Converter transformer excitation curve transition parameter measurement platform and calculation method
Through the no-load and saturation experiments of power frequency, an excitation curve transition parameter measurement platform was built, which solved the accuracy of the measurement of the excitation characteristics of the converter transformer core, achieved accurate measurement of different models and voltage levels, and improved the accuracy of low-frequency transient simulation.
Patent Information
- Application Number
- CN202510515432.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-23
- Publication Date
- 2025-08-05
AI Technical Summary
The prior art cannot accurately measure the excitation characteristics of converter transformer cores of different models and voltage levels, resulting in low simulation accuracy of excitation inrush current, and the existing modeling methods cannot fully cover the depth saturation zone and saturation process of core materials.
Through the no-load experiment of power frequency and saturation experiment, an excitation curve transition parameter measurement platform is built, voltage and current data are recorded, the magnetic flux and dynamic inductor are calculated using formulas, and a complete excitation characteristic curve is drawn, including the working area and the saturation area.
Accurate measurement of the excitation characteristics of the core of the converter transformer is achieved, and the accuracy of the transformer equipment in low-frequency transient simulation is improved, and the error is controlled within ±3%.
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Figure CN120428007A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of transformer detection, and relates to a measurement platform and calculation method for a converter transformer excitation curve transition parameter. Background Art
[0002] Converter transformers (CTs) are the core power transmission equipment in HVDC transmission systems. The core excitation characteristics are crucial parameters for modeling converter stations or individual CTs and are essential for accurately analyzing low-frequency transient phenomena. Magnetizing inrush currents are transient high currents generated when a transformer is switched on or reconnected to power without load. Peak values can reach 6-8 times the rated current, significantly impacting power system stability and potentially causing malfunctions in differential protection, loosening of transformer windings, and shortened transformer life. This is primarily due to the nonlinear nature of the excitation characteristics and the presence of boundary values in the core magnetic flux. To better study magnetizing inrush currents, an accurate representation of the excitation characteristic curve is necessary.
[0003] The current excitation characteristic testing methods widely used in engineering have significant limitations. When testing converter transformers with capacities exceeding 500MVA, the conventional power-frequency step-up method is limited to a maximum test voltage of only 1.1 times the rated voltage (approximately 550kV) due to the test power supply capacity. In actual operation, converter transformers can experience transient surges of up to 6-8 times the rated current. These limitations prevent existing excitation characteristic curves from fully capturing the deep saturation region of the core material and provide a relatively rough description of the core saturation process.
[0004] In terms of modeling methods, most existing research uses electromagnetic transient simulation models (such as PSCAD / EMTDC) for modeling and simulation. The equivalent inductance models employed suffer from the following drawbacks: They provide a relatively rough representation of excitation characteristics, often using a two-segment equation to approximate the complete curve. Converter transformers, with their fixed operating frequency, larger capacity, greater leakage reactance, and higher voltage levels, exhibit excitation characteristics that differ from those of traditional transformers. Traditional linear inductance models cannot accurately represent these excitation characteristics, necessitating the development of more precise models to describe them.
[0005] In terms of engineering applications, existing research often focuses on the following two areas: 1. Laboratory-level research often targets small transformers (typically less than 1 / 1000 of the capacity of a commutator transformer) or silicon steel laminations, failing to accurately replicate the excitation characteristics of a full-scale commutator transformer core. 2. The parameter settings for simulation models are often simplified, failing to fully consider the transition from non-saturated to saturated conditions. Consequently, a parameter transition mechanism has yet to be established, resulting in unsatisfactory simulation accuracy of the magnetizing inrush current waveform at relatively low saturation levels.
[0006] Therefore, due to the large capacity and high voltage level of the converter transformer, it is necessary to characterize the excitation characteristics more accurately and comprehensively in order to achieve accurate simulation of low-frequency transient phenomena. Summary of the Invention
[0007] In view of this, the purpose of the present invention is to provide a measurement platform and calculation method for the transition parameters of the excitation curve of a converter transformer, so as to solve the problem in the prior art that there is a lack of complete measurement of the excitation characteristic curves of the core of converter transformers of different models and different voltage levels, and to achieve accurate measurement of the excitation curves of the core of converter transformers of different models.
