CN105588985A - Dielectric loss on-line accurate measurement method based on phase factor transformation and interpolation - Google Patents

Abstract

The invention relates to a dielectric loss on-line accurate measurement method based on phase factor transformation and interpolation. The method includes following steps of: 1) performing digital sampling on voltages and currents at both ends of electric power capacitive devices, and obtaining discrete sampling values of the voltages and the currents; 2) performing discrete Fourier transform in which a Hanning window is added on the discrete sampling values of the voltages and the currents, and performing phase factor transform on frequency spectra of the voltages and the currents and obtaining new frequency spectra of the voltages and the current; 3) performing three-spectral line superposition and interpolation on fundamental components of the new frequency spectra of the voltages and the currents, and obtaining fundamental phase values of the voltages and the currents; and 4) performing conversion on the obtained fundamental phase values of the voltages and the current, and calculating a dielectric loss angle delta and a dielectric value tan delta. Compared with the prior art, the dielectric loss on-line accurate measurement method based on the phase factor transformation and interpolation is simple and accurate.

Description

A kind of online accurate measurement method of dielectric loss based on phase factor conversion interpolation

Technical field

The present invention relates to the fields of measurement of electric variable, especially relate to a kind of Jie based on phase factor conversion interpolationDamage online accurate measurement method.

Background technology

Dielectric loss angle tangent, as an index of concentrated expression dielectric loss characteristic quality, is to measure and prisonControl the important references amount of various Electric Power Equipment Insulation performances, can reflect apparatus insulatedly make moist, cracking, air gap putThe defects such as electricity are the big events of prevention power system device fault, monitoring equipment insulating properties. In recent years, withThe fast development of electrical equipment state inspection, people more and more pay attention to the line Measurement Technique of dielectric loss, thereforeForm diverse ways. According to the difference of the metering system of dielectric loss and principle, it is two large that its measuring method can be divided intoClass: the one, based on the measuring method of " hardware ", the 2nd, rely on " software " to realize measurement. Based on " hardware "Dielectric loss On-line Measuring Method be mainly to rely on hardware circuit device to realize electric current, the voltage phase difference of insulator arrangementRelatively, as traditional bridge method and document " digitized measurement of dielectric loss angle " (author: Zhao Xiushan, Tan KeHero, Tsing-Hua University's journal, 1996,36 (9): 51-56.) in phase-comparison method etc. at zero point, because it is subject to hardwareAffect greatlyr, certainty of measurement is lower, and dielectric loss angle itself is less, and certainty of measurement is had relatively high expectations, therefore based onThe dielectric loss On-line Measuring Method of " hardware " is less use at present. Rely on the dielectric loss On-line Measuring Method of " software "Typical case be harmonic analysis method, by the voltage and current analog signal at online insulator arrangement two ends is passed through to sensorIn device, then carry out analog-to-digital conversion, obtain the data signal of voltage and current, data signal is carried out to harmonic signalAnalysis can be obtained Dielectric loss angle. Dielectric loss On-line Measuring Method based on frequency analysis is because energy harmonic carcellation is abnormal at presentBecome, direct current biasing, and there is anti-interference and temperature and the more conventional measurement means that becomes.

The core concept of the dielectric loss On-line Measuring Method based on frequency analysis is that voltage, current digital signal are carried outDiscrete Fourier or FFT (DFT/FFT), therefore intrinsic fence effect and the frequency of Fourier transformIt is the key factor that affects dielectric loss measurement precision that spectrum is leaked. Meanwhile, the frequency in power system in dynamic fluctuation,Cause being difficult to voltage, electric current are carried out integer-period sampled, non-synchronous sampling has caused spectrum leakage to eliminate completely.For ubiquitous fence effect in harmonic analysis method and spectrum leakage problem, document is " with adding HanningWindow interpolation Higher-order Sine fitting process is surveyed Dielectric loss angle " (author: Xu Zhi button, rule side becomes, Wang Fochi, Li Heming, heightVoltage Technique, 2007,33 (4): 50-53) having proposed to add Hanning window interpolation measures Dielectric loss angle, has improvedThe real-time of Dielectric loss angle and precision, algorithm has been realized the on-line measurement of dielectric loss, but its angle-measurement accuracy is limited,In high interference and large noise circumstance, measurement result is influenced larger.

