A method and system for correcting voltage across low-voltage capacitors of a capacitive voltage divider

Abstract

The present invention discloses a voltage correction method and system at both ends of a low-voltage capacitor of a capacitive voltage divider, comprising: obtaining a ground current of a capacitive voltage divider and a measured voltage at both ends of a low-voltage capacitor of the capacitive voltage divider; performing signal decomposition on the measured voltage and the ground current respectively, and determining a fundamental wave and harmonic signals corresponding to the measured voltage and a fundamental wave and harmonic signals corresponding to the ground current; calculating the impedance of the low-voltage capacitor end according to the fundamental wave and harmonic signals corresponding to the measured voltage and the fundamental wave and harmonic signals corresponding to the ground current; calculating an equivalent capacitive reactance according to the high-voltage capacitor and the medium-voltage capacitor of the capacitive voltage divider; determining a voltage correction coefficient according to the impedance of the low-voltage capacitor end and the equivalent capacitive reactance; and correcting the measured voltage according to the correction coefficient to obtain a corrected voltage. The method of the present invention can improve the measurement accuracy of power frequency and harmonic signals, and meet the high accuracy requirements of a power quality monitoring system for data sources.

Description

Technical Field

[0001] The present invention relates to the field of high voltage insulation technology, and more specifically, to a method and system for correcting voltage across a low voltage capacitor of a capacitive voltage divider. Background Art

[0002] The harmonic voltage signal of the power grid needs to be measured through the secondary winding of the voltage transformer using power analyzers, power quality monitoring terminals and other equipment. This requires the voltage transformer to have accurate harmonic transmission characteristics to achieve accurate measurement of harmonics. In my country, capacitor voltage transformer (CVT) is the main sensing terminal for measuring system voltage in power systems of 110kV and above. However, it has obvious passband or bandstop characteristics in certain frequency bands, which causes the harmonic voltage waveform measured by the secondary winding to be distorted to varying degrees. Therefore, it is difficult to accurately obtain the true level of the power grid harmonic voltage directly through CVT.

[0003] To solve this problem, researchers have proposed a technical idea for CVT with harmonic measurement function, that is, adding low-voltage capacitor C3 to the capacitor voltage divider part of the conventional CVT, and using the voltage division principle to measure the harmonic voltage of the power grid at both ends of the low-voltage capacitor. When conducting power quality measurement on site, the voltage signal obtained from both ends of the low-voltage capacitor contains both fundamental and harmonic waves. The measurement accuracy of fundamental and harmonic waves will directly affect the accuracy of subsequent calculations of indicators such as harmonic content rate and total distortion rate, and is the core key to the accuracy of the harmonic measurement data source. Limited by the load capacity of low-voltage capacitors, and considering the safety of secondary equipment and personnel, the output signals at both ends of low-voltage capacitors often need to be sent to the power quality signal acquisition unit through shielded cables for on-site digitization. This load (mainly including C3 terminal impedance, cable impedance and on-site module impedance) has a great influence on the signal measurement accuracy at both ends of the low-voltage capacitor, especially the fundamental signal, which has a certain gap with the national standard "GB / T19862-2016 General Requirements for Power Quality Monitoring Equipment" for fundamental voltage measurement accuracy of ±0.1%. The current solution is: under the premise of specifying the measurement accuracy of the voltage fundamental signal at the low-voltage capacitor end, the manufacturer obtains its upper limit load through test methods as a reference data for on-site load arrangement. However, limited by the manufacturing process and technical characteristics of the CVT body, the measurement accuracy of the voltage fundamental signal at the low-voltage capacitor end cannot be too small. At present, it can only reach the error limit level of ±2%, which is much larger than the CVT fundamental error limit specified in the standard. Moreover, for CVTs with harmonic measurement functions, since the harmonic measurement function is implemented on a capacitor voltage divider, it is impossible to use a tap method to achieve capacitance control due to the capacitance of a single capacitor core. Therefore, after the equipment is manufactured, if it is found during the test that the error of the harmonic measurement part does not meet the requirements, it is impossible to intervene and control it.

