CN105842596A - High-sensitivity local defect diagnosis method for power cable - Google Patents
High-sensitivity local defect diagnosis method for power cable Download PDFInfo
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- CN105842596A CN105842596A CN201610351358.8A CN201610351358A CN105842596A CN 105842596 A CN105842596 A CN 105842596A CN 201610351358 A CN201610351358 A CN 201610351358A CN 105842596 A CN105842596 A CN 105842596A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
- G01R31/1272—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
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Abstract
The invention discloses a high-sensitivity local defect diagnosis method for a power cable. According to the method, on the basis of a power cable reflection coefficient spectrum of a frequency domain, a reflection coefficient spectrum of a power cable is measured and analyzed by using a non-destructive test technology; positioning of a local defect of a power cable is realized by combining a strobing gate and a modern digital signal processing technology; and a wave velocity obtained by a rear part or a virtual part of the reflection coefficient spectrum after conversion, of the measured cable is compared with a wave velocity of a new cable and the difference between the reflection coefficient spectrum value after conversion and a corresponding simulated fitting curve are combined, thereby realizing evaluation on the severity degree of the local defect. Compared with the prior art, positioning of a local defect with a weak changing degree and multi-defect identification are realized; and the severity degree of the local defect of the power cable can be evaluated.
Description
Technical field
The present invention relates to power cable operating defect diagonsis technology, more specifically, relate to a kind of electric power electricity
The diagnostic method of cable local defect.
Background technology
Crosslinked polyethylene (XLPE) power cable is because it is the most electric and mechanical performance, at present in China's power industry
It is widely used.China in the early 1990s, has carried out the work of substantial amounts of urban network restructuring, and substantial amounts of cable is opened
Begin to be applied to urban distribution network.But, due to processing technology and be in the impact under different operating conditions for a long time, electricity
Power cable often owing to making moist, overheated, extruding, the reason such as curved transitions cause power cable to produce water tree, insulation
The local defects such as deformation of media, copper shield loosen, if the local defect of power cable is not processed, electric power
Cable local defect will develop rapidly under the effect of highfield, ultimately results in the inefficacy of power cable insulation, thus
Maintenance, replacing for power cable bring substantial amounts of work, cause substantial amounts of manpower, financial resources to be wasted.Additionally, due to
Power cable is embedded in underground, and concentrates on inner city, and being replaced whole cable is also a difficult job.
From cost-effective angle, if can carry out power cable local defect diagnosing, repairing, then can save in a large number manpower,
Financial resources.
The time domain reflectometry (TDR) of existing comparative maturity can utilize pulse signal to realize the diagnosis of power cable fault,
Application No. 201310063871.3, the Chinese invention patent of entitled " Time Domain Reflectometry system and method ", it is provided that
A kind of use time domain reflectometry to determine the method and system that conductor is abnormal, but the method to there is no method more weak to intensity of variation
Defect diagnoses, and the resolution that TDR is in many defect recognition and near-end defect recognition is not high enough.Electric power
The shelf depreciation diagnosis of cable is a kind of method of detection cable local defect, but owing to local discharge signal amplitude is little,
Decay the reasons such as serious, the separation difficulty of signal and multiple faults identification difficulty so that is difficulty with in reality is measured
Local defect is diagnosed.Meanwhile, a kind of destructive test of shelf depreciation off-line test experiment, itself
The structure of cable can be produced certain impact.Existing power cable Examination and diagnosis remains in fault diagnosis
Aspect, lacks and diagnoses the local defect that construction of cable Parameters variation degree is more weak, it is impossible to lack the early stage of cable
Being trapped into row investigation, the local defect diagnosis new technique therefore carrying out cable is significant.
Summary of the invention
The high sensitivity power cable local that it is an object of the invention to provide a kind of electrically-based cable reflection coefficient spectrum lacks
Fall into diagnostic method, it is achieved the local defect of cable is accurately positioned and state estimation, simultaneously also can be to power cable
Transition joint well distinguish.There is advanced technology, the advantage that easily operated, cost is relatively low, highly sensitive.
