Direct-current demagnetization quantization method and device based on time-current curve and electronic medium

Abstract

The invention provides a time-current curve-based direct current demagnetization quantification method, which comprises the following steps of: in a direct current demagnetization process, acquiring a time-current change curve of a transformer through a current monitoring device; marking intersection points where the current drops from a positive value to zero, and determining time corresponding to the intersection points to obtain residual magnetism points; and based on the time information of each residual magnetism point, calculating the percentage of each residual magnetism in the initial residual magnetism. According to the method, the direct-current demagnetization process can be accurately quantified through the curve of the current changing along with time, and the defect that the demagnetization effect cannot be accurately evaluated through a traditional method is overcome.

Description

Technical Field

[0001] The invention belongs to the field of transformer demagnetization, and in particular relates to a direct current demagnetization quantification method, equipment and electronic medium based on a time-current curve. Background Art

[0002] During long-term operation, transformers often produce residual magnetism, which will have a certain impact on the performance, reliability and operating efficiency of the transformer. Existing demagnetization methods mainly use direct current to demagnetize, but there is a lack of effective quantitative standards and it is impossible to accurately evaluate the demagnetization effect, so it is difficult to guide actual operations.

[0003] Existing demagnetization effect evaluation methods are mostly based on residual magnetism polarity judgment, but this method cannot quantify the demagnetization process and cannot achieve precise control. Quantification of DC demagnetization process is still an urgent problem to be solved in the field of transformer maintenance. Summary of the invention

[0004] The purpose of the present invention is to provide a DC demagnetization quantification method based on a time-current curve. The method quantifies the effect of the demagnetization process by real-time monitoring of the curve of current changing with time during the demagnetization process and combining it with the physical properties of the transformer, so as to more accurately evaluate the DC demagnetization effect and optimize the demagnetization process.

[0005] The technical solution of the present invention is as follows:

[0006] A direct current demagnetization quantification method based on a time-current curve, the method comprising the following steps:

[0007] During the DC demagnetization process, the time-current variation curve of the transformer is obtained through the current monitoring device;

[0008] Mark the intersection points where the current drops from positive to zero, and determine the time corresponding to these intersection points to obtain the residual magnetization points;

[0009] Based on the time information of each residual magnetization point, the percentage of each residual magnetization is calculated.

[0010] Furthermore, the remanence point is the intersection of the current with the horizontal axis when the current decreases from a positive value to zero, and is defined as B i points, where i represents the number of times the reverse voltage is applied.

[0011] Furthermore, the percentage of residual magnetism calculated each time is specifically:

[0012] Read the time it takes for the current to reach the forward and reverse peaks;

[0013] According to the time difference between adjacent residual magnetization points, calculate the change of residual magnetization each time;

[0014] All the residual magnetization changes are accumulated to obtain the reduction of magnetic induction intensity during the entire demagnetization process, and the percentage of residual magnetization each time is calculated based on the reduction.

[0015] Furthermore, the formula for calculating the change in residual magnetism each time according to the time difference between adjacent residual magnetization points is:

[0016] |Δt j |=(t Nj -t 0j )+(t Nj+1 -t Pj )-(t Pj+1 -t Nj )

[0017] Among them, Δt j It represents the time difference corresponding to the change of magnetic flux from the jth positive remanent magnetization point to the j+1th positive remanent magnetization point, t Nj is the time when the demagnetization current reaches the negative peak value for the jth time, t 0j is the time it takes for the demagnetization current to decay from the positive half zone to 0 for the jth time, t Pj It is the time when the demagnetization current reaches the positive peak value for the jth time.

[0018] Furthermore, the formula for accumulating all residual magnetization changes to obtain the reduction in magnetic induction intensity during the entire demagnetization process is:

[0019]

[0020] Where |Δt j | indicates the demagnetization process of the transformer residual magnetism from B j Change to B j+1 The amount of change.

[0021] Furthermore, the percentage formula for calculating the residual magnetism each time by the reduction amount is:

[0022]

[0023] Among them, t sum Indicates the initial remanence B r The time difference corresponding to the difference between Br and 0, Δt is the forward voltage time required for the magnetic induction intensity to rise from Br to Bs.

