CN102156250A - Dielectric loss factor measurement method based on equivalent model - Google Patents

Abstract

The invention discloses a dielectric loss factor measurement method based on an equivalent model, belonging to the technical field of electrical equipment test. The method comprises the following steps: measuring a voltage signal and a current signal on equipment insulation to obtain signal frequency and subharmonic waves; and calculating the dielectric loss factor in that way that the insulation is equivalent to two models, namely parallel connection of a resistor and a capacitor and series connection of a resistor and a capacitor. By the method, the signal frequency fluctuation and the measurement error of the dielectric loss factor caused by the existence of the harmonic wave can be inhibited; and the method has strong anti-interfere capacity and high calculation accuracy.

Description

A kind of dielectric dissipation factor measuring method based on equivalent model

Technical field

The invention belongs to the electrical equipment technical field of measurement and test, relate in particular to a kind of dielectric dissipation factor measuring method based on equivalent model.

Background technology

Dielectric dissipation factor is the ratio of medium total active power and total reactive power under the sinusoidal alternating electric field action, active power is usually by diminishing polarization and the loss that causes of insulation resistance is formed, if the insulation of electrical equipment exist make moist, situations such as penetrability conductive channel, bubble ionization, layering, shelling, aging, deterioration, dielectric insulation resistance descended, diminished the polarization increase this moment, and corresponding dielectric loss will increase.Therefore, the measuring media loss factor can effectively reflect the situation of insulation of electrical installation.For high voltage electric equipment, the damage of insulation is its main cause that breaks down.According to statistics, account for 23.1% of accident total amount by the direct power grid accident that causes of the damage of insulation of electrical installation.Therefore, the detection of electrical equipment dielectric dissipation factor has important in theory meaning and economic worth to the safe operation of electric system.

Under the normal condition, it is very little that the loss in the insulation of electrical installation is idle relatively, so the dielectric dissipation factor value is less, so extraneous interference exerts an influence to its measurement result easily, the influence of the fluctuation of its medium frequency is comparatively outstanding.Stipulate according to electric system, the frequency of signal allows to change in 49.5～50.5 hertz of scopes, if in the time of can't obtaining 50 hertz of frequency information and frequency departures and acquire a certain degree, conventional Fourier algorithm etc. all exists than mistake when the calculation medium loss factor.

Summary of the invention

Because frequency jitter causes the bigger deficiency of the error of calculation, the present invention proposes a kind of dielectric dissipation factor measuring method at the existing calculation medium loss factor method of mentioning in the above-mentioned background technology based on equivalent model.

Technical scheme of the present invention is based on the dielectric dissipation factor measuring method of equivalent model, to it is characterized in that described method comprises the following steps:

Step 1: obtain voltage signal and current signal on apparatus insulated;

Step 2:, obtain the frequency and the signal each harmonic of voltage signal and current signal according to the data of step 1;

Step 3: with the apparatus insulated equivalent-circuit model that is thought of as, utilize the linear least-squares algorithm to obtain the resistance in the model, capacitance parameter, directly calculate then and obtain dielectric dissipation factor.

Described voltage signal obtains by voltage transformer (VT) or capacitive divider.

Described current signal is by the centre path current sensor or seal in the acquisition of formula current sensor.

The process of described picked up signal frequency and signal each harmonic is:

Earlier with adding Hanning window interpolation Fourier algorithm picked up signal frequency, if signal frequency in 49.9～50.1 hertz of scopes, then obtains the each harmonic of voltage signal and current signal with fast Fourier algorithm; Otherwise according to the each harmonic of the signal frequency that obtains with the desirable sample frequency method picked up signal of correction.

Described equivalent-circuit model is resistance and electric capacity parallel connection.

Described equivalent-circuit model is resistance and capacitances in series.