The high sensitivity power cable local defect diagnostic method that the present invention provides, comprises the following steps:
1, cable under test DATA REASONING
Low-pressure linear frequency modulation, pseudorandom or the signal V of high-frequency narrow-pulse is launched to tested power cablei, measure from electricity
The reflected signal V that cable end reflection is returnedr, pass throughObtain the amplitude of the reflection coefficient spectrum of cable | Γd(f)|
And the real part Real (Γ of reflection coefficient spectrumd(f)) and the imaginary part Imag (Γ of reflection coefficient spectrumd(f)), wherein f is letter
Number frequency；
2, cable under test data process
Utilize transfer function f → t ', tested frequency-region signal f is converted to t ' territory signal, then to being converted to
Real(Γd(t ')) or Imag (Γd(t ')) carry out fast Fourier (FFT) conversion or discrete fourier (DFT) change
Change, record the Frequency point f that energy is maximum0′；Then to the Real (Γ being converted tod(t ')) or Imag (Γd(t ')) with
Kaiser (Kai Se) window function is multiplied, and carries out fast Fourier transform or discrete Fourier transform, is tentatively located
Reason data K Γd；
To the preliminary treatment data K Γ obtaineddDo 0 hertz to Frequency point f0' discrete Fourier transform, by conversion tie
Fruit is mapped to initial range diagnosis collection of illustrative plates D0In, initial range is diagnosed collection of illustrative plates D0Carry out adding distance window to process, obtain
Distance diagnosis collection of illustrative plates D, wherein mapping distance is 0 meter at 0 hertz, Frequency point f0' place mapping distance is power cable
Length l；
3, reference cable DATA REASONING and process
Using the non-tested phase power cable in three-phase system as with reference to power cable, then utilize step 1 same way
Obtain the amplitude of the reflection coefficient spectrum with reference to power cable | Γd1(f) | and the real part Real (Γ of reflection coefficient spectrumd1(f))
Imaginary part Imag (Γ with reflection coefficient spectrumd1(f)), and carry out the process of same way in step 2, after being processed
Distance diagnosis collection of illustrative plates E；
4, power cable local defect position determines
Distance diagnosis collection of illustrative plates E after contrast distance diagnosis collection of illustrative plates D and process, utilizes storbing gate technology to eliminate distance and examines
In disconnected collection of illustrative plates D with process after distance diagnosis collection of illustrative plates E same position at distortion point, obtain local defect distance and examine
Disconnected collection of illustrative plates F, the distortion point found from local defect distance diagnosis collection of illustrative plates F, it is power cable local defect position；
5, power cable local defect judges
The local defect distance diagnosis collection of illustrative plates obtained is carried out inverse discrete Fourier transform change or Fast Fourier Transform Inverse,
T ' territory reflection coefficient spectral curve after conversion, and utilize transfer function t ' → f reflection coefficient spectrum in t ' territory to be converted to
Real(Γd2(f)) or Imag (Γd2(f)), then find Real (Γd2(f)) or Imag (Γd2(f)) in each greatly
Frequency f that value is put or minimum point is correspondingk, utilize formulaObtain tested electric power electricity
The average velocity of wave of cable, and by vcNew power cable velocity of wave v with same specification0Compare, if vcWith v0Difference 1% and
Above, illustrating that tested cable exists local defect, wherein N is Real (Γd2) or Imag (Γd2In) maximum point or
The number of minimum point.
The present invention also can take following method to assess the order of severity of tested power cable local defect further:
Set up cable reflection coefficient spectrum modulus value mathematical model
abs(Γd2(f))=a eb·f+c·ed·f
After the reflection coefficient spectrum utilizing the mathematical model set up to obtain tested power cable measurement uses storbing gate technology
Modulus value | Γd2(f) | carry out data matching, seek upper frequency extreme point fkThe match value that place is corresponding, and by formula below
It is calculated defect level error to be estimated:
Error=std ((| Γd2(fk)|-abs(Γd2(fk)))/abs(Γd2(fk))) × 100%
As error ＜ 5%, cable local defect is relatively light, and the most tested power cable there may be a small amount of copper shield and loosens
There is the defects such as tool marks scuffing in defect or dielectric；When 5%≤error≤10%, power cable defect level
Medium, the most tested power cable there may be the defects such as dielectric makes moist or larger areas of copper screen layer is damaged；When
During error ＞ 10%, electric cable stoppage is very serious, and the most tested power cable there may be dielectric gross distortion
Etc. defect.Std in formula is standard deviation.
