A method for measuring the voltage dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning

Abstract

The present invention provides a method for measuring the voltage-dividing capacitance of a capacitor voltage transformer based on short-circuit frequency scanning, which belongs to the field of electrical insulation detection of power equipment. The method comprises: performing a first short-circuit impedance test on the capacitor voltage transformer, measuring the frequency-variable short-circuit impedance including the second capacitor, and obtaining a first frequency-variable short-circuit impedance; performing a second short-circuit impedance test, measuring the frequency-variable short-circuit impedance including the first capacitor and the second capacitor, and obtaining a second frequency-variable short-circuit impedance; drawing a frequency-variable short-circuit impedance curve based on the first frequency-variable short-circuit impedance and the second frequency-variable short-circuit impedance, and calculating a first capacitance reference value and a second capacitance reference value; using the first capacitance reference value and the second capacitance reference value, combined with the ratio of the intermediate voltage transformer, calculating the measured value of the voltage-dividing capacitance, and completing the voltage-dividing capacitance measurement of the capacitor voltage transformer. The present invention solves the problems of existing capacitance value measurement methods, such as complex wiring and a large influence of the wiring method on the accuracy.

Description

Technical Field

[0001] The present invention belongs to the field of electrical insulation detection of power equipment, and in particular relates to a method for measuring the voltage dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning. Background Art

[0002] Capacitor voltage transformers (CVTs) age over their lifetime. This aging process can reduce their measurement accuracy and even lead to serious failures such as sudden explosions. Therefore, regular insulation testing and inspections are necessary, including capacitance measurement and power frequency withstand voltage testing. Capacitance measurement is the most widely used field testing method, but existing methods suffer from complex wiring and accuracy that is significantly affected by the wiring method. Summary of the Invention

[0003] In response to the above-mentioned deficiencies in the prior art, the present invention provides a method for measuring the voltage divider capacitance of a capacitive voltage transformer based on short-circuit frequency scanning, which solves the problem that the existing capacitance value measurement method has complex wiring and the accuracy is greatly affected by the wiring method.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: a method for measuring the voltage dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning, comprising the following steps:

[0005] S1. Perform a first short-circuit impedance test on the capacitor voltage transformer to obtain a first frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the second capacitor is measured;

[0006] S2. Perform a second short-circuit impedance test on the capacitor voltage transformer to obtain a second frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the first capacitor and the second capacitor is measured;

[0007] S3. Draw a frequency-dependent short-circuit impedance curve of the capacitor voltage transformer according to the first frequency-dependent short-circuit impedance and the second frequency-dependent short-circuit impedance, and calculate a first capacitance reference value and a second capacitance reference value according to the frequency-dependent short-circuit impedance curve;

[0008] S4. Using the first capacitance reference value and the second capacitance reference value, combined with the ratio of the intermediate voltage transformer, calculate the measured values ​​of the first capacitance, the second capacitance, and the total capacitance, and complete the capacitance divider capacitance measurement of the capacitive voltage transformer.

[0009] The beneficial effects of the present invention are as follows: the present invention determines the capacitance value of the voltage divider capacitor through two short-circuit impedance tests, thereby achieving simple wiring, improving measurement accuracy, and reducing the influence of the wiring method on the measurement accuracy.

[0010] Furthermore, the S1 includes the following steps:

[0011] S101, connecting the variable frequency AC power supply and the secondary side of the voltage and ammeter to the capacitive voltage transformer;

[0012] S102. Perform a first short-circuit impedance test on the capacitor voltage transformer, disconnect the high-voltage terminal of the capacitor voltage transformer from the system and keep it open, and keep the NHF / CAR terminal grounded to obtain a first frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the second capacitor is measured.

[0013] The beneficial effect of the above further scheme is: the present invention only measures the frequency-variable short-circuit impedance of the second capacitor through the first short-circuit impedance test, and can obtain the parameters of the second capacitor separately, providing accurate basic data for subsequent capacitance value calculation, avoiding the complexity of multiple capacitors in parallel, and improving the pertinence and accuracy of the measurement.

[0014] Furthermore, the S2 is specifically as follows:

[0015] A second short-circuit impedance test is performed on the capacitor voltage transformer, and the high-voltage terminal and the NHF / CAR terminal of the capacitor voltage transformer are connected to the ground wire to obtain a second frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the first capacitor and the second capacitor is measured.