[0008] In order to achieve the above object, the present invention provides the following technical solutions:
[0009] A method for calculating transition parameters of a converter transformer core excitation curve comprises the following steps:
[0010] S1: For the excitation characteristic curve of the working area, conduct a no-load test at the power frequency and record the effective value of the voltage U during the no-load test. rms With the current amplitude I peak ;
[0011] S2: Calculate the flux corresponding to all the effective values of voltage in the no-load test, convert the relationship between the effective value of voltage and current amplitude in the no-load test into the relationship between the current amplitude and flux in the working area of the commutation transformer, and draw the working area curve of the excitation characteristic. The end current and flux of the working area curve measured in the no-load test are recorded as I0 and
[0012] S3: For the saturation region excitation characteristic curve, a converter transformer excitation curve transition parameter measurement platform is built, and a saturation experiment of the converter transformer to be tested is carried out based on the platform to obtain the DC current, AC voltage and AC current on the grid side of the converter transformer; and based on the saturation experimental data, the saturation region curve of the excitation characteristic is drawn.
[0013] Furthermore, in step S1, a no-load experiment is conducted at the power frequency, specifically, the converter transformer valve side is open, and AC voltage excitation is applied to the grid side until the rated voltage of the converter transformer is reached, with a step size of 0.1 times the rated voltage, and the voltage effective value and current amplitude are recorded during the experiment.
[0014] Furthermore, in step S2, the magnetic flux corresponding to the effective value of the voltage in the no-load test is calculated according to the following formula:
[0015]
[0016] in, is the magnetic linkage, U rms is the effective value of the no-load test voltage, N1 is the number of turns on the grid side of the transformer, f is the operating frequency, and the operating frequency of the commutation transformer is 50Hz.
[0017] Furthermore, in step S3, the constructed converter transformer excitation curve transition parameter measurement platform includes a DC power supply, an AC power supply, a converter transformer to be measured, and a host computer.
[0018] Furthermore, in step S3, a saturation experiment of the converter transformer to be tested is performed based on the converter transformer excitation curve transition parameter measurement platform. Specifically, the valve side of the converter transformer is opened, and the grid side is connected to the measurement power supply. The DC excitation is adjusted from small to large through the control of the upper computer to allow the converter transformer to reach different saturation states; under the current DC excitation, an AC small signal voltage excitation is applied to put the converter transformer into operation; the AC voltage is kept unchanged, and the test range and number of data points are selected according to actual needs. Each time the DC excitation is adjusted, the grid-side DC current, AC voltage and AC current at this time are recorded.
[0019] Further, step S3 specifically includes: different saturation points of the core are controlled by the DC current i dc As the DC current increases, the core saturation deepens. The dynamic inductance L(i dc ):
[0020]
[0021] Where, L(i dc ) represents the dynamic inductance at different saturation points, U1 represents the measured grid-side alternating voltage of the converter transformer, I1 represents the measured grid-side alternating current of the converter transformer, and f represents the operating frequency.
[0022] In particular, it should be noted that the DC current corresponding to the first saturation point is consistent with the end point current value of the excitation characteristic curve in the working area in step S2. The second saturation point is greater than the first saturation point, and so on. During the measurement process, the adjustment amplitude of the DC excitation can be unevenly distributed. In the low saturation region, the number of measurement points can be appropriately increased. In the deep saturation region, the adjustment interval can be increased and the number of measurement points can be appropriately reduced.