In the technique scheme of the present invention, the β value in described kaiser window function should meet:
Wherein α is side lobe attenuation multiple.
In the technique scheme of the present invention, initial range diagnosis collection of illustrative plates D0Preferential use following formula carry out adding away from
Process from window:
Wherein s is length of window, and value is not more than distance diagnosis collection of illustrative plates D0In spatial resolution, D be process after obtain
Distance diagnosis collection of illustrative plates.
In the technique scheme of the present invention, the velocity of wave v of same specification new cable described in step 50Can be by formula
Calculating and obtain, wherein L and C is respectively inductance and the electric capacity of same specification new cable unit length；May be used without time domain
Bounce technique measures acquisition.
Owing to intermediate joint of electric cable position also there will be distortion point during measuring, affect the judgement of defective locations,
In order to eliminate the impact that defective locations is judged by the transition joint of power cable, the present invention draws in diagnostic method step 3
Entered and contrasted with reference to power cable, will non-tested phase power cable in three-phase system as with reference to electric power electricity
Cable, then utilizes step 1 same way to obtain the amplitude of the reflection coefficient spectrum with reference to power cable | Γd1(f) | and anti-
Penetrate the real part Real (Γ of coefficient spectrumd1(f)) and the imaginary part Imag (Γ of reflection coefficient spectrumd1(f)), and carry out phase in step 2
With the process of mode, the distance diagnosis collection of illustrative plates E after being processed.
Owing to each phase of power cable under normal circumstances all can make transition joint in same position, in order to eliminate centre
The joint impact on cable local defect position judgment, the present invention, in diagnostic method step 4, have employed contrast distance
Diagnosis collection of illustrative plates D and distance diagnosis collection of illustrative plates E method, utilize storbing gate technology eliminate distance diagnosis collection of illustrative plates D in away from
Distortion point away from diagnosis collection of illustrative plates E same position, obtains local defect distance diagnosis collection of illustrative plates F, from local defect distance
The distortion point found in diagnosis collection of illustrative plates F, distortion point is exactly local defect position.
In power cable local defect diagnoses, there is power cable long, signal attenuation is serious, required signal band
Narrower；Power cable is short, and signal attenuation is less, and required signal band is wider.Simultaneously when signal does not decays to zero,
The frequency band of signal is the widest, and positioning precision is the highest with sensitivity.
The power cable local defect diagnostic method that the present invention provides, has the most prominent advantage and Advantageous
Effect:
1. the defect diagnostic method of the present invention uses low pressure measurement mode rather than damage type test metering system, no
Only cable insulation will not be caused damage, also can reduce the weight and volume of measurement equipment.
2. the present invention utilizes the mode processing frequency domain information to make cable local defect be easier to show,
By the combination with kaiser window function on the basis of this, substantially increase the sensitivity to cable local defect location.
3., compared to TDR, the present invention is for the identification ability of the more weak local defect of intensity of variation and many places defect
Accuracy of identification and identification sensitivity are higher, and it is the most higher to the identification ability of near-end defect simultaneously.
4. due to the fact that taking the method added apart from window process by diagnosis collection of illustrative plates of adjusting the distance makes distortion point be more easy to table
Reveal to come, substantially increase positioning precision.
5. this invention takes contrast and the storbing gate technology being diagnosed collection of illustrative plates by cable under test and reference cable distance,
Find out the distortion point at same position and eliminate, eliminating cable intermediate joint with this and cable local defect position is sentenced
Disconnected impact.
6. the present invention is calculated by the velocity of wave of cable and the cable local defect order of severity is carried out entry evaluation, basis at this
Upper combination gating back reflection coefficient spectrum modulus value matched curve has carried out further assessment to the local defect order of severity, can be accurate
Really assess the order of severity of cable local defect.
7. the electric cable stoppage diagnostic method of the present invention is not only restricted to the electric pressure of cable under test, traditional electric cable stoppage
Diagnostic method needs to select different test equipment according to different electric pressures.