The computing formula of described dielectric dissipation factor is:

When resistance and electric capacity were in parallel, computing formula was: tg δ=1/ ω RC;

Wherein: tg δ is a dielectric dissipation factor; ω is an angular frequency; R is the equivalent resistance of insulation; C is the equivalent capacity of insulation.

The computing formula of described dielectric dissipation factor is:

When resistance and capacitances in series, computing formula is: tg δ=ω RC.

Beneficial effect of the present invention comprises:

(1) accuracy height

Because the inventive method when the calculation medium loss factor, has not only been considered voltage and current signal fundametal compoment, and has been considered the each harmonic component, reduced and do not considered the error of calculation that harmonic component causes, the result who obtains is more accurately with reliable;

(2) can accurately obtain equivalent resistance and electric capacity

The resistance of capacitance type equipment insulation and electric capacity also are its important parameters, obtain its resistance value and capacitance and help the capacitance type equipment insulation state is monitored, to safeguard its operation better;

(3) anti-frequency jitter and harmonic interference ability are strong

Owing to adopted the Fourier algorithm of windowed interpolation during to the frequency departure ideal value, so the present invention can suppress the signal frequency fluctuation and there is the error that measurement causes to dielectric dissipation factor in harmonic wave, antijamming capability is stronger.

Description of drawings

Fig. 1 is a process flow diagram of the present invention;

Fig. 2 is the result of casing leak electric current with the match of series connection simplified model;

Fig. 3 is the result of casing leak electric current with simplified model match in parallel.

Embodiment

Below in conjunction with accompanying drawing, preferred embodiment is elaborated.Should be emphasized that following explanation only is exemplary, rather than in order to limit the scope of the invention and to use.

Step of the present invention is as shown in Figure 1:

1. utilize voltage transformer (VT) or capacitive divider to obtain to put on voltage signal on the capacitance type equipment insulation, utilize the centre path current sensor or seal in the formula current sensor to obtain the current signal that flows through in the capacitance type equipment insulation.

2. utilize windowed interpolation Fourier algorithm picked up signal frequency, utilize fast Fourier algorithm then or revise desirable sample frequency method picked up signal each harmonic.

2.1 the frequency of picked up signal

This method is used and is added Hanning window interpolation Fourier algorithm picked up signal frequency, and principle is as follows:

If the discrete Fourier transformation DFT of signal x (n) (Discrete Fourier Transformer) gained result is X (n), add then that the discrete Fourier transformation DFT gained result of signal is behind the Hanning window:

$X_w\left(n\right)=\frac{1}{2}X\left(n\right)-\frac{1}{4}X(n-1)-\frac{1}{4}X(n+1)---\left(1\right)$

If frequency resolution is Δ f, then fundamental frequency f can be expressed as:

f＝(k+Δk)Δf (2)

In the formula: k is an integer; Δ k is a decimal.

The approximate treatment of Δ k is as follows:

Can calculate the frequency of acquisition according to formula (2).Because sample frequency is a definite value normally, it is not the integral multiple of signal frequency, can't directly intercept according to sampling gained signal and obtain partly to obtain complete cycle each harmonic;

2.2 obtain the harmonic wave of voltage and current signal

Discrete Fourier transformation is handled is the signal that adds behind the rectangular window, and according to Fourier transform principle, the time domain product equals frequency domain convolution, has caused signal frequency spectrum leakage to other frequency range, Here it is spectrum leakage.When signal frequency is not on the frequency discrimination point in discrete Fourier transformation, directly use Fourier transform gained result and original signal different, Here it is fence effect.Under the synchronized sampling situation, the Fourier transform gained frequency of correspondence as a result just is a signal place frequency, and spectrum leakage and fence effect just do not manifest.Fourier transform gained frequency is not the actual frequency of signal when non-synchronous sampling, has just produced spectrum leakage and fence effect.

$s\left(t\right)=\underset{k=0}{\overset{N}{\mathrm{\Σ}}}{s}_k\sin (\mathrm{k\ωt}+{\mathrm{\θ}}_k)---\left(4\right)$

In the formula: N is the high reps of harmonic wave; s _kIt is k subharmonic amplitude; ω is a signal first-harmonic angular frequency; θ _kIt is the initial phase angle of k subharmonic.