[0004] In summary, the existing CVT harmonic measurement technical measures still have certain deficiencies, and therefore a method is needed to correct the voltage at the low-voltage capacitor end of the capacitive voltage divider of the CVT. Summary of the invention

[0005] The present invention provides a method and system for correcting the voltage across a low-voltage capacitor of a capacitive voltage divider, so as to solve the problem of how to correct the voltage across a low-voltage capacitor of a capacitive voltage divider in a capacitive voltage transformer with a harmonic measurement function.

[0006] In order to solve the above problem, according to one aspect of the present invention, a method for correcting the voltage across a low-voltage capacitor of a capacitive voltage divider is provided, the method comprising:

[0007] Obtaining a ground current of the capacitive voltage divider and a measured voltage across a low voltage capacitor of the capacitive voltage divider;

[0008] Decomposing the measured voltage and the ground current respectively to determine the fundamental wave and harmonic signals corresponding to the measured voltage and the fundamental wave and harmonic signals corresponding to the ground current;

[0009] Calculating the impedance of the low-voltage capacitor terminal according to the fundamental wave and harmonic signals corresponding to the measured voltage and the fundamental wave and harmonic signals corresponding to the ground current;

[0010] Calculating an equivalent capacitive reactance based on the high voltage capacitor and the medium voltage capacitor of the capacitive voltage divider;

[0011] Determining a voltage correction coefficient according to the impedance of the low-voltage capacitor end and the equivalent capacitive reactance;

[0012] The measured voltage is corrected according to the correction coefficient to obtain a corrected voltage.

[0013] Preferably, the step of performing signal decomposition on the measured voltage and the ground current respectively to determine the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current comprises:

[0014]

[0015]

[0016] Among them, U 3 is the measured voltage; I d is the ground current; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

[0017] Preferably, the calculating the impedance of the low-voltage capacitor terminal according to the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current comprises:

[0018]

[0019] Among them, Z h is the impedance of the low voltage capacitor end; and The measured voltage U 3 and the ground current Id The vector form of the hth harmonic component of , when h is 1, it is the vector form of the fundamental wave components of the two; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component.

[0020] Preferably, the calculating of the equivalent capacitive reactance according to the high voltage capacitor and the medium voltage capacitor of the capacitive voltage divider comprises:

[0021]

[0022] Among them, Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; ω h is the hth harmonic angular frequency, ω h =2πhf, f is the industrial frequency; j represents a complex number.

[0023] Preferably, determining the voltage correction coefficient according to the impedance of the low-voltage capacitor terminal and the equivalent capacitive reactance includes:

[0024]

[0025]

[0026] Among them, K d-h is the voltage correction factor; Z h is the impedance of the low voltage capacitor end; Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; K C3 is the no-load voltage divider ratio; C 1 , C 2 and C 3 They are the high voltage capacitor, medium voltage capacitor and low voltage capacitor of the capacitive voltage divider respectively.

[0027] Preferably, the step of correcting the measured voltage according to the correction coefficient to obtain a corrected voltage comprises:

[0028]

[0029] Among them, U 3d is the correction voltage; K d-his the voltage correction coefficient; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

[0030] According to another aspect of the present invention, a voltage correction system for a low-voltage capacitor of a capacitive voltage divider is provided, the system comprising:

[0031] A data acquisition unit, used for acquiring a ground current of the capacitive voltage divider and a measured voltage across the low-voltage capacitor of the capacitive voltage divider;

[0032] A signal decomposition unit, used to perform signal decomposition on the measured voltage and the ground current respectively, and determine the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current;

[0033] An impedance calculation unit of the low-voltage capacitor end, used to calculate the impedance of the low-voltage capacitor end according to the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current;

[0034] An equivalent capacitive reactance calculation unit, used for calculating an equivalent capacitive reactance according to a high voltage capacitor and a medium voltage capacitor of the capacitive voltage divider;

[0035] A voltage correction coefficient determination unit, used to determine a voltage correction coefficient according to the impedance of the low-voltage capacitor terminal and the equivalent capacitive reactance;

[0036] The correction unit is used to correct the measured voltage according to the correction coefficient to obtain a corrected voltage.