[0024] Furthermore, the t sum The specific formula is:

[0025]

[0026] Δt=t2-t1

[0027] Among them, t1 is the time required for the transformer flux to reach the positive and negative saturation points and the reverse voltage to act, and t2 is the time required for the transformer flux to reach the positive and negative saturation points and the forward voltage to act.

[0028] The present invention also provides an electronic device, comprising a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to perform the above-mentioned DC demagnetization quantization method.

[0029] The present invention also provides a computer-readable storage medium storing a computer program, wherein the computer program implements the DC demagnetization quantization method as described above when executed by a processor.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] The present invention can accurately quantify the DC demagnetization process through the curve of current changing with time, thus overcoming the deficiency that the traditional method cannot accurately evaluate the demagnetization effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings generally illustrate various embodiments by way of example and not limitation, and together with the description and claims, serve to illustrate the embodiments of the invention. Where appropriate, the same reference numerals are used throughout the drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be exhaustive or exclusive embodiments of the present apparatus or method.

[0033] Figure 1 The schematic diagram of the demagnetization voltage and current curve of the present invention is shown;

[0034] Figure 2 A schematic diagram of the simulation structure of the present invention is shown;

[0035] Figure 3 A schematic diagram showing the corresponding relationship between the time-current curve and the positive residual magnetism of the present invention is shown;

[0036] Figure 4 A schematic diagram of residual magnetic polarity determination of the present invention is shown;

[0037] Figure 5 A schematic diagram of a hysteresis loop of the polarity judgment process of the present invention is shown. DETAILED DESCRIPTION

[0038] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0039] An embodiment of the present invention provides a direct current demagnetization quantification method based on a time-current curve, comprising:

[0040] The residual magnetism percentage of the transformer refers to the relationship between the residual magnetism generated by the transformer at different periods of DC demagnetization and the initial residual magnetism of the transformer. Therefore, the residual magnetism percentage can directly reflect the elimination of the residual magnetism of the transformer and the progress of demagnetization. At the same time, the increase and decrease and change of the magnetic flux inside the transformer core can also be analyzed according to the residual magnetism percentage. Applying it to engineering can help people better analyze the DC demagnetization process and strengthen the understanding and mastery of the internal magnetic flux and magnetic induction intensity of the transformer.

[0041] During the DC demagnetization process, the hysteresis loop still has intersections with the ordinate, that is, the remanence that occurs during the demagnetization process. It is not difficult to find that the moments corresponding to these points are when the magnetic field intensity is zero, that is, the transformer current is zero, and the current crosses the coordinate axis from positive to negative. Therefore, the moment when the remanence appears during the demagnetization process can correspond to the moment when the current decreases from a positive value to zero in the demagnetization process time-current curve.

[0042] The transformer can be equivalent to a series connection of resistance and inductance. Every time a voltage is applied across the transformer, the change in current can be analyzed using a first-order RL series circuit. At the beginning of the demagnetization process, the residual magnetism inside the transformer is a positive saturation value. A reverse voltage is applied to it to reduce it to the positive saturation residual magnetism B1, and then the current continues to decrease until it reaches the reverse peak. After that, the voltage gradually reverses, causing the current amplitude to gradually decrease until the demagnetization requirements are met, and the entire process ends. In this process, the direction of the external voltage is opposite to the direction of the residual magnetism inside the transformer, so it has the same change law.

[0043] Analyzing the above voltage-current relationship diagram, finding the points corresponding to two adjacent positive remanent magnetizations in the diagram, we can find that:

[0044] The current between two adjacent positive residual magnetization points undergoes three changes. They are: applying a reverse voltage to make it reach the reverse peak; applying a forward voltage to reduce it to zero and reach the forward peak; applying a reverse voltage to reduce it to 0. According to formula (13), it can be found that the magnitude of the weakening between two adjacent positive residual magnetizations is related to the magnitude of the difference in the time of applying the forward and reverse voltages within this period. The entire DC demagnetization process is to gradually apply a voltage with the opposite polarity to the residual magnetization to the transformer to reduce it to zero. Therefore, it is only necessary to completely eliminate the residual magnetization of magnitude B with the transformer. r Taking the net reverse time required for the residual magnetism as the reference value, the residual magnetism percentage of each positive residual magnetism that occurs during the demagnetization process can be determined.