According to Taylor series expansion:

sin(kωt+θ _k)＝sin(kωt ₀+θ _k)+kω(t-t ₀)cos(kωt ₀+θ _k)+o ¹(t-t ₀)(5)

When the relatively higher hamonic wave frequency of sample frequency is big, 0 ¹(t-t ₀) less can ignoring, formula (5) just becomes:

sin(kωt+θ _k)＝sin(kωt ₀+θ _k)+kω(t-t ₀)cos(kωt ₀+θ _k)

So,

s(t)＝s(t ₀)+a(t-t ₀) (6)

In the formula:

$a=\underset{k=0}{\overset{N}{\mathrm{\Σ}}}{s}_k\mathrm{k\ω}\cos \left(\mathrm{k\ω}{t}_0\right)---\left(7\right)$

Work as o ¹(t-t ₀) during less can ignoring, can think that s (t) is around t ₀In the distribution from formula (6) more for oral administration, owing to do not know the each harmonic component, can obtain the value of a in the formula (6) with linear fitting, just can obtain t according to formula (6) again ₀The value of neighbor point.

After having determined interpolation formula, need to obtain revised sample frequency and sampling number, the original signal sequence could be modified to the sequence that meets the synchronized sampling requirement like this.If f _rFundamental frequency for signal reality; f _sSample frequency for reality; f _SiBe desirable sample frequency; N is that actual samples is counted; N _iBe desirable sampling number, need make f _SiAnd N _iTwo formulas could satisfy the requirement of synchronized sampling below satisfying:

f _si＝k ₁f _r (8)

N _i＝k ₂f _si/f _r (9)

In the formula: k ₁, k ₂Be positive integer; Require f simultaneously _SiAnd N _iAs far as possible near f _sAnd N.

The present invention adopts linear interpolation to obtain the signal value corresponding with approximate ideal sample frequency point, obtains each harmonic with Fourier transform then.

3. the acquisition of dielectric dissipation factor

This method is considered the equivalent resistance and the equivalent capacity of insulation in two kinds of situation:

3.1 the least square model of capacitance-resistance parallel connection

If resistance and electric capacity are respectively R and C in the parallel model, after putting on voltage in the insulation, current signal discretize, be respectively u (n), i (n), n=0,1 ..., N-1, signal first-harmonic angular frequency is ω, when fundamental frequency during near 50 hertz, directly use Fourier algorithm picked up signal harmonic component, otherwise with revising desirable sample frequency method.Obtaining direct current, first-harmonic, the second harmonic of voltage signal, current signal, is U (n) and I (n) up to the M order harmonic components, n=0, and 1,2 ..., M, then following equation is set up:

U(n)(1/R+jnωC)＝I(n)，n＝0，1，2，...，M (10)

The real part and the imaginary part of formula (10) left and right sides should equate then have respectively:

$\frac{\mathrm{real}\left(U\left(n\right)\right)}{R}-\mathrm{n\ωimag}\left(U\left(n\right)\right)C=\mathrm{real}\left(I\left(n\right)\right)$

$\frac{\mathrm{imag}\left(U\left(n\right)\right)}{R}+\mathrm{n\ωreal}\left(U\left(n\right)\right)C=\mathrm{imag}\left(I\left(n\right)\right)---\left(11\right)$

In the formula: n=0,1,2 ..., M, real and imag obtain real and imaginary part respectively.

