CN105388444B - The capacitance type potential transformer harmonic measure bearing calibration being fitted using no-load voltage ratio - Google Patents
The capacitance type potential transformer harmonic measure bearing calibration being fitted using no-load voltage ratio Download PDFInfo
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Abstract
The present invention proposes a kind of capacitance type potential transformer harmonic measure bearing calibration being fitted using no-load voltage ratio, consistent equivalent circuit is established for the capacitance type potential transformer of same voltage class, it is fitted first according to the equivalent-circuit component parameter of preset model, obtain no-load voltage ratio amplitude-frequency response and phase versus frequency response charac t curve, then curve is adjusted using modes such as translations based on fitting result to the different equivalent circuit element parameter of other models, realizes correction.The present invention is using capacitance type potential transformer broadband properties as the standard for weighing the actual no-load voltage ratio of capacitance type potential transformer, the measurement result of capacitance type potential transformer under harmonic frequency is corrected, solve capacitance type potential transformer and may not apply to harmonic measure this problem, with computational methods are simple and the advantages of real-time, expand the application bandwidth of capacitance type potential transformer.
Description
Technical Field
The invention relates to the field of voltage measurement of a capacitor voltage transformer, in particular to a harmonic measurement correction method of the capacitor voltage transformer by adopting transformation ratio fitting.
Background
The Capacitor Voltage Transformer (CVT) is widely used for voltage measurement of a high-voltage system with a directly grounded neutral point, and is the most main secondary signal source for harmonic measurement of the high-voltage level system at present. However, it is clearly specified in the national standard GB/T "harmonic of power quality utility grid" that "capacitive voltage transformers cannot be used for harmonic measurement".
The current research focuses on the principle analysis of harmonic measurement errors of a Capacitor Voltage Transformer (CVT). A harmonic equivalent circuit is established, a calculation method of corresponding parameters is given, and theoretical research on the harmonic measurement precision of a Capacitor Voltage Transformer (CVT) is carried out; researching the measurement precision change rule of a Capacitor Voltage Transformer (CVT) by changing the secondary side load and adopting dampers of different models; the influence of stray capacitance and coupling capacitance on the measurement error of a Capacitance Voltage Transformer (CVT) is analyzed from the point of view of the transfer function. However, the existing research is mainly directed to qualitative analysis of a Capacitor Voltage Transformer (CVT), and does not relate to a quantitative analysis and calculation method of each error peak point source, and a correction method for the error characteristic of the Capacitor Voltage Transformer (CVT) is not provided.
The current research is not deep about the mechanism research of CVT measurement error generation under the harmonic condition, and the quantitative analysis of CVT harmonic measurement error influenced by different factors still has shortcomings, especially the analysis of CVT harmonic measurement error with different dampers is lacked. There is also a lack of correction for CVT harmonic measurement errors. The invention aims to obtain an amplitude-frequency curve and a phase-frequency curve of a transformation ratio frequency response by utilizing the broadband characteristic of the capacitor voltage transformer and realize accurate measurement of the harmonic frequency of the capacitor voltage transformer based on the actual value of the transformation ratio corresponding to the curve.
Disclosure of Invention
The invention provides a broadband characteristic of a Capacitor Voltage Transformer (CVT) adopting a fast saturation damper, and a transformation ratio distortion value of the capacitor voltage transformer under harmonic frequency is obtained. Fitting the amplitude-frequency characteristic and the phase-frequency characteristic curve of the transformation ratio, and realizing the correction of the harmonic measurement of the capacitor voltage transformer by using the obtained fitting curve.