Because Dielectric loss angle is generally very little, often between 0.001～0.02rad, easy when it is carried out to on-line measurementBe subject to the impacts such as noise jamming, non-synchronous sampling and nonperiodic signal block. Therefore, seek a kind of high accuracy, anti-The measuring method of interference, real-time is necessary.

Summary of the invention

Object of the present invention be exactly provide in order to overcome the defect that above-mentioned prior art exists a kind of based on phase place because ofThe online accurate measurement method of dielectric loss of son conversion interpolation.

Object of the present invention can be achieved through the following technical solutions:

Based on the online accurate measurement method of dielectric loss of phase factor conversion interpolation, comprise the following steps:

1) voltage to electric power capacitive device two ends, electric current carry out digital sample, obtain the discrete of voltage and currentSampled value;

2) the discrete sampling value of voltage and current is added to the discrete fourier transform after Hanning window, and to itFrequency spectrum is made phase factor and is converted the new frequency spectrum that obtains voltage and current;

3) fundamental component of the new frequency spectrum to voltage and current carries out 3 Spectral Overlapping interpolation respectively, obtain voltage andThe fundamental frequency phase value of electric current;

4) the voltage and current fundamental frequency phase value obtaining is converted, ask for Dielectric loss angle δ and dielectric loss value tan δ.

Described step 1) in voltage discrete sampling value u (m Δ t)_N(m Δ t) with electric current discrete sampling value i_NExpressionFormula is:

Wherein, M is the frequency component number in voltage sampling signal, and P is current sampling signal medium frequency componentNumber, U_iBe the voltage magnitude of i component, I_jBe the current amplitude of j component, f_iBe i componentElectric voltage frequency, f_jBe the power frequency of j component,Be the voltage-phase of i component,It is jThe current phase of component, Δ t is the sampling interval, N is number of samples, m be natural number and m=0,1 ..., N-1.

Described step 2) specifically comprise the following steps:

21) discrete fourier transform discrete sampling value of voltage and current being added after Hanning window is convertedAfter voltage spectrum value X (k) and current spectrum value Y (k):

${\mathrm{\β}}_i=\frac{f_i}{\mathrm{\Δ}f}$

${\mathrm{\β}}_i^{\′}=\frac{f_i^{\′}}{\mathrm{\Δ}f}$

$W\left(\mathrm{\θ}\right)=e^{-\frac{N-1}{N}\mathrm{\π}\mathrm{\θ}}\frac{sin\left(\mathrm{\π}\mathrm{\θ}\right)}{2\mathrm{\π}\mathrm{\θ}(1-{\mathrm{\θ}}^2)}$

Wherein, k is spectral line sequence number, and Δ f is frequency resolution, and W () is Hanning window spectral function, f_i、f_i' beThe electric voltage frequency of i component, power frequency, U_i、I_iBe voltage magnitude, the current amplitude of i component, Be i the voltage-phase factor, the current phase factor that positive frequency component is corresponding,It is iThe voltage-phase factor, the current phase factor that negative frequency components is corresponding, N is number of samples, θ is window spectral functionVariable Factors,For the phase factor of window spectral function, β_i、β′_iBe i component normalized voltage frequency,Normallized current frequency;

22) voltage spectrum value X (k) and current spectrum value Y (k) are taken advantage of to phase factorConversion, obtains newVoltage spectrum valueWith new current spectrum value

β_i＝k_i+σ_i，β′_i＝k_i+σ′_i

$\mathrm{\Δ}\left(k_i\right)=\underset{m=0,m\≠i}{\overset{M}{\Σ}}\mathrm{\Δ}\left(k_m\right),{\mathrm{\Δ}}^{\′}\left(k_i\right)=\underset{m=0,m\≠i}{\overset{M}{\Σ}}{\mathrm{\Δ}}^{\′}\left(k_m\right)$

Wherein, k_iBe i frequency component f_iPeak spectral line sequence number, σ_i、σ′_iBe i frequency component f_i、f_i'Frequency deviation value, Δ (k_i)、Δ′(k_i) be that interference components is to frequency component f_i、f_i' interference superposition value, U_i、I_iBe iThe voltage magnitude of individual component, current amplitude, N is number of samples, β_i、β′_iIt is the normalized voltage of i componentFrequency, normallized current frequency,Be i the voltage-phase factor, the electric current that positive frequency component is correspondingPhase factor.

