A transformer star side winding equivalent electrical parameter measurement method and deformation fault diagnosis system

Abstract

The application discloses a transformer star side winding equivalent electric parameter measurement method and a deformation fault diagnosis system, and the method steps are as follows: 1) extracting the short-circuit natural frequency omega of a driving point impedance curve of a neutral point open circuit sci , the short-circuit natural frequency of a driving point impedance curve of a neutral point grounded through a capacitor and calculating equivalent electric parameters L eq ; 2) judging whether the winding of a transformer to be detected is faulty based on the equivalent electric parameters L eq and the equivalent electric parameters of the transformer to be detected under normal conditions; the system comprises a voltage transformer, a current transformer, a data processing unit, a fault diagnosis unit and a diagnosis result display unit; the application can timely and accurately diagnose the winding state of the transformer through the measured equivalent electric parameters, meanwhile, the sensitivity and reliability are considered, and the stable operation of the power grid is ensured.

Description

Technical Field

[0001] This invention relates to the fields of electrical parameter measurement technology and fault detection technology, specifically a method for measuring the equivalent electrical parameters of the star-side winding of a transformer and a system for diagnosing deformation faults. Background Technology

[0002] Transformer winding damage is one of the main causes of transformer failure. Transformer windings are mostly made of copper conductors, and the deformation they undergo under the influence of short-circuit electrodynamic forces is elasto-plastic deformation, which accumulates after repeated short-circuit impacts. When the deformation of the transformer windings is small, this cumulative effect usually does not trigger the relay protection devices in the power system. Therefore, slight deformation of the transformer windings is often overlooked by maintenance personnel. However, as the number of short-circuit impacts increases, this cumulative effect alters the winding structure. When the insulation protection of the windings is damaged to a certain extent, a massive short-circuit impact may cause the windings to break or collapse.

[0003] Due to the enclosed structure of transformers, conventional fault detection methods sometimes fail to accurately diagnose winding deformation. Currently, my country commonly uses the frequency response method to detect transformer winding deformation, comprehensively evaluating the winding condition by comparing the frequency response curves before and after deformation. However, in the high-frequency range, the frequency response curve is easily affected by factors such as the wiring method of the measuring device, the wire arrangement, personnel experience, and the electromagnetic environment, resulting in poor test repeatability due to the influence of stray capacitance parameters. Other low-frequency detection methods, such as the short-circuit impedance method, lack sufficient sensitivity and are difficult to detect minute deformations in the windings. Therefore, balancing the sensitivity and reliability of transformer winding fault detection is of great significance for preventing potential transformer faults and extending the service life of transformers. Summary of the Invention

[0004] The purpose of this invention is to provide a method for measuring the equivalent electrical parameters of a transformer star-side winding, comprising the following steps:

[0005] 1) Set the scanning frequency, the excitation voltage frequency, and the initial value of the iteration number m = 1;

[0006] 2) Open the neutral point of the three-phase transformer to be tested, and apply a scanning frequency excitation voltage to phase X. Use voltage transformers and current transformers to measure the port voltage and port current of the three-phase transformer under the current wiring condition. The number of measurements is n. X can be any one of phases A, B, and C.

[0007] 3) Ground the neutral point of the three-phase transformer to be tested through a capacitor, and apply the same scanning frequency excitation voltage as in step 1) to phase X. Measure the port voltage and port current of the three-phase transformer under the current wiring condition using voltage transformers and current transformers. The number of measurements is n.

[0008] 4) Calculate the average value of the port voltage and port current measured in step 2), and calculate the driving point impedance of the neutral point open circuit at the current frequency based on the average value of the port voltage and port current.

[0009] Calculate the average value of the port voltage and port current measured in step 3), and calculate the driving point impedance of the neutral point grounded through the capacitor at the current frequency based on the average value of the port voltage and port current.

[0010] 5) Determine if m≥M holds true. If not, adjust the frequency of the scanning frequency excitation voltage, let m=m+1, and return to step 2). If yes, proceed to step 6. M is the maximum number of iterations.