Accompanying drawing explanation
Fig. 1 is the schematic flow sheet of the power cable defect diagnostic method of the present invention.
Fig. 2 is the tested power cable drawn in the embodiment of the present invention 1 and the contrast distance diagnostic graph with reference to power cable
Spectrum, wherein solid line represents the distance diagnosis collection of illustrative plates of tested power cable, and dotted line represents the distance diagnosis with reference to power cable
Collection of illustrative plates.
Fig. 3 is the spectrum comparison diagram of the reflection coefficient amplitude after storbing gate technology drawn in the embodiment of the present invention 1.Its
Middle dotted line represents the reflection coefficient amplitude spectrum using tested power cable after storbing gate technology, and solid line represents according to reflection system
The curve that number spectrum modulus value Model fitting obtains.
Fig. 4 is the local defect distance diagnosis collection of illustrative plates drawn in the embodiment of the present invention 2.
Detailed description of the invention
Below by embodiment, the present invention is specifically described.Be necessary it is pointed out here that be that the present embodiment is served only for
The present invention is further described, it is impossible to be interpreted as limiting the scope of the invention.Being skilled in technique of this field
Personnel can make some nonessential improvement and adjustment according to the content of the invention described above.
Embodiment 1
The flow process of the power cable local defect diagnostic method of the present embodiment is as it is shown in figure 1, tested power cable and reference
The contrast distance diagnosis collection of illustrative plates of power cable is as in figure 2 it is shown, be for 100m ZR-YJV22-8.7/15 power cable
Local defect diagnosis, defect type is that copper shield loosens defect.Diagnostic method comprises the following steps:
(1) cable under test DATA REASONING
Low pressure pseudo-random signal V is launched to tested 100m ZR-YJV22-8.7/15 power cablei, measure from cable end piece
The reflected signal V reflectedr, pass throughObtain the amplitude of the reflection coefficient spectrum of cable | Γd(f) | and anti-
Penetrate the real part Real (Γ of coefficient spectrumd(f)) and the imaginary part Imag (Γ of reflection coefficient spectrumd(f))。
(2) cable under test data process
Utilize transfer function f → t ', tested frequency-region signal is converted to t ' territory signal, then to being converted to
Real(Γd(t ')) carry out fast Fourier (FFT) conversion, record the Frequency point f that energy is maximum0′；Then to turning
Real (the Γ got in returnd(t ')) it is multiplied with kaiser (Kai Se) window and carries out at the beginning of fast Fourier (FFT) conversion obtains
Step processes data K Γd, the β value in kaiser window is 6；
To K ΓdDo 0 hertz to Frequency point f0' DFT transform, transformation results is mapped to initial range diagnosis collection of illustrative plates
D0In, wherein mapping distance is 0 meter at 0 hertz, f0' place mapping distance is cable length 100 meters.
Carrying out adding the windowing process that distance window length s is 5 meters by the initial range obtained diagnosis collection of illustrative plates, processing mode is:
(3) reference cable DATA REASONING and process
Using the non-tested phase cable in three-phase system as reference cable, step (1) same way is then utilized to obtain
Amplitude with reference to the reflection coefficient spectrum of power cable | Γd1(f) | and the real part Real (Γ of reflection coefficient spectrumd1(f)) and anti-
Penetrate the imaginary part Imag (Γ of coefficient spectrumd1(f)), and the process carried out in step (2) under the same terms, after being processed
Distance diagnosis collection of illustrative plates E.
(4) power cable local defect position determines
Contrast distance diagnosis collection of illustrative plates D and distance diagnosis collection of illustrative plates E, as in figure 2 it is shown, utilize storbing gate technology to eliminate distance
Diagnosis collection of illustrative plates D diagnoses the distortion point at collection of illustrative plates E same position with distance, obtains local defect distance diagnosis collection of illustrative plates F.
From Fig. 2 it appeared that there is an obvious distortion point, the local defect arranged just at this point the position of 70 meters.