The technical scheme of the invention provides a capacitor voltage transformer harmonic measurement correction method adopting transformation ratio fitting, wherein consistent equivalent circuits are established for CVTs with the same voltage class, firstly, fitting is carried out according to equivalent circuit element parameters of a preset model, then, correction is carried out on different equivalent circuit element parameters of other models based on fitting results, and the CVT is a capacitor voltage transformer;
the fitting according to the equivalent circuit element parameters of the preset model comprises respectively fitting a transformation ratio amplitude-frequency response curve F (x) and a phase-frequency response characteristic curve H (x) obtained according to the equivalent circuit element parameters of the preset model to obtain F i (x) And H i_ (x) Wherein F is i (x) For the i-th step of the transformation ratio amplitude error in F (x), the unit is divided by 20lgKIn decibels (dB), K is the amplitude of the transformation ratio; h i_ (x) The unit is degree, and the unit is the phase angle error of the i-th section; x is the logarithmic value of frequency, i =1,2,3,4;
the correction based on the fitting result includes the following steps,
(1) According to the equivalent circuit element parameters of the target to be corrected, calculating the resonant frequency f of the resonance of the compensating reactor, the voltage-dividing capacitor and the primary side stray capacitance of the intermediate transformer 1 And compensating the internal resonance frequency f of the reactor 2 (ii) a Two resonance frequencies of the preset model higher than the power frequency are respectively marked as f 10 And f 20 ；
(2) Amplitude K of corresponding transformation ratio K Amplitude The manner in which the partial pressure ratio is adopted is as follows,
where ω =2 π f, ω is the angular frequency, f is the frequency, C 1 And C 2 High and medium voltage capacitors of the capacitive voltage divider, respectively; l is a radical of an alcohol Lc 、L Lce And R Lce And C Lc Respectively the reactance of a compensation reactor coil, the reactance and the resistance of an iron core and stray capacitance; l is a radical of an alcohol Tf For connecting leakage reactance of damper winding, C f Is a damper stray capacitance to ground;
for amplitude K Amplitude Using 20lgK linear graduation, according to the equivalent circuit element parameter of the target to be corrected, f is divided 1 And f 2 Substituting into the above formula, and adopting linear graduation to obtain corresponding transformation ratio amplitude and recording as K 1 And K 2 ；
(3) The resonant frequencies higher than the power frequency according to the preset model are respectively f 10 And f 20 A frequency difference c can be obtained 1 ＝f 1 -f 10 ，c 2 ＝f 2 -f 20 ；
(4) The amplitude-frequency response curve adjustment is performed as follows,
i) If K 1 ≥F 2 (lgf 10 ) Let F 2 (x)＝K 1 To find the value x corresponding to x 11 If the frequency difference c 11 ＝lgf 1 -x 11 If not less than 0, then F 2 (x) Curve shifting to right c 11 A unit; if c is 11 <, 0, then F 2 (x) Curve left shift c 11 A unit;
ii) if K 1 ＜F 2 (lgf 10 ) Let F 2 (x)＝K 1 To find the value x corresponding to x 12 If the frequency difference c 12 ＝lgf 1 -x 12 If not less than 0, then F 2 (x) Curve is shifted to right c 12 A unit; if c is 12 <, 0, then F 2 (x) Curve left shift c 12 A unit;
iii) If K 2 ≥F 4 (lgf 20 ) Let F 4 (x)＝K 2 To find the value x corresponding to x 21 (ii) a If the frequency difference c 21 ＝lgf 2 -x 21 If not less than 0, then F 4 (x) Curve is shifted to right c 21 A unit; if c is 21 &0, then F 4 (x) Curve left shift c 21 A unit;
iv) if K 2 ＜F 4 (lgf 20 ) Let F 4 (x)＝K 2 To find the value x corresponding to x 22 (ii) a If the frequency difference c 22 ＝lgf 2 -x 22 If not less than 0, F is added 4 (x) Curve is shifted to right c 22 A unit; if c is 22 <, 0, then F 4 (x) Curve left shift c 22 A unit;
v) for frequency f 1 ＜f＜f 2 Is fitted with a straight line from the resonance frequency peak point (lgf) 1 ,K 1 ) And (lgf) 2 ,K 2 ) Determining a fitting function F 3 (x) (ii) a Let F 1 (x)＝0；
(5) Fitting the phase-frequency response curve by using a translation method, setting P i Is composed of
i) If f 1 <f 10 Then H will be 2 (x) Left shift | c 1 |＝|f 1 -f 10 L units; if f 1 >f 10 Then H will be 2 (x) Translate | c to the right 1 |＝|f 1 -f 10 L units;
ii) if f 2 <f 20 Then H will be 4 (x) Left shift | c 2 |＝|f 2 -f 20 L units; if f 2 >f 20 Then H is added 4 (x) Translate | c to the right 2 |＝|f 2 -f 20 L units;
iii) At a frequency of f 1 And f 2 Response curve H in between 3 (x) Fitting by quadratic function, taking actual data from the ordinate of the curve vertex, and respectively taking (f) from the two end points 1 ,H 2 (f 1 ))，(f 2 ,H 4 (f 2 ) ); let H 1 (x)＝0；
(6) Obtaining the rated transformation ratio K of CVT harmonic measurement according to the measurement error ratio of the transformation ratio in the transformation ratio amplitude-frequency response curve F (x) N Amplitude K of the ratio K Amplitude By multiplying the voltage magnitude measurement of the CVT at the harmonic frequency by the ratioObtaining an accurate voltage amplitude measurement value; subtracting H (x) from the voltage phase angle measured value of the CVT under the harmonic frequency to obtain an accurate voltage phase angle measured value; and completing the correction of the CVT measured value at the harmonic frequency.