[0011] 6) Based on the driving point impedance and corresponding frequency of the neutral point open circuit, construct the driving point impedance curve of the neutral point open circuit;

[0012] Based on the driving point impedance with the neutral point grounded by a capacitor and the corresponding frequency, a driving point impedance curve with the neutral point grounded by a capacitor is constructed.

[0013] 7) Extract the short-circuit natural frequency ω from the driving point impedance curve of the neutral point open circuit. sci And the short-circuit natural frequency of the impedance curve of the drive point with the neutral point grounded by a capacitor. And calculate the equivalent electrical parameter L eq ;

[0014] 8) Based on equivalent electrical parameter L eq The equivalent electrical parameters of the transformer under test under normal conditions are used to determine whether the windings of the transformer under test have a fault.

[0015] Furthermore, in step 1), the frequency range of the scanning frequency excitation voltage is 1Hz-2MHz.

[0016] Furthermore, in step 2), the three-phase transformer to be tested is a Y-connected three-phase transformer.

[0017] Furthermore, in step 7), the short-circuit natural frequency ω of the driving point impedance curve with the neutral point open circuit is... sci As shown below:

[0018]

[0019] In the formula, L ii C is the self-inductance of the i-th winding unit of the transformer. si and C gi M is the series capacitance and grounding capacitance of the i-th winding unit. 0i Let N be the total inductance between the wire end and the i-th winding unit end. N is the number of winding units.

[0020] Furthermore, in step 7), the short-circuit natural frequency of the impedance curve of the drive point with the neutral point grounded via a capacitor is... As shown below:

[0021]

[0022] In the formula, C ext For external pf level capacitors; M 0N This represents the total inductance between the neutral and neutral terminals of the winding when all capacitors are open-circuited. C gN This is the grounding capacitance of the Nth winding unit.

[0023] Furthermore, in step 7), the equivalent electrical parameter L eq As shown below:

[0024]

[0025] In the formula, The short-circuit natural frequency of the driving point impedance curve with the neutral point grounded by a capacitor.

[0026] Furthermore, in step 8), the step of determining whether the winding of the transformer under test has a fault is as follows:

[0027] Calculate the percentage difference in equivalent electrical parameters L eq,0 The equivalent electrical parameters of the transformer under test under normal conditions; L eq Equivalent electrical parameters;

[0028] If ΔL eq >ΔL eq,max If ΔL eq ≤ΔL eq,max If the transformer winding under test is normal, then it is determined that the transformer winding is normal; ΔL eq,max This is a preset threshold for the percentage difference.

[0029] Furthermore, a preset difference percentage threshold ΔL is defined. eq,max =20%.

[0030] Furthermore, in step 8), after determining whether a fault has occurred in the winding of the transformer under test, the determination result and the short-circuit natural frequency ω are... sci Short-circuit natural frequency Equivalent electrical parameter L eq Visualization.

[0031] A system for measuring the equivalent electrical parameters of the star-side winding of a transformer using the aforementioned method includes a voltage transformer, a current transformer, a data processing unit, a fault diagnosis unit, and a diagnosis result display unit.

[0032] The voltage transformers measure the three-phase transformer port voltages under the conditions of neutral point open circuit and neutral point grounded via capacitor, and transmit the data to the data processing unit.

[0033] The current transformers measure the three-phase transformer port currents under the conditions of neutral point open circuit and neutral point grounded via capacitor, and transmit the data to the data processing unit.

[0034] The data processing unit calculates the average values ​​of the three-phase transformer port voltage and current corresponding to different frequency excitation voltages when the neutral point is open, and constructs the drive point impedance curve when the neutral point is open.

[0035] The data processing unit calculates the average values ​​of the three-phase transformer port voltage and current corresponding to different frequency excitation voltages when the neutral point is grounded through a capacitor, and constructs the driving point impedance curve when the neutral point is grounded through a capacitor.

[0036] The data processing unit extracts the short-circuit natural frequency ω from the driving point impedance curve of the neutral point open circuit. sci And the short-circuit natural frequency of the impedance curve of the drive point with the neutral point grounded by a capacitor. Calculate the equivalent electrical parameter L eq The results are transmitted to the fault diagnosis unit and the diagnosis result display unit.