(5) cable local defect Severity
The local defect distance diagnosis collection of illustrative plates obtained is carried out Fast Fourier Transform Inverse (IFFT), after being converted
Reflection coefficient spectrum t ' territory curve, and utilize transfer function t ' → f to be converted to Real (Γd2(f)).Find Real (Γd2(f))
In frequency f corresponding to each maximum pointk, utilize formulaObtain tested electric power electricity
The average velocity of wave v of cablec=1.7247 × 108Meter per second, records new cable velocity of wave v0=1.7261 × 108Meter per second.Wherein N is
Real(Γd2) or Imag (Γd2Maximum point or the number of minimum point in).vcWith v0Both differences 0.81% < 1%,
Illustrate that tested cable local defect is lighter.
In order to assess the order of severity of tested cable local defect further, set up cable reflection coefficient spectrum modulus value mathematical modulo
Type:
abs(Γd2(f))=a eb·f+c·ed·f
The reflection coefficient spectrum utilizing the mathematical model set up to obtain tested cable measurement uses storbing gate
Modulus value after technology | Γd2(f) | carrying out data matching, fitting result is
abs(Γd2(f))=0.137 e-1.23×10-7·f+0.8095·e-5.474×10-9·f, as it is shown on figure 3, obtain upper frequency extreme point
fkLocate corresponding match value and by formula
Error=std ((| Γd2(fk)|-abs(Γd2(fk)))/abs(Γd2(fk))) × 100%
Obtain | Γd2(f) | with standard deviation error=1.16% of the relative difference of matched curve < 5%, tested electric power electricity is described
The local defect of cable is relatively light, has confirmed the most tested power cable and there is the defect that copper shield loosens.
Embodiment 2
The flow process of the power cable local defect diagnostic method of the present embodiment is as it is shown in figure 1, tested power cable and reference
The contrast distance diagnosis collection of illustrative plates of power cable as shown in Figure 4, carries out office for 1500m10kV XLPE power cable
Portion's defect diagonsis, defect type also dielectric gross distortion defect, comprise the following steps:
(1) cable under test DATA REASONING
Low-voltage high-frequency burst pulse V is launched to tested 1500m ZR-YJV22-8.7/15 power cablei, measure from cable end
The reflected signal V that end reflectsr, pass throughObtain the amplitude of the reflection coefficient spectrum of cable | Γd(f) | and
Real part Real (the Γ of reflection coefficient spectrumd(f)) and the imaginary part Imag (Γ of reflection coefficient spectrumd(f))。
(2) cable under test data process
Utilize transfer function f → t ', tested frequency-region signal is converted to t ' territory signal, then to being converted to
Imag(Γd(t ')) carry out discrete fourier (DFT) conversion, record the Frequency point f that energy is maximum0′；Then to turning
Imag (the Γ got in returnd(t ')) it is multiplied with kaiser (Kai Se) window and carries out at the beginning of discrete fourier (DFT) transforms to
Step processes data K Γd, the β value in kaiser window is 8；
To K ΓdDo 0 hertz to Frequency point f0' DFT transform, transformation results is mapped to initial range diagnosis collection of illustrative plates
D0In, wherein at 0Hz, mapping distance is 0 meter, f0' place mapping distance is cable length 1500 meters.
Carry out adding the windowing process that distance window length s is 30 meters, processing mode by the initial range obtained diagnosis collection of illustrative plates
For:
(3) reference cable DATA REASONING and process
Using the phase cable non-to be measured in three-phase system as reference cable, step (1) same way is then utilized to obtain
Amplitude with reference to the reflection coefficient spectrum of power cable | Γd1(f) | and the real part Real (Γ of reflection coefficient spectrumd1(f)) and anti-
Penetrate the imaginary part Imag (Γ of coefficient spectrumd1(f)), and the process carried out in step (2) under the same terms, after being processed
Distance diagnosis collection of illustrative plates E.
(4) power cable local defect position determines
Contrast distance diagnosis collection of illustrative plates D and distance diagnosis collection of illustrative plates E, utilizes storbing gate technology to eliminate distance diagnosis collection of illustrative plates D
In with distance diagnosis collection of illustrative plates E same position at distortion point, obtain local defect distance diagnosis collection of illustrative plates F, such as Fig. 3 institute
Show.From Fig. 3 it appeared that there is obvious distortion point at 500 meters and 1200 meters, the local arranged just at this
Defect point.