Have according to the principle of least square:

$E=\frac{1}{2}\underset{n=0}{\overset{M}{\mathrm{\Σ}}}{[\frac{\mathrm{real}\left(U\left(n\right)\right)}{R}-\mathrm{n\ωimag}\left(U\left(n\right)\right)C-\mathrm{real}\left(I\left(n\right)\right)]}^2$

$+\frac{1}{2}\underset{n=0}{\overset{M}{\mathrm{\Σ}}}{[\frac{\mathrm{imag}\left(U\left(n\right)\right)}{R}+\mathrm{n\ωreal}\left(U\left(n\right)\right)C-\mathrm{imag}\left(I\left(n\right)\right)]}^2$

In the formula: resistance R, capacitor C are for treating the match variable.

Following formula is the nonlinear function about R, C, belongs to the non-linear least square problem, can adopt the civilian Burger of row-Ma Kuaerte algorithm (Levenberg-Marquardt) optimization, but calculated amount is relatively large.If but regard 1/R as variable, then following formula is the linear least-squares problem, thus the iterative computation process of having avoided nonlinear least square method to need has reduced the programming difficulty when greatly having accelerated computing velocity.

Formula (11) has after being converted into the form of matrix:

U _MZ＝I _M(12)

In the formula:

$U_M=\left[\begin{array}{cc}\mathrm{real}\left(U\left(0\right)\right)& 0\\ \mathrm{real}\left(U\left(1\right)\right)& -\mathrm{\ωimag}\left(U\left(1\right)\right)\\ \mathrm{imag}\left(U\left(1\right)\right)& -\mathrm{\ωreal}\left(U\left(1\right)\right)\\ \mathrm{real}\left(U\left(2\right)\right)& -2\mathrm{\ωimag}\left(U\left(2\right)\right)\\ \mathrm{imag}\left(U\left(2\right)\right)& 2\mathrm{\ωreal}\left(U\left(2\right)\right)\\ M& M\\ \mathrm{real}\left(U\left(M\right)\right)& -\mathrm{M\ωimag}\left(U\left(M\right)\right)\\ \mathrm{imag}\left(U\left(M\right)\right)& \mathrm{M\ωreal}\left(U\left(M\right)\right)\end{array}\right];$ $Z=\left[\begin{array}{c}\frac{1}{R}\\ C\end{array}\right];$ $I_M=\left[\begin{array}{c}\mathrm{real}\left(I\left(0\right)\right)\\ \mathrm{real}\left(I\left(1\right)\right)\\ \mathrm{imag}\left(I\left(1\right)\right)\\ \mathrm{real}\left(I\left(2\right)\right)\\ \mathrm{imag}\left(U\left(2\right)\right)\\ M\\ \mathrm{real}\left(I\left(M\right)\right)\\ \mathrm{imag}\left(I\left(M\right)\right)\end{array}\right].$

Z is a variable in the following formula, and according to the linear least-squares principle, the optimum solution of resistance and electric capacity is:

Z＝(U _M ^TU _M) ^-1U _M ^TI _M (13)

Resistance, electric capacity are separated and are R=1/Z (1), C=Z (2).If sampling time sequence t (n)=n/f _s, n=0,1 ..., N-1, f _sBe sample frequency, then get match gained current signal and be according to resistance, electric capacity, voltage signal:

$i_1\left(n\right)=\frac{u\left(n\right)}{R}+\underset{k=1}{\overset{M}{\mathrm{\Σ}}}[-\mathrm{k\ωCreal}\left(\frac{2U\left(k\right)}{N}\right)]\sin \left(\mathrm{k\ωt}\left(n\right)\right)-\mathrm{k\ωCimag}(2U\left(k\right)/N)\cos \left(\mathrm{k\ωt}\left(n\right)\right)---\left(14\right)$

The gained dielectric dissipation factor is:

tgδ＝1/ωRC (15)

3.2 the least square model of capacitance-resistance series connection

Have following formula to set up according to the series connection equivalent model:

I(n)(R-j/(nωC))＝U(n)，n＝0，1，2，...，M (16)

Set up respectively according to real part in the following formula and imaginary part:

$\mathrm{real}\left(I\left(n\right)\right)R+\frac{\mathrm{imag}\left(I\left(n\right)\right)}{\mathrm{n\ωC}}=\mathrm{real}\left(U\left(n\right)\right)---\left(17\right)$

$\mathrm{imag}\left(I\left(n\right)\right)R-\frac{\mathrm{real}\left(I\left(n\right)\right)}{\mathrm{n\ωC}}=\mathrm{imag}\left(U\left(n\right)\right)$

In the formula: n=0,1,2 ..., M.