[0037] Preferably, the signal decomposition unit performs signal decomposition on the measured voltage and the ground current respectively to determine the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current, including:

[0038]

[0039]

[0040] Among them, U 3 is the measured voltage; I d is the ground current; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

[0041] Preferably, the impedance calculation unit of the low-voltage capacitor terminal calculates the impedance of the low-voltage capacitor terminal according to the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current, including:

[0042]

[0043] Among them, Z h is the impedance of the low voltage capacitor end; and The measured voltage U 3 and the ground current I d The vector form of the hth harmonic component of , when h is 1, it is the vector form of the fundamental wave components of the two; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component.

[0044] Preferably, the equivalent capacitive reactance calculation unit calculates the equivalent capacitive reactance according to the high voltage capacitor and the medium voltage capacitor of the capacitive voltage divider, including:

[0045]

[0046] Among them, Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; ω h is the hth harmonic angular frequency, ω h =2πhf, f is the industrial frequency; j represents a complex number.

[0047] Preferably, the voltage correction coefficient determining unit determines the voltage correction coefficient according to the impedance of the low-voltage capacitor terminal and the equivalent capacitive reactance, including:

[0048]

[0049]

[0050] Among them, K d-h is the voltage correction factor; Z h is the impedance of the low voltage capacitor end; Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; K C3 is the no-load voltage divider ratio; C 1 , C 2 and C 3 They are the high voltage capacitor, medium voltage capacitor and low voltage capacitor of the capacitive voltage divider respectively.

[0051] Preferably, the correction unit corrects the measured voltage according to the correction coefficient to obtain the corrected voltage, including:

[0052]

[0053] Among them, U 3d is the correction voltage; K d-h is the voltage correction coefficient; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

[0054] The present invention provides a method and system for correcting voltage at both ends of a low-voltage capacitor of a capacitive voltage divider, comprising: obtaining a ground current of a capacitive voltage divider and a measured voltage at both ends of a low-voltage capacitor of the capacitive voltage divider; performing signal decomposition on the measured voltage and the ground current respectively, and determining a fundamental wave and harmonic signals corresponding to the measured voltage and a fundamental wave and harmonic signals corresponding to the ground current; calculating the impedance of the low-voltage capacitor end according to the fundamental wave and harmonic signals corresponding to the measured voltage and the fundamental wave and harmonic signals corresponding to the ground current; calculating an equivalent capacitive reactance according to a high-voltage capacitor and a medium-voltage capacitor of the capacitive voltage divider; determining a voltage correction coefficient according to the impedance of the low-voltage capacitor end and the equivalent capacitive reactance; and correcting the measured voltage according to the correction coefficient to obtain a corrected voltage. The method of the present invention can correct the signals output from both ends of the low-voltage capacitor of the capacitive voltage divider, improve the measurement accuracy of power frequency and harmonic signals, and meet the high accuracy requirements of a power quality monitoring system for data sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0056] Figure 1is a flow chart of a method 100 for correcting the voltage across a low-voltage capacitor of a capacitive voltage divider according to an embodiment of the present invention;

[0057] Figure 2 is an equivalent schematic diagram of a capacitive voltage divider of a capacitive voltage transformer with a harmonic measurement function according to an embodiment of the present invention;

[0058] Figure 3 A schematic diagram of voltage correction based on a capacitive voltage transformer with a harmonic measurement function according to an embodiment of the present invention;

[0059] Figure 4 A structural diagram of a capacitive voltage transformer body with a harmonic measurement function according to an embodiment of the present invention;

[0060] Figure 5 Schematic diagram of the structure of a voltage correction system 500 for a low-voltage capacitor of a capacitive voltage divider according to an embodiment of the present invention. DETAILED DESCRIPTION