[0037] The fault diagnosis unit is based on the equivalent electrical parameter L. eq The system obtains the equivalent electrical parameters of the transformer under normal conditions, determines whether the winding of the transformer under test has a fault, and transmits the determination result to the diagnostic result display unit.

[0038] The diagnostic result display unit will display the judgment result and the short-circuit natural frequency ω. sci Short-circuit natural frequency Equivalent electrical parameter L eq Visualization.

[0039] The technical effects of this invention are undeniable. This invention provides a method and system for measuring equivalent electrical parameters for detecting deformation faults in the star-side winding of a transformer. The measured equivalent electrical parameters can be used to diagnose the winding status of the transformer in a timely and accurate manner, thus ensuring the stable operation of the power grid. Attached Figure Description

[0040] Figure 1 The principle of measuring equivalent electrical parameters for detecting transformer winding deformation faults;

[0041] Figure 2 The established transformer fully coupled N-segment ladder network model;

[0042] Figure 3The two driving point impedance curves are the measured values ​​with the neutral point open and the neutral point grounded via a 58pF capacitor.

[0043] Figure 4 This is a schematic diagram of the fault detection system interface. Detailed Implementation

[0044] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0045] Example 1:

[0046] See Figures 1 to 4 A method for measuring the equivalent electrical parameters of a transformer star-side winding includes the following steps:

[0047] 1) Set the scanning frequency, the excitation voltage frequency, and the initial value of the iteration number m = 1;

[0048] 2) Open the neutral point of the three-phase transformer to be tested, and apply a scanning frequency excitation voltage to phase X. Use voltage transformers and current transformers to measure the port voltage and port current of the three-phase transformer under the current wiring condition. The number of measurements is n. X can be any one of phases A, B, and C.

[0049] 3) Ground the neutral point of the three-phase transformer to be tested through a capacitor, and apply the same scanning frequency excitation voltage as in step 1) to phase X. Measure the port voltage and port current of the three-phase transformer under the current wiring condition using voltage transformers and current transformers. The number of measurements is n.

[0050] 4) Calculate the average value of the port voltage and port current measured in step 2), and calculate the driving point impedance of the neutral point open circuit at the current frequency based on the average value of the port voltage and port current.

[0051] Calculate the average value of the port voltage and port current measured in step 3), and calculate the driving point impedance of the neutral point grounded through the capacitor at the current frequency based on the average value of the port voltage and port current.

[0052] 5) Determine if m≥M holds true. If not, adjust the frequency of the scanning frequency excitation voltage, let m=m+1, and return to step 2). If yes, proceed to step 6. M is the maximum number of iterations.

[0053] 6) Based on the driving point impedance and corresponding frequency of the neutral point open circuit, construct the driving point impedance curve of the neutral point open circuit;

[0054] Based on the driving point impedance with the neutral point grounded by a capacitor and the corresponding frequency, a driving point impedance curve with the neutral point grounded by a capacitor is constructed.

[0055] 7) Extract the short-circuit natural frequency ω from the driving point impedance curve of the neutral point open circuit. sci And the short-circuit natural frequency of the impedance curve of the drive point with the neutral point grounded by a capacitor. And calculate the equivalent electrical parameter L eq ;

[0056] 8) Based on equivalent electrical parameter L eq The equivalent electrical parameters of the transformer under test under normal conditions are used to determine whether the windings of the transformer under test have a fault.

[0057] In step 1), the frequency range of the scanning frequency excitation voltage is 1Hz-2MHz.

[0058] In step 2), the three-phase transformer to be tested is a Y-connected three-phase transformer.

[0059] In step 7), the short-circuit natural frequency ω of the driving point impedance curve with the neutral point open circuit is... sci As shown below:

[0060]

[0061] In the formula, L ii C is the self-inductance of the i-th winding unit of the transformer. si and C gi M is the series capacitance and grounding capacitance of the i-th winding unit. 0i Let N be the total inductance between the wire end and the i-th winding unit end. N is the number of winding units.

[0062] In step 7), the short-circuit natural frequency of the impedance curve of the drive point with the neutral point grounded via a capacitor. As shown below:

[0063]

[0064] In the formula, C ext For external pf level capacitors; M 0N This represents the total inductance between the neutral and neutral terminals of the winding when all capacitors are open-circuited. C gN This is the grounding capacitance of the Nth winding unit.