Formula (17) has after being converted into the form of matrix:

I _MZ＝U _M (18)

In the formula: $I_M=\left[\begin{array}{cc}\mathrm{real}\left(I\left(1\right)\right)& \frac{\mathrm{imag}\left(I\left(1\right)\right)}{\mathrm{\ω}}\\ \mathrm{imag}\left(I\left(1\right)\right)& -\frac{\mathrm{real}\left(I\left(1\right)\right)}{\mathrm{\ω}}\\ \mathrm{real}\left(I\left(2\right)\right)& \frac{\mathrm{imag}\left(I\left(2\right)\right)}{2\mathrm{\ω}}\\ \mathrm{imag}\left(I\left(2\right)\right)& -\frac{\mathrm{real}\left(I\left(2\right)\right)}{2\mathrm{\ω}}\\ M& M\\ \mathrm{real}\left(I\left(M\right)\right)& \frac{\mathrm{imag}\left(I\left(M\right)\right)}{\mathrm{M\ω}}\\ \mathrm{imag}\left(I\left(M\right)\right)& -\frac{\mathrm{real}\left(I\left(M\right)\right)}{\mathrm{M\ω}}\end{array}\right];$ $Z=\left[\begin{array}{c}R\\ \frac{1}{C}\end{array}\right];$ $U_M=\left[\begin{array}{c}\mathrm{real}\left(U\left(1\right)\right)\\ \mathrm{imag}\left(U\left(1\right)\right)\\ \mathrm{real}\left(U\left(2\right)\right)\\ \mathrm{imag}\left(U\left(2\right)\right)\\ M\\ \mathrm{real}\left(U\left(M\right)\right)\\ \mathrm{imag}\left(U\left(M\right)\right)\end{array}\right].$

Z is a variable to be optimized in the following formula, if with 1/C but not C regards variable as, then formula (18) becomes the linear least-squares problem, and the optimum solution of resistance and electric capacity is:

Z＝(I _M ^TI _M) ^-1I _M ^TU _M (19)

Then resistance, electric capacity are separated and are R=Z (1), C=1/Z (2).Getting match gained current signal according to resistance, electric capacity, voltage signal is:

$i_1\left(n\right)=\underset{k=1}{\overset{M}{\mathrm{\Σ}}}[\frac{-\mathrm{k\ωC}}{1+{\left(\mathrm{k\ωRC}\right)}^2}\mathrm{real}\left(\frac{2U\left(k\right)}{N}\right)+\frac{-R{\left(\mathrm{k\ωC}\right)}^2}{1+{\left(\mathrm{k\ωRC}\right)}^2}\mathrm{imag}\left(\frac{2U\left(k\right)}{N}\right)]\sin \left(\mathrm{k\ωt}\left(n\right)\right)$

$+\underset{k=1}{\overset{M}{\mathrm{\Σ}}}[\frac{R{\left(\mathrm{k\ωC}\right)}^2}{1+{\left(\mathrm{k\ωRC}\right)}^2}\mathrm{real}\left(\frac{2U\left(k\right)}{N}\right)-\frac{\mathrm{k\ωC}}{1+{\left(\mathrm{k\ωRC}\right)}^2}\mathrm{imag}\left(\frac{2U\left(k\right)}{N}\right)]\cos \left(\mathrm{k\ωt}\left(n\right)\right)---\left(20\right)$

The gained dielectric dissipation factor is:

tgδ＝ωRC (21)

Experimental verification:

It is 10 kilovolts power-frequency voltage that one 110 kilovolts of covers are applied effective value on the pipe insulations, voltage signal obtains by capacitive divider, current signal in the insulation obtains by the noninductive resistance that seals between sleeve pipe low pressure end and the ground wire, and the gained two paths of signals all inserts Tyke TDS2024 oscillograph.Choose one group wantonly and gather gained voltage, current signal, carry out match, get primary current signal, match gained current signal respectively as Fig. 2, shown in Figure 3 with capacitance-resistance series connection and simplification dielectric Type Equivalent Circuit Model in parallel.