[0045] After obtaining the DC demagnetization process time-current curve, do the following processing: first mark the intersection of the current with the horizontal axis when the current decreases from a positive value to 0, and call these points B ipoint, where i is the number of times reverse DC power is applied to the transformer (positive residual magnetism can occur when reverse voltage is applied), and the corresponding time is read and named t 0i Then read the time when the current reaches each forward and reverse peak, named t Pi ,t Ni It can be found that the net reverse voltage time |Δt between two adjacent residual magnetic points j |(1≤j≤i) has the following relationship:

[0046] |Δt j |=(t Nj -t 0j )+(t Nj+1 -t Pj )-(t Pj+1 -t Nj )

[0047]

[0048] |Δt j | can represent the demagnetization process of transformer residual magnetism from B j Change to B j+1 The degree of change of all the calculated |Δt j | The sum of the Σt obtained can be used to obtain the reduction in magnetic induction intensity during the entire demagnetization process. The demagnetization process changes from the saturation magnetic induction intensity B s All the above analysis processes are based on the premise that the voltage remains unchanged. It is not difficult to see that the net reverse voltage time can be used to represent the difference between any two magnetic induction intensities t sum Indicates the initial remanence B r The difference between Σt and 0; Σt represents the positive saturation value B s The difference between the final remanence B0.

[0049] After obtaining the magnitude of the changes between the various values, the demagnetization process and results can be quantified (in B r The calculation formula is:

[0050]

[0051] like Figure 4 As shown, a reverse voltage is first applied to the transformer to make it reach the reverse saturation point, and then a forward voltage is applied to make it reach the forward saturation point. This process is similar to measuring the hysteresis loop. The current signal of the entire process is monitored and sampled to obtain the time-current curve. The final method for determining the residual magnetic polarity is as follows:

[0052] The above process can be regarded as two stages: the magnetic flux inside the transformer rises from the initial value to the reverse saturation value; the magnetic flux changes from the reverse saturation value to the forward saturation value, and the magnetic flux change value in this stage is twice the saturation magnetic flux. If the transformer contains forward residual magnetism, the magnitude of the magnetic flux change in the first stage should be greater than the saturation magnetic flux; conversely, the magnitude of the magnetic flux change in the first stage should be less than the saturation magnetic flux. The magnitude of the magnetic flux change is proportional to the integral of the voltage. Since the voltage does not change during the process, the residual magnetic polarity can be determined by analyzing the magnitude of the time of the two stages.

[0053] The definitions of t1 and t2 correspond to the reverse and forward voltage action times required for the transformer flux to reach the positive and reverse saturation points, respectively. They are also the time required for the transformer current to rise from zero to the reverse peak saturation excitation current and to change from the reverse saturation excitation current to the forward saturation excitation current.

[0054] Use the following method to determine the residual magnetic polarity of the transformer: The transformer residual magnetism is positive; if The residual magnetism of the transformer is reverse; if This method can be used to directly and accurately determine whether the transformer has residual magnetism and the polarity of residual magnetism without complicated calculations, and a conclusion can be drawn quickly.

[0055] In addition to determining the residual magnetic polarity, this process is mainly used to obtain the important parameter t for quantifying the DC demagnetization process. sum , that is, the net reverse voltage time required to completely eliminate the residual magnetism inside the transformer. The above article discusses the relationship between the magnetic induction intensity and the voltage action time during the operation process. Based on this conclusion and the hysteresis loop of the process, we can get Figure 5 ,

[0056]

[0057]

[0058] Therefore, the corresponding t sum and Δt (which makes the magnetic induction intensity change from B r Rise to B s The required forward voltage time) is calculated as follows:

[0059]