[0065] In step 7), the equivalent electrical parameter L eq As shown below:

[0066]

[0067] In the formula, The short-circuit natural frequency of the driving point impedance curve with the neutral point grounded by a capacitor.

[0068] In step 8), the steps for determining whether the winding of the transformer under test has a fault are as follows:

[0069] Calculate the percentage difference in equivalent electrical parameters L eq,0 These are the equivalent electrical parameters of the transformer under test when it is in normal condition.

[0070] If ΔL eq >ΔL eq,max If ΔL eq ≤ΔL eq,max If the transformer winding under test is normal, then it is determined that the transformer winding is normal; ΔL eq,max This is a preset threshold for the percentage difference.

[0071] Preset difference percentage threshold ΔL eq,max =20%.

[0072] In step 8), after determining whether a fault has occurred in the winding of the transformer under test, the determination result and the short-circuit natural frequency ω are... sci Short-circuit natural frequency Equivalent electrical parameter L eq Visualization.

[0073] Example 2:

[0074] A method for measuring the equivalent electrical parameters of a transformer star-side winding includes the following steps:

[0075] 1) Set the scanning frequency, the excitation voltage frequency, and the initial value of the iteration number m = 1;

[0076] 2) Open the neutral point of the three-phase transformer to be tested, and apply a scanning frequency excitation voltage to phase X. Use voltage transformers and current transformers to measure the port voltage and port current of the three-phase transformer under the current wiring condition. The number of measurements is n. X can be any one of phases A, B, and C.

[0077] 3) Ground the neutral point of the three-phase transformer to be tested through a capacitor, and apply the same scanning frequency excitation voltage as in step 1) to phase X. Measure the port voltage and port current of the three-phase transformer under the current wiring condition using voltage transformers and current transformers. The number of measurements is n.

[0078] 4) Calculate the average value of the port voltage and port current measured in step 2), and calculate the driving point impedance of the neutral point open circuit at the current frequency based on the average value of the port voltage and port current.

[0079] Calculate the average value of the port voltage and port current measured in step 3), and calculate the driving point impedance of the neutral point grounded through the capacitor at the current frequency based on the average value of the port voltage and port current.

[0080] 5) Determine if m≥M holds true. If not, adjust the frequency of the scanning frequency excitation voltage, let m=m+1, and return to step 2). If yes, proceed to step 6. M is the maximum number of iterations.

[0081] 6) Based on the driving point impedance and corresponding frequency of the neutral point open circuit, construct the driving point impedance curve of the neutral point open circuit;

[0082] Based on the driving point impedance with the neutral point grounded by a capacitor and the corresponding frequency, a driving point impedance curve with the neutral point grounded by a capacitor is constructed.

[0083] 7) Extract the short-circuit natural frequency ω from the driving point impedance curve of the neutral point open circuit. sci And the short-circuit natural frequency of the impedance curve of the drive point with the neutral point grounded by a capacitor. And calculate the equivalent electrical parameter L eq ;

[0084] 8) Based on equivalent electrical parameter L eq The equivalent electrical parameters of the transformer under test under normal conditions are used to determine whether the windings of the transformer under test have a fault.

[0085] Example 3:

[0086] A method for measuring the equivalent electrical parameters of a transformer star-side winding, with the same technical content as in Embodiment 2, further wherein, in step 1), the frequency range of the scanning frequency excitation voltage is 1Hz-2MHz.

[0087] Example 4:

[0088] A method for measuring the equivalent electrical parameters of the star-side winding of a transformer, the technical content of which is the same as any one of embodiments 2-3, further wherein, in step 2), the three-phase transformer to be tested is a three-phase transformer with a Y-type connection.

[0089] Example 5:

[0090] A method for measuring the equivalent electrical parameters of a transformer star-side winding, with technical content identical to any one of embodiments 2-4, further comprising, in step 7), the short-circuit natural frequency ω of the driving point impedance curve with the neutral point open circuit. sci As shown below:

[0091]

[0092] In the formula, L ii C is the self-inductance of the i-th winding unit of the transformer. si and Cgi M is the series capacitance and grounding capacitance of the i-th winding unit. 0i Let be the total inductance between the line end and the i-th winding unit end.