Annotate: the reality/dotted line among Fig. 2 (1), Fig. 3 (1) is represented measurement/match gained current signal.

By Fig. 2, Fig. 3 as can be known, no matter be capacitance-resistance series connection equivalent model or capacitance-resistance equivalent model in parallel, the current signal on the cover of the match preferably pipe insulation, but by contrast, the parallel model fitting precision is wanted a little higher than series connection model.To the leakage current of other insulation of electrical installation, also verified above analysis as the match of insulator leakage current under the drying regime, good fitting effect is that the accurate calculating of subsequent medium loss factor is laid a good foundation.

Measured 27 groups of voltages and leakage current data, the average that parallel model obtains equivalent resistance and equivalent capacity is respectively 160.7 megohms and 144.6 pico farads, and standard deviation is respectively 0.6 megohm and 0.07 pico farad; The average that the series connection model obtains equivalent resistance and equivalent capacity is respectively 2.87 megohms and 147.6 pico farads, and standard deviation is respectively 9153 ohm and 0.09 pico farad, and stability is very high.Usually, insulation is making moist, is having penetrability conductive channel or discharge back insulation resistance to descend, and the back electric capacity that makes moist simultaneously can increase, therefore can be as a reference quantity of insulation status according to equivalent resistance and electric capacity.

Insulation with the non-simplification circuit model of dielectric artificial capacitor type equipment is an example, produces discrete voltage and current signal by emulation mode, and the dielectric dissipation factor actual value is 1.16 * 10 in the time of 50 hertz ^-2(the dielectric dissipation factor actual value changed less than 1% when frequency changed in 49.5～50.5 hertz of scopes), voltage signal 2,3 subharmonic are 0.03,0.04 with the fundamental voltage amplitude ratio, signal frequency is got 5 points in 49.5～50.5 hertz of scopes, sample frequency is chosen as 5 KHz, sampling time length is 0.1 second, quantization digit is 14, adopts based on Fourier algorithm and the inventive method calculation medium loss factor, and the error of gained dielectric dissipation factor is as shown in the table.

Following two kinds of method gained Error Absolute Value/10 of table 1 different frequency ^-5

By table 1 as seen, with the increase of 50 hertz of degree of frequency departure, the Fourier algorithm error increases, and maximum error can reach 1064 * 10 ^-5, average error also reaches 579 * 10 when frequency departure is 0.5 hertz ^-5, this error is greater than the dielectric dissipation factor value that present capacitance type equipment allows probably.What the present invention proposed has higher degree of accuracy based on capacitance-resistance series connection/parallel model, is 12 * 10 based on the max value of error of parallel model method ^-5, the max value of error of series connection model method is 26.5 * 10 ^-5, all more much smaller than true dielectric dissipation factor value, precision should be able to meet the demands.At the signal under different frequency, the initial phase, parallel model obtains equivalent resistance and the equivalent capacity average is respectively 1001 megohms and 272.0 pico farads, and standard deviation is respectively 6.73 megohms and 0.01 pico farad; The series connection model obtains equivalent resistance and the equivalent capacity average is respectively 0.13 megohm and 272.0 pico farads, and standard deviation is respectively 1231 ohm and 2.01 pico farads, all has good stability.