[0023] According to the endpoint data of the working area curve in step S2, combined with the dynamic inductance obtained through the transition parameter measurement platform, the incremental flux is calculated. The calculation formula is as follows:
[0024]
[0025] Where, is the incremental magnetic flux, I k is the Kth saturation point, N1 is the number of turns on the grid side;
[0026] After calculating the incremental flux at the Kth saturation point, the flux at the K+1th saturation point can be further calculated, thereby transitioning the excitation characteristic curve from the linear region to the saturation region. The calculation method is shown in the following formula:
[0027]
[0028] It should be noted that the starting point of the saturation region curve should be the magnetic flux calculated from the end point data of the working region curve in step S2. That is, the first saturation point (I1) corresponds to the magnetic flux
[0029] The dynamic inductance at the starting point of the saturation region curve is calculated as follows: adjust the DC current value to be consistent with the AC current I0 measured in the no-load test, and reapply small-signal AC excitation to calculate the dynamic inductance;
[0030] After calculating the flux linkage at all saturation points, the working area curves are connected and extended to obtain the complete excitation characteristic curve. For easier viewing, the current-magnetism curve can be converted into a current-voltage curve by performing the inverse operation of formula (2).
[0031] The parameters required for the saturation region curve calculation process are measured by the transition parameter measurement platform. For different types of converter transformers, the complete excitation characteristic curve of the converter transformer core can be calculated and obtained according to the method provided by the present invention.
[0032] The beneficial effects of the present invention are as follows: the present invention provides a converter transformer excitation curve transition parameter measurement platform and calculation method, which can realize convenient and accurate measurement of the excitation characteristics of the core of different types of converter transformers, and improve the low-frequency transient simulation accuracy of transformer equipment.
[0033] 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
[0034] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:
[0035] Figure 1 This is a schematic diagram of the working area curve parameter measurement;
[0036] Figure 2 This is a schematic diagram of the excitation curve transition parameter measurement platform;
[0037] Figure 3It is the actual curve and the calculated curve of the excitation characteristics;
[0038] Figure 4 This is the error analysis diagram. DETAILED DESCRIPTION
[0039] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.
[0040] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.
[0041] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.
[0042] See also Figures 1 to 4 The embodiment of the present invention provides a method for measuring the excitation characteristics of the core of a converter transformer, with a primary side rated voltage of Taking the commutation ratio model as an example, the specific steps include:
[0043] Step 1: Measure the parameters required to calculate the working area excitation characteristic curve, such as Figure 1 As shown, AC excitation was applied to the converter transformer's high-voltage winding, with the secondary side open-circuited. The RMS voltage and current amplitude of the converter transformer were measured and recorded at 10% to 100% of the rated voltage, with a rated voltage step size of 0.1 pu. Some of this data is shown in Table 1.
[0044] Table 1 Voltage RMS and current amplitude in the working area of the excitation curve
[0045] Voltage RMS / V Current amplitude / A 1120 0.0280 2021 0.0460 2943 0.0676 3214 0.0758 3730 0.0946 4092 0.1112 4867 0.1607 5491 0.2468 5819 0.5167
[0046] Step 2: Measure the parameters required to calculate the saturation region excitation characteristic curve, such as Figure 2 As shown in the figure, a converter transformer excitation curve transition parameter measurement platform is built, the AC power supply and the DC power supply are connected in series, the grid-side wiring of the converter transformer to be tested is connected to the AC / DC hybrid power supply, and the secondary side is kept open.
[0047] Step 3: Since the transformer loop impedance under test is already determined, adjust the DC voltage via the host computer to control the DC current. Set the AC excitation to a fixed small signal value, adjust the DC voltage, and record the AC voltage and AC current at different DC currents.
[0048] Step 4: For this embodiment, the operating frequency is 50Hz, and the number of turns N1 on the primary side of the transformer is 468 turns. According to formula (1), calculate the flux corresponding to all the effective values of the voltage in step 1 The relationship between the effective value of voltage and current amplitude is converted into the relationship between the current amplitude and magnetic flux in the working area of the commutation transformer.