[0093] Example 6:

[0094] A method for measuring the equivalent electrical parameters of the star-side winding of a transformer, with the same technical content as any one of embodiments 2-5, further comprising, in step 7), the short-circuit natural frequency of the impedance curve of the driving point with the neutral point grounded by a capacitor. As shown below:

[0095]

[0096] In the formula, C ext For external pf level capacitors; M 0N This represents the total inductance between the neutral and neutral terminals of the winding when all capacitors are open.

[0097] Example 7:

[0098] A method for measuring the equivalent electrical parameters of a transformer star-side winding, with the same technical content as any one of embodiments 2-6, further comprising, in step 7), the equivalent electrical parameter L eq As shown below:

[0099]

[0100] In the formula, The short-circuit natural frequency of the driving point impedance curve with the neutral point grounded by a capacitor.

[0101] Example 8:

[0102] A method for measuring the equivalent electrical parameters of a transformer star-side winding, with the same technical content as any one of embodiments 2-7, further comprising the following step 8): determining whether a fault has occurred in the transformer winding to be tested.

[0103] Calculate the percentage difference in equivalent electrical parameters L eq,0 The equivalent electrical parameters of the transformer under test under normal conditions; L eq Equivalent electrical parameters;

[0104] If ΔL eq >ΔL eq,max If ΔL eq ≤ΔL eq,max If the transformer winding under test is normal, then it is determined that the transformer winding is normal; ΔL eq,max This is a preset threshold for the percentage difference.

[0105] Example 9:

[0106] A method for measuring the equivalent electrical parameters of a transformer star-side winding, with the same technical content as any one of embodiments 2-8, further comprising a preset difference percentage threshold ΔL. eq,max =20%.

[0107] Example 10:

[0108] A method for measuring the equivalent electrical parameters of a transformer star-side winding, with technical content identical to any one of embodiments 2-9, further comprising the following step 8): after determining whether a fault has occurred in the transformer winding under test, the determination result and the short-circuit natural frequency ω are... sci Short-circuit natural frequency Equivalent electrical parameter L eq Visualization.

[0109] Example 11:

[0110] A system for measuring the equivalent electrical parameters of the star-side winding of a transformer according to any one of embodiments 1-10 includes a voltage transformer, a current transformer, a data processing unit, a fault diagnosis unit, and a diagnosis result display unit.

[0111] The voltage transformers measure the three-phase transformer port voltages under the conditions of neutral point open circuit and neutral point grounded via capacitor, and transmit the data to the data processing unit.

[0112] The current transformers measure the three-phase transformer port currents under the conditions of neutral point open circuit and neutral point grounded via capacitor, and transmit the data to the data processing unit.

[0113] The data processing unit calculates the average values ​​of the three-phase transformer port voltage and current corresponding to different frequency excitation voltages when the neutral point is open, and constructs the drive point impedance curve when the neutral point is open.

[0114] The data processing unit calculates the average values ​​of the three-phase transformer port voltage and current corresponding to different frequency excitation voltages when the neutral point is grounded through a capacitor, and constructs the driving point impedance curve when the neutral point is grounded through a capacitor.

[0115] The data processing unit extracts the short-circuit natural frequency ω from the driving point impedance curve of the neutral point open circuit. sci And the short-circuit natural frequency of the impedance curve of the drive point with the neutral point grounded by a capacitor. Calculate the equivalent electrical parameter L eq The results are transmitted to the fault diagnosis unit and the diagnosis result display unit.

[0116] The fault diagnosis unit is based on the equivalent electrical parameter L. eq The system obtains the equivalent electrical parameters of the transformer under normal conditions, determines whether the winding of the transformer under test has a fault, and transmits the determination result to the diagnostic result display unit.

[0117] The diagnostic result display unit will display the judgment result and the short-circuit natural frequency ω. sci Short-circuit natural frequency Equivalent electrical parameter L eq Visualization.