[0016] The beneficial effect of the above further scheme is: the present invention measures the frequency-variable short-circuit impedance including the first capacitor and the second capacitor through a second short-circuit impedance test, obtains the impedance characteristics under the joint action of the first capacitor and the second capacitor, provides the necessary data for calculating the total capacitance, and enhances the comprehensiveness and reliability of the measurement results.

[0017] Furthermore, the S3 includes the following steps:

[0018] S301. Draw a frequency-dependent short-circuit impedance curve of a capacitor voltage transformer according to a first frequency-dependent short-circuit impedance and a second frequency-dependent short-circuit impedance;

[0019] S302: Obtain a total inductance reference value including the compensation inductance and the leakage inductance of the intermediate voltage transformer based on the frequency-dependent short-circuit impedance curve, define a frequency corresponding to a zero-degree phase response in the frequency-dependent short-circuit impedance curve as a resonant frequency, and obtain the resonant frequency of the second capacitor and the resonant frequency of the total capacitor;

[0020] S303 : Calculate a first capacitance reference value and a second capacitance reference value according to the total inductance reference value, the resonant frequency of the second capacitor, and the resonant frequency of the total capacitor.

[0021] Furthermore, the expression of the second capacitance reference value is as follows:

[0022]

[0023] C1″=C t ' o ' t -C2″;

[0024] Wherein, C2″ represents the second capacitance reference value, C t ' o ' t Indicates the total capacitance reference value, L t ' o ' t Indicates the total inductance reference value, represents the resonant frequency of the second capacitor, represents the resonant frequency of the total capacitance, and C1″ represents the first capacitance reference value.

[0025] The beneficial effect of the above further scheme is: the present invention can accurately determine the capacitance value by drawing the frequency-dependent short-circuit impedance curve and calculating the reference values ​​of the first capacitor and the second capacitor. Through graphical display and precise calculation, the intuitiveness and accuracy of the capacitance value measurement are improved, making the measurement results more stable and reliable.

[0026] Furthermore, the S4 includes the following steps:

[0027] S401: Using a first capacitance reference value and a second capacitance reference value, combined with a ratio of an intermediate voltage transformer, convert the capacitance reference value to a primary side of the intermediate voltage transformer by calculation to obtain a measured value of the first capacitance and a measured value of the second capacitance;

[0028] S402. Calculate the measured value of the total capacitance based on the measured value of the first capacitance and the measured value of the second capacitance, and compare the measured value of the first capacitance, the measured value of the second capacitance, and the measured value of the total capacitance with the calibrated rated capacitance to complete the capacitance voltage transformer divider capacitance measurement.

[0029] Furthermore, the expression for converting the first capacitance reference value and the second capacitance reference value to the primary side of the intermediate voltage transformer is as follows:

[0030]

[0031] Wherein, C1′ represents the measured value of the first capacitance, C2′ represents the measured value of the second capacitance, C1″ represents the first capacitance reference value, C2″ represents the second capacitance reference value, K IVT Indicates the ratio of the intermediate voltage transformer.

[0032] The beneficial effect of the above further scheme is: the present invention uses the first capacitance reference value and the second capacitance reference value, and combines the ratio of the intermediate voltage transformer to calculate the measurement values ​​of the first capacitance, the second capacitance and the total capacitance, thereby completing the accurate measurement of the voltage divider capacitance of the capacitive voltage transformer, improving the measurement accuracy, and by considering the ratio of the intermediate voltage transformer, making the measurement results more consistent with actual working conditions, enhancing the practicality and application value of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Flow chart of the method of the present invention.

[0034] Figure 2 2 is a structural diagram of the capacitive voltage transformer in this embodiment.

[0035] Figure 3 4 is a structural diagram of a capacitive voltage transformer for performing the first short-circuit impedance test in this embodiment.

[0036] Figure 4 4 is a structural diagram of a capacitive voltage transformer for performing the second short-circuit impedance test in this embodiment.

[0037] Figure 5 : is a typical frequency-dependent short-circuit impedance curve of the capacitive voltage transformer in this embodiment.