[0061] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0062] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0063] Figure 1 FIG. 1 is a flow chart of a method 100 for correcting the voltage across a low-voltage capacitor of a capacitive voltage divider according to an embodiment of the present invention. Figure 1 As shown, the voltage correction method at both ends of the low-voltage capacitor of the capacitive voltage divider provided in the embodiment of the present invention can correct the signal outputted at both ends of the low-voltage capacitor of the capacitive voltage divider, can improve the measurement accuracy of the power frequency and harmonic signals, and meet the high accuracy requirements of the power quality monitoring system for the data source. The voltage correction method 100 at both ends of the low-voltage capacitor of the capacitive voltage divider provided in the embodiment of the present invention starts from step 101, and in step 101, the ground current of the capacitive voltage divider and the measured voltage at both ends of the low-voltage capacitor of the capacitive voltage divider are obtained.

[0064] The method of the embodiment of the present invention acts on a capacitive voltage transformer CVT with a harmonic measurement function. The CVT with a harmonic measurement function mainly consists of a capacitive voltage divider and an electromagnetic unit. The high-voltage capacitor C1, the medium-voltage capacitor C2, and the low-voltage capacitor C3 are connected in series to form a capacitive voltage divider, wherein the value of the capacitor C3 is much larger than the values ​​of the capacitors C1 and C2. Within the fundamental and harmonic frequency bands of interest, the output voltage across the capacitor C3 is basically not affected by the electromagnetic unit. Considering the influence of the low-voltage capacitor C3 load, establish Figure 2 The equivalent model shown, Figure 2 C is the equivalent capacitance of high voltage capacitor C1 and medium voltage capacitor C2 in series, Z L It is the load of the low-voltage capacitor C3, which mainly includes the terminal impedance, cable impedance and local module impedance. The terminal impedance and local module impedance are generally fixed values, and the cable impedance varies with its model and length.

[0065] Depend on Figure 2 It can be seen that the load Z L Connecting in parallel with the low-voltage capacitor C3 will affect the voltage divider ratio of the capacitor voltage divider, and thus affect the output voltage across the low-voltage capacitor. At this time, the output voltage across the low-voltage capacitor is:

[0066]

[0067]

[0068] Among them, K C3 is the no-load voltage divider ratio; X C3 is the capacitive reactance of low voltage capacitor C3; U 1 From the theoretical calculation results, even if the cable length is 0, the power frequency voltage error is close to 1%, which exceeds the error limit requirement. Therefore, it is necessary to correct the output signal at both ends of the low-voltage capacitor.

[0069] Therefore, in an embodiment of the present invention, by measuring the ground current I d The measured voltage U output across the low voltage capacitor C3 3 , the total impedance value Z at the low-voltage capacitor C3 end is calculated in reverse, and the voltage correction coefficient at both ends of the low-voltage capacitor is obtained by combining the capacitive reactance values ​​of the high-voltage capacitor C1 and the medium-voltage capacitor C2, and then the corrected voltage at both ends of the low-voltage capacitor is obtained.

[0070] Combination Figure 3 and Figure 4 As shown, the embodiment of the present invention realizes voltage correction based on the local module 3, and the local module 3 includes a data acquisition module and a voltage correction module. Based on the data acquisition module, the ground current of the capacitor voltage divider and the measured voltage across the low-voltage capacitor of the capacitor voltage divider are obtained. Based on the voltage correction module, the voltage across the low-voltage capacitor is corrected.

[0071] In an embodiment of the present invention, a CVT body 1 with a harmonic measurement function is composed of a capacitive voltage divider 4 and an electromagnetic unit 5, and the capacitive voltage divider 4 is stacked on the oil tank of the electromagnetic unit 5. The harmonic measurement terminal H and the low-voltage terminal of the capacitive voltage divider 4 are led out to the h terminal and the N terminal of the secondary outlet box 6 of the electromagnetic unit 5 through the outlet bushing. During normal operation, the h terminal of the secondary outlet box 6 is connected to the local module 3 through a shielded cable, and the output voltage U3 signal at both ends of the low-voltage capacitor is sent to the local module 3 for data sampling and processing; the N terminal is connected to the ground terminal of the secondary outlet box 6. The ground terminal of the secondary outlet box 6 is provided with a fixing flange 7.