[0118] Example 12:

[0119] A method for measuring the equivalent electrical parameters of a transformer star-side winding, comprising the following steps:

[0120] Step 1: Open the neutral point of a Y-connected three-phase transformer, apply a scanning frequency excitation voltage (1Hz-2MHz) to one phase, and use a voltage transformer and a current transformer to measure the port voltage and port current 5 times, and save the data in the system working area.

[0121] Step 2: Ground the neutral point of the transformer through a capacitor, keeping the rest of the wiring unchanged. Apply the same scanning frequency excitation voltage (1Hz-2MHz) to the same phase as in Step 1. Use a voltage transformer and a current transformer to measure the port voltage and port current 5 times and save the results in the system working area.

[0122] Step 3: Using the five collected voltage and current data, take the average value of the data and plot the two driving point impedance curves: one with the neutral point open and the other with the neutral point grounded through a capacitor.

[0123] Step 4: Calculate the equivalent electrical parameters using the formula by extracting the short-circuit natural frequencies (SCNF) from the impedance curves of the two driving points.

[0124] Step 5: Compare the equivalent electrical parameters with the equivalent electrical parameters of the transformer under normal conditions, and display the curve, the extracted SCNF, and the calculation results on the fault detection system interface. If the difference in equivalent electrical parameters is greater than 20%, it is determined that the transformer winding has a fault. If the difference in equivalent electrical parameters is less than 20%, it is determined that the transformer winding is normal.

[0125] Example 13:

[0126] A verification of the method for measuring the equivalent electrical parameters of the star-side winding of the transformer according to any one of Embodiments 1-12 is as follows:

[0127] In step one, this example uses the star-side winding of a three-phase oil-immersed transformer with a rated capacity of 2kVA-300kVA as the experimental object, such as... Figure 2The fully coupled N-segment stepped network model of the transformer is established as shown, where each segment represents a unit of the winding. The neutral point of the transformer is opened, and a scanning frequency voltage with a frequency range of 1Hz to 2MHz and an amplitude of 10V is applied to phase A. The port voltage and port current data are collected five times using voltage transformers and current transformers and stored in the system working area.

[0128] In step two, the neutral point of the transformer is grounded through a capacitor of pF level, and the rest of the wiring remains unchanged. The same sweep frequency voltage is applied to phase A, and the port voltage and port current are measured 5 times using voltage transformers and current transformers, and the data is saved in the system working area.

[0129] In step three, the five voltage and current data collected are used to calculate the average value of the voltage and current data, and two driving point impedance curves are plotted for the neutral point open circuit and the neutral point grounded through a capacitor.

[0130] In step four, the SCNF of the drive point impedance curve under the neutral point open-circuit condition is extracted. The relationship between SCNF and the winding electrical parameters (capacitance and inductance) is as follows:

[0131]

[0132] In the formula, L ii It is the self-perception of the i-th cake, C si and C gi M is the series capacitance of the i-th cake and the grounding capacitance. 0i ω is the total inductance between the line end and the i-th disc end. sci It is SCNF.

[0133] Extract the SCNF of the drive point impedance curve when the neutral point is grounded through a pF-level capacitor. The relationship between SCNF and winding electrical parameters (capacitance and inductance) is as follows:

[0134]

[0135] In the formula, except for the grounding capacitor in the last segment, which is C gN Change to C gN +C ext In addition, each parameter of the ladder network remains constant, C ext For external pF level capacitors, For the new SCNF.

[0136] (2) Subtracting (1) gives:

[0137]

[0138] M 0iThis refers to the total inductance between node 0 (line terminal) and node N (neutral terminal) of the winding when all capacitors are open-circuited. That is, M... 0i It is the inductance between the winding terminals and the neutral terminal when the same current flows through all the cakes. Therefore, M 0i =L eq The above expression can be rewritten as:

[0139]

[0140] The equivalent electrical parameters (inductance) of the test transformer can be obtained by substituting into equation (4).

[0141] In step five, the equivalent electrical parameters are compared with those under normal conditions, and the curves, the extracted SCNF, and the calculation results are displayed as follows: Figure 4 The fault detection system interface shown has functions such as parameter setting, data acquisition and display, and diagnostic result display. If the difference in equivalent electrical parameters is greater than 20%, the transformer winding is judged to have a fault. If the difference in equivalent electrical parameters is less than 20%, the transformer winding is judged to be normal.