[0049]
[0050] in, is the magnetic linkage, U rms is the effective value of the no-load test voltage, N1 is the number of turns on the primary side of the transformer, f is the operating frequency, and the operating frequency of the commutation transformer is 50Hz.
[0051] The working area data of the excitation characteristic curve are shown in Table 2. The end current I0 of the curve measured in the no-load experiment is 0.5167A, and the flux linkage is It is 0.05601Wb.
[0052] Table 2 Corresponding relationship between current flux linkage in working area of excitation characteristic curve
[0053]
[0054] Step 5: Based on the experimental parameters obtained in steps 2 and 3, the DC current i dc Determine the number of saturation points, and further calculate the dynamic inductance L(i dc ).
[0055]
[0056] Where, L(i dc) represents the dynamic inductance at different saturation points, U1 represents the measured grid-side alternating voltage of the converter transformer, I1 represents the measured grid-side alternating current of the converter transformer, and f represents the operating frequency.
[0057] The dynamic inductances at some saturation points in this embodiment are shown in Table 3.
[0058] Table 3 Calculated values of dynamic inductance
[0059] DC current / A Dynamic inductance / H 1.069 0.927321 15.025 0.054241 25.010 0.046468 39.961 0.042731 79.332 0.039193
[0060] In particular, the last point of the no-load test data has an AC voltage of 5819 V, a current of 0.5617 A, and an adjusted DC current of 0.5617 A. The corresponding dynamic inductance here is 3.073 H.
[0061] Step 6: Based on the data of the last point of the working area curve in Table 2, combined with the dynamic inductance obtained by the AC / DC hybrid measurement device, use formula (3) to calculate the incremental flux at each saturation point.
[0062] Where, is the incremental magnetic flux, I k is the Kth saturation point, and N1 is the number of turns on the grid side.
[0063] Step 7: After calculating the incremental flux at the Kth saturation point, the flux at the K+1th saturation point can be further calculated, thereby transitioning the excitation characteristic curve from the linear region to the saturation region. The calculation method is shown in formula (4).
[0064]
[0065] An example, based on the results of Table 2 and Table 3, the first saturation point =(1.069-0.5167)*3.07315 / 468=0.00362671Wb, so the first saturation point =0.05601+0.00362671=0.05963671Wb. According to the inverse operation of formula (2), the calculated voltage effective value is 6196.0156V. Similarly, the next saturation point = (2.058-1.069)*0.927321 / 468=0.00195966Wb, the next data point The value is 0.05963671+0.00195966=0.06159637Wb. According to the inverse operation of formula (2), the calculated effective value of the voltage is 6399.616V, and so on.
[0066] Figure 3The comparison between the excitation characteristic curve calculated value and the actual value corresponding to the method provided by the present invention is Figure 4 The results show the variation in error between the two curves as the core transitions from low saturation to deep saturation as current increases, within a verifiable measured range. The error in the excitation curve calculated based on the transition parameters does not exceed ±3%, validating the effectiveness of the proposed method.
[0067] In summary, the method of the present invention can realize the convenient measurement of the excitation characteristics of the core of different types of converter transformers and improve the accuracy of low-frequency transient simulation of transformer equipment.
[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention 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 invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.
Claims
1. A method for calculating the transition parameters of the core excitation curve of a converter transformer, characterized in that: The method specifically comprises the following steps: S1: For the excitation characteristic curve of the working area, conduct a no-load test at the power frequency and record the effective value of the voltage and the current amplitude during the no-load test; S2: Calculate the flux linkage corresponding to all voltage RMS values in the no-load test, convert the relationship between voltage RMS value and current amplitude in the no-load test into the relationship between current amplitude and flux linkage in the commutation transformer working area, and draw the excitation characteristic working area curve; S3: For the saturation region excitation characteristic curve, a converter transformer excitation curve transition parameter measurement platform is built, and a saturation experiment of the converter transformer to be tested is carried out based on the platform to obtain the DC current, AC voltage and AC current on the grid side of the converter transformer; and based on the saturation experimental data, the saturation region curve of the excitation characteristic is drawn.