[0038] Figure 6 Graph showing the short-circuit impedance and phase as a function of frequency in this embodiment. DETAILED DESCRIPTION

[0039] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0040] Before describing this embodiment, the following terms are explained:

[0041] CVT: Capacitor Voltage Transformer;

[0042] IVT: Intermediate Voltage Transformer;

[0043] FSC: Ferro-resonance suppression circuit;

[0044] NHF / CAR terminal: Fuse type load switch terminal.

[0045] Example 1

[0046] In this embodiment, a new method for determining the capacitance values ​​of the voltage divider capacitors C1 and C2 of a capacitive voltage transformer is proposed. The method is independent of the specific CVT design, and the accuracy is not affected by the wiring method.

[0047] like Figure 1 As shown, the present invention provides a method for measuring the voltage divider capacitance of a capacitive voltage transformer based on short-circuit frequency scanning, and its implementation method is as follows:

[0048] S1. Perform a first short-circuit impedance test on the capacitor voltage transformer to obtain a first frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the second capacitor is measured. The specific steps are as follows:

[0049] S101, connecting the variable frequency AC power supply and the secondary side of the voltage and ammeter to the capacitive voltage transformer;

[0050] S102. Perform a first short-circuit impedance test on the capacitor voltage transformer, disconnect the high-voltage terminal of the capacitor voltage transformer from the system and keep it open, and keep the NHF / CAR terminal grounded to obtain a first frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the second capacitor is measured.

[0051] In this embodiment, Figure 2 As shown in the figure, the main components of CVT include a capacitor unit composed of the same capacitor elements C1 and C2 in series, a series compensation reactor (L comp ), an intermediate voltage transformer and an iron resonance suppression circuit; the capacitor unit reduces the system voltage to an intermediate voltage level between 8kV and 20kV, and the intermediate voltage is then converted to the secondary output voltage of the CVT by the intermediate voltage transformer; the FSC is used to damp oscillation to protect the CVT.

[0052] In this embodiment, the new measurement method proposed mainly determines the capacitance values ​​of the first capacitor C1 and the second capacitor C2 through two short-circuit impedance tests; Figure 3 As shown, the first short-circuit impedance test Z SC1 Measure the frequency-dependent short-circuit impedance of the second capacitor C2, disconnect the high-voltage terminal (A / H1) from the system and keep it open, and keep the NHF / CAR terminal grounded; Figure 3 The devices connected to the secondary side of the CVT are a variable frequency AC power supply and a voltage and current meter.

[0053] S2. Perform a second short-circuit impedance test on the capacitor voltage transformer, measuring the frequency-dependent short-circuit impedance including the first capacitor and the second capacitor, and obtaining a second frequency-dependent short-circuit impedance, as follows:

[0054] A second short-circuit impedance test is performed on the capacitor voltage transformer, and the high-voltage terminal and the NHF / CAR terminal of the capacitor voltage transformer are connected to the ground wire to obtain a second frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the first capacitor and the second capacitor is measured.

[0055] In this embodiment, Figure 4 As shown, the second short-circuit impedance test Z SC2 The frequency-dependent short-circuit impedance including the first capacitor C1 and the second capacitor C2 is measured, and the high voltage terminal (A / H1) and the NHF / CAR terminal are connected to the ground line.

[0056] S3. Draw a frequency-dependent short-circuit impedance curve of the capacitor voltage transformer according to the first frequency-dependent short-circuit impedance and the second frequency-dependent short-circuit impedance, and calculate a first capacitance reference value and a second capacitance reference value according to the frequency-dependent short-circuit impedance curve. The specific steps are as follows:

[0057] S301. Draw a frequency-dependent short-circuit impedance curve of a capacitor voltage transformer according to a first frequency-dependent short-circuit impedance and a second frequency-dependent short-circuit impedance;

[0058] S302: Obtain a total inductance reference value including the compensation inductance and the leakage inductance of the intermediate voltage transformer based on the frequency-dependent short-circuit impedance curve, define a frequency corresponding to a zero-degree phase response in the frequency-dependent short-circuit impedance curve as a resonant frequency, and obtain the resonant frequency of the second capacitor and the resonant frequency of the total capacitor;

[0059] S303 : Calculate a first capacitance reference value and a second capacitance reference value according to the total inductance reference value, the resonant frequency of the second capacitor, and the resonant frequency of the total capacitor.

