Transformer star-side winding equivalent electrical parameter measurement method and deformation fault diagnosis system

Abstract

The invention discloses a transformer star side winding equivalent electrical parameter measurement method and a deformation fault diagnosis system. The method comprises the following steps: 1) extracting a short-circuit inherent frequency omega sci of a driving point impedance curve of which a neutral point is open-circuited and a short-circuit inherent frequency # imgabs0 # of a driving point impedance curve of which the neutral point is grounded through a capacitor, and calculating an equivalent electrical parameter Leq; 2) based on the equivalent electrical parameter Leq and the equivalent electrical parameter of the to-be-detected transformer under the normal condition, judging whether the winding of the to-be-detected transformer has a fault; the system comprises a voltage transformer, a current transformer, a data processing unit, a fault diagnosis unit and a diagnosis result display unit. According to the invention, the winding state of the transformer can be timely and accurately diagnosed through the measured equivalent electrical parameters, sensitivity and reliability are considered at the same time, and a guarantee is provided for stable operation of a power grid.

Description

Technical Field

[0001] The invention relates to the technical field of electrical parameter measurement and fault detection, and in particular to a transformer star-side winding equivalent electrical parameter measurement method and a deformation fault diagnosis system. Background Art

[0002] Transformer winding damage is one of the main causes of transformer failure. Transformer windings are mostly made of copper wires. The deformation caused by the short-circuit electromotive force is elastic-plastic deformation, and it will accumulate after the winding is subjected to multiple short-circuit shocks. When the deformation of the transformer winding is small, this cumulative effect usually does not cause the relay protection device in the power system to operate. Therefore, slight deformation of the transformer winding is usually ignored by maintenance personnel. However, as the number of short-circuit shocks increases, this cumulative effect will change the structure of the winding. When the insulation protection of the winding is damaged to a certain extent, the huge short-circuit shock may cause the winding to break or collapse.

[0003] Due to the closed structure of the transformer, conventional fault detection methods are sometimes unable to accurately diagnose winding deformation. At present, my country generally uses the frequency response method to detect the deformation of transformer windings, and comprehensively judges the winding status of the transformer by comparing the frequency response curves before and after the winding deformation. However, in the high-frequency band, due to the influence of stray capacitance parameters, the frequency response curve is easily affected by factors such as the wiring method of the measuring device, wire layout, personnel experience, and electromagnetic environment, and the test repeatability is poor. Other low-frequency detection methods, such as the short-circuit impedance method, are not sensitive enough and it is difficult to detect small deformations of the winding. Therefore, taking into account the sensitivity and reliability of transformer winding fault detection is of great significance for preventing potential failures of the transformer and prolonging the service life of the transformer. Summary of the invention

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

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

[0006] 2) Open the neutral point of the three-phase transformer to be tested, and pass the scanning frequency excitation voltage to the X phase. Use the voltage transformer and current transformer to measure the port voltage and port current of the three-phase transformer under the current connection state. The number of measurements is n; X is selected from any phase of A, B, and C;

[0007] 3) The neutral point of the three-phase transformer to be tested is grounded via a capacitor, and the same scanning frequency excitation voltage as in step 1) is applied to the X phase, and the port voltage and port current of the three-phase transformer under the current connection state are measured using a voltage transformer and a current transformer, and the number of measurements is n;

[0008] 4) calculating the average values ​​of the port voltage and the port current measured in step 2), and calculating the driving point impedance of the neutral point open circuit at the current frequency based on the average values ​​of the port voltage and the port current;

[0009] Calculate the average value of the port voltage and 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 port current;

[0010] 5) Determine whether m≥M is established. If not, adjust the frequency of the scanning frequency excitation voltage to set 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 a driving point impedance curve of the neutral point open circuit;

[0012] Based on the driving point impedance of the neutral point grounded through the capacitor and the corresponding frequency, a driving point impedance curve of the neutral point grounded through the capacitor is constructed;

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

[0014] 8) Based on the equivalent electrical parameter L eq , and the equivalent electrical parameters of the transformer to be tested under normal conditions, to determine whether the winding of the transformer to be tested is faulty.

