CN101464235A - Test method and apparatus for polymer power cable insulation accelerated electric tree aging - Google Patents

Abstract

The invention provides a polymer power cable insulation acceleration electrical tree aging test method and a device, which relate to a testing device for monitoring polymer power cable insulation electrical tree aging and a method thereof. The device provided by the invention comprises a non-vignetting testing transformer, an induction voltage regulator, a capacitance voltage divider, a testing electrode, a broad band current sensor, an amplification filter, a digital oscillograph, a microcomputer and an electrothermal combined aging oven. The method provided by the invention comprises the following steps: the testing preparation is carried out with the device provided by the invention; a test sample is subjected to local discharge data acquisition and processing through a program; and the image and the basic data of the insulation electrical tree branching of the test sample are obtained through slicing and photographing. The device provided by the invention has the advantages of high pressure resistance and heat resistance level, small amount of self-local discharge, and safe and reliable use. The method provided by the invention has the characteristics of convenient and accurate use, and the like. The invention can be widely applied to the field of monitoring the insulation aging of a power cable, in particular to the field of monitoring the insulation electrical tree aging of a polymer power cable.

Description

The test method of polymer power cable insulation accelerated electric tree aging and device

Technical field

The invention belongs to the insulating monitoring technical field of polymer power cable, be specifically related to the test method and the device of monitoring polymer power cable insulation electric tree aging.

Background technology

Polymer insulation power cable particularly crosslinked polyethylene (XLPE) cable is widely used in electric system owing to its superior electric, mechanical, mechanical property.The insulation of polymer power cable electricity, heat, machinery, water is wet and the multiple stress of environmental stress under, will show with the aging form of water tree, electric branch, finally ascribe electric branch to and cause insulation breakdown.Because electric branchization is the bottleneck of polymer power cable long-term safety operation, influence the safe and reliable operation of electric system, its branch The Characteristic Study is subjected to the world, domestic extensive concern.Facts have proved that electric branchization is the water tree under single stress such as electricity, heat, machinery or the many stress conditions, the ageing process of electric branch.Therefore, by quickening the aging test unit of polymer power cable insulation, initiation, growth mechanism and the inhibition method of electric branch in the insulation of research polymkeric substance cable, thereby seek the incipient fault that polymer power cable is in operation, for the manufacturing of polymer power cable, the on-line monitoring and the diagnosis of insulation ag(e)ing provide reliable foundation, thereby improve the reliability of polymer power cable long-term safety reliability service, guarantee the safe and reliable operation of electric system.So the electric branch process of research polymer power cable has very important meaning.

Test unit and method to the polymer power cable insulation electric branchization mainly contains two kinds at present, a kind of accelerated deterioration research that is based on material block, and biasing toward is the electric branch The Characteristic Study of insulating material of polymer.As rolling up " electric branch structure and growth characteristics thereof in the XLPE cable insulation " civilian disclosed pilot system in the 6th phase " High-Voltage Technology " in June the 33rd in 2007, comprise frequency conversion high-voltage generator, high-field electrode, pin-plate electrode, digital camera and the micro-computer system formed by function signal generator and variable ratio frequency changer high-voltage amplifier, silicone oil etc., sample is the hollow disk of 5mm that XLPE cable is made, and adopts pin-template die type pilot system.The actual operating state difference of this pilot system and polymer power cable is bigger, and is unable to estimate the influence of the inside and outside shield semiconductors layer of cable etc., with the electric branch growth course of actual motion cable differ bigger, test figure relatively poor with reference to property.Another kind is based on the aging test of final polymer insulated cable, it is makers' product testing, the ageing process of this method and actual motion cable is very approaching, but accelerated deterioration is difficult to realize, digestion time is longer, and test operation is miscellaneous, and consumptive material is big, need large-scale test site, economic needs is huge.

Summary of the invention

The objective of the invention is weak point at existing polymer power cable insulation electric branch device and method, a kind of test method and device of polymer power cable insulation accelerated electric tree aging are provided, has the energy simulate electric field, thermal field, machinery, a plurality of stress conditions that make insulation ag(e)ing such as water is wet, to reach the electric branchization of both quickening the cable sample, do not destroy electric branch mechanism again, the electric branch process of true dummycable sample, simultaneously can be easily to the shelf depreciation in the electric branch process, electrical specification parameters such as leakage current carry out on-line measurement, and it is convenient to ensure, carry out the characteristics of the test of electric branch aging characteristics safely.