Furthermore, the resonance frequency f is calculated 1 And f 2 The implementation is as follows, and the method,
X L2 ＝j×ω×(L Lc +L Lce )
wherein X C1 And X L1 Equivalent capacitive reactance and inductive reactance of a compensation reactor, a voltage division capacitor and a primary side stray capacitance resonance circuit of the intermediate transformer are respectively arranged; x C2 And X L2 Respectively the capacitive reactance and the inductive reactance of a resonance circuit in the compensation reactor; ω =2 π f, ω is the angular frequency, f is the frequency; c 1 And C 2 High and medium voltage capacitors of the capacitive voltage divider, respectively; c T1 A stray capacitance to ground at the primary side of the intermediate transformer; l is Lc 、L Lce And C Lc Respectively the reactance of a compensation reactor coil, the reactance of an iron core and the stray capacitance; l is a radical of an alcohol Tf Leakage reactance for switching-in damper winding, C f Is the damper stray capacitance to ground.
The invention takes the broadband characteristic of the capacitor voltage transformer as the standard for measuring the actual transformation ratio of the capacitor voltage transformer, corrects the measurement result of the capacitor voltage transformer under the harmonic frequency, solves the problem that the capacitor voltage transformer can not be applied to the harmonic measurement, has the advantages of simple calculation method and real-time performance compared with the harmonic measurement methods based on algorithms such as an instantaneous reactive power theory, a wavelet transformation theory and the like, avoids the problem that the harmonic result is obtained by carrying out data analysis after a large number of measurement results of the capacitor voltage transformer are collected within a certain time period, and enlarges the application bandwidth of the capacitor voltage transformer.
Drawings
FIG. 1 is a circuit diagram of a capacitor voltage transformer employing a fast saturation type damper according to an embodiment of the present invention;
FIG. 2 is a graph of a magnitude-frequency curve fit based on polynomial fitting according to an embodiment of the invention;
FIG. 3 is a phase frequency curve fit graph based on polynomial fit and fractional fit according to an embodiment of the present invention;
fig. 4 is a flowchart of a method for correcting the transformation ratio amplitude-frequency fitting according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of a method application of an embodiment of the invention.
Detailed Description
The technical solution of the present invention is described in detail below with reference to the accompanying drawings and examples.
The invention applies equal voltage values with different frequencies on the primary side of the capacitance voltage transformer adopting the rapid saturation type damper, and the ratio of the secondary side measurement result and the primary side applied voltage is the actual transformation ratio of the capacitance voltage transformer. And obtaining a fitting function of the transformation ratio frequency response characteristic curve by using polynomial fitting and fractional fitting. And obtaining the frequency of each resonance point according to the equivalent circuit parameters of the capacitor voltage transformer, and obtaining the actual ratio of the resonance frequency by using a voltage division formula. And according to the resonance frequency and the actual variable ratio, realizing translation and transformation of the fitting function to obtain an accurate fitting function formula of the capacitor voltage transformer. Based on the formula, the measurement result of the capacitor voltage transformer is corrected, so that the capacitor voltage transformer can be applied to voltage measurement of a power frequency system and voltage measurement under harmonic frequency.