[0060] Δt=t2-t1

[0061] After determining the residual magnetism polarity using the time-current curve data, the DC demagnetization operation can begin. After applying a DC power supply with different polarities, the residual magnetism inside the transformer is at the positive saturation residual magnetism value. Under normal circumstances, the transformer will also be magnetized in the initial stage of the DC demagnetization process, and then gradually eliminated. Therefore, the above method has a limited impact on the DC demagnetization process, but the above operation can be used to evaluate the demagnetization process and the final effect. Moreover, the saturation magnetic flux of the direct transformer is known, and the magnetic flux polarity must be positive after the above treatment. It is easier to demagnetize the magnetic flux with known polarity and size.

[0062] like Figure 2 As shown, the present invention uses the PSACAD platform to complete the construction of this simulation model. A single-phase full-bridge inverter circuit is added on both sides of the DC voltage source to achieve voltage direction conversion, and the voltage and current signals on both sides of the transformer are sampled and monitored. According to the change of the signal, the opening and closing of the switch tube inside the inverter circuit and the opening and closing of the short-circuit circuit part are controlled.

[0063] This simulation uses a bipolar pulse demagnetization method with a gradually decreasing pulse width. The control circuit analyzes and processes the current flowing through the transformer during the demagnetization process, and controls the switch tube inside the inverter circuit to gradually reduce the peak value that the current can reach each time. The voltage remains unchanged during the entire demagnetization process, and only the action time of different voltage directions is changed to achieve the demagnetization effect. At the end of demagnetization, a short-circuit loop is connected to prevent the transformer state from continuing to change. The voltage is set to achieve demagnetization after 10 commutations, that is, the current reaches the forward and reverse peaks and the number of forward residual magnetism in the demagnetization process is 5.

[0064] During the simulation process, the transformer is first set to contain a positive remanent magnetism of 1.36, and the relationship between the current, voltage, and magnetic induction intensity during the demagnetization process and time is recorded. Since the magnetic field intensity is proportional to the current, a hysteresis loop can be formed with the current and magnetic induction intensity as the horizontal and vertical axes respectively. The magnetic induction intensity corresponding to the point where the current is zero is the remanent magnetism of the demagnetization process.

[0065] The time-current curve of the residual magnetism measurement process is analyzed. First, the residual magnetism polarity is determined based on it. According to the method proposed above, the data is read to obtain: t1 = 1.444S, t2 = 1.632S. It can be found that t1 < 0.5*t2. Based on this, it can be determined that the initial residual magnetism polarity of the transformer is positive, which is consistent with the experimental preset value. In addition, t sum =0.63925S, Δt=0.1945S At this time, the residual magnetism inside the transformer is in the positive saturation state and continues to start the demagnetization process.

[0066] To determine the residual magnetism percentage, we must first record the time for each forward and reverse peak value on the time-current curve and the time for the current to decrease from a positive value to 0; find out the length of time the forward and reverse voltages between two adjacent residual magnetisms act on both ends of the transformer; the difference between the above two times and then take the absolute value to get the degree of change between two adjacent residual magnetisms, and then calculate, and the predicted value and actual value are shown in the following table.

[0067] Table 1 Comparison table of predicted and actual values ​​of residual magnetism percentage

[0068]

[0069]

[0070] The above table selects several forward remanent magnetization points of the demagnetization process for analysis and prediction. From the previous principle description, it can be found that this method can be used to analyze the entire process of the DC demagnetization process with equal amplitude and frequency, and obtain the percentage of the internal magnetic induction intensity of the transformer after demagnetization to the initial remanence. From the above table, it can be found that the difference between the predicted value and the true value does not exceed 2%, and the average error is 1.889%. The method has a high accuracy in predicting the remanence percentage, and can accurately predict the remanence percentage during the DC demagnetization process.

[0071] The following shows the relationship between the predicted value of the residual magnetism percentage of the demagnetization process generated by this method and the actual residual magnetism percentage of the simulation process. It can be found that the difference between the two is very small. The residual magnetism percentage gradually decreases as the demagnetization process proceeds and finally reaches a very small value, proving that the demagnetization process is well completed.