(4) cable local defect Severity
The local defect distance diagnosis collection of illustrative plates obtained is carried out inverse discrete Fourier transform and changes (IDFT), after being converted
Reflection coefficient spectrum t ' territory curve, and utilize transfer function t ' → f to be converted to Imag (Γd2(f)).Find
Imag(Γd2(f)) in frequency f corresponding to each minimum pointk, utilize formulaAsk
Go out the average velocity of wave v of tested power cable0=1.7217 × 108Meter per second, records new cable velocity of wave v0=1.7261 × 108Rice/
Second.Wherein N is Imag (Γd2Maximum point or the number of minimum point in).vcWith v0Both differences 2.55% > 1%,
Illustrate that tested cable local defect ratio is more serious.
In order to assess the order of severity of tested cable local defect further, set up cable reflection coefficient spectrum modulus value mathematical modulo
Type:
abs(Γd2(f))=a eb·f+c·ed·f
The reflection coefficient spectrum utilizing the mathematical model set up to obtain tested cable measurement uses the mould after storbing gate technology
Value | Γd2(f) | carrying out data matching, fitting result is
abs(Γd2(f))=0.3406 e-9.535×10-7·f+0.2823·e-2.032×10-7·f, obtain upper frequency extreme point fkPlace's correspondence
Match value by formula
Error=std ((| Γd2(fk)|-abs(Γd2(fk)))/abs(Γd2(fk))) × 100%
Obtain | Γd2(f) | with standard deviation error=16.14% of the relative difference of matched curve > 10%, tested power cable is described
Local defect ratio more serious, confirmed the most tested power cable and there is the major defect of dielectric gross distortion.
Claims (9)
1. a high sensitivity power cable local defect diagnostic method, it is characterised in that: comprise the following steps:
(1) cable under test DATA REASONING
Low-pressure linear frequency modulation, pseudorandom or the signal V of high-frequency narrow-pulse is launched to tested power cablei, measure from electricity
The reflected signal V that cable end reflection is returnedr, pass throughObtain the amplitude of the reflection coefficient spectrum of cable | Γd(f)|
And the real part Real (Γ of reflection coefficient spectrumd(f)) and the imaginary part Imag (Γ of reflection coefficient spectrumd(f)), wherein f is letter
Number frequency；
(2) cable under test data process
Utilize transfer function f → t ', tested frequency-region signal f is converted to t ' territory signal, then to being converted to
Real(Γd(t ')) or Imag (Γd(t ')) carry out fast Fourier transform or discrete Fourier transform, record energy
Big Frequency point f0′；Then to the Real (Γ being converted tod(t ')) or Imag (Γd(t ')) it is multiplied with kaiser window function
And carry out fast Fourier transform or discrete Fourier transform, obtain preliminary treatment data K Γd；
To the preliminary treatment data K Γ obtaineddDo 0 hertz to Frequency point f0' discrete Fourier transform, by conversion tie
Fruit is mapped to initial range diagnosis collection of illustrative plates D0In, initial range is diagnosed collection of illustrative plates D0Carry out adding distance window to process, obtain
Distance diagnosis collection of illustrative plates D, wherein mapping distance is 0 meter at 0 hertz, Frequency point f0' place mapping distance is power cable
Length l；
(3) reference cable DATA REASONING and process
Using the non-tested phase power cable in three-phase system as with reference to power cable, then utilize step (1) identical
Mode obtains the amplitude of the reflection coefficient spectrum with reference to power cable | Γd1(f) | and the real part of reflection coefficient spectrum
Real(Γd1(f)) and the imaginary part Imag (Γ of reflection coefficient spectrumd1(f)), and carry out the place of same way in step (2)
Reason, the distance diagnosis collection of illustrative plates E after being processed；
(4) power cable local defect position determines
Distance diagnosis collection of illustrative plates E after contrast distance diagnosis collection of illustrative plates D and process, utilizes storbing gate technology to eliminate distance and examines
In disconnected collection of illustrative plates D with process after distance diagnosis collection of illustrative plates E same position at distortion point, obtain local defect distance and examine
Disconnected collection of illustrative plates F, the distortion point found from local defect distance diagnosis collection of illustrative plates F, it is power cable local defect position；
(5) power cable local defect judges
The local defect distance diagnosis collection of illustrative plates obtained is carried out inverse discrete Fourier transform change or Fast Fourier Transform Inverse,
T ' territory reflection coefficient spectral curve after conversion, and utilize transfer function t ' → f reflection coefficient spectrum in t ' territory to be converted to
Real(Γd2(f)) or Imag (Γd2(f)), then find Real (Γd2(f)) or Imag (Γd2(f)) in each greatly
Frequency f that value is put or minimum point is correspondingk, utilize formulaObtain tested electric power electricity
The average velocity of wave of cable, and by vcNew power cable velocity of wave v with same specification0Compare, if vcWith v0Difference 1% and
Above, illustrating that tested cable exists local defect, wherein N is Real (Γd2) or Imag (Γd2In) maximum point or
The number of minimum point.