The technical scheme that realizes the object of the invention is: a kind of test unit of polymer power cable insulation accelerated electric tree aging comprises not having dizzy experimental transformer, induction voltage regulator, capacitive divider, test electrode, wide band flow sensor, amplifilter, digital oscilloscope, microcomputer.Its test electrode mainly is made up of glass fibre reinforced plastics casing, anti-corona cover, round end electrode, column type copper electrode, gland nut, cable sample, binding clip, ground link, insulating oil, fuel outlet valve, insulating support, support insulator and rosette base.Upper surface at glass fibre reinforced plastics casing is provided with top cover, so that installing test electrode and injection insulating oil, the two ends at center are equiped with the column type copper electrode respectively in glass fibre reinforced plastics casing.Both ends at each column type copper electrode, be respectively arranged with screw thread, be equiped with gland nut respectively, so that affixed cable sample in the inner of two column type copper electrodes, the other end of two column type copper electrodes passes glass fibre reinforced plastics casing respectively, so that affixed with anti-corona cover and round end electrode.Two anti-corona covers are installed in the outside, two ends of glass fibre reinforced plastics casing respectively, the center of two anti-corona covers penetrates the end that two column type copper electrodes stretch out glass fibre reinforced plastics casing respectively, the intracardiac screw thread that is respectively arranged with in two round end electrodes, one end, to stretch out the end of glass fibre reinforced plastics casing affixed with two column type copper electrodes respectively, and compress two anti-corona covers affixed respectively.In glass fibre reinforced plastics casing, fill insulating oil, cable sample is flooded, be equiped with fuel outlet valve,, guarantee the insulating property of insulating oil in the glass fibre reinforced plastics casing so that bleed off the insulating oil of deterioration in the lower end of glass fibre reinforced plastics casing.Glass fibre reinforced plastics casing is positioned on the insulating support, and insulating support is fixed on the support insulator, and support insulator is positioned on the rosette base, so that test electrode is applied high pressure.Test electrode is positioned in the electric heating associating ageing oven, so that the actual motion environment of simulating polymer power cable.Test electrode and capacitive divider parallel connection, one end of capacitive divider is with in parallel with the secondary of induction voltage regulator again after resistance is connected, the former limit of induction voltage regulator is in parallel with the secondary that does not have dizzy testing transformer, when the former limit of not having dizzy testing transformer applies the 380V industrial-frequency alternating current, just can be test electrode trial voltage is provided.The ground wire of test electrode passes the wide band flow sensor, the local discharge signal that is produced in the process when being used for detecting cable sample electric branch in the test electrode, the secondary of wide band flow sensor is connected with amplifilter, in order to detected local discharge signal is amplified and filtering, amplifilter links to each other with digital oscilloscope by signal wire, and digital oscilloscope will be analyzed and handle data through amplifying with the local discharge signal storage of filtering and with data transmission to microcomputer.

Experimentation is: one section cable getting certain-length on the finished cable after going to protect armor, remove copper shield band and segment outer semiconductor screen layer, cut the termination on both sides, do small stress defective at the cable body middle part, as infiltrate pure water etc. after inserting the metal needle of certain depth or inserting a pin hole, recover copper shield then and take shield semiconductors layer place to, utilize insulating tape that the copper shield band at two ends is compressed, in an electrode in one of them termination insertion case, another section is fixed with cheese head screw; Electrode system is put in the electric heating associating ageing oven rises to required temperature, regulate induction voltage regulator, rise to the experiment required voltage, local discharge signal is by copper shield process ground link, fuel outlet valve, wide band flow sensor induced flow cross ground wire (current impulse produce voltage signal through after the amplification filtering of amplifilter, gather waveform signal by digital oscilloscope, and deliver to analysis and the diagnosis that microcomputer carries out local discharge signal; Discharge develops into to a certain degree when the part, and step-down and cable sample section utilize digit microscope observation and record electric branch form, analyze the physicochemical characteristics in electric branch deterioration district.

A kind of test method of polymer power cable insulation accelerated electric tree aging, utilize apparatus of the present invention, test preparation earlier, the back is carried out data processing by program to the shelf depreciation data that collect, through cutting into slices and taking pictures, obtain the image and the basic data of cable sample insulated electro branchization again.Concrete steps are as follows:

1) test is prepared

At first, its two ends are successively peelled off, and on the insulation course at sample center, artificially make a defective, to producing the cable sample of insulation defect one section of polymer power cable intercepting.Elder generation is with the core at cable sample two ends, gland nut by test electrode is fixed on the two column type copper electrodes of test electrode respectively, and the copper shield of cable sample linked to each other with ground link, ground link links to each other with fuel outlet valve, then electrode system is placed with electric heating and united in the ageing oven, fuel outlet valve links to each other with ground wire, closes electric heating associating ageing oven, electric heating united be warming up to the required temperature of test in the ageing oven, so that quicken the insulation ag(e)ing of cable sample.

2) gather the shelf depreciation data

The 1st) after the step finishes, apply the 380V industrial-frequency alternating current on the former limit of the dizzy transformer of the nothing of apparatus of the present invention, output voltage to the insulation defect on the cable sample of adjusting induction voltage regulator again produces shelf depreciation.The digital oscilloscope collection of apparatus of the present invention is amplified and filtered local discharge signal through amplifilter, and sends microcomputer to and carry out data processing.