Described step 3) specifically comprise the following steps:

31) new frequency spectrum is carried out to 3 Spectral Overlapping interpolation, suppress spectrum leakage and eliminate by the stack of adjacent spectra valueFence effect, obtains phase place initial valueFor:

Wherein, arg () is for asking for Circular measure phase function,For spectral line sequence number k_iThe new frequency spectrum of ± 1 correspondenceValue sum,For spectral line sequence number k_iCorresponding new spectrum value,For normalized frequency β_iPhase factor.

32) according to phase place initial valueObtain the voltage fundamental frequency phase value of same period capacitive apparatusWith electric current baseFrequently phase value

Wherein, k₁、k′₁For the peak spectral line sequence number of fundamental voltage, fundamental current,For spectral line sequence number k₁±1Corresponding new voltage spectrum value sum,For spectral line sequence number k '₁The new current spectrum value sum of ± 1 correspondence,For peak spectral line sequence number k₁、k′₁Corresponding new voltage spectrum value, new current spectrum value, For normalization fundamental frequency β₁、β′₁The voltage-phase factor, the current phase factor.

Described step 4) in the expression formula of Dielectric loss angle δ be:

Described electric power capacitive device comprises bushing shell for transformer, coupling capacitor and cable.

Compared with prior art, the present invention has the following advantages:

One, the inventive method is for electric power capacitive device (as bushing shell for transformer, coupling capacitor, cable etc.)Dielectric carries out on-line measurement, can in the situation that not having a power failure, carry out analysis to measure by simple sampled signal,The bridge method of comparing the test that has a power failure has more operability and practical significance.

Two, the inventive method has higher authenticity and flexibility, and its automatization level is higher, can establish completelyDetermine automation mechanized operation, for electrical equipment online supervision provides good method, be able to measure at any time and notCarry out discontinuously continuous measurement.

Three, the inventive method converts interpolation by phase factor and can suppress spectrum leakage and eliminate fence effect, logicalCross adjacent Spectral Overlapping and eliminated the interference of other component, principle simple possible, compares all the other harmonic analysis method toolsThere are higher certainty of measurement and noiseproof feature, can find in time, exactly that the globality of Electric Power Equipment Insulation device lacksFall into or compared with centrality local defect, the generation of minimizing accident.

Brief description of the drawings

Fig. 1 is dielectric loss value measuring circuit schematic diagram;

Fig. 2 is Dielectric loss angle polar plot;

Fig. 3 is overall flow figure of the present invention;

Fig. 4 is time-domain diagram and the frequency domain figure of voltage signal.

Detailed description of the invention

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

Embodiment:

In Fig. 1, the circuit reduction schematic diagram of electric power capacitive device, has provided the relation between current vector.

In Fig. 2, the relation between power equipment voltage, current phase and Dielectric loss angle δ, by measuring voltage,Current first harmonics phase angle calculates Dielectric loss angle δ.

In Fig. 3, comprise overall flow figure of the present invention, comprised the following steps:

A, the voltage to capacitive apparatus two ends, electric current carry out digital sample, obtain voltage, electric current discrete sampling value;

B, voltage, the current signal of sampling are added to FFT after Hanning window, and to its frequency spectrum do phase place because ofSon conversion obtains voltage, the new frequency spectrum of electric current;

C, the fundamental component of new frequency spectrum is carried out to 3 Spectral Overlapping interpolation, obtain respectively voltage, electric current fundamental frequency phase placeValue;

D, the voltage of gained, electric current fundamental frequency phase value are converted, ask for Dielectric loss angle δ and dielectric loss value tan δ.