[0072] A high-precision current sensor 2 is connected between the low-voltage terminal N and the ground terminal of the capacitive voltage divider. The current sensor 2 is a high-precision through-type micro-current sensor, which is installed in the groove of the fixed flange 7 and is used to measure the ground current Id of the capacitive voltage divider 4. Its output terminal D is connected to the local module 3 through a shielded cable, and the ground current Id of the capacitive voltage divider is sent to the local module 3 for data sampling and processing.

[0073] In an embodiment of the present invention, the above process is realized and the measured value is sent to the local module.

[0074] In step 102, the measured voltage and the ground current are respectively subjected to signal decomposition to determine the fundamental wave and harmonic signals corresponding to the measured voltage and the fundamental wave and harmonic signals corresponding to the ground current.

[0075] Preferably, the step of performing signal decomposition on the measured voltage and the ground current respectively to determine the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current comprises:

[0076]

[0077]

[0078] Among them, U 3 is the measured voltage; I d is the ground current; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

[0079] In the embodiment of the present invention, the output voltage U across the low voltage capacitor is converted into 3 and the voltage divider to ground current I d Decompose into fundamental wave and harmonic signals. Specifically, the calculation formula is:

[0080]

[0081]

[0082] Where h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order of interest; U 3-h and θ 3-h The signal U 3 The effective value and phase angle of the hth harmonic component, I d-n and θ d-h Signal I d The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

[0083] In step 103, the impedance of the low-voltage capacitor terminal is calculated according to the fundamental wave and harmonic signals corresponding to the measured voltage and the fundamental wave and harmonic signals corresponding to the ground current.

[0084] Preferably, the calculating the impedance of the low-voltage capacitor terminal according to the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current comprises:

[0085]

[0086] Among them, Z h is the impedance of the low voltage capacitor end; and The measured voltage U 3 and the ground current I d The vector form of the hth harmonic component of , when h is 1, it is the vector form of the fundamental wave components of the two; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component.

[0087] In step 104, an equivalent capacitive reactance is calculated according to the high voltage capacitor and the medium voltage capacitor of the capacitive voltage divider.

[0088] Preferably, the calculating of the equivalent capacitive reactance according to the high voltage capacitor and the medium voltage capacitor of the capacitive voltage divider comprises:

[0089]

[0090] Among them, Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; ω h is the hth harmonic angular frequency, ω h =2πhf, f is the industrial frequency; j represents a complex number.

[0091] In the embodiment of the present invention, the impedance value Z of the low voltage capacitor terminal under the fundamental wave and each harmonic is calculated. h And the equivalent capacitive reactance value Z of capacitors C1 and C2 in series C-h The method is:

[0092]

[0093]

[0094] Among them, Z h is the impedance of the low-voltage capacitor end, which is the parallel value of the capacitive reactance value of the low-voltage capacitor C3 and the impedance value ZL at both ends of the low-voltage capacitor; and The measured voltage U 3 and the ground current I d The vector form of the hth harmonic component of , when h is 1, it is the vector form of the fundamental wave components of the two; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component; Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; ω h is the hth harmonic angular frequency, ω h =2πhf, f is the industrial frequency; j represents a complex number.

[0095] In step 105, a voltage correction coefficient is determined according to the impedance of the low voltage capacitor terminal and the equivalent capacitive reactance.

[0096] Preferably, determining the voltage correction coefficient according to the impedance of the low-voltage capacitor terminal and the equivalent capacitive reactance includes:

[0097]

[0098]

[0099] Among them, K d-h is the voltage correction factor; Z h is the impedance of the low voltage capacitor end; Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; K C3 is the no-load voltage divider ratio; C 1 , C 2 and C 3 They are the high voltage capacitor, medium voltage capacitor and low voltage capacitor of the capacitive voltage divider respectively.