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

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

[0017] Further, 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] Where, L ii is the self-inductance of the i-th winding unit of the transformer, C si and C gi is the series capacitance and ground capacitance of the ith winding unit, M 0i is the total inductance between the line end and the end of the i-th winding unit. N is the number of winding units.

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

[0021]

[0022] In the formula, C ext is an external pf level capacitor; M 0N It represents the total inductance between the neutral end and the neutral end of the winding when all capacitors are open circuit. gN is the grounding capacitance of the Nth winding unit.

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

[0024]

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

[0026] Further, in step 8), the step of determining whether the transformer winding to be detected is faulty is as follows:

[0027] Calculate the difference percentage of equivalent electrical parameters L eq,0 is the equivalent electrical parameter of the transformer to be tested under normal conditions; L eq is the equivalent electrical parameter;

[0028] If ΔL eq >ΔL eq,max , then it is judged that the transformer winding to be tested is faulty. If ΔL eq ≤ΔL eq,max , then it is judged that the transformer winding to be tested is normal; ΔL eq,max is the preset difference percentage threshold.

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

[0030] Further, in step 8), after determining whether the transformer winding to be detected is faulty, 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 using the transformer star-side winding equivalent electrical parameter measurement method comprises a voltage transformer, a current transformer, a data processing unit, a fault diagnosis unit and a diagnosis result display unit;

[0032] The voltage transformer measures the voltage at the three-phase transformer port when the neutral point is open and the neutral point is grounded via a capacitor, respectively, and transmits the voltage to the data processing unit;

[0033] The current transformer measures the three-phase transformer port currents when the neutral point is open and the neutral point is grounded via a capacitor, respectively, and transmits the currents 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 the excitation voltages of different frequencies when the neutral point is open, and constructs a driving 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 the excitation voltages of different frequencies when the neutral point is grounded through a capacitor, and constructs a 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 of the driving point impedance curve of the neutral point open circuit sci , and the short-circuit natural frequency of the driving point impedance curve with the neutral point grounded by a capacitor Calculate the equivalent electrical parameter L eq , and transmit it 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 , and the equivalent electrical parameters of the transformer to be detected under normal conditions, determine whether the winding of the transformer to be detected is faulty, and transmit the determination result to the diagnosis result display unit;

[0038] The diagnosis result display unit displays the judgment result, the short-circuit natural frequency ω sci , short circuit natural frequency Equivalent electrical parameter L eq Visualization.

[0039] The technical effect of the present invention is unquestionable. The present invention provides an equivalent electrical parameter measurement method and system for detecting transformer star-side winding deformation faults, which can timely and accurately diagnose the winding status of the transformer through the measured equivalent electrical parameters, thereby providing guarantee for the stable operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The equivalent electrical parameter measurement principle for detecting transformer winding deformation fault;

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

[0042] Figure 3These are the two driving point impedance curves measured when the neutral point is open circuited and the neutral point is grounded via a 58pF capacitor;

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

[0044] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0045] Embodiment 1:

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

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

[0048] 2) Open the neutral point of the three-phase transformer to be tested, and pass the scanning frequency excitation voltage to the X phase. Use the voltage transformer and current transformer to measure the port voltage and port current of the three-phase transformer under the current connection state. The number of measurements is n; X is selected from any phase of A, B, and C;

[0049] 3) The neutral point of the three-phase transformer to be tested is grounded via a capacitor, and the same scanning frequency excitation voltage as in step 1) is applied to the X phase, and the port voltage and port current of the three-phase transformer under the current connection state are measured using a voltage transformer and a current transformer, and the number of measurements is n;

[0050] 4) calculating the average values ​​of the port voltage and the port current measured in step 2), and calculating the driving point impedance of the neutral point open circuit at the current frequency based on the average values ​​of the port voltage and the port current;

[0051] Calculate the average value of the port voltage and 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 port current;

[0052] 5) Determine whether m≥M is established. If not, adjust the frequency of the scanning frequency excitation voltage to set 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 a driving point impedance curve of the neutral point open circuit;

[0054] Based on the driving point impedance of the neutral point grounded through the capacitor and the corresponding frequency, a driving point impedance curve of the neutral point grounded through the capacitor is constructed;

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

[0056] 8) Based on the equivalent electrical parameter L eq , and the equivalent electrical parameters of the transformer to be tested under normal conditions, to determine whether the winding of the transformer to be tested is faulty.