[0060] In this embodiment, Figure 5 As shown, a typical frequency-variable short-circuit impedance curve is drawn by the first short-circuit impedance test and the second short-circuit impedance test. The red curve in the curve represents the first short-circuit impedance test, and the black curve represents the second short-circuit impedance test. The measurement curve in the typical frequency-variable short-circuit impedance curve shows that the second capacitance C2 and the total capacitance C tot and the total inductance L tot The behavior of a series resonant circuit of components; where the total capacitance C tot The first capacitor C1 and the second capacitor C2 are connected in parallel, and the total inductance L tot Including compensation inductor L comp and the leakage inductance of the IVT.

[0061] In this embodiment, Figure 6 As shown, the short-circuit impedance and phase change as a function of frequency, the resonant frequency f resThe frequency corresponding to the phase response is zero degrees, so the first capacitance reference value C1″, the second capacitance reference value C2″ and the total capacitance reference value C on the secondary side of the IVT are t ' o ' t , can be calculated by the following formula;

[0062]

[0063] C1″=C t ' o ' t -C2″;

[0064] Among them, L t ' o ' t Indicates the total inductance reference value, represents the resonant frequency of the second capacitor, Indicates the resonant frequency of the total capacitance.

[0065] Using the first and second capacitance reference values, combined with the ratio of the intermediate voltage transformer, the measured values ​​of the first capacitance, the second capacitance, and the total capacitance are calculated to complete the capacitance divider capacitance measurement of the capacitive voltage transformer. The specific steps are as follows:

[0066] S401: Using a first capacitance reference value and a second capacitance reference value, combined with a ratio of an intermediate voltage transformer, convert the capacitance reference value to a primary side of the intermediate voltage transformer by calculation to obtain a measured value of the first capacitance and a measured value of the second capacitance;

[0067] S402. Calculate the measured value of the total capacitance based on the measured value of the first capacitance and the measured value of the second capacitance, and compare the measured value of the first capacitance, the measured value of the second capacitance, and the measured value of the total capacitance with the calibrated rated capacitance to complete the capacitance voltage transformer divider capacitance measurement.

[0068] In this embodiment, the capacitance reference value can be converted to the IVT primary side by a calculation formula, and combined with the ratio of the intermediate voltage transformer, the first capacitance measurement value C1′ and the second capacitance measurement value C1′ can be obtained, and then the total capacitance measurement value C can be obtained. r ;

[0069] The expression for converting the capacitance reference value to the primary side of the intermediate voltage transformer is as follows:

[0070]

[0071] Among them, K IVT Indicates the ratio of the intermediate voltage transformer;

[0072] The calculated first capacitance measurement value, the second capacitance measurement value, and the total capacitance measurement value are compared with the rated capacitance on the upper surface of the nameplate to complete the voltage divider capacitance measurement of the capacitive voltage transformer.

[0073] Example 2

[0074] In this example, to verify the accuracy of the method proposed in this article, three 110kV CVTs of the same specifications were measured in a laboratory environment using a dielectric loss meter and the method of the present invention. Each was measured three times, and the average value was taken as the final result. To prevent damage to the insulation layer of the secondary terminal box, the test voltage of the dielectric loss meter and the short-circuit frequency sweep method was selected to be 1kV, and the test results at a frequency of 50Hz were selected for comparison. The test wiring is as follows: Figure 3 and Figure 4 The test results and errors are shown in Table 1.

[0075] Table 1

[0076]

[0077] As can be seen from Table 1, compared with the traditional dielectric loss meter test method, the short-circuit frequency sweep method has higher measurement accuracy and the capacitance value is closer to the nameplate data.

[0078] In this example, to further verify the applicability of the proposed method for field testing, a 220 kV CVT in a substation that had been in operation for five years was subjected to a power outage test. Its capacitance was measured using a dielectric loss meter and the proposed method. The average results and errors after five measurements are shown in Table 2.