Table 1 is the Dielectric Loss Angle result of l-G simulation test gained. Wherein method of the present invention (method 1) and document" with adding Hanning window interpolation Higher-order Sine fitting process survey Dielectric loss angle " method (method 2), method 2 suppose mutuallyMethod 1 error has increased 1 times.

Table 1 Dielectric Loss Angle result

Visible, in signal, contain under harmonic wave, a harmonic wave and very noisy disturbed condition, and asynchronous adoptingUnder the spectrum leakage acting in conjunction that sample causes, the inventive method has showed higher certainty of measurement and anti-noise ability, toolThere are reliability and accuracy, can be used for the measurement of actual survey dielectric loss value.

Below technical scheme of the present invention is elaborated from principle angle:

1, the electric current and voltage digital sample model of capacitive apparatus

Capacitive apparatus both end voltage and electric current to on-line operation carry out digitized sampling, obtains voltage and currentDiscrete sample signals value:

In formula, u, i are the voltage and current signal of sampling, and M, P are that voltage, current sampling signal medium frequency divideAmount number, voltage and current amplitude, frequency and the phase place of the corresponding a certain component of Ui and Ij, fi and fj, i and j,Δ t is the sampling interval, m=0,1,, N-1, N is number of samples.

2, to the factor transformation of sampled signal spectral phase

From formula (1) and formula (2), voltage and current sample signal has similar expression-form, withVoltage signal is that example is analyzed. Formula (1) is added to Hanning window Spectrum Conversion to be obtained:

X in formula (k) is the voltage spectrum value that spectral line sequence number k is corresponding, β_i＝f_i/ Δ f, Δ f is frequency resolution, W ()For Hanning window spectral function, wherein

Frequency spectrum U (k) to formula (3) takes advantage of phase factorConversion, obtains new spectrum value:

$\stackrel{\‾}{X}\left(k\right)=X\left(k\right)\·e^{j\frac{N-1}{N}\mathrm{\π}k}---\left(4\right)$

Formula (4) is reduced to following form:

β in formula_i＝k_i+σ_i，k_i、σ_iFor frequency component f_iPeak spectral line sequence number and frequency deviation value, σ_i∈(-0.5,0.5]，For interference components is to f_iThe interference superposition value of component, each Δ (k_m) close, the phase place of amplitudeOn the contrary.

3, new frequency spectrum is carried out to 3 spectral line interpolations

Choose 3 spectral line ki, ki ± 1 at the spectral line place, peak of component fi to be analyzed and carry out interpolation processing, its widthValue scale factor is defined as:

${\mathrm{\α}}_i=\frac{|\stackrel{\‾}{X}\left(k_i\right)+\stackrel{\‾}{X}(k_i-1)|}{|\stackrel{\‾}{X}\left(k_i\right)+\stackrel{\‾}{X}(k_i+1)|}---\left(6\right)$

Formula (5) substitution formula (6) abbreviation is obtained:

${\mathrm{\α}}_i=\frac{2-{\mathrm{\σ}}_i}{2+{\mathrm{\σ}}_i}---\left(7\right)$

The anti-frequency deviation value solving in formula (7):

${\mathrm{\σ}}_i=2\frac{\left|\stackrel{\‾}{X}(k_i+1)\right|-\left|\stackrel{\‾}{X}(k_i-1)\right|}{|\stackrel{\‾}{X}(k_i-1)+2\stackrel{\‾}{X}\left(k_i\right)+\stackrel{\‾}{X}(k_i+1)|}---\left(8\right)$

Respective frequencies f_iThe unit frequency values of component:

β_i＝k_i+σ_i(9)

On the basis of formula (8), formula (9), structure k_i、k_iThe spectral overlay value at ± 1 place is:

Formula (8) is updated in formula (10), and the phase value that obtains a certain component of voltage is:

In formula, arg () represents to ask for Circular measure phase place.