[0100] according to Figure 2 It can be seen that there exists:

[0101]

[0102] In the formula, is the no-load voltage divider ratio.

[0103] Therefore, the correction factor can be obtained as:

[0104]

[0105] Among them, K d-h is the voltage correction factor; C 1 , C 2 and C 3 They are the high voltage capacitor, medium voltage capacitor and low voltage capacitor of the capacitive voltage divider respectively.

[0106] In step 106, the measured voltage is corrected according to the correction coefficient to obtain a corrected voltage.

[0107] Preferably, the step of correcting the measured voltage according to the correction coefficient to obtain a corrected voltage comprises:

[0108]

[0109] Among them, U 3d is the correction voltage; K d-h is the voltage correction coefficient; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; ω h=2πhf is the hth harmonic angular frequency, and f is the power frequency.

[0110] In the embodiment of the present invention, the voltage U across the low-voltage capacitor after correction is calculated. 3d The formula is:

[0111]

[0112] Among them, U 3d is the correction voltage; K d-h is the voltage correction coefficient; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

[0113] Combination Figure 3 As shown, in the embodiment of the present invention, the data acquisition module simultaneously acquires the output voltage U across the low-voltage capacitor C3. 3 and the capacitive voltage divider to ground current I d The sampling rate is 25.6kHz and sent to the voltage correction module. The voltage correction module uses U 3 and I d The impedance value of the low-voltage capacitor is calculated by reverse calculation. Combined with the capacitive reactance value of the voltage divider 4, the voltage correction coefficient of the low-voltage capacitor is calculated. The output voltage U 3 Correction is made, and the corrected voltage U 3d It will be output in the form of a serial digital optical signal through the optical fiber in accordance with the agreed format, and can be directly used by the power quality monitoring terminal; among them, the signal output protocol is IEC61850-9-2, which can be directly used by the power quality monitoring terminal.

[0114] In addition, if Figure 3 As shown, the local module of the embodiment of the present invention further includes: a signal monitoring alarm module, the signal monitoring alarm module monitors U 3 The size of the voltage divider is used to judge the performance status of the voltage divider.

[0115] The present invention can effectively improve the measurement accuracy of the output signal of the port by correcting the output signal of the low-voltage capacitor at both ends of the CVT with a harmonic measurement function, and can solve the problem of difficulty in error control of the output signal of the low-voltage capacitor end in the prior art.

[0116] Figure 5 FIG. 5 is a schematic diagram of a voltage correction system 500 for a low-voltage capacitor of a capacitive voltage divider according to an embodiment of the present invention. Figure 5As shown, the voltage correction system 500 at both ends of the low-voltage capacitor of the capacitive voltage divider provided in an embodiment of the present invention includes: a data acquisition unit 501, a signal decomposition unit 502, an impedance calculation unit 503 at the low-voltage capacitor end, an equivalent capacitive reactance calculation unit 504, a voltage correction coefficient determination unit 505 and a correction unit 506.

[0117] Preferably, the data acquisition unit 501 is used to acquire the ground current of the capacitive voltage divider and the measured voltage across the low-voltage capacitor of the capacitive voltage divider.

[0118] Preferably, the signal decomposition unit 502 is used to perform signal decomposition on the measured voltage and the ground current respectively, and determine the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current.

[0119] Preferably, the signal decomposition unit 502 performs signal decomposition on the measured voltage and the ground current respectively to determine the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current, including:

[0120]

[0121]

[0122] Among them, U 3 is the measured voltage; I d is the ground current; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

[0123] Preferably, the impedance calculation unit 503 of the low-voltage capacitor end is used to calculate the impedance of the low-voltage capacitor end according to the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current.