3) data processing

The 2nd) after the step finishes, to the 2nd) local discharge signal gathered of step, utilize microcomputer, carry out following data processing by program:

(1) small echo denoising

At first carrying out wavelet decomposition, to the 2nd) local discharge signal gathered of step carries out wavelet decomposition by following formula

$f_{A_j}\left(t\right)=f_{A_{j+1}}\left(t\right)+f_{D_{j+1}}\left(t\right)---\left(1\right)$

In the formula: Be analyzed signal,

For

Low frequency component,

For

High fdrequency component.

The local discharge signal that collects is decomposed in the different frequency bands, obtain the wavelet coefficient in each frequency band.

Generate threshold value by thresholding algorithm or the minimax variance threshold values algorithm of partially estimating based on this smooth nothing again, the wavelet coefficient of each frequency band that the wavelet decomposition step is obtained deducts threshold value and generates the threshold value that step generates, and obtains new wavelet coefficient.Carry out wavelet reconstruction to handling the new wavelet coefficient that obtains then through wavelet coefficient, generate real part, imaginary part and phase signal that small echo removes signal after the dry conversion, at last with real part, imaginary part and the phase signal of the signal after the small echo denoising conversion, generate composite signal according to real part imaginary part or real part phase place or imaginary part phase method for position.

(2) Characteristic Extraction

The 3rd)-after (1) step finishes, to the 3rd)-composite signal that (1) step generates extracts its characteristic quantity.At first carry out the frequency of single waveform and extract, single discharge pulse is carried out fast fourier transform, obtain the spectrum distribution of discharge pulse, the average frequency W that counts single discharge pulse is:

$W=\frac{\underset{i=0}{\overset{K}{\mathrm{\Σ}}}{f}_i^2\·{\left|X_i\left(f_i\right)\right|}^2}{\underset{i=0}{\overset{K}{\mathrm{\Σ}}}{\left|X_i\left(f_i\right)\right|}^2}---\left(2\right)$

In the formula: f _iBe the energy component in the frequency collection of illustrative plates; X _i(f _i) be the frequency component in the frequency collection of illustrative plates.

Carry out the phase extraction of single waveform then, the sampling width is set equals a power frequency period, then the waveform of being taked just is the shelf depreciation in the one-period, and the phase place Ph of single partial discharge pulse is

$\mathrm{Ph}=\frac{360\×N_i}{N_o}---\left(3\right)$

$N_i=\frac{N_{\mathrm{ai}}+N_{\mathrm{bi}}}{2}---\left(4\right)$

In the formula: N _iIt is the position of i pulse center; N _Ai, N _BiBe the reference position and the final position of i pulse; N ₀Be the sum of sampling.

(3) identification of discharge mode

The 3rd)-after (2) step finishes, to the 3rd)-characteristic quantity that extracts of (1) step, adopt possibility clustering algorithm (FCM) that it is classified, its objective function is:

$J_m(U,V)=\underset{i=1}{\overset{c}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{\left(u_{\mathrm{ij}}\right)}^{\mathrm{<figure-callout\; id="2"\; label="m\; d\; ij"\; filenames="A200910103045E00161.png,A200910103045E00181.png"\; state="\{\{state\}\}">m</figure-callout>}}{d}_{\mathrm{ij}}^{}{}_2^{}+\underset{i=1}{\overset{c}{\mathrm{\&Sigma;}}}{\mathrm{\&eta;}}_i\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{(1-u_{\mathrm{ij}})}^m---\left(5\right)$

In the formula: N is a number of samples; C is the cluster centre number; u _Ij=u _i(x _j) represent that j sample belongs to the degree of membership of i class; M is the weight index, characterizes the obfuscation degree; d _IjBe that j sample is to i distances of clustering centers.The 2nd is penalty, requires u _IjBig as far as possible, thus solution trivial avoided.η _iBe a suitable positive number, recommend value to be:

${\mathrm{\&eta;}}_i=K\frac{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^{\mathrm{<figure-callout\; id="2"\; label="m\; d\; ij"\; filenames="A200910103045E00161.png,A200910103045E00181.png"\; state="\{\{state\}\}">m</figure-callout>}}{d}_{\mathrm{ij}}^{}{}_2^{}}{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^m}---\left(6\right)$

K is a positive integer in the formula, gets K=1 usually.

The cluster intermediate formulas is:

$v_i^l=\frac{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^{m}K\&CenterDot;x_j}{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^{m}K}---\left(7\right)$

Degree of membership u _IjFormula is:

$u_{\mathrm{ij}}=\frac{1}{1+{\left[\frac{{\mathrm{<figure-callout\; id="2"\; label="d\; ij"\; filenames="A200910103045E00161.png,A200910103045E00181.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{ij}}^{}}{{\mathrm{\&eta;}}_i}\right]}^{\frac{1}{m-1}}}---\left(8\right)$

The FCM algorithm flow is as follows:

1. determine at first that cluster centre counts C, the weight exponent m, maximum iteration time 1 and iteration stop error ε, and with its degree of membership of cluster result initialization u of FCM _Ij

2. secondly calculate η according to (6) formula _i

3. calculate cluster centre according to (7) formula then

And obtain degree of membership according to degree of membership computing formula (8)

4. judge at last $\left|\right|u_{\mathrm{ij}}^l-u_{\mathrm{ij}}^{l+1}<\mathrm{\&epsiv;}\left|\right|,$ Satisfying condition then, iteration stops; Otherwise returned for the 3. step, continue iteration.