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

[0058] In step 2), the three-phase transformer to be detected is a three-phase transformer with a Y-type connection.

[0059] 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:

[0060]

[0061] Where, L ii is the self-inductance of the i-th winding unit of the transformer, C si and C gi is the series capacitance and ground capacitance of the ith winding unit, M 0i is the total inductance between the line end and the end of the i-th winding unit. N is the number of winding units.

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

[0063]

[0064] In the formula, C ext is an external pf level capacitor; M 0N It represents the total inductance between the neutral end and the neutral end of the winding when all capacitors are open circuit. gN 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, It is the short-circuit natural frequency of the driving point impedance curve with the neutral point grounded through a capacitor.

[0068] In step 8), the step of determining whether the transformer winding to be detected is faulty is as follows:

[0069] Calculate the difference percentage of equivalent electrical parameters L eq,0 is the equivalent electrical parameter of the transformer to be tested under normal conditions;

[0070] If ΔL eq >ΔL eq,max , then it is judged that the transformer winding to be tested is faulty. If ΔL eq ≤ΔL eq,max , it is judged that the transformer winding to be tested is normal; ΔL eq,max is the preset difference percentage threshold.

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

[0072] In step 8), after determining whether the transformer winding to be detected is faulty, the determination result and the short-circuit natural frequency ω are sci , short circuit natural frequency Equivalent electrical parameter L eq Visualization.

[0073] Embodiment 2:

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

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

[0076] 2) Open the neutral point of the three-phase transformer to be tested, and pass the scanning frequency excitation voltage to the X phase. Use the voltage transformer and current transformer to measure the port voltage and port current of the three-phase transformer under the current connection state. The number of measurements is n; X is selected from any phase of A, B, and C;

[0077] 3) The neutral point of the three-phase transformer to be tested is grounded via a capacitor, and the same scanning frequency excitation voltage as in step 1) is applied to the X phase, and the port voltage and port current of the three-phase transformer under the current connection state are measured using a voltage transformer and a current transformer, and the number of measurements is n;

[0078] 4) calculating the average values ​​of the port voltage and the port current measured in step 2), and calculating the driving point impedance of the neutral point open circuit at the current frequency based on the average values ​​of the port voltage and the port current;

[0079] Calculate the average value of the port voltage and 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 port current;

[0080] 5) Determine whether m≥M is established. If not, adjust the frequency of the scanning frequency excitation voltage to set 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 a driving point impedance curve of the neutral point open circuit;

[0082] Based on the driving point impedance of the neutral point grounded through the capacitor and the corresponding frequency, a driving point impedance curve of the neutral point grounded through the capacitor is constructed;

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

[0084] 8) Based on the equivalent electrical parameter L eq , and the equivalent electrical parameters of the transformer to be tested under normal conditions, to determine whether the winding of the transformer to be tested is faulty.

[0085] Embodiment 3:

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

[0087] Embodiment 4:

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

[0089] Embodiment 5:

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

[0091]

[0092] Where, L ii is the self-inductance of the i-th winding unit of the transformer, C si and Cgi is the series capacitance and ground capacitance of the ith winding unit, M 0i is the total inductance between the line end and the end of the i-th winding unit.

[0093] Embodiment 6:

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

[0095]

[0096] In the formula, C ext is an external pf level capacitor; M 0N It represents the total inductance between the midline and neutral ends of a winding when all capacitors are open circuited.

[0097] Embodiment 7:

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

[0099]

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

[0101] Embodiment 8:

[0102] A method for measuring equivalent electrical parameters of a transformer star-side winding, the technical content of which is the same as any one of embodiments 2-7, further, in step 8), the step of determining whether a transformer winding to be detected is faulty is:

[0103] Calculate the difference percentage of equivalent electrical parameters L eq,0 is the equivalent electrical parameter of the transformer to be tested under normal conditions; L eq is the equivalent electrical parameter;

[0104] If ΔL eq >ΔL eq,max , then it is judged that the transformer winding to be tested is faulty. If ΔL eq ≤ΔL eq,max , then it is judged that the transformer winding to be tested is normal; ΔL eq,max is the preset difference percentage threshold.

