Capacitive voltage transformer partial voltage capacitance measurement method based on short circuit frequency scanning

Abstract

The invention provides a capacitor voltage transformer partial voltage capacitance measuring method based on short circuit frequency scanning, and belongs to the field of electrical insulation detection of electrical equipment, and the method comprises the steps: carrying out the first short circuit impedance test of a capacitor voltage transformer, measuring the frequency-dependent short circuit impedance containing a second capacitor, and obtaining the first frequency-dependent short circuit impedance; performing a second short-circuit impedance test, and measuring frequency-dependent short-circuit impedance including the first capacitor and the second capacitor to obtain second frequency-dependent short-circuit impedance; drawing a frequency-dependent short-circuit impedance curve according to the first frequency-dependent short-circuit impedance and the second frequency-dependent short-circuit impedance, and calculating to obtain a first capacitance reference value and a second capacitance reference value; the first capacitance reference value and the second capacitance reference value are combined with the ratio of the intermediate voltage transformer, a measured value of the voltage dividing capacitance is calculated, and measurement of the voltage dividing capacitance of the capacitor voltage transformer is completed. The problems that wiring is complex and the precision is greatly influenced by a wiring mode in an existing capacitance value measuring method are solved.

Description

Technical Field

[0001] The 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 will age during their service life, which may reduce the measurement accuracy of capacitor voltage transformers and even cause serious faults such as sudden explosions. Therefore, it is necessary to regularly test and inspect the insulation performance of capacitor voltage transformers, such as capacitance measurement and power frequency withstand voltage test. Among them, capacitance measurement is the most widely used on-site testing method, but the existing capacitance measurement method has problems such as complex wiring and accuracy is greatly affected by the wiring method. Summary of the invention

[0003] In view of 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 capacitive voltage transformer to obtain a first frequency-variable short-circuit impedance, wherein the frequency-variable short-circuit impedance including the second capacitor is measured;

[0006] S2, performing a second short-circuit impedance test on the capacitive 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 capacitive 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 and combining 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 voltage 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-dividing 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 comprises the following steps:

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

[0012] S102, performing a first short-circuit impedance test on the capacitor voltage transformer, disconnecting the high-voltage terminal of the capacitor voltage transformer from the system and keeping it open, and keeping the NHF / CAR terminal grounded to obtain a first frequency-variable short-circuit impedance, wherein the frequency-variable 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 including 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 when multiple capacitors are connected 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 capacitive voltage transformer, and the high-voltage terminal and the NHF / CAR terminal of the capacitive 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 necessary data for calculating the total capacitance, and enhances the comprehensiveness and reliability of the measurement results.

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

[0018] S301, drawing a frequency-dependent short-circuit impedance curve of a capacitive voltage transformer according to the first frequency-dependent short-circuit impedance and the second frequency-dependent short-circuit impedance;

[0019] S302, according to the frequency-dependent short-circuit impedance curve, obtain a total inductance reference value including the compensation inductance and the leakage inductance of the intermediate voltage transformer, define a frequency corresponding to a phase response of zero degrees 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 Represents 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 capacitance and the second capacitance. Through graphical display and precise calculation, the intuitiveness and accuracy of the capacitance value measurement are improved, making the measurement result more stable and reliable.

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

[0027] S401, using the first capacitance reference value and the second capacitance reference value, combined with the ratio of the intermediate voltage transformer, converting the capacitance reference value to the primary side of the intermediate voltage transformer by calculation, and obtaining a measurement value of the first capacitance and a measurement value of the second capacitance;

[0028] S402. Calculate the measured value of the total capacitance according to 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 voltage divider capacitance measurement of the capacitive voltage transformer.

[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, and K IVT Indicates the ratio of the intermediate voltage transformer.

[0032] The beneficial effects of the above further scheme are as follows: the present invention utilizes 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 precise 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 in line with actual working conditions, thereby enhancing the practicality and application value of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a flow chart of the method of the present invention.

[0034] Figure 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 a second short-circuit impedance test in this embodiment.

[0037] Figure 5 Graph showing 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 implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept 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 dividing 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-dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning, and the implementation method thereof is as follows:

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

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

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

[0051] In this embodiment, Figure 2 As shown in the figure, the main components of the 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 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 proposed new measurement method 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 The frequency-variable short-circuit impedance including the second capacitor C2 is measured, so that the high-voltage terminal (A / H1) in the circuit is disconnected from the system and remains open-circuited, and the NHF / CAR terminal remains 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 capacitive voltage transformer, measure the frequency-dependent short-circuit impedance including the first capacitor and the second capacitor, and obtain a second frequency-dependent short-circuit impedance, as follows:

[0054] A second short-circuit impedance test is performed on the capacitive voltage transformer, and the high-voltage terminal and the NHF / CAR terminal of the capacitive 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 capacitive 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, drawing a frequency-dependent short-circuit impedance curve of a capacitive voltage transformer according to the first frequency-dependent short-circuit impedance and the second frequency-dependent short-circuit impedance;

[0058] S302, according to the frequency-dependent short-circuit impedance curve, obtain a total inductance reference value including the compensation inductance and the leakage inductance of the intermediate voltage transformer, define a frequency corresponding to a phase response of zero degrees 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-dependent 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 measured curve in the typical frequency-dependent short-circuit impedance curve shows that the second capacitor C2 and the total capacitor 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 resCorresponding to the frequency of zero degree phase response, 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 Represents the total inductance reference value, represents the resonant frequency of the second capacitor, Represents the resonant frequency of the total capacitance.