4) cut into slices and take pictures

The 3rd) step finish after, the output voltage of pressure regulator is reduced to 0, the closing test power supply hangs up ground rod at the round end electrode place of test electrode, closes electric heating associating ageing oven, open electric heating associating ageing oven, electric heating is united aging the temperature inside the box reduce to room temperature, take out cable sample, fault location is cut into slices in the people work area, slice thickness 2-5mm will cut into slices to place with microscopically and take pictures.

After the present invention adopts technique scheme, mainly contain following technique effect:

1 convenience: cable sample is made simple, need not the stress cone terminal, only just both can finish with the cable bite; The selection of aging factor is convenient, but arbitrary combination, heating arrangement is provided by outside ageing oven, and temperature control is convenient; The on-line measurement continuously of electricity parameter such as shelf depreciation, leakage current behind aging the end, is removed screen layer and can be carried out the test of physical and chemical performance to cable sample, and convenience is good.

2 economy: each test only need not have about 1 meter of armor finished cable, and manufacture craft is simple, and Master Cost is saved; During heat ageing, utilize the heating of test ageing oven, it is slower to dispel the heat, and consumed power is little, good economy performance.

3 securities: select glass-reinforced plastic material high temperature resistant, maximum operating temperature is above 200 ℃, good flame resistance, and thermal expansivity is little, convenient sealing, to put into the heat ageing case behind this device filling insulating oil, pressurization power frequency 15kV heats to 130 ℃, keeps 1 day time, good airproof performance takes place in the unusual imagination such as no leakage of oil.

4 withstand voltage levels: during no cable sample, add the no abnormal phenomenon of power frequency voltage 40kV under the room temperature, when cable sample is arranged, apply the no abnormal phenomenon of power-frequency voltage 35kV, the withstand voltage level height.

5 thermal levels: because resistant to elevated temperatures condition has all been considered in the selection of all material, the theoretical work temperature is above 200 ℃, put into the heat ageing case after apparatus of the present invention are irritated insulating oil, heat to 150 ℃, keep 1 day time, abnormal conditions such as no leakage of oil take place, consider the volatilization of oil, be the security of ensuring equipment, actual maximum operating temperature is no more than 130 ℃, the thermal level height.

6 local discharging level: during no cable sample, power-frequency voltage 30kV, partial discharge quantity be less than 2pc, the following corona free sound of 35kV, and when adding zero defect cable sample, power-frequency voltage 35kV, partial discharge quantity are less than 5pc, and apparatus of the present invention self partial discharge quantity is little.

7 the present invention adopt wide band current sensor, have the monitoring bandwidth, and are highly sensitive, the characteristics that accuracy is good.

The present invention is widely used in the insulation ag(e)ing of monitoring power cable, is specially adapted to the insulation ag(e)ing of monitoring polymer power cable.To guarantee the safe and reliable operation of power cable.

Description of drawings

Fig. 1 is the principle assumption diagram of apparatus of the present invention;

Fig. 2 is that structural drawing is clicked in the test of apparatus of the present invention;

Fig. 3 is a cable sample structural representation of the present invention;

Fig. 4 is A-A sectional view of Fig. 3;

Fig. 5 is the flow chart of data processing figure of the inventive method;

Fig. 6 is the electric branch figure that the cable sample of present embodiment produces under different tests voltage;

Fig. 7 is the electric branch figure that the cable sample of present embodiment produces under different tests voltage and different temperatures;

The phase frequency distribution collection of illustrative plates of the shelf depreciation impulse discharge that Fig. 8 obtains for present embodiment

Among the figure: 1 does not have dizzy testing transformer, 2 induction voltage regulators, 3 capacitive dividers, 4 test electrodes, 5 wide band flow sensor, 6 amplifilters, 7 digital oscilloscopes, 8 microcomputers, 9 electric heating associating ageing oven, 10 glass fibre reinforced plastics casings, 11 anti-corona covers, 12 round end electrodes, 13 column type copper electrodes, 14 gland nuts, 15 cable samples, 16 binding clips, 17 ground links, 18 insulating oils, 19 fuel outlet valves, 20 insulating supports, 21 support insulators, 22 rosette bases, 23 cable cores, 24 internal shields, 25 insulation courses, 26 external shielding layers, 27 copper shields, 28 defectives, 29 ground wires

Embodiment

Below in conjunction with accompanying drawing technical scheme of the present invention is further detailed:

Embodiment 1

Shown in Fig. 1～4, a kind of test unit of polymer power cable insulation accelerated electric tree aging comprises not having dizzy experimental transformer 1, induction voltage regulator 2, capacitive divider 3, test electrode 4, wide band flow sensor 5, amplifilter 6, digital oscilloscope 7, microcomputer 8.Its test electrode 4 mainly is made up of with rosette base 22 glass fibre reinforced plastics casing 10, anti-corona cover 11, round end electrode 12, column type copper electrode 13, gland nut 14, cable sample 15, binding clip 16, ground link 17, insulating oil 18, fuel outlet valve 19, insulating support 20, support insulator 21.Upper surface at glass fibre reinforced plastics casing 10 is provided with top cover, so that installing test electrode 4 and injection insulating oil 18, the two ends at center are equiped with the column type copper electrode respectively in glass fibre reinforced plastics casing 10.Both ends at each column type copper electrode 13, be respectively arranged with screw thread, the inner at two column type copper electrodes 13 is equiped with gland nut 14 respectively, so that affixed cable sample 15, the other end of two column type copper electrodes 13 passes glass fibre reinforced plastics casing 10 respectively, so that affixed with anti-corona cover 11 and round end electrode 12.Two anti-corona covers 11 are installed in the outside, two ends of glass fibre reinforced plastics casing 10 respectively, the center of two anti-corona covers 11 penetrates the end that two column type copper electrodes 13 stretch out glass fibre reinforced plastics casing 10 respectively, the intracardiac screw thread that is respectively arranged with in two round end electrodes, 12 1 ends, to stretch out the end of glass fibre reinforced plastics casing 10 affixed with two column type copper electrodes 13 respectively, and compress two anti-corona covers 11 affixed respectively.In glass fibre reinforced plastics casing 10, fill insulating oil 18, cable sample 15 is flooded, be equiped with fuel outlet valve 19,, guarantee the insulating property of insulating oil 18 in the glass fibre reinforced plastics casing 10 so that bleed off the insulating oil 18 of deterioration in the lower end of glass fibre reinforced plastics casing 10.Glass fibre reinforced plastics casing 10 is positioned on the insulating support 20, and insulating support 20 is fixed on the support insulator 21, and support insulator 21 is positioned on the rosette base 22, so that test electrode 4 is applied high pressure.Test electrode 4 is positioned in the electric heating associating ageing oven 9, so that the actual motion environment of simulating polymer power cable.Test electrode 4 and capacitive divider 3 parallel connections, one end of capacitive divider 3 is with in parallel with the secondary of induction voltage regulator 2 again after resistance is connected, the former limit of induction voltage regulator 2 is in parallel with the secondary that does not have dizzy testing transformer 1, when the former limit of not having dizzy testing transformer 1 applies the 380V industrial-frequency alternating current, just can be test electrode 4 trial voltage is provided.The ground wire 29 of test electrode 4 passes wide band flow sensor 5, the local discharge signal that is produced in the process when being used for detecting cable sample 15 electric branch in the test electrode 4, the secondary of wide band flow sensor 5 is connected with amplifilter 6, in order to detected local discharge signal is amplified and filtering, amplifilter 6 links to each other with digital oscilloscope 7 by signal wire, and digital oscilloscope 7 will be analyzed and handle through amplifying with the local discharge signal storage of filtering and with data transmission to 8 pairs of data of microcomputer.

Embodiment 2

A kind of test method of polymer power cable insulation accelerated electric tree aging, concrete steps are as follows:

1) test is prepared

At first, its two ends are successively peelled off, and on the insulation course 25 at cable sample 15 centers, artificially make a defective 28, to the cable sample 15 of producing insulation defect 28 one section of polymer power cable intercepting.Elder generation is with the cable core 23 at cable sample 15 two ends, gland nut 14 by test electrode 4 is fixed on the two column type copper electrodes 12 of test electrode 4 respectively, and the copper shield 27 of cable sample 15 linked to each other with ground link 17, ground link 29 links to each other with the end of fuel outlet valve 19 in the electrode of exerting pressure, then electrode system 4 is placed with electric heating and united in the ageing oven 9, the end of fuel outlet valve 19 outside test electrode links to each other with ground wire 29, close electric heating associating ageing oven 9, electric heating united be warming up to the required temperature of test in the ageing oven 9, so that quicken the insulation ag(e)ing of cable sample 15

2) gather the shelf depreciation data

The 1st) after the step finishes, apply the 380V industrial-frequency alternating current on the former limit of the dizzy transformer 1 of the nothing of apparatus of the present invention, output voltage to the insulation defect 28 on the cable sample 15 of adjusting induction voltage regulator 2 again produces shelf depreciations.The digital oscilloscope 7 of apparatus of the present invention is gathered through amplifilters 6 and is amplified and filtered local discharge signals, and sends microcomputer 8 to and carry out data processing.

3) data processing

The 2nd) after the step finishes, to the 2nd) local discharge signal gathered of step, utilize microcomputer 8, carry out following data processing by program:

(1) small echo denoising

At first carrying out wavelet decomposition, to the 2nd) local discharge signal gathered of step carries out wavelet decomposition by following formula

$f_{A_j}\left(t\right)=f_{A_{j+1}}\left(t\right)+f_{D_{j+1}}\left(t\right)---\left(1\right)$

In the formula:

Be analyzed signal,

For

Low frequency component, For

High fdrequency component.

