are generated according to a progressive process of demagnetization, precise magnetization, and dynamic inductance adjustment.

2. The method according to claim 1, characterized in that, The standard demagnetization stage involves the following steps: (2.1) Connect an adjustable constant current source capable of generating sinusoidal excitation current to the primary winding of the power transformer; (2.2) The initial excitation current amplitude is 1.414 times the rated current of the transformer, and the amplitude decays at twice the rated frequency of the transformer; (2.3) The current amplitude decreases by one-W times in each decay, and a total of W rapid decays are performed. The duration of this demagnetization cycle is W / 2 / rated frequency. (2.4) The residual magnetism of the iron core is monitored in real time by a high-precision magnetic flux sensor. If the residual magnetism value is less than the allowable value, it is determined to be in a magnetically neutral state, that is, the demagnetization is completed. If the residual magnetism value is greater than or equal to the allowable value, the amplitude of the new initial excitation current is adjusted to half of the original initial excitation current amplitude. (2.5) If demagnetization has been completed, then the process ends; otherwise, repeat steps 2.3 and 2.

4.

3. The method according to claim 1, characterized in that, The precise magnetization stage involves the following steps: (3.1) The excitation current of the transformer primary side generated by the constant current power supply changes from zero to the negative saturation current Imin. After the negative saturation excitation is completed, the current increases to a certain positive current, and then the excitation current gradually decreases to zero. Record the maximum positive current after the negative saturation excitation and the final iron core remanence during this process. (3.2) Repeat the previous step M times. After completing the negative saturation excitation, the maximum positive current increases from zero. Each increment is one-M times the positive saturation current Imax. (3.3) Based on the test results of the above two steps, formulate a table showing the relationship between the maximum positive current and the residual magnetism after completing negative saturation excitation; (3.4) According to the residual magnetism value of the magnetization command, look up the table to obtain the maximum positive current after negative saturation excitation corresponding to the residual magnetism value that is closest to the command residual magnetism value in the table; (3.5) The primary excitation current of the transformer generated by the constant current power supply changes from zero to negative saturation current. After completing negative saturation excitation, the current increases to the maximum positive current obtained in the previous step, and then the excitation current gradually decreases to zero. Record the residual magnetism of the iron core. (3.6) Determine whether the residual magnetism of the iron core meets the accuracy requirements. If it does, the magnetization ends. Otherwise, use a sinusoidal small pulse excitation current that is opposite to the last excitation current to fine-tune the residual magnetism of the iron core until the residual magnetism of the iron core meets the accuracy requirements. The specific parameters of the sinusoidal small pulse excitation current are: the amplitude is one-Y of the rated current of the transformer, the frequency is the rated frequency of the transformer, and the initial phase is 180°.

4. The method according to claim 1, characterized in that, The dynamic inductance adjustment stage involves the following process: (4.1) After the transformer core is precisely magnetized and a certain residual magnetism is fixed, a sinusoidal AC excitation current with an initial phase angle of zero and a frequency of power frequency is passed through the primary winding. After one cycle of the rated frequency, the inductance of the transformer primary winding is calculated according to the formula L=N2S / l*dB / dH based on the measured BH curve. In the formula, L is the inductance, N is the number of turns, S is the core area, l is the magnetic path length, B is the magnetic flux density, and H is the magnetic field strength. (4.2) Repeat the previous step X times, and the amplitude of the AC excitation current increases from zero, with each increment being one-Xth of the positive saturation current Imax; (4.3) Based on the test results of the above two steps, formulate a table showing the relationship between the AC excitation current amplitude and the inductance; (4.4) Based on the table data prepared in the previous step, the relationship expression between the AC excitation current amplitude and the inductance is obtained by fitting a quadratic polynomial; (4.5) Substitute the command inductance value into the relational expression to obtain the corresponding AC excitation current amplitude; (4.6) A sinusoidal AC excitation current is passed through the primary winding. The initial phase angle of this current is zero, the frequency is the rated frequency, and the amplitude is the amplitude calculated in the previous step. After one cycle of the rated frequency, the required primary winding inductance value is obtained.

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