2. The method for calculating the transition parameters of the converter transformer core excitation curve according to claim 1, characterized in that: In step S1, a no-load test is performed at the power frequency. Specifically, the converter transformer valve side is open, and AC voltage excitation is applied to the grid side until the rated voltage of the converter transformer is reached. The step size is 0.1 times the rated voltage, and the voltage effective value and current amplitude are recorded during the experiment.
3. The method for calculating the transition parameters of the converter transformer core excitation curve according to claim 1, characterized in that: In step S2, the magnetic flux corresponding to the effective value of the voltage in the no-load test is calculated according to the following formula: in, is the magnetic linkage, U rms is the effective value of the no-load test voltage, N1 is the number of turns on the transformer grid side, and f is the operating frequency.
4. The method for calculating the transition parameters of the converter transformer core excitation curve according to claim 1, characterized in that: In step S3, the constructed AC / DC hybrid measurement device includes a DC power supply, an AC power supply, a converter transformer to be measured, and a host computer.
5. The method for calculating the transition parameters of the converter transformer core excitation curve according to claim 4, characterized in that: In step S3, a saturation experiment of the converter transformer to be tested is performed based on the excitation curve transition parameter measurement platform. Specifically, the valve side of the converter transformer is opened, and the grid side is connected to the measurement power supply. The DC excitation is adjusted from small to large through the control of the upper computer to allow the converter transformer to reach different saturation states; under the current DC excitation, an AC small signal voltage excitation is applied to put the converter transformer into operation; the AC voltage is kept unchanged, and the test range and number of data points are selected according to actual needs. Each time the DC excitation is adjusted, the grid-side DC current, AC voltage and AC current at this time are recorded.
6. The method for calculating the transition parameters of the converter transformer core excitation curve according to claim 5, characterized in that: Step S3 specifically includes: different saturation points of the core are controlled by the DC current i dc As the DC current increases, the core saturation deepens. The dynamic inductance L(i dc ): In the formula, L(i dc ) represents the dynamic inductance at different saturation points, U1 represents the grid-side alternating voltage of the converter transformer measured at the operating frequency, I1 represents the grid-side alternating current of the converter transformer measured at the operating frequency, and f represents the operating frequency; According to the endpoint data of the working area curve in step S2, combined with the dynamic inductance obtained through the transition parameter measurement platform, the incremental flux is calculated. The calculation formula is as follows: Where, is the incremental magnetic flux, I k is the Kth saturation point, N1 is the number of turns on the grid side; After calculating the incremental flux at the Kth saturation point, the flux at the K+1th saturation point is further calculated, thereby transitioning the excitation characteristic curve from the linear region to the saturation region. The calculation method is shown in the following formula: The starting point of the saturation zone curve should be the magnetic flux calculated from the end point data of the working zone curve That is, the first saturation point (I1) corresponds to the magnetic flux The dynamic inductance at the starting point of the saturation region curve is calculated as follows: adjust the DC current value to be consistent with the AC current I0 measured in the no-load test, and reapply small-signal AC excitation to calculate the dynamic inductance; After calculating the flux linkage size at all saturation points, the working area curves are connected and extended to obtain the complete excitation characteristic curve.
7. The method for calculating the transition parameters of the converter transformer core excitation curve according to claim 6, characterized in that: In step S3, the DC current corresponding to the first saturation point is consistent with the end point current value of the excitation characteristic curve in the working area, the second saturation point is greater than the first saturation point, and so on; during the measurement process, the adjustment amplitude of the DC excitation is non-uniformly distributed to improve the measurement accuracy in the low saturation area, increase the measurement points in the low saturation area, increase the adjustment spacing in the deep saturation area, and reduce the measurement points.
8. The method for calculating the transition parameters of the converter transformer core excitation curve according to claim 6, characterized in that: In step S3, the current-magnetism curve is converted into a current-voltage curve by performing the inverse operation of formula (2).