[0079] Table 2

[0080]

[0081] As can be seen in Table 2, the results obtained using the dielectric loss meter have a larger error, while the maximum error obtained using the short-circuit frequency sweep method is only 0.6137%. Laboratory and field test results demonstrate that the short-circuit frequency sweep method proposed in this paper is more accurate than traditional methods for measuring CVT voltage divider capacitance. Furthermore, it does not require consideration of CVT structural design during measurement, making it more applicable.

Claims

1. A method for measuring the voltage dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning, characterized in that: Measuring the voltage divider capacitance in a capacitive voltage transformer includes the following steps: S1. Perform a first short-circuit impedance test on the capacitor voltage transformer to obtain a first frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the second capacitor is measured; S2. Perform a second short-circuit impedance test on the capacitor voltage transformer to obtain a second frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the first capacitor and the second capacitor is measured; S3. Draw a frequency-dependent short-circuit impedance curve of the capacitor voltage transformer according to the first frequency-dependent short-circuit impedance and the second frequency-dependent short-circuit impedance, and calculate a first capacitance reference value and a second capacitance reference value according to the frequency-dependent short-circuit impedance curve, specifically: S301. Draw a frequency-dependent short-circuit impedance curve of a capacitor voltage transformer according to a first frequency-dependent short-circuit impedance and a second frequency-dependent short-circuit impedance; S302: Obtain a total inductance reference value including the compensation inductance and the leakage inductance of the intermediate voltage transformer based on the frequency-dependent short-circuit impedance curve, define a frequency corresponding to a zero-degree phase response in the frequency-dependent short-circuit impedance curve as a resonant frequency, and obtain the resonant frequency of the second capacitor and the resonant frequency of the total capacitor; S303: Calculate a first capacitance reference value and a second capacitance reference value according to the total inductance reference value, the resonant frequency of the second capacitor, and the resonant frequency of the total capacitor; The expression of the second capacitance reference value is as follows: ； ； ； in, represents the second capacitance reference value, Indicates the total capacitance reference value, Indicates the total inductance reference value, represents the resonant frequency of the second capacitor, represents the resonant frequency of the total capacitance, represents a first capacitance reference value; S4. Using the first capacitance reference value and the second capacitance reference value, combined with the ratio of the intermediate voltage transformer, calculate the measured values ​​of the first capacitance, the second capacitance, and the total capacitance, and complete the capacitance divider capacitance measurement of the capacitive voltage transformer.

2. The method for measuring the voltage dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning according to claim 1, wherein: Said S1 comprises the following steps: S101, connecting the variable frequency AC power supply and the secondary side of the voltage and ammeter to the capacitive voltage transformer; S102. Perform a first short-circuit impedance test on the capacitor voltage transformer, disconnect the high-voltage terminal of the capacitor voltage transformer from the system and keep it open, and keep the NHF / CAR terminal grounded to obtain a first frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the second capacitor is measured.

3. The method for measuring the voltage dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning according to claim 1, wherein: The S2 is specifically as follows: A second short-circuit impedance test is performed on the capacitor voltage transformer, and the high-voltage terminal and the NHF / CAR terminal of the capacitor voltage transformer are connected to the ground wire to obtain a second frequency-dependent short-circuit impedance, wherein the frequency-dependent short-circuit impedance including the first capacitor and the second capacitor is measured.

4. The method for measuring the voltage dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning according to claim 1, wherein: The S4 comprises the following steps: S401: Using a first capacitance reference value and a second capacitance reference value, combined with a ratio of an intermediate voltage transformer, the first capacitance reference value and the second capacitance reference value are converted to a primary side of the intermediate voltage transformer by calculation to obtain a measured value of the first capacitance and a measured value of the second capacitance; S402. Calculate the measured value of the total capacitance based on the measured value of the first capacitance and the measured value of the second capacitance, and compare the measured value of the first capacitance, the measured value of the second capacitance, and the measured value of the total capacitance with the calibrated rated capacitance to complete the capacitance voltage transformer divider capacitance measurement.

5. The method for measuring the voltage dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning according to claim 4, characterized in that: The expression for converting the first capacitance reference value and the second capacitance reference value to the primary side of the intermediate voltage transformer is as follows: ； ； in, represents the measured value of the first capacitance, represents the measured value of the second capacitance, represents the first capacitance reference value, represents the second capacitance reference value, Indicates the ratio of the intermediate voltage transformer.

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