The capacitor voltage transformer is composed of a capacitive voltage divider (composed of a high-voltage capacitor C) 1 And a medium voltage capacitor C 2 Formed), an electromagnetic unit (formed by a compensation reactor L) C An intermediate transformer T and a damper Z f Form), load (by measuring winding load Z 1 And a protective winding load Z 2 Composition). In the embodiment of the invention, a harmonic equivalent circuit is established according to the capacitor voltage transformer adopting the rapid saturation damper. C in FIG. 1 1 And C 2 High and medium voltage, respectively, of capacitive voltage dividersAccommodating; l is Lc And R Lc 、L Lce And R Lce And C Lc Respectively the reactance and resistance of a compensation reactor coil, the reactance and resistance of an iron core and stray capacitance; l is a radical of an alcohol T1 And R T1 、L T2 And R T2 And L Tf And R Tf Leakage reactance and resistance of a primary side of the intermediate transformer, a winding for measurement and protection and a winding connected into the damper are respectively, wherein the winding for measurement and protection is equivalently combined because the capacity and the output voltage are generally the same; c T1 A stray capacitance to ground at the primary side of the intermediate transformer; l is a radical of an alcohol Tm And R Tm Respectively an exciting reactance and a resistance of the intermediate transformer; l is f And R f The reactance and the resistance of the fast saturation type damper; c f Is a damper stray capacitance to ground; l is a radical of an alcohol z And R z Measuring and protecting the reactance and resistance of the equivalent load of the winding; the load ground constitutes a loop. Because the number of turns of the secondary winding of the intermediate transformer is small, the stray capacitance to the ground of each winding on the secondary side is ignored in the model; a is power supply voltage; n is ground.
Then, the difference of parameter values of products produced by various manufacturers under the same voltage level is considered. The invention provides that aiming at the same voltage level, the parameters of equivalent circuit elements of a preset model are fitted, and then the parameters of different equivalent circuit elements of other models are processed in modes of translation curves and the like. The embodiment takes a 400kV CVT as an example for processing, and the implementation manner of other voltage grades is the same. Fig. 2 and 3 show transformation ratio amplitude-frequency response and phase-frequency response characteristic curves obtained by the embodiment of the present invention for a 400kV CVT capacitor voltage transformer using a fast saturation type damper based on equivalent circuit element parameters of a preset model shown in table 1, and polynomial fitting is used for an amplitude-frequency response characteristic curve F (x) line and polynomial fitting and fractional fitting are used for a phase-frequency response characteristic curve H (x). The fitting results are given below, where x is the logarithm of the frequency; f i (x) Dividing the variation ratio amplitude error of the ith section in F (x) by 20lgK, wherein the unit is decibel (dB), and K is the variation ratio amplitude; h i (x) And (3) the unit of the transformation ratio phase angle error of the ith section is degree, and i =1,2,3,4.
TABLE 1 Preset model equivalent Circuit element parameters
| Equivalent capacitor C of voltage-dividing capacitor | 57.18nF |
| Compensation reactor winding resistance R Lc | 766Ω |
| Iron core resistance R of compensation reactor Lce | 9.288MΩ |
| Compensation reactor winding inductance L Lc | 24.71H |
| Compensation reactor iron core inductance L Lce | 148.9H |
| Iron core capacitor C of compensation reactor Lc | 61.17pF |
| Primary side winding resistor R of intermediate transformer T1 | 1403Ω |
| Primary side winding inductance L of intermediate transformer T1 | 1.27H |
| Winding resistance R for measurement and protection T2 | 1054Ω |
| Winding inductance L for measurement and protection T2 | 6.95H |
| Exciting resistor R of intermediate transformer Tm | 1070Ω |
| Intermediate transformer excitation reactance L Tm | 53kH |
| Intermediate variable primary side-to-ground stray capacitance C T1 | 267pF |
| Leakage reactance resistance R of damper winding Tf | 5904Ω |
| Leakage reactance inductance L of damper winding Tf | 6.18H |
| Stray capacitance to ground C of damping circuit f | 30pF |
| Transformer winding resistor R of damping circuit f | 2725Ω |
| Self-inductance L of damping circuit transformer winding f | 3002H |
Relevant parameters can be found in:
H.J.Vermeulen,L.R.Dann,J.van Rooijen.Equivalent circuit modeling of a capacit ive voltage transformer for power system harmonic frequencies[J].IEEE Trans.On Power Delivery,1995,10(4):1743-1749.
in specific implementation, other value-taking schemes can be adopted as equivalent circuit element parameters of the preset model, and the realization principles are the same
Fitting results of amplitude-frequency response characteristic curves:
phase-frequency response characteristic curve fitting result:
as can be seen in FIG. 2, F 1 (x) Approximately equal to zero, so the fitting function can be directly equivalent with 0, let F 1 (x) =0, and can be applied to 400kV CVTs of other models; f 3 (x) Is a linear function and is obtained by connecting amplitude points of two resonant frequencies of a preset model of the 400kV CVT, and for 400kV CVTs of other models, the same method can be adopted to determine a straight line from two points to obtain F 3 (x) The fitting function of (2).