[0124] Preferably, the impedance calculation unit 503 of the low-voltage capacitor terminal calculates the impedance of the low-voltage capacitor terminal according to the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current, including:

[0125]

[0126] Among them, Z h is the impedance of the low voltage capacitor end; and The measured voltage U 3 and the ground current I d The vector form of the hth harmonic component of , when h is 1, it is the vector form of the fundamental wave components of the two; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component.

[0127] Preferably, the equivalent capacitive reactance calculation unit 504 is used to calculate the equivalent capacitive reactance according to the high voltage capacitor and the medium voltage capacitor of the capacitive voltage divider.

[0128] Preferably, the equivalent capacitive reactance calculation unit 504 calculates the equivalent capacitive reactance according to the high voltage capacitor and the medium voltage capacitor of the capacitive voltage divider, including:

[0129]

[0130] Among them, Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; ω h is the hth harmonic angular frequency, ω h =2πhf, f is the industrial frequency; j represents a complex number.

[0131] Preferably, the voltage correction coefficient determining unit 505 is used to determine the voltage correction coefficient according to the impedance of the low-voltage capacitor terminal and the equivalent capacitive reactance.

[0132] Preferably, the voltage correction coefficient determining unit 505 determines the voltage correction coefficient according to the impedance of the low voltage capacitor terminal and the equivalent capacitive reactance, including:

[0133]

[0134]

[0135] Among them, K d-h is the voltage correction factor; Z h is the impedance of the low voltage capacitor end; Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2Equivalent capacitive reactance after series connection; K C3 is the no-load voltage divider ratio; C 1 , C 2 and C 3 They are the high voltage capacitor, medium voltage capacitor and low voltage capacitor of the capacitive voltage divider respectively.

[0136] Preferably, the correction unit 506 is used to correct the measured voltage according to the correction coefficient to obtain a corrected voltage.

[0137] Preferably, the correction unit 506 corrects the measured voltage according to the correction coefficient to obtain the corrected voltage, including:

[0138]

[0139] Among them, U 3d is the correction voltage; K d-h is the voltage correction coefficient; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

[0140] The voltage correction system 500 across the low-voltage capacitor of the capacitive voltage divider of the embodiment of the present invention corresponds to the voltage correction method 100 across the low-voltage capacitor of the capacitive voltage divider of another embodiment of the present invention, which will not be described in detail herein.

[0141] The invention has been described above with reference to a few embodiments. However, it is readily apparent to a person skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

[0142] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / said / the [means, components, etc.]" are to be openly interpreted as at least one instance of the means, components, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily have to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0143] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0144] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0145] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0146] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0147] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for correcting the voltage across a low-voltage capacitor of a capacitive voltage divider, It is characterized in that The method comprises: Obtaining a ground current of the capacitive voltage divider and a measured voltage across a low voltage capacitor of the capacitive voltage divider; Decomposing the measured voltage and the ground current respectively to determine the fundamental wave and harmonic signals corresponding to the measured voltage and the fundamental wave and harmonic signals corresponding to the ground current; Calculating the impedance of the low-voltage capacitor terminal according to the fundamental wave and harmonic signals corresponding to the measured voltage and the fundamental wave and harmonic signals corresponding to the ground current; Calculating an equivalent capacitive reactance based on the high voltage capacitor and the medium voltage capacitor of the capacitive voltage divider; Determining a voltage correction coefficient according to the impedance of the low-voltage capacitor end and the equivalent capacitive reactance; Correcting the measured voltage according to the correction coefficient to obtain a corrected voltage; Wherein, determining the voltage correction coefficient according to the impedance of the low-voltage capacitor end and the equivalent capacitive reactance includes: Among them, K d-h is the voltage correction factor; Z h is the impedance of the low voltage capacitor end; Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; K C3 is the no-load voltage divider ratio; C 1 , C 2 and C 3 They are high voltage capacitor, medium voltage capacitor and low voltage capacitor of the capacitive voltage divider respectively; The step of correcting the measured voltage according to the correction coefficient to obtain a corrected voltage includes: Among them, U 3d is the correction voltage; h is the harmonic order, when h=1 it is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

2. The method according to claim 1, It is characterized in that The signal decomposition of the measured voltage and the ground current is respectively performed to determine the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current, including: Among them, U 3 is the measured voltage; I d is the ground current; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

3. The method according to claim 1, It is characterized in that Calculating the impedance of the low-voltage capacitor terminal according to the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current includes: Among them, Z h is the impedance of the low voltage capacitor end; and The measured voltage U 3 and the ground current I d The vector form of the hth harmonic component of , when h is 1, it is the vector form of the fundamental wave components of the two; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component.