[0105] Embodiment 9:

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

[0107] Embodiment 10:

[0108] A method for measuring equivalent electrical parameters of a transformer star-side winding, the technical content of which is the same as any one of embodiments 2-9, further, in step 8), after determining whether the transformer winding to be detected is faulty, the determination result, the short-circuit natural frequency ω sci , short circuit natural frequency Equivalent electrical parameter L eq Visualization.

[0109] Embodiment 11:

[0110] A system for measuring equivalent electrical parameters of a transformer star-side winding using any one of the methods described in Examples 1 to 10, comprising a voltage transformer, a current transformer, a data processing unit, a fault diagnosis unit, and a diagnosis result display unit;

[0111] The voltage transformer measures the voltage at the three-phase transformer port when the neutral point is open and the neutral point is grounded via a capacitor, respectively, and transmits the voltage to the data processing unit;

[0112] The current transformer measures the three-phase transformer port currents when the neutral point is open and the neutral point is grounded via a capacitor, respectively, and transmits the currents 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 the excitation voltages of different frequencies when the neutral point is open, and constructs a driving 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 the excitation voltages of different frequencies when the neutral point is grounded through a capacitor, and constructs a 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 of the driving point impedance curve of the neutral point open circuit sci , and the short-circuit natural frequency of the driving point impedance curve with the neutral point grounded by a capacitor Calculate the equivalent electrical parameter L eq , and transmit it 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 , and the equivalent electrical parameters of the transformer to be detected under normal conditions, determine whether the winding of the transformer to be detected is faulty, and transmit the determination result to the diagnosis result display unit;

[0117] The diagnosis result display unit displays the judgment result, the short-circuit natural frequency ω sci , short circuit natural frequency Equivalent electrical parameter L eq Visualization.

[0118] Embodiment 12:

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

[0120] Step 1: Open the neutral point of a Y-type three-phase transformer, apply a sweep frequency excitation voltage to one phase, with a frequency of 1Hz-2MHz, use a voltage transformer and a current transformer to measure the port voltage and port current five times, and save them in the system workspace;

[0121] Step 2: Ground the neutral point of the transformer through a capacitor, and keep the other connections unchanged. Apply the same scanning frequency excitation voltage as in step 1, with a frequency of 1Hz-2MHz. Use a voltage transformer and a current transformer to measure the port voltage and port current five times, and save them in the system work area.

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

[0123] Step 4: By extracting the short circuit natural frequencies (SCNF) of the two driving point impedance curves, use the formula to calculate the equivalent electrical parameters;

[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 the equivalent electrical parameters is greater than 20%, it is judged that the transformer winding is faulty. If the difference in the equivalent electrical parameters is less than 20%, it is judged that the transformer winding is normal.

[0125] Embodiment 13:

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

[0127] In step 1, in this example, the star-side winding of a three-phase oil-immersed transformer with a rated capacity of 2kVA-300kVA is used as the experimental object. Figure 2As shown in the figure, a fully coupled N-segment ladder network model of the transformer is established, in which each segment represents a unit of the winding. The neutral point of the transformer is open, and a sweep 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 5 times using a voltage transformer and a current transformer, and saved in the system workspace;

[0128] In the step 2, the neutral point of the transformer is grounded via a capacitor of pF level, the other 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 a voltage transformer and a current transformer, and the results are saved in the system work area;

[0129] In the step three, the five collected voltage and current data are used to take the average values ​​of the voltage and current data, and two driving point impedance curves are drawn respectively, one with the neutral point open and the other with the neutral point grounded through a capacitor.

[0130] In the step 4, the SCNF of the driving point impedance curve when the neutral point is open is extracted. The relationship between the SCNF and the winding electrical parameters (capacitance and inductance) is as follows:

[0131]

[0132] Where, L ii is the self-inductance of the ith pie, C si and C gi is the series capacitance and ground capacitance of the ith pancake, M 0i is the total inductance between the line end and the i-th pie end, ω sci It is SCNF.