The calibration is performed based on the fitting result, and the specific implementation steps of the embodiment are as follows:
(1) Because the harmonic equivalent circuits are the same, when CVTs of other models of 400kV CVTs adopting speed saturation type dampers are targets to be corrected, the resonance frequency f of resonance of the compensation reactor, the voltage dividing capacitor and the primary side stray capacitance of the intermediate transformer is calculated according to the equivalent circuit element parameters 1 And compensating the internal resonance frequency f of the reactor 2 . The calculation method is as follows:
X L2 ＝j×ω×(L Lc +L Lce )
wherein X C1 And X L1 Equivalent capacitive reactance and inductive reactance of a compensating reactor, a voltage-dividing capacitor and a primary side stray capacitance resonance circuit of an intermediate transformer are respectively adopted; x C2 And X L2 Respectively the capacitive reactance and the inductive reactance of a resonance circuit in the compensation reactor.
ω =2 π f, ω is the angular frequency, f is the frequency; c 1 And C 2 High and medium voltage capacitors of the capacitive voltage divider, respectively; c T1 A stray capacitance to ground at the primary side of the intermediate transformer; l is Lc 、L Lce And C Lc Respectively the reactance of a compensation reactor coil, the reactance of an iron core and a stray capacitance; l is Tf Leakage reactance for switching-in damper winding, C f Is the damper stray capacitance to ground. And adopting the equivalent circuit element parameters of the target to be corrected during calculation.
In this embodiment, there are two resonant frequencies, denoted as f, of the preset models higher than the power frequency 10 And f 20 。
(2) Transformation ratioAmplitude K of K Amplitude The method can be expressed by adopting a partial pressure ratio as follows:
where ω =2 π f, ω is the angular frequency and f is the frequency. C 1 And C 2 High and medium voltage capacitors of the capacitive voltage divider, respectively; l is Lc 、L Lce And R Lce And C Lc Respectively the reactance of a compensation reactor coil, the reactance and the resistance of an iron core and stray capacitance; l is Tf Leakage reactance for switching-in damper winding, C f Is the damper stray capacitance to ground. And adopting the equivalent circuit element parameters of the target to be corrected during calculation.
It is linearly graduated by 20lgK and converted into the form of ordinate of the waveform chart in FIG. 2. Will f is 1 And f 2 Substituting in formula (1), and obtaining corresponding transformation ratio amplitude value by linear division and recording as K 1 And K 2 。
(3) The resonant frequencies of the preset models higher than the power frequency are respectively f 10 And f 20 A frequency difference c can be obtained i 。c i ＝f i -f i0 (i =1, 2), i.e. c 1 ＝f 1 -f 10 ，c 2 ＝f 2 -f 20 。
(4) Adjusting an amplitude-frequency response curve:
i) If K is 1 ≥F 2 (lgf 10 ) Let F 2 (x)＝K 1 To find the value x corresponding to x 11 . If the frequency difference c 11 ＝lgf 1 -x 11 If not less than 0, F is added 2 (x) Curve is shifted to right c 11 A unit; if c is 11 &0, then F 2 (x) Curve left shift c 11 And (4) units.
ii) if K 1 ＜F 2 (lgf 10 ) Let F 2 (x)＝K 1 To find the value x corresponding to x 12 . If the frequency difference c 12 ＝lgf 1 -x 12 If not less than 0, F is added 2 (x) Curve shifting to right c 12 A unit; if c is 12 &0, then F 2 (x) Curve left shift c 12 And (4) units.
iii) If K 2 ≥F 4 (lgf 20 ) Let F 4 (x)＝K 2 To find the value x corresponding to x 21 . If the frequency difference c 21 ＝lgf 2 -x 21 If not less than 0, F is added 4 (x) Curve is shifted to right c 21 A unit; if c is 21 &0, then F 4 (x) Curve left shift c 21 And (4) units.
iv) if K 2 ＜F 4 (lgf 20 ) Let F 4 (x)＝K 2 To find the value x corresponding to x 22 . If the frequency difference c 22 ＝lgf 2 -x 22 If not less than 0, then F 4 (x) Curve is shifted to right c 22 A unit; if c is 22 &0, then F 4 (x) Curve left shift c 22 And (4) units.