4. The method according to claim 1, It is characterized in that The calculating the equivalent capacitive reactance according to the high voltage capacitor and the medium voltage capacitor of the capacitive voltage divider comprises: Among them, Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; ω h is the hth harmonic angular frequency, ω h =2πhf, f is the industrial frequency; j represents a complex number.

5. A voltage correction system across the low voltage capacitor of a capacitive voltage divider, It is characterized in that The system comprises: A data acquisition unit, used for acquiring a ground current of the capacitive voltage divider and a measured voltage across the low-voltage capacitor of the capacitive voltage divider; A signal decomposition unit, used to perform signal decomposition on the measured voltage and the ground current respectively, and determine the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current; An impedance calculation unit of the low-voltage capacitor end, used to calculate the impedance of the low-voltage capacitor end according to the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current; An equivalent capacitive reactance calculation unit, used for calculating an equivalent capacitive reactance according to a high voltage capacitor and a medium voltage capacitor of the capacitive voltage divider; A voltage correction coefficient determination unit, used to determine a voltage correction coefficient according to the impedance of the low-voltage capacitor terminal and the equivalent capacitive reactance; A correction unit, used for correcting the measured voltage according to the correction coefficient to obtain a corrected voltage; The voltage correction coefficient determining unit determines the voltage correction coefficient according to the impedance of the low-voltage capacitor terminal and the equivalent capacitive reactance, including: Among them, K d-h is the voltage correction factor; Z h is the impedance of the low voltage capacitor end; Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; K C3 is the no-load voltage divider ratio; C 1 , C 2 and C 3 They are high voltage capacitor, medium voltage capacitor and low voltage capacitor of the capacitive voltage divider respectively; The correction unit corrects the measured voltage according to the correction coefficient to obtain the corrected voltage, including: Among them, U 3d is the correction voltage; h is the harmonic order, when h=1 it is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

6. The system according to claim 5, It is characterized in that The signal decomposition unit performs signal decomposition on the measured voltage and the ground current respectively to determine the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current, including: Among them, U 3 is the measured voltage; I d is the ground current; h is the harmonic order, h=1 is the fundamental wave; n is the highest harmonic order; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component; ω h =2πhf is the hth harmonic angular frequency, and f is the power frequency.

7. The system according to claim 5, It is characterized in that The impedance calculation unit of the low-voltage capacitor end calculates the impedance of the low-voltage capacitor end according to the fundamental wave and each harmonic signal corresponding to the measured voltage and the fundamental wave and each harmonic signal corresponding to the ground current, including: Among them, Z h is the impedance of the low voltage capacitor end; and The measured voltage U 3 and the ground current I d The vector form of the hth harmonic component of , when h is 1, it is the vector form of the fundamental wave components of the two; U 3-h and θ 3-h The measured voltage U 3 The effective value and phase angle of the hth harmonic component; I d-n and θ d-h are the ground current I d The effective value and phase angle of the hth harmonic component.

8. The system according to claim 5, It is characterized in that The equivalent capacitive reactance calculation unit calculates the equivalent capacitive reactance according to the high voltage capacitor and the medium voltage capacitor of the capacitive voltage divider, including: Among them, Z C-h is the high voltage capacitor C of the capacitive voltage divider 1 and medium voltage capacitor C 2 Equivalent capacitive reactance after series connection; ω h is the hth harmonic angular frequency, ω h =2πhf, f is the industrial frequency; j represents a complex number.

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