The local discharge signal that collects is decomposed in the different frequency bands, obtain the wavelet coefficient in each frequency band.

Generate threshold value by thresholding algorithm or the minimax variance threshold values algorithm of partially estimating based on this smooth nothing again, the wavelet coefficient of each frequency band that the wavelet decomposition step is obtained deducts threshold value and generates the threshold value that step generates, and obtains new wavelet coefficient.Carry out wavelet reconstruction to handling the new wavelet coefficient that obtains then through wavelet coefficient, generate real part, imaginary part and phase signal that small echo removes signal after the dry conversion, at last with real part, imaginary part and the phase signal of the signal after the small echo denoising conversion, generate composite signal according to real part imaginary part or real part phase place or imaginary part phase method for position.

(2) Characteristic Extraction

The 3rd)-after (1) step finishes, to the 3rd)-composite signal that (1) step generates extracts its characteristic quantity.At first carry out the frequency of single waveform and extract, single discharge pulse is carried out fast fourier transform according to following formula, obtain the spectrum distribution of discharge pulse, the average frequency W that counts single discharge pulse is:

$W=\frac{\underset{i=0}{\overset{\mathrm{<figure-callout\; id="2"\; label="K\; f\; i"\; filenames="A200910103045E00161.png,A200910103045E00181.png"\; state="\{\{state\}\}">K</figure-callout>}}{\mathrm{\&Sigma;}}}{f}_i^{}{}_2^{}\&CenterDot;{\left|X_i\left(f_i\right)\right|}^2}{\underset{i=0}{\overset{K}{\mathrm{\&Sigma;}}}{\left|X_i\left(f_i\right)\right|}^2}---\left(2\right)$

In the formula: f _iBe the energy component in the frequency collection of illustrative plates; X _i(f _i) be the frequency component in the frequency collection of illustrative plates.

Carry out the phase extraction of single waveform then, the sampling width is set equals a power frequency period, then the waveform of being taked just is the shelf depreciation in the one-period, and the phase place Ph of single partial discharge pulse calculates according to following formula

$\mathrm{Ph}=\frac{360\&times;N_i}{N_o}---\left(3\right)$

$N_i=\frac{N_{\mathrm{ai}}+N_{\mathrm{bi}}}{2}---\left(4\right)$

In the formula: N _iIt is the position of i pulse center; N _Ai, N _BiBe the reference position and the final position of i pulse; N ₀Be the sum of sampling.

(3) identification of discharge mode

The 3rd)-after (2) step finishes, to the 3rd)-characteristic quantity that (1) step extracts adopts possibility clustering algorithm (FCM) that it is classified, and its objective function is:

$J_m(U,V)=\underset{i=1}{\overset{c}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{\left(u_{\mathrm{ij}}\right)}^m{\mathrm{<figure-callout\; id="2"\; label="d\; ij"\; filenames="A200910103045E00161.png,A200910103045E00181.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{ij}}^{}+\underset{i=1}{\overset{c}{\mathrm{\&Sigma;}}}{\mathrm{\&eta;}}_i\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{(1-u_{\mathrm{ij}})}^m---\left(5\right)$

In the formula: N is a number of samples; C is the cluster centre number; u _Ij=u _i(x _j) represent that j sample belongs to the degree of membership of i class; M is the weight index, characterizes the obfuscation degree; d _IjBe that j sample is to i distances of clustering centers.The 2nd is penalty, requires u _IjBig as far as possible, thus solution trivial avoided.η _iBe a suitable positive number, its value is

${\mathrm{\&eta;}}_i=K\frac{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^m{d}_{\mathrm{ij}}^2}{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^m}---\left(6\right)$

In the formula: K is a positive integer, gets K=1.

The cluster intermediate formulas is:

$v_i^l=\frac{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^{m}K\&CenterDot;x_j}{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^{m}K}---\left(7\right)$

Degree of membership u _IjFormula is:

$u_{\mathrm{ij}}=\frac{1}{1+{\left[\frac{d_{\mathrm{<figure-callout\; id="2"\; label="ij"\; filenames="A200910103045E00161.png,A200910103045E00181.png"\; state="\{\{state\}\}">ij</figure-callout>}}^2}{{\mathrm{\&eta;}}_i}\right]}^{\frac{1}{m-1}}}---\left(8\right)$

The FCM algorithm flow is as follows:

1. determine at first that cluster centre counts C, the weight exponent m, maximum iteration time 1 and iteration stop error ε, and with its degree of membership of cluster result initialization u of FCM _Ij

2. secondly calculate η according to (6) formula _i

3. calculate cluster centre according to (7) formula then

And obtain degree of membership according to degree of membership computing formula (8)

4. judge at last $\left|\right|u_{\mathrm{ij}}^l-u_{\mathrm{ij}}^{l+1}<\mathrm{\&epsiv;}\left|\right|,$ Satisfying condition then, iteration stops; Otherwise returned for the 3. step, continue iteration.