4, ask for dielectric loss value

According to formula (11) can be in the hope of capacitive apparatus fundamental voltage phase valueBecause electric current has and electricityPress similar discrete expression, in like manner can obtain same period capacitive apparatus fundamental current phase value and beCauseThis is according to the Dielectric Loss Angle principle of Fig. 1 and Fig. 2, obtains Dielectric loss angle to be:

Therefore, the Dielectric loss angle tangent value of reflection dielectric loss characteristic quality is:

Dielectric loss value ask for flow chart as shown in Figure 3. The inventive method is laggard by the phase factor of change frequency spectrumRow 3 spectral line interpolations, have been eliminated by non-synchronous sampling and non-integer-period signal and have been cut by the stack interpolation of adjacent spectral lineThe disconnected spectrum leakage causing and fence effect impact, promoted the certainty of measurement of phase value, finally make Dielectric loss angle andThe certainty of measurement of dielectric loss value is greatly improved.

Voltage, the current signal data length of setting the sampling of electric power capacitive device two ends are 10 cycles of fundamental frequency,Sample frequency fs=12800Hz, wherein in signal, contain 3 times and 78.2Hz between harmonic wave, detail parameters is as table 2Shown in, measurement environment is the white Gaussian noise environment of 20dB signal to noise ratio.

Table 2 voltage, current parameters theoretical value

Shown in his-and-hers watches 1, signal carries out spectrum analysis, and its voltage signal time-domain diagram and spectrogram are as shown in Figure 4. Profit" survey dielectric loss with adding Hanning window interpolation Higher-order Sine fitting process with method of the present invention (method 1) and documentAngle " to carry out comparing result as shown in table 3 for method (method 2).

Table 3 Dielectric Loss Angle result

In table 3, method 1 is owing to having carried out phase factor conversion interpolation, and its fundamental voltage phase place and current phase are surveyedAccuracy of measurement is higher, measures relative error and is respectively-0.024% ,-0.004%, and Dielectric Loss Angle error is-0.571%; The fundamental voltage phase place of method 2 and current phase measure relative error be respectively-1.102%,-0.046%, Dielectric Loss Angle error is 1.143%, and phase ratio method 1 error has increased 1 times. Meanwhile, signalThe non-strict 50Hz of fundamental frequency contains under harmonic wave, a harmonic wave and very noisy disturbed condition in signal, withAnd under the spectrum leakage acting in conjunction that causes of non-synchronous sampling, the inventive method showed higher certainty of measurement andAnti-noise ability, has reliability and accuracy, can be used for the measurement of actual survey dielectric loss value.

Claims (6)

1. the online accurate measurement method of dielectric loss based on phase factor conversion interpolation, is characterized in that, comprisesFollowing steps:

1) voltage to electric power capacitive device two ends, electric current carry out digital sample, obtain the discrete of voltage and currentSampled value;

2) the discrete sampling value of voltage and current is added to the discrete fourier transform after Hanning window, and to itFrequency spectrum is made phase factor and is converted the new frequency spectrum that obtains voltage and current;

3) fundamental component of the new frequency spectrum to voltage and current carries out 3 Spectral Overlapping interpolation respectively, obtain voltage andThe fundamental frequency phase value of electric current;

4) the voltage and current fundamental frequency phase value obtaining is converted, ask for Dielectric loss angle δ and dielectric loss value tan δ.

2. the online accurately measurement side of a kind of dielectric loss based on phase factor conversion interpolation according to claim 1Method, is characterized in that, described step 1) in voltage discrete sampling value u (m Δ t)_NWith electric current discrete sampling valuei(mΔt)_NExpression formula be:

Wherein, M is the frequency component number in voltage sampling signal, and P is current sampling signal medium frequency componentNumber, U_iBe the voltage magnitude of i component, I_jBe the current amplitude of j component, f_iBe i componentElectric voltage frequency, f_jBe the power frequency of j component,Be the voltage-phase of i component,It is jThe current phase of component, Δ t is the sampling interval, N is number of samples, m be natural number and m=0,1 ..., N-1.