High sensitivity power cable local defect diagnostic method the most according to claim 1, it is characterised in that
The order of severity of tested power cable local defect is assessed further by following method:
Set up cable reflection coefficient spectrum modulus value mathematical model
abs(Γd2(f))=a eb·f+c·ed·f
The reflection coefficient spectrum utilizing the mathematical model set up to obtain tested power cable measurement uses the mould after storbing gate technology
Value | Γd2(f) | carry out data matching, seek upper frequency extreme point fkThe match value that place is corresponding, and calculated by formula below
Obtain defect level error to be estimated:
Error=std ((| Γd2(fk)|-abs(Γd2(fk)))/abs(Γd2(fk))) × 100%
As error ＜ 5%, power cable local defect is relatively light, and when 5%≤error≤10%, power cable local lacks
The degree of falling into is medium, and as error ＞ 10%, power cable local defect is very serious, and in formula, std is standard deviation.
High sensitivity power cable local defect diagnostic method the most according to claim 1 and 2, it is characterised in that
β value in described kaiser window function meets:
Wherein α is side lobe attenuation multiple.
High sensitivity power cable local defect diagnostic method the most according to claim 1 and 2, it is characterised in that
Initial range diagnosis collection of illustrative plates D0Use following formula to carry out adding distance window to process:
Wherein s is length of window, and value is not more than distance diagnosis collection of illustrative plates D0In spatial resolution, D for process after obtain
Distance diagnosis collection of illustrative plates.
High sensitivity power cable local defect diagnostic method the most according to claim 3, it is characterised in that former
The distance that begins diagnosis collection of illustrative plates D0Use following formula to carry out adding distance window to process:
Wherein s is length of window, and value is not more than distance diagnosis collection of illustrative plates D0In spatial resolution, D for process after obtain
Distance diagnosis collection of illustrative plates.
High sensitivity power cable local defect diagnostic method the most according to claim 1 and 2, its feature exists
In: the new cable velocity of wave v of same specification in step (5)0By formulaCalculating and obtain, wherein L and C is respectively
The inductance of the new cable unit length of same specification and electric capacity, or use time domain reflectometry to measure.
High sensitivity power cable local defect diagnostic method the most according to claim 3, it is characterised in that:
The new cable velocity of wave v of same specification in step (5)0By formulaCalculating and obtain, wherein L and C is respectively same specification
The inductance of new cable unit length and electric capacity, or use time domain reflectometry to measure.
High sensitivity power cable local defect diagnostic method the most according to claim 4, it is characterised in that:
The new cable velocity of wave v of same specification in step (5)0By formulaCalculating and obtain, wherein L and C is respectively same specification
The inductance of new cable unit length and electric capacity, or use time domain reflectometry to measure.
High sensitivity power cable local defect diagnostic method the most according to claim 5, it is characterised in that:
The new cable velocity of wave v of same specification in step (5)0By formulaCalculating and obtain, wherein L and C is respectively same specification
The inductance of new cable unit length and electric capacity, or use time domain reflectometry to measure.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201610351358.8A CN105842596B (en) | 2016-05-24 | 2016-05-24 | A kind of high sensitivity power cable local defect diagnostic method |
Applications Claiming Priority (1)
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