v) for frequency f 1 ＜f＜f 2 Is fitted with a straight line from the resonance frequency peak point (lgf) 1 ,K 1 ) And (lgf) 2 ,K 2 ) Determining a fitting function thereof, i.e. F 3 (x) Is (lgf) 1 ,K 1 ) And (lgf) 2 ,K 2 ) The connection line of (2). Let F 1 (x)＝0。
(5) The adjustment of the phase-frequency response curve mainly adopts a translation method, and is realized as follows,
i) If f 1 <f 10 Then H will be 2 (x) Left shift | c 1 |＝|f 1 -f 10 L units; if f 1 >f 10 Then H will be 2 (x) Shift to right | c 1 |＝|f 1 -f 10 L units.
ii) if f 2 <f 20 Then H will be 4 (x) Left shift | c 2 |＝|f 2 -f 20 L units; if f 2 >f 20 Then H is added 4 (x) Shift to right | c 2 |＝|f 2 -f 20 L units.
iii) At a frequency of f 1 And f 2 Response curve H in between 3 (x) Fitting by quadratic function, taking actual data 0.289 from the ordinate of the curve vertex, and respectively taking (f) from two end points 1 ,H 2 (f 1 ))，(f 2 ,H 4 (f 2 )). F in two coordinate points 1 And f 2 Taking logarithm. Let H 1 (x)＝0。
(6) Error ratio 10 measured from the ratio of change given by the curve shown in FIG. 2 F(x) /20, the rated transformation ratio K of CVT harmonic measurement can be obtained N To the actual ratio (i.e. the amplitude K of the ratio K) Amplitude ) The ratio of (a) to (b).
In the formula, K N Is the rated transformation ratio of the CVT.
Multiplying the voltage magnitude measurement of the CVT at the harmonic frequency by the ratioAccurate voltage amplitude measurement values can be obtained; and subtracting H (x) from the voltage phase angle measured value of the CVT at the harmonic frequency to obtain an accurate voltage phase angle measured value. Thereby enabling correction of CVT measurements at harmonic frequencies.
In specific implementation, the transformation ratio amplitude-frequency fitting correction process of the embodiment of the invention can be seen in fig. 4, and the transformation ratio phase-frequency fitting correction process is similar. As shown in fig. 4, the amplitude-frequency response curve adjustment can be performed in three stages:
first, it is judged whether K is present 1 ≥F 2 (lgf 10 )，
If K is 1 ≥F 2 (lgf 10 ) Let F 2 (x)＝K 1 To find the value x corresponding to x 11 . And judging whether c is 11 ＝lgf 1 -x 11 ≧ 0, if the frequency difference c 11 ＝lgf 1 -x 11 If not less than 0, F is added 2 (x) Curve is shifted to right c 11 A unit; if c is 11 &0, then F 2 (x) Curve left shift c 11 And (4) units.
If K 1 ＜F 2 (lgf 10 ) Let F 2 (x)＝K 1 To find the value x corresponding to x 12 . And judging whether c is 12 ＝lgf 1 -x 12 Is greater than or equal to 0 if the frequency difference c 12 ＝lgf 1 -x 12 If not less than 0, F is added 2 (x) Curve is shifted to right c 12 A unit; if c is 12 &0, then F 2 (x) Curve left shift c 12 And (4) units.
Then, it is judged whether K is present 2 ≥F 4 (lgf 20 )，
If K is 2 ≥F 4 (lgf 20 ) Let F 4 (x)＝K 2 To find the value x corresponding to x 21 . And judging whether c is 21 ＝lgf 2 -x 21 Is greater than or equal to 0 if the frequency difference c 21 ＝lgf 2 -x 21 If not less than 0, F is added 4 (x) Curve is shifted to right c 21 A unit; if c is 21 &0, then F 4 (x) Curve left shift c 21 And (4) units.
iv) if K 2 ＜F 4 (lgf 20 ) Let F 4 (x)＝K 2 To find the value x corresponding to x 22 . And judging whether c is 22 ＝lgf 2 -x 22 ≧ 0, if the frequency difference c 22 ＝lgf 2 -x 22 If not less than 0, then F 4 (x) Curve is shifted to right c 22 A unit; if c is 22 &0, then F 4 (x) Curve left shift c 22 And (4) units.
Finally, let F 1 (x)＝0，F 3 (x) Is (lgf) 1 ,K 1 ) And (lgf) 2 ,K 2 ) The connecting line of (2).
Referring to fig. 5, the present capacitive voltage transformer generally comprises a capacitive voltage divider (consisting of a high voltage capacitor C) 1 And a medium voltage capacitor C 2 Composition), electromagnetic sheetElement (by compensating reactor L) C Intermediate transformer T and damper Z f Form), load (by measuring winding load Z 1 And a protective winding load Z 2 The device comprises a variable ratio correcting device and a signal generator, and can be used for realizing the method provided by the invention. Furthermore, G is a guard gap, L d The carrier frequency leakage coil is used, and V is a voltmeter for measurement. Compensation reactor L C One end of the capacitor is connected with a high-voltage capacitor C 1 And a medium voltage capacitor C 2 The other end of the intermediate transformer T is connected with a primary winding of the intermediate transformer T and a damper Z f Measuring winding load Z 1 And a protective winding load Z 2 Respectively connected with the secondary windings of the intermediate transformer T. The input end of the voltmeter for measurement is connected with the load Z of the measurement winding 1 Two ends, the output end is connected with the first input end of the transformation ratio correcting device, and the winding load Z is measured by the voltmeter 1 And the output results of the capacitor voltage transformers collected at the two ends are connected to the transformation ratio correction device and used for collecting and outputting the output results of the capacitor voltage transformers. The high-voltage end of the capacitor voltage transformer is marked as A, the ground is marked as N, and the voltage division point is marked as M. The output end of the signal generator is connected with the second input end of the transformation ratio correcting device, and the harmonic frequency to be detected output by the signal generator is connected to the transformation ratio correcting device. The signal generator transmits the harmonic frequency to be detected to the transformation ratio correcting device, and during specific implementation, the signal generator can generate the corresponding harmonic frequency to be detected according to the received harmonic frequency signal. And after receiving the frequency to be measured sent by the signal generator, the transformation ratio correction device corrects the output result of the capacitor voltage transformer according to a transformation ratio fitting curve established based on the broadband characteristic of the capacitor voltage transformer and outputs the correction result. The transformation ratio correcting device can adopt DSP and is realized based on the method provided by the invention.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments, or alternatives may be employed, by those skilled in the art, without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (2)
1. A capacitance voltage transformer harmonic measurement correction method adopting transformation ratio fitting is characterized in that: the method comprises the steps that a consistent equivalent circuit is established for CVTs with the same voltage class, fitting is carried out according to equivalent circuit element parameters of a preset model, and then correction is carried out on different equivalent circuit element parameters of other models based on fitting results, wherein the CVT is a capacitor voltage transformer;
the fitting according to the equivalent circuit element parameters of the preset model comprises respectively fitting a transformation ratio amplitude-frequency response curve F (x) and a phase-frequency response characteristic curve H (x) obtained according to the equivalent circuit element parameters of the preset model to obtain F i (x) And H i (x) wherein F i (x) Dividing the variation ratio amplitude error of the ith section in F (x) by 20lgK, wherein the unit is decibel (dB), and K is the variation ratio amplitude; h i (x) The unit is degree, and the unit is the phase angle error of the i-th section; x is the logarithmic value of frequency, i =1,2,3,4;
the correction based on the fitting result includes the following steps,
(1) According to the equivalent circuit element parameters of the target to be corrected, calculating the resonant frequency f of the resonance of the compensating reactor, the voltage-dividing capacitor and the primary side stray capacitance of the intermediate transformer 1 And compensating the internal resonance frequency f of the reactor 2 (ii) a Two resonance frequencies of the preset model higher than the power frequency are respectively marked as f 10 And f 20 ；
(2) Amplitude K of corresponding transformation ratio K Amplitude The manner in which the partial pressure ratio is adopted is as follows,
where ω =2 π f, ω is the angular frequency, f is the frequency, C 1 And C 2 High and medium voltage capacitors of the capacitive voltage divider, respectively; l is a radical of an alcohol Lc 、L Lce And R Lce And C Lc Respectively the reactance of the coil of the compensation reactor, the reactance and the resistance of the iron core and the stray capacitance；L Tf For connecting leakage reactance of damper winding, C f Is a stray capacitance of the damper to ground, C T1 A stray capacitance to ground at the primary side of the intermediate transformer;
for amplitude K Amplitude Using 20lgK linear graduation, according to the equivalent circuit element parameter of the target to be corrected, f is divided 1 And f 2 Substituting into the above formula, and adopting linear graduation to obtain corresponding transformation ratio amplitude and recording as K 1 And K 2 ；
(3) The resonant frequencies higher than the power frequency according to the preset model are respectively f 10 And f 20 A frequency difference c can be obtained 1 ＝f 1 -f 10 ，c 2 ＝f 2 -f 20 ；
(4) The amplitude-frequency response curve adjustment is performed as follows,
i) If K 1 ≥F 2 (lgf 10 ) Let F 2 (x)＝K 1 To find the value x corresponding to x 11 If the frequency difference c 11 ＝lgf 1 -x 11 If not less than 0, then F 2 (x) Curve is shifted to right c 11 A unit; if c is 11 &0, then F 2 (x) Curve left shift c 11 A unit;
ii) if K 1 ＜F 2 (lgf 10 ) Let F 2 (x)＝K 1 To find the value x corresponding to x 12 If the frequency difference c 12 ＝lgf 1 -x 12 If not less than 0, then F 2 (x) Curve is shifted to right c 12 A unit; if c is 12 <, 0, then F 2 (x) Curve left shift c 12 A unit;
iii) If K 2 ≥F 4 (lgf 20 ) Let F 4 (x)＝K 2 To find the value x corresponding to x 21 (ii) a If the frequency difference c 21 ＝lgf 2 -x 21 If not less than 0, F is added 4 (x) Curve shifting to right c 21 A unit; if c is 21 &0, then F 4 (x) Curve left shift c 21 A unit;
iv) if K 2 ＜F 4 (lgf 20 ) Let F 4 (x)＝K 2 To find the value x corresponding to x 22 (ii) a If the frequency difference c 22 ＝lgf 2 -x 22 If not less than 0, F is added 4 (x) Curve is shifted to right c 22 A unit; if c is 22 <, 0, then F 4 (x) Curve left shift c 22 A unit;
v) for frequency f 1 ＜f＜f 2 Is fitted with a straight line from the resonance frequency peak point (lgf) 1 ,K 1 ) And (lgf) 2 ,K 2 ) Determining a fitting function F 3 (x) (ii) a Let F 1 (x)＝0；
(5) Fitting the phase-frequency response curve by using a translation method, setting P i Is composed of
i) If f 1 <f 10 Then H will be 2 (x) Left shift | c 1 |＝|f 1 -f 10 L units; if f is 1 >f 10 Then H will be 2 (x) Shift to right | c 1 |＝|f 1 -f 10 L units;
ii) if f 2 <f 20 Then H will be 4 (x) Left shift | c 2 |＝|f 2 -f 20 L units; if f 2 >f 20 Then H will be 4 (x) Shift to right | c 2 |＝|f 2 -f 20 L units;
iii) At a frequency of f 1 And f 2 Response curve H in between 3 (x) Fitting by quadratic function, taking actual data from the ordinate of the curve vertex, and respectively taking (f) from the two end points 1 ,H 2 (f 1 ))，(f 2 ,H 4 (f 2 ) ); let H 1 (x)＝0；
(6) Obtaining the rated transformation ratio K of CVT harmonic measurement according to the measurement error ratio of the transformation ratio in the transformation ratio amplitude-frequency response curve F (x) N Amplitude K of the ratio K Amplitude By multiplying the voltage magnitude measurement of the CVT at the harmonic frequency by the ratioObtaining accurate voltage amplitude measurements(ii) a Subtracting H (x) from the voltage phase angle measured value of the CVT under the harmonic frequency to obtain an accurate voltage phase angle measured value; and completing the correction of the CVT measured value at the harmonic frequency.
2. The method for correcting harmonic measurement of a capacitor voltage transformer by adopting transformation ratio fitting according to claim 1, characterized in that: calculating the resonant frequency f 1 And f 2 The implementation mode is as follows,
X L2 ＝j×ω×(L Lc +L Lce )
wherein X C1 And X L1 Equivalent capacitive reactance and inductive reactance of a compensating reactor, a voltage-dividing capacitor and a primary side stray capacitance resonance circuit of an intermediate transformer are respectively adopted; x C2 And X L2 Respectively the capacitive reactance and the inductive reactance of a resonance circuit in the compensation reactor; ω =2 π f, ω is the angular frequency, f is the frequency; c 1 And C 2 High and medium voltage capacitors of the capacitive voltage divider, respectively; c T1 A stray capacitance to ground at the primary side of the intermediate transformer; l is Lc 、L Lce And C Lc Electricity of compensating reactor coils respectivelyReactance of the reactance, iron core and stray capacitance; l is Tf Leakage reactance for switching-in damper winding, C f Is the damper stray capacitance to ground.
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