3. the online accurately measurement side of a kind of dielectric loss based on phase factor conversion interpolation according to claim 1Method, is characterized in that, described step 2) specifically comprise the following steps:

21) discrete fourier transform discrete sampling value of voltage and current being added after Hanning window is convertedAfter voltage spectrum value X (k) and current spectrum value Y (k):

${\mathrm{\β}}_i=\frac{f_i}{\mathrm{\Δ}f}$

${\mathrm{\β}}_i^{\′}=\frac{f_i^{\′}}{\mathrm{\Δ}f}$

$W\left(\mathrm{\θ}\right)=e^{-j\frac{N-1}{N}\mathrm{\π}\mathrm{\θ}}\frac{sin\left(\mathrm{\π}\mathrm{\θ}\right)}{2\mathrm{\π}\mathrm{\θ}(1-{\mathrm{\θ}}^2)}$

Wherein, k is spectral line sequence number, and Δ f is frequency resolution, and W () is Hanning window spectral function, f_i、f′_iForThe electric voltage frequency of i component, power frequency, U_i、I_iBe voltage magnitude, the current amplitude of i component, Be i the voltage-phase factor, the current phase factor that positive frequency component is corresponding,Be respectivelyI the voltage-phase factor, the current phase factor that negative frequency components is corresponding, N is number of samples, θ is window spectrum letterThe Variable Factors of number,For the phase factor of window spectral function, β_i、β′_iIt is the normalized voltage of i componentFrequency, normallized current frequency;

22) voltage spectrum value X (k) and current spectrum value Y (k) are taken advantage of to phase factorConversion, obtains newThe voltage spectrum value of frequency spectrumWith current spectrum value

β_i＝k_i+σ_i，β′_i＝k_i+σ′_i

$\mathrm{\Δ}\left(k_i\right)=\underset{m=0,m\≠i}{\overset{M}{\Σ}}\mathrm{\Δ}\left(k_m\right),{\mathrm{\Δ}}^{\′}\left(k_i\right)=\underset{m=0,m\≠i}{\overset{M}{\Σ}}{\mathrm{\Δ}}^{\′}\left(k_m\right)$

Wherein, k_iBe i frequency component f_iPeak spectral line sequence number, σ_i、σ′_iBe i frequency component f_i、f′_i'sFrequency deviation value, Δ (k_i)、Δ′(k_i) be that interference components is to frequency component f_i、f′_iInterference superposition value, U_i、I_iBe iThe voltage magnitude of individual component, current amplitude, N is number of samples, β_i、β′_iIt is the normalized voltage of i componentFrequency, normallized current frequency,Be i the voltage-phase factor, the electric current that positive frequency component is correspondingPhase factor.

4. the online accurately measurement side of a kind of dielectric loss based on phase factor conversion interpolation according to claim 1Method, is characterized in that, described step 3) specifically comprise the following steps:

31) new frequency spectrum is carried out to 3 Spectral Overlapping interpolation, suppress spectrum leakage and eliminate by the stack of adjacent spectra valueFence effect, obtains phase place initial valueFor:

Wherein, arg () is for asking for Circular measure phase function,For spectral line sequence number k_iThe new frequency spectrum of ± 1 correspondenceValue sum,For spectral line sequence number k_iCorresponding new spectrum value,For normalized frequency β_iPhase factor.

32) according to phase place initial valueObtain the voltage fundamental frequency phase value of same period capacitive apparatusWith electric current baseFrequently phase value

Wherein, k₁、k′₁For the peak spectral line sequence number of fundamental voltage, fundamental current,For spectral line sequence number k₁±1Corresponding new voltage spectrum value sum,For spectral line sequence number k '₁The new current spectrum value sum of ± 1 correspondence,For peak spectral line sequence number k₁、k′₁Corresponding new voltage spectrum value, new current spectrum value, For normalization fundamental frequency β₁、β′₁The voltage-phase factor, the current phase factor.

5. the online accurately measurement side of a kind of dielectric loss based on phase factor conversion interpolation according to claim 4Method, is characterized in that, described step 4) in the expression formula of Dielectric loss angle δ be:

6. the online accurately measurement side of a kind of dielectric loss based on phase factor conversion interpolation according to claim 1Method, is characterized in that, described electric power capacitive device comprises bushing shell for transformer, coupling capacitor and cable.