[0142] Example 14:

[0143] A verification of the method for measuring the equivalent electrical parameters of the star-side winding of the transformer according to any one of Embodiments 1-12 is as follows:

[0144] In step one, this example uses the star-side winding of a three-phase oil-immersed transformer with a rated capacity of 2kVA-300kVA as the experimental object. The neutral point of the transformer is opened, and a scanning frequency voltage with a frequency range of 1Hz to 2MHz and an amplitude of 10V is applied to phase A. Voltage and current transformers are used to collect five sets of port voltage and port current data, which are then stored in the system's working area.

[0145] In step two, the neutral point of the transformer is grounded through a 58pF capacitor, and the rest of the wiring remains unchanged. A scanning frequency voltage with a frequency range of 1Hz to 2MHz and an amplitude of 10V is applied to phase A. The port voltage and port current are measured five times using a voltage transformer and a current transformer, and the data is saved in the system working area.

[0146] In step three, using the five collected voltage and current data points, the average values ​​of the voltage and current data are taken respectively, and two drive point impedance curves are plotted for the neutral point open circuit and the neutral point grounded through a capacitor, as shown below. Figure 3 As shown.

[0147] In step four, the SCNF of the two drive point impedance curves with the neutral point open and the neutral point grounded through a 58pF capacitor is extracted, as shown in the table below.

[0148]

[0149]

[0150] Substituting into equation (4), the equivalent electrical parameter (inductance) of the test transformer can be calculated to be 0.92mH.

[0151] In step five, the equivalent electrical parameters are compared with those under normal conditions, and the curves, extracted SCNF, and calculation results are displayed on the fault detection system interface. If the difference is greater than 20%, the transformer winding is judged to have a fault; if the difference is less than 20%, the transformer winding is judged to be normal. After the above method was used to diagnose the star-side winding of a 10kVA three-phase oil-immersed transformer, deformation of the internal winding was found.

Claims

1. A method for measuring the equivalent electrical parameters of a transformer star-side winding, characterized in that, Includes the following steps: 1) Set the scanning frequency, the excitation voltage frequency, and the initial value of the iteration number m = 1; 2) Open the neutral point of the three-phase transformer to be tested, and apply a scanning frequency excitation voltage to phase X. Use voltage transformers and current transformers to measure the port voltage and port current of the three-phase transformer under the current wiring condition. The number of measurements is n. X can be any one of phases A, B, and C. 3) Ground the neutral point of the three-phase transformer to be tested through a capacitor, and apply the same scanning frequency excitation voltage as in step 1) to phase X. Measure the port voltage and port current of the three-phase transformer under the current wiring condition using voltage transformers and current transformers. The number of measurements is n. 4) Calculate the average value of the port voltage and the average value of the port current measured in step 2), and calculate the driving point impedance of the neutral point open circuit at the current frequency based on the average value of the port voltage and the average value of the port current. Calculate the average value of the port voltage and the average value of the port current measured in step 3), and calculate the driving point impedance of the neutral point grounded through the capacitor at the current frequency based on the average value of the port voltage and the average value of the port current. 5) Determine if m≥M holds true. If not, adjust the frequency of the scanning frequency excitation voltage, let m=m+1, and return to step 2). If yes, proceed to step 6. M is the maximum number of iterations. 6) Based on the driving point impedance and corresponding frequency of the neutral point open circuit, construct the driving point impedance curve of the neutral point open circuit; Based on the driving point impedance with the neutral point grounded by a capacitor and the corresponding frequency, a driving point impedance curve with the neutral point grounded by a capacitor is constructed. 7) Extract the short-circuit natural frequency ω from the driving point impedance curve of the neutral point open circuit. sci And the short-circuit natural frequency of the impedance curve of the drive point with the neutral point grounded by a capacitor. And calculate the equivalent electrical parameter L eq ; 8) Based on equivalent electrical parameter L eq The equivalent electrical parameters of the transformer under test under normal conditions are used to determine whether the windings of the transformer under test have a fault.

2. The method for measuring the equivalent electrical parameters of a transformer star-side winding according to claim 1, characterized in that, In step 1), the frequency range of the scanning frequency excitation voltage is 1Hz-2MHz.