4) cut into slices and take pictures

The 3rd) step finish after, the output voltage of induction voltage regulator 2 is reduced to 0, close the power supply that does not have dizzy testing transformer 1, hang up ground rod at round end electrode 12 places of test electrode 4, close the power supply of electric heating associating ageing oven 9, open electric heating associating ageing oven 9, electric heating is united ageing oven 9 interior temperature reduce to room temperature, take out cable sample 15, cut into slices in 28 places in artificial defect, slice thickness 2-5mm is positioned over microscopically with section and takes pictures, shown in Fig. 6,7,8.

Claims (2)

1, a kind of test unit of polymer power cable insulation accelerated electric tree aging, comprise and do not have dizzy experimental transformer (1), induction voltage regulator (2), capacitive divider (3), test electrode (4), wide band flow sensor (5), amplifilter (6), digital oscilloscope (7), microcomputer (8), it is characterized in that test electrode (4) is mainly by glass fibre reinforced plastics casing (10), anti-corona cover (11), round end electrode (12), column type copper electrode (13), gland nut (14), cable sample (15), binding clip (16), ground link (17), insulating oil (18), fuel outlet valve (19), insulating support (20), support insulator (21) is formed with rosette base (22), upper surface at glass fibre reinforced plastics casing (10) is provided with top cover, so that installing test electrode (4) and injection insulating oil (18), the two ends at center are equiped with the column type copper electrode respectively in glass fibre reinforced plastics casing (10), both ends at each column type copper electrode (13), be respectively arranged with screw thread, be equiped with gland nut (14) respectively in the inner of two column type copper electrodes (13), the other end of two column type copper electrodes (13) passes glass fibre reinforced plastics casing (10) respectively, affixed with anti-corona cover (11) and round end electrode (12), two anti-corona covers (11) are installed in the outside, two ends of glass fibre reinforced plastics casing (10) respectively, the center of two anti-corona covers (11) penetrates the end that two column type copper electrodes (13) stretch out glass fibre reinforced plastics casing (10) respectively, the intracardiac screw thread that is respectively arranged with in two round end electrodes (12) one ends, to stretch out the end of glass fibre reinforced plastics casing (10) affixed with two column type copper electrodes (13) respectively, and compress two anti-corona covers (11) affixed respectively, in glass fibre reinforced plastics casing (10), fill insulating oil (18), be equiped with fuel outlet valve (19) in the lower end of glass fibre reinforced plastics casing (10), glass fibre reinforced plastics casing (10) is positioned on the insulating support (20), insulating support (20) is fixed on the support insulator (21), support insulator (21) is positioned on the rosette base (22), test electrode (4) is positioned in the electric heating associating ageing oven (9), test electrode (4) and capacitive divider (3) parallel connection, one end of capacitive divider (3) is with in parallel with the secondary of induction voltage regulator (2) again after resistance is connected, and the former limit of induction voltage regulator (2) is in parallel with the secondary that does not have dizzy testing transformer (1).

2, a kind of test method of polymer power cable insulation accelerated electric tree aging is utilized apparatus of the present invention, by program the shelf depreciation data of gathering is carried out data processing, it is characterized in that concrete steps are as follows:

1) test is prepared

At first with one section of polymer power cable intercepting, its two ends are successively peelled off, and in the upward artificial defective (28) of making of the insulation course (25) at cable sample (15) center, to the cable sample (15) of producing insulation defect (28), elder generation is with the cable core (23) at cable sample (15) two ends, gland nut (14) by test electrode (4) is fixed on the two column type copper electrodes (12) of test electrode (4) respectively, and the copper shield (27) of cable sample (15) linked to each other with ground link (17), ground link (29) links to each other with the end of fuel outlet valve (19) in the electrode of exerting pressure, electrode system (4) is placed with electric heating then and united in the ageing oven (9), the end of fuel outlet valve (19) outside test electrode links to each other with ground wire (29), close electric heating associating ageing oven (9), electric heating is united to be warming up in the ageing oven (9) test required temperature;

2) gather the shelf depreciation data

The 1st) step finish after, former limit at the dizzy transformer (1) of the nothing of apparatus of the present invention applies the 380V industrial-frequency alternating current, output voltage to the insulation defect (28) on the cable sample (15) of adjusting induction voltage regulator (2) again produces shelf depreciation, the digital oscilloscope of apparatus of the present invention (7) is gathered through amplifilter (6) and is amplified and filtered local discharge signal, and sends microcomputer (8) to and carry out data processing;

3) data processing

The 2nd) after the step finishes, to the 2nd) local discharge signal gathered of step, utilize microcomputer (8), carry out following data processing by program:

(1) small echo denoising

At first carrying out wavelet decomposition, to the 2nd) local discharge signal gathered of step carries out wavelet decomposition by following formula

$f_{A_j}\left(t\right)=f_{A_{j+1}}\left(t\right)+f_{D_{j+1}}\left(t\right)---\left(1\right)$