With resistance and capacity cell series connection artificial capacitor type equipment is example, by AWG (Arbitrary Waveform Generator) Agilent33120A produce that peak value is about 10 volts, frequency is 49.5～50.5 hertz sinusoidal voltage, each Frequency point is measured 10 groups of signals, sample frequency is 25 KHz, sampling number is 2500, and it is as follows with frequency change that Fourier algorithm and the inventive method obtain dielectric dissipation factor.

Dielectric dissipation factor result of calculation/10 of table 2 measured signal ^-2

From finding that according to the data the table 2 three kinds of method gained results are close, reliable in the time of 50 hertz.But increase along with the frequency departure degree, the Fourier algorithm error also increases gradually, the gained dielectric dissipation factor is near 3 times of original value during to 49.5 hertz, and during to 50.5 hertz even negative value can occur, obviously the Fourier algorithm resultant error is excessive when frequency departure is serious.And no matter the present invention adopts capacitance-resistance still capacitance-resistance in parallel series connection equivalent model, the gained dielectric dissipation factor has all kept advantages of higher stability in frequency is 49.5～50.5 hertz of scopes, the result is very little with the frequency change fluctuation, and two kinds of equivalent model gained dielectric dissipation factors are also very close.Measured the signal of 50 groups of different frequencies, parallel model obtains equivalent resistance and the equivalent capacity average is respectively 26.0 kilohms and 23.3 microfarads, and standard deviation is respectively 2644 ohm and 29.5 nanofarads; The series connection model obtains equivalent resistance and the equivalent capacity average is respectively 0.72 ohm and 23.3 microfarads, and standard deviation is respectively 0.07 ohm and 0.24 microfarad.

The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claim.

Claims (8)

1. the dielectric dissipation factor measuring method based on equivalent model is characterized in that described method comprises the following steps:

Step 1: obtain voltage signal and current signal on apparatus insulated;

Step 2:, obtain the frequency and the signal each harmonic of voltage signal and current signal according to the data of step 1;

Step 3: with the apparatus insulated equivalent-circuit model that is thought of as, utilize the linear least-squares algorithm to obtain the resistance in the model, capacitance parameter, directly calculate then and obtain dielectric dissipation factor.

2. according to the described a kind of dielectric dissipation factor measuring method of claim 1, it is characterized in that described voltage signal obtains by voltage transformer (VT) or capacitive divider based on equivalent model.

3. according to the described a kind of dielectric dissipation factor measuring method of claim 1, it is characterized in that described current signal is by the centre path current sensor or seal in the formula current sensor and obtain based on equivalent model.

4. according to the described a kind of dielectric dissipation factor measuring method of claim 1, it is characterized in that the process of described picked up signal frequency and signal each harmonic is based on equivalent model:

Earlier with adding Hanning window interpolation Fourier algorithm picked up signal frequency, if signal frequency in 49.9～50.1 hertz of scopes, then obtains the each harmonic of voltage signal and current signal with fast Fourier algorithm; Otherwise according to the each harmonic of the signal frequency that obtains with the desirable sample frequency method picked up signal of correction.

5. according to the described a kind of dielectric dissipation factor measuring method of claim 1, it is characterized in that described equivalent-circuit model is resistance and electric capacity parallel connection based on equivalent model.

6. according to the described a kind of dielectric dissipation factor measuring method of claim 1, it is characterized in that described equivalent-circuit model is resistance and capacitances in series based on equivalent model.

7. according to the described a kind of dielectric dissipation factor measuring method of claim 5, it is characterized in that the computing formula of dielectric dissipation factor was when described resistance and electric capacity were in parallel based on equivalent model:

tgδ＝1/ωRC

Wherein: tg δ is a dielectric dissipation factor; ω is an angular frequency; R is the equivalent resistance of insulation; C is the equivalent capacity of insulation.

8. according to the described a kind of dielectric dissipation factor measuring method based on equivalent model of claim 6, the computing formula of dielectric dissipation factor is when it is characterized in that described resistance and capacitances in series:

tgδ＝ωRC。

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