3. The method for measuring the equivalent electrical parameters of a transformer star-side winding according to claim 1, characterized in that, In step 2), the three-phase transformer to be tested is a Y-connected three-phase transformer.

4. The method for measuring the equivalent electrical parameters of a transformer star-side winding according to claim 1, characterized in that, In step 7), the short-circuit natural frequency ω of the driving point impedance curve with the neutral point open circuit is... sci As shown below: In the formula, L ii C is the self-inductance of the i-th winding unit of the transformer. si and C gi M is the series capacitance and grounding capacitance of the i-th winding unit. 0i is the total inductance between the wire end and the i-th winding unit end; N is the number of winding units.

5. The method for measuring the equivalent electrical parameters of a transformer star-side winding according to claim 4, characterized in that, In step 7), the short-circuit natural frequency of the impedance curve of the drive point with the neutral point grounded via a capacitor. As shown below: In the formula, C ext For external pf level capacitors; M 0N This represents the total inductance between the neutral and neutral terminals of the winding when all capacitors are open; C gN This is the grounding capacitance of the Nth winding unit.

6. The method for measuring the equivalent electrical parameters of a transformer star-side winding according to claim 5, characterized in that, In step 7), the equivalent electrical parameter L eq As shown below: In the formula, The short-circuit natural frequency of the driving point impedance curve with the neutral point grounded by a capacitor.

7. The method for measuring the equivalent electrical parameters of a transformer star-side winding according to claim 1, characterized in that, In step 8), the steps for determining whether the winding of the transformer under test has a fault are as follows: Calculate the percentage difference in equivalent electrical parameters L eq,0 The equivalent electrical parameters of the transformer under test under normal conditions; L eq Equivalent electrical parameters; If ΔL eq >ΔL eq,max If ΔL eq ≤ΔL eq,max If the transformer winding under test is normal, then it is determined that the transformer winding is normal; ΔL eq,max This is a preset threshold for the percentage difference.

8. The method for measuring the equivalent electrical parameters of a transformer star-side winding according to claim 7, characterized in that, Preset difference percentage threshold ΔL eq,max =20%.

9. The method for measuring the equivalent electrical parameters of a transformer star-side winding according to claim 1, characterized in that, In step 8), after determining whether a fault has occurred in the winding of the transformer under test, the determination result and the short-circuit natural frequency ω are... sci Short-circuit natural frequency Equivalent electrical parameter L eq Visualization.

10. A system for measuring the equivalent electrical parameters of a transformer star-side winding according to any one of claims 1-9, characterized in that, It includes voltage transformers, current transformers, data processing units, fault diagnosis units, and diagnosis result display units; The voltage transformers measure the three-phase transformer port voltages under the conditions of neutral point open circuit and neutral point grounded via capacitor, and transmit the data to the data processing unit. The current transformers measure the three-phase transformer port currents under the conditions of neutral point open circuit and neutral point grounded via capacitor, and transmit the data to the data processing unit. The data processing unit calculates the average value of the three-phase transformer port voltage and the average value of the current corresponding to different frequency excitation voltages when the neutral point is open, and constructs the drive point impedance curve when the neutral point is open. The data processing unit calculates the average value of the three-phase transformer port voltage and the average value of the current corresponding to different frequency excitation voltages when the neutral point is grounded through a capacitor, and constructs the driving point impedance curve when the neutral point is grounded through a capacitor. The data processing unit extracts the short-circuit natural frequency ω from the driving point impedance curve of the neutral point open circuit. sci And the short-circuit natural frequency of the impedance curve of the drive point with the neutral point grounded by a capacitor. Calculate the equivalent electrical parameter L eq The results are transmitted to the fault diagnosis unit and the diagnosis result display unit. The fault diagnosis unit is based on the equivalent electrical parameter L. eq The system obtains the equivalent electrical parameters of the transformer under normal conditions, determines whether the winding of the transformer under test has a fault, and transmits the determination result to the diagnostic result display unit. The diagnostic result display unit will display the judgment result and the short-circuit natural frequency ω. sci Short-circuit natural frequency Equivalent electrical parameter L eq Visualization.

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