[0065] The first capacitance reference value and the second capacitance reference value are used in combination with the ratio of the intermediate voltage transformer to calculate the measured values ​​of the first capacitance, the second capacitance and the total capacitance, and the capacitor voltage transformer voltage divider capacitance measurement is completed. The specific steps are as follows:

[0066] S401, using the first capacitance reference value and the second capacitance reference value, combined with the ratio of the intermediate voltage transformer, converting the capacitance reference value to the primary side of the intermediate voltage transformer by calculation, and obtaining a measurement value of the first capacitance and a measurement value of the second capacitance;

[0067] S402. Calculate the measured value of the total capacitance according to 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 voltage divider capacitance measurement of the capacitive voltage transformer.

[0068] In this embodiment, the capacitance reference value can be converted to the IVT primary side by a calculation formula, and the first capacitance measurement value C1′ and the second capacitance measurement value C1′ can be obtained by combining the ratio of the intermediate voltage transformer, and then the total capacitance measurement value C 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 embodiment, in order 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. In order 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 scanning method was selected as 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] It can be seen from Table 1 that compared with the traditional dielectric loss meter test method, the short-circuit frequency scanning method has higher measurement accuracy and the capacitance value is closer to the nameplate data.

[0078] In this embodiment, in order to further verify the applicability of the method proposed in the present invention for field testing, a 220kV CVT in operation for 5 years in a substation was subjected to a power outage test, and its capacitance was measured by a dielectric loss meter and the method proposed in this article, respectively. The average results and errors after 5 measurements are shown in Table 2.

[0079] Table 2

[0080]

[0081] It can be seen from Table 2 that the result measured by the dielectric loss meter has a large error, and the maximum error of the short-circuit frequency scanning method is only 0.6137%. The laboratory and field test results show that in the field of CVT voltage-dividing capacitance measurement, the short-circuit frequency scanning method proposed in the present invention has higher accuracy than the traditional method, and it does not need to consider the CVT structure design during measurement, and has stronger applicability.

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 dividing capacitance in the capacitive voltage transformer includes the following steps: S1. Perform a first short-circuit impedance test on the capacitive voltage transformer to obtain a first frequency-variable short-circuit impedance, wherein the frequency-variable short-circuit impedance including the second capacitor is measured; S2. Perform a second short-circuit impedance test on the capacitive 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 capacitive 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; S4. Using the first capacitance reference value and the second capacitance reference value and combining 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 voltage 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, characterized in that: The S1 comprises the following steps: S101, connecting a variable frequency AC power supply and a secondary side of a voltage and current meter to a capacitive voltage transformer; S102, performing a first short-circuit impedance test on the capacitor voltage transformer, disconnecting the high-voltage terminal of the capacitor voltage transformer from the system and keeping it open, and keeping the NHF / CAR terminal grounded to obtain a first frequency-variable short-circuit impedance, wherein the frequency-variable 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, characterized in that: The S2 is specifically as follows: A second short-circuit impedance test is performed on the capacitive voltage transformer, and the high-voltage terminal and the NHF / CAR terminal of the capacitive 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, characterized in that: The S3 comprises the following steps: S301, drawing a frequency-dependent short-circuit impedance curve of a capacitive voltage transformer according to the first frequency-dependent short-circuit impedance and the second frequency-dependent short-circuit impedance; S302, according to the frequency-dependent short-circuit impedance curve, obtain a total inductance reference value including the compensation inductance and the leakage inductance of the intermediate voltage transformer, define a frequency corresponding to a phase response of zero degrees 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.

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 of the second capacitance reference value is as follows: C1″=C t ′ o ′ t -C2″; Wherein, C2″ represents the second capacitance reference value, C t ' o ' t Indicates the total capacitance reference value, L t ' o ' t Represents 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.

6. The method for measuring the voltage dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning according to claim 1, characterized in that: The S4 comprises the following steps: S401, using the first capacitance reference value and the second capacitance reference value, combined with the ratio of the intermediate voltage transformer, converting the capacitance reference value to the primary side of the intermediate voltage transformer by calculation, and obtaining a measurement value of the first capacitance and a measurement value of the second capacitance; S402. Calculate the measured value of the total capacitance according to 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 voltage divider capacitance measurement of the capacitive voltage transformer.

7. The method for measuring the voltage dividing capacitance of a capacitive voltage transformer based on short-circuit frequency scanning according to claim 6, 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: 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, and K IVT Indicates the ratio of the intermediate voltage transformer.

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