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

[0134]

[0135] In the formula, except for the last segment of grounding capacitance composed of C gN Change to C gN +C ext In addition, each parameter of the ladder network remains unchanged, C ext For an external pf level capacitor, For the new SCNF.

[0136] Subtracting (1) from (2) yields:

[0137]

[0138] M 0iIt refers to the total inductance between node 0 (line end) and node N (neutral end) in the winding when all capacitors are open circuit. 0i is the inductance between the winding line end and the neutral end when the same current flows through all the pies, so M 0i =L eq . The above expression can be rewritten as:

[0139]

[0140] Substituting into formula (4) to calculate the equivalent electrical parameters (inductance) of the test transformer can be obtained.

[0141] In step 5, the equivalent electrical parameters are compared with the equivalent electrical parameters under normal conditions, and the curve, the extracted SCNF, and the calculation results are displayed in the following manner: Figure 4 The fault detection system interface shown has functions such as parameter setting, collected data display, and diagnostic result display. If the difference in equivalent electrical parameters is greater than 20%, it is judged that the transformer winding is faulty. If the difference in equivalent electrical parameters is less than 20%, it is judged that the transformer winding is normal.

[0142] Embodiment 14:

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

[0144] In step 1, in this example, the star-side winding of a three-phase oil-immersed transformer with a rated capacity of 2kVA-300kVA is used as the experimental object. The neutral point of the transformer is open, 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 5 times using a voltage transformer and a current transformer, and saved in the system workspace;

[0145] In the step 2, the neutral point of the transformer is grounded via a 58pF capacitor, and the other connections remain 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 5 times using a voltage transformer and a current transformer, and the results are saved in the system work area.

[0146] In step 3, the five collected voltage and current data are used to take the average values ​​of the voltage and current data, and two driving point impedance curves are drawn, respectively, when the neutral point is open and the neutral point is grounded through a capacitor. Figure 3 shown.

[0147] In the step 4, the SCNF of the two driving point impedance curves, one with the neutral point open and the other with the neutral point grounded via a 58 pF capacitor, are extracted respectively, as shown in the following table.

[0148]

[0149]

[0150] Substituting into formula (4) to calculate, the equivalent electrical parameter (inductance) of the test transformer is 0.92mH.

[0151] In step 5, the equivalent electrical parameters are compared with the equivalent electrical parameters under normal conditions, and the curve, the extracted SCNF, and the calculation results are displayed on the fault detection system interface. If the difference is greater than 20%, it is determined that the transformer winding is faulty. If the difference is less than 20%, it is determined that the transformer winding is normal. After the star side winding of a 10kVA three-phase oil-immersed transformer was diagnosed by the above method, it was found that its internal winding was deformed.

Claims

1. A method for measuring equivalent electrical parameters of a transformer star-side winding, characterized in that: The following steps are involved: 1) Set the frequency of the sweep frequency excitation voltage and the initial value of the number of iterations m=1. 2) Open the neutral point of the three-phase transformer to be tested, and pass the scanning frequency excitation voltage to the X phase. Use the voltage transformer and current transformer to measure the port voltage and port current of the three-phase transformer under the current connection state. The number of measurements is n; X is selected from any phase of A, B, and C; 3) The neutral point of the three-phase transformer to be tested is grounded via a capacitor, and the same scanning frequency excitation voltage as in step 1) is applied to the X phase, and the port voltage and port current of the three-phase transformer under the current connection state are measured using a voltage transformer and a current transformer, and the number of measurements is n; 4) calculating the average values ​​of the port voltage and the port current measured in step 2), and calculating the driving point impedance of the neutral point open circuit at the current frequency based on the average values ​​of the port voltage and the port current; Calculate the average value of the port voltage and 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 port current; 5) Determine whether m≥M is established. If not, adjust the frequency of the scanning frequency excitation voltage to set 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 a driving point impedance curve of the neutral point open circuit; Based on the driving point impedance of the neutral point grounded through the capacitor and the corresponding frequency, a driving point impedance curve of the neutral point grounded through the capacitor is constructed; 7) Extract the short-circuit natural frequency ω of the driving point impedance curve with the neutral point open sci , and the short-circuit natural frequency of the driving point impedance curve with the neutral point grounded by a capacitor And calculate the equivalent electrical parameter L eq ; 8) Based on the equivalent electrical parameter L eq , and the equivalent electrical parameters of the transformer to be tested under normal conditions, to determine whether the winding of the transformer to be tested is faulty.