In the formula: Be analyzed signal,

Low frequency component,

For

High fdrequency component,

The local discharge signal that collects is decomposed in the different frequency bands, obtain the wavelet coefficient in each frequency band;

Generate threshold value by thresholding algorithm or the minimax variance threshold values algorithm of estimating partially based on this smooth nothing again, the wavelet coefficient of each frequency band that the wavelet decomposition step is obtained, deduct threshold value and generate the threshold value that step generates, obtain new wavelet coefficient, carry out wavelet reconstruction to handling the new wavelet coefficient that obtains then through wavelet coefficient, generate real part, imaginary part and phase signal that small echo removes signal after the dry conversion, at last with real part, imaginary part and the phase signal of the signal after the small echo denoising conversion, generate composite signal according to real part imaginary part or real part phase place or imaginary part phase method for position;

(2) Characteristic Extraction

The 3rd)-(1) step finish after, to the 3rd)-composite signal that (1) step generates extracts its characteristic quantity, at first carrying out the frequency of single waveform extracts, single discharge pulse is carried out fast fourier transform according to following formula, obtain the spectrum distribution of discharge pulse, the average frequency W that counts single discharge pulse is:

$W=\frac{\underset{i=0}{\overset{K}{\mathrm{\&Sigma;}}}{f_i}^2\&CenterDot;{\left|X_i\left(f_i\right)\right|}^2}{\underset{i=0}{\overset{K}{\mathrm{\&Sigma;}}}{\left|X_i\left(f_i\right)\right|}^2}---\left(2\right)$

In the formula: f _iBe the energy component in the frequency collection of illustrative plates, X _i(f _i) be the frequency component in the frequency collection of illustrative plates,

Carry out the phase extraction of single waveform then, the sampling width is set equals a power frequency period, then the waveform of being taked just is the shelf depreciation in the one-period, and the phase place Ph of single partial discharge pulse is:

$\mathrm{Ph}=\frac{360\&times;N_i}{N_o}---\left(3\right)$

$N_i=\frac{N_{\mathrm{ai}}+N_{\mathrm{bi}}}{2}---\left(4\right)$

In the formula: N _iBe the position of i pulse center, N _Ai, N _BiBe the reference position and the final position of i pulse, N ₀Be the sum of sampling;

(3) identification of discharge mode

The 3rd)-after (2) step finishes, to the 3rd)-characteristic quantity that extracts of (1) step, adopt the possibility clustering algorithm, promptly FCM classifies to it, and its objective function is:

$J_m(U,V)=\underset{i=1}{\overset{c}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{\left(u_{\mathrm{ij}}\right)}^m{d}_{\mathrm{ij}}^2+\underset{i=1}{\overset{c}{\mathrm{\&Sigma;}}}{\mathrm{\&eta;}}_i\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{(1-u_{\mathrm{ij}})}^m---\left(5\right)$

In the formula: N is a number of samples, and C is the cluster centre number, u _Ij=u _i(x _j) representing that j sample belongs to the degree of membership of i class, m is the weight index, characterizes the obfuscation degree, d _IjBe j sample to i distances of clustering centers, the 2nd is penalty, requires u _IjBig as far as possible, thus solution trivial avoided, η _iFor-suitable positive number, its value is

${\mathrm{\&eta;}}_i^{\&prime;}=K\frac{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^m{d}_{\mathrm{ij}}^2}{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^m}---\left(6\right)$

In the formula: K is a positive integer, gets K=1,

The cluster intermediate formulas is

$v_i^l=\frac{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^m{K\&CenterDot;x}_j}{\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{u_{\mathrm{ij}}}^{m}K}---\left(7\right)$

Degree of membership u _IjFormula is

$u_{\mathrm{ij}}=\frac{1}{1+{\left[\frac{d_{\mathrm{ij}}^2}{{\mathrm{\&eta;}}_i}\right]}^{\frac{1}{m-1}}}---\left(8\right)$

The FCM algorithm flow is as follows:

1. determine at first that cluster centre counts C, the weight exponent m, maximum iteration time 1 and iteration stop error ε, and with its degree of membership of cluster result initialization u of FCM _Ij

2. secondly calculate η according to (6) formula _l

3. calculate cluster centre according to (7) formula then

And obtain degree of membership according to degree of membership computing formula (8)

4. judge at last $\left|\right|u_{\mathrm{ij}}^l-u_{\mathrm{ij}}^{l+1}<\mathrm{\&epsiv;}\left|\right|,$ The iteration that satisfies condition then stops, otherwise returns for the 3. step, continues iteration;

4) cut into slices and take pictures

The 3rd) step finish after, the output voltage of induction voltage regulator (2) is reduced to 0, close the power supply that does not have dizzy testing transformer (1), locate to hang up ground rod, close the power supply of electric heating associating ageing oven (9) at the round end electrode (12) of test electrode (4), open electric heating associating ageing oven (9), electric heating is united the interior temperature of ageing oven (9) reduce to room temperature, take out cable sample (15), locate to cut into slices in artificial defect (28), slice thickness 2-5mm is positioned over microscopically with section and takes pictures.

Images