[0072] By combining the position and time of the predicted data in the time-current curve and the hysteresis loop of the demagnetization process, the demagnetization time can be used as the horizontal coordinate and the predicted residual magnetism percentage as the vertical coordinate to obtain a curve combining the residual magnetism percentage and the demagnetization process predicted by this method. The actual residual magnetism percentage-time curve is a curve whose direction gradually changes with time and whose amplitude decreases. Since the above curve only predicts the positive residual magnetism of the demagnetization process and the demagnetization result, the number of samples is small and cannot have the same change trend as the actual one. However, as long as more points are analyzed and predicted according to the method of the present invention, the actual curve can be closer and closer. After enough collection points are collected, the entire demagnetization process can also be better analyzed and predicted with reference to the curve.

[0073] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A DC demagnetization quantification method based on time-current curve, characterized in that: The method comprises the following steps: During the DC demagnetization process, the time-current variation curve of the transformer is obtained through the current monitoring device; Mark the intersection points where the current drops from positive to zero, and determine the time corresponding to these intersection points to obtain the residual magnetization points; Based on the time information of each residual magnetization point, the percentage of each residual magnetization to the initial residual magnetization is calculated.

2. The DC demagnetization quantification method based on time-current curve according to claim 1 is characterized in that: The residual magnetic point is the intersection of the current and the horizontal axis when the current decreases from a positive value to zero, and is defined as B i points, where i represents the number of times the reverse voltage is applied.

3. The DC demagnetization quantification method based on time-current curve according to claim 1, characterized in that: The percentage of residual magnetism calculated each time is specifically: Read the time it takes for the current to reach the forward and reverse peaks; According to the time difference between adjacent residual magnetization points, calculate the change of residual magnetization each time; All the residual magnetization changes are accumulated to obtain the reduction of magnetic induction intensity during the entire demagnetization process, and the percentage of residual magnetization each time is calculated based on the reduction.

4. The DC demagnetization quantification method based on time-current curve according to claim 3 is characterized in that: The formula for calculating the change of residual magnetism each time according to the time difference between adjacent residual magnetization points is: |Δt j |=(t Nj -t 0j )+(t Nj+1 -t Pj )-(t Pj+1 -t Nj ) Among them, Δt j It represents the time difference corresponding to the change of magnetic flux from the jth positive remanent magnetization point to the j+1th positive remanent magnetization point, t Nj is the time when the demagnetization current reaches the negative peak value for the jth time, t 0j is the time it takes for the demagnetization current to decay from the positive half zone to 0 for the jth time, t Pj It is the time when the demagnetization current reaches the positive peak value for the jth time.

5. The DC demagnetization quantification method based on time-current curve according to claim 3 is characterized in that: The formula for accumulating all residual magnetization changes to obtain the reduction in magnetic induction intensity during the entire demagnetization process is: Where |Δt j | indicates the demagnetization process of the transformer residual magnetism from B j Change to B j+1 The amount of change.

6. The DC demagnetization quantification method based on time-current curve according to claim 3 is characterized in that: The formula for calculating the percentage of residual magnetism each time by the reduction amount is: Among them, t sum Indicates the initial remanence B r The time difference corresponding to the difference between B and 0, Δt is the time difference between the magnetic induction intensity and r Rise to B s Required forward voltage time.

7. The DC demagnetization quantification method based on time-current curve according to claim 6, characterized in that: The sum and Δt are obtained by the time required for the transformer flux to reach the positive and negative saturation points under the action of reverse and forward voltages. The specific formula is: Δt=t2-t1 Among them, t1 is the time required for the transformer flux to reach the positive and negative saturation points and the reverse voltage to act, and t2 is the time required for the transformer flux to reach the positive and negative saturation points and the forward voltage to act.

8. An electronic device, characterized in that: The electronic device comprises a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to perform the DC demagnetization quantization method according to any one of claims 1 to 7.

9. A computer-readable storage medium, characterized in that: A computer program is stored therein, and when the computer program is executed by a processor, the DC demagnetization quantization method according to any one of claims 1 to 7 is implemented.

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