2. A method for measuring 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 1 Hz-2 MHz.

3. The method for measuring 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 detected is a three-phase transformer with a Y-type connection.

4. The method for measuring 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 sci As shown below: Where, L ii is the self-inductance of the i-th winding unit of the transformer, C si and C gi is the series capacitance and ground capacitance of the ith winding unit, M 0i is the total inductance between the line end and the end of the i-th winding unit; N is the number of winding units.

5. The method for measuring equivalent electrical parameters of a transformer star-side winding according to claim 1, characterized in that: In step 7), the short-circuit natural frequency of the driving point impedance curve with the neutral point grounded through a capacitor is As shown below: In the formula, C ext is an external pf level capacitor; M 0N Indicates the total inductance between the neutral end and the neutral end of the winding when all capacitors are open circuited; C gN is the grounding capacitance of the Nth winding unit.

6. A method for measuring equivalent electrical parameters of a transformer star-side winding according to claim 1, characterized in that: In step 7), the equivalent electrical parameter L eq As shown below: In the formula, It is the short-circuit natural frequency of the driving point impedance curve with the neutral point grounded through a capacitor.

7. A method for measuring equivalent electrical parameters of a transformer star-side winding according to claim 1, characterized in that: In step 8), the step of determining whether the transformer winding to be detected is faulty is as follows: Calculate the difference percentage of equivalent electrical parameters L eq,0 is the equivalent electrical parameter of the transformer to be tested under normal conditions; L eq is the equivalent electrical parameter; If ΔL eq >ΔL eq,max , then it is judged that the transformer winding to be tested is faulty. If ΔL eq ≤ΔL eq,max , then it is judged that the transformer winding to be tested is normal; ΔL eq,max is the preset difference percentage threshold.

8. A method for measuring 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 equivalent electrical parameters of a transformer star-side winding according to claim 1, characterized in that: In step 8), after determining whether the transformer winding to be detected is faulty, 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 using the method for measuring equivalent electrical parameters of a transformer star-side winding according to any one of claims 1 to 9, characterized in that: It includes a voltage transformer, a current transformer, a data processing unit, a fault diagnosis unit and a diagnosis result display unit; The voltage transformer measures the voltage at the three-phase transformer port when the neutral point is open and the neutral point is grounded via a capacitor, respectively, and transmits the voltage to the data processing unit; The current transformer measures the three-phase transformer port currents when the neutral point is open and the neutral point is grounded via a capacitor, respectively, and transmits the currents to the data processing unit; The data processing unit calculates the average values ​​of the three-phase transformer port voltage and current corresponding to the excitation voltages of different frequencies when the neutral point is open, and constructs a driving point impedance curve when the neutral point is open; The data processing unit calculates the average values ​​of the three-phase transformer port voltage and current corresponding to the excitation voltages of different frequencies when the neutral point is grounded through a capacitor, and constructs a driving point impedance curve when the neutral point is grounded through a capacitor; The data processing unit extracts the short-circuit natural frequency ω of the driving point impedance curve of the neutral point open circuit sci , and the short-circuit natural frequency of the driving point impedance curve with the neutral point grounded by a capacitor Calculate the equivalent electrical parameter L eq , and transmit it to the fault diagnosis unit and the diagnosis result display unit; The fault diagnosis unit is based on the equivalent electrical parameter L eq , and the equivalent electrical parameters of the transformer to be detected under normal conditions, determine whether the winding of the transformer to be detected is faulty, and transmit the determination result to the diagnosis result display unit; The diagnosis result display unit displays the judgment result, the short-circuit natural frequency ω sci , short circuit natural frequency Equivalent electrical parameter L eq Visualization.

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