CN102435816B - Working method of MOA (Metal Oxide Arrester) resistive current tester - Google Patents

Abstract

The invention discloses a working method of MOA (Metal Oxide Arrester) resistive current tester; the resistive leakage current fundamental wave parameters are acquired normally by a projection method, comprising the following steps of: sampling leakage current signals of power grid voltage and MOA at the same time; acquiring the fundamental wave amplitude value V1=(a<2>k+b<2>k)<1/2> and an initial phase angle psi v1=tg<-1>(ak/bk) of the power grid voltage by a changeable fence plesiochronous DFT (Discrete Fourier Transformation) harmonic wave analyzing technology; acquiring the fundamental wave amplitude value I1=(a<2>k+b<2>k)<1/2> and initial phase angle psi I1=tg<-1>(ak/bk) of the MOA leakage current by the changeable fence plesiochronous DFT harmonic wave analyzing technology; acquiring the projection angle psi=psi I1-psi v1 of the leakage current fundamental wave on the power grid voltage fundamental wave based on the projection method; acquiring the MOA resistive leakage current fundamental wave I<R1>=I1*cos(pis) and outputting and displaying the fundamental wave. The analyzing error of the plesiochronous DFT harmonic wave analyzing technology is effectively reduced and high-precision harmonic wave analyzing result is acquired by the working method of MOA resistive current tester provided by the invention. Consequently, the reliability of MOA resistive current test based on harmonic wave analyzing theory is improved.

Description

A kind of method of work of MOA testing current in resistance property instrument

Technical field

The present invention relates to the technical field of MOA testing current in resistance property, specifically a kind of method of work of the MOA testing current in resistance property instrument based on high-precision harmonic analysis method.

Background technology

Metal oxide arrester (hereinafter to be referred as MOA) is used widely because of its superior overvoltage protection characteristic in electric system; but MOA resistor disc is aging and cause fault through being heated with impact failure meeting; seriously may cause its blast; lightning arrester also punctures can cause substation bus bar short circuit; affect system safety operation, therefore must carry out strictly effective detection and regularly preventive trial to operating MOA.In the detection and test of Zinc-Oxide Arrester, leakage current measurement under ac operation voltage is an important project, and the size of the resistive current first harmonics composition in leakage current can reflect the defects such as Zinc-Oxide Arrester makes moist, the aging and built-in electrical insulation of valve block is impaired more accurately.Therefore, the parameters such as resistive leakage current first-harmonic being carried out to Measurement accuracy just can differentiate MOA performance comparatively exactly.

Frequency analysis technology is widely used in various fields such as electric energy quality monitoring, electronic product production testing, electric equipment monitoring, is the important technical of carrying out power system monitor, quality inspection, monitoring of tools.The most widely used technology of frequency analysis is discrete Fourier transformation (DFT) and Fast Fourier Transform (FFT) (FFT) at present.The frequency analysis technology that accurate synchronous sampling technique and DFT technology combine (that is: accurate synchronous DFT frequency analysis technology) can improve the precision of frequency analysis, and its formula is:

，

In formula: k is for needing the number of times (as first-harmonic k=1,3 subharmonic k=3) of the harmonic wave of acquisition; Sin and cos are respectively sine and cosine functions; And a _kand b _kbe respectively real part and the imaginary part of k subharmonic; N is iterations; W determines by integration method, while adopting complexification trapezoidal integration method, and W=nN; it is a weighting coefficient;

, be all weighting coefficient sums; I the sampled value that f (i) is analysis waveform; N is sampling number in the cycle.

In engineering application, frequency analysis is always carried out the sampling of finite point and is difficult to accomplish the synchronized sampling of stricti jurise.Like this, when the accurate synchronous DFT of application carries out frequency analysis, the short scope leakage that will exist the long scope causing due to truncation effect to leak and cause due to fence effect, makes analysis result precision not high, even not credible.

Summary of the invention

The technical problem to be solved in the present invention is to provide the method for work of the MOA testing current in resistance property instrument that a kind of precision is higher, effectively to improve the analytical error of accurate synchronous DFT frequency analysis technology, obtain high-precision frequency analysis result, thereby improve the reliability of the MOA testing current in resistance property based on frequency analysis theory.

For solving the problems of the technologies described above, the method for work of MOA testing current in resistance property instrument provided by the invention comprises the following steps:

(1), simultaneously the sample Leakage Current I of line voltage V and MOA of the CPU of MOA testing current in resistance property instrument, and respectively to line voltage V and W+2 sampling number certificate of Leakage Current I equal interval sampling: f (i), i=0,1 ..., w+1};

(2), described CPU starts the accurate synchronous DFT formula of application from the sampled point i=0 of described line voltage V:

analyze W+1 data acquisition first-harmonic information with ;

Then, described CPU starts the accurate synchronous DFT formula of application from the sampled point i=1 of described line voltage V:

analyze W+1 data acquisition first-harmonic information ;

Application of formula:

, calculate the frequency drift of described line voltage V

;

Application of formula:

, draw the real part of the first-harmonic of described line voltage V

and imaginary part

, then calculate the amplitude of the first-harmonic of described line voltage V

and initial phase angle

;

(3), described CPU starts the accurate synchronous DFT formula of application from the sampled point i=0 of described Leakage Current I:

analyze W+1 data acquisition first-harmonic information

with ;

Then, described CPU applies accurate synchronous DFT formula from the sampled point i=1 of Leakage Current I:

Analyze W+1 data acquisition first-harmonic information

;

Application of formula:

, calculate the frequency drift of described Leakage Current I

;

Application of formula:

, draw respectively the real part of the first-harmonic of described Leakage Current I and imaginary part

, then calculate the amplitude of the first-harmonic of described Leakage Current I

and initial phase angle

;

(4) projected angle of the first-harmonic that, obtains Leakage Current I according to sciagraphy on the first-harmonic of line voltage V

;

(5), obtain the first-harmonic of the resistive Leakage Current of MOA

, and output display.

The method of work of MOA testing current in resistance property instrument has adopted a kind of harmonic analysis method, and the position that the accurate synchronous DFT of its application carries out the sampling of frequency analysis time-frequency domain changes according to the drift of signal frequency, and described frequency domain sampling position is μ 2 π/N, wherein:

for the drift of signal frequency, during without drift

be 1.

The thought of described harmonic analysis method of the present invention based on variable fence, realizes by 5 analytical procedures.

The thought of variable fence: the main cause of accurate synchronous DFT analytical error is position and the ideal position generation deviation that the drift of signal frequency causes spectrum peak to occur, if the analysis result still obtaining to sample in frequency domain according to 2 π/N is extremely incorrect.Variable fence refers to: the position of frequency domain sampling be not the 2 π/N fixing, but change according to the drift of signal frequency, frequency sampling position is the drift that μ 2 π/N(μ is signal frequency).Frequency domain sampling fence changes along with the drift of signal frequency can accurately estimate the position that each harmonic peak value occurs, and then obtains high-precision amplitude and phase angle information.

Accurate synchronous DFT frequency analysis can effectively suppress long scope and leak, the main cause of its spectrum leakage is that the short scope that signal frequency drift causes is leaked, and signal frequency drift causes principal character that short scope leaks is spectrum peak-to-peak value occurs position along with signal frequency drift synchronous change, so variable fence frequency domain sample can effectively catch according to signal drift the position that spectrum peak-to-peak value occurs, thereby obtains high-precision harmonic information.

Equal interval sampling is according to cycle T and the frequency f (if power frequency component frequency f is 50Hz, the cycle is 20mS) of carrying out the ideal signal of frequency analysis, the N point of sampling in one-period, and sample frequency is f _s=Nf, and N>=64.

Described sampling W+2 sampling number is according to being to do corresponding selection according to selected integration method, if adopt complexification trapezoidal integration method, W=nN; If adopt complexification rectangular integration method, W=n (N-1); If adopt iterative Simpson integration method, W=n (N-1)/2.Then according to sample frequency f _s=Nf, acquisition sampled point data sequence f (i), and i=0,1 ..., w+1}, n>=3, finally carry out frequency analysis to this data sequence.

An iteration coefficient

by integration method, ideal period sampled point N and iterations n, determined, concrete derivation referring to document [Dai Xianzhong. the some problems [J] in accurate synchronized sampling application. electrical measurement and instrument, 1988, (2): 2-7.].

for imaginary part and the real part of k subharmonic, according to just can obtain harmonic amplitude and initial phase angle.

The drift of signal frequency

to obtain according to the fixed relationship of sampling number N in neighbouring sample point first-harmonic phase angle difference and ideal period, the drift of signal frequency

also can be used for revising the frequency f of first-harmonic ₁frequency f with higher hamonic wave _k.

MOA testing current in resistance property instrument application frequency analysis technology of the present invention detects the parameters such as resistive leakage current first-harmonic of operating MOA, and then the performance of judgement MOA.MOA testing current in resistance property instrument is comprised of MOA Leakage Current sensor, line voltage sensor, signal conditioning circuit, data acquisition circuit, CPU, LCD unit and corresponding analysis software.MOA Leakage Current sensor generally adopts current transformer, in the ground wire of the lower end at MOA in tandem, obtains the Leakage Current of MOA; Line voltage sensor generally adopts voltage transformer (VT), for obtaining the voltage signal of electrical network; The voltage signal that signal conditioning circuit is sent sensor here, Leakage Current signal are transformed to the voltage signal that is applicable to Acquisition Circuit sampling; By data acquisition circuit, the signal after conditioning is sampled, then completed the analysis of harmonic wave and detection by analysis software by CPU.

The method of work of MOA testing current in resistance property instrument of the present invention, for improvement of the quality with improving frequency analysis, obtains fundamental voltage amplitude, the phase angle of high-precision line voltage and MOA Leakage Current.

The harmonic analysis method that MOA testing current in resistance property instrument of the present invention adopts, the frequency analysis technology for based on variable fence thought, has following technical advantage:

(1) high-precision frequency analysis result.No matter the analysis result that frequency analysis technology of the present invention obtains is that amplitude or phase angle error improve 4 more than the order of magnitude.

(2) frequency analysis technology of the present invention has fundamentally solved the low problem of accurate synchronous DFT analysis precision, and without carrying out complicated inverting and correction, algorithm is simple.

(3) with respect to the synchronous DFT of standard, frequency analysis technology of the present invention only need to increase a sampled point and just solve the large problem of accurate synchronous DFT analytical error, is easy to realize.

(4) application the present invention improves existing instrument and equipment, and technical is feasible, and does not need to increase any hardware spending and just can make analysis result can improve 4 more than the order of magnitude.

(5) variable fence thought is also applicable to carry out repeatedly iteration and the frequency analysis process of non-once iteration too, now only an iteration need to be resolved into repeatedly to iteration and realize just passable.Iteration is the same with iteration repeatedly in essence, and just when calculating, repeatedly iteration is carried out substep calculating, and iteration is that the process of iteration is repeatedly merged to iteration coefficient

in once calculated, so the present invention is equally applicable to repeatedly iterative process.

Embodiment

The method of work of MOA testing current in resistance property instrument of the present invention, comprises the following steps:

(1), simultaneously the sample Leakage Current I of line voltage V and MOA of the CPU of MOA testing current in resistance property instrument, and respectively to line voltage V and W+2 sampled point of Leakage Current I equal interval sampling, to obtain discrete series { f (k), k=0,1 of analyzed signal,, w+1}.W is determined jointly by sampling number N in integration method, iterations n and ideal period.Equal interval sampling refers to according to the frequency f (if power frequency component frequency is 50Hz, the cycle is 20mS) of carrying out the ideal signal of frequency analysis determines sample frequency f _s=Nf, at sample frequency f _seffect under the N point of sampling equably in one-period.Usually, periodic sampling point N=64 or just can obtain good frequency analysis result above, and iterations n=3-5 just can obtain comparatively ideal frequency analysis result.Integration method has complexification trapezoidal integration method W=nN, complexification rectangular integration method W=n (N-1), Simpson's integration method W=n (N-1)/2 etc. multiple, can select according to actual conditions.

(2), described CPU starts the accurate synchronous DFT formula of application from the sampled point i=0 of line voltage V

analyze W+1 data acquisition first-harmonic information

with

.Wherein, an iteration coefficient

by integration method, ideal period sampled point N and iterations n, determined, and

for all weighting coefficient sums.

From the sampled point i=1 of described line voltage V, start the accurate synchronous DFT formula of application:

analyze W+1 data acquisition first-harmonic information

;

Application of formula:

, calculate the frequency drift of described line voltage V

;

Application of formula:

, draw the real part of the first-harmonic of described line voltage V

and imaginary part

, then calculate the amplitude of the first-harmonic of described line voltage V

and initial phase angle

;

(3), described CPU starts the accurate synchronous DFT formula of application from the sampled point i=0 of described Leakage Current I:

analyze W+1 data acquisition first-harmonic information

with

;

The accurate synchronous DFT formula of sampled point i=1 application from Leakage Current I:

Analyze W+1 data acquisition first-harmonic information ;

Application of formula:

, calculate the frequency drift of described Leakage Current I

;

Application of formula:

, draw respectively the real part of the first-harmonic of described Leakage Current I and imaginary part

, then calculate the amplitude of the first-harmonic of described Leakage Current I

and initial phase angle ;

(4) projected angle of the first-harmonic that, described CPU obtains Leakage Current I according to sciagraphy on the first-harmonic of line voltage V

;

(5), described CPU obtains the first-harmonic of the resistive Leakage Current of MOA

, and output display.

Those skilled in the art will be appreciated that, above embodiment is only for the present invention is described, and not as limitation of the invention, the present invention can also be varied to more mode, as long as within the scope of connotation of the present invention, to the variation of the above embodiment, modification, all will drop within the scope of claims of the present invention.

Claims (4)

1. a method of work for MOA testing current in resistance property instrument, is characterized in that comprising the following steps:

(1), simultaneously the sample Leakage Current I of line voltage V and MOA of the CPU of MOA testing current in resistance property instrument, and respectively to line voltage V and W+2 sampling number certificate of Leakage Current I equal interval sampling: f (i), i=0,1 ..., w+1};

(2), described CPU starts the accurate synchronous DFT formula of application from the sampled point i=0 of described line voltage V:

$\left\{\begin{array}{c}{a}_k={2F}_{a_k}^n=\frac{2}{Q}\underset{i=0}{\overset{W}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\cos \left(k\frac{2\mathrm{\&pi;}}{N}i\right)\\ b_k={2F}_{b_k}^n=\frac{2}{Q}\underset{i=0}{\overset{W}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\sin \left(k\frac{2\mathrm{\&pi;}}{N}i\right),\end{array}\right.$ Analyze W+1 data acquisition first-harmonic information

with

Then, described CPU starts the accurate synchronous DFT formula of application from the sampled point i=1 of described line voltage V:

$\left\{\begin{array}{c}{a}_k={2F}_{a_k}^n=\frac{2}{Q}\underset{i=0}{\overset{W+1}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\cos \left(k\frac{2\mathrm{\&pi;}}{N}(i-1)\right)\\ b_k={2F}_{b_k}^n=\frac{2}{Q}\underset{i=0}{\overset{W+1}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\sin \left(k\frac{2\mathrm{\&pi;}}{N}(i-1)\right),\end{array}\right.$ Analyze W+1 data acquisition first-harmonic information

with

Application of formula: $\mathrm{\&mu;}=N\frac{{\mathrm{tg}}^{-1}\left[\frac{F_{a_0}^n\left(1\right)}{F_{b_0}^n\left(1\right)}\right]-{\mathrm{tg}}^{-1}\left[\frac{F_{a_0}^n\left(0\right)}{F_{b_0}^n\left(0\right)}\right]}{2\mathrm{\&pi;}},$ Calculate the frequency drift μ of described line voltage V;

Application of formula: $\left\{\begin{array}{c}{a}_k=\frac{2}{Q}\underset{i=0}{\overset{W}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\cos \left(k\frac{\mathrm{\&mu;}2\mathrm{\&pi;}}{N}i\right)\\ b_k=\frac{2}{Q}\underset{i=0}{\overset{W}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\sin \left(k\frac{\mathrm{\&mu;}2\mathrm{\&pi;}}{N}i\right),\end{array}\right.$ Draw the real part a of the first-harmonic of described line voltage V _kwith imaginary part b _k, then calculate the amplitude of the first-harmonic of described line voltage V $V_1=\sqrt{a_k^2+b_k^2}$ And initial phase angle

(3), described CPU starts the accurate synchronous DFT formula of application from the sampled point i=0 of described Leakage Current I:

$\left\{\begin{array}{c}{a}_k={2F}_{a_k}^n=\frac{2}{Q}\underset{i=0}{\overset{W}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\cos \left(k\frac{2\mathrm{\&pi;}}{N}i\right)\\ b_k={2F}_{b_k}^n=\frac{2}{Q}\underset{i=0}{\overset{W}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\sin \left(k\frac{2\mathrm{\&pi;}}{N}i\right),\end{array}\right.$ Analyze W+1 data acquisition first-harmonic information

with

Then, described CPU applies accurate synchronous DFT formula from the sampled point i=1 of Leakage Current I:

$\left\{\begin{array}{c}{a}_k={2F}_{a_k}^n=\frac{2}{Q}\underset{i=0}{\overset{W+1}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\cos \left(k\frac{2\mathrm{\&pi;}}{N}(i-1)\right)\\ b_k={2F}_{b_k}^n=\frac{2}{Q}\underset{i=0}{\overset{W+1}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\sin \left(k\frac{2\mathrm{\&pi;}}{N}(i-1)\right),\end{array}\right.$

Analyze W+1 data acquisition first-harmonic information

with

Application of formula: $\mathrm{\&mu;}=N\frac{{\mathrm{tg}}^{-1}\left[\frac{F_{a_0}^n\left(1\right)}{F_{b_0}^n\left(1\right)}\right]-{\mathrm{tg}}^{-1}\left[\frac{F_{a_0}^n\left(0\right)}{F_{b_0}^n\left(0\right)}\right]}{2\mathrm{\&pi;}},$ Calculate the frequency drift μ of described Leakage Current I;

Application of formula: $\left\{\begin{array}{c}{a}_k=\frac{2}{Q}\underset{i=0}{\overset{W}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\cos \left(k\frac{\mathrm{\&mu;}2\mathrm{\&pi;}}{N}i\right)\\ b_k=\frac{2}{Q}\underset{i=0}{\overset{W}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{i}f\left(i\right)\sin \left(k\frac{\mathrm{\&mu;}2\mathrm{\&pi;}}{N}i\right),\end{array}\right.$

, draw respectively the real part a of the first-harmonic of described Leakage Current I _kwith imaginary part b _k, then calculate the amplitude of the first-harmonic of described Leakage Current I $I_1=\sqrt{a_k^2+b_k^2}$ And initial phase angle

(4) projected angle of the first-harmonic that, described CPU obtains Leakage Current I according to sciagraphy on the first-harmonic of line voltage V

(5), described CPU obtains the first-harmonic of the resistive Leakage Current of MOA

and output display.

2. the method for work of MOA testing current in resistance property instrument according to claim 1, is characterized in that: described equal interval sampling is according to cycle T and the frequency f of carrying out the ideal signal of frequency analysis, the N point of sampling in one-period, and sample frequency is f _s=Nf, and N>=64.

3. the method for work of MOA testing current in resistance property instrument according to claim 1 and 2, is characterized in that: described sampling W+2 sampling number is according to being to do corresponding selection according to selected integration method, if adopt complexification trapezoidal integration method, W=nN; If adopt complexification rectangular integration method, W=n (N-1); If adopt iterative Simpson integration method, W=n (N-1)/2;

Then according to sample frequency f _s=Nf, acquisition sampled point data sequence f (i), and i=0,1 ..., w+1}, n>=3.

4. the method for work of MOA testing current in resistance property instrument according to claim 3, it is characterized in that: described frequency drift μ obtains according to the fixed relationship of sampling number N in neighbouring sample point first-harmonic phase angle difference and ideal period, frequency drift μ is for revising the frequency